3a 3f Research Articles

One‐Pot Synthesis of Oxime Derivatives of 1,3‐Diphenylpyrazole‐4‐carboxaldehydes from Acetophenone Phenylhydrazones Using Vilsmeier—Haack Reagent.

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Structural and theoretical investigation of 2-iminoimidazolines ? carbene analogues of iminophosphoranes

The preparation of 2-iminoimidazolines - has been accomplished by the Staudinger reaction of the carbenes 1,3-di-tert-butylimidazolin-2-ylidene (), 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene (), 1,3-diisopropylimidazolin-2-ylidene (), 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (), 1,3-bis(2,6-diisopropylphenylimidazolin-2-ylidene () and 1,3,4,5-tetramethylimidazolin-2-ylidene () with trimethylsilyl azide (Me3SiN3) followed by desilylation of the resulting 2-trimethylsilyliminoimidazolines -. The X-ray crystal structures of and have been established, revealing C1-N1-Si1 angles that are more obtuse than the corresponding P-N-Si angles observed in related trimethylsilyl iminophosphoranes. Together with , the disilylated side product 1,3-diisopropyl-2-(trimethylsilylimino)-4-trimethylsilylimidazoline () has been isolated and structurally characterized. Cleavage of the N-Si bonds in and formation of is easily achieved by stirring in methanol. The molecular structures of the 2-iminoimidazolines are reported, indicating that the structural parameters are best described by non-ylidic resonance structures and that electron delocalization within the imidazole heterocycle does not play a crucial role in these imine systems. Compound forms a head-to-head dimer in the solid state via weak intermolecular N-H...N contacts, which have additionally been characterized by means of compliance constants. To further analyze the electronic structure of these imines in comparison to related guanidine ligands, the proton affinities (PAs) of the model compounds 2-imino-1,3-dimethylimidazoline (), 2-imino-1,3-dimethylimidazolidine () and tetramethylguanidine () have been calculated by means of density functional theory. Finally, the charge distribution in - and the relative contribution of relevant resonance structures have been determined using natural bond orbitals (NBO) and natural resonance theory (NRT).

One‐Pot Synthesis of Oxime Derivatives of 1,3‐Diphenylpyrazole‐4‐carboxaldehydes from Acetophenone Phenylhydrazones Using Vilsmeier–Haack Reagent

A one‐pot synthesis of oxime derivatives 3a–3f of 1‐phenyl‐3‐arylpyrazole‐4‐carboxaldehydes has been accomplished by the Vilsmeier–Haack reaction of acetophenone phenylhydrazones 1a–1f under a new workup procedure.

Selenium-Containing Heterocycles from Isoselenocyanates: Use of Hydrazine for the Synthesis of 1,3,4-Selenadiazine Derivatives

Aryl isoselenocyanates 1 react with different phenacyl halides 2 in the presence of hydrazine hydrate in a one-pot reaction to give selenadiazines 3a–3f in good-to-excellent yields.

An Efficient Synthesis of Benzofurans and Their Application in the Preparation of Natural Products of the Genus Calea.

Abstract The intramolecular cyclization of the β-substituted olefins methyl 2-aryloxy-3-dimethylaminopropenoates 3a–3f catalyzed by Lewis acids leads to a short and novel synthesis of benzofurans 2a–2f . When the olefins 4-dimethylamino-3-aryloxy-3-buten-2-ones 4a–4f were used, the cyclization process was faster and provided the corresponding substituted 2-acetylbenzofurans 1a–1f . Among the latter, naturally occurring compounds calebertin ( 1a ), caleprunin A ( 1b ), and caleprunin B ( 1c ) were prepared in good overall yields. These benzofurans were also obtained by direct treatment under MW irradiation of the precursors 1-aryloxypropan-2-ones 7a–7c with DMFDMA, followed by addition of the catalyst, resulting in a route that was one step shorter.

Isomeric dinuclear gold(i) complexes with highly functionalised ditertiary phosphines: Self-assembly of dimers, rings and 1-D polymeric chains

