Cesium carbonate → 4-(6-Nitropyridin-3-yl)-3-oxopiperazine-1-carboxylic acid tert-butyl ester

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Reaction Steps

A 250-mL single-neck round-bottomed flask equipped with a magnetic stirrer and reflux condenser was charged with 2-nitro-5-bromopyridine (1.00 g, 5.00 mmol), 2-oxo-4-(tert-butoxycarbonyl)piperazine (1.01 g, 5.00 mmol), cesium carbonate (3.58 g, 11.0 mmol) and 1,4-dioxane (40 mL). After bubbling nitrogen through the resulting solution for 30 min, Xantphos (246 mg, 0.425 mmol) and tris(dibenzylidene-acetone)dipalladium(0) (230 mg, 0.250 mmol) were added, and the reaction mixture was heated at reflux for 6 h. Water (30 mL) and ethyl acetate (150 mL) were added after the reaction mixture was cooled to room temperature. The resulting mixture was filtered through a bed of Celite 521. The organic layer of the filtrate was separated and the aqueous layer was extracted with ethyl acetate (2×50 mL). The combined organic layers were washed with brine (30 mL), dried over sodium sulfate and purified by column chromatography to afford a 96% yield (1.55 g) of 121a as an amber oil: 1H NMR (300 MHz, CDCl3) δ 8.67 (d, 1H, J=2.4 Hz), 8.32 (d, 1H, J=8.7 Hz), 8.15 (dd, 1H, J=8.7, 2.4 Hz), 4.33 (s, 1H), 3.89 (m, 4H), 1.48 (s, 9H); MS (ESI+) m/z 323.1 (M+H).

Provenance & Evidence