Intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)cyclohexane induced by N-heterocyclic carbene and thiourea

Intermolecular Stetter reaction of aromatic aldehydes with (E)-(2-nitrovinyl)cyclohexane catalyzed by thiazolium A has been developed. The reaction rate and efficiency are profoundly impacted by the presence of thiourea B. The reaction affords moderate to good yields of the Stetter product. Some factors influencing yield were discussed.     

N-heterocyclic carbene-catalysed intermolecular Stetter reactions of acetaldehyde

A facile method for the intermolecular Stetter reaction of various Michael acceptors with acetaldehyde as a biomimetic acylanion source was realized using N-heterocyclic carbene catalysis. This catalytic system has also been applied to the enantioselective Stetter reaction and resulted in moderate to good enantioselectivities for the corresponding Stetter products.     

Catalytic asymmetric intermolecular Stetter reaction of glyoxamides with alkylidenemalonates

An asymmetric intermolecular Stetter reaction of glyoxamide and alkylidenemalonates has been developed. Catalyzed by a novel N-heterocyclic carbene, the Stetter adducts are formed in good yield and excellent enantioselectivity. The presence of a sensitive epimerizable stereocenter is tolerated under these mildly basic reaction conditions if a bulky amine base is used. The products may be further elaborated to provide synthetically useful intermediates.     

Isa‒NHC‒catalyzed intermolecular Stetter reaction of aromatic aldehydes with maleimides: An efficient access to 3‒aroylsuccinimides

An intermolecular Stetter reaction of aromatic aldehydes with maleimides has been developed using thiazolylidene salt derived Isa?NHC as an efficient organocatalyst. The synthesized Stetter products “3?aroylsuccinimides” are important building blocks for the synthesis of natural products and bioactive compounds. The reaction conditions are mild, and various substituents on aromatic aldehyde and maleimide nitrogen were tolerated.     

Synthesis of (1R,2R)-DPEN-derived triazolium salts and their application in asymmetric intramolecular Stetter reactions

A series of novel chiral triazolium salts has been synthesized from readily available (1R,2R)-DPEN and found to be efficient for the enantioselective intramolecular Stetter reaction. With 10 mol% of the catalyst, the intramolecular Stetter reaction was realized in excellent yields with up to 97% ee.     

The effect of pre-existing stereocenters in the intramolecular asymmetric Stetter reaction

A series of disubstituted cyclopentanones have been synthesized by the intramolecular Stetter reaction. Racemic substrates containing one chiral center were used, allowing us the opportunity to observe a parallel kinetic resolution in the synthesis of 2,3- and 2,4-disubstituted cyclopentanones. The Stetter reaction of 2,5-disubstituted cyclopentanones proved to be substrate controlled, resulting in the selective formation of the cis-diasteromers with low ee.     

Scope of the asymmetric intramolecular stetter reaction catalyzed by chiral nucleophilic triazolinylidene carbenes

A highly enantioselective intramolecular Stetter reaction of aromatic and aliphatic aldehydes tethered to different Michael acceptors has been developed. Two triazolium scaffolds have been identified that catalyze the intramolecular Stetter reaction with good reactivity and enantioselectivity. The substrate scope has been examined and found to be broad; both electron-rich and -poor aromatic aldehydes undergo cyclization in high yield and enantioselectivity. The tether can include oxygen, sulfur, nitrogen, and carbon linkers with no detrimental effects. In addition, the incorporation of various tethered Michael acceptors includes amides, esters, thioesters, ketones, aldehydes, and nitriles. The catalyst loading may be reduced to 3 mol % without significantly affecting the reactivity or selectivity of the reaction.     

