Diastereoselectivity in a Ring Closing Metathesis Reaction with a Remote Stereogenic Centre Leading to Quaternary Dihydropyrans

Starting from α-allyloxy esters, divinyl carbinols with diastereotopic vinyl groups become accessible. Diastereoselectivity for ring closing metathesis reactions of these trienes was investigated. Formation of a spirocyclic derivative proceeds with significant diastereoselectivity, and a mechanistic proposal for the diastereoselective formation of spirocyclic derivatives is presented.