Addition, Substitution, and Ring-Contraction Reactions of Quinones with N-Heterocyclic Carbenes.

Despite the common use of quinones as oxidizing agents in N-heterocyclic carbene (NHC)-based organocatalysis and transition-metal catalysis, the direct reactivity of quinones with NHCs remains underexplored. In this paper, we report the reactivity of NHCs with common p- and o-quinones, uncovering three unreported reactions involving contractions of the quinone ring that lead to push-pull furanolactone chromophores, NHC fulvalenes, and α-acylimidazolium cyclopentenone derivatives. These experiments also provide a rationale for the superior compatibility of tetra- tert-alkylated diphenoquinones in NHC-based oxidative transformations.

Transition metal-catalyzed site- and regio-divergent C-H bond functionalization.

Recent advances in transition metal-catalyzed C-H bond functionalization have profoundly impacted synthetic strategy. Since organic substrates typically contain several chemically distinct C-H bonds, controlling the regioselectivity of C-H bond functionalization is imperative to harness its full potential. Moreover, the ability to alter reaction pathways to selectively functionalize different C-H bonds in a substrate represents a greater opportunity and challenge. The choice of catalysts, ligands, solvents, and even more subtle variations of the reaction conditions have been shown to allow the formation of regioisomeric C-H functionalization products starting from the same precursors. This review describes recent advances in transition metal-catalyzed divergent C-H bond functionalization that highlight its potential in organic synthesis.