Research Projects

Enantioselective allylation constitutes one of the more actively studied reaction types in which chiral phosphoric acids and palladium catalysts have been employed. Efforts have been made to incorporate a variety of allyl electrophiles with and without a preinstalled leaving group as well as to integrate a variety of nucleophilic coupling partners. The combination of CPAs with transition metal catalysts imparts new reactivity (and selectivity) manifolds that are not accessible by their individual catalytic components.Specifically, enantioselective allylic substitution reactions of nonderivatized (unactivated) allylic alcohols are desirable as a step-economic approach to the formation of key carbon–carbon and carbon–heteroatom bonds. The synergy between two distinct catalysts allows for unique reactivity of these substrates, often with enhanced enantio- and diastereocontrol. It has been found that trivalent phosphorus ligands are capable of facilitating Pd-catalyzed allylic C−H functionalization of α-alkenes upon using p-quinone as an oxidant. In these reactions, a 16-electron Pd(0) complex bearing a monodentate phosphorus ligand, a p-quinone, and an α-alkene has been identified as a key intermediate. Through a concerted proton and two-electron transfer process, electrophilic π-allylpalladium is subsequently generated and can be leveraged to forge versatile chemical bonds with a wide range of nucleophiles. In few cases, the combination of chiral phosphoric acid and a palladium complex of a chiral phosphoramidite ligand becomes fruitful for the the allylic C−H alkylation of α-alkenes. The enantioselective allylic C−H functionalization reactions are tolerant of a wide range of nucleophiles and α-alkenes, providing a large library of optically active building blocks. However, most of the reported methods are intermolecular processes and intramolecular reactions are hardly reported. Thus the PI likes to develop asymmetric organocatalytic syntheses of chiral 1-aryl-4,9-dihydrocarbazoles,1,3-dihydroisobenzofurans, cyclohexanones/cyclopentanones/carbocycles and pyrrolidines via intramolecular allylic substitution reactions. Asymmetric intramolecular allylic C−H functionalization can thus provide straightforward entry to chiral cyclic compounds, featuring either atom- or step-economy.