Epoxides complex

Figure 5.1 Ternary organolithium(RLi) sparteine epoxide complex in which the proton on the (R)-epoxide stereocenter is held closer to the organolithium.

The [3-hydroxy amines are a class of compounds falling within the generic definition of Eq. 6A.6. When the alcohol is secondary, the possibility for kinetic resolution exists if the Ti-tartrate complex is capable of catalyzing the enantioselective oxidation of the amine to an amine oxide (or other oxidation product). The use of the standard asymmetric epoxidation complex (i.e., T2(tartrate)2) to achieve such an enantioselective oxidation was unsuccessful. However, modification of the complex so that the stoichiometry lies between Ti2 (tartrate) j and Ti2(tartrate)1 5 leads to very successful kinetic resolutions of [3-hydroxyamines. A representative example is shown in Eq. 6A.11 [141b,c]. The oxidation and kinetic resolution of more than 20 secondary [3-hydroxyamines [141,145a] provides an indication of the scope of the reaction and of some... 

According to the Baldwin rule, the exo cyclization mode is favored in intramolecular reactions of alkynyloxiranes with alcohols to afford cyclic ethers. However, the unfavorable endo cyclization mode is observed by the complexation. Thus exclusive endo cyclization of epoxide complex 146 takes place regioselectively to give 147, without forming the five-membered ether 148 by exo mode reaction [37]. 

Vitamin K reductase epoxide complex International normalized ratio Thiopurine methyltransferase... 

The first isolated and characterised species that could be envisioned as intermediates in the initiation step for the coordination polymerisation of epoxides when using metal carboxylate catalysts were complexes formed between cadmium carboxylates, solubilised in organic solvents by the tris-3-phenylpyrazole hydroborate ligand, and epoxides such as propylene oxide and cyclohexene oxide [68]. Other epoxide complexes with various metal derivatives have also been reported in the literature [69-72],... 

A final possibility was raised by the observation that (Cp Re0)2(jU.-0)2 deoxygenated epoxides. Migration of carbon not to rhenium but to oxygen would result in a Re(V)-epoxide complex ... 

The allylic alcohol binds to the remaining axial coordination site where stereochemical and stereoelec-tronic effects dictate the conformation shown in Figure 5. The structural model of catalyst, oxidant and substrate shown in Figure 5 illustrates a detailed version of the formalized rule presented in Figure 1. Ideally, all the observed stereochemistry of epoxy alcohol and kinetic resolution products can be rationalized according to the conq>atibility of their binding with the stereochemistry and stereoelectronic requirements imposed by this site. A transition state model for the asymmetric epoxidation complex has been calculated by a frontier orbital preach and is consistent with the formulation portrayed in Figure... 

Studies in a cryogenic matrix provide evidence for epoxide complexes of chromium(iv) complexes <1999IC2106>. The mechanism of chromyl chloride epoxidation has been evaluated <2003JA11188>. 

The mechanism of the Jacobsen HKR and ARO are analogous. There is a second order dependence on the catalyst and a cooperative bimetallic mechanism is most likely. Both epoxide enantiomers bind to the catalyst equally well so the enantioselectivity depends on the selective reaction of one of the epoxide complexes. The active species is the Co(lll)salen-OH complex, which is generated from a complex where L OH. The enantioselectivity is counterion dependent when L is only weakly nucleophilic, the resolution proceeds with very high levels of enantioselectivity. 

Absorbance vs time curves for guanosine-5 -monophosphate (GMP) are not monoexponential, as observed with the other substrates. The decay curves for GMP oxidation are sigmoidal in shape, as shown in Fig. 15. This behavior is consistent with formation of a bound, colored intermediate and eventual overoxidation of the substrate where the first step is much slower than the subsequent steps. Thus, initial oxidation of GMP produces a species that is oxidized more rapidly than GMP itself Oxidation of trans-stilbene by Ru(IV)0 occurs with an initial rate-determining step corresponding to the formation of a bound epoxide complex Ru(III)(epoxide), and other oxo-transfer reactions of Ru(IV)0 proceed via similar initial steps 130, 190). These bound... 

Proton removal at the J -epoxide stereocentre is consistently seen in the enan-tioselective a-deprotonation-rearrangement of epoxides using the sparteines this enantioselectivity may be explained by considering a sparteine-RLi-epoxide complex 86, where the C-H bond on the epoxide R stereocentre is held closer to the organolithium than the S stereocentre, minimising non-bonded interactions between sparteine and the epoxide (Scheme 14). 

A catalytic cycle starting from the formation of a catalyst-epoxide complex that further reacts with the thione tautomer of the thiobenzoic add 17 (Scheme 3.7) was computed. Full molecule of the catalyst was used in the PCM-M06-2X/6-31H-G V/M06-2X/6-31G computations. 

A series of Ceo complexes of the type [Rh(acac)(T 2-C6o)(pyridine)2] have been reported and the X-ray crystal structure with 3,S-dimethylpyridine has been determined. The formation and structural characterisation of the fullerene epoxide complex [Ir(r -C6oO)(CO)Cl(PPh3)2] has been described. The synthesis of [Ir(li2.C6o)(CO)(H)(PPh3)2] has been reported. Multiple additions of Vaska-type iridium complexes to have been shown to result in preferential crystallisation of the "para" double addition products C6o) If(CO)Cl(PR3)2 2l (R = Me, Et). The X-ray crystal structure of [ (112-C84)(CO)Cl(PKi3)2l has been reported . 

Some 0X0 complexes of manganese have been found to be capable of transferring the oxygen atom selectively to an alkene to give an epoxide. Complex 8.28 shows a general structure for such complexes. 

A remarkably simple and effective Mn-based epoxidation system, using 1.0-0.1 mol% of MnS04, no ligands and 30% aqueous H2O2 as the oxidant in the presence of bicarbonate, was introduced by Burgess [9, 87]. Bicarbonate and H2O2 form the actual oxidant peroxy monocarbonate (Scheme 10.14), which is proposed to react with the Mn-ion to generate the active epoxidation complex, as was supported by EPR studies [87, 88]. 

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