Phosphine–phosphite ligands in the palladium-catalyzed asymmetric allylic alkylation: Electronic and steric effects

• Phosphine–phosphite ligands with different tether lengths were tested in asymmetric allylation.
• The reaction rate and enantioselectivity were strongly sensitive to the chain length.
• A steady relationship was observed between the ligands' basicity and their catalytic activity.
• The role of the biaryl terminal moiety and the stereogenic elements in the backbone was also studied (ees up to 74%).
• Alkylene carbonates were successfully used as green solvents for the catalytic reaction (ees up to 69%).

The asymmetric allylic alkylation of rac-1,3-diphenyl-2-propenyl acetate catalyzed by the palladium-complexes of phosphine–phosphite ligands with 1,1'-binaphthyl- or 1,1'-octahydrobinaphthyl- moiety is reported. The roles of (i) the tether length in directly analogous phosphine–phosphite ligands, (ii) the stereogenic elements in the backbone of PC3OP type of ligands, and (iii) the BINOL moiety in the activities and enantioselectivities of the catalysts are studied. The applicability of these ligands was also evaluated in ethylene and propylene carbonates as green solvents obtaining up to 69% ees with good activity. By using directly analogous phosphine–phosphite ligands the catalytic activity increases steadily with the length of the backbone and with the basicity of the phosphine moiety.

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