Palladium-catalyzed weak chelation-assisted
regioselective C4-arylation
of indoles has been accomplished using a readily available arene at
moderate temperature. The C4-arylation, weak chelating benzoyl (Bz)
directing group, cross-dehydrogenative coupling (CDC), broad substrate
scope, and late-stage diversifications are the important practical
features.
A Rh-catalyzed weak chelation-guided C4-alkylation of
indoles has
been accomplished using cyclopropanols as an alkylating agent via
the cascade C–H and C–C bond activation. The substrate
scope, functional group tolerance, and late-stage mutation of drug
molecules are the important practical features.
C8-Substituted quinoline (QN) and 1,2,3,4-tetrahydroquinoline (THQ) scaffolds are featured largely in a plethora of bio-active compounds and natural products. Appreciable efforts have thus been made towards the development of elegant techniques to functionalize the C8-H bond of QNs and THQs. Transition-metal-catalyzed chelation assisted C-H activation strategy has emerged as an effective synthetic tool among existing methods. This review focuses on the recent advances in the transition-metal-catalyzed directed carbon-carbon bond forming reactions for the C8-H functionalization of QNs and THQs (till February 2023). The discussion has been summarized categorically on the type of reactions.
C4-Functionalized indole scaffold is ubiquitous in natural products, bio-active compounds and pharmaceuticals. Much efforts have thus been made to develop the effective synthetic strategies for the C4 functionalization of indole core. Among them, the chelation assisted synthetic approach using transition-metal-catalysis for the C4-selective C-H functionalization of indole is attractive. This account highlights the progress of the C4-carbon-carbon bond formation of indole using directing group assisted transition-metal-catalyzed C-H functionalization (till May 2022). These studies have been performed using Ru, Rh, Pd and Ir-based catalytic systems, while attention has been devoted on the use of first-row abundant catalytic systems.
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