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A novel route to stereoselective synthesis of (4R,5S)-O- acetylosmundalactone and (4S,5R)-O-acetylosmundalactone
A route has been developed for the enantioselective synthesis of (4R,5S)-O-acetylosmundalactone 1 and (4S,5R)-O-acetylosmundalactone 2 by using sharpless kinetic resolution of the racemic 1-(2-furyl)ethanol 6 as a key step.
Yonghong, Gan,Fangning, Zhang,Xinfu, Pan
p. 488 - 489
(1999)
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Pseudocine Substitution of 4-(Mesyloxy)-2-cyclopentenones: An Efficient Route to 2,4-Disubstituted 2-Cyclopentenones
Readily available mesylates 1a-d were found to undergo a novel substitution reaction.In the presence of a variety of nucleophiles, 1a-d underwent a net substitution in which the nucleophile was introduced vicinally (C-3) to the departing mesylate (C-4) and the double bond migrated to C-4/C-5.Lithium bromide, thiophenol, benzylamine, sodium azide, and the potassium salt of dimethyl malonate all led to substitution products in good yield.The reaction is thought to proceed by way of initial conjugate addition of the nucleophile, followed by enolate equilibration and β-elimination of mesylate.
West, F. G.,Gunawardena, Gamini
p. 2402 - 2406
(1993)
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Cationic Ru complexes anchored on POM via non-covalent interaction towards efficient transfer hydrogenation catalysis
The ionic materials consisting of cationic Ru complexes and Wells-Dawson polyoxometalate anion (POM, K6P2W18O62) have been constructed via a non-covalent interaction. The as-synthesized catalysts have been characterized thoroughly by NMR, XRD, FESEM, and FT-IR, etc. The characterization suggested that a hydrogen bond interaction occurred between the proton of the amine ligand in the cationic Ru complexes and the oxygen atom of the POM anion. The hydrogen bond played an important role in enhancing catalytic activity for the transfer hydrogenation of methyl levulinate (ML) to γ-valerolactone (GVL) under very mild conditions. Especially, the transfer hydrogenation reaction proceeded via a heterogeneous catalysis approach and the heterogenized catalysts even afforded much better catalytic performance than homogeneous analogs. Notably, the catalysts can be recycled without an obvious loss of activity, and further extended to highly selective transfer hydrogenation of α,β-unsaturated ketones and aldehydes, etc. into the corresponding α,β-unsaturated alcohols without any base external additives. The high catalytic performance of these anchored catalysts was highly related to the hydrogen bond interaction and the basicity of the polyanion. The obtained knowledge from this work could lead us to a new catalysis concept of tethering active homogeneous complexes for constructing highly active anchored Ru complex catalysts for hydrogenation reaction.
Chen, Manyu,Cui, Kai,Hou, Zhenshan,Peng, Qingpo,Wang, Jiajia,Wei, Xinjia,Zhao, Xiuge
(2021/12/22)

Cinchona-Alkaloid-Derived NNP Ligand for Iridium-Catalyzed Asymmetric Hydrogenation of Ketones
Most ligands applied for asymmetric hydrogenation are synthesized via multistep reactions with expensive chemical reagents. Herein, a series of novel and easily accessed cinchona-alkaloid-based NNP ligands have been developed in two steps. By combining [Ir(COD)Cl]2, 39 ketones including aromatic, heteroaryl, and alkyl ketones have been hydrogenated, all affording valuable chiral alcohols with 96.0-99.9% ee. A plausible reaction mechanism was discussed by NMR, HRMS, and DFT, and an activating model involving trihydride was verified.
Zhang, Lin,Zhang, Ling,Chen, Qian,Li, Linlin,Jiang, Jian,Sun, Hao,Zhao, Chong,Yang, Yuanyong,Li, Chun
supporting information
p. 415 - 419
(2022/01/12)

2, 4, 5-Trideoxyhexopyranosides Derivatives of 4’-Demethylepipodophyllotoxin: De novo Synthesis and Anticancer Activity
Background: Podophyllotoxin is a natural lignan which possesses anticancer and antiviral activities. Etoposide and teniposide are semisynthetic glycoside derivatives of podophyllotoxin and are increasingly used in cancer medicine. Objective: The present work aimed to design and synthesize a series of 2, 4, 5-trideoxyhexopyrano-sides derivatives of 4’-demethylepipodophyllotoxin as novel anticancer agents. Methods: A divergent de novo synthesis of 2, 4, 5-trideoxyhexopyranosides derivatives of 4’-demethylepipodophyllotoxin has been established via palladium-catalyzed glycosylation. The abili-ties of synthesized glycosides to inhibit the growth of A549, HepG2, SH-SY5Y, KB/VCR and HeLa cancer cells were investigated by MTT assay. Flow cytometric analysis of cell cycle with propidium iodide DNA staining was employed to observe the effect of compound 5b on cancer cell cycle. Results: Twelve D and L monosaccharide derivatives 5a-5l have been efficiently synthesized in three steps from various pyranone building blocks employing de novo glycosylation strategy. D-monosaccharide 5b showed the highest cytotoxicity on five cancer cell lines with the IC50 values ranging from 0.9 to 6.7 μM. It caused HepG2 cycle arrest at G2/M phase in a concentration-dependent manner. Conclusion: The present work leads to the development of novel 2, 4, 5-trideoxyhexopyranosides derivatives of 4’-demethylepipodophyllotoxin. The biological results suggest that the replacement of the glucosyl moiety of etoposide with 2, 4, 5-trideoxyhexopyranosyl is favorable to their cytotoxic-ity. D-monosaccharide 5b was observed to cause HepG2 cycle arrest at the G2/M phase in a concen-tration-dependent manner.
Cai, Rui,Li, Yu,Lu, Yapeng,Zhao, Yu,Zhu, Li
p. 130 - 139
(2022/03/09)

Dynamic Kinetic Resolution of Alcohols by Enantioselective Silylation Enabled by Two Orthogonal Transition-Metal Catalysts
A nonenzymatic dynamic kinetic resolution of acyclic and cyclic benzylic alcohols is reported. The approach merges rapid transition-metal-catalyzed alcohol racemization and enantioselective Cu-H-catalyzed dehydrogenative Si-O coupling of alcohols and hydrosilanes. The catalytic processes are orthogonal, and the racemization catalyst does not promote any background reactions such as the racemization of the silyl ether and its unselective formation. Often-used ruthenium half-sandwich complexes are not suitable but a bifunctional ruthenium pincer complex perfectly fulfills this purpose. By this, enantioselective silylation of racemic alcohol mixtures is achieved in high yields and with good levels of enantioselection.
Oestreich, Martin,Seliger, Jan
p. 247 - 251
(2020/10/29)

