Controlled interconversion of macrocyclic atropisomers via defined intermediates

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2024年8月2日

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Xin Sun,
Jin-Ku Bai,
Yu-Dong Yang,
Ke-Lin Zhu,
Jia-Qi Liang,
Xin-Yue Wang,
Jun-Feng Xiang,
Xiang Hao,
Tong-Ling Liang,
Ai-Jiao Guan,
Ning-Ning Wu,
Han-Yuan Gong

摘要

Macrocyclic conformations play a crucial role in regulating their properties. Our understanding of the determinants to control macrocyclic conformation interconversion is still in its infancy. Here we present a macrocycle, octamethyl cyclo[4](1,3-(4,6)-dimethylbenzene)[4]((4,6-benzene)(1,3-dicarboxylate) (OC-4), that can exist at 298 K as two stable atropisomers with C_2v and C_4v symmetry denoted as C_2v-OC-4 and C_4v-OC-4, respectively. Heating induces the efficient stepwise conversion of C_2v- to C_4v-OC-4 via a C_s-symmetric intermediate (C_s-OC-4). It differs from the typical transition state-mediated processes of simple C–C single bond rotations. Hydrolysis and further esterification with a countercation dependence promote the generation of C_2v- and C_s-OC-4 from C_4v-OC-4. In contrast to C_2v-OC-4, C_4v-OC-4 can bind linear guests to form pseudo-rotaxans, or bind C₆₀ or C₇₀ efficiently. The present study highlights the differences in recognition behavior that can result from conformational interconversion, as well as providing insights into the basic parameters that govern coupled molecular rotations.