Reductive elimination hydroxy sulfoxides

Trisubstituted alkenes are prepared by reductive elimination of (3-hydroxy sul-fones but, in general, the reverse reaction competes.214 The reverse reaction is favored when the P-alkoxy sulfone adduct is sterically encumbered. The ole-fination of ketones to prepare trisubstituted alkenes employing Na/Hg affords moderate yields, unpredictable stereoselectivities, and large amounts of retroal-dol products from the intermediate P-alkoxy sulfones. High yields and moderate stereoselectivities of trisubstituted alkenes are obtained by a modification of the Julia-Lythgoe oleflnation reaction involving the in situ capture of the intermediate P-alkoxy sulfones with a suitable oxophilic electrophile and the employment of Smb/HMPA to promote, under neutral conditions, the reductive elimination at low temperatures (Eq. 128).223 A recent modification of this protocol, using sulfoxides instead of sulfones, is very efficient in the stereoselective preparation of di-, tri-, and tetrasubstituted alkenes.224,225... 

Mention has already been made of attempts to obtain 2-hydroxy- and 3-hydroxypenams (compounds 301 and 303), from which penems might have been generated by loss of the elements of water. The reductive elimination performed on the 2,3-diphenylthiopenam 316 by Kametani [182], and the oxidative elimination accomplished by Hanessian on the 2-methylthio compound 298 [29], are successful examples of penem synthesis achieved from isolated penam intermediates. Other examples of this strategy involve Pummerer-type rearrangements. The preparation of penem 306 by treatment of penam sulfoxide... 

The reductive elimination of yS-hydroxy sulfoxides reported by Satoh et al. deserves special attention [52, 53]. The reaction of yS-mesyloxy (or acetoxy) sulfoxides 196 with alkyl metals (nBuLi, tBuLi or EtMgBr) at low temperature affords the corresponding olefins in good to excellent yields (Table 3.8). 

Besides simple alkyl-substituted sulfoxides, (a-chloroalkyl)sulfoxides have been used as reagents for diastereoselective addition reactions. Thus, a synthesis of enantiomerically pure 2-hydroxy carboxylates is based on the addition of (-)-l-[(l-chlorobutyl)sulfinyl]-4-methyl-benzene (10) to aldehydes433. The sulfoxide, optically pure with respect to the sulfoxide chirality but a mixture of diastereomers with respect to the a-sulfinyl carbon, can be readily deprotonated at — 55 °C. Subsequent addition to aldehydes afforded a mixture of the diastereomers 11A and 11B. Although the diastereoselectivity of the addition reaction is very low, the diastereomers are easily separated by flash chromatography. Thermal elimination of the sulfinyl group in refluxing xylene cleanly afforded the vinyl chlorides 12 A/12B in high chemical yield as a mixture of E- and Z-isomers. After ozonolysis in ethanol, followed by reductive workup, enantiomerically pure ethyl a-hydroxycarboxylates were obtained. 

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