Synthesis and molecular structure of 3-(2-benzyloxy-6-hydroxyphenyl)-5-styrylpyrazoles. Reaction of 2-styrylchromones and hydrazine hydrate

3-(2-Benyloxy-6-hydroxyphenyl)-5-styrylpyrazoles 7a-e were prepared from th e reaction of 2-styrylchromones and hydrazine hydrate. 3-(2-Benzyloxy-6-hyd roxyphenyl)-5-(2-phenylethyl)-pyrazoles pyrazoles 8a,d,e and 3-(2-benzyloxy -beta,6-dihydroxystyryl)-5-aryl-2-pyrazolines 9a-e were also obtained as by -products. The crystal and molecular structure of two 3-(2-benzyloxy-6-hydr oxyphenyl)-5-styrylpyrazoles 7a,b have been determined by X-Ray analysis. A lthough the substitution of an hydrogen by a methyl group on the double bon d of the styryl moiety seems to be a minor perturbation, it produces drasti c changes in the crystal packing where only one conformer is present. The O H group is involved as donor of an intramolecular hydrogen bond and the NH group is responsible for the formation of chains via intermolecular hydroge n bonds. (C) 1999 Elsevier Science Ltd. All rights reserved.