Reductive Dimerization of Macrocycles Activated by BBr3.

A macrocyclic motif composed of carbazole and pyridine subunits linked by a carbonyl bridge (C═O) forms a skeleton with a peripheral reactivity that leads to a pinacol-like coupling activated by BBr3, eventually entrapping a substantially elongated C-C bond. Slightly modified conditions lead to the efficient transformation of the C═O unit to a CH2 linker that, after exposure to air, gives a dimeric molecule with multiple bonds between two macrocyclic units, as documented in spectroscopy and X-ray analysis.