A facile two-step synthesis of aza[7]helicenes possessing a 6-5-6-6-6-5-6 skeleton from commercially available 2,9-dichloro-1,10-phenanthroline via double amination with aniline derivatives followed by hypervalent iodine reagent-mediated intramolecular double-NH/CH couplings was developed. Single-crystal X-ray analyses of the helicenes revealed unique structures, including both a significantly twisted center and planar terminals of the skeleton. The azahelicenes show high fluorescent quantum yields (Φs) under both neutral (Φ: 0.25-0.55) and acidic conditions (Φ: up to 0.80). An enantiomerically pure aza[7]helicene showed high circularly polarized luminescence (CPL) activity under both neutral and acidic conditions (g : up to 0.009).

A facile two‐step synthesis of aza[7]helicenes possessing a 6‐5‐6‐6‐6‐5‐6 skeleton from commercially available 2,9‐dichloro‐1,10‐phenanthroline via double amination with aniline derivatives followed by hypervalent iodine reagent‐mediated intramolecular double‐NH/CH couplings was developed. Single‐crystal X‐ray analyses of the helicenes revealed unique structures, including both a significantly twisted center and planar terminals of the skeleton. The azahelicenes show high fluorescent quantum yields (Φs) under both neutral (Φ: 0.25–0.55) and acidic conditions (Φ: up to 0.80). An enantiomerically pure aza[7]helicene showed high circularly polarized luminescence (CPL) activity under both neutral and acidic conditions (glum: up to 0.009).

Acid-responsive fluorescent compounds were prepared by introducing a nitrophenyl group to L-shaped pentacycles with a pyrrolo[1,2-a][1,8]naphthylidine backbone. These compounds show almost no fluorescence under neutral conditions, but emit green to orange fluorescence upon addition of trifluoroacetic acid. Acid titration experiments and NMR spectroscopy, plus DFT calculations, show that formation of a pyridinium cation species is responsible for the appearance of fluorescence.

Brønsted acid-promoted intramolecular hydroarylation of alkynylbenzenes carrying an arylalkyl group at the ortho-position leads to alkylidenedibenzo[a,d]cycloheptenes, -octenes and -nonenes in up to quantitative yield with complete regioselectivity. The scope and limitation of this reaction and application to the synthesis of tricyclic antidepressants are described.