Phase Separation-Promoted Redox Deracemization of Secondary Alcohols over a Supported Dual Catalysts System
Unification of oxidation and reduction in a one-pot deracemization process has great significance in the preparation of enantioenriched organic molecules. However, the intrinsic mutual deactivation of oxidative and reductive catalysts and the extrinsic incompatible reaction conditions are unavoidable challenges in a single operation. To address these two issues, we develop a supported dual catalysts system to overcome these conflicts from incompatibility to compatibility, resulting in an efficient one-pot redox deracemization of secondary alcohols. During this transformation, the TEMPO species onto the outer surface of silica nanoparticles catalyze the oxidation of racemic alcohols to ketones, and the chiral Rh/diamine species in the nanochannels of the thermoresponsive polymer-coated hollow-shell mesoporous silica enable the asymmetric transfer hydrogenation (ATH) of ketones to chiral alcohols. To demonstrate the general feasibility, a series of orthogonal oxidation/ATH cascade reactions are compared to prove the compatible benefits in the elimination of their deactivations and the balance of the cascade directionality. As presented in this study, this redox deracemization process provides various chiral alcohols with enhanced yields and enantioselectivities relative to those from unsupported dual catalysts systems. Furthermore, the dual catalysts can be recycled continuously, making them an attractive feature in the application.
Zhao, Zhitong,Wang, Chengyi,Chen, Qipeng,Wang, Yu,Xiao, Rui,Tan, Chunxia,Liu, Guohua
p. 4055 - 4063
(2021/08/12)

Preparation method of 2-acetylfuran
The invention discloses a preparation method of 2-acetylfuran, which comprises the following steps: taking furfural as a raw material, carrying out Grignard reaction to obtain furfuryl alcohol, and carrying out oxidation reaction on furfuryl alcohol in the presence of a catalyst in an oxygen-containing atmosphere to obtain 2-acetylfuran, wherein the catalyst is a 4-hydroxy-2, 2, 6, 6-tetramethylpyridine oxide (Temp) and potassium bromide. The method is simple in process, simple in catalyst and suitable for large-scale industrial production, the stability meets the market requirements of products, the product cost is lower than that of existing industrial production, and the product quality is better.
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Paragraph 0034-0036

(2021/06/23)

Reduction of carbonyl compounds via hydrosilylation catalyzed by well-defined PNP-Mn(I) hydride complexes
Reduction reactions of unsaturated compounds are fundamental transformations in synthetic chemistry. In this context, the reduction of polarized double bonds such as carbonyl or C=C motifs can be achieved by hydrogenation reactions. We describe here a highly chemoselective Mn(I)-based PNP pincer catalyst for the hydrosilylation of aldehydes and ketones employing polymethylhydrosiloxane (PMHS) as inexpensive hydrogen donor. Graphic abstract: [Figure not available: see fulltext.]
Weber, Stefan,Iebed, Dina,Glatz, Mathias,Kirchner, Karl
p. 635 - 639
(2021/06/17)

Manganese-Catalyzed Hydrogenation of Ketones under Mild and Base-free Conditions
In this paper, several Mn(I) complexes were applied as catalysts for the homogeneous hydrogenation of ketones. The most active precatalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe) (CO)3(CH2CH2CH3)]. The reaction proceeds at room temperature under base-free conditions with a catalyst loading of 3 mol % and a hydrogen pressure of 10 bar. A temperature-dependent selectivity for the reduction of α,β-unsaturated carbonyls was observed. At room temperature, the carbonyl group was selectively hydrogenated, while the C=C bond stayed intact. At 60 °C, fully saturated systems were obtained. A plausible mechanism based on DFT calculations which involves an inner-sphere hydride transfer is proposed.
Brünig, Julian,Kirchner, Karl,Veiros, Luis F.,Weber, Stefan
supporting information
p. 1388 - 1394
(2021/05/31)

Asymmetric reduction of aromatic heterocyclic ketones with bio-based catalyst Lactobacillus kefiri P2
Abstract: Chiral heterocyclic secondary alcohols have received much attention due to their widespread use in pharmaceutical intermediates. In this study, Lactobacillus kefiri P2 biocatalysts isolated from traditional dairy products, were used to catalyze the asymmetric reduction of prochiral ketones to chiral secondary alcohols. Secondary chiral carbinols were obtained by asymmetric bioreduction of different prochiral substrates with results up to > 99% enantiomeric excess (ee). (R)-1-(benzofuran-2-yl)ethanol 5a, which can be used in the synthesis of pharmaceuticals such as bufuralols potent nonselective β-blockers antagonists, Amiodarone (cardiac anti-arrhythmic), and Benziodarone (coronary vasodilator), was produced in gram-scale, high yield and enantiomerically pure form using L. kefiri P2 biocatalysts. The gram-scale production was carried out, and 9.70?g of (R)-5a in enantiomerically pure form was obtained in 96% yield. Also, production of (R)-5a in terms of yield and gram scale through catalytic asymmetric reduction using the biocatalyst was the highest report so far. This is a cost-effective, clean and eco-friendly process for the preparation of chiral secondary alcohols compared to chemical processes. From an environmental and economic perspective, this biocatalytic method has great application potential, making it a green and sustainable way of synthesis. Graphical Abstract: [Figure not available: see fulltext.]
Bayda?, Yasemin,Kalay, Erbay,?ahin, Engin
p. 1147 - 1155
(2020/10/06)

Highly Active Cooperative Lewis Acid—Ammonium Salt Catalyst for the Enantioselective Hydroboration of Ketones
Enantiopure secondary alcohols are fundamental high-value synthetic building blocks. One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe a new concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5–3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule. Control experiments reveal that both catalytic centers are essential for the observed activity. Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via a concerted mechanism, in which hydride at Boron is continuously displaced by iodide, reminiscent to an SN2 reaction. The catalyst, which is accessible in high yields in few steps, was found to be stable during catalysis, readily recyclable and could be reused 10 times still efficiently working.
Titze, Marvin,Heitk?mper, Juliane,Junge, Thorsten,K?stner, Johannes,Peters, René
supporting information
p. 5544 - 5553
(2021/02/05)

Ruthenium-catalyzed hydrogenation of aromatic ketones using chiral diamine and monodentate achiral phosphine ligands
The Ru-catalyzed asymmetric hydrogenation of ketones with chiral diamine and monodentate achiral phosphine has been developed. A wide range of ketones were hydrogenated to afford the corresponding chiral secondary alcohols in good to excellent enantioselectivities (up to 98.1% ee). In addition, an appropriate mechanism for the asymmetric hydrogenation was proposed and verified by NMR spectroscopy.
Wang, Mengna,Zhang, Ling,Sun, Hao,Chen, Qian,Jiang, Jian,Li, Linlin,Zhang, Lin,Li, Li,Li, Chun
(2021/03/24)

