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Discriminating non-ylidic carbon-sulfur bond cleavages of sulfonium ylides for alkylation and arylation reactions
A sulfonium ylide participated alkylation and arylation under transition-metal free conditions is described. The disparate reaction pattern allowed the separate activation of non-ylidic S-alkyl and S-aryl bond. Under acidic conditions, sulfonium ylides serve as alkyl cation precursors which facilitate the alkylations. While under alkaline conditions, cleavage of non-ylidic S-aryl bond produces O-arylated compounds efficiently. The robustness of the protocols were established by the excellent compatibility of wide variety of substrates including carbohydrates.
Cai, Lei,Chen, Qi,Fang, Jing,Li, Ting,Liao, Zhiwen,Ma, Xiang,Meng, Lingkui,Sun, Jiuchang,Wan, Qian,Zeng, Jing
supporting information

(2021/07/25)

Disproportionation of aliphatic and aromatic aldehydes through Cannizzaro, Tishchenko, and Meerwein–Ponndorf–Verley reactions
Disproportionation of aldehydes through Cannizzaro, Tishchenko, and Meerwein–Ponndorf–Verley reactions often requires the application of high temperatures, equimolar or excess quantities of strong bases, and is mostly limited to the aldehydes with no CH2 or CH3 adjacent to the carbonyl group. Herein, we developed an efficient, mild, and multifunctional catalytic system consisting AlCl3/Et3N in CH2Cl2, that can selectively convert a wide range of not only aliphatic, but also aromatic aldehydes to the corresponding alcohols, acids, and dimerized esters at room temperature, and in high yields, without formation of the side products that are generally observed. We have also shown that higher AlCl3 content favors the reaction towards Cannizzaro reaction, yet lower content favors Tishchenko reaction. Moreover, the presence of hydride donor alcohols in the reaction mixture completely directs the reaction towards the Meerwein–Ponndorf–Verley reaction. Graphic abstract: [Figure not available: see fulltext.].
Sharifi, Sina,Sharifi, Hannah,Koza, Darrell,Aminkhani, Ali
p. 803 - 808
(2021/07/20)

N-Heterocyclic Carbene Catalyzed Ester Synthesis from Organic Halides through Incorporation of Oxygen Atoms from Air
Oxygenation reactions with molecular oxygen (O2) as the oxygen source provides a green and straightforward strategy for the construction of O-containing compounds. Demonstrated here is a novel N-heterocyclic carbene (NHC) catalyzed oxidative transformation of simple and readily available organic halides into valuable esters through the incorporation of O-atoms from O2. Mechanistic studies prove that the deoxy Breslow intermediate generated in situ is oxidized to a Breslow intermediate for further transformation by this oxidative protocol. This method broadens the field of NHC catalysis and promotes oxygenation reactions with O2.
Tan, Hui,Wang, Shen-An,Yan, Zixi,Liu, Jianzhong,Wei, Jialiang,Song, Song,Jiao, Ning
supporting information
p. 2140 - 2144
(2020/12/01)

Iodine-catalyzed synthesis of β-uramino crotonic esters as well as oxidative esterification of carboxylic acids in choline chloride/urea: a desirable alternative to organic solvents
Abstract: Iodine-mediated selective synthesis of β-uramino crotonic esters was achieved via the reaction of β-dicarbonyls and urea at room temperature. Choline chloride/urea mixture, as an eco-friendly, cheap, non-toxic, and recyclable deep eutectic solvent (DES), was employed as sustainable media as well as reagent at the same time in these transformations. Some derivatives of β-uramino crotonic esters were synthesized with good to high yields without a tedious work-up. The process could be done to synthesize the above-mentioned compounds in gram scale. Moreover, oxidative cross-esterification of carboxylic acids with alkyl benzenes was carried out in the above-mentioned DES by the employment of tetrabutylammonium iodide (TBAI) as the catalyst and tert-butyl hydroperoxide (TBHP) as the oxidant at 80?°C. DES/TBAI system was reused up to five consecutive times. Graphic abstract: Iodine-catalyzed C–N and C–O bond formation in choline chloride/urea as a green solvent under the mild reaction conditions. Providing the clean procedure toward synthesis of β-uramino crotonic esters and benzylic esters.[Figure not available: see fulltext.].
Moayyed, Mohammadesmaeil,Saberi, Dariush
p. 445 - 455
(2020/09/07)

Dual utility of a single diphosphine-ruthenium complex: A precursor for new complexes and, a pre-catalyst for transfer-hydrogenation and Oppenauer oxidation
The diphosphine-ruthenium complex, [Ru(dppbz)(CO)2Cl2] (dppbz = 1,2-bis(diphenylphosphino)benzene), where the two carbonyls are mutually cis and the two chlorides are trans, has been found to serve as an efficient precursor for the synthesis of new complexes. In [Ru(dppbz)(CO)2Cl2] one of the two carbonyls undergoes facile displacement by neutral monodentate ligands (L) to afford complexes of the type [Ru(dppbz)(CO)(L)Cl2] (L = acetonitrile, 4-picoline and dimethyl sulfoxide). Both the carbonyls in [Ru(dppbz)(CO)2Cl2] are displaced on reaction with another equivalent of dppbz to afford [Ru(dppbz)2Cl2]. The two carbonyls and the two chlorides in [Ru(dppbz)(CO)2Cl2] could be displaced together by chelating mono-anionic bidentate ligands, viz. anions derived from 8-hydroxyquinoline (Hq) and 2-picolinic acid (Hpic) via loss of a proton, to afford the mixed-tris complexes [Ru(dppbz)(q)2] and [Ru(dppbz)(pic)2], respectively. The molecular structures of four selected complexes, viz. [Ru(dppbz)(CO)(dmso)Cl2], [Ru(dppbz)2Cl2], [Ru(dppbz)(q)2] and [Ru(dppbz)(pic)2], have been determined by X-ray crystallography. In dichloromethane solution, all the complexes show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry on the complexes shows redox responses within 0.71 to -1.24 V vs. SCE. [Ru(dppbz)(CO)2Cl2] has been found to serve as an excellent pre-catalyst for catalytic transfer-hydrogenation and Oppenauer oxidation.
Mukherjee, Aparajita,Bhattacharya, Samaresh
p. 15617 - 15631
(2021/05/19)

