Synthesis of the macrolactone core of (+)-neopeltolide by transannular cyclization.

The synthesis of the macrolactone core of (+)-neopeltolide has been achieved. The key synthetic strategy involves the highly diastereoselective synthesis of the 2,6-cis-disubstituted tetrahydropyran ring by a transannular cyclization of δ-hydroxy alkene using mercuric trifluoroacetate. Two of the six stereocenters C-5 and C-11 were realized from L-malic acid, while the remaining stereocenters C-3 (Sharpless asymmetric epoxidation), C-7 (transannular cyclization), C-9 (regioselective epoxide opening) and C-13 (chelation controlled reduction) were derived by asymmetric synthesis. The macrolactone ring was synthesized by macrocyclization using a RCM protocol.