Tandem Double [3 + 2] Cycloaddition Reactions at Both C-1 and C-3 Atoms of N-Cyanomethylisoquinolinium Ylide

[Image: see text] The base-promoted cycloaddition reaction of N-cyanomethylisoquinolinium chloride with 2-arylidene-1,3-indanediones in dry tetrahydrofuran resulted in the expected spiro[indene-2,1′-pyrrolo[2,1-a]isoquinoline] derivatives. However, the triethylamine-promoted three-component reaction of N-cyanomethylisoquinolinium chloride, aromatic aldehydes, and two molecules of 1,3-indanediones in acetonitrile afforded unique spiro[benzo[f]imidazo[5,1,2-cd]indolizine-4,2′-indene] derivatives in satisfactory yields through tandem double [3 + 2] cycloaddition reactions.