A,P-Unsaturated sulfoxides and

This review continues from one entitled The Chemistry of a,P-Unsaturated Sulfoxides which was recently published in a monograph of organosulfur chemistry. 1 In addition, the coverage has been extended to include the analogous a,P-unsaturated sulfones. The focus of the present review are recent advances in the chemistry of a,P-unsaturated sulfoxides and sulfones, especially those which have been published since 1993. The synthesis of a,P-unsaturated sulfoxides and sulfones has already been reviewed extensively by Rayner2 and hence will not be covered here. Only the chemistry of vinyl (alkenyl) sulfoxides and sulfones will be considered. The chemistry of other a,P-unsaturated sulfoxides and sulfones such as dienyl, allenyl, and propargyl (alkynyl) sulfoxides and sulfones is beyond the scope of this review. Considerable emphasis has been placed on stereo- and enantioselective reactions, reflecting the current interest in this area. 

Dipolar cycloaddition of nitrones to alkenes has been widely utilized for the synthesis of many nitrogen-containing natural products. Indeed, in this process, up to three stereogenic centers are built up in a single step, often in a highly stereoselective manner. Louis and Hootele recently reported the first highly selective 1,3-dipolar cycloaddition between an a,P-unsaturated sulfoxide and a cyclic ni-... 

RECENT ADVANCES IN THE CHEMISTRY OF a,P-UNSATURATED SULFOXIDES AND SULFONES Ian Forristal and Christopher M. Rayner 155... 

NaBHj/NiC or Raney nickel, the menthyloxy group is removed with NaBH /KOH to give 3,4-disubstituted butyrolactones with a high diastereo- and enantioselectivity (Figure 7.69). Corey and Houpis [1458] have described asymmetric Michael reactions of ketone enolates with a 2-thiophenyl crotonate of 8-phenmenthol. Chirality has also been introduced on the amino group of 2-ami-nomethyiacrylates to perform the asymmetric addition of the anion of the tert-Bu ester of cyclopentanecarboxylate [1459], More important developments have been reported with chiral a,p-unsaturated sulfoxides and nitro compounds as Michael acceptors (see below). 

Pyne and coworkers have studied both the inter- and intramolecular reaction between amines and optically active a,P-unsaturated sulfoxides, and have applied this methodology to synthesis of natural products [109,110,112-114]. 

Maignan and coworkers have reported the preparation and Diels-Alder reaction of a-keto-a,P-unsaturated sulfoxides and have observed exclusive formation of cjro-sulfinyl cycloadducts albeit with poor diastereoselectivity [29]. 

The palladium-catalyzed [3+2] cycloaddition reaction between enantiomerically pure a,P-unsaturated sulfoxides and trimethylenemethane (266), using the methodology developed by Trost [198], has been reported [199]. Thus, reaction of the sulfoxide (31), 2-acetoxymethyl-3-allyltrimethylsilane (2eq), palladium acetate (5mol%), and triisopropylphosphite (20 eq) in THF under reflux gave the major cycloadduct (267) in 80% yield and 80% de (Scheme 5.87). Moderate to good levels of asymmetric induction were observed for various a,P unsaturated sulfoxides. 

Sigmatropic rearrangements have been described above as part of the proposed mechanism of additive Pummerer rearrangements such as the reaction between a,P-unsaturated sulfoxides and dichloroketene [220]. De Lucchi et al. have observed a similar type of rearrangement with isopropenyl acetate under acidic conditions [232]. 

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