A novel and efficient synthesis of 1-acylindoxyls (3) from 1-acylindoles (1) is described. The procedure involves the demethoxylation with stannic chroride of 1-acyl-3-hydroxy-2-methoxy-indoline (2), which were obtained by the MoO5 oxidation of 1in methoanol. Since the MoO5 oxidation of 2-substituted 1-acylindoles (1f and 1g) gave not the corresponding indolines (2f and 2g), but 2-hydroxyindoxyls (4f and 4g), 2f and 2g were obtained by the methylation of 4f and 4g with diazomethane to give 5f and 5g, followed by the reduction of 5f and 5g with sodium borohydride, respectively.
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CHIEN et al. (1986) studied this question.