Catalytic transfer hydrogenation
Catalytic, enantioselective transfer hydrogenation reactions involve the enantioselective formal addition of a proton (H+) and hydride (H–) to a reducible functional group such as a carbonyl group, alkene, or aromatic heterocycle from an oxidizable hydrogen source. Transfer hydrogenation reactions eliminate the need for high pressures and temperatures, which are typically required in catalytic hydrogenation reactions employing H2. Metal catalysts containing ruthenium, rhodium, or iridium are employed to facilitate transfer hydrogenation; organocatalysts such as chiral secondary amines or phosphoric acid derivatives can also be used in some cases. Common hydrogen sources include secondary alcohols, Hantzsch esters, and formate.