Construction of indeno[1,2-a]fluorene via domino reaction of 1,3-indanedione and 3-arylideneindolin-2-ones or chalcones

An efficient synthetic protocol for novel indeno[1,2-a]fluorene derivatives was successfully developed by the base promoted domino reaction of 1,3-indanedione with 3-arylideneindolin-2-ones. The domino reaction in different solvents selectively gave carbamato- or amino-substituted indeno[1,2-a]fluorene in satisfactory yields. Additionally, a similar domino reaction of 1,3-indanediones with chalcones also gave polysubstituted indeno[1,2-a]fluorenes in high yields. The reaction mechanism is believed to proceed with base-promoted dimerization of 1,3-indanedione, Michael condensation, annulation, ring-opening of indolin-2-one and aromatization process.