Cross-metathesis approach to a (2E,4E)-dienoic acid intermediate for the synthesis of elaiolide

A (2E,4E)-7-hydroxy-2,4-dienoic acid, previously employed as a key intermediate for the total synthesis of the macrodiolide antibiotic elaiolide, was prepared stereoselectively and concisely from (S)-2-methyl-3-trityloxypropanal by a three-step sequence consisting of Brown’s asymmetric crotylboration, olefin cross-metathesis, and alkaline treatment. Ethyl 3-pivaloyloxy-4-pentenoate was used as a masked dienoate in the cross-metathesis step.