Recyclable organotungsten Lewis acid and microwave assisted Diels–Alder reactions in water and in ionic liquids

The water-soluble, organotungsten Lewis acid, [Odouble bond; length as m-dashP(2-py)3W(CO)(NO)2](BF4)2 (), was synthesized and characterized. A series of -catalyzed Diels–Alder reactions were investigated under conventional heating or microwave heating conditions. The cycloaddition reactions were efficiently conducted in either water or in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate. The ionic liquid acts as a powerful medium not only for rate- and selectivity enhancements but also for facilitating catalyst recycling. Dramatic rate acceleration via microwave flash heating as compared to thermal heating was observed.