Palladium-Catalyzed, Site-Selective C(sp2)8-H Halogenation and Nitration of 4-Quinolone Derivatives

Selective installation of halo and nitro groups in heterocyclic backbone through a transition-metal-catalyzed C-H bond activation strategy is immensely alluring to access high-value scaffolds. Here in, we disclosed N-pyrimidyl-directed assisted palladium(II)-catalyzed C(sp2)8-H halogenation and nitration of substituted 4-quinolone derivatives in the presence of N-halosuccinimide and tert-butyl nitrite, respectively, offering structurally diversified 8-halo/nitro-embedded 4-quinolone frameworks in high yields. Mechanistic studies indicated that the reaction follows an organometallic pathway with a reversible C-H metalation step. This operationally simple protocol is scalable with a broad substrate scope and excellent functional group compatibility. Moreover, the postdiversifications of the synthesized derivatives are also showcased to ensure the synthetic versatility of the methodology.

Copper(II)-catalyzed, site-selective C(sp)2-H amination using 8-aminoimidazo[1,2-a]pyridine (8-AIP) as a directing group

An efficient copper(II)-catalyzed regioselective ortho C(sp2)-H amination of arenes/heteroarenes has been developed with the assistance of 8-AIP (8-aminoimidazo[1,2-a]pyridine) as an efficacious 6,5-fused bicyclic removable chelating auxiliary. This operationally simple approach is scalable, has a broad substrate scope, and is highly compatible with functional groups. Furthermore, post-diversification of the synthesized derivatives demonstrates the methodology's synthetic adaptability.

Palladium-Catalyzed Arylation of C(sp2)-H Bonds and C(sp3)-H Bonds with 4-Amino-benzotriazole as the Bidentate Directing Group

The arylation of C(sp2)-H and C(sp3)-H bonds in carboxylic acids catalyzed by Pd(II) with 4-aminobentriazole as the directing group was investigated. In addition to activation of the C(sp2)-H bond, selective arylation of alkyl carboxylic acids and amino acids in the β position can also be achieved. This strategy involved a 5,5-bicyclic Pd intermediate complex whose structure was determined by X-ray single crystal diffraction analysis. Importantly, the DG (directing group) can be easily removed under mild conditions.

Copper(II)-Mediated, Site-Selective C(sp2)-H Sulfonamidation of 1-Naphthylamines

An operationally simple and efficient protocol for copper(II)-mediated, picolinamido-directed C8-H sulfonamidation of 1-naphthylamine derivatives with various sulfonamides has been developed. Remarkably, this cross-dehydrogenative C-H/H-N coupling reaction exhibits a broad substrate scope with excellent functional group tolerance, is scalable, and enables an expeditious route to a library of unsymmetrical N-arylated sulfonamides in good to excellent yields with exclusive site selectivity.

Organocatalytic synthesis of (Het)biaryl scaffolds via photoinduced intra/intermolecular C(sp2)-H arylation by 2-pyridone derivatives

A unique N,O-bidentate ligand 6-oxo-1,6-dihydro-pyridone-2-carboxylic acid dimethylamide (L1) catalyzed direct C(sp²)-H (intra/intermolecular) arylation of unactivated arenes has been developed to expedite access to (Het)biaryl scaffolds under UV-irradiation at room temperature. The protocol tolerated diverse functional groups and substitution patterns, affording the target products in moderate to excellent yields. Mechanistic investigations were also carried out to better understand the reaction pathway. Furthermore, the synthetic applicability of this unified approach has been showcased via the construction of biologically relevant 4-quinolone, tricyclic lactam and sultam derivatives.

8-Aminoimidazo[1,2-a]pyridine (AIP) directed Pd(ii) catalysis: site-selective ortho-C(sp2)–H arylation in aqueous medium

An efficient and facile Pd(ii) catalyzed selective ortho and β-C(sp²)–H arylation reaction employing the 8-AIP (aminoimidazo[1,2-a]pyridine) auxiliary as a removable N,N-bidentate directing group in a green solvent (water) has been reported.

Palladium-catalyzed directed synthesis of ortho-deuterated phenylacetic acid and analogues

The synthesis of deuterium-labeled organic compounds is of increased interest, especially after the approval of deutetrabenazine by the Food and Drug Administration in 2014. The selective incorporation of deuterium in the place of hydrogen not only represents uniqueness in terms of a novel chemical class, but it also can improve the pharmacokinetic profiles of drug molecules while retaining potency and other parameters; thus, hydrogen-deuterium (H/D) exchange methods have been proven to be powerful additions in different areas of chemical science. In that regard, metal-catalyzed deuterium labeling via C-H activation mediated by a unique inbuilt directing group (DG) can play a significant role in the synthesis of novel deuterated chemical entities. In this context, herein, we divulge our results relating to Pd(ii)-catalyzed deuterium incorporation (>97%) at the γ C(sp2)-position of pyridone-containing phenylacetic acid derivatives, where 3-amino-1-methyl-1H-pyridin-2-one (AMP) not only acts as an efficient N,O-directing group, but it also constitutes a part of the target molecules of medicinal importance. Our methodology, which has been optimized based on the effects of temperature, catalyst, time, and substrate scope, shows advantages over existing protocols, with non-selectivity or meager deuteration or the use of an expensive metal (catalytic or super stoichiometric) and a deuterated solvent, reported previously for the deuteration of phenylacetic acid and its derivatives. Moreover, towards our aim of synthesizing deuterium-labeled biologically relevant compounds, the gram scale synthesis of a deuterated analogue of biphenyl acetic acid (3), known to have activity against epileptic seizures, has also been successfully accomplished in high yields and with excellent isotope enrichment via implementing this protocol.