Palladium-catalyzed alkoxycarbonylation and aminocarbonylation of terminal alkynes: Synthesis and applications of alpha,beta-unsaturated esters and amides. Computational study of the reaction mechanism

Palladium-catalyzed carbonylation reactions, carried out in the presence of various nucleophiles like amines and alcohols, belong to the most widely used homogeneous catalytic reactions in synthetic chemistry. The alpha,beta-unsaturated amides and esters produced from the above reactions are important intermediates in a wide range of organic reactions. In the present study, we have successfully developed a catalyst system for the alkoxycarbonylation of phenylacetylene using palladium-dppb-salicylborate catalyst system with high regioselectivity towards the formation of trans isomer under mild reaction conditions. Milder reaction conditions for the alkoxycarbonylation and aminocarbonylation of terminal mono and dialkynes have been obtained using the catalyst system Pd(OAc)2/dppb/p-TsOH/CH3CN/CO in acetonitrile. Results showed significant disparity in the conversion of terminal alkynes and in the selectivity towards the gem or trans unsaturated esters or amides by changing the type of nucleophile. The catalyst systems have been optimized by screening various reaction parameters (catalyst precursor, ligand, CO pressure, solvent and temperature).;Furthermore, an effective synthesis of mono and dicyclic succinimides has been achieved via palladium-catalyzed alkoxycarbonylation of gem-enamides followed by ring closure. New palladium-binuclear complexes based on chelating diimines and bridging diphosphine or diimine ligands have been successfully synthesized and characterized. The new complexes showed a promising activity in the coupling of arylboronic compounds to various electron-rich and deficient olefins.;We have carried out computational investigation of mechanisms proposed for alkoxycarbonylation and aminocarbonylation reactions in order to account for the interesting activity and regioselectivity of the developed palladium catalyst systems.