Diethyl chlorophosphate → tert-Butyl 6-Fluoro4,5-dihydro-5-[(pyrrolidino)carbonyl]imidazo[1,5-a]quinoxaline-3-carboxylate

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Reaction Steps

Potassium tert-butoxide (1M, 3.8 ml) is added to 5-fluoro-1,2,3,4-tetrahydro-4-[(pyrrolidino)carbonyl]quinoxalin-2-one (XXXII, EXAMPLE 29, 0.908 g) at 0° in THF (20 ml). The mixture is stirred for 30 min and then diethylchlorophosphate (0.55 ml) is added. The reaction is stirred for 1 hr at 0°, then cooled at -78°. tert-butyl isocyanoacetate (0.58 g) is added, followed by potassium tert-butoxide (1M, 4.14 ml). The reaction is stirred at -78° for 4 hr, then allowed to warm to 20°-25° over 1 hr. The mixture is then partitioned between ethyl acetate, water, and saline. The organic layers are dried over magnesium sulfate and concentrated. The crude product is chromatographed on silica gel (250 ml) eluting with a gradient of ethyl acetate/dichloromethane (20/80 to 40/60). The appropriate fractions are pooled, concentrated and crystallized from dichloromethane/hexane to give the title compound; mp 213.5°-214.5°; MS (m/z) at 386; IR (mineral oil) 1689, 1677, 1217, 1363 and 1157 cm-1 ; NMR (CDCl3) 1.63, 1.88, 3.36, 5.08, 7.08, 7.20, 7.33 and 8.00 δ.

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