Synthesis of γ-lactones and unsaturated bis γ-lactones via Cu–Fe-mediated reductive cyclization of di- and tri-α-halogenated carboxylic esters

A new synthetic route to γ-substituted γ-butyrolactones from alkenes and α-dichloro ester, in the presence of CuCl (catalytic) and Fe(0) (stoichiometric) in acetonitrile, was established. A study of this reaction has demonstrated that the overall process consists of the following reaction steps: (a) addition of the dichloro ester to the olefin via CuCl catalysis; (b) selective reduction of the α-chloro atom in the resulting adduct by Fe(0); (c) cyclization of the resulting γ-chloro ester to γ-butyrolactone. Yields were improved by first carrying out step (a), then steps (b) and (c) in one pot. Selectivity was improved in the presence of a small amount of water. α-Trichloro esters also generated the γ-substituted γ-butyrolactone, albeit in lower yields and selectivity. The latter reaction gave rise to the formation of interesting by-products, namely new unsaturated bis-lactones.