Chlorination of quinoxalino[2,3-c]cinnolines : mechanistic studies

Abstract

Section 1 (Introduction) gives a brief outline of some cyanide-induced cyclisation reactions of ortho-substituted nitrobenzene derivatives, and the proposed mechanism for the cyclisation of N-(o-nitrobenzylidene)-o-phenylenediamines to quinoxalino[2,3-c]cinnolines. An overview of the mechanism for the chlorination of the quinoxalinocinnoline ring and the reasoning behind the hypothesis is also given, as are the aims of the project. Section 2 (Results and Discussion) develops the mechanistic ideas outlined in Section 1 relating to the chlorination reaction, and attempts to divert the course of this reaction by hindering the protonation of the quinoxalinocinnoline at the preferred location. Chlorination of l-methylquinoxalino-[2,3-c]cinnoline, however, still follows the usual pathway, although the reaction is both slow and incomplete. These results therefore support the previous proposal that protonation occurs preferentially at N-12. Attempts to synthesise the analogous ring system in which N-12 is lacking have so far met with no success. Section 3 (Experimental) details the synthetic procedures used and this is followed by the Bibliography.