Palladium-Catalyzed Regioselective and Diastereoselective C-Glycosylation by Allyl-Allyl Coupling
A Pd-catalyzed C-glycosylation reaction was developed by allyl-allyl coupling process using Achmatowicz rearrangement products as donors and methylcoumarins as acceptors under mild conditions. This method featured regio- and diastereoselectivities, stereo
Li, Junhao,Zheng, Nan,Duan, Xuelun,Li, Rui,Song, Wangze
supporting information
p. 846 - 850
(2020/12/13)

Arene-Immobilized Ru(II)/TsDPEN Complexes: Synthesis and Applications to the Asymmetric Transfer Hydrogenation of Ketones
The Noyori-Ikariya (arene)Ru(II)/TsDPEN precatalyst has been anchored to amorphous silica and DAVISIL through the η6-coordinated arene ligand via a straightforward synthesis and the derived systems, (arene)Ru(II)/TsDPEN@silica and (arene)Ru(II)/TsDPEN@DAVISIL, form highly efficient catalysts for the asymmetric transfer hydrogenation of a range of electron-rich and electron-poor aromatic ketones, giving good conversion and excellent ee's under mild reaction conditions. Moreover, catalyst generated in situ immediately prior to addition of substrate and hydrogen donor, by reaction of silica-supported [(arene)RuCl2]2 with (S,S)-TsDPEN, was as efficient as that generated from its preformed counterpart [(arene)Ru{(S,S)-TsDPEN}Cl]@silica. Gratifyingly, the initial TOFs (up to 1085 h?1) and ee's (96–97 %) obtained with these catalysts either rivalled or outperformed those previously reported for catalysts supported by either silica or polymer immobilized through one of the nitrogen atoms of TsDPEN. While the high ee's were also maintained during recycle studies, the conversion dropped steadily over the first three runs due to gradual leaching of the ruthenium.
Doherty, Simon,Knight, Julian G.,Alshaikh, Hind,Wilson, James,Waddell, Paul G.,Wills, Corinne,Dixon, Casey M.
supporting information
p. 226 - 235
(2020/12/31)

Abiotic reduction of ketones with silanes catalysed by carbonic anhydrase through an enzymatic zinc hydride
Enzymatic reactions through mononuclear metal hydrides are unknown in nature, despite the prevalence of such intermediates in the reactions of synthetic transition-metal catalysts. If metalloenzymes could react through abiotic intermediates like these, then the scope of enzyme-catalysed reactions would expand. Here we show that zinc-containing carbonic anhydrase enzymes catalyse hydride transfers from silanes to ketones with high enantioselectivity. We report mechanistic data providing strong evidence that the process involves a mononuclear zinc hydride. This work shows that abiotic silanes can act as reducing equivalents in an enzyme-catalysed process and that monomeric hydrides of electropositive metals, which are typically unstable in protic environments, can be catalytic intermediates in enzymatic processes. Overall, this work bridges a gap between the types of transformation in molecular catalysis and biocatalysis. [Figure not available: see fulltext.]
Ji, Pengfei,Park, Jeeyoung,Gu, Yang,Clark, Douglas S.,Hartwig, John F.
p. 312 - 318
(2021/02/26)

Synthetic Studies toward the Berkeleyacetal Core Architecture
Berkeleyacetals are structurally complex natural products that have shown potent anti-inflammatory activity. The presence of a highly dense oxygen functionality and a polycyclic ring system presents significant synthetic challenges. Herein, we report an e
Márquez-Cadena, Miguel Adrián,Zhang, Wei,Tong, Rongbiao
supporting information
p. 9227 - 9231
(2021/11/30)

N-Heterocyclic Carbene (NHC)-Stabilized Ru0 Nanoparticles: In Situ Generation of an Efficient Transfer Hydrogenation Catalyst
Tethered and untethered ruthenium half-sandwich complexes were synthesized and characterized spectroscopically. X-ray crystallographic analysis of three untethered and two tethered Ru N-heterocyclic carbene (NHC) complexes were also carried out. These RuNHC complexes catalyze transfer hydrogenation of aromatic ketones in 2-propanol under reflux, optimally in the presence of (25 mol %) KOH. Under these conditions, the formation of 2–3 nm-sized Ru0 nanoparticles was detected by TEM measurements. A solid-state NMR investigation of the nanoparticles suggested that the NHC ligands were bound to the surface of the Ru nanoparticles (NPs). This base-promoted route to NHC-stabilized ruthenium nanoparticles directly from arene-tethered ruthenium–NHC complexes and from untethered ruthenium–NHC complexes is more convenient than previously known routes to NHC-stabilized Ru nanocatalysts. Similar catalytically active RuNPs were also generated from the reaction of a mixture of [RuCl2(p-cymene)]2 and the NHC precursor with KOH in isopropanol under reflux. The transfer hydrogenation catalyzed by these NHC-stabilized RuNPs possess a high turnover number. The catalytic efficiency was significantly reduced if nanoparticles were exposed to air or allowed to aggregate and precipitate by cooling the reaction mixtures during the reaction.
Kathuria, Lakshay,Din Reshi, Noor U.,Samuelson, Ashoka G.
supporting information
p. 7622 - 7630
(2020/05/29)

RETRACTED ARTICLE: The Manganese(I)-Catalyzed Asymmetric Transfer Hydrogenation of Ketones: Disclosing the Macrocylic Privilege
The bis(carbonyl) manganese(I) complex [Mn(CO)2(1)]Br (2) with a chiral (NH)2P2 macrocyclic ligand (1) catalyzes the asymmetric transfer hydrogenation of polar double bonds with 2-propanol as the hydrogen source. Ketones (43 substrates) are reduced to alcohols in high yields (up to >99 %) and with excellent enantioselectivities (90–99 % ee). A stereochemical model based on attractive CH–π interactions is proposed.
Passera, Alessandro,Mezzetti, Antonio
supporting information
p. 187 - 191
(2019/12/11)

Chemoenzymatic Synthesis of 5-Hydroxymethylfurfural (HMF)-Derived Plasticizers by Coupling HMF Reduction with Enzymatic Esterification
Biobased plasticizers, as substitutes for phthalates, have been synthesized from 5-hydroxymethylfurfural (HMF) and carboxylic acids (or esters) through a chemoenzymatic cascade process that involves as its first step the reduction of 5-hydroxymethylfurfural into 2,5-bis(hydroxymethyl)furan (BHMF), followed by the esterification of BHMF with carboxylic acids (or esters) by using a supported lipase (Novozym 435). The reduction of HMF into BHMF is performed by using monodisperse metallic Co nanoparticles with a thin carbon shell (Co@C) with high activity and selectivity. After optimization of reaction conditions (temperature, hydrogen pressure, and solvent), it is possible to achieve 97 % conversion of HMF with 99 % selectivity to BHMF after 2 h reaction time. The reduction of HMF and esterification of BHMF using carboxylic acids or vinyl esters as acyl donors by lipase are optimized separately in batch and in fixed-bed continuous reactors. The coupling of two flow reactors (for reduction and subsequent esterification) working under optimized reaction conditions affords the diesters of BHMF in roughly 90 % yield with no loss of activity during 60 h of operation.
Arias, Karen S.,Carceller, Jose M.,Climent, Maria J.,Corma, Avelino,Iborra, Sara
p. 1864 - 1875
(2020/03/11)

