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

[GRAPHICS] A new method for the synthesis of alpha,beta-unsaturated lactones from beta -acetoxy aldehydes by reaction with the lithium enolate of methyl acetate w as developed. The reaction is relatively insensitive to structural changes in the aldehyde substrates. The process was extended to the synthesis of fi ve-ring lactones from alpha-acetoxy aldehydes, Experimental evidence regard ing the mechanism of this one-pot transformation was obtained. The observat ions 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.