The oxidation profile at C-18 of furanocembranolides may provide a taxonomical marker for several genera of octocorals

The furanocembranolides 1-3 along with the known compounds pukalide, pukalidealdehyde, epoxypukalide, and leptolide were isolated from Leptogorgia spp. and their structures were determined by spectroscopic evidences. An NMR-based method using Pirkle's reagent at low temperature allowed us to determine the absolute configuration at C-10 of a γ-butenolide unit embedded in a flexible furanocembranolide network. The C-18 of furanocembranolides undergoes an oxidation cascade leading from a methyl group to a carboxylic acid/ester that appears to be genus specific. We introduce the concept genus-specific oxidation, a feature that provides a chemotaxonomical marker for several genera of octocorals. This concept also allowed us to propose a biogenetic pathway for these compounds.     

Application of laccase/DDQ as a new bioinspired catalyst system for the aerobic oxidation of tetrahydroquinazolines and Hantzsch 1,4-dihydropyridines

Laccase/DDQ as a new bioinspired quinone-based cooperative catalytic system was used for the biomimetic aerobic oxidative synthesis of 2-substituted quinazolines and Hantzsch pyridines from the oxidative cyclocondensation of 2-aminobenzylamine and aldehydes and the oxidative aromatization of 1,4-dihydropyridines, respectively. The products were obtained in good to high yields in a phosphate buffer (0.1 M, 12.5 mL, pH 4.5) and acetonitrile (4 vol%) mixture as a solvent. These methods are more eco-friendly, efficient, simple, and practical than other currently available ones because of mild reaction conditions and because they are free from any halide and toxic and expensive transition metals. Therefore, these methods can be applied in pharmaceutical and other sensitive synthetic procedures.     

Water as an additive for selective synthesis of saturated 1,4-diketones and tetrasubstituted furans directly from 1,4-enediones

Water-controlled and phosphine-mediated selective synthesis of saturated 1,4-diketones and tetrasubstituted furans has been developed directly from 1,4-enediones. Saturated 1,4-diketones were selectively obtained in acetone with water as an additive, whereas tetrasubstituted furans were selectively obtained in anhydrous 1,2-dichloroethane. A large variety of functional groups are tolerated under these reaction conditions, including electron-rich, electron-poor, halogen, and heteroaryl substituents. This method also has significant advantages in easily available substrates, mild reaction conditions, and high reaction efficiency.     

Methods for the Synthesis of Heteroaryl-substituted 1,4-Benzo- and 1,4-Naphthoquinones. (Review)

Methods for the synthesis of heteroaryl-substituted 1,4-benzo- and 1,4-naphthoquinones with a C-C bond between the heterocycle and quinone fragments are reviewed. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 803–833, June, 2005.     

Investigation of methylaluminoxane as a cocatalyst for the polymerization of 1,3-butadiene to high cis-1,4-polybutadiene

The catalytic system Co/methylaluminoxane/tert-butyl chloride has been studied and optimized for the polymerization of 1,3-butadiene to high cis-1,4-polybutadiene. The ratio of the individual catalyst components was investigated to achieve maximum conversion, stereoregularity, and molecular weight. It was found that the specific order of addition of catalyst components to the feedstock and aging time therein has critical influence in the polymerization reaction. This can be attributed to the rate of chlorinating the aluminoxane and the stability of the active catalyst sites obtained. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3277–3284, 1999     

Synthesis of novel aza analogues of 2-substituted-2,3-dihydro-1,4-benzodioxins as potential new scaffolds for drug discovery

New synthesis approaches that have led to a series of novel aza analogues of the 2-substituted-2,3-dihydro-1,4-benzodioxin core, bearing versatile bromomethyl group on the non aromatic oxygenated ring, are described. According to their structures these novel scaffolds can be useful intermediates for the preparation of potential new therapeutic agents.     

