SYNTHESIS OF SOME FLUORONITROBENZIMIDAZOLES AND THEIR REACTIVITIES TOWARD PEPTIDE NUCLEOPHILES

A series of monomtro- and dmitro-4-fluorobenzimidazoles has been prepared using 2-fluoroacetanilide as starting point. Assignment of position to the nitro groups is based on analyses of nmr hydrogen-fluorine coupling constants. Orientation in nitration is controlled by the fluorine atom rather than by the fused imidazole ring, except where steric factors intercede. At 25°, 5,7-dmitro-4-fluorobenzimidazole is 84 times as reactive as 2,4-dinitrofluorobenzene toward a peptide nucleophile. The enhanced reactivity is attributed primarily to the ability of the fused imidazole ring to participate in stabilization of the Meisenheimer adduct. The corresponding benzimidazole anion, as well as a series of mononitrofluorobenzimidazoles, are unreactive under the same conditions. © 1969, American Chemical Society. All rights reserved.