“On Water” Direct C-3 Arylation of 2H-Pyrazolo[3,4-b]pyridines

Unlocking the Potential of Deep Eutectic Solvents for C-H Activation and Cross-Coupling Reactions: A Review

Green chemistry principles have underpinned the development of deep eutectic solvents (DESs). In this brief overview, we discuss the potential of DESs as a greener alternative to volatile organic solvents for cross-coupling and C-H activation reactions in organic chemistry. DESs offer numerous benefits, such as easy preparation, low toxicity, high biodegradability, and the potential to replace volatile organic compounds. The ability of DESs to recover the catalyst-solvent system enhances their sustainability. This review highlights recent advances and challenges in utilizing DESs as a reaction media, as well as the impact of physicochemical properties on the reaction process. Several types of reactions are studied to highlight their effectiveness at promoting C-C bond formation. Aside from demonstrating the success of DESs in this context, this review also discusses the limitations and future prospects of DESs in organic chemistry.

A regioselective C7 bromination and C7 palladium-catalyzed Suzuki-Miyaura cross-coupling arylation of 4-substituted NH-free indazoles

A direct and efficient regioselective C7-bromination of 4-substituted 1H-indazole has been achieved. Subsequently, a successful palladium-mediated Suzuki–Miyaura reaction of C7-bromo-4-substituted-1H-indazoles with boronic acids has been performed under optimized reaction conditions. A series of new C7 arylated 4-substituted 1H-indazoles was obtained in moderate to good yields.

A regioselective C7-bromination of 4-substituted 1H-indazoles followed by a palladium-catalyzed Suzuki–Miyaura reaction with boronic acids is described.

Palladium in biological media: Can the synthetic chemist's most versatile transition metal become a powerful biological tool?

Palladium catalysed reactions are ubiquitous in synthetic organic chemistry in both organic solvents and aqueous buffers. The broad reactivity of palladium catalysis has drawn interest as a means to conduct orthogonal transformations in biological settings. Successful examples have been shown for protein modification, in vivo drug decaging and as palladium-protein biohybrid catalysts for selective catalysis. Biological media represents a challenging environment for palladium chemistry due to the presence of a multitude of chelators, catalyst poisons and a requirement for milder reaction conditions e.g. lower temperatures. This review looks to identify successful examples of palladium-catalysed reactions in the presence of proteins or cells and analyse solutions to help to overcome the challenges of working in biological systems.

"On Water" Palladium Catalyzed Direct Arylation of 1H-Indazole and 1H-7-Azaindazole

The C3 direct arylation of 1H-indazole and 1H-7-azaindazole has been a significant challenge due to the lack of the reactivity at this position. In this paper, we describe a mild and an efficient synthesis of new series of C3-aryled 1H-indazoles and C3-aryled 1H-7-azaindazoles via a C3 direct arylation using water as solvent. On water, PPh₃ was effective as a ligand along with a lower charge of the catalyst Pd(OAc)₂ (5 mol%) at 100 °C, leading to C3-aryled 1H-indazoles or C3-aryled 1H-7-azaindazoles in moderate to good yields.

Selective N7 Alkylation of 7-Azaindazoles

A general and mild procedure for alkylation of 7-azaindazoles at the N7 position using alkyl halides in butanone is reported, which requires no additives such as acids or bases. The scope of the reaction regarding substituents on 7-azaindazoles and the alkyl electrophiles is presented.

A one-pot three-component strategy for highly diastereoselective synthesis of spirocycloalkane fused pyrazolo[3,4-b]pyridine derivatives using recyclable solid acid as a catalyst

An efficient and eco-friendly approach for highly diastereoselective synthesis of spirocycloalkane fused pyrazolo[3,4-b]pyridine derivatives has been developed.

Unusual rearrangement of imidazo[1,5-a]imidazoles and imidazo[1,2-b]pyrazoles into imidazo[1,5-a]pyrimidines and pyrazolo[1,5-a]pyrimidines

A multicomponent reaction giving easy and cheap access to a variety of bicyclic 5,5-fused hetero-rings has been developed.

Synthesis of 3,6-diaryl-1H-pyrazolo[3,4-b]pyridines via one-pot sequential Suzuki–Miyaura coupling

A practical synthesis of diarylpyrazolo[3,4-b]pyridine derivatives by a combination of chemoselective Suzuki–Miyaura cross-coupling reactions was developed. The sequential arylation strategy can be performed in a one-pot manner without much loss of efficiency when compared to the corresponding stepwise synthesis. These conditions are applicable to the coupling of a wide variety of aryl and heteroaryl-boronic acids with pyrazolo[3,4-b]pyridines with high selectivity of the C3 over the C6 position, thus enabling the rapid construction of a diverse array of medicinally important diarylpyrazolo[3,4-b]pyridines.

An efficient method to produce diarylpyrazolo[3,4-b]pyridines derivatives via combination of chemoselective Suzuki–Miyaura cross-coupling reactions has been developed.