4828-96-0Relevant academic research and scientific papers
Diboron-mediated palladium-catalyzed asymmetric transfer hydrogenation using the proton of alcohols as hydrogen source
Wu, Bo,Yang, Jimin,Hu, Shu-Bo,Yu, Chang-Bin,Zhao, Zi-Biao,Luo, Yi,Zhou, Yong-Gui
, p. 1743 - 1749 (2021/09/06)
The developments of hydrogen sources stand at the forefront of asymmetric reduction. In contrast to the well-studied alcohols as hydrogen sources via β-hydride elimination, the direct utilization of the proton of alcohols as a hydrogen source for activator-mediated asymmetric reduction is rarely explored. Herein we report the proton of alcohols as a hydrogen source in diboron-mediated palladium-catalyzed asymmetric transfer hydrogenation of 1,3-diketones and indoles, providing a series of chiral β-hydroxy ketones and indolines with excellent yields and enantioselectivities. This strategy would be useful for the synthesis of chiral deuterium-labelled compounds due to the ready availability of deuterium-labelled alcohols. Mechanistic investigations and DFT calculations revealed that active chiral Pd-H species was generated from the proton of alcohols by activating of tetrahydroxydiboron, hydrogen transfer was the rate-determining step, and the reaction preferred Pd(0)-catalyzed mechanism. [Figure not available: see fulltext.]
Asymmetric Transfer Hydrogenation of N-Unprotected Indoles with Ammonia Borane
Zhao, Weiwei,Zhang, Zijia,Feng, Xiangqing,Yang, Jing,Du, Haifeng
supporting information, p. 5850 - 5854 (2020/08/05)
A metal-free asymmetric transfer hydrogenation of unprotected indoles was successfully realized using a catalyst derived from HB(C6F5)2 and (S)-tert-butylsulfinamide with ammonia borane as a hydrogen source. A variety of indolines were achieved in 40-78percent yields with up to 90percent ee.
Aerobic Dehydrogenation of N-Heterocycles with Grubbs Catalyst: Its Application to Assisted-Tandem Catalysis to Construct N-Containing Fused Heteroarenes
Kawauchi, Daichi,Noda, Kenta,Komatsu, Yoshiyuki,Yoshida, Kei,Ueda, Hirofumi,Tokuyama, Hidetoshi
supporting information, p. 15793 - 15798 (2020/10/12)
An aerobic dehydrogenation of nitrogen-containing heterocycles catalyzed by Grubbs catalyst is developed. The reaction is applicable to various nitrogen-containing heterocycles. The exceptionally high functional group compatibility of this method was confirmed by the oxidation of an unprotected dihydroindolactam V to indolactam V. Furthermore, by taking advantage of the oxygen-mediated structural change of the Grubbs catalyst, we integrated ring-closing metathesis and subsequent aerobic dehydrogenation to develop the novel assisted-tandem catalysis using molecular oxygen as a chemical trigger. The utility of the assisted-tandem catalysis was demonstrated by the concise synthesis of N-containing fused heteroarenes including a natural antibiotic, pyocyanine.
Br?nsted-Acid-Promoted Rh-Catalyzed Asymmetric Hydrogenation of N-Unprotected Indoles: A Cocatalysis of Transition Metal and Anion Binding
Wen, Jialin,Fan, Xiangru,Tan, Renchang,Chien, Hui-Chun,Zhou, Qinghai,Chung, Lung Wa,Zhang, Xumu
, p. 2143 - 2147 (2018/04/30)
The incorporation of Br?nsted acid, thiourea anion binding, and transition metal catalysis enables an efficient method to synthesize chiral indolines via hydrogenation of indoles. Catalyzed by a rhodium/ZhaoPhos complex, asymmetric hydrogenation of unprotected indoles is performed smoothly with excellent enantioselectivities (up to 99% ee, up to 400 TON). Br?nsted acid HCl activates indoles to form iminium ion intermediates. Mechanistic studies support the assumption that anion binding plays a crucial role as a secondary interaction. DFT calculations reveal an outer-sphere mechanism in this chemical transformation.
Kinetic Resolution of 2-Substituted Indolines by N-Sulfonylation using an Atropisomeric 4-DMAP-N-oxide Organocatalyst
Murray, James I.,Flodén, Nils J.,Bauer, Adriano,Fessner, Nico D.,Dunklemann, Daniel L.,Bob-Egbe, Opetoritse,Rzepa, Henry S.,Bürgi, Thomas,Richardson, Jeffery,Spivey, Alan C.
supporting information, p. 5760 - 5764 (2017/05/12)
The first catalytic kinetic resolution by N-sulfonylation is described. 2-Substituted indolines are resolved (s=2.6–19) using an atropisomeric 4-dimethylaminopyridine-N-oxide (4-DMAP-N-oxide) organocatalyst. Use of 2-isopropyl-4-nitrophenylsulfonyl chloride is critical to the stereodiscrimination and enables facile deprotection of the sulfonamide products with thioglycolic acid. A qualitative model that accounts for the stereodiscrimination is proposed.
