Controlling the chemoselectivity of Palladium catalysed cyclizations of (2-iodoanilino)-carbonyl compounds

Abstract

The factors which control the chemoselectivity of palladium catalyzed cyclizations of (2- haloanilino) carbonylic compounds have been explored by an extensive experimental-computational (DFT) study. It was found that the selectivity of the process, i.e. the formation of fused six versus fivemembered rings, can be controlled by the proper selection of the initial reactant, reaction conditions and the additives. Thus, esters or amides produce ketones by a nucleophilic addition process, whereas the addition of PhO- leads to the formation of indolines by an α-arylation reaction. In contrast, the corresponding ketone reactants yield mixture of both reaction products in the presence of phenol whose ratio depends on the base used. The outcome of the processes can be explained by the formation of a common four-membered palladacycle intermediate from which the competitive nucleophilic addition and α-arylation reactions occur. The remarkable effect of phenol in the process, which makes the αarylation reaction easier, was found to favor the formation of enol-complexes which are stabilized by an intramolecular hydrogen bond between the hydroxyl group of the enol moiety and the oxygen atom of the phenoxy ligand. Moreover, the chemoselectivy of the process can be also controlled by the addition of bidendate ligands leading to the almost exclusive formation of indoles at expenses of the corresponding alcohols.