Hydroxyindoles Somei 1-hydroxyindole synthesis

The synthesis of 7-methoxyindole was accomplished starting from 1-acetylindoline (34). Regioselec-tive intr uction of iodine was achieved using thallium trifluoroacetate, then potassium iodide. Deacetylation and oxidation to the indole (35), followed by reaction with sodium methoxide in DMF, gave the 7-methoxyindole (36) in 48% overall yield (Scheme 13). More recently, Somei et al have reported that treating the intermediate thallium species with copper(II) sulfate pentahydrate gives directly the l-acetyl-2,3-dihydro-7-hydroxyindole (37) in 42% yield (Scheme 14). It remains to be seen whether this is a general process. 

As for many reductions of the nitro group, the reaction often stops at an intermediate stage (NO, NHOH). Somei was the first to observe this in the Leimgruber-Batcho indole synthesis [60-62]. Although 1-hydroxyindole itself is very unstable, Somei and his coworkers were able to isolate 1-hydroxyindoles bearing an electron-withdrawing... 

---