Stereoselective Intramolecular Nicholas Reaction Using Epoxides as Nucleophiles

Abstract

The intramolecular nucleophilic attack of the epoxides on the exo-Co2(CO)6-propargylic cations provided cyclic ethers in good yields. The use of substrates with stereochemically defined oxiranes provided polysubstituted tetrahydropyrans and oxepanes with a high degree of stereocontrol. The cyclization is sensitive to the nature of the protecting group used at the primary alcohol, the use of tert-butyl carbonates being highly effective in terms of regioselectivity and yields.