A rutheniumcis-dihydride with 2-phosphinophosphinine ligands catalyses the acceptorless dehydrogenation of benzyl alcohol
The first ruthenium dihydride complex featuring a phosphinine ligandcis-[Ru(H)2(2-PPh2-3-Me-6-SiMe3-PC5H2)2] was synthesised exclusively as thecis-isomer. When formedin situfrom the reaction ofcis-[Ru(Cl)2(2-PPh2-3-Me-6-SiMe3-PC5H2)2] with two equivalents of Na[BHEt3], as demonstrated by31P and1H NMR spectroscopy, the catalysed acceptorless dehydrogenation of benzyl alcohol was observed leading to benzyl benzoate in up to 70% yield.
Andresen, John M.,Delve, Matthew P.,Luz, Christian,Mansell, Stephen M.,Newland, Robert J.,Trodden, Elizabeth C.
supporting information
p. 13407 - 13411
(2021/10/12)

Sodium organoaluminate containing bidentate pyrrolyl ligand: Synthesis, structure, and catalytic activity for the Tishchenko reaction
An novel sodium organoaluminate containing bidentate pyrrolyl ligand [C4H3NH(2-CH2NHtBu)] was efficiently synthesized and characterized by X-ray crystallography. The molecular structure shows it is a monodimensional infinite chain structures with linear arrangements. Its basic repeat unit comprises the Al atom bonded to two deprotonated pyrrole rings and Na atom coordinated to of nitrogen atoms of –NtBu fragment, which undergoes further to coordinates a pyrrolyl ring of an adjacent molecule in a ?2-fasion. Furthermore, this sodium organoaluminate exhibited high catalytic activities for Tishchenko reaction.
Liu, Yu,Guo, Zhiqiang,Wang, Yakong
(2021/05/26)

Thermally regulated molybdate-based ionic liquids toward molecular oxygen activation for one-pot oxidative cascade catalysis
One-pot oxidative cascade catalysis plays a central role in the synthesis of key pharmaceutical and industrial molecules. Although ionic liquids are one of the most promising solvents and reaction media, the breakthrough of their catalysis in aerobic oxidation is very challenging due to the difficulty in the direct activation of molecular oxygen. Herein, a family of novel thermally regulated molybdate-based ionic liquids (Mo-ILs) has been designed and developed for the first time toward molecular oxygen activation for highly efficient tandem oxidative catalysis. Three diverse one-pot oxidative cascade processes for the syntheses of various flavones, imines, and benzyl benzoates were achieved with good to excellent yields using the Mo-IL [Bmim]2[MoO4] as a catalyst under air conditions. The results of spectroscopic investigations and quantum-chemical calculations further demonstrated that a thermally regulated proton migration between the cation [Bmim] and anion [MoO4] was the key to forming N-heterocyclic carbene and thereby to effortlessly promoting the generation of O2- active species from molecular oxygen, which results in excellent catalytic performance in these three aerobic tandem oxidations. Our work extends the application area of ILs as the sole catalyst to one-pot aerobic oxidative cascade catalysis, which could have pronounced implications in future work.
Song, Zhibin,Huang, Wei,Zhou, Yan,Tian, Zi-Qi,Li, Zhang-Min,Tao, Duan-Jian
supporting information
p. 103 - 109
(2020/01/21)

A metal-free approach for the synthesis of amides/esters with pyridinium salts of phenacyl bromides via oxidative C–C bond cleavage
An efficient, simple, and metal-free synthetic approach for the N- and O-benzoylation of various amines/benzyl alcohols with pyridinium salts of phenacyl bromides is demonstrated to generate the corresponding amides and esters. This protocol facilitates the oxidative cleavage of a C–C bond followed by formation of a new C–N/C–O bond in the presence of K2CO3. Various pyridinium salts of phenacyl bromides can be readily transformed into a variety of amides and esters which is an alternative method for the conventional amidation and esterification in organic synthesis. High functional group tolerance, broad substrate scope and operational simplicity are the prominent advantages of the current protocol.
Manasa, Kesari Lakshmi,Tangella, Yellaiah,Krishna, Namballa Hari,Alvala, Mallika
p. 1864 - 1871
(2019/08/12)

Synthesis of Unsymmetrical N-Heterocyclic Carbene-Nitrogen-Phosphine Chelated Ruthenium(II) Complexes and Their Reactivity in Acceptorless Dehydrogenative Coupling of Alcohols to Esters
Two novel ruthenium complexes RuH(CO)Cl(PPh3)(κ2-CP) (1) and [fac-RuH(CO)(PPh3)(κ3-CNP)]Cl (2) bearing unsymmetrical N-heterocyclic carbene-nitrogen-phosphine (CNP) were synthesized and characterized with 1H NMR, 31P NMR, and HRMS. The structure of complex 2 was further confirmed by single-crystal X-ray diffraction. An anion exchange experiment proved that complex 2 could transform into complex 1 in solution. The two complexes exhibited a highly catalytic performance in acceptorless dehydrogenative coupling of alcohols to esters, and the excellent isolated yields of esters were given in a catalyst loading of 1% for para- and meta-substituted benzyl alcohols and long-chain primary alcohols. Although some ortho-substituted benzyl alcohols displayed a relatively low reactivity due to the steric hindrance and the coordination of electron donor with the ruthenium center, the good product yields were still obtained by prolonging the reaction time. Especially, this system successfully realized the dehydrogenative cross-coupling to esters between two different primary alcohols.
He, Xiaochun,Li, Yaqiu,Fu, Haiyan,Zheng, Xueli,Chen, Hua,Li, Ruixiang,Yu, Xiaojun
p. 1750 - 1760
(2019/04/17)

