Selective conversion of bromo oxirane into tetrahydropyranylacrylate by epoxide ring opening

Abstract

In order to construct the tetrahydropyran ring of rhopaloic acid A and hippospongic acid A, the ring-expansion of methyl 2-bromomethyl-6,7-epoxyhept-2-enoate with various acids was studied; treatment of the bromo oxirane with Lewis acids (TiBr 4 , MgBr 2 and ZnBr 2 ) afforded a tetrahydrofuran derivative as the major product, while reaction of the oxirane with silver salt (AgNO 3 /KPF 6 ) gave a tetrahydropyran derivative as the major product.