Dynamic and Persistent Cyclochirality in Hydrogen-Bonded Derivatives of Medium-Ring Triamines

David T J Morris; Steven M Wales; Javier Echavarren; Matej Žabka; Giulia Marsico; John W Ward; Natalie E Pridmore; Jonathan Clayden

doi:10.1021/jacs.3c06570

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Dynamic and Persistent Cyclochirality in Hydrogen-Bonded Derivatives of Medium-Ring Triamines

Journal article

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Peer reviewed

Dynamic and Persistent Cyclochirality in Hydrogen-Bonded Derivatives of Medium-Ring Triamines

David T J Morris, Steven M Wales, Javier Echavarren, Matej Žabka, Giulia Marsico, John W Ward, Natalie E Pridmore and Jonathan Clayden

Journal of the American Chemical Society, Vol.145, pp.19030-19041

2023

DOI: https://doi.org/10.1021/jacs.3c06570

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Abstract

chemical structure

conformation

molecular structure

noncovalent interactions

solvents

Cyclic triureas derived from 1,4,7-triazacyclononane (TACN) were synthesized; X-ray crystallography showed a chiral bowl-like conformation with each urea hydrogen-bonded to its neighbor with uniform directionality, forming a “cyclochiral” closed loop of hydrogen bonds. Variable-temperature 1H NMR, 1H-1H exchange spectroscopy, Eyring analysis, computational modeling, and studies in various solvents revealed that cyclochirality is dynamic (ΔG‡25°C = 63–71 kJ mol–1 in noncoordinating solvents), exchanging between enantiomers by two mechanisms: bowl inversion and directionality reversal, with the former subject to a slightly smaller enantiomerization barrier. The enantiomerization rate substantially increased in the presence of hydrogen-bonding solvents. Population of only one of the two cyclochiral hydrogen-bond directionalities could be induced by annulating one ethylene bridge with a trans-cyclohexane. Alternatively, enantiomerization could be inhibited by annulating one ethylene bridge with a cis-cyclohexane (preventing bowl inversion) and replacing one urea function with a formamide (preventing directionality reversal). Combining these structural modifications resulted in an enantiomerization barrier of ΔG‡25°C = 93 kJ mol–1, furnishing a planar-chiral, atropisomeric bowl-shaped structure whose stereochemical stability arises solely from its hydrogen-bonding network.

Details

Title: Dynamic and Persistent Cyclochirality in Hydrogen-Bonded Derivatives of Medium-Ring Triamines
Authors: David T J Morris (Author) - University of Bristol
Steven M Wales (Author) - University of Bristol
Javier Echavarren (Author) - University of Bristol
Matej Žabka (Author) - University of Bristol
Giulia Marsico (Author) - University of Bristol
John W Ward (Author) - University of Bristol
Natalie E Pridmore (Author) - University of Bristol
Jonathan Clayden (Corresponding Author) - University of Bristol
Publication details: Journal of the American Chemical Society, Vol.145, pp.19030-19041
Publisher: American Chemical Society
Date published: 2023
DOI: 10.1021/jacs.3c06570
ISSN: 1520-5126; 0002-7863
Copyright note: This publication is licensed under CC-BY 4.0.
Organisation Unit: School of Science, Technology and Engineering; Student Services and Engagement
Language: English
Record Identifier: 99748297302621
Output Type: Journal article

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