Asymmetric Hydroboration of Heteroaryl Ketones by Aluminum Catalysis

A series of methyl aluminum complexes bearing chiral biphenol-type ligands were found to be highly active catalysts in the asymmetric reduction of heterocyclic ketones (S/C = 100–500, ee up to 99%). The protocol is suitable for a wide range of substrates and has a high tolerance to functional groups. The formed 2-heterocyclic-alcohols are valuable building blocks in drug discovery or can be used as ligands in asymmetric catalysis. Isolation and comprehensive characterization of the reaction intermediates support a catalysis cycle proposed by DFT calculations.