A series of single-walled carbon nanotube precursors, C3h-symmetric cyclotri(ethynylene)(biphenyl-2,4'-diyl) and cyclotri(ethynylene)(p-terphenyl-2,4″-diyl), have been prepared by a linear stepwise oligomerization-cyclization route and by statistical intermolecular cyclooligomerization. In addition to producing these members of a novel class of arylene ethynylene macrocycles, 1 and 2, the latter statistical process produces the smaller cyclic dimer, cyclodi(ethynylene)(p-terphenyl-2,4″-diyl) and the larger cyclic tetramer cyclotetra(ethynylene)(biphenyl-2,4'-diyl). These macrocycles display large Stokes shifts in their fluorescence spectra. Their biphenyl or terphenyl connectivity prevents these macrocycles from achieving full planarity in the ground state, and the ethynylene moieties could provide synthetic access to cyclic arylene oligomers and discrete carbon nanotube segments.
A series of single-walled carbon nanotube precursors, C3h-symmetric <span class="Chemical">cyclotri(ethynylene)(biphenyl-2,4'-diyl) and cyclotri(ethynylene)(p-terphenyl-2,4″-diyl), have been prepared by a linear stepwise oligomerization-cyclization route and by statistical intermolecular cyclooligomerization. In addition to producing these members of a novel class of arylene ethynylene macrocycles, 1 and 2, the latter statistical process produces the smaller cyclic dimer, cyclodi(ethynylene)(p-terphenyl-2,4″-diyl) and the larger cyclic tetramer cyclotetra(ethynylene)(biphenyl-2,4'-diyl). These macrocycles display large Stokes shifts in their fluorescence spectra. Their biphenyl or terphenyl connectivity prevents these macrocycles from achieving full planarity in the ground state, and the ethynylene moieties could provide synthetic access to cyclic arylene oligomers and discrete carbon nanotube segments.
Conjugated shape-persistent
macrocycles[1] and, in particular, arylene
<span class="Chemical">ethynylene macrocycles (AEMs)[2] have received
much attention in recent years
because advances in synthetic techniques have made them more accessible,
and they have potential in many applications. AEMs are relatively
thermally, photolytically, and oxidatively stable;[3] they often have strong UV absorptions and are often highly
fluorescent.[4] Their rigid shape makes them
suitable for host–guest interactions.[5] Additionally, these macrocycles have been of interest because their
high polarizability makes them desirable as second-order nonlinear
optical materials[6] and as materials for
organic semiconductors[7] and devices.[8] Their unique two-dimensional structure could
potentially allow these materials to circumvent the trade-off between
efficiency and transparency observed in linear systems, and C3-symmetric systems can be derivatized to give
noncentrosymmetric materials. Planar AEMs have been shown to aggregate
in solution,[9] in the liquid crystalline
phase,[10] and in the solid phase[11] through weak van der Waals interactions. AEMs
can aggregate into columnar mesophases as well as vesicles[12] and have the potential to act as model systems
for organic nanotubes.[13]
Arylene
<span class="Chemical">ethynylene macrocycles are synthetically accessible either
by statistical cyclization of a single aryl halide ethynyl monomer[14,15] or by the cyclization of a linear oligomer via a palladium catalyzed
cross coupling,[16] in either case at low
concentrations. This latter approach requires a linear, stepwise,
and often tedious synthesis of the linear oligomer but usually gives
a single discrete macrocycle as the sole product. Alternatively, the
former methodology employs more synthetically accessible precursors
but often yields various cyclic and linear oligomers[17] unless specific macrocycle ring sizes are excluded by ring
strain or steric interactions on neighboring monomer units.[18] More recently, alkyne metathesis has proven
to be an efficient synthetic method to prepare the arylene ethynylene
scaffold.[19] Metathesis allows the formation
of the thermodynamically most favored product(s) but may not offer
the functional group tolerance of the palladium-catalyzed protocols.
Derivatization of the monomers should allow the formation of electron-rich
and/or electron-poor ring systems and thus the tuning of their physical
properties. The incorporation of side chains is often crucial to allow
the solubility of the highly rigid macrocycles.
Despite the
recent attention given arylene ethynylene macrocycles,
the incorporation of <span class="Chemical">biphenyl and terphenyl moieties is rare, and
such macrocycles have not been fully explored. The few reported examples
of biphenyl or teraryl units include bipyridyl,[20]m-terphenyl,[21]m-terpyridinyl,[22] and
11,12-dihydroindolo[2,3-a]carbazole[23] (nominal p-terphenylenes) and tetram-phenylene[24] subunits but no
simple biphenyl or p-terphenylene containing macrocycles
have been reported. The presence of such biphenyl units disrupts the
fully planar geometry of the macrocycle and would therefore be expected
to attenuate any aggregation via stacking of the planar rings. The
deviation from planarity also would affect the conjugation around
the macrocycle, and change their electronic properties in comparison
to their fully planar analogs. The macrocycles depicted in Figure 1 represent novel classes of arylene ethynylene macrocycles.
Figure 1
Biphenyl
and terphenyl macrocycles.
Biphenyl
and terphenyl macrocycles.More significantly, the title C3 macrocycles
offer the possibility to synthesize short segments of single-walled
<span class="Chemical">carbon nanotubes. Ethynylene units in shape-persistent macrocycles
are usually used as rigid spacers that prevent diaryl steric interactions.
However, alkynes are also reactive moieties, and if the alkynes in
the title macrocycles can be incorporated into ortho-substituted aromatic rings via cycloaddition reactions with cyclopentadienone
synthons, the vertices of the triangular macrocycles could be folded
out of the plane to form the walls of the nanotube segment.[25] The phenylene rings in such a cycloaddition
product are geometrically disposed to produce a fully fused nanotube
segment upon oxidative cyclodehydrogenation (Figure 2). This synthetic path toward carbon nanotube segments relies
on the title macrocycles as relatively strain-free templates that
are elaborated with additional phenyl rings in a stepwise increase
of strain until the fused tube is achieved. Alternatively, macrocycles
containing cyclopentadienone moieties could be constructed and undergo
cycloadditions with diarylalkynes to give similar cyclooligophenylenes.[26]
Figure 2
Potential conversion
of title macrocycles to nanotube segments.
A similar strain strategy pioneered by
Bertozzi and Jasti[27] converts a more highly
curved precursor containing
sp3 centers to the all-<span class="Gene">sp2 nanotube segment.
Jasti,[28] Itami,[29] and others[30] have used this route to
prepare a variety of [n]cycloparaphenylenes, and
Jasti[31] and Mullen[32] have recently prepared [n]cycloparaphenylenes that
could in principle give belts of longer length upon oxidative cyclodehydrogenation
of pendant phenyl substituents. Bodwell[33] has also prepared highly curved nanotube segments by incorporating
polycyclic arenes in cyclophanes. Scott has proposed a slightly different
approach that uses bowl-shaped templates upon which the nanotube can
be grown.[34] To further our synthetic proposal,
the synthesis of C3-symmetric biphenyl
and terphenyl arylene ethynylene macrocycles and their alkyl derivatives,
along with their photophysical properties, are described below.
Potential conversion
of title macrocycles to nanotube segments.
Results and Discussion
Monomer Synthesis
As discussed above,
the construction
of cyclooligomers is usually achieved by one of two means: a statistical
coupling of simple monomer units or a cyclization of a linear oligomer
of appropriate length. The former method involves a shorter synthetic
route and was the first one attempted for the construction of the C3-symmetric macrocycles 1a, 1b, 2a, and 2b. Since both synthetic
approaches require monomers 3a, 3b, 4a, and 4b, they were prepared first. The diethyltriazene
and triisopropylsilyl groups on the termini of 3 and 4 are protecting groups that can be removed under orthogonal
reaction conditions to give the <span class="Chemical">aryl iodide or terminal alkyne, respectively.
A statistical macrocyclization would require both groups to be deprotected
to give the AB monomer, while the synthesis of a linear trimer which
could be subsequently cyclized could be accomplished using a split-pool
strategy (Scheme 1).
Scheme 1
Retrosynthetic Analysis
Compound 3a was
prepared via a convergent approach
(Scheme 2). Triazene 5 was prepared
in 97% yield by diazotization of <span class="Chemical">4-iodoaniline followed by quenching
with diethylamine. Boronation of 5 with 1.2 equiv of
bis(pinacalato)diboron, Cl2Pd(dppf), and dry KOAc in DMSO
gave 6 in 74% yield. However, this boronation also produced
a significant quantity of biphenyl 7 which could only
be removed by recrystallization from 2-propanol. In an attempt to
minimize the formation of this undesired homodimer, a 3-fold excess
of bis(pinacalato)boron was used. No homodimerization was observed,
but the excess diboron proved equally difficult to remove during purification.
The most effective purification protocol involves recrystallization
from 2-propanol to remove the homodimer 7 followed by
column chromatography to remove the residual palladium and excess
diboron. Alternatively, 6 was prepared by diethylamine
addition to the diazotized aminophenylboronic acid pinacol ester in
85% yield. This second protocol not only provided an overall higher
yield of the phenylene synthon 6 but also a high enough
purity after workup that the crude product could be used in further
reactions without further purification, in stark contrast to the first
protocol. Alkyne coupling partner 8 was prepared in 99%
yield according to literature procedures from 1-bromo-2-iodobenzene
and triisopropylsilylacetylene.
Scheme 2
Convergent Approach to Biphenyl 3a and Terphenyl 4a Monomers
Suzuki coupling of the boronate ester 6 and <span class="Chemical">alkyne 8 was performed using Cl2Pd(dppf) and K3PO4 in DME to give the biphenyl
monomer 3a in 95% yield. It should be noted that other
palladium catalysts
(notably Pd(PPh4)3), bases, and solvents did
not give comparable yields. Terphenyl monomer 4a was
prepared in 65% yield from triazene 3a by treatment with
iodomethane to give 9 followed by a Suzuki coupling with
triazene 6. Despite the more reactive iodide and lack
of hindering ortho group in 9 compared
to 8, the lower yield for the second Suzuki coupling
was the result of competitive protiodeiodination[35] to give 2-(triisopropylsilylethynyl)biphenyl. The terphenyl
triazene also undergoes photolytic decomposition, especially in the
presence of silica gel or Florisil; alumina was used in the chromatography
of all terphenyl triazenes described, and little such decomposition
was observed on this stationary phase.
