Catalytic approach to unsymmetrical [7]-helical indenofluorenes: Cyclotrimerization vs. dehydro-Diels-Alder reaction pathways

Synthesis of unsymmetrical [7]-helical compounds possessing the dispiro[2,1-c]indenofluorene motif was ach-ieved for the first time in good yields. The crucial step of the whole reaction sequence was catalytic intra-molecular [2 + 2 + 2] cycloaddition of triynediols by using various transition metal compounds (Co, Ni, etc.). The cyclotrimerizations were accompanied by dehydro-Diels-Alder reaction giving rise to other types of aromatic compounds depending on the respective reaction conditions. Limits of enantioselective cyclotrimerization were assessed. The subsequent transformations of the cyclotrimerization products provided the respective dis-piroindenofluorenes. Structures of both unsymmetrical [7]helical cyclotrimerization products as well as three dehydro-Diels-Alder products were unequivocally confirmed by single-crystal X-ray diffraction analyses. Pho-tophysical properties of selected products were determined as well.

Automated summary

The synthesis of unsymmetrical [7]-helical compounds containing the dispiro[2,1-c]indenofluorene motif has been achieved for the first time, with good yields. The key step in the reaction sequence is the catalytic intramolecular [2 + 2 + 2] cycloaddition of triynediols using various transition metal compounds (Co, Ni, etc.). The resulting cyclotrimerizations are accompanied by dehydro-Diels-Alder reactions, leading to different aromatic compounds depending on the reaction conditions. The enantioselective cyclotrimerization limits were assessed, and the structures of the products were confirmed by single-crystal X-ray diffraction analysis. Additionally, the photophysical properties of selected products were determined.