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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Vydáno v:	Angewandte Chemie International Edition Ročník 59; číslo 27; s. 11073 - 11079
Hlavní autoři:	Zhou, Minghui, Lankelma, Marianne, Vlugt, Jarl Ivar, Bruin, Bas
Médium:	Journal Article
Jazyk:	angličtina
Vydáno:	WEINHEIM Wiley 26.06.2020 Wiley Subscription Services, Inc John Wiley and Sons Inc
Vydání:	International ed. in English
Témata:	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
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Popis
Shrnutí:	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.
Bibliografie:	https://doi.org/10.26434/chemrxiv.11871501.v1 . A previous version of this manuscript has been deposited on a preprint server ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 14 content type line 23 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