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

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.