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Styrene epoxidation stereochemistry

Sharpless epoxidation of alkenylsilanols.1 Allylic silanols also undergo highly enantioselective Sharpless epoxidation. This reaction furnishes simple epoxides such as styrene oxide in high optical purity. Thus reaction of fram-(3-lithiostyrene il) with ClSi(CH,)2H gives 2, which can be oxidized to the alkenylsilanol 3. ShaTp-less epoxidation of 3 gives the epoxide 4, which is converted to styrene epoxide 5 by cleavage with fluoride ion. The stereochemistry of epoxidation of 3 is similar to that of the corresponding allylic alcohol. [Pg.55]

Figure 4. Ferryl transfer versus protein-mediated co-oxidation of styrene proposed for the myoglobin-catalyzed formation of styrene epoxides with, respectively, (a) retention of stereochemistry and incorporation of oxygen from H2O2, and (b) loss of stereochemistry and incorporation of oxygen from O2. Figure 4. Ferryl transfer versus protein-mediated co-oxidation of styrene proposed for the myoglobin-catalyzed formation of styrene epoxides with, respectively, (a) retention of stereochemistry and incorporation of oxygen from H2O2, and (b) loss of stereochemistry and incorporation of oxygen from O2.
Improved catalysis of styrene epoxidation by protein-polyion films was related to their better mechanical stability compared to the surfactant films. Product stereochemistry for the epoxidation of cw- 3-methylstyrene depended on oxygen availability. There appear to be two pathways for olefin oxidation. The stereoselective pathway utilizes the high valent iron-oxygen intermediate (Figure 24), as does the natural enzyme system. The non-stereoselective pathway may involve a peroxyl radical near the protein surface that forms in the presence of oxygen [91]. The competing reactions are summarized in Figure 26. [Pg.225]

By-products in the reactions in Table 3 are mainly cleavage products (carbonyls) An interesting by-product is found in the oxidation of styrene, as phenyl acetate is produced. It has been found that phenyl acetate is formed via oxidation of either styrene oxide or acetophenone. Nearly the same yield and stereochemical mixture of the epoxides, as in Table 3, can be obtained by oxidation with Ag202. It appears from Table 3 that the epoxidation of alkenes catalyzed by discrete silver complexes also takes place without maintaining the stereochemistry of the alkene, as in the silver-surface catalyzed reaction. [Pg.382]

Although (salen)manganese(III) complexes are widely studied, those with other metals are largely unexplored. The stereochemistry of Cr-salen-catalysed epoxidation of dimethylchromenes and styrenes was found to be highly solvent-dependent, with polar solvents giving the opposite sense of induction to non-polar.17 This may be explained by competitive collapse of diastereomeric metalloxetanes either directly to epoxide or via a cationic intermediate. [Pg.181]

Mg-Al oxides with a Mg/Al ratio of 5, calcined at 400 °C, are the most active catalysts for the reaction of CO2 and styrene oxide, and DMF is the best solvent. Using this Mg-Al oxide, various kinds of epoxides could be quantitatively converted into the corresponding cyclic carbonates. This addition reaction proceeds with retention of the stereochemistry of epoxides the reaction of CO2 with (R)- and (S j-benzyl glycidyl ether gave and ( Sj-4-(benzyloxymethyl)-l,3-dioxolane-2-one with >99% e.e., respectively. [Pg.153]

Nucleophilic ring opening of epoxides usually occurs with anti stereochemistry, with nucleophilic attack at the less substituted carbon. On the other hand, the acid-catalyzed epoxidation-hydrolysis sequence is not always stereospecific. In the case of (5 )-l-phenyloxirane (styrene oxide), the acid-catalyzed ring opening is regiose-lective and proceeds through the more stable (benzylic) carbocation there is extensive racemization because of the involvement of a carbocation. ... [Pg.186]

Fruetel, J.A., J.R. Collins, D.L. Camper, G.H. Loew, and PR. Ortiz de Montellano (1992). Calculated and experimental absolute stereochemistry of the styrene and 3-methylstyrene epoxides formed by cytochrome P450cam. J. Am. Chem. Soc. 114, 6987-6993. [Pg.84]

Table 1. Experimental and calculated absolute stereochemistries of the styrene and cis and rr(3 5-P-methylstyrene epoxides produced by cytochrome P450cam. Table 1. Experimental and calculated absolute stereochemistries of the styrene and cis and rr(3 5-P-methylstyrene epoxides produced by cytochrome P450cam.
Studies of the epoxidation of styrene and sulfoxidation of thioanisoles by cytochrome P450, a monooxygenase of known structure, show that the absolute stereochemistry of the reaction can be predicted by molecular dynamics calculations. Extension of this approach to other reactions, and to more complicated substrates, should provide an important step towards the rationalization of oxidative metabolism and the construction of tailor made oxidative catalysts. [Pg.264]


See other pages where Styrene epoxidation stereochemistry is mentioned: [Pg.58]    [Pg.15]    [Pg.15]    [Pg.6427]    [Pg.59]    [Pg.242]    [Pg.31]    [Pg.108]    [Pg.833]    [Pg.833]    [Pg.404]    [Pg.72]    [Pg.263]    [Pg.529]    [Pg.527]    [Pg.155]    [Pg.259]    [Pg.260]    [Pg.262]    [Pg.833]    [Pg.27]   
See also in sourсe #XX -- [ Pg.27 , Pg.33 , Pg.65 ]




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