| Experimental. (2-Chloro-5-methyl-phenyl)-(4-ethoxy-phenyl)-methanone (2):To a solution of 2-chloro-5-methyl-benzoic acid (1.0 g, 5.86 mmol) in
dichloromethane (12 ml) was added at room temperature (~23°C) oxalyl
chloride (0.54 ml, 6.2 mmol) followed by the dropwise addition of
N,N-dimethylformamide (0.1 ml). The resulting solution was
allowed to stir overnight at room temperature before being concentrated under
reduced pressure to produce crude 2-chloro-5-methylbenzoyl chloride which was
used in the next step without further purification. The crude
2-chloro-5-methylbenzoyl chloride (1.15 g, 5.86 mmol) and ethoxybenzene (0.75 g, 6.14 mmol) were dissolved in 10 ml of dichloromethane and the resulting
solution was cooled to 0°C. Aluminum trichloride (0.85 g, 6.38 mmol) was
added and the reaction mixture was allowed to stir at 0°C for 4 hours before
being allowed to warm to room temperature overnight (~16 hours). The reaction
was quenched by pouring the solution over ice. The mixture was diluted with
water and extracted three times with dichloromethane. The combined organic
layers were successively washed with aqueous 1 N hydrochloric acid solution,
aqueous 1 N sodium hydroxide solution, brine, dried over sodium sulfate,
filtered and concentrated under reduced pressure. The crude material was
chromatographed using an ISCO automated chromatography unit (40 g silica gel
column) and eluting with a gradient of 0-40% ethyl acetate in heptane yielding
650 mg (30% yield) of an oil that solidified upon standing. MS (LCMS) 274.9
(M+H+; positive mode). HRMS calculated for C16H16ClO2 (M+H+)
275.0833 found 275.0832. 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.43 (t,
J=7.0 Hz, 3 H), 2.34 (s, 3 H), 4.09 (q, J=7.0 Hz, 2 H), 6.90 (d, J=8.8 Hz, 2
H), 7.14 (s, 1 H), 7.17 - 7.22 (m, 1 H), 7.30 (d, J=8.2 Hz, 1 H), 7.76 (d,
J=8.8 Hz, 2 H); 13C NMR (100 MHz, CHLOROFORM-d) δ ppm 194.3, 163.7, 139.0,
136.9, 132,7 (2 C), 132.5, 131.7, 129.8, 129.5, 128.4, 114.4 (2 C), 64.0,
21.0, 14.8.(5-Bromomethyl-2-chloro-phenyl)-(4-ethoxy-phenyl)-methanone (3):To a solution of (2-chloro-5-methyl-phenyl)-(4-ethoxy-phenyl)-methanone
(2; 650 mg, 2.37 mmol) and N-bromosuccinimide (465 mg, 2.61 mmol) in carbon tetrachloride (8 ml) was added 2,2'-azobisisobutyronitrile
(AIBN, 8 mg, 0.047 mmol) and the reaction mixture was heated to reflux for 26
hours under nitrogen. The reaction was cooled to room temperature, quenched
with water (50 ml) and the mixture diluted with dichloromethane (25 ml). The
layers were separated and the aqueous layer was extracted two additional times
with dichloromethane (25 ml). The combined organic layers were washed with
brine, dried over magnesium sulfate, filtered through a pad of celite, and
concentrated under reduced pressure. The crude material was chromatographed
with an ISCO automated chromatography unit (40 g silica gel column) eluting
with a gradient of 0-20% ethyl acetate in heptane to produce 434 mg (52%
yield) of the desired product as a white solid. HRMS calculated for
C16H15BrClO2 (M+H+) 352.9938 found 352.9939. 1H NMR (400 MHz,
CHLOROFORM-d) δ ppm 1.43 (t, J=7.0 Hz, 3 H), 4.10 (q, J=6.9 Hz, 2 H), 4.45
(s, 2 H), 6.91 (d, J=8.8 Hz, 2 H), 7.36 (s, 1 H), 7.37 - 7.40 (m, 2 H), 7.76
(d, J=9.0 Hz, 2 H). 13C NMR (100 MHz, CHLOROFORM-d) δ ppm 193.3, 163.3,
139.6, 136.9 132.7 (2 C), 131.5, 131.3, 130.6, 129.5, 129.1, 114.6 (2 C),
64.1, 31.8, 14.8.4-Bromomethyl-1-chloro-2-(4-ethoxy-benzyl)-benzene (4):To a solution of (5-bromomethyl-2-chloro-phenyl)-(4-ethoxy-phenyl)-methanone
(3; 400 mg, 1.13 mmol) dissolved in dichloromethane (2 ml) and
acetonitrile (4 ml) cooled to 0°C was added triethylsilane (0.7 mL, 4 mmol).
