Substituent effects on ligands on asymmetric induction in a prototypical palladium-catalyzed allylation reaction: Making both enantiomers of a product in high optical purity using the same source of chirality

The substituent effects of the ligands 1 through 8 play a crucial role in d etermining the enantioselectivity in the palladium-catalyzed asymmetric all ylation reaction between 1,3-diphenylprop-2-en-1-yl acetate and the sodium salt of diethyl malonate. For a given chirality of the backbone, electron-d eficient and electron-rich ligands generally gave opposite enantiomers, whi le sterically hindered ligands bad the same enantioselectivity as electron- rich ligands. In the case of flexible backbones with ligands of comparable size, a variation of the enantioselectivity with the electronic properties of the ligand is predictable. In Ligands with rigid backbones, the steric e ffects of the substituents appear; to play a more decisive role, and cautio n should be exercised in interpreting the role of electronic effects in suc h cases. Examples are provided for maximizing both the chemical yield and t he enantioselectivity of the allylation reaction through the tuning of the electronic properties of the ligands. In selected cases, the major sense of the asymmetric induction could be reversed solely by changing the electron ic properties of the ligands. Bisphosphinites from (R)-(+)-1,1'-bi-2-naphth ol (BINOL) can be tuned to produce both (R)- and (S)-products in 80 and 87% ee, respectively. Stoichiometric reaction of complexes 10e* and 10j* with the sodium salt of diethyl malonate gave malonate adducts with enantiomeric excesses in agreement with those obtained under the catalytic conditions. Also reported are the details of an NMR study of the Pd-(eta(3)-1,3-dipheny lallyl)bis-diphenylphosphinite and the corresponding bis-dicyclohexylphosph inite complexes 10e* and 10j*.