Spiro[4H-pyran-3,3-oxindoles] Derived from 9,10-dihydroacridine

Reaction 6H-pyrrolo[3,2,1-de]acridine-1,2-dione (7) with cyclic 1,3-dicarbonyl compounds in the presence of malononitrile or ethyl cyanoacetate generates spiro[4H-pyran-3,3-oxindoles] 8.