Synthesis of thioethers, arenes and arylated benzoxazoles by transformation of the C(aryl)-C bond of aryl alcohols
Transformation of aryl alcohols into high-value functionalized aromatic compounds by selective cleavage and functionalization of the C(aryl)-C(OH) bond is of crucial importance, but very challenging by far. Herein, for the first time, we report a novel and versatile strategy for activation and functionalization of C(aryl)-C(OH) bonds by the cooperation of oxygenation and decarboxylative functionalization. A diverse range of aryl alcohol substrates were employed as arylation reagents via the cleavage of C(aryl)-C(OH) bonds and effectively converted into corresponding thioether, arene, and arylated benzoxazole products in excellent yields, in a Cu based catalytic system using O2 as the oxidant. This study offers a new way for aryl alcohol conversion and potentially offers a new opportunity to produce high-value functionalized aromatics from renewable feedstocks such as lignin which features abundant C(aryl)-C(OH) bonds in its linkages.
Chen, Bingfeng,Han, Buxing,Liu, Mingyang,Meng, Qinglei,Song, Jinliang,Zhang, Pei,Zhang, Zhanrong
p. 7634 - 7640
(2020/08/14)

Chiral amino-pyridine-phosphine tridentate ligand, manganese complex, and preparation method and application thereof
The invention discloses a chiral amino-pyridine-phosphine tridentate ligand, a manganese complex, and a preparation method and application thereof. The chiral amino-pyridine-phosphine tridentate ligand is shown as a formula II, and the manganese complex of the chiral amino-pyridine-phosphine tridentate ligand can be used for efficiently catalyzing and hydrogenating ketone compounds to prepare chiral alcohol compounds in a high enantioselectivity mode. The chiral amino-pyridine-phosphine tridentate ligand and the manganese complex are simple in synthesis process, good in stability, high in catalytic activity and mild in reaction conditions.
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Paragraph 0597-0600; 0602

(2020/07/13)

A simple and efficient asymmetric hydrogenation of heteroaromatic ketones with iridium catalyst composed of chiral diamines and achiral phosphines
An efficient iridium catalyst composed of a simple and commercially available o-methoxytriphenylphosphine and 9-Amino (9-deoxy) epi-cinchonine was applied to the asymmetric hydrogenation of heteroaromatic ketones. A range of simple heteroaromatic ketones could be hydrogenated with good to excellent enantioselectivities and high activities. In particular, thiophene ketones and furyl ketones furnished 98.6% ee with up to 2.18 × 104(1/h) TOF. This catalytic system can be of practical value.
Li, Chun,Lu, Xunhua,Wang, Mengna,Zhang, Ling,Jiang, Jian,Yan, Shunfa,Yang, Yuanyong,Zhao, Yonglong,Zhang, Lin
(2020/09/02)

ILLUDIN ANALOGS, USES THEREOF, AND METHODS FOR SYNTHESIZING THE SAME
This invention provides illudin derivatives, intermediates, preparation methods, pharmaceutical compositions and uses thereof. Specific examples include novel synthetic routes to prepare illudin derivatives and an illudin derivative having a positive optical rotation, which has therapeutic value.
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(2020/03/29)

Method for preparing 2-acyl furan
The invention relates to a method for preparing 2-acyl furan. The method is characterized by comprising the following steps: (1) controlling the temperature to -10-40 DEG C, and adding 70-98% of a water phase or 10-90% of a mixed liquid of the water phase and an organic phase, 0.0001-2.0% of an osmium compound and 0.001-5.0% of an amine compound into a reaction container so as to obtain a reactionliquid; (2) feeding the reaction liquid into a sealed reactor, and performing gas exchange to provide an aerobic environment for reactions; (3) adding 1-(2-furyl)-1-alkyl methanol into the sealed reactor, and controlling the pressure to 0-20MPa and the temperature to 0-200 DEG C for 1-74 hours; and (4) after the reaction is stopped, performing cooling to the room temperature, performing pressurerelease to the barometric pressure, adding sodium hydrogen sulfate and acetic acid, performing extraction, and performing organic phase vacuum distillation refining, so as to obtain a 2-acyl furan product. The method has the advantages that technical and economical defects of a conventional synthesis route can be avoided, process procedures can be reduced, consumption and emission can be reduced,the energy consumption and the cost can be lowered, and the method is applicable to capacity increase industrial production.
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Paragraph 0020

(2019/12/25)

A Practical and Stereoselective In Situ NHC-Cobalt Catalytic System for Hydrogenation of Ketones and Aldehydes
Homogeneous catalytic hydrogenation of carbonyl groups is a synthetically useful and widely applied organic transformation. Sustainable chemistry goals require replacing conventional noble transition metal catalysts for hydrogenation by earth-abundant base metals. Herein, we report how a practical in situ catalytic system generated by easily available pincer NHC precursors, CoCl2, and a base enabled efficient and high-yielding hydrogenation of a broad range of ketones and aldehydes (over 50 examples and a maximum turnover number [TON] of 2,610). This is the first example of NHC-Co-catalyzed hydrogenation of C=O bonds using flexible pincer NHC ligands consisting of a N-H substructure. Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized by fine-tuning of the steric bulk of pincer NHC ligands. Additionally, a bis(NHCs)-Co complex was successfully isolated and fully characterized, and it exhibits excellent catalytic activity that equals that of the in-situ-formed catalytic system. Catalytic hydrogenation is a powerful tool for the reduction of organic compounds in both fine and bulk chemical industries. To improve sustainability, more ecofriendly, inexpensive, and earth-abundant base metals should be employed to replace the precious metals that currently dominate the development of hydrogenation catalysts. However, the majority of the base-metal catalysts that have been reported involve expensive, complex, and often air- and moisture-sensitive phosphine ligands, impeding their widespread application. From a mixture of the stable CoCl2, imidazole salts, and a base, our newly developed catalytic system that formed easily in situ enables efficient and stereoselective hydrogenation of C=O bonds. We anticipate that this easily accessible catalytic system will create opportunities for the design of practical base-metal hydrogenation catalysts. A practical in situ catalytic system generated by a mixture of easily available pincer NHC precursors, CoCl2, and a base enabled highly efficient hydrogenation of a broad range of ketones and aldehydes (over 50 examples and up to a turnover number [TON] of 2,610). Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized in high selectivities. Moreover, the preparation of a well-defined bis(NHCs)-Co complex via this pincer NHC ligand consisting of a N-H substructure was successful, and it exhibits equally excellent catalytic activity for the hydrogenation of C=O bonds.
Zhong, Rui,Wei, Zeyuan,Zhang, Wei,Liu, Shun,Liu, Qiang
supporting information
p. 1552 - 1566
(2019/06/14)

