HETEROCYCLES, Vol. 27, No 12, 1988 A ONE STEP SYNTHESIS OF 4-CYANOPYRAZOLES Hamdi M. Hassaneen*, Hamed A Ead, M h a i M. Elwan, and Atnned S Shawali Department of Chemistry, Faculty of Science, University of Caim, Giza, Egypt Abstract - Reaction of nitrilimines 2 with fumamnitrile 6 yielded 4-cyanopyra- zoles 8 in good yielm. The structures of 8 were substantiated by comparison with their regioisornerr5-cyanopyrazoles 5, prepared by addition of 2 to acrylo- nitrile followed by oxidation of the 2-pyrazoline cycloadducts 4 . 1,s-Dipolar cycloaddition of nitrilimines 2 to acrylonitriie 3 is known to be regioseiective yielding 5-cyano-2-pyrazolines 4 exclusivelyl" (Scheme I). Oxidation of 4 affords the corresponding 5-cyam- pyrazole derivatives 5. We now wish to report one step synthesis for their regioisorners, 4-cyanopyra- zoies 8 via the reaction of 2 with fumamnitrile 6 (Scheme I). The principle upon which this synthesis is based is that hydrogen cyanide was reported to be eliminated readily from nitrogen heterocycles having a cyam group in the oc-position with rdpect to the hetero-nitrogen atom and an acidic phydmgen atom. 9-11 Reaction of Za-h, generated in sit" by treatment of the corresponding hydrazidoyl halides la-h with triethylamine in chiomform, with fumaronitrile 6 gave in each case one product as evidenced by thin layer chromatographic analysis The products obtained were identified as 1,)-disubstituted b-cyano- pyrazoies Ea-h (Scheme 1). Their structures were assigned on the basis of elemental analyses and I spectral data. The H nmr spctra of Ba-h showed in each case a characteristic singlet signal near 68.35 ppm assignable to the 5-CH of pyraroie ring residue.'' in their infrared spectra the pmducB I 8a-h exhibit a nitrile absorption band near 2230 cm- . I t seems pmbable that the intermediate cycloadducts 7a-h have undergone elimination of hydmgen cyanide as soon as they are formed to give Ea-h (Scheme 1) since the crude reaction mixture revealed the abence of the doublet signals expected far the 4-CH and 5-CH of the 2-pyrazoline ring residue of intermediates 7a-h. The elirni- nation of hydrogen cyanide from 7 is analogous to the elimination of benrenesulflnic acid, hydrazoic acid and benraldehyde from 5-benzenesuifonyl-, 5-azidn- and 5-benzoyl substituted 2-pyrazoilnes, respectively. 13-15