1,4-Cyclohexadiene with Pd/C as a rapid, safe transfer hydrogenation system with microwave heating

A method for the rapid, safe hydrogenation of alkenes and deprotection of benzyl ethers and carboxybenzyl amides is described using catalytic transfer hydrogenation under microwave heating conditions. Commonly available Pd/C catalyst is extremely effective with 1,4-cyclohexadiene as the hydrogen transfer source. In general, the reactions are complete within five minutes at 100 °C.     

Oxidation of cationic 1,4-dihydropyridine derivatives as model compounds for putative gene delivery agents

A new synthetic approach to cationic pyridine derivatives is described here. Two different strategies for the synthesis of 1,1′-{[3,5-bis(ethoxycarbonyl)-4-phenylpyridine-2,6-diyl]dimethylene}bispyridinium salts have been developed. The key step of the first strategy relies on electrochemical and chemical oxidation of cationic 1,4-dihydropyridines; the second one involves nucleophilic substitution of pyridine dibromo derivatives.     

Stereoselective synthesis of highly enantioenriched 3-methyl-2-cyclohexen-1-ones possessing an asymmetric quaternary carbon as C-4 or C-6: a sugar template approach

The 1,4-addition of the enolate generated from α-methylated acetoacetate incorporated at C-4 of methyl 6-deoxy-2,3-di-O-(tert-butyldimethylsilyl)-α-d-glucopyranoside to methyl vinyl ketone, followed by aldol condensation of the resulting 1,4-addition product under two base-mediated conditions, provided 4-O-functionalized d-glucose derivatives with high diastereoselectivity. These products install a 3-methyl-2-cyclohexen-1-one-4- (or -6-) carboxylic acid as the O-4 ester, in which C-4 or C-6 is an asymmetric quaternary carbon. Removal of the sugar template from those aldol condensation products provided synthetically useful 3,6-dimethyl-2-cyclohexen-1-one-6-carboxylic acid and 3,4-dimethyl-2-cyclohexen-1-one-4-carboxylic acid derivatives both in high enantioenriched forms.     

Silica Chloride/NaNO 2 as a Novel Heterogeneous System for the Oxidation of 1,4-Dihydropyridines Under Mild Conditions via In Situ Generation of NOCl

A combination of silica chloride and sodium nitrite in the presence of wet SiO 2 were used as an effective oxidizing agent for the oxidation of dihydropyridines to their corresponding pyridine derivatives under mild and heterogeneous conditions in moderate to excellent yields.     

A novel one-pot synthesis of carbazole-1,4-quinones through Pd-catalyzed cyclocarbonylation,desilylation and oxidation processes from 3-iodo-2-propenylindoles

A novel one-pot synthesis of carbazole-1,4-quinone by consecutive Pd-catalyzed cyclocarbonylation, desilylation, and oxidation reactions is described. We propose a possible mechanism of the cyclocarbonylation reaction between 3-iodo-2-propenylindole and CO (1 atm) in the presence of a tributyl(vinyl)tin and Pd-catalyst and the resulting acylpalladium species was directly coupled with a terminal alkene to produce the carbazole-1,4-quinone. To our knowledge, this is the first example of this type of reaction. A new formal total synthesis of a carbazole-1,4-quinone alkaloid, murrayaquinone A was established using this reaction.     

13X分子筛负载Fe催化剂上1,4-二氧六环在空气中完全氧化(英文)

采用浸渍法制备了不同Fe含量的13X分子筛负载的Fe催化剂(Fe/X13),运用N_2吸附-脱附法测得其BET比表面积和BJH孔径分布,采用X射线衍射、扫描电镜、程序升温还原和NH_3程序升温脱附法表征了该催化剂的织构性质.在固定床流动反应器中,以空气为氧化剂、在100-400℃范围内考察了Fe/X13催化剂上1,4-二氧六环的完全氧化反应性能,研究了反应温度、金属担载量和气体空速(GHSV)等条件对催化氧化降解二氧六环反应性能的影响,并在400℃测定了该催化剂反应50h的稳定性,结果表明,6 wt%Fe/13X催化剂表现出最高的催化性能,在400℃,GHSV=24000 h~(-1)的条件下,二氧六环转化率为97%,生成CO和CO_2的选择性达95%,降解产物还包括少量的乙醛、乙二醇-甲酸酯、乙二醇二甲酸、1,4-二氧六环-2醇、1,4-二氧六环-2酮及2-甲氧基1,3二氧戊环.基于这些经色谱-质谱联用仪检测出的产物,提出了可能的1,4-二氧六环降解机理。     

