Regioselectivity Switching in the Tandem Reaction of Skipped Diynones with Allylic Alcohols: Stereoselective Synthesis of 4-Allyl-2-Methylene-3(2<i>H</i>)-Furanones

A novel base-catalyzed synthesis of hitherto unknown 4-allyl-2-methylene-3(2<i>H</i>)-furanones from skipped diynones and allylic alcohols via nucleophilic addition/Claisen rearrangement/cyclization reaction is described. An important role of the employed catalytic system for the regioselective switching in the cyclization step from 3-allyl-4-pyrones to isomeric 4-allyl-3(2<i>H</i>)-furanones is discussed. The isolation of main intermediates of the tandem reaction and study of their reactivity allowed us to develop a convenient two-stage protocol for stereoselective 4-allyl-2-methylene-3(2<i>H</i>)-furanone formation featuring a good substrate tolerance and good yields of target products.