An isomeric series of six linear, dinuclear, gold(I) complexes (AuCl)2{P,P-C6H4N(CH2PPh2)2(CO2H)(OH)} 6a–6f have been synthesised in high yields (>90%) from AuCl(tht) (tht = tetrahydrothiophene) and the appropriate building blocks C6H4N(CH2PPh2)2(CO2H)(OH) 3a–3f in CH2Cl2. The diphosphine ligands C6H4N(CH2PPh2)21, 4-CO2HC6H4N(CH2PPh2)22 and their corresponding digold(I) complexes 4 and 5 have also been prepared. Solution NMR (31P{1H}, 1H), FT-IR and microanalytical data are in full agreement with the proposed structures. Single crystal X-ray studies confirm that in each case, compounds 4, 5, 6a–6e are linear, with typical Au–P [2.227(4)–2.2349(17) A]/Au–Cl [2.271(2)–2.325(4) A] bond lengths and P–Au–Cl [169.37(1)–179.05(4)°] bond angles. Furthermore these studies demonstrate the relationship between regioselectivity, with respect to the –N(CH2PPh2)2, –CO2H and –OH functionalities around the benzene core, and solid state structures of the gold(I) complexes 6a–6e. In 6a, molecules are associated into pairs through classical intermolecular O–H⋯O hydrogen bonding, whilst in 6b and 6c, dimer pairs are formed using intermolecular O–H⋯Cl hydrogen bonds. 1-D chains of alternate 20-/22- or 8-/18-membered hydrogen bonded rings are propagated using O–H⋯Cl and/or O–H⋯O hydrogen bonds in compounds 6d and 6e. The Au⋯Au separation decreases from 6.179(3) A (for 6a) to 3.0722(9) A (for 6e) suggesting that aurophilicity increases within this series. The X-ray structure of a representative diphosphine 3a is also presented.

Rapid and High‐Yield Synthesis of Aryloxyacetates under Microwave Irradiation and Phase‐Transfer Catalysis Conditions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Trifluoromethanesulfonic Acid Catalyzed Alkylation of Arenes with Methyl (2R)‐Glycidate.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Microwave- and ultrasound-assisted semisynthesis of natural methoxylated propiophenones from isomeric mixture of phenylpropenes in minutes

A rapid and practical semisynthesis of natural methoxylated propiophenones (3a–3f) is realized by reacting stereo- and regio-isomeric mixture of phenylpropenes (1a–1f) with a catalytic amount of palladium chloride – sodium formate in formic acid, methanol, and water (2:1:2) into single product phenylpropanes (2a–2f) followed by its oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in wet dioxane, containing a few drops of formic acid. Conventional, ultrasound, and microwave heating were compared through these studies.Key words: focused microwave, ultrasound, phenylpropene, propiophenone, DDQ.

Rapid and High‐Yield Synthesis of Aryloxyacetates Under Microwave Irradiation and Phase‐Transfer Catalysis Conditions

A series of methyl aryloxyacetates (3a–3f) have been synthesized by the reaction of substituted phenol with methyl chloroacetate under the conditions of microwave irradiation and phase‐transfer catalysis. By the optimization of the reaction conditions, we developed a good method for the preparation of methyl aryloxyacetates, which have the advantages of high yields, short reaction times, ease of workup, and simple operation.

Trifluoromethanesulfonic Acid Catalyzed Alkylation of Arenes with Methyl (2R)‐Glycidate

AbstractMethyl (R)‐glycidate (=methyl (R)‐oxiranecarboxylate; 2) in superacidic trifluoromethanesulfonic acid medium reacts with electron‐rich arenes to give α‐hydroxy‐β‐arylpropanoate derivatives 3a–3f with high stereospecificity. At the same time, the observed high regioselectivity has been attributed to superelectrophilic activation of the glycidate.

Semaphorin/neuropilin signaling influences the positioning of migratory neural crest cells within the hindbrain region of the chick

Within the hindbrain region, neural crest cell migration is organized into three streams that follow the segmentation of the neuroepithelium into distinct rhombomeric compartments. Although the streaming of neural crest cells is known to involve signals derived from the neuroepithelium, the molecular properties underlying this process are poorly understood. Here, we have mapped the expression of the signaling component of two secreted class III Semaphorins, Semaphorin (Sema) 3A and Sema 3F, at time points that correspond to neural crest cell migration within the hindbrain region of the chick. Both Semaphorins are expressed within rhombomeres at levels adjacent to crest-free mesenchyme and expression of the receptor components essential for Semaphorin activity by neural crest cells suggests a function in restricting neural crest cell migration. By using bead implantation and electroporation in ovo, we define a role for both Semaphorins in the maintenance of neural crest cell streams in proximity to the neural tube. Attenuation of Semaphorin signaling by expression of soluble Neuropilin-Fc resulted in neural crest cells invading adjacent mesenchymal territories that are normally crest-free. The loss or misguidance of specific neural crest cell populations after changes in Semaphorin signaling also affects the integration of the cranial sensory ganglia. Thus, Sema 3A and 3F, expressed and secreted by the hindbrain neuroepithelium contributes to the appropriate positioning of neural crest cells in proximity to the neural tube, a process crucial for the subsequent establishment of neuronal connectivity within the hindbrain region.

Role of class 3 semaphorins in the development and maturation of the septohippocampal pathway.

