cycloaddition with suitable dienophiles in one-pot operations gave hexahydroindenes 8 and 9 in yields of 40–78%, an hexahydro-s-indacene derivative 13 could be obtained in up to 25% yield with cyclopent-2-en-1-one (10) as a dienophile in the presence of different Lewis acids, and a spirocyclopentane-hexahydroindenone 18 could be isolated in 72% yield. When in-situ-formed iminium salts were used as heterodienophiles