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.