New synthetic methods for α,β -unsaturated ketones, aldehydes, esters and lactones by the palladium-catalyzed reactions of silyl enol ethers, ketene silyl acetals, and enol acetates with allyl carbonates

Abstract

Silyl enol ethers and ketene silyl acetals derived from ketones, aldehydes, esters and lactones are converted into α,β-unsaturated ketones, aldehydes, esters and lactones by treatment with allyl carbonates in high yields using the palladium—bis(diphenylphosphino)ethane (dppe) complex as catalyst. Phosphine-free palladium catalyst instead of the palladium—phosphine complex gives a higher selectivity for the preparation of cyclopentenone, cyclooctenone, dienones, α,β-unsaturated esters and lactones. As a solvent, the use of nitriles such as acetonitrile is essential. In other solvents, allylation takes place. Enol acetates derived from ketones are converted into α,β-unsaturated ketones by reaction with allyl carbonate in acetonitrile using the palladium complex and tributyltin methoxide as bimetallic catalysts.