Microwave irradiation and selectivities in organic reactions

The different selectivities, including chemoselectivity, regioselectivity, syn/trans selectivity, diastereoselectivity, and enantioselectivity, of organic reactions under the microwave-assisted and conventional heating conditions are reviewed. The effect of microwave irradiation on these selectivities is discussed. According to a survey of literature, although some differences on the selectivities between the microwave-assisted and classical heating conditions are observed in some reactions, most of the reactions are not conducted under the strict same conditions except for heating mode, such as in different solvents, even under solvent-free conditions, under the catalysis of different catalysts or additives, at different temperatures. Some examples are conducted under the same reaction systems, but at different temperatures. For most of examples, the effects of the microwave irradiation on the selectivities are possibly caused by the actually different temperature and could be explained by the thermal effect. I am prone to consider that no specific athermal. effect exists generally in the microwave-assisted organic reactions. The microwave-assisted technology can tune selectivities via changing reaction temperature for some organic reactions. I hope this review will provide some useful information to understand the microwave effect on the organic reactions and the origin of the microwave-induced organic reaction enhancement chemical techniques.