Phosphine-Free Ru-Catalyzed Regio- and Stereoselective Addition of Benzoic Acids to Trifluoromethylated Alkynes toward Facile Access to Trifluoromethyl Group-Substituted (E)-Enol Esters.

A combination of ruthenium catalyst with silver salt and copper salt was proved to be a highly efficient protocol for the direct addition reaction of benzoic acids with unsymmetrical trifluoromethylated internal alkynes. Diverse trifluoromethyl group-substituted (E)-enol esters were readily obtained for a broad substrate scope in moderate to good yields with excellent regio- and stereoselectivities under mild reaction conditions.

Introduction

Enol esters represent a kind of important and versatile synthon, which have broad applications in both organic synthesis and polymer as well as material science.[1] Among the numerous synthetic methods toward such kind of valuable compounds, the direct addition of carboxylic acids to alkynes constitutes one of the most straightforward and atom-economical approaches without generation of byproduct or waste.[2] Consequently, substantial attention has been attracted from the synthetic community and a diverse set of different catalytic systems has been well established by the employment of various typical transition-metal catalysts, including Ru,[3] Rh,[4] Ir,[5] Pd,[6] Au,[7] Ag,[8] Re,[9] Co,[10] Cu,[11] Hg,[12] etc. Undoubtedly, ruthenium complexes turned out to be the most extensively utilized catalyst due to the high catalytic efficiency and relatively low cost of ruthenium compared to noble metals such as Rh, Ir, Pd, and Au. However, the vast majority of current state of the art has focused on the usage of terminal or symmetrical internal alkynes to avoid the regioselectivity issues. In contrast, unsymmetrical internal alkynes have so far received much less attention because of the inherent challenges, such as stereo- and regiospecific selectivities and it could generate a mixture of four isomers.[13] Toward this end, it is highly desirable to establish a novel method to circumvent the above limitations.

Trifluoromethyl group as a representative unique fluorine-containing moiety can be found in a large number of important drugs and pesticides, and therefore, the development of a simple and highly efficient protocol to incorporate trifluoromethyl group into organic molecules has become an important research topic for chemists.[14] Unsymmetrical trifluoromethylated internal alkynes[15] as a type of readily available trifluoromethyl group-containing building blocks have been widely used by our and other groups to construct a variety of trifluoromethyl group-substituted carbonic or heterocyclic molecules (Scheme a).[16−23] During the course of our previous work about the synthesis of trifluoromethylated isocoumarins (Scheme a),[17] an unexpected formation of trifluoromethyl group substituted (E)-enol ester was noticed (Scheme d). With respect to the importance of multisubstituted enol ester, this preliminary experimental result promoted us to continue to study the addition reaction in detail. However, literature survey showed that there are only three examples about the preparation of trifluoromethyl group-substituted enol esters (Scheme b,c).[24−26] Kawatsura and Itoh reported a triphenylphosphine-assisted ruthenium-catalyzed addition of carboxylic acids to aryl and trifluoromethyl group-substituted unsymmetrical internal alkynes for the synthesis of trifluoromethyl group-substituted (E)-enol esters (Scheme b).[24]

Scheme 1

Transition-Metal-Catalyzed Diverse Transformations of Trifluoromethylated Alkynes

Later, Szabó group developed a copper-catalyzed addition of Togni’s electrophilic CF3 transfer reagent to terminal alkynes for the access of trifluoromethyl group-substituted (E)-enol esters (Scheme c).[25] Very recently, Zhang and co-workers have demonstrated a syn-carboxylation–trifluoromethylation reaction of terminal alkynes with a Cu(III)–CF3 complex to produce trifluoromethyl group-substituted (Z)-enol esters (Scheme c).[26] Herein, a simple and useful phosphine-free Ru-catalyzed addition reaction of benzoic acids with trifluoromethylated internal alkynes to deliver trifluoromethyl group-substituted (E)-enol esters with excellent regio- and stereoselectivities was developed.

Results and Discussion

To start the initial investigation, the model reaction of benzoic acid 1a with trifluoromethylated para-fluorophenylacetylene 2a was used to optimize the reaction conditions. The results are listed in Table . Our previous work[17] indicated that the catalyst was of importance for the successful transformation. Therefore, a series of typical noble-metal catalysts were initially assessed in combination of silver salt and copper salt (Table , entries 1–5). The reaction occurred in excellent regio- and stereoselective manner, and no other possible stereoisomers were detected. Both Ir and Rh catalysts could generate comparable moderate yields for the desired (E)-enol ester product 3a. Then, several Ru catalysts were further screened hoping to enhance the efficiency. Unfortunately, neither (PPh3)3RuCl2 nor RuCl3 could promote the transformation. And [Ru(p-cymene)Cl2]2 turned out to be the optimal catalyst in terms of yield and selectivity. Next, a group of silver salts were screened; however, no one could provide better results (Table , entries 6–10). On the other hand, several copper salts were also evaluated to deliver comparable efficiencies (Table , entries 11–13). Final solvent investigation indicated that DCM and toluene could generate moderate yields, while methanol was completely inert for the reaction (Table , entries 14–16). The yield for expected (E)-enol ester product could further improve to 66% by usage of a bit more Ru catalyst and silver salt with prolonged reaction time (Table , entry 17). Control experimental results indicated that both Ru catalyst and silver salt were pivotal to the reaction, whereas the yield decreased to 52% in the absence of copper salt (Table , entries 18–20).

