Metal-Free Selective Borylation of Arenes by a Diazadiborinine via C–H/C–F Bond Activation and Dearomatization

A newly developed annulated 5-chlorinated 1,3,2,5-diazadiborinine derivative (4) selectively activates a C–H bond of benzene (C₆H₆) and 1,3-di­(trifluoromethyl)­benzene, as well as a C–F bond in partially fluorinated arenes, to furnish borylation products under catalyst-, metal-, and irradiation-free conditions. Moreover, 4 readily undergoes a reversible dearomative coupling reaction with polycyclic aromatic hydrocarbons to afford diboration products. The latter represents the first reversible intermolecular dearomative diboration of arenes.