B(C6F5)3-Catalyzed Reductive Deoxygenation of Isatins for Indole Synthesis

An efficient method for reductive deoxygenation of isatin derivatives using catalyst B(C6F5)3 and methylphenylsilane is described. This reaction proceeds rapidly under mild conditions, and the protocol provides a broad substrate scope. Notably, while general synthetic methods utilizing a combination of B(C6F5)3 and hydrosilanes smoothly reduce indoles to generate indolines, the present strategy represents the first reductive deoxygenation reaction for the formation of indoles without further reduction.

Ruthenium-catalyzed monodeuterium-methylenation of two indole units with vinylene carbonate as a novel methylene precursor

A new example of deuteration, involving ruthenium-catalyzed monodeuterium-methylenation of indole units with vinylene carbonate, is described. This reaction was used to build an array of promising highly deuterated bisindolylmethanes (d-BIMs). This methodology featured excellent functional group compatibility with diverse substrate categories such as indoles, N,N-dialkylanilines, and 1,3-dicarbonyls as well as having showcased the distinct chemical function of VC as an innovative methylene precursor.

Rongalite induced metal-free C(sp2)-H functionalization of indoles: direct access to 3-(sulfonylmethyl) indoles

A rongalite-induced C(sp2)-H functionalization reaction has been developed for the synthesis of 3-(phenylsulfonylmethyl) indole derivatives from indole and arylsulfonyl hydrazides. This regioselective C-H functionalization provides a wide range of C-3 sulfonylmethyl indoles with upto 90% yields. Here, rongalite functions as a C1 unit source and a single electron donor. The use of inexpensive rongalite (ca. $0.03 per 1 g), mild reaction conditions and gram-scale synthesis are some of the key features of this methodology.

Efficient Ru-Catalyzed Electrochemical Homo- and Heterocoupling Reaction of Terminal Alkynes: Synthesis, In Vitro Anticancer Activity, and Docking Study

With the objective to identify novel anticancer leads, herein ruthenium-catalyzed electrochemical homo- and heterocoupling reactions of terminal alkynes have been developed for the synthesis of the desired products. Among the synthesized 1,3-diynes, some of them were rigorously examined for possible in vitro anticancer activity against HeLa (human cervical cancer) and L6 normal (rat skeletal muscle) cell lines. Additionally, the docking study was also performed toward 16 ovarian cancer targets with binding affinity calculations with respect to the standard. To the best of our knowledge, this is the first scientific report on the ruthenium-catalyzed electrochemical homocoupling reaction between terminal alkynes with its in vitro anticancer and in silico docking studies.

Copper-catalysed dehydrogenative self-coupling/cyclization of 5-aminopyrazoles: synthesis and photophysical study of pyridazines

An interesting self-coupling/cyclization of 5-aminopyrazoles is revealed, which provides a variety of pyridazine cores in reasonable yields. In this reaction, C(sp²)-C(sp²) and N-N bond formation occurs simultaneously in one reaction vessel. The photophysical properties of the synthesized compounds were also studied and some of them exhibited fluorescence properties with good quantum yields. A radical mediated reaction mechanism is proposed with the help of control experiments.

Strategies Toward the Catalyst-Free α-C-H Functionalizations of Tertiary Amines

α-C-H functionalization of tertiary amines has been a highly studied field for the past two decades because several important nitrogen containing heterocycles or compounds can be synthesized through this strategy. Though transition metal catalysts and some metal-free catalysts are mainly used for these reactions, a few catalyst-free reactions have recently been efficiently performed. Catalyst-free reactions are cost-effective, less sensitive to air/moisture, easier to operate, have a simple purification process, and are relatively environment-friendly. In this article, we have summarized all the α-C-H functionalization reactions of tertiary amines performed without using any external catalysts. The content of this article will undoubtedly encourage readers to do more work in this area.

