Acetic anhydride generated imidazolium ylide in ring closures onto carboxylic acids; part of the synthesis of new potential bioreductive antitumor agents

Acetic anhydride behaves as a traceless activating agent allowing thermal intramolecular condensation of 2-(benzimidazol-1-ylmethyl) benzoic and nicotinic acids. Autoxidation gives benzimidazo[1,2-b]isoquinoline-6,11-diones (intermediates characterized) and benzimidazo[2,1-g]-1,7-naphthyridine-5,12-diones in a facile, one-pot transformation. The 1,4-dimethoxy analogue of the former is converted into benzimidazo[1,2-b]isoquinoline-1,4,6,11-tetrone using cerium ammonium nitrate (CAN). The 1,7-naphthyridine-5,12-dione system readily ring-opens, and an X-ray crystal structure of the methanol adduct was obtained.