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. 2019 Dec 27;5(1):904-913.
doi: 10.1021/acsomega.9b03884. eCollection 2020 Jan 14.

Regioselective Arylation of Quinoline N-Oxides (C8), Indolines (C7) and N- tert-Butylbenzamide with Arylboronic Acids

Shiv Shankar Gupta  1 , Rakesh Kumar  1 , Upendra Sharma  1
Affiliations

Regioselective Arylation of Quinoline N-Oxides (C8), Indolines (C7) and N- tert-Butylbenzamide with Arylboronic Acids

Shiv Shankar Gupta et al. ACS Omega. .

Abstract

Herein, we disclose Ru(II)-catalyzed regioselective distal C(sp2)-H arylation of quinoline N-oxide with arylboronic acids to 8-arylquinolines. In the developed method, the Ru(II)-catalyst shows dual activity, that is, distal C-H activation of quinoline N-oxides followed by in situ deoxygenation of arylated quinoline N-oxide in the same pot. The current catalytic method features use of Ru metal as the catalyst and arylboronic acids as the arylating source under mild reaction conditions. Use of the Rh(III)-catalyst in place of Ru(II) under the same conditions afforded 8-arylquinoline N-oxides with excellent regioselectivity. Furthermore, the developed Ru(II) catalytic system is also extended for the C(sp2)-H arylation of indolines, N-tert-butylbenzamide, and 6-(5H)-phenanthridinone. Formation of the quinoline N-oxide coordinated ruthenium adduct is found to be the key reaction intermediate, which has been characterized by single crystal X-ray diffraction and NMR spectroscopy.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Selected Example of Bioactive 8-Arylquinoline Scaffolds
Scheme 2
Scheme 2. Regioselective C8 Functionalization of Quinoline N-Oxide
Scheme 3
Scheme 3. Parallel Experiment for KIE.
Scheme 4
Scheme 4. Synthesis of the Ruthenium Adduct and Its Utility as an Catalyst.
Scheme 5
Scheme 5. Preliminary Experiment Showing Ru as a Deoxygenating Agent.
Scheme 6
Scheme 6. Proposed Mechanistic Pathway
See this image and copyright information in PMC

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