Photoluminescent and Liquid‐Crystalline Properties of Donor–Acceptor‐Type 2,5‐Diarylthiazoles

The synthesis of donor–acceptor‐type 2,5‐diarylthiazoles that bear electron‐donating N,N‐dialkylamine and electron‐withdrawing cyano groups at the 2‐ and 5‐position, respectively, were carried out with transition‐metal‐catalyzed C? H arylation reactions developed by us. The compounds were synthesized by the C? H arylation of unsubstituted thiazole at the 2‐position with a palladium/copper catalyst in the presence of tetrabutylammonium fluoride (TBAF) as an activator. Further C? H arylation of the 2‐arylated thiazole at the 5‐position was carried out by the palladium‐catalyzed reaction in the presence of silver(I) fluoride to afford the donor–acceptor‐type 2,5‐diarylthiazoles with N,N‐dialkylamine groups of different chain lengths. The UV/Vis absorption, photoluminescence, and electrochemical behavior were similar regardless of chain length, whereas liquid‐crystalline behavior and thermal characteristics were found to be dependent on the alkyl‐chain length. The compounds with N,N‐diethylamine or N‐butyl‐N‐methyl groups showed a stable liquid‐crystalline phase over a wide temperature range as well as higher stability to thermal decomposition.     

Novel Bulky Esters of Biopolymers: Dendritic Cellulose

Dendronized cellulose derivatives are discussed. Regarding our own studies, novel bulky esters of cellulose were synthesized homogeneously in N,N- dimethyl acetamide/LiCl or dimethyl sulfoxide in combination with fluoride ions by conversion of the biopolymer with 3,5-dihydroxybenzoic acid based aryl polyester dendrons. The carboxylic acid moieties were efficiently activated in situ with N,N′-carbonyldiimidazole or the acid chloride was applied. Cellulose esters with values of the degree of substitution of up to 0.7 were obtained. The functionalization analyzed by NMR spectroscopy occurs not only at position 6 (primary hydroxyl group) but also the secondary one at position 2.     

Synthesis of Diverse N‐Substituted Muramyl Dipeptide Derivatives and Their Use in a Study of Human NOD2 Stimulation Activity

A flexible synthetic strategy toward the preparation of diverse N‐substituted muramyl dipeptides (N‐substituted MDPs) from different protected monosaccharides is described. The synthetic MDPs include N‐acetyl MDP and N‐glycolyl MDP, known NOD2 ligands, and this methodology allows for structural variation at six positions, including the muramic acid, peptide, and N‐substituted moieties. The capacity of these molecules to activate human NOD2 in the innate immune response was also investigated. It was found that addition of the methyl group at the C1 position of N‐glycolyl MDP significantly enhanced the NOD2 stimulating activity.     

A Study of alkylation regioselectivity of 5-substituted tetrazoles with chloroacetamides

Alkylation of 5-aryltetrazoles with N-arylchloroacetamides commonly proceeds regioselectively at 2 position of the tetrazole ring. The ratio of 1,5- and 2,5-regioisomers depends on the nature of a substituents in the benzene ring of the N-arylchloroacetamide and position of a substituent in the aryltetrazole aryl group. Features of ¹H NMR spectra of the synthesized compounds are discussed.     

Preferential protonation and methylation at the nitrogen atoms of N,N-dimethylamino derivatives of pyridine

The relative reactivity toward protonation and methylation of the two nitrogen atoms in N,N-dimethylaminopyridines has been examined by ¹H NMR. The ring position of the dimethylamino group has no influence on protonation, which occurs in all the derivatives at the heterocyclic nitrogen. The N-methylation reaction does not follow a homogeneous behaviour, occurring at the exocyclic nitrogen in the 2-substituted dimethylamino derivative. The electronic characteristics of the molecules, determined by MO calculations at a semi-empirical level, indicate that both protonation and methylation should occur at the heterocyclic nitrogen; the calculated relative stabilites, however, of the N-protonated and N-methylated forms are in full agreement with the experimental results, and it appears that the anomalous behaviour of 2-dimethylaminopyridine in the N-methylation reaction is caused by steric factors.     

