Stereoselective synthesis of tetrasubstituted 2,3-dihydrofurans by one-step cyclization of β-ketosulfides of benzothiazole and aldehydes in ionic liquids

A stereoselective synthesis of tetrasubstituted 2,3-dihydrofurans was carried out in n-butylpyridinium tetrafluoroborate ([bpy(+)] [BF4-]) as solvent. The reaction proceeds smoothly in one step starting from simple materials such as aldehydes and beta-ketosulfides of benzothiazole. A comparison between several ionic liquids (ILs) is presented, and the role of the benzothiazolyl moiety is discussed. Workup proved to be very easy and recycling of IL possible.