Asymmetric Hydrogenation of Quinoxalines Catalyzed by Iridium/PipPhos
作者:Nataša Mršić、Thomas Jerphagnon、Adriaan J. Minnaard、Ben L. Feringa、Johannes G. de Vries
DOI:10.1002/adsc.200900522
日期:2009.11
from the (cyclooctadiene)iridium chloride dimer, [Ir(COD)Cl]2, and the monodentate phosphoramidite ligand (S)-PipPhos was used in the enantioselective hydrogenation of 2- and 2,6-substituted quinoxalines. In the presence of piperidine hydrochloride as additive full conversions and enantioselectivities of up to 96% are obtained.
Water as a hydride source: A new pathway to form metal–hydride bonds has been developed through the reaction of easily available metal–silyl compounds with water. This method has been successfully applied to asymmetrichydrogenation of heteroaromatic compounds with up to 93 % ee under mild autoclave‐free conditions (see scheme).
terminal epoxides into valuable 1,2,3,4-tetrahydroquinoxalines in a highly enantioselective fashion. This procedure operates through relay zinc and iridiumcatalysis, and achieves redox-neutral and stereoconvergent production of valuable chiral heterocycles from racemic starting materials with water as the only side product. The use of commercially available reagents and catalysts and a convenient procedure