Asymmetric hydrogenation of unprotected indoles using iridium complexes derived from P-OP ligands and (reusable) Bronsted acids
Nunez-Rico, Jose Luis,Fernandez-Perez, Hector,Vidal-Ferran, Anton
, p. 1153 - 1157 (2014/03/21)
Unprotected indoles have been efficiently converted to enantiomerically enriched indolines (up to 91% ee) by a stepwise process: (reusable) Bronsted acid-mediated C=C isomerisation and asymmetric hydrogenation using enantioselective iridium catalysts derived from P-OP ligands. This straightforward combination of (reusable) Bronsted acids, which activate the indole ring for hydrogenation by breaking its aromaticity, and enantiomerically pure [Ir(P-OP)]+ complexes as hydrogenation catalysts affords the resulting indolines with high enantioselectivities.
Homogenous Pd-catalyzed asymmetric hydrogenation of unprotected indoles: Scope and mechanistic studies
Duan, Ying,Li, Lu,Chen, Mu-Wang,Yu, Chang-Bin,Fan, Hong-Jun,Zhou, Yong-Gui
supporting information, p. 7688 - 7700 (2014/06/10)
An efficient palladium-catalyzed asymmetric hydrogenation of a variety of unprotected indoles has been developed that gives up to 98% ee using a strong Br?nsted 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 in this reaction. The important proposed active catalytic Pd-H species was observed with 1H NMR spectroscopy. It was found that proton exchange between the Pd-H active species and solvent trifluoroethanol (TFE) did not occur, although this proton exchange had been previously observed between metal hydrides and alcoholic solvents. Density functional theory calculations were also carried out to give further insight into the mechanism of Pd-catalyzed asymmetric hydrogenation of indoles. This combination of experimental and theoretical studies suggests that Pd-catalyzed hydrogenation goes through a stepwise outer-sphere and ionic hydrogenation mechanism. The activation of hydrogen gas is a heterolytic process assisted by trifluoroacetate of Pd complex via a six-membered-ring transition state. The reaction proceeds well in polar solvent TFE owing to its ability to stabilize the ionic intermediates in the Pd-H generation step. The strong Br?nsted acid activator can remarkably decrease the energy barrier for both Pd-H generation and hydrogenation. The high enantioselectivity arises from a hydrogen-bonding interaction between N-H of the iminium salt and oxygen of the coordinated trifluoroacetate in the eight-membered-ring transition state for hydride transfer, while the active chiral Pd complex is a typical bifunctional catalyst, effecting both the hydrogenation and hydrogen-bonding interaction between the iminium salt and the coordinated trifluoroacetate of Pd complex. Notably, the Pd-catalyzed asymmetric hydrogenation is relatively tolerant to oxygen, acid, and water.
Highly enantioselective hydrogenation of N-unprotected indoles using (S)-C10-BridgePHOS as the chiral ligand
Li, Chao,Chen, Jianzhong,Fu, Guanghong,Liu, Delong,Liu, Yangang,Zhang, Wanbin
, p. 6839 - 6844 (2013/07/26)
(S)-C10-BridgePHOS was successfully applied to a highly efficient Pd-catalyzed enantioselective hydrogenation of substituted indoles. The methodology was suitable for the hydrogenation of indoles substituted at the 2-, 3- and 2,3-positions. Products were obtained in quantitative conversion and up to 98% ee. The role the 2-position substituent plays in the hydrogenation process has been proposed. The methodology could be used as an alternative method to synthesize extremely important chiral indolines from N-unprotected indoles.
Stereoselective synthesis of 2,3-disubstituted indoline diastereoisomers by chemoenzymatic processes
Lopez-Iglesias, Maria,Busto, Eduardo,Gotor, Vicente,Gotor-Fernandez, Vicente
, p. 8049 - 8055,7 (2020/10/15)
Racemic indolines including a variety of structural motifs such as C-2 and C-3 substitutions (alkyl or aryl), cis/trans relative stereochemistry and functionalization of the aromatic ring (fluoro, methyl or methoxy groups) have been efficiently prepared through Fischer indolization and subsequent diastereoselective reduction of the unprotected indoles. Combination of Candida antarctica lipase type A and allyl 3-methoxyphenyl carbonate has been identified as the best tandem for their kinetic resolutions, observing excellent stereodiscriminations for most of the tested indolines.
Direct asymmetric hydrosilylation of indoles: Combined Lewis base and bronsted acid activation
Xiao, You-Cai,Wang, Chao,Yao, Yuan,Sun, Jian,Chen, Ying-Chun
supporting information; experimental part, p. 10661 - 10664 (2011/12/05)
Quite a pair: The first organocatalytic direct asymmetric reduction of unprotected 1H-indoles to chiral indolines has been developed. The reaction proceeds through the generation of electrophilic indolenium ions by a Bronsted acid, and then chiral Lewis base (1) mediated enantioselective hydride transfer with HSiCl3. A variety of chiral indolines were obtained with moderate to excellent enantioselectivity. MOM=methoxymethyl. Copyright
