Competition between Two Modes of 6 pi-Photocyclization: A Case Study for 3-(1,2-Diarylvinyl)-2-arylimidazo[1,2-a]pyridines

The photochemical 6 pi-electrocyclization of diarylethenes (DAE), 2-vinylbiaryls (VBA) and their derivatives is widely used in organic synthesis. Combination of these motifs in one molecule opens the issue of selectivity of the photochemical reaction. We have found that upon UV irradiation, 3-(1,2-diarylvinyl)-2-arylimidazo[1,2-a]pyridines comprising both DAE and VBA moieties form products of VBA cyclization followed by oxidation. The selectivity of the process was rationalized by DFT calculations. The presented reaction gave access to highly fluorescent 5,6-diarylnaphtho[1 ',2 ':4,5]imidazo[1,2-a]pyridine derivatives.