Electron-deficient Alkynes Research Articles

Decarboxylative olefination of potassium benzoates via bimetallic catalysis strategy

A novel synthesis of styrene derivatives through decaroxylative olefination of potassium benzoates with alkynes using Pd2dba3/CuBr as catalyst system has been developed. The protocol proceeded smoothly and in most cases Z-alkene was the main product. Electron-rich potassium benzoates reacted more efficiently than those of electron-deficient substrates. Heteroaromatic and electron-deficient aryl alkynes were not consistent with this transformation.

Direct Regioselective [3 + 2] Cycloaddition Reactions of Masked Difluorodiazoethane with Electron-Deficient Alkynes and Alkenes: Synthesis of Difluoromethyl-Substituted Pyrazoles

Phenylsulfone difluorodiazoethane (PhSO2CF2CHN2), an easy-to-prepare and bench-stable masked CF2-building block, has been developed. The synthetic utility of this reagent is demonstrated by a direct regioselective [3 + 2] cycloaddition with electron-deficient alkynes and alkenes. This protocol enables facile construction of an array of difluoromethyl-substituted pyrazoles in good to high yields under mild reaction conditions.

Inorganic base-mediated stereoselective hydroamination of arylalkynes with imidazole: An efficient access to N-vinylimidazoles

A metal-free inorganic base-mediated highly stereoselective hydroamination of arylalkynes with imidazoles has been developed, and the corresponding N-vinylimidazoles were obtained in good yields and with moderate to excellent stereoselectivities (up to 99:1). For the electron rich alkynes, the reaction system of CsOH·H2O/NMP/140 °C led to the predominant formation of E-addition products, while the reaction system of KOH/NMP/90 °C afforded the Z-isomers as the major product. The electron deficient alkynes furnished predominantly the E-addition products in both reaction systems. This study essentially provides a general and an efficient protocol for the synthesis of E-isomer of the N-vinylimidazoles.

Benzocyclobutadienes: An Unusual Mode of Access Reveals Unusual Modes of Reactivity.

The reaction of an aryne with an alkyne to generate a benzocyclobutadiene (BCB) intermediate is rare. We report here examples of this reaction, revealed by Diels-Alder trapping of the BCB by either pendant or external electron-deficient alkynes. Mechanistic delineation of the reaction course is supported by DFT calculations. A three-component process joining the benzyne first with an electron-rich and then with an electron-poor alkyne was uncovered. Reactions in which the BCB functions in a rarely observed role as a 4π diene component in Diels-Alder reactions are reported. The results also shed new light on aspects of the hexadehydro-Diels-Alder reaction used to generate the benzynes.

Gold-Catalyzed Hydrofluorination of Electron-Deficient Alkynes: Stereoselective Synthesis of β-Fluoro Michael Acceptors.

The gold(I)-catalyzed, stereoselective hydrofluorination of electron-deficient alkynes with triethylamine trihydrogen fluoride (Et3N·3HF) is described. Fluorinated α,β-unsaturated aldehydes, amides, esters, ketones, and nitriles were isolated in moderate to good yields as single diastereomers. In all but four cases, the (Z)-vinyl fluorides were initially formed in ≥97% diastereoselectivity. This work constitutes the first catalytic example of the diastereoselective preparation of a variety of β-alkyl, β-fluoro Michael acceptors from alkynes. Additionally, the described work expands access to β-aryl, β-fluoro Michael acceptors to the synthesis of β-fluoro-α,β-unsaturated amides and nitriles. The monofluoroalkenes formed through this strategy were readily transformed into other fluorine-containing compounds, and the developed method was applied to the synthesis of a fluorinated analogue of Exoderil, a topical antimycotic.

PPh3 Mediated Stereoselective Synthesis of 4‐Fumarate Substituted 3‐AcylCoumarins: A Cascade Reaction of 3‐Acyl Coumarin with Alkyne Derivatives

AbstractA novel strategy has been developed for the stereoselective synthesis of 4‐fumarate substituted 3‐acyl coumarins. The cascade reaction between electron deficient alkynes like dialkylacetylenedicarboxylates and 3‐acyl coumarin has been achieved in presence of triphenylphosphine. This methodology offers an efficient one‐pot access to a new class of 4‐fumarate substituted 3‐acyl coumarins in high yields under mild reaction condition. The reaction proceeds in a highly stereoselective manner.

