Catalytic Synthesis of 8‐Membered Ring Compounds via Cobalt(III)‐Carbene Radicals

The metalloradical activation of o‐aryl aldehydes with tosylhydrazide and a cobalt(II) porphyrin catalyst produces cobalt(III)‐carbene radical intermediates, providing a new and powerful strategy for the synthesis of medium‐sized ring structures. Herein we make use of the intrinsic radical‐type reac...

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Bibliographic Details
Published in:Angewandte Chemie International Edition Vol. 59; no. 27; pp. 11073 - 11079
Main Authors: Zhou, Minghui, Lankelma, Marianne, Vlugt, Jarl Ivar, Bruin, Bas
Format: Journal Article
Language:English
Published: WEINHEIM Wiley 26.06.2020
Wiley Subscription Services, Inc
John Wiley and Sons Inc
Edition:International ed. in English
Subjects:
8-membered diene rings
Aldehydes
Aromatic compounds
carbene radicals
Catalysts
Chemical synthesis
Chemistry
Chemistry, Multidisciplinary
Cobalt
Cyclic compounds
Density functional theory
dibenzocyclooctenes
Divergence
Enantiomers
Hydrogen bonds
Intermediates
Mathematical analysis
metalloradicals
Physical Sciences
Ring structures
Science & Technology
CYCLOADDITION
carbene radicals
8-membered diene rings
CONSTRUCTION
dibenzocyclooctenes
metalloradicals
CYCLOPROPANATION
INDOLINES
cobalt
LIGAND
VERSATILE SYNTHONS
CYCLIZATION
ISSN:1433-7851, 1521-3773, 1521-3773
Online Access:Get full text
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Summary:The metalloradical activation of o‐aryl aldehydes with tosylhydrazide and a cobalt(II) porphyrin catalyst produces cobalt(III)‐carbene radical intermediates, providing a new and powerful strategy for the synthesis of medium‐sized ring structures. Herein we make use of the intrinsic radical‐type reactivity of cobalt(III)‐carbene radical intermediates in the [CoII(TPP)]‐catalyzed (TPP=tetraphenylporphyrin) synthesis of two types of 8‐membered ring compounds; novel dibenzocyclooctenes and unprecedented monobenzocyclooctadienes. The method was successfully applied to afford a variety of 8‐membered ring compounds in good yields and with excellent substituent tolerance. Density functional theory (DFT) calculations and experimental results suggest that the reactions proceed via hydrogen atom transfer from the bis‐allylic/benzallylic C−H bond to the carbene radical, followed by two divergent processes for ring‐closure to the two different types of 8‐membered ring products. While the dibenzocyclooctenes are most likely formed by dissociation of o‐quinodimethanes (o‐QDMs) which undergo a non‐catalyzed 8π‐cyclization, DFT calculations suggest that ring‐closure to the monobenzocyclooctadienes involves a radical‐rebound step in the coordination sphere of cobalt. The latter mechanism implies that unprecedented enantioselective ring‐closure reactions to chiral monobenzocyclooctadienes should be possible, as was confirmed for reactions mediated by a chiral cobalt‐porphyrin catalyst. Back in the ring! An efficient strategy based on metalloradical catalysis leads to 8‐membered ring compounds. Both dibenzocyclooctenes and monobenzocyclooctadienes can be obtained in high yields under mild reaction conditions. DFT calculations indicate different ring‐closure pathways for the formation of these two structures.
Bibliography:https://doi.org/10.26434/chemrxiv.11871501.v1
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A previous version of this manuscript has been deposited on a preprint server
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A previous version of this manuscript has been deposited on a preprint server (https://doi.org/10.26434/chemrxiv.11871501.v1).
ISSN:1433-7851
1521-3773
1521-3773
DOI:10.1002/anie.202002674