Table 1

Optimization of Reaction Conditionsa

entry	catalyst	Ag salt	Cu salt	solvent	yield (%) of 3a
1	[Cp*IrCl2] 2	AgSbF6	Cu(OAc)2·H2O	DCE	35
2	[Cp*RhCl2] 2	AgSbF6	Cu(OAc)2·H2O	DCE	41
3	(PPh3)3RuCl2	AgSbF6	Cu(OAc)2·H2O	DCE	trace
4	RuCl3	AgSbF6	Cu(OAc)2·H2O	DCE	NRb
5	[Ru(p-cymene)Cl2]2	AgSbF6	Cu(OAc)2·H2O	DCE	45
6	[Ru(p-cymene)Cl2]2	AgPF6	Cu(OAc)2·H2O	DCE	26
7	[Ru(p-cymene)Cl2]2	AgBF4	Cu(OAc)2·H2O	DCE	29
8	[Ru(p-cymene)Cl2]2	AgOTf	Cu(OAc)2·H2O	DCE	30
9	[Ru(p-cymene)Cl2]2	AgOAc	Cu(OAc)2·H2O	DCE	35
10	[Ru(p-cymene)Cl2]2	Ag2CO3	Cu(OAc)2·H2O	DCE	37
11	[Ru(p-cymene)Cl2]2	AgSbF6	CuCO3	DCE	40
12	[Ru(p-cymene)Cl2]2	AgSbF6	CuBr2	DCE	36
13	[Ru(p-cymene)Cl2]2	AgSbF6	CuO	DCE	39
14	[Ru(p-cymene)Cl2]2	AgSbF6	Cu(OAc)2·H2O	DCM	40
15	[Ru(p-cymene)Cl2]2	AgSbF6	Cu(OAc)2·H2O	PhMe	31
16	[Ru(p-cymene)Cl2]2	AgSbF6	Cu(OAc)2·H2O	MeOH	trace
17c	[Ru(p-cymene)Cl2]2	AgSbF6	Cu(OAc)2·H2O	DCE	66
18d		AgSbF6	Cu(OAc)2·H2O	DCE	NRb
19e	[Ru(p-cymene)Cl2]2		Cu(OAc)2·H2O	DCE	NRb
20f	[Ru(p-cymene)Cl2]2	AgSbF6		DCE	52

Reaction conditions: 1a (0.2 mmol), 2a (0.3 mmol, 1.5 equiv), catalyst (2.5 mol %), silver salt (10 mol %), and copper salt (20 mol %) in 3 mL solvent at 100 °C for 12 h.

No reaction.

3.5 mol % [Ru(p-cymene)Cl2]2 in combination of 30 mol % AgSbF6 were used. Reaction time was extended to 21 h.

No Ru catalyst was used.

No silver salt was used.

No copper salt was used, while 3.5 mol % [Ru(p-cymene)Cl2]2 in combination of 30 mol % AgSbF6 were used for 21 h.

Subsequently, the substrate scope was investigated, and the results are depicted in Scheme . At first, the scope of benzoic acid part was explored. The absolute structure of 3q was unambiguously confirmed to be (E)-configuration by X-ray crystallographic diffraction, while the others were assigned by analogy. In contrast to our previous work about Ir catalysis,[17] herein electron density of benzoic acids did not affect the reaction too much. Both electron-rich and electron-poor benzoic acids reacted well to generate the desired adducts in moderate to good yields along with excellent regio- and stereoselectivities. It is worth noting that sulfur-containing benzoic acid (1f) could generate moderate yield, which indicates that the sulfur atom did not poison Ru catalyst. A group of halogen atoms, including fluorine, chloride, and bromide (3h–j) were well tolerated to produce satisfactory outcomes, which permit valuable opportunities for further derivatizations via various classical transition-metal-mediated cross-couplings. A strong electron-withdrawing group like the trifluoromethyl group also gave acceptable result (3k). On the other hand, the steric hindrance also had limited effect on the reaction. Para-, meta-, and even ortho-substituents were compatible in this catalytic system (3l–n).

Scheme 2

Substrate Scope Investigation

The yield in parentheses was for 1 mmol scale reaction.

Reaction conditions: 1 (0.2 mmol), 2 (0.3 mmol, 1.5 equiv), 3.5 mol % [Ru(p-cymene)Cl2]2, 30 mol % AgSbF6, and 20 mol % Cu(OAc)2·H2O in 3 mL of 1,2-dichloroethene (DCE) at 100 °C for 21 h.

Next, some disubstituted benzoic acids were also exploited, and all of the tested substrates afforded satisfied results (3o–q). Moreover, this catalytic system could further extend to aromatic heterocyclic furan-2-carboxylic acid, furnishing the highest yield of 87% under standard condition (3s). In addition, to enhance the practical usage of this newly developed method, an enlarged scale reaction of 1s (1 mmol) was carried out, and 80% yield was obtained. Unfortunately, aliphatic acids failed to provide the corresponding enol ester product.

After completing exploration of the scope of benzoic acids, the scope of trifluoromethylated internal alkynes was further explored. It was delighting to find that these used trifluoromethylated alkynes reacted well under the standard conditions. A group of substituents on the benzene ring of internal alkynes were well accommodated for the process. Diverse halogenated substrates, such as alkynes containing F, Cl, Br, and I atoms, were all suitable to afford the expected products smoothly (3t–v). Ester group and tert-butyl group could also be tolerated under the standard catalytic conditions to obtain moderate yields (3w and 3z). However, trifluoromethylated internal alkyl alkynes were not suitable for this reaction.

On the basis of the previous reports[3d,3f,24] and experimental results, a plausible reaction pathway is suggested to comment the generated excellent regio- and stereoselectivity, which is demonstrated in Scheme . First, by treatment of silver and copper salt, ruthenium dimer catalyst produces the active monomer species A. Subsequent anion exchange with benzoic acid 1 leads to the formation of intermediate B. Then, coordination of trifluoromethylated phenylacetylene 2 to Ru catalyst center generates intermediate C, followed by alkyne migratory insertion into the ruthenium–oxygen bond to provide the six-membered cycloruthenium complex D. Ultimately, there are two possible pathways to fulfill the catalytic cycle. Protodemetalation of cycloruthenium intermediate D by either acid HX, which is generated by anion exchange before (path a), or another molecule of benzoic acid 1 (path b) affords the final product trifluoromethyl group-substituted (E)-enol ester 3. Meanwhile, the catalyst species A or B could be revived for next catalytic cycle.

