Copper-catalyzed aerobic oxidative amidation of terminal alkynes: efficient synthesis of ynamides

A copper-catalyzed method for the preparation of ynamides has been identified that proceeds via aerobic oxidative coupling of terminal alkynes with various nitrogen nucleophiles, including cyclic carbamates, amides and ureas, and N-alkyl-arylsulfonamides and indoles.     

Intramolecular "hydroiminiumation and -amidiniumation" of alkenes: a convenient, flexible, and scalable route to cyclic iminium and imidazolinium salts

Addition of a stoichiometric amount of HCl to alkenylaldimines, -formamidines, and -amidines results in the protonation of the sp2-nitrogen atom. The resulting alkenylaldiminium, -formamidinium, and -amidinium salts can be isolated and fully characterized, including single-crystal X-ray diffraction studies. Heating solutions of these salts induces ring closure cleanly and regioselectively via formal "exo" addition of the nitrogen-hydrogen bond to the pendent carbon-carbon double bond, affording the corresponding cyclic aldiminium, dihydroisoquinolinium, and imidazolinium salts. Of special interest, novel 4,4-disubstituted imidazolinium salts are accessible via this synthetic route. Similarly, addition of phosgene to alkenyl ureas and alkenyl amides, followed by gentle heating, cleanly affords C-chloro imidazolinium, and cyclic C-chloro iminium salts, respectively. Treatment of the latter with tetrakis(triphenylphosphine)palladium allows for the preparation of the first transition-metal complex bearing a cyclic arylaminocarbene as ligand. Deuterium labeling experiments suggest that the mechanism of the hydroiminiumation and -amidiniumation reactions involves an intramolecular proton transfer to the double bond in the rate-determining step. This novel synthetic methodology gives access to a variety of N-heterocyclic carbene (NHC) and cyclic alkyl- and arylaminocarbene (CAAC) precursors.     

The scope and mechanism of phosphonium-mediated S(N)Ar reactions in heterocyclic amides and ureas

An efficient "one-step" synthesis of cyclic amidines and guanidines has been developed. Treatment of cyclic amides and ureas with benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate (BOP), base, and nitrogen nucleophiles leads to the formation of the corresponding cyclic amidines and guanidines, typically in good to excellent yields. This method has also been used to prepare heteroaryl ethers and thioethers using phenol and thiophenol nucleophiles. Time course NMR and HPLC-MS studies have facilitated explicit characterization of the proposed intermediates (the phosphonium salt and HOBt adduct); the data reveal a stepwise reaction pathway.     

Solid-phase synthesis of urea and amide libraries using the T2 triazene linker

Starting from Merrifield resin, primary amines were immobilized in two steps by triazene linkage (T2-linker). While reaction with isocyanates gave rise to resin-bound urea derivatives, acylation by acid chlorides or anhydrides furnished amides bound to solid support via the nitrogen atom, therefore representing a novel backbone amide linker. Cleavage from the resin was conducted using dilute trimethylsilyl chloride or trifluoroacetic acid, respectively, to yield ureas and amines/amides in a library format (altogether 60 examples; manual synthesis: 17 ureas, 6 mono-alkylated ureas [including dihydroxylation and ozonolysis/Wittig reaction]; automated synthesis: 15 ureas, 15 amides) in high purities and good overall yields. The synthesis of a small library (4 x 4 member) was successfully conducted on a Bohdan Neptune synthesizer.     

Visible-Light-Induced Decarboxylation of Dioxazolones to Phosphinimidic Amides and Ureas

A visible-light-induced external catalyst-free decarboxylation of dioxazolones was realized for the bond formation of N=P and N–C bonds to access phosphinimidic amides and ureas. Various phosphinimidic amides and ureas (47 examples) were synthesized with high yields (up to 98%) by this practical strategy in the presence of the system’s ppm Fe.     

