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.

Transition metal-free-C-H functionalization of tertiary amines catalysed/promoted by acids: A brief review

Abstract:

C-H Functionalization of -carbon of tertiary amines has been of great importance for the past two decades as N-heterocycles can be synthesized by this approach and these heterocycles are highly useful as drugs or drug precursors in the pharmaceutical industry. In this review article, we have summarized only the -C-H functionalization reactions of tertiary amines that are catalysed or promoted by acids. These C-H functionalization reactions are usually catalysed by transition metal salts, although metal-free catalysts are also used. However, several such reactions have been reported that are efficiently catalysed by acids. They are cost-effective, have a simple purification process, less sensitive to air/moisture, and are relatively environmentally benign. However, this area has not received enough focus due to the lack of review articles, which encouraged us to write this review.

Iodine-Catalyzed Synthesis of Alkylthio-Substituted 1,4-Enediones from Styrenes and Dialkyl Sulfoxides

We have developed an efficient iodine-catalyzed route for the synthesis of 2-(alkylthio)-substituted 1,4-enedione derivatives from styrenes under an open air atmosphere. Styrenes are heated with a range of sulfoxides in the presence of iodine and potassium persulfate to afford the desired products in high yields. Except for DMSO, all the sulfoxides are synthesized in the laboratory and are used crude. The products are formed as mixtures of E and Z stereoisomers that are easily separable by column chromatography. Both oxygen atoms of 1,4-enedione product originate from aerial oxygen. A mechanism is proposed based on control experiments and literature reports.

Visible-light-promoted sulfenylation of 6-aminouracils under catalyst-free conditions

Visible-light-promoted reactions have proven to be a decent strategy for the synthesis of complex molecules.

Ten Years of Glory in the α-Functionalizations of Acetophenones: Progress Through Kornblum Oxidation and C-H Functionalization

This review article focuses on the α-functionalization of acetophenones involving Kornblum oxidation and C-H functionalizations. Although various other strategies, such as classical approaches, enamine approaches and umpolung strategy are also known for this functionalization, here we discuss mainly the Kornblum oxidation approach and C-H functionalization strategy as they have advantages over the others. In Kornblum oxidation, the reaction uses iodine and dimethylsulfoxide and proceeds through the formation of arylglyoxal as the key intermediate. In C-H functionalization, the reaction requires metal, or metal-free catalyst, and generates radical intermediate in most cases. α-Functionalization of acetophenones is very important because of their huge applications in the synthesis of various natural products and pharmaceuticals and, therefore, a number of research articles have been published in this area. However, no review articles are available so far. In this article, we present a succinct discussion of various important and novel reactions, along with their mechanisms, published since 2012 to date. We believe that this first review article in this field will give readers one-stop information on this topic and encourage further intriguing work in this area.

Visible-Light-Driven Z-Selective Reaction of Methyl Ketones with DMSO: A Mild Synthetic Approach to Methylthio-Substituted 1,4-Enedione Promoted by Selectfluor™

Here we disclose a simple, visible-light-driven Z-selective synthesis of methylthio-substituted 1,4-enedione in a single step promoted by Selectfluor. Dimethyl sulfoxide is used as both the ‘thio’ source and the solvent. Molecular iodine and potassium persulfate are used as catalyst and oxidant, respectively. White light (CFL-30W) is used as the light source. The proposed mechanism involves a Kornblum reaction followed by aldol reaction.

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.

α-C–H functionalization of tertiary amines catalyzed/promoted by molecular iodine/derivatives

A recent review on the α-C–H functionalization of tertiary amines using low-cost and benign I₂ or its derivatives.

L-Proline-catalyzed regioselective C1 arylation of tetrahydroisoquinolines through a multicomponent reaction under solvent-free conditions

Here we disclose the C1 arylation of tetrahydroisoquinolines (THIQ) through regioselective C(sp3)-H functionalization using a multicomponent reaction. The reaction was performed by reacting THIQ, aldehydes and aminopyrazoles or indoles under neat conditions with l-proline as a catalyst. The regioselectivity of the products was confirmed by X-ray analysis and spectroscopic data. The formation of an azomethine ylide intermediate is crucial for obtaining the regioselectivity.

Recent advances in intramolecular C–O/C–N/C–S bond formationviaC–H functionalization

This review presents the construction of C–X bonds (X = O/N/S) by using intramolecular C–H functionalization for the synthesis of heterocyclic compounds.

Multi-component synthesis of 3-substituted indoles and their cyclisation to α-carbolines via I2-promoted intramolecular C2 oxidative amination/aromatisation at room temperature

Condensation of indoles, aldehydes and pyrazol-5-amine in the presence of ceric ammonium nitrate gives 3-substituted indoles. These then cyclise to α-carbolines at room temperature through I2-promoted intramolecular C2 amination and aromatisation in open air. A plausible mechanism is proposed based on some controlled experiments.

Introducing tetramethylurea as a new methylene precursor: a microwave-assisted RuCl3-catalyzed cross dehydrogenative coupling approach to bis(indolyl)methanes

The microwave-assisted synthesis of symmetrical/unsymmetrical bis(indolyl)methanes using tetramethylurea as a methylene source.

Copper catalyzed oxidative deamination of Betti bases: an efficient approach for benzoylation/formylation of naphthols and phenols

A copper-catalyzed benzoylation/formylation of naphthols and phenols via oxidative deamination of Betti bases.

Synthesis of some novel annulated pyrido[2,3-d]pyrimidines via stereoselective intramolecular hetero Diels-Alder reactions of 1-oxa-1,3-butadienes

Some novel annulated pyrido[2,3-d]pyrimidines 6 and 7 were synthesized stereoselectively by intramolecular hetero Diels-Alder reactions involving 1-oxa-1,3-butadienes.