Selective 5‐<i>exo‐dig</i> Cyclization of <i>in Situ</i> Synthesized <i>N</i>‐Boc‐2‐aminophenyl Ethoxyethynyl Carbenols: Synthesis of Multifunctional Indoles and Their Derivatives

Abstract

Abstract A method to prepare 3‐substituted‐2‐formylindole derivatives from N ‐Boc‐ ortho ‐aminoaryl ketones and ethoxyacetylene through a cascade of reactions in a single operation that included a nucleophile‐triggered 5‐ exo‐dig cyclization and an acid‐mediated 1,3‐allyl alcohol isomerization (1,3‐AAI) is described. A variety of aryl, vinyl and alkynyl groups can be introduced at C‐3 of indole‐2‐carboxaldehyde while having a high functional group compatibility. The 3‐alkynyl adducts, which are highly valuable substrates for diversity‐oriented synthesis, can be further transformed to useful carboline and carbazole derivatives through novel pathways. magnified image