1H, 13C and 15N NMR spectra of the reaction product of benzenediazonium fluoroborates with 1-phenyl-3-methyl-4-(α-acet-ethylidene)-pyrazol-5-one

Abstract Contrary to previously published data (Mustroph and Bach, Z. Chem, 1985), we have found that the reaction product of 4-X-benzenediazonium fluoroborates (X = H, NO 2 ) with 1-phenyl-3-methyl-4(α-acet-ethylidene)-pyrazol-5-one corresponds to 5′-hydroxy-5,5′-dimethyl-2-phenyl-1′-(4-X-phenyl)-1′,5′-dihydro-2 H -[4,4′]bipyrazolylidene-3-ones ( 4a,b ) and not to compounds 3 . The structural elucidation is based on analysis of 1 H, 13 C and 15 N NMR spectra of non- and 15 N-selectively labelled samples.