Post-spin crossing dynamics determine the regioselectivity in open-shell singlet biradical recombination

Zhu, Min; Zheng, Chao

doi:10.1039/d1qo01757h

Cited by 3 publications

(3 citation statements)

References 107 publications

(20 reference statements)

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“…We first focused on determining the first nonreversible step of the reaction as it is important for understanding the origins of the observed selectivities. , To probe this, we conducted the standard reaction with the E - 2 D-labeled alkene 59 . If the intermolecular radical addition step was selectivity-determining, we would expect to isolate 60a and/or 60b with recovered unchanged 59 (Scheme A).…”

Section: Resultsmentioning

confidence: 74%

Photochemical Dearomative Cycloadditions of Quinolines and Alkenes: Scope and Mechanism Studies

et al. 2022

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Photochemical dearomative cycloaddition has emerged as a useful strategy to rapidly generate molecular complexity. Within this context, stereo- and regiocontrolled intermolecular para-cycloadditions are rare. Herein, a method to achieve photochemical cycloaddition of quinolines and alkenes is shown. Emphasis is placed on generating sterically congested products and reaction of highly substituted alkenes and allenes. In addition, the mechanistic details of the process are studied, which revealed a reversible radical addition and a selectivity-determining radical recombination. The regio- and stereochemical outcome of the reaction is also rationalized.

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Section: Resultsmentioning

confidence: 74%

Photochemical Dearomative Cycloadditions of Quinolines and Alkenes: Scope and Mechanism Studies

et al. 2022

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“…Besides, the Gibbs free energy of 23 was higher than the unobserved [5 + 2] cycloadduct by 10.9 kcal/mol. Therefore, this regioselectivity did not originate from either the electronic property or the thermodynamic preference of the system (Figure c) . Instead, a transition state ( TS-5 ) of radical type 1,3-migration that connected the [5 + 2] and [5 + 4] cycloadducts was located.…”

Section: Comprehensive Mechanistic Studiesmentioning

confidence: 98%

“…Therefore, this regioselectivity did not originate from either the electronic property or the thermodynamic preference of the system (Figure 15c). 61 Instead, a transition state (TS-5) of radical type 1,3-migration that connected the [5 + 2] and [5 + 4]…”

Section: Post-spin Crossing Dynamicsmentioning

confidence: 99%

Energy-Transfer-Enabled Dearomative Cycloaddition Reactions of Indoles/Pyrroles via Excited-State Aromatics

et al. 2022

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Metrics & MoreArticle Recommendations CONSPECTUS: Exploring the enormous chemical space through an expedient buildingup of molecular diversity is an important goal of organic chemistry. The development of synthetic methods toward molecules with unprecedented structural motifs lays the foundation for wide applications ranging from pharmaceutical chemistry to materials science. In this regard, the dearomatization of arenes has been recognized as a unique strategy since it provides novel retrosynthetic disconnections for various spiro or fused polycyclic molecules with increased saturation and stereoisomerism. However, inherent thermodynamic challenges are associated with dearomatization processes. The disruption of the aromaticity of arene substrates usually requires large energy inputs, which makes harsh conditions necessary for many ground-state dearomatization reactions. Therefore, further expansion of the scope of dearomatization reactions remains a major problem not fully solved in organic chemistry.The past decade has witnessed tremendous progress on photocatalytic reactions under visible light. Particularly, reactions via an energy transfer mechanism have unlocked new opportunities for dearomatization reactions. Mediated by appropriately chosen photosensitizers, aromatic substrates can be excited. This kind of precise energy input might make feasible some dearomatization reactions that are otherwise unfavorable under thermal conditions because of the significant energy increases of the substrates. Nevertheless, the lifetimes of key intermediates in energy-transfer-enabled reactions, such as excited-state aromatics and downstream biradical species, are quite short. How to regulate the reactivities of these transient intermediates to achieve exclusive selectivity toward a certain reaction pathway among many possibilities is a crucial issue to be addressed. Since 2019, our group has reported a series of visible-light-induced dearomative cycloaddition reactions for indole and pyrrole derivatives. It was found that the aromatic units in substrates can be excited under the irradiation of visible light in the presence of a suitable photosensitizer. These excited aromatics readily undergo various [m + n] cycloaddition reactions with appropriately tethered unsaturated functionalities including alkenes, alkynes, N-alkoxy oximes, (hetero)arenes, and vinylcyclopropanes. The reactions yield polycyclic indolines and pyrrolines with highly strained small-and/or medium-sized rings embedded, some of which possess unique bridge-or cagelike topologies. Systematic mechanistic studies confirmed the involvement of an energy transfer process. Density functional theory (DFT) calculations revealed the correlation between the substrate structure and the excitation efficiency, which accelerated the optimization of the reaction parameters. Meanwhile, DFT calculations demonstrated the competition between kinetically and thermodynamically controlled pathways for the open-shell singlet biradical intermediates, which allowed the complete s...

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Visible‐Light‐Induced Diradical‐Mediatedipso‐Cyclization towards Double Dearomative [2+2]‐Cycloaddition or Smiles‐Type Rearrangement

Zhen

Zeng

Jiang

et al. 2023

Chemistry A European J

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When mono‐radical ipso‐cyclization of aryl sulfonamides tend to undergo Smiles‐type rearrangement through aromatization‐driven C−S bond cleavage, diradical‐mediated cyclization must perform in a distinct reaction pathway. It is interesting meanwhile challenging to tune the rate of C−S bond cleavage to achieve a chemically divergent reaction of (hetero) aryl sulfonamides in a visible‐light induced energy transfer (EnT) reaction pathway involving diradical species. Herein a chemically divergent reaction based on the designed indole‐tethered (hetero)arylsulfonamides is reported which involves a diradical‐mediated ipso‐cyclization and a controllable cleavage of an inherent C−S bond. The combined experimental and computational results have revealed that the cleavage of the C−S bond in these substrates can be controlled by tuning the heteroaryl moieties: a) If the (hetero)aryl is thienyl, furyl, phenanthryl, etc., the radical coupling of double dearomative diradicals (DDDR) precedes over C−S bond cleavage to afford cyclobutene fused indolines by double dearomative [2+2]‐cycloaddition; b) if the (hetero)aryl is phenyl, naphthyl, pyridyl, indolyl etc., the cleavage of C−S bond in DDDR is favored over radical coupling to afford biaryl products.

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Post-spin crossing dynamics determine the regioselectivity in open-shell singlet biradical recombination

Abstract: Radical recombination is among the fastest reactions in organic chemistry. Achieving high level of selectivities in this type of reactions is rather challenging. In a recent report on visible-light-induced dearomative...

Cited by 3 publications

References 107 publications

Photochemical Dearomative Cycloadditions of Quinolines and Alkenes: Scope and Mechanism Studies

Photochemical Dearomative Cycloadditions of Quinolines and Alkenes: Scope and Mechanism Studies

Energy-Transfer-Enabled Dearomative Cycloaddition Reactions of Indoles/Pyrroles via Excited-State Aromatics

Visible‐Light‐Induced Diradical‐Mediatedipso‐Cyclization towards Double Dearomative [2+2]‐Cycloaddition or Smiles‐Type Rearrangement

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