Butyrolactone Synthesis via Polar Radical Crossover Cycloaddition Reactions: Diastereoselective Syntheses of Methylenolactocin and Protolichesterinic Acid

A direct catalytic synthesis of γ-butyrolactones from simple alkene and unsaturated acid starting materials is reported. The catalytic system consists of the Fukuzumi acridinium photooxidant and substoichiometric quantities of a redox-active cocatalyst. Oxidizable alkenes such as styrenes and trisubstituted aliphatic alkenes are cyclized with unsaturated acids via polar radical crossover cycloaddition (PRCC) reactions. This method has been applied to the diastereoselective total synthesis of methylenolactocin and protolichesterinic acid.