Since the macrocycles
constructed from 3a and 4a were anticipated
to have low solubility, alkyl-substituted
analogues 3b and 4b were also prepared (Scheme 3). <span class="Chemical">Octylaniline 10 was iodinated with
an ammonium dichloroiodate with high regiospecificity give iodoarene 11, which was diazotized and quenched with diethylamine gave
triazene 12. The Sonogashira coupling of 12 with triisopropylsilylacetylene gave 13, which was
then converted to iodoarene 14 in 86% yield over four
steps.
Scheme 3
Convergent Approach to Alkyl-Substituted Biphenyl 3b and Terphenyl 4b Monomers
As with the unsubstituted analogues, biphenyl monomer 3b was obtained by Suzuki–Miyaura coupling of 6 and 14, and terphenyl monomer 4b was obtained
from 3b by deprotection of the <span class="Chemical">triazene in 3b with methyl iodide to give iodoarene 15 (in 94% yield)
which was then coupled with another equivalent of 6.
Initial attempts to couple 6 and 14 produced
very poor yields of 3b along with significant quantities
of (3-octylphenylethynyl)triisopropylsilane, the protiodeiodination
product of 14. The concentration of reactants was increased
5-fold in an attempt to make the coupling more competitive with protiodeiodination,
and the yield of the desired biphenyl 3b was increased
to 82%. The careful exclusion of water, a potential source of protons,[36] did not increase the yield of coupled product 3b appreciably. Additionally, the yield of the Suzuki coupling
to produce the terphenyl monomer 4b was 68%, lower than
that for 3b, presumably for the same reasons discussed
above for 3a.
Statistical Macrocyclization
The
doubly deprotected
monomeric iodoalkynes <span class="Gene">16a and 17a were obtained
by diethyltriazene removal in methyl iodide followed by fluoride deprotection
of the ethynyl protecting groups (Scheme 2)
in 88% and 71% yields over two steps, respectively. The instability
of terphenyl 17a required that this free alkyne be utilized
immediately after preparation and explains the lower yield of its
preparation in comparison to the biphenyl16a. Biphenyl
monomer 16a was subjected to Sonogashira reaction conditions
using Cl2Pd(PPh3)2 at low concentration
(18 mM) for 10 days at room temperature to give a product mixture
containing a mixture of linear and cyclic oligomers. Poor solubility
and similar polarities of the reaction products precluded chromatographic
separation or purification, but the presence of 1a was
evident by peaks in the 1H NMR (Figure 3) that matched those in pure samples of 1a obtained
by the alternate synthesis described below.
Figure 3
(Top) statistical macrocyclization
of 16a. (Bottom)
stepwise construction of 1a.
(Top) statistical macrocyclization
of 16a. (Bottom)
stepwise construction of 1a.Stephens–Castro coupling of terphenyl monomer 17a at 182 mM and Sonogashira coupling at 155 mM with Pd(<span class="Gene">PPh3)2Cl2 gave only an insoluble yellow
product,
which had an 1H NMR spectrum consistent with a mixture
of linear and cyclic oligomers. The Sonogashira coupling of 17a was attempted again, using Pd(PPh3)4 and at lower concentration, 18 mM. After 12 days at room temperature,
this reaction yielded a solid that when washed repeatedly with methylene
chloride proved to be macrocycle 2a. The cyclic trimer
was isolated in 20% crude yield but could not be separated from an
impurity of unknown structure.
Similar protocols were used to
convert the alkyl-substituted monomers 3b and 4b to cyclooligomers. Double deprotection
of 3b and 4b to give 16b and <span class="Chemical">17b proceeded as with the unsubstituted analogues in 68% and
98% yields over two steps, respectively. Compound 16b was subjected to Sonogashira coupling conditions at 28 mM; four
fluorescent compounds were identified by TLC, but only two compounds
were isolated by five iterations of flash chromatography, the cyclic
trimer 1b in 36% yield, and the cyclic tetramer 1c in 24%. In an effort to improve the yield of the cyclooligomers,
the concentration was lowered to 1.5 mM in the Sonogashira coupling
reaction of 17b. A 51% yield of the cyclic trimer 2b was recovered by column chromatography as well as cyclic
dimer 2c in 12% yield. The yield of the cyclic trimer
may also have been higher in the cyclooligomerization of 17b because of the use of Pd(PPh3)4 instead of
PdCl2(PPh3)2. The isolation of the
substituted macrocycles was greatly facilitated by their much higher
solubility, attributable to their long alkyl side chains.
Macrocyclization
of Linear Oligomers
Analytically pure
samples of 1a and 2a were obtained by constructing
each through a linear, stepwise approach (Schemes 4 and 5, respectively). This split pool
approach began with the removal of the diethyltriazene of 3a to give 18a in 98% yield and the removal of the ethynyl
protecting group of 3a using <span class="Chemical">TBAF to yield 19a in 90% yield (Scheme 3). Sonogashira coupling
of fragments 18a and 19a gave the protected
dimer 20a in 75% yield. Unmasking the aryl iodide by
removal of the diethyltriazene was followed by a second coupling with
fragment 19a, which led to the linear trimer 22a in 67% yield over the two steps. Compound 22a was then
quantitatively converted to the iodide 23a. Deprotection
of 23a with TBAF gave an iodoarylethyne which was immediately
subjected to Sonogashira coupling conditions without purification.
The cyclization was performed by slowly adding a solution of the linear
trimer iodoarylethyne with a syringe pump to a solution of the catalysts
in triethylamine. The final and highest concentration of the linear
trimer was 3.7 mM, and after the addition was complete, the reaction
was stirred for another 12 h before workup. Column chromatography
gave pure 1a in 45% yield (Scheme 6).
Scheme 4
Cyclization of Unsubstituted and Alkyl-Substituted Free Monomers
Scheme 5
Cyclization of Alkyl-Substituted and
Alkyl-Substituted Free Monomers
Scheme 6
Linear Approach to Macrocycle 1a
A split-pool approach to the terphenyl macrocycle 2a also occurred in a similar sequence, but the additional p-phenylene unit within the monomer unit contributed to
solubility problems (Scheme 4). Both deprotections
of 3b proceeded in 91% yield to give the <span class="Chemical">iodide 18b and terminal alkyne 19b, which were coupled
under Sonogashira conditions to give dimer 20b in 76%
yield. A significant quantity of unreacted 18b was also
recovered, along with a similar amount of a third organic product
which is presumed to be the Hay coupled dialkyne arising from dimerization
of 19b. Conversion of the triazene to the iodide 21b and Sonogashira coupling with another 1.3 equiv of 19b gave the trimer 22b in 52% combined yield.
The lower yield compared to the biphenyl system can be attributed
to losses during chromatography of the sparingly soluble synthons,
and the larger excess of the terminal alkyne was utilized to minimize
yield loss due to Hay coupling. Deprotection of the triazene to give
iodide 23b proceeded in quantitative yield. Removal of
the TIPS group gave the sparingly soluble iodoarylethyne linear trimer;
the loss of the relatively small alkyl groups in the TIPS group significantly
lowered its solubility, and its subsequent cyclization was carried
out without further chromatographic purification or complete characterization.
As with the biphenyl trimer, the cyclization was carried out under
high dilution Sonogashira conditions (2.1 mM) achieved using a syringe
pump. The product mixture was purified by removing the solvent and
centrifugation of the residue slurried with dichloromethane. The insoluble
organic products floated on the chlorinated solvent while the inorganic
catalysts and byproducts thereof formed a solid pellet. Macrocycle 2b was thus isolated in 21% yield (Scheme 7).
Scheme 7
Linear Synthesis of Macrocycle 2b
Computational Modeling
of Cyclooligomer Strain
The
formation of both linear and cyclic oligomers of various sizes during
cyclooligomerization is not unexpected and has been shown to occur
in various systems under a wide array of reaction conditions.[14] In some of these reports, the <span class="Chemical">cyclotrimeric
and cyclotetrameric products isolated from o-iodoethynylenebenzene
precursors were relatively unstrained.[15] Other studies have reported the production of strained cyclic dimeric
species along with unstrained cyclotrimers and cyclotetramers.[37]
On the basis of the macrocycles described
above, the cyclic dimer, <span class="Chemical">cyclic trimer, and cyclotetramer of the 1,2-phenylene,
1,4′-biphenylene, and 1,4″-terphenyleneethynylene macrocycles
were computationally modeled. Geometry optimization and single-point
energies were calculated at various levels of theory using Gaussian
03,[38] and the alkyl chains were omitted
for computational ease. The structures shown are from the B3LYP/6-31G(d)
geometry optimization, but the structures for the geometries optimized
with every method do not differ appreciably. The energies tabulated
in Table 3 are per repeat unit and normalized
to the cyclotrimer for each analogous series.
Table 3
λmax (nm) and ε
(M–1 cm–1) of n-Octyl Terphenyl Cyclodimer and Cyclotrimer
solvent
1a λmax (ε)
1b λmax (ε)
1c λmax (ε)
2a λmax (ε)
2b λmax (ε)
2c λmax (ε)
nC5H12
296 (20300)
282 (14700)
312 (−)
306 (−)
301 (14500)
C6H6
298 (19800)
303 (34100)
309 (7400)
303 (12600)
309 (11200)
307 (9800)
THF
295 (13000)
302 (15800)
285 (7500)
305 (10900)
305 (4800)
307 (7500)
CHCl3
297 (19900)
302 (21700)
285 (12300)
303 (8200)
315 (12000)
307 (6200)
306 (12200)
For the o-arylene ethynylene cyclooligomers, it
is no surprise that the D2 cyclodimer 24c is much higher in energy than
either the D3 <span class="Chemical">cyclotrimer 24a or D2 tetramer 24b. The incomplete treatment of the closed π-system
in the molecular mechanics force field is most likely the source of
the difference in repeat unit strain calculated for the cyclotetramer 24b; the puckered ring of 24b is predicted to
be as nearly strainless as cyclotrimer 24a by semiempirical,
ab initio, and density functional methods but not by molecular mechanics.
