C(sp3)-H Bond Functionalization of 8-Methylquinolines

Quinolines have emerged as essential components in various medicinal agents, playing a key role in treating various ailments. Numerous drugs with a quinoline core have been recognized for their antimalarial, antibacterial, and anticancer activities and have been successfully commercialized, including chloroquine, ciprofloxacin, topotecan, etc. Over the past two decades, a tremendous expansion in the C-H bond functionalization of quinoline scaffolds to widen this chemical space for drug discovery have been witnessed. This review article summarizes the efforts toward C(sp3)-H functionalization of 8-methylquinolines for C(sp3)-C/X bond formation under metal and metal-free strategies. Each section briefly overviews the C(sp3)-H functionalization of 8-methylquinoline, highlighting the metal and metal-free approaches.

Dual C(sp3)-H and C(sp2)-H Activation of 8-Methylquinoline N-Oxides: A Route to Access C7-H Bond

A Pd(II)-catalyzed regioselective dual C(sp3)-H/C7(sp2)-H activation and annulation of 8-methylquinoline N-oxides with maleimide has been accomplished. The use of N-oxide as a weak directing group under Pd(II)-complex catalysis activates the initial C(sp3)-H and triggers a relayed, second C7(sp2)-H activation. The dual C-H bond activation, [3 + 2]-annulation, facile introduction and removal of the directing group, substrate scope, and functional group diversity are the important practical features.

Rh(III)-Catalyzed Alkylation of 8-Methylquinolines with Oxabenzonorbornadienes

Herein, a concise Rh(III)-catalyzed C(sp³)-H alkylation of 8-methylquinolines with oxabenzonorbornadiene scaffolds and other strained olefins has been disclosed. The retention of the oxabenzonorbornadiene skeleton, broad substrate scope, and wide-ranging functional group tolerance are the key features of the developed catalytic methodology. Mechanistic studies revealed that the reaction does not involve a radical pathway, and the five-membered rhodacycle is the key intermediate. This is the first report on the C(sp³)-H alkylation of 8-methylquinolines with strained oxabenzonorbornadiene scaffolds (with ring retention).

Rh(III)-Catalyzed [4 + 1] Annulation of Sulfoximines with Maleimides: Access to Benzoisothiazole Spiropyrrolidinediones

Rh(III)-catalyzed synthesis of benzoisothiazole spiropyrrolidinediones using sulfoximine as a directing group under a C-H activation and [4 + 1] annulation strategy with maleimides as a coupling partner is reported. The cyclization reaction was compatible with various substituted sulfoximine and maleimides. The deuterium-labeling studies were performed to investigate the mechanism of the reaction.

Recent advances in transition-metal-catalyzed directed C-H alkenylation with maleimides

Transition-metal-catalyzed directed C-H alkenylation with maleimides has attracted much attention in recent years, as maleimide core moieties are present in various natural products and pharmaceuticals. In addition, these derivatives can be readily modified into biologically important compounds including succinimides, pyrrolidines and γ-lactams. The efficient chelation-assisted inert C-H bond activation strategy provides straightforward access to a wide array of structurally diverse molecules containing maleimide units. This review describes the major progress and mechanistic investigations on Heck-type reaction/cyclization of maleimides with organic molecules until early 2022.

Pd(II)-Catalyzed oxidative alkenylation of 4-hydroxycoumarin with maleimide via a C-H bond activation strategy

A Pd(ii)-catalyzed oxidative alkenylation of 4-hydroxycoumarins with maleimides for the synthesis of 4-hydroxy-3-maleimidecoumarins has been described. This methodology proceeds via C-H activation and C(sp2)-C(sp2) bond formation providing a series of alkenylated Heck-type products.