Transition metal-mediated N-heterocyclisation reactions. Synthesis of 2-phenylindole by reduction by CO of 2-nitrostilbene catalysed by [Rh(CO)(4)](-)

The complex [PPN][Rh(CO)(4)] is a very efficient catalyst for the conversion of 2-nitrostilbene to 2-phenylindole by reduction by CO followed by cyclisation. The reaction is quite selective (up to 85%) and the only observable by-product is the amine corresponding to the starting material. The addition of 2-hydroxypyridine increases both conversion and selectivity. but simple pyridine deactivates the catalytic system. The reaction conditions have been optimised.