Current Organic Chemistry - Volume 14, Issue 4, 2010

During the past decades, many novel multicomponent reactions (MCRs) have been added to the chemist's armamentarium and successfully applied to all fields of organic chemistry. By virtue of their inherent convergence and high productivity, together with their exploratory and complexity-generating power, MCRs have naturally become a rapidly evolving field of research and have attracted the attention of both academic and industrial scientists.The literature of multicomponent reactions is extremely wide but I do hope that these four reviews piled up in the issue will supply new and relevant information for many chemists working in the field of synthetic organic chemistry. The first review was written by Prof. Yadav on the topic of multicomponent reactions using Indium(III) Salts. Indium metal salts emerged as potent tools to achieve various functionalized molecules through multi-component reactions. Their review focuses the recent developments regarding the Indium(III) salts catalysed multicomponent reactions. This compiled reactions include amino Diels-Alder reactions, imino Diels-Alder reactions, oxa-Diels-Alder reactions, reactions of sugars and named reactions. The second review came from Prof. Lavilla' group. They provide a detailed overview on the mechanistic variations of the Povarov multicomponent reaction and related processes. The Povarov reaction is a multicomponent process involving anilines, carbonyl compounds and activated olefins to afford terahydroquinolines. The mechanism of this domino reaction comprises a sequence of steps linking imine formation, a Mannich-type reaction and an intramolecular aromatic electrophilic substitution. In their contribution, they are discussing the scope of the methodology, with a particular emphasis on mechanistic variations, new synthetic inputs, reaction modes, structural diversity originated from this process and its applications to organic chemistry. The third review has been provided by Prof. Tu on the topic of microwave-assisted multicomponent reactions in the heterocyclic chemistry. The MW-assisted MCRs offer rapid and efficient procedures for the introduction of many points of structural diversity into heterocyclic compounds prepared in a straightforward manner in a single synthetic step. In many cases, MW-assisted MCRs offers considerable improvements in selectivity, chemical yield and purity and constitutes a very simple and extremely rapid method to access a diverse range of heterocyclic motifs. Their review focuses recent developments in MW-assisted MCRs for the construction of five-, six-, and seven-membered heterocyclic skeletons as well as dicyclic system. The last review was contributed by Prof. Xia. The current review comprises 166 references and covers extensively the multicomponent synthesis of cyclic frameworks on Knoevenagel-initiated domino reactions from recent publication. In their contribution, they presents the exhaustively collected examples of Knoevenagel-initiated muticomponent domino reactions in the last decade in order to describe the comprehensive profile of such important synthetic strategy. It has been a pleasure to be involved as a Guest Editor of this multicomponent reactions issue of Current Organic Chemistry. I would like to thank all of the authors contributing to this special issue for their valuable work, their patience and understanding. I am sure that their contributions will be noticeable for many organic chemists and help the development of the chemical science.

The Povarov reaction is a multicomponent process involving anilines, carbonyl compounds and activated olefins to afford tetrahydroquinolines. The mechanism of this domino reaction comprises a sequence of steps linking imine formation, a Mannich-type reaction and an intramolecular aromatic electrophilic substitution. Here we analyze the scope of the methodology, with a particular emphasis on mechanistic variations, new synthetic inputs, reaction modes, structural diversity originated from this process and its applications to organic chemistry.

The use of emerging multicomponent reactions (MCRs) in conjunction with microwave (MW)-assisted chemistry techniques is dramatically reducing chemical waste and reaction times in several organic syntheses and chemical transformations. The MW-assisted MCRs offer rapid and efficient procedures for the introduction of many points of structural diversity into heterocyclic compounds prepared in a straightforward manner in a single synthetic step. The present review summarizes recent developments in MW-assisted MCRs for the construction of five-, six-, and seven-membered heterocyclic skeletons as well as dicyclic system. Methods for the generation of both simple and fused heterocyclic targets are described, with particular emphasis on the introduction of structural diversity and complexity. In many cases, MW-assisted MCRs offer considerable improvements in selectivity, chemical yield and purity and constitute a very simple and extremely rapid method to access a diverse range of heterocyclic motifs.

Major aspects of multicomponent synthesis of cyclic frameworks are reviewed with special focus on Knoevenagel-based domino reactions. Particularly, the Knoevenagel-Cycloaddition and the Knoevenagel-Michael cascades are the majority of reaction types which contribute to the building of complicated cyclic molecular scaffolds. Although samples of the other Knoevenagel-induced reactions are not abundant, their creativity in production of novel cyclic structures should not be neglected. The presented reports herein are sufficient enough to confirm that Knoevenagel-induced domino reactions have been one of the most powerful and productive tools for the construction of novel and complicated frameworks.

Multi-component coupling reactions (MCRs) are a powerful synthetic tool to access complex structures from simple precursors via one-pot procedure. Due to various advantages, it provides, over the conventional two component methods, the investigation for the possibility of an MCR in a multi-sequential synthetic strategy towards the total synthesis of a natural product is of prime importance. Indium (III) salts have been shown to catalyse a variety of MCR reactions in the recent past. In this review, the recently reported methodology which provides new route to functionalized organic molecules are discussed.