REACTIONS OF FUSED DIHYDRO-1,2,4-THIADIAZOLES WITH ISOCYANATES AND ISOTHIOCYANATES TO GIVE 6A-LAMBDA(4)-THIA-1,3,4,6-TETRAAZAPENTALENE DERIVATIVES

3-Methyl-6, 7-dihydro-5H-1,2,4-thiadiazolo[4, 5-a]pyrimidine 4a reacte d with isocyanates and isothiocyanates with elimination of acetonitril e and concomitant addition of two molecules of the heterocumulene to g ive the 2, 3-disubstituted-6, 7-dihydro-5H-2-alambda4-thia-2, 3, 4a, 7 a-tetraazacyclopent[cd]indene-1 (2H), 4(3H)-diones 8a-8e and the corre sponding dithiones 9a-9h, respectively. 3-Methyl-5, 10-dihydrobenzo[e] -1,2,4-thiadiazolo[4, 5-a][1,3]diazepine 5a likewise reacted with isoc yanates and isothiocyanates to give the 2, 3-disubstituted-5, 10-dihyd ro-2alambda4-thia-2, 3, 4a, 10a-tetraazapentaleno[3, 3a, 4-gh]benzocyc loheptene-1, 4-diones 10a-10f and the corresponding dithiones 11a-11f. The base 4a reacted with phenyl isocyanate, methyl isothiocyanate, an d phenyl isothiocyanate in toluene at room temperature to give the zwi tterions 14a, 14b, and 14c, respectively, and the diazepine 5a reacted with phenyl isothiocyanate to give the zwitterion 17.