Enantioselective Synthesis of the Unsaturated Fragment of Callyspongiolide.

A synthesis of the unsaturated side chain of callyspongiolide has been accomplished from two chiral building blocks prepared by catalytic asymmetric procedures applied on simple starting materials. The synthesis of the chiral benzylic alcohol was based on an enantioselective aldol reaction of a substituted benzaldehyde catalyzed by a chiral amine, whereas the chiral homoallyl alcohol was prepared by the enantioselective crotylboration of iodomethacryl aldehyde catalyzed by a chiral phosphoric acid. Both fragments were joined together by using standard Sonogashira coupling conditions.