Aldehyde effect and ligand discovery in Ru-catalyzed dehydrogenative cross-coupling of alcohols to esters
The presence of different aldehydes is found to have a significant influence on the catalytic performance when using PN(H)P type ligands for dehydrogenation of alcohols. Accordingly, hybrid multi-dentate ligands were discovered based on an oxygen-transfer alkylation of PNP ligands by aldehydes. The relevant Ru-PNN(PO) system provided the desired unsymmetrical esters in good yields via acceptorless dehydrogenation of alcohols. Hydrogen bonding interactions between the phosphine oxide moieties and alcohol substrates likely assisted the observed high chemoselectivity.
Jiang, Xiaolin,Zhang, Jiahui,Zhao, Dongmei,Li, Yuehui
p. 2797 - 2800
(2019/03/27)

Direct oxidative esterification of primary alcohols and oxidation of secondary alcohols over mesoporous spherical silica encapsulated MnO2 nanoparticles
In this work, a simple and efficient strategy for the fabrication of novel encapsulated MnO2 nanoparticles inside spherical mesoporous silica hollow-nanoparticles was described. They were synthesized by consecutively anchoring MnO2 nanoparticles on poly(styrene-co-methacrylic acid) particles, coating with a mesoporous silica shell, and subsequently removing the polymeric core by dissolving in acetone. The catalytic activity of the nanoparticles was examined in the aerobic oxidation of various primary and secondary alcohols, which showed good activity and selectivity for the transformation of primary alcohols to the corresponding esters through the oxidative esterification process and secondary alcohols to ketones in short reaction times under mild reaction conditions. In addition, the catalyst system was utilized for the oxidation of primary alcohols to aldehydes using tert-butyl hydroperoxide (TBHP) as an oxidant under mild conditions and produced an excellent product yield.
Hosseinzadeh, Shahram Zare,Babazadeh, Mirzaagha,Shahverdizadeh, Gholam Hossein,Hosseinzadeh-Khanmiri, Rahim
p. 9491 - 9499
(2019/06/21)

Iridium catalysts for acceptorless dehydrogenation of alcohols to carboxylic acids: Scope and mechanism
We introduce iridium-based conditions for the conversion of primary alcohols to potassium carboxylates (or carboxylic acids) in the presence of potassium hydroxide and either [Ir(2-PyCH2(C4H5N2))(COD)]OTf (1) or [Ir(2-PyCH2PBu2t)(COD)]OTf (2). The method provides both aliphatic and benzylic carboxylates in high yield and with outstanding functional group tolerance. We illustrate the application of this method to a diverse variety of primary alcohols, including those involving heterocycles and even free amines. Complex 2 reacts with alcohols to form the crystallographically characterized catalytic intermediates [IrH(η1,η3-C8H12)(2-PyCH2PtBu2)] (2a) and [Ir2H3(CO)(2-PyCH2PtBu2){μ-(C5H3N)CH2PtBu2}] (2c). The unexpected similarities in reactivities of 1 and 2 in this reaction, along with synthetic studies on several of our iridium intermediates, enable us to form a general proposal of the mechanisms of catalyst activation that govern the disparate reactivities of 1 and 2, respectively, in glycerol and formic acid dehydrogenation. Moreover, careful analysis of the organic intermediates in the oxidation sequence enable new insights into the role of Tishchenko and Cannizzaro reactions in the overall oxidation.
Cherepakhin, Valeriy,Williams, Travis J.
p. 3754 - 3763
(2018/05/23)

Rhodium-catalyzed synthesis of imines and esters from benzyl alcohols and nitroarenes: Change in catalyst reactivity depending on the presence or absence of the phosphine ligand
The [Rh(COD)Cl]2/xantphos/Cs2CO3 system efficiently catalyzes the reductive N-alkylation of aryl nitro compounds with alcohols by a borrowing-hydrogen strategy to afford the corresponding imine products in good to excellent yields. In the absence of xantphos, the [Rh(COD)Cl]2/Cs2CO3 catalytic system behaves as an effective catalyst for the dehydrogenative coupling of alcohols to esters, with nitrobenzene as a hydrogen acceptor. The reactivity of the rhodium catalytic system can be easily manipulated to selectively afford the imine or ester.
Song, Taemoon,Park, Ji Eun,Chung, Young Keun
p. 4197 - 4203
(2018/04/14)

Cobalt-Catalyzed Acceptorless Dehydrogenative Coupling of Primary Alcohols to Esters
A novel catalytic system with a tripodal cobalt complex is developed for efficiently converting primary alcohols to esters. KOtBu is found essential to the transformation. A preliminary mechanistic study suggests a plausible reaction route that involves an initial Co-catalyzed dehydrogenation of alcohol to aldehyde, followed by a Tishchenko-type pathway to ester mediated by KOtBu.
Paudel, Keshav,Pandey, Bedraj,Xu, Shi,Taylor, Daniela K.,Tyer, David L.,Torres, Claudia Lopez,Gallagher, Sky,Kong, Lin,Ding, Keying
supporting information
p. 4478 - 4481
(2018/08/09)

Base-Free and Acceptorless Dehydrogenation of Alcohols Catalyzed by an Iridium Complex Stabilized by a N, N, N-Osmaligand
The preparation of a N,N,N-osmaligand, its coordination to iridium to afford an efficient catalyst precursor, and the catalytic activity of the latter in dehydrogenation reactions of hydrogen carriers based on alcohols are reported. Complex OsH2Cl2(PiPr3)2 (1) reacts with 3-(2-pyridyl)pyrazol to give the osmium(II) complex 2H, which contains an acidic hydrogen atom. Deprotonation of the latter by the bridging methoxy groups of the dimer [Ir(μ-OMe)(n4-COD)]2 (COD = 1,5-cyclooctadiene) leads to Ir(2)( n 4-COD) (3), where osmaligand 2 has a free-nitrogen atom. Iridium complex 3 catalyzes the dehydrogenation of secondary and primary alcohols to ketones and aldehydes or esters, respectively, and the dehydrogenation of diols to lactones. Cyclooctatriene is detected during the catalysis by GC-MS, suggesting that the true catalyst of the reactions is a dihydride IrH2(2)-species with osmaligand 2 acting as N,N,N-pincer. The presence of a phenyl group in the substrates favors the catalytic processes. The dehydrogenative homocoupling of primary alcohols to esters appears to take place via the transitory formation of hemiacetals.
Alabau, Roberto G.,Esteruelas, Miguel A.,Martínez, Antonio,Oliván, Montserrat,O?ate, Enrique
p. 2732 - 2740
(2018/09/10)