Regio- and stereoselective reaction of 3-fluoropyridine, electron-deficient alkynes and bis(fluoroalkyl) phosphites: Catalyst- and solvent-free synthesis of polyfluoroalkylphosphonylated 3-fluoro-1,2-dihydropyridines

The catalyst- and solvent-free reaction between 3-fluoropyridine, electron-deficient alkynes and bis(fluoroalkyl) phosphites occurs under mild conditions (20–22 °C, 1–8.5 h) to stereo- and regioselectively afford 2-bis(polyfluoroalkoxy)phosphoryl- (E)-N-ethenyl-3-fluoro-1,2-dihydropyridines in 53–69% yield.

Thermally induced formal [4+2] cycloaddition of 3-aminocyclobutenones with electron-deficient alkynes: facile and efficient synthesis of 4-pyridones.

A thermally induced novel formal [4+2] cycloaddition of cyclobutenones with electron-deficient alkynes under metal-free conditions has been developed for the first time. The reaction can proceed in a highly regioselective manner and provides a straightforward and efficient method for the synthesis of 4-pyridone derivatives from readily available starting materials in a single step.

Functionalized geminal-diborylalkanes from various electron-deficient alkynes and B2pin2

An environmentally benign and convenient method is developed to access a variety of functionalized geminal-diborylalkanes from various electron-deficient alkynes and B2pin2 with the DBP (Domino-Borylation–Protodeboronation) strategy.

Transition metal-free one-pot double C-H functionalization of quinolines with disubstituted electron-deficient acetylenes.

Transition metal-free one-pot reaction of quinolines with acylarylacetylenes and water proceeds in the presence of KOH (55-60 °C, MeCN, 48 h) to afford 2-aryl-3-acylquinolines in up to 66% yield. Here, a formal replacement of the acetylene moiety by the aryl and acyl substituents in the quinoline scaffold takes place. In fact, it has been proved experimentally that the reaction involves the ring cleavage, accompanied by the rearrangement and insertion of the electron-deficient acetylene moiety to form a dihydroquinoline intermediate with an aldehyde functional group in position 4. This intermediate gives the corresponding doubly functionalized quinolines.

Iodine-promoted stereoselective amidosulfenylation of electron-deficient alkynes.

Iodine-promoted three-component synthesis of substituted β-amino sulfides has been developed starting from a propargyl ester, aliphatic secondary amine, and disulfide. This protocol provides a step-economic and highly regioselective entry to trisubstituted olefins with good substrate scope and functional group tolerance.

Ring opening in 1,2,3,4-tetrahydrochromeno[3,2-c]pyridines under the action of electron-deficient alkynes

2-Vinyl substituted chromones were obtained by the reaction between 1,2,3,4-tetrahydrochromeno[3,2-c]pyridines and electron-deficient alkynes.

Rhodium-Catalyzed Chemo- and Regioselective Intermolecular Cross-Cyclotrimerization of Nonactivated Terminal and Internal Alkynes.

It has been established that a cationic rhodium(I)/BIPHEP complex is able to catalyze the unprecedented intermolecular cross-cyclotrimerization of nonactivated terminal and internal alkynes at room temperature. In this transformation, the use of arylacetylenes as terminal alkynes and 1,4-butynediol derivatives as internal alkynes afforded the cross-cyclotrimerization products with good chemo- and regioselectivity. The present study clearly demonstrated that an electronically biased combination of nonactivated and electron-deficient alkynes is not necessary to realize good chemo- and regioselectivity in the cationic rhodium(I) complex-catalyzed intermolecular cross-cyclotrimerization.

Direct [3+2]-cycloaddition of electron-deficient alkynes with CF3CHN2: Regioselective one-pot synthesis of 3-trifluoromethylpyrazoles

A direct and facile cycloaddition reaction of electron-deficient terminal alkynes with 2,2,2-trifluorodiazoethane under mild conditions to afford a series of 5-substituted 3-trifluoromethylpyrazoles in high yields is described. The potential application of this cycloaddition reaction was demonstrated via the efficient synthesis of a key intermediate of the antiviral drug AS-136A and a fluorinated analog of Tebufenpyrad.

