Distinguishing Between Linear and Nonlinear (Cooperative) Mechanisms of Substrate Activation Under “Ligand- and Copper-Free” Conditions of the Sonogashira Reaction

A comparative study was made of the differential selectivity of the Sonogashira reaction with a pair of competing arylacetylenes under “ligand- and copper-free” conditions by varying nature and concentration of aryl halides and bases common to competing substrates. The change in the differential selectivity with varying nature of aryl halides is consistent with the proposal that aryl halide and arylacetylene are activated sequentially according to a mechanism that is linear in terms of chemical kinetics. The observed lack of influence of the nature and concentration of the base on the selectivity of the reaction under competition between arylacetylenes indicates that the step of their activation is virtually irreversible.