Novel synthesis of γ-lactones starting from β,γ-unsaturated carboxylic esters

Article abstract of DOI:10.1246/bcsj.68.3599

A novel synthetic route to highly substituted γ-lactones was achieved by an intermolecular radical addition to 4-(methylthio)-4-(p-tolylsulfonyl)-3-butenoic ester (1) and its 2-(ethoxycarbonyl) derivative (2), which were easily prepared from (methylthio)methyl p-tolyl sulfone. Upon the irradiation of a solution of 1 and benzophenone in an alcohol (R¹R²CHOH), the 1-hydroxyalkyl radical (R¹R²C-OH) was generated and added regiospecifically to the 3-position of 1 to form an adduct that led to a γ-lactone by spontaneous intramolecular condensation. Similarly, 2 reacted with the alcohol to give α-(ethoxycarbonyl)-γ-lactones. The alcohol, which is a high boiling liquid or solid, can be employed in the form of a solution (10 molar amounts in acetonitrile) without greatly lowering the reaction efficiency.