Abstract
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.
Highlights
The Pschorr reaction involves intramolecular carbon-carbon bond formation between two aromatic rings of an aryl or heteroaryl diazonium salt through a carbonium or radical intermediate.[1]
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
The ionic pathway was characterized by an increased yield of 1,4-dimethyl3-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
Summary
The Pschorr reaction involves intramolecular carbon-carbon bond formation between two aromatic rings of an aryl or heteroaryl diazonium salt through a carbonium or radical intermediate.[1]. The product 4 of ring closure of the Pschorr reaction was obtained in low yield and only by thermal transformation of 1,10,8 which is expected to follow an ionic pathway.[2,3,4] On the basis of the above results, it appeared interesting to perform the transformation of the diazonium ion derived from 1, in non-aqueous media or in the absence of solvent, in order to establish the fate of the 3 and 7 spiro intermediates under these conditions With this aim, we have studied the thermal decomposition of the analogous diazonium tetrafluoroborate 11 in dry acetonitrile solution at reflux (about 82 °C) (Scheme 2) and at its melting point (143-144 °C) (Scheme 3). For a radical pathway of the reaction, an electrochemical reduction of 11 was performed in acetonitrile, according to Scheme 4
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