Overcoming solid handling issues in continuous flow substitution reactions through ionic liquid formation
Substitutions such as acylations, arylations, and alkylations are some of the most commonly run reactions for building complex molecules. However, the requirement of a stoichiometric base to scavange acid by-products creates significant challenges when operating in continuous flow due to solid handling issues associated with precipitating base·HX salts. We present a general and simple strategy to overcome these solid handling issues through the use of acid scavenging organic bases that generate low- to moderate-melting ionic liquids upon protonation. The application of these bases towards the most commonly run substitutions are demonstrated, enabling reactions to be run in flow without requiring additional equipment, specific solvents, or dilute reaction conditions to prevent clogging.
Kashani, Saeed,Sullivan, Ryan J.,Andersen, Mads,Newman, Stephen G.
supporting information
p. 1748 - 1753
(2018/04/30)

Synthesis, characterization and catalytic performances of benzimidazolin-2-iminato actinide (IV) complexes in the Tishchenko reactions for symmetrical and unsymmetrical esters
A new family of benzimdazolin-2-iminato actinide?(IV) complexes [(Bim7-MeDipp/MeN)An(N(SiMe3)2)3] (An = U (3), Th (4)) and [(Bim4-MeDipp/MeN)An(N(SiMe3)2)3] (An = U (5), Th (6)) were synthesized and their solid state structures were established by single-crystal X-ray diffraction analysis. The catalytic performances of complexes 3–6 towards the homo- and cross-coupling of aldehydes (Tishchenko reaction) were studied and the thorium complexes 4 and 6 displayed moderate to high activities for the production of the corresponding symmetric and unsymmetrical esters. Coupling of aldehyde and alcohols, known as the tandem proton-transfer esterification, and the intermolecular coupling reaction between aldehyde and trifluoromethylketones were also investigated by these thorium complexes, indicating a complementary method to obtain unsymmetrical esters selectively. Plausible mechanisms for these reactions are proposed based on stoichiometric studies.
Liu, Heng,Khononov, Maxim,Fridman, Natalia,Tamm, Matthias,Eisen, Moris S.
p. 123 - 137
(2017/10/25)

Nickel-Catalyzed Decarbonylation of Aromatic Aldehydes
We report here the first systematic study of nickel-catalyzed decarbonylation of aromatic aldehydes under relatively mild conditions. Aldehydes with electron donating groups at para and ortho positions are generally successful with our method. For aldehydes with electron-withdrawing groups, significantly higher yields were achieved for ortho-substituted substrates than para ones, probably due to the effects of steric hindrance or electron donors at the ortho position to suppress the Tishchenko reaction, an undesirable side reaction toward homocoupled esters.
Ding, Keying,Xu, Shi,Alotaibi, Rajeh,Paudel, Keshav,Reinheimer, Eric W.,Weatherly, Jessie
p. 4924 - 4929
(2017/05/12)

Manganese Pincer Complexes for the Base-Free, Acceptorless Dehydrogenative Coupling of Alcohols to Esters: Development, Scope, and Understanding
Aliphatic PNP pincer-supported earth-abundant manganese(I) dicarbonyl complexes behave as effective catalysts for the acceptorless dehydrogenative coupling of a wide range of alcohols to esters under base-free conditions. The reaction proceeds under neat conditions, with modest catalyst loading and releasing only H2 as byproduct. Mechanistic aspects were addressed by synthesizing key species related to the catalytic cycle (characterized by X-ray structure determination, multinuclear (1H, 13C, 31P, 15N, 55Mn) NMR, infrared spectroscopy, inter alia), by studying elementary steps connected to the postulated mechanism, and by resorting to DFT calculations. As in the case of related ruthenium and iron PNP catalysts, the dehydrogenation results from cycling between the amido and amino-hydride forms of the PNP-Mn(CO)2 scaffold. For the dehydrogenation of alcohols into aldehydes, our results suggest that the highest energy barrier corresponds to the hydrogen release from the amino-hydride form, although its value is close to that of the outer-sphere dehydrogenation of the alcohol into aldehyde. This contrasts with the ruthenium and iron catalytic systems, where dehydrogenation of the substrate into aldehyde is less energy-demanding compared to hydrogen release from the cooperative metal-ligand framework.
Nguyen, Duc Hanh,Trivelli, Xavier,Capet, Frédéric,Paul, Jean-Fran?ois,Dumeignil, Franck,Gauvin, Régis M.
p. 2022 - 2032
(2017/08/14)

RUTHENIUM COMPLEXES AND THEIR USES AS CATALYSTS IN PROCESSES FOR FORMATION AND/OR HYDROGENATION OF ESTERS, AMIDES AND RELATED REACTIONS
The present invention relates to novel Ruthenium complexes of formulae A1-A4 and their use, inter alia, for (1) dehydrogenative coupling of alcohols to esters; (2) hydrogenation of esters to alcohols (including hydrogenation of cyclic esters (lactones) or cyclic di-esters (di-lactones), or polyesters); (3) preparing amides from alcohols and amines—(including the preparation of polyamides (e.g., polypeptides) by reacting dialcohols and diamines and/or polymerization of amino alcohols and/or forming cyclic dipeptides from p-aminoalcohols; (4) hydrogenation of amides (including cyclic dipeptides, polypeptides and polyamides) to alcohols and amines; (5) hydrogenation of organic carbonates (including polycarbonates) to alcohols or hydrogenation of carbamates (including polycarbamates) or urea derivatives to alcohols and amines; (6) dehydrogenation of secondary alcohols to ketones; (7) amidation of esters (i.e., synthesis of amides from esters and amines); (8) acylation of alcohols using esters; (9) coupling of alcohols with water and a base to form carboxylic acids; and (10) preparation of amino acids or their salts by coupling of amino alcohols with water and a base. The present, invention further relates to the use of certain known Ruthenium complexes for the preparation of amino acids or their salts from amino alcohols.
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Paragraph 0274; 0275

