Asymmetric Transfer Hydrogenation of Aryl Heteroaryl Ketones using Noyori‐Ikariya Catalysts

Abstract

AbstractA range of ketones flanked by a combination of an aromatic and a heterocyclic ring (furan, thiophene, N‐methylimidazole) were reduced under asymmetric transfer hydrogenation (ATH) conditions. Using a range of [(arene)Ru(TsDPEN)Cl] precatalysts, including tethered derivatives, the reduction enantioselectivity was high (up to 99 % ee) in cases where the aromatic ring contained an ortho‐substituent. The enantioselectivity is influenced by a combination of steric and electronic factors which for the furan and thiophene series, follow literature precedents. In the case of the N‐methylimidazole‐containing ketones, an unexpected switch in enantioselectivity took place upon variation of the opposing aromatic group. Pyrrole‐ containing ketones were resistant to reduction. This study demonstrates the asymmetric transfer hydrogenation (ATH) of a range of hindered heterocyclic ketones, in high conversion and ee, using Noyori‐Ikariya catalysts.