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Silver salts and DBU cooperatively catalyzed nucleophilic addition/cyclization of propargylic alcohols with trifluoromethyl ketones† Jingjing Wang,* Wei-Guang Kong, Feng Li, Jie Liu, Qin Shen, Lantao Liu and Wen-Xian Zhao*

Received 5th March 2015, Accepted 2nd April 2015

A general and efficient synthesis of trifluoromethyl substituted 5-alkylidene-1,3-dioxolane using a silver

DOI: 10.1039/c5ob00438a

salt and DBU cooperatively catalyzed nucleophilic addition/cyclization of propargylic alcohols and trifluoromethyl ketones is described. The procedure produced 5-alkylidene-1,3-dioxolane derivatives with

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good to excellent yields and can be used with a broad range of substrates.

Introduction The efficient and facile construction of promising heterocycles is a continuing challenge for synthetic chemistry. In particular, heterocyclic compounds containing a trifluoromethyl group have emerged as attractive synthetic targets due to their applications in various fields like pharmacy, medicine, agriculture and materials science.1 Therefore, the development of useful methods to produce organofluorine compounds bearing a CF3 group is highly desirable. Carbonyl compounds such as ketones and aldehydes are essential building blocks for the synthesis of fine chemicals, pharmaceuticals and other materials. Since trifluoromethyl ketones have higher electrophilicities than their nonfluorinated counterparts, they are more prone to attack by nucleophiles. Therefore, trifluoromethyl ketones are ideal building blocks for synthesizing trifluoromethylated heterocycles.2 Trifluoromethyl ketones have been utilized as versatile reagents in a wide range of organic reactions, such as Henry reactions,3 1,2-addition reactions,4 annulation reactions,5 and Friedel–Crafts reactions.6 Although many studies have reported the annulation of trifluoromethyl ketones, the reaction of trifluoromethyl ketones and propargylic alcohols are very rare. Therefore, the synthesis of trifluoromethylated compounds via the annulation of trifluoromethyl ketones and propargylic alcohols is desired. Propargylic alcohols are valuable intermediates in organic syntheses,7 and can be easily prepared by coupling aryl halides

College of Chemistry and Chemical Engineering, Shangqiu Normal University, 298 Wenhua Road, Shangqiu, Henan 476000, China. E-mail: [email protected] † Electronic supplementary information (ESI) available. CCDC 1045554. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/ c5ob00438a

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with 2-methyl-3-butyn-2-ol.8 Currently, propargylic alcohols are used in coupling9 and cycloaddition10 reactions. Many reactions have been reported for the synthesis of 1,3-dioxanone by the [3 + 2] annulation of propargylic alcohols and carbon dioxide.11 To the best of our knowledge, only a few annulation reactions have been developed to synthesize 5-alkylidene-1,3dioxolane.12 Herein, an efficient method for the synthesis of trifluoromethyl substituted 5-alkylidene-1,3-dioxolane derivatives via a silver salt and DBU cooperatively catalyzed nucleophilic addition/cyclization reaction of propargylic alcohols and trifluoromethyl ketones is reported.

Results and discussion Initially, 2,2,2-trifluoroacetophenone (1a) and propargylic alcohol (2a) were chosen as the model substrates to evaluate the catalyst activity of different metal salts under various reaction conditions. The results are summarized in Table 1. When the organic base DBU was used with toluene as the solvent, no desired product was isolated (Table 1, entry 1). The reaction of 1a and 2a also did not proceed when only AgOAc was used as the catalyst (Table 1, entry 2). These disappointing results demonstrate the existence of great challenge and force us to further optimize the reaction conditions more carefully. Next, AgOAc was used in combination with DBU and the reaction gave the desired product 3aa in 96% yield (Table 1, entry 3). Other organic bases, such as DABCO and DMAP, were not effective in promoting this reaction (Table 1, entries 4 and 5). The highest yield (99%) occurred for the reaction using AgNO3 as the catalyst with DBU as the base (Table 1, entry 6). Other metal catalysts like AgOTf and Ag2O showed much lower efficacies (Table 1, entries 7 and 8), and CuI and Cu(OAc)2 did

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Table 1 Screening of reaction conditions of 2,2,2-trifluoro-acetophenone and propargylic alcohola

Entry

Metal salt

Base

Solvent

Yieldb (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14c

— AgOAc AgOAc AgOAc AgOAc AgNO3 AgOTf Ag2O CuI Cu(OAc)2 AgNO3 AgNO3 AgNO3 AgNO3

DBU — DBU DABCO DMAP DBU DBU DBU DBU DBU DBU DBU DBU DBU

Toluene Toluene Toluene Toluene Toluene Toluene Toluene Toluene Toluene Toluene THF DCM DMF Toluene

— — 96 — — 99 30 46 — — 74 65 69 86

a Reaction conditions: 1a (0.3 mmol), 2a (0.36 mmol), metal salt (10 mol%), base (10 mol%), solvent (2.0 mL). b Isolated yield. c 5 mol% AgNO3 was used.

not show any catalytic ability even in the presence DBU (Table 1, entries 9 and 10). Other solvents, such as THF, DCM and DMF, were tested and lower yields than that achieved with toluene were obtained (Table 1, entries 11–13). When the catalyst loading was reduced to 5 mol%, 3aa was obtained in 86% yield (Table 1, entry 14). Thus, the optimal catalytic system for this reaction is AgNO3 (10 mol%) with DBU (10 mol%) in toluene. To determine the importance of the trifluoromethyl ketone in this reaction, benzaldehyde and acetophenone were used instead of 2,2,2-trifluoroacetophenone under the same reaction conditions. No desired product was observed for either substrate. Next, the scope of the substrates was explored with respect to both the trifluoromethyl ketones and the propargylic alcohols using the optimized reaction conditions. The results are summarized in Table 2. The reaction of 2,2,2-trifluoroacetophenone (1a) with 2-methyl-4-phenylbut-3-yn-2-ol (2a) proceeded smoothly to give the corresponding product 3aa in 99% yield (Table 2, entry 1). In addition, 2,2,2-trifluoro-1( p-tolyl)ethanone (1b) and 1-(4-(tert-butyl)phenyl)-2,2,2-trifluoroethanone (1c) showed good reactivity with 2a, giving the desired product in 92% and 99% yields, respectively (Table 2, entries 2 and 3). Trifluoromethyl ketones with a methoxy group at the para- or meta-positions of the phenyl ring also showed good reactivity with 2a, giving the desired product in 96% or 99% yields, respectively (Table 2, entries 4 and 5). However, when there was a methoxy group at the ortho-position, the yield of the reaction decreased dramatically to 34%