(2017/10/18)

Thorium complexes possessing expanded ring N-heterocyclic iminato ligands: Synthesis and applications
Six and seven membered N-heterocyclic iminato ligands (L) are introduced allowing access a new class of Th(iv) complexes of the type Cp?2Th(L)(CH3). These complexes were studied in the Tishchenko reaction. Stoichiometric reactions together with kinetic and thermodynamic studies permit us to propose a plausible mechanism.
Ghatak, Tapas,Drucker, Shani,Fridman, Natalia,Eisen, Moris S.
supporting information
p. 12005 - 12009
(2017/09/25)

Dicopper Complexes with Anthyridine-Based Ligands: Coordination and Catalytic Activity
Two new anthyridine-based ligands, 5-phenyl-2,8-bis(2-pyridinyl)-1,9,10-anthyridine (L3) and 5-phenyl-2,8-bis(6′-bipyridinyl)-1,9,10-anthyridine (L4), were designed for accommodation of dimetallic systems with the metal ions separated by 5 ?. Complexation of Cu(ClO4)2 with L3 and L4 provided the corresponding dicopper complexes [{Cu2(L3)(H2O)4(CH3CN)2}(ClO4)4] (3) and [{Cu2(L4)(μ-ClO4)2}(PF6)2] (4), respectively. Both complexes were characterized by spectroscopic methods, and the detail structural features were further confirmed by X-ray crystallography. Structural analyses of 3 and 4 reveal the Cu···Cu distances in the complexes being 4.9612(7) and 5.013 (2) ?, respectively. Both complexes are active in the catalytic oxidation of benzyl alcohols into the corresponding aldehydes. Furthermore, complex 4 appears to be a good catalyst for the oxidative coupling of primary alcohols into the corresponding esters with the use of hydrogen peroxide as the oxidant in an aqueous medium. The possible cooperative interactions between the metal ions during the catalysis are discussed.
Huang, Da-Wei,Liu, Yi-Hung,Peng, Shie-Ming,Liu, Shiuh-Tzung
p. 151 - 158
(2016/02/05)

Nitrous Oxide as a Hydrogen Acceptor for the Dehydrogenative Coupling of Alcohols
The oxidation of alcohols with N2O as the hydrogen acceptor was achieved with low catalyst loadings of a rhodium complex that features a cooperative bis(olefin)amido ligand under mild conditions. Two different methods enable the formation of either the corresponding carboxylic acid or the ester. N2 and water are the only by-products. Mechanistic studies supported by DFT calculations suggest that the oxygen atom of N2O is transferred to the metal center by insertion into the Rh-H bond of a rhodium amino hydride species, generating a rhodium hydroxy complex as a key intermediate.
Gianetti, Thomas L.,Annen, Samuel P.,Santiso-Quinones, Gustavo,Reiher, Markus,Driess, Matthias,Grützmacher, Hansj?rg
supporting information
p. 1854 - 1858
(2016/02/03)

Formamides as Lewis Base Catalysts in SNReactions—Efficient Transformation of Alcohols into Chlorides, Amines, and Ethers
A simple formamide catalyst facilitates the efficient transformation of alcohols into alkyl chlorides with benzoyl chloride as the sole reagent. These nucleophilic substitutions proceed through iminium-activated alcohols as intermediates. The novel method, which can be even performed under solvent-free conditions, is distinguished by an excellent functional group tolerance, scalability (>100 g) and waste-balance (E-factor down to 2). Chiral substrates are converted with excellent levels of stereochemical inversion (99 %→≥95 % ee). In a practical one-pot procedure, the primary formed chlorides can be further transformed into amines, azides, ethers, sulfides, and nitriles. The value of the method was demonstrated in straightforward syntheses of the drugs rac-Clopidogrel and S-Fendiline.
Huy, Peter H.,Motsch, Sebastian,Kappler, Sarah M.
supporting information
p. 10145 - 10149
(2016/08/16)

Aluminum complexes of β-hydroxy-imino ligands: Synthesis, structures and application in the Tishchenko reaction
Four aluminum alkoxide complexes containing β-hydroxy-imino ligands, [(2,6-Me2C6H3)NCPhCH2CPh2O]2AlMe (3a), [(2,6-iPr2C6H3)NCPhCH2CPh2O]2AlMe (3b), [(2,6-Me2C6H3)NCPhCH2C(C12H8)OAlMe2]2 (3c) and [(2,6-iPr2C6H3)NCPhCH2C(C12H8)OAlMe2]2 (3d) were synthesized in high yields, and their structural features were provided. The catalytic behavior of those four complexes about the Tishchenko reaction with a range of aromatic aldehydes as substrates were assessed, and it present a synthetically useful protocol to the solvent-free Tishchenko reaction under mild conditions.
Guo, Zhiqiang,Wang, Song,Wei, Xuehong
p. 115 - 122
(2016/07/06)

Facile and selective deprotection of PMB ethers and esters using oxalyl chloride
Oxalyl chloride, (0.5 equiv) was found to cleave the PMB group from alkyl, aryl PMB ethers, and esters to give corresponding alcohol and acid in good yields. This method offers simple and efficient protocol for the selective deprotection of PMB ether and ester in DCE at ambient temperature.
Ilangovan, Andivelu,Anandhan, Karnambaram,Kaushik, Mahabir Prasad
p. 1081 - 1084
(2015/02/19)

The promoted Tishchenko reaction and catalytic intermediate by 2-aminopyrrolyl dilithium compounds
The dimerization of aldehydes to the analogous carboxylic esters (Tischenko reaction) has been achieved in impressive yields using the dilithium compounds containing bidentate di-anionic pyrrolyl ligands as initiators. The initiated intermediate {[2-(tBuNCH)C4H3NLi][PhCH2OLi(TMEDA)]}2 was isolated and characterized by satisfactory C, H and N microanalysis, 1H, 13C{1H} and 7Li NMR spectra in pyridine-d5 at ambient temperature, and single crystal X-ray structural data. The processes involve a redox reaction of 2-aminopyrrolyl dilithium compound with aldehyde.
Guo, Zhiqiang,Wei, Xuehong,Tong, Hongbo,Chao, Jianbin,Liu, Diansheng
supporting information
p. 73 - 76
(2015/03/14)

