An Efficient Flow‐Photochemical Synthesis of 5<i>H</i>‐Furanones Leads to an Understanding of Torquoselectivity in Cyclobutenone Rearrangements

Harrowven, David C.; Mohamed, Mubina; Gonçalves, Théo P.; Whitby, Richard J.; Bolien, David; Sneddon, Helen F.

doi:10.1002/ange.201200281

Cited by 17 publications

(5 citation statements)

References 39 publications

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“…Entry 12 describes a reaction previously developed by us involving the irradiation of pyrrole 24 to tricyclic aziridine 25 through a complex photochemical two‐step process 17. Consistent with the rest of the 1‐layer/36 W reactors used in this study, the yields between batch and flow were essentially identical, with a minor increase in batch productivity when the power correction was factored in.…”

Section: Resultssupporting

confidence: 55%

Batch versus Flow Photochemistry: A Revealing Comparison of Yield and Productivity

Elliott

Knowles

Koovits

et al. 2014

Chemistry A European J

188

120

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The use of flow photochemistry and its apparent superiority over batch has been reported by a number of groups in recent years. To rigorously determine whether flow does indeed have an advantage over batch, a broad range of synthetic photochemical transformations were optimized in both reactor modes and their yields and productivities compared. Surprisingly, yields were essentially identical in all comparative cases. Even more revealing was the observation that the productivity of flow reactors varied very little to that of their batch counterparts when the key reaction parameters were matched. Those with a single layer of fluorinated ethylene propylene (FEP) had an average productivity 20% lower than that of batch, whereas three-layer reactors were 20% more productive. Finally, the utility of flow chemistry was demonstrated in the scale-up of the ring-opening reaction of a potentially explosive [1.1.1] propellane with butane-2,3-dione.

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Section: Resultssupporting

confidence: 55%

Batch versus Flow Photochemistry: A Revealing Comparison of Yield and Productivity

Elliott

Knowles

Koovits

et al. 2014

Chemistry A European J

188

120

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“…The photochemical rearrangement of 4‐hydroxycyclobutenones to yield 5 H ‐furanones was achieved in continuous flow (Scheme A) 61. The reaction was difficult in batch since extended irradiation times resulted in substantial photodegradation of the desired product (27 % yield after 4 h).…”

Section: Photochemistry In Continuous‐flow Reactorsmentioning

confidence: 99%

Photochemical Transformations Accelerated in Continuous‐Flow Reactors: Basic Concepts and Applications

Straathof

Hessel

et al. 2014

Chemistry A European J

465

271

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Continuous-flow photochemistry is used increasingly by researchers in academia and industry to facilitate photochemical processes and their subsequent scale-up. However, without detailed knowledge concerning the engineering aspects of photochemistry, it can be quite challenging to develop a suitable photochemical microreactor for a given reaction. In this review, we provide an up-to-date overview of both technological and chemical aspects associated with photochemical processes in microreactors. Important design considerations, such as light sources, material selection, and solvent constraints are discussed. In addition, a detailed description of photon and mass-transfer phenomena in microreactors is made and fundamental principles are deduced for making a judicious choice for a suitable photomicroreactor. The advantages of microreactor technology for photochemistry are described for UV and visible-light driven photochemical processes and are compared with their batch counterparts. In addition, different scale-up strategies and limitations of continuous-flow microreactors are discussed.

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“…Torquoselectivity is defined to be the preference for either the transition state (TS) inward conrotatory reaction pathway (TSIC) or the transition state outward conrotatory (TSOC) reaction pathway . Rondan and Houk first postulated the mechanism of torquoselectivity using orbital symmetry to understand electrocyclic reactions but only for reactions where a high degree of symmetry was present . Realistic conrotatory ring‐opening reactions are not highly symmetrical and, therefore, only reaction measures that possess directional character can correctly predict the TSIC or TSOC pathways consequently, that is, only vector‐based and not scalar measures can be used.…”

Section: Introductionmentioning

confidence: 99%

A vector‐based representation of the chemical bond for predicting competitive and noncompetitive torquoselectivity of thermal ring‐opening reactions

Azizi

Momen

Morales-Bayuelo

et al. 2018

Int J of Quantum Chemistry

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We present a new vector-based representation of the chemical bond referred to as the bondpath frame-work set B = {p, q, r}, where p, q, and r represent three paths with corresponding eigenvector-following paths with lengths H*, H, and the bond-path length from the quantum theory of atoms in molecules (QTAIM). We find that longer path lengths H of the ring-opening bonds predict the preference for the transition state inward (TSIC) or transition state outward (TSOC) of thermal ring opening reactions in agreement with experiment for all five reactions R1-R5. Competitiveness and noncompetitiveness have traditionally been considered using activation energies within transition state theory that is known to fail for thermal ring-opening reactions. Consequently, we find that the activation energy for R3 does not satisfactorily determine competitiveness or provide consistent agreement with experimental yields. We choose a selection of five competitive and noncompetitive reactions; methyl-cyclobutene (R1), ethyl-methylcyclobutene (R2), iso-propyl-methyl-cyclobutene (R3), ter-butyl-methyl-cyclobutene (R4), and phenyl-methyl-cyclobutene (R5). Therefore, in this investigation we provide a new criterion, within the QTAIM framework, to determine whether the reactions R1-R5 are competitive or noncompetitive. We that find R2, R3, and R5 are competitive and R1 and R4 are noncompetitive reactions in contrast to the results from the activation energies, calling into question the reliability of activation energies.

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An Efficient Flow‐Photochemical Synthesis of 5H‐Furanones Leads to an Understanding of Torquoselectivity in Cyclobutenone Rearrangements

Cited by 17 publications

References 39 publications

Batch versus Flow Photochemistry: A Revealing Comparison of Yield and Productivity

Batch versus Flow Photochemistry: A Revealing Comparison of Yield and Productivity

Photochemical Transformations Accelerated in Continuous‐Flow Reactors: Basic Concepts and Applications

A vector‐based representation of the chemical bond for predicting competitive and noncompetitive torquoselectivity of thermal ring‐opening reactions

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