Dephosphinylative [4 + 2] Benzannulation of Phosphinyl Ynamines: Application to the Modular Synthesis of Polycyclic Aromatic Amines

A series of 9-amino-10-halophenanthrenes were synthesized through a one-pot process, including dephosphinylative Sonogashira–Hagihara coupling of 2-bromobiphenyls with air-stable phosphinyl ynamines, followed by halonium-promoted [4 + 2] benzannulation of the resulting 2-(aminoethynyl)­biphenyls. Nonsubstituted and methyl-substituted 2-bromobiphenyls rapidly underwent the Sonogashira–Hagihara aminoethynylation and the halogenative Friedel–Crafts benzannulation to provide the corresponding amino­(halo)­phenanthrenes in high yields, while electron-sufficient and -deficient substrates did slowly undergo the former and the latter to result in low yields, respectively. This protocol worked well for the syntheses of highly π-extended aminophenanthrenes and aminobenzonaphthothiophenes with different optical properties. Further application of this approach between 2,2″- and 2′,5′-dibromo-p-terphenyls with phosphinyl ynamines led to the regioselective formation of 6,13-diamino-5,12-dihalo- and 5,12-diamino-6,13-dihalo-dibenz­[a,h]­anthracenes via dual aminoethynylation and [4 + 2] benzannulation. The obtained analogues showed different ultraviolet–visible absorption and photoluminescence spectra with different emission quantum yields in CH2Cl2 solution and the powder state.