File(s) under permanent embargo
Enhanced synthesis of oxo-verdazyl radicals bearing sterically-and electronically-diverse C3-substituents
journal contribution
posted on 2023-05-21, 06:42 authored by Rebecca FullerRebecca Fuller, Madeleine TaylorMadeleine Taylor, Margot DugginMargot Duggin, Alexander BissemberAlexander Bissember, Allan CantyAllan Canty, Judd, MM, Cox, N, Moggach, SA, Turner, GFThe 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.
Funding
Australian Research Council
History
Publication title
Organic and Biomolecular ChemistryVolume
19Issue
46Pagination
10120-10138ISSN
1477-0520Department/School
School of Natural SciencesPublisher
Royal Soc ChemistryPlace of publication
Thomas Graham House, Science Park, Milton Rd, Cambridge, England, Cambs, Cb4 0WfRights statement
© The Royal Society of Chemistry 2021Repository Status
- Restricted