Thiophosgene ring closure with

This approach is suitable for the formation of mesoionic 1,3,4-thiadiazoles. The thiohydrazide (427) with phosgene, thiophosgene or an isocyanide dichloride leads to ready ring closure and formation of the mesoionic 1,3,4-thiadiazoles (428 X = 0, S, NR, respectively) (b-79MI40300). 

The synthesis of bis-carbene ligands on a p-biphenyl scaffold starts with 3,3 -diami-nobenzidine [375,376], Ring closure to the bis-benzimidazole compounds can be achieved by at least two routes (i) using thiophosgene [260] and (ii) using formic acid (see Figure 3.118). The linchpin in the thiophosgene method is the reduction of the thione to the carbene, which in this case was achieved by KC (potassium or K/Na alloy are alternatives). 

A soln. of l-thiocyano-2-aminonaphthalene in acetone added dropwise with stirring to a cooled soln. of thiophosgene in the same solvent 1-thiocyano-2-isothiocyanonaphthalene. Y 95%. Reactions of the product s. R. Pohloudek-Fabini and F. Friedrich, Arch. Pharm. 298, 51 (1965) 2-mercaptothiazole ring closure s. Pharmazie 20, 114 (1965). 

---