Transition-Metal-Catalyzed Radical Cyclization: Copper-Catalyzed Cyclization of Allyl Trichloroacetates to Trichlorinated γ-Lactones

Cuprous salts in acetonitrile catalyzed the cyclization of allyl trichloroacetates to trichlorinated γ-lactones by way of an intramolecular atom-transfer radical cyclization. Various trichlorinated γ-lactones having a variety of alkyl substituents were prepared by this method. γ-Lactones were generally obtained as a singleproduct except the cyclization of methallyl trichloroacetate, which afforded a mixture of γ- and δ-lactones. The addition of a dichloroacetyl moiety and a chlorine atom to olefins was not stereospecific, Trichloroacetates of secondary allylic alcohols provided a mixture of diastereomers. The stereochemical outcome was dependent on the structure of the starting trichloroacetates; 2-cyclohexenyl trichloroacetate gave the corresponding cis-fused bicyclic lactone, whereas the reaction of acyclic trichloroacetates derived from l-buten-3-ol and its analogues generally provided the trans-substituted lactones. A mechanism of this reaction based on the stereochemical outcome is discussed.