Double head-to-tail direct arylation as a viable strategy towards the synthesis of the aza-analog of dihydrocyclopenta[]aceanthrylene - an intriguing antiaromatic heterocycle

The first case of double head-to-tail direct arylation of aromatic compounds and the unusual photophysical properties of the resulting 2,2 a 1,5 b 1,7 -tetraazacyclopenta[ hi ]aceanthrylene are reported. This molecule, comprising of two imidazo[1,2- a ]pyridine units, is antiaromatic due to the changes in the efficiency of π-electron ring current and it belongs to a class of seldom encountered compounds with a dark lowest electronically excited singlet state. Straightforwardly prepared head-to-tail bis-imidazo[1,2- a ]pyridine displays antiaromaticity and no fluorescence.