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Table 2 Scope of AgNO3 and DBU cooperatively catalyzed nucleophilic addition/cyclization of propargylic alcohols with trifluoromethyl ketonesa

Trifluoromethyl ketone

Propargylic alcohol

Product

Entry

1

Ar

2

R

3

Yieldb (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

1a 1b 1c 1d 1e 1f 1g 1h 1i 1j 1k 1l 1m 1a 1a 1a 1a 1a 1a 1a 1a 1a 1a 1a 1a 1a 1a

Ph 4-Me-C6H4 4-t-Bu-C6H4 4-MeOC6H4 3-MeOC6H4 2-MeOC6H4 3,5-Me2C6H3 1-Naphthyl 4-FC6H4 4-ClC6H4 4-BrC6H4 4-PhC6H4 2-Thienyl Ph Ph Ph Ph Ph Ph Ph Ph Ph Ph Ph Ph Ph Ph

2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2b 2c 2d 2e 2f 2g 2h 2i 2j 2k 2l 2m 2n 2o

Ph Ph Ph Ph Ph Ph Ph Ph Ph Ph Ph Ph Ph 4-MeC6H4 4-MeOC6H4 3-MeOC6H4 2-MeOC6H4 3,5-Me2C6H3 1-Naphthyl 4-FC6H4 4-BrC6H4 3-BrC6H4 2-BrC6H4 4-NCC6H4 4-O2NC6H4 2-Pyridyl Butyl

3aa 3ba 3ca 3da 3ea 3fa 3ga 3ha 3ia 3ja 3ka 3la 3ma 3ab 3ac 3ad 3ae 3af 3ag 3ah 3ai 3aj 3ak 3al 3am 3an 3ao

99 92 99 96 99 34 90 97 99 99 99 99 55 96 99 92 84 93 60 81 87 84 88 90 84 20 Trace

a

Reaction conditions: 1 (0.3 mmol), 2 (0.36 mmol), AgNO3 (10 mol%), DBU (10 mol%), toluene (2.0 mL), rt, 24 h. b Isolated yield.

(Table 2, entry 6). These results suggest that a steric effect plays a significant role in the reaction. In addition, 1-(3,5-dimethylphenyl)-2,2,2-trifluoroethanone (1g) reacted with 2a to give the desired product 3ga in 90% yield (Table 2, entry 7) and 2,2,2-trifluoro-1-(naphthalen-1-yl)ethanone (1h) showed excellent reactivity (Table 2, entry 8). Trifluoromethyl ketones with an electron-withdrawing group such as F, Cl, Br, or Ph at the 4 position (li–ll), reacted with 2a to give 3ia, 3ja, 3ka, and 3la in 99% yields (Table 2, entries 9–12), thus indicating that the reaction is not very sensitive to the electron density of the phenyl group. The configuration of 3ia was identified using X-ray crystallographic analysis (Fig. 1).13 Heteroaryl groups such as thiophenyl was also tested, and the desired product was obtained albeit in only a moderate yield (3ma) (Table 2, entry 13). The scope of propargylic alcohols was also investigated. As shown in Table 2, 2-methyl-4-( p-tolyl)but-3-yn-2-ol (2b) reacted smoothly with 1a to give the desired product 3ab in 96% yield

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Fig. 1

The X-ray structure of the product 3ia.

(entry 14). Propargylic alcohols with a methoxy group at the para-, meta- or ortho-positions of the phenyl ring all exhibited good to excellent reactivities (3ac, 3ad and 3ae), indicating that steric hindrance in the alcohol did not significantly affect the efficiency of the reaction (Table 2, entries 15–17). In addition, 4-(3,5-dimethylphenyl)-2-methylbut-3-yn-2-ol (2f ) reacted with 1a to give the desired product 3af in 93% yield (Table 2, entry 18) and 2-methyl-4-(naphthalen-1-yl)but-3yn-2-ol (2g) reacted with 1a to give the desired product 3ag in moderate yield (Table 2, entry 19). Propargylic alcohols with a F or Br substituent on the phenyl ring reacted with 1a to give the desired product 3ah–3ak in good yield (81–88%) (Table 2, entries 20–23). Propargylic alcohols with a strong electron-withdrawing group at the 4 position, such as CN or NO2, gave products 3al and 3am in 90% and 84% yields, respectively (Table 2, entries 24 and 25). A pyridyl group was also tested, and the desired product was obtained in a lower yield (3an), which may be due to the strong complexation of the nitrogen atom with the metal and its competition with the substrate (Table 2, entry 26).14 The propargylic alcohol with a butyl group reacted with 1a to only give a trace amount of the desired product (Table 2, entry 27). To investigate the stereoselectivity of the reaction, 3-diphenylprop-2-yn-1-ol (4) was chosen as a reaction substrate, and reacted with 1a to give the desired product 5 in 93% yield and 1.8 : 1 dr (Fig. 2). Next, 3-methyl-1,5-diphenylpenta-1,4-diyn-3-ol (6) was tested under similar reaction conditions. The substrate 6 also reacted with 2,2,2trifluoroacetophenone (1a) to give the desired product 7 in 89% yield and with a high diastereoselectivity (dr = 3.9 : 1) (Fig. 2).

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Scheme 1

Proposed mechanism.

Based on these experimental results and previous reports,11 a plausible mechanism for the reaction is postulated in Scheme 1. Initially, the alcohol I is activated by the strong DBU base to generate the alkoxide anion II. Then, the alkoxide anion II attacks the carbonyl carbon of the trifluoromethyl ketone 2 to generate the nucleophilic addition product. Subsequently, intermediate IV is obtained by an intramolecular nucleophilic ring-closing reaction of intermediate III activated by the silver(I) catalyst. Finally, the release of the metal catalyst gives the corresponding product V.

Conclusions A general and efficient synthesis of trifluoromethyl substituted 5-alkylidene-1,3-dioxolane derivatives using a silver salt and DBU cooperatively catalyzed nucleophilic addition/annulation reaction of propargylic alcohols and trifluoromethyl ketones is described. The reaction tolerates a broad range of functional groups, and the desired products were obtained in moderate to excellent yields (20%–99%) under mild reaction conditions. Moreover, 3-diphenylprop-2-yn-1-ol and 3-methyl-1,5-diphenylpenta-1,4-diyn-3-ol were also used to obtain the desired products in good yield (89%–93%) with moderate diastereoselectivities. Further investigations on the scope of this reaction are currently underway in our laboratories.

Experimental section General information and materials 1

Fig. 2

The application of other propargylic alcohols.

