Chiral D 2-symmetric figure-eight macrocycles with extended π-conjugated systems represent versatile scaffolds for developing advanced chiroptical materials. Here, we present a dynamic covalent platform that transforms a preorganized alkaloidal bispyrrolidinoindoline (BPI) scaffold into a series of chiroptically tunable figure-eight macrocycles through thermodynamically controlled imine formation. Strategic installation of aryl-ethynyl substituents precisely preorganized the BPI scaffold, enabling highly efficient macrocyclization (up to a 81% yield) under reversible imine-forming conditions. This modular approach allowed systematic assembly of diverse intercrossing chromophores, affording 44-90-membered macrocycles exhibiting predictable variations in both optical and chiroptical responses. Postsynthetic conversion of dynamic imine linkages into rigid π-extended B-N chelates via boranil formation further fixed the macrocyclic conformation, producing a bright orange emitter (Φfl = 0.54) with enhanced circularly polarized luminescence (CPL) activity (g lum = 1.97 × 10-3). This work establishes a general design principle integrating dynamic covalent chemistry and conformational preorganization to generate functional figure-eight macrocycles, translating natural-product-inspired molecular architecture into tunable chiroptical materials.
Murakami et al. (Thu,) studied this question.