Asymmetric construction of the core of C6,
C7-epoxy daphnane diterpenoid orthoesters is developed
through a convergent
synthetic strategy. The salient features include a diastereoselective
nucleophilic assembly of two bulky cyclic fragments, an oxidative
cleavage/transesterification/aldol cascade to fashion the seven-membered
ring, and a base-mediated transesterification/retro-aldol/aldol/epoxidation
cascade to install the epoxy moiety with proper stereochemistry.