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H, 13C, and 19F were recorded using a Bruker 400 MHz (1H NMR), 100 MHz (13C NMR), as well as 376 MHz (19F NMR). Chemical shifts were reported in ppm from the solvent resonance as the internal standard (CDCl3: 7.26 ppm, 77.0 ppm). Multiplicity was indicated as follows: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), dd (doublet of doublet), br (broad). Coupling constants were reported in hertz (Hz). HRMS were recorded on an APEXIII 7.0 TESLA FTMS (EI resource). All commercially available reagents and solvents were used without further purification. Analytical thin layer chromato-

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graphy was performed using 0.20 mm silica gel plates. Silica gel (200–300 mesh) was used for flash chromatography. Trifluoromethyl ketones15 and propargylic alcohols16 were prepared according to the literature.

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General procedure for the nucleophilic addition/cyclization of propargylic alcohols with trifluoromethyl ketones To a solution of the trifluoromethyl ketone 1 (0.3 mmol) and propargylic alcohols 2 (0.36 mmol) in toluene (2.0 mL) was added AgNO3 (0.03 mmol, 10 mol%) and DBU (0.03 mmol, 10 mol%). Then, the mixture was vigorously stirred at room temperature for 24 h. After the reaction was complete, the reaction mixture was concentrated under vacuum, and the residue was purified by column chromatography on silica gel ( petroleum ether–ethyl acetate 50/1) to furnish the corresponding product. (Z)-5-Benzylidene-4,4-dimethyl-2-phenyl-2-(trifluoromethyl)1,3-dioxolane (3aa). White solid; 99.3 mg, 99% yield; mp 80–81 °C.1H NMR (400 MHz, CDCl3) δ 1.31 (s, 3H), 1.67 (s, 3H), 5.24 (s, 1H), 7.21 (t, J = 7.2 Hz, 1H), 7.37 (t, J = 7.6 Hz, 2H), 7.39–7.42 (m, 3H), 7.62 (d, J = 7.2 Hz, 2H), 7.69–7.71 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 156.1, 134.7, 134.5, 129.9, 128.5, 128.1, 127.8, 126.7, 126.1, 121.8 (q, JC–F = 285.5 Hz), 105.8 (q, JC–F = 33.1 Hz), 97.0, 85.2, 29.3, 27.6; 19F NMR (376 MHz, CDCl3) δ −83.30 (s, 3F); IR (KBr) ν 3066, 2982, 1694, 1493, 1450, 1368, 1187, 1135, 1084, 1038, 959, 692 cm−1; HRMS (EI) found: m/z 335.1257 [M + H]+; calcd for C19H17F3O2 335.1253. (Z)-5-Benzylidene-4,4-dimethyl-2-(p-tolyl)-2-(trifluoromethyl)1,3-dioxolane (3ba). Yellow solid; 96.1 mg, 92% yield; mp 95–96 °C. 1H NMR (400 MHz, CDCl3) δ 1.40 (s, 3H), 1.74 (s, 3H), 2.44 (s, 3H), 5.30 (s, 1H), 7.26–7.30 (m, 3H), 7.44 (t, J = 8.0 Hz, 2H), 7.65–7.70 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 156.2, 140.0, 134.8, 131.6, 128.8, 128.4, 127.8, 126.6, 126.1, 121.8 (q, JC–F = 285.5 Hz), 105.9 (q, JC–F = 32.9 Hz), 96.8, 85.1, 29.3, 27.6, 21.2; 19F NMR (376 MHz, CDCl3) δ −83.38 (s, 3F); IR (KBr) ν 3040, 2982, 2929, 1693, 1608, 1499, 1371, 1285, 1184, 1134, 1083, 1040, 959, 812, 741 cm−1; HRMS (EI) found: m/z 349.1413 [M + H]+; calcd for C20H19F3O2 349.1410. (Z)-5-Benzylidene-2-(4-(tert-butyl)phenyl)-4,4-dimethyl-2(trifluoromethyl)-1,3-dioxolane (3ca). Light yellow solid; 116.0 mg, 99% yield; mp 64–65 °C. 1H NMR (400 MHz, CDCl3) δ 1.35 (s, 9H), 1.37 (s, 3H), 1.70 (s, 3H), 5.25 (s, 1H), 7.23 (t, J = 7.6 Hz, 1H), 7.39 (t, J = 7.6 Hz, 2H), 7.45 (d, J = 8.4 Hz, 2H), 7.65 (d, J = 7.6 Hz, 4H); 13C NMR (100 MHz, CDCl3) δ 156.3, 153.0, 134.8, 131.4, 128.4, 127.8, 126.4, 126.1, 125.1, 121.9 (q, JC–F = 285.6 Hz), 106.0 (q, JC–F = 32.9 Hz), 96.8, 85.2, 34.6, 31.2, 29.4, 27.7; 19F NMR (376 MHz, CDCl3) δ −83.23 (s, 3F); IR (KBr) ν 2966, 2866, 1693, 1602, 1485, 1344, 1275, 1185, 1133, 1079, 1039, 958, 824, 748, 700 cm−1; HRMS (EI) found: m/z 391.1881 [M + H]+; calcd for C23H25F3O2 391.1879. (Z)-5-Benzylidene-2-(4-methoxyphenyl)-4,4-dimethyl-2-(trifluoromethyl)-1,3-dioxolane (3da). Pale oily liquid; 104.9 mg, 96% yield; 1H NMR (400 MHz, CDCl3) δ 1.36 (s, 3H), 1.69 (s, 3H), 3.83 (s, 3H), 5.26 (s, 1H), 6.95 (d, J = 8.8 Hz, 2H), 7.23 (d, J = 7.6 Hz, 1H), 7.39 (d, J = 8.0 Hz, 2H), 7.63–7.66 (m, 4H);

