Diels–Alder reactions of activated 2H-thiopyrans

Abstract

The Diels–Alder reactivity of various 2H-thiopyrans bearing electron-donating substituents has been investigated. The approximate order of reactivity among the 2H-thiopyrans studied was 4,6-disubstituted [Formula: see text] 5-substituted > 4-substituted, 3,5-disubstituted [Formula: see text] 3-substituted. Good yields of predominantly endo adducts are obtained with reactive dienophiles. With less reactive dienophiles, reactions are much slower and yields are attenuated due to the competing thermal decomposition of the dienes under the reaction conditions. The adducts obtained are equivalent (via desulfurization) to those from unreactive cis-substituted dienes. Key words: Diels–Alder, 2H-thiopyran.