Highly efficient regioselective synthesis of pyrroles via a tandem enamine formation–Michael addition–cyclization sequence under catalyst- and solvent-free conditions

Abstract

An efficient three-component, catalyst-, solvent-, and column chromatography-free procedure was developed for the synthesis of 3-(1H-pyrrol-3-yl)indolin-2-ones.

Highly Regioselective Synthesis of Oxindolyl-Pyrroles and Quinolines via a One-Pot, Sequential Meyer–Schuster Rearrangement, Anti-Michael Addition/C(sp3)–H Functionalization, and Azacyclization

“…It also indicated that the catalyst is not required for the conjugate addition and annulation (eqs v and vi). 14 , 15 However, the presence of a catalyst is compulsory for the MS rearrangement of propargyl alcohol ( Table 1 , entry 8). On the basis of these observations, the mechanism for the one-pot synthesis of oxindolyl-pyrrole is presented in Scheme 6 .…”

Green Synthesis of Pyrrole Derivatives

“…Automation of the Hantzsch reaction was performed by Herath et al [53] with an approach to continuous flow chemistry [54]. The process takes place in a microreactor containing pyrrole-3carboxilic acids (17) and pyrrole-3-carboxilic highly substituted esters (18) with yields above 40%. The technique involves a 1 mL glass reactor with two injection points at which the preheated solutions of the reactants in DMF are introduced, the reactor temperature is maintained at 200°C, and the time in the reactor is no longer than 8 min (Scheme 16).…”

“…Another multicomponent reaction was developed by Vivekanand [17]; the procedure follows a catalyst-free methodology in which a number of green solvents, such as ethanol, water, PEG-200, glycerol and lactic acid, are tested for the sequential reaction that involves enamine formation, Michael addition and cyclization of primary amines, 1,3-dicarbonyl compounds and isatin-derived compounds that afforded 3-(1H-pyrrol-3-yl)indolin-2-ones (20) (Scheme 23). Using water, glycerol, PEG-200 and a solvent-free medium, they showed that the solvent-free conditions are better regardless of the nature of the starting materials.…”

“…Due to the diverse applications of pyrroles, there is a constant search for environmentally compatible processes for their preparation following the principles of Green Chemistry, i.e., cleaner, efficient and safe processes. Within this framework, a wide variety of catalysts and sustainable methodologies have been developed, such as the use of microwave and ultrasound activation techniques [17], and the replacement of conventional solvents with green solvents such as ethanol, water and ionic liquids or processes performed under solvent-free conditions [18]. This paper reports the latest results in pyrrole synthesis that aims to make the common reactions more eco-friendly for the preparation of these heterocyclic compounds using green methodologies.…”

A Unique Blend of Water, DES and Ultrasound for One‐Pot Knorr Pyrazole Synthesis and Knoevenagel‐Michael Addition Reaction

“…A lot of syntheses of heterocycles from the early days are MCR, and these reaction sequences paved the way to a multitude of applications. Since last one decade, numerous efforts have been taken for development of these technique for synthesis of various organic …”