A highly enantio- and diastereoselective catalytic intramolecular Stetter reaction

A highly enantio- and diastereoselective intramolecular Stetter reaction has been developed. Subjection of alpha,alpha-disubstituted Michael acceptors to an asymmetric intramolecular Stetter reaction results in a highly enantioselective conjugate addition and a diastereoselective proton transfer. Available evidence suggests the diastereoselective protonation occurs via intramolecular delivery to the sterically more hindered face of the enolate. The scope of the trisubstituted Michael acceptors has been examined and found to be broad with respect to the size of the alpha-substituent and nature of the Michael acceptor. Aliphatic and aromatic aldehydes were examined and found to afford the desired product in good overall yield with high enantio- and diastereoselectivity.     

Heterocyclic alpha-alkylidene cyclopentenones obtained via a Pauson-Khand reaction of amino acid derived allenynes. A scope and limitation study directed toward the preparation of a tricyclic pyrrole library

The synthesis of a novel class of tricyclic pyrroles has been accomplished by using a Pauson-Khand/Stetter/Paal-Knorr reaction sequence. Full details of the Pauson-Khand reaction of amino acid tethered allenynes 4a-e and 9a-d are disclosed. The study of this reaction led to the discovery of an unprecedented substituent effect on the diastereoselectivity of the Mo(CO)6 mediated allenic Pauson-Khand reaction. It was found that amino acid tethered allenynes with aromatic side chains afford alpha-alkylidene cyclopentenones with the opposite diastereoselectivity compared to those with aliphatic side chains. This effect has been attributed to complexation of the metal mediator to the aromatic ring in the substrate. Furthermore, an isomerization of one of the diastereomers of the alpha-alkylidene cyclopentenones was encountered, leading to eventual decomposition. The stable diastereomers were found to react well in the Stetter reaction leading to 1,4-diketones that were converted to pyrroles. The observation that the first generation of 2-alkyl-substituted pyrroles was unstable led to a second generation of 2-carboxamide pyrroles with sufficient stability for biological tests which are in progress.     

Synthesis of thermoregulated phase-separable triazolium ionic liquids catalysts and application for Stetter reaction

A series of polyether-substituted triazolium ionic liquids catalysts have been first synthesized for resolving the problem of separation and reuse of Stetter catalysts. The catalysts possess the properties of critical solution temperature (CST) and inverse temperature-dependent solubility in toluene/heptane solvents. Based on these properties, the catalysts can achieve the catalytic process named as thermoregulated phase-separable catalysis (TPSC) with the characteristic of homogeneous reaction at higher temperature and phase-separation at lower temperature. The novel TPSC system has been successfully applied for Stetter reaction of furfural or butanal with ethyl acrylate. The experimental results have showed that the novel catalysts exhibit excellent TPSC with high recycling efficiency.     

Enantioselective formation of quaternary stereocenters using the catalytic intramolecular Stetter reaction

Asymmetric formation of quaternary stereocenters has been accomplished using the catalytic intramolecular Stetter reaction. A variety of tethered aldehydes and Michael acceptors are cyclized in excellent yields and enantioselectivities.     

Enantioselective synthesis of quaternary stereocenters via a catalytic asymmetric Stetter reaction

A new electron-deficient chiral triazolium salt has been shown to catalyze the formation of quaternary stereocenters by an asymmetric intramolecular Stetter reaction. Pentafluorophenyl substitution on an aminoindanol-derived catalyst affords tertiary ether, thioether, and quaternary stereocenters in typically greater than 90% ee and very good chemical yield. Aromatic and aliphatic aldehydes are equally competent substrates for this reaction. The reaction proceeds at room temperature under mild conditions to provide quaternary stereocenters with functional group relationships that are particularly difficult to access by other methods.     

A formal total synthesis of roseophilin: cyclopentannelation approach to the macrocyclic core

[formula: see text] The formal total synthesis of the macrocyclic core of roseophilin 4 has been accomplished in 12 steps from 5-hexenal 8. The cyclopentannelation reaction was used to form the aliphatic five-membered ring of 3. Diene 2 was assembled by means of a Stetter reaction. Ring-closing metathesis of 2, reduction, and Knorr reaction of the 1,4-diketone 5 gave the ketopyrrole 3.     

