Silver-Mediated C–H
Activation: Oxidative Coupling/Cyclization
of
<i>N</i>-Arylimines and Alkynes for the Synthesis of
Quinolines
- Publication date
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Abstract
A silver-mediated tandem protocol for the synthesis of
quinolines
involving the oxidative coupling/cyclization of <i>N</i>-arylimines and alkynes has been developed. We demonstrated that
scenario-dependent metalation could occur either at the <i>ortho</i> C–H bond of an <i>N</i>-arylimine through protonation-driven
enhancement of acidity or at the terminal C–H bond of an alkyne
by virtue of the carbophilic π-acidity of silver. The diverse
set of mechanistic manifolds implemented with a single type of experimental
protocol points toward the importance of stringent reactivity analysis
of each individual potentially reactive molecular site. Importantly,
the direct arene C–H bond activation provides a unique and
distinct mechanistic handle for the expansion of reactivity paradigms
for silver. As expected, the protocol allows for the incorporation
of both internal and terminal alkynes into the products, and in addition,
both electron-withdrawing and -donating groups are tolerated on <i>N</i>-arylimines, thus enabling the vast expansion of substituent
architectures on quinoline framework. Further, an intriguing phenomenon
of structural isomerization and chemical bond cleavage has been observed
for aliphatic internal alkynes