Asymmetric synthesis using chiral piperazines. Part 3. Enantioselective addition of dialkylzincs to aryl aldehydes catalysed by chiral piperazines

Abstract

The use of chiral piperazines (cyclic diamines) 1 as chiral catalysts for the enantioselective addition of dialkylzincs to aldehydes is described. (2S,5S)-2,5-Dialkyl substituted piperazines 1 catalysed the enantioselective addition of dialkylzincs to aryl aldehydes. It was found that the presence of the dilithium salt of 1 was more effective in producing the corresponding alcohols in high e.e.s (up to 96% e.e.) and that the catalyst 1 with branched carbon chains as the substituents on the piperazine ring was effective for highly enantioselective reaction.