Modular Synthesis of Biaryl-Substituted Phosphine Ligands: Application in Microwave-Assisted Palladium-Catalyzed C-N Cross-Coupling Reactions
Résumé
Biaryl-substituted monophosphine-based ligands, I, II, III and IV, have been synthesized by transition-metal-free "ARYNE" cross-coupling reaction of aryllithiums with 1,2-dibromobenzene and subsequent regioselective functionalization through bromine-lithium interconversion. These ligands were employed in palladium-catalyzed C-N bond-forming reactions. The reaction was found to be general with wide substrate applicability. A wide variety of both primary and secondary amines were successfully coupled with an array of differently substituted halobenzenes under microwave irradn. to give the expected products in good to excellent yields. A no. of biaryl-substituted phosphine ligands screened for the coupling reaction showed that steric bulk and the electronic properties of substituents on phosphorus play a crucial role in governing the catalytic activity of C-N cross-coupling reactions.