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C NMR (100 MHz, CDCl3) δ 160.8, 156.2, 134.8, 128.4, 128.2, 127.8, 126.5, 126.1, 121.8 (q, JC–F = 285.5 Hz), 113.5, 105.9 (q, JC–F = 32.9 Hz), 96.8, 85.2, 55.2, 29.3, 27.6; 19F NMR (376 MHz, CDCl3) δ −83.48 (s, 3F); IR (KBr) ν 2984, 2927, 1693, 1610, 1511, 1453, 1346, 1254, 1181, 1038, 960, 827, 747, 697 cm−1; HRMS (EI) found: m/z 365.1364 [M + H]+; calcd for C20H19F3O3 365.1359. (Z)-5-Benzylidene-2-(3-methoxyphenyl)-4,4-dimethyl-2-(trifluoromethyl)-1,3-dioxolane (3ea). Pale oily liquid; 108.2 mg, 99% yield; 1H NMR (400 MHz, CDCl3) δ 1.24 (s, 3H), 1.58 (s, 3H), 3.71 (s, 3H), 5.15 (s, 1H), 6.87 (dt, J = 2.4 Hz, 1H), 7.11 (t, J = 7.2 Hz, 1H), 7.15 (s, 1H), 7.20–7.29 (m, 4H), 7.52 (d, J = 7.2 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 159.2, 156.0, 135.9, 134.7, 129.3, 128.4, 127.8, 126.1, 121.8 (q, JC–F = 285.7 Hz), 119.1, 115.3, 112.6, 105.6 (q, JC–F = 33.0 Hz), 97.0, 85.2, 55.2, 29.2, 27.6; 19F NMR (376 MHz, CDCl3) δ −83.16 (s, 3F); IR (KBr) ν 3061, 2985, 2942, 2840, 1694, 1599, 1487, 1452, 1314, 1280, 1186, 1043, 975, 817, 740, 694 cm−1; HRMS (EI) found: m/z 365.1362 [M + H]+; calcd for C20H19F3O3 365.1359. (Z)-5-Benzylidene-2-(2-methoxyphenyl)-4,4-dimethyl-2-(trifluoromethyl)-1,3-dioxolane (3fa). Light yellow oily liquid; 37.1 mg, 34% yield; 1H NMR (400 MHz, CDCl3) δ 1.38 (s, 3H), 1.69 (s, 3H), 3.93 (s, 3H), 5.23 (s, 1H), 6.97–7.00 (m, 2H), 7.20 (t, J = 7.2 Hz, 1H), 7.34–7.43 (m, 3H), 7.68–7.72 (m, 3H); 13C NMR (100 MHz, CDCl3) δ 158.0, 156.5, 135.0, 131.6, 129.4, 128.3, 127.8, 125.9, 122.3, 122.0 (q, JC–F = 286.5 Hz), 120.0, 112.2, 106.3 (q, JC–F = 34.6 Hz), 96.5, 84.5, 55.8, 29.2, 27.6; 19 F NMR (376 MHz, CDCl3) δ −82.74 (s, 3F); IR (KBr) ν 2992, 2936, 1694, 1596, 1493, 1341, 1259, 1187, 1084, 1040, 952, 750 cm−1; HRMS (EI) found: m/z 365.1363 [M + H]+; calcd for C20H19F3O3 365.1359. (Z)-5-Benzylidene-2-(3,5-dimethylphenyl)-4,4-dimethyl-2-(trifluoromethyl)-1,3-dioxolane (3ga). White solid; 97.8 mg, 90% yield; mp 108–109 °C; 1H NMR (400 MHz, CDCl3) δ 1.25 (s, 3H), 1.58 (s, 3H), 2.26 (s, 6H), 5.15 (s, 1H), 6.97 (s, 1H), 7.12 (t, J = 7.2 Hz, 1H), 7.21 (s, 2H), 7.29 (t, J = 8.0 Hz, 2H), 7.54 (d, J = 7.2 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 155.8, 137.8, 134.6, 134.5, 129.9, 128.1, 127.9, 126.7, 125.7, 121.8 (q, JC–F = 285.7 Hz), 105.7 (q, JC–F = 33.1 Hz), 97.0, 85.1, 29.3, 27.5, 21.4; 19 F NMR (376 MHz, CDCl3) δ −83.24 (s, 3F); IR (KBr) ν 3035, 2985, 1689, 1557, 1442, 1370, 1308, 1185, 1139, 1027, 973, 837, 722, 686 cm−1; HRMS (EI) found: m/z 363.1570 [M + H]+; calcd for C21H21F3O2 363.1566. (Z)-5-Benzylidene-4,4-dimethyl-2-(naphthalen-1-yl)-2-(trifluoromethyl)-1,3-dioxolane (3ha). White solid; 111.8 mg, 97% yield; mp 119–120 °C; 1H NMR (400 MHz, CDCl3) δ 1.25 (s, 3H), 1.73 (s, 3H), 5.27 (s, 1H), 7.20–7.26 (m, 1H), 7.39 (t, J = 8.0 Hz, 2H), 7.43–7.51 (m, 3H), 7.66 (d, J = 7.2 Hz, 2H), 7.85 (d, J = 8.0 Hz, 1H), 7.89–7.94 (m, 2H), 8.02 (d, J = 7.2 Hz, 1H); 13 C NMR (100 MHz, CDCl3) δ 156.3, 153.0, 134.8, 131.4, 130.2, 130.1, 128.4, 127.8, 127.3, 126.4, 126.1, 125.1, 121.9 (q, JC–F = 285.7 Hz), 106.0 (q, JC–F = 33.1 Hz), 96.8, 85.2, 29.4, 27.7; 19 F NMR (376 MHz, CDCl3) δ −81.96 (s, 3F); IR (KBr) ν 3056, 2984, 2934, 1694, 1596, 1502, 1352, 1184, 1144, 1038, 928, 785, 740 cm−1; HRMS (EI) found: m/z 385.1412 [M + H]+; calcd for C23H19F3O2 385.1410. 13

