One-Pot Rh(III)-Catalyzed Twofold C-H Activation/Oxidative Annulation of N-Arylpyrroles with Alkynes to Fluorescent Ullazines

A range of densely functionalized ullazines have been synthesized by a one-pot Rh(III)-catalyzed twofold C-H activation/oxidative annulation of N-arylpyrroles with alkynes. Electrophilic bromination at 5- or 5,7- positions of the EWG-substituted ullazine core offers an interesting single or double entry for further extended functionalization. Mechanistic considerations suggest two complementary paths, EWG-assisted and SEAr, for the C-H activations. All ullazines exhibit strong fluorescence emissions. Ullazines bearing thiophene and triarylamine units at 5- and 5,7- positions show a significant bathochromic shift in their emission spectra, attributed to the more extended electronic circuits present.