Microwave assisted organic synthesis-a review

Microwave assisted organic reactions

Claisen rearrangement over the past nine decades.

Conventional methods for carrying out carbon–hydrogen functionalization and carbon–nitrogen bond formation are typically conducted at elevated temperatures, and rely on expensive catalysts as well as the use of stoichiometric, and perhaps toxic, oxidants. In this regard, electrochemical synthesis has recently been recognized as a sustainable and scalable strategy for the construction of challenging carbon–carbon and carbon–heteroatom bonds. Here, electrosynthesis has proven to be an environmentally benign, highly effective and versatile platform for achieving a wide range of nonclassical bond disconnections via generation of radical intermediates under mild reaction conditions. This review provides an overview on the use of anodic electrochemical methods for expediting the development of carbon–hydrogen functionalization and carbon–nitrogen bond formation strategies. Emphasis is placed on methodology development and mechanistic insight and aims to provide inspiration for future synthetic applications in the field of electrosynthesis.

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Electrochemical strategies for C-H functionalization and C-N bond formation.

Microwave, ultrasound, sunlight and mechanochemical mixing can be used to augment conventional laboratory techniques. By applying these alternative means of activation, a number of chemical transformations have been achieved thereby improving many existing protocols with superior results when compared to reactions performed under traditional conditions. The purpose of this critical review is to highlight the advances in this general area by presenting such newer applications in organic synthesis (175 references).

Alternative energy input: mechanochemical, microwave and ultrasound-assisted organic synthesis

Vilsmeier-haack reactoin of glycals-a short route to C-2-formyl glycals☆

Microwave Induced Ferrier Rearrangement

Syntheis of tri-O-benzyl-2-C-acetoxymethylglycals and subsequent Ferrier rearangement to give 2-C-methylene glycosides is described.

A new ferrier system: 2-C-acetoxymethylglycals. A covenient entry to 2-C-methylene glycosides

In recent years, intramolecular aryl radical cyclisation has emerged as a useful route for the synthesis of benzannulated heterocycles and carbocycles. The aryl radicals are generated in situ from aryl halides (iodides or bromides) with tributylstannyl hydride–AIBN, SmI2, Co(I) or under photochemical conditions. The present work envisages the generation of aryl radicals by cathodic reduction of the carbon–iodine bond of N-(2-iodophenyl)-N-alkylcinnamides and their intramolecular cyclisation. The cathodic reduction of N-(2-iodophenyl)-N-alkylcinnamides under deaerated conditions in DMF gave 1-alkyl-3-benzylindolin-2-ones regioselectively and in the presence of oxygen yielded surprisingly 1-alkyl-3-hydroxy-3-benzylindolin-2-ones. Both these products were formed by a 5-exo-trig process in good yields. A mechanism for the formation of the products has been proposed through the use of cyclic voltammetry, coulometry and controlled-potential electrolysis as well as deuterium labelling.

K. K. Balasubramanian

Papers

Vilsmeier-haack reactoin of glycals-a short route to C-2-formyl glycals☆

Microwave Induced Ferrier Rearrangement

A new ferrier system: 2-C-acetoxymethylglycals. A covenient entry to 2-C-methylene glycosides

Cathodic reduction of N-(2-iodophenyl)-N-alkylcinnamides: a novel sequential electrochemical radical cyclisation and hydroxylation

A novel synthesis of flav-3-enes by claisen rearrangement