posted on 2022-12-16, 14:05authored byCaiyun Yu, Yuanshuang Xu, Xinying Zhang, Xuesen Fan
Presented
herein is a condition-controlled selective synthesis
of pyrazolonyl spirodihydroquinolines or pyrazolonyl spiroindolines
through formal [5 + 1] or [4 + 1] spiroannulation of 2-alkenylanilines
with diazopyrazolones. Mechanistically, the formation of the title
products involves initial generation of a pyrazolonyl spiro-fused
seven-membered ruthenacycle species serving as a key intermediate
through Ru(II)-catalyzed C–H/N–H bonds metalation, carbene
formation, and its migratory insertion. When the reaction is carried
out under air, the key intermediate undergoes reductive elimination
to afford spirodihydroquinoline. When the reaction is run under argon,
the key intermediate undergoes protonation and intramolecular nucleophilic
addition to furnish spiroindoline. This work provides an atom-economical
protocol for the effective functionalization of alkenyl C(sp2)–H bond, allowing rapid and selective assembly of valuable
spiroscaffolds with a broad range of substrates.