Palladium-catalyzed diastereoselective and enantioselective allylic alkylations of ketone enolates

Lithium and magnesium enolates of cyclohexanone undergo palladium-catalyzed allylic alkylations under mild conditions. Diastereoselectivity and enantioselectivity are observed when the diphenyl-and dimethyl-substituted allylic substrates 1a and 1b are reacted with cyclohexanone or ethyl mesityl ketone. The lithium enolates of cyclohexanone, cyclopentanone and a-tetralone lead to the alkylations products 12-14 in an enantioselective manner. Axially chiral biphenyl- and binaphthyl-bisphosphanes provide high enantioselectivity and/or diastereoselectivity. In the case of the lithium enolates, the presence of lithium chloride is also crucial to reactivity and stereoselectivity. The stereochemical outcome of the allylic alkylation of cyclohexanone and acetophenone has been investigated by the palladium-catalyzed reaction of their lithium enolates with the cis/trans isomeric alkenes (Z)-18 and (E)-19. It turns out that the preformed, non-stabilized enolates attack pi-allyl-palladium complexes generated in situ from the face opposite to the noble metal thus following the stereochemical pathway of soft, stabilized carbanions.