Diastereoselectivity asymmetric Heck reaction

Another significant development in oxazoline chemistry is the application of oxazoline-containing ligands for asymmetric catalysis, such as palladium-catalyzed allylic substimtions, Heck reactions, hydrogenations, dialkylzinc additions to aldehydes, and Michael reactions. The discovery of diastereoselective metalation of chiral ferrocenyloxazolines has further expanded the availability of chiral ligands for metal-catalytic reactions. 

Overman s group [67] enlisted an intramolecular Heck reaction to form a quaternary center in their synthesis of gelsemine. When the cyclization precursor 68 was subjected to ligandless conditions [Pd ldbajj, Et N] in the weakly coordinating solvent toluene, the quaternary center was formed with 9 1 diastereoselectivity (70 69 = 89 11). In contrast, use of the coordinating solvent THF and a stoichiometric amount of an added silver salt completely reversed the sense of asymmetric induction in the cyclization reaction (70 69 = 3 97). 

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