Ethyl phenyl sulfoxide

Sulfoxides are known to form both 0-alkyl and S-alkyl derivatives. The latter are obtained when so-called soft alkylating agents are employed. This behavior of sulfoxides was utilized (172) in the stereospecific synthesis of chiral 135. The reaction of the optically active (+)-ethyl phenyl sulfoxide 136 with methyl iodide in the presence of mercuric iodide followed by anion exchange was found to give the optically active salt 135. 

The behavior of chiral phenyl /-butyl sulfoxide 219 and a-phenyl-ethyl phenyl sulfoxide 220 is completely different in strongly acidic media and in the presence of halide ions. Two reactions were found (266) to occur in parallel. One results in the loss of optical activity, and the second leads to the decomposition of the sulfoxide. It was observed that the racemization process is not accompanied by [ 0] oxygen exchange. In the case of sulfoxide 220 the complete loss of optical activity at chiral sulfur is accompanied by partial racemization at the chiral carbon center. These results are consistent with a sulfenic acid-ion-pair mechanism formulated by Modena and co-workers (266) as follows (it is obvious that the formation of achiral sulfenic acid is responsible for racemization). 

As mentioned earlier (see page 373), methylation of (+)-(i )-ethyl phenyl sulfoxide 136 with methyl iodide in the presence of mercury iodide affords the corresponding oxosulfonium salt (+)-(/ )-l 35 (172). That its demethylation by iodide anion yields sulfoxide 136 with the same configuration as that of the starting one indicates that 5-methylation of sulfoxides occurs with retention of configuration. 

By Methods A and B, isopropyl phenyl sulfoxide was included in crystalline 1 with high ( -enantioselectivity (86 and 87% ee, respectively). Ethyl phenyl sulfoxide formed no inclusion compound by Method A, but the inclusion compound of its (5)-enantiomer was obtained by Method B. The inclusion crystal of (.V)-e(hyl phenyl sulfoxide is isostructural with that of (S)-isopropyl phenyl sulfoxide (Figure 3). As mentioned above, (6>ethyl phenyl sulfoxide was not included by Method A. The lack of one methyl group may make enthalpy (interaction with the inclusion cavity) and entropy disadvantageous in crystal packing to result in no inclusion of ethyl phenyl sulfoxide via Method A. 

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%. 

When (6), prepared from (1) and the anion of ethyl phenyl sulfoxide, is heated with (4), the cyclized product (7) is obtained in 35% yield. Probably benzene-sulfenic acid, produced by elimination of (6), serves as an acid catalyst for cyclization of (5) to (7). 

Preparative Methods by lithiation of phenyl vinyl sulfide with lithium diisopropylamide, followed by silylation, or the base-induced elimination of 2-chloro-l-trimethylsilyl-l-phenylthioethane, or the lithiation of ethyl phenyl sulfoxide with LDA followed by silylation, or the Pd-catalyzed coupling reactions of trimethylstannyl phenyl sulfide with 1-bromo-1-trimethylsily lethylene. ... 

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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