Sulfoxides formation

During the synthesis of peptides that contain 4-methoxybenzyl-protected cysteine residues, sulfoxide formation may occur. These sulfoxides, when treated with HF/ anisole, form thiophenyl ethers that cannot be deprotected therefore, the peptides should be subjected to a reduction step prior to deprotection. ... 

M CF3SO3H, PhSCH3 or Tl(OCOCF3)3. The 5-adamantyl group is less prone to sulfoxide formation than is the 5-4-methoxybenzyl group. It is also more stable to CF3COOH. 

Two attractive routes to thiolene oxide and dioxide are the diene-SO104 and diene-S02298 cycloadditions, respectively. These cycloadditions are highly stereoselective at both carbons of the diene systems and at sulfur (see equation 62 for specifics) which, in the case of sulfoxide formation, proceed via attack of triplet SO on the diene. Equation 112 shows an example of such a cycloaddition104. The overall yields are significantly improved by running the cycloadditions in the absence of oxygen and by the use of excess diene. 

Parallel to the modification of the catalytic performance in Baeyer-Villiger oxidations, random mutagenesis was successfully applied to improve the stereoselectivity of CHMOAcineto hi cascs of essentially racemic sulfoxide formation. In addition, enantiodivergent clones with >98% ee for both antipodal products were identified (Table 9.5) [205]. However, improvement in stereoselectivity of mutant enzymes was often accompanied by increased formation of sulfone. This effect can also be utilized to resolve racemic sulfoxides. 

Scheme 4.29 Diastereoselective sulfoxide formation in the axial series.

Oxidations. Hydroxylations, epoxide formation, sulfoxide formation, dealkylation, deamination. For example, benzene is oxidized into phenol, and toluene (methylben-zene) is oxidized into benzoic acid. 

Sulfoxide formation requires much milder conditions and traditionally bromine in wet ether was used although this is very successful, modern practice makes use of f-butyl... 

DFIT-induced fluoro-Pummerer reactions of N-substituted-2-(phenylsul-fanyl)acetamides have also been reported (Scheme 37) [107]. With some amides, cyclization of the Pummerer intermediate was competitive with fluorination, and in other cases, fluorination was preempted by sulfoxide formation. 

However, the (M)-phenyl methyl sulfoxide has the opposite configuration to (Mi-styrene oxide (Fig. 8, inset) (49). A possible structural difference between styrene and thioanisole is the fact that the ethylene group in styrene is in the plane of the phenyl ring while the S-methyl group in thioanisole is perpendicular to the phenyl group. If the Mb mutants discriminate this steric difference, one could expect (S)-sulfoxide formation if cyclic sulfides are employed as substrates, since the cyclic sulfides should have planar structures (Fig. 8c) similar to styrene. Table III lists representative results of cyclic and acyclic sulfide... 

The enantioselective sulfoxidation of thioanisole for the (R)-isomer by H64D/V68A and H64D/V68S Mbs suggest the sulfoxidation intermediate shown in Scheme 9 could be stabler for (R)-sulfoxide formation over the (S)-isomer. The chiral discrimination for (R)- and ( -intermediates is caused by steric interaction between the transition state and the heme cavity. However, it is... 

Scheme 9. Expected oxidation intermediate for (R)-methylphenyl sulfoxide formation.

Cephalosporins in the sulfoxide or sulfone oxidation states can easily be obtained by treatment with different oxidants. This sulfur oxidation is usually accomplished for one of the following reasons (1) sulfoxide formation to obtain reactive intermediates for further transformations (2) sulfoxide formation with subsequent reduction in cephems to shift the double bond from position 2 to position 3 (3) preparation of sulfones as /3-lactamase or elastase inhibitors. 

Enantiopure Sulfoxides Formation by Double Nucleophilic Displacement of Oxathiazolidine 101... 

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