Efficient Pd-catalyzed allene synthesis from alkynes and aryl bromides through an intramolecular base-assisted deprotonation (iBAD) mechanism

Abstract

An optimized ligand-controlled palladium-catalyzed allene synthesis starting from alkynes and aryl bromides giving rise to allene products in a simple and direct manner is described. The methodology is performed in an inter- and intramolecular fashion with unprecedented scope and excellent yields. Based on mechanistic investigations and on DFT calculations, the role played by the carboxylic additive (i.e., PivOH) in controlling the selectivity of the reaction is discussed, allowing us to propose an intramolecular base-assisted deprotonation (iBAD) mechanism for this process.

Keywords: Heck reaction; allenes; density functional calculations; palladium; reaction mechanisms.