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(Z)-5-Benzylidene-2-(4-fluorophenyl)-4,4-dimethyl-2-(trifluoromethyl)-1,3-dioxolane (3ia). White solid; 104.6 mg, 99% yield; mp 72–73 °C; 1H NMR (400 MHz, CDCl3) δ 1.32 (s, 3H), 1.66 (s, 3H), 5.25 (s, 1H), 7.09 (t, J = 8.4 Hz, 2H), 7.21 (t, J = 7.6 Hz, 1H), 7.36 (t, J = 8.0 Hz, 2H), 7.60 (d, J = 7.6 Hz, 2H), 7.66–7.70 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 163.7 (d, JC–F = 247.8 Hz), 155.9, 134.6, 130.5 (d, JC–F = 3.1 Hz), 128.9 (d, JC–F = 8.6 Hz), 128.5, 127.8, 126.3, 121.7 (q, JC–F = 285.5 Hz), 115.2 (d, JC–F = 21.8 Hz), 105.4 (q, JC–F = 33.3 Hz), 97.2, 85.4, 29.3, 27.5; 19F NMR (376 MHz, CDCl3) δ −83.47 (s, 3F), −111.02 (s, 1F); IR (KBr) ν 3066, 2985, 2934, 1694, 1605, 1507, 1450, 1341, 1187, 1137, 1085, 1044, 961, 828, 745, 695 cm−1; HRMS (EI) found: m/z 353.1165 [M + H]+; calcd for C19H16F4O2 353.1159. (Z)-5-Benzylidene-2-(4-chlorophenyl)-4,4-dimethyl-2-(trifluoromethyl)-1,3-dioxolane (3ja). White solid; 109.5 mg, 99% yield; mp 97–98 °C; 1H NMR (400 MHz, CDCl3) δ 1.32 (s, 3H), 1.66 (s, 3H), 5.25 (s, 1H), 7.21 (t, J = 7.6 Hz, 1H), 7.35–7.40 (m, 4H), 7.58–7.64 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 155.8, 136.2, 134.5, 133.1, 128.6, 128.5, 128.2, 127.8, 126.3, 121.6 (q, JC–F = 285.7 Hz), 105.4 (q, JC–F = 33.1 Hz), 97.3, 85.4, 29.3, 27.5; 19F NMR (376 MHz, CDCl3) δ −83.40 (s, 3F); IR (KBr) ν 2981, 2925, 1694, 1597, 1493, 1368, 1192, 1133, 1085, 1043, 957, 822, 743, 694 cm−1; HRMS (EI) found: m/z 369.0867 [M + H]+; calcd for C19H16ClF3O2 369.0864. (Z)-5-Benzylidene-2-(4-bromophenyl)-4,4-dimethyl-2-(trifluoromethyl)-1,3-dioxolane (3ka). White solid; 122.7 mg, 99% yield; mp 101–102 °C; 1H NMR (400 MHz, CDCl3) δ 1.31 (s, 3H), 1.66 (s, 3H), 5.25 (s, 1H), 7.21 (t, J = 7.6 Hz, 1H), 7.36 (t, J = 8.0 Hz, 2H), 7.53–7.60 (m, 6H); 13C NMR (100 MHz, CDCl3) δ 155.8, 134.5, 133.7, 131.5, 128.5, 127.9, 126.4, 124.6, 121.6 (q, JC–F = 285.6 Hz), 105.4 (q, JC–F = 33.3 Hz), 97.4, 85.5, 29.3, 27.6; 19F NMR (376 MHz, CDCl3) δ −83.37 (s, 3F); IR (KBr) ν 3066, 2986, 2933, 1695, 1592, 1490, 1345, 1193, 1135, 1080, 1043, 956, 820, 744, 696 cm−1; HRMS (EI) found: m/z 413.0363 [M + H]+; calcd for C19H16BrF3O2 413.0359. (Z)-2-([1,1′-Biphenyl]-4-yl)-5-benzylidene-4,4-dimethyl-2-(trifluoromethyl)-1,3-dioxolane (3la). White solid; 121.9 mg, 99% yield; mp 109–110 °C; 1H NMR (400 MHz, CDCl3) δ 1.38 (s, 3H), 1.71 (s, 3H), 5.28 (s, 1H), 7.24 (t, J = 7.6 Hz, 1H), 7.36–7.42 (m, 3H), 7.46 (t, J = 7.6 Hz, 2H), 7.60–7.66 (m, 6H), 7.78 (d, J = 8.0 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 156.1, 142.8, 140.2, 134.7, 133.3, 128.8, 128.5, 127.8, 127.7, 127.2, 127.1, 126.9, 126.2, 121.8 (q, JC–F = 285.7 Hz), 105.8 (q, JC–F = 33.0 Hz), 97.0, 85.3, 29.4, 27.6; 19F NMR (376 MHz, CDCl3) δ −83.21 (s, 3F); IR (KBr) ν 3064, 2986, 1692, 1606, 1435, 1369, 1188, 1131, 1081, 1040, 960, 831, 748, 700 cm−1; HRMS (EI) found: m/z 411.1567 [M + H]+; calcd for C25H21F3O2 411.1566. (Z)-5-Benzylidene-4,4-dimethyl-2-(thiophen-2-yl)-2-(trifluoromethyl)-1,3-dioxolane (3ma). Yellow oily liquid; 56.2 mg, 55% yield; 1H NMR (400 MHz, CDCl3) δ 1.47 (s, 3H), 1.69 (s, 3H), 5.28 (s, 1H), 7.06 (t, J = 4.4 Hz, 1H), 7.20–7.25 (m, 1H), 7.36 (t, J = 8.0 Hz, 2H), 7.41 (d, J = 4.8 Hz, 2H), 7.60 (d, J = 7.2 Hz, 2H); 13 C NMR (100 MHz, CDCl3) δ 156.2, 137.7, 134.8, 134.2, 131.6, 128.4, 127.8, 126.1, 124.4, 121.9 (q, JC–F = 285.9 Hz), 105.9 (q, JC–F = 32.8 Hz), 96.8, 85.1, 29.4, 27.4; 19F NMR (376 MHz,

