To a solution of hydrazine hydrate diluted in 16 ml of dimethylsulfoxide under argon are added dropwise a solution of 4.76 g (16.41 mmol) of tert-butyl 4-(4-formylphenyl)piperazine-1-carboxylate dissolved in 32 ml of dimethylsulfoxide. The reaction mixture is stirred at room temperature for 3 h before being cooled over an ice bath. Then, the successive addition is made of 11.45 ml (82 mmol) of triethylamine, 162 mg of copper (I) chloride and, in 5 min, a solution of 8.23 ml (82 mmol) of trichloroacetonitrile diluted in 16 ml of dimethylsulfoxide. The reaction mixture is stirred at room temperature for 18 h then poured onto an aqueous 0.1N hydrochloric acid solution. The product is extracted several times with dichloromethane. The organic phases are combined, dried over magnesium sulfate, and concentrated. The residue is purified by chromatography on silica (cyclohexane/ethyl acetate eluent: 8:2) to yield 1.52 g (26%) of tert-butyl 4-(4-(2-chloro-2-cyanovinyl)phenyl)piperazine-1-carboxylate in the form of a yellow solid (mixture of the two isomers Z/E).
