Asymmetric reactions enantiotopic leaving group

The exact ee (enantiomeric excess) is very sensitive to reaction variables, such as solvent and additives (such as R4NX salts), which influence the amount of ion pairing in the nucleophile. For substrates with enantiotopic leaving groups, the degree of asymmetric induction depends on the ionization step, and is relatively independent of the nucleophile (equation 64). 

Asymmetrically induced Heck reactions can also be performed with substrates containing two enantiotopic leaving groups. Starting from dimedone, novel cyclohexa-l,4-diene-l,5-diol bis(nonafluorobutanesulfonates) such as 309 have been prepared and cycUzed under palladium catalysis to cleanly give bicy-clo[4.2.0]octadienes 370 and bicyclo[4.2.0]octenones, respectively, by an unprecedented 4-exo-trig process (Scheme 8.77, cf. Scheme 8.66). In the presence of a chiral phosphine ligand, the products could be obtained with modest enantiomeric excesses (up to 52% ee) [239]. 

Enantiotopic leaving groups can also differentiated by asymmetric Heck reactions (for a possible substrate, see Scheme 5-30). 

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