Pyrrolidinopyridines in palladium-catalyzed allylic substitutions - Conformation of the ligand

The (R,R)-2-[(2,5-dimethylpyrrolidin-1-yl)methyl]pyridines 4, 5, and 6 carr ying a 2-hydroxyalkyl, 2-alkoxyalkyl or 2-siloxyalkyl substituent in the 6- position of the pyridine ring were prepared and assessed in palladium-catal yzed allylations of 1,3-diphenylpropenyl acetate with malonate. All ligands having g-substituents with an S absolute configuration afforded the produc t with an R configuration in 80-84% ee, whereas those having substituents w ith an R absolute configuration gave the opposite product with a selectivit y depending on the nature of the substituent (8-74% ee). It is believed tha t the enantioselectivity is dependent on the conformation of that substitue nt.