Halogen lamp irradiation of benzo[e][1,2,4]triazines 2[X] in CH2Cl2 solutions leads to planar ring-fused 1,4-dihydro[1,2,4]triazin-4-yl radicals 1 through a novel, potentially general, cyclization mechanism. The scope and efficiency of the method were established for unsubstituted and ortho-substituted (X = NH2, Br, NO2) phenoxy, naphthyloxy, and quinolinoxy derivatives 2[X]. The regioselectivity of 2[X] photocyclization was rationalized with DFT computational methods. Radicals 1 were characterized by spectroscopic (UV-vis, EPR), electrochemical, and XRD methods.
Bibliographical noteFunding Information:
Support for this work was provided by the National Science Center (2017/25/B/ST5/02851) and Foundation for Polish Science (TEAM/2016-3/24). ChemMatCARS Sector 15 is supported by the NSF under Grant Number CHE-1834750. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Authors thank Ms. Małgorzata Celeda for her technical assistance.
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