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The tunable reactions of enaminones with phosphine oxides/phosphonates in the form of vicinal- and geminal diphosphorylation, C–N bond phosphorylation have been developed, providing new methods for the synthesis of divergent phosphorylated molecules.

The reactions of enaminones, hydrazine hydrochlorides and internal alkynes for the synthesis of N-naphthyl pyrazoles are achieved via Rh(iii) catalysis, representing the first three-component Satoh–Miura benzannulation.

A metal-free dioxygenative reaction of aryl diazonium salts with aryl alkynes for vicinal diketone synthesis is developed.

The Dess-Martin periodinane (DMP) reagent-mediated reactions of tertiary enaminones with potassium thiocyanate for the synthesis of thiazole-5-carbaldehydes are developed. The product formation involves cascade hydroxyl thiocyanation of the C═C double bond, intramolecular hydroamination of the C≡N bond, and thiazole annulation by condensation on the ketone carbonyl site, representing novel reaction pathways in the reactions between enaminones and thiocyanate salt. DMP plays dual roles in mediating the free radical thiocyanation and inducing the unconventional selective thiazole-5-carbaldehyde formation by masking the in situ generated formyl group during the reaction process.

The selective synthesis of N2-sulfonyl and N2-H 1,2,3-triazoles via organocatalytic annulation of enaminone/enaminoester with sulfonyl azide has been realized. The unconventional selectivity providing N2-sulfoyl 1,2,3-triazoles takes place in pure water, wherein the hydrogen bond effect between water and the intermediate resulting from enamine-azide corporation accounts for the novel reaction selectivity. On the other hand, the reactions conducted in DMSO specifically afford N2-H 1,2,3-triazoles in the absence of such hydrogen bond effect.

Enaminones and analogous stable enamines are well known as platform building blocks in organic synthesis for the construction of heterocyclic compounds, especially N-heterocycles. To date, enaminones have been successfully employed in the synthesis of various 5- or 6- membered heterocycles. Recently, synthetic protocols accomplished by diversity-oriented annulation reactions based on the C-N bond cleavage of enamines have gained notable success. In this review, the development of the transition metal-free heterocyclic product synthesis based on the annulation reactions of enaminones or analogous enamines featuring a C-N bond cleavage is reviewed.

An efficient visible-light-mediated tandem phosphorylation/cyclization of N-arylacrylamides with H-phosphine oxides is described, providing a series of phosphorylated oxindoles in good yields.

The electrochemical annulation of enaminones/analogous enamines and thioureas providing 2-aminothiazoles has been realized. Modulating the electrolyte enables the diastereoselective synthesis of 4,5-dialkoxyl thiazolines by dearomatization.

The synthesis of 2-vinyl pyrroles has been achieved via copper-catalyzed cascade reactions of enaminones and alkyl propiolates. The synthesis of 2,3-dicarboxylate-functionalized products has been tuned by using internal alkynyl dicarboxylates.

This review highlights recent progress in electrochemical cascade cyclization reactions for the synthesis of carbon rings and heterocycles, such as pyridines, quinolines, phenanthridines, cinnolines, 1,4-dihydroquinolines, oxindoles, imidazo[1,5-α]pyridines, imidazoles, etc. The works included herein are introduced in two major sections of heterocycle construction and carbocycle construction reactions, covering the works reported from 2012 to 2022.1 Introduction2 Electrochemical Cascade Cyclization for the Synthesis of Heterocycles2.1 Synthesis of Pyridines, Quinolines, Phenanthridines, and Cinnolines2.2 Synthesis of 1,4-Dihydroquinolines, Hexacyclic Sulfonamides, and Thiazines2.3 Synthesis of Hydroisoquinolinones and Hydroquinolinones2.4 Synthesis of Quinazolin-4(3H)-ones2.5 Synthesis of 4H-3,1-Benzoxazines2.6 Synthesis of Oxindoles2.7 Synthesis of Indolines and Indoles2.8 Synthesis of Imidazo[1,5-α]pyridines and Imidazoles2.9 Synthesis of Imidazolones, Imidazolidinones, Oxazolones, and Oxazolidinones2.10 Synthesis of Benzoxazoles, Oxazolines, and Isoxazolines2.11 Synthesis of Furans and Dihydrofurans2.12 Synthesis of Indolizines, Pyrazoles, and Triazolium Inner Salts2.13 Synthesis of Sulfonated Benzothiophenes, Thiazoles, Dihydrothiazoles, and 1,3,4-Thiadiazoles2.14 Synthesis of Lactones3 Electrochemical Cascade Cyclization for the Construction of Carbocycles3.1 Synthesis of Carbon Polycycles and Spiroindenes3.2 Synthesis of Difluoroacyl (Hetero)arenes and Sulfonated Indenones4 Conclusion

The selectivity tunable synthesis of functionalized indoles and benzofurans has been achieved via the reactions of enaminones with quinonediimides and quinoneimides under modified conditions, respectively.

