Tin(II) Chloride Mediated Coupling Reactions between Alkynes and Aldehydes

Tin(II) chloride, which is insensitive to water and air, mediated the coupling reaction between alkynes and aldehydes as a Lewis acid in nitromethane to produce (E)-,-unsaturated ketones by a skeletal transformation in which one alkynic carbon atom changed into an oxo carbon atom accompanied by the cleavage of a C=O bond in the starting aldehydes. This coupling reaction was promoted by a catalytic amount of a primary or secondary alkanol. The coupling reaction between 1-deuterio-2-phenylethyne and benzaldehyde with BuOH afforded 1,3-diphenyl-2-deuterio-2-propenone (2-deuteriation: 94% D), whereas the coupling reaction between phenylethyne and benzaldehyde with BuOD afforded 1,3-diphenyl-2-propenone (2-deuteriation: 0% D). Because almost no exchange between hydrogen and deuterium at the 2-position of 1,3-diphenyl-2-propenone occurs in either of the reactions, the coupling reaction between alkynes and aldehydes with tin(II) chloride is presumed to proceed by nucleophilic addition of alkynes to aldehydes. The cleavage of the C-O single bond generated by the nucleophilic addition might be induced by the strong oxophilicity of tin.