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.
Highlights
We reported the transformation of diazonium hydrogen sulphate 2 derived from2-amino-N-methyl-N-(3-methyl-1-phenyl-1H-pyrazol-5-yl)benzamide (1)
As regards the transformation of the diazonium salt 11, performed under the identical conditions followed for the chemical analogues 10 and 2, the production of the dichloro spiro compound 29 was observed, which demonstrates that substitution at the 4-position of the pyrazoline nucleus does not hinder the ligand radical transfer process from the copper(II)-chloro complex to radical species 38 (Scheme 6)
The solid product obtained was washed with cold water, dried in desiccator and crystallized from diethyl ether to give the epimeric mixture of (1S,4′R)- (or (1S,4′S)-) and (1S,4′S)- (or (1S,4′R)-)4′-chloro-2,2′,5′trimethy-2′,4′-dihydrospiro[isoindoline-1,3′-pyrazol]-3-one (18) and 19, respectively in 8% overall yield; GLC-MS: two peaks, 228 (m/z) for each, (M+-Cl); IR (KBr, cm−1): 1,710 (CO); 1H-NMR
Summary
We reported the transformation of diazonium hydrogen sulphate 2 derived from. This reaction was carried out with CuSO4 and NaCl, in the presence of ascorbic acid as a reducing agent [1] (Scheme 1). Transformation of the diazonium salt 2 by reaction with CuSO4/NaCl/ascorbic acid. CuSO4/NaCl/ascorbic acid has allowed to establish that a demethylation process takes place to give N-(3-methyl-1-phenyl-1H-pyrazol-5-yl)benzamide 4 (for the mechanism see Scheme 5, below). We describe the CuSO4/ascorbic acid-catalyzed decomposition in the presence of NaCl of the diazonium hydrogen sulfates 10 and 11 (Figure 1). These intermediates bear a methyl group or a chloro atom on the pyrazole nucleus, at positions 1 or 4, respectively
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