A safe and selective method for reduction of 2-nitrophenylacetic acid systems to N-aryl hydroxamic acids using continuous flow hydrogenation

The cyclic hydroxamic acid functional group is critical to the biological activity of numerous natural products and drug candidates. Efficient, reliable, and green synthetic methods to produce cyclic hydroxamic acids are needed. Herein, flow hydrogenation has been explored as a novel approach toward achieving the selective partial reduction of 2-nitrophenylacetic acid to 1-hydroxyindolin-2-one. The bidentate ligand, 1,10-phenanthroline, has been identified as a unique inhibitor for modulating product selectivity in this Pt/C-catalyzed process. Under the newly optimized reaction conditions, the targeted hydroxamic acid is produced with high selectivity (49:1) over the lactam by-product. The scope of the reaction is demonstrated for a variety of 2-nitrophenylacetic acid derivatives.