Enantioselective hydrogenation of dialkyl ketones

Chiral catalyst development is a key to asymmetric catalysis research. The enantioselectivity of a chiral catalyst relies on its ability to distinguish the prochiral centres or faces of substrates, which is difficult when the two groups attached to the centre or face are spatially and electronically similar. For example, dialkyl ketones are difficult to reduce enantioselectively. Here we report a protocol for the highly enantioselective hydrogenation of dialkyl ketones catalysed by a rationally designed chiral spiro iridium complex. The tridentate spiro structure and the bulky phosphino groups of the chiral ligand imparted a remarkable stability and enantioselectivity to the catalyst. The protocol is highly efficient for generating chiral aliphatic alcohols, and has potential for a wide application in pharmaceuticals and fine chemicals. Achieving high enantioselective control in the hydrogenation of aliphatic ketones is a long-standing challenge. Now, the design of a spiro iridium catalyst with a narrow, crowded chiral pocket allows highly enantioselective hydrogenation of these compounds.