5589-62-8Relevant academic research and scientific papers
Combined Cyanoborylation, C-H Activation Strategy for Styrene Functionalization
Ansel, Annabel Q.,Montgomery, John
supporting information, p. 8538 - 8543 (2020/11/12)
A one-pot multicomponent copper-catalyzed protocol for borylation/ortho-cyanation of styrene derivatives followed by a Suzuki-Miyaura coupling provides a platform to explore the factors that control the selectivity between distal or proximal functionalization of arenes. The development of divergent nitrile-directed C-H functionalization (acetoxylation, pivalation, and methoxylation) offers an effective approach to rapidly increase synthetic complexity. Finally, the development of a mild reductive decyanation allows a traceless method to access functionalized biaryl motifs.
Mechanistic Studies of Hydride Transfer to Imines from a Highly Active and Chemoselective Manganate Catalyst
Freitag, Frederik,Irrgang, Torsten,Kempe, Rhett
supporting information, p. 11677 - 11685 (2019/08/20)
We introduce a highly active and chemoselective manganese catalyst for the hydrogenation of imines. The catalyst has a large scope, can reduce aldimines and ketimines, and tolerates a variety of functional groups, among them hydrogenation sensitive examples such as an olefin, a ketone, nitriles, nitro groups, and an aryl iodo substituent or a benzyl ether. We could investigate the transfer step between imines and the hydride complex in detail. We found that double deprotonation of the ligand is essential and excess base does not lead to a higher rate in the transfer step. We identified the actual hydrogenation catalyst as a K-Mn-bimetallic species and could obtain a structure of the K-Mn complex formed after hydride transfer by X-ray analysis. NMR experiments indicate that the hydride transfer is a well-defined reaction, which is first order in imine, first order in the bimetallic (K-Mn) hydride, and independent in rate from the concentration of the potassium base. We propose an outer-sphere mechanism in which protons do not seem to be involved in the rate-determining step, leading to a transiently negatively charged nitrogen atom in the substrate which reacts rapidly with HOtBu (2-methylpropan-2-ol) to produce the amine. This is based on several observations, such as no dependency of the reaction rate on the HOtBu concentration, no observable manganese amide complex, and a high reaction constant in a conducted Hammett study. Furthermore, hydrogen transfer of the catalytic cycle was experimentally probed and monitored by NMR with subsequent quantitative regeneration of the catalyst by H2.
Borrowing Hydrogen-Mediated N-Alkylation Reactions by a Well-Defined Homogeneous Nickel Catalyst
Bains, Amreen K.,Kundu, Abhishek,Yadav, Sudha,Adhikari, Debashis
, p. 9051 - 9059 (2019/10/02)
We report herein a well-defined and bench-stable azo-phenolate ligand-coordinated nickel catalyst which can efficiently execute N-alkylation of a variety of anilines by alcohol. We demonstrate that the redox-active azo ligand can store hydrogen generated during alcohol oxidation and redelivers the same to an in-situ-generated imine bond to result in N-alkylation of amines. The reaction has wide scope, and a large array of alcohols can directly couple to a variety of anilines. Mechanistic studies including deuterium labeling to the substrate establishes the borrowing hydrogen method from alcohols and pinpoints the crucial role of the redox-active azo moiety present on the ligand backbone. Isolation of the ketyl intermediate in its trapped form with a radical quencher and higher kH/kD for the alcohol oxidation step suggest altogether a hydrogen-atom transfer (HAT) to the reduced azo backbone to pave alcohol oxidation as opposed to the conventional metal-ligand bifunctional mechanism. This example clearly demonstrates that an inexpensive base metal catalyst can accomplish an important coupling reaction with the help of a redox-active ligand backbone.
Chemoselectivity for Alkene Cleavage by Palladium-Catalyzed Intramolecular Diazo Group Transfer from Azide to Alkene
Frost, Grant B.,Mittelstaedt, Michaela N.,Douglas, Christopher J.
supporting information, p. 1727 - 1732 (2019/01/09)
Alkenes can be cleaved by means of the (3+2) cycloaddition and subsequent cycloreversion of 1,3-dipoles, classically ozone (O3), but the azide (R?N3) variant is rare. Chemoselectivity for these azide to alkene diazo group transfers (DGT) is typically disfavored, thus limiting their synthetic utility. Herein, this work discloses a palladium-catalyzed intramolecular azide to alkene DGT, which grants chemoselectivity over competing aziridination. The data support a catalytic cycloreversion mechanism distinct from other known metal-catalyzed azide/alkene reactions: nitrenoid/metalloradical and (3+2) cycloadditions. Kinetics experiments reveal an unusual mechanistic profile in which the catalyst is not operative during the rate-controlling step, rather, it is active during the product-determining step. Catalytic DGT was used to synthesize N-heterocyclic quinazolinones, a medicinally relevant structural core. We also report on the competing aziridination and subsequent ring expansion to another N-heterocyclic core structure of interest, benzodiazepinones.
