Stereoselective Wittig Olefination as a Macrocyclization Tool. Synthesis of Large Carbazolophanes

Z-Selective Wittig olefination was applied to
the synthesis of large carbazolophanes containing up to eight heteroaromatic
subunits. A number of strategies were devised and tested, showing
that cyclooligomerization yields can be significantly improved by
using one-component schemes involving heterobifunctional reactants.
[4]- and [6]­Carbazolophanes were characterized in the solid state,
revealing compact, highly folded structures. Electronic and steric
effects of substitution and chain length on the Wittig olefination
rates and Z-selectivities were explored theoretically
using DFT calculations.