Oxazoline Moiety Research Articles

Modular Preparation of 5-Halomethyl-2-oxazolines via PhI(OAc)2-Promoted Intramolecular Halooxygenation of N-Allylcarboxamides.

A new method for the construction of oxazoline moiety was detailed. Using (diacetoxyiodo)benzene (PIDA) as the reaction promoter and halotrimethylsilane as the halogen source, intramolecular halooxygenation and halothionation of N-allylcarboxamides/N-allylcarbothioamides proceeded readily, leading to the corresponding 5-halomethyloxazolines/5-halomethylthiazolines in good to excellent isolated yields. The 5-halomethyl products could be converted to different derivatives via conventional nucleophilic substitution methods. The reactions were carried out using easily available starting materials, and did not need harsh reaction conditions. All these features made this reaction a viable method for the construction of different oxazoline and thiazoline structures.

Convenient and rapid strategies towards 6-(hetero)aryl pyridylmethylamines: first catalytic issues

The convenient preparation of new pyridylmethylamines is described using a short two step sequence. The first step involved the straightforward microwave-assisted construction of 6-aryl and 6-heteroaryl pyridine scaffolds bearing carboxaldehyde and nitrile fragments. The pendant arm comprising a second nitrogen atom by mean of amine and oxazoline moieties is installed in the second step. Finally, a first entry towards catalytic activity is given. In this context, modification of the ligand pattern and steric crowding around the central pyridine ring is examined and led to modest to fair ee’s in the construction of binaphthyl substrates.

Synthesis, Characterization and Antimicrobial Screening of Some Bioactive 1,8-Naphthalimide Derivatives.

This research include developing new heterocyclic derivatives of 1,8-naphthalimides bearing oxazoline, thiazoline, oxadiazole, thiadiazole and aminotriazole moieties as the following steps: N-ester-1,8-naphthalimide (1) was obtained by direct imidation of 1,8- naphthalic anhydride with ethylglycinate in dimethylsulfoxide. Compound (1) was treated with hydrazine hydrate in absolute ethanol to give N-acetohydrazide-1,8-naphthalimide (2).N-Acetophenylsemicarbazide-1,8-naphthalimide (3) and N-Aceto phenylthiosemicarbazide- 1,8-naphthalimide (7) were synthesized via reaction of compound (2) with phenylisocyanate and phenylisothiocyanate in absolute ethanol respectively.Cyclization of compounds (3) and (7) with p-substituted phenacyl bromide gives the oxazoline derivatives (4-6) and thiazoline derivatives (9-11) respectively. N-Methyl-[(5- (phenyl amino)-1,3,4-thiadiazol-2-yl)]-1,8-naphthalimide (8) prepared via treatment of compound (7) with phosphoric acid. Reaction of the prepared hydrazide (2) with carbon disulfide in the presence of potassium hydroxide producing N-Methyl-[potassium dithiocarbazate]-1,8-naphthalimide (12). Acidifying of the obtained salt (12) with 4N hydrochloric acid give N-Methyl-[1,3,4-oxadiazol-2-yl-5-thiol]-1,8-naphthalimide (13). The obtained salt (12) also treated with hydrazine hydrate to afford the desirable N-Methyl-[1,2,4- triazol-3-yl-4-amino-5-thiol]-1,8-naphthalimide (14).All the prepared compounds in this research were characterized by recording their melting points, FTIR, 1HNMR, 13CNMR spectra, checked by TLC, physical properties and some specific chemical tests also. Some of the new prepared compounds were evaluated for the antimicrobial screening in vitro against two types of Gram positive bacteria including (Staphylococcus aureus, Bacillus subtilis) and two types of Gram negative bacteria including (Escherichia coli, Pseudomonas aeuroginosa).More, antifungal activities of some prepared compounds performed against the yeastlike pathogenic fungus (Candida albicans). The antimicrobial screening carried out in three concentrations of prepared compounds. Sulfamethoxazole/Clotrimazole was used as standard drugs. The results showed that most of the tested compounds have good biological activity against the mentioned organisms compared with standard drugs above

Radical Polymerizations of Optically Active Methacrylamides Having Oxazoline Moieties

A novel type of chiral N-substituted methacrylamide derivatives bearing an oxazoline pendant (OPMAM) had been synthesized. Radical polymerization were carried out to produced corresponding polymers with high specific rotation in moderate yields. The polymerization characteristics and the chiroptical behavior of the resultant polymers have been examined in detail by using HPLC and CD and UV-vis spectra. The polymers showed relatively high molecular weights(Mn=5000-15000). The abolutely value of the specific rotation of poly(OPMAM)s basically increased with increasing the molecular weights.