Nitrogen-15 nuclear magnetic resonance spectroscopy. Pyridine N-oxides and quinoline N-oxides

The noise-decoupled nitrogen-15 NMR spectra of ten pyridine N-oxides and two quinoline N-oxides have been obtained at the natural-abundance level by high-resolution NMR spectroscopy. Substituents at the 4-ring position of pyridine N-oxide, capable of resonance interaction with the N-O moiety, give fairly large shifts in the expected directions. Spectra taken in dimethyl sulfoxide solution give 5–20 ppm and 33–55 ppm downfield shifts with respect to the solutions of the same substances in 2,2,2-trifluoroethanol and trifluoroacetic acid. Solvent influences are discussed in terms of hydrogen bonding and protonation of the N-oxide oxygen. Carbon-13 chemical shifts and one-bond carbon-hydrogen coupling constants of some substituted pyridine N-oxides are reported and discussed.     

Nucleophilic displacements of N-aryl and heteroaryl groups. Part 8 . Intermolecular reactions of N-aryl-pyridinium, -quinolinium,and -acridinium salts with nucleophiles

N-Aryl-mono-, -tri- and -pentacyclic pyridinium cations react with S- and C-nucleophiles to give: (i) simple addition of hydride at the α-ring position, (ii) nucleophilic addition of thiophenoxide at the γ-ring position, (iii) deprotonation at the 6-position of a 5,6-dihydroquinolinium ring followed by prototropic shift to give a 1,2-dihydroquinoline derivative, (iv) ring contraction of a pyridine to a pyrrole ring, and (v) nucleophilic displacement of the N-aryl group.     

Synthesis and oxidation of vinyl derivatives of <Emphasis Type="Italic">N</Emphasis>-methyl[60]fullereno[<Emphasis Type="Italic">c</Emphasis>]pyrrolidine

Novel organometallic derivatives of N-methyl[60]fullereno[c]pyrrolidine bearing the vinyl fragment at the position 2 of the pyrrolidine ring were synthesized. Their oxidation with 3-chloroperoxybenzoic acid to give N-oxides and epoxides was studied in detail.     

An intramolecular N‐arylation approach to 3‐functionalized 4,9‐dihydropyrrolo[2,1‐b]quinazolines

A series of 4,9‐dihydropyrrolo[2,1‐b]quinazolines containing electron withdrawing groups at the 3‐position have been prepared by the palladium‐catalyzed intramolecular N‐arylation of some 2‐aminopyrroles having a 2‐bromobenzyl group at the N‐1 position. Important for success of the reaction is the use of X‐phos, a biphenyl mono‐phosphine ligand, instead of xantphos, a more standard diphosphine ligand, and the use of t‐BuOH as reaction solvent. J. Heterocyclic Chem., (2011).     

Annelated Pyrrolo[1,2‐a][1,4]diazepines in Mannich Reaction

New Mannich bases were synthesized through an interaction of fused pyrrolo[1,2‐a][1,4]diazepines with secondary amines and formaldehyde. The reaction appears to be regioselective, yielding the monosubstituted products bearing N,N‐dialkylaminomethyl group at position 2 of the pyrrolodiazepine moiety.     

Derivatives of 2,3‐dihydroimidazo[1,5,4‐ef][1,2,5]‐benzothiadiazepin‐6(4h,7h)‐thione 1,1‐dioxide,a new heterocyclic system related to tibo

