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Synlett 2006(9): 1343-1346  
DOI: 10.1055/s-2006-941574
LETTER
© Georg Thieme Verlag Stuttgart · New York

Unexpected Formation of Trifluoromethylated Spiro or Fused Cyclic Compounds from 4-Ethyloxy-1,1,1-trifluoro-3-buten-2-one and Silyl Enol Ethers

Huiling Jiang, Shizheng Zhu*
Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, P. R. of China
e-Mail: zhusz@mail.sioc.ac.cn;
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Publication History

Received 5 January 2006
Publication Date:
22 May 2006 (online)

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Abstract

Two kinds of trifluoromethylated spiro or fused cyclic compounds were synthesized via the unexpected direct α,α′-di­alkylation of (E)-4-ethoxy-1,1,1-trifluoro-3-buten-2-one (1) with silyl enol ethers in the presence of boron trifluoride etherate.

Key words

trifluoromethylated spiro or fused cyclic compounds - silyl enol ethers - (E)-4-ethoxy-1,1,1-trifluoro-3-buten-2-one - boron trifluoride etherate

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General Procedure. BF3·OEt2 (1.6 mL, 6 mmol) was added dropwise to a mixture of 1 (1.01 g, 6 mmol) and silyl enol ether (3 mmol) in CH2Cl2 (5 mL) at 0 °C under a nitrogen atmosphere. After 12 h TLC analysis showed the reaction was complete. H2O (10 mL) was added to the reaction mixture to quench the reaction, and then the organic layer was extracted with CH2Cl2 and dried over Na2SO4. The residue was subjected to column chromatography on silica gel (hexane-EtOAc, 60:1) to provide pure products.
( E )-1,1,1-Trifluoro-4-(2-trifluoromethyl-5,6-dihydro-cyclopenta[ b ]pyran-7-yl)but-3-en-2-one ( 3a): Yield: 92%; red solid; mp 88-89 °C. IR: 2976, 1687, 1587, 1515, 1252, 1078, 1018, 834 cm-1. 1H NMR (CDCl3): δ = 7.95 (1 H, d, 3 J HH = 15.0 Hz, CH), 6.21 (1 H, d, 3 J HH = 6.3 Hz, CH), 6.20 (1 H, d, 3 J HH = 15.0 Hz, CH), 6.10 (1 H, d, 3 J HH = 6.3 Hz, CH), 2.71 (2 H, m, CH2), 2.69 (2 H, m, CH2). 13C NMR (CDCl3): δ = 174.9 (C3 ′, 2 J CF = 34.7 Hz), 159.99 (C4a), 146.02 (C7a), 142.5 (C2, 2 J CF = 38.8 Hz), 139.31 (C4), 118.8 (C1 ′′, 1 J CF = 271.5Hz), 116.8 (C4 ′, 1 J CF = 292.5 Hz), 116.22 (C7), 115.78 (C2 ′), 112.88 (C3), 107.50 (C1 ′), 25.49 (C6), 24.89 (C5). 19F NMR (CDCl3, CHF3 as internal standard): δ = -71.12, -77.18 (s, CF3). LRMS: m/z (%) = 310 (M+, 64.38), 291 (M+ - F, 4.69), 263 (1.33), 241 (M+ - CF3, 100), 213 (M+ - COCF3, 17.80), 115 (30.22), 69 (CF3, 8.09). Anal. Calcd for C13H8F6O2 (310.195): C, 50.33; H, 2.60. Found: C, 49.98; H, 2.68.
( E )-1,1,1-Trifluoro-4-(2-trifluoromethyl-6,7-dihydro-5 H -1-benzopyran-8-yl)but-3-en-2-one ( 3b): Yield: 68%; red solid; mp 99-101 °C. IR: 2925, 1689, 1533, 1307, 1143 cm-1. 1H NMR (CDCl3): δ = 8.22 (1 H, d, 3 J HH = 15.3 Hz, CH), 6.31 (1 H, d, 3 J HH = 15.6 Hz, CH), 6.20 (2 H, s, CH), 2.54 (2 H, t, 3 J HH = 5.7 Hz, CH), 2.45 (2 H, t, 3 J HH = 6 Hz, CH2), 1.81 (2 H, m, CH2). 13C NMR (CDCl3): δ = 179.2 (C3 ′, 2 J CF = 33.6 Hz), 155.3 (C4a), 143.9 (C2, 2 J CF = 38.5 Hz), 142.8 (C8a), 134.7 (C4), 122.1 (C8), 116.9 (C1 ′′, 1 J CF = 269.6 Hz), 116.9 (C4 ′, 1 J CF = 288.8 Hz), 112.5 (C2 ′), 110.6 (C3), 105.7 (C1 ′), 29.7 (C7), 24.4 (C5), 19.7 (C6). 19F NMR (CDCl3, CHF3 as internal standard): δ = -71.92, -77.37. LRMS: m/z (%) = 324 (M+, 29.59), 305 (M+ - F, 2.33), 255 (M+ - CF3, 100), 199 (7.47), 69 (CF3, 13.18). HRMS: m/z calcd for C14H10F6O2: 324.059; found: 324.062.
