Studies On Oxidative Decarboxylation Of N-Aroylglycine

Oxidative decarboxylation of N-Aroylglycine catalyzed by silver(I) was investigated. We found that using ammonium persulfate as a oxidant and water/CHCl3 as solvents, N-aroylglycine underwent oxidative decarboxylation to afford N-formylbenzamides at 60°C. Using hippuric acid as a model compound, N-formylbenzamide was obtained in the best yield (71%) when using two equivalents of ammonium persulfate. For hippuric acids with 4-Cl, 4-Br, 4-Me, 2-OMe or 3-NO2, N-formylbenzamides were obtained in 20~68% yield. N-Phenyl-N-benzoylglyine gave N-formyl-N-phenylbenzamide in 78% yield. Since the reaction was carried out in aqueous solution and used inexpensive reagents, this provides a facile synthesis of N-formylbenzamides starting from aroyl chloride and glycine. Attempts to synthesize N-formyl compounds from N-phenylsulfonylglycine or phthalylglycine, and synthesize N-acetylbenzamide from N-benzoylalanine failed. The reaction probably includes an amidomethyl radical intermediate, which formed via oxidative decarboxylation, and further oxidized to be N-formylbenzamide after oxidation and hydrolysis. However, attempts to capture amidomethyl radical using intramolecular C=N, i. e., to synthesize 6,7-dihydropyrrolo[3,4-b]pyrridin-5-one from N-nicotinoylphenylalanine or N-nicotinoyl-α-phenylglycine failed.