Sulfoxide- and Phosphorus-Stabilized Carbanions

Carbanions derived from sulfoxides, phosphonates, and phosphonium salts have a rich preparative chemistry. The fact that sulfoxides are configuration-ally stable and partake in a wide range of reactions as nucleophiles has inspired a number of investigators to examine chiral sulfoxides as auxiliaries for asymmetric synthesis [21-23]. The chemistry of phosphonates and phosphonium salts is largely dominated by their use in olefination reactions. Consequently, the applications of chiral phosphorus-stabilized carbanions in asymmetric synthesis are primarily found in the desymmetrization reaction of ketones, leading to optically active olefins. 

A discussion of the use of chiral sulfoxides requires a brief introduction of the fundamental approach to their synthesis involving auxiliary displacement the classic method of Andersen [62], This method is based on treat- 

Numerous diastereoselective transformations using chiral carbanions derived from a-deprotonation of sulfoxides have been reported [21-23]. In 1973, Maniwa reported the addition of sulfoxide anions to imines [65]. In subsequent work, Kagan established the preparative utility of these additions to provide the corresponding adducts 101 and 103 with useful selectivities and yields (Equations 10 and 11) [66]. 

Pioneering studies in the area of chiral phosphorus reagents for asymmetric synthesis were reported by Bestmann (Equation 12) [68]. Treatment of phosphorus ylide 109 with 4-substituted cyclohexanones thus led to the formation of enantioenriched benzylidenecyclohexanes, such as 111 in 

This seminal work inspired the development of chiral phosphorus reagents that furnished related products with higher optical purity. Hanessian, for example, documented the synthesis and use of chiral bicyclic phosphona-mide reagents such as 112, conveniently prepared from 1,2-diaminocyclo-hexane (Equation 13) [69]. 

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