2,11-Ditriflouromethyl-5,6,7,8-tetrahydrocyclohepta[1,2- b ;1,7- b ]di(dihydropyran) ( 3c): Yield: 71%; colorless solid; mp 123-125 °C. IR: 2948, 1683, 1449, 1349, 1306, 1189, 1070 cm-1. 1H NMR (CDCl3): δ = 6.22 (2 H, d, 3 J HH = 6.3 Hz, CH), 6.05 (2 H, d, 3 J HH = 6.3 Hz, CH), 2.48 (2 H, m, CH2), 2.34 (2 H, m, CH2), 2.03 (2 H, m, CH2), 1.48 (2 H, m, CH2). 13C NMR (CDCl3): δ = 137.43 (C2,11, 2 J CF = 37.7 Hz), 134.28 (C4a,8a), 119.54 (CF3, 1 J CF = 271.8 Hz), 120.28 (C8,9), 103.46 (C13), 102.69 (C3,10), 33.423 (C7,6), 31.81 (C5,8). 19F NMR (CDCl3, CHF3 as internal standard): δ = -72.00 (s, CF3). LRMS: m/z (%) = 338 (M+, 27.94), 319 (M+ - F, 3.27), 291 (3.98), 269 (M+ - CF3, 100), 115 (11.52), 69 (CF3, 5.64). Anal. Calcd for C15H12F6O2 (338.248): C, 53.26; H, 3.57. Found: C, 53.18; H, 3.57. X-ray data C15H12F6O2: FW = 338.25; temperature 293 K; monoclinic,C2/c; wavelength 0.71 Å; a = 14.504 (4) Å, b = 13.383 (4) Å, c = 9.806 (3) Å, α = 90o, β = 130.413 (34)o, γ = 90o; V = 1449.2 (8) Å3; Z = 4, Dc = 1.550 mg/m3; absorption coefficient 0.153 mm-1; F(000) = 688; size 0.515 × 0.371 × 0.128 mm; 2.39<θ<27.00; reflections collected 4052; absorption correction empirical; transmission 1.00mix - 0.602min; goodness-of-fit on F2 1.026; final R indices R 1 = 0.0518, wR 2 = 0.1294.
( E )-1,1,1-Trifluoro-4-(7-methyl-2 trifluoromethyl-6,7-dihydro-5 H -1-benzopyran-8-yl)but-3-en-2-one ( 3d): Yield: 64%; colorless solid; mp 70-72 °C. IR: 3096, 1689, 1534, 1142 cm-1. 1H NMR (CDCl3): δ = 8.20 (1 H, d, 3 J HH = 15.6 Hz, CH), 6.30 (1 H, d, 3 J HH = 15.0 Hz, CH), 6.21 (2 H, m, CH), 2.55 (2 H, m, CH2), 2.50 (1 H, m, CH2), 2.05 (1 H, m, CH2), 2.00 (1 H, m, CH2), 1.08 (3 H, d, 3 J HH = 6.3 Hz, CH3). 13C NMR (CDCl3): δ = 179.7 (C3 ′, 2 J C-F = 30 Hz), 152.2 (C4a), 143.7 (C2, 2 J CF = 38.5 Hz), 142.8 (C8a), 134.5 (C4), 122.1 (C8), 116.7 (C1 ′′, 1 J CF = 269.4 Hz), 116.5 (C4 ′, 1 J CF = 288.6 Hz), 112.6 (C2 ′), 111.3 (C3), 105.4 (C1 ′), 37.5 (C7), 32.6 (C5), 26.1 (C6), 20.7 (CH3). 19F NMR (CDCl3, CHF3 as internal standard): δ = -71.85, -77.39 (s, CF3). LRMS: m/z (%) = 338 (M+, 32.12), 319 (M+ - F, 2.78), 269 (M+ - CF3, 100), 270 (16.35), 69 (CF3, 11.55). Anal. Calcd for C15H12F6O2 (338.248): C, 53.26; H, 3.58. Found: C, 53.26; H, 3.84.
5,5′-Dimethyl-2,2′-trifluoromethyl-6,6′-spirobis-dihydropyra ( 3e): Yield: 67%; red solid; mp 109-110 °C. IR: 2998, 1688, 1347, 1306, 1187, 1061, 911, 838 cm-1. 1H NMR (CDCl3): δ = 6.18 (2 H, d, 3 J HH = 5.1 Hz, CH), 5.96 (2 H, d, 3 J HH = 6 Hz, CH), 1.92 (6 H, s, CH3). 13C NMR (CDCl3): δ = 138.69 (C2,10, 2 J CF = 36.5 Hz), 128.5 (C5,7), 119.94 (CF3, 1 J CF = 269.6 Hz), 120.28 (C4,8), 109.46 (C6), 101.21 (C3,9), 43.41 (CH3). 19F NMR (CDCl3, CHF3 as internal standard): δ = -72.19 (s, CF3). LRMS: m/z (%) = 312 (M+, 86.06), 297 (29.52), 265 (9.90), 245 (100), 215 (30.13), 146 (35.40), 69 (30.27). Anal. Calcd for C13H10F6O2 (312.210): C, 50.01; H, 3.28. Found: C, 49.71; H, 3.30.