Microwave-assisted organic synthesis instrumentation

Due to the importance of substituted 2-pyridones, many preparative methods have been reported (see Sect. 2.1), and some of these, but for from all, have been further developed into methods suitable for microwave-assisted organic synthesis (MAOS). Here we describe mainly methods performed with instruments specially designed for MAOS, thus excluding synthesis per-... 

Although many of the early experiments in microwave-assisted organic synthesis have been carried out in domestic microwave ovens, the current trend clearly is to use specialized instruments for this type of chemical synthesis. Experiments carried out in domestic ovens have been found to be difficult to reproduce, owing to the lack of temperature and pressure control, pulsed irradiation, uneven electromagnetic field distributions, and the unpredictable formation of hotspots. 

Abstract 2-pyridones are important heterocydes with great applicability in medicinal chemistry and this core structure can be found in compounds with various biological/medicinal applications. Here we show how microwave-assisted chemistry can be used to effectively synthesize and functionalize substituted monocydic 2-pyridones, 2-quinolones and other ring-fused 2-pyridones. The chapter covers recent advancements in this field mainly describing methods developed with instruments specially designed for microwave-assisted organic synthesis (MAOS). 

Since the first appearance of industrially designed microwave instruments for organic synthesis in the early 1990s, the interest in microwave-assisted synthesis has grown tremendously. 

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. 

Microwave acceleration of reactions is a valuable tool for organic synthesis [39], and various specialized instruments are now commercially available. Tye and co-workers have reported the microwave-assisted Petasis borono-Mannich reaction of arylboron-ic acids and primary or secondary amines with either glyoxylic acid or salicylaldehyde [40]. Optimized reaction conditions employed didiloromethane as solvent, and microwave assisted heating at 120 °C for 10 min. Products were obtained in generally modest yields (10-83%), in part due to incomplete reaction conversion imder the reported conditions. 

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