The synthesis of derivatives of 2,3‐dihydroimidazo[1,5,4‐ef][1,2,5]benzothiadiazepin‐6(4H,7H)‐thione 1,1‐dioxide is reported starting from N‐substituted ethyl 2‐(5‐chloro‐2‐nitrobenzenesulfonamido)‐2‐alkyl‐acetates. Fundamental steps of the synthetic pathway were: i) intramolecular cyclization of N‐substituted 2‐(2‐amino‐5‐chlorobenzenesulfonamido)‐2‐alkylacetic acids in the presence of N‐(3‐dimethyl‐aminopropyl)‐N′‐ethyl carbodiimide hydrochloride‐N,N‐dimethylaminopyridine complex; ii) building of imidazole ring from 2‐alkyl‐8‐chloro‐2,3‐dihydro‐3‐methyl‐1,2,5‐benzothiadiazepin‐4(5H)‐one 1,1‐dioxide to achieve 2‐alkyl‐9‐chloro‐2,3‐dihydro‐3‐methylimidazo[1,5,4‐ef][1,2,5]benzothiadiazepin‐6(4H,7H)‐one 1,1‐dioxide; iii) preparation of thiocarbonyl derivative by treatment with Lawesson's reagent. Introduction of a 3‐methyl‐2‐butenyl chain at position 2 of above imidazobenzothiadiazepinone required protection at the 7 position with thermally removable tert‐butoxycarbonyl moiety, due to the fact that alkylation of unprotected structure proved to be regioselective for the 7 position.     

Tautomerism and electron impact mass spectra of pyrimidin-4(3H)- and -4(1H)-ones

A mass spectrometric identification and differentiation of pyrimidin-4(3H)- and -4(1H)-ones was carried out. N-Substitution at position 1 or 3 made the distinction of the two sets of compounds very easy because of their characteristic fragmentation pathways. Most interesting were the spectra of the N-unsubstituted derivatives, which illustrated a predominance of the two possible NH tautomers in relation to the 4-hydroxy structure.     

Reductive Amination of ω‐Oxoecdysteroids in the Synthesis of Dimeric Ecdysteroids

N‐Alkyl‐ and N‐arylaminoecdysteroids were synthesized for the first time by reductive amination of ω‐oxoecdysteroids. By using aliphatic or aromatic diamines, dimeric ecdysteroids with an ethylenediamine or p‐phenylenediamine bridge at the C(24), C(24′)‐position of the monomeric moieties were obtained.     

Synthesis and Biological Evaluation of Glycosides and Acyclic Nucleosides Derived 2‐Oxonicotinonitriles

Synthesis and biological evaluations of a series of 2‐oxonicotinonitriles (2‐ONNs) derivatives are described. Incorporation of branching and solubilizing groups to the 2‐ONN derivative 7 was attained by coupling with several organo‐halides/alkylating agents including three glycosyl bromides under basic conditions. Coupling of 2‐ONNs occurred mainly at the ring nitrogen position and to a lesser extent at the 2‐oxo position giving the O‐alkylated products. Alkylated ONNs and free nucleosides/glycosides derived from the 2‐ONN derivative 7 were tested for their antibacterial, antifungal, and antiviral activities. N‐propargyl and N‐allyl derivatives 23 and 25 showed significant anti‐SARS‐CoV. The N‐butylacetate and O‐allyl derivatives 18 and 26 showed potent antibacterial activities against both Gram‐positive (Staphylococcus aureus, Micrococci luteus) and Gram‐negative (Pseudomonas aeruginosa, Escherichia coli) bacterial strains. The N‐glucoside derivative 8 showed significant antifungal activity.     

Site‐Selective Linear Alkylation of Anilides by Cooperative Nickel/Aluminum Catalysis

We report meta‐ and para‐selective linear alkylation reactions of anilides with alkenes by nickel/N‐heterocyclic carbene (NHC) and aluminum catalysis. With a less bulky NHC, the alkylation reaction of N‐methyl‐N‐phenylcyclohexanecarboxamides proceeded mainly at the meta position. In contrast, a bulky NHC ligand led to the para‐selective alkylation of N‐sec‐alkyl anilides.     