Design and synthesis of 4H-1,4-benzothiazines containing thiazole ring system for use as potential biopharmaceuticals

Synthesis of 4H-1,4-benzothiazines containing thiazole ring system is reported by condensation of substituted 2-amino-benzenethiols with N-(substituted benzothiazol-2-yl)-3-oxo-butyr-amides in the presence of DMSO.     

Synthesis of a functionalized tetrahydro-1,4-thiazepine in water as the solvent and theoretical investigation of its tautomeric structures

Reaction of sodium 2,2-dicyanoethene-1,1-bis(thiolate) with 2-chloroethylamine hydrochloride in water afforded the novel (Z)-5-amino-7-thioxo-2,3,4,7-tetrahydro-1,4-thiazepine-6-carbonitrile. The molecular geometry of the most stable tautomeric structure was investigated with DFT and AIM at the B3LYP level of theory using the standard 6-31G** basis set. Correspondence: Mehdi Bakavoli, Department of Chemistry, School of Science, Ferdowsi University, 91775-1436 Mashhad, Iran.     

ZrCl4/Hantzsch 1,4-dihydropyridine as a new and efficient reagent combination for the direct reductive amination of aldehydes and ketones with weakly basic amines

ZrCl4/Hantzsch 1,4-dihydropyridine is a mild and highly efficient reagent combination for the direct reductive amination.Weakly basic amines such as anilines substituted by electron-withdrawing group and heteroaromatic amines can be reductivelyalkylated with electron rich aldehydes and ketones under mild conditions to form the secondary amines in excellent yields.     

Selective oxidation of acetylenic 1,4-diols with dioxiranes in comparison with the methyltrioxorhenium-hydrogen peroxide oxidant

Dimethyldioxirane (1a) and its trifluoro analog (1b) were employed to achieve selectively the direct transformation of hex-3-yne-2,5-diol 3a and 1,4-diphenyl-but-2yne-1,4-diol 3b (two representative acetylenic 1,4-diols) into the corresponding carbonyls, leaving the carbon-carbon triple bond moiety untouched. The results are compared with those recorded in the analogous oxidation using the methyltrioxorhenium (MTO)/85% H₂O₂ homogeneous system. The powerful methyl(trifluoromethyl)dioxirane (1b) is the reagent of choice to achieve optimum yields of the target alkyne-1,4-diones, which are extremely versatile synthons.     

