Site-selective Suzuki cross-coupling reactions of 2,3-dibromobenzofuran

The Suzuki-Miyaura reaction of 2,3-dibromobenzofuran with two equivalents of boronic acids gave 2,3-diarylbenzofurans. The reaction with one equivalent of arylboronic acids resulted in site-selective formation of 2-aryl-3-bromobenzofurans. 2,3-Diarylbenzofurans containing two different aryl groups were prepared from 2,3-dibromobenzofuran in a one-pot protocol by sequential addition of two different boronic acids.     

A facile synthesis of 2,3-disubstituted furo[2,3-b]pyridines

In a three-step sequence starting from readily available starting materials, 2,3-carbon disubstituted furo[2,3-b]pyridines can be accessed in good yields and purity. Furo[2,3-b]pyridines bearing ester, amide and ketone groups at the 2-position can be prepared with a variety of aryl and alkyl groups at the 3-position.     

Reaction of 2,3-diphenylpyrazine 1-oxides with acetic anhydride

Some 2,3-diphenylpyrazine 1-oxides were heated with acetic anhydride to give the corresponding 2,3-di-acetoxy-2,3-dihydro-5,6-diphenylpyrazines. By X-ray diffraction analysis, the configuration of two acetoxyl groups was determined to be trans.     

Competitive adsorption of organic matter with phosphate on aluminum hydroxide

The effects of orthophosphate on the adsorption of natural organic matter (NOM) on aluminum hydroxide were investigated using three organic compounds as surrogates, including humic acid (HA), phthalic acid, and 2,3-dihydroxybenzoic acid (2,3-DHBA). The adsorption of phthalic acid and 2,3-DHBA was very limited compared to that of HA, whereas their adsorption was reduced much more significantly than that of HA by phosphate. The efficiency of phosphate in reducing HA adsorption increased with increasing phosphate concentration. Phosphate adsorption was slightly reduced by phthalic acid and 2,3-DHBA but moderately suppressed by HA. The adjacent carboxylic groups mainly contributed to the adsorption of humic acid at low pH, while the adjacent phenol groups were responsible for the adsorption of humic acid at high pH. HPLC-SEC and SUVA analysis revealed that HA molecules with high molecular weight were adsorbed preferentially but were easily displaced by the specifically adsorbed phosphate. TM-AFM images revealed that the aggregation of HA molecules and the protonation of carboxylic groups at low pH facilitated the adsorption under acidic conditions. The presence of phosphate increases the coagulant dosage for NOM removal as some sites on the coagulant precipitates become utilized by phosphate.     

Aromatic condensation monomers and polymers containing quinoxal-2,3-diyl groups

The main achievements in the synthesis of aromatic condensation monomers and polymers containing quinoxal-2,3-diyl groups are surveyed. Two general approaches to incorporation of such groups into macromolecules are considered: (i) the synthesis of polymers with α-diketone groups (polybenzyls) followed by their polymer-analogous transformations under the influence of o-phenylenediamine and its derivatives and (ii) the synthesis of target polymers of various classes from monomers containing quinoxal-2,3-diyl groups. Particular attention is focused on the properties of the polymers of interest.     

The rearrangement of 2,3-epoxysulfonates and its application to natural products syntheses: formal synthesis of (-)-aphanorphine and total syntheses of (-)-alpha-herbertenol and (-)-herbertenediol

The Lewis acid treatment of 2,3-epoxysulfonates with 2,3-dialkyl substituents or 2-alkyl-3-aryl substituents produced the rearrangement products via C3-cleavage of the oxirane ring in high yields. On the other hand, 2-aryl-3-alkyl-2,3-epoxysulfonates produced the products via C2-cleavage of the oxirane ring. The sulfonyloxy groups of the alpha-sulfonyloxy ketones, having a chiral benzylic quaternary carbon center obtained by the rearrangement of 2-alkyl-3-aryl-2,3-epoxysulfonates, were reductively eliminated to give the ketones with a chiral benzylic quaternary carbon center. The method was applied to the formal synthesis of (-)-aphanorphine and total syntheses of (-)-alpha-herbertenol and (-)-herbertenediol.     

Efficient regioselective heterocyclisation leading to fluorescent fused pyrazine derivatives

The regioselective syntheses of substituted pyrrolo[2,3-b]quinoxaline, pyrido[2,3-b]pyrrolo[2,3-e]pyrazine, pyrido[2,3-b]pyrrolo[3,2-e]pyrazine and pyrido[3,4-b]pyrrolo[3,2-e]pyrazine are reported. Differential reactivity between two amino groups in ortho-diaminopyridine can be exploited to obtain new regio-defined unsymmetrical pyridopyrrolopyrazine derivatives. Weak electron-donating methyl or moderately electron-withdrawing carboxylic groups attached to the aromatic ortho-diamines reduce the regioselectivity of obtaining unsymmetrical substituted pyrrolo[2,3-b]quinoxaline. The fluorescence properties of the resultant 1-alkyl pyridopyrrolopyrazine and substituted pyrrolo[2,3-b]quinoxaline derivatives are presented.     

