Heterocyclic systems containing bridgehead nitrogen atom: syntheses of s-triazolo[3,4-b][1,3,4]thiadiazole-6-(5H)-thiones, s-triazolo[3,4-b][1,3,4]-thiadiazines and related heterocycles - Mohan, J; Anjaneyulu, GSR (Indian J Chem., 1988)