二甲二氧环烷的制备和一些碳碳双键的环氧化

通过过一硫酸和丙酮反应, 合成了新型高效的氧化剂二甲二氧环烷。其光谱数据和理化性能与文献报道一致, 制得的氧化剂应用于一系列天然化合物的碳碳双键环氧化反应, 取得较好结果。反应转化率高, 副反应很少, 产物纯化方便。     

活化二甲亚砜选择性氧化醇的反应

介绍活化二甲亚砜在醇类选择性氧化方面的反应及机理     

二氧杂环丙烷参与的烯烃环氧化反应

酮是催化烯烃环氧化反应的一类重要催化剂, 酮与氧化剂KHSO₅ (Oxone)可原位产生二氧杂环丙烷中间体, 然后二氧杂环丙烷中间体将氧原子传递给烯烃使之成为环氧化物, 而自身又生成原来的酮. 酮的催化效能大小与酮产生二氧杂环丙烷的能力、二氧杂环丙烷将氧原子传给烯烃的能力以及反应条件下酮的稳定性有关. 本工作对各种脂肪酮、脂环酮、杂环酮对烯烃环氧化催化能力的大小及其影响因素进行了评述.     

3,4—亚甲二氧基正丙基苯的氯甲基化反应

在季铵盐四乙基溴化铵存在下，３，４－亚甲二氧基正丙基进行氯甲基化反应的转化率达９６．６％，定位选择性达１００％，对产物进行了气相色谱，红外光谱，核磁共振测定及元素分析。     

α-氧代烯酮环二硫代缩酮化学——α,α-二氧代烯酮环二硫代缩酮与乙二胺反应

由α，α－二氧代烯酮环二硫代缩酮与乙二胺反应制得五种α，α－二氧代烯酮环二氮代缩酮化合物，所有产物均经元素分析、ＩＲ、１ＨＮＭＲ和１３ＣＮＭＲ确证。     

α—氧代烯酮环二硫代缩酮化学：α,α—二氧代烯酮环二硫代缩酮与乙二…

由α，α－二氧代烯酮环二硫代缩酮与乙二胺反应制得五种α，α－二氧代烯酮环二氮代缩酮化合物，所有产物均经元素分析，ＩＲ＾１ＨＮＭＲ和＾１３ＣＮＭＲ确证。     

氧化苯乙烯和氧化二苯乙烯的区域选择性和立体选择性开环

本文报道 NaBH_4-CoCl_2可使氧化苯乙烯类化合物发生区域选择性开环,主要生成β-苯乙醇衍生物。对于氧化二苯乙烯类化合物,由于受到苯环的空间阻碍,使其开环能力减弱,如反式氧化二苯乙烯比顺式异构体更难于开环。     

N-羟基邻苯二甲酰亚胺及其类似物催化下的分子氧氧化反应

本文综述了近年来N-羟基邻苯二甲酰亚胺（NHPI）及其类似物催化下分子氧氧化的各种反应,并对它们的催化机理作了简要介绍。NHPI与过渡金属离子组成的催化体系能高效的催化乙烷氧化为乙酸、环烷烃氧化为二元羧酸、甲苯氧化为苯甲酸、烯烃氧化为环氧化物、炔烃氧化为炔酮、酰胺氧化为酰亚胺;NHPI单独使用能催化金刚烷发生氧化羰基化反应、催化氧化醇制取过氧化氢;NHPI与有机助催化剂如：偶氮二异丁腈、溴化季铵盐、蒽醌、醇等也能催化分子氧氧化反应。     

过氧化氢与苯乙烯环氧化的反应机理及溶剂效应

以过氧化氢与苯乙烯环氧化为模型反应, 采用Materials Studio软件中Dmol³模块, 模拟计算了过氧化氢与苯乙烯的环氧化反应机理. 并用连续介质-类导体屏蔽模型(COSMO)研究了反应体系分别在三种质子性溶剂(水, 乙醇, 叔丁醇)中的溶剂化效应. 为研究溶剂分子直接参与反应的微观过程, 用离散介质模型模拟了单个水分子、乙醇分子和叔丁醇分子分别对反应的影响. 两种溶剂模型所得的结果一致, 叔丁醇作溶剂时反应活性最好, 乙醇次之; 质子性溶剂能够促进过氧化氢分子的异裂, 形成活性氧物种, 从而使反应能垒降低.     

