Synthetic approach toward cis-disubstituted γ- and δ-lactones through enantioselective dialkylzinc addition to aldehydes: application to the synthesis of optically active flavors and fragrances

A versatile and straightforward approach to optically active cis-4,5-disubstituted γ- and δ-lactones by catalytic enantioselective addition of dialkyzincs to cinnamic aldehydes and RCM ring closure has been reported. The synthetic importance of the enantioselective dialkylzinc alkylation of aldehydes has been thus widened. Such an approach has then been employed for the enantioselective synthesis of naturally occurring γ-lactone flavors like (S)-5-ethyl-butanolide (6a) and (4S,5S)-cis-whisky lactone (6b) and extended to the preparation of δ-lactones like (5S,6S)-5-methyl-6-ethylpentanolide (9a), precursor of the pheromone serricornin.