Three-Carbon Homologation of Diorganozincs with Lithiated Acetylenic Epoxides

Reaction of dialkylzincs with lithiated acetylenic epoxides
is
described to give zincates that undergo a 1,2-metallate rearrangement
by an anti-SN2′ pathway. This rearrangement
occurs with the transfer of an alkyl or a silyl group affording allenylzinc
intermediates. Allenic and/or homopropargylic alcohols are obtained
upon hydrolysis. Quenching the reaction mixture with aldehydes or
ketones is shown to give access to 2-alkynyl-1,3-diols in a stereoselective
manner.