Hydroxyindoles Leimgruber-Batcho indole synthesis

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... 

A few type la reductive cycUzations leading to indoles have been reported. A palladium (II) trifluoroacetate catalyst was effective in the reductive cyclization of orfho-nitrostyrenes to 2-substituted indoles <05T6425>. The Batcho-Leimgruber indole synthesis, the reductive cyclization of p-amino-2-nitrostyrenes, was utilized in a synthesis of 5-formylindole <05JHC137>. A partial reduction of a nitroarene provided a route to iV-hydroxyindoles <05AG(E)3736>. Treatment of nitro ketoester 90 with tin chloride in the presence of a primary alcohol nucleophile provided Al-hydroxyindole 93 via hydroxylamine intermediate 91. 

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