A versatile preparation of alpha,beta-unsaturated lactones from homoallylic alcohols.

[formula: see text] A new method for the synthesis of alpha,beta-unsaturated lactones from beta-acetoxy aldehydes by reaction with the lithium enolate of methyl acetate was developed. The reaction is relatively insensitive to structural changes in the aldehyde substrates. The process was extended to the synthesis of five-ring lactones from alpha-acetoxy aldehydes. Experimental evidence regarding the mechanism of this one-pot transformation was obtained. The observations are consistent with a pathway involving an initial aldol condensation with subsequent acyl migration, lactonization, and beta-elimination and not an enolate equilibration-aldol mechanism.