Boron trifluoride diethyl ether complex (0.34 ml, 2.71 mmol) was added
dropwise to the stirring solution and the reaction mixture was allowed to warm
to room temperature overnight. The reaction was quenched by addition of
aqueous 1 N sodium hydroxide (30 ml) and the resulting biphasic mixture was
extracted three times with ethyl acetate (30 ml). The combined organic layers
were successively washed with aqueous 1 N sodium hydroxide solution (50 ml),
brine (50 ml), dried over sodium sulfate, filtered and concentrated under
reduced pressure. The crude material was chromatographed using an ISCO
automated chromatography unit (12 g silica gel column) eluting with a gradient
of 0-50% ethyl acetate in heptane to produce 310 mg (81% yield) of the desired
product as a clear oil. HRMS calculated for C16H17BrClO (M+H+) 339.0145
found 339.0137. 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.39 (t, J=7.0 Hz, 3
H), 4.00 (q, J=8.4 Hz, 2 H), 4.01 (s, 2 H), 4.38 (s, 2 H), 6.82 (d, J=8.6 Hz,
2 H), 7.08 (d, J=8.6 Hz, 2 H), 7.12 (d, J=2.0 Hz, 1 H), 7.17 (dd, J=8.1, 2.0 Hz, 1 H), 7.32 (d, J=8.2 Hz, 1 H). 13C NMR (100 MHz, CHLOROFORM-d) δ ppm
157.7, 139.8, 136.7, 134.4, 131.5, 131.1, 130.2, 130.1 (2 C), 128.4, 114.7 (2 C), 63.6, 38.4, 32.8, 15.1.[4-Chloro-3-(4-ethoxy-benzyl)-phenyl]-methanol (5):A solution of 4-bromomethyl-1-chloro-2-(4-ethoxy-benzyl)-benzene (4; 300 mg, 0.883 mmol) and sodium acetate (217 mg, 2.65 mmol) in
N,N-dimethylformamide (2 ml) was heated at 100°C for 18 hours.
After cooling to room temperature, the reaction was quenched with water (30 ml) and the resulting mixture was extracted with ethyl acetate (30 ml). The
aqueous layer was extracted with ethyl acetate (30 ml) two additional times.
