The versatility of the addition of Lithium-cyclopropyl-carbenoids to cyclopentenone has been tested with respect to the attempted synthesis of 5,6-dihydro-calicenes (= 1-cyclopropylidene-cyclopentadienes). The Li-carbenoids prepared by reaction of butyllithium with some 2-mono- or 2,3-disubstituted 1,1-dihalo-cyclopropanes 1 attack the carbonyl-C-atom of cyclopentenone as long as the substituents are small. Otherwise the main reaction consists in a deprotonation of cyclopentenone. By this reaction sequence (schemes 1 and 3) two unknown 5,6-dihydrocalicenes 5f and 5h have been prepared.
