A Chiral Dicationic [8]Circulenoid: Photochemical Origin and Facile Thermal Conversion into a Helicene Congener

Abstract

Doubly positive: A circulene‐like species has been transformed into its helical counterpart exclusively by the application of heat (see scheme). The synthesis of the chiral dicationic [8]circulenoid is based on a key [6+6] photocycloaddition and requires only five steps and no chromatographic purification.

Single‐Crystal‐to‐Single‐Crystal Transition in an Enantiopure [7]Helquat Salt: The First Observation of a Reversible Phase Transition in a Helicene‐Like Compound

“…For instance, resolution of some racemic helquats has been achieved by crystallization of diastereomeric salts7a–c and preferential crystallization 7b,c. Moreover, crystallization and precipitation of various helquats have been instrumental in X‐ray crystal structure determinations and purifications 5a,b,g6, 7…”

“…The possibility of racemization of the enantiopure helical dicationic salt 1 during the phase transition α→β was studied by chiral capillary electrophoresis 5a–c. 7, 11 As evidenced by the electropherograms of three crystals that were heated to 426 K (Figure 3), enantiocomposition analysis did not show any loss of the stereointegrity during this phase transition.…”

Cationic Nitrogen‐Doped Helical Nanographenes

“…Considering the intrinsic challenge of forming the five‐membered cyclometalated species with sterically hindered helical aromatic backbones during the rhodium‐catalyzed C−H activation step, according to the mechanism proposed by Huang and co‐workers, the yields of charged aza[6]‐ and aza[7]helicenium cations ( 1 b + , 1 c + , and 1 e + ) are remarkable. To the best of our knowledge, the charged aza[7]helicene 1 c + is the largest helicene with fully conjugated six‐membered rings and cationic nitrogen doping ,…”

Kationische stickstoffdotierte helikale Nanographene

“…Die Ausbeuten an Aza[6]‐ und Aza[7]helicenium‐Kationen in diesem Fall ist daher beachtlich. Nach unserer Auffassung stellt das Aza[7]helicenium‐Kation 1 c + das bisher ausgedehnteste vollständig aus konjugierten sechsgliedrigen Ringen aufgebaute Helicen mit kationischer Stickstoffdotierung dar ,…”