Related Experiment Video
Updated: May 22, 2026

Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
Published on: September 18, 2016
Surprisingly difficult resolution of N-methylated cationic [4]helicenes
Nathalie Mehanna1, Stéphane Grass, Jérôme Lacour
1Department of Organic Chemistry, University of Geneva, Geneva, Switzerland.
Abstract:
1,13-Dimethoxyquinacridinium ions of type 3 are highly configurationally stable [4]helicenes that can be synthesized in racemic form in a single step from tris(2,6-dimethoxyphenyl)methylium ion. Previously, it had been shown that the single enantiomers can be routinely obtained from racemic mixtures through Pummerer fragmentations of diastereomerically pure sulfoxide adducts that release the enantiopure cations after a C-C bond rupture. This resolution protocol is readily performed because of a (normally) large retention difference of the diastereomers over silica gel. Herein, we report that it is not always the case. Introduction of N-methyl side chain(s) at the periphery of the helical quinacridinium cations, which are needed for photophysical and biological studies, has a large negative effect of this separation. Instead of simple, rapid, and multigram separations by flash chromatography, extensive semi-preparative high-performance liquid chromatography sequences are now required.
Related Concept Videos
Aromatic Hydrocarbon Cations: Structural Overview
Removing one hydrogen from the intervening CH2 group with both...
Electrophilic Addition to Alkynes: Halogenation
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Nucleophilic Aromatic Substitution: Elimination–Addition
Thermal Electrocyclic Reactions: Stereochemistry
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Aromatic Hydrocarbon Anions: Structural Overview
Due to the absence of continuous overlap of p...
Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration

