Prefece IX 1 Microwave Synthesis -An Introduction 1 References 5 2 Microwave Theory 11 2.1 Microwave Radiation 11 2.2 Microwave Dielectric Heating 12 2.3 Dielectric Properties 25 2.4 Microwave versus Conventional Thermal Heating 19 2.5 Microwave Effects 20 2.5.1 Temperature Monitoring in Microwave Chemistry 22 2.5.2 Thermal Effects (Kinetics) 28 2.5.3 Specific Microwave Effects 31 2.5.4 Non-Thermal (Athermal) Microwave EfFects 37 References 42 3 Equipment Review 45

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In the past few years, using microwave energy to heat and drive chemical reactions has become increasingly popular in the medicinal chemistry community. First described 20 years ago, this non-classical heating method has matured from a laboratory curiosity to an established technique that is heavily used in academia and industry. One of the many advantages of using rapid 'microwave flash heating' for chemical synthesis is the dramatic reduction in reaction times--from days and hours to minutes and seconds. As will be discussed here, there are good reasons why many pharmaceutical companies are incorporating microwave chemistry into their drug discovery efforts.

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.