Synthesis of 3-aminooxindoles via acid-promoted cyclization of α-imino-N-arylamides and α-azido-N-arylamides

This paper reports a new method for the synthesis of 3-aminooxindole derivatives. Ethyl 2-(N-arylcarbamoyl)-2-iminoacetates, which can be prepared from the reaction of α-ethoxycarbonyl-α-bromo-N-phenylacetamides with sodium azide, were found to undergo Friedel-Crafts cyclization to afford 3-aminooxindoles in high yield by the catalysis of an acid such as BF3⋅OEt2. α-Aryl-α-azido-N-arylamides, on the other hand, were transformed to 3-arylaminooxindoles via a tandem 1,2-aryl migration-dinitrogenation and cyclization by the action of triflic acid. As both ethyl 2-(N-arylcarbamoyl)-2-iminoacetates and α-aryl-α-azido-N-arylamides are easily accessible, the current reactions are expected to be practically useful in the synthesis of 3-aminooxindole derivatives.