Acetic Acid → 2-[4-(Biphenyl-4-ylmethyl)piperazin-1-ylmethyl]-6-nitro-2,3-dihydroimidazo[2,1-b]oxazole

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Reaction Steps

A mixture of tert-butyl 4-(6-nitro-2,3-dihydroimidazo[2,1-b]oxazol-2-ylmethyl)piperazine-1-carboxylate prepared in Example 319 (400 mg, 1.13 mmol) and trifluoroacetic acid (10 ml) was stirred at room temperature for 4 hours. The reaction mixture was concentrated. The residue was dissolved in methylene chloride (10 ml) and neutralized with triethylamine (2 ml, 14.35 mmol). The resulting solution was concentrated under reduced pressure, and the residue was dissolved in methanol (10 ml). To the solution, 4-phenylbenzaldehyde (515 mg, 2.83 mmol), sodium cyanotrihydroborate (214 mg, 3.41 mmol) and acetic acid (0.21 mg, 3.67 mmol) were added in this order followed by stirring at room temperature overnight. The reaction mixture was concentrated. To the residue, water was added, and the solution was extracted with methylene chloride twice. The organic phases were combined, washed with a saturated sodium hydrogen-carbonate solution and a saturated saline solution in this order, dried over magnesium sulfate and then filtered. The filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography (methylene chloride/methanol=20/1) to afford 2-[4-(biphenyl-4-ylmethyl)piperazin-1-ylmethyl]-6-nitro-2,3-dihydroimidazo[2,1-b]oxazole (188 mg, yield 40%) as a white powder.

Provenance & Evidence