Formation of seven-membered oxacycles through ring expansion of cyclopropanated carbohydrates

The cyclopropanation and ring expansion of 4,6-O-(di-tert-butylsilanediyl)-D-glucal (1) to produce oxepanes have been investigated. Using catalytic amounts of TMSOTf and an excess of a silylated nucleophile, a wide range of substituted oxepanes have been synthesized. Good to excellent yields are obtained; however, only modest diastereoselectivity resulted. This new methodology should provide convenient access into the synthesis of optically active oxepanes.