Selective access to dihydrophenanthridines and phenanthridinones via cyclisation of aryl amines onto N -tethered arynes.

5,6-Dihydrophenanthridines are prepared from aryl amines via intramolecular addition to N -tethered arynes under mild conditions. A new o -silylaryl triflate precursor was developed to increase reactivity and enable electron-rich and electron-poor aryl amines to undergo cyclisation. A complete switch in product selectivity occurs when the reaction is conducted in air, affording the corresponding phenanthridin-6(5 H )-one as the sole product under otherwise identical reaction conditions.