Synthesis of Indoles by Palladium-Catalyzed Reductive Cyclization of -Nitrostyrenes with Carbon Monoxide as the Reductant

An efficient catalytic cyclization of -nitrostyrenes to indoles was developed. The reaction was applied to the synthesis of 3-arylindoles and 2-alkylindoles. Given that in the latter case the starting -nitrostyrenes can be easily obtained by a Henry reaction, the present method allows indoles to be obtained in a two-step sequence starting from cheap reactants.