Carbonyl compounds a, -acetylenic

Stereospecific synthesis of 1,3-dienes. Corey et a .3 have described a new synthesis of 1,3-dienes based on the highly stereospecific cis addition of alkylcopper reagents to a, -acetylenic carbonyl compounds (3, 108). Thus the reaction of methyl 4-trimethyl-siloxy-2-nonynoate (l)4 in THF with divinylcopperlithium (1.25 eq) at —90° and then at — 78° affords the pure e(r adduct (2) in > 90% yield. Treatment of (2) with methanolic hydrochloric acid effects cleavage of the trimethylsilyl ether and lactonization to give (3). 

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