The nucleophilic aromatic substitution(SNAr)reactions of activated substrates have been well studied and continue to draw attention as a synthetic method.The two-step reaction mechanism,the addition of the nucleophile to form a tetrahedron Meisenheimer complex and the elimination of the leaving group from the substituted cyclohexadienide anion,is commonly accepted to account for the so-called element effect and for SNAr reactivity in general.