Chromic Acid → N-Carbobenzyloxy-4-keto-L-proline

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Reaction Steps

21.5 g. (0.81 mole) of N-carbobenzyloxy-4-hydroxy-L-proline is oxidized in 1.2 liters of acetone with 83 ml. of 8 N chromic acid in sulfuric acid as described in J.A.C.S. 79, 189 (1957). In order to facilitate the subsequent filtration of chromium salts, 30 g. of Celite (diatomaceous earth) is added to the acetone solution before introduction of the oxidizing agent. An air stirrer is employed. The reaction mixture is filtered and the acetone filtrate is concentrated to approximately 300 ml. before diluting with 1 liter of chloroform. The solution is washed with 300 ml. of saturated sodium chloride (four times), dried (MgSO4), filtered and the solvent evaporated to give N-carbobenzyloxy-4-keto-L-proline (22.8 g.) which is crystallized from ether (50 ml.)-hexane (150 ml.) to obtain 17.2 g. (81%) of product, m.p. 99°-101°, [α]D26 +17° (c, 1% in chloroform).

Provenance & Evidence