Methyl phenyl selenide

Sodium periodate is also frequently used as an oxidant for selenides, the reaction proceeds slowly in aqueous methanol. Various selenoxides such as methyl phenyl and benzyl phenyl selenoxides, (3B), (39),2 (40) and 2-azidocyclohexyl phenyl selenoxide have been isolated in this way. Other solvents and reaction conditions may also be employed. " °... 

Until quite recently the isolation of optically active seienoxides has been limited to those contained in steroids (isolated as diastereoisomeis). < The difficulty in obtaining these compounds was attributed to the racemization through the achiral hydrated intermediates. Simple optically active sel enoxides (S-11% ee) were first prepared by kinetic resolution. Direct oxidation of selenides to seienoxides was first reported using optically active oxaziridine derivatives under anhydrous conditions, but the extent of the asymmetric induction was somewhat unsatisfactory with methyl phenyl selenide as substrate (8-9% Recently much improved enantiomeric excesses (45-73%) were achieved with new oxaziridine reagents such as (70). An attempt at the asymmetric oxidation of more bulky selenides was independently carried out using Bu OCl in the presence of (-)-2-octanol (equation 55), but resulted in unsatisfactory enantioselectivities (ee 1%). Much better results were obtained by the oxidation of p-oxyalkyl aryl selenides (ee 18-40% equation 56) 27 gjyj selenides (ee 1-28%) using... 

In the former case, almost complete stereoselective oxidation to the chiral selenoxides has been accomplished quite recently. The Davis oxidant, 3,3-di-chloro-l,7,7-trimethyl-2 -(phenylsulfonyl)spirobicyclol2.2.11heptane-2,3 -oxa-ziridine, was found to be the most efficient reagent for the enantioselective oxidation of a variety of prochiral alkyl aryl selenides [81. Asymmetric oxidation was accomplished by the treatment of the selenides with 1 molar equivalent of the Davis oxidant at 0°C to afford the corresponding chiral alkyl aryl selenoxides in quantitative yields with 91-95% ee (Scheme 1). The oxidation of methyl phenyl selenide was complete within 1 min, whereas that of triiso-propyl(a bulkier alkyl) phenyl selenide required a few hours. Typical results are... 

Like sulfides, selenides can be oxidized to the corresponding oxides, selenoxides, or to selenones. Oxidation to selenoxides is much faster and, with some oxidants, final. Reaction conditions are specified in equation 592 for the oxidation of methyl phenyl selenide [325, 711, 773, 1034]. 

The presence of a group able to delocalize the charge from the caibanionic center favors the synthesis of the carbanion whatever the method used, whereas substitution of the carbanionic center by alkyl groups disfavors it. Thus, whereas methyl phenyl and dimethyl selenide cannot be metallated wiA LDA at -78 °C or 0 C, phenylseleno and methylseleno acetates and propionates lead, on reaction with the same base at -78 °C, to the corresponding organometallics (Scheme 10). - ... 

Alkyl aryl and dialkyl selenides, aside from the parent compounds methyl phenyl selenide (Scheme 13, a) and trifluoromethylphenyl methyl selenide (Scheme 13, b), cannot be easily metallated. It was expected that the extra stabilization provided by the cyclopropyl group would be sufficient to permit the metallation of cyclopropyl selenides, but that proved not to be the case. ... 

Bu"Li, which usually performs the Se-Li exchange in selenides, effects the metallation of some functionalized selenides. This is p cularly the case of phenylselenomethyl phosphonates and phosphonium salts (Scheme 28, c). b6.w >p g t),g methyl phenyl selenide (Scheme 13, a... 

Treatment of benzylmethylphenylselenonium tetrafluoroborate with potassium r-butoxide gave a 9 1 mixture of methyl phenyl and benzyl phenyl selenides but no products which would have resulted had the appropriate ylide been formed (Scheme 66, a). This demonstrated that at least this salt is extremely susceptible to nucleophilic attack, even by nucleophiles as hindered as the r-butoxide anion (Scheme 66, a). ... 

Di- and trisubstituted epoxides. j3-Hydroxyselenides (1), prepared by the method illustrated above, can be converted into epoxides. Alkylation with methyl iodide in the presence of silver tetrafluoroborate gives the resulting salts (2), which are treated with potassium -butoxide in DMSO. An epoxide (3) and methyl phenyl selenide are formed by way of the betaine (a). Unfortunately, when two alkyl groups are attached to the carbon bearing the SeCeHs group. 

Methyl phenyl selenide in CCI4 added dropwise with water cooling during 20 min. to a soln. of benzoyl peroxide in the same solvent methylphenyldibenzoyloxy-selenurane (Y 92%) dissolved in CCI4 and refluxed 2 hrs. benzoyloxymethyl phenyl selenide (Y 60%). F. e. s. Y. Okamoto, K. L. Chellappa, and R. Homsany, J.Org. Chem. 38, 3172 (1973). 

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