Scheme 3

Proposed Catalytic Cycle

Herein, it is worth noting that the excellent regio- and stereoselectivity should come from the coordination-insertion process. Although the detailed mechanism has not been clearly documented in previous report,[24] we conceive that the excellent regio- and stereoselectivity should be attributed to the unique electronic property of trifluoromethyl group. In this proposed catalytic cycle, we give some new insights to clarify both regio- and stereoselectivity for the addition process. On the one hand, due to the high electronegativity of the fluorine atom making trifluoromethyl group a strong electron-withdrawing group, Cβ of the alkyene is much more electron-poor than Cα. Therefore, the carboxylic acid prefers adding to Cβ position regioselectively, whereas the cationic ruthenium center adds to Cα. On the other hand, the carbonyl oxygen atom of the ester could coordinate to the Ru center to form the energy-favorable six-membered ring cycloruthenium complex D, which results in the phenyl and trifluoromethyl group to be on the same side on the alkene.[3f] Consequently, the subsequent protodemetalation furnishes (E)-enol ester 3 stereoselectively.

Conclusions

To conclude, a practically useful phosphine-free Ru-catalyzed direct addition of benzoic acids to unsymmetrical trifluoromethylated internal alkynes was successfully developed for the facile access to diverse trifluoromethyl group-substituted (E)-enol esters. The substrate scope was broad with good functional group tolerance. Moderate to good yields along with excellent regio- and stereoselectivities were achieved for the reaction. A plausible reaction pathway was suggested to explain the obtained excellent regio- and stereoselectivities for the addition of benzoic acid to unsymmetric trifluoromethylated internal alkynes. Further synthetic application of trifluoromethylated internal alkynes is ongoing in our laboratory and the results will be reported soon.

Experimental Section

General Information

Unless otherwise noted, all reagents and transition-metal catalysts were purchased and used as received. Petroleum ether and ethyl acetate for column chromatography were purified prior to use by evaporation on a rotary evaporator. Reactions were monitored by thin-layer chromatography (TLC) analysis, which was performed on aluminum plates precoated with silica gel (Merck, 60 F-254), and visualized by UV fluorescence (λmax = 254 nm) and/or by staining with 1% w/v KMnO4 in 0.5 M aqueous K2CO3. Products were purified by flash column chromatography, which was performed using silica gel 60 (300–400 mesh). Solvents: petroleum ether and ethyl acetate for column chromatography were purified prior to use by evaporation on a rotary evaporator. Unless performing reactions sensitive to air and/or moisture, the solvents were bought in p.a. quality and used without further purification. Flasks for absolute solvents were flame-dried three times under oil pump vacuum and backfilled with argon. Transition-metal catalysts were purchased and used as received.

Nuclear magnetic resonance (NMR) spectra were acquired on a Bruker Avance 400 spectrometer. Chemical shifts for 1H NMR spectra are reported in parts per million (ppm) from tetramethylsilane with the solvent resonance as the internal standard (CDCl3, 7.26 ppm). Data are reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, br = broad), coupling constants (Hz), and integration. Chemical shifts for 13C NMR spectra are reported in ppm from the tetramethylsilane with the solvent resonance as internal standard (CDCl3, 77.16 ppm) and with complete proton decoupling. No internal standard was used for 19F NMR spectra. High-resolution mass spectroscopy (HRMS) was conducted on an instrument equipped with an atmospheric pressure chemical ionization (APCI) or electrospray ionization (ESI) source in the positive-ion mode. The structures of 3e were assigned by X-ray crystallography analysis. Melting points for solids were measured on a melting point apparatus and are given uncorrected.

General Procedure for the Synthesis of Trifluoromethyl Group-Substituted (E)-Enol Esters 3

A 10 mL reaction tube was charged with benzoic acid 1 (0.2 mmol, 1.0 equiv), trifluoromethylated internal alkyne 2 (0.3 mmol, 1.5 equiv), [Ru(p-cymene)Cl2]2 (4.3 mg, 0.007 mmol, 3.5 mol %), AgSbF6 (20.6 mg, 0.06 mmol, 30 mol %), and Cu(OAc)2·H2O (8.0 mg, 0.04 mmol, 20 mol %). Then, 3 mL of DCE was added by a syringe under atmosphere. The reaction tube was sealed, and the resulting mixture was stirred at 100 °C for 21 h. The mixture was cooled down to room temperature and the solvent was removed with a rotary evaporator. The residue was purified with column chromatography on silica gel, eluting with petroleum ether and ethyl acetate to afford the corresponding product 3.

1 mmol Scale Reaction for 3s

A 50 mL flask was charged with furan-2-carboxylic acid 1s (1.0 mmol, 1.0 equiv), methyl trifluoromethylated para-fluorophenylacetylene 2a (1.5 mmol, 1.5 equiv), [Ru(p-cymene)Cl2]2 (21.5 mg, 0.035 mmol, 3.5 mol %), AgSbF6 (103 mg, 0.3 mmol, 30 mol %), and Cu(OAc)2·H2O (40.0 mg, 0.2 mmol, 20 mol %). Then, 15 mL of DCE was added by a syringe under atmosphere. The reaction tube was sealed, and the resulting mixture was stirred at 100 °C for 21 h. The mixture was cooled down to room temperature and the solvent was removed with a rotary evaporator. The residue was purified with column chromatography on silica gel, eluting with petroleum ether and ethyl acetate to afford the corresponding product 3s (240 mg, yield 80%).

