Directive effects in hydroborations of 1-(trialkylsilyl)-1,3-diynes. Syntheses of (Z)-enynes and α-ketoacetylenes

✍ Scribed by Elain C. Stracker; William Leong; Joseph A. Miller; Timothy M. Shoup; George Zweifel

• Publisher: Elsevier Science
• Year: 1989
• Tongue: French
• Weight: 300 KB
• Volume: 30
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)89001-8

✦ Synopsis

Chemo-and regioselective hydroborations of I-(dimethylthexylsilyl)-1,3-diynes with dicyclohexylborane or with [bis(l,2-dimethylpropyl)borane] furnishes organoboranes which afford on protonation (Zj-enynes and on oxidation alkynyl ketones. We have previously shown that monohydroborations of symmetrically dialkyl-substituted 1,3-diynes with dialkylboranes proceed to place the boron preferentially ar the internal positions of the diyne system. Protonolysis of the organoboron intermediates with acetic acid affords the corresponding (Zj-enynes.1 However, this jZ)-cnyne synthesis unfortunately cannot be employed for the preparation of unsymmetrical enynes since hydroborating agents do not discriminate in their addition between the triple bonds of unsymmetrically alkyl-substituted diynes. On the other hand, we have recently shown rhat rhe presence of a trimethylsilyl moiety imparts appreciably different reactivities to the mple bonds of l-(trimethylsilyl)-l,%diynes in reactions with lithium diisobutyl-n-butylaluminum hydride, providing an efficient method for preparing (E)-l-(trimethylsilyl)-3-alken-l-ynes.2 R= = SiMe,