Trifluoroacetic acid → 4-trifluoromethylbenzyl (S)-4-(2-methyl-6-nitro-2,3-dihydroimidazo[2,1-b]oxazol-2-ylmethyl)piperazine-1-carboxylate

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Reaction Steps

A mixture of tert-butyl (S)-4-(2-methyl-6-nitro-2,3-dihydroimidazo[2,1-b]oxazol-2-ylmethyl)piperazine-1-carboxylate prepared in Example 393 (1.87 g, 5.09 mmol) and methylene chloride (20 ml) was added trifluoroacetic acid (20 ml) followed by stirring for 5 minutes, and then concentrated under reduced pressure. The residue was dissolved in DMF (20 ml). To the solution, a mixture of 1,1′-carbonyldiimidazole (1.76 g, 10.9 mmol), 4-(trifluoromethyl)benzyl alcohol (1.92 g, 10.9 mmol) and DMF (20 ml) stirred at room temperature for 3 hours was added followed by stirring at room temperature overnight. The reaction mixture was extracted with ethyl acetate. The organic phases were combined, washed with water and a saturated saline solution, dried over sodium sulfate and then filtered. The resulting filtrate was concentrated under reduced pressure, and the residue was purified by silica gel column chromatography (n-hexane/acetone=3/1), recrystallized from isopropyl alcohol. The resulting solids were filtered off and then dried under reduced pressure to afford 4-trifluoromethylbenzyl (S)-4-(2-methyl-6-nitro-2,3-dihydroimidazo[2,1-b]oxazol-2-ylmethyl)piperazine-1-carboxylate (1.48 g, yield 53%) as a light yellow powder.

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