ChemInform Abstract: New Chiral Iodooxazoline Catalysts for the I(III)‐Mediated α‐Tosyloxylation of Ketones: Refining the Stereoinduction Model.

AbstractThe catalyst with the best performance is shown.

Oxorhenium(V) complexes with naphtholate-oxazoline ligands in the catalytic epoxidation of olefins

Four oxorhenium(V) complexes 3a–d equipped with naphtholate-oxazoline based ligands 2a–d have been prepared and characterized by NMR, IR and mass spectroscopy as well as elemental analysis. Ligands 2a–d were prepared in a two-step procedure from commercially available starting materials. Ligands 2a–b and 2c–d are regioisomers to each other regarding the position of the –OH group and oxazoline moiety on the naphthol ring. Reaction of 2a–d with (NBu4)[ReOCl4] in methanol under reflux gave oxorhenium(V) complexes 3a–d of the type [ReOCl(L)2] as green solids in acceptable to good yields. The molecular structures of complexes 3b and 3d have been determined via single crystal X-ray diffraction analysis and both display a distorted octahedral geometry. Complexes 3a–d are active catalysts for the epoxidation of cyclooctene with tert-butylhydroperoxide (TBHP) showing moderate conversions between 41% and 65%.

Cationic half-sandwich quinolinophaneoxazoline-based (η6-p-cymene)ruthenium(ii) complexes exhibiting different chirality types: synthesis and structural determination by complementary spectroscopic methods

Novel, optically pure 2-{4-methyl[2]paracyclo[2](5,8)quinolinophan-2-yl}-4-aryl/alkyloxazolines (QUIPHANOX) exhibiting both planar and central chirality have been prepared by reacting (Rp)- and (Sp)-2-cyano-4-methyl[2]paracyclo[2](5,8)quinolinophane with 2-aryl/alkyl-2-aminoethanols. The reaction of each of the above N,N-ligands with [Ru(η(6)-p-cymene)Cl2]2 in methanol, in the presence of either NH4PF6 or NaBPh4, gave the corresponding half-sandwich [(η(6)-p-cymene)Ru(QUIPHANOX)Cl](+)Y(-), (Y(-) = PF6(-), BPh4(-)) as stable complex salts exhibiting planar and carbon- and metal-centered chirality. The unknown absolute configuration (AC) at the metal was determined by (1)H NMR and by theoretical calculations of electronic circular dichroism (ECD) spectra and subsequently confirmed by crystallographic X-ray analysis. (Rp) and (Sp)-ligands afforded (RRu)- and (SRu)-configured complexes, respectively, independent of the AC at the chiral carbon of the oxazoline moiety.

New chiral iodooxazoline catalysts for the I(III)-mediated α-tosyloxylation of ketones: refining the stereoinduction model

A new family of iodooxazoline catalysts, derived from widely available chiral ketones (menthone and camphor), was developed to promote the iodine(III)-mediated α-tosyloxylation of ketone derivatives. The reaction conditions to achieve the direct formation of the oxazoline moieties from the corresponding aminoalcohols and an aldehyde were explored and optimized. These catalysts were tested for the α-tosyloxylation of propiophenone and led to new information on the stereoinduction process. The results demonstrate that modulation of the steric hindrance around the iodane center is critical to obtain good activity. Additionally, from the selectivities observed, a preliminary predictive model is proposed.

Oxazolochlorins. 9. meso-Tetraphenyl-2-oxabacteriochlorins and meso-Tetraphenyl-2,12/13-dioxabacteriochlorins

