Sulfoxide influence

Extrusion of S02 provides a unique opportunity for diene preparation Because of the sulfoxide influence, substitution at these positions quite easy. 

The effect of an additional site of complexation, as well as the influence of additional stereogenic centers, was demonstrated with the diastereomeric sulfoxides 2 A -2D40. Addition of the racemic,... 

The steric requirements of the enhanced interaction between arylsulfinyl or arylsulfonyl groups and the benzene ring in bis(4-hydroxyphenyl)sulfoxides or sulfones were examined by Oae and colleagues through the introduction of methyl groups in two or four of the positions ortho to SO or S02. As in the work described earlier for S02Me, effective values for the combined influence of the substituents o (obs.) were determined and compared with o (calc.) computed on the basis of strict additivity of substituent effects on the dissociation... 

C. The Influence of the Hydrogen Bond on the Conformation and Configuration of Sulfoxides.562... 

The relative ease of H/D exchange of the methylene protons of benzyl methyl sulfoxide is markedly influenced by the nature of the base and the solvent used, as shown in Table 12. The data reveal that rather high stereoselectivities can be observed when alkyllithium-THF is used. 

Successful applications of these stereocontrolled conjugate additions have led to asymmetric syntheses of several natural products such as (+ )-cuparenone (39) which involves formation of a quaternary carbon center81, (- )-/ -vetivone (40)8° and steroidal equilenin 4182 the wavy lines in these structures indicate that C—C bond formed stereoselectively under the influence of a temporarily-attached stereogenic sulfoxide auxiliary group. 

The influence of the solvent on the oxidation of film under conformational relaxation control is illustrated in Fig. 47, which shows chronoamperograms obtained by steps from -2000 to 300 mV vs. SCE at room temperature (25°C) over 50 s in 0.1 M LiC104 solutions of different solvents acetonitrile, acetone, propylene carbonate, (PC), dimethyl sulfoxide (DMSO), and sulfolane. Films were reduced over 120 s in the corresponding background solution. Despite the large differences observed in the relative shape of the curves obtained in different solvents, shifts in the times for the current maxima (/max) are not important. This fact points to a low influence of the solvent on the rate at which confor-... 

Carbanions derived from optically active sulfoxides react with esters, affording generally optically active )S-ketoesters ° . Kunieda and coworkers revealed that treatment of (-t-)-(R)-methyl p-tolyl sulfoxide 107 with n-butyllithium or dimethy-lamine afforded the corresponding carbanion, which upon further reaction with ethyl benzoate gave (-l-)-(R)-a-(p-tolylsulfinyl)acetophenone 108. They also found that the reaction between chiral esters of carboxylic acids (R COOR ) and a-lithio aryl methyl sulfoxides gave optically active 3-ketosulfoxides The stereoselectivity was found to be markedly influenced by the size of the R group of the esters and the optical purity reached to 70.3% when R was a t-butyl group. 

Acid-catalyzed migration of an oxygen atom from a sulfoxide to sulfide is one of the first examples where an intermediate formation of a S-S dication was proposed.26 Recently, such intermediates were observed by physical methods. Kinetic studies suggested that an intramolecularly formed S-S dication 54 was involved in isomerization of sulfoxide 53 to 55 under influence of trifluoroacetic acid (Scheme 18).82... 

Certain chalcogen structures display the phenomenon of chirality (Chapter 10.2). As with carbon,2 chirality at sulfur can influence physiological events there are many stereoselectivities in the interactions of chiral sulfur compounds with enzymes and receptor molecules. Sulfur chirality in secondary metabolites is most commonly observed with sulfonium salts, sulfoxides and sulfoximines.3... 

The sulfoxide method was employed in the direct synthesis of a P-l,2-man-nooctaose (Scheme 4.60) [362-364]. The synthesis of a p-mannosyl phosphoiso-prenoid illustrates the possibility of employing even such weak nucleophiles as phosphates (Scheme 4.61) [365]. Both syntheses rely on the presence of 4,6-0-benzylidene acetal, and its effect on the covalent triflate-contact ion-pair equilibrium [366,367], to influence the stereochemistry of the glycosylation process [295,323],... 

---