A novel synthesis of indole derivatives by the reaction of N ‐arylhydroxamic acids with malononitrile

An approach to indole derivatives from N ‐arylhydroxamic acids and malononitrile via a [3,3]‐sigmatropic rearrangement and intramolecular cyclization is described. Reactions of N ‐arylhydroxamic acids 1a‐c, 2a‐c and 3a‐c with malononitrile in the presence of triethylamine at room temperature gave the corresponding α‐cyanoacetamide derivatives 4a‐c, 5a‐c, 6a‐c, 7a‐c and 8a‐c . Thermal treatment of 4a‐c, 5a‐c and 7a‐c with a base, e.g. triethylamine and sodium methoxide, caused intramolecular cyclization and deacylation to afford the corresponding indole derivatives 9‐11 .