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The reactions of thiapyrylium salts 3a–c with hydrazine and methylhydrazine yield the 3,5,7-triphenyl-1,2(4H)-diazepines 4a–c and 1-methyl-3,5,7-triphenyl-1,2(1H)-diazepines 5a–c in good to excellent yields. Although numerous 1-acyl-1,2(1H)-diazepines are now known, compounds 5a–c represent the first examples of 1-alkyl-1,2(1H)-diazepine derivatives. With a slight variation in work up conditions, the reaction of thiapyrylium salts 3a and 3c with methylhydrazine leads to the formation of the pyrazoline derivatives 6a and 6c, respectively; on the other hand, only pyrazolines 9a and 9b can be obtained from the corresponding reaction with phenylhydrazine. Pyrolysis of the pyrazolines 6a, 6c, 9a, and 9b provides the pyrazoles 7a, 7c, 10a, and 10b, respectively. The mechanism of some of these transformations is briefly discussed.

The reaction of pyrylium salts 1a–e with methylhydrazine gives pyrazolines (2), pyrazoles (3), pyridines (4), 1,2-diazepine (5), and N-methylaminopyridinium salts (6). Product composition has been studied as a function of pyrylium salt counter anion, concentration of methylhydrazine, and conditions of the reaction (Table 1). Pyridines (4) and 1,2-diazepines (5) are minor components, the major products being the pyrazolines (2) and pyrazoles (3). The reactions of more unusual pyrylium salts (1f–i, 8a, 9a, 9c, and 11a) with hydrazine have been shown to provide 1,2(4H)-diazepines (10, 12–15) and N-aminopyridinium salts (8b, 9b) (Table 2), the nature of the product apparently depending on the absence or presence of 2-methyl substitution respectively in the starting pyrylium salts.