Synthesis, Characterization, and unique catalytic activities of a fluorinated nickel enolate
We have synthesized a new nickel enolate [(PhCOCF2)Ni(dcpe)][FB(C6F5)3] featuring fluorine atoms on the enolate moiety via B(C6F5)3-promoted C-F bond activation of α,α,α-trifluoroacetophenone. X-ray diffraction study of [(PhCOCF2)Ni(dcpe)][FB(C6F5)3] revealed that the complex had adopted an η3-oxallyl coordination mode in the crystal lattice. The reaction of tBuNC with [(PhCOCF2)Ni(dcpe)][FB(C6F5)3] resulted in the coordination of isocyanide to the nickel center to form a C-bound enolate complex. The reactions of [(PhCOCF2)Ni(dcpe)][FB(C6F5)3] with aldehydes gave insertion products quantitatively which were fully characterized by NMR spectroscopy. Furthermore, we established unique catalytic applications for [(PhCOCF2)Ni(dcpe)][FB(C6F5)3] toward a Tishchenko reaction, along with a highly selective crossed-esterification of α,α,α-trifluoroacetophenones with aldehydes.
Doi, Ryohei,Kikushima, Kotaro,Ohashi, Masato,Ogoshi, Sensuke
supporting information
p. 3276 - 3282
(2015/03/30)

Bulky guanidinate stabilized homoleptic magnesium, calcium and zinc complexes and their catalytic activity in the Tishchenko reaction
Bulky guanidinate stabilized homoleptic complexes of [LM(thf)nL] [L = {ArNC (NiPr2)NAr} (Ar = 2,6- Me2-C6H3)]; M = Mg, Ca, and Zn; n = 0-1) have been synthesized with three different synthetic routes. First, treatment of bis{bis(trimethylsilyl)amide}s of Mg, Ca, and Zn i.e. [M{(N(SiMe3)2}2] (M = Mg, Ca(thf)2, and Zn) with free guanidine ligand (LH) at 80 °C, elimination of NH(SiMe3)2 and formation of [LM(thf)nL] (M = Mg, Ca and Zn; n = 0-1) (3-5) complexes were occurred. Second, the reaction of two equivalents of potassium salt of LH with metal dihalides via salt metathesis led to the formation of homoleptic complexes. Third, the reaction between MR2 (M = Mg, Ca, Zn; R = alkyl or OTf) and LH at reflux temperature, formation of bis(guanidinate) magnesium, calcium, and zinc complexes have been observed. The solid state structures of LH(1), LK(2) and all three bis(guanidinate) magnesium, calcium and zinc complexes (3-5) were confirmed by X-ray structural analysis. Furthermore, dimerization of a range of aromatic, heteroaromatic and aliphatic aldehydes (Tishchenko reaction) has been demonstrated by using catalysts 3-5.
Barman, Milan Kr,Baishya, Ashim,Nembenna, Sharanappa
p. 52 - 60
(2015/03/30)

Proton-exchanged montmorillonite-mediated reactions of methoxybenzyl esters and ethers
Proton-exchanged montmorillonite (H-mont) was found to be an eco-friendly and cost-effective catalyst for the generation of O-methylated quinone methides (QM) from the corresponding p or o-methoxybenzyl esters and ethers. Nucleophilic trapping of the O-methylated QM with arenes, alcohols, 1,3-dicarbonyl compounds, silyl enol ethers, and allylsilanes has been carried out, respectively, leading to eco-friendly benzylation reactions. Using this protocol, H-mont-mediated deprotection of PMB-protected esters and ethers have been realized for the first time. This work would pave the way for further exploration in O-alkylated QM that are of chemical and biological significance.
Chen, Dongyin,Xu, Chang,Deng, Jie,Jiang, Chunhuan,Wen, Xiaoan,Kong, Lingyi,Zhang, Ji,Sun, Hongbin
p. 1975 - 1983
(2014/03/21)

Spontaneous formation of PMB esters using 4-methoxybenzyl-2,2,2- trichloroacetimidate
Carboxylic acids are converted to the corresponding 4-methoxybenzyl (PMB) esters with 4-methoxybenzyl-2,2,2-trichloroacetimidate in the absence of an acid catalyst. This operationally simple procedure is a highly effective method for the formation of PMB esters. The reaction is promoted by the carboxylic acids themselves in excellent yields (72-99%). Sterically hindered carboxylic acids, which provide lower yields with other imidates, are esterified in higher yield with the more reactive PMB imidate. No racemization is observed in the case of carboxylic acids bearing an α-stereocenter, and no isomerization is observed with Z-α,β-unsaturated acids. This method may therefore find use in the esterification of complex or sensitive substrates where more common techniques lead to decomposition.
Shah, Jigisha P.,Russo, Christopher M.,Howard, Kyle T.,Chisholm, John D.
supporting information
p. 1740 - 1742
(2014/03/21)

A convenient approach for the deprotection and scavenging of the PMB group using POCl3
A convenient and high yielding approach for the deprotection and scavenging of the p-methoxybenzyl (PMB) group in PMB ethers and PMB esters was developed using POCl3 as the reagent. 4-Methoxybenzyl chloride, a starting material used for the preparation of PMB ethers and esters was regenerated in the deprotection step. This mild and selective procedure tolerates several acid sensitive functional groups. The Royal Society of Chemistry 2013.
Ilangovan, Andivelu,Saravanakumar, Shanmugasundar,Malayappasamy, Subramani,Manickam, Govindaswamy
p. 14814 - 14828
(2013/09/02)

Easy access to benzylic esters directly from alkyl benzenes under metal-free conditions
An efficient metal free protocol has been developed for the synthesis of benzylic esters via a cross dehydrogenative coupling (CDC) involving alkylbenzene(s) as a self- or as a cross-coupling partner(s) via the intermediacy of Ar-COOH and the benzylic carbocation obtained from the other half of the alkylbenzene; both symmetrical as well as unsymmetrical esters can be prepared using Bu4NI and TBHP. The Royal Society of Chemistry.
Majji, Ganesh,Guin, Srimanta,Gogoi, Anupal,Rout, Saroj Kumar,Patel, Bhisma K.
supporting information
p. 3031 - 3033
(2013/05/09)

