Synthesis of chiral diphosphine ligands derived from diols and tartaric acid derivative via diastereomeric coupling

Abstract

Asymmetric hydrogenation utilizing molecular hydrogen is one of the most efficient methods for constructing chiral compounds as this method is the simplest, cleanest, efficient, environmentally friendly and economical. It is most widely applied in both industry and academia. This thesis focused on the development of novel C2-symmetric biphenyl diphosphine ligands with chiral linkers and their applications in asymmetric hydrogenations. A C2-symmetric biphenyl diphosphine ligand (R)-[6,6'-(2S',3S'-butadioxy)]-(2,2')-bis(diphenylphosphino)-(1,1')-biphenyl 117 with a chiral linker was synthesized. Complete atropdiastereoselectivity was observed in asymmetric intramolecular Ullmann coupling. (S)-[6,6'-(2S',3S'-butadioxy)]-(2,2')-bis(diphenylphosphino)-(1,1')-biphenyl 124, (S)-[6,6'-(2R,4R-pentadioxy)]-(2,2')-bis(diphenylphosphino)-(1,1')-biphenyl 128 and (S)-[6,6'-(2R,5R-hexadioxy)]-(2,2')-bis(diphenylphosphino)-(1,1')-biphenyl 132 were synthesized via ring closure process. The enantioselectivities of the corresponding Ir and Ru complexes compared well with MeO-BIPHEP 5a. The configuration of the product was controlled by the axial chirality rather than the additional central chirality. Another novel C2-symmetric biphenyl diphosphine ligand, [6,6'-(4S,5S'-2,2-dimethyl-1,3-dioxolane-4,5-dimethoxy)]-(2,2')-bis(diphenylphosphino)-(1,1)-biphenyl 141 and 142 were synthesized via asymmetric Ullmann coupling. However, no atropdiastereoselectivity was observed. The enantioselectivities of the corresponding Ru complexes compared favorably with MeO-BIPHEP 5a. The corresponding Rh complexes showed better enantioselectivities than MeO-BIPHEP 5a. The configuration of product was also controlled by the axial chirality rather than the additional central chirality.