Optically active triple helicenes (TH-1) were prepared via a palladium-catalyzed enantioselective cross-cyclotrimerization of two helicenyl arynes 5, which are generated in situ from 3, with dialkyl acetylenedicarboxylate 4. Enantiomeric ratios of up to 98:2 were obtained when using 4a and (S)-QUINAP as the alkyne and chiral ligand, respectively. The absolute stereochemistry of TH-1a was revealed to be (M,P,M) by a single-crystal X-ray diffraction analysis. Kinetic studies of the racemization of enantiomerically pure TH-1a at elevated temperatures were conducted based on a high-performance liquid chromatography analysis. The activation energy for the racemization was found to be 29.1 kcal mol −1 . Density functional theory calculations revealed that the palladium-catalyzed enantioselective cross-cyclotrimerization reactions proceed via the dynamic kinetic resolution of a five-membered palladacycle 6a with two [5]helicenes. Several initially formed stereoisomers of 6a eventually isomerize into the most thermodynamically stable palladacycle intermediate (M,P,M)-6a by inversion of the [5]helicenyl moiety. Then, the insertion of 4 into 6a to form (M,P,M)-12a, followed by a reductive elimination, leads to the formation of (M,P,M)-TH-1a in a stereoselective manner. The optical properties of TH-1a were studied by circular dichroism and circularly polarized luminescence.

Heteroatom-embedded buckybowl molecules provide a fundamental molecular framework that has potential applications in various research fields. However, selective introduction of heteroatoms into buckybowls is challenging, and thus, studies investigating the effect of introduced heteroatoms have been limited. Here, we report the synthesis of pyridine-fused azacorannulene molecules. The influence of nitrogen atoms introduced into the peripheral positions on the structural, electronic, and optical properties is discussed.

Transformation of triple helicene (TH) to double helicene (DH) with adjacent stereogenic carbon atoms and axial stereogenicity was achieved by the unexpected conjugate addition to the central aromatic ring of...