Construction of Terminal Conjugated Enynes: Regio- and Stereoselective Syntheses of 3-Alken-1-ynes and 1-Trimethylsilyl-3-alken-1-ynes from Alkenyldialkylboranes and (Trimethylsilyl)ethynyl Bromide

Masayuki Hoshi; Kazuya Shirakawa

doi:10.1055/s-2002-32604

LETTER

Construction of Terminal Conjugated Enynes: Regio- and Stereoselective Syntheses of 3-Alken-1-ynes and 1-Trimethylsilyl-3-alken-1-ynes from Alkenyldialkylboranes and (Trimethylsilyl)ethynyl Bromide

Masayuki Hoshi*, Kazuya Shirakawa
Department of Applied and Environmental Chemistry, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan
Fax: +81(157)247719; e-Mail: hoshi-m@chem.kitami-it.ac.jp;

Abstract

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Abstract

The cross-coupling reaction of (E)- and (Z)-1-alkenyldialkylboranes with (trimethylsilyl)ethynyl bromide proceeds in the presence of a base and a catalytic amount of Cu(acac)₂ under very mild conditions to provide conjugated enynes whose carbon-carbon triple bond is in distal position. The use of 1 M NaOMe as a base exclusively affords both (E)- and (Z)-3-alken-1-ynes with high regio- and stereoselectivity, while the use of LiOH·H₂O instead of 1 M NaOMe preferentially gives both (E)- and (Z)-1-trimethylsilyl-3-alken-1-ynes regio- and stereoselectively.

Key words

cross-coupling - 3-alken-1-yne - 1-trimethylsilyl-3-alken-1-yne - alkenyldialkylborane - (trimethylsilyl)ethynyl bromide

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References

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To a stirred solution of (E)-1-octenylbis(1,2-dimethyl-propyl)borane (4 mmol) in THF (12 mL) at -15 °C, Cu(acac)₂ (0.052 g, 0.2 mmol) was added under an argon flow. (Trimethylsilyl)ethynyl bromide (0.474 g, 2.68 mmol) and 1 M NaOMe (4 mL, 4 mmol) were then added dropwise to the solution, and the resulting mixture was allowed to warm gradually to room temperature and to stir overnight. The reaction mixture was treated with 3 M NaOH (4 mL) and 30% H₂O₂ (2 mL) at 0 °C and stirred for 1 h at the same temperature to decompose the residual organoboron compound. The resultant mixture was extracted with ether, washed with brine, and dried over anhydrous Na₂SO₄. The solvent was removed on a rotary evaporator under reduced pressure, and the crude product was purified by column chromatography on silica gel, with n-pentane as eluent, to give product 2a (0.255 g, 70% yield) as a colorless liquid. Compound 2a: ¹H NMR (CDCl₃) δ: 0.88 (t, 3 H), 1.1-1.5 (m, 8 H), 2.0-2.2 (m, 2 H), 2.76 (dd, J = 2.2, 0.4 Hz, 1 H), 5.47 (ddt, J = 16.0, 2.2, 1.5 Hz, 1 H), 6.22 (dtd, J = 16.0, 6.8, 0.4 Hz, 1 H); ¹³C NMR (CDCl₃) δ: 14.04, 22.60, 28.58, 28.79, 31.68, 33.02, 75.49 (CH), 82.66 (C-), 108.52
(CH-), 146.96 (=CH-); IR(neat) 3315, 3024, 2956, 2927, 2856, 2104, 1629, 1465, 1436, 954, cm^-1; HRMS (EI) C₁₀H₁₆: requires 136.1252; found 136.1254.

To a stirred solution of (E)-1-octenyldicyclohexylborane (4 mmol) in THF (12 mL) at -15 °C, Cu(acac)₂ (0.052 g, 0.2 mmol) was added under an argon flow. (Trimethyl-silyl)ethynyl bromide (0.474 g, 2.68 mmol) was added dropwise to the solution, and then LiOH·H₂O (0.168 g, 4 mmol) was introduced into the solution under an argon flow. The resulting mixture was allowed to warm gradually to room temperature and to stir overnight. After the reaction mixture was neutralized with sat. NH₄Cl, the resultant mixture was treated with NaBO₃·4H₂O (1.846 g, 12 mmol) and H₂O (4 mL) at room temperature with vigorous stirring for 2 h to decompose the residual organoboron compound. Workup is the same as described in ref. 9. The crude product was purified by column chromatography on silica gel, with n-pentane as eluent, to give product 3a (0.401 g, 72% yield) as a colorless liquid. Compound 3a: ¹H NMR (CDCl₃) δ: 0.17 (s, 9 H), 0.88 (t, 3 H), 1.1-1.5 (m, 8 H), 2.0-2.2 (m, 2 H), 5.52 (dt, J = 15.8, 1.5 Hz, 1 H), 6.20 (dt, J = 15.8, 6.8 Hz, 1 H); ¹³C NMR (CDCl₃) δ 0.00 (Me × 3), 14.00, 22.55, 28.58, 28.78, 31.63, 33.06, 92.43 (C-), 104.28 (C-), 109.61 (=CH-), 146.26 (=CH-); IR(neat) 2958, 2927, 2856, 2175, 2133, 1249, 1085, 952, 842, 759 cm^-1; HRMS (EI) C₁₃H₂₄Si: requires 208.1647, found 208.1664.