The formal replacement of one or two pyrrole groups in meso-tetraphenylporphyrin by oxazole moieties is described, generating inter alia the bacteriochlorin-type chromophores oxazolobacteriochlorins (oxabacteriochlorins) and bisoxazolobacteriochlorins (dioxabacteriochlorins). The key step is the conversion of a β,β'-dihydroxy-functionalized pyrroline group into an oxazolone or (substituted) oxazole. Depending on the substitution pattern on the oxazole or oxazoline moieties, mono- and dioxabacteriochlorins may have chlorin- or bacteriochlorin-like spectra. The optical properties (as measured by UV-vis and fluorescence spectroscopies) of the novel oxa- and dioxabacteriochlorins are described and contrasted against benchmark chlorins and bacteriochlorins. The conformations of a representative number of mono- and dioxabacteriochlorins, as their free bases or Zn(II) complexes, were determined by single-crystal X-ray diffractometry. They proved to be essentially planar, showing that the modulation of their optical properties is primarily due to their intrinsic electronic structures and electronic substituent effects and are not largely affected by conformational effects. The mono- and bisoxazolobacteriochlorins are a novel class of readily prepared and oxidatively stable chlorin and bacteriochlorin analogues with tunable optical spectra that, in part, reach into the NIR.

Unexpected Formation of Chiral Pincer CNN Nickel Complexes with β-Diketiminato Type Ligands via C–H Activation: Synthesis, Properties, Structures, and Computational Studies

Reaction of lithiated chiral, unsymmetric β-diketimine type ligands HL(2a-e) containing oxazoline moiety (HL(2a-e) = 2-(2'-R(1)NH)-phenyl-4-R(2)-oxazoline) with trans-NiCl(Ph)(PPh(3))(2) afforded a series of new chiral CNN pincer type nickel complexes (3a-3e) via an unexpected cyclometalation at benzylic or aryl C-H positions. Single crystal X-ray diffraction analysis established the pincer coordination mode and the strained conformation. Chirality, and in one case, racemization of the target nickel complexes were confirmed by circular dichroism (CD) spectroscopy. Electronic structure and band assignments in experimental UV-vis and CD spectra were discussed on the basis of Density Functional Theory (DFT) and time-dependent (TD) DFT calculations.

Catalytic Enantioselective α-Tosyloxylation of Ketones Using Iodoaryloxazoline Catalysts: Insights on the Stereoinduction Process

A family of iodooxazoline catalysts was developed to promote the iodine(III)-mediated α-tosyloxylation of ketone derivatives. The α-tosyloxy ketones produced are polyvalent chiral synthons. Through this study, we have unearthed a unique mode of stereoinduction from the chiral oxazoline moiety, where the stereogenic center alpha to the oxazoline oxygen atom is significant. Computational chemistry was used to rationalize the stereoinduction process. The catalysts presented promote currently among the best levels of activity and selectivity for this transformation. Evaluation of the scope of the reaction is presented.

Pharmacophore Development and SAR Studies of Imidazoline Receptor Ligands

Relationship between biological responses and binding affinities at I(1)/I(2)/I(3) imidazoline receptors of compounds with imidazoline, pyrroline or oxazoline moieties was studied by 2D-QSAR, 3D-QSAR and quantitative pharmacophore development approaches. Since the I(1) imidazoline receptor is involved in central inhibition of sympathicus that produce hypotensive effect, the I(2) receptor is allosteric modulator of monoamine oxidase B (MAO-B) and the I(3) receptor regulates insulin secretion from pancreatic β-cells, design and synthesis of selective I(1)/I(2)/I(3) imidazoline ligands are very important for the development of new effective therapeutic agents. New agonists and antagonists with high selectivity for I(1)/I(2)/I(3) imidazoline receptor classes have been recently synthesized and examined. The present review will highlight the main chemical diversity and pharmacophore features of selective I(1)/I(2)/I(3) imidazoline receptor ligands.

Carbon- and Sulfur-Bridged Diiron Carbonyl Complexes Containing N,C,S-Tridentate Ligands Derived from Functionalized Dibenzothiophenes: Mimics of the [FeFe]-Hydrogenase Active Site

