Direct and rapid heating by microwave irradiation in combination with sealed vessel processing in many cases enables reactions to be carried out in a fraction of the time generally required using conventional conditions. This makes microwave chemistry an ideal tool for rapid reaction scouting and optimization of conditions, allowing very rapid progress through hypotheses–experiment–results iterations. The speed at which multiple variations of reaction conditions can be performed allows a morning discussion of “What should we try?” to become an after-lunch discussion of “What were the results” Not surprisingly, therefore, many scientists both in academia and industry have turned to microwave synthesis as a front-line methodology for their projects. In this review, more than 220 published examples of microwave-assisted synthetic organic transformations from the 2004 to 2008 literature are discussed. An additional ca. 500 reaction schemes are presented in the Electronic Supplementary Material, providing the reader with an overall number of ca. 930 references in this fast-moving and exciting field.

Controlled microwave heating in modern organic synthesis: highlights from the 2004–2008 literature

Metal-Free Multicomponent Syntheses of Pyridines

Multicomponent domino reactions (MDRs) serve as a rapid and efficient tool for the synthesis of versatile heterocycles, particularly those containing structural diversity and complexity, by a one-pot operation. These reactions can dramatically reduce the generation of chemical wastes, costs of starting materials, and the use of energy and manpower. Moreover, the reaction period can be substantially shortened. This Review covers recent advances on multicomponent domino reactions for the construction of five-, six-, and seven-membered heterocyclic skeletons and their multicyclic derivatives.

Multicomponent Reactions for the Synthesis of Heterocycles

Deep eutectic solvents (DESs) as eco-friendly and sustainable solvent/catalyst systems in organic transformations

A new four-component domino reaction has been discovered. The reaction is easy to perform simply by mixing four common reactants and K2CO3 in ethylene glycol under microwave irradiation. The reaction proceeds rapidly and can be finished within 10−24 min with water as the major byproduct, making workup convenient. Four stereogenic centers with one quaternary carbon−amino function are controlled very well; the stereochemistry was unequivocally determined by X-ray structural analysis. The resulting pyrido[3,4-i]quinazoline derivatives are of importance for organic and medicinal research.

Four-Component Domino Reaction Leading to Multifunctionalized Quinazolines

1,2-dihydro-pyrimido[1,2-a]benzimidazole-3-carbonitrile derivatives were synthesized via the three-component reaction of aldehyde, malonodinitrile and 2-aminobenzimidazole in water under microwave irradiation. The new protocol has the advantages of excellent yield, low cost, reduced environment impact, wide scope and convenient procedure.

Green Multicomponent Synthesis of 1,2‐Dihydro‐pyrimido[1,2‐a]benzimidazole‐3‐carbonitrile.

Aza-helicenes are one of the most important series of heterohelicenes; herein, a series of novel aza-helicenes (5H, 6H, 6S, and 8S) were prepared via Bischler-Napieralski cyclization, and the interconversion dynamic process of these aza-helicenes was revealed using density functional theory calculations. The novel nitrogen-doped [6]helicene (6H) possesses a very high interconversion energy barrier of 36.0 kcal/mol. Two enantiomers of 6H were successfully resolved by high-performance liquid chromatography and showed desired chiral optical properties. 6H with chiral optical activity and lone electrons can be a potential candidate for chiral switches, which was demonstrated using the UV and circular dichroism spectra obtained upon titration with an acid and a base.

Synthesis of Nitrogen-Doped Aza-Helicenes with Chiral Optical Properties.

A Simple Three‐Component Condensation: Highly Efficient Microwave‐Assisted One‐Pot Synthesis of Polyfunctional Pyridine Derivatives.

Solid acid-catalyzed one-pot multi-step cascade reaction: Multicomponent synthesis of indol-3-yl acetates and indol-3-yl acetamides in water

A Green Approach to the Synthesis of Biologically Important Indeno[2,1-d]pyrazolo[5,4-b]pyridines via Microwave-Assisted Multicomponent Reactions in Water.

Chunmei Li

Papers

Green Multicomponent Synthesis of 1,2‐Dihydro‐pyrimido[1,2‐a]benzimidazole‐3‐carbonitrile.

Synthesis of Nitrogen-Doped Aza-Helicenes with Chiral Optical Properties.

A Simple Three‐Component Condensation: Highly Efficient Microwave‐Assisted One‐Pot Synthesis of Polyfunctional Pyridine Derivatives.

Solid acid-catalyzed one-pot multi-step cascade reaction: Multicomponent synthesis of indol-3-yl acetates and indol-3-yl acetamides in water

A Green Approach to the Synthesis of Biologically Important Indeno[2,1-d]pyrazolo[5,4-b]pyridines via Microwave-Assisted Multicomponent Reactions in Water.