Convenient synthesis of substituted tetrahydrofuran via Lewis base catalyzed [3 + 2] domino reactions

A DABCO catalyzed domino reaction between 3-oxo-4-(2-oxoindolin-3-ylidene) butanoates and allenoates furnished 2,3,5-substituted tetrahydrofuran furan derivatives with oxindole moieties and two exocyclic double bonds in high yield. During this reaction, two carbon atoms and one oxygen atom of 3-oxo-4-(2-oxoindolin-3-ylidene) butanoates participated. Moreover, four isomers were synthesized and two of them can be isolated in this reaction.