Transfer Hydrogenation of Carbonyl Groups, Imines and N-Heterocycles Catalyzed by Simple, Bipyridine-Based MnI Complexes
Utilization of hydroxy-substituted bipyridine ligands in transition metal catalysis mimicking [Fe]-hydrogenase has been shown to be a promising approach in developing new catalysts for hydrogenation. For example, MnI complexes with 6,6′-dihydroxy-2,2′-bipyridine ligand have been previously shown to be active catalysts for CO2 hydrogenation. In this work, simple bipyridine-based Mn catalysts were developed that act as active catalysts for transfer hydrogenation of ketones, aldehydes and imines. For the first time, Mn-catalyzed transfer hydrogenation of N-heterocycles was reported. The highest catalytic activity among complexes with variously substituted ligands was observed for the complex bearing two OH groups in bipyridine. Deuterium labeling experiments suggest a monohydride pathway.
Dubey, Abhishek,Rahaman, S. M. Wahidur,Fayzullin, Robert R.,Khusnutdinova, Julia R.
p. 3844 - 3852
(2019/04/08)

β-Amino Phosphine Mn Catalysts for 1,4-Transfer Hydrogenation of Chalcones and Allylic Alcohol Isomerization
Mn complexes with amino acid derived PN ligands were used in the catalytic transfer hydrogenation (TH) of ketone and chalcone substrates in 2-propanol with mild heating. Moreover, chalcones are reduced selectively to the saturated ketone at short times and can be fully converted to the alcohol when reactions are prolonged. The mechanism of chalcone reduction was briefly considered. Allylic alcohols are not reactive in 2-propanol, but quantitative isomerization occurs in toluene. Thus, we suspect that the allylic alcohols are dehydrogenated and the resulting ketone is formed through a direct 1,4-hydrogenation of the chalcone. Finally, several other related ligands that have been used in Mn-based TH reactions were explored to test the viability of ligand design in favoring chemoselectivity. The β-amino phosphine ligands proved most effective in this regard.
Vigneswaran, Vipulan,MacMillan, Samantha N.,Lacy, David C.
supporting information
p. 4387 - 4391
(2019/11/14)

Heteroditopic Ru(II)-And Ir(III)-NHC Complexes with Pendant 1,2,3-Triazole/Triazolylidene Groups: Stereoelectronic Impact on Transfer Hydrogenation of Unsaturated Compounds
Imidazol-2-ylidene (ImNHC) and 1,2,3-Traizol-5-ylidene (tzNHC) have been established as important classes of carbene ligands in homogeneous catalysis. To develop Ru(II)/Ir(III) complexes based on these ligand systems considering their electronic as well as steric profiles for hydride transfer reactions, we employed chelating ligands featuring combinations of ImNHC and triazole-N or mesoionic tzNHC donors bridged by a CH2 spacer with possible modifications at triazole backbone. In general, synthesized Ru(II) complexes were found to perform significantly better than analogous Ir(III) complexes in ketone and aldimine reduction. Among the Ru(II) complexes, electron-rich complexes 8/9 of the general formula [(p-cymene)(ImNHC-CH2-TzNHC)RuII(Cl)]BF4 with two different carbene donors (ImNHC and tzNHC) were found to perform appreciably better in ketone reduction than analogous complexes with a combination of ImNHC and triazole-N-donor ([(p-cymene)(ImNHC-CH2-Tz-N)RuII(Cl)]BF4; 4) explaining the electronic fine-Tuning of the catalytic systems. No appreciable variation in activity was observed between complexes 8 and 9 having almost similar electronic profiles. However, less bulky Ru(II) complex 9 with a triazole N-phenyl substituent is more suitable for aldimine reduction than is complex 8, having a triazole N-3,5-dimethylphenyl substituent that explains the steric influence in addition to electronic effect on the reduction process.
Illam, Praseetha Mathoor,Donthireddy,Chakrabartty, Sayantan,Rit, Arnab
supporting information
p. 2610 - 2623
(2019/07/31)

Synthetic Versatility of Lipases: Application for Si-O Bond Formation and Cleavage
Several commercially available lipases were examined in a study on O-Si bond formation and cleavage applying silicon-based protecting groups and alcohols or the corresponding silyl ethers. With regard to deprotection, from silyl ether to the corresponding alcohol, only the solvent and the lipase were necessary. The influence of the protecting group, the lipase source, and the substituent was investigated to optimize the results. The TMS moiety could be removed in 24 hours of reaction at room temperature in aqueous systems (conv. up to 99%, depending on the substrate and lipase). The reverse reactions, that is, with the protection of the alcohols, were carried out in hexane using different silyl chlorides. The TMS, TES, and TBS moieties were successfully inserted in the primary and secondary alcohols without the need for dry conditions or an inert atmosphere, presenting conversions of up to 99%, depending on the substrate.
Brondani, Patrícia Bulegon,Mittersteiner, Mateus,Voigt, Morgana Aline,Klinkowski, Bruna Heloisa,Riva Scharf, Dilamara,De Jesus, Paulo Cesar
p. 477 - 485
(2019/01/10)

n-Butyllithium (1 mol %)-catalyzed Hydroboration of Aldehydes and Ketones with Pinacolborane
A practical and efficient protocol for the hydroboration of aldehydes and ketones using a pinacolborane and alkyl lithium system is demonstrated. A systematic evaluation showed that 1 mol % n-butyllithium afforded catalyzed hydroboration of aldehydes and ketones in a short reaction time under ambient conditions. Excellent yield, functional group tolerance, short reaction time, low catalyst loading, and gram-scale synthesis are the salient features of the proposed protocol.
Yang, Su Jin,Jaladi, Ashok Kumar,Kim, Jea Ho,Gundeti, Shankaraiah,An, Duk Keun
p. 34 - 38
(2019/01/04)

Design, Synthesis, and Application of NNN Pincer Ligands Possessing a Remote Hydroxyl Group for Ruthenium-Catalyzed Transfer Hydrogenation of Ketones
A new family of pyridyl-based NNN pincer ligands bearing a remote pendent OH group were developed. Considerable acceleration effects on the activity of Ru-catalyzed transfer hydrogenation of ketones were imparted by the pendent OH group, and importantly, introducing a CH2OH group to the 4′-position of the pyrazolyl moiety is an appropriate choice. The results present a general strategy for exploring bifunctional ligands to construct effective catalysts.
Cao, Zhengqiang,Qiao, Hong,Zeng, Fanlong
p. 797 - 804
(2019/03/04)

