Mild Hydroxylation of 2-Oxindoles

Mild Hydroxylation of 2-Oxindoles

Author: ChemViews Magazine

3-Hydroxy-2-oxindoles (example pictured) are useful biologically active molecules, and there is a need for efficient methods for their synthesis under mild conditions.

Wen-Ting Wei, Ningbo University, China, have developed a base- and metal-free C(sp3)–H hydroxylation of 2-oxindoles. The reaction is promoted by TEMPO (2,2,6,6-tetramethylpiperidine N-oxide) and uses atmospheric air as a hydroxylation reagent in THF (tetrahydrofuran) at room temperature.

The proposed reaction mechanism involves TEMPO reacting with the enol form of the 2-oxindole, followed by a reaction with O2 that generates a superoxide anion. This anion regenerates TEMPO and is converted to a peroxide. In a final step, the peroxide is cleaved to give the desired product.

This protocol provides a mild and simple strategy for the construction of C–O bonds in moderate to good yields. The reaction can convert a wide range of substituted 2-oxindoles with a variety of functional groups.


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