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CDCl3) δ −83.35 (s, 3F); IR (KBr) ν 3062, 2985, 2929, 1694, 1598, 1440, 1352, 1266, 1189, 1128, 1071, 1039, 915, 837, 737 cm−1; HRMS (EI) found: m/z 341.0821 [M + H]+; calcd for C17H15F3O2S 341.0818. (Z)-4,4-Dimethyl-5-(4-methylbenzylidene)-2-phenyl-2-(trifluoromethyl)-1,3-dioxolane (3ab). White solid; 100.4 mg, 96% yield; mp 70–71 °C; 1H NMR (400 MHz, CDCl3) δ 1.34 (s, 3H), 1.70 (s, 3H), 2.39 (s, 3H), 5.25 (s, 1H), 7.21 (d, J = 8.0 Hz, 2H), 7.41–7.45 (m, 3H), 7.55 (d, J = 8.0 Hz, 2H), 7.73–7.75 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 155.4, 135.8, 134.6, 131.8, 129.9, 129.2, 128.1, 127.7, 126.8, 121.8 (q, JC–F = 285.8 Hz), 105.6 (q, JC–F = 33.1 Hz), 96.9 (d, JC–F = 4.9 Hz), 85.1, 29.3, 27.6, 21.2 (d, JC–F = 5.2 Hz); 19F NMR (376 MHz, CDCl3) δ −83.29 (s, 3F); IR (KBr) ν 2985, 2929, 1692, 1510, 1452, 1346, 1187, 1134, 1084, 1039, 959, 838, 724 cm−1; HRMS (EI) found: m/z 349.1414 [M + H]+; calcd for C20H19F3O2 349.1410. (Z)-5-(4-Methoxybenzylidene)-4,4-dimethyl-2-phenyl-2-(trifluoromethyl)-1,3-dioxolane (3ac). White solid; 108.3 mg, 99% yield; mp 101–102 °C; 1H NMR (400 MHz, CDCl3) δ 1.33 (s, 3H), 1.68 (s, 3H), 3.84 (s, 3H), 5.22 (s, 1H), 6.95 (d, J = 8.8 Hz, 2H), 7.41–7.44 (m, 3H), 7.58 (d, J = 8.8 Hz, 2H), 7.71–7.74 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 157.9, 154.4, 134.6, 129.9, 129.0, 128.1, 127.4, 126.7, 121.9 (q, JC–F = 285.7 Hz), 113.9, 105.5 (q, JC–F = 32.9 Hz), 96.5, 85.0, 55.2, 29.3, 27.6; 19 F NMR (376 MHz, CDCl3) δ −83.28 (s, 3F); IR (KBr) ν 2984, 1695, 1609, 1511, 1368, 1252, 1184, 1132, 1036, 960, 842, 721 cm−1; HRMS (EI) found: m/z 365.1363 [M + H]+; calcd for C20H19F3O3 365.1359. (Z)-5-(3-Methoxybenzylidene)-4,4-dimethyl-2-phenyl-2-(trifluoromethyl)-1,3-dioxolane (3ad). White oily liquid; 100.6 mg, 92% yield; 1H NMR (400 MHz, CDCl3) δ 1.28 (s, 3H), 1.63 (s, 3H), 3.81 (s, 3H), 5.19 (s, 1H), 6.74 (dd, J = 7.6 Hz, 2.0 Hz, 1H), 7.12 (d, J = 8.0 Hz, 1H), 7.19–7.24 (m, 2H), 7.35–7.39 (m, 3H), 7.64–7.66 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 159.6, 156.3, 136.0, 134.4, 130.0, 129.3, 128.1, 126.7, 121.8 (q, JC–F = 285.7 Hz), 120.5, 112.8, 112.2, 105.8 (q, JC–F = 33.0 Hz), 96.9, 85.3, 55.0, 29.2, 27.5; 19F NMR (376 MHz, CDCl3) δ −83.35 (s, 3F); IR (KBr) ν 3064, 2985, 2940, 2835, 1691, 1593, 1484, 1458, 1344, 1256, 1190, 1086, 1041, 960, 872, 761, 724 cm−1; HRMS (EI) found: m/z 365.1361 [M + H]+; calcd for C20H19F3O3 365.1359. (Z)-5-(2-Methoxybenzylidene)-4,4-dimethyl-2-phenyl-2-(trifluoromethyl)-1,3-dioxolane (3ae). Light yellow solid; 91.9 mg, 84% yield; mp 77–78 °C; 1H NMR (400 MHz, CDCl3) δ 1.24 (s, 3H), 1.60 (s, 3H), 3.73 (s, 3H), 5.64 (s, 1H), 6.77 (d, J = 7.2 Hz, 1H), 6.95 (t, J = 7.6 Hz, 1H), 7.08–7.13 (m, 1H), 7.29–7.32 (m, 3H), 7.61 (t, J = 4.0 Hz, 2H), 8.00 (dd, J = 8.0 Hz, 1.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 156.0, 155.5, 134.6, 129.9, 128.6, 128.1, 127.2, 126.8, 123.5, 121.9 (q, JC–F = 285.7 Hz), 120.7, 110.2, 105.6 (q, JC–F = 32.9 Hz), 90.1, 85.4, 55.4, 29.4, 27.7; 19F NMR (376 MHz, CDCl3) δ −83.25 (s, 3F); IR (KBr) ν 3072, 2983, 1690, 1588, 1453, 1371, 1248, 1186, 1137, 1082, 1037, 960, 754 cm−1; HRMS (EI) found: m/z 365.1364 [M + H]+; calcd for C20H19F3O3 365.1359. (Z)-5-(3,5-Dimethylbenzylidene)-4,4-dimethyl-2-phenyl-2(trifluoromethyl)-1,3-dioxolane (3af ). Yellow oily liquid;

