Alkyl aryl sulfoxides reduction

Asymmetric synthesis of sulfoxides can be achieved by biocatalytic oxidation of sulfides and reduction of sulfoxides (Figure 33). i4-27s One example is the reduction of alkyl aryl sulfoxides by intact cells of Rhodobacter sphaeroides f.sp. denitrificans (Figure 33 (a)). 341 In the reduction of methyl -substituted phenyl sulfoxides, ( S )-cnanliomcrs were exclusively deoxygenated while enantiomerically pure (W)-isomcrs were recovered in good yield. For poor substrates such as ethyl phenyl sulfoxide, the repetition of the incubation after removing the toxic product was effective in enhancing the ee of recovered (f )-enantiomers to 100%. 

The use of THF as solvent with organolithium nucleophiles, as described by Wudl and Lee, resulted in significant reduction in the levels of diastereoselectivity. Entries 7-9 of Table 2.9 highlight the limitations of this procedure for the synthesis of diaryl sulfoxides and therefore dictate that alkyl aryl sulfoxides are synthesized... 

Peroxidases have been used very frequently during the last ten years as biocatalysts in asymmetric synthesis. The transformation of a broad spectrum of substrates by these enzymes leads to valuable compounds for the asymmetric synthesis of natural products and biologically active molecules. Peroxidases catalyze regioselective hydroxylation of phenols and halogenation of olefins. Furthermore, they catalyze the epoxidation of olefins and the sulfoxidation of alkyl aryl sulfides in high enantioselectivities, as well as the asymmetric reduction of racemic hydroperoxides. The less selective oxidative coupHng of various phenols and aromatic amines by peroxidases provides a convenient access to dimeric, oligomeric and polymeric products for industrial applications. 

A useful survey of the chemistry of phosphite radicals, prepared by pulse radiolysis, has been presentedThese can take part in oxidation, reduction, substitution, and addition reactions. Reports have been published on the oxidation by peroxodiphosphate of alkyl aryl sulfides,methyl phenyl sulfoxide,and hexacyanoferrate(II). The oxidation of dialkyl sulfides by peroxomonophos-... 

Reduction of Sulfiir Compounds. Alkyl and aryl sulfoxides are reduced by BBrs to the corresponding sulfides in good yields. Addition of Potassium Iodide and a catalytic amount of Tetra-n-... 

The at complex from DIB AH and butyllithium is a selective reducing agent.16 It is used tor the 1,2-reduction of acyclic and cyclic enones. Esters and lactones are reduced at room temperature to alcohols, and at -78 C to alcohols and aldehydes. Acid chlorides are rapidly reduced with excess reagent at -78 C to alcohols, but a mixture of alcohols, aldehydes, and acid chlorides results from use of an equimolar amount of reagent at -78 C. Acid anhydrides are reduced at -78 C to alcohols and carboxylic acids. Carboxylic acids and both primary and secondary amides are inert at room temperature, whereas tertiary amides (as in the present case) are reduced between 0 C and room temperature to aldehydes. The at complex rapidly reduces primary alkyl, benzylic, and allylic bromides, while tertiary alkyl and aryl halides are inert. Epoxides are reduced exclusively to the more highly substituted alcohols. Disulfides lead to thiols, but both sulfoxides and sulfones are inert. Moreover, this at complex from DIBAH and butyllithium is able to reduce ketones selectively in the presence of esters. 

Sulfides, or thioethers, are sulfur analogues of ethers, and like ethers they can be either symmetrical (R2S) or unsymmetrical (RSR1, where R and R are different). Sulfides can be prepared from alkyl halides by a Williamson-type synthesis with sodium hydrogen sulfide, sodium thiolate or sodium sulfide from alkyl or aryl halides via the Grignard reagent (11) from alkenes by radical-catalysed addition of thiols or by reduction of sulfoxides (Scheme 9).2b... 

Curran et al. have studied reductions of 1,3-diphenylpropanone, ethyl cinna-mate, diphenyl sulfoxide, 1-iodododecane, and o-allyloxyiodobenzene with Sml2 in the presence of water [98] (Scheme 46). The accelerating role of water in the reduction of alkyl and aryl iodide has been readily demonstrated [99]. 

In situ method for reduction and sulfurization. The combination of Me SiCl and Na2S successfully reduces arylamines and sulfoxides, converts nitriles to thioamides, alkyl halides to sulfides, as well as demethylates aryl methyl ethers. 

A variety of methods for the reduction of sulfoxides to sulfides are available. PI3 rapidly reduces aryl alkyl and dialkyl sulfoxides and selenoxides, usually at —78 °C (eq 3). For example, treatment of ethyl phenyl sulfoxide with 1 equiv of PI3 (CH2CI2, -78 °C, 15 min) affords ethyl phenyl sulfide in 91% yield. Others have successfully employed this procedure. Dialkyl sulfoxides generally react in somewhat lower yield. A phenyl vinyl sulfoxide (eq 3, entry c) requires ambient temperatures to react. Selenoxides behave similarly, and P2I4 can usually be used in place of PI3. Treatment of decyl phenyl selenone with PI3 (CH2CI2, 0 °C, 30 min) affords a mixture of the reduced product, decyl phenyl se-lenide (69%), and the substitution product, n-decyl iodide. ... 

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