MTHPP monoacetic ester: unexpected formation, zinc metalation, thermal and photophysical properties

In the current investigation we report an unexpected methyl esterification occurred during the coupling reaction of mTHPP monoacetic acid 2 with 3-amino-1,2,4-triazole in the presence of HBTU/DIPEA. The mechanism of this unexpected methyl esterification was studied, and the structure of the formed methyl ester 5 was confirmed by the means of 1H, 13C NMR in addition to (MALDI-TOF and ESI-HRMS) spectrometry. The formation of 5 during the coupling reaction was also chemically supported by an alternative synthetic method involving a direct monosubstitution reaction of mTHPP 1 with methyl bromoacetate. We also investigated the metalation of 5 with zinc and studied the thermal properties along with differential scanning calorimetry (DSC) of the zinc porphyrin 6. The photophysical properties of porphyrin methyl ester 5 and its zinc complex 6 were also investigated.

Graphical Abstract

Selectfluor facilitated bridging of indoles to bis(indolyl)methanes using methyl tert-butyl ether as a new methylene precursor

A novel, green and efficient method is developed for the synthesis of methylene bridged bis(indolyl)methanes in good to excellent yields. The reaction employs methyl tert-butyl ether (MTBE) as the methylene source and selectfluor as an oxidizing agent. The scope and versatility of the methods have been successfully demonstrated with 48 examples. The metal-free transformation process is suitable for scale-up production. A selectfluor-promoted oxidative reaction mechanism is proposed based on the results of the experimental studies.

Catalyst-free and additive-free reactions enabling C-C bond formation: a journey towards a sustainable future

This review focuses on the catalyst- and additive-free C-C bond forming reactions reported mostly from the year 2005 to date. C-C bond forming reactions are highly important as large and complex organic molecules can be derived from simpler ones via these reactions. On the other hand, catalyst- and additive-free reactions are economical, environmentally friendly and less sensitive to air/moisture, allow easy separation of products and are operationally simple. Hence, a large number of research articles have been published in this area. Though a few reviews are available on the catalyst-free organic reactions, most of them were published a few years ago. The current review excludes catalysts as well as additives and is specific to only C-C bond formation. Besides many organic name reactions, catalyst/additive-free C-H functionalizations, coupling reactions and UV-visible-light-promoted reactions are also discussed. Undoubtedly, the contents of this review will motivate readers to do more novel work in this area which will accelerate the journey towards a sustainable future.

Copper Ferrite Superparamagnetic Nanoparticle-Catalyzed Cross-coupling Reaction to Form Diindolylmethane (DIM): Effect of Experimental Parameters

Superparamagnetic copper ferrite (CuFe2O4) nanoparticles were utilized as a heterogenous catalyst for the cross-coupling reaction of indole to form 3,3’-diindolylmethane (DIM) as the desirable product. High reaction yield, at around 82%, was achieved under optimal conditions. The CuFe2O4 material could be easily separated from the reaction mixture by an external magnetic field and could be reutilized several times without a significant decrease in catalytic activity. We also showed that no sites of catalyst material leached into reaction solution was detected. To our best knowledge, the above cross-coupling reaction was not previously conducted under catalysis of superparamagnetic nanoparticles. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Generation of indole derivatives by an endophytic fungus Chaetomium sp. through feeding 1,2-dimethylindole

Through feeding 1,2-dimethylindole, two new bisindoles, chaetoindolone E and F (1 and 2) and five known indole derivatives (3-7) were isolated from the cultures of an endophytic fungus Chaetomium sp. The structures of these compounds were elucidated based on HR-MS, NMR and single-crystal X-ray crystallography. Compounds 1 and 2 were undescribed before, compounds 3-7 were first reported from natural sources, and NMR spectrums of compounds 4 and 5 were first reported. The cytotoxity of the bisindole compounds (1-3) was also tested.

Solvent-free ruthenium trichloride-mediated [2 + 2 + 2] cycloaddition of α,ω-diynes and cyanamides: a convenient access to 2-aminopyridines

A convenient access to functionalized 2-aminopyridinesviaa solventless Ru-catalyzed [2 + 2 + 2] cycloaddition reaction of α,ω-diynes and cyanamides is described.