Planar Blatter radicals through Bu3SnH- and TMS3SiH-assisted cyclization of aryl iodides: azaphilic radical addition

Abstract

Bu₃SnH- and TMS₃SiH-assisted cyclizations of iodoarene derivatives of benzo[e][1,2,4]triazine lead to the formation of planar Blatter radicals (2-phenyl-3H-[1,2,4]triazino[5,6,1-kl]phenoxazin-3-yls and 2-phenyl-3H-[1,2,4]triazino[5,6,1-kl]phenothiazin-3-yls) in yields of up to 96%. The cyclization step involves the thermodynamically favored (DFT: ΔG^‡₂₉₈ = 3.1 kcal mol⁻¹ and ΔH = –55.3 kcal mol⁻¹) unprecedented attack of a C-centered radical on the heterocyclic N atom. This method opens up access to functionalized sulfur-containing planar Blatter radicals for the first time. New radicals were characterized using spectroscopic (UV–vis, EPR), electrochemical, and single-crystal X-ray diffraction methods.