The oxidation of 1-acylindoles, 1, 15, 20, and 22, with (hexamethylphosphoramide) oxodiperoxomolybdenum (VI), MoO5·HMPA, in dry methanol gives a variety of products depending on the indole substituents ; trans- and cis-1-acyl-3-hydroxy-2-methoxyindolines 2 and 3 are obtained from 2, 3-unsubstituted 1-acylindoles 1, 1-acetyl-2-hydroxy-3-methoxy-3-methylindoline (16) from 1-acetyl-3-methylindole (15), 1-acetyl-2, 3-dihydroxy-2, 3-dimethylindoline (21) from 1-acetyl-2, 3-dimethylindole (20), and 1-acetyl-2-hydroxy-2-methylindoxyl (23) from 1-acetyl-2-methylindole (22). Reaction of 2 and 3 with acids gives 1-acylindoxyl 10, respectively, while reaction of 16 with the acid gives 3-methyloxindole (19). Treatment of 3-acetoxy-1-acetyl-2-methoxyindoline (5) with stannic chloride gives 1-acetylindoxyl (10a) and 1-acetyl-3-chloroindole (14).