5 + 2] Cycloaddition reaction of 2-vinylaziridines and sulfonyl isocyanates. Synthesis of seven-membered cyclic ureas

The [5 + 2] cycloaddition reaction of 2-vinylaziridines with sulfonyl isocyanates proceeded smoothly under mild conditions, and various cyclic ureas were isolated in high yields. The remarkable solvent effect on the reaction was observed, and the preferential formation of the seven-membered ring occurred when the reaction was carried out in CH(2)Cl(2). The scope and limitation were studied, and the mechanism of this reaction was discussed. This study provides a new and simple method for the synthesis of seven-membered cyclic ureas.     

Microwave-assisted preparation of cyclic ureas from diamines in the presence of ZnO

A microwave-assisted facile method for the preparation of various ureas, cyclic ureas, and urethanes has been developed that affords nearly quantitative yield of products at 120 °C (150 W), 71 kPa within 10 min using ZnO as a catalyst. The enhanced selectivity in this reaction is attributed to the deployment of ZnO whose absence results in poor yield and the generation of byproducts.     

Infrared spectra of cyclic and non-cyclic ureas in solution: structures and interactions

Infrared spectra of 1,3-dimethyl-2-imidazolidinone, 2-imidazolidinone, 1,1,3,3-tetramethylurea, 1,3-dimethylurea, and 1,1-dimethylurea have been collected in a variety of solvents. When the C=O stretching frequencies for the molecules in a common solvent were recorded, higher frequencies were found for the cyclic ureas as compared to the non-cyclic ureas. When data were analyzed within each class of urea derivatives, it was found that an increase in the number of methyl groups present on the nitrogen atoms contributed to a decrease in the C=O stretching frequency values. The frequencies of the C=O stretching modes have been correlated with the electron accepting ability of each solvent (represented by Gutmann electron acceptor numbers). The urea derivatives in the studied series exhibit similar behavior with respect to changing solvent environment despite the differences that exist among the ureas. These observations have been interpreted in terms of the structural characteristics of the ureas.     

Planar chiral cyclic amine and its derivatives: synthesis and stereochemical behavior

[STRUCTURE: SEE TEXT] Nine-membered diallylic cyclic amines and amides have remarkably stable planar chirality. The transformation of enantiomerically enriched amides provides optically active nitrogen heterocycles containing stereogenic centers in a stereospecific fashion.     

Microwave-assisted cyclic amidine synthesis using TiCl4

Microwave-assisted treatment of various heterocyclic amides (benzodiazepinone, phthalazone) with TiCl(4) in the presence of primary or secondary amines provides the corresponding amidines. In addition to the interest of the microwaves for this reaction, our study highlights the higher reactivity of the cyclic acetamide moiety compared to the cyclic benzamide moiety towards this TiCl(4)-mediated reaction.     

Solvent extraction of technetium(VII) by cyclic amides

The extraction behavior of heptavalent technetium with cyclic amides inn-dodecane from nitric acid solution was studied. The amides investigated are N-(2-ethyl)hexylbutyrolactam(EHBLA). N-(2-ethyl)hexylvalerolactam(EHVLA), N-(2-ethyl)hexyl-caprolactam (EHCLA), N-octylcaprolactam(OCLA), a mixture of 3-octyl-N-(2-ethyl)hexylvalerolactam and 4-octyl-N-(2-ethyl)hexylvalerolactam (3,4,OEHVLA), 2-octyl-N-(2-ethyl)hexylcaprolactam(2OEHCLA), a mixture of 3-octyl-N-(2-ethyl)hexylcaprolactam and 5-octyl-N-(2-ethyl)hexylcaprolactam(3,5,OEHCLA) and that of 3-octyl-N-octylcaprolactam and 5-octyl-N-octylcaprolactam(3,5,OOCLA). From the results of the distribution ratio of Tc(VII) as a function of acid concentration, cyclic amides concentration and HTcO₄ concentration, the effects of both the ring size of cyclic amide and structure of the substituents attached to different positions of the cyclic ring on the extraction behavior of Tc(VII) were discussed. A clear steric hindrance was observed. For applications, 3,4,OEHVLA is proposed as the best extractant for Tc from acidic solution.     