Characterization Data of the Products

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl Benzoate (3a)

Colorless oil, 40.9 mg, yield 66%. 1H NMR (400 MHz, CDCl3) δ 8.07 (dd, J = 7.2, 1.6 Hz, 2H), 7.63 (t, J = 7.4 Hz, 1H), 7.55 (dd, J = 8.4, 5.2 Hz, 2H), 7.48 (t, J = 7.8 Hz, 2H), 7.08 (t, J = 8.6 Hz, 2H), 5.92 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9, 163.8 (d, JC–F = 249.7 Hz), 156.2 (q, C–F = 6.5 Hz), 134.1, 130.6 (qd, JC–F = 8.7, 1.8 Hz), 130.2, 128.7, 128.6 (d, JC–F = 3.5 Hz), 128.5, 122.5 (q, JC–F = 267.5 Hz), 115.5 (d, JC–F = 22.0 Hz), 110.0 (q, JC–F = 35.8 Hz); 19F NMR (376 MHz, CDCl3) δ −55.73, −109.24; HRMS (pos. ESI): m/z [M + H]+ for C16H11F4O2 calcd: 311.0690, found: 311.0699.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 4-Methylbenzoate (3b)

Colorless oil, 50.5 mg, yield 78%. 1H NMR (400 MHz, CDCl3) δ 7.95 (d, J = 8.0 Hz, 2H), 7.55 (dd, J = 8.8, 5.5 Hz, 2H), 7.27 (d, J = 8.0 Hz, 2H), 7.07 (t, J = 8.8 Hz, 2H), 5.91 (q, J = 8.0 Hz, 1H), 2.42 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 164.0, 163.8 (d, JC–F = 249.5 Hz), 156.3 (q, JC–F = 6.3 Hz), 145.2, 130.6 (qd, JC–F = 8.6, 1.8 Hz), 130.2, 129.5, 128.8 (d, JC–F = 3.4 Hz), 125.8, 122.6 (q, JC–F = 267.4 Hz), 115.5 (d, JC–F = 21.9 Hz), 109.9 (q, JC–F = 35.7 Hz), 21.7; 19F NMR (376 MHz, CDCl3) δ −55.66, −109.36; HRMS (pos. ESI): m/z [M + H]+ for C17H13F4O2 calcd: 325.0846, found: 325.0848.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 4-tert-Butylbenzoate (3c)

Colorless oil, 60.0 mg, yield 82%. 1H NMR (400 MHz, CDCl3) δ 8.00 (d, J = 8.8 Hz, 2H), 7.55 (dd, J = 8.8, 5.5 Hz, 2H), 7.49 (d, J = 8.4 Hz, 2H), 7.06 (t, J = 8.6 Hz, 2H), 5.90 (q, J = 8.0 Hz, 1H), 1.34 (s, 9H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9, 163.8 (d, JC–F = 249.6 Hz), 158.2, 156.3 (q, JC–F = 6.3 Hz), 130.6 (qd, JC–F = 8.6, 1.7 Hz) 130.1, 128.8 (d, JC–F = 3.4 Hz), 125.8, 125.7, 122.6 (q, JC–F = 267.4 Hz), 115.5 (d, JC–F = 22.0 Hz), 109.8 (q, JC–F = 35.8 Hz), 35.3, 31.0; 19F NMR (376 MHz, CDCl3) δ −55.65, −109.35; HRMS (pos. ESI): m/z [M + H]+ for C20H19F4O2 calcd: 367.1316, found: 367.1325.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 4-Phenoxybenzoate (3d)

Colorless oil, 48.2 mg, yield 60%. 1H NMR (400 MHz, CDCl3) δ 8.02 (dt, J = 8.8, 2.4 Hz, 2H), 7.54 (dd, J = 8.6, 5.2 Hz, 2H), 7.40 (t, J = 8.0 Hz, 2H), 7.21 (t, J = 7.4 Hz, 1H), 7.09–7.05 (m, 4H), 7.00 (d, J = 8.8 Hz, 2H), 5.91 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.8 (d, JC–F = 249.6 Hz), 163.4, 163.0, 156.2 (q, JC–F = 6.3 Hz), 155.2, 132.4, 130.6 (qd, JC–F = 8.7, 1.8 Hz), 130.2, 128.7 (d, JC–F = 3.5 Hz), 124.9, 122.6 (q, JC–F = 267.4 Hz), 122.5, 120.3, 117.4, 115.5 (d, JC–F = 21.9 Hz), 109.9 (q, JC–F = 35.8 Hz); 19F NMR (376 MHz, CDCl3) δ −55.64, −109.26; HRMS (pos. ESI): m/z [M + H]+ for C22H15F4O3 calcd: 403.0952, found: 403.0959.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 4-Methoxybenzoate (3e)

White solid, 52.4 mg, yield 77%, mp: 83–85. 1H NMR (400 MHz, CDCl3) δ 8.01 (d, J = 8.8 Hz, 2H), 7.54 (dd, J = 8.8, 5.2 Hz, 2H), 7.07 (t, J = 7.6 Hz, 2H), 6.94 (d, J = 8.8 Hz, 2H), 5.90 (q, J = 8.0 Hz, 1H), 3.86 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 164.4, 163.8 (d, JC–F = 249.4 Hz), 163.6, 156.3 (q, JC–F = 6.3 Hz), 132.4, 130.6 (qd, JC–F = 7.2, 1.8 Hz), 128.8 (d, JC–F = 3.4 Hz), 122.6 (q, JC–F = 267.3 Hz), 120.8, 115.4 (d, JC–F = 21.9 Hz), 114.1, 109.8 (q, JC–F = 35.7 Hz), 55.5; 19F NMR (376 MHz, CDCl3) δ −55.62, −109.44; HRMS (pos. ESI): m/z [M + H]+ for C17H13F4O3 calcd: 341.0795, found: 341.0809.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 4-(Methylthio)benzoate (3f)