Calculations on the biphenyl cyclooligomers exhibit similar energy
trends. The <span class="Chemical">C14H8 repeat units in cyclodimer C21d are ∼10
kcal/mol higher in energy than those in C31a, and the two para-substituted rings
are predicted to be coplanar with one another, which gives C21d the appearance of an extended
cyclophane. The aryl–aryl dihedral angle decreases from 90°
in 1d to 56° in cyclotrimer 1a. Cyclic
tetramer 1e shows a similar aryl–aryl dihedral
angle (57°) as well as a similar alkyne bond angle to that of
the cyclic trimer. These structural similarities, despite the pucker
in the cyclotetramer ring, contribute its lack of strain; the cyclotrimer
and cyclotetramer are nearly isoenergetic on the basis of each repeat
unit.
The constrained cyclic array of the terphenyl dimer C symmetric 2d forces the
two para-substituted rings to be nearly coplanar,
while being orthogonal to the ortho-substituted ring.
The <span class="Chemical">C20H12 repeat units are calculated to be
∼8 kcal/mol more strained in 2d than in 2a, a smaller difference than that calculated in the biphenyl
macrocycles. The optimized geometry of the cyclotrimer 2a is C3 symmetric and features a nearly
all-planar system in which only the central p-phenylene
of the terphenyl unit is twisted out of the plane. As a result, there
are three planar diphenylacetylene moieties within 2a, a structural feature that is shared by the optimized geometry of C2 symmetric 2e. The lack of angle
strain in the alkykyl moieties in both 2a and 2e is a contributing factor making them nearly isoenergetic.
In all cases, the cyclodimers have the highest energy per monomer
unit compared to the respective cyclotrimers or cyclotetramers, which
in each case are nearly isoenergetic. There is a relationship between
the number of <span class="Chemical">p-phenylene units in the macrocycle
and the relative strain of the cyclodimer; presumably, the angle strain
of the alkynyl moieties is shared among additional phenylene units
and the overall strain of the repeat unit is reduced. The average
spcarbon bond angle is 155.4° in 24c, 166.5°
in 1d, and 170.0° in 2d, and it is
evident that smaller deviations from the ideal bond angle in the alkynylcarbons is accompanied by a reduction in the strain energy. The structural
similarities shared between 1a and 1e as
well as 2a and 2e shown in Table 1 reflect their isoenergetic relationships. There
is one close nonbonded C–H interaction present in the biphenyl
and terphenyl macrocycles that is as significant in setting the aryl–aryl
dihedral as the distance between the 2- and 2′-hydrogens; these
distances are only significant in the cyclic trimers and tetramers
since the cyclic dimer has a near orthogonal biphenyl dihedral angle
(Table 2).
Table 1
Energies and Geometries of Various
Arylene Ethynylene Macrocyclesa
Energies are in kcal mol–1 per repeat
unit of cyclooligomer and are referenced to the cyclic
trimer repeat unit energy for each set of cyclooligomers.
Table 2
Structural Features
of Various Arylene
Ethynylene Macrocycles
avg sp C bond angle (deg)
H–C (Å)
Ar–C≡C–Ar dihedral angle (deg)
other Ar–Ar
dihedral angles (deg)
24c
155.4
0.0
24a
179.4
0.0
24b
178.0
60.5
1d
166.5
3.60
95.0
1a
177.8
2.72
47.6
1e
177.6
2.74
47.9
2d
170.0
3.07
87.4
29.0, 68.3
2a
177.2
2.72
6.5
39.4, 46.5
2e
177.4
2.66
18.1
38.4, 52.8
The observation of
cyclic dimer 2c in the macrocyclization
of 3b suggests that the strain calculated per repeat
unit is not great enough to prevent the irreversible, kinetic formation
of 2c. The larger strain calculated for the <span class="Chemical">biphenyl
dimer 1d suggests that strain may be playing a role in
favoring the formation of cyclotrimer 1b and cyclotetramer 1c in the macrocyclization of 3a.
Energies are in kcal mol–1 per repeat
unit of cyclooligomer and are referenced to the cyclic
trimer repeat unit energy for each set of cyclooligomers.
Optical Properties
The absorption and emission spectra
of the novel macrocycles described above were recorded in a variety
of solvents, since solvent polarity has been shown to affect the absorption
and emission wavelength as well as the quantum yields (Φ) of
organic molecules.[39] Their poor solubility
in some solvents such as pentane limited full comparisons of all of
the macrocycles, but in <span class="Chemical">benzene, THF and CHCl3, their λmax and εmax were determined.
Compounds 1a and 2a were not sufficiently soluble in pentane
to record UV–vis absorption spectra, but the <span class="Chemical">alkyl-substituted
cyclooligomers were. Compound 1b exhibited an absorption
maximum at 296 nm, with shoulders near 264 and 330 nm. Cyclotetramer 2b exhibited two nearly equally intense absorptions at 282
and 301 nm, and these two maxima were observed in other solvents as
well. Cyclotrimer and cyclodimer 2b and 2c exhibited more similar spectra in pentane, with single dominant
absorption maxima at 312 and 306 nm, respectively. It should be noted
that accurate molar absorptivities were not obtained for 2b and 2c because of the formation of insoluble precipitate
during the measurement of the spectra in pentane.
All of the
macrocycles were more soluble in benzene, and their
absorption spectra are shown in Figure 4. The
spectra of linear trimers 23a and 23b were
also obtained in <span class="Chemical">benzene. The λmax of biphenylene
linear trimer 23a, 299 nm, does not change appreciably
upon cyclization to 1a, which has a λmax of 298 nm. Alternatively, the λmax of terphenylene
linear trimer 23b, 295 nm, is shifted bathochromatically
by 8 nm upon cyclization to cyclic trimer 2a (λmax = 303 nm). This could arise from an increase in conjugation
upon moving from the linear to the cyclic system.[40] Both 1b and 2b are red-shifted
by 5–6 nm compared to their unsubstituted analogs, 1a and 2a. Cyclic tetramer 1c is also red-shifted
6 nm compared to cyclic trimer 1b and has a much broader
and less intense UV absorption band. All of the terphenylene macrocycles
also showed broad absorptions, but cyclic dimer 2c and
cyclic trimer 2b had very similar spectra. The absorption
spectra of the macrocycles in THF show similar trends to those seen
in the less polar benzene and pentane.
Figure 4
UV–vis absorbance
spectra of macrocycles in benzene.
UV–vis absorbance
spectra of macrocycles in benzene.All of the terphenylene macrocycles 2a–c exhibit a bathochromatic shift in their absorption maxima
in <span class="Chemical">CHCl3 compared to THF, while no such shift is observed
for the biphenylene macrocycles 1a–c. Just as was observed in benzene, the λmax of linear
trimer 23a, 298 nm, is very similar to that of cyclic
trimer 1a, 297 nm, while terphenylene linear trimer 23b has a λmax of 293, 10 nm blueshifted
compared to the cyclic trimer 2a which has a λmax of 303 nm. Alkyl substitution again redshifts the λmax of cyclic trimers, from 297 nm for 1a to 302
nm for 1b and from 303 for 2a to 315 nm
for 2b, which was the largest λmax observed
in the solvents examined. As observed in previous solvents, biphenyl
cyclotetramer 1c exhibits two λmax at
286 and 308 nm, and cyclic dimer 2c exhibits a broad
maximum with a relatively small molar absorptivity (Figure 5).
Figure 5
UV–vis absorption spectra of macrocycles in CHCl3.
UV–vis absorption spectra of macrocycles in CHCl3.There is little to no solvent
dependence on absorption for macrocycles 1a–c and 2a–c. cyclotrimers 1a, 1b and 2a or for cyclotetramer 1c or cyclodimer 2c. Only substituted <span class="Chemical">biphenylenecyclotrimer 1b and terphenylenecyclotrimer 2b exhibited a significant
solvatochromic shifts, and while cyclotetramer 1c exhibits
two nearly identical λmax in pentane, THF and chloroform,
it has only a single broad λmax in benzene.
The relationship between the structure of the macrocycle and its
absorption spectrum should depend on the extent of conjugation around
the macrocyclic ring. The three central <span class="Chemical">p-phenylene
aromatic rings of the terphenylene moiety in 2b are ∼47°
out of the macrocyclic plane, as are the three p-phenylenes
in 1b. It is possible that the conjugation around the
macrocyclic ring is not interrupted to a significant extent, thus
causing 2b to exhibit a more red-shifted λmax compared to 1b which has a smaller π
system. This trend exists in all solvents tested, although the extent
of the shift increases as solvent polarity decreased. CHCl3 and THF show a shift of 1–2 nm each, while nonpolar solvents
benzene and pentane cause a larger red shift of 9 and 18 nm, respectively.
Several groups have examined the varying effects of ring strain
on absorption properties of conjugated ethynylic systems.[41] In the case of the biphenylene and <span class="Chemical">terphenylene
systems, ring strain is accompanied with perturbation of the aryl–aryl
dihedral angles. The structures and energies predicted by the computations
described above for cyclic trimer 1a and cyclic tetramer 1e suggest that all biphenylene macrocycles synthesized, 1a, 1b, and 1c, are all essentially
strain-free. The aryl–aryl dihedral angle is also nearly identical
in 1a and 1e, and both the planar cyclic
trimer and puckered cyclic tetramer differ only in the disposition
of the identical biphenylene–ethynylene units; these units
are coplanar in the cyclic trimer and are not in the cyclic tetramer.
