Chemistry of substituted pyrazolo[1,5-a]pyrimidines. Part 4. A structural correction of a series of pyrazolo[5′,1′ : 2,3]pyrimido[5,4-d][1,2]diazepines on the basis of NMR spectroscopy and X-ray diffraction analysis

Abstract

The reaction of a series of 6-acetyl-7-(2-dimethylaminovinyl)pyrazolo[1,5-a]pyrimidines 3 with hydrazine hydrate has been re-investigated and the nature of the reaction product unambiguously established on the basis of both NMR spectroscopy and X-ray diffraction. 7-Methyl-6-(pyrazol-3′-yl)pyrazolo[1,5-a]pyrimidines 1 and not, as formerly claimed, 6-methylpyrazolo[5′,1′ : 2,3]pyrimido[5,4-d][1,2]diazepines 2 are shown to be the final products in the reaction of compounds 3 with hydrazine hydrate. The structures of compounds 1 have been rationalised on the basis of some diagnostic coupling constants' values and confirmed by the X-ray structure of 2,7-dimethyl-6-(pyrazol-3′-yl)pyrazolo[1,5-a]pyrimidine 1b. The literature assignments for the quaternary carbon resonances have been revised and the signals unambiguously attributed by means of 2D experiments.