Oxidation of Methyl Function of 3,3-(3-Fluorobenzyl)-2-Propanone by Thionyl Chloride

Abstract

In the presence of a catalytic amount of a tertiary amine, thionyl chloride generally oxidizes carboxylic acids^1,2 and ketones¹ at α carbon atoms to form α-chloro-α-chlorosulfenyl derivatives and their subsequent reaction products. Examination of reaction mixtures of thionyl chloride with a number of variously substituted 4-aryl-2-butanones revealed that in the case of the 3-methoxy or 3-hydroxy derivatives, cyclization onto the aromatic ring to form a benzo[b] thiophene competes quite favorably with cyclization onto enol to form a thietanone.⁴ The results were consistent only with thionyl chloride oxidation proceeding exclusively at the methylene position.