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101.2 mg, 93% yield; 1H NMR (400 MHz, CDCl3) δ 1.35 (s, 3H), 1.70 (s, 3H), 2.39 (s, 6H), 5.23 (s, 1H), 6.91 (s, 1H), 7.30 (s, 2H), 7.43–7.47 (m, 3H), 7.74–7.76 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 155.8, 137.8, 134.6, 134.5, 129.9, 128.1, 127.9, 126.7, 125.7, 121.8 (q, JC–F = 285.7 Hz), 105.7 (q, JC–F = 33.1 Hz), 97.0, 85.1, 29.3, 27.5, 21.4; 19F NMR (376 MHz, CDCl3) δ −83.29 (s, 3F); IR (KBr) ν 2986, 2923, 1691, 1594, 1454, 1398, 1338, 1288, 1186, 1134, 1087, 1042, 959, 849, 718 cm−1; HRMS (EI) found: m/z 363.1568 [M + H]+; calcd for C21H21F3O2 363.1566. (Z)-4,4-Dimethyl-5-(naphthalen-1-ylmethylene)-2-phenyl-2-(trifluoromethyl)-1,3-dioxolane (3ag). Yellow solid; 69.2 mg, 60% yield; mp 89–90 °C; 1H NMR (400 MHz, CDCl3) δ 1.47 (s, 3H), 1.83 (s, 3H), 5.95 (s, 1H), 7.41–7.46 (m, 3H), 7.51–7.55 (m, 2H), 7.59 (t, J = 8.0 Hz, 1H), 7.71–7.73 (m, 2H), 7.78 (d, J = 8.4 Hz, 1H), 7.88–7.90 (m, 1H), 8.05–8.11 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 157.3, 134.5, 133.7, 131.0, 130.6, 129.8, 128.7, 128.1, 126.9, 126.8, 126.1, 125.8, 125.7, 125.5, 123.6, 121.8 (q, JC–F = 285.8 Hz), 105.7 (q, JC–F = 32.9 Hz), 92.7, 85.2, 29.6, 27.8; 19 F NMR (376 MHz, CDCl3) δ −83.14 (s, 3F); IR (KBr) ν 3050, 2984, 1689, 1507, 1275, 1186, 1137, 1087, 1041, 958, 776, 726 cm−1; HRMS (EI) found: m/z 385.1414 [M + H]+; calcd for C23H19F3O2 385.1410. (Z)-5-(4-Fluorobenzylidene)-4,4-dimethyl-2-phenyl-2-(trifluoromethyl)-1,3-dioxolane (3ah). White solid; 85.7 mg, 81% yield; mp 98–99 °C; 1H NMR (400 MHz, CDCl3) δ 1.34 (s, 3H), 1.69 (s, 3H), 5.23 (s, 1H), 7.05–7.10 (m, 2H), 7.41–7.45 (m, 3H), 7.58–7.61 (m, 2H), 7.70–7.72 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 161.1 (d, JC–F = 244.3 Hz), 155.7 (d, JC–F = 2.3 Hz), 134.4, 130.8 (d, JC–F = 3.0 Hz), 130.0, 129.3 (d, JC–F = 7.6 Hz), 128.1, 126.7, 121.8 (q, JC–F = 285.7 Hz), 115.3 (d, JC–F = 21.3 Hz), 105.8 (q, JC–F = 33.1 Hz), 96.0, 85.2, 29.3, 27.5; 19F NMR (376 MHz, CDCl3) δ −83.33 (s, 3F), −115.66 (s, 1F); IR (KBr) ν 2988, 1699, 1509, 1363, 1187, 1134, 1085, 1040, 960, 844, 724 cm−1; HRMS (EI) found: m/z 353.1162 [M + H]+; calcd for C19H16F4O2 353.1159. (Z)-5-(4-Bromobenzylidene)-4,4-dimethyl-2-phenyl-2-(trifluoromethyl)-1,3-dioxolane (3ai). Yellow solid; 107.9 mg, 87% yield; mp 106–107 °C; 1H NMR (400 MHz, CDCl3) δ 1.33 (s, 3H), 1.68 (s, 3H), 5.20 (s, 1H), 7.41–7.51 (m, 7H), 7.68–7.70 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 156.7, 134.2, 133.7, 131.5, 130.0, 129.3, 128.2, 126.7, 121.7 (q, JC–F = 285.6 Hz), 119.7, 106.0 (q, JC–F = 32.9 Hz), 96.0, 85.3, 29.2, 27.5; 19F NMR (376 MHz, CDCl3) δ −83.33 (s, 3F); IR (KBr) ν 2983, 2925, 1692, 1488, 1339, 1276, 1187, 1137, 1083, 1039, 959, 840, 721 cm−1; HRMS (EI) found: m/z 413.0366 [M + H]+; calcd for C19H16BrF3O2 413.0359. (Z)-5-(3-Bromobenzylidene)-4,4-dimethyl-2-phenyl-2-(trifluoromethyl)-1,3-dioxolane (3aj). Yellow solid; 104.2 mg, 84% yield; mp 60–61 °C; 1H NMR (400 MHz, CDCl3) δ 1.31 (s, 3H), 1.66 (s, 3H), 5.17 (s, 1H), 7.22 (t, J = 8.0 Hz, 1H), 7.31–7.33 (m, 1H), 7.39–7.43 (m, 3H), 7.57 (d, J = 8.0 Hz, 1H), 7.67–7.72 (m, 3H); 13 C NMR (100 MHz, CDCl3) δ 157.3, 136.8, 134.2, 130.7, 130.1, 129.9, 129.0, 128.2, 126.7, 126.2, 122.5, 121.7 (q, JC–F = 285.6 Hz), 106.1 (q, JC–F = 33.0 Hz), 95.7, 85.4, 29.2, 27.5; 19F NMR (376 MHz, CDCl3) δ −83.32 (s, 3F); IR (KBr) ν 2988, 1688, 1592, 1442, 1359, 1289, 1190, 1136, 1085, 1040, 960, 725 cm−1;

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HRMS (EI) found: m/z 413.0362 [M + H]+; calcd for C19H16BrF3O2 413.0359. (Z)-5-(2-Bromobenzylidene)-4,4-dimethyl-2-phenyl-2-(trifluoromethyl)-1,3-dioxolane (3ak). Yellow solid; 109.1 mg, 88% yield; mp 87–88 °C; 1H NMR (400 MHz, CDCl3) δ 1.38 (s, 3H), 1.73 (s, 3H), 5.69 (s, 1H), 7.07 (dt, J = 8.0 Hz, 1.6 Hz, 1H), 7.36–7.48 (m, 4H), 7.58 (dd, J = 8.0 Hz, 1.2 Hz, 1H), 7.68–7.70 (m, 2H), 8.10 (dd, J = 8.0 Hz, 1.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 157.6, 134.2, 134.0, 132.6, 130.0, 129.2, 128.2, 127.5, 126.7, 123.0, 121.7 (q, JC–F = 285.7 Hz), 106.1 (q, JC–F = 33.2 Hz), 95.5, 95.4, 85.6, 29.4, 27.6; 19F NMR (376 MHz, CDCl3) δ −83.28 (s, 3F); IR (KBr) ν 3060, 2982, 1692, 1465, 1345, 1278, 1189, 1133, 1085, 1035, 960, 751 cm−1; HRMS (EI) found: m/z 413.0365 [M + H]+; calcd for C19H16BrF3O2 413.0359. (Z)-4-((5,5-Dimethyl-2-phenyl-2-(trifluoromethyl)-1,3-dioxolan-4-ylidene)methyl)benzonitrile (3al). White solid; 97.2 mg, 90% yield; mp 135–136 °C; 1H NMR (400 MHz, CDCl3) δ 1.35 (s, 3H), 1.70 (s, 3H), 5.28 (s, 1H), 7.41–7.48 (m, 3H), 7.62–7.69 (m, 6H); 13C NMR (100 MHz, CDCl3) δ 159.1, 139.5, 133.8, 132.2, 130.2, 128.2, 128.0, 126.6, 121.6 (q, JC–F = 285.5 Hz), 119.2, 109.0, 106.5 (q, JC–F = 33.1 Hz), 95.8, 85.8, 29.1, 27.4; 19F NMR (376 MHz, CDCl3) δ −83.36 (s, 3F); IR (KBr) ν 3070, 2986, 2225, 1686, 1604, 1502, 1358, 1278, 1188, 1139, 1082, 1038, 960, 851, 724 cm−1; HRMS (EI) found: m/z 360.1210 [M + H]+; calcd for C20H16F3NO2 360.1206. (Z)-4,4-Dimethyl-5-(4-nitrobenzylidene)-2-phenyl-2-(trifluoromethyl)-1,3-dioxolane (3am). Yellow solid; 95.6 mg, 84% yield; mp 114–115 °C; 1H NMR (400 MHz, CDCl3) δ 1.38 (s, 3H), 1.72 (s, 3H), 5.36 (s, 1H), 7.43–7.48 (m, 3H), 7.69–7.75 (m, 4H), 8.22–8.25 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 159.8, 145.4, 141.6, 133.7, 130.3, 128.3, 128.0, 126.6, 123.9, 121.5 (q, JC–F = 285.3 Hz), 106.7 (q, JC–F = 33.3 Hz), 95.5, 85.9, 29.1, 27.4; 19 F NMR (376 MHz, CDCl3) δ −83.35 (s, 3F); IR (KBr) ν 3070, 2986, 2930, 1684, 1594, 1514, 1340, 1190, 1082, 1037, 960, 859, 723 cm−1; HRMS (EI) found: m/z 380.1105 [M + H]+; calcd for C19H16F3NO4 380.1104. (Z)-2-(5-Benzylidene-4,4-dimethyl-2-(trifluoromethyl)-1,3dioxolan-2-yl)pyridine (3an). Yellow oily liquid; 20.2 mg, 20% yield; 1H NMR (400 MHz, CDCl3) δ 1.65 (s, 3H), 1.90 (s, 3H), 6.15 (s, 1H), 6.99 (dd, J = 7.6 Hz, 4.8 Hz, 1H), 7.07 (d, J = 8.0 Hz, 1H), 7.40–7.43 (m, 3H), 7.54 (dt, J = 7.6 Hz, 1.6 Hz, 1H), 7.68 (t, J = 3.6 Hz, 2H), 8.47 (d, J = 3.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 155.9, 138.0, 136.9, 134.4, 129.1, 128.4, 127.9, 127.7, 127.2, 126.3, 121.4 (q, JC–F = 285.4 Hz), 104.7 (q, JC–F = 34.3 Hz), 97.5, 85.9, 29.3, 27.7; 19F NMR (376 MHz, CDCl3) δ −83.12 (s, 3F); IR (KBr) ν 3066, 2976, 2930, 1669, 1585, 1472, 1349, 1263, 1185, 1137, 1095, 1055, 958, 849, 769, 725 cm−1; HRMS (EI) found: m/z 336.1214 [M + H]+; calcd for C18H16F3NO2 336.1206. (Z)-4-Benzylidene-2,5-diphenyl-2-(trifluoromethyl)-1,3-dioxolane (5). White solid; 106.8 mg, 1.8 : 1 dr, 93% yield; mp 103–105 °C; IR (KBr) ν 3064, 2921, 1695, 1495, 1453, 1370, 1276, 1190, 1089, 961, 696 cm−1; HRMS (EI) found: m/z 383.1256 [M + H]+; calcd for C23H17F3O2 383.1253. Major diastereoisomer: 1H NMR (400 MHz, CDCl3) δ 4.94 (d, J = 1.6 Hz, 1H), 5.54 (d, J = 1.6 Hz, 1H), 7.19–7.21 (m, 1H),