In examining the role of Class 3 secreted semaphorins in the prenatal and postnatal development of the septohippocampal pathway, we found that embryonic (E14-E16) septal axons were repelled by the cingulate cortex and the striatum. We also found that the hippocampus exerts chemorepulsion on dorsolateral septal fibers, but not on fibers arising in the medial septum/diagonal band complex, which is the source of septohippocampal axons. These data indicate that endogenous chemorepellents prevent the growth of septal axons in nonappropriate brain areas and direct septohippocampal fibers to the target hippocampus. The embryonic septum expressed np-1 and np-2 mRNAs, and the striatum and cerebral cortex expressed sema 3A and sema 3F. Experiments with recombinant semaphorins showed that Sema 3A and 3F, but not Sema 3C or 3E, induce chemorepulsion of septal axons. Sema 3A and 3F also induce growth cone collapse of septal axons. This indicates that these factors are endogenous cues for the early guidance of septohippocampal fibers, including cholinergic and gamma-aminobutyric acid (GABA)ergic axons, during the embryonic stages. During postnatal stages, when target cell selection and synaptogenesis take place, np-1 and np-2 were expressed by septohippocampal neurons at all ages tested. In the target hippocampus, pyramidal and granule cells expressed sema 3E and sema 3A, whereas most interneurons expressed sema 3C, but few expressed sema 3E or 3A. Combined tracing and expression studies showed that GABAergic septohippocampal fibers terminated preferentially onto sema 3C-positive interneurons. In contrast, cholinergic septohippocampal fibers terminated onto sema 3E and sema 3A-expressing pyramidal and granule cells. The data suggest that Class 3 secreted semaphorins are involved in postnatal development. Moreover, because GABAergic and cholinergic axons terminate onto neurons expressing distinct, but overlapping, patterns of semaphorin expression, semaphorin functions may be regulated by different signaling mechanisms at postnatal stages.

A Rapid and Efficient Microwave‐Assisted Synthesis of Substituted 3‐Phenylpropionic Acids from Benzaldehydes in Minutes.

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Synthesis and properties of fluorinated polyimides based on 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐2,5‐di‐tert‐butylbenzene and various aromatic dianhydrides

AbstractA novel fluorinated diamine monomer, 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐2,5‐di‐tert‐butylbenzene (2), was prepared through the nucleophilic substitution reaction of 2‐chloro‐5‐nitrobenzotrifluoride and 2,5‐di‐tert‐butylhydroquinone in the presence of potassium carbonate, followed by catalytic reduction with hydrazine and Pd/C. Fluorinated polyimides (5a–5f) were synthesized from diamine 2 and various aromatic dianhydrides (3a–3f) via thermal or chemical imidization. These polymers had inherent viscosities of 0.77–1.01 dL/g. The 5 series polyimides were soluble in N‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, and N,N‐dimethylformamide and were even soluble in dioxane, tetrahydrofuran, and dichloromethane. 5(C) showed cutoff wavelengths between 363 and 404 nm and yellowness index (b*) values of 6.5–40.2. The polyimide films had tensile strengths of 93–114 MPa, elongations to break of 9–12%, and initial moduli of 1.7–2.1 GPa. The glass‐transition temperatures were 255–288 °C. The temperatures of 10% weight loss were all above 460 °C in air or nitrogen atmospheres. In comparison with a nonfluorinated polyimide series based on 1,4‐bis(4‐aminophenoxy)‐2,5‐di‐tert‐butylbenzene, the 5 series showed better solubility and lower color intensity, dielectric constants, and moisture absorption. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2272–2284, 2004

A Rapid and Efficient Microwave-Assisted Synthesis of Substituted 3-Phenylpropionic Acids from Benzaldehydes in Minutes

Abstract A convenient, inexpensive, and efficient synthesis of 3-phenylpropionic acids (1a–1f) by reacting benzaldehyde (2a–2f) and malonic acid in acetic acid and piperidine into cinnamic acid (3a–3f) in 77 to 89% followed by its reduction with PdCl2 in the biphase of formic acid and aqueous sodium hydroxide is reported under microwave irradiation which utilizes short reaction time ranging 5 to 7 min to provide 1a–1f in moderate to high yield (69–86%) depending upon methoxy, methylenedioxy, and hydroxy groups present at the phenyl ring.

