1,2-Dibromopropane → Ethyl 6,7-dihydro-5H-pyrazolo[5,1-B][1,3]oxazine-3-carboxylate

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Reaction Conditions

Reaction Steps

3-Oxo-2,3-dihydro-1H-pyrazole-4-carboxylic acid ethyl ester (13.2 g, 84.5 mmol), potassium carbonate (50 g, 0.3 mol) and N,N-dimethylformamide (500 mL) were combined in a 250 mL round bottom flask, and the mixture was heated to 130° C. 1,2-Dibromo-propane (10.4 mL, 0.10 mol) was added. After 30 minutes, the mixture was partitioned between DCM and water. The aqueous layer was extracted with DCM and the combined organics were washed with brine, dried (Na2SO4), filtered and concentrated in vacuo. The yellow solid was purified by column chromatography (DCM/MeOH) to afford the ester (9.67 g, 58%) as a solid. 1H NMR (400 MHz, DMSO-d6) δ7.62 (s, 1H), 4.41-4.38 (m, 2H), 4.13 (q, 2H), 4.08 (t, 2H, J=6.03 Hz), 2.21-2.15 (m, 2H), 1.21 (t, 3H, J=7.09 Hz).

Provenance & Evidence