In all solvents examined excepting benzene where the solvent may have
partially obscured the spectrum, trimer 1b showed a single,
broad λmax at around 300 nm, and tetramer 1c showed two λmax, one ∼15 nm shorter and
another ∼5 nm longer wavelength (Table 3). It should be noted
that the two-dimensional π-network is disrupted in the cyclotetramer
by the ring pucker, which may explain the lower molar absorptivities
of the cyclic tetramer in each solvent examined. Cyclic dimer 2c and cyclic trimer 2b exhibit very similar
spectra in benzene and THF, and slightly shifted spectra in pentane
and chloroform. Deformation from planarity by the ethynyl-substituted p-phenylene ring in the terphenyl cyclotrimer, 2b is amplified from 6° to near orthongonality, 87°, by removing
a single repeat unit to form the terphenyl cyclodimer 2c. Despite this interruption in the cyclic π-nework, the UV–vis
spectra are similar. This suggests that either π-conjugation
is not occurring in both systems and absorptions are a result of individual
subunits or that delocalization about the macrocycles is not disrupted.
In all cases, 2b exhibits greater molar absorptivity
which could be the result of a larger number of absorbing moieties
in the cyclic trimer versus the cyclic dimer.
Solutions of all of the macrocycles 1 and 2 as well as the linear trimers 23a and 23b are highly fluorescent (Figure 6). The emission
properties of these compounds were analyzed in benzene and their fluorescence
quantum yields were determined using <span class="Chemical">pyrene as a standard. All macrocycles
displayed large Stokes shifts which are indicative of large conjugated
arylene ethynylene macrocycles (see Table 4).[40]
Figure 6
Fluorescence spectra in benzene of macrocycles
and linear trimers.
Table 4
Absorbance and Emission
Optical Properties
of Macrocycles and Linear Trimers
λabs (nm)
λem (nm)
Stokes Shift
(nm)
Φ
23a
300
381
81
1a
298
418
120
0.03
1b
303
422
119
0.02
1c
309
382
73
0.04
401
92
23b
296
381
85
399
103
2a
303
390
87
0.04
406
103
2b
309
387
78
0.06
405
96
2c
307
387
80
0.05
405
98
Fluorescence spectra in benzene of macrocycles
and linear trimers.The absorbance spectrum
of biphenylene linear trimer 23a and <span class="Chemical">biphenylenecyclic
trimer 1a are very similar,
but the single emission maximum exhibited by linear trimer 23a at 381 nm shifts to 418 nm upon ring closure to form 1a. No such large shift is observed upon ring closure of terphenylene
linear trimer 23b with an emission maxima of 381 and
399 nm to terphenylenecyclic trimer 2a with emission
maxima of 390 and 406 nm. Comparison of the fluorescence spectra of 1a to 1b and 2a to 2b indicates that n-octyl substitution causes only
small shifts in the emission maxima. Cyclic tetramer 1c displays two λem at 382 and 401 nm, at much shorter
wavelengths than 1a and 1b; the puckering
of the macrocyclic ring not only affects the absorbance spectrum of
1c, but its emission spectrum. All terphenylene macrocycles emit two
λem at similar wavelengths to 1c, at ∼390
and ∼405 nm. Cyclic dimer 2c shows similar emission
properties to that of the cyclic trimer even though the p-phenylenes are orthogonal to the o-phenylene. The
dihedral angles of the terphenyl moiety do not appear to perturb the
optical properties of these systems.
While 1a and 1b exhibit Stokes shifts
of 120 nm, all of the other macrocycles exhibit Stokes shifts of ∼80
and 100 nm. The larger Stokes shifts for the biphenylene cyclic trimers
could indicate a more complete planarization of the macrocycle in 1a and 1b than the other macrocycles; extending
the conjugation throughout the <span class="Chemical">biphenylenecyclotrimers requires only
a single close H–H and a single close C–H contact, while
the biphenylene cyclotetramer cannot achieve planarity and greater
conjugation without involving a significant amount of angle strain
and the terphenylenes would require four close H–H contacts
to achieve full planarity and conjugation.
One possible cause
for the Stokes shifts observed could be aggregation
of the macrocycles in solution, which has been observed for similar
structures. To test this hypothesis, we obtained the NMR spectra of
solutions of 1b in benzene at concentrations higher than
those used to obtain the fluorescence spectrum of 1b (Figure 7). If 1b had been aggregating in the
0.066 mM solution used in the fluorescence experiment, it should be
doing so at higher concentrations as well. Since the NMR chemical
shifts of all of the aromatic protons in 1b show no concentration
dependence above that concentration, it seems likely that no aggregation
would have taken place at the lower concentration.
Figure 7
Concentration-dependent
NMR chemical shifts of 1b in
C6D6; fluorescence spectra were observed at
0.066 mM.
Concentration-dependent
NMR chemical shifts of 1b in
C6D6; fluorescence spectra were observed at
0.066 mM.All macrocycles exhibit fairly
low quantum yields (Φ) in
benzene compared to larger <span class="Chemical">arylene ethynylene macrocycles (Table 4).[13] However, these systems do not contain long linear conjugated
pathways which has been correlated to high quantum yields.[28] Quantum yields for the biphenyl macrocycles
range from 0.02 for 1b to 0.04 for 1c while
the quantum yields for terphenyl macrocycles are slightly more efficient
ranging 0.04 for both 2a and 23b to 0.06
for 2b.
Conclusions
In an effort to synthesize
precursors of short carbon single-walled
nanotubes, <span class="Chemical">cyclic trimers containing biphenylene and p-terphenylene ethynylene units were constructed via linear, split-pool
approaches to give unsubstituted macrocycles 1a and 2a. More soluble alkyl-substituted analogues 1b and 2b were also synthesized, utilizing statistical
macrocyclizations of monomers made possible by the increased solubility.
These statistical macrocyclizations also yielded a cyclotetramer 1c in the biphenylene system and a cyclodimer 2c in the p-terphenylene system; these alternative
cyclooligomers were separable from the cyclotrimers by exhaustive
column chromatography. Computational geometry optimizations suggest
that the cyclic dimer is not energetically accessible in the statistical
macrocyclization of 16b, while a lesser degree of angle
strain in the terphenylene monomer 17b allows formation
of cyclodimer 2c. All of the macrocycles obtained absorb
around 300 nm, but the cyclotrimers 1a and 1b exhibit larger Stokes shifts in their fluorescence emission spectra
than the other macrocycles observed. Further studies are currently
being conducted to determine if multiple cycloadditions can be carried
out on the alkynes present in these macrocycles to convert them into
arylene cyclooligomers that can be oxidized to make carbon nanobelts.
Experimental Section
3,3-Diethyl-1-(4-iodophenyl)triaz-1-ene
(5)[42]
4-Iodoaniline
(10.004 g, 45.67 mmol,
1.00 equiv) was dissolved in 380 mL of <span class="Chemical">acetonitrile, 160 mL of water,
and 16.0 mL of concentrated hydrochloric acid and cooled to 0 °C.
A solution of 1.1 equiv of NaNO2 (3.321 g, 48.14 mmol,
1.05 equiv) in 20 mL water was added slowly via syringe and the mixture
stirred 45 min at 0 °C. The mixture was transferred to a flask
containing K2CO3 (21.001 g, 151.9 mmol, 3.32
equiv) and diethylamine (9.5 mL, 91.81 mmol, 2.00 equiv) in 250 mL
of H2O at 0 °C. The reaction was allowed to slowly
warm to room temperature and stirred for 2 h before being extracted
with diethyl ether. The combined organic layers washed with brine,
dried over magnesium sulfate, filtered, and concentrated in vacuo.
The crude product was then purified by flash chromatography using
5% diethyl ether in hexanes to afford 13.43 g of the desired product
as an orange oil (97% yield): 1H NMR (500 MHz, CDCl3) δ 7.61 (d, J = 8.8 Hz, 2H), 7.16
(d, J = 8.8 Hz, 2H), 3.74 (q, J = 7.3, 4H), 1.25 (br t, 6H); 13C NMR (125 MHz, CDCl3) δ 150.9, 137.6, 122.4, 88.9; IR (cm–1) 2974, 2933, 2871, 1475, 1420, 1391, 1341, 1238, 1198, 1108, 1093,
1001, 828; MS (CI-isobutane) [MH+] 304.6 m/z.
A 25 mL round-bottomed
flask
was charged with 1-bromo-2-iodobenzene (2.697 g, 9.53 mmol, 1.00 equiv),
<span class="Chemical">Cl2Pd(PPh3)2 (0.198 g, 0.282 mmol,
0.03 equiv), CuI (0.051 g, 0.267 mmol, 0.03 equiv), triisopropylsilylethynylene
(2.3 mL, 10.25 mmol, 1.07 equiv), and 20 mL of 1:1 THF/Et3N. The solution was stirred at room temperature for 24 h before being
concentrated in vacuo. The crude residue was dissolved in diethyl
ether and washed with saturated NH4Cl (aq). The organic
layers were dried over MgSO4, filtered, and concentrated
in vacuo. Purification of the crude material by flash column chromatography
yielded 3.18 g of the product as a yellow oil (99% yield): 1H NMR (500 MHz, CDCl3) δ 7.56 (d, J = 8.2 Hz, 1H), 7.50 (d J = 7.74 Hz, 1H), 7.22 (t, J = 7.74 Hz, 1H), 7.13 (t, J = 7.95 Hz,
1H), 1.13 (br s, 21H); 13C NMR (125 MHz, CDCl3) δ 134.1, 132.6, 129.6, 127.0, 126.0, 125.9, 105.0, 96.4,
18.9, 11.6; IR (cm–1) 2943, 2865, 2161, 1464, 1220,
1047, 908, 883, 834, 753, 678; MS (CI-isobutane) [MH+]
295.5, 296.4 m/z
Method A: 1,1-Diethyl-3-(4-iodophenyl)triazene
(1.931 g, 6.370 mmol, 1.00 equiv) was combined with bis(pinacolato)<span class="Chemical">diboron
(1.947 g, 7.667 mmol, 1.20 equiv), Cl2Pd(dppf) (0.143 g,
0.195 mmol, 0.03 equiv), and KOAc that had been dried under vacuum
(1.875 g, 19.11 mmol, 3.00). Deoxygenated DMSO (52 mL) was added,
and the reaction was heated to 80 °C and monitored by TLC (5%
diethyl ether in hexanes). Upon consumption of triazene starting material,
the reaction was diluted with water and extracted with EtOAc. The
organic layers were combined, washed with satd NH4Cl (aq),
dried over MgSO4, and concentrated in vacuo. Crude material
was purified by flash chromatography using 5% diethyl ether in hexanes
as the eluent to afford 1.931 g (74% yield) of the desired product
as a white solid, mp 119–120 °C. The product can also
be purified by filtration through a silica plug (10% ethyl acetate
in hexanes) followed by recrystallization from 2-propanol: 1H NMR (500 MHz, CDCl3) δ 7.77 (d, J = 8.3 Hz, 2H), 7.40 (d, J = 8.3 Hz, 2H), 3.77 (q, J = 7.3, 4H), 1.35 (s, 12H), 1.27 (br t, J = 6.8 Hz, 6H); 13C NMR (125 MHz, CDCl3) δ
153.6, 135.5, 119.7, 83.5, 24.8; IR (cm–1) 2979,
1602, 1391, 1351, 1320, 1139, 1087, 857, 655; HRMS (ESI) m/z calc’d for C16H26BN3O2H ([M + H+]) 304.2196, found
304.2194.
