Erbium Triflate Promoted Multicomponent Synthesis of Highly Substituted Imidazoles

Abstract

The synthesis of highly substituted imidazole derivatives has been achieved from various α-azido chalcones, aryl aldehydes, and anilines. This multicomponent protocol employs erbium triflate as a catalyst resulting in excellent yield of the imidazoles.

Iron(III)/Iodine‐Catalyzed C(sp2)H Activation of α,β‐Unsaturated Aldehydes/Ketones with Amidines: Synthesis of 1,2,4,5‐Tetrasubstituted Imidazoles

“…Moreover, when 2equiv.o f 2,2,6,6-tetramethyl-1-piperidinyl oxyl (TEMPO) were addedi nto the standard reactiont he isolated yield of 1ab was reducedf rom 92% to 63% (Scheme2D), indicatingt hat this transformation might not proceed via ar adical pathway, anditm ay be that the weak oxidizing effect of TEMPO affected the reaction. Accordingt ot he aforementioned results and previous reports, [15,[23][24][25] ap lausible mechanism is outlined in Scheme 3. Initially,aMichael addition of amidine to the chalcone takes place to form the corresponding Michaela dduct A in the presence of FeCl 3 ·6 H 2 O. Subsequently,t he iodo compound B is formed from the Michaela dduct A aftera ttack by am olecule of iodine,atthe same time with releaseofH + + .T here follows an intramolecular cyclization of the iodo compound B to form the immediate C,w ith am olecule of HI beingreleased.…”

“…[14] Subsequently, Bhuvanesh and co-workers preparedh ighly substituted imidazoles from Er(OTf) 3 -catalyzed reaction of aazidochalconesa nd aryl aldehydesi n2 013. [15] Althoughe ffective as they are,t hey may suffer from some drawbackss uch as complex starting materials, low yields,p oor atom economy and poorly accessible synthetic precursors.…”

“…Comparatively,t he substitution on R 4 provided excellentr esults,e ither as ah eteroaromatic ring such as 2-pyridyl as wella se lectron-donating or electronwithdrawing groups (Table 3, entries8-14). Bifunctional and trifunctional amidines were also studied, and were wellc ompatible in this transformation in 84-97% yields ( Table 3, entries [15][16][17][18][19]. Ther eaction tolerated ortho-substitutioni nt he aromatic ring and gave comparable yields to the ones with substitution at the para-position (Table 3, entries 3, 4, 13 and 14).…”

Nano Copper Ferrite Catalyzed Sonochemical, One-Pot Three and Four Component Synthesis of Poly Substituted Imidazoles

“…Melting points of the products were recorded on an electrochemical apparatus and they were compared with literature values. 1 HNMR and 13 CNMR spectral data were performed on the Bruker-Avance 400 MHz and 100 MHz spectrometers respectively in DMSO-d 6 /CDCl 3 . The chemical shift values were reported on the δ scale in parts per million (ppm), downfield from tetramethylsilane (TMS) as an internal standard.…”

“…Owing to their enormous collection of pharmacological and biological activities many synthetic strategies has been developed for synthesis of substituted imidazoles such as the hetero-cope rearrangement [11], four component condensation of arylglyoxals, primary amines, carboxylic acids and isocyanides on wangresin [12] and three component condensation of α-azido chalcones, aromatic aldehyde and substituted aniline in presence of Erbiumtriflate [13]. Later on a first, simple and convenient synthetic methodology has been reported by Radziszewski and japp for the synthesis of 2,4,5-tri phenyl imidazoles by using 1,2 dicarbonyl compounds, ammonia, various aldehydes [14].…”