Lithium borohydride → benzyl tetrahydro-3-oxo-1H-oxazolo[3,4-a]pyrazine-7(3H)-carboxylate

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Reaction Steps

To a flask containing methyl N,N'-dibenzyloxycarbonylpiperazine-2-carboxylate (Step 2, 12.60 g, 30.60 mmol) and tetrahydrofuran (65 mL) at 0° C. under an inert atmosphere is added lithium borohydride (2 M in THF) (23.00 mL, 45.9 mmol). The solution is warmed to ambient temperature, stirred 19 hours, cooled to 0° C., and quenched with water (50 mL). The mixture is diluted with ethyl acetate (100 mL) and the pH is adjusted to 2 with 1N HCl. The layers are separated and the aqueous phase is extracted with ethyl acetate (50 mL). The organics are combined, washed with water (50 mL) and saline, dried over MgSO4, concentrated in vacuo, and chromatographed on silica gel (70-230 mesh, 500 g), eluting with hexane/ethyl acetate (50/50) then ethyl acetate (100). The appropriate fractions are combined (Rf =0.17, TLC, hexane/ethyl acetate, 50/50) and concentrated in vacuo to give the title compound, mp 85.5-86.5° C.

Provenance & Evidence