Trifluoroacetic acid → 1,1-Diphenyltetrahydro-1H-oxazolo[3,4-a]pyrazin-3(5H)-one

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Reaction Steps

To a solution of (1,1-dimethylethyl)tetrahydro-3-oxo-1,1-diphenyl-3H-oxazolo[3,4-a]pyrazine-7(1H)-carboxylate (99 mg, 0.25 mmol) in dichloromethane (2 mL) was added trifluoroacetic acid (0.19 mL, 2.5 mmol), and the mixture was stirred at room temperature for 4 hours. The reaction solution was concentrated under reduced pressure, and the residue was dissolved in ethyl acetate. This solution was washed with sodium hydrogen carbonate, dried over anhydrous magnesium sulfate and concentrated under reduced pressure to obtain hexahydro-1,1-diphenyl-3H-oxazolo[3,4-a]pyrazin-3-one as a crude product. The product was dissolved in tetrahydrofuran (2 mL). Diisopropylethylamine (60 μL, 0.35 mmol) and phenyl chlorocarbonate (44 μL, 0.35 mmol) were added thereto, and the mixture was stirred at room temperature for 1 hour. To the reaction solution was added ethyl acetate, and the resulting mixture was washed with water and saturated brine, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was crystallized from ethyl acetate-hexane to obtain the title compound (70 mg, yield 67%).

Provenance & Evidence