Catalytic C−C bond cleavage processes followed by further transformations are some of the most fascinating reactions in chemistry and valuable organic synthesis tools. Herein, we demonstrate that the regioselectivity of C−C bond cleavage in 1-azabiphenylene and its derivatives can be switched by using neutral or cationic transition metal catalysts. The use of the former leads to selective distal C−C bond cleavage (with respect to the position of the nitrogen atom), whereas use of the latter leads to selective proximal bond cleavage. This process enables synthesis of a variety of complex heterocycles by regioselective C−C bond cleavage switched on demand. Density functional theory calculations (SMD/M06/DGDZVP level of theory) show that the regioselectivity is a result of kinetically controlled oxidative addition into the C−C bond. In neutral complexes the transition states (TS) for distal cleavage have lower energy, in agreement with experiments. For the cationic catalyst, the proximal TSs are stabilized presumably by relieving the Cl−N dipole−dipole repulsion when the Rh-bound Cl is removed whereas the distal TSs remain largely unaffected.

The reaction of biphenylene with various nitriles in the presence of catalytic amount of [Rh(cod) 2 BF 4 ]/dppe under microwave irradiation afforded 9-substituted phenanthridines. The reaction with alkyl and aromatic nitriles provided the corresponding 9-substituted phenanthridines in 26-79% isolated yields. The reaction was also carried out with cyanopyridines and it provided heterocyclic compounds with the bipyridine and terpyridine scaffold. The synthesized bipyridine and terpyridine were complexed with [Rh(cod)Cl] 2. The former provided a Rh(III) complex in which the cyclooctadiene moiety was oxidized to the tetrahydrofuran ring, whereas the latter gave a structurally fluxional complex (in solution) with only one pyridine ring coordinated to the rhodium atom.

9‐Substituted phenanthridines are prepared by microwave‐assisted reaction of biphenylene with various (hetero)aromatic and aliphatic nitriles.