Potentiometric and spectroscopic studies on yttrium(III) complexes of dihydroxybenzoic acids

The equilibrium reactions of yttrium(III) ion with dihydroxybenzoic acids (2,3-dihydroxybenzoic acid (2,3-DHBA) and 3,4-dihydroxybenzoic acid (3,4-DHBA)) (H(3)L) were investigated in aqueous solution by means of potentiometric and spectroscopic methods, in 0.1 mol.l(-1) ionic strength medium at 25 degrees C. The stability constants are reported for YL, YL(HL)(2-) and YL(2)(3-)- type mononuclear complexes. 2,3-DHBA can bind Y(III) ion strongly and the salicylate mode is effective over the acidic pH range. But in higher pH range, 2,3-DHBA and 3,4-DHBA act more efficiently through catecholate groups. The complexes of 2,3-DHBA are more stable than the complexes of 3,4-DHBA.     

Synthesis of pyrazine-2,3-dicarbonitriles via the one-pot three-component reaction of 4-benzoyl-5-phenylamino-2,3-dihydrothiophene-2,3-dione,diaminomaleonitrile, and functionalized alcohols in acetonitrile

An efficient one-pot three-component reaction of 4-benzoyl-5-phenylamino-2,3-dihydrothiophene-2,3-dione, diaminomaleonitrile, and alcohols with hetero-atom substituents or several hydroxyl groups in acetonitrile solvent under reflux led to the formation of 5-(2-substituted ethoxy or propoxy-2-phenyl-1-N-phenylthiocarbamoylethenyl)-6-oxo-1,6-dihydropyrazine-2,3-dicarbonitrile derivatives in good yields.     

Further characterization of the binding of heparin to granulocyte colony-stimulating factor: importance of sulfate groups

Heparin mediates fundamental biological mechanisms through interaction with proteins. Previously, we have shown that standard heparin binds to granulocyte colony-stimulating factor (G-CSF) with an affinity of 4.8 x 10(5) M(-1). To further study the structural features in heparin that are responsible for this interaction, we studied the bindings of G-CSF and N-desulfated and 2,3-O-desulfated heparin by CZE. Results showed that the N-desulfated heparin had a similar affinity for G-CSF ((5.4 +/- 0.9) x 10(5) M(-1)), but the 2,3-O-desulfated heparin had a 1000-fold lower affinity ((3.4 +/- 1.2) x 10(2) M(-1)) in comparison to standard heparin. The results showed that 2,3-O-sulfate groups are more important than N-sulfate groups in heparin-G-CSF interaction.     

Induction of a preferred sense of twist in flexible diphenyls by carbohydrate scaffolds. Synthesis of two "naked" ellagitannin analogous.

The synthesis of "naked" ellagitannin analogues 1 and 2, having a preferred sense of twist of the diphenyl moiety, with a rhamnose and a glucose template, is reported. A clear induction in the chirality of the diphenyl moiety, mediated through a 10-membered ring via ester linkages, was observed. The chiral scaffold of glucose (diequatorial 2,3-hydroxyl groups) exerts a remarkable stronger atropdiastereoselective effect onto the diphenoyl group than the rhamnose ring (axial-equatorial 2,3-hydroxyl groups), according to the Schmidt-Haslam hypothesis.     

A simple synthesis of natural spinazarins and their analogues

A short simple synthesis of spinazarins (2,3-dihydroxy-naphthazarins or 2,3,5,8-tetrahydroxy-1,4-naphtho-quinones) from available 2,3-dichloronaphthazarin derivatives involves replacement of chlorine atoms with azido groups followed by their acidic hydrolysis. The procedure can be used for the preparative synthesis of natural biologically active spinazarins and their analogues.     

Site-selective Suzuki-Miyaura reactions of 2,3-dibromo-1H-inden-1-one

The first transition metal-catalyzed cross-coupling reactions of 2,3-dibromo-1H-inden-1-one are reported. The Suzuki-Miyaura reaction of 2,3-dibromo-1H-inden-1-one with 2 equiv of arylboronic acid gave 2,3-diaryl-1H-inden-1-ones. The reaction with 1 equiv of arylboronic acid gave 2-bromo-3-aryl-1H-inden-1-ones with very good site-selectivity. The one-pot reaction of 2,3-dibromo-1H-inden-1-one with two different arylboronic acids afforded 2,3-diaryl-1H-inden-1-ones containing two different terminal aryl groups.     

Synthesis and Thermal Properties of Crosslinked Poly(2,3-Tetrahydrofurandiyl)s

Abstract

Bi- and trifunctional monomers with 2,3-dihydrofuranyl moieties were synthesized. The polymerizable dihydrofuranyl groups were connected to each other with ester and ether linkages. Alkyl-, alkenyl- and arylspacers were used. The synthesized monomers were copolymerized with 2,3-dihydrofuran by photoinduced cationic polymerization. As photo acid (η⁵-cyclopentadienyl)-Fe(II)-(η⁶-isopropylbenzene) hexafluorophosphate was used. The thermal stability of the crosslinked poly(2,3-tetrahydrofurandiyl)s is dependent of the monomer structure. Higher stability was observed for poly(tetrahydrofurandiyl)s crosslinked with bis(2,3-dihydrofuranyl) compounds instead of tetraethyleneglycol bis-2-propenyl-ether.     

