Unique reactivity of diphenylacetylene
has been uncovered through
weak chelation-assisted cobalt-catalyzed regioselective C(4)–H
activation of 3-pivolyl indole. α-Hydroxy ketone and α,β-unsaturated
ketone derivatives have been synthesized in good yields from indole
and alkynes. Notably, the indole C(4)–H-functionalized α,β-unsaturated
ketone product was obtained with high stereo- and regioselectivity
simply by changing the coupling partner from symmetrical alkynes to
unsymmetrical aromatic-aliphatic alkynes. Most importantly, trifluoroethanol
acts as a sole source of water for this conversion. Quantitative detection
of bis(2,2,2-trifluoroethyl) ether from dry trifluoroethanol through 19F NMR and LCMS studies indirectly confirms the in situ formation
of water. A six-membered cobaltacycle intermediate was detected in
HRMS, and also, this was further confirmed by the quantum mechanical
calculations, which accounts for the highly regioselective C(4)–H
functionalization.
Herein, we disclosed the first report
on the selective C(4)–H functionalization of 3-acetylindole
derivatives using first-row transition metal cobalt where an acetyl
group is acting as a weakly coordinating directing group. Selective
C(4)–H functionalization has been achieved using diverse Michael
acceptors (acrylate and maleimide) simply by switching the additive
from copper acetate to silver carbonate. Further the formation of
a cobaltacycle intermediate was also detected through HRMS for mechanistic
insight.
This review focuses on providing comprehensive highlights of the recent advances in the field of cobalt-catalysed C−H functionalization and related synthetic concepts relying on these through oxygen atom coordination. In...
A cobalt(III) catalyzed
hydroarylation of Michael acceptors using indolines, selectively at
the C-7 position, has been reported. For the selective C-7 functionalization
of indoline, we have used a weakly coordinating amide carbonyl group.
During the process of optimization, we have also discovered the unusual
cocatalytic activity of zinc triflate in the C–H functionalization
reaction. Hydroarylation of unprotected maleimide using indolines
was a challenging substrate and never accomplished before, we were
able to achieve this with our methodology in good yields.
The stereoselective synthesis of 1,3-enynes from 1,3-diynes is demonstrated by the palladium-catalyzed selective C-C bond cleavage of cyclopropanol. Exclusive formation of mono-alkenylated adduct was achieved by eliminating the possibility of...
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