Selective Synthesis of 5-Nitroindoles through a Ag-Catalyzed Nitro Rearrangement/Cyclization Cascade of N-(o-Alkynylphenyl)nitramines.

The reactions of N-(o-alkynylphenyl)nitramines in the presence of catalytic amounts of AgNTf₂ afforded 5-nitroindoles in good to acceptable yields in a site-selective manner. This cascade reaction is initiated by selective migration of the nitro group to the para position relative to the aniline nitrogen, followed by cyclization of the resulting o-alkynylaniline. This sequence is different from typical cascade reactions of o-alkynylanilines having a migrating group on the nitrogen atom, which proceed through cyclization, followed by rearrangement of the migrating group. Mechanistic studies suggest that both migration of the nitro group and cyclization are promoted by the silver catalyst.