Silver-catalyzed chemoselective annulation of propargyl amines with alkynes for access to pyridines and pyrroles

The annulation of propargyl amines with electron-deficient alkynes in the presence of silver salts affording pyridines and pyrroles has been developed. The chemoselective [4+2] or [3+2] annulation approach to pyridines or pyrroles depends on the structures of propargyl amines and the different reaction conditions.

Gold-Catalyzed [4+2] Annulation/Cyclization Cascades of Benzisoxazoles with Propiolate Derivatives to Access Highly Oxygenated Tetrahydroquinolines.

This work describes gold-catalyzed annulations of electron-deficient alkynes with benzisoxazoles to yield quinoline oxides chemoselectively. Chemical functionalizations of these resulting azacyclic compounds afforded various oxygenated tetrahydroquinolines which are present as the cores of many bioactive molecules. With the same reactants, a new relay catalysis using gold and zinc(II) catalysts affords highly oxygenated tetrahydroquinoline derivatives stereoselectively.

Reactivity of Seven-Membered-Ring trans-Alkenes with Electrophiles

Seven-membered-ring trans-alkenes containing a silicon–oxygen bond reacted rapidly with oxygen gas and electron-deficient alkenes and alkynes to give products with high selectivity. Addition of an electron-donating substituent or incorporating additional strain increased the reactivity by over two orders of magnitude. These results indicate that release of strain is not the only driving force for reactivity.

Phosphazene Catalyzed Addition to Electron-Deficient Alkynes: The Importance of Nonlinear Allenyl Intermediates upon Stereoselectivity.

An ONIOM(QM/MM) study on the mechanism of the Michael addition to triple bonds catalyzed by chiral diiminophosphorane catalysts has been performed to understand the stereoselectivity of the product olefin. Our results are consistent with the experimental enantioselectivity, but more importantly, reveal that the Z vs E preference depends on the influence of the catalyst upon the geometry of the allenyl enolate formed in the addition step. These intermediates show an innate preference for a (Z)-configuration, although this can be suppressed by steric interactions due to a catalyst. This leads to two distinct mechanisms in which the kinetic basis for (E) or (Z)-stereoselectivity is determined by a different step. Bifunctional iminophosphorane catalysts are found to use steric interactions to override innate stereoelectronic effects of the allenyl enolate reactive intermediate.

Microwave-assisted synthesis and crystal structure of some novel 1,2,4-oxadiazol-5-ylmethyl-1,2,3-triazoles

ABSTRACTMicrowave-assisted 1,3-dipolar cycloaddition of 5-azidomethyl 3-aryl-substituted 1,2,4-oxadiazoles to electron-deficient alkyne; phenyl propiolic acid affords a series of 1,2,3-triazole derivatives carrying 3-p-substitutedphenyl-1,2,4-oxadiazolyl methyl unit. The structures of all the cycloadducts were elucidated by IR, NMR (1H, 13C, 2D), MASS (low and high resolution) spectra, X-ray diffraction data, and physical characteristics (melting points and Rf values).

Physicochemical properties and antimicrobial activity of new spirocyclic thieno[2,3-d]pyrimidin-4(3H)-one derivatives

A number of 6'-methylidene-2,3-dihydro-1H-spiro[pyridine-4,5'-thieno[2,3-d]pyrimidin]-4'(3'H)-one derivatives, obtained as major products of a domino reaction between 5,6,7,8-tetrahydropyrido[4',3':4,5]thieno[2,3-d]pyrimidines and electron-deficient alkynes, were characterized for their acid-base properties and lipophilicity and evaluated for the antimicrobial activity against a number of clinical isolates of bacterial and fungal strains. The cytotoxicity against four tumor cell lines was also screened for some compounds. The dissociation constants (pK a) and partition coefficients (log P) in 1-octanol–water system were determined using a potentiometric technique. The negative difference between the observed and calculated log P values could be explained in the light of the conformational rigidity. Most of the studied compounds showed a moderate and selective activity against Gram-positive bacteria strains (S. agalactiae, E. faecalis, S. epidermidis), whereas did not exhibit any effect against Gram-negative bacteria and fungi at the maximum test concentration (500 μM). Implications of the physicochemical properties in modulating the antimicrobial activity and cytotoxicity of the examined spirocyclic thieno[2,3-d]pyrimidin-4(3H)-one derivatives are also discussed.