Comparative studies of the Pschorr reaction in the pyrazole series. Access to the new dibenzo[e,g]pyrazolo[1,5-a][1,3]diazocine system of pharmaceutical interest

The diazonium tetrafluoroborate 11 obtained from 2-amino-N-methyl-N-(1- phenyl-3-methylpyrazol-5-yl)benzamide was transformed in dry acetonitrile via an ionic or radical pathway. Differences were observed with respect to ionic or radical transformations in aqueous media of the analogous diazonium hydrogen sulfate 1 derived from the same amine. In acetonitrile solution, the ionic pathway was characterized by an increased yield of 1,4-dimethyl-3-phenyl- pyrazolo[3,4-c]isoquinolin-5-one 4 and by the formation of its isomer, the new derivative 7,9-dimethyldibenzo[e,g]pyrazolo[1,5-a][1,3]diazocin-10(9H)-one 12. When the reaction followed a radical pathway, the pyrazolo[3,4-c]isoquinoline derivative 4 and N-methyl-2-(1-phenyl-3-methylpyrazol-5-yl)benzamide 17, the latter due to a 1,4-pyrazolyl transfer process, were isolated in low yields. Decomposition of the solid diazonium tetrafluoroborate at its melting point gave compounds 4, 12 and the N-(1-phenyl-3-methylpyrazol-5-yl)-2-fluorobenzamide 17. The crystal structure of compound 12 was also determined.