Ring Synthesis of Indoxyls

Indoxyls are normally prepared from anthranilic acids via alkylation with a haloacetic acid followed by a cyclising condensation with loss of carbon dioxide. Indoxyl itself is best prepared by Friedel-Crafts type ring closure of iV-phenylglycine activated with triphenylphosphine oxide/triflic anhydride in the presence of triethylamine at room temperature.  

C02H CICH2C02H C02H AC2O, NaOAc heat rA aq. 

It is possible to directly chloroacylate an aniline using chloroacetonitrile and boron trifluoride, ortho to the nitrogen. After (V-acylation, ring closure produces iV-acetyl-indoxyls. The Sugasawa synthesis of indoles utilises these same orf/to-chloroacetyl-anilines, via borohydride reduction and ring closure.  

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