Oxidative resolution

Whereas the chiral TEMPO analog 87 was used to resolve racemic secondary alcohols, the D-fructose-derived ketone 88 [137] proved useful for oxidative resolution of racemic diols (Table 10.13) [138, 139], Persulfate in the form of Oxone, Curox, etc., served as the final oxidizing agent, and the dioxirane generated from the ketone 88 is the chiral active species. Because of the relatively low conversions (except for unsubstituted dihydrobenzoin) at which the ee stated were achieved, the method currently seems to be of less practical value. Furthermore, typically 3 equiv. ketone 88 had to be employed [138, 139]. 

The bis(phosphane oxide) resolution route to (S)-MeOBIPHEP (S-29), the ligand for the geraniol hydrogenation, was successfully developed to a larger scale process (Fig. 11). In this process, phosphinoylation of 3-bromoanisole was realized... 

CTEM enables particle size to be measured but without making it possible to distinguish between the precious metal particles and the particles of Ce and/or Fe oxides (resolution of the apparatus used = 0.7 nm). 

Dziuba K, Flis A, Szmigielska A, Pietrusiewicz KM (2010) Efficient oxidative resolution of a F-stereogenic triarylphosphine and asymmetric synthesis of a F-stereogenic atropoisomeric biphenyl diphosphine dioxide. Tetrahedron Asymmetry 21 1401-1405... 

A special variant of resolution is called oxidative resolution, because it yields optically pure phosphine oxides from racemic phosphines. To this end, Keay and co-workers" used the Staudinger reaction between racemic phosphines and an optically pure azide (Scheme 2.3). 

Pietrusiewicz and co-workers" resolved a bicyclic phosphole by an oxidative resolution protocol via a phosphonium salt (Scheme 2.4). 

Scheme 2.3 Oxidative resolution of phosphines using intermediate phosphinimines.

Scheme 2.4 Oxidative resolution of rac-Vl using an intermediate phosphonium salt.

Ru(II) (15, 25 )-iV-/ -toluenesulfonyl-l,2-diphenylethylenediamine [Ru(II) S,S)-TsDPEN] has catalysed the oxidative resolution of the allylic alcohols (4) (Scheme 2). The hydrogen transfer occurs from the secondary allylic site rather than the primary... 

Recently, a cascade process for the simultaneous preparation of two enantiopure secondary alcohols by the same ADH was investigated [12]. In this work, a kinetic oxidative resolution of different secondary alcohols was coupled with the irreversible asymmetric reduction of selected prochiral activated ketones, that is, a-chloro ketones (Scheme 11.5a). The proposed strategy, named PIKAT (parallel intercoimected kinetic asymmetric transformations), represents an example of redox neutral (or self-sufficient) cascade, with no additional reducing or oxidizing reagents being required. Moreover, the reaction was catalyzed by a single enzyme in the presence of catalytic amounts of the cofactor. As the outcome of the cascade process is a mixture of two different enantioenriched products, substrates were properly selected on the basis of different physical properties. 

Figure Bl.25.2 shows the XPS spectra of two organoplatinum complexes which contain different amounts of chlorine. The spectrum shows the peaks of all elements expected from the compounds, the Pt 4f and 4d doublets (the 4f doublet is iimesolved due to the low energy resolution employed for broad energy range scans). Cl 2p and Cl 2s, N Is and C Is. Flowever, the C Is caimot be taken as characteristic for the complex only. All surfaces that have not been cleaned by sputtermg or oxidation in the XPS spectrometer contain carbon. The reason is that adsorbed hydrocarbons from the atmosphere give the optimum lowering of the surface free energy and hence, all surfaces are covered by hydrocarbon fragments [9].

Because of these difficulties, special mechanisms were proposed for the 4-nitrations of 2,6-lutidine i-oxide and quinoline i-oxide, and for the nitration of the weakly basic anilines.However, recent remeasurements of the temperature coefficient of Hq, and use of the new values in the above calculations reconciles experimental and calculated activation parameters and so removes difficulties in the way of accepting the mechanisms of nitration as involving the very small equilibrium concentrations of the free bases. Despite this resolution of the difficulty some problems about these reactions do remain, especially when the very short life times of the molecules of unprotonated amines in nitration solutions are considered... 

Enzymatic fat splitting Enzymatic hydrolysis Enzymatic methods Enzymatic oxidation Enzymatic resolutions... 

Deamination, Transamination. Two kiads of deamination that have been observed are hydrolytic, eg, the conversion of L-tyrosiae to 4-hydroxyphenyUactic acid ia 90% yield (86), and oxidative (12,87,88), eg, isoguanine to xanthine and formycia A to formycia B. Transaminases have been developed as biocatalysts for the synthetic production of chiral amines and the resolution of racemic amines (89). The reaction possibiUties are illustrated for the stereospecific synthesis of (T)-a-phenylethylamine [98-84-0] (ee of 99%) (40) from (41) by an (5)-aminotransferase or by the resolution of the racemic amine (42) by an (R)-aminotransferase. 

Although x-rays probe inner rather than valence electrons, in light elements the chemical state of the emitting atom may affect inner-shell energies enough to be detected at high resolution. Thus the K d lines of sulfur at 0.537 nm shift by 0.3 pm between the oxidation states and. ... 

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