Preparation of 2,5-disubstituted oxazoles from N-propargylamides

[reaction: see text] 2,5-Disubstituted oxazoles have been prepared through the reaction of N-propargylamides with aryl iodides in the presence of Pd(2)(dba)(3), tri(2-furyl)phosphine, and NaO(t)()Bu. The reaction appears to proceed through a palladium-catalyzed coupling step followed by the in situ cyclization of the resultant coupling product.     

Copper(II)-mediated oxidative cyclization of enamides to oxazoles

The copper(II)-mediated oxidative cyclization of enamides to oxazoles is reported. A range of 2,5-disubstituted oxazoles were prepared in moderate to good yields in two steps from simple amide and alkyne precursors.     

Sequential copper-catalyzed vinylation/cyclization: an efficient synthesis of functionalized oxazoles

A modular and practical synthesis of highly substituted oxazoles has been developed. The transformation consists of a sequential copper-catalyzed amidation of vinyl halides followed by cyclization promoted by iodine. A wide variety of functionalized oxazoles and polyazoles can be obtained in a selective manner from simple and easily accessible precursors.     

Synthesis of 2,4- and 2,4,5-substituted oxazoles via a silver triflate mediated cyclization

2,4- and 2,4,5-substituted oxazoles were prepared from a broad range of bromo-ketones and amides in high yield and purity.     

TBHP/I2-mediated domino oxidative cyclization for one-pot synthesis of polysubstituted oxazoles

A facile type of one-pot, transition-metal-free domino process was developed for the synthesis of oxazoles. Thus, a variety of polysubstituted oxazoles were easily synthesized via t-BuOOH/I(2)-mediated domino oxidative cyclization from readily available starting materials under mild conditions.     

Gold- and silver-mediated cycloisomerizations of N-propargylamides

Substituted N-propargylamides have proven to be valuable substrates for alkyne-activated cycloisomerization reactions. N-Tosyl- N'-propargylurea underwent reaction with AuCl 3 to give the corresponding dihydroimidazolone, while N-propargyl-3-oxobutanamides and esters were used to construct furanyl fused pyrrolidinones and dihydrofuranones via Ag(I)-mediated alkyne activation.     

Unexpected intramolecular nucleophilic cyclization of ureidoacetamide: A novel route towards the synthesis of 2,4,5-trisubsituted oxazoles

A variety of N, 2-diaryl-2-ureidoacetamide prepared from the condensation of N-aryl-α-aminoamide with potassium cyanate (KOCN) undergo efficient Hendrickson’s reagent-mediated nucleophilic cyclization to afford 2,5-diamine-4-aryloxazoles. The two-step synthesis provides seven target products in yields of 61–78% under mild conditions. This reaction involves an unusual pathway in which the electrophilic amide carbonyl carbon is activated by Hendrickson’s reagent and attacked by a nucleophilic ureido oxygen in a 5-exo-trig O-cycloisomerization.     

Base-Catalyzed Autocondensation of Cyclohexanone

Autocondensation of cyclohexanone in air at 119-137°C, catalyzed with a solid alkali, was studied.     

Direct arylation of oxazoles at C2. A concise approach to consecutively linked oxazoles

The synthesis of bis- and trisoxazoles via direct arylation is discussed. A variety of aryl groups can be installed at the 2-position of 5-aryl and 5-carboxy-substituted oxazoles under mild conditions using palladium catalysis on water. The direct arylation method can be extended to the synthesis of bis- and trisoxazoles if 2-triisopropylsilyl-4-iodooxazole is used as the electrophile in the arylation.     

Studies of oxazoles

Mercuration of oxazole derivatives is studied. As a result mono- and disubstituted mercury derivatives, hitherto not described in the literature, are obtained. The ability of the oxazole ring to undergo mercuration decreases in the order C-5>C-4 C-2. It is shown that phenyl-substituted oxazoles are mercurated solely, or mainly at least, at an unsubstituted carbon atom in the heterocyclic ring, actual phenyl substituents in the oxazoles remaining inert towards mercuration.     

Base-Catalyzed Keto-Enol Tautomerism of Diazepam

The hydrogens at 3-position of diazepam, a frequently prescribed anxiolytic drug worldwide, undergo an efficient exchange with deuterium atoms in alkaline deuterated methanol. The position of deuterium exchange is confirmed by proton nuclear magnetic resonance and mass spectral analyses. A base-catalyzed keto-enol tautomerism is proposed to be responsible for the observed deuterium exchange. This finding has been applied to the preparation of tritium-labeled diazepam in which only aromatic protons are labeled with tritium atoms. A tritium-labeled diazepam lacking tritium atoms at 1 and 3 positions is valuable as a substrate for quantitative metabolism studies.     

Base-Catalyzed Reaction of Cyanoalkylphosphonates with Methanol

The equilibrium conversion of nitriles in the reaction of cyanoalkylphosphonates with methanol in the presence of sodium methylate, as determined by potentiometric titration with perchloric acid in nitromethane, varies from 58 to 17.7%. The practical yields of imidates were evaluated by a preparative procedure of isolation of purified imidates from the reaction mixtures (56-14%). Because of the low conversions of nitriles, the reaction is expedient to use only for preparing alkyl (dialkoxyphosphoryl)acetimidates.     

甾酮类化合物的碱催化自氧化反应的研究

酮类化合物的碱催化自氧化反应受底物的结构和反应条件的影响较大。不同的底物或不同的反应条件,可得不同类型的产物。在油菜甾醇内酯 B 环的合成中,曾探索了用该反应来合成内酯环。本文报道一些与三元环共     

Cycloaddition of fluorinated oxazoles

Cycloaddition reactions of polyfluorinated 1,3-oxazoles with cyclic and acyclic alkenes were studied. The results of these reactions were interpreted using quantum chemical calculations. An unusual product, viz., fluorine-containing acylpyrrole, was studied by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1630–1635, July, 2005.     

Pyrroles from oxazoles

The review is devoted to the transformation of oxazoles (including those with cationoid and mesoionic structures) into compounds of the pyrrole series.     

Researches on oxazoles

Bromine, and, for the first time, iodine, are inserted at various positions in the 1, 3-oxazole ring by halogenating mercury derivatives of oxazole. Thus, unlike what is obtained by direct halogenation, halogen derivatives of oxazole are available independently of alkyl or phenyl substituents already present in the ring. Direct halogenation of phenyl-substituted oxazoles is reviewed, and in this connection 2, 4-diphenyloxazole is brominated directly. -Bromo derivatives of 1, 3-oxazole are also synthesized.For Part I see [1].     

Suzuki coupling of oxazoles

A protocol for the functionalization of the oxazole 2- and 4-positions using the Suzuki coupling reaction is described. 2-Aryl-4-trifloyloxazoles undergo rapid, microwave-assisted coupling with a range of aryl and heteroaryl boronic acids in good to excellent yields. The methodology is similarly effective using 4-aryl-2-chlorooxazoles as the coupling partner and has been extended to the synthesis of a novel class of homo- and heterodimeric 4,4-linked dioxazoles. [reaction: see text]     

New four-component condensations leading to 2,4,5-trisubstituted oxazoles

A one-pot reaction leading to the title compounds has been developed based on the in situ acylation and hydroxyarylation of 5-aminooxazoles at the 4-position of the heterocycle.