Diastereoselective formation of seven-membered oxacycles by ring-expansion of cyclopropanated galactal

The cyclopropanation and ring-expansion of 4,6-O-di-(tert-butyl)silanediyl-d-galactal using catalytic amounts of TMSOTf and silated nucleophiles gave a range of substituted oxepanes. Good to excellent yields were obtained in addition to very high selectivities.