A novel and practical chiral ruthenium NHC-diamine system is disclosed for the enantioselective hydrogenation of isocoumarins, which provides a new concept to apply (chiral) NHC ligands in asymmetric catalysis. A variety of optically active 3-substituted 3,4-dihydroisocoumarins were obtained in excellent enantio-selectivities (up to 99% ee). Moreover, this methodology was utilized in the synthesis of O-methylmellein, mellein, and ochratoxin A.