一步法合成Pt@ZIF-8及其在1,4-丁炔二醇选择加氢中的应用

1,4-丁炔二醇(BYD)部分加氢生成1,4-丁烯二醇(BED),BED进一步加氢生成1,4-丁二醇(BDO).此外,BYD,BED和BDO还会发生脱水反应生成单醇类产物.工业上BYD加氢反应主要用于生产BDO.由于传统的单金属加氢催化剂很难控制反应的加氢程度,因此一般通过提高反应温度和压力使BYD尽量转化为完全加氢产物BDO,以减少部分加氢产物BED对最终产品收率的影响.部分加氢产物BED在精细化工领域也具有重要的应用,所以选择合适的催化剂和反应条件来提高部分加氢产物BED的选择性具有重要的理论意义和潜在应用价值.文献中常采用Zn、微生物等活性抑制剂来降低贵金属催化剂的加氢活性.这些方法往往比较复杂,所使用的添加剂不仅存在毒性和污染产物,还会增加成本.这些方法得到的催化材料虽然可以提高烯醇的选择性,但是仍需要严格控制反应条件才能得到较高收率的部分加氢产物.本文基于MOFs材料独特的结构和性质,探索了MOFs负载型贵金属催化剂在选择加氢反应中的催化性能.首先制备了一种羧酸根保护的Pt纳米溶胶,并以水为溶剂,增加2-甲基咪唑的加入量,实现了室温下ZIF-8晶体的快速生成.在室温合成ZIF-8的过程中加入羧酸根保护的Pt纳米溶胶,通过羧酸根与ZIF-8之间存在的化学吸附力,实现ZIF-8对Pt纳米粒子的包覆.羧酸根不仅可以稳定溶液中的纳米粒子,同时还起着“桥梁”的作用.羧酸根中的C=O基团与ZIF-8中的Zn原子或有机骨架之间弱的配位作用,增加了纳米粒子和ZIF-8之间的亲和力,实现了金属纳米粒子被ZIF-8包围.Pt纳米粒子的引入对ZIF-8的形成也没有影响,得到的Pt@ZIF-8材料拥有良好的晶体结构和高的比表面积.采用XRD、N2吸附和TEM等表征揭示了Pt@ZIF-8的结构特点,并研究了其在水相1,4-丁炔二醇加氢反应中的催化性能.结果显示,该材料不仅具有很高的活性,还具有突出的部分加氢选择性.在5次循环反应中,BYD转化率没有明显变化,说明催化剂在反应过程中活性没有降低.在多次反应之后,反应产物的分布也没有发生明显变化,1,4-丁烯二醇选择性在5次反应中都保持在94％以上.结构表征结果则显示,在4次循环使用之后,催化剂的结构已经遭到破坏;5次循环使用之后,催化剂的XRD谱图中ZIF-8的特征衍射峰完全消失.其余谱峰为ZnO特征衍射峰,说明由于反应温度较高,催化剂在多次反应之后其载体ZIF-8发生了分解.循环寿命实验说明,ZIF-8中Zn离子和含氮有机骨架的抑制作用是导致1,4-丁烯二醇高选择性的重要原因.ZIF-8的分解虽然会使孔道塌陷,但是结构中的Zn和含氮的有机骨架组成依然存在,仍然可以达到抑制烯醇进一步加氢的效果,并且Pt纳米溶胶主要存在于外表面,所以催化剂的活性和选择性没有发生明显变化.     

Pyrazolo[1,4]diazepines as non-peptidic probes of the oxytocin and vasopressin receptors

An improved synthesis of differently substituted pyrazolo[1,4]diazepine compounds is reported. In addition, we have used this methodology to obtain non-peptidic compounds to probe the oxytocin and vasopressin receptors.     

Phase-transfer oxidation of 2-methyl-1-naphthol into 2-methyl-1,4-naphthoquinone in the presence of vanadomolybdophosphoric heteropolyacids

2-Methyl-1-naphthol is oxidized into 2-methyl-1,4-naphthoquinone (menadione) by air in the presence of vanadomolybdophosphoric heteropolyacids and their salts. The reaction proceeds in a biphasic system, and the yield of menadione is up to 85 %. The influence of the composition of the heteropolyacids on the rate and the selectivity of the reaction was studied, and the reaction mechanism was proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1208–1211, July, 1994.     

Studies on the chemistry of 1,4-oxazines,XV: Synthesis of ethyl 3,4-dihydro-4-tosyl-2H-1,4-benzoxazine-3-carboxylate

A four step synthesis of ethyl 3,4-dihydro-4-tosyl-2H-1,4-benzoxazine-3-carboxylate (4) from the acetal5 is described.

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Studien zur Chemie der 1,4-Oxazine, 15. Mitt.: Synthese des 3,4-Dihydro-4-tosyl-2H-1,4-benzoxazin-3-carbonsäureethylesters (Kurze Mitteilung)

Zusammenfassung Eine Synthese des 3,4-Dihydro-4-tosyl-2H-1,4-benzoxazin-3-carbon-säureethylesters (4) über vier Stufen wird, ausgehend vom Acetal5, beschrieben.