2,2,2-Trifluoroethylhydrazine → 3,3a,4,5,6,7-Hexahydro-5-methyl-3-phenyl-7-(phenylmethylene)-2-(2,2,2-trifluoroethyl)-2H-pyrazolo[4,3-c]pyridine, hydrochloride

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Reaction Steps

A stirred suspension of 12.5 g of 3,5-dibenzylidene-1-methyl-4-piperidone, hydrochloride in 225 ml of methanol is treated with 6.9 g of 70% aqueous 2,2,2-trifluoroethylhydrazine, heated, and the resulting solution refluxed for four hours. The solvent is removed on a rotary evaporator and the light yellow foamy residue (18 g) is dissolved in 90 ml of acetonitrile and treated with 7.5 ml of 5.1 N alcoholic hydrogen chloride; the solid salt rapidly separates after a few seconds. Following cooling for about 16 hours, the material is filtered under nitrogen, washed with cold acetonitrile and ether, and dried in vacuo yielding 9.7 g of material, melting point 185°-187° C (foaming); sintering at 181° C. Crystallization from 50 ml of methanol and 50 ml of ether yields 7.9 g of product, melting point 185°-187° C (foaming).

Provenance & Evidence