Asymmetric Magnesium-Catalyzed Hydroboration by Metal-Ligand Cooperative Catalysis
Asymmetric catalysis with readily available, cheap, and non-toxic alkaline earth metal catalysts represents a sustainable alternative to conventional synthesis methodologies. In this context, we describe the development of a first MgII-catalyzed enantioselective hydroboration providing the products with excellent yields and enantioselectivities. NMR spectroscopy studies and DFT calculations provide insights into the reaction mechanism and the origin of the enantioselectivity which can be explained by a metal-ligand cooperative catalysis pathway involving a non-innocent ligand.
Falconnet, Alban,Magre, Marc,Maity, Bholanath,Cavallo, Luigi,Rueping, Magnus
supporting information
p. 17567 - 17571
(2019/11/13)

Water soluble Ru (II)–p-cymene complexes of chiral aroylthiourea ligands derived from unprotected D/L-alanine as proficient catalysts for asymmetric transfer hydrogenation of ketones
The newfangled chiral aroylthiourea ligands (L1-L6) were produced from unprotected D/L-alanine and their water soluble Ru (II) organometallic catalysts (1–6) were designed from their reaction with [RuCl2(η6-p-cymene)]2. The analytical and spectral methods were used to confirm the structure of the ligands and complexes. The solid state structure of L1, 5 and 6 was confirmed by single crystal XRD. The organometallic compounds (1–6) catalyzed the asymmetric transfer hydrogenation of aromatic, heteroaromatic and bulky ketones to yield respective enantiopure secondary alcohols with admirable conversions (up to 99%) and attractive enantiomeric excesses (ee up to 98%), in presence of formic acid and triethylamine in water medium under non-inert atmospheric conditions.
Sheeba, Mani Mary,Tamizh, Manoharan Muthu,Bhuvanesh, Nattamai S.P.,Karvembu, Ramasamy
(2019/01/04)

Manganese Catalyzed Asymmetric Transfer Hydrogenation of Ketones Using Chiral Oxamide Ligands
The asymmetric transfer hydrogenation of ketones using isopropyl alcohol (IPA) as hydrogen donor in the presence of novel manganese catalysts is explored. The selective and active systems are easily generated in situ from [MnBr(CO)5] and inexpensive C2-symmeric bisoxalamide ligands. Under the optimized reaction conditions, the Mn-derived catalyst gave higher enantioselectivity compared with the related ruthenium catalyst.
Schneek?nig, Jacob,Junge, Kathrin,Beller, Matthias
supporting information
p. 503 - 507
(2019/02/26)

Asymmetric transfer hydrogenation of ketones using Ru(0) nanoparticles modified by Chiral Thiones
The catalytic asymmetric transfer hydrogenation (ATH) of acetophenone in isopropanol by Ru(0) nanoparticles (NPs) obtained by the in-situ reduction of Ru (II) half-sandwich complexes of chiral 2-oxazolidinethiones and 2-thiozolidinethiones was examined and compared with the catalytic activity of Ru(0) NPs formed in-situ by the reduction of [Ru(p-cymene)(Cl)2]2 in presence of optically active ligands such as (S)-4-isobutylthiazolidine-2-thione, (S)-4-Isopropyl-2(?2-pyridinyl)-2-oxazoline, (8S, 9R)-(?)-cinchonidine, (S)-leucinol, (S)-phenylalaninol, and (S)-leucine. Three of the best catalytic systems were then examined for ATH of thirteen aromatic ketones with different electronic and steric properties. A maximum of 24% ee was obtained using NPs generated from the Ru (II) half-sandwich complex with (S)-4-isobutylthiazolidine-2-thione in the TH of acetophenone. The NPs were characterized by TEM and DLS measurements. Kinetic studies and poisoning experiments confirmed that the reaction is catalyzed by the chiral NPs formed in-situ. Complete characterization of the complexes, including the X-ray crystallographic characterization of two complexes, was also carried out.
Din Reshi, Noor U.,Senthurpandi, Dineshchakravarthy,Samuelson, Ashoka G.
(2019/03/21)

Lutidine-Based Chiral Pincer Manganese Catalysts for Enantioselective Hydrogenation of Ketones
A series of MnI complexes containing lutidine-based chiral pincer ligands with modular and tunable structures has been developed. The complex shows unprecedentedly high activities (up to 9800 TON; TON=turnover number), broad substrate scope (81 examples), good functional-group tolerance, and excellent enantioselectivities (85–98 % ee) in the hydrogenation of various ketones. These aspects are rare in earth-abundant metal catalyzed hydrogenations. The utility of the protocol have been demonstrated in the asymmetric synthesis of a variety of key intermediates for chiral drugs. Preliminary mechanistic investigations indicate that an outer-sphere mode of substrate–catalyst interactions probably dominates the catalysis.
Zhang, Linli,Tang, Yitian,Han, Zhaobin,Ding, Kuiling
supporting information
p. 4973 - 4977
(2019/03/17)

Manganese complex and preparation method and application thereof
The invention discloses a manganese complex taking (RC,SP)-N-5,6,7,8-tetrahydroquinoline-1-(2-diphenylphosphino)ferrocene ethyl amine as a ligand, a preparation method and application of the manganesecomplex in catalyst ketone compound asymmetric hydrogen transfer reduction preparing chiral alcohol. The manganese complex is a cheap metal chiral catalyst, the cost is low, the thermal stability isgood, and the preparation method of the manganese complex has the advantages of mild condition, short period, simple operation condition and the like. The catalyst is used for reducing the chiral alcohol for ketone hydrogen transfer, has higher catalytic activity, and a method for preparing the chiral alcohol is simple, less in environment pollution, and high in yield.
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Paragraph 0063-0066; 0069-0079

(2020/01/03)

Divergent Synthesis of Dihydropyranone Stereoisomers via N-Heterocyclic Carbene Catalysis
We recently developed a novel chiral N-heterocyclic carbene (NHC) catalyzed dynamic kinetic enantioselective acylation (DKEA) and dynamic kinetic diastereoselective acylation (DKDA) of Achmatowicz rearrangement products to generate useful intermediates for the further synthesis of carbohydrates. In this update, we describe a divergent NHC catalytic strategy for the stereoselective preparation of all four isomers starting from a common racemic precursor. The present report provides easy access to diverse optically pure dihydropyranones. (Figure presented.).
Zhao, Changgui,Wang, Jian
supporting information
p. 1668 - 1672
(2019/02/19)

Lipase-Induced Oxidative Furan Rearrangements
Lipase B from Candida antarctica catalyzes the oxidative ring expansion of furfuryl alcohols using aqueous hydrogen peroxide to yield functionalized pyranones under mild conditions. The method further allows for the preparation of corresponding piperidinone derivatives by enzymatic rearrangement of N-protected furfurylamines.
Blume, Fabian,Sprengart, Petra,Deska, Jan
p. 1293 - 1296
(2018/01/27)

