共查询到20条相似文献,搜索用时 15 毫秒
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Prof. Ryoichi Kuwano Yuta Hashiguchi Ryuhei Ikeda Dr. Kentaro Ishizuka 《Angewandte Chemie (International ed. in English)》2015,54(8):2393-2396
The asymmetric hydrogenation of pyrimidines proceeded with high enantioselectivity (up to 99 % ee) using an iridium catalyst composed of [IrCl(cod)]2, a ferrocene‐containing chiral diphosphine ligand (Josiphos), iodine, and Yb(OTf)3 (cod=1,5‐cyclooctadiene). The chiral catalyst converted various 4‐substituted pyrimidines into chiral 1,4,5,6‐tetrahydropyrimidines in high yield. The lanthanide triflate is crucial for achieving the high enantioselectivity as well as for activating the heteroarene substrate. 相似文献
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Dr. Mingxin Chang Yuhua Huang Shaodong Liu Dr. Yonggang Chen Dr. Shane W. Krska Dr. Ian W. Davies Prof. Xumu Zhang 《Angewandte Chemie (International ed. in English)》2014,53(47):12761-12764
Iridium‐catalyzed asymmetric hydrogenation 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 and practical procedure for the synthesis of chiral piperidines. 相似文献
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Ryuhei Ikeda Prof. Ryoichi Kuwano 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(25):8610-8618
The iridium catalyst [IrCl(cod)]2–phosphine–I2 (cod=1,5‐cyclooctadiene) selectively reduced isoxazolium triflates to isoxazolines or isoxazolidines in the presence of H2. The iridium‐catalyzed hydrogenation proceeded in high‐to‐good enantioselectivity when an optically active phosphine–oxazoline ligand was used. The 3‐substituted 5‐arylisoxazolium salts were transformed into 4‐isoxazolines with up to 95:5 enantiomeric ratio (e.r.). Chiral cis‐isoxazolidines were obtained in up to 89:11 e.r., with no formation of their trans isomers, when the substrates had a primary alkyl substituent at the 5‐position. The mechanistic studies indicate that the hydridoiridium(III) species prefers to deliver its hydride to the C5 atom of the isoxazole ring. The hydride attack leads to the formation of the chiral isoxazolidine via a 3‐isoxazoline intermediate. Meanwhile, in the selective formation of 4‐isoxazolines, hydride attack at the C5 atom may be obstructed by steric hindrance from the 5‐aryl substituent. 相似文献
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Alejandro Baeza Dr. Andreas Pfaltz Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(10):2266-2269
Optically active tertiary amines are readily prepared by iridium‐catalyzed asymmetric hydrogenation of unfunctionalized enamines (see scheme). The best enantioselectivities with >90 % ee were obtained with N‐aryl‐ and N‐benzyl‐substituted enamines with a terminal double bond. The hydrogenation of enamines derived from cyclic ketones, which has not been reported yet with other catalysts, gave enantiomeric excesses of up to 87 %.
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Alejandro Baeza Dr. Andreas Pfaltz Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(13):4003-4009
We have evaluated a wide range of iridium complexes derived from chiral oxazoline‐based N,P ligands for the asymmetric hydrogenation of imines and identified three efficient catalysts. These catalysts are readily synthesized by straightforward convenient routes and are air and moisture stable. In the reduction of acetophenone N‐arylimines and related acyclic substrates, excellent enantioselectivities (up to 96 % ee) were obtained by using 0.1–0.5 mol % of catalyst at ?20 °C and 5–50 bar hydrogen pressure. 相似文献
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Raphael Bigler Kyle A. Mack Jeff Shen Paolo Tosatti Chong Han Stephan Bachmann Haiming Zhang Michelangelo Scalone Andreas Pfaltz Scott E. Denmark Stefan Hildbrand Francis Gosselin 《Angewandte Chemie (International ed. in English)》2020,59(7):2844-2849
Asymmetric hydrogenation has evolved as one of the most powerful tools to construct stereocenters. However, the asymmetric hydrogenation of unfunctionalized tetrasubstituted acyclic olefins remains the pinnacle of asymmetric synthesis and an unsolved challenge. We report herein the discovery of an iridium catalyst for the first, generally applicable, highly enantio‐ and diastereoselective hydrogenation of such olefins and the mechanistic insights of the reaction. The power of this chemistry is demonstrated by the successful hydrogenation of a wide variety of electronically and sterically diverse olefins in excellent yield and high enantio‐ and diastereoselectivity. 相似文献
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J. Johan Verendel Jia‐Qi Li Xu Quan Byron Peters Taigang Zhou Dr. Odd R. Gautun Prof. Thavendran Govender Prof. Pher G. Andersson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(21):6507-6513
Several types of chiral hetero‐ and carbocyclic compounds have been synthesized by using the asymmetric hydrogenation of cyclic alkenes. N,P‐Ligated iridium catalysts reduced six‐membered cyclic alkenes with various substituents and heterofunctionality in good to excellent enantioselectivity, whereas the reduction of five‐membered cyclic alkenes was generally less selective, giving modest enantiomeric excesses. The stereoselectivity of the hydrogenation depended more strongly on the substrate structure for the five‐ rather than the six‐membered cyclic alkenes. The major enantiomer formed in the reduction of six‐membered alkenes could be predicted from a selectivity model and isomeric alkenes had complementary enantioselectivity, giving opposite optical isomers upon hydrogenation. The utility of the reaction was demonstrated by using it as a key step in the preparation of chiral 1,3‐cis‐cyclohexane carboxylates. 相似文献
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Dr. Jian‐Bo Xie Prof. Jian‐Hua Xie Xiao‐Yan Liu Qian‐Qian Zhang Prof. Qi‐Lin Zhou 《化学:亚洲杂志》2011,6(3):899-908
