3-Cyano-l-hydroxyindoles

Hydroxyindole-3-glyoxylic acid (113) with hydroxylamine hydrochloride yielded 3-cyano-l-hydroxyindole 115, presumably by the cyclic process indicated (114), but if sodium hydrogen carbonate was present, the presumably formed anion (116) underwent an alternative decomposition, yielding the remarkably stable nitrile oxide (117) [78JCS(P1)1117]. 

There is one more way for conversion of ort/to-nitroarylacetonitriles into indoles. Alkylation of such nitriles with allyl or benzyl halides followed by treatment of the compounds obtained with basic agents results in a multistep transformation, which is likely to proceed via intermediate nitrosoarenes, to produce 1-hydroxyindoles. For instance, alkylation of ort/io-nitroarylacetonitriles with 3-phenylallyl bromide gives the compounds that in the presence of chlorotri-methylsilane and triethylamine undergo cyclization into 3-cyano-l-hydroxy-2-vinylindoles (Scheme 70) [188]. Presumably, this reaction proceeds via 0-silylation of the nitronate anion and 1,5-elimination of trimethylsilanol from the intermediate trimethylsilyl nitronate, followed by cyclization and a hydrogen shift. 

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