Investigation of the electro-oxidation and oxidation of catechol in the presence of sulfanilic acid

The electrochemical oxidation of catechol (1) in the presence of sulfanilic acid (2) was investigated. Some electrochemical (EC) techniques such as cyclic voltammetry and controlled-potential coulometry were used. The oxidation reaction of catechol (1) with periodate in the presence of sulfanilic acid (2) was also investigated spectrophotometrically. The results indicate that the o-quinone derived from catechol participate in Michael addition reaction with sulfanilic acid (2). In addition, according to the ECE mechanism, the observed homogeneous rate constant (k_obs) for the reaction of o-quinone derived from catechol (1) with sulfanilic acid (2) has been estimated by digital simulation of cyclic voltammograms.     

A peptide-catalyzed asymmetric Stetter reaction

Thiazolylalanine, in appropriately functionalized form, has been found to function as an enantioselective catalyst for an intramolecular Stetter reaction. Incorporation of the residue in a number of environments has resulted in a family of catalysts that promote the cyclization of a test substrate with up to 81% enantiomeric excess.     

Catalytic asymmetric stetter reaction onto vinylphosphine oxides and vinylphosphonates

An intramolecular Stetter reaction of vinylphosphine oxides and vinylphosphonates has been developed. Treatment of an aldehyde with a nucleophilic N-heterocyclic carbene catalyst allows for addition of an acyl anion equivalent into a vinylphosphine oxide or vinylphosphonate Michael acceptor in yields up to 99% and ee values up to 96%.     

A highly enantioselective catalytic intramolecular Stetter reaction

A family of chiral triazolium salts has been developed for inducing the asymmetric intramolecular Stetter reaction. The use of an aminoindanol-derived catalyst affords optimal results, with the product keto esters formed in 82-97% ee and very good chemical yield. Aromatic and aliphatic aldehydes are equally competent substrates for this reaction. The reaction conditions are reasonably mild and allow the isolation of the newly formed stereocenter without epimerization, although the presumed carbenic intermediates are strong bases.     

Efficient synthesis of benzofuranones: N-heterocyclic carbene (NHC)/base-catalyzed hydroacylation-Stetter-rearrangement cascade

A N-heterocyclic carbene/base-catalyzed cascade reaction leading to the formation of functionalized benzofuranones is reported. The reaction proceeds via an intramolecular hydroacylation of unactivated alkynes followed by an intermolecular Stetter reaction and a base-catalyzed chromanone to benzofuranone rearrangement.     

纳米铂修饰玻碳电极对邻苯二酚的电化学氧化及测定

应用循环伏安法研究了邻苯二酚在纳米铂修饰玻碳(PtNPs/GC)电极上的电化学氧化行为。实验表明,PtNPs/GC电极对邻苯二酚有很强的电催化作用,其伏安扫描氧化峰电流随着温度的升高而增大,但氧化峰电位略有负移。常温下,邻苯二酚能自发在电极表面发生聚合反应,生成具有导电性的聚合膜,其催化氧化电流与邻苯二酚浓度在1.0×10-6mol/L~5.0×10-5mol/L范围内呈良好的线性关系,检出限为2.9×10-7mol/L。     

CHEMISTRY OF SINGLET OXYGEN—48. ISOLATION and STRUCTURE OF THE PRIMARY PRODUCT OF PHOTOOXYGENATION OF 3,5-DI-t-BUTYL CATECHOL

The dye-sensitized photooxygenation of t -butyl substituted catechols has been investigated. The primary product from 3,5-di- t -butyl catechol has been isolated and shown to be a hydroperoxydienone by single crystal X-ray diffraction. The absence of sensitizer effects and the faster reaction rate in polar solvents suggest that the reaction proceeds with singlet oxygen as the primary oxygenating species. Charge-transfer or full electron-transfer from the catechol to singlet oxygen is probably involved. Substituent effects are in agreement with this mechanism. The products from thermal breakdown of the hydroperoxydienone are inconsistent with a Baeyer-Villiger mechanism.