Chiral electrophilic selenium reagents

Recently, the semi-synthesis of Vancomycin (48) on solid supports was accomplished using an allylic linker (Scheme 3.2) [123, 124]. Polymer-bound chiral electrophilic selenium reagents have been developed and applied to stereoselective se-lenylation reactions of various alkenes (Tab. 3.9) [125]. 

There have been many studies on the use of chiral electrophilic selenium reagents for stereoselective additions to alkenes <1998JA3376, B-1999MI35, 1999T1, 2000AGE3740> with notable diastereoselectivity in some cases. 

Synthesis of furans with chiral substituents with high diastereoselectivity was achieved by using an optically active electrophilic selenium reagent via a carboselenenylation reaction of simple aryl-conjugated alkenes <05AG(E)3588>. 

A number of useful enantioselective syntheses can be performed by attaching a chiral auxihary group to the selenium atom of an appropriate reagent. Examples of such chiral auxiliaries include (49-53). Most of the asymmetric selenium reactions reported to date have involved inter- or intramolecular electrophilic additions to alkenes (i.e. enantioselective variations of processes such as shown in equations (23) and (15), respectively) but others include the desymmefrization of epoxides by ringopening with chiral selenolates, asymmetric selenoxide eliminations to afford chiral allenes or cyclohexenes, and the enantioselective formation of allylic alcohols by [2,3]sigmafropic rearrangement of allylic selenoxides or related species. 

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