Mechanisms epoxide ring opening

CRV737) A critical discussion of the mechanisms of ring-opening of epoxides by nucleophiles. 

Scheme 60 Mechanism for titanocene-catalyzed epoxide ring opening and tandem reaction...

In the first step, a cyclic intermediate is generated by a suprafacial addition, followed by a SN2-type ring opening (e.g., halogenation or epoxidation ring opening). In this manner, olefin 1 may either be converted into diastereomer 2 or 3, which may be optically active or racemic. Mechanism control thus means that the relative, but not the absolute, configuration of the two vicinal centers is defined. 

Investigation of the mechanism and of the selectivity of epoxide ring openings have been performed 84 100-102 117 120 however, further systematic investigations are necessary. 

Write the steps in the mechanism for ring-opening reactions of ethylene oxide and other epoxides. 

Characteristic of these models of active sites is the appearance of the OZn O Zn(0)Et species. Considering the structural properties of the discussed catalysts as well as the polymer chain microstructure and the structure of the end groups of poly(propylene oxide) obtained with the PhOZnOCeHi ( -Bu)OZnEt catalyst, a concerted mechanism of epoxide ring-opening polymerisation with catalysts containing multinuclear species, including those with condensed zinc atoms, has been postulated [65,74] ... 

Mechanism 14-4 Base-Catalyzed Opening of Epoxides 653 14-14 Orientation of Epoxide Ring Opening 654 14-15 Reactions of Epoxides with Grignard and Organolithium Reagents 656 14-16 Epoxy Resins The Advent of Modern Glues 656 Summary Reactions of Epoxides 658 EssentialTerms 660 Study Problems 662... 

A variety of mechanisms may participate in the displacement reactions surveyed above. Some displacements, including tosylates and some epoxide ring openings, occm with the high degrees of inversion of configmation expected... 

Enzyme-catalyzed epoxide ring opening including discussion of convergent families of epoxide hydrolases, the catalytic mechanism of microsomal epoxide hydrolases, epoxide hydrolases in metabolism, and the synthesis, structure, and mechanism of leukotriene A4 hydrolase, and glutathione transferase has been reviewed by Armstrong <1999CONAP(5)51>. 

The mechanism of the Wharton transposition is very simiiar to that of the Woiff-Kishner reaction. The epoxyhydrazone is first deprotonated, which triggers the faciie and irreversible epoxide ring-opening. The C-N bond of the resuiting vinyi diazene is broken upon another deprotonation, releasing N2 and a vinyl anion, which in turn affords the desired aiiyiic aicohoi. Aiternativeiy, the formation of a vinyi radical has been proposed. ... 

BES buffers (pKa<7.5) with 76 to form benzylic carbocation 77 is solely rate limiting, whereas increase in Tris, HEPES and CHES (p/fa >7.5) buffer concentrations bring about a change in mechanism from rate-determining epoxide ring opening at low buffer concentration to attack of solvent on the carbocation at high buffer concentration. 

Hinshelwood (LH) process. It has been found that the ER mechanism with the epoxide ring opened via H abstraction from N2H4 is more favorable. After H transfer, the newly formed OH group can easily obtain another H from NHNH2 and desorb from the surface. Gao et al. [80] then systematically investigated the reduction of GO based on DFT calculations with cluster models. For hydrazine reduction, three possible mechanisms for epoxide reduction have been identified. However, reduction path for hydroxyl, carboxyl, and carbonyl groups has not been found. Those groups are expected to be removed by thermal reduction. 

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