Synthetic Studies on Indoles and Related Compounds. XII. A Simple General Method for the C-3 Acylation of Ethyl Indole-2-carboxylates

Abstract

Ethyl indole-2-carboxylate (1a) and its derivatives were reacted with various carboxylic acids by using trifluoroacetic anhydride and phosphoric acid (or polyphosphoric acid) to yield effectively the corresponding ethyl 3-acylindole-2-carboxylates (3). However, strongly acidic carboxylic acids and nitrogen-containing carboxylic acids were poor acylating agents. Ethyl 3-acylindole-2-carboxylate (3) could easily be converted to 3-acylindole (5)