Synthesis of (-)-deoxypukalide, the enantiomer of a degradation product of the furanocembranolide pukalide.

A convergent stereoselective synthesis of (-)-deoxypukalide is described. This substance has not yet been found in Nature but is obtained through deoxygenation of pukalide, the first naturally occurring furanocembrane to be structurally elucidated. The route features a new intraannular furan synthesis that entails treatment of a 4-oxopropargylic beta-keto ester with silica gel. The product of this novel reaction, a 3-carboxy 2,5-bridged furan, is formed in 96% yield. The synthetic strategy was strongly directed by molecular mechanics calculations, which provided valuable insight into stereodefining steps including double bond stereochemistry and butenolide configuration.