Polymethine dyes derived from heterocyclic bases containing condensed thiophene rings

The synthesis of polymethine dyes of the cyanine and merocyanine series derived from 3-methylthionaphtheno[2,3-b]pyridine, 3-methylthionaphtheno[3,2-b]-pyridine, 6-methylthieno[2,3-b]thieno[2,3-b]-pyridine, and 6-methylthieno[3,2-b]thieno[2,3-b]pyridine is described. The color of the dyes obtained is discussed. It has been shown that the replacement of vinylene groups by sulfur atoms in one of the two benzene rings of the hetero residue in 2-substituted 5,6-benzoquinolines in cyanine dyes leads to a bathochromic shift of the absorption maxima.For part VI, see [8].     

Armed-disarmed effect of remote protecting groups on the glycosylation reaction of 2,3-dideoxyglycosyl donors

The armed-disarmed effect of remote protecting groups at the C-4 and/or C-6 position(s) on the glycosylation reactions of 2,3-dideoxyglycosyl donors was investigated. It was found that under various glycosylation conditions, 4- or 6-O-Bn 2,3-dideoxyglycosyl donors were much more reactive than the corresponding 4,6-di-O-Bz 2,3-dideoxyglycosyl donors. Based on these results, an effective and chemoselective glycosylation reaction using 4,6-di-O-Bn glycosyl acetate and 4-OH-6-O-Bz glycosyl acetate was realized, producing a 2,3-dideoxydisaccharide in good yield with high α-stereoselectivity.     

含有热引发转移终止剂的引发体系在反向原子转移自由基聚合中的应用

原子转移自由基聚合 (ATRP)是实现活性聚合的一种颇为有效的途径 ,可以实现多种单体的活性自由基聚合 .反向原子转移自由基聚合 (ReverseATRP)的概念始提出于 1995年 ,是对传统ATRP的改进和拓展 .近年来关于此体系的引发剂的拓展、过渡金属及单体的适用性都得到了很大发展 .本文简要综述了我们研究组在反向原子转移自由基聚合方面的研究进展     

Hydrogen bonding. Part 75. Infrared, titrametric and molecular orbital study of the structure, solubility and reaction with fluoride ion of 2,3-dicarboxypyrazine

2,3-Dicarboxypyrazine (2,3-H₂DCPz), unlike 2,3-dicarboxypyridine (2,3-H₂DCPy), does not exist as a zwitterion in the solid state. This is due to the remarkably low base strength of nitrogen in the pyrazine ring relative to that of pyridine. The decrease in the base strength of pyrazine relative to pyridine may result from greater disruption of the aromatic π-system of pyrazine on protonation than is the case with pyridine. We propose that 2,3-H₂DCPz has a structure of C_s symmetry in the solid state in which one carboxyl group forms an internal hydrogen bond to carbonyl of adjacent carboxyl in the same molecule, and the second carboxyl forms an intermolecular hydrogen bond to carbonyl in an adjacent molecule. The monoanion in 2,3-NaHDCPz has a strong O–H–O covalent three-center hydrogen bond between carboxylate groups. When saturated solutions of 2,3-H₂DCPz are treated with F⁻, one additional diacid molecule is taken into solution for each 1.5 F⁻ added. As is the case with 2,3-H₂DCPy, the high solubility and acid strength of 2,3-H₂DCPz (pK_a=2.87) leads to formation of the hydrogen-rich H₂F₃⁻ ion instead of HF₂⁻.     

用环糊精合成楔筒状主体分子新模型

用四醋酸铅将七元（6-O-二甲基叔丁基硅基）-β-环糊精选择氧化、并用三氟 化硼乙醚脱硅基保护基后,再经分离、纯化,可获得具有“楔筒状”空腔的单-2, 3-二醛基-β-环糊精。单-2,3-二醛基-β-环糊精较β-环糊精有更好的水溶性。 用单-2,3-二醛基-β-环糊精作TLC流动相手性添加剂时,可将肾上腺素对映体在 硅胶薄层板上有效拆分。     

N-heterocyclic carbene-catalyzed cascade annulation reaction of o-vinylarylaldehydes with nitrosoarenes: one-step assembly of functionalized 2,3-benzoxazin-4-ones

The NHC-catalyzed reactions of ortho electron-deficient vinyl substituted arylaldehydes with nitrosoarenes were studied. The reactions produced multifunctional 2,3-benzoxazin-4-ones in good to excellent yields via a cascade aza-benzoin reaction between aldehyde and nitroso groups followed by an intramolecular oxo-Michael addition. The resulting 1-acetate substituted 2,3-benzoxazinones were transformed into a new type of β-hydroxycarboxylate derivatives or 3-oxo-1-isobenzofuranacetates, respectively, under different reductive conditions. This work not only provides a simple and efficient method for the construction of multifunctional 2,3-benzoxazin-4-ones of potential pharmacological interest, but also expands the application of NHC-catalyzed cascade reactions in the formation of carbon-heteroatom and heteroatom-heteroatom bonds.