Relaxing Conformational Constraints in Dynamic Macrocycle Synthesis

The preparation of functional macrocycles via dynamic covalent chemistry (DCC) is an attractive synthetic strategy due to its thermodynamic control over the products. The use of alkyne metathesis has emerged as an efficient DCC method for synthesis of conjugated arylene-ethynylene macrocycles (AEMs), but the scope has been mostly limited to rigid and angle-persistent benzenoid-based structures. Introducing functional groups to macrocycle backbones increases flexibility by relaxing conformational constraints, which often leads to broad product distributions. Here we expand the scope of alkyne metathesis to functionalized macrocycles by systematically exploring how conformation and connectivity interplay to affect product distribution. With a divergent approach, we prepared a series of conjugated polymer analogues and synthesized the corresponding macrocycles via depolymerization. The importance of conformational constraints was reinforced by the results, but it was discovered that minimizing the monomer's torsional axes provides high yields of functional macrocycles, even those with increased flexibility. We believe that this strategy is applicable in other areas of DCC and self-assembly to enable efficient preparation of organic materials with flexible functional groups.