A series of chiral cyclometalated iridiumcomplexes have been synthesised by cyclometalating chiral 2-aryl-oxazoline and imidazoline ligands with [Cp*IrCl2]2. These iridacycles were studied for asymmetric transfer hydrogenation reactions with formic acid as the hydrogen source and were found to display various activities and enantioselectivities, with the most effective ones affording up to 63% ee
Asymmetric Hydrogenation of Pyridinium Salts with an Iridium Phosphole Catalyst
作者:Mingxin Chang、Yuhua Huang、Shaodong Liu、Yonggang Chen、Shane W. Krska、Ian W. Davies、Xumu Zhang
DOI:10.1002/anie.201406762
日期:2014.11.17
Iridium‐catalyzedasymmetrichydrogenation of N‐alkyl‐2‐alkylpyridinium salts provided 2‐aryl‐substituted piperidines with high levels of enantioselectivity. Simple benzyl and other alkyl groups successfully activated the challenging pyridine substrates toward hydrogenation. The use of the unusual chiral‐phosphole‐based MP2‐SEGPHOS was the key to the success of this approach which provides a versatile
Enantioselective Synthesis of α-(Hetero)aryl Piperidines through Asymmetric Hydrogenation of Pyridinium Salts and Its Mechanistic Insights
作者:Bo Qu、Hari P. R. Mangunuru、Sergei Tcyrulnikov、Daniel Rivalti、Olga V. Zatolochnaya、Dmitry Kurouski、Suttipol Radomkit、Soumik Biswas、Shuklendu Karyakarte、Keith R. Fandrick、Joshua D. Sieber、Sonia Rodriguez、Jean-Nicolas Desrosiers、Nizar Haddad、Keith McKellop、Scott Pennino、Heewon Lee、Nathan K. Yee、Jinhua J. Song、Marisa C. Kozlowski、Chris H. Senanayake
DOI:10.1021/acs.orglett.8b00067
日期:2018.3.2
α-heteroaryl piperidines is reported. The key step is an iridium-catalyzed asymmetric hydrogenation of substituted N-benzylpyridinium salts. High levels of enantioselectivity up to 99.3:0.7 er were obtained for a range of α-heteroaryl piperidines. DFT calculations support an outersphere dissociative mechanism for the pyridinium reduction. Notably, initial protonation of the final enamine intermediate
报道了 α-芳基和 α-杂芳基哌啶的对映选择性合成。关键步骤是取代的N-苄基吡啶鎓盐的铱催化不对称氢化。一系列 α-杂芳基哌啶获得了高达 99.3:0.7 er 的高水平对映选择性。DFT 计算支持吡啶还原的外层解离机制。值得注意的是,最终烯胺中间体的初始质子化决定了转化的立体化学结果,而不是所得亚胺中间体的氢化物还原。
Iridium-Catalyzed Asymmetric Hydrogenation of Pyridinium Salts
Highly efficient iridium‐catalyzed asymmetrichydrogenations of simple 2‐substituted pyridinium salts gives the chiral 2‐substituted piperidines with up to 93 % ee (see picture; cod=1,5‐cyclooctadiene; synphos=(5,6),(5′,6′)‐bis(ethylenedioxy)‐2,2′‐bis(diphenylphosphino)‐1,1′‐biphenyl). The key feature of this strategy is the activation of simple pyridines as the pyridinium salts, thus eliminating substrate
A Mixed Ligand Approach for the Asymmetric Hydrogenation of 2-Substituted Pyridinium Salts
作者:Marc Renom-Carrasco、Piotr Gajewski、Luca Pignataro、Johannes G. de Vries、Umberto Piarulli、Cesare Gennari、Laurent Lefort
DOI:10.1002/adsc.201600348
日期:2016.8.18
describe a new methodology for the asymmetric hydrogenation (AH) of 2‐substituted pyridinium salts. An iridium catalyst based on a mixture of a chiralmonodentate phosphoramidite and an achiral phosphine was shown to hydrogenate N‐benzyl‐2‐arylpyiridinium bromides to the corresponding N‐benzyl‐2‐arylpiperidines with full conversion and good enantioselectivity. The mechanism of the reaction under optimized