Synthesis of Silafluorenes by Iridium-Catalyzed [2 + 2 + 2] Cycloaddition of Silicon-Bridged Diynes with Alkynes

Silicon-bridged 1,6-diynes underwent [2 + 2 + 2] cycloaddition with alkynes in the presence of an iridium(I)−phosphine catalyst to afford densely substituted silafluorene derivatives. Extended silafluorene skeletons were constructed by the [2 + 2 + 2] cycloaddition of tetraynes.