Heterocyclic syntheses. Part XXVIII. ortho-Dialkylamino-benzenesulphonyl azides, -benzoyl azides, and -benzoyldiazomethanes

Abstract

A series of the title compounds incorporating ortho-dimethylamino, diethylamino, dipropylamino, pyrrolidin-1-yl, piperidino, morpholino, 4-methylpiperazin-1-yl, perhydroazepin-1-yl, perhydroazocin-1-yl, and perhydroazonin-1-yl groups were prepared. Thermal decomposition of the sulphonyl azides in solution in chlorobenzene or dimethyl sulphoxide resulted in attack on the ortho-nitrogen atom to give mesoionic spirobenzothiadiazoles or (by ring-opening or dealkylation) 3-substituted benzothiadiazoles. The pyrrolidinyl system was unique in giving a variety of products derived by Curtius rearrangement or otherwise from an intermediate sulphonylnitrene. Thermolysis in the presence of a catalytic amount of base hydrochloride, or an excess of piperidine or of copper, gave a dihydrobenzothiadiazine by attack on an N-methylene group. Photolysis of the sulphonyl azides in solution in dimethyl sulphoxide gave the benzothiadiazines, but by a mechanism different from that of the thermal reaction which did not involve oxidation by dimethyl sulphoxide. The carbonyl azides spontaneously decomposed to give conventional products of a Curtius rearrangement, and one diazo-ketone gave a mesoionic system analogous to those derived from the sulphonyl azides. Unusual properties are associated with some of the intermediates prepared, and are accounted for by a neighbouring group effect. Mechanisms are proposed for the observed reaction pathways.