Evans catalysis

Linear relations between the activation energies and heats of adsorption or heats of reaction have long been assumed to be valid. Such relations are called Bronsted-Evans-Polanyi relations [N. Bronsted, Chem. Rev. 5 (1928) 231 M.G. Evans and M. Polanyi, Trans. Faraday Soc. 34 (1938) 11]. In catalysis such relations have recently been found to hold for the dissociation reactions summarized in Pig. 6.42, and also for a number of reactions involving small hydrocarbon fragments such as the hydro-... 

Bligaard T, Nprskov JK, Dahl S, Matthiesen J, Chistensen CH, Sehested J. 2004. The Br0nsted-Evans-Polanyi relation and the volcano curve in heterogeneous catalysis. J Catal 224 206-217. 

The standard work of Evans [2] as well as a survey of the papers produced in the Journal of Labeled Compounds and Radiopharmaceuticals over the last 20 years shows that the main tritiation routes are as given in Tab. 13.1. One can immediately see that unlike most 14C-labeling routes they consist of one step and frequently involve a catalyst, which can be either homogeneous or heterogeneous. One should therefore be able to exploit the tremendous developments that have been made in catalysis in recent years to benefit tritiation procedures. Chirally catalyzed hydrogenation reactions (Knowles and Noyori were recently awarded the Nobel prize for chemistry for their work in this area, sharing it with Sharpless for his work on the equivalent oxidation reactions) immediately come to mind. Already optically active compounds such as tritiated 1-alanine, 1-tyrosine, 1-dopa, etc. have been prepared in this way. 

Evans et al. (219, 220) examined the use of electron-poor heterodienes as partners in cycloadditions with electron-rich alkenes under copper catalysis. In particular, a,p-unsaturated acylphosphonates and keto-esters afford hetero-Diels-Alder adducts in high selectivities when treated with enol ethers in the presence of catalysts 269c and 269d. 

This was his first venture into theorising about unexplained facts. Its central point is an extension of the new idea of co-catalysis and the application of a thermochemical argument to decide which of two reactions is the more likely. This type of argument, which goes back to M. Polanyi and M.G. Evans, was the small change of the tea-room discussions in the Chemistry Department at the University of Manchester, where H.A. Skinner, a thermochemist, was the writer s research supervisor and S.D. Hamann was a fellow research student working under A.G. Evans. 

For suitable substances the average life-time of the hydrated or unhydrated species can be deduced from the broadening of nuclear magnetic resonance lines. This has recently been applied to acetaldehyde (Evans et al., 1965 Ahrens and Strehlow, 1965) and to isobuty-raldehyde (Hine and Houston, 1965) the velocities deduced for catalysis by hydrogen ions are in fair agreement with those obtained by other methods. 

It has been shown by H naff (1963) that the rate of reaction of several carbonyl reagents (bisulphite, hydrazine, phenylhydrazine, semi-carbazide and hydroxylamine) with aqueous formaldehyde solutions is independent of the nature and concentration of the reagent, and is therefore determined by the rate of dehydration of methylene glycol. He obtained catalytic constants for hydrogen and hydroxide ions, and a detailed study of acid-base catalysis has been made by the same method by Bell and Evans (1966). 

Evans and coworkers developed C2-symmetrical copper(II) complexes as chiral Lewis acids that rely on two-dentate substrates for their catalysis. Consequently,... 

G.S.BROWN, in Synchrotron radiation research, eds. H.WINICK S.DONIACH (Plenum Press, New York 1980), p. 387 J.EVANS, in Catalysis, Royal Society of Chemistry, Specialist Periodical Report 8, 1 (1989). 

Evans DA, Johnson JS (1999) In Jacobsen EN, Pfalz A, Yamamoto H (eds) Comprehensive asymmetric catalysis, vol 3, chap 33.1. Springer, Berlin Heidelberg New York... 

The initial work on the asymmetric [4-1-2] cycloaddition reactions of A -sulfinyl compounds and dienes was performed with chiral titanium catalysts, but low ee s were observed <2002TA2407, 2001TA2937, 2000TL3743>. A great improvement in the enantioselectivity for the reaction of AT-sulfinyl dienophiles 249 or 250 and acyclic diene 251 or 1,3-cyclohexadiene 252 was observed in the processes involving catalysis with Cu(ll) and Zn(ii) complexes of Evans bis(oxazolidinone) (BOX) ligands 253 and 254 <2004JOC7198> (Scheme 34). While the preparation of enantio-merically enriched hetero-Diels-Alder adduct 255 requires a stoichometric amount of chiral Lewis acid complex, a catalytic asymmetric synthesis of 44 is achieved upon the addition of TMSOTf. 

Br0nsted-Evans-Polanyi relationships in heterogeneous catalysis... 

The Evans Cu(II)- and Sn(II)-catalyzed processes are unique in their ability to mediate aldol additions to pyruvate. Thus, the process provides convenient access to tertiary a-hydroxy esters, a class of chiral compounds not otherwise readily accessed with known methods in asymmetric catalysis. The process has been extended further to include a-dike-tone 101 (Eqs. 8B2.22 and 8B2.23). It is remarkable that the Cu(II) and Sn(II) complexes display enzyme-like group selectivity, as the complexes can differentiate between ethyl and methyl groups in the addition of thiopropionate-derived Z-silyl ketene acetal to 101. As discussed above, either syn or anti diastereomers may be prepared by selection of the Cu(II) or Sn(II) catalyst, respectively. 

Apparently, these results implied an inverse relationship between reactivity and selectivity, with the reactivity of the carbocation measured by the inverse of the rate constant for solvolysis. This indeed was not unexpected in the context of a general perception that highly reactive reagents, especially reactive intermediates such as carbocations, carbanions, or carbenes are unselective in their reactions.257 259 Such a relationship is consistent with a natural inference from the Hammond postulate258 and Bell-Evans-Polanyi relationship,260 and is illustrated experimentally by the dependence of the Bronsted exponent for base catalysis of the enolization of ketones upon the reactivity of the ketone,261,262 and other examples21,263 including Richard s careful study of the hydration of a-methoxystyrenes.229... 

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