Photochemical reactions of [Fe(CO)5] with dibenzothiophene (DBT) derivatives bearing a N-donor group produced a series of C,S-bridged diiron carbonyl complexes [{Fe(μ-L′-κ3N,C,S)(CO)2}Fe(CO)3], as previously reported for 4-(2′-pyridyl)dibenzothiophene (L1), where L′ represents the N,C,S-tridentate ligands L1′–L5′, formed by C–S bond cleavage of L1–L5, respectively. The DBT derivatives used in this study have Schiff base or oxazoline moieties at the 4-position: L2 = PhCH2N═CH-DBT, L3 = 2-MeOC6H4CH2N═CH-DBT, L4 = (S)-PhC(Me)HN═CH-DBT, L5 = (R)-4-isopropyl-2-oxazolinyl-DBT. The diiron complexes were characterized by NMR, absorption, and circular dichroism spectroscopy, and the dinuclear structures bridged by thiolate S and aryl C atoms were established by X-ray crystallography. The diiron complex [{Fe(μ-L′-κ3N,C,S)(CO)2}Fe(CO)3] consists of two units, Fe(L′)(CO)2 and Fe(CO)3: the latter unit is located on a thiolate-containing metallacycle in the former one. The chiral Schiff base ligand precursor L4 gave a 55:45 mixture of two diastereomers for [{Fe(μ-L4′-κ3N,C,S)(CO)2}Fe(CO)3], while chiral L5 with an (R)-4-isopropyl-2-oxazolinyl group afforded [{Fe(μ-L5′-κ3N,C,S)(CO)2}Fe(CO)3] in a 9:1 diastereomeric ratio. The diiron carbonyl complexes of the N,C,S-tridentate ligands (L1′—L5′) showed two reversible redox couples for [Fe2(μ-L′)(CO)5]0/– and [Fe2(μ-L′)(CO)5]−/2–. The two-electron-reduced forms undergo protonation and act as electrocatalysts for proton reduction of acetic acid in acetonitrile.

Chiral (Mercaptophenyl)oxazolines as Auxiliaries for Asymmetric Coordination Chemistry

Abstract(4S)‐2‐(4‐Isopropyl‐4,5‐dihydrooxazol‐2‐yl)‐4‐nitrobenzenethiol {(S)‐TS} and its tert‐butyl derivative {(S)‐TS′} were developed as chiral auxiliaries for the asymmetric synthesis of polypyridyl ruthenium complexes. In their deprotonated form, these (mercaptophenyl)oxazolines were used as bidentate ligands and allowed the efficient transfer of chirality from the oxazoline moiety to the ruthenium stereocenter. After the induction of the absolute metal‐centered configuration, the auxiliaries were labilized by converting the coordinated thiolate into a thioether ligand upon methylation with Meerwein salt, followed by the thermal replacement with 2,2′‐bipyridine or 1,10‐phenanthroline ligands under retention of configuration to afford octahedral polypyridyl ruthenium complexes with high enantiomeric excesses. These thiol‐based auxiliaries complement our previously developed acid‐labile chiral auxiliaries and thus expand the toolbox for the asymmetric synthesis of chiral ruthenium complexes.

Gas-phase reactivity of protonated 2-oxazoline derivatives: mass spectrometry and computational studies

Oxazolines have attracted the attention of researchers worldwide due to their versatility as carboxylic acid protecting groups, chiral auxiliaries, and ligands for asymmetric catalysis. Electrospray ionization tandem mass spectrometric (ESI-MS/MS) analysis of five 2-oxazoline derivatives has been conducted, in order to understand the influence of the side chain on the gas-phase dissociation of these protonated compounds under collision-induced dissociation (CID) conditions. Mass spectrometric analyses were conducted in a quadrupole time-of-flight (Q-TOF) spectrometer fitted with electrospray ionization source. Protonation sites have been proposed on the basis of the gas-phase basicity, proton affinity, atomic charges, and a molecular electrostatic potential map obtained on the basis of the quantum chemistry calculations at the B3LYP/6-31 + G(d,p) and G2(MP2) levels. Analysis of the atomic charges, gas-phase basicity and proton affinities values indicates that the nitrogen atom is a possible proton acceptor site. On the basis of these results, two main fragmentation processes have been suggested: one taking place via neutral elimination of the oxazoline moiety (99 u) and another occurring by sequential elimination of neutral fragments with 72 u and 27 u. These processes should lead to formation of R(+). The ESI-MS/MS experiments have shown that the side chain could affect the dissociation mechanism of protonated 2-oxazoline derivatives. For the compound that exhibits a hydroxyl at the lateral chain, water loss has been suggested to happen through an E2-type elimination, in an exothermic step.

