Planar Chirality Controls Diastereotopicity in [2.2]Paracyclophanyl Cyclopropenes
Tilman Köhler1, Maximilian Hartmann2, Olaf Fuhr3
1Institute of Organic Chemistry (IOC), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|March 26, 2026
Summary
Researchers synthesized cyclopropenes using rhodium-catalyzed reactions. The [2.2]paracyclophane structure created unique stereochemical differences in the cyclopropenes, which disappeared upon oxidation.
Area of Science:
- Organic Chemistry
- Organometallic Chemistry
- Stereochemistry
Background:
- Cyclopropenes are strained three-membered ring systems with unique reactivity.
- Rhodium-catalyzed reactions are powerful tools for C-C bond formation.
- [2.2]Paracyclophane (pCp) is a rigid macrocycle that can impart specific stereochemical properties.
Purpose of the Study:
- To report the synthesis of [2.2]paracyclophanyl (pCp) cyclopropenes.
- To investigate the stereochemical outcomes of this cyclopropene synthesis.
- To explore the effect of oxidation on the stereochemistry of the resulting cyclopropenium ions.
Main Methods:
- Rhodium-catalyzed [2+1] cycloaddition reaction.
- Use of a [2.2]paracyclophane-derived carbene precursor.
- Synthesis of cyclopropenes from alkynes.
- 1H Nuclear Magnetic Resonance (NMR) spectroscopy.
- Oxidation of cyclopropenes to cyclopropenium ions.
Main Results:
- Successful synthesis of [2.2]paracyclophanyl (pCp) cyclopropenes.
- Observation of diastereotopic differentiation of alkyl substituents in cyclopropenes due to the pCp topology.
- 1H NMR spectra consistently showed this stereochemical bias.
- Oxidation to cyclopropenium ions eliminated the stereochemical bias, restoring substituent equivalence.
- Increased symmetry observed upon aromatization.
Conclusions:
- The [2.2]paracyclophane framework effectively induces and differentiates stereocenters in cyclopropene synthesis.
- The observed stereochemical bias is a direct consequence of the rigid macrocyclic structure.
- Aromatization to cyclopropenium ions leads to loss of stereochemical information and increased molecular symmetry.
More Related Videos
09:22Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives
Published on: February 7, 2017
8.3K
09:35Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
Published on: September 18, 2016
12.2K
Related Concept Videos
02:05Prochirality
5.3K
The concept of prochirality leads to the nomenclature of the individual faces of a molecule and plays a crucial role in the enantioselective reaction. It is a concept where two or more achiral molecules react to produce chiral products. A typical process is the reaction of an achiral ketone to generate a chiral alcohol. Here, the achiral reactant reacts with an achiral reducing agent, sodium borohydride, to generate an equimolar mixture of the chiral enantiomers of the product. For example, an...
5.3K
02:33Stereoisomerism of Cyclic Compounds
11.8K
In this lesson, we delve into the role of ring conformation and its stability, which determines the spatial arrangement and, consequently, the molecular symmetry and stereoisomerism of cyclic compounds. 1,2-Dimethylcyclohexane is used as a case study to evaluate the possible number of stereoisomers. Here, given the multiple (n = 2) chiral centers, there are 2n = 4 possible configurations that lack a plane of symmetry, as the ring skeleton exists in a non-planar chair conformation. In addition,...
11.8K
02:25Chirality
32.2K
Chirality is a term that describes the lack of mirror symmetry in an object. In other words, chiral objects cannot be superposed on their mirror images. For example, our feet are chiral, as the mirror image of the left foot, the right foot, cannot be superposed on the left foot.
Chiral objects exhibit a sense of handedness when they interact with another chiral object. For example, our left foot can only fit in the left shoe and not in the right shoe. Achiral objects — objects that have...
Chiral objects exhibit a sense of handedness when they interact with another chiral object. For example, our left foot can only fit in the left shoe and not in the right shoe. Achiral objects — objects that have...
32.2K
02:37Disubstituted Cyclohexanes: cis-trans Isomerism
15.1K
Depending upon the different spatial orientation of the substituents, the disubstituted cycloalkanes exhibit two types of stereoisomers. The cis isomers have the substituents on the same side of the ring, whereas the trans isomers have the substituents on the opposite sides. These stereoisomers exhibit different physical properties and cannot be interconverted without breaking the carbon-carbon bonds.
In cyclohexane, the substituents can occupy different positions generating distinct isomers....
In cyclohexane, the substituents can occupy different positions generating distinct isomers....
15.1K
02:25Molecules with Multiple Chiral Centers
16.4K
Molecules that possess multiple chiral centers can afford a large number of stereoisomers. For instance, while some molecules like 2-butanol have one chiral center, defined as a tetrahedral carbon atom with four different substituents attached, several molecules like butane-2,3-diol have multiple chiral centers. A simple formula to predict the number of stereoisomers possible for a molecule with n chiral centers is 2n. However, there can be a lower number where some of the stereoisomers are...
16.4K
02:21Naming Enantiomers
27.7K
The naming of enantiomers employs the Cahn–Ingold–Prelog rules that involve assigning priorities to different substituent groups at a chiral center. Each enantiomer, being a distinct molecule, is assigned a unique name by the Cahn–Ingold–Prelog (CIP) rules, also called the R–S system. The prefix R- or S- attached to the chiral centers in an enantiomer is dependent on the spatial arrangement of the four substituents on the chiral center. The R–S system essentially comprises three...
27.7K