One-Pot Reaction of Carboxylic Acids and Ynol Ethers for The Synthesis of β-Keto Esters

Phototriggered Generation of Ynol Ethers and Their Rearrangement to Ketenes

This study developed reactions for the phototriggered generation of reactive ynol ethers using alkoxycyclopropenones. The resulting ynol ethers underwent rearrangement to ketenes, which subsequently participated in cycloaddition with alkynes and the acylation of amines. The alkoxy groups in the ynol ethers significantly influenced on the reactivity toward their rearrangement to ketenes. Reasonable transition state structures for the rearrangement reaction were found through density functional theory calculations, and the reactivity of the ynol ethers could be predicted by these calculations.

Gold-Catalyzed Regio- and Stereoselective α-Acyloxy-β-Alkynylation of Ynol Ethers

Enol esters and conjugated enynes are valuable structural motifs for synthetic chemistry and material sciences. Herein, the synthesis of tetra-substituted enol ester 2-iodobenzoate derivatives was achieved in good yields at room temperature through a gold-catalyzed acyloxyalkynylation of sensitive ynol ethers with ethynylbenziodoxolones (EBXs), the latter acting as bifunctional reactants. The conversion is highly regioselective with a broad substrate scope. Mechanistically, an Au(III) species is the key intermediate of an Au(I)/Au(III) redox cycle. The reaction is synthetically useful and can easily be scaled up to gram scale.

Ag2O versus Cu2O in the Catalytic Isomerization of Coordinated Diaminocarbenes to Formamidines: A Theoretical Study

DFT theoretical calculations for the Ag₂O-induced isomerization process of diaminocarbenes to formamidines, coordinated to Mn(I), have been carried out. The reaction mechanism found involves metalation of an N-H residue of the carbene ligand by the catalyst Ag₂O and the formation of a key transition state showing a μ-η²:η² coordination of the formamidinyl ligand between manganese and silver, which allows a translocation process of Mn(I) and silver(I) ions between the carbene carbon atom and the nitrogen atom, before the formation of the formamidine ligand is completed. Calculations carried out using Cu₂O as a catalyst instead of Ag₂O show a similar reaction mechanism that is thermodynamically possible, but highly unfavorable kinetically and very unlikely to be observed, which fully agrees with experimental results.

Copper-Promoted Conjugate Addition of Carboxylic Acids to Ethenesulfonyl Fluoride (ESF) for Constructing Aliphatic Sulfonyl Fluorides

A CuO-promoted direct hydrocarboxylation of ethenesulfonyl fluoride (ESF) was developed using carboxylic acid as a nucleophile under mild conditions. A variety of molecules containing both ester group and aliphatic sulfonyl fluoride moiety exhibit great potential in medicinal chemistry and chemical biology. Furthermore, the modification of the known drugs Ibuprofen and Aspirin was also demonstrated.

Iridium(III)-Catalyzed C−H Functionalization of Triarylphosphine Oxides with Diazo Dicarbonyl Compounds: Synthesis of α-Aryl 1,3-Dicarbonyl Derivatives

A novel (pentamethylcyclopenta-1,3-dienyl)iridium(III)-catalyzed direct C–H functionalization of triarylphosphine oxides with diazo dicarbonyl compounds through carbene insertion has been developed. This strategy provides a simple and efficient route to the construction of α-arylated 1,3-dicarbonyl compounds, which are important building blocks in pharmaceutical chemistry.

Synthetic Scope of Brønsted Acid-Catalyzed Reactions of Carbonyl Compounds and Ethyl Diazoacetate

The comprehensive study of the reactions of carbonyl compounds and ethyl diazoacetate in the presence of a Brønsted acid catalyst is described. In result, a broad range of 3-oxo-esters were synthesized from a variety of ketones and aliphatic aldehydes by 1,2-aryl/alkyl/hydride shift. Aryl-methyl ketones produced only aryl-migrated products, whereas other ketones yielded a mixture of products. For diaryl ketones, the identity of two inseparable migrated products was confirmed by two-dimensional NMR spectroscopy.

Directing-Group-Enabled Cycloaddition of Azides and Alkynes toward Functionalized Triazoles

Herein, we report a directing-group-enabled Huisgen cycloaddition of azides and alkynes for the synthesis of functionalized triazoles in which the triazene group could act as a directing group to enable this regioselective [3 + 2] cycloaddition and further replacement by diverse groups, including amino, amide, halogen, and heterocycle substituents. This method represents a general and practical synthesis of triazoles under mild reaction conditions and broad substrate scope.

Iridium(i)-catalyzed hydration/esterification of 2-alkynylphenols and carboxylic acids

A mild and efficient iridium(i)-catalyzed hydration/esterification of 2-alkynylphenols and carboxylic acids has been successfully developed.

One-Pot Reaction of Carboxylic Acids, Ynol Ethers, and m-CPBA for Synthesis of α-Carbonyloxy Esters

A novel one-pot reaction of carboxylic acids, ynol ethers, and m-CPBA for the synthesis of α-carbonyloxy esters in the presence of Ag₂O is described. This process provides a direct approach to α-carbonyloxy esters with the achievement of formation of three C-O bonds. The protocol is featured with readily available starting materials and broad substrate scope. Control reactions and isotope-labeling reactions were conducted to elucidate a plausible mechanism.

Quick construction of a C–N bond from arylsulfonyl hydrazides and Csp2–X compounds promoted by DMAP at room temperature

A mild C–N coupling reaction with arylsulfonyl hydrazides and 2(5H)-furanones shows good yields, excellent reaction regioselectivity and functional group tolerance.