Novel oxidations of 1,3-disubstituted indoles

A study of oxidation versus nitration of 1,3-disubstituted indole derivatives with nitric acid in acetic acid was carried out. Oxidation of methyl and ethyl 2-cyano-2-(1-alkoxycarbonyl-1H-indol-3-yl)acetates 1 and 2 under the above conditions gave rise to novel functionalized 2-hydroxyindolenines as single products possessing the Z-configuration, 8 and 10 , respectively. The structure of 10 was determined by an X-ray analysis. In contrast, 1-methoxycarbonyl-1H-indol-3-acetonitrile ( 3 ) was nitrated to the corresponding 6-nitroindole derivative 11 , whereas the reaction of ethyl 2-cyano-2-(1-methyl-1H-indol-3-yl)acetate ( 4 ) with nitric acid effected an oxidative nitration to provide the corresponding ethyl Z-5-nitroisatyliene cyanoacetate ( 12 ), which in solution isomerized to the E isomer.