Copper-Catalyzed Radical Cascade Cyclization of N-Substituted Indole-3-Aldehydes with Aryl Alkenes: Access to Pyrrolo[1,2-a]indole Scaffolds

Herein, we report a Cu-DTBP-catalyzed [3 + 2] cycloaddition reaction between 1-(2-oxo-2-phenylethyl)-1H-indole-3-aldehyde and arylalkene, using DMF as the solvent. Under relatively mild reaction conditions, a series of indole compounds were synthesized in moderate yields (up to 73%). This protocol features good functional group tolerance and high atom economy. In addition, we synthesized a total of 20 target compounds, providing a reliable and straightforward method to obtain structurally diverse pyrrolo[1,2-a]indole derivatives.

Iron(II)-Catalyzed Synthesis of Nitrated Dihydropyrazole via a Nitrification and C-H Activation/Cyclization Cascade Reaction

A route for nitrification and C-H activation/cyclization of (E)-N-allyl-N'-benzylidenebenzenesulfonohydrazide and cobalt nitrate via an iron(II)-catalyzed cascade reaction to synthesize nitrated dihydropyrazoles has been developed. The method features convenient operation and good functional group tolerance. In addition, it employs insensitive and inexpensive FeSO4 as the catalyst and provides a direct approach for the preparation of dihydropyrazoles.

Electrochemical Phenyl-Carbonyl Coupling Reaction of Aromatic Aldehydes or Ketones

An electrochemical phenyl-carbonyl coupling reaction of aromatic aldehydes or ketones to synthesize 4-(hydroxy(phenyl)methyl)benzaldehyde derivatives has been developed. The method shows high chemoselectivity, broad functional group compatibility, atom economy, and environmental benignity and has good potential applicability.

Access to Fully Substituted Dihydroindazoles Via Hexadehydro-Diels-Alder/[3 + 2] Cycloaddition

A cascade hexadehydro-Diels-Alder (HDDA)/[3 + 2] cycloaddition reaction between tetrayne and N,N'-cyclic acylhydrazone is described. This strategy allows the efficient construction of fully substituted 2,3-dihydro-1H-indazole scaffolds which have insecticidal activity against the third instar larvae of Mythimna separata.

Nitration of Pyrrolo[2,1-a]isoquinolines

We have successfully modified a series of pyrrolo[2,1-a]isoquinolines via direct nitration under mild reaction conditions. Easily accessible nitrates including CAN, Cu(NO₃)₂·H₂O, and Fe(NO₃)₃·9H₂O all can serve as effective nitrating reagents for functionalizing pyrrolo[2,1-a]isoquinolines. Various nitro-bearing pyrrolo[2,1-a]isoquinolines have been efficiently prepared in acceptable to good yields.

Recent Strategies in Transition-Metal-Catalyzed Sequential C–H Activation/Annulation for One-Step Construction of Functionalized Indazole Derivatives

Designing new synthetic strategies for indazoles is a prominent topic in contemporary research. The transition-metal-catalyzed C–H activation/annulation sequence has arisen as a favorable tool to construct functionalized indazole derivatives with improved tolerance in medicinal applications, functional flexibility, and structural complexity. In the current review article, we aim to outline and summarize the most common synthetic protocols to use in the synthesis of target indazoles via a transition-metal-catalyzed C–H activation/annulation sequence for the one-step synthesis of functionalized indazole derivatives. We categorized the text according to the metal salts used in the reactions. Some metal salts were used as catalysts, and others may have been used as oxidants and/or for the activation of precatalysts. The roles of some metal salts in the corresponding reaction mechanisms have not been identified. It can be expected that the current synopsis will provide accessible practical guidance to colleagues interested in the subject.

Practical chemoselective aromatic substitution: the synthesis of N-(4-halo-2-nitrophenyl)benzenesulfonamide through the efficient nitration and halogenation of N-phenylbenzenesulfonamide

A novel route involving the metal-promoted tandem nitration and halogenation of N-phenylbenzenesulfonamide to synthesize N-(4-halo-2-nitrophenyl)benzenesulfonamide derivatives has been developed. The method shows highly practical chemoselective and functional group compatibility. In addition, it employs insensitive and inexpensive Cu(NO3)2·3H2O, Fe(NO3)3·9H2O, and NH4NO3 as the nitration reagents, and it provides a direct approach for the preparation of 4-halo-2-nitroaniline, which is a crucial intermediate for the synthesis of benzimidazoles and quinoxaline derivatives.

