Ethyl 1-benzyloxycarbonyl-4-(tert-butoxycarbonyl)-2-piperazinecarboxylate → 1-tert-Butyl 3-ethyl piperazine-1,3-dicarboxylate

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Reaction Steps

To a solution of ethyl 1-benzyloxycarbonyl-4-(tert-butoxycarbonyl)-2-piperazinecarboxylate (2.49 g) (Tet. Lett. 30(39), 5193-5196) in EtOH was added Pd/C (0.25 g). The solution was degassed with nitrogen and hydrogen gas was bubbled into the mixture. The reaction mixture was stirred for 3 hours under hydrogen atmosphere. The mixture was filtered through Celite and concentrated to give 1.15 g of ethyl 4-(tert-butoxycarbonyl)-2-piperazinecarboxylate. (2) To a solution of the compound obtained above in THF (10 mL) was added 3,5-dichlorophenyl isocyanate (1.00 g). After stirring overnight, the solution was concentrated. Purification by chromatography (Silica gel: EtOAc/hexane: 1/4, Chromatotron) afforded ethyl 1-[N-(3,5-dichlorophenyl)carbamoyl]-4-tert-butoxycarbonyl-2-piperazinecarboxylate (1.36 g). MS (m/z) 446 (MH+). (3) The compound obtained above was treated in a manner similar to Example 1 (4) to yield 4-(tert-butoxycarbonyl)-8-(3,5-dichlorophenyl)-1,4,8-triazabicyclo[4.3.0]nonane-7,9-dione (0.72 g). MS (m/z) 422 (M++Na) mp 60.2° C.

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