Colorless oil, 37.7 mg, yield 53%. 1H NMR (400 MHz, CDCl3) δ 7.94 (d, J = 8.4 Hz, 2H), 7.54 (dd, J = 8.8, 5.2 Hz, 2H), 7.27 (d, J = 8.4 Hz, 2H), 7.08 (t, J = 8.4 Hz, 2H), 5.91 (q, J = 8.0 Hz, 1H), 2.52 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.8 (d, JC–F = 249.6 Hz), 163.7, 156.2 (q, JC–F = 6.3 Hz), 147.6, 130.6 (qd, JC–F = 8.7, 1.8 Hz), 130.4, 128.7 (d, JC–F = 3.5 Hz), 125.1, 124.4, 122.6 (q, JC–F = 267.4 Hz), 115.5 (d, JC–F = 21.9 Hz), 109.9 (q, JC–F = 35.8 Hz), 14.7; 19F NMR (376 MHz, CDCl3) δ −55.67, −109.27; HRMS (pos. ESI): m/z [M + H]+ for C17H13F4O2S calcd: 357.0567, found: 357.0573.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 4-Phenylbenzoate (3g)

White solid, 24.7 mg, yield 32%, mp: 78–79. 1H NMR (400 MHz, CDCl3) δ 8.12 (d, J = 8.4 Hz, 2H), 7.69 (d, J = 8.4 Hz, 2H), 7.63–7.61 (m, 2H), 7.58 (dd, J = 8.8, 5.2 Hz, 2H), 7.48 (t, J = 7.2 Hz, 2H), 7.43–7.41 (m, 1H), 7.10 (t, J = 8.6 Hz, 2H), 5.94 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.8 (d, JC–F = 249.7 Hz), 163.7, 156.2 (q, JC–F = 6.2 Hz), 147.0, 139.6, 130.7, 130.6 (qd, JC–F = 8.7, 1.7 Hz), 129.0, 128.7 (q, JC–F = 3.4 Hz), 128.5, 127.4, 127.3, 127.2, 122.6 (q, JC–F = 267.3 Hz), 115.5 (d, JC–F = 21.9 Hz), 110.0 (q, JC–F = 35.7 Hz); 19F NMR (376 MHz, CDCl3) δ −55.69, −109.23; HRMS (pos. ESI): m/z [M + H]+ for C22H15F4O2 calcd: 387.1003, found: 387.1009.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 4-Fluorobenzoate (3h)

Colorless oil, 53.8 mg, yield 82%. 1H NMR (400 MHz, CDCl3) δ 8.11–8.06 (m, 2H), 7.54 (dd, J = 8.8, 5.2 Hz, 2H), 7.15 (t, J = 8.4 Hz, 2H), 7.08 (t, J = 8.4 Hz, 2H), 5.92 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 166.5 (d, JC–F = 254.8 Hz), 163.8 (d, JC–F = 249.9 Hz), 162.9, 156.1 (q, JC–F = 6.2 Hz), 132.9 (d, JC–F = 9.5 Hz), 130.6 (qd, JC–F = 8.7, 1.8 Hz), 128.5 (d, JC–F = 3.5 Hz), 124.8 (d, JC–F = 3.0 Hz), 122.5 (q, JC–F = 267.5 Hz), 116.0 (d, JC–F = 22.1 Hz), 115.6 (d, JC–F = 21.9 Hz), 110.2 (q, JC–F = 35.9 Hz); 19F NMR (376 MHz, CDCl3) δ −55.80, −103.10, −109.10; HRMS (pos. ESI): m/z [M + H]+ for C16H10F5O2 calcd: 329.0595, found: 329.0607.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 4-Chlorobenzoate (3i)

Colorless oil, 32.3 mg, yield 47%. 1H NMR (400 MHz, CDCl3) δ 8.00 (d, J = 8.4 Hz, 2H), 7.53 (dd, J = 8.8, 5.2 Hz, 2H), 7.45 (d, J = 8.4 Hz, 2H), 7.09 (t, J = 8.6 Hz, 2H), 5.92 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9 (d, JC–F = 250.0 Hz), 163.1, 156.0 (q, JC–F = 6.3 Hz), 140.8, 131.5, 130.6 (qd, JC–F = 8.8, 1.8 Hz), 129.2, 128.4 (d, JC–F = 3.5 Hz), 127.0, 122.4 (q, JC–F = 267.5 Hz), 115.6 (d, JC–F = 22.0 Hz), 110.2 (q, JC–F = 35.9 Hz); 19F NMR (376 MHz, CDCl3) δ −55.82, −109.01; HRMS (pos. ESI): m/z [M + H]+ for C16H10F4O2Cl calcd: 345.0300, found: 345.0309.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 4-Bromobenzoate (3j)

Colorless oil, 41.1 mg, yield 53%. 1H NMR (400 MHz, CDCl3) δ 7.91 (d, J = 8.8 Hz, 2H), 7.63 (d, J = 8.8 Hz, 2H), 7.53 (dd, J = 8.4, 5.2 Hz, 2H), 7.09 (t, J = 8.4 Hz, 2H), 5.92 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9 (d, JC–F = 250.0 Hz), 163.2, 156.0 (q, JC–F = 6.4 Hz), 132.2, 131.6, 130.6 (qd, JC–F = 8.6, 1.8 Hz), 129.6, 128.4 (d, JC–F = 3.5 Hz), 127.4, 122.4 (q, JC–F = 267.5 Hz), 115.6 (d, JC–F = 21.9 Hz), 110.2 (q, JC–F = 36.0 Hz); 19F NMR (376 MHz, CDCl3) δ −55.83, −108.99; HRMS (pos. ESI): m/z [M + H]+ for C16H10F4O2Br calcd: 388.9795, found: 388.9801.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 4-(Trifluoromethyl)benzoate (3k)