“Inverse” Frustrated Lewis Pairs: An Inverse FLP Approach to the Catalytic Metal Free Hydrogenation of Ketones
For the first time have boron-containing weak Lewis acids been demonstrated to be active components of Frustrated Lewis Pair (FLP) catalysts in the hydrogenation of ketones to alcohols. Combining the organosuperbase (pyrr)3P=NtBu with the Lewis acid 9-(4-CF3-C6H4)-BBN generated an “inverse” FLP catalyst capable of hydrogenating a range of aliphatic and aromatic ketones including N-, O- and S-functionalized substrates and bio-mass derived ethyl levulinate. Initial computational and experimental studies indicate the mechanism of catalytic hydrogenation with “inverse” FLPs to be different from conventional FLP catalysts that contain strong Lewis acids such as B(C6F5)3.
Mummadi, Suresh,Brar, Amandeep,Wang, Guoqiang,Kenefake, Dustin,Diaz, Rony,Unruh, Daniel K.,Li, Shuhua,Krempner, Clemens
supporting information
p. 16526 - 16531
(2018/10/20)

Constructing reactive Fe and Co complexes from isolated picolyl-functionalized N-heterocyclic carbenes
We report the isolation of free picolyl-functionalized N-heterocyclic carbenes (NHCs), which serve as versatile precursors to access low coordinate iron and cobalt complexes. The reactivities of these new iron and cobalt complexes towards catalytic hydrosilylation of ketones have also been explored. For example, low loadings (0.05-1 mol%) of a four-coordinate iron complex bearing two deprotonated picolyl-NHC ligands can effect the fast catalytic reduction of ketones using the inexpensive industrial byproduct polymethylhydrosiloxane (PMHS) as the reductant at ambient temperature.
Liang, Qiuming,Liu, Nina Jiabao,Song, Datong
supporting information
p. 9889 - 9896
(2018/08/06)

Iridium-catalyzed efficient reduction of ketones in water with formic acid as a hydride donor at low catalyst loading
A highly efficient and chemoselective transfer hydrogenation of ketones in water has been successfully achieved with our newly developed catalyst. Simple ketones, as well as α- or β-functionalized ketones, are readily reduced. Formic acid is used as a traceless hydride source. At very low catalyst loading (S/C = 10:000 in most cases; S/C = 50:000 or 100:000 in some cases), the iridium catalyst is impressively efficient at reducing ketones in good to excellent yields. The TOF value can be as high as up to 26:000 mol mol-1 h-1. A variety of functional groups are well tolerated, for example, heteroaryl, aryloxy, alkyloxy, halogen, cyano, nitro, ester, especially acidic methylene, phenol and carboxylic acid groups.
Liu, Ji-Tian,Yang, Shiyi,Tang, Weiping,Yang, Zhanhui,Xu, Jiaxi
supporting information
p. 2118 - 2124
(2018/05/24)

A mechanistic study of transfer hydrogenation catalyzed by cyclometallated ruthenium half-sandwich complexes
Transfer hydrogenation of aromatic ketones catalyzed by eight cyclometallated ruthenium half-sandwich complexes, including three new complexes, was examined. The catalytic process was studied using different ratios of substrate to base and base to catalyst and using a deuterated reductant. Optimum conditions for catalysis were shown to be in the presence of higher amounts of base in refluxing isopropanol. Under these conditions, the complexes were reduced in situ to give Ru(0) nanoparticles invisible to the naked eye. The nanoparticles were characterized by TEM, DLS and XPS. The catalytic transfer hydrogenation, under conditions in which nanoparticles were generated, was found to be far greater than the transfer hydrogenation by the molecular catalyst. Complete characterization of the three new complexes, including the X-ray crystallographic characterization of these complexes was carried out.
Din Reshi, Noor U.,Senthurpandi, Dineshchakravarthy,Samuelson, Ashoka G.
p. 189 - 199
(2018/05/04)

Chemoselective transfer hydrogenation of nitroarenes, ketones and aldehydes using acylthiourea based Ru(II)(p-cymene) complexes as precatalysts
A new series of Ru(II)(η6-p-cymene) complexes (1–5) was synthesized from pyridine based acylthiourea ligands (L1-L5) and [Ru(η6-p-cymene)Cl2]2. All the ligands and complexes were well characterized by UV-Visible, FT-IR, mass and 1H & 13C NMR spectroscopic techniques. The molecular structures of the ligands (L1, L2, L4 and L5) and complex 1 were confirmed using single crystal X-ray diffraction study. The Ru(II)(η6-p-cymene) complexes (1–5) were proved to be efficient precatalysts for the transfer hydrogenation of carbonyl compounds and nitroarenes in the presence of 2-propanol as a hydrogen donor and KOH as a base. The catalytic transfer hydrogenation reactions were chemoselective towards the nitro group in presence of carbonyl group, which is a rare scenario in homogeneous catalysis. The catalyst was compatible with broad range of substrates which include furfural, quinone and many heterocycles. The catalytic reactions exhibited very high conversions (upto 100%) and excellent yields (upto 99%). Turn Over Number (TON) was found upto 990.
Sathishkumar, Pushpanathan N.,Raveendran, Neethi,Bhuvanesh, Nattamai S.P.,Karvembu, Ramasamy
p. 57 - 65
(2018/10/05)

Aminotriazole Mn(I) Complexes as Effective Catalysts for Transfer Hydrogenation of Ketones
A catalytic system based on complexes comprising abundant and cheap manganese together with readily available aminotriazole ligands is reported. The new Mn(I) complexes are catalytically competent in transfer hydrogenation of ketones with 2-propanol as hydrogen source. The reaction proceeds under mild conditions at 80 °C for 20 h with 3 % of catalyst loading using either KOtBu or NaOH as base. Good to excellent yields were obtained for a wide substrate scope with broad functional group tolerance. The obtained results by varying the substitution pattern of the ligand are consistent with an out-sphere mechanism for the H-transfer.
Martínez-Ferraté, Oriol,Werlé, Christophe,Franciò, Giancarlo,Leitner, Walter
p. 4514 - 4518
(2018/10/20)

Effect of Ancillary Ligand in Cyclometalated Ru(II)-NHC-Catalyzed Transfer Hydrogenation of Unsaturated Compounds
In an effort to develop efficient Ru(II)-NHC-based catalyst considering their stereoelectronic effect for hydride-transfer reaction, we found that the ancillary NHC ligand can play a significant role in its catalytic performance. This effect is demonstrated by comparing the activity of two different types of orthometalated precatalysts of general formula [(p-cymene)(NHC)RuII(X)] (NHC = an imidazolylidene-based ImNHC, compound 2a-c, or a mesoionic triazolylidene-based tzNHC, compound 4) in transfer hydrogenation of carbonyl substrates. The electron-rich precatalyst, 2c, containing p-OMe-substituted NHC ligand performed significantly better than both unsubstituted complex 2a and p-CF3 substituted electron-poor complex 2b in ketone reduction. Whereas bulky mesoionic triazolylidene ligand containing complex 4 was found to be superior catalyst for aldehyde reduction and the precatalyst 2a is more suitable for the selective transfer hydrogenation of a wide range of aromatic aldimines to amines. To the best of our knowledge, this is the first systematic study on the effect of stereoelectronic tuning of ancillary orthometalated NHC ligand in Ru(II)-catalyzed transfer hydrogenations of various types of unsaturated compounds with broad substrate scope.
Bauri, Somnath,Donthireddy,Illam, Praseetha Mathoor,Rit, Arnab
supporting information
p. 14582 - 14593
(2018/11/25)

