Allylic Alkylations Catalyzed by Palladium Systems Containing Modular Chiral Dithioethers. A Structural Study of the Allylic Intermediates

Palladium allylic systems containing modular chiral dithioether ligands were chosen as
catalysts for a systematic study of homodonor ligands in allylic alkylation reactions. For
this purpose, new type-DMPS (4−6) and -DEGUS (8, 9) ligands were synthesized.
Dithioethers 4−6 afforded high activities and excellent selectivities in all Pd-catalyzed allylic
reactions. Particularly the Pd/6 catalytic system provided b-VIII with an ee > 99% and a
regioselectivity l/b (VIII) = 1/1.6. A family of intermediate complexes containing several
allyl groups (symmetrical, 13−16 and 20, and nonsymmetrical, 17−19, moieties) and
dithioether ligands (4−6, 8, 9, 11, and 12) is described. The complexes were fully
characterized both in solution and in the solid state. X-ray structures of four of these
complexes (16−18 and 20) were determined. The diastereomers present in solution were
studied by NMR spectroscopy, and in some cases it was possible to establish a relationship
between the diastereomeric excesses and the selectivities found in the catalytic process.