Pt, Pd and Au nanoparticles supported on a DNA-MMT hybrid: Efficient catalysts for highly selective oxidation of primary alcohols to aldehydes, acids and esters
Novel DNA-MMT hybrid supported metal nanoparticle catalysts, such as Pt/DNA-MMT, Pd/DNA-MMT, Au/DNA-MMT, were prepared for application in highly selective aerobic oxidation of primary alcohols to aldehydes, acids and esters, respectively. Taking advantage of the water-soluble reversibility of these catalysts, all the transformations could be performed smoothly in water and reuse of the catalysts has also been accomplished by a very simple phase separation process.
Tang, Lin,Guo, Xuefeng,Li, Yunfeng,Zhang, Shuai,Zha, Zhenggen,Wang, Zhiyong
supporting information
p. 5213 - 5215
(2013/06/27)

Ruthenium-catalyzed self-coupling of primary and secondary alcohols with the liberation of dihydrogen
The dehydrogenative self-condensation of primary and secondary alcohols has been studied in the presence of RuCl2(IiPr)(p-cymene). The conversion of primary alcohols into esters has been further optimized by using magnesium nitride as an additive, which allows the reaction to take place at a temperature and catalyst loading lower than those described previously. Secondary alcohols were dimerized into racemic ketones by a dehydrogenative Guerbet reaction with potassium hydroxide as the additive. The transformation gave good yields of the ketone dimers with a range of alkan-2-ols, whereas more substituted secondary alcohols were unreactive. The reaction proceeds by dehydrogenation to the ketone, followed by an aldol reaction and hydrogenation of the resulting enone.
Makarov, Ilya S.,Madsen, Robert
p. 6593 - 6598
(2013/07/26)

Solvent-controlled copper-catalyzed oxidation of benzylic alcohols to aldehydes and esters
A procedure for the copper-catalyzed selective oxidation of primary alcohols to esters and aldehydes was developed. Under solvent-free conditions, self-oxidative esterification and cross-esterification of benzyl alcohols with various aliphatic alcohols proceed smoothly to give the corresponding esters in good yields. If DMF was used as a solvent, the benzyl alcohols were selectively converted into the corresponding aldehydes in excellent yields. Depend on solvent! Under solvent-free conditions, Cu-catalyzed oxidative self-esterification and cross-esterification of benzylic alcohols with various aliphatic alcohols proceed smoothly to give the corresponding esters in good yields. If DMF is used as a solvent, the benzylic alcohols are selectively converted into the corresponding aldehydes in excellent yields. DTBP = di-tert-butyl peroxide. Copyright
Zhu, Yefeng,Wei, Yunyang
supporting information
p. 4503 - 4508
(2013/07/26)

Oxidant controlled Pd-catalysed selective oxidation of primary alcohols
The oxidant controlled palladium catalysed selective oxidation of primary alcohols to aldehydes or esters was investigated. The electronic properties of the benzylic alcohols and the structure of the oxidant are both important factors in controlling the selectivity between aldehydes and esters. A covalent benzyl ligand derived from BnCl provides η3 coordination to the Pd centre. This covalent ligand is the key to the selective oxidative esterification of primary alcohols.
Liu, Chao,Tang, Shan,Lei, Aiwen
supporting information
p. 1324 - 1326
(2013/03/13)

Alkali metal tert-butoxides, hydrides and bis(trimethylsilyl)amides as efficient homogeneous catalysts for Claisen-Tishchenko reaction
Shelf-available alkali metal tert-butoxides, hydrides and bis(trimethylsilyl)amides were shown to be highly efficient homogeneous precatalysts for the disproportionation of aldehydes to the corresponding carboxylic esters. Potassium compounds in combination with 18-crown-6 ether could drastically increase the rate of reaction in a few cases. Alternatively, efficient aldol condensations were found for aldehydes possessing an enolizable methylene group at the α-position to the aldehyde functionality. The active species involved in this esterification using any of these alkali metal catalysts is expected to be the metal alkoxide. Potassium compounds were found to be much more efficient when compared to analogous sodium compounds and kinetic studies revealed the rate-determining step to be a second order concerted hydride transfer from a potassium hemiacetal species to another molecule of aldehyde. Copyright
Rajesh, Kunjanpillai,Berke, Heinz
supporting information
p. 901 - 906
(2013/05/08)

Synthesis, structures, and reactivities of guanidinatozinc complexes and their catalytic behavior in the Tishchenko reaction
Treatment of a secondary amine (pipH, Bz2NH, Et2NH) with sequentially diethylzinc and N,N′-dicyclohexylcarbodiimide in hexane has afforded in good yield the new crystalline guanidinatozinc complexes. Each has been X-ray and solution NMR spectrally characterized. Three are dimeric (mono)guandinatozinc alkyls, two are dinuclear (tris)guanidinatozinc amides, and one is a homoleptic zinc bis(guanidinate). The reactions of dinuclear (tris)guanidinatozinc amides with diethylzinc and N,N′- dicyclohexylcarbodiimide in the molar ratios of 1:2:1 led to the dimeric (mono)guandinatozinc alkyls; homoleptic zinc bis(guanidinate) with an equimolar portion of diethylzinc also yielded dimeric (mono)guandinatozinc alkyls. Each of the complexes exhibited good to excellent catalytic activity for the solvent-free Tishchenko reaction under mild conditions.
Li, Jie,Shi, Jingchao,Han, Hongfei,Guo, Zhiqiang,Tong, Hongbo,Wei, Xuehong,Liu, Diansheng,Lappert, Michael F.
p. 3721 - 3727
(2013/07/26)

The thiolate-catalyzed intermolecular crossed tishchenko reaction: Highly chemoselective coupling of two different aromatic aldehydes
Crossed products: Ortho-substituted benzaldehydes react with other aromatic aldehydes in a highly selective, atom-economical Tishchenko disproportionation (see scheme) in the presence of a readily prepared, inexpensive thiolate-based catalyst. The methodo
Curran, Simon P.,Connon, Stephen J.
supporting information
p. 10866 - 10870
(2013/01/15)

