Sulfuric Acid → (2S)-1-(tert-butoxycarbonyl)-4-oxopyrrolidine-2-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

Commercial (2S, 4R)-1-(tert-butoxycarbonyl)-4-hydroxy-2-pyrrolidinecarboxylic acid (30 g, 0.13 mol) was dissolved in acetone (1500 ml). A mechanical stirrer was placed in the flask and the solution stirred vigorously. A freshly made solution of 8N chromic acid was prepared by dissolving chromium trioxide (66.7 g, 0.667 mol) in water (40 ml), adding concentrated sulphuric acid (53.3 ml) and adding enough water to bring the solution volume to 115 ml. The 8N chromic acid solution (115 ml) was then added dropwise over a period of 30 min with continued vigorous stirring, the reaction's exotherm being maintained at the optimal temperature of 25° C. by the use of an ice bath. After the complete addition of the chromic acid, the reaction mixture was stirred for a further 15 minutes—maintaining the optimal temperature of 25° C. The reaction mixture was then quenched by the addition of methanol (20 ml). Exotherm was controlled by the use of an ice bath and, if necessary, direct addition of a small amount of crushed ice to the reaction mixture itself. The reaction mixture was filtered through a Celite pad and then concentrated in vacuo. The resulting acidic solution was then extracted with ethyl acetate (3×300 ml) and the combined organic layers washed with brine (2×100 ml), then dried with magnesium sulfate and concentrated in vacuo. The crude product was recrystallized from ethyl acetate to give a white crystalline product, (2S)-1-(tert-butoxycarbonyl)-4-oxo-2-pyrrolidinecarboxylic acid (22.55 g, 76%) (1a). (1H NMR (360 MHz, CDCl3): 1.4 (m, 9H), 2.5–3.0 (m, 2H), 3.7–3.9 (m, 2H), 4.75 (dd, 1H)).

Provenance & Evidence