Synthesis Of P,N Ligands Based On Biphenyl Backbones And Their Applications In Asymmetric 1, 4-conjugate Additions

Using asymmetric activation strategy, phosphite-pyridine ligands derivedfrom racemic or achiral biphenyl backbones have been developed in the Cu(I)-catalyzed enantioselective 1,4-conjugate additions of Et₂Zn to acyclic enones.Furthermore, the selective reductions of 2,2'-dinitrobiphenyl have been detailedstudied in the synthesis of achiral biphenyl backbones.Diastereomeric P,N-ligands were conveniently synthesized from racemicbiphenyl backbones ((±)-2-amine-2'-hydroxy-4,4',6,6'-tetramethyl-1,1'-biphenyl)and (S)-BINOL in two steps. In the Cu(I)-catalyzed enantioselective 1,4-conjugateadditions of Et₂Zn to acyclic enones, the developed catalysts derived from theseligands exhibited high enantioselectivity and good catalytic activity. Up to 96.1 %ee with 70.5 % yield was achieved with 4-Cl-chalcone as substrate, which wasequivalent to the result obtained bythe corresponding enantiopure ligands.The achiral biphenyl backbones (substituted 2-amine-2'-hydroxy-1,1'-biphenyl) were synthesized via diazotation/iodination, Ullmann coupling,selective reduction, diazotation/hydrolysis and hydrogenation from 4-substituted-2-nitroaniline in five steps. The process of diazotation/iodination was carefullyoptimized in the research. New flexible ligand derived from this achiral biphenylbackbone was applied in Cu(I)-catalyzed enantioselective 1,4-conjugate additionsof Et₂Zn to chalcone.In the studies on the selective reductions of 2,2'-dinitrobiphenyl,benzo[c]cinnoline N-oxide, benzo[c]cinnoline N,N-dioxide, 2,2'-diaminobiphenyland 2-amine-2'-nitrobiphenyl could be selectively obtained, using aqueous Na2S2as the reductant and by tuning the reaction conditions, such as, solvents,temperature, the pH of the reaction system and quantity of Na2S2. Among of theselective reduction of 2,2'-dinitrobiphenyls to their corresponding 2-amine-2'-nitrobiphenyls, up to 80-90 % of isolated yields were obtained. which are thebest results to date.