Reduction of sulfoxides and pyridine-N-oxides over iron powder with water as hydrogen source promoted by carbon dioxide

A green process was developed for efficient reduction of sulfoxides and pyridine-N-oxides using the iron powder in the presence of H2O–CO2 to sulfides and pyridines, respectively. Notably, H2O is employed as the terminal hydrogen source, and CO2 could enhance hydrogen generation through in situ formation of carbonic acid. Thus carbonic acid offers simple neutralization by depressurizing CO2 and the system can eliminate unwanted byproducts. The high generality and chemo-selectivity of this protocol were demonstrated by the scope of substrates, in which chlorine, vinyl group and benzene ring can be tolerated.