Regioselective iminophosphorane-mediated annelation of a 1,3,4-thiadiazole ring into a 1,2,4-triazine ring: Preparation of novel mesoionic compounds derived from [1,3,4]thiadiazolo[2,3-c]- and [1,3,4]thiadiazolo[3,2-d][1,2,4]triazines

Article abstract of DOI:10.1016/S0040-4020(01)82326-7

Aza Wittig-type reaction of iminophosphorane 1 derived from 4-amino-2,6-dimethyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro-1,2,4-triazine with several types of iso(thio)cyanates leads to [1,3,4]thiadiazolo[2,3-c][1,2,4]triazines 2, 3 and 6 which display mesoionic