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

Abstract

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.

Realizing Metal-Free Carbene-Catalyzed Carbonylation Reactions with CO

“…On the other hand, all attempts to use BiCAAC and CAAC Me as catalysts failed, even when more forcing experimental conditions were used. We discovered that BiCAAC and the small CAAC Me readily react with Quin , leading irreversibly to adducts I and II , respectively, thus quenching the catalytic cycle (Scheme ). As a control experiment, we confirmed that the bulky CAAC did not react with the o -quinone even at 80 °C and thereby leads to a viable catalyst.…”