One-Pot Synthesis of Symmetrical and Asymmetrical 3-Amino Diynes via Cu(I)-Catalyzed Reaction of Enaminones with Terminal Alkynes

Platform of Oxidative Transformation of α-Methyl Secondary Enaminones toward Tetrahydropyridines

In this paper, the application of α-methyl secondary enaminones in the synthesis of tetrahydrofuropyridines is described. The key step of the methodology is the in situ generation of 1-azadiene from oxidation of α-methyl secondary enaminone, followed by a subsequent inverse-electron-demand hetero-Diels-Alder reaction proceeded to give the desired product. Mechanistic studies and density functional theory (DFT) calculations revealed the detailed reaction pathway. Gram-scale preparation experiments and further transformation of the product demonstrate the potential applicability of this method. In addition, the amide derivatives could be obtained by employing β-methyl secondary enaminones as substrates under similar oxidative conditions. The present work opens a new window to the application of rarely reported α-methyl secondary enaminones.

Synthesis of Multisubstituted Arylnitriles via Tf2O-Mediated Benzannulation of Enaminones with Acylacetonitriles

A novel and efficient method for the synthesis of multisubstituted arylnitriles via Tf2O-mediated [3 + 2 + 1] benzannulation of enaminones and acylacetonitriles has been developed. This reaction proceeds under mild conditions with excellent functional group compatibility. Mechanistic studies have revealed that the cyclization involves two consecutive nucleophilic additions, followed by a cascade Knoevenagel condensation and aromatization. Additionally, trifluoromethanesulfonate 6 has been identified as a crucial intermediate in this process.

Divergent Synthesis of Enynals and Dihydrobenzo[f]isoquinolines via Deoxyalkynylation of Enaminones Enabled by the Cooperative Action of Tf2O/Pd/Cu

A variety of enynals and dihydrobenzo[f]isoquinolines were effectively synthesized with favorable functional group compatibility via deoxyalkynylation of enaminones enabled by the cooperative action of Tf2O/Pd/Cu. The reaction system demonstrated the ability to be expanded to the deoxyarylation/deoxyaryloxylation of enaminones with arylboronic acids or phenols, facilitating the efficient formation of C-C/C-O bonds and showcasing the practicality and versatility of the methodology.

Tf2O-Mediated Tandem Reaction of Enaminones for the Synthesis of Functionalized Conjugated-Enals/β-Naphthalaldehydes

A highly efficient and regioselective method for constructing functionalized conjugated enals via the Tf2O-mediated tandem reaction of enaminones with thiophenols has been described. Chain products with excellent stereoselectivity could be obtained through substrate regulation. Additionally, a feasible method for synthesizing β-naphthalaldehydes through PhSO2Na/DABCO promoting hydrogen atom transfer process has also been reported here. Mechanism studies have shown that 2-formyl vinyl triflate 8 and sulfonylated enal 9 were the key intermediates in this process.

A General Synthesis of Cross-Conjugated Enynones through Pd Catalyzed Sonogashira Coupling with Triazine Esters

The palladium-catalyzed Sonogashira coupling of α, β-unsaturated acid derivatives offers a diversity-oriented synthetic strategy for cross-conjugated enynones. However, the susceptibility of the unsaturated C-C bonds adjacent to the carbonyl group toward Pd catalysts makes the direct conversion of α, β-unsaturated derivatives as acyl electrophiles to cross-conjugated ketones rare. This work presents a highly selective C-O activation approach to prepare cross-conjugated enynones using α, β-unsaturated triazine esters as acyl electrophiles. Under base and phosphine ligand-free conditions, NHC-Pd(II)-Allyl precatalyst alone catalyzed the cross-coupling of α, β-unsaturated triazine esters with terminal alkynes efficiently, yielding 31 cross-conjugated enynones with diverse functional groups. This method demonstrates the potential of triazine-mediated C-O activation for preparing highly functionalized ketones.

Synthesis of Indolizines via Tf2O-Mediated Cascade Reaction of Pyridyl-enaminones with Thiophenols/Thioalcohols

A cost-effective, highly regioselective and metal-free version for the synthesis of indolizine derivatives by means of Tf₂O-mediated cascade reaction of pyridyl-enaminones and thiophenols/thioalcohols under mild reaction conditions has been reported. Diverse electron-rich indolizine derivatives could be obtained in up to 94% yield via the selective 1,4-addition of vinyl iminium triflate tandem cyclization/aromatization, which allowed the simultaneous construction of C-N and C-S/and one example of C-Se bonds.

Cobalt Homeostatic Catalysis for Coupling of Enaminones and Oxadiazolones to Quinazolinones

Transition metal catalysis has revolutionized modern synthetic chemistry for its diverse modes of coordination reactivity. However, this versatility in reactivity is also the predominant cause of catalyst deactivation, a persisting issue that can significantly compromise its synthetic value. Homeostatic catalysis, a catalytic process that can sustain its productive catalytic cycle even when chemically disturbed, is proposed herein as an effective tactic to address the challenge. In particular, a cobalt homeostatic catalysis process has been developed for the water-tolerant coupling of enaminones and oxadiazolones to quinazolinones. Dynamic covalent bonding serves as a mechanistic handle for the preferred buffering of water onto enaminone and reverse exchange by a released secondary amine, thus securing reversible entry into cobalt's dormant and active states for productive catalysis. Through this homeostatic catalysis mode, a broad structural scope has been achieved for quinazolinones, enabling further elaboration into distinct pharmaceutically active agents.

Ultrasound-Promoted Synthesis of α-Thiocyanoketones via Enaminone C═C Bond Cleavage and Tunable One-Pot Access to 4-Aryl-2-aminothiazoles

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.