Synthesis of Rigid Stepladder Polymers via Scandium-Catalyzed Polyspiroannulation of Quinoline with Alkyne

Polymers with rigid three-dimensional architectures have attracted significant attention due to their high rigidity and intrinsic microporosity. Here, we report the synthesis of a new class of rigid stepladder polymers featuring unique spirodihydroquinoline skeletons. Under the catalysis of a half-sandwich scandium catalyst, quinoline compounds bearing both an aryl substituent (e.g., phenyl or naphthyl) and an alkynyl group (e.g., C≡CSiMe₃) selectively undergo dearomative polyspiroannulation between the quinoline skeleton and the alkyne unit via ortho-C-H activation of the aryl group. This reaction efficiently yields rigid stepladder polymers comprising a spirodihydroquinoline skeleton with a quaternary carbon stereocenter and an unprotected N-H group. Treatment of the N-H-containing polymers with an alkyl lithium reagent followed by methyl iodide leads to quantitative formation of the corresponding N-methylated polymers, which exhibit enhanced thermal stability and porosity compared to their N-H counterparts.