Convenient Synthesis of Indolines by Reduction of Indoles With Sodium Cyanoborohydride in Carboxylic Acids

Abstract The reduction of indoles to indolines has received considerable attention during the l a s t few years1,2. A recent report from Gribble et al 3, 4 has shown that sodium borohydride in neat acetic acid or formic acid reduces the indole double bond and at the same time alkylates the nitrogen to give Nalkyl indolines, while sodium cyanoborohydride in acetic acid or sodium borohydride in trifluoroacetic acid only reduces the double bond of indole to give indoline.