Pentatomic heteroaromatic cations. Part V. A convenient general method for the preparation of aldehydes from acyl chlorides via 2-substituted 1,3-benzoxathiolylium tetrafluoroborates

Abstract

Reactions at 35 °C of acyl chlorides with o-mercaptophenol in tetrafluoroboric acid–ether or boron trifluoride–ether complex gave excellent yields of the corresponding 2-substituted 1,3-benzoxathiolylium tetrafluoroborates. Reduction of the products with sodium borohydride (or sodium borodeuteride) in acetonitrile at 0–20 °C gave 2-substituted 1,3-benzoxathioles. These were hydrolysed with mercury(II) chloride to the corresponding aldehydes. Overall yields were equally good (70–90%) in the preparation of aliphatic, alicyclic, and aromatic aldehydes.