E)-and (Z)-3(5)-(2-hydroxyphenyl)-4-styrylpyrazoles from (E)-and (Z)-3-styrylchromones: the unexpected case of (E)- Abstract—An efficient synthetic method for the preparation of (E)-and (Z)-3(5)-(2-hydroxyphenyl)-4-styrylpyrazoles has been developed. The reaction of (E)-and (Z)-3-styrylchromones with hydrazine hydrate afforded the corresponding (E)-and (Z)-4-styr-ylpyrazoles, respectively, saved 4 0 -nitro-derivatives where both (E)-and (Z)-4 0 -nitro-3-styrylchromones afforded (E)-3(5)-(2-hydroxyphenyl)-4-(4-nitrostyryl)pyrazoles. The reaction mechanism for these transformations was discussed and the stereochemis-try of all products was assigned by NMR experiments. Pyrazoles are widely studied five-membered heterocyclic compounds which possess promising pharmacological, agrochemical and analytical applications. 1 In the last decade, these compounds received considerable atten-tion since some well-known drugs such as sildenafil (Via-gra) and celecoxib (Celebrex) are pyrazole derivatives. 2 Furthermore, derivatives containing pyrazole ring systems have demonstrated potent activities, such as anti-inflammatory activity, 3,4 cytotoxicity against several human cancer cell lines, 5 and inhibitory activity against monoamine oxidase which is crucial in compounds used in the treatment of Parkinson's and Alzheimer's diseases. 6 Certain 3(5)-(2-hydroxyphenyl)-pyrazoles can be used as ultraviolet stabilisers, 7 as analytical reagents in the complexation of transition metal ions, 8 as analgesic agents and platelet aggregation inhibitors, 9 and also as potent inhibitors of Hsp90 ATP-ase activity. 10–14