iron(II) trifluoromethanesulfonate; 2-((4R,5R)-1-((4-(tert-butyl)phenyl)sulfonyl)-4,5-diphenylimidazolidin-2-yl)-6-((4R,5R)-1-((4-(tert-butyl)phenyl)sulfonyl)-4,5-diphenylimidazolidin-2-yl)pyridine; oxygen T=60°C; P=760.051 Torr; 16 h; Green chemistry; Catalytic behavior; regioselective reaction;