Silver-catalyzed nitration/annulation of 2-alkynylanilines for a tunable synthesis of nitrated indoles and indazole-2-oxides

Abstract

Two new types of silver-catalyzed nitration–annulations of 2-alkynylanilines with tert-butyl nitrite (TBN) were reported, leading to the selective formation of a variety of nitrated indoles and indazole-2-oxides by changing the N-protection of 2-alkynylanilines. Ag-Catalyzed nitration–annulation of N-sulfonyl 2-alkynylanilines without C4 substituents afforded 5-nitroindoles under neutral-redox conditions, whereas the presence of C5 substituents gave 7-nitroindoles through silver catalysis. N-Methyl 2-alkynylanilines underwent a completely different process to furnish aroyl indazole-2-oxides.