Oxalamide-based bisdiamidophosphites: synthesis, coordination, and application in asymmetric metallocatalysis

Abstract

A series of easy-to-prepare and modular chiral bisdiamidophosphites with oxalamide linkers were synthesized. The structures of the novel ligands were elucidated by means of 2D-NMR and confirmed by single-crystal X-ray diffraction. The reactions of such ligands with [Pd(Cod)Cl₂] at molar ratios of L/Pd = 1 and 0.5 were studied by ¹H, ¹³C, ¹³C DEPT, ³¹P, ¹H–¹³C HSQC, ¹H–¹³C HMBC, ¹H–¹H COSY, ¹H–¹H ROESY, ¹H–¹⁵N HMBC and DOSY spectroscopy, as well as by DFT calculations. Stereoselectors of this type exhibited high enantioselectivities in the Pd-catalyzed allylic substitution reactions of (E)-1,3-diphenylallyl acetate with pTolSO₂Na (up to 92% ee), CH₂(CO₂Me)₂ (up to 97% ee), (CH₂)₄NH (up to 96% ee), (EtO)₂P(O)CH₂NH₂ (up to 96% ee) and (CH₂)₄N(CCH(CH₂)₄) (up to 92% ee). ee values of up to 90%, 97% and 83% were obtained in the Pd-mediated allylic alkylation of cinnamyl acetate with ethyl 2-oxocyclohexane-1-carboxylate, allylic amination of cyclohex-2-en-1-yl ethyl carbonate with dibenzylamine and desymmetrization of N,N’-ditosyl-meso-cyclopent-4-ene-1,3-diol biscarbamate, respectively. In addition, ee values of up to >99% were achieved in the Rh-catalyzed asymmetric hydrogenation of methyl esters of unsaturated acids.