One-Pot Synthesis of 2-Cyano-1,4-diketones: Applications to Synthesis of Cyanosubstituted Furans, Pyrroles, and Dihydropyridazines

Direct Construction of 1,4-Dihydropyridazines and Pyrazoles via Annulation of Alkyl 2-Aroyl-1-chlorocyclopropanecarboxylates

An efficient and chemodivergent synthesis of highly functionalized 1,4-dihydropyridazines and pyrazoles has been accomplished via base-promoted annulation between hydrazones and alkyl 2-aroyl-1-chlorocyclopropanecarboxylates, respectively. This transition-metal-free domino reaction proceeded rapidly under mild basic conditions, affording potentially bioactive 1,4-dihydropyridazine and pyrazole derivatives in moderate yields. The conversion of 1,4-dihydropyridazine to pyrazole was confirmed by adjusting the quantity of the base.

Electro-oxidative Synthesis of Unsymmetrical Alkyne-1,4-diones via Sequential Ring Formation and Cleavage

Synthesis of unsymmetrical but-2-yne-1,4-diones is reported through oxidative alkyne translocation of readily accessible homopropargylic alcohols. The developed method consists of an unprecedented one-pot sequential electro-oxidative annulation-fragmentation-chemical selenoxide elimination process. Excellent functional group compatibility was observed, and an array of yne-1,4-diones were synthesized. Derivatization of the alkyne gave access to other valuable scaffolds. Detailed mechanistic studies through the isolation of key intermediates clarified the cascade transformation.

Synthesis of 1,4-ketoaldehydes and 1,4-diketones by Mo-catalyzed oxidative cleavage of cyclobutane-1,2-diols

A new two-step procedure for the synthesis of 1,4-dicarbonyls has been developed involving an efficient and clean Mo-catalyzed oxidative cleavage of cyclobutane-1,2-diols with DMSO, which is used as solvent and oxidant. The required starting glycols were prepared by nucleophilic additions of organolithiums and Grignard reagents to easily available 2-hydroxycyclobutanones.

Synthesis of β-Ketonitriles via N-Heterocyclic-Carbene-Catalyzed Radical Coupling of Aldehydes and Azobis(isobutyronitrile)

Herein, an NHC (N-heterocyclic carbene)-catalyzed radical coupling reaction between aldehydes and azobis(isobutyronitrile) (AIBN) has been developed. This method provides an efficient and convenient approach for the synthesis of β-ketonitriles containing a quaternary carbon center (31 examples, up to >99% yield) utilizing commercially available substrates. This protocol features broad substrate scope, good functional group tolerance, and high efficiency under metal-free and mild reaction conditions.

Regio- and diastereoselective synthesis of unsymmetrical 1,4-diketone-derived (Z)-monosilyl enol ethers via siloxyallylpotassium intermediates

This paper describes the regio- and diastereoselective synthesis of unsymmetrical 1,4-diketone-derived (Z)-monosilyl enol ethers from 1-arylallyloxysilanes and Weinreb amides using (trimethylsilyl)methylpotassium as a base. The metalation of 1-arylallyloxysilanes to generate siloxyallylpotassiums is the key step in this transformation. The products can be transformed into diverse α-monofunctionalized unsymmetrical 1,4-diketones.

Copper‐Catalyzed 1,2‐Dicarbonylative Cyclization of Alkenes with Alkyl Bromides via Radical Cascade Process

Herein, we developed a new procedure on 1,2-dicarbonylative cyclization of 4-aryl-1-butenes with alkyl bromides. Using simple copper catalyst, two molecules of carbon monoxide were introduced into the double bond with the formation of four new C-C bonds and a new ring. Various α-tetralones and 2,3-dihydroquinolin-4-ones were formed in moderate to good yields.

Transition-metal-catalyst-free reaction of amides and acetonitriles: synthesis of β-ketonitriles

The first example of the coupling reaction between amide and acetonitrile for the synthesis of β-ketonitriles was developed. Various amides provide the corresponding β-ketonitriles in good yields.

Metal-Free Tandem Oxidative Cyclization for the Synthesis of 1,2-Dihydropyridazines and Pyrazoles

Mediated by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), a novel oxidative coupling of hydrazones and 1,3-diarylpropenes has been disclosed to generate appealing β,γ-unsaturated hydrazones, which further undergo 5-exo-trig or 6-endo-trig cascade cyclization to give the respective 1,2-dihydropyridazines or pyrazoles selectively under metal-free conditions. The mechanisms of the coupling and subsequent cyclization are proposed.

