Hemilabile Diamidophosphite-Thioether Ligands with a β-Hydroxy Sulfide Backbone: Palladium(II) Complexes and Asymmetric Allylic Substitution

A series of structurally diverse diamidophosphite-sulfides were synthesized from 1,2-thioether alcohols. With respect to Pd(II), these hemilabile ligands showed the ability to form both P,S-chelates and complexes with two ligands connected to the metal P-monodentately. The structures of the ligands and complexes were confirmed by two-dimensional (2D) NMR spectroscopy and single-crystal X-ray diffraction. These stereoselectors provided up to 98% ee in the Pd-catalyzed asymmetric allylic substitution of (E)-1,3-diphenylallyl acetate with C- and N-nucleophiles and up to 78% ee in the Pd-mediated allylic alkylation of cinnamyl acetate with β-ketoesters. Furthermore, up to 71% ee was achieved in the rare reaction between 2-(diethoxyphosphoryl)-1-phenylallyl acetate and aniline. The effects of the structural parameters, reaction conditions, and ligand-to-metal ratio on the catalytic results are discussed. Due to the ability of the ligands to form structurally different catalytic species, a pronounced dependence of the asymmetric induction on the ligand-to-metal ratio is shown.