A practical synthesis of 6-[2-(2,5-dimethoxyphenyl)ethyl]-4-ethylquinazoline and the art of removing palladium from the products of Pd-catalyzed reactions

A concise large-scale synthesis of 1, a new antimitotic agent is described. The key step was a one-pot Sonogashira cross-coupling of an aryl halide with a heteroaryl halide through an acetylene using the readily available 2-methyl-3-butyn-2-ol (7). An innovative approach for palladium removal was designed and successfully scaled-up on a multikilogram scale. The product was crystallized from the crude reaction mixture while keeping the residual palladium in the mother liquor by using Pd-scavenging agents such as N-acetylcysteine or thiourea.