Hexapole [9]Helicene

Abstract

Herein we present the first hexapole [9]helicene (H9H). Co‐catalyzed [2+2+2] cyclotrimerization of a dinaphthopyrene (DNP) functionalized alkyne provides the hexaaryl benzene precursor 2, which is transformed into H9H via a dehydrocyclization reaction. Formation of each embedded [9]helicene involves forging of a new C−C bond, which stitches together two [4]helicene subunits of the neighboring DNP blades, reminiscent of the initial method Martin developed for the preparation of [9]helicene in the 1960s. Single‐crystal X‐ray analysis of both 2 and H9H discloses their extremely distorted and crowded structural features. Chiral resolution, optical and electronic properties of H9H are also presented.

A Nitrogen‐Doped Hexapole [7]Helicene versus Its All‐Carbon Analogue

“…A significant red‐shift in absorption for the C 138 N 6 N‐H7H ( λ max =683 nm) was noted not only with respect to the C 150 C‐H7H ( λ max =593 nm), but also in comparison with all other propeller‐shaped NG homologues previously synthesized by our group (see Figure S10), including a methoxy‐substituted C 150 H7H ( λ max =618 nm), an all‐carbon C 198 H9H ( λ max =605 nm), and even a much larger C 258 superhelicene ( λ max =650 nm) . These results suggest a stronger effect of N‐doping in modulating the transition energy relative to other factors, such as the shape, size, and functional groups of these propeller‐shaped NG compounds.…”

“…The title compounds were prepared using our previous method for making hexapole [9]helicenes (H9Hs), with indispensable modifications. The key steps in the synthesis of the DBU and DBP subunits involve palladium‐catalyzed C−H activation and tert ‐butyl nitrite promoted Pschorr cyclization, respectively (Figure ).…”

Negative Charge as a Lens for Concentrating Antiaromaticity: Using a Pentagonal “Defect” and Helicene Strain for Cyclizations

“…Injecting an egative charge into al arge p-system is known to lead to C À Cb ond formations through, for example,d imerization [9] and annulations. [10] In 1992, Rabinovitz and co-workers reported ar eductive annulation of a [ 5]helicene by alkali metals with putative products characterized spectroscopically. [11] Thep resent work shows that this reductive coupling is applicable to helicenes that are already anionic.…”

“…In conclusion, crystallographic and computational analysis illustrate the effect of negative-charge injection in twisted and planar polyaromatics.T he non-planarity of the helicene core compromises their efficient crystal packing and assists in the formation of "porous" supramolecular arrangements, creating afavorable situation for multi-component solid-state packing.D eprotonation of fused [5]bis-helicenes with ap entagonal "defect" adds charge to the twisted polyaromatic core and converts it into an attractive anionic component of hybrid organic-inorganic ion-pair architectures.…”

“…[2] Recently, considerable progress has been achieved in the synthesis and applications of various helicenes, [3] including heterohelicenes [4] and fused "multipole" helicenes. [5] Theh elical twist depends on the length of the helicenes,t he nature of the substituents,a nd the presence of defects in the backbone. Defects,for example,heteroatoms or smaller rings,can affect helicity as well as local trends in aromaticity.…”