Selective Propargylation of Carbonyl Compounds and Imines with Barium Reagents

摘要

Propargylation of electrophiles is a useful method to introduce a carbon-carbon triple bond into organic compounds.One problem of this reaction employing a propargylic or allenylic metal reagent is to control its regioselectivity.Organomagnesium and organozinc reagents prepared from gamma-alkylated propargyl bromides are known to add to aldehydes selectively at the gamma-position to give allenylic alcohols.On the other hand,there are not many satisfactory methods for the selective synthesis of homopropargylic alcohols.We have previously shown that reactive barium promotes a Barbier-type reaction of a Me3Si-substituted propargyl bromide with aldehydes and ketones which provides homopropargylic alcohols exclusively.We report here further studies about the regioselective propargylation using carbonyl compounds and imines as electrophiles (Scheme 1).