Selective Ring-expansion of Oxirane into Tetrahydropyran and Tetrahydrofuran by Reagent-controlled Conditions

Abstract

Ring-expansion of methyl 2-bromomethyl-5-oxiranylpent-2-enoate (7) with various acids was studied; treatment with Lewis acids (TiBr₄, MgBr₂ and ZnBr₂) afforded the tetrahydrofuran derivative 4-Br as a major product, while reaction with silver salt (AgNO₃/KPF₆), which is known to have a high halide affinity, gave preferentially the tetrahydropyran 3-ONO₂ derivatives as the major products.