Selective Mono- and Diamination of Ketones in a Combined Copper-Organocatalyst System

Herein, we report a simple and mild protocol for the chemoselective mono- and diamination of ketone using pyrazole as the amine source in a combined copper-organocatalyst system. Various substrates are compatible, providing the corresponding products in moderate to good yields. This strategy gives an efficient and convenient solution for the synthesis of α-pyrazole and α,α-dipyrazole ketone derivatives. The control experiment demonstrates that in situ generated hydrazone is a key intermediate in the transformation.

Cobalt(II) nitrate promoted cyclization of benzoyl hydrazone for the synthesis of 2,5-diphenyl-1,3,4-oxadiazole derivatives

A Co(NO3)2 method to promote cyclization of benzoyl hydrazone for the formation of 2,5-diphenyl-1,3,4-oxadiazoles has been developed. The reaction proceeded smoothly and was promoted by Co(NO3)2 under air at 110 °C in DCE; 16 examples of products were obtained.

Photo-Induced N-N Coupling of o-Nitrobenzyl Alcohols and Indolines To Give N-Aryl-1-amino Indoles

A novel method to synthesize N-aryl-1-amino indoles was established by the photoinduced N-N coupling reaction. This protocol is by treatment of o-nitrobenzyl alcohols and indolines in the presence of TEAI and acetic acid with a 24 W ultraviolet (UV) light-emitting diode (LED) (385-405 nm) irradiation. The products bearing an aldehyde group can be further transformed to fluorescent probes based on Rhodamine 6G derivative 11, which shows a high specificity and sensitivity for Fe³⁺.

Metal-free regioselective C-H amination for the synthesis of pyrazole-containing 2H-indazoles

A general and practical regioselective approach for the C-H amination of 2H-indazoles under transition-metal-free conditions was developed. A series of substrates were tested showing eminent functional group tolerance and affording the C-N functionalization products in good to excellent yields. Mechanism studies revealed that a radical process was involved in this transformation.

Synthesis of 1H-Indazoles via Silver(I)-Mediated Intramolecular Oxidative C-H Bond Amination

We described a silver(I)-mediated intramolecular oxidative C-H amination that enables the construction of assorted 1H-indazoles that are widely applicable in medicinal chemistry. The developed amination was found to be efficient for the synthesis of a variety of 3-substituted indazoles that are otherwise difficult to be synthesized by other means of C-H aminations. Preliminary mechanistic studies suggested that the current amination proceeds via single electron transfer (SET) mediated by Ag(I) oxidant.

Sulfonylimination of Proline with Sulfonylazides Involving Aldehyde-Induced Decarboxylation Coupling

In the presence of aldehyde, a facile method was developed to obtain N-sulfonyl amidines under metal- and oxidant-free conditions by the decarboxylative of proline. This transformation features a double C-N bond formation and allows for the green synthesis of the N-sulfonyl amidines on the basis of mild conditions.

Transition-metal-free sulfonylations of methylthiolated alkynones to synthesize 3-sulfonylated thioflavones

A set of transition-metal-free NaI/TBHP-mediated sulfonylation cyclization reactions of methylthiolated alkynones with sulfonyl hydrazides was developed, by which various 3-sulfonylated thioflavones were prepared under mild reaction conditions.

Transition-metal- and oxidant-free three-component reaction of quinoline N-oxides, sodium metabisulfite and aryldiazonium tetrafluoroborates via a dual radical coupling process

A convenient and straightforward three-component transformation of quinoline N-oxides, sodium metabisulfite and aryldiazonium tetrafluoroborates has been developed, providing the target products in moderate to good yields. Compared with previous studies, the present methodology avoids the use of transition-metal catalysts and excess oxidants, providing a simple and practical alternative approach for the construction of 2-sulfonylquinolines. Control experiments indicate that a dual radical coupling process is responsible for this reaction.