An efficient and robust Rh(III)-catalyzed C–H homoallylation of indolines has been developed. Using 4-vinyl-1,3-dioxan-2-one as coupling partner, a range of homoallylic alcohols were prepared in excellent stereoselectivities. The current strategy features high efficiency, good yields, and exceptional functional group tolerance.

The combination of visible light irradiation and Pd-catalysis has been practically employed for the C-H alkylation reactions of naphthylamines and α-diazo esters, leading to the synthesis of α-naphthyl functionalized acetates via C-C bond construction under mild reaction conditions and under solvent-free conditions. The light irradiation has been proven to play a pivotal role in the reactions, probably by promoting the generation of active carbene species from α-diazo esters.

The perfluoroalkylsulfonylation (CF3SO2, C2F5SO2 and CHF2SO2) in the enaminone C H bonds has been developed simply via the promotion of molecular iodine by using stable and cheap sodium perfluoroalkyl sulfinates as coupling partners. The stereoselective synthesis of E-configurated α-perfluoroalkylsulfonyl enaminones has been realized via unprecedented C H bond elaboration and C C double bond configuration inversion by free radical process.

An unprecedented method for the synthesis of dichlorinated and dibrominated 2-amino-substituted chromanones is developed by employing enaminones and NCS/NBS as starting materials under microwave irradiation. The reactions proceed quickly to deliver products without using any catalyst or additive, thus providing practical access to 3,3-dihalogenated 2-aminochromanones.

An efficient zinc-catalyzed amination of free anilines and free phenols with quinoneimides has been disclosed, which proceeds smoothly under simple and mild conditions. The

Without employing an external oxidant, the simple synthesis of 3-halochromones and various halogenated electron-rich arenes has been realized with electrode oxidation by employing the simplest sodium halide (NaX, X = Cl, Br, I) as halogen source. This electrochemical method is advantageous for the simple and mild room temperature operation, environmental friendliness as well as broad substrate scope in both C-H bond donor and halogen source components.

A direct enaminone C-N bond coupling functionalization that generates a new C-P bond using dialkyl phosphonate for the efficient and stereoselective synthesis of (E)-alkenylphosphonates is reported. The reactions toward target products proceed well with a broad scope, disclosing a valuable new synthetic application of enaminones by the interesting C(sp2)-N bond elaboration.

The synthesis of NH-free pyrroles via Pd-catalyzed annulation of enaminones and alkenes is reported. With the catalysis of Pd(II), the activation of triple C(sp2)-H bonds, including one internal C(sp2)-H bond in enaminone, has been activated to provide various pyrroles. The interesting evolution of hydrogen gas from the reactions has been observed by a hydrogen detector.

A highly practical method for C–CN bond formation by C–N bond cleavage on enaminones leading to the efficient synthesis of β-cyano enones is developed. The reactions take place efficiently to provide (E)-β-cyano enones with only a molecular iodine catalyst. In addition, the additional employment of oxalic acid enables the selective synthesis of (Z)-β-cyano enones.

The C═C double bond cleavage on tertiary enaminones, enabling the formation of a new C–CF3 bond, has been realized as a practical method for the synthesis of α-trifluoromethyl ketones with only the...

Chromone and flavone are both central backbones of natural products and clinical medicines. Synthesis of diversely functionalized chromones and flavones constitutes significant research contents of the modern synthetic science because abundant molecular libraries of such types are crucial in providing candidate compounds for the discovery of new pharmaceuticals and functional materials. The direct C H bond activation or functionalization on these heterocyclic backbones provides highly powerful tools for the rapid accesses to densely functionalized chromone and flavone derivatives. Considering the importance of the functionalized chromone and flavone compounds as well as the notable advances in the synthesis of such products by direct C H activation or functionalization, we review herein the research advances in the C H bond activation and functionalization reactions of chromone and flavones, in hope of showing the current states and promise of the research domain.

Ultrasound has been successfully employed to promote the thiocyanation of the C═C bond in enaminones for the synthesis of α-thiocyanoketones and 2-aminothiazoles. The reactions of enaminones with ammonium thiocyanate provide α-thiocyanoketones with ultrasound irradiation at room temperature. More interestingly, simply further heating the vessel after ultrasonic irradiation leads to the selective synthesis of 2-aminothiazoles with an unconventional 4-aryl substructure.