Method B: 6 N HCl (27.10 mL, 162.51 mmol,
8.9 equiv) was added dropwise to a solution of 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline
(4.035 g, 18.42 mmol, 1 equiv) in 62.40 mL of <span class="Chemical">diethyl ether, 48.00
mL of tetrahydrofuran, and 9.60 mL of acetonitrile chilled to −5
°C in an ice–salt bath. A solution of NaNO2 (4.3255 g, 62.69 mmol, 3.5 equiv) in 21.60 mL of water and 9.69
mL of acetonitrile was added dropwise, and the reaction was stirred
at −5 °C for 30 min before being slowly transferred via
cannula to a flask containing diethylamine (43.45 mL, 419.98 mmol,
23 equiv) and K2CO3 (12.640 g, 91.46 mmol, 5
equiv) in 79.20 mL of water and 174.00 mL of acetonitrile at 0 °C.
The reaction was stirred for 45 min while being warmed to room temperature
before being diluted with satdNaCl and extracted with Et2O. The organics were washed with H2O, dried over MgSO4, filtered, and concentrated in vacuo to give a brown crystal.
Crude material was purified by extraction with hexanes and concentration
in vacuo to afford 4.7567 g (85% yield) of orange crystals: 1H NMR (500 MHz, CDCl3) δ 7.77 (d, J = 8.3 Hz, 2H), 7.40 (d, J = 8.3 Hz, 2H), 3.77 (q, J = 7.3, 4H), 1.35 (s, 12H), 1.27 (br t, J = 6.8 Hz, 6H); 13C NMR (125 MHz, CDCl3) δ
153.6, 135.5, 119.7, 83.5, 24.8; IR (cm–1) 2979,
1602, 1391, 1351, 1320, 1139, 1087, 857, 655; HRMS (ESI) m/z calcd for C16H26BN3O2H ([M + H+]) 304.2196, found 304.2194.
(2-Bromophenylethynyl)triisopropylsilane
(2.067 g, 6.13 mmol, 1.00 equiv) was added to a flask fitted with
a sealed reflux condenser and charged with 3,3-diethyl-1-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)triaz-1-ene
(2.787 g, 9.19 mmol, 1.5 equiv), powdered <span class="Chemical">potassium phosphate (tribasic)
(6.51 g, 30.65 mmol, 5 equiv), and PdCl2(dppf) (0.150 g,
0.184 mmol, 0.03 equiv). The flask was purged with nitrogen, and 50
mL of dexoygenated 1,2-dimethoxyethane was added via syringe. The
reaction was stirred at reflux for 6–24 h, until TLC indicated
completion (some side products run at the same R as the bromide, making exact assignment
of completion difficult). The reaction mixture was then cooled, and
the DME was removed in vacuo. The reaction mixture was then extracted
with water and diethyl ether. The combined organic layers were washed
with brine, dried over magnesium sulfate, filtered, and concentrated
in vacuo. Purification was effected by flash column chromatography
over neutral alumina with a mobile phase of 5% diethyl ether in hexanes
to obtain 2.66 g of the biphenyl product as an orange oil (95% yield): 1H NMR (500 MHz, CDCl3) δ 7.59 (d, J = 8.3 Hz, 3H), 7.43 (d, J = 8.3 Hz, 2H),
7.38 (d, J = 7.8 Hz, 1H), 7.33 (t, J = 7.3 Hz, 1H), 7.23 (t, J = 7.8 Hz, 1H), 3.76 (q, J = 7.3 Hz, 4H), 1.27 (t, J = 7.3 Hz, 6H),
1.03 (s, 21H); 13C NMR (125 MHz, CDCl3) δ
150.48, 144.0, 137.1, 133.9, 129.7, 129.3, 128.4, 126.5, 121.7, 119.9,
106.6, 93.9, 18.6, 11.3; IR (cm–1) 2940, 2864, 2151,
1464, 1397, 1330, 1235, 1096, 883, 835, 761, 677; HRMS (ESI) m/z calcd for C27H39N3SiH ([M + H+]) 434.2992, found 434.2991.
Compound 3a (1.855 g, 4.277 mmol,
1.00 equiv) was dissolved in 10 mL of methyl iodide in a sealable
reaction flask, degassed, backfilled with <span class="Chemical">nitrogen, sealed, and heated
to 125 °C for 44 h. After cooling, the methyl iodide was removed
by evaporation and the product purified by flash chromatography over
silica with 5% diethyl ether in hexanes to isolate 1.950 g of a yellow
oil (99% yield): 1H NMR (500 MHz, CDCl3) δ
7.70 (d, J = 8.3 Hz, 2H), 7.59 (d, J = 7.8 Hz, 1H), 7.27–7.37 (m, 5H), 1.01 (s, 21H); 13C NMR (125 MHz, CDCl3) δ 143.1, 140.1, 137.0, 133.7,
131.2, 129.0, 128.5, 127.2, 121.9, 105.9, 94.6, 93.1, 18.5, 11.3;
IR (cm–1) 2940, 2863, 2152, 1469, 1386, 1000, 883,
820, 758, 677; HRMS (EI) m/z calcd
for C23H29ISi ([M+]) 460.1083, found
460.1091.
2-Ethynyl-1-(4-iodophenyl)benzene (16a)
TBAF (1 M) in <span class="Chemical">THF (2.0 mL, 2.00 mmol, 4.35 equiv) was added to a
solution of 9 (0.212 g, 0.460 mmol, 1.00 equiv) in 3
mL of THF. The reaction was stirred at room temperature and monitored
by TLC. Upon disappearance of starting material, the reaction was
concentrated to one-third of its original volume, diluted with 25
mL of H2O, and extracted with diethyl ether (3 × 50
mL). The organic layers were combined, dried over MgSO4, and concentrated in vacuo. The crude material was purified via
flash chromatography using 5% diethyl ether in hexane to afford 0.134
g (96% yield) of a reddish oil: 1H NMR (500 MHz, CDCl3) δ 7.78 (d, J = 7.0 Hz, 2H), 7.64
(d, J = 7.5 Hz, 1H), 7.42 (t, J =
6.5 Hz, 1H), 7.37–7.34 (m, 4H), 3.08 (s, 1H); 13C NMR (125 MHz, CDCl3) δ 143.1, 139.7, 137.1, 133.9,
131.1, 129.2, 129.0, 127.3, 120.3, 93.6, 80.6; IR (neat, cm–1) 3274, 3061, 1583,1472; HRMS (ESI) m/z calcd for C14H10I ([M + H+]) 304.9827,
found 304.9821.
Attempted Synthesis of Cyclotri(ethynylene)(biphenyl-2,4′-diyl)
(1a)
16a (0.060 g, 0.197 mmol,
1.00 equiv), <span class="Chemical">Cl2Pd(PPh3)2 (0.007
g, 0.010 mmol, 0.05 equiv),
and CuI (0.004 g, 0.020 mmol, 0.11 equiv) were combined and dissolved
in 10.6 mL of THF and 0.2 mL of Et3N. The reaction was
stirred for 10 days at room temperature before being diluted with
H2O and extracted with Et2O (3 × 20 mL).
The organics were washed over brine, dried over MgSO4,
filtered, and concentrated in vacuo. The crude material was run through
a flash column to afford a white solid mixture of cyclic and linear
oligomers that resisted further purification.
Compound 3a (0.655 g, 1.510
mmol,
1 equiv) was dissolved in 5 mL of methanol. A solution of 1 M <span class="Chemical">TBAF
in THF (7.6 mL, 7.50 mmol, 4.97 equiv) was added; the reaction was
then stirred at room temperature and monitored by TLC. Upon disappearance
of starting material, the reaction was concentrated to one-third its
original volume, diluted with 50 mL of H2O, and extracted
with diethyl ether (3 × 50 mL). The organic layers were combined,
dried over MgSO4, and concentrated in vacuo. The crude
material was purified via flash chromatography using 5% diethyl ether
in hexane to afford 0.376 g (90% yield) of a yellow oil: 1H NMR (500 MHz, CDCl3) δ 7.62 (d, J = 8.0 Hz, 1H), 7.59 (d, J = 8.2 Hz, 2H), 7.50 (d, J = 8.2 Hz, 2H), 7.41–7.40 Hz (m, 2H), 7.30–7.27
(m, 1H), 3.80 (q, J = 7.0 Hz, 4H), 3.06 (s, 1H),
1.30 (t, J = 7.0 Hz, 6H); 13C NMR (125
MHz, CDCl3) δ 150.6, 144.4, 136.9, 133.8, 129.7,
129.5, 128.9, 126.6, 120.3, 119.9, 83.3, 80.0. IR (cm–1) 3284, 1330, 1229, 837; HRMS (photospray ionization) m/z calcd for C18H20N3 ([M + H+]) 278.1657, found 278.1664.
