Late-stage ortho-C-H alkenylation of 2-arylindazoles in aqueous medium by Manganese(i)-catalysis

One-Pot Manganese (I)-Catalyzed Oxidant-Controlled Divergent Functionalization of 2-Arylindazoles

The oxidant-controlled divergent synthesis of C-2' formyl 2H-indazoles and indazoloindazolediones has been developed through Mn(I)- catalyzed ortho C-H functionalization of 2H-indazoles with para-formaldehyde to afford C-2' hydroxymethylated 2H-indazoles and subsequently oxidation with varying the amount of DDQ in one-pot. By employing selectfluor as the oxidant instead of DDQ, this reaction exclusively provided indazolebenzoxazine derivatives. This strategy delivered unsymmetrical indazoloindazoledione and indazolobenzoxazine with varied functional group tolerance in moderate to good yields.

Iso-Pentadienyl Carbonate as a Five Carbon Synthon in Manganese(I)-Catalyzed Selective Linear 1,3-Dienylation

Selective linear 1,3-dienylations are essential transformations, and numerous synthetic efforts have been documented. However, a general method enabling access to electron-rich, -poor, and biologically relevant dienyl molecules is in high demand. Hence, we report a straightforward method of manganese(I)-catalyzed C-H dienylation of arenes by using iso-pentadienyl carbonate as a five carbon synthon. This is a highly unprecedented report for selective linear 1,3-dienylation using manganese C-H activation catalysis. Our method facilitates the synthesis of varieties of dienes, including those suitable for normal or inverse electron demand Diels-Alder reactions, dienyl glycoconjugates, and unnatural amino acids. Extensive mechanistic studies, including isolation of C-H activated organo-manganese complex and isotopic analyses, have supported the proposed mechanism of this dienylation. The synthetic applicability of this method eased to deliver a 6/6/5-fused tricyclic nagilactone scaffold.

Robust Synthesis of Terpenoid Scaffolds under Mn(I)-Catalysis

The 6/6/5-fused tricyclic scaffold is a central feature of structurally complex terpenoid natural products. A step-economical cascade transformation that leads to a complex molecular skeleton is regarded as a sustainable methodology. Therefore, we report the first Mn(I)-catalyzed C(sp²)-H chemoselective in situ dienylation and diastereoselective intramolecular Diels-Alder reaction using iso-pentadienyl carbonate to access 6/6/5-fused tricyclic scaffolds. To the best of our knowledge, there is no such report thus far to utilize iso-pentadienyl carbonate as a substrate in C-H activation catalysis. Extensive mechanistic studies, such as the isolation of catalytically active organo-manganese(I) complexes, 1,3-dienyl-intermediates, and isotopic labeling experiments have supported the proposed mechanism of this cascade reaction.

Synthesis and Antitumor Evaluation of Biotin-SN38-Valproic Acid Conjugates

Despite the strong anticancer activity of SN38 (7-ethyl-10-hydroxy-camptothecin), the severe side effects and loss of anticancer activity caused by the lack of selectivity to cancer cells and hydrolysis of ring E prevent its clinical application. To address the issue, herein a multifunctional SN38 derivative (compound 9) containing biotin (tumor-targeting group) and valproic acid (histone deacetylase inhibitor, HDACi) was synthesized via click chemistry and evaluated using MTT assay. The in vitro cytotoxicity study showed that compound 9 exhibited superior cytotoxicity than irinotecan against human cervical cancer HeLa cells, albeit it was inferior to SN38. More significantly, compound 9 significantly reduced toxicity in mouse embryonic fibroblast NIH3T3 cells, indicating that compound 9 had the capacity to enhance tumor targeting due to its cell selectivity. Further studies demonstrated that, compared with irinotecan, compound 9 induced similar apoptosis of cancer cells. Consequently, compound 9 can not only improve its tumor-targeting ability mediated by biotin but also exert potent anticancer activity through the effect of SN38 and valproic acid, indicating that the design concept is an effective strategy for the structural modification of SN38.

Manganese-catalyzed hydroarylation of multiple bonds

Transition metal-catalyzed C-H activation has become a promising strategy in organic synthesis due to its improved atom-, step- and resource economy. Considering the Earth's abundance, economic benefits, and low toxicity, 3d metal catalysts for C-H activation have received a significant focus. In particular, organometallic manganese-catalyzed C-H activation has proven to be versatile and suitable for a wide range of transformations such as C-H addition to π-components, arylation, alkylation, alkynylation, amination, and many more. Among them, manganese-catalyzed C-H addition to C-C and C-heteroatom multiple bonds exhibited unique and promising reactivity to construct a wide range of complex organic molecules. In this review, we highlight the developments in the field of manganese-catalyzed hydroarylation of multiple bonds via C-H activation with a range of applications until August 2022.

Homogeneous Manganese-Catalyzed Hydrofunctionalizations of Alkenes and Alkynes: Catalytic and Mechanistic Tendencies

In recent years, many manganese-based homogeneous catalytic precursors have been developed as powerful alternatives in organic synthesis. Among these, the hydrofunctionalizations of unsaturated C-C bonds correspond to outstanding ways to afford compounds with more versatile functional groups, which are commonly used as building blocks in the production of fine chemicals and feedstock for the industrial field. Herein, we present an account of the Mn-catalyzed homogeneous hydrofunctionalizations of alkenes and alkynes with the main objective of finding catalytic and mechanistic tendencies that could serve as a platform for the works to come.