Palladium-catalyzed oxidative C-H/C-H cross-coupling of pyrazolo[1,5-a]azines with five-membered heteroarenes

Advances in pyrazolo[1,5-a]pyrimidines: synthesis and their role as protein kinase inhibitors in cancer treatment

Pyrazolo[1,5-a]pyrimidines are a notable class of heterocyclic compounds with potent protein kinase inhibitor (PKI) activity, playing a critical role in targeted cancer therapy. Protein kinases, key regulators in cellular signalling, are frequently disrupted in cancers, making them important targets for small-molecule inhibitors. This review explores recent advances in pyrazolo[1,5-a]pyrimidine synthesis and their application as PKIs, with emphasis on inhibiting kinases such as CK2, EGFR, B-Raf, MEK, PDE4, BCL6, DRAK1, CDK1 and CDK2, Pim-1, among others. Several synthetic strategies have been developed for the efficient synthesis of pyrazolo[1,5-a]pyrimidines, including cyclization, condensation, three-component reactions, microwave-assisted methods, and green chemistry approaches. Palladium-catalyzed cross-coupling and click chemistry have enabled the introduction of diverse functional groups, enhancing the biological activity and structural diversity of these compounds. Structure-activity relationship (SAR) studies highlight the influence of substituent patterns on their pharmacological properties. Pyrazolo[1,5-a]pyrimidines act as ATP-competitive and allosteric inhibitors of protein kinases, with EGFR-targeting derivatives showing promise in non-small cell lung cancer (NSCLC) treatment. Their inhibitory effects on B-Raf and MEK kinases are particularly relevant in melanoma. Biological evaluations, including in vitro and in vivo studies, have demonstrated their cytotoxicity, kinase selectivity, and antiproliferative effects. Despite these advances, challenges such as drug resistance, off-target effects, and toxicity persist. Future research will focus on optimizing synthetic approaches, improving drug selectivity, and enhancing bioavailability to increase clinical efficacy.

Direct C7-H Arylation of Pyrazolo[1,5-a]azines with Aryl Chlorides

C7-Arylated pyrazolo[1,5-a]azines are important structural motifs with profound applications in drug and material research. Here, we report a general and straighforward synthesis of these bi(hetero)aryls via palladium-catalyzed direct C-H arylation, employing low-cost and abundant (hetero)aryl chlorides as the aryl source. The catalytic system is robust and covers a wide substrate scope regarding heteroarenes as well as (hetero)aryl chlorides, with possible extension to the C-H arylation of [1,2,4]triazolo[1,5-a]pyrimidines. This study also presents a rare example of using (hetero)aryl chlorides for the direct C-H arylation of six-membered heteroarenes.

Palladium-Catalyzed C7–H (Hetero)arylation of Pyrazolo[1,5-a]pyrazines with Heteroarenes and Aryl Iodides with the Assistance of Silver Salts

Pyrazolo[1,5-a]pyrazines coupled with heteroarenes and aryl iodides selectively at the C7 position to afford a broad library of bi(hetero)aryl structures under ligand-free palladium-catalyzed conditions. The key to the success of the reaction is the use of silver salts as the oxidant or the base, allowing the regioselective C–H bond functionalization to occur under relatively mild conditions.

Rh(III)-catalysed C-H/C-H cross-coupling of S-aryl sulfoximines with thiophenes: facile access to [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and benzothiazines

Reported herein is rhodium-catalysed oxidative C-H/C-H cross-coupling of S-aryl sulfoximines with thiophenes via a chelation-assisted strategy, which provides an efficient approach for the construction of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and benzothiazine skeletons from easily available substrates. This protocol exhibits a good compatibility with halogen substituents, thus paving the way for further transformation to prepare various organic functional molecules. The resulting benzothiazine derivative shows a deep blue emission with Commission Internationale de 'Eclairage (CIE) coordinates of (0.15, 0.04), a high quantum yield, and a delayed fluorescence lifetime.