Gold-Catalyzed Ascorbic Acid-Induced Arylative Carbocyclization of Alkynes with Aryldiazonium Tetrafluoroborates

Abstract

We describe, herein, arylative carbocyclization of alkynes catalyzed by gold. In this process, Au(I) is oxidized to Au(III) with aryldiazonium tetrafluoroborates following a photosensitizer-free and irradiation-free protocol. Ascorbic acid acts as a radical initiator, generating aryl radicals. According to DFT calculations, these radicals are added to Au(I), leading to a Au(II) species that is further oxidized to Au(III) with the assistance of a tetrafluoroborate anion. The overall arylative carbocyclization process is very energetically favorable, transforming arylpropargyl ethers into valuable 3,4-diaryl-2H-chromenes in a completely regio- and stereoselective fashion. Furthermore, we show that one of the synthesized 3,4-diaryl-2H-chromenes exhibits polymorphism with marked differences in the color of its crystals, a property that could lead to the development of colored derivatives in the future.