Significant promoting effects of Lewis acidity on Au-Pd systems in the selective oxidation of aromatic hydrocarbons
An unprecedented synergistic effect, obtained for rationally designed Au-Pd alloy nanoparticles supported on an acidic metal-organic framework (MOF), in the aerobic oxidation of the primary C-H bonds in toluene and derivates is reported.
Liu, Hongli,Li, Yingwei,Jiang, Huanfeng,Vargas, Carolina,Luque, Rafael
supporting information
p. 8431 - 8433
(2012/10/29)

Novel triarylimidazole redox catalysts: Synthesis, electrochemical properties, and applicability to electrooxidative C-H activation
A new class of metal-free, easy to synthesize redox catalysts based on a triarylimidazole framework is described. With those synthesized thus far, one can access a potential range of ca. 410 mV. They proved to be useful mediators for the activation of benzylic C-H bonds under mild conditions.
Zeng, Cheng-Chu,Zhang, Ni-Tao,Lam, Chiu Marco,Little, R. Daniel
supporting information; experimental part
p. 1314 - 1317
(2012/04/23)

Copper catalyzed oxidative esterification of aldehydes with alkylbenzenes via cross dehydrogenative coupling
Copper(II) as the catalyst in a cross dehydrogenative coupling (CDC) reaction has been demonstrated for the synthesis of benzylic esters using aldehydes and alkylbenzenes as coupling partners.
Rout, Saroj Kumar,Guin, Srimanta,Ghara, Krishna Kanta,Banerjee, Arghya,Patel, Bhisma K.
supporting information; experimental part
p. 3982 - 3985
(2012/09/22)

Dehydrogenation of alcohols under ambient atmosphere by a recyclable sol-gel encaged iridium pincer catalyst
We demonstrate that a sol-gel entrapped iridium-pincer catalyst 1 is capable of promoting acceptorless dehydrogenation of primary and secondary alcohols. Although the dehydrogenations by the non-heterogenized catalyst are faster than by the sol-gel encaged complex, recyclability and significant stabilization of the organometallic species toward non-inert conditions represent a clear advantage from the environmental and practical points of view.
Oded, Kobi,Musa, Sanaa,Gelman, Dmitri,Blum, Jochanan
experimental part
p. 68 - 70
(2012/06/16)

Selenide ions as catalysts for homo- and crossed-Tishchenko reactions of expanded scope
Selenide ions have been shown to catalyze the Tishchenko reaction for the first time. These catalysts are superior to previously reported thiolate analogues and promote the disproportionation of aldehydes with increased reaction rates and broader scope at lower catalyst loadings and temperatures. Significantly improved catalyst performance was also observed in the aryl selenide mediated crossed intermolecular Tishchenko reaction.
Curran, Simon P.,Connon, Stephen J.
supporting information; experimental part
p. 1074 - 1077
(2012/03/27)

Solvent-free oxidation of primary carbon-hydrogen bonds in toluene using Au-Pd alloy nanoparticles
Selective oxidation of primary carbon-hydrogen bonds with oxygen is of crucial importance for the sustainable exploitation of available feedstocks. To date, heterogeneous catalysts have either shown low activity and/or selectivity or have required activated oxygen donors. We report here that supported gold-palladium (Au-Pd) nanoparticles on carbon or TiO2 are active for the oxidation of the primary carbon-hydrogen bonds in toluene and related molecules, giving high selectivities to benzyl benzoate under mild solvent-free conditions. Differences between the catalytic activity of the Au-Pd nanoparticles on carbon and TiO2 supports are rationalized in terms of the particle/support wetting behavior and the availability of exposed corner/edge sites.
Kesavan, Lokesh,Tiruvalam, Ramchandra,Rahim, Mohd Hasbi Ab,Saiman, Mohd Izham Bin,Enache, Dan I.,Jenkins, Robert L.,Dimitratos, Nikolaos,Lopez-Sanchez, Jose A.,Taylor, Stuart H.,Knight, David W.,Kiely, Christopher J.,Hutchings, Graham J.
scheme or table
p. 195 - 199
(2011/09/30)

N-heterocyclic carbene based ruthenium-catalyzed direct amide synthesis from alcohols and secondary amines: Involvement of esters
A well-defined N-heterocyclic carbene based ruthenium complex was developed as a highly active precatalyst for the direct amide synthesis from alcohols and secondary amines. Notably, reaction of 1-hexanol and dibenzylamine afforded 60% of the corresponding amide using our catalytic system, while no amide formation was observed for this reaction with the previously reported catalytic systems. Unlike the previously reported amidation with less sterically hindered alcohols and amines, involvement of ester intermediates was observed (Figure presented).
Chen, Cheng,Zhang, Yao,Hong, Soon Hyeok
experimental part
p. 10005 - 10010
(2012/02/05)

Dehydrogenative coupling of primary alcohols to form esters catalyzed by a ruthenium N-heterocyclic carbene complex
The ruthenium complex [RuCl2(IiPr)(p-cymene)] catalyzes the direct condensation of primary alcohols into esters and lactones with the release of hydrogen gas. The reaction is most effective with linear aliphatic alcohols and 1,4-diols and is believed to proceed with a ruthenium dihydride as the catalytically active species.
Solvhoj, Amanda,Madsen, Robert
experimental part
p. 6044 - 6048
(2012/01/13)

A remarkable effect of ionic liquids in transition-metal-free aerobic oxidation of benzylic alcohols
The transition-metal-free aerobic oxidation of benzylic alcohols is uniquely accelerated by a 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6)/PhCF3 biphasic system and Cs2CO 3 to afford the corresponding ketones in good yields. The reaction system is also applicable to an oxidative cross-esterification of primary benzyl alcohols with a higher aliphatic alcohol.
Oda, Yoshiro,Hirano, Koji,Satoh, Tetsuya,Kuwabata, Susumu,Miura, Masahiro
scheme or table
p. 5392 - 5394
(2011/10/19)