Unusual direction of three-component reaction involving 2-amino-4-arylimidazoles and carbonyl compounds leading to Knoevenagel-Michael adducts

Abstract

Three-component reaction of 2-amino-4-arylimidazoles, aldehydes and dimedone or barbituric acid proceeds in an unusual direction and instead of imidazo[1,2-a]pyrimidine derivatives gives Knoevenagel-Michael adducts having abnormally low reactivity in heterocyclizations.

Novel (2-amino-4-arylimidazolyl)propanoic acids and pyrrolo[1,2-c]imidazoles via the domino reactions of 2-amino-4-arylimidazoles with carbonyl and methylene active compounds

“…Previously, an unusual direction of the three-component reaction between 2-aminoimidazoles, aldehydes and 5,5-dimethyl-1,3-cyclohexanedione has led to the formation of the Knoevenagel–Michael adducts (Fig. 2) [24]. By analogy with our results obtained with the use of other aminoazoles in the reactions with benzaldehydes and Meldrum’s acid [25] we expected the formation of one or several isomers of tetrahydroimidazopyrimidinone derivatives (Fig.…”

Dihydroazolopyrimidines: Past, Present and Perspectives in Synthesis, Green Chemistry and Drug Discovery

“…Sometimes the dehydration of dihydro derivatives (reaction I) can occur as a secondary process during their synthesis. [23,87,88] However, it was found that under the conditions of the well-known method of heteroaromatization of dihydroazines by the action of acidic NaNO 2 solutions, electrophilic substitution and formation of oximes (reaction m, Scheme 8) are observed in the case of dihydroazolopyrimidines with R 1 =H. [34,35,55,65] The increased stability of dihydro systems to heteroaromatization processes is also reflected in their relative resistance to the action of atmospheric oxygen and trinitrobenzene.…”

“…The synthesis of 5,6-dihydroimidazo[1,2a]pyrimidines 134 via two component sequential microwaveassisted reactions of 2-amino-4-arylimidazoles 132 with chalcones 133 was described by Andriushchenko et al (Scheme 50). [87] The treatment of thiophene chalcone with 2-aminobenzimidazole in ethanol in the presence of a catalytic amount of AcOH under microwave irradiation was studied in paper. [116] It was found that microwave irradiation was more effective than thermal heating.…”

“…A common property of the dihydro derivatives of azolopyrimidines is their ability to heteroaromatize, which can be achieved preparatively by the action of N‐bromosuccinimide, [16,18,19,34,35,56,64,66,73–75] Br 2 /HOAc, [35,60,76,77] I 2 , [78] SeO 2 , [35] PhI(OAc) 2 , [79] CrO 3 , [80] NaNO 2 /HOAc (R 1= COOEt), [81] 2,3‐dicyano‐5,6‐dichloro‐p‐benzoquinone, [72,82,83] Na 2 S 2 O 8 , [84] ammonium cerium (IV) nitrate, [85] potassium permanganate, [86] manganese (IV) oxide [50] (reaction l ). Sometimes the dehydration of dihydro derivatives (reaction I ) can occur as a secondary process during their synthesis [23,87,88] …”