Copper(I)‐catalyzed Cyclization Reactions of Ethyl (E)‐α‐Ethynyl‐β‐Aryl‐α,β‐Unsaturated Esters with N‐Sulfonyl Azides: Synthesis of 1‐Aminonaphthalene, 3‐Aminobenzofuran, and 3‐Aminothiobenzofuran Derivatives

Abstract

A synthetic method for ethyl 4‐(alkyl or arylsulfonamido)‐2‐naphthoates from ethyl (E)‐α‐ethynyl‐β‐aryl‐α,β‐unsaturated esters (1) and N‐sulfonyl azides (2) in the presence of 2,6‐lutidine in THF at 60 °C for 3 h was developed in one step, in which a copper(I)‐catalyzed 1,3‐dipolar cycloaddition, ketenimine formation, and 6π‐electrocyclization followed by [1,3]‐H shift tandem reaction took place. This method enabled efficient synthesis of a wide range of 1‐aminonaphthalene and 3‐aminobenzofuran and 3‐aminobenzothiophene derivatives with the release of molecular nitrogen.