Fragmentation of Nitrone Triflates to 9-Membered Rings

A new fragmentative rearrangement of nitrone derivatives to form 9-membered rings is reported. The fragmentations are triggered when nitrones are treated with triflic anhydride; a C−C bond antiperiplanar to the cleaving N−O bond is activated either by an oxygen lone pair or by an electron-rich aromatic ring. In the former case, further cyclization of the 9-membered intermediate leads to a rearranged condensed ring system, but when triggered by arenes, 9-membered ring amides are isolated.