The iridium complexes of chiral spiro aminophophine ligands, especially the ligand with 3,5‐di‐tert‐butylphenyl groups on the P atom ( 1c ) were demonstrated to be highly efficient catalysts for the asymmetric hydrogenation of alkyl aryl ketones. In the presence of KOtBu as a base and under mild reaction conditions, a series of chiral alcohols were synthesized in up to 97 % ee with high turnover number (TON up to 10 000) and high turnover frequency (TOF up to 3.7×104 h−1). Investigation on the structures of the iridium complexes of ligands (R)‐ 1a and 1c by X‐ray analyses disclosed that the 3,5‐di‐tert‐butyl groups on the P‐phenyl rings of the ligand are the key factor for achieving high activity and enantioselectivity of the catalyst. Study of the catalysts generated from the Ir‐(R)‐ 1c complex and H2 by means of ESI‐MS and NMR spectroscopy indicated that the early formed iridium dihydride complex with one (R)‐ 1c ligand was the active species, which was slowly transformed into an inactive iridium dihydride complex with two (R)‐ 1c ligands. A plausible mechanism for the reaction was also suggested to explain the observations of the hydrogenation reactions. 相似文献
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Jędrzej Wysocki Dr. Nuria Ortega Prof. Dr. Frank Glorius 《Angewandte Chemie (International ed. in English)》2014,53(33):8751-8755
An enantioselective hydrogenation of disubstituted furans has been developed by using a chiral ruthenium catalyst with N‐heterocyclic carbene ligands. This reaction converts furans into valuable enantioenriched disubstituted tetrahydrofurans. 相似文献
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Dr. Maurizio Bernasconi Marc‐André Müller Prof. Dr. Andreas Pfaltz 《Angewandte Chemie (International ed. in English)》2014,53(21):5385-5388
Asymmetric hydrogenation of maleic and fumaric acid derivatives with iridium catalysts based on N,P ligands provides an efficient route to chiral enantioenriched succinates. A new catalyst derived from a 2,6‐difluorophenyl‐substituted pyridine‐phosphinite ligand was developed and enables the conversion of a wide range of 2‐alkyl and 2‐arylmaleic acid diesters into the corresponding succinates in high enantiomeric purity. Mixtures of cis/trans substrates can be hydrogenated in an enantioconvergent fashion with high enantioselectivity, and further enhances the scope of this transformation. The products are valuable chiral building blocks with a structural motif found in many bioactive compounds, such as metalloproteinase inhibitors. 相似文献
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Dr. Agnieszka Bartoszewicz Dr. Nanna Ahlsten Prof. Dr. Belén Martín‐Matute 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7274-7302
The preparation of chiral alcohols and amines by using iridium catalysis is reviewed. The methods presented include the reduction of ketones or imines by using hydrogen (hydrogenations), isopropanol, formic acid, or formate (transfer hydrogenations). Also dynamic and oxidative kinetic resolutions leading to chiral alcohols and amines are included. Selected literature reports from early contributions to December 2012 are discussed. 相似文献
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Zhou J Ogle JW Fan Y Banphavichit V Zhu Y Burgess K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(25):7162-7170
Asymmetric hydrogenations of monoenes and dienes were performed to obtain terminal deoxypolyketide fragments A and the corresponding internal chirons B and C. The chiral N-heterocyclic carbene catalyst 1 was used throughout. Modest selectivities for hydrogenations of simple monoenes relayed into high selectivities for preparations of the terminal deoxypolyketide fragments in which either two hydrogenations or one and an optically pure starting material were used. Curiously, the face selectivities for hydrogenation of alpha,beta-unsaturated esters were consistently opposite to those that had been observed for styrene and stilbene derivatives in previous work, and to closely related allylic alcohol and ether derivatives in this work. Plausible mechanisms for this differing behavior were deduced by using DFT calculations. It appears that the origin of the unusual stereoselectivity for the ester derivatives is transient metal-coordination of the ester carbonyl whereas there is no evidence that the allylic alcohol or ethers coordinate. The routes developed to alpha,omega-functionalized internal deoxypolyketide fragments are extremely practical. These begin with the Roche ester being converted into alkene and, in one case, diene derivatives. Catalyst control prevails in the hydrogenations of these substrates, but there is a significant "substrate vector" (a term we used to describe the influence of the substrate on a catalyst-controlled reaction). This is determined by minimization of 1,3-allylic strain and, in some cases, syn pentane interactions. This substrate vector can be constructively paired with the (dominant) catalyst vector by use of the appropriate enantiomer of 1. In the hydrogenation of a diene derivative, two chiral centers could be formed simultaneously with overall 11:1.0 selectivity; this is the first time this has been achieved in any asymmetric synthesis of a deoxypolyketide fragment. Throughout, diastereoselectivities of the crude material in the syntheses of alpha,omega-functionalized internal deoxypolyketide fragments were in excess of 11:1.0 and chromatographically purified samples could be isolated in high yields with dr (dr=diastereomeric ratio) values consistently in excess of 40:1.0. 相似文献
19.
Dr. Chinna Ayya Swamy P Andrii Varenikov Dr. Graham de Ruiter 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(11):2333-2337
A chiral iridium carbene-oxazoline catalyst is reported that is able to directly and efficiently hydrogenate a wide variety of ketones in excellent yields and good enantioselectivity (up to 93 % ee). Moreover, when using racemic α-substituted ketones, excellent diastereoselectivities were obtained (dr 99:1) by dynamic kinetic resolution of the in situ formed enolate. Overall, the herein described hydrogenation occurs under ambient conditions using low hydrogen pressures, providing a direct and atom efficient method towards chiral secondary alcohols. 相似文献