Hydrogenation of Nitriles and Ketones Catalyzed by an Air-Stable Bisphosphine Mn(I) Complex
Efficient hydrogenations of nitriles and ketones with molecular hydrogen catalyzed by a well-defined bench-stable bisphosphine Mn(I) complex are described. These reactions are environmentally benign and atomically economic, implementing an inexpensive, earth-abundant nonprecious metal catalyst. A range of aromatic and aliphatic nitriles and ketones were efficiently converted into primary amines and alcohols, respectively, in good to excellent yields. The hydrogenation of nitriles proceeds at 100 °C with catalyst loading of 2 mol % and 20 mol % base (t-BuOK), while the hydrogenation of ketones takes place already at 50 °C, with a catalyst loading of 1 mol % and 5 mol % of base. In both cases, a hydrogen pressure of 50 bar was applied.
Weber, Stefan,St?ger, Berthold,Kirchner, Karl
supporting information
p. 7212 - 7215
(2018/11/25)

Preparation method of natural maltol
The invention provides a preparation method of natural maltol. The preparation method has the characteristics that methyl metal halide is not prepared and used, 2-furan ethanol is directly prepared through the reduction of natural 2-acetylfuran, and the like. The method is simple in process and easy and convenient to operate, few devices are adopted, the pollution and occupational hazard caused bymethyl halide to air and operators are avoided, and the method is suitable for industrial production.
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Paragraph 0031-0041

(2019/01/08)

Iridium and Rhodium Complexes Containing Enantiopure Primary Amine-Tethered N-Heterocyclic Carbenes: Synthesis, Characterization, Reactivity, and Catalytic Asymmetric Hydrogenation of Ketones
The imidazolium salt [(S,S)-tBuNC3H3NCHPhCHPhNH2]PF6, (S,S)-11·HPF6 is a precursor to the enantiopure "Kaibene" ligand, tBu-Kaibene, (S,S)-11 featuring a tert-butyl group on the N-heterocyclic carbene (NHC) ring-nitrogen atoms. It has been prepared in high yield and purity by refluxing a chiral cyclic sulfamidate with 1-tert-butylimidazole. Similarly (S,S)-12·HPF6 with a mesityl group at the imidazolium ring-nitrogen atom has been prepared in the same fashion and serves as a source of Mes-Kaibene, (S,S)-12. These bidentate Kaibene ligands feature an NHC and a primary amine separated by a chiral linker. Salts (S,S)-11·HPF6 or (S,S)-12·HPF6 react with base and AgI or CuI to give a total of four M(Kaibene)2I compounds (M = Ag or Cu). At 22 °C, the amine-functionalized imidazolium cations undergo oxidative addition to iridium(I) in [IrCl(cod)]2 (cod = 1,5-cyclooctadiene) to generate iridium(III) hydride R-Kaibene compounds [IrHCl(cod)((S,S)-11)](PF6) (17) and [IrHCl(cod)((S,S)-12)](PF6) (18), respectively, each as a mixture of six configurational isomers. In contrast, the salt (S,S)-11·HPF6 reacts with [Ir(OtBu)(cod)]2 to produce a bimetallic iridium compound with (S,S)-11 as the bridging ligand. This compound contains interesting NH···Cl and NH···Ir noncovalent intramolecular interactions. Salt (S,S)-12·HPF6 reacts with silver oxide to yield [Ag2((S,S)-12)2](PF6)2 (20). Reagent 20 serves as an efficient transmetalation reagent to deliver to each rhodium in [RhCl(cod)]2 1 equiv of (S,S)-12 as a bidentate ligand to give [Rh(cod)((S,S)-12)](PF6). In the reaction between [IrCl(cod)]2 and 20, (S,S)-12 ends up coordinated in an iridium(III) hydride complex (22) as a tridentate ligand via the NHC, NH2, and a cyclometalated phenyl group. The two iridium hydride compounds, 18 and 22, are catalysts for the hydrogenation of a range of ketones (turnover number up to 499, turnover frequency up to 249 h-1, with er (enantiomeric ratio) up to 35:65 R:S).
Wan, Kai Y.,Roelfes, Florian,Lough, Alan J.,Hahn, F. Ekkehardt,Morris, Robert H.
supporting information
p. 491 - 504
(2018/02/17)

CHIRAL METAL COMPLEX COMPOUNDS
The invention comprises novel chiral metal complex compounds of the formula (I) wherein M, PR2, R3 and R4 are outlined in the description, its stereoisomers, in the form as a neutral complex or a complex cation with a suitable counter ion. The chiral metal complex compounds can be used in asymmetric reactions, particularly in asymmetric reductions of ketones, imines or oximes.
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Page/Page column 18; 19; 20

(2018/11/10)

Piano-stool Ru(II)-benzene complexes bearing D/L-alanine derived chiral aroylthiourea ligands for asymmetric transfer hydrogenation of ketones in water
Abstract: The new water soluble chiral Ru(II)-benzene complexes of the type [RuCl 2(η6-C 6H 6) L] were obtained from the reactions between [RuCl2(η6-C6H6)]2 and the chiral aroylthiourea ligands (L) derived from unprotected D/L-alanine and characterized. The solid-state structure of representative complexes was confirmed by single crystal X-ray diffraction technique. The Ru(II)-benzene complexes catalyzed the asymmetric transfer hydrogenation (ATH) of aromatic ketones to their enantiopure secondary alcohols. The reactions were carried out in the presence of formic acid–triethylamine mixture in water, and the product alcohols were obtained with excellent conversions (up to 99%) and enantiomeric excesses (up to 99%). The scope of the catalytic system was extended to various aromatic ketones. The catalytic activity of the present water-soluble Ru-benzene complexes toward enantioselective reduction of ketones was considerably higher than that of p-cymene analogues in water. Graphical Abstract: The water-soluble chiral Ru(II)-benzene complexes were produced from the reactions between [RuCl2(η6-C6H6)]2 and the chiral aroylthiourea ligands derived from unprotected D/L-alanine. The catalytic activity of the Ru(II)-benzene complexes toward enantioselective reduction of ketones was found to be good in water medium.[Figure not available: see fulltext.].
Sheeba, Mani Mary,Bhuvanesh, Nattamai S P,Karvembu, Ramasamy
(2018/12/04)