Photocyclization of 8-Aryloxybenzo[e][1,2,4]triazines Revisited: Unambiguous Structural Assignment of Planar Blatter Radicals by Correlation NMR Spectroscopy

The recent discovery of a photo-Smiles rearrangement and the development of effective analytical methods prompted structural investigation of the previously reported planar Blatter radicals obtained by photocyclization of 8-aryloxy-3-phenylbenzo[e][1,2,4]triazines. Thus, seven freshly prepared radicals were cleanly converted to their leuco forms and analyzed by 2D correlation 1H NMR methods (COSY, TOCSY, and ROSEY). Results demonstrate that all investigated 8-aryloxy-3-phenylbenzo[e][1,2,4]triazines undergo photocyclization with Smiles rearrangement and exclusive formation of a single rearranged product. This work corrects the previously reported structural assignment and DFT data of planar Blatter radicals and further demonstrates the generality of this new variation of the photo-Smiles rearrangement.