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