Alkyne Trifunctionalization via Divergent Gold Catalysis: Combining π-Acid Activation, Vinyl-Gold Addition, and Redox Catalysis

Here we report the first example of alkyne trifunctionalization through simultaneous construction of C-C, C-O, and C-N bonds via gold catalysis. With the assistance of a γ-keto directing group, sequential gold-catalyzed alkyne hydration, vinyl-gold nucleophilic addition, and gold(III) reductive elimination were achieved in one pot. Diazonium salts were identified as both electrophiles (N source) and oxidants (C source). Vinyl-gold(III) intermediates were revealed as effective nucleophiles toward diazonium, facilitating nucleophilic addition and reductive elimination with high efficiency. The rather comprehensive reaction sequence was achieved with excellent yields (up to 95%) and broad scope (>50 examples) under mild conditions (room temperature or 40 °C).

A Practical Synthesis of Densely Functionalized Pyrroles via a Three-Component Cascade Reaction between Carbohydrates, Oxoacetonitriles, and Ammonium Acetate

A practical three-component reaction between unactivated carbohydrates, oxoacetonitriles, and ammonium acetate gave densely functionalized pyrroles in 75-96% yields. Disaccharides afforded novel pyrrolo-glycosides. This metal-free, Et₃N-catalyzed cascade reaction proceeded with exclusive chemo-, regio-, and stereoselectivities and showed a wide substrate scope with high atom economy. It also proceeded successfully at a 2 g scale, demonstrating potential for large-scale synthesis. The functional groups on the pyrroles permit easy transformation to other handles for the construction of more complex structures. The reaction proceeded through a cascade mechanism involving several intermediates identified by mass spectrometric analysis. This work has great potential for the sustainable production of densely functionalized pyrroles from cheap and widely available carbohydrates and represents a key advancement in the sustainable synthesis of these ubiquitous heterocycles.

I2-Promoted [4 + 2] cycloaddition of in situ generated azoalkenes with enaminones: facile and efficient synthesis of 1,4-dihydropyridazines and pyridazines

A facile and efficient strategy for the synthesis of 1,4-dihydropyridazines and pyridazines through I2-promoted [4 + 2] cycloaddition of in situ generated azoalkenes with enaminones has been developed. The switch in selectivity is attributed to the judicious choice of different reaction temperatures. The key features of this work include controllable and selective synthesis, good functional group tolerance, good to excellent reaction yields, metal/base-free conditions, and also applicability to one-pot methodology.

Base-Mediated Tunable Synthesis of 2-Trifluoromethylated Furans and Dihydrofuranols: Extraordinary Stable in Sulfuric Acid

2-Trifluoromethylated furans and dihydrofuranols were tunably synthesized from the cyclization of β-ketonitriles with 3-bromo-1,1,1-trifluoroacetone mediated by bases. In addition, dehydration of dihydrofuranol compounds with concentrated sulfuric acid gave another 2-(trifluoromethyl)furans isomer. The developed methodology exhibits an excellent functional group tolerance for both aromatic and aliphatic β-ketonitriles.

One-Pot Tandem Approach to Functionalized 3-Hydroxy-2-furanyl-acrylamides

A novel one-pot tandem process involving Knoevenagel condensation, Michael addition, selective amidation, and Paal-Knorr cyclization to diverse functionalized 3-hydroxy-2-furanyl-acrylamides from simple 2-oxoaldehydes and aroylacetonitriles was presented. Attempts were also made to expand the scope of the reaction to different 2-heteroarylfurans. The packing diagram of the molecules viewed down along the α-axis of the unit cell showed a characteristic intramolecular classical O-H···O hydrogen bond between hydroxyl and carbonyl O atoms leading to self-associated (Z)-2-furanyl-acrylamides.

Copper-Promoted 6- endo-trig Cyclization of β,γ-Unsaturated Hydrazones for the Synthesis of 1,6-Dihydropyridazines

A novel and efficient strategy for the synthesis of 1,6-dihydropyridazines via copper-promoted 6- endo-trig cyclization of readily available β,γ-unsaturated hydrazones have been developed. A series of 1,6-dihydropyridazines have been synthesized by this method with good yields, high functional group tolerance, and remarkable regioselectivity under mild conditions. Importantly, the 1,6-dihydropyridazines can be efficiently converted to biologically important pyridazines in the presence of NaOH.

Synthesis and characterization of poly(ethene–ketone–arylene–ketone)s containing pendant methylthio groups via metal-free catalyzed copolymerization of aryldiynes with DMSO

A metal-free copolymerization of aryldiynes with DMSO as a monomer gave polyeneketones in good yields and high molecular weight.