1,1'-Thiocarbonyldiimidazole → 1-(4-Isothiocyanatophenyl)-4-(sec-butyl)piperazine

A solution of 4-[4-(sec-butyl)-1-piperazinyl]benzenamine (3.5 g, 15 mmol) (from Step B above) in N,N-dimethylformamide (40 mL) was added dropwise over 20 min to a cooled (−15° C.) solution of thiocarbonyidiimidazole (2.68 g, 15.03 mmol) (Aldrich) in N,N-dimethylformamide (15 mL). After the addition was complete, the mixture was stirred at −15° C. for 20 min, then the cooling bath was removed and the solution was stirred for 1 h. Ice-water (800 ml) was added and the mixture was stirred for 30 min. The solid was filtered off and washed with water and dried under vacuum to give 1-(4-isothiocyanatophenyl)-4-(sec-butyl)piperazine (3.6 g, 87%) as a purple solid.