Isomeric sulfoxides

Owing to the reversible nature of the allylic sulfenate/allylic sulfoxide interconversion, the stereochemical outcome of both processes is treated below in an integrated manner. However, before beginning the discussion of this subject it is important to point out that although the allylic sulfoxide-sulfenate rearrangement is reversible, and although the sulfenate ester is usually in low equilibrium concentration with the isomeric sulfoxide, desulfurization of the sulfenate by thiophilic interception using various nucleophiles, such as thiophenoxide or secondary amines, removes it from equilibrium, and provides a useful route to allylic alcohols (equation 11). 

Bromide ion-mediated electrolyses of substituted cyclic sulfides result in cis and trans isomeric sulfoxides [76] ... 

This transannular addition of a-sulfinyl carbanions to nonactivated double bonds is utilized as the key step in a synthesis of trans-1-thiadecalin (70) in enantiomerically pure form. The required ( )-thiacy-clodec-4-ene 5-oxide (66a,b) was prepared via several steps frtm (/ ,/ )-l,6-dibromo-3,4-hexanediol. Upon treatment with butyllithium, a 4 1 mixture of isomeric sulfoxides (66a and 66b) undergoes smooth cyclizadon to give a mixture of isomeric bicyclic sulfoxides (67a and 67b) in the same 4 1 ratio as the starting material, suggesting that the cyclizadon is essentially stereospecific. The major isomer (67a) is reduced with PCb to a sulfide (68) from which the desired (70) is derived via a thiaoctaline (69 heme 16). 

Even though the sulfenate ester is usually in low equilibrium concentration with the isomeric sulfoxide, it can be trapped by thiophiles like trimethyl phosphite, leading eventually to complete formation of the alcohol. 

The exo-methylenecyclopentane (197) is also functionalized on the less hindered side upon rearrangement (Scheme 24). The isomeric sulfoxide epi-(197) gave the same product (198) but more slowly. The retarding effect is due to the enforced exo orientation of the phenyl group in the transition state while endo is preferred (c/. Scheme 23). 

Many organosulfur compounds can be resolved into optically active forms (enantiomers) owing to the presence of a chiral (asymmetric) sulfur atom 5 important examples include sulfoxides and sulfonium salts. Chiral sulfoxides containing amino or carboxylic acid groups have been resolved by formation of the diastereoisomeric salts with d-camphor-10-sulfonic acid or d-brucine. The salts can then be separated by fractional crystallisation and the free optically isomeric sulfoxides liberated by acid hydrolysis. However, a more convenient synthetic procedure for the preparation of chiral sulfoxides of high optical purity is Andersen s method (see p. 30). 

This S—O bond, however, is not strong since addition of RS- to O2 will lead to the formation of a derivative of sulfenic acid, RSOR. Such derivatives are very unstable. Stable S—O bonds are the ones present in the isomeric sulfoxides, RR SO, which are coordinate covalent bonds. In HSAB terms, RSOR is a combination of a soft acid, RS , with a hard base, R O, while sulfoxide is a combination of a soft acid, oxene (the oxygen atom), with a soft base, RSR. ... 

Sulfenic esters and sultenes are relatively stable thermodynamically, lying only several kcal/mol over the sulfoxides, all other things being equal [50]. However, in the laboratory, sulfenic esters are very difficult to handle without significant decomposition, in the absence of stabilizing substitutions [51], Their absorption spectra often extend to the red of the isomeric sulfoxides, which contributes further to difficulty in their isolation by way of sulfoxide photochemistry. Thus it is exciting that two independent laboratories isolated stable sultene derivatives in the 1980s, derived from sulfoxide photolysis. 

Janecke and Voege (119) attempted to determine biotin and its oxidation products in commercial multivitamin preparations using the silylation technique. However, the separation of biotin, biotin sulfone, and sulfoxides from a multivitamin mixture was not complete, and the two isomeric sulfoxides could not be separated. 

The reaction is fast and results in a mixture of isomeric sulfoxides in the ratio 2,0 (( ), This observation is in analogy with that of Mislow who studied this isomerization for a number of aliphatic sulfoxides and proposed the mechanism which includes formation of an intermediate with the structure of sulfur dichloride type. 

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