A 50 mL round-bottomed flask was charged
with 9 (0.223 g, 0.484 mmol, 1.00 equiv), 19a (0.180 g, 0.649 mmol, 1.34 equiv), and <span class="Chemical">Cl2Pd(PPh3)2 (0.020 g, 0.0285 mmol, 0.06 equiv) and flushed
with N2. To this 20 mL of deoxygenated THF/Et3N (1:1 v/v) was added, and the reaction flask was sparged with N2 for 5 min. CuI was added and the reaction stirred at 40 °C
for 18 h. Upon completion, the reaction was diluted with 25 mL of
H2O and extracted with diethyl ether (3 × 25 mL).
The organics were combined, washed with satd NH4Cl, dried
over MgSO4, and concentrated in vacuo. The crude material
was purified via flash chromatography using 5% diethyl ether in hexanes
to give 0.226 g (77%) of the desired product as a yellow oil: 1H NMR (500 MHz, CDCl3) δ 7.72 (d, J = 8.5 Hz, 2H), 7.70 (d, J = 7.9 Hz, 1H),
7.62 (d, J = 7.8 Hz, 1H), 7.57–7.54 (m, 4H),
7.48 (d, J = 8.0 Hz, 1H), 7.43 (d, J = 7.9 Hz, 2H), 7.40 (d, J = 8.3 Hz, 1H), 7.38–7.27
(m, 4H), 3.82 (q, 7.2 Hz, 4H), 1.31 (t, J = 7.1 Hz,
6H), 1.05 (s, 21H); 13C NMR (125 MHz, CDCl3)
δ 150.6, 143.7, 143.5, 140.2, 137.2, 133.8, 133.0 130.9, 129.8,
129.5, 129.2, 129.1, 128.5, 127.1, 126.7, 122.5, 121.8, 121.4, 119.9,
106.0, 94.4, 92.3, 89.8, 18.55, 11.3; IR (cm–1)
2942, 2860, 2356, 1460, 1334, 1229, 830; HRMS (MALDI) m/z calcd for C41H48N3Si ([M + H+]) 610.3618, found 610.3616.
Compound 20a (0.206 g, 0.338
mmol, 1.00 equiv) and 4 mL of MeI were placed in a sealed tube flask
under an atmosphere of N2. The reaction was heated to 125
°C for 18 h before being allowed to cool to room temperature.
Excess MeI was allowed to evaporate. The residue was dissolved in
10 mL of CH2Cl2, washed with <span class="Chemical">H2O,
dried over MgSO4, and concentrated in vacuo. The crude
product was purified via flash chromatography using 5% EtOAc in hexanes
as the eluent and afforded 0.202 g (94% yield) of the desired product
as a yellow oil: 1H NMR (500 MHz, CDCl3) δ
7.81 (d, J = 8.5 Hz, 2H), 7.69 (d, J = 7.7 Hz, 1H), 7.62 (d, J = 7.5 Hz, 1H), 7.59 (d, J = 8.0 Hz, 2H), 7.46 (d, J = 8.0 Hz, 2H),
7.41–7.38 (m, 2H), 7.37–7.35 (m, 5H), 7.32–7.29
(m, 1H) 1.05 (s, 21H); 13C NMR (125 MHz, CDCl3) δ 143.3, 142.5, 140.5, 140.0, 137.0, 133.8, 133.0, 131.3,
130.9, 129.3, 129.2, 128.6, 128.5, 127.4, 127.2, 122.1, 121.8, 121.5,
106.0, 94.5, 93.4, 92.8, 89.1, 18.6, 11.3; IR (cm–1) 2940, 2865, 2148, 1467, 1000, 756; HRMS (ESI) m/z calcd for C37H38ISi ([M
+ H+]) 637.1787, found 637.1777.
Compound 23a (0.039 g, 0.0463 mmol, 1.00 equiv) was dissolved in 0.25 mL of THF
before 0.100 mL of 1 M <span class="Chemical">TBAF in THF (0.100 mL, 0.100 mmol, 2.16 equiv)
was added. After 5 min, the reaction showed no signs of starting material
by TLC and was diluted with Et2O. The organics were washed
with satd NH4Cl (aq), dried over MgSO4, filtered,
and rotovapped. The crude material was purified by flash chromatography
using 5% EtOAc in hexanes to afford the desired compound which was
used in the following reaction without further characterization.
Cyclotri(ethynylene)(biphenyl-2,4′-diyl) (1a)
Compound 24a (assuming 100%
conversion in previous reaction: 0.032 g, 0.0463 mmol, 1.00 equiv)
was dissolved in 1 mL of Et3N and charged in a gastight
syringe in a syringe pump. <span class="Gene">Pd(dba)2 (0.039 g 0.068 mmol,
1.42 equiv), CuI (0.015 g, 0.079 mmol, 1.71 equiv), and PPh3 (0.076 g, 0.290 mmol, 6.26 equiv) were dissolved in 11.6 mL of Et3N. The iodoalkyne trimer was added at a rate of 0.1 mL per
hour, and the reaction was allowed to stir for an additional 12 h
after the addition was complete. The reaction was diluted with sat
NH4Cl (aq) and extracted with EtOAc. The organic phases
were dried over MgSO4, filtered, and concentrated in vacuo.
The crude material was purified using 15% CH2Cl2 in hexanes to afford 11 mg (45% yield) of the desired macrocycle
as a white solid: mp 282–291 °C; 1H NMR (500
MHz, CDCl3) δ 7.75 (d, J = 8.4 Hz,
6H), 7.67 (d, J = 7.4 Hz, 3H), 7.50–7.48 (m,
9H), 7.45 (t, J = 7.8 Hz, 3H), 7.36 (t, J = 7.4 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ
143.7, 140.9, 133.4, 131.5, 130.0, 129.9, 129.5, 128.1, 123.1, 122.2,
93.4, 90.3; HRMS (MALDI) m/z calcd
for C42H24 ([M+]) 528.1872, found
528.1864.
Compound 9 (1.923 g, 4.18
mmol, 1.00 equiv) was added to a flask with 6 (1.90 g,
6.27 mmol, 1.5 equiv), boronate, <span class="Chemical">K3PO4 (4.52
g, 21.3 mmol, 5.1 equiv), and PdCl2(dppf) (0.10 g, 0.125
mmol, 0.03 equiv). The flask was purged with nitrogen and 30 mL of
deoxygenated DME added. The reaction was refluxed for 20 h and cooled
to room temperature, the solvent was removed in vacuo, and the organic
products were extracted from water with diethyl ether. The combined
organic layers were washed with brine, dried over magnesium sulfate,
filtered, and concentrated in vacuo. Purification over neutral alumina
with 25% methylene chloride in hexanes afforded 1.38 g of the product
as a pale yellow solid: mp 110–111 °C (65% yield);. 1H NMR (500 MHz, CDCl3) δ 7.58–7.65
(m, 7H), 7.51 (d, J = 8.3 Hz, 2H), 7.36–4.42
(m, 2H), 7.29 (t, J = 7.3 Hz, 1H), 3.79 (q, J = 7.3 Hz, 4H), 1.29 (t, J = 7.3 Hz, 6H),
1.01 (s, 21H); 13C NMR (125 MHz, CDCl3) δ
150.6, 144.0, 140.0, 139.1, 137.7, 133.7, 129.7, 129.2, 128.4, 127.5,
126.8, 126.4, 122.0, 120.8, 106.4, 94.1, 18.6, 11.3; IR (cm–1) 2940, 2864, 2361, 2151, 1463, 1329, 1233, 1092, 995, 882, 823,
764, 674, 639; HRMS (ESI) m/z calcd
for C33H43N3SiH ([M + H+]) 510.3305, found 510.3309.
Compound 4a (0.096
g, 0.188 mmol, 1 equiv) was dissolved in 2.5 mL of methyl iodide in
a sealable reaction flask, degassed, backfilled with <span class="Chemical">nitrogen, sealed,
and heated to 125 °C for 40 h. After cooling, the methyl iodide
was removed by evaporation and the product purified by flash chromatography
over neutral alumina with 50% methylene chloride in hexanes to afford
0.092 mg of the product as a yellow solid: mp 81–83 °C
(91% yield); 1H NMR (500 MHz, CDCl3) δ
7.77 (d, J = 8.3 Hz, 2H), 7.64 (d, J = 8.3 Hz, 2H), 7.61 (d, J = 7.8 Hz, 1H), 7.54 (d, J = 8.3 Hz, 2H), 7.27–7.38 (m, 5H), 1.00 (s, 21H); 13C NMR (125 MHz, CDCl3) δ 143.7, 140.5, 140.1,
138.9, 137.9, 137.8, 129.9, 128.91, 128.87, 128.5, 127.0, 126.4, 122.0,
106.2, 95.2, 93.0, 18.6, 11.3. IR (cm–1) 2939, 2862,
2152, 1473, 1384, 1064, 1000, 882, 837, 812, 578, 662; HRMS (photospray
ionization) m/z calcd for C29H33SiI ([M+]) 536.1396, found 536.1383.
