Cycloisomerization of Alkyne‐Tethered N‐Acyloxycarbamates to 2‐(3H)Oxazolones through Nitrenoid‐Mediated Carboxyamidation

The cycloisomerization of alkyne‐tethered N‐benzoyloxycarbamates to 2‐(3H)oxazolones is described. Two catalytic systems are tailored for intramolecular 5‐exo‐alkyne carboxyamidation and concomitant alkene isomerization. PtCl2/CO (5 mol%, toluene, 100 °C) promotes both carboxyamidation and alkene is...

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Bibliographic Details
Published in:Chemistry : a European journal 2023-04, Vol.29 (19), p.e202203371-n/a
Main Authors: Su, Siyuan, Wu, Tongtong, Xia, Yuanzhi, Wink, Donald J., Lee, Daesung
Format: Article
Language:English
Subjects:
alkene isomerization
Alkenes
Alkynes
benzoyloxycarbamate
carboxyamidation
Chemistry
Ferric chloride
Intermediates
Isomerization
nitrenoid
Organic compounds
oxazolones
Substrates
Toluene
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Summary:The cycloisomerization of alkyne‐tethered N‐benzoyloxycarbamates to 2‐(3H)oxazolones is described. Two catalytic systems are tailored for intramolecular 5‐exo‐alkyne carboxyamidation and concomitant alkene isomerization. PtCl2/CO (5 mol%, toluene, 100 °C) promotes both carboxyamidation and alkene isomerization but has a limited substrate scope. On the other hand, FeCl3 (5 mol%, CH3CN, 100 °C) promotes carboxyamidation effectively but a cocatalyst is required for the exocyclic alkene isomerization. Thus, a two‐step one‐pot protocol has been developed for a broader reaction scope, which involves FeCl3‐catalyzed carboxyamidation and base‐induced alkene isomerization. Crossover experiments suggest that these reactions proceed mainly through a mechanism involving acylnitrenoid intermediates rather than carbenoid intermediates. Zip and shift: Activation of alkyne‐tethered N‐benzoyloxycarbamates with PtCl2/CO or FeCl3 promotes 5‐exo‐cyclization to form carboxyamidation products and subsequent in situ double bond migration catalyzed by Pt‐catalyst or DMAP generates the final product 2‐(3H)oxazolones. Experimental evidence suggests a concerted mechanism of nitrenoid‐mediated C−N and C−O bond formation.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.202203371