Friedel–Crafts chemistry. Part 64. Facile syntheses of fused azepinoindoles by Jourdan–Ullmann and Friedel–Crafts approaches
Hassan A. K. Abd El-Aal
A
Abstract
Facile and concise procedures for the construction of indole fused N-heterocyclic systems were described. A series of benzo-, pyrido-, thieno-, naphtho-fused azepinoindolones and indolo-azepinoquinolinones has been prepared starting from indol-2-acetic acids. The required starting carboxylic acids 3a–e were readily obtained by the N-arylations of indoleacetic acid 1 with various aromatic halides 2a–e. Subsequent carboxylic acids were esterified, followed by the addition of Grignard reagents to afford the corresponding indole-based alcohols 5a–e. The key step in this protocol is the Friedel–Crafts cyclisations of these precursors promoted by AlCl3/CH3NO2 or trifluoromethanesulfonic acid (TfOH) or polyphosphoric acid (PPA) catalysts to form the desired condensed indoles in moderate to good yields.
Keywords: azepino[3,4-b]quinolinones, azepinoindolones, carbocations, Friedel–Crafts reactions, Grignard reagents, indole-fused N-heterocycles, TfOH, trifluoromethanesulfonic acid.
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