Axially Chiral Stable Radicals: Resolution and Characterization ofBlatter Radical Atropisomers

Abstract

Atropisomers of three Blatter radicals were obtainedby the addition of 8-substituted 1-naphthyllithiums to 3-phenyl and3-t-butylbenzo[e][1,2,4]triazine and separated by chiral high-performance liquid chromatography. Their absolute configurationswere assigned by a comparison of experimental and time-dependent density functional theory calculated electronic circulardichroism spectra. The free energy of activation,ΔG‡298, and thehalf life of racemization,t1/2, at 298 K were determined at∼25 kcal mol−1and <130 h, respectively. Intramolecularπ−πinteractionsin radicals were evident from single-crystal X-ray diffraction, density functional theory, and electrochemical analyses.