Catalytic Action of Azolium Salts. VIII. Oxidative Aroylation with Arenecarbaldehydes Catalyzed by 1,3-Dimethylbenzimidazolium Iodide.

N-Heterocyclic carbene-catalyzed oxidations

“…Several reports exist of thiazolium or benzimidazolium reagents catalyzing the oxidation of aromatic aldehydes to esters. 29–33,35 A representative example is the recent disclosure by Connon and co-workers of an approach utilizing a thiazolium catalyst and azobenzene as an oxidant 55. While this method gives good yields for the oxidation of substituted benzaldehydes (46–97% yield, 8 substrates), application to unactivated substrates results in poor yields of the ester.…”

“…Using a non-enzymatic thiazolium-based N -heterocyclic carbene (NHC), very brief studies concerning the oxidative transformation converting aromatic aldehydes to esters were reported 29–32. More recently, Miyashita33 has demonstrated that other NHCs derived from triazolium and benzimidazolium salts, are capable of catalyzing the oxidation of aryl aldehydes. These processes generally employed organic oxidants such as substituted nitrobenzenes, azobenzene derivatives, and flavin.…”

N-heterocyclic carbene-catalyzed rearrangements of vinyl sulfones

“…3 Carbene catalysis is highly versatile and allows access to acyl anions, 4 homoenolates, 5 enolates, 6 Cannizarro-type reductions, 3 c and oxidations. 7 The majority of NHC catalysis currently involves the 1,2-addition of the carbene to a carbonyl-containing species which then proceeds to produce an acyl anion or homoenolate equivalent. A different mode for these nucleophilic catalysts is a conjugate addition manifold.…”

N-Heterocyclic Carbene-Promoted Rauhut–Currier Reactions between Vinyl Sulfones and ?,?-Unsaturated Aldehydes

“…[3] Inspired by the biological conversion of pyruvate into acetyl Co-A by a thiamin cofactor, NHC catalysis utilizes the electron lone pair of nitrogen-containing heterocycles (i.e., thiazolium, imidazolium, and triazolium-derived carbenes) to promote a variety of reactions including acyl anion chemistry, [4] homoenolate [5] and enolate [6] equivalents, reductions, [3c] and oxidations. [7] Carbene catalysis is well known for the 1,2-addition of the carbene to a carbonyl group of a substrate, affording an acyl anion or homoenolate equivalent (Scheme 1). A less developed reactivity mode for these Lewis base catalysts is the conjugate addition of an α,β-unsaturated carbonyl-containing compound to generate a reactive enolate intermediate.…”