Catalytic asymmetric decomposition

Electronically conducting polymers (ECPs) such as polyaniline (PANI), polypyrrole (PPy) and po 1 y(3.4-cthy 1 cncdi oxyth iophcnc) (PEDOT) have been applied in supercapacitors, due to their excellent electrochemical properties and lower cost than other ECPs. We demonstrated that multi-walled carbon nanotubes (CNTs) prepared by catalytic decomposition of acetylene in a solid solution are very effective conductivity additives in composite materials based on ECPs. In this paper, we show that a successful application of ECPs in supercapacitor technologies could be possible only in an asymmetric configuration, i.e. with electrodes of different nature. 

The seminal report of an asymmetric homogeneous metal-catalyzed reaction described the copper-catalyzed group-transfer reaction from a diazoester to an alkene, Eq. 3 (2). This article provided experimental verification of the intervention of copper carbenoid olefin complexes in the catalytic decomposition of diazo com-... 

In summary, the metal-catalyzed decomposition of diazo compounds results in a broad array of opportunities for the development of new asymmetric catalytic transformations. In the last few years considerable advances have been made in enantioselective intermolecular C-H insertion, novel cycloadditions, and tandem cyclization/cycloadditions. These new transformations offer new strategies for the rapid enantioselective construction of complex structures. 

However, at this stage relatively little progress has been made in research on asymmetric catalytic carbene transfer to imines. In 1995, Jacobsen and Jorgensen reported independently that reaction of ethyl diazoacetate with selected imines can be catalyzed by copper salts [27,28]. In the former case [27], moderate levels of enantioselection were found to be imparted by bisoxazoline ligands associated with the copper catalyst (Scheme 11). The observation of racemic pyrrolidine byproducts in the reaction was taken to support a mechanism of catalysis involving initial formation of a copper-bound azomethine yhde intermediate (Scheme 12 ). Collapse of this intermediate to the optically active aziridine apparently competes with dissociation of the copper to a free azomethine ylide. The latter can react with fumarate formed by diazoester decomposition in a dipolar cycloaddition to afford racemic pyrrolidine. 

An elegant example of the combination of infrared studies with kinetic and thermodynamic data to determine the overall mechanism of a catalytic reaction is the catalytic decomposition of formic acid. Its decomposition on silica-supported nickel has been investigated by several groups namely, Fahrenfort and co-workers (17, 69), Clarke and Pullin (70) and Hirota, Kuwata, and Nakai (71). Fahrenfort and Coworkers identified the prominent bands at 1575 and 1360 cm-1 as typical of carboxylate ions by comparison with the spectrum of nickel formate. These bands were assigned to the symmetrical and asymmetrical vibration of the O-C-O group, respectively. They showed that these bands were absent in the spectrum of formic acid adsorbed on the support. The formation of carboxylate ion (1575 cm-1 band) at room temperature was faster than the response time of the instrument, which was about 10 sec. The proposed mechanism is ... 

The chemistry of copper carbenoids involved in the catalytic decomposition of diazo compounds and related tosylhydrazones has been reviewed. Many aspects of these catalytic transformations are covered including not only the classical cyclopropanation and X-H insertion processes but also a range of formal cycloaddition reactions, the reactions involving ylide formation, and the various coupling reactions of diazo derivatives. An account more focused on asymmetric metal-catalysed X-H insertion has been published. Through this review, the dependence on the nature of the metal and its i ligands can be evaluated for these 0-H, N-H, S-H, and Si-H insertions of carbenoids. 

From all of them, highly enantioseleetive eyelopropanes are formed by asymmetric catalytic insertion of carbene to prochiral olefins. This method, first employed by Noyori in 1966 [72] consists in the metal-catalyzed decomposition of substituted diazo compounds in the presence of various prochiral alkenes. 

Catalytic, enantioselective cyclopropanation enjoys the unique distinction of being the first example of asymmetric catalysis with a transition metal complex. The landmark 1966 report by Nozaki et al. [1] of decomposition of ethyl diazoacetate 3 with a chiral copper (II) salicylamine complex 1 (Scheme 3.1) in the presence of styrene gave birth to a field of endeavor which still today represents one of the major enterprises in chemistry. In view of the enormous growth in the field of asymmetric catalysis over the past four decades, it is somewhat ironic that significant advances in cyclopropanation have only emerged in the past ten years. 

Certain transition metal complexes catalyze the decomposition of diazo compounds. The metal-bonded carbene intermediates behave differently from the free species generated via photolysis or thermolysis of the corresponding carbene precursor. The first catalytic asymmetric cyclopropanation reaction was reported in 1966 when Nozaki et al.93 showed that the cyclopropane compound trans- 182 was obtained as the major product from the cyclopropanation of styrene with diazoacetate with an ee value of 6% (Scheme 5-56). This reaction was effected by a copper(II) complex 181 that bears a salicyladimine ligand. 

