Stereoselective Access to Hydroxy Oxetanes and Tetrahydrooxepines through Isomerization of Oxiranyl Ethers

Substituted trans-oxetanemethanols and cis-substituted tetrahydrooxepines are prepared regioselectively by lithiation of substituted glycidyl ethers with lithium bases derived from either butyllithium or lithium diisopropylamide and potassium tert-butoxide. The regiochem. of nucleophilic cyclization depends upon the substitution next to the glycidyl ether oxygen; when the pendant group is either a Ph or ethynyl group, the cyclization gives oxetanemethanol derivs. selectively, while when the pendant group is a vinyl group, tetrahydrooxepine derivs. are obtained as the sole products. Superbase-promoted isomerization of oxiranyl ethers thus allows convenient access to oxetane and tetrahydrooxepane derivs with high regio- and stereoselectivities.