1-(4-(4-Iodophenyl)phenyl)-2-ethynylbenzene (17a)
Compound 18b (0.229 g, 0.427
mmol, 1.00 equiv) was stirred with TBAF (1 M in <span class="Chemical">THF) (5.55 mL, 5.55
mmol, 13 equiv) with 4 mL of THF and 1 mL of methanol for 3 days at
room temperature. The solvent was removed in vacuo, and the organic
products were extracted from water with methylene chloride. The combined
organic layers were dried over magnesium sulfate, filtered, and concentrated
to produce 0.127 g of an orange solid (78% yield): 1H NMR
(500 MHz, CDCl3) δ 7.78 (d, J = 8.6 Hz, 2H), 7.68 (d, J = 8.1 Hz, 2H), 7.61–7.65
(m, 3H), 7.38–7.43 (m, 4H), 7.30–7.34 (m, 1H), 3.08
(s, 1H); 13C NMR (125 MHz, CDCl3) δ 143.7,
140.2, 139.6, 139.1, 137.8, 134.0, 129.7, 129.5, 129.0, 128.9, 127.1,
126.4, 120.3, 93.1, 83.0, 80.4; HRMS (photospray ionization) m/z calcd for C20H14I ([M + H+]) 381.0140, found 381.0151
Compound 22b (0.067 g, 0.066 mmol, 1.00 equiv) was dissolved in 2.5 mL of methyl
iodide in a sealable reaction flask, degassed, backfilled with <span class="Chemical">nitrogen,
sealed, and heated to 125 °C for 40 h. After cooling, the methyl
iodide was removed by evaporation. The residue was filtered through
a silica plug with methylene chloride to provide 0.068 g of the product
iodide (99% yield) as a colorless waxy solid, which was reacted without
further purification since poor solubility precluded further chromatography: 1H NMR (500 MHz, CDCl3) δ 7.78 (d, J = 8.8 Hz, 6H), 7.52–7.70 (m, 15H), 7.35–7.48
(m, 14H), 7.29 (m, 1H), 0.99 (s, 21H); 13C NMR (125 MHz,
CDCl3) δ 143.7, 143.1, 140.7, 140.5, 140.3, 139.9,
139.2, 139.1, 139.0, 137.9, 133.7, 133.0, 131.8, 131.7, 129.9, 129.9,
129.8, 129.4, 128.9, 128.6, 127.2, 126.9, 126.8, 126.4, 126.4, 126.3,
122.3, 122.2, 122.0, 121.5, 106.2, 94.1, 93.1, 92.3, 90.1, 18.6, 11.3;
IR (cm–1) 2921, 2860, 2360, 2342, 2155, 1473, 1441,
1384, 1000, 822, 814, 761, 667.
Cyclotri(ethynylene)(p-terphenyl-2,4″-diyl)
(2a)
Method A (Sonogashira Cyclization)
Compound 23b (0.070 g, 0.067 mmol, 1.00 equiv)
was stirred with 4.0
mL of THF, 6 drops of <span class="Chemical">methanol, and TBAF (1 M in THF) (0.20 mL, 0.20
mmol, 3.0 equiv) for 48 h, during which time a precipitate was observed
in the reaction. Extraction from water with methylene chloride, drying
of the organic layers with magnesium sulfate, filtration, and concentration
in vacuo yielded 0.53 g of crude trimer (90% yield), which was used
in the next step without further purification or characterization.
The crude linear iodoarylethyne trimer was dissolved in 10 mL of deoxygenated
THF and placed in a syringe pump. 1.5 equiv of Pd(dba)2 (0.046 g, 0.080 mmol, 1.5 equiv), 1.3 equiv of CuI (0.013 g, 0.068
mmol, 1.3 equiv), and 5.9 equiv of triphenylphosphine (0.082 g, 0.313
mmol, 5.9 equiv) were dissolved in 5.0 mL of deoxygenated triethylamine
and 10 mL of deoxygenated THF. The catalyst solution was heated to
reflux under nitrogen, and the trimer solution was added at 0.6 mL/h,
followed by continued refluxing overnight. The solvents were then
removed in vacuo and the organic products extracted from saturated
ammonium chloride solution with methylene chloride, washed with water
and brine, and concentrated. The solids were then filtered with Whatman
quantitative filter paper (1 μm pore size) and washed with methylene
chloride; centrifugation in methylene chloride yielded 0.008 g (21%
yield) of a colorless solid floating on top of the supernatant. No
melting transition was observed below 300 °C: 1H NMR
(500 MHz, CDCl3) δ 7.81 (d, J = 8.3
Hz, 2H), 7.70 (d, J = 7.8 Hz, 2H), 7.69 (d, J = 6.3 Hz, 1H)7.64 (d, J = 8.3 Hz, 2H),
7.52 (d, J = 7.8 Hz, 1H), 7.49 (d, J = 7.8 Hz, 2H), 7.44 (t, J = 6.8 Hz, 1H), 7.37 (t, J = 7.3 Hz, 1H); 1H NMR (500 MHz, C6D4Cl2) δ 7.82 (d, J = 8.0 Hz, 6H), 7.70 (d, J = 7.5 Hz, 3H), 7.67 (d, J = 8.0 Hz, 6H), 7.58 (d, J = 8.5 Hz, 6H),
7.51 (d, J = 8.5 Hz, 6H), 7.47 (d, J = 7.5 Hz, 3H), 7.36 (t, J = 7.3 Hz, 3H), 7.29 (t, J = 7.3 Hz, 3H); COSY (500 MHz, o-C6D4Cl2) δ 7.82 × 7.67, 7.70
× 7.29, 7.58 × 7.51, 7.47 × 7.36, 7.36 × 7.29;
HMQC (500 MHz, o-C6D4Cl2) δ 7.82 × 130.3, 7.70 × 133.0, 7.68 ×
126.6, 7.59 × 127.1, 7.52 × 132.0, 7.47 × 129.5, 7.36
× 128.9, 7.29 × 127.5; HMBC (o-500 MHz,
C6D4Cl2, selected peaks) δ
7.82 × 143.3, 7.82 × 139.5, 7.70 × 143.3, 7.70 ×
90.7, 7.68 × 140.4, 7.68 × 139.8, 7.59 × 139.5, 7.59
× 122.6, 7.52 × 140.4, 7.52 × 92.7, 7.47 × 139.8,
7.47 × 121.6, 7.36 × 143.3, 7.29 × 121.6; IR (cm–1) 3056, 3031, 2217, 1922, 1498, 1473, 1442, 1395,
1104, 1004, 819, 758, 733, 703; HRMS (MALDI) m/z calcd for C60H36 ([M+]) 756.2817, found 756.2822.
Method B (Sonogashira Cyclotrimerization)
Compound 17a (0.053 g, 0.139 mmol, 1.00 equiv) was
dissolved in 0.8
mL of THF and 0.1 mL of <span class="Chemical">triethylamine (both solvents distilled and
deoxygenated) with CuI (0.3 mg, 0.0016 mmol, 0.01 equiv) and PdCl2(Ph3P)2 (0.005 g, 0.007 mmol, 0.05 equiv)
and stirred at room temperature. The reaction was monitored by TLC
and periodically reloaded with catalysts and solvent until TLC failed
to indicate a significant change over a 24 h period. The solid precipitate
formed was filtered from solution and washed with methylene chloride
to yield a solid: 1H NMR (500 MHz, C6D4Cl2) δ 7.80 (d), 7.26–7.7.2 (m), 3.07 (s).
Method C (Sonogashira Cyclotrimerization)
Compound 17a (0.053 g, 0.139 mmol, 1.00 equiv) was dissolved in 7.5
mL of THF and 0.1 mL of <span class="Chemical">triethylamine (both solvents were distilled
and deoxygenated) with CuI (0.3 mg, 0.0016 mmol, 0.01 equiv) and Pd(Ph3P)4 (0.005 g, 0.007 mmol, 0.05 equiv) and stirred
at room temperature. The reaction was monitored by TLC and periodically
reloaded with catalysts and solvent until TLC failed to indicate a
significant change over a 24 h period. The solid precipitate formed
was filtered from solution and washed with methylene chloride to yield
20% yield of macrocycle 2a with slight contamination
evidenced by: 1H NMR (500 MHz, CDCl3) δ
7.78 (d, J = 7.8 Hz), 7.62 (d, J = 7.8 Hz).
2-Iodo-4-n-octylaniline
(11)
[BnN(CH3)3]·ICl2 (3.535 g,
10.15 mmol, 1.05 equiv) and CaCO3 (3.141 g, 31.38 mmol,
3.21 equiv) were added to a stirred solution of <span class="Chemical">4-n-octylaniline (1.995 g, 9.72 mmol, 1 equiv) in 80 mL of dry CH2Cl2 and 35 mL of anhydrous MeOH. The reaction stirred
at room temperature for 2 h prior to being vacuum filtered through
a pad of Celite. The filtrate was washed with satdNa2SO4 (40 mL) followed by satd NH4Cl (40 mL). The organics
were dried over MgSO4, filtered, and concentrated in vacuo
to give a brown oil that was purified by chromatography (10% ethyl
acetate in hexane on silica) to give 3.08 g of a brown oil (96% yield).
This product was used in subsequent reactions without further purification: 1H NMR (500 MHz, CDCl3) δ 7.43 (d, J = 1.9 Hz, 1H), 6.93 (dd, J = 1.9, 8.3
Hz, 1H), 6.65 (d, J = 8.3 Hz, 1H), 3.93 (br s, 2H),
2.44 (t, J = 7.3 Hz, 2H), 1.52 (m, 2H), 1.23–1.31
(m, 10H), 0.88 (t, J = 7.3 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 144.4, 138.4, 134.8, 129.4,
114.6, 84.4, 34.5, 31.8, 31.6, 29.5, 29.4, 29.2, 22.6, 14.0; IR (cm–1) 3407, 3317, 2954, 2916, 2850, 1617, 1496, 1467,
1405, 1306, 1152, 1028, 819, 665; HRMS (MALDI) m/z calcd for C14H22NI ([M + H]+) 332.0870, found 332.0870.
