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Enhanced synthesis of oxo-verdazyl radicals bearing sterically-and electronically-diverse C3-substituents

Citation

Fuller, RO and Taylor, MR and Duggin, M and Bissember, AC and Canty, AJ and Judd, MM and Cox, N and Moggach, SA and Turner, GF, Enhanced synthesis of oxo-verdazyl radicals bearing sterically-and electronically-diverse C3-substituents, Organic and Biomolecular Chemistry, 19, (46) pp. 10120-10138. ISSN 1477-0520 (2021) [Refereed Article]

Copyright Statement

The Royal Society of Chemistry 2021

DOI: doi:10.1039/d1ob01946e

Abstract

The synthetic viability of the hydrazine- and phosgene-free synthesis of 1,5-dimethyl oxo-verdazyl radicals has been improved via a detailed study investigating the influence of the aryl substituent on tetrazinanone ring formation. Although it is well established that functionalisation at the C3 position of the tetrazinanone ring does not influence the nature of the radical, it is crucial in applications development. The synthetic route involves a 4-step sequence: Schiff base condensation of a carbohydrazide with an arylaldehyde, alkylation, ring closure then subsequent oxidation to the radical. We found that the presence of strong electron-donating substituents and electron rich heterocycles, result in a significant reduction in yield during both the alkylation and ring closure steps. This can, in part, be alleviated by milder alkylation conditions and further substitution of the aryl group. In comparison, more facile formation of the tetrazine ring was observed with examples containing electron-withdrawing groups and with meta- or para-substitution. Density functional theory suggests that the ring closure proceeds via the formation of an ion pair. Electron paramagnetic resonance spectroscopy provides insight into the precise electronic structure of the radical with small variations in hyperfine coupling constants revealing subtle differences.

Item Details

Item Type:Refereed Article
Keywords:oxo-verdazyl radicals, heterocyclic chemistry
Research Division:Chemical Sciences
Research Group:Organic chemistry
Research Field:Organic chemical synthesis
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the chemical sciences
UTAS Author:Fuller, RO (Dr Rebecca Fuller)
UTAS Author:Taylor, MR (Miss Madeleine Taylor)
UTAS Author:Duggin, M (Miss Margot Duggin)
UTAS Author:Bissember, AC (Associate Professor Alex Bissember)
UTAS Author:Canty, AJ (Professor Allan Canty)
ID Code:149425
Year Published:2021
Funding Support:Australian Research Council (DE180100112)
Web of Science® Times Cited:2
Deposited By:Chemistry
Deposited On:2022-03-30
Last Modified:2022-04-08
Downloads:0

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