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

Tian-Shu Zhang, Rong Wang, Pei-Jun Cai,* Wen-Juan Hao, Shu-Jiang Tu, Bo Jiang*

Two new types of silver-catalyzed nitration-annulation of 2-alkynylanilines with TBN were reported, leading to the selective formation of a variety of nitrated indoles and indazole-2-oxides by changing 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 direct to furnish aroyl indazole-2-oxides.

Org. Chem. Front. 2019, 6, 2968-2973