The synthesis of 4, 5-diphenyl-l-oxo-l, 2, 3, 5-thiaoxa-diazole (IIIa), a representative of a new heterocyclic system, and its pyrolysis t'o diphenylcarbodiimide (IVa) with the concomitant extrusion of sulfur dioxide were described in a recent communication. 2 We have examined this reaction in detail to find that the pyrolysis of this novel class of compounds (111) is indeed a general one and that it constitutes a new
