Carbon–Carbon Bond Formation between N‑Heterocyclic Carbene Ligand on Ruthenium Carbene Catalysts and 1,4-Naphthoquinone via Intramolecular Carbon(sp3)–Hydrogen Bond Activation

Reactions of ruthenium carbene catalysts, including their metathesis, nonmetathesis, and decomposition reactions, have been extensively studied because of their importance in organic synthesis. Here, we developed a novel cross-coupling reaction between 1,4-naphthoquinone and NHC ligands on ruthenium benzylidene complexes via intramolecular C­(sp3)–H bond activation. Also, we discovered a novel tricyclic blue pigment, 2-(1-mesityl-5,7-dimethyl-2,3-dihydro-1H-imidazo­[1,2-a]­indol-9-yl)­naphthalene-1,4-dione, as a product of the reaction.