The combined organic layers were washed with brine, dried over sodium sulfate,
filtered and concentrated under reduced pressure. The crude material was
chromatographed using an ISCO automated chromatography unit (12 g silica gel
column) eluting with a gradient of 0-50% ethyl acetate in heptane yielding 237 mg (84% yield) of acetic acid 4-chloro-3-(4-ethoxy-benzyl)-benzyl ester as a
clear oil. HRMS calculated for C18H19ClNaO3 (M+Na+) 341.0914 found
341.0925. 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.39 (t, J=6.9 Hz, 3 H),
2.06 (s, 3 H), 3.99 (q, 2 H), 4.02 (s, 2 H), 4.99 (s, 2 H), 6.81 (d, J=8.6 Hz,
2 H), 7.08 (d, J=8.8 Hz, 2 H), 7.10 (br. s., 1 H), 7.13 (dd, J=8.2, 2.0 Hz, 1
H), 7.34 (d, J=8.0 Hz, 1 H). 13C NMR (100 MHz, CHLOROFORM-d) δ ppm 170.9,
157.7, 139.6, 134.9, 134.2, 131.3, 130.9 (2 C), 130.1, 129.8, 127.5, 114.7 (2 C), 67.7, 63.6, 38.5, 21.2, 15.1.To a solution of acetic acid 4-chloro-3-(4-ethoxy-benzyl)-benzyl ester (221 mg,
0.693 mmol) dissolved in methanol (8 ml) was added 25% sodium methoxide in
methanol (1 ml) until pH = 12 was reached and the reaction mixture was allowed
to stir at room temperature under nitrogen for 18 hours. The mixture was
neutralized with the addition of Dowex Monosphere 650 C (H) cation exchange
resin (the resin was washed with methanol 3 times before using) until the pH
of the solution was ~7. The reaction mixture was filtered and the filtrate
was concentrated under reduced pressure. The crude material was
chromatographed using an ISCO automated chromatography unit (12 g silica gel
column) eluting with a gradient of 0-60% ethyl acetate in heptane to produce
167 mg (87% yield) of the desired product as a clear gum. HRMS calculated for
C16H17ClNaO2 (M+Na+) 299.0809 found 299.0813. 1H NMR (400 MHz,
CHLOROFORM-d) δ ppm 1.38 (t, J=7.0 Hz, 3 H), 1.63 (t, J=6.0 Hz, 1 H), 3.94 -
4.05 (m, 2 H), 4.02 (s, 2 H), 4.59 (d, J=5.9 Hz, 2 H), 6.81 (d, J=8.6 Hz, 2
H), 7.08 (d, J=8.6 Hz, 2 H), 7.12 (s, 1 H), 7.13 - 7.17 (m, 1 H), 7.34 (d,
J=8.0 Hz, 1 H). 13C NMR (100 MHz, CHLOROFORM-d) δ ppm 157.7, 139.8, 139.5,
133.5, 131.5, 130.1 (2 C), 129.8, 129.6, 126.3, 114.7 (2 C), 64.8, 63.6, 38.5,
15.1.4-Chloro-3-(4-ethoxy-benzyl)-benzaldehyde (6):A solution of [4-chloro-3-(4-ethoxy-benzyl)-phenyl]-methanol (5; 150 mg,
0.542 mmol), N,N-diisopropylethylamine (0.54 ml, 3.1 mmol) and
dimethylsulfoxide (0.52 ml, 7.32 mmol) in dichloromethane (3 ml) was cooled to
0°C using an ice bath. Sulfur trioxide pyridine complex (150 mg, 0.94 mmol)
was added portionwise and the reaction mixture was allowed to stir at 0°C for
1 hour before being warmed to room temperature and stirred at this temperature
for 2 hours. The reaction was quenched with water (50 ml), the resulting
mixture was diluted with dichloromethane (25 ml) and the layers were
separated. The aqueous phase was extracted with dichloromethane (25 ml) two
additional times and the combined organic layers were successively washed with
water (25 ml), brine (25 ml), dried over magnesium sulfate, filtered through a
plug of celite, and concentrated under reduced pressure. The crude material
was chromatographed using an ISCO automated chromatography unit (12 g silica
gel column) eluting with a gradient of 0-40% ethyl acetate in heptane yielding
127 mg (85%) of the desired product as a clear oil which solidified upon
standing. HRMS calculated for C16H16ClO2 (M+H+) 275.0833 found
275.0831. 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.39 (t, J=7.0 Hz, 3 H),
