Microwave-Assisted 1,3-Dipolar Cycloaddition: an Eco-Friendly Approach to Five-Membered Heterocycles

The review describes the use of microwave technology to carry out 1,3-dipolar cycloaddition reactions, an important tool for the construction of five-membered heterocycles. Microwave methodology can be applied to generate 1,3-dipoles (nitrones, nitrile oxides, azomethine ylides, azomethine imines, nitrile imines, azides, carbonyl ylides) and to promote the subsequent cycloaddition and usually avoids harsh reaction conditions. This nonconventional energy source is able to reduce chemical reaction times and to increase yields and in some cases can lead to different outcomes from those obtained with conventional heating. The review highlights the more recent developments in the area with particular emphasis on aspects related to efficiency and to regio- and stereo-selectivity. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)