A Synthetic Methodology for Pyrroles from Nitrodienes

Palladium complexes containing the ligand 4,7-dimethoxy-1,10-phenanthroline have been used to catalyze the reductive cyclization of nitrodienes using carbon monoxide as the reductant to give pyrroles. Carbon dioxide was the only stoichiometric byproduct of the reaction. The yields were good and the starting materials can be easily synthesized in two steps by a cross-aldol condensation reaction followed by a Henry reaction. Different substitution patterns are tolerated by this novel synthetic strategy.