Applications of Clauson-Kaas Reaction in Organic Synthesis

Pyrrole-embedded organic molecules received a considerable importance due to their numerous biological and material applications. Hence, several synthetic strategies have been devised for the construction of diverse pyrrole analogues over the years. Among these, the Clauson-Kaas reaction is one of the most widely used protocols for the synthesis of various N-substituted pyrroles. This review briefly describes the Clauson-Kaas reaction along with modifications and a detailed account on its applications in the various sectors of organic synthesis.

Toward Biomass-Based Organic Electronics: Continuous Flow Synthesis and Electropolymerization of N-Substituted Pyrroles

Pyrroles are foundational building blocks in a wide array of disciplines, including chemistry, pharmaceuticals, and materials science. Currently sourced from nonrenewable fossil sources, there is a strive to explore alternative and sustainable synthetic pathways to pyrroles utilizing renewable feedstocks. The utilization of biomass resources presents a compelling solution, particularly given that several key bulk and fine chemicals already originate from biomass. For instance, 2,5-dimethoxytetrahydrofuran and aniline are promising candidates for biomass-based chemical production. In this study, we present an innovative approach for synthesizing N-substituted pyrroles by modifying the Clauson-Kaas protocol, starting from 2,5-dimethoxytetrahydrofuran as the precursor. The developed methodology offers the advantage of producing pyrroles under mild reaction conditions with the potential for catalyst-free reactions depending upon the structural features of the substrate. We devised protocols suitable for both continuous flow and batch reactions, enabling the conversion of a wide range of anilines and sulfonamides into their respective N-substituted pyrroles with good to excellent yields. Moreover, we demonstrate the feasibility of depositing thin films of the corresponding polymers onto electrodes through in situ electropolymerization. This innovative application showcases the potential for sustainable, biomass-based organic electronics, thus, paving the way for environmentally friendly advancements in this field.

Nickel ferrite nanoparticles doped on hollow carbon microspheres as a novel reusable catalyst for synthesis of N-substituted pyrrole derivatives

Pyrroles are widely spread worldwide because of their critical applications, especially pharmacology. An expedition method for one-pot synthesis of N-substituted pyrrole derivatives has been presented by a reaction between 2,5-dimethoxytetrahydrofuran and various primary aromatic amines in the presence of NiFe₂O₄ anchored to modified carbon hollow microspheres (NiFe₂O₄@MCHMs) as a recoverable reactive catalyst. The Classon-Kass method has been used to synthesize the pyrroles in excellent yields and short reaction times in the same direction with green chemistry rules. This reaction was carried out by employing NiFe₂O₄@MCHMs as a catalyst to make a simple procedure with short activation energy in water as an accessible, non-toxic, and biodegradable solvent. This catalyst provides a promising pathway to synthesize N-substituted pyrroles several times in a row through the recyclability without remarkable loss of its catalytic activity. The NiFe₂O₄@MCHMs nanocatalyst was characterized by applying FT-IR, XRD, FE-SEM, TEM, EDS, BET, TGA, VSM, and elemental mapping techniques. Also, the synthesized N-substituted pyrrole derivatives were identified using melting point, FT-IR, and ¹H NMR analyses.

Clauson-Kaas pyrrole synthesis using diverse catalysts: a transition from conventional to greener approach

Pyrrole is an important aromatic heterocyclic scaffold found in many natural products and predominantly used in pharmaceuticals. Continuous efforts are being made to design and synthesize various pyrrole derivatives using different synthetic procedures. Among them, the Clauson-Kaas reaction is a very old and well-known method for synthesizing a large number of N-substituted pyrroles. In recent years, due to global warming and environmental concern, research laboratories and pharmaceutical industries around the world are searching for more environmentally friendly reaction conditions for synthesizing compounds. As a result, this review describes the use of various eco-friendly greener protocols to synthesize N-substituted pyrroles. This synthesis involves the reaction of various aliphatic/aromatic primary amines, and sulfonyl primary amines with 2,5-dimethoxytetrahydrofuran in the presence of numerous acid catalysts and transition metal catalysts. The goal of this review is to summarize the synthesis of various N-substituted pyrrole derivatives using a modified Clauson-Kaas reaction under diverse conventional and greener reaction conditions.