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7.30–7.35 (m, 5H), 7.42–7.46 (m, 5H), 7.56 (d, J = 1.2 Hz, 2H), 7.76–7.78 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 151.4, 135.9, 134.4, 133.0, 130.4, 129.6, 128.8, 128.5, 128.4, 127.9, 127.2, 126.4, 121.6 (q, JC–F = 284.7 Hz), 106.3 (q, JC–F = 33.4 Hz), 100.7, 82.0; 19F NMR (376 MHz, CDCl3) δ −82.16. Minor diastereoisomer: 1H NMR (400 MHz, CDCl3) δ 5.03 (d, J = 1.6 Hz, 0.57H), 6.05 (s, 0.57H), 7.16–7.18 (m, 0.57H), 7.26–7.29 (m, 1.67H), 7.46–7.50 (m, 3.90H), 7.54 (d, J = 2.0 Hz, 1.13H), 7.45 (d, J = 2.0 Hz, 1.12H); 13C NMR (100 MHz, CDCl3) δ 151.7, 137.5, 134.3, 133.1, 130.2, 129.2, 128.7, 128.5, 128.4, 128.0, 126.6, 126.4, 122.6 (q, JC–F = 288.7 Hz), 107.0 (q, JC–F = 32.7 Hz), 100.5, 83.6; 19F NMR (376 MHz, CDCl3) δ −81.75. (Z)-5-Benzylidene-4-methyl-2-phenyl-4-( phenylethynyl)-2-(trifluoromethyl)-1,3-dioxolane (7). White liquid; 112.3 mg, 3.9 : 1 dr, 89% yield; IR (KBr) ν 3064, 2988, 1696, 1590, 1491, 1446, 1364, 1272, 1191, 1111, 1030, 958, 828, 750, 694 cm−1; HRMS (EI) found: m/z 421.1413 [M + H]+; calcd for C26H19F3O2 421.1410. Major diastereoisomer: 1H NMR (400 MHz, CDCl3) δ 1.99 (s, 3H), 5.53 (s, 1H), 6.97–7.00 (m, 2H), 7.14–7.16 (m, 2H), 7.35–7.43 (m, 5H), 7.65 (d, J = 7.2 Hz, 2H), 7.78–7.80 (m, 2H); 13 C NMR (100 MHz, CDCl3) δ 152.4, 134.3, 133.1, 131.5, 130.1, 128.6, 128.5, 128.2, 128.1, 128.0, 127.3, 126.6, 121.6, 121.5 (q, JC–F = 284.7 Hz), 106.6 (q, JC–F = 33.4 Hz), 99.0, 87.7, 86.0, 78.6, 27.6; 19F NMR (376 MHz, CDCl3) δ −82.96. Minor diastereoisomer: 1H NMR (400 MHz, CDCl3) δ 1.75 (s, 0.76H), 5.64 (s, 0.26H), 7.24–7.26 (m, 0.28H), 7.30–7.34 (m, 1.03H), 7.43–7.45 (m, 1.04H), 7.48–7.52 (m, 0.77H), 7.72–7.75 (m, 0.76H); 13C NMR (100 MHz, CDCl3) δ 152.8, 134.2, 133.7, 131.9, 130.2, 128.9, 128.6, 128.2, 128.1, 128.0, 127.3, 126.6, 121.8, 121.5 (q, JC–F = 286.7 Hz), 106.6 (q, JC–F = 33.5 Hz), 99.4, 87.1, 85.8, 80.2, 30.7; 19F NMR (376 MHz, CDCl3) δ −82.26.

Acknowledgements We are thankful for financial support from the National Natural Science Foundation of China (no. 21402116, 21202095 and 21172139).

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cyclization of propargylic alcohols with trifluoromethyl ketones.

A general and efficient synthesis of trifluoromethyl substituted 5-alkylidene-1,3-dioxolane using a silver salt and DBU cooperatively catalyzed nucleo...
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