Photo aldol reactions with 5-methoxyoxazoles: Highly regio- and diastereoselective synthesis of α-amino β-hydroxy carboxylic acid derivatives

A versatile route to derivatives of α-amino β-hydroxy carboxylic acids, either with tertiary (from a corresponding glycine equivalent) or a quaternary α-carbon center is described. The key reaction is the cycloaddition of electronically excited carbonyl compounds (aromatic and aliphatic aldehydes, respectively) to oxazoles. To make the products hydrolytically more labile, a methoxy substituent at position C-5 was introduced leading to the formation of cycloadducts with an orthoester substructure. The photocycloaddition, either with triplet excited (aromatic) carbonyls or with singlet excited (aliphatic) carbonyls, led to the formation of mixtures of endo- and exo-diastereoisomers with moderate to very high exo-selectivities. The 4-unsubstituted 5-methoxyoxazole 1 (glycine equivalent) gave the [2 + 2]-adducts 3a–3f with aldehydes 2a–2f in high yields and excellent diastereoselectivities. Hydrolysis of these compounds resulted in the α-amino β-hydroxy esters 4a–4f with preferred erythro (S*,S*) configuration. As an extension of this process, 4-alkylated 5-methoxyoxazoles 5a–5f were applied as alkene components and the corresponding cycloadducts with benzaldehyde 6a–6f were obtained. Again, the exo-diastereoisomers were formed as the major products in diastereoselectivities from 73:27 (exo:endo) up to >95:5. Hydrolysis of these adducts resulted in the formation of α-amino β-hydroxy esters 7a–7f with like (S*,S*) configuration of the major diastereoisomers.Key words: photo aldol reaction, oxazoles, oxetanes, photocycloaddition, amino acids, hydroxy acids.

Effects of diamines and their fluorinated groups on the color lightness and preparation of organosoluble aromatic polyimides from 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]‐hexafluoropropane

AbstractTo investigate the position and amount of the CF3 group affecting the coloration of polyimides (PIs), we prepared 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]hexafluoropropane (2) with four CF3 groups with 2‐chloro‐5‐nitrobenzotrifluoride and 2,2‐bis(4‐hydroxyphenol)hexafluoropropane. A series of soluble and light‐colored fluorinated PIs (5) were synthesized from 2 and various aromatic dianhydrides (3a–3f). 5a–5f had inherent viscosities ranging from 0.80 to 1.19 dL/g and were soluble in amide polar solvents and even in less polar solvents. The glass‐transition temperatures of 5 were 221–265 °C, and the 10% weight‐loss temperatures were above 493 °C. Their films had cutoff wavelengths between 343 and 390 nm, b* values (a yellowness index) ranging from 5 to 41, dielectric constants of 2.68–3.01 (1 MHz), and moisture absorptions of 0.03–0.29 wt %. In a comparison of the PI series 6–8 based on 2,2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane, 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]propane, and 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane, we found that the CF3 group close to the imide group was more effective in lowering the color; this means that CF3 of 5, 7, and 8f was more effective than that of 6c. The color intensity of the four PI series was lowered in the following order: 5 > 7 > 6 > 8. The PI 5f, synthesized from diamine 2 and 4,4′‐hexafluoroisopropylidenediphthalic anhydride, had six CF3 groups in a repeated segment, so it exhibited the lightest color among the four series. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 922–938, 2003

Ontogeny of semaphorins 3A and 3F and their receptors neuropilins 1 and 2 in the kidney

Semaphorins 3A and 3F are axon guidance proteins during nervous system development. Their expression pattern and function outside the nervous system are unknown. Neuropilin 1 and 2 (NP-1, NP-2) are natural ligands for semaphorins 3A and 3F, respectively. NP-1 is also a co-receptor for vascular endothelial growth factor (VEGF) required for normal vascular development. We showed that VEGF is a direct chemoattractant for glomerular endothelial cells towards developing nephrons. To examine whether semaphorins could modulate VEGF endothelial cell guidance cues in the developing kidney, we studied the expression of semaphorin 3A and semaphorin 3F and their receptors NP-1 and NP-2 in the kidney during ontogeny using Northern blot analysis, in situ hybridization, Western blot analysis and immunohistochemistry. All four genes are developmentally regulated, with abundant expression during organogenesis and downregulation in the adult kidney. Semaphorin 3A and 3F are expressed by podocytes and tubules whereas their receptors NP-1 and NP-2 are localized to endothelial cells. In vitro, renal tubular epithelial cell lines (tsMPT, IRPT and MDCK) and glomerular endothelial cells express both semaphorins and their receptors, suggesting the presence of an autocrine system. The distribution of the receptors NP-1 and NP-2 in endothelial cells and developing vessels is complementary to that of the ligands in adjacent epithelial cells during kidney development. The sum of the guidance cues provided by VEGF and semaphorins 3A and 3F may be important determinants of the pattern of endothelial cell migration during kidney morphogenesis.

Sodium sulfate supported synthesis of cationic cyclophanes using microwaves

A facile microwave-assisted synthesis of a series of cationic cyclophanes, viz. benzimidazolophanes 3a–3f, benzotriazolophanes 3g–3j, through efficient double quaternization of the corresponding precyclophanes 1a–1j with appropriate dibromides 2a–2d in solid phase medium, is described.