<i>C</i>₂-Symmetric Bisphosphinobioxazoline as a Chiral Ligand. Highly Enantioselective Palladium-Catalyzed Allylic Substitutions and Formation of <i>P</i>,<i>N</i>,<i>N</i>,<i>P</i> Tetradentate Palladium (II) Complexes

Abstract

The C 2 -symmetric bisphosphinobioxazoline [( S, S )-Phos-Biox] 4 was found to be a highly efficient chiral ligand for Pd-catalyzed enantioselective allylic substitution of rac -1,3-diphenyl-2-propenyl acetate with dimethyl malonate and afforded enantioselectivities of up to 97% ee. Moderate enantioselectivities have been observed in Pd-catalyzed desymmetrizations of cis -1,4-bis(benzoyloxy)cyclopent-2-ene ( 12) with dimethyl malonate (51−78% yield, 38−58% ee) and N -benzyl- N -methylamine (87% yield, 33% ee) nucleophiles and of biscarbamate 15 of cis -1,4-dihydroxycyclopent-2-ene (90% yield, 50% ee). A 1:1 molar mixture of ( S, S )-Phos-Biox 4 with Pd(CH 3 CN) 2 Cl 2 and [( η 3 -C 3 H 5 )PdCl] 2 afforded the P, N, N, P -tetradentate Pd(II) complexes 19a and 19b, respectively. The structures of the complexes 19a, b were determined by X-ray analysis. The complex 19a also exhibited high enantioselectivity (86% yield, 92% ee) in allylic substitution of rac -1,3-diphenyl-2-propenyl acetate with dimethyl malonate.