Critical Assessment of the Reducing Ability of Breslow?type Derivatives and Implications for Carbene?Catalyzed Radical Reactions**

We report the synthesis of acyl azolium salts stemming from thiazolylidenes CNS, triazolylidenes CTN, mesoionic carbenes CMIC and generation their corresponding radicals enolates, covering about 60 Breslow-type derivatives. This study highlights role additives in redox behavior these compounds unveils several critical misconceptions radical transformations aldehyde derivatives under N-heterocyclic carbene catalysis. In particular, reducing ability enolates has been dramatically underestimated case biomimetic CNS. contrast with previous electrochemical studies, we show that catalytic intermediates can transfer electrons to iodobenzene within minutes at room temperature. Enols derived are not previously claimed super electron donors, although enolate CNS powerful agents.