Synthesis of functionalized γ-spiroiminolactones from isocyanides, acetylenic esters, and cyclopenta[a]acenaphthylen-8-ones

The reaction between dialkyl 8-oxo-8H-cyclopenta[a]acenaphthylene-7,9-dicarboxylates and zwitterionic intermediates, generated in situ from alkyl isocyanides and dialkyl acetylenedicarboxylates, is described. This reaction leads to the formation of tetraalkyl 5′-(alkylimino)-5′H-spiro[cyclopenta[a]acenaphthylene-8,2′-furan]-3′,4′,7,9-tetracarboxylates. The structure of a typical product was confirmed by X-ray crystallographic analysis.