Synthesis of imidazo[1, 2‐a]pyridines via the silver acetate‐catalyzed Groebke‐Blackburn‐Bienayme reaction with ethylene glycol as a biodegradable and sustainable solvent

Abstract

An efficient, silver‐based catalytic system has been designed for the synthesis of biologically important 3‐aminoimidazo‐fused heterocycles via the Groebke‐Blackburn‐Bienayme reaction, in which AgOAc was used as a catalyst and ethylene glycol as a solvent from isocyanides, various aryl aldehydes and an 2‐amino heterocycle were also used. Good to excellent yields, high atomic economy and environmentally friendly conditions are the potential features of this one‐pot process.

Silver-catalyzed synthesis of nitrogen heterocycles: recent advancements

“…Imidazo[1,2-a]pyridines 20, which are prominent bioactive candidates possessing 3-aminoimidazo ring, were efficiently synthesized by Hussain et al in 2020. 57 They designed an efficient one-pot strategy catalyzed by AgOAc 19 through the Scheme 1 Silver-catalyzed cycloisomerization of propargylic ureas 1.…”

“…Imidazo[1,2- a ]pyridines 20 , which are prominent bioactive candidates possessing 3-aminoimidazo ring, were efficiently synthesized by Hussain et al in 2020. 57 They designed an efficient one-pot strategy catalyzed by AgOAc 19 through the Groebke–Blackburn–Bienayme reaction pathway. This three-component reaction was carried out by reacting various aldehydes 12 , amines 10 and isocyanates 16 in the presence of 20 mol% AgOAc 19 for 2 h in ethylene glycol (EG) at 90 °C (Scheme 5).…”

Recent Advances in the Synthesis of Imidazo[1,2‐a]pyridines: A Brief Review

“…[56] No groups have used silver acetate as a catalyst in ethylene glycol (EG) as a promoter solvent for the synthesis of imidazopyridine. Hussain et al [57] in 2020 developed the synthesis of imidazo[1,2-a]pyridines 56 via the silver acetate catalyzed GBBR with EG as a solvent from isocyanides 55, various aryl aldehydes 54 and 2-amino heterocycle 53 with good to excellent yields, high atomic economy and environmentally friendly conditions. The relatively cheap silver catalyst, simple work-up procedures and generation of no side products constituted the unique features of this protocol.…”

Diaza-1,3-butadienes as Useful Intermediate in Heterocycles Synthesis

“…Several catalyst were used for his reaction, for example, L -proline [ 63 ], Yb(OTf) 3 [ 64 ], Candida antarctica lipase B (CALB) enzyme [ 65 ], NH 4 Cl [ 66 , 67 ], K-10 clay [ 68 ], AgOAc [ 69 ], thiamine hydrochloride [ 70 ], Sc(OTf) 3 [ 71 , 72 ], In(OTf) 3 [ 73 ], InCl 3 [ 74 ], and HClO 4 [ 75 , 76 ]. Nevertheless, catalyst and solvent-free conditions have also been reported [ 77 , 78 ].…”

“…An advantage of this reaction is that it is not limited to the exclusive use of 2-aminopyridine, but also can be used with amines with the cyclic H 2 N-C=N structure (2-aminoazines or amidines), so this reaction allows to obtain different imidazo[1,2-a]-heterocyclic compounds ( Scheme 33 ). Among the recently reported amidines we have: 2-aminothiazoles [ 64 , 69 , 72 , 78 , 81 ], 2-aminopyrazine [ 72 , 73 , 81 ], 2-aminobenzothiazole [ 70 , 78 ], 2-aminopyrimidine [ 69 , 71 ], 5-(trifluoromethyl)-1,3,4-thiadiazol-2-amine [ 77 ] and 2-aminoquinoline [ 70 , 72 ].…”