Synthesis of erythronolide a via a very efficient macrolactonization under usual acylation conditions with the Yamaguchi reagent

Abstract Macrolactonization of 3,5- O -(3,4-dimethoxybenzylidene)-9,11- O -(2,4,6-trimethylbenzylidene)(9 S )-9-dihydroerythronolide A seco-acid ( 4 ) was reexamined under various conditions and found to proceed rapidly only by treatment of 4 with Yamaguchi's reagent, 2,4,6-trichlorobenzoyl chloride, in the presence of a large excess of TEA and a small amount of DMAP at room temperature to give the corresponding 14-membered erythronolide A derivative ( 7 ) in almost quantitative yield.