Cyclizations. Part 3. Use of a mild-steel cathode in the electrochemical intramolecular cyclization of aryl halides

Abstract

One electron reduction of aryl halides is known to generate the aryl radical and halide ion. These aryl radicals will cyclize onto an adjacent benzene ring in a reaction that is potentially useful in organic synthesis and which is well documented at a mercury cathode. 5-(2-Halophenyl)-1-(4-fluorophenyl)tetrazoles are used here as representative substrates and the cyclization reaction to 7-fluorotetrazolo[1,5-f]phenanthridine is developed at cathodes of cadmium, zinc and mild-steel. A high yield of the desired cyclization product is achieved using a mild-steel cathode and a sacrificial magnesium anode in an undivided cell with acetonitrile, 0.1 M tetraethyl ammonium tetrafluoroborate as electrolyte and under an air atmosphere.