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Mateos J, Rigodanza F, Costa P, Natali M, Vega-Peñaloza A, Fresch E, Collini E, Bonchio M, Sartorel A, Dell'Amico L. Unveiling the impact of the light-source and steric factors on [2+2] heterocycloaddition reactions. NATURE SYNTHESIS 2023; 962:26-36. [PMID: 37325160 PMCID: PMC7614650 DOI: 10.1038/s44160-022-00191-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Accepted: 10/11/2022] [Indexed: 07/13/2023]
Abstract
Information gained from in-depth mechanistic investigations can be used to control the selectivity of reactions, leading to the expansion of the generality of synthetic processes and the discovery of new reactivity. Here, we investigate the mechanism of light-driven [2+2] heterocycloadditions (Paternò-Büchi reactions) between indoles and ketones to develop insight into these processes. Using ground-state UV-Vis absorption and transient absorption spectroscopy (TAS), together with DFT calculations, we found that the reactions can proceed via an exciplex or electron-donor-acceptor (EDA) complex, which are key intermediates in determining the stereoselectivity of the reactions. We used this discovery to control the diastereoselectivity of the reactions, gaining access to previously inaccessible diastereoisomeric variants. When moving from 370 to 456 nm irradiation, the EDA complex is increasingly favoured, and the diastereomeric ratio (d.r.) of the product moves from >99:<1 to 47:53. In contrast, switching from methyl to ipropyl substitution favours the exciplex intermediate, reversing the d.r. from 89:11 to 16:84. Our study shows how light and steric parameters can be rationally used to control the diastereoselectivity of photoreactions, creating mechanistic pathways to previously inaccessible stereochemical variants.
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Affiliation(s)
- Javier Mateos
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
| | - Francesco Rigodanza
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
| | - Paolo Costa
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
| | - Mirco Natali
- Dipartimento di Scienze Chimiche e Farmaceutiche, University of Ferrara, Via Luigi Borsari 46, 44121 Ferrara, Italy
| | - Alberto Vega-Peñaloza
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
| | - Elisa Fresch
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
| | - Elisabetta Collini
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
| | - Marcella Bonchio
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
| | - Andrea Sartorel
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
| | - Luca Dell'Amico
- Department of Chemical Sciences, University of Padova, Via Marzolo 1, 35131 Padova, Italy
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Mori T. Asymmetric Photochemical Synthesis Based on Selective Excitation of Charge-Transfer Complexes. J SYN ORG CHEM JPN 2017. [DOI: 10.5059/yukigoseikyokaishi.75.144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Tadashi Mori
- Graduate School of Engineering, Osaka University
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Matsuki N, Inoue Y, Mori T. Orbital Control of Photochemical Rearrangement of 4-Aryl-1,1-dicyano-1-butenes through the Hyperconjugative Substitution on the Linker Chain. J Phys Chem Lett 2016; 7:4957-4961. [PMID: 27973867 DOI: 10.1021/acs.jpclett.6b02632] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Hyperconjugative interaction was demonstrated to play a vital role in the photochemistry of 4-aryl-1,1-dicyano-1-butenes. Thus a simple substituent on the benzylic position effectively induced a new photoreactivity to afford an allylic rearrangement product that is not obtained for the parent substrate. The natural bond orbital analysis was employed to reveal the enhanced relative contributions of hyperconjugation in the excited state, which dramatically alter the photochemical outcomes not only by reducing the strength of the allylic/benzylic bond but more crucially by affecting the conformer distribution.
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Affiliation(s)
- Nobuo Matsuki
- Department of Applied Chemistry, Graduate School of Engineering, Osaka University , 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Yoshihisa Inoue
- Department of Applied Chemistry, Graduate School of Engineering, Osaka University , 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Tadashi Mori
- Department of Applied Chemistry, Graduate School of Engineering, Osaka University , 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan
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Enhanced asymmetric photocycloaddition of anthracene tethered to maleate versus fumarate through non-fluorescent exciplex intermediate. J Photochem Photobiol A Chem 2016. [DOI: 10.1016/j.jphotochem.2015.09.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Vayá I, Gustavsson T, Markovitsi D, Miranda MA, Jiménez MC. Influence of the spacer on the photoreactivity of flurbiprofen-tyrosine dyads. J Photochem Photobiol A Chem 2016. [DOI: 10.1016/j.jphotochem.2016.03.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Nagasaki K, Inoue Y, Mori T. Contrasting Behaviour of Exciplex Ensembles in the Diastereodifferentiating Paternò–Büchi Reaction of Chiral Cyanobenzoate with Naphthyl- and Phenylethenes on Direct or Charge-Transfer Excitation. Aust J Chem 2015. [DOI: 10.1071/ch15404] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The diastereodifferentiating Paternò–Büchi reaction of chiral cyanobenzoate with 1-(1-naphthyl)-1-phenylethene was compared with those with 1,1-diphenylethene on direct and charge-transfer excitations. By desymmetrization of the donor, four diastereomeric oxetane products were formed on photolysis in excellent combined yields. Increase in donor strength induced a stronger charge-transfer interaction both in ground and excited states. Thus, the difference in diastereoselectivities with two different excitation modes (i.e. direct versus charge-transfer) became less significant with a naphthyl derivative as donor. A subtle change of donor–acceptor interaction was shown to have profound effect on the nature of the excited-state complexes and thus the product (stereo)selectivities. Despite a small temperature dependence, an Eyring-type study on the diastereoselectivities confirmed that the excited charge-transfer complex is an excited species distinct from the conventional exciplex.
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