Benzophenone → Hexahydro-1,1-diphenyl-7-(phenylmethyl)-3H-oxazolo[3,4-a]pyrazin-3-one

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Reaction Conditions

Reaction Steps

1,1-Dimethylethyl 4-(phenylmethyl)-1-piperazine carboxylate (20 g, 72 mmol) and tetramethylethylenediamine (18 g, 0.16 mol) were dissolved in tetrahydrofuran (100 mL), and the solution was cooled to −78° C. A 1.0 M solution of sec-butyllithium in hexane and cyclohexane (150 mL, 0.15 mol) was added thereto, and the mixture was stirred for 2 hours and the temperature was elevated to −30° C. After cooling to −78° C. again, a solution of benzophenone (28 g, 0.15 mol) in tetrahydrofuran (70 mL) was added dropwise thereto, and the mixture was stirred for 18 hours while elevating the temperature to room temperature. To the reaction solution was added an aqueous saturated ammonium chloride solution, and the resulting mixture was extracted with ethyl acetate. The extract was washed with water and concentrated under reduced pressure. The residue was purified with silica gel column chromatography (hexane:ethyl acetate=3:1) to obtain the title compound (18 g, yield 64%) as crystals.

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