Impact of Excited-State Antiaromaticity Relief in a Fundamental Benzene Photoreaction Leading to Substituted Bicyclo[3.1.0]hexenesShow others and affiliations
2020 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 142, no 25, p. 10942-10954Article in journal (Refereed) Published
Abstract [en]
Benzene exhibits a rich photochemistry which can provide access to complex molecular scaffolds that are difficult to access with reactions in the electronic ground state. While benzene is aromatic in its ground state, it is antiaromatic in its lowest ππ∗ excited states. Herein, we clarify to what extent relief of excited-state antiaromaticity (ESAA) triggers a fundamental benzene photoreaction: the photoinitiated nucleophilic addition of solvent to benzene in acidic media leading to substituted bicyclo[3.1.0]hex-2-enes. The reaction scope was probed experimentally, and it was found that silyl-substituted benzenes provide the most rapid access to bicyclo[3.1.0]hexene derivatives, formed as single isomers with three stereogenic centers in yields up to 75% in one step. Two major mechanism hypotheses, both involving ESAA relief, were explored through quantum chemical calculations and experiments. The first mechanism involves protonation of excited-state benzene and subsequent rearrangement to bicyclo[3.1.0]hexenium cation, trapped by a nucleophile, while the second involves photorearrangement of benzene to benzvalene followed by protonation and nucleophilic addition. Our studies reveal that the second mechanism is operative. We also clarify that similar ESAA relief leads to puckering of S1-state silabenzene and pyridinium ion, where the photorearrangement of the latter is of established synthetic utility. Finally, we identified causes for the limitations of the reaction, information that should be valuable in explorations of similar photoreactions. Taken together, we reveal how the ESAA in benzene and 6π-electron heterocycles trigger photochemical distortions that provide access to complex three-dimensional molecular scaffolds from simple reactants.
Place, publisher, year, edition, pages
American Chemical Society , 2020. Vol. 142, no 25, p. 10942-10954
Keywords [en]
Addition reactions, Benzene, Ground state, Isomers, Photoreactivity, Protonation, Quantum chemistry, Scaffolds, Electronic ground state, Molecular scaffolds, Nucleophilic additions, Photorearrangement, Quantum chemical calculations, Stereogenic centers, Substituted benzenes, Synthetic utility, Excited states, bicyclo[3.1.0]hexene derivative, cyclohexene derivative, heterocyclic compound, molecular scaffold, pyridinium derivative, silabenzene, solvent, unclassified drug, Article, chemical phenomena, controlled study, electron, excited state antiaromaticity, isomer, nucleophilicity, photochemistry, synthesis
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:ri:diva-57302DOI: 10.1021/jacs.9b13769Scopus ID: 2-s2.0-85087034116OAI: oai:DiVA.org:ri-57302DiVA, id: diva2:1616708
Note
Funding details: 19-20467Y; Funding details: National Science Foundation, NSF, 1800329, 2016-03398, CHE-1465142; Funding details: Fayetteville State University, FSU; Funding details: VINNOVA, 2016-04572; Funding details: Vetenskapsrådet, VR, 2015-04538, 2019-05618; Funding details: Ústav organické chemie a biochemie Akademie věd České republiky, ÚOCHB AV ČR; Funding text 1: The Olle Engkvist Byggmästare Foundation is greatly acknowledged for postdoctoral fellowships to T.S., J.T., and W.R. (184-390 and 194-677). T.S. appreciates support from the Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences and the Czech Grant Academy (19-20467Y). H.O. is grateful to the Swedish Research Council (VR) for financial support (2015-04538 and 2019-05618) and to the Vinnova agency for an academia-industry exchange grant (2016-04572). R.A. is grateful to the Liljewalch Foundation for a travel grant allowing a research visit at FSU. I.A. is grateful for the support by the National Science Foundation (CHE-1465142). R.L. and I.F.G. are grateful to the Swedish Research Council (VR) for financial support (grant 2016-03398). M.N. is grateful for an Erasmus+ scholarship that allowed for a summer internship at UU. The computations were enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputer Center (NSC) in Linköping and at UPPMAX in Uppsala.
2021-12-032021-12-032021-12-03Bibliographically approved