Base-Promoted Annulation of Amidoximes with Alkynes: Simple Access to 2,4-Disubstituted Imidazoles

Abstract

An efficient construction of imidazole ring by a Cs2CO3-promoted annulation of amidoximes with terminal alkynes in DMSO has been developed. This protocol provides a simple synthetic route with high atom-utilization for the synthesis of 2,4-disubstituted imidazoles in good yields under transition-metal-free and ligand-free conditions. Internal alkynes can also undergo the annulation to give 2,4,5-trisubstituted imidazoles.

Unusual Formation of 1,2,4-Oxadiazine Core in Reaction of Amidoximes with Maleic or Fumaric Esters

“…Amidoximes are polynucleophilic species that are widely used in synthetic chemistry to assemble diverse heterocyclic [ 1 , 2 , 3 , 4 ] and organometallic systems [ 5 , 6 ]. The type of the formed heterocyclic core depends mainly on the structure of the electrophile.…”

TMSOTf-catalyzed synthesis of trisubstituted imidazoles using hexamethyldisilazane as a nitrogen source under neat and microwave irradiation conditions

“…Because of their versatile applications, several approaches have been developed for the chemical synthesis of imidazoles. 6,31–39 The most commonly known synthetic methods are (i) the three-component condensation reaction of benzils with -aryl aldehydes, primary alcohols, and ammonium acetate (NH 4 OAc)/amines using a microwave (MW) irradiation under ionic liquid, 13 HOAc, 35,36,40,41 Fe, 42,43 Ni, 44 and Co 45 catalysis system, in the presence of acids, 6,17,36,39,46,47 urea/hydrogen peroxide (UHP), 48 organic bases, 49 carbon, 50 and transition-metal (TM) catalysts such as TiCl 4 /SiO 2 , 4 Cu 32 and Fe/Ag nanoparticles (NPs), 51 Zr NPs, 33 La/Mn NPs, 52 Au( i ) 38 and Ru( ii ) 53,54 complexes, urea/ZnCl 2 , 55 MoO 3 /SiO 2 , 56 I 2 , 57 ZrO 2 /Al 2 O 3 , 58 and sulfated SnO 2 59 ( Scheme 1a ) (ii) via reaction of α,β-unsaturated ketones/aldehydes and internal alkynes with amidoximes using Fe( ii )-catalyzed cross-dehydrogenative coupling 60 and Cs 2 CO 3 -promoted annulation 61 ( Scheme 1b ) (iii) from α-nitro-epoxides and amidines with an excess base as promoter 62 ( Scheme 1c ), and (iv) from base-promoted nitrile-alkyne domino-type cyclization 63 ( Scheme 1d ).…”