ABSTRACT
Reactions of 2-carbonyl- and 2-hydroxy(or methoxy)alkylbenzimidazoles with arenes in the Brønsted superacid TfOH resulted in the formation of the corresponding Friedel-Crafts reaction products, 2-diarylmethyl and 2-arylmethyl-substituted benzimidazoles, in yields up to 90%. The reaction intermediates, protonated species derived from starting benzimidazoles in TfOH, were thoroughly studied by means of NMR and DFT calculations and plausible reaction mechanisms are discussed.
ABSTRACT
The reaction of 5-hydroxymethylfurfural (5-HMF) with arenes in superacidic trifluoromethanesulfonic acid (triflic acid, TfOH) as the solvent at room temperature for 1-24 h gives rise to 5-arylmethylfurfurals (yields of 17-91%) and 2-arylmethyl-5-(diarylmethyl)furans (yields of 10-37%). The formation of these two types of reaction products depends on the nucleophilicity of the arene. The same reactions under the action of acidic zeolites H-USY in high pressure tubes at 130 °C for 1 h result in the formation of only 5-arylmethylfurfurals (yields of 45-79%). 2,5-Diformylfuran (2,5-DFF) in the reaction with arenes under the action of AlBr3 at room temperature for 1 h leads to 5-(diarylmethyl)furfurals (yields of 51-90%). The reactive protonated species of 5-HMF and 2,5-DFF were characterized by NMR spectroscopy in TfOH and studied by DFT calculations. These reactions show possibilities of organic synthesis based on biomass-derived 5-HMF and 2,5-DFF.
