Intermolecular reductive coupling of hindered N-aryl imines towards the modular synthesis of chiral N-heterocyclic carbenes

We describe a simple method for the synthesis of hindered N-aryl diamines. The diastereoselectivity for these processes are relatively low but the diamines can be separated using either chromatography or selective crystallization. Separation of enantiomers can be accomplished using HPLC equipped with a chiral stationary phase.     

Synthesis of substituted benzimidazoles via tosylation of N-aryl amidoxime

Tosylation of N-aryl amidoxime in the presence of TEA produces the corresponding benzimidazoles in high yields.     

Synthesis of new N-aryl oxindoles as intermediates for pharmacologically active compounds

Various new N-aryl oxindoles were synthesized as intermediates for the preparation of pharmacologically active 2-(N-arylamino)-phenylacetic acids. Two novel approaches were explored for the construction of diarylamine and N-aryl oxindole core structures, in addition to Buchwald-arylamination and Smiles rearrangement. Condensation of anilines with 2-oxo-cyclohexylidene-acetic acid derivatives and subsequent dehydrogenation is a new and viable method for the preparation of N-aryl oxindoles.     

Cyclometalated Ir(III) complexes containing N-aryl picolinamide ancillary ligands

The reaction of the cyclometalated chloro-bridged iridium(III) dimer, [(ppy)₂ Ir(μ-Cl)]₂ (ppy - 2-phenyl pyridine) with N-aryl picolinamides (LH, LH-NO₂, LH-CH₃, LH-l, LH-F) resulted in the formation of neutral heteroleptic complexes [Ir(ppy)₂L] (1), [Ir(ppy)₂L-NO₂](2), [Ir(ppy)₂L-CH₃](3), [Ir(ppy)₂L-Cl](4) and [Ir(ppy)₂L-F] (5). These complexes contain a six-coordinate iridium with a 2C, 4N coordination environment. The N-aryl picolinamide ligands are deprotonated during complexation and the resulting amidates bind to iridium in a chelating manner (N, N). Optical spectroscopic studies revealed that the complexes 1-5 exhibited intense π→π^∗ absorptions in the ultraviolet region. In addition low energy transitions due to ¹MLCT, ¹LLCT and ³MLCT are also seen. The emission spectra of 1-5, upon excitation at 450 nm, show a single emission with a λ_max around 513 nm. The lifetimes of this emission are in between 7.4 and 9.6 μs while the quantum yields are quite high and range from 0.2 to 0.5. Based on density functional theory (DFT) calculations on 1 and 3, the three highest occupied orbitals are composed of ligand π orbitals mixed with Ir-d orbitals while the three lowest unoccupied orbitals are mostly π orbitals of the ligands. From the time dependent DFT calculations it is revealed that the lowest energy electronic singlet and triplet excitations are a mixture of MLCT and LLCT.     

Synthesis and reactivity of N-aryl substituted N-heterocyclic silylenes

The synthesis of two N-aryl substituted 2-silaimidazolidenes 9a, b by metal-reduction of the appropriate silicon(IV) heterocycles is reported. Structural as well as spectroscopic data obtained for the N-aryl substituted N-heterocyclic silylenes (NHSi) are very close to those obtained previously for their N-alkyl substituted counterparts. NHSis 9a, b are used as starting materials for the synthesis of a series of dichalcogenadisiletanes 19-24 and for of a mono silylene tungsten complex 29. The reactivity studies revealed only marginally differences between the N-aryl substituted NHSis 9a, b and previously described N-alkyl substituted silylenes.     

A convenient and efficient method for the synthesis of mono- and N,N-disubstituted thioureas

A convenient method for the synthesis of mono- and N,N-disubstituted thioureas by the debenzoylation of N-substituted- and N,N-disubstituted-N′-benzoylthioureas with hydrazine hydrate under solvent-free conditions has been developed. N-Substituted-N′-benzoylthioureas and hydrazine hydrate were mixed, and stirred at room temperature without a solvent to give the corresponding N-substituted thioureas in high yields.     