Colorless oil, 36.3 mg, yield 48%. 1H NMR (400 MHz, CDCl3) δ 8.19 (d, J = 8.0 Hz, 2H), 7.75 (d, J = 8.0 Hz, 2H), 7.55 (dd, J = 8.8, 5.2 Hz, 2H), 7.10 (t, J = 8.8 Hz, 2H), 5.95 (q, J = 7.6 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9 (d, JC–F = 250.2 Hz), 162.7, 155.9 (q, JC–F = 6.3 Hz), 135.6 (q, JC–F = 32.8 Hz), 131.8, 130.7 (qd, JC–F = 8.8, 1.8 Hz), 130.6, 128.2 (d, JC–F = 3.6 Hz), 125.8 (q, JC–F = 3.7 Hz), 123.4 (q, JC–F = 271.2 Hz), 122.3 (q, JC–F = 267.6 Hz), 115.6 (d, JC–F = 22.0 Hz), 110.4 (q, JC–F = 36.0 Hz); 19F NMR (376 MHz, CDCl3) δ −55.92, −63.36, −108.80; HRMS (pos. ESI): m/z [M + H]+ for C17H10F7O2 calcd: 379.0564, found: 379.0572.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 2-Methylbenzoate (3l)

Colorless oil, 38.9 mg, yield 60%. 1H NMR (400 MHz, CDCl3) δ 8.03 (dd, J = 8.0, 0.8 Hz, 1H), 7.56 (dd, J = 8.8, 5.2 Hz, 2H), 7.47 (td, J = 7.6, 1.2 Hz, 1H), 7.31–7.27 (m, 2H), 7.09 (t, J = 8.8 Hz, 2H), 5.89 (q, J = 8.0 Hz, 1H), 2.57 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 164.2, 163.8 (d, JC–F = 249.5 Hz), 156.3 (q, JC–F = 6.3 Hz), 141.8, 133.3, 132.1, 131.2, 130.6 (qd, JC–F = 8.7, 1.8 Hz), 128.8 (d, JC–F = 3.4 Hz), 127.3, 126.1, 122.6 (q, JC–F = 267.5 Hz), 115.5 (d, JC–F = 21.9 Hz), 110.0 (q, JC–F = 35.7 Hz), 21.8; 19F NMR (376 MHz, CDCl3) δ −55.66, −109.37; HRMS (pos. ESI): m/z [M + H]+ for C17H13F4O2 calcd: 325.0846, found: 325.0853.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 3-Methylbenzoate (3m)

Colorless oil, 46.0 mg, yield 71%. 1H NMR (400 MHz, CDCl3) δ 7.87–7.86 (m, 2H), 7.57–7.53 (m, 2H), 7.43 (d, J = 7.6 Hz, 1H), 7.36 (t, J = 8.0 Hz, 1H), 7.08 (t, J = 8.8 Hz, 2H), 5.91 (q, J =8.0 Hz, 1H), 2.41 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 164.1, 163.8 (d, JC–F = 249.6 Hz), 156.3 (q, JC–F = 6.3 Hz), 138.7, 134.9, 130.7, 130.6 (qd, JC–F = 8.5, 1.8 Hz), 128.7 (d, JC–F = 3.8 Hz), 128.6, 128.5, 127.3, 122.6 (q, JC–F = 267.4 Hz), 115.5 (d, JC–F = 21.9 Hz), 109.9 (q, JC–F = 35.7 Hz), 21.2; 19F NMR (376 MHz, CDCl3) δ −55.70, −109.31; HRMS (pos. ESI): m/z [M + H]+ for C17H13F4O2 calcd: 325.0846, found: 325.0848.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 3-Methoxybenzoate (3n)

Colorless oil, 35.4 mg, yield 52%. 1H NMR (400 MHz, CDCl3) δ 7.67 (d, J = 7.6 Hz, 1H), 7.57–7.53 (m, 3H), 7.38 (t, J = 8.0 Hz, 1H), 7.17 (ddd, J = 8.0, 2.4, 0.8 Hz, 1H), 7.08 (t, J = 8.8 Hz, 2H), 5.92 (q, J = 8.0 Hz, 1H), 3.85 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9 (d, JC–F = 249.7 Hz), 163.8, 159.8, 156.2 (q, JC–F = 7.3 Hz), 130.6 (qd, JC–F = 8.7, 1.9 Hz), 129.8, 129.7, 128.6 (d, JC–F = 3.4 Hz), 122.6 (q, JC–F = 267.4 Hz), 122.5, 120.6, 115.5 (d, JC–F = 21.9 Hz), 114.6, 110.0 (q, JC–F = 35.8 Hz), 55.5; 19F NMR (376 MHz, CDCl3) δ −55.74, −109.22; HRMS (pos. ESI): m/z [M + H]+ for C17H13F4O3 calcd: 341.0796, found: 341.0809.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 3,5-Dimethylbenzoate (3o)

Colorless oil, 51.4 mg, yield 76%. 1H NMR (400 MHz, CDCl3) δ 7.68 (s, 2H), 7.55 (dd, J = 8.8, 5.6 Hz, 2H), 7.25 (s, 1H), 7.07 (t, J = 8.8 Hz, 2H), 5.89 (q, J = 8.0 Hz, 1H), 2.36 (s, 6H); 13C{1H} NMR (100 MHz, CDCl3) δ 164.2, 163.8 (d, JC–F = 249.6 Hz), 156.3 (q, JC–F = 6.3 Hz), 138.5, 135.8, 130.6 (qd, JC–F = 8.7, 1.8 Hz), 128.7 (d, JC–F = 3.5 Hz), 128.4, 127.9, 122.6 (q, JC–F = 267.4 Hz), 115.5 (d, JC–F = 21.9 Hz), 110.0 (q, JC–F = 35.8 Hz), 21.1; 19F NMR (376 MHz, CDCl3) δ −55.68, −109.38; HRMS (pos. ESI): m/z [M + H]+ for C18H15F4O2 calcd: 339.1003, found: 339.1013.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 3,4-Dimethylbenzoate (3p)

