Microwave-Assisted Intramolecular Stetter Reaction in Ionic Liquids

Significance

An efficient microwave-assisted intramolecular Stetter reaction of 4-(2-formylphen­oxy)but-2-enoate derivatives to chroman-4-ones under thiazolium salt and Et₃N catalysis in ionic liquids at room temperature is described. Although structural variation of starting materials has been modestly tested, a comparison of reaction conditions was carried out: ionic liquid versus DMF, ionic liquid and heating versus ionic liquid and microwave irradiation. The results show clearly that the presented conditions lead to higher yields in much shorter times. The E-stereochemistry of the starting material is relevant in that the Z-isomer gives only traces of product. The starting materials are readily available from the condensation of salicylaldehydes with 4-halocrotonate esters with high E-selectivity.