The breakthrough came already in 1996, one year after Curd s prediction, when Yang and coworkers reported the C2-symmetric binaphthalene-derived ketone catalyst 6, with which ee values of up to 87% were achieved. A few months later, Shi and coworkers reported the fructose-derived ketone 7, which is to date still one of the best and most widely employed chiral ketone catalysts for the asymmetric epoxidation of nonactivated alkenes. Routinely, epoxide products with ee values of over 90% may be obtained for trans- and trisubstituted alkenes. Later on, a catalytic version of this oxygen-transfer reaction was developed by increasing the pH value of the buffer. The shortcoming of such fructose-based dioxirane precursors is that they are prone to undergo oxidative decomposition, which curtails their catalytic activity. 

The results do not prove that in the reaction conditions used the alkyl formation is not reversible, but only that, if it is reversible, the carbon monoxide insertion on both diastereomeric rhodium-alkyls must be much faster than the rhodium-alkyls decomposition. Restricting this analysis of the asymmetric induction phenomena to the rhodium-alkyl complexes formation, two 7r-olefin complexes are possible for each diastereomer of the catalytic rhodium complex (see Scheme 11). The induction can take place in the 7r-olefin complexes formation (I — II(S) or I — II(R)) or in the equilibrium between the diastereomeric 7r-olefin complexes (II(r) and... 

The first reports on iron-catalyzed aziridinations date back to 1984, when Mansuy et al. reported that iron and manganese porphyrin catalysts were able to transfer a nitrene moiety on to alkenes [90]. They used iminoiodinanes PhIN=R (R = tosyl) as the nitrene source. However, yields remained low (up to 55% for styrene aziridination). It was suggested that the active intermediate formed during the reaction was an Fev=NTs complex and that this complex would transfer the NTs moiety to the alkene [91-93]. However, the catalytic performance was hampered by the rapid iron-catalyzed decomposition of PhI=NTs into iodobenzene and sulfonamide. Other reports on aziridination reactions with iron porphyrins or corroles and nitrene sources such as bromamine-T or chloramine-T have been published [94], An asymmetric variant was presented by Marchon and coworkers [95]. Biomimetic systems such as those mentioned above will be dealt with elsewhere. 

The importance, for catalytic activity, of metal sites exhibiting different coordination environments has been evaluated by using asymmetrically coordinated dinuclear species [103b]. A mixture of l,4,7-trimethyl-l,4,7-triazacyclono-nane (Me3tacn) and bpy yielded bis(p-oxo)p-carboxylato) [Me3(tacn)MnmMnIV (bpy)], 54, the first such complex. This was indeed catalytically active, but still at the same low level (105 slower than catalase) as other symmetrical models. Nevertheless, the requirement for two metals for catalysis was confirmed since decomposition of the dinuclear species yields inactive, but similarly coordinated mononuclear complexes. 

Some optically active 3-alkoxycarbonyl-2-methylisoxazolidines were obtained by asymmetric decomposition in the presence of catalytic amount of Pd-BINAP complex. For instance, the kinetic resolution of racemic 105 by 106 afforded (+)-105 in 48% yield and with... 

The Sharpless AE of allylic alcohols has become a benchmark classic in catalytic asymmetric synthesis [52a,b] and has found use in some industrial applications [52c]. Although this catalytic process seems to be well understood, a heterogeneous system would be advantageous as it could avoid a complicated separation of the product from the catalyst, which can lead to decomposition of the epoxide formed [52c]. However, only a few heterogeneous versions of this important reaction have been conducted successfully [43, 51c, 53]. 

Davies has further exploiled his previously reporied approach to (he tropanc skeleton related to cocaine based on the rhodium catalyzed decomposition of the vinyidiazomethane 81 in the presence of A/-Boc-pyrroIe (82) <01BMCL487>. Reduction of the non-conjugated double bond followed by A -deprotection and N-alkylation provided substrate 83 which was susceptible to conjugate addition of nucleophiles such as 84 in the presence of CuBr to afford 3-p-aryl tropanes which exhibited potent binding affinity for both the dopamine and serotonin transporters. Additionally, this author described the synthesis of various methyl heteroaryldiazoacetate analogues of 81, (me of which possessed an indole function, for use in catalytic asymmetric cyclopropanations . 

Terent yev A.P. and Klabunovskii E.I. (1953) Catal54ic asymmetric synthesis. I. Asymmertric decomposition of racemic 2-butanol over Cu-quartz catalysts. Comm. I., in Collection of papers on General Chemistry russ.), V.2, 1521-1529 Chem. Abstr. 1955,49,5262E Terent yev A.P. and Klabunovskii E.I. (1953) Catalytic asymmetric synthesis. Comm. II. Asymmetric decomposition of 2-butanol over quartz-catalysts, in Collection of papers on General Chemistry (russ.)y.2, 1598-1604 Chem. Abstr. 1955,49, 5262g. 

Method c) is exemplified in the chiral modification of surfaces of zeolites with chiral compounds. Sundarababu et al. modified NaX and NaY zeolites with (-)-ephedrine and used them in the asymmetric photolysis of ketones with ee s above 10%. A strange behavior of the nature of carriers for the configuration of products in the latter reaction was observed the NaY-(-)-ephedrine zeolite system gave (+)-rotating products, while the NaX-(-)-ephedrine zeolite system gave (-)-rotating products. Zeolite H-Y modified with R)- or (5)-dithiane-l-oxide showed catalytic activity in the asymmetric decomposition of racemic 2-butanol (Hutchings)... 

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