Direct n.c.a. electrophilic radioiodination of deactivated arenes with N-chlorosuccinimide

An efficient method for the direct electrophilic no-carrier-added (n.c.a.) radioiodination of deactivated arenes has been developed using N-chlorosucc inimide (NCS)/radioiodide in trifluoromethanesulfonic acid (triflic acid). Optimization of the one pot labelling procedure using chlorobenzene as a mo del substrate resulted in a radiochemical yield of 75% within 15 min at roo m temperature. Drying of the aqueous radioiodide solution prior to radiolab elling was not required. Radioiodination of weakly activated and deactivate d monosubstituted benzene derivatives gave rise to radiochemical yields of about 80% with an electrophilic substitution pattern. Strongly deactivated aromatic compounds were radioiodinated with high radiochemical yields of ab out 70% exclusively in their meta-position using a reaction temperature of 75 degrees C and a reaction time of 1 h. With regard to the reaction mechan ism, in situ formed radioiodo(I) trifluoromethanesulfonate (triflyl [I-131] hypoiodite) is discussed as electrophilic reagent.