Sulphines. Part IV. Reactions of aromatic sulphines with diazoalkanes

Abstract

The cycloaddition reactions of aromatic sulphines, such as thiobenzophenone S-oxide and thiofluorenone S-oxide, with 2-diazopropane lead to 1,3,4-thiadiazoline 1-oxides in high yields. Diazomethane reacts more sluggishly with sulphines: only with thiofluorenone S-oxide was a cycloadduct obtained. The structure of the cycloadducts has been proven by photochemical extrustion of sulphur monoxide from 2,2-dimethyl-5,5-di-(p-tolyl)-1,3,4-thiadiazoline 1-oxide. In solution the cycloadducts readily undergo a retro-cycloaddition. The adduct from thioxanthen-9-thione SSS′-trioxide and 2-diazopropane not only reverts to the starting sulphine, but also shows a reversed retro-cycloaddition reaction to give diazothioxanthen SS-dioxide and thioacetone S-oxide.