Non-classical transformation of benzendiazonium hydrogen sulfates. access to 1,3-dimethylisochromeno[4,3-c]pyrazol-5(1h)-one, a potential benzodiazepine receptor ligand

Abstract

The compound 2-((1,3-dimethyl-1H-pyrazol-5-yl)(methyl)carbamoyl) benzenediazonium hydrogen sulfate (10) was reacted with copper sulfate and sodium chloride, in the presence of ascorbic acid as reducing agent, to afford a mixture of the chlorinated epimers 4′-chloro-2,2′,5′- trimethyl-2′,4′-dihydrospiro[isoindoline-1,3′-pyrazol]-3-one (18) and (19), the epimers 4′-hydroxy-2,2′,5′-trimethyl- 2′,4′-dihydrospiro[isoindoline-1,3′- pyrazol]-3-one (20) and (21), and N-(1,3-dimethyl-1H-pyrazol-5-yl)benzamide (22). Under the foregoing conditions, diazonium salt 10 affords neither the 2-chloro-N-(1,3-dimethyl- 1H-pyrazol-5-yl)-N-methylbenzamide (23) nor the tricyclic derivative 24, the classical products of the Sandmeyer and Pschorr reactions, respectively. Finally, by heating 20 at 210 °C the compound 1,3-dimethylisochromeno[4,3-c] pyrazol-5(1H)-one (24) was obtained. The transformation under the above conditions of 2-((4-chloro-3-methyl-1-phenyl- 1H-pyrazol-5-yl)(methyl)carbamoyl) benzendiazonium hydrogen sulphate (11) afforded 4′,4′-dichloro-2, 5′-dimethyl-2′-phenyl-2′,4′-dihydrospiro[isoindoline-1, 3′-pyrazol]-3-one (29) as the sole reaction product. © 1996-2013 MDPI AG.