A convenient method for the synthesis of N-hydroxyureas

Treatment of amines with 1-(4-nitrophenol)-N-(O-benzylhydroxy)carbamate yields the O-benzyl protected N-hydroxyureas. Hydrogenation of the O-benzyl protected N-hydroxyureas over 5% Pd/BaSO₄ cleanly gives the N-hydroxyureas in good yield. In addition to primary and secondary aliphatic and aromatic amines, this method converts amino sugars to the corresponding N-hydroxyureas without extensive protecting group chemistry.     

Superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids: synthesis of quinolin-2(1H)-one derivatives

The superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids by Bronsted superacids (CF₃SO₃H, HSO₃F) or strong Lewis acids AlX₃ (X=Cl, Br) results in the formation of 4-aryl quinolin-2(1H)-ones in quantitative yields. The vinyl triflates or vinyl chlorides may be formed as additional reaction products. The investigated amides in reactions with benzene give 4,4-diaryl 3,4-dihydroquinolin-2-(1H)-ones under the superelectrophilic activation. 4-Aryl quinolin-2(1H)-ones in POCl₃ are converted into 4-aryl 2-chloroquinolines. 4-Fluorophenyl-4-phenyl 3,4-dihydroquinolin-2-(1H)-one give N-formylation products in a yield of 79% under the Vilsmeier–Haack reaction conditions.     

A convenient synthesis of iminosugar-C-glycosides via organometallic addition to N-benzyl-N-glycosylhydroxylamines

N-Benzyl-N-glycosylhydroxylamines were prepared in very good yield via condensation of furanoses and pyranoses with N-benzylhydroxylamine at 110°C for 30 min under solvent-free conditions. These anomeric sugar-hydroxylamines exist in equilibrium with the open-chain nitrone form. In fact upon treatment with various organometallic reagents, the corresponding adducts were obtained with good to high diastereoselectivity. These adducts were converted into iminosugar-C-glycosides by reductive dehydroxylation and intramolecular cyclization.     

A convenient synthesis of the core trisaccharide of the N-glycans

A convenient synthesis of the core trisaccharide of the N-glycans was described. Orthogonal one-pot glycosylation of three monosaccharide building blocks was performed to furnish β-glucosyl chitobiose, which was then transformed to β-mannosyl chitobiose by intramolecular epimerization of the C-2 position of the β-glucoside. The key glucosyl donor 7c with differentiated 2,3-OH was prepared following the 4,6-O-benzylidene-protected 1,2-orthoester strategy.     

One step synthesis of 1,5-diaryl pyridin-2(1H)-ones from 2-aryl vinamidinium salts and N-aryl cyanoacetamides

A one step, direct method for the synthesis of 1,5-diaryl pyridin-2(1H)-one derivatives by condensation of 2-aryl vinamidinium salts with N-aryl cyanoacetamides has been developed. This method can conveniently provide the corresponding 1,5-diaryl pyridin-2(1H)-one derivatives with various substituents in good yields and overcome the drawbacks of existing methods such as poor substrate scope, heavy metal pollution, and low yields. The formation mechanism of the products was illustrated.     

A convenient microwave-assisted synthesis of N-glycosyl amino acids

Optimization of coupling reactions of glycosylamines with Fmoc-protected aspartic acid, by microwave approach, is described. Different reaction conditions, quantities of substrates and solvents were tested to develop simple and reproducible methodologies. The best results were obtained using new triazine-based coupling reagents with a monomode microwave Discover® BenchMate™ instrument (CEM). The N-glycosyl amino acids were then deprotected to achieve final products for SPPS.     

Preparation of N-arylpiperazines and other N-aryl compounds from aryl bromides as scaffolds of bioactive compounds

Aryl bromides are coupled with N-compounds to give the corresponding arylamines in the presence of a palladium catalyst, a suitable ligand, and a weak base. The catalysts perform well for a large number of different starting material combinations at 100-150 °C with drops of toluene or without solvent, and with low catalyst levels (0.12 mol % Pd). The low catalyst amount makes the process environment friendly.     

