A highly active catalyst for the reductive cyclization of ortho-nitrostyrenes under mild conditions

Abstract A mild and efficient method for the palladium-catalyzed reductive cyclization of ortho -nitrostyrenes to afford indoles is reported. Treatment of ortho -nitrostyrenes with 0.1 mol% palladium (II) trifluoroacetate [Pd(TFA) 2 ] and 0.7 mol% 3,4,7,8-tetramethyl-1,10-phenanthroline (tm-phen) in DMF at 15 psig CO and 80 °C afforded indoles in good to excellent yields. When the reaction was conducted in toluene, the corresponding N -hydroxyindole was isolated. A mechanism that accounts for the formation of N -hydroxyindole is proposed.