A new synthesis of aryl isothiocyanates: carbon disulfide as a dipolarophile. The reaction of (4,5,6,7-tetrahydro-2H-1,2,3-benzotriazolium-1-yl)arylaminide 1,3-dipoles with carbon disulfide: synthesis, kinetics, mechanism. Azolium 1,3-dipoles

Abstract

A new synthesis of aryl isothiocyanates in which the aryl nitrogen moiety ultimately comes from an arylhydrazine is described. Treatment of (4,5,6,7-tetrahydro-2H-1,2,3-benzotriazolium-1-yl)arylaminide 1,3-dipoles (derived from cyclohexane-1,2-dione bis(arylhydrazones)) with carbon disulfide in acetone at ambient temperatures gives high yields of aryl isothiocyanates and 2-aryl-4,5,6,7-tetrahydro-2H-1,2,3-benzotriazole as a leaving group. The kinetics and mechanism of the reaction were investigated. The mechanism involves a polar cycloaddition of the triazolium-aminide to the CS₂ generating a partially ring-closed intermediate which fragments to the aryl isothiocyanate. Carbon disulfide is not a kinetic superdipolarophile with (1,2,3-benzotriazolium-1-yl)aminide 1,3-dipoles.