1-Hydroxy- and 1-Methoxy-2,3-dimethylindoles

1-Hydroxyindoles having an electron-donating group on the indole ring are generally unstable [5]. 1-Hydroxy-2,3-dimethylindole (1a) is not easily pre pared and is even more difficult to store (Scheme 1) [10]. Although the application of the tungstate method to 2,3-dihydro-2,3-dimethylindole (3), obtained from 2,3-dimethylindole (2), generates 1a in the reaction mixture, its isolation is cumbersome. During the work-up, 1a is oxidized rapidly to 3-hydroxy-2,3-dimethyl-3H-indole N-oxide (4) under air. The structure (4) is determined by X-ray single-crystal analysis.

Once the unstable 1a is converted to 1-acetoxy-2,3-dimethylindole (1b) in situ, its isolation and purification is easy because of its stability. 1-Methoxy-2,3-dimethylindole (1c) is also a stable compound. Mild hydrolysis of 1b gives rise to pure 1a. As a result, the half-life of 1a in CHCl3 at room temperature under air is shown to be about 4 h. In the pure state in the refrigerator, the half-life of 1a is determined to be 24 h [10].

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