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(5H)-one as the sole product under otherwise identical reaction conditions.

A simple Hückel model-driven strategy to overcome electronic barriers to retro-Brook silylation relevant to aryne and bisaryne precursor synthesis.

ortho-Silylaryl triflate precursors (oSATs) have been responsible for many recent advances in aryne chemistry and are most commonly accessed from the corresponding 2-bromophenol. A retro-Brook O- to C-silyl transfer is a key step in this synthesis but not all aromatic species are amenable to the transformation, with no functionalized bisbenzyne oSATs reported. Simple Hückel models are presented which show that the calculated aromaticity at the brominated position is an accurate predictor of successful retro-Brook reaction, validated synthetically by a new success and a predicted failure. From this, the synthesis of a novel difunctionalized bisaryne precursor has been tested, requiring different approaches to install the two C-silyl groups. The first successful use of a disubstituted o-silylaryl sulfonate bisbenzyne precursor in Diels-Alder reactions is then shown.