Arylseleninic acids

An analogous sequence appears in trifluoroseleninic acid as compared to -selenonic acid CF3SeO3H resonates at 3 = 981 whereas the Se chemical shift of CF3SeO2H is only 5=1231 The 3-value of benzeneseleninic acid Ph-SeO2H in a chloroform-methanol mixture is 1188 (3=1152, 1182) and its methyl ester 3= 1236 protonation leads to a ca. 20 ppm shielding. Recently, some further arylseleninic acids have been reported with Se chemical shifts between 3=1200 for Ar = 2,4,6-triisopropylphenyl and 3= 1276 for Ar = 2,4,6-triethylphenyl. These were optically resolved, partially to 100% e.g., on a chiral column and their racemization studied. ... 

Some p-hydroxyamides (246) in different diastereomic mixtures were cyclized to tetrahydrofurane derivatives (247) in the presence of Ph-SeCl, and subsequently, their diastereomeric ratios could be determined by Se NMR analysis.Some arylseleninic acids (Ar-SeO2H S = 1200-1276) were optically resolved by chiral columns and their racemization studied. 

T. Hori, K. B. Sharpless, Synthetic applications of arylselenenic and arylseleninic acids. Conversion of olefins to allylic alcohols and epoxides, J. Org. Chem. 43, 1689-1697 (1978). 

Baeyer-Villiger oxidation of alkyl- and aryl-substituted C -C, cycloalkanones, steroid ketones and branched chain aliphatic ketones is catalysed by arsonated polystyrene resins [53], Larger size cycloalkanones and linear ketones react much slower. Water miscible and immiscible solvents can be used. With the latter, the resin behaves as an effective catalyst and a phase-transfer agent (triphase catalysis). The same compounds are also epoxidation catalysts. More recently, a method for the preparation of phenols by the oxidation of aromatic aldehydes and ketones has been reported. The most convenient catalysts are nitro-substituted arylseleninic acids and corresponding diselenides [54]. 

The direct oxidation of alkenes to oxirans by hydrogen peroxide is, of course, only possible when a catalyst is used. In the past the main choice of catalyst has been oxides of the metals of Groups 5a, 5b, 6a, or 6b. In 1978, however. Sharpless put the use of arylseleninic acids as catalysts on a firm practical footing.Using the nitrophenylseleninic acids (25 R = H, R = NO2) and (25 R = R = NO2), 95 % preparative yields of cyclo-octene oxide were obtained from the alkene in CH2CI2 with 30% H2O2. 

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