Synthesis of cyclic sulfamoyl carbamates and ureas via ring-closing metathesis

Synthetic routes to a diverse set of cyclic sulfamoyl carbamates and ureas are reported. These routes utilize 3-component coupling, Mitsunobu alkylation, and ring-closing metathesis using the second-generation Grubbs catalyst to achieve the synthesis of the target S-heterocyclic compounds. Cyclic S-heterocycles ranging from 9- to 11-membered rings have been obtained.     

Synthesis and properties of novel dialkylaminocarbenium salts

Novel dialkylaminocarbenium salts with metallocomplex counter ions were prepared by the reaction of phosgene with either DMF or tetramethylurea in the presence of metal chlorides. Reactions of organosilicon amides with phosgene gave corresponding carbenium salts, while organosilicon ureas yielded aminoiminocarbenium salts. Dialkylaminochlorocarbenium salts were reduced with hydrosilanes to give dialkylaminocarbenium, salts and can be easily hydrolyzed to afford either amides or ureas. Pathways of the reaction with water and alcohols depend on the nature of reagent and the reaction conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1035–1040, May 1997.     

Activation of carboxylic acids by Burgess reagent: an efficient route to acyl ureas and amides

Carboxylic acids upon treatment with Burgess reagent are converted to novel mixed sulfocarboxy anhydrides. Subsequent treatment of such mixed anhydrides with amines at elevated temperatures yields acyl ureas and amides. The ratio of the two products appears to be temperature controlled. The method provides a simple and convenient route to diverse acyl ureas starting from carboxylic acids and amines.     

New substituted amides, ureas, and thioureas based on cage quinopimaric acid derivatives

Optically active amides, ureas, and thioureas were synthesized from cage acid chloride derived from quinopimaric acid.     

13C NMR spectra of some spiro cyclic glycidic esters

The ¹³C NMR of fourteen spiro cyclic glycidic esters and two amides have been investigated.     

15N NMR spectroscopy 24—chemical shifts and coupling constants of α-amino acid N-carboxyanhydrides and related heterocycles

The chemical shifts of amino acid N-carboxyanhydrides (NCAs) and cyclic or linear urethanes are less sensitive to solvent effects than those of amides and lactams. The values of the one-bond ¹⁵N? ¹H coupling constants depend on the solvent and are 5-8 Hz larger than those of ureas and amides. The ¹⁵N? ¹³C coupling constant of the N? CO group is also unusually high, while that of the N—CH group lies within the range known for N-acylated aliphatic amines. The one-bond ¹⁵N? ¹³C coupling constant was found to be insensitive to conformational changes.     

Triflic acid-mediated phenylation of N-acylaminoalkyl diethylacetals and N-acyl-2-phenyl cyclic amides

The reaction of N-acylaminoalkyl diethylacetals with triflic acid in benzene gave N-acylamino-diphenylalkyls. The proposed intermediates are the N-acyl-2-phenyl cyclic amides, which themselves are similarly converted to N-acylamino-diphenylalkyls.     

Calix[3]amides—bowl-shaped cyclic trimers toward building block for molecular recognition: self-complementary dimeric structure in the crystal

Bowl-shaped cyclic trimers of aromatic amides were simply synthesized in high yield by condensation reaction of meta-substituted 3-(alkylamino)benzoic acid using dichlorotriphenylphosphorane. The cyclic amides exist in syn conformation, which has a small chiral cavity, and a pair of each enantiomeric conformer formed a dimeric structure in the crystal.     

Facile Desulfurization of Thioamides and Thioureas with Tetrabutylammonium Periodate under Mild Conditions

Summary. Thioamides and thioureas were reacted with tetrabutylammonium periodate at room temperature to afford the corresponding amides and ureas, respectively, under aprotic conditions.