Highly Enantioselective Synthesis of Indolines: Asymmetric Hydrogenation at Ambient Temperature and Pressure with Cationic Ruthenium Diamine Catalysts
作者:Zhusheng Yang、Fei Chen、Yanmei He、Nianfa Yang、Qing-Hua Fan
DOI:10.1002/anie.201607890
日期:2016.10.24
asymmetric hydrogenation of 1H‐indoles and 3H‐indoles at ambient temperature and pressure, catalyzed by chiral phosphine‐free cationic ruthenium complexes, has been developed. Excellent enantio‐ and diastereoselectivities (up to >99 % ee, >20:1 d.r.) were obtained for a wide range of indolederivatives, including unprotected 2‐substituted and 2,3‐disubstituted 1H‐indoles, as well as 2‐alkyl‐ and 2‐aryl‐substituted
The first highly enantioselective hydrogenation of simple indoles was developed with a Brønstedacid as an activator to form the iminium intermediate in situ, which was hydrogenated using Pd(OCOCF(3))(2)/(R)-H8-BINAP catalyst system with up to 96% ee. The present method provides an efficient route to enantioenriched 2-substituted and 2,3-disubstituted indolines.
98% ee using a strong Brønsted acid as the activator. This methodology was applied in the facile synthesis of biologically active products containing a chiral indoline skeleton. The mechanism of Pd-catalyzed asymmetric hydrogenation was investigated as well. Isotope-labeling reactions and ESI-HRMS proved that an iminium salt formed by protonation of the C═C bond of indoles was the significant intermediate
application of binaphthyl-stabilized palladium nanoparticles (Bin-PdNPs) with chiral modifiers in asymmetric hydrogenation of N-heteroaromatics is revealed. With an appropriate ratio of R-BINAP/Bin-PdNPs used, the pre-prepared chiral nanocatalyst achieves asymmetric hydrogenations of 2-substituted quinolines with good to excellent yields and moderate enantioselectivities, which showed superior catalytic properties
The developments of hydrogensources stand at the forefront of asymmetric reduction. In contrast to the well-studied alcohols as hydrogensources via β-hydride elimination, the direct utilization of the proton of alcohols as a hydrogensource for activator-mediated asymmetric reduction is rarely explored. Herein we report the proton of alcohols as a hydrogensource in diboron-mediated palladium-catalyzed