HCl (1.1 mL, 13.2 mmol, 7.8 equiv) was
added dropwise
to a solution of 11 (0.558 g, 1.68 mmol, 1 equiv) in
10.0 mL of <span class="Chemical">tetrahydrofuran and 0.6 mL of acetonitrile chilled to −5
°C in an ice–salt bath. A solution of NaNO2 (0.415 g, 6.02 mmol, 3.58 equiv) in 1.8 mL of water and 0.8 mL acetonitrile
was added dropwise, and the reaction was stirred at −5 °C
for 30 min before being slowly transferred via cannula to a flask
containing diethylamine (3.5 mL, 42.5 mmol, 25 equiv) and K2CO3 (2.32 g, 16.8 mmol, 10 equiv) in 7.0 mL of water at
0 °C. The reaction was stirred for 45 min while warming to room
temperature before being diluted with satdNaCl and extracted with
Et2O. The organics were washed with H2O, dried
over MgSO4, filtered, and concentrated in vacuo. Crude
material was purified by flash chromatography using hexanes to afford
0.686 g of an orange oil (98% yield): 1H NMR (500 MHz,
CDCl3) δ 7.66 (d, J = 1.9 Hz, 1H),
7.25 (d, J = 8.6 Hz, 1H), 7.08 (dd, J = 1.9, 8.2 Hz, 1H), 3.78 (q, J = 7.2 Hz, 4H), 2.52
(t, J = 7.5 Hz, 2H), 1.57 (m, 2H), 1.23–1.33
(m, 12H), 0.88 (t, J = 6.4 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 148.3, 141.5, 138.6, 128.8,
117.1, 96.5, 34.9, 31.8, 31.4, 29.4, 29.22, 29.16, 22.6, 14.1; IR
(cm–1) 2923, 2853, 1463, 1432, 1389, 1331, 1266,
1234, 1202, 1105; HRMS (MALDI) m/z calcd for C18H30N3I ([M + H]+) 416.1563, found 416.1558.
Compound 12 (0.250
g, 0.602 mmol, 1.00 equiv), (triisopropylsilyl)acetylene (0.21 mL,
0.934 mmol, 1.55 equiv), Cl2Pd(<span class="Gene">PPh3)2 (0.0227 g, 0.0323 mmol, 0.054 equiv), and CuI (0.0039 g, 0.0204
mmol, 0.034 equiv) were combined in a 50 mL round-bottomed flask and
purged with N2. Ten milliliters of deoxygenated THF and
10 mL of deoxygenated Et3N were added by syringe, and the
reaction was stirred at 40 °C for 18 h. The reaction mixture
was then diluted with H2O (50 mL) and extracted with EtOAc
(3 × 50 mL). The combined organic phases were washed with satdNH4Cl (2 × 50 mL), dried over MgSO4, filtered,
and concentrated in vacuo. The crude material was purified by flash
chromatography using 5% Et2O in hexanes to give 0.256 g
of a brown/orange oil (92% yield): 1H NMR (500 MHz, CDCl3) δ 7.34 (d, J = 8.3 Hz, 1H), 7.28
(d, J = 1.9 Hz, 1H), 3.77 (q, J = 7.3 Hz, 4H), 2.53 (t, J = 7.3 Hz, 2H), 1.55–1.60
(m, 2H), 1.22–1.32 (m, 18H), 1.13 (s, 21H), 0.88 (t, J = 6.3 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 150.5, 139.2, 133.5, 129.2, 118.2, 116.5, 105.9, 35.2,
31.9, 31.5, 29.5, 29.2, 22.7, 18.8, 14.1, 11.4; IR (cm–1) 2925, 2862, 2147, 1463, 1398, 1330, 1242, 1201, 1092, 883; HRMS
(MALDI) m/z calcd for C29H51N3Si ([M + H]+) 470.3930, found
470.3917.
Compound 13 (0.485
g, 1.032
mmol, 1 equiv) was dissolved in 5 mL of MeI in a sealed tube. The
reaction flask was evacuated and backfilled with N2 before
being sealed and heated to 125 °C for 20 h. The reaction was
cooled to room temperature before excess MeI was evaporated by N2 bubbling. The crude residue was purified by flash chromatography
using hexanes as eluent to afford 0.51 g of a yellow <span class="Chemical">oil (99% yield): 1H NMR (500 MHz, CDCl3) δ 7.70 (d, J = 8.2 Hz, 1H), 7.29 (d, J = 2.1 Hz, 1H),
6.81 (dd, J = 2.1, 8.0 Hz, 1H), 2.51 (t, J = 7.7 Hz, 2H), 1.23–1.31 (m, 10H), 1.16 (s, 21H),
0.88 (t, J = 7.1, 3H); 13C NMR (125 MHz,
CDCl3) δ 142.8, 138.4, 133.2, 129.9, 129.8, 108.2,
97.1, 94.6, 31.9, 31.2, 29.4, 29.2, 22.6, 18.7, 14.1, 11.4; IR (cm–1) 2923, 2862, 2366, 2150, 1459, 1394, 1017, 883, 765,
735, 665; HRMS (MALDI) m/z calcd
for C25H41ISi ([M + H]+) 497.2100,
found 497.2098.
Boronic ester 6 (0.620 g,
2.04 mmol, 2.00 equiv) and 14 (0.508 g, 1.02 mmol, 1.00
equiv) were dissolved in deoxygenated <span class="Chemical">DME and further deoxygenated
for 10 min by N2 bubbling. To this solution were added
Cl2Pd(dppf) (0.061 g, 0.0834 mmol, 0.082 equiv) and dry
K3PO4 (1.045 g, 4.922 mmol, 4.83 equiv), and
the reaction was deoxygenated by N2 bubbling for an additional
10 min. The reaction was heated to 90 °C for 20 h before being
cooled to room temperature and diluted with H2O. The reaction
was extracted with Et2O (3 × 30 mL), and organics
were washed with satdNaCl before being dried over MgSO4, filtered, and concentrated in vacuo. Purification by flash chromatography
over neutral alumina with 5% diethyl ether in hexanes gave 0.56 g
of a yellow oil (82% yield): 1H NMR (500 MHz, CDCl3) δ 7.58 (d, J = 8.3 Hz, 2H), 7.41
(d, J = 8.8 Hz, 3H), 7.29 (d, J = 7.8 Hz, 1H), 7.16 (d, J = 7.8 Hz, 1H), 3.77 (q, J = 7.0 Hz, 4H), 2.60 (t, J = 7.8 Hz, 2H),
1.64 (m, 2H), 1.25–1.38 (m, 16 H), 1.03 (s, 21H), 0.88 (t, J = 6.8 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 150.3, 141.5, 141.3, 137.2, 133.7, 129.8, 129.2, 128.8,
121.5, 119.9, 106.9, 93.2, 35.3, 31.9, 31.4, 29.5, 29.4, 29.3, 22.7,
18.7, 14.1, 11.3; IR (cm–1) 2926, 2862, 2363, 2341,
2146, 1463, 1380, 1234, 1095, 908, 883, 827, 734, 666; HRMS (ESI) m/z calcd for C35H55N3SiH ([M + H+]) 546.4244, found 546.4235.
Compound 3b (0.349
g, 0.639 mmol, 1.00 equiv) was dissolved in 5 mL of MeI in a sealed
tube. The flask was evacuated and purged with N2 before
being sealed and heated to 125 °C for 44 h. The reaction was
cooled to room temperature before excess MeI was removed by N2 bubbling. The crude residue was purified by flash chromatography
using 5% Et2O in <span class="Chemical">hexanes to afford 0.336 g of the desired
compound as a colorless oil (92% yield): 1H NMR (500 MHz,
CDCl3) δ 7.69 (d, J = 8.3 Hz, 2H),
7.39 (s, 1H), 7.30 (d, J = 8.8 Hz, 2H), 7.21 (d, J = 7.8 Hz, 1H), 7.17 (dd, J = 7.8, 1.5
Hz, 1H), 2.60 (t, J = 7.8 Hz, 2H), 1.63 (m, 2H),
1.25–1.37 (m, 10H), 1.01 (s, 21H), 0.88 (t, J = 7.3 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ
142.3, 140.5, 140.1, 136.9, 133.5, 131.3, 128.9, 128.8, 106.2, 93.9,
92.8, 35.4, 31.9, 31.4, 29.4, 29.3, 29.2, 22.7, 18.6, 14.1, 11.3;
IR (cm–1) 2924, 2861, 2366, 2333, 2145, 1464, 1385,
1000, 883, 816, 667; HRMS (ESI) m/z calcd for C31H45SiI ([M+]) 572.2335,
found 572.2344.
4-Octyl-1-(4-iodophenyl)-2-ethynylbenzene
(16b)
Compound 15 (0.299
g, 0.522 mmol, 1.00
equiv) was dissolved in 2 mL of THF before 0.63 mL of 1 M <span class="Chemical">TBAF (in
THF containing 5% H2O) was added. TLC showed disappearance
of starting material within 5 min. The reaction was then concentrated,
and the residue was dissolved in Et2O and washed with satdNH4Cl. The organic phase was dried over MgSO4, filtered, and concentrated in vacuo. The crude material was purified
by flash chromatography using hexanes to afford 0.22 g of a colorless
oil (74% yield): 1H NMR: (CDCl3, 500 MHz) δ
7.90 (d, J = 7.0 Hz, 2H), 7.49 (s, 1H), 7.37 (d, J = 7.0 Hz, 2H), 7.28–7.24 (m, 2H), 3.07 (s, 1H),
2.64 (t, J = 7.8 Hz, 2H), 1.68 (m, 2H), 1.25–1.37
(m, 10H), 0.88 (t, J = 7.3 Hz, 3H); 13C NMR (CDCl3, 125 MHz) δ 142.3, 140.6, 139.7, 137.1,
133.9, 131.1, 129.4, 129.2, 120.0, 93.4, 83.2, 80.2, 77.1, 35.3, 31.9,
31.2, 29.5, 29.3, 29.2, 22.7, 14.2; IR (neat, cm–1) 3293, 1479.7, 1384, 1007, 814; HRMS (ESI) m/z calcd for C22H25IH ([M + H+]) 417.1071, found 417.1090.
Authors: Michael Brettreich; Michael Bendikov; Sterling Chaffins; Dmitrii F Perepichka; Olivier Dautel; Hieu Duong; Roger Helgeson; Fred Wudl Journal: Angew Chem Int Ed Engl Date: 2002-10-04 Impact factor: 15.336
Authors: Sang Hyuk Seo; Ticora V Jones; Helga Seyler; Jack O Peters; Tae Hyung Kim; Ji Young Chang; Gregory N Tew Journal: J Am Chem Soc Date: 2006-07-26 Impact factor: 15.419
Figure 1
Figure 2
Scheme 1
Scheme 2
Scheme 3
Figure 3
Scheme 4
Scheme 5
Scheme 6
Scheme 7
Figure 4
Figure 5
Figure 6
Figure 7