Stereoselective synthesis of (Z)-α-(alkoxycarbonyl)methylene β- and γ-lactones by palladium-catalysed oxidative carbonylation of alkynols

Abstract

(Z)-α-(Alkoxycarbonyl)methylene β- and γ-lactones can be obtained in fair to excellent yields and with high catalytic efficiencies by PdI₂/KI-catalysed oxidative dialkoxycarbonylation of propynyl alcohols (α,α-dialkyl substituted, or α-monoalkyl substituted with a sufficiently bulky alkyl group) and but-3-yn-1-ols, respectively. Reactions are carried out in alcoholic media under mild conditions (70–80 °C and 20 atm of a 3∶1 mixture of carbon monoxide and air). Reaction pathways are discussed.