EFFICIENT SYNTHESIS OF t-BUTYL 3-ALKYL-N-HYDROXY-OXINDOLE-3-CARBOXYLATES FROM DI-t-BUTYL 2-NITROPHENYLMALONATES

A selective and efficient synthesis of t-butyl 3-alkyl-N-hydroxy-oxindole-3-carboxylates from di-t-butyl 2-nitrophenylmalonates is described. A tandem reduction-cyclization approach involving reduction of di-t-butyl 2-methyl-(2-nitrophenyl)malonate to di-t-butyl 2-(2-(hydroxyamino)phenyl)-2-methylmalonate followed by accelerated cyclization reaction using a combination of Rh/C and hydrazine monohydrate smoothly and selectively afforded the N-hydroxy-oxindole scaffold. This methodology was successfully applied to gram-scale-synthesis of the t-butyl N-hydroxy-3-methyl-oxindole-3-carboxylate 1 without silica gel column chromatographic separation step.