Synthesis of Indoles by Palladium-Catalyzed Reductive Cyclization of ?-Nitrostyrenes with Phenyl Formate as a CO Surrogate

The reductive cyclization of suitably substituted organic nitro compounds by carbon monoxide is a very appealing technique for the synthesis heterocycles because its atom efficiency and easiness separation only stoichiometric byproduct CO2, but need pressurized CO has hampered diffusion. We have recently reported on indoles o-nitrostyrenes using phenyl formate as surrogate, palladium/1,10-phenanthroline complex catalyst. However, depending desired substituents structure, use ?-nitrostyrenes alternative reagents may be advantageous. report here results our study possibility to surrogate in ?-nitrostyrenes, PdCl2(CH3CN)2 + phenanthroline It turned out that good can obtained when starting nitrostyrene bears an aryl substituent alpha position. no such present, fair yield indole base required decompose also catalyzes oligo-polymerization styrene. reaction performed single glass pressure tube, cheap easily available piece equipment.