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Configurationally stable dithia[7]helicene and dithia-quasi[8]circulene fused dithiolones

Abstract : Dithia-[7]helicene and quasi[8]circulene have been formed on the 1,3-dithiol-2-one ring by oxidative dehydrocyclisation of bis-naphthothiophenyl-1,3-dithiol-2-one. Quasi-circulenes are easily obtained at room temperature by successive dehydrocyclisations regardless the amount of oxidation reagent whereas selectivity towards helicene, involving a single dehydrocyclisation, has been achieved only at low temperature. DFT calculations suggest a mechanism via a dication intermediate rather than a mono-cation for the formation of the quasicirculenes whereas the helicene should be formed via a radical cation intermediate. While dithia[7]helicene is known to give stable stereoisomers, here the unsubstituted dithiaquasi[8]circulene shows unprecedented configurational stability of the enantiomers, with a theoretically estimated enantiomerisation energy barrier of 30.4 kcal/mol, in excellent agreement with the experimentally determined value of 29.8 kcal/mol. The enantiomers of both helicene and quasi-circulene have been separated by chiral chromatography and their absolute configuration assigned from the calculated CD spectra.
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https://hal.univ-angers.fr/hal-03855078
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Soumis le : mercredi 16 novembre 2022 - 10:51:44
Dernière modification le : jeudi 17 novembre 2022 - 04:12:54

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Maxime Baudillon, Thomas Cauchy, Nicolas Vanthuyne, Narcis Avarvari, Flavia Pop. Configurationally stable dithia[7]helicene and dithia-quasi[8]circulene fused dithiolones. Organic Chemistry Frontiers, 2022, 9 (16), pp.4260-4270. ⟨10.1039/D2QO00921H⟩. ⟨hal-03855078⟩

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