tert-Butyl piperazine-1-carboxylate → Tert-butyl 4-(4-chloro-1,2,5-thiadiazol-3-yl)piperazine-1-carboxylate

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Reaction Steps

Piperazine-1-carboxylic acid tert-butyl ester (10 g, 0.054 m) was dissolved in anhydrous dimethylformamide (DMF, 50 mL) under nitrogen in a single-necked round bottomed flask. The clear solution was placed in a preheated oil bath (50 C-60 C). 4,5-Dichloro-[1,2,5]thiadiazole (5.0 mL, 0.054 m) was added and the reaction mixture was allowed to stir for 24 h. A yellow solution containing a white solid was observed. After cooling to room temperature, the mixture was diluted with an equal volume of anhydrous ethyl ether and stirred for 5 minutes. The solid was removed by filtration and the yellow filtrate was concentrated under aspirator vacuum to remove ether and then evaporated under oil pump vacuum to remove DMF. The yellow residue was dried at oil pump vacuum overnight to give 9.91 g of 4-(4-chloro-[1,2,5]thiadiazol-3-yl)piperazine-1-carboxylic acid tert-butyl ester. Two recrystallizations of crude product from hexane gave white crystals: mp 83-86° C.

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