Hydrogenation of aromatic rings catalysts

The catalytic hydrogenation of aromatic rings is a well-established transformation used to produce industrially relevant molecules. Aromatic rings such as benzenes, pyridines, quinolines, and isoquinolines are crucial building blocks and their hydrogenation is key to producing a wide variety of cyclic structures that are essential components of many small molecules. In general, heterocycles are easier to hydrogenate than carbocycles and product stereochemistry depends on the catalyst used and the nature of any ring substituents.

A wide variety of catalysts can be used for this transformation. A ruthenium catalyst is often recommended to avoid C-O or C-N bond hydrogenolysis. Often times, hydrogenolysis during ring reduction is decreased with increased pressure and lower reaction temperatures. Phenols can be converted directly to cyclohexanones under basic conditions using palladium catalysts. Also, palladium catalysts are preferred for selective hydrogenation of nitrogen-containing heterocyclic rings in the presence of carbocylic rings.