Molecules 2013, 18(10), 13096-13110; doi:10.3390/molecules181013096
Article

Non-Classical Transformation of Benzendiazonium Hydrogen Sulfates. Access to 1,3-Dimethylisochromeno[4,3-c]pyrazol-5(1H)-one, a Potential Benzodiazepine Receptor Ligand

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Received: 13 September 2013; in revised form: 12 October 2013 / Accepted: 15 October 2013 / Published: 22 October 2013
(This article belongs to the Section Organic Synthesis)
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract: The compound 2-((1,3-dimethyl-1H-pyrazol-5-yl)(methyl)carbamoyl)benzene-diazonium 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.
Keywords: heterocycles; Pschorr reaction; Sandmeyer reaction; 1,5-hydrogen atom transfer; isochromeno[4,3-c]pyrazol-5(1H)-one
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MDPI and ACS Style

Maggio, B.; Raffa, D.; Raimondi, M.V.; Daidone, G. Non-Classical Transformation of Benzendiazonium Hydrogen Sulfates. Access to 1,3-Dimethylisochromeno[4,3-c]pyrazol-5(1H)-one, a Potential Benzodiazepine Receptor Ligand. Molecules 2013, 18, 13096-13110.

AMA Style

Maggio B, Raffa D, Raimondi MV, Daidone G. Non-Classical Transformation of Benzendiazonium Hydrogen Sulfates. Access to 1,3-Dimethylisochromeno[4,3-c]pyrazol-5(1H)-one, a Potential Benzodiazepine Receptor Ligand. Molecules. 2013; 18(10):13096-13110.

Chicago/Turabian Style

Maggio, Benedetta; Raffa, Demetrio; Raimondi, Maria V.; Daidone, Giuseppe. 2013. "Non-Classical Transformation of Benzendiazonium Hydrogen Sulfates. Access to 1,3-Dimethylisochromeno[4,3-c]pyrazol-5(1H)-one, a Potential Benzodiazepine Receptor Ligand." Molecules 18, no. 10: 13096-13110.

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