Colorless oil, 53.4 mg, yield 79%. 1H NMR (400 MHz, CDCl3) δ 7.82 (s, 1H), 7.79 (d, J = 8.0 Hz, 1H), 7.54 (dd, J = 8.4, 5.6 Hz, 2H), 7.22 (d, J = 8.0 Hz, 1H), 7.06 (t, J = 8.8 Hz, 2H), 5.90 (q, J = 8.0 Hz, 1H), 2.32 (s, 3H), 2.30 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 164.1, 163.8 (d, JC–F = 249.4 Hz), 156.3 (q, JC–F = 6.4 Hz), 143.9, 137.2, 131.2, 130.6 (qd, JC–F = 8.6, 1.8 Hz), 130.0, 128.8 (d, JC–F = 3.5 Hz), 127.8, 126.1, 122.6 (q, JC–F = 267.3 Hz), 115.4 (d, JC–F = 21.9 Hz), 109.8 (q, JC–F = 35.7 Hz), 20.1, 19.6; 19F NMR (376 MHz, CDCl3) δ −55.65, −109.44; HRMS (pos. ESI): m/z [M + H]+ for C18H15F4O2 calcd: 339.1003, found: 339.1010.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 3,4-Dimethoxybenzoate (3q)

White solid, 43.7 mg, yield 59%, mp: 81–83. 1H NMR (400 MHz, CDCl3) δ 7.73 (dd, J = 8.4, 2.0 Hz, 1H), 7.55 (dd, J = 8.8, 5.6 Hz, 2H), 7.51 (d, J = 2.0 Hz, 1H), 7.08 (t, J = 8.8 Hz, 2H), 6.91 (d, J = 8.4 Hz, 1H), 5.91 (q, J = 8.0 Hz, 1H), 3.95 (s, 3H), 3.92 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.8 (d, JC–F = 249.6 Hz), 163.7, 156.3 (q, JC–F = 6.4 Hz), 154.2, 149.0, 130.6 (qd, JC–F = 8.6, 1.8 Hz), 128.8 (d, JC–F = 3.4 Hz), 124.6, 122.6 (q, JC–F = 267.4 Hz), 120.8, 115.5 (d, JC–F = 21.9 Hz), 112.4, 110.5, 109.8 (q, JC–F = 35.8 Hz), 56.1, 56.0; 19F NMR (376 MHz, CDCl3) δ −55.67, −109.37; HRMS (pos. ESI): m/z [M + H]+ for C18H15F4O4 calcd: 371.0901, found: 371.0910.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl 2-Naphthoate (3r)

Colorless oil, 47.5 mg, yield 66%. 1H NMR (400 MHz, CDCl3) δ 8.65 (s, 1H), 8.03 (dd, J = 8.4, 1.6 Hz, 1H), 7.96 (d, J = 8.4 Hz, 1H), 7.89 (dd, J = 8.4, 6.0 Hz, 2H), 7.64–7.54 (m, 4H), 7.08 (t, J = 8.8 Hz, 2H), 5.98 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 164.1, 163.9 (d, JC–F = 249.7 Hz), 156.3 (q, JC–F = 6.4 Hz), 136.0, 132.4, 132.2, 130.7 (qd, JC–F = 8.6, 1.8 Hz), 129.5, 129.0, 128.7 (d, JC–F = 3.4 Hz), 128.6, 127.9, 127.1, 125.7, 125.1, 122.6 (q, JC–F = 267.4 Hz), 115.6 (d, JC–F = 21.9 Hz), 110.1 (q, JC–F = 35.8 Hz); 19F NMR (376 MHz, CDCl3) δ −55.64, −109.17; HRMS (pos. ESI): m/z [M + H]+ for C20H13F4O2 calcd: 361.0846, found: 361.0850.

(E)-3,3,3-Trifluoro-1-(4-fluorophenyl)prop-1-enyl Furan-2-carboxylate (3s)

Colorless oil, 52.2 mg, yield 87%. 1H NMR (400 MHz, CDCl3) δ 7.64–7.63 (m, 1H), 7.54 (dd, J = 8.8, 5.2 Hz, 2H), 7.31 (d, J = 3.6 Hz, 1H), 7.08 (t, J = 8.8 Hz, 2H), 6.56 (dd, J = 3.6, 1.6 Hz, 1H), 5.94 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9 (d, JC–F = 249.8 Hz), 155.5 (q, JC–F = 6.3 Hz), 155.4, 147.7, 143.1, 130.7 (qd, JC–F = 8.7, 1.8 Hz), 128.3 (d, JC–F = 3.5 Hz), 122.4 (q, JC–F = 267.5 Hz), 120.3, 115.5 (d, JC–F = 21.9 Hz), 112.4, 110.2 (q, JC–F = 35.9 Hz); 19F NMR (376 MHz, CDCl3) δ −55.83, −109.09; HRMS (pos. ESI): m/z [M + H]+ for C14H9F4O3 calcd: 301.0482, found: 301.0489.

(E)-1-(4-Chlorophenyl)-3,3,3-trifluoroprop-1-enyl Benzoate (3t)

Colorless oil, 35.9 mg, yield 55%. 1H NMR (400 MHz, CDCl3) δ 8.06 (dd, J = 8.0, 1.2 Hz, 2H), 7.63 (t, J = 7.6 Hz, 1H), 7.51–7.46 (m, 4H), 7.38–7.36 (m, 2H), 5.94 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9, 156.1 (q, JC–F = 6.3 Hz), 136.7, 134.2, 130.9, 130.2, 129.8 (q, JC–F = 1.8 Hz), 128.8, 128.7, 128.5, 122.5 (q, JC–F = 267.6 Hz), 110.3 (q, JC–F = 35.9 Hz); 19F NMR (376 MHz, CDCl3) δ −55.68; HRMS (pos. ESI): m/z [M + H]+ for C16H11F3O2Cl calcd: 327.0394, found: 327.0397.

