Gold‐Catalyzed Oxidation of Internal Alkynes into Benzils and its Application for One‐Pot Synthesis of Five‐, Six‐, and Seven‐Membered Azaheterocycles

Abstract

Internal alkynes have been shown to undergo oxidation to substituted benzils (1,2‐diarylethane‐1,2‐diones) by α ‐picoline N ‐oxide in the presence of Ph 3 PAuNТf 2 (5 mol‐%). In addition to the unsubstituted benzil, the method allows preparing, under markedly mild conditions (50 °C in chlorobenzene), various non‐symmetrical products, including heteroaromatic versions thereof which are much more difficult to obtain otherwise. This gold(I)‐catalyzed transformation was integrated into one‐pot reaction sequence delivering a range of 5‐ to 7‐membered ring systems (imidazoles, quinoxalines, 1,2,4‐triazines, pyrazines, and 1,4‐diazepines), thus linking these important heterocyclic motifs to the internal alkyne reagent space.