Epoxide opening reactions of aryl substituted dihydropyran oxides: regio- and stereochemical studies directed towards deoxy-aryl-C-glycosides

Abstract

2-Aryl-substituted tetrahydropyrans with 3,4- or 4,5-trans-configured oxo substituents have been synthesized via ring-closing metathesis of allyl homoallyl ethers, epoxidation of the resulting dihydropyrans and opening of the epoxides with O-nucleophiles under different conditions. The substituent in the 2-position serves as an anchor group and adopts the equatorial configuration. Cleavage of the epoxide leads to the selective formation of trans-diaxial or trans-diequatorially substituted tetrahydropyrans, depending on the conditions and on the relative configuration of the starting epoxide. A mechanism for the formation of trans-diequatorial cleavage products via a sequential epoxide opening/anomerization is presented.