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(Z)-3-Decen-1-yne(5a): ¹H NMR (CDCl₃) δ: 0.88 (t, 3 H), 1.1-1.55 (m, 8 H), 2.2-2.45 (m, 2 H), 3.05 (d, J = 2.2 Hz, 1 H), 5.45 (ddt, J = 11.0, 1.3, 0.9 Hz, 1 H), 5.98 (dtd, J = 11.0, 7.3, 0.9 Hz, 1 H); ¹³C NMR (CDCl₃) δ: 14.04, 22.60, 28.74, 28.87, 30.29, 31.68, 80.62 (C-), 81.11 (CH), 108.03 (=CH-), 146.22 (=CH-); IR(neat) 3313, 3024, 2956, 2927, 2856, 2358, 1465, 738 cm^-1; HRMS (EI) C₁₀H₁₆: requires 136.1252, found 136.1253.

(Z)-1-Trimethylsilyl-3-decen-1-yne(6a): ¹H NMR (CDCl₃) δ: 0.19 (s, 9 H), 0.88 (t, 3 H), 1.1-1.55 (m, 8 H), 2.2-2.45 (m, 2 H), 5.48 (dt, J = 11.0, 1.3 Hz, 1 H), 5.94 (dt, J = 11.0, 7.3 Hz, 1 H); ¹³C NMR (CDCl₃) δ: 0.00 (Me × 3), 14.00, 22.59, 28.66, 28.78, 30.25, 31.59, 98.41 (C-), 102.24 (C-), 109.16 (=CH-), 145.57 (=CH-); IR(neat) 3020, 2958, 2927, 2856, 2148, 1249, 842, 759 cm^-1; HRMS (EI) C₁₃H₂₄Si: requires 208.1647, found 208.1671.

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<A NAME="RY05402ST-17">17</A> Mori A. Shimada T. Kondo T. Sekiguchi A. Synlett 2001, 649

(E)-1-Phenyl-3-decen-1-yne: ¹H NMR (CDCl₃) δ: 0.88 (t, 3 H), 1.1-1.5 (m, 8 H), 2.05-2.3 (m, 2 H), 5.70 (dt, J = 15.8, 1.4 Hz, 1 H), 6.22 (dt, J = 15.8, 7.0 Hz, 1 H), 7.2-7.5 (m, 5 H); ¹³C NMR (CDCl₃) δ: 14.04, 22.60, 28.79(-CH₂- × 2), 31.68, 33.22, 87.91 (C-), 88.44 (C-), 109.57 (=CH-), 123.79 (=C<), 127.82 (=CH-), 128.22 (=CH- × 2), 131.44 (=CH- × 2), 145.16 (=CH-); IR (neat) 3080, 3055, 3020, 2954, 2927, 2854, 2202, 1596, 1571, 1488, 1463, 1454, 1442, 1379, 1303, 1068, 952, 912, 754, 690 cm^-1; MS (EI) m/z 212 (M⁺, 51%), 183(3), 169(6), 155(24), 141(78), 128(100), 115(41), 102(6), 91(13), 77(7), 63(4). (Z)-1-Phenyl-3-decen-1-yne: ¹H NMR (CDCl₃) δ: 0.88 (t, 3 H), 1.1-1.5 (m, 8 H), 2.25-2.55 (m, 2 H), 5.67 (dt, J = 10.8, 1.1 Hz, 1 H), 5.96 (dt, J = 10.8, 7.0 Hz, 1 H), 7.2-7.5 (m, 5 H); ¹³C NMR (CDCl₃) δ: 14.08, 22.64, 28.87(-CH₂- × 2), 30.41, 31.72, 86.57 (C-), 93.45 (C-), 109.05 (=CH-), 123.87 (=C<), 127.94 (=CH-), 128.27 (=CH- × 2), 131.40 (=CH- × 2), 144.31 (=CH-); IR (neat) 3080, 3058, 3020, 2956, 2927, 2856, 1595, 1571, 1488, 1467, 1456, 1440, 1398, 1377, 1068, 1028, 1014, 912, 754, 732, 690 cm^-1; HRMS (EI) C₁₆H₂₀: requires 212.1565, found 212.1559.