Synthesis of Imidazoles from Fatty 1,2‐Diketones

Abstract

Unsaturated vegetable oils and their corresponding fatty acid derivatives constitute interesting renewable platforms for the preparation of heterocycles, notably through the formation of oxygenated intermediates. In this work, fatty imidazoles were prepared from the corresponding 1,2‐diketones through Debus‐Radziszewski reaction. The reaction was optimized under microwave irradiation using a 1,2‐diketone derived from methyl oleate and ammonium acetate as a nitrogen source. Using benzaldehyde as a model substrate, the reaction occurs at 180 °C for 5 min and the desired imidazole was formed in 96 % GC yield. A range of aldehydes was tested under the optimized conditions and the corresponding imidazoles were obtained in 33–99 % isolated yields (20 examples).

Kinetic and Thermodynamic Evidence of the Paal–Knorr and Debus–Radziszewski Reactions Underlying Formation of Pyrroles and Imidazoles in Hydrothermal Liquefaction of Glucose–Glycine Mixtures

“…The reduction of butane-2,3-diimine concentration in the acid-catalyzed HTL was due to the cycloaddition of the carbonyl carbon of formaldehyde toward the −NH 2 groups of butane-2,3-diimine, yielding 4,5-dimethyl-imidazole in biocrude. 47 This result showed that the cycloaddition favored acidic conditions, agreeing with its higher frequency factor and lower activation energy for r 39 under more acidic feedstock pH (see Table 1). Moreover, Table S33 shows an increased concentration of 4,5dimethyl-imidazole at higher temperatures, highlighting the endothermic (r 39 ; ΔH = 66.7 kJ/mol) cycloaddition as the rate-controlling step.…”

“…Given that the HTL of acidic feedstocks in scenarios 2a and 2b producing 4,5dimethyl-imidazole and 1,3,4,5-tetramethyl-2,3-dihydro-1Himidazole employed phosphoric acid as the acidifying agent to pH 2, this result demonstrated that the Debus− Radziszewski reaction involving biacetyl was only catalyzed by a high concentration of homogeneous strong acid catalysts, consistent with the literature. 40,47 Scenario 2e (i.e., HTL of pyruvaldehyde, glycine, and fumaric acid mixtures) validated the precipitation of (Z)-1,13diimino-2,5,9,12,13,14,14a,14b-octahydro-1H,7H-azepino-[1′,2′:3,4]-imidazo[1,5-a]azocine-3,11-dicarbonitrile (DOAIAD) in hydrochar from the HTL of the acidic feedstock mixture. Figure 6E shows a decreasing concentration of fumaric acid (i.e., the oxidation product of furfural, r 46 ) with reaction time under acid-catalyzed and alkaline-catalyzed processes due to the amidation and dehydration into fumaronitrile.…”

Reactivity and Stability of Natural Clay Minerals with Various Phyllosilicate Structures as Catalysts for Hydrothermal Liquefaction of Wet Biomass Waste

“…The Debus–Radziszewski reaction ( R 22) was responsible for the imidazole formation. This reaction included the formation of a diamine intermediate from monosaccharide-derived α-dicarbonyl and 1° amine before condensing with an aldehyde forming an imidazole . The formation of pyrazoles followed the Knorr-type reaction ( R 20) involving a hydrazine and a 1,3-dicarbonyl .…”

“…This reaction included the formation of a diamine intermediate from monosaccharidederived α-dicarbonyl and 1°amine before condensing with an aldehyde forming an imidazole. 88 The formation of pyrazoles followed the Knorr-type reaction (R20) involving a hydrazine and a 1,3-dicarbonyl. 89 The formation of dialkylhydrazines (R39) occurred through the Raschig mechanism (i.e., direct nucleophilic attack by the 2°amine) that required a reaction between dialkylamine and chloramine, generated in situ by the reaction of ammonia with potassium hypochlorite.…”

Understanding desaturation/hydroxylation activity of castor stearoyl Δ9-Desaturase through rational mutagenesis

“…Methyl erythro - and threo -9,10-dihydroxystearates ( erythro / threo -9,10-bisOH-18:Me) as well as methyl cis –9,10–epoxystearate ( cis -9,10-epoxy-18:Me) were prepared according to published procedures (Scheme S1 in the Supporting Information ) [41] , [42] . The synthesis of 9-, 10- and 11–hydroxystearic acids was based on a modular method starting from corresponding ω -hydroxyalkanoic acids (Schemes S2–S4).…”