(E)-1-(4-Bromophenyl)-3,3,3-trifluoroprop-1-enyl Benzoate (3u)

Colorless oil, 48.8 mg, yield 66%. 1H NMR (400 MHz, CDCl3) δ 8.06 (d, J = 7.6 Hz, 2H), 7.63 (t, J = 7.6 Hz, 1H), 7.54 (d, J = 8.4 Hz, 2H), 7.48 (t, J = 8.0 Hz, 2H), 7.43 (d, J = 8.4 Hz, 2H), 5.95 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9, 156.1 (q, JC–F = 6.3 Hz), 134.2, 131.6, 131.4, 130.2, 130.0 (q, JC–F = 1.8 Hz), 128.8, 128.4, 125.0, 122.4 (q, JC–F = 267.6 Hz), 110.3 (q, JC–F = 35.9 Hz); 19F NMR (376 MHz, CDCl3) δ −55.67; HRMS (pos. ESI): m/z [M + H]+ for C16H11F3O2Br calcd: 370.9889, found: 370.9896.

(E)-3,3,3-Trifluoro-1-(4-iodophenyl)prop-1-enyl Benzoate (3v)

Colorless oil, 50.2 mg, yield 60%. 1H NMR (400 MHz, CDCl3) δ 8.05 (dd, J = 7.2, 0.8 Hz, 2H), 7.75 (d, J = 8.4 Hz, 2H), 7.63 (t, J = 7.6 Hz, 1H), 7.48 (t, J = 7.6 Hz, 2H), 7.28 (d, J = 8.4 Hz, 2H), 5.94 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9, 156.2 (q, JC–F = 6.3 Hz), 137.6, 134.2, 132.0, 130.2, 130.0 (q, JC–F = 1.7 Hz), 128.8, 128.4, 122.4 (q, JC–F = 267.6 Hz), 110.3 (q, JC–F = 35.9 Hz), 97.1; 19F NMR (376 MHz, CDCl3) δ −55.65; HRMS (pos. ESI): m/z [M + H]+ for C16H11F3O2I calcd: 418.9750, found: 418.9755.

Methyl (E)-4-(1-(benzoyloxy)-3,3,3-trifluoroprop-1-en-1-yl)benzoate (3w)

Colorless oil, 36.4 mg, yield 52%. 1H NMR (400 MHz, CDCl3) δ 8.08–7.06 (m, 4H), 7.65–7.62 (m, 3H), 7.48 (t, J = 8.0 Hz, 2H), 6.01 (q, J = 8.0 Hz, 1H), 3.92 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 166.2, 163.8, 156.1 (q, JC–F = 6.3 Hz), 136.7, 134.2, 131.8, 130.2, 129.5, 128.8, 128.5 (q, JC–F = 1.8 Hz), 128.4, 122.4 (q, JC–F = 267.6 Hz), 110.8 (q, JC–F = 35.9 Hz), 52.3; 19F NMR (376 MHz, CDCl3) δ −55.69; HRMS (pos. ESI): m/z [M + H]+ for C18H14F3O4 calcd: 351.0839, found: 351.0845.

(E)-3,3,3-Trifluoro-1-phenylprop-1-enyl Benzoate (3x)

Colorless oil, 38.0 mg, yield 65%. 1H NMR (400 MHz, CDCl3) δ 8.07 (d, J = 7.2 Hz, 2H), 7.62 (t, J = 7.2 Hz, 1H), 7.57–7.55 (m, 2H), 7.47 (t, J = 8.0 Hz, 2H), 7.43–7.37 (m, 3H), 5.93 (q, J = 8.0 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9, 157.2 (q, JC–F = 6.4 Hz), 134.0, 132.5, 130.4, 130.2, 128.7, 128.4 (q, JC–F = 1.7 Hz), 128.3, 122.6 (q, JC–F = 267.4 Hz), 109.8 (q, JC–F = 35.8 Hz); 19F NMR (376 MHz, CDCl3) δ −55.60; HRMS (pos. ESI): m/z [M + H]+ for C16H12F3O2 calcd: 293.0784, found: 293.0789.

(E)-3,3,3-Trifluoro-1-(p-tolyl)prop-1-en-1-yl Benzoate (3y)

Colorless oil, 30.6 mg, yield 50%; 1H NMR (400 MHz, CDCl3) δ 8.08 (d, J = 7.6 Hz, 2H), 7.62 (t, J = 7.6 Hz, 1H), 7.49–7.44 (m, 4H), 7.20 (d, J = 8.0 Hz, 2H), 5.88 (q, J = 8.0 Hz, 1H), 2.36 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 163.9, 157.3 (q, JC–F = 6.4 Hz), 140.8, 133.9, 130.2, 129.6, 129.0, 128.8 (q, JC–F = 1.5 Hz), 128.6, 128.3, 122.5 (q, JC–F = 266.6 Hz), 109.2 (q, JC–F = 35.8 Hz), 21.4; 19F NMR (376 MHz, CDCl3) δ −55.53; HRMS (pos. ESI): m/z [M + H]+ for C17H14F3O2 calcd: 307.0940, found: 307.0942.

(E)-1-(4-(tert-Butyl)phenyl)-3,3,3-trifluoroprop-1-en-1-yl Benzoate (3z)

Colorless oil, 49.4 mg, yield 71%; 1H NMR (400 MHz, CDCl3) δ 8.08 (d, J = 7.6 Hz, 2H), 7.62 (t, J = 6.4 Hz, 1H), 7.50–7.46 (m, 4H), 7.39 (d, J = 8.0 Hz, 2H), 5.88 (q, J = 8.0 Hz, 1H), 1.31 (s, 9H); 13C{1H} NMR (100 MHz, CDCl3) δ 164.0, 157.2 (q, JC–F = 6.5 Hz), 153.8, 133.9, 130.2, 129.5, 128.8, 128.7, 128.1 (q, JC–F = 1.6 Hz), 125.2, 122.7 (q, JC–F = 267.4 Hz), 109.3 (q, JC–F = 36.0 Hz), 34.8, 31.1; 19F NMR (376 MHz, CDCl3) δ −55.50; HRMS (pos. ESI): m/z [M + H]+ for C20H20F3O2 calcd: 349.1410, found: 349.1414.