Lead Tetraacetate Oxidation on Caryachine,A Phenolic Pavine

Lead tetraacetate oxidation on caryachine, a pavine alkaloid possessing a phenolic group at the position para to the N-methine, in dichloromethane yielded four products — 10-acetoxy-O-acetyl-caryachine, 10-acetoxycaryachine, 7-acetoxy-O-acetylcaryachine and (6S, 11R, 12R)-11-acetoxy-O-acetyl-caryachine. The reaction took place via adoption of an acetoxy group at a position majorly ortho to the phenolic group, but very minorly at the desired benzylic position para to the phenolic group.     

Synthesis of N4‐substituted[1,3,4]oxadiazinan‐2‐ones derived from norephedrine

[1,3,4]‐Oxadiazinan‐2‐ones bearing substitution at the N₄‐position have been synthesized from norephedrine in good yield via N‐alkylation, nitrosation, reduction and cyclization.     

14H-Naphtho[1′,2′:5,6] pyrano[2,3-b]quinoline derivatives

Reaction of (N-alkyl-N-phenyl)ethoxycarbonylacetamides with β-naphthol in the presence of phosphorus oxychloride afforded 1-oxo-3-(N-alkyl-N-phenyl)amino-1H-naphtho[2,1-b]pyrans. These compounds underwent reaction with N,N-dimethylformamide-phosphorus oxychloride at 95° yielding a mixture of 14H-naphtho[1′,2′:5,6]pyrano[2,3-b]quinoline derivatives and 1-oxo-2-formyl-3-(N-alkyl-N-phenyl)amino-9-oxy-1H-phenalene. When the same reaction was performed at 140°, only 14-oxo-14H-naphtho[1′,2′:5,6]pyrano[2,3-b]quinoline was obtained in a very good yield. The structures of such compounds were demonstrated by spectral data and by chemical transformations. On the other hand, the expected formylation in the 2 position was achieved when 1-oxo-3-(N-alkyl-N-benzyl)amino-1H-naphtho[2,1-b]pyrans reacted with N,N-dimethylformamide-phosphorus oxychloride.     

Synthesis of Chlorins Fused with Nitrogen‐Containing Heterocycle by the Modification along Their N21–N23 axis

Quinoxalinodeoxopyropheophorbide‐a and benzimidazolopurpurin‐18 imide were obtained from methyl pheophorbide‐a by one‐pot method. The synthesis of a series of chlorins fused with nitrogen‐containing heterocycle was fulfilled by chemical modifications along their N²¹–N²³ axis such as LiOH‐promoted allomerization of C12‐methyl group, electrophilic addition to C3‐vinyl group, substitution at 20‐meso‐position and 1, 3‐dipolar cycloaddition with diazomethane at 3‐position. The structures of new chlorins were characterized by UV–vis, MS, ¹H NMR spectra, and elemental analysis.     

Substitution effects on the molecular structures and the longitudinal molecular polarizabilities of all‐trans polyacetylene oligomers of increasing size

AM1 calculations have been performed on all‐trans polyacetylene (PA) oligomers with an increasing number of unit cells to study the effect of donor or acceptor groups capped at opposite ends of PA chains, substituents included in the monomers, substituents' number and position in the monomers, on the molecular structures, and the static longitudinal polarizabilities (α_L) and second‐order hyperpolarizabilities (γ_L). Substitution of CH₃, Cl, or F group at opposite ends of an oligomer results in an increase of α_L and γ_L, but the substitution effects on Δα_L(N) and Δγ_L(N) are very small. The asymptotic limit values are unaffected by the substitution. F substituent included in the monomer of an oligomer enhances the Δα_L(N) and Δγ_L(N) values, especially at large N, but including monomers with CH₃ or Cl substituents substantially reduces the Δα_L(N) and Δγ_L(N) values. We alter the number of F substituents included in the monomers of oligomers and find that including two F substituents in the monomer leads to the larger enhancement of Δγ_L(N). The effect of F substituents' position in the monomers of oligomers on Δα_L and Δγ_L is obvious. The results may be helpful for the design of new materials for applications in nonlinear optics, particularly in the area of poled polymer films. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001