N-(Diethoxyphosphoryl)-O-benzylhydroxylamine—a convenient substrate for the synthesis of N-substituted O-benzylhydroxylamines

Easily available N-(diethoxyphosphoryl)-O-benzylhydroxylamine was shown to be convenient, orthogonally protected substrate for regioselective N-alkylation by means of diverse halides under basic conditions (sodium hydride/tetrabutylammonium bromide). An efficient procedure for dephosphorylation of N-substituted N-(diethoxyphosphoryl)-O-benzylhydroxylamine to provide N-substituted O-benzylhydroxylamines was also established.     

N-ferrocenoyl benzotriazole: A convenient tool for the synthesis of ferrocenoyl esters

A new synthesis methodology has been presented for the preparation of the ferrocenoyl esters. Ferrocene carboxylic acid was derivatized using direct 1H-benzotriazole/SOCl₂ methodology to prepare N-ferrocenoyl benzotriazole as a convenient tool for the functionalization of ferrocene ring. N-ferrocenoyl benzotriazole was reacted with alcohols in mild conditions to prepare ferrocenoyl esters in high purity and in good yield. The solid state structure of benzyl-1-ferrocenoate, 2f, has also been determined by X-ray crystallography. In the crystal structure, intermolecular C-H···O hydrogen bonds link the molecules into a two-dimensional network. The π···π contacts between the cyclopentadiene rings and cyclopentadiene and phenyl rings, [centroid-centroid distances = 3.296(1) and 3.750(1) Å] may further stabilize the structure. Two weak C-H···π interactions are also found.     

Facile synthesis of C-aryl glycals from sugar-derived lactones

A general entry to C(1) aryl-substituted glycals from the corresponding sugar lactones is described. This approach features one-pot access to aryl glycals. A variety of aryllithium reagents can be used and the method is compatible with various 2-deoxysugar lactones.     

Mild, convenient and versatile Cu-mediated synthesis of N-aryl-2-imidazolidinones

A mild, general, convenient and practical methodology for the selective copper-mediated mono N-arylation of unprotected 2-imidazolidinone was developed. Strong electron-donating groups and free hydroxy and amino groups on the aryl iodide substrates were well tolerated. The use of n-butanol as the solvent for the copper-catalysed mono-arylation of 2-imidazolidinone is unprecedented.     

A practical synthesis of N-tosylimines of arylaldehydes

Synthesis of N-tosylimines of arylaldehydes was carried out by the reaction of arylaldehydes and p-toluenesulfonamide in methylene chloride in the presence of trifluoroacetic anhydride as a dehydrating agent.     

Synthesis of N-acyl-N,O-acetals from N-aryl amides and acetals in the presence of TMSOTf

Secondary amides undergo in situ silyl imidate formation mediated by TMSOTf and an amine base, followed by addition to acetal acceptors to provide N-acyl-N,O-acetals in good yields. An analogous, high-yielding reaction is observed with 2-mercaptothiazoline as the silyl imidate precursor. Competing reduction of the acetal to the corresponding methyl ether via transfer hydrogenation can be circumvented by the replacement of CY₂NMe with 2,6-lutidine under otherwise identical reaction conditions.     

N,N′-Diisopropyl- and N,N′-dicyclohexylthiourea cadmium(II) complexes as precursors for the synthesis of CdS nanoparticles

Crystals of the cadmium(II) complexes of N,N-diisopropylthiourea and N,N-dicyclohexylthiourea were obtained and their X-ray single crystal structures determined. These complexes are air-stable, easy to prepare and inexpensive and decompose cleanly to give good quality crystalline CdS. The nanoparticles of CdS thus obtained showed quantum confinement effects in their optical spectra, with close to band-edge emission in luminescence experiments. The broad diffraction patterns observed are typical of nanodimensional particles. The variation of concentration of precursor-to-HDA ratio change the isolated materials from spheres to rod-shaped. TEM images showed agglomerates of needle-like plate of particles.