New chiral synthesis of methyl and allyl disubstituted butyro lactone:a formal synthesis of (-)-Ngaione

摘要

A new chiral synthesis fo butyrolactone[(-)-7]bearing methyl and allyl substituents at te gamma-position has been established via diasftereoselective continuousnucleophilic addition ot th echiral tricyclic lactone[(-)-1] as the key stepl.In practice,continuous nucleophilic addition to the tricyclic lactone [(-)-1] by using the combination of methyllithium and allylmagnesium bromide proceeded to yield thecorresponding diol(8) diastereoselectively.After oxidation of 8,enantiopure methyl and allyl disubstituted butenolide (10) was obtained via retro-Diels-alder reaction.Selective 1,4-reduction of 10 afforded the corresponding butyrolactone[(-)-7],which is thekey intermediate fro (-)-ngainone synthesis.