ReviewMetal-catalyzed asymmetric sulfoxidation, epoxidation and hydroxylation by hydrogen peroxide
Graphical abstract
Introduction
Oxidation catalysis is an important domain of chemical research. Numerous applications exist nowadays in the fine chemical industry. The nature of the terminal oxidant is often crucial for the efficiency of oxidation reactions, and typical oxygen-transfer reagents include alkyl hydroperoxides, iodosylbenzene, peroxycarboxylic acids, hypochlorite, dioxygen and oxone. Despite significant efforts to utilize H2O2 in asymmetric oxidation catalysis, only a few general systems work well with this abundant, environmentally benign, atom-economical and relatively safe oxidant [1], [2]. However hydrogen peroxide is probably the best terminal oxidant after dioxygen with respect to environmental and economic consideration [1], [3]. It is also very attractive because its solubility in water and many organic solvents is quite large. As a result, oxidation systems that use hydrogen peroxide in conjunction with catalytic amount of cheap, relatively non-toxic metals such as iron, and to a less extent manganese, are highly desired for application in pharmaceutical area. Despite significant efforts to utilize H2O2 in asymmetric oxidation catalysis, only a few general systems are efficient with this environmentally benign oxidant [2]. The only side-product when using hydrogen peroxide as oxidant is a water molecule. However, the two main difficulties of using hydrogen peroxide in the presence of transition metal complexes are the homolytic cleavage generating OH radicals and the catalase reaction with formation of dioxygen [4].
Recently, however, there has been a revival in developing original and efficient system in asymmetric catalysis [5]. Thus we have now the development of new generations of metal complexes which are able to selectively catalyze various oxidation reactions. In this review the focus is on promising asymmetric oxidation systems using hydrogen peroxide as oxidant and metal-based catalysts. Organic catalysts designed for asymmetric oxidation may also operate with hydrogen peroxide [2], [6], [7], [8] but they are beyond the scope of this review. Direct use of hydrogen peroxide as primary oxidant, in the Baeyer–Villiger oxidation has also been reported [9]. However, only a few catalysts are used in combination with hydrogen peroxide as the oxidant for enantioselective reactions [10], [11], [12]. Consequently, this reaction will not be developed in the present review, there are excellent reviews on this topic [9], [13], [14].
Section snippets
Asymmetric sulfoxidation
The selective oxidation of sulfides to sulfoxides has attracted much attention over the years after the pioneering work of Kagan and coworkers [15] and Modena and coworkers [16]. Hydrogen peroxide, however, has to be used in a controlled manner, due to the possibility of an over-oxidation reaction since possible formation of sulfones is also observed in various reactions as by-products [17]. This formation may suggest the existence of a kinetic resolution process during the course of the
Asymmetric epoxidation of alkenes
Catalytic asymmetric epoxidation reactions play a major role in organic chemistry since the optically active epoxides are important building blocks [1], [115], [116]. In particular, catalytic asymmetric reactions in aqueous solutions are attractive, but rare [7]. Therefore until 2006, results obtained in the asymmetric epoxidation with H2O2 and chiral metal catalysts have been rather disappointing [5]. It is only quite recently, however, that the metal-catalyzed asymmetric epoxidation of
Asymmetric dihydroxylation of alkenes
The development of the osmium catalyzed asymmetric cis-dihydroxylation of alkenes by Sharpless and coworkers [192], [193] is invaluable to synthetic organic chemistry. However, the cost and toxicity of the osmium based asymmetric cis-dihydroxylation system, prevents their widespread industrial application. This has provided a strong driving force for the identification and development of economically viable and environmentally benign methods based on first row transition metals and H2O2 [194],
Asymmetric hydroxylation of alkanes
The functionalization of CH bonds of alkanes is one of the most difficult transformation in synthetic chemistry [203], [204], [205]. Nevertheless, these reactions are catalyzed by a variety of metalloenzymes, among which the most diverse are the many members of the cytochrome P-450 family [206]. Thus the extracellular heme-thiolate peroxygenase from Agrocybe aegerita hydroxylates alkanes and numerous other substrates using hydrogen peroxide as the terminal oxidant [207], [208]. However the
Conclusion
Most of the work presented herein indicates that the asymmetric oxidation using chiral metal complexes as catalysts and hydrogen peroxide as oxidant is possible, with good results. Diastereo- and enantioselectivities comparable to those obtained with different oxidants are observed in organic solvents and in water. This is true for sulfoxidation reaction and in a less extent for epoxidation reaction. Although the number of efficient systems is relatively high, their development must be widened
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2022, PolyhedronCitation Excerpt :Metalloenzymes such as Cytochrome P-450, which contains Fe at the active site, catalyze various oxidation reactions, including alkene epoxidation under mild conditions [14-17]. This inspired chemists to develop biomimetic catalysts using first-row-transition metals like Fe, Co and Mn under mild conditions [5,18-29]. Several Mn-containing complexes modelled on Cytochrome P-450 were reported to efficiently catalyze olefin epoxidation [30-35].
Peroxides in metal complex catalysis
2021, Coordination Chemistry ReviewsCitation Excerpt :For example, [Ti(OiPr)4] catalyzed enantioselective oxidation (Sharpless epoxidation) of prochiral allylic alcohols with tBuOOH was achieved in the presence of chiral non racemic tartrates (Scheme 3) [74–76]. The metal-mediated/catalyzed peroxidative functionalization of organic compounds has been intensively developed, and a number of reviews have already been published: dioxygen complexes for catalytic oxidations [77,78], peroxo complexes of vanadium, molybdenum and tungsten for oxidation of organic compounds [79], peroxy, peroxo and oxo metal complexes in catalytic oxidations [80], transition metal peroxides for oxidation reactions [81], oxoperoxomolybdenum(VI) complexes for olefin epoxidation [82], metal complexes catalyzed peroxidative oxidation of hydrocarbons [83], vanadium and molybdenum peroxides in oxidation reactions [84], organocatalytic and metal complex catalyzed asymmetric oxidations with dioxygen and peroxides [85,86], selective C−H oxidations and epoxidations/cis-dihydroxylations with hydrogen peroxide, catalysed by non-heme iron and manganese complexes [87], metal-catalyzed asymmetric sulfoxidation, epoxidation and hydroxylation by hydrogen peroxide [88], manganese catalysed oxidation of alkenes with hydrogen peroxide [89], metal catalyzed oxidation of alkanes, arenes and alkenes with hydrogen peroxide [90] and amphoteric reactivity of metal–oxygen complexes in oxidation reactions [91]. In contrast to the above reviews, herein we discuss selected recent examples on the role of peroxides in metal complex catalyzed functionalization of different and relevant classes of organic compounds, namely alkanes, alkenes, alkynes, aromatics, heterocycles, aldehydes, ketones and alcohols.