Synthesis of gamma,delta-unsaturated-beta-keto lactones via sequential cross metathesis-lactonization: a facile entry to macrolide antibiotic (-)-A26771B.

A simple access to gamma,delta-unsaturated-beta-keto lactones is presented, allowing a rapid total synthesis of the naturally occurring 16-membered macrolide antibiotic (-)-A26771B via cross metathesis, asymmetric dihydroxylation, and lactonization as the key steps.