Palladium-Catalyzed C3-Arylations of 1H- and 2H-Pyrazolo[4,3-b]pyridines on Water

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.

"Walking the nitrogen around the ring": Chemical synthesis and spectroscopic characterization of novel 4-, 5-, 6-, and 7-azaindazole analogs of the synthetic cannabinoid receptor agonist MDMB-PINACA

Over the past decade, synthetic cannabinoid receptor agonists (SCRAs) have rapidly evolved to encompass a wide range of structurally diverse new psychoactive substances (NPS), including derivatives that incorporate indole, indazole, 7-azaindole, γ-carbolinone, or carbazole heterocyclic scaffolds. The introduction of legislative measures seeking to control the availability of NPS on the recreational drug scene has likely contributed to the continued emergence of novel SCRA analogs, which often evade regulatory control. However, the detection and/or identification of azaindazole-type SCRAs in seized material has not yet been reported (September, 2021). It is plausible that SCRAs bearing a 1,3-disubstituted azaindazole scaffold may possess cannabimimetic activity, given their structural similarity with known indole, indazole, and azaindole SCRAs. In view of these antecedents, a set of four novel isomeric 4-, 5-, 6-, and 7-azaindazole analogs of the known potent indazole SCRA, MDMB-PINACA, were synthesized using a Pd-catalyzed aminocarbonylation strategy. The complementary use of ultraviolet (UV) and infrared (IR) spectroscopy, gas chromatography-mass spectrometry (GC-MS), high resolution mass spectrometry (HRMS), 1D- and 2D-nuclear magnetic resonance (NMR) spectroscopy, and high performance liquid chromatography (HPLC) has permitted the spectroscopic differentiation, unambiguous structural assignment, and rapid separation of novel isomeric 4-, 5-, 6-, and 7-azaindazole analogs of the indazole SCRA, MDMB-PINACA.

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.

"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.

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.