Uncatalysed hydrogen-transfer reductions of aldehydes and ketones

Bagnell, Laurence; Strauss, Christopher R.

doi:10.1039/a808977i

Cited by 26 publications

(11 citation statements)

References 11 publications

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“…Catalysts capable of this kind of reactivity are generally based on electropositive metals like Al or lanthanides, even if some examples have been reported with Ir catalysts (Scheme 4) [15,[31][32][33]. Even if some examples of reduction of aldehydes or ketones by 2-propanol or ethanol in absence of any catalyst at high temperature (225°C, 30 h) have been reported [29], the metal catalyzed process is the best option for the synthesis of alcohols by reduction of the corresponding ketones. The mechanism of the catalytic transfer hydrogenation is related to the catalyst employed.…”

Section: Scheme 3 Transfer Hydrogenation From a Generic Donor Agent mentioning

confidence: 99%

“…On the short list of hydrogen donors employed for the TH there are also the Hantzsch's esters ( Figure 1) [28], which have been used as mimics of the reactivity of the biofactor NADH. Even if some examples of reduction of aldehydes or ketones by 2-propanol or ethanol in absence of any catalyst at high temperature (225 ℃, 30 h) have been reported [29], the metal catalyzed process is the best option for the synthesis of alcohols by reduction of the corresponding ketones. The mechanism of the catalytic transfer hydrogenation is related to the catalyst employed.…”

Section: Scheme 3 Transfer Hydrogenation From a Generic Donor Agent mentioning

confidence: 99%

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Transfer Hydrogenation from 2-propanol to Acetophenone Catalyzed by [RuCl2(η6-arene)P] (P = monophosphine) and [Rh(PP)2]X (PP = diphosphine, X = Cl−, BF4−) Complexes

2020

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The reduction of ketones through homogeneous transfer hydrogenation catalyzed by transition metals is one of the most important routes for obtaining alcohols from carbonyl compounds. The interest of this method increases when opportune catalytic precursors are able to perform the transformation in an asymmetric fashion, generating enantiomerically enriched chiral alcohols. This reaction has been extensively studied in terms of catalysts and variety of substrates. A large amount of information about the possible mechanisms is available nowadays, which has been of high importance for the development of systems with excellent outcomes in terms of conversion, enantioselectivity and Turn Over Frequency. On the other side, many mechanistic aspects are still unclear, especially for those catalytic precursors which have shown only moderate performances in transfer hydeogenation. This is the case of neutral [RuCl 2 (η 6 -arene)(P)] and cationic [Rh(PP) 2 ]X (X = anion; P and PP = monoand bidentate phosphine, respectively) complexes. Herein, a summary of the known information about the Transfer Hydrogenation catalyzed by these complexes is provided with a continuous focus on the more relevant mechanistic features. Abstract:The reduction of ketones through homogeneous transfer hydrogenation catalyzed by transition metals is one of the most important routes for obtaining alcohols from carbonyl compounds. The interest of this method increases when opportune catalytic precursors are able to perform the transformation in an asymmetric fashion, generating enantiomerically enriched chiral alcohols. This reaction has been extensively studied in terms of catalysts and variety of substrates. A large amount of information about the possible mechanisms is available nowadays, which has been of high importance for the development of systems with excellent outcomes in terms of conversion, enantioselectivity and Turn Over Frequency. On the other side, many mechanistic aspects are still unclear, especially for those catalytic precursors which have shown only moderate performances in transfer hydeogenation. This is the case of neutral [RuCl2( 6 -arene)(P)] and cationic [Rh(PP)2]X (X = anion; P and PP = mono-and bidentate phosphine, respectively) complexes. Herein, a summary of the known information about the Transfer Hydrogenation catalyzed by these complexes is provided with a continuous focus on the more relevant mechanistic features.The possibility to reduce ketones to alcohols in an enantioselective way through ATH represents a milestone in the asymmetric catalysis, as chiral alcohols are employed as intermediates, as well as end-products in many industries, including fragrancies and pharmaceutics [2]. In addition, the protocol can be extended to a general C=X polar substrate (X = O, N), allowing the synthesis of chiral alcohols [2], amines, and many corresponding derivatives [3].Recent applications of such protocol have allowed the valorization of biomass by extracting lignin [4], or for the production of biofuels [5].Historically, a ...