Rare earth metal oxazoline complexes in asymmetric catalysis

Polydentate oxazolines have been employed as highly effective stereodirecting ligands for asymmetric catalysis with metals from across most of the periodic table. Despite their highly versatile coordination chemistry, the use of these ligands tends to be polarised towards late transition metals; their use with early transition metals and the f-elements is significantly less developed. This current article aims to review the coordination chemistry and catalytic applications of Group 3 and lanthanide complexes supported by ligands possessing oxazoline moieties. Oxazoline-containing ligands were first employed in molecular lanthanide catalysis as early as 1997, yet there is still a significant void in the chemical literature in this respect. The ligands generally employed include bis(oxazolinyl)methane ("BOX"), 2,6-bis(oxazolinyl)pyridine ("pybox"), 1,1,1-tris(oxazolinyl)ethane ("trisox"), and others. The complexes are employed in a wide-range of catalytic applications, especially in Lewis acid catalysis, but also in the stereospecific polymerisation of olefins.

Synthesis and polymerization reactions of cyclic imino ethers. 5: naphthalene unit-containing poly(ether amide)s

Poly(ether amide)s containing naphthalene unit were prepared either by the polyaddition reaction of aromatic bis(2-oxazoline)s with the different dihydroxynaphthalenes or by the homopolyaddition of a monomer containing an oxazoline, a hydroxy, and naphthalene moieties. First, polymerization method represents AA + BB mode where 1,4-phenylene-2,2′-bis(2-oxazoline) (A) and 1,3-phenylene-2,2′-bis(2-oxazoline) (B) were used as AA monomers and four different dihydroxynaphthalenes 1–4 were used as BB monomers. In the second case, 2-(6-hydroxynaphthalene-2-yl)-2-oxazoline (5) was used as AB-type monomer in thermally induced polymerizations. The time dependences of polyadditions in bulk as well as in the solution were examined. The reduction of molar mass was observed after the initial fast increase of molar mass. This can be explained by the presence of side and degradation reactions. In both cases, polyadditions resulted in the linear poly(ether amide)s, which were characterized by 1H and 13C NMR spectroscopy. Thermal properties of the prepared polymers were studied by differential scanning calorimetry (DSC) measurements. Comparison of the temperatures of glass transition for polymers prepared in AA + BB mode shows the strong dependence of thermal properties on the structure of the polymers. The values were in the range of 136–171°C. The glass-transition temperature (Tg) of poly[2-(6-hydroxynaphthalene-2-yl)-2-oxazoline] prepared by AB-type polyaddition is 183°C, which corresponds to the higher contents of hard aromatic segments in the latter type of polymers compared to the polymers prepared in the AA + BB-type polyadditions. The described polymers represent novel naphthalene unit-containing poly(ether amide)s for different applications in material science. Copyright © 2011 John Wiley & Sons, Ltd.

ChemInform Abstract: Rapid Synthesis of an Electron‐Deficient t‐BuPHOX Ligand: Cross‐Coupling of Aryl Bromides with Secondary Phosphine Oxides.

AbstractCopper‐catalyzed coupling of aryl bromides, containing a chiral oxazoline moiety, with secondary phosphine oxides provides tertiary phosphine oxides which can be reduced to PHOX‐type ligands as demonstrated for the example (S)‐IIIa.

Mechanistic investigations on the efficient catalytic decomposition of peroxynitrite by ebselen analogues

In this study, ebselen and its analogues are shown to be catalysts for the decomposition of peroxynitrite (PN). This study suggests that the PN-scavenging ability of selenenyl amides can be enhanced by a suitable substitution at the phenyl ring in ebselen. Detailed mechanistic studies on the reactivity of ebselen and its analogues towards PN reveal that these compounds react directly with PN to generate highly unstable selenoxides that undergo a rapid hydrolysis to produce the corresponding seleninic acids. The selenoxides interact with nitrite more effectively than the corresponding seleninic acids to produce nitrate with the regeneration of the selenenyl amides. Therefore, the amount of nitrate formed in the reactions mainly depends on the stability of the selenoxides. Interestingly, substitution of an oxazoline moiety on the phenyl ring stabilizes the selenoxide, and therefore, enhances the isomerization of PN to nitrate.

Chelated Ruthenium Complexes of Functionalized Pentaarylcyclopentadienes

The Pd-catalyzed arylation of tetraphenylcyclopentadiene (7) and the classical “tetracyclone route” are tested as preparative entries to a variety of pentaarylcyclopentadienes 4 monofunctionalized in the ortho-position. The corresponding chelated ruthenium complexes 6 can be formed either thermally induced or by photochemical irradiation. These complexes contain stereogenic ruthenium centers. Enantiopure complexes 6f and 6g, with chiral oxazoline moieties, were tested for the asymmetric transfer hydrogenation of phenyl ketones 9.