An efficient Rh -catalyzed direct C2-alkenylation of indoles using readily available potassium vinyltrifluoroborate under mild conditions has been developed. This protocol features wide substrate scope and excellent functional group compatibility, enabling a facile access to diverse terminal vinylindoles in moderate to good yields. Furthermore, the C2-alkenylated indole can be easily transformed into 9H-carbazole through a ring-closing metathesis/aromatization cascade.
Main observation and conclusion
A new Rh(III)‐catalyzed direct C—H alkenylation of 2,3‐unsubstitued indoles with alkenyl borates through C—H activation followed by transmetallation was described. This protocol provides an efficient method for the synthesis of terminal C2‐alkenylindoles under mild conditions, and also shows broad substrate scope and high functional group tolerance with respect to both components. Furthermore, the C2‐alkenylated indole can be easily transformed into carboline derivative, which is an important polycyclic indole moiety in natural products and drug molecules.
Over the last few decades, transition metal-catalyzed direct C-H activation with
the assistance of a coordinating directing group has emerged as an atom- and stepeconomical
synthetic tools to transform C–H bonds into carbon-carbon or carbonheteroatom
bonds. Although the strategies involving regioselective C–H cleavage assisted
by various directing groups have been extensively reviewed in the literature, we now attempt
to give an overview of the recent advances on phosphorus-containing functional
group assisted C-H activation reactions catalyzed by transition-metal catalysts including
mechanistic study and synthetic applications. The discussion is directed towards C-H olefination,
C-H activation/cyclization, C-H arylation, C-H amination, C-H hydroxylation
and acetoxylation as well as miscellaneous C-H activation.
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