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Section: Scheme 3 Transfer Hydrogenation From a Generic Donor Agent mentioning

confidence: 99%

Section: Scheme 3 Transfer Hydrogenation From a Generic Donor Agent mentioning

confidence: 99%

Transfer Hydrogenation from 2-propanol to Acetophenone Catalyzed by [RuCl2(η6-arene)P] (P = monophosphine) and [Rh(PP)2]X (PP = diphosphine, X = Cl−, BF4−) Complexes

2020

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“…It has been reported that this process is feasible and that aryl and alkyl aldehydes and, to a lesser extent, ketones can be reduced to the relevant alcohols upon simple heating at high temperature with ethanol or 1 -or 2 -propanol (but not methanol) [15] . One possibility is that the migration of covalently bonded hydrogen from the hydroxy -substituted sp 3 -C of an alcohol to the sp 2 -C of a carbonyl group takes place under purely thermal conditions in the absence of any metal, base or acid catalyst.…”

Section: Mechanismsmentioning

confidence: 99%

Reduction of Carbonyl Compounds by Hydrogen Transfer

Gladiali

Taras

2008

Modern Reduction Methods

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“…We recently reported a modified Meerwein±Ponndorf±Verley reduction in which low-boiling alcohols such as EtOH and n-PrOH, but preferably i-PrOH, were used at temperatures near 225 8C in the absence of aluminum alkoxides [42]. The carbonyl moiety of an olefinic aldehyde such as cinnamaldehyde was reduced selectively to the alcohol without the carbon±carbon double bond being affected (Scheme 2.7).…”

Section: Uncatalyzed Hydrogen-transfer Reductionmentioning

confidence: 99%

Microwave‐Assisted Organic Chemistry in Pressurized Reactors

Strauss

2002

Microwaves in Organic Synthesis

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The highest priorities for the chemical industry now are process and product safety and the environment [1±5]. New technologies and methods for ªgreenº and sustainable chemistry are subjects of intense activity [6]. In that regard, the potential of microwave heating for organic synthesis attracted interest soon after the first reports [7, 8] appeared in 1986. Early reactions were performed with domestic microwave ovens and relatively primitive containers. Rate enhancement of up to three orders of magnitude was observed, but the time savings were offset by hazards such as deformation of the vessels and explosions.Thus, the major challenge confronting the early microwave chemists was to retain or enhance the benefits of the technology while concurrently avoiding the risks. Several groups concluded that microwave heating was incompatible with organic solvents and investigated solvent-free conditions including ªdryº media, usually with open vessels in domestic microwave ovens [9±12]. That area expanded rapidly, aided by the ready availability of inexpensive microwave equipment and encouraged by a diverse range of reactions awaiting exploration.Synthetic chemists desire well defined reaction conditions. Process chemists demand them. Nonuniform heating and difficulties with mixing and temperature measurement are technical constraints that initially limited the scale of microwave chemistry with ªdryº media and have not yet been overcome. Poor reproducibility also has been reported, probably resulting from differences in performance and operation of individual domestic microwave ovens [13±15]. Consequently, most, if not all, of the disclosed applications of ªdryº media are laboratory-scale preparations. However, as discussed in other chapters, this does not prevent their being interesting and useful.An alternative approach, developed by Bose [16±19] and termed ªmicrowave-induced organic reaction enhancementº (MORE) chemistry, employed polar, high-boiling solvents with open vessels in unmodified domestic microwave ovens. The solvents had dielectric properties suitable for efficient coupling of microwave energy and rapid heating to temperatures that although high, were typically some 20±30 8C 35Microwaves in Organic Synthesis. Edited by Andr Loupy

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Uncatalysed hydrogen-transfer reductions of aldehydes and ketones

Cited by 26 publications

References 11 publications

Transfer Hydrogenation from 2-propanol to Acetophenone Catalyzed by [RuCl2(η6-arene)P] (P = monophosphine) and [Rh(PP)2]X (PP = diphosphine, X = Cl−, BF4−) Complexes

Transfer Hydrogenation from 2-propanol to Acetophenone Catalyzed by [RuCl2(η6-arene)P] (P = monophosphine) and [Rh(PP)2]X (PP = diphosphine, X = Cl−, BF4−) Complexes

Reduction of Carbonyl Compounds by Hydrogen Transfer

Microwave‐Assisted Organic Chemistry in Pressurized Reactors

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