Ionic Liquid Promoted Multicomponent Reaction: A Good Strategy for the Eco‐Compatible Synthesis of Functionalized Pyrroles

Abstract

Task specific [bmim]BF4 was found to be reusable, alternative, and effective reaction media for multicomponent synthesis of highly functionalized pyrroles. Generality of the procedure was established by synthesizing various pyrroles from wide range of aromatic/aliphatic amine, phenacyl bromide, and electrophilic alkynes by utilizing this protocol without any acid or metal catalyst. Ecocompatibility, short reaction time, excellent yield, recyclability of [bmim]BF4, low cost, easy work‐up, and mild reaction conditions are additional advantages of the procedure in the context of sustainable and green chemistry.

Recent advances in the synthesis of pyrroles by multicomponent reactions

“…73 Other groups have published variations of this reaction, including the use of polyethyleneglycol as solvent under catalyst-free conditions, 74 the use of b-cyclodextrin as a catalyst in aqueous medium 75 and reactions in ionic liquids. 76 A recent catalyst-free synthesis of polysubstituted pyrroles involves refluxing in ethanol an arylglyoxal monohydrate, an aniline, a dialkyl alkynedioate and malononitrile (Scheme 60). 77 Scheme 55 Three-component synthesis of pyrroles from amines and alkynoates reported by Jiang.…”

[Bmim]BF4: A Versatile Ionic Liquid for the Synthesis of Diverse Bioactive Heterocycles

“…Siddiqui et al . (Table ) successfully employed ionic liquid [bmim]BF 4 as a task specific, efficient reaction media for the one‐pot three‐component synthesis of densely functionalized pyrroles ( 4 ) from the reaction of a wide range of aromatic/aliphatic amine ( 1 ), phenacyl bromide ( 2 ), and diethyl but‐2‐ynedioate ( 3 ) or dimethyl but‐2‐ynedioate ( 3 a ) without any added catalyst at room temperature. The ionic liquid was successfully recovered, and reused four times for the same batch of reaction without any substantial loss in activity.…”

Synthesis of methyl 1,5‐diaryl‐1H‐pyrrole‐2‐carboxylates via acid‐catalyzed ring‐opening/ring‐closure sequence

“…The construction patterns for pyrrole core mainly include [3+2] annulation, [4+1] annulation, and three‐component reactions with or without transition metal catalysis. Dimethyl acetylenedicarboxylate (DMAD) as a valuable electrophile in [3+2] annulation, is commonly used to react with α‐amino ketones, or α‐amino ketones generated in situ from the reaction of phenacyl bromides with aliphatic/aromatic amines, or α‐nitroepoxides and primary amines [3–7]. The reaction of DMAD with β‐enamino ketones or esters, or C‐acylimines formed in situ from anilines and arylglyoxals, or treatment of α‐silylaryl triflates, Schiff bases, and alkynes with CsF also afforded the muti‐substituted pyrroles [2,8–11].…”