A new synthesis of lactones from tertiary alkenylcarbinols by cobaltcatalyzed photocarbonylation under ambient conditions

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In the presence of a Co catalyst, tertiary vinyl-, propenyl-, and allylcarbinols were chelatively cycloadded to carbon monoxide to produce lactones by xanthone-sensitized photoreaction in tetrahydrofuran, under CO at 1 atmosphere and at room temperature. At lower temperatures the isomerization of alkenylcarbinols was suppressed and lactones were obtained with improved selectivity. The photoprocess was facilitated by addition of pyridine or hydrogen and retarded in presence of amines or phosphines. Mechanistic interpretations for the process and the accompanying effects are discussed.