Redox-Neutral [4 + 2] Annulation of -Methoxybenzamides with Alkynes Enabled by an Osmium(II)/HOAc Catalytic System.

Org Lett

Guangzhou Municipal and Guangdong Provincial Key Laboratory of Protein Modification and Degradation & Molecular Target and Clinical Pharmacology, State Key Laboratory of Respiratory Disease, School of Pharmaceutical Sciences & the Fifth Affiliated Hospital , Guangzhou Medical University, Guangzhou , Guangdong 511436 , China.

Published: December 2019

By making use of a direct C-H activation strategy, an efficient osmium(II)-catalyzed redox-neutral [4 + 2] annulation of -methoxybenzamides with alkynes has been accomplished. Computational and experimental studies revealed that such transformation leading to the synthesis of the isoquinolone core might follow an Os(II)-Os(IV)-Os(II) catalytic pathway, in which an unusual HOAc-assisted oxidative addition of osmium(II) into the N-O bond to generate the osmium(IV) species was involved as one of the key transition states. Further exploration of divergent C-H activation reaction modes enabled by the osmium(II) catalyst has also been exemplified for one-pot assembly of other either linear or cyclic products.

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http://dx.doi.org/10.1021/acs.orglett.9b03827DOI Listing

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