[6]Saddlequat: a [6]helquat captured on its racemization pathway

Abstract

A dicationic [6]helicene congener captured on the racemization pathway in its saddle-shaped geometry is introduced. Synthesis, structure, resolution, and dynamic properties of this chiral [6]saddlequat in-between and its highly stereocontrolled transformation into enantiopure [6]helquat are discussed and demonstrated. The dynamic aspects established by experiment and supported by detailed DFT-D calculations are presented visually in the form of a movie (electronic table-of-contents and electronic supplementary information). The title [6]saddlequat was found to be an isolable chiral species on the entirely chiral enantiomerization pathway of a [6]helquat that is discussed as an example of Mislow's ''rubber glove'' molecule. Scheme 1 (a) Racemization of [6]helicene via achiral saddle-shaped transition state, (b) racemization of [9]helicene via saddle-shaped intermediate, and the corresponding energy profiles. r.c. ¼ reaction coordinate.

Preferential Crystallization of a Helicene–Viologen Hybrid – An Efficient Method to Resolve [5]Helquat Enantiomers on a 20 g Scale

“…[18] This resolution gave enantiopure [P-1][TfO] 2 in milligram quantities. During our studies on helquats, [12,18] we realized that the preparative power of PC to separate enantiomers of helical aromatics in multigram quantities is attractive and remains unexplored. Because of this, we became interested in the demonstration of the mass throughput advantage of this method with our helicene-viologen hybrids such as [1][TfO] 2 .…”

“…[1][TfO] 2 , Figure 2), which represent a structural link between helicenes and viologens. [12] To explore the emerging potential of helquats and to address issues that depend on their helical chirality, multigram preparative access to nonracemic series is desirable. However, from the beginning of our studies, we were aware that reports on obtaining helical aromatics as separate enantio- mers in quantities larger than 1 g are relatively rare (Figure 2).…”

Kann gehinderter intramolekularer Schwingungsenergietransfer nichtergodisches Verhalten mittelgroßer Ionenpaare bewirken?

“…So untersuchten wir die nichtkovalenten Ionenpaare von Triflat (TfO À = CF 3 SO 3 À ) mit einem Bispyridinium-Ion, das in zwei auftrennbaren Konformeren existiert (siehe die Strukturformeln in Abbildung 1), die wir als Helquat (h-1 2+ ) und Saddlequat (s-1 2+ ) bezeichnen. [13] Neben anderweitigen massenspektrometrischer Studien haben wir die Infrarot-Mehrphotonendissoziation (IRMPD) [14] [16] als IRMPD-aktiv zugelassen werden. In diesem Zusammenhang ist es wichtig darauf hinzuweisen, dass IRMPD eine Wirkungsspektroskopie ist, in der die IR-Absorption der Gasphasen-Ionen über deren Fragmentierung verfolgt wird.…”

Dutch Resolution of a configurationally stable [5]helquat

“…In the course of our studies of helquats and other chiral cations, we benefited from unexpectedly high success rate of racemate resolutions via diastereomeric salts with dibenzoyltartrate anions (L‐DBT ‐ in Figure ) . However, there are some racemic helquats, we have not been able to resolve with this anion .…”

“…18,20 In our research into nonracemic helquats, we mainly explored preparative resolutions relying on diastereomeric ion pairs with inexpensive dibenzoyltartrate anion. 31,33,[51][52][53][54] Besides this, we developed efficient multigram scale resolutions of two different helquats via preferential crystallization. 53,54 Herein we present synthesis and nontrivial resolution of racemic helicene-like dication, helquat 1.…”