The deracemization of racemic material is an important synthetic technology of optical pure compounds. Dynamic kinetic resolution(DKR)/asymmetric transformation(DYKAT) represent the outstanding technologies in this field. Compared with the conventional enzyme-catalyzed kinetic resolution, transition metal-catalyzed DKR could transform racemic material 100% to the single enantiomer. Recent developed DYKAT strategies enhanced the practice of deracemization technologies.
Prof. LIAO Jian's lab at the Chengdu Institute of Biology, Chinese Academy of Sciences reported an unprecedented example of palladium-catalyzed DYKAT using a novel bifunctional ligand(Angew. Chem. Int. Ed. 2013, 52, 4207 –4211). Bisulfoxide-phosphine ligands were designed based on the concept of cooperative catalysis, one sulfinyl group acting as a metal-binding site and the other one serving as a bronsted base. Such a conception was applied in the palladium-catalyzed asymmetric reaction of 1,3-unsymmetric allylic acetate and indole with highly regio-(85/15-96/4) and enantioselectivities(84-95%).
In this deracemization example, a DYKAT mechanism via Pd(0)-promoted epimerization of allylpalladium species was proved by control experiments and each enantiopure-material convergent transformation. Particularly, a hydrogen-bond binding interaction of the secondary sulfinyl group with (N)H-indole was confirmed by 1H NMR titration experiments. And the comparison experiments demonstrated the key role of the existence of such hydrogen-bond interaction.
More results entitled "Hydrogen-Bond-Promoted Palladium Catalysis: Allylic Alkylation of Indoles with Unsymmetrical 1,3-Disubstituted Allyl Acetates Using Chiral Bis(sulfoxide) Phosphine Ligands" have been published on Angewandte Chemie International Edition,in April of 2013.