Oxalic amide ligands, and uses thereof in copper-catalyzed coupling reaction of aryl halides
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Page/Page column 77-78, (2020/01/09)
The present invention provides oxalic amide ligands and uses thereof in copper-catalyzed coupling reaction of aryl halides. Specifically, the present invention provides a use of a compound represented by formula I, wherein definitions of each group are described in the specification. The compound represented by formula I can be used as a ligand in copper-catalyzed coupling reaction of aryl halides for the formation of C—N, C—O and C—S bonds.
Synthesis of Quinazolines via an Iron-Catalyzed Oxidative Amination of N-H Ketimines
Chen, Cheng-Yi,He, Fengxian,Tang, Guangrong,Yuan, Huiqing,Li, Ning,Wang, Jinmin,Faessler, Roger
, p. 2395 - 2401 (2018/02/23)
An efficient synthesis of quinazolines based on an iron-catalyzed C(sp3)-H oxidation and intramolecular C-N bond formation using tert-BuOOH as the terminal oxidant is described. The reaction of readily available 2-alkylamino benzonitriles with various organometallic reagents led to 2-alkylamino N-H ketimine species. The FeCl2-catalyzed C(sp3)-H oxidation of the alkyl group employing tert-BuOOH followed by intramolecular C-N bond formation and aromatization afforded a wide variety of 2,4-disubstituted quinazolines in good to excellent yields.
Cu-catalyzed reduction of azaarenes and nitroaromatics with diboronic acid as reductant
Pi, Danwei,Zhou, Haifeng,Zhou, Yanmei,Liu, Qixing,He, Renke,Shen, Guanshuo,Uozumi, Yasuhiro
, p. 2121 - 2129 (2018/03/23)
A ligand-free copper-catalyzed reduction of azaarenes with diboronic acid as reductant in an aprotic solvent under mild conditions has been developed. Most interestingly, the nitroazaarenes could be reduced exclusively to give the corresponding amines without touching the azaarene moieties. Furthermore, the reductive amination of aromatic nitro compounds and aromatic aldehydes has also been realized. A series of hydrogenated azaarenes and secondary amines were obtained with good functional group tolerance.
Water as a hydrogen source in palladium-catalyzed reduction and reductive amination of nitroarenes mediated by diboronic acid
Zhou, Yanmei,Zhou, Haifeng,Liu, Sensheng,Pi, Danwei,Shen, Guanshuo
, p. 3898 - 3904 (2017/06/13)
An unprecedented palladium-catalyzed chemoselective reduction and reductive amination of nitroarenes with water as a hydrogen source mediated by diboronic acid have been discovered. A series of aryl amines containing various reducible functional groups were obtained in good to excellent yields.
Borrowing Hydrogen Methodology for N-Benzylation using a π-Benzylpalladium System in Water
Hikawa, Hidemasa,Koike, Toshitaka,Izumi, Kyoko,Kikkawa, Shoko,Azumaya, Isao
, p. 784 - 791 (2016/03/09)
We demonstrate a borrowing hydrogen methodology using the unique reactivity of the π-benzylpalladium system in water, which offers an efficient and environmentally friendly N-monobenzylation of electron-deficient anilines or 2-aminopyridine with non-activated benzylic alcohols under neutral conditions. The crossover experiment using benzyl-α,α-d2 alcohol and 3-methylbenzyl alcohol afforded H/D scrambling products, suggesting that the borrowing hydrogen pathway occurred in our catalytic system. Our simple protocol can accomplish a gram scale reaction of 2-aminobenzonitrile (76 % isolated yield), and is performed with the use of only 1 mol % Pd(OAc)2 and 2 mol % TPPMS without other additives in water.
A General and Direct Reductive Amination of Aldehydes and Ketones with Electron-Deficient Anilines
Pletz, Jakob,Berg, Bernhard,Breinbauer, Rolf
supporting information, p. 1301 - 1317 (2016/05/02)
In our ongoing efforts in preparing tool compounds for investigating and controlling the biosynthesis of phenazines, we recognized the limitations of existing protocols for C-N bond formation of electron-deficient anilines when using reductive amination. After extensive optimization, we have established three robust and scalable protocols for the reductive amination of ketones with electron-deficient anilines, by using either BH3·THF/AcOH/CH2Cl2 (method A), with reaction times of several hours, or the more powerful combinations BH3·THF/TMSCl/DMF (method B) and NaBH4/TMSCl/DMF (method C), which give full conversions for most substrates within 10 to 25 minutes. The scope and limitations of these reactions have been defined for 12 anilines and 14 ketones.
