Abstract Post-synthetic modification of non-planar π-systems represents a pivotal technique in materials science. Cyclobisbiphenylenecarbonyl (CBBC) is a readily available figure-eight macrocycle, which has recently proven its effectiveness for the design of chiral functional materials. CBBC features two carbonyl groups in its macrocyclic conjugation. Herein, we report nucleophilic transformations of the carbonyl groups in CBBC with NaBH4 as well as alkyl, alkynyl, and aryl lithium reagents. These reactions selectively yield either mono-adducts or bis-adducts, depending on the choice of reagents. The carbonyl transformation effectively tunes physical properties and molecular conformations. For instance, mono-adducts undergo reversible conformational switching between figure-eight and bathtub conformations through intramolecular hydroxyketone–hemiacetal tautomerization. The bathtub conformation exhibits a lower racemization barrier compared to the figure-eight form. The conversion of sp2-hybridized carbonyl carbons to sp3-hybridized centers is accompanied by an increase in strain energy.
Moribe et al. (Tue,) studied this question.