Microwave-assisted organic synthesis techniques

In modern microwave synthesis, a variety of different processing techniques can be utilized, aided by the availability of diverse types of dedicated microwave reactors. While in the past much interest was focused on, for example, solvent-free reactions under open-vessel conditions [1], it appears that nowadays most of the published examples in the area of controlled microwave-assisted organic synthesis (MAOS) involve the use of organic solvents under sealed-vessel conditions [2] (see Chapters 6 and 7). Despite this fact, a brief summary of alternative processing techniques is presented in the following sections. 

In this chapter we discuss the new speeding-up techniques, optimized during the last decade, such as solid-phase extraction, polymer-assisted solution-phase synthesis, microwave-assisted organic synthesis, and flow chemistry. The improvements obtained with these techniques are not limited to a subset of chemical reactions (e.g., the reported examples), but they are fully applicable to the entire set of chemistry involved in the synthetic drug discovery process. 

Microwave-assisted organic synthesis is an eco-friendiy technique, it is iikeiy to repiace other conventionai syntheses in years to come. 

This book is written primarily to help students at undergraduate and graduate levels to understand and apply microwave techniques to organic synthesis, using commercially available microwave reactors. It is hoped that the application of different kind of microwave reactors will help to spread ideas of microwave technologies. It should also serve as an introduction to the field for the industrial chemists with no prior training in microwave assisted organic chemistry. 

Parallel to these developments in solid-phase synthesis and combinatorial chemistry, microwave-enhanced organic synthesis has attracted much attention in recent years. As is evident from the other chapters in this book and the comprehensive reviews available on this subject [5, 6], high-speed microwave-assisted synthesis has been applied successfully in many fields of synthetic organic chemistry. Any technique which can speed the process of rather time-consuming solid-phase synthesis is of substantial interest, particularly in research laboratories involved in high-throughput synthesis. 

Microwave technology has now matured into an established technique in laboratory-scale organic synthesis. In addition, the application of microwave heating in microreactors is currently being investigated in organic synthesis reactions [9-11] and heterogeneous catalysis [12, 13]. However, most examples of microwave-assisted chemistry published until now have been performed on a... 

Most examples of microwave-assisted chemistry published to date and presented in this book (see Chapters 6 and 7) were performed on a scale of less than 1 g (typically 1-5 mL reaction volume). This is in part a consequence of the recent availability of single-mode microwave reactors that allow the safe processing of small reaction volumes under sealed-vessel conditions by microwave irradiation (see Chapter 3). While these instruments have been very successful for small-scale organic synthesis, it is clear that for microwave-assisted synthesis to become a fully accepted technology in the future there is a need to develop larger scale MAOS techniques that can ultimately routinely provide products on a multi kg (or even higher) scale. 

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