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Synthesis of 3-oxindoles

Recent Literature

A Hg(OTf)2-catalyzed N-oxide addition to alkynes forms an enolonium species, that can undergo intramolecular nucleophilic attack by hydroxyl or amino groups, providing various coumaran-3-ones and indolin-3-ones via an enolate umpolung reactivity.
Z. Rong, W. Hu, N. Dai, G. Qian, Org. Lett., 2020, 22, 3245-3250.

RuCl33H2O catalyzes an oxidative dearomatization of N-Boc indoles into indolin-3-ones in acetonitrile using sodium periodate as oxidant.
X. Chen, X.-Y. Zhou, X.-J. Feng, M. Bao, Synthesis, 2021, 53, 1121-1126.

Efficient and operationally simple reactions using a combination of B(C6F5)3 and BnMe2SiH or B(C6F5)3 and Et2SiH2 provide various indolin-3-ones and indolines under mild conditions, without the need for multistep procedures and metal catalysts.
H. Jeong, N. Han, D. W. Hwang, H. M. Ko, Org. Lett., 2020, 22, 8096-8100.

A TEMPO oxoammonium salt mediates a metal-free oxidative dearomatization of indoles with aromatic ketones in the presence of H2SO4 to provide 2,2-disubstituted indolin-3-ones in good yields. The dearomatization proceeds smoothly and displays a broad substrate scope with respect to both indoles and aromatic ketones.
J. Liu, J. Huang, K. Jia, T. Du, C. Zhao, R. Zhu, X. Liu, Synthesis, 2020, 52, 763-768.