From Carbonohydrazide

From carbonohydrazide. Equimolar quantities of carbonohydrazide (71) and aroyl isothiocyanates undergo an addition-cyclization in dimethyl-formamide at 100 °C, with elimination of hydrazine, resulting in moderate yields of 2-aroylamido-5-hydroxy-l,3,4-thiadiazoles (73). The postulated intermediate mono-adducts (72) are not isolable, but stable addition 

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Monohydrazones 9, derived from carbonohydrazide and monocarbonyl compounds, exist in solution as tautomeric mixtures of the /Z-hydrazone 9 and hexahydro-1,2,4,5-tetrazine forms 10 (Scheme 2) <1999RJ0357>. 

From Thio)carbonohy dr azides. 1,3,4-Thiadiazoles arise in the acidic cyclization of thioacylated (thio)carbonohydrazides. Thioaroylthioacetic acids" convert carbonohydrazide into 1-thioaroylcarbonohydrazides (95 R = H, X = O). 1-Phenyl- and 1-benzylidene-carbonohydrazide react to give similar compounds. All are readily cyclized by mineral acids to 2-aryl-5-hydroxy-l,3,4-thiadiazoles (96), with loss of hydrazine or its appropriate derivative. The action of acetic anhydride produces 2-acetoxy-5-phenyl-l,3,4-thiadiazoles directly, in one stage."... 

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