Ring expansions of beta-keto lactones with zinc carbenoids: syntheses of (+)-patulolide A and (+/-)-patulolide B.

A one-pot ring expansion/oxidation/elimination method has been developed in which beta-keto lactones are converted efficiently to alpha,beta-unsaturated-gamma-keto lactones. The reaction can be successfully applied to a variety of ring sizes. Alkene stereochemistry is dependent upon ring size and reaction conditions. The method was applied to the synthesis of (+)-patulolide A.