Important consequences for gas chromatographic analysis of the Sonogashira cross-coupling reaction

On following the kinetics of the Sonogashira alkynylation reaction of halogenated 2-pyrone 1 with phenylacetylene we have found that turnover continues to occur in sample vials even after quenching by commonly employed silica adsorption methods and product elution with small quantities of CH2Cl2. Trace quantities of Pd are carried through the silica plug. Addition of a CH2Cl2 solution of 1,2-bis(diphenylphosphino)ethane (dppe) to the quenched sample inhibits the reaction and represents a more reliable method for determining yields and reaction kinetics.