4.00 (q, J=7.0 Hz, 2 H), 4.08 (s, 2 H), 6.83 (d, J=8.6 Hz, 2 H), 7.09 (d,
J=8.4 Hz, 2 H), 7.52 (d, J=8.2 Hz, 1 H), 7.62 (d, J=1.8 Hz, 1 H), 7.64 - 7.69
(m, 1 H), 9.89 (s, 1 H); 13C NMR (100 MHz, CHLOROFORM-d) δ ppm 191.4,
157.9, 141.0, 140.7, 135.2, 132.1, 130.6, 130.4, 130.1 (2 C), 128.5, 114.9 (2 C), 63.6, 38.5, 15.1.Alternative synthesis of 6:To a solution of 4-bromomethyl-1-chloro-2-(4-ethoxy-benzyl)-benzene (4;
26.6 mg, 0.078 mmol) in dimethylsulfoxide (0.3 ml) was added
2,4,6-trimethyl-pyridine (0.03 ml, 0.2 mmol) and the reaction was heated to
125°C for 30 minutes. The reaction mixture was cooled to room temperature,
water (25 ml) was added and the resulting mixture was extracted three times
with ethyl acetate (20 ml). The combined organic layers were successively
washed with water, brine, dried over sodium sulfate, filtered and concentrated
under reduced pressure. The crude material was chromatographed using an ISCO
automated chromatography unit (4.0 g silica gel column) and eluting with a
gradient of 0-50% ethyl acetate in heptane yielding 11 mg (51% yield) of an
oil that solidified upon standing.Alternatively 6 could be prepared in an analogous way by using the
appropriate starting material: To a solution of 1-bromomethyl-4-methoxybenzene
(153 mg, 0.766 mmol) in 1,2-dimethoxyethane (3 ml) was added (185 mg, 0.996 mmol), 2-chloro-5-formyl-phenyl-boronic acid a solution of 2M aqueous sodium
carbonate (1.5 ml) followed by the addition
[1,1'-bis(diphenyl-phosphino)ferrocene]dichloro-palladium, dichloromethane (65 mg, 0.1 mmol). The reaction mixture was purged with nitrogen before being
sealed and heated to 80°C in the microwave for 30 minutes. The organic layer
was separated and concentrated under reduced pressure. The crude material was
chromatographed using an ISCO automated chromatography unit (12.0 g silica gel
column) and eluting with a gradient of 0-70% ethyl acetate in heptane yielding
17.4 mg (9% yield) of 4-chloro-3-(4-methoxy-benzyl)-benzaldehyde as an oil.2-(4-Chloro-3-(4-ethoxy-benzyl)phenyl)-1,3-dithiane (1):To a solution of 4-chloro-3-(4-ethoxy-benzyl)benzaldehyde (8.4 g, 31 mmol) in
dichloromethane (113 ml) was added 1,3-propanedithiol (3.38 ml, 33.6 mmol) and
the solution was stirred at room temperature for 1 hour before cooling down to
0°C. To the solution was added boron trifluoride diethyl etherate (5 ml, 39.7 mmol) and the reaction was warmed up to room temperature over 12 hours. The
mixture was diluted with dichloromethane and the reaction was quenched by
dropwise addition of saturated aqueous solution of sodium bicarbonate. The
organic phase was successively washed with a solution of sodium hydroxide
(1M), brine, dried over magnesium sulfate, filtered and concentrated. The
crude product was purified by chromatography over silica gel (0% to 30% EtOAc
in heptane) to give 1 as a white solid (8.25 g, 74% yield). MS (LCMS)
365.1 (M+H+; positive mode). HRMS calculated for C19H22ClOS2 (M+H+)
365.0795 found 365.0796. 1H NMR (500 MHz, CHLOROFORM-d) δ ppm 1.42 (t,
J=7.0 Hz, 3 H), 1.87 - 1.99 (m, 1 H), 2.13 - 2.21 (m, 1 H), 2.86 - 2.94 (m, 2
H), 2.99 - 3.09 (m, 2 H), 3.98 - 4.07 (m, 4 H), 5.08 (s, 1H), 6.80 - 6.88 (m,
2 H), 7.07 - 7.14 (m, 2 H), 7.23 - 7.38 (m, 3 H). 13C NMR (100 MHz,
CHLOROFORM-d) δ ppm 15.1, 25.2, 32.2 (2 C), 38.6, 50.9, 63.6, 114.7 (2 C),
127.1, 130.1, 130.2 (2 C), 130.5, 131.2, 134.3, 138.1, 139.7, 157.7. |