Natural Products with Anti‐Bredt and Bridgehead Double Bonds

Well over a hundred years ago, Professor Julius Bredt embarked on a career pursuing and critiquing bridged bicyclic systems that contained ring strain induced by the presence of a bridgehead olefin. These endeavors founded what we now know as Bredt’s rule (Bredtsche Regel). Physical, theoretical, and synthetic organic chemists have intensely studied this premise, pushing the boundaries of such systems to arrive at a better understood physical phenomenon. Mother nature has also seen fit to construct molecules containing bridgehead double bonds that encompass Bredt’s rule. For the first time, this topic is reviewed in a natural product context.     

Epoxidation of Polyunsaturated Fatty Acid Double Bonds by Dioxirane Reagent: Regioselectivity and Lipid Supramolecular Organization

The use of dimethyldioxirane (DMD) as the epoxidizing agent for polyunsaturated fatty acids was investigated. With fatty acid methyl esters, this is a convenient method for avoiding acidic conditions, using different solvents, and simplifying the isolation procedures, with less contamination due to by‐products. The reagent was also tested with free fatty acids in water. In this case, the supramolecular organization of fatty acids influenced the reaction outcome, and the epoxidation showed interesting regioselective features. The C?C bonds closest to the aqueous‐micelle interface is the most favored for the interaction with dimethyldioxirane. The preferential epoxidation of linoleic acid (= (9Z,12Z)‐octadeca‐9,12‐dienoic acid) to the 9,10‐monoepoxy derivative was achieved, with a high yield and 65% regioselectivity. In case of arachidonic acid (= (5Z,8Z,11Z,14Z)‐eicosa‐5,8,11,14‐tetraenoic acid) micelles, the regioselective outcome with formation of the four possible monoepoxy isomers was studied under different conditions. It resulted to be a convenient synthesis of ‘cis‐5,6‐epoxyeicosatrienoic acid’ (= 3‐[(2Z,5Z,8Z)‐tetradeca‐2,5,8‐trienyl]oxiran‐2‐butanoic acid), whereas in reverse micelles, epoxidation mostly gave ‘cis‐14,15‐epoxyeicosatrienoic acid (= (5Z,8Z,11Z)‐13‐(3‐pentyloxiran‐2‐yl)trideca‐5,8,11‐trienoic acid).     

Use of acyl substituents to favour 2,3-epoxidation of 5,7-dioxygenated flavones with dimethyldioxirane

The reaction of 5,7-dimethoxyflavone with dimethyldioxirane (DMDO) gives the 2,3-epoxide rapidly at first. However, low levels of ring A hydroxylated by-products are also formed. With increasing proportions of DMDO, demethylation at C-5 becomes apparent and consumption of substrate is not matched by further significant build-up of the epoxide. Deactivation of ring A by the use of acyl groups removes this complication. 5,7-Diacylflavones give excellent yields of epoxides and monoacyl derivatives also react in good yield. Ionization potential maps derived from density functional theory calculations (B3LYP/6-31G^∗), provide good visual indicators of the relative reactivity of the key nucleophilic loci. The epoxides may be isolated as such, or transformed into flavonols by treatment with p-toluenesulfonic acid.     

Orbital Interaction of Epoxidation on the Same Curvature Bonds of Single-walled Carbon Nanotubes

The epoxidation of different bonds with the same bond curvature in one nano-tube including armchair,zigzag and chiral tubes was studied. The calculated results showed that for the adducts with opened C–O–C configuration,the magnitude of the binding energies was related with their corresponding bonding characteristics in HOMO,and the larger binding energies were attributed to stronger orbital interaction between one O atom and the nanotube; whereas for the adducts with 3MR structures,the binding energies were related with the changes of C–C bond length and independent of the frontier orbital interaction before and after epoxidation.     

Triphenylphosphine in Some Nucleophilic Additions to Double Bonds Containing Electrophilic Carbon

Abstract

Phosphorus (III) componds like 1 possess basic and nucleophilic properties (phosphonium salt formation) as well as SET properties (i.e. reduction of peroxides). Typical examples of both reaction types are discussed in schemes I and II.     

Syntheses of Polycyclic Natural Products Employing the Intramolecular Double Michael Reaction

The one-pot intramolecular double Michael reaction of compounds having two different α, β-unsaturated carbonyl groups to form polycyclic compounds can be carried out by three different methods: in the first the substrate is treated with lithium hexamethyldisilazide, in the second with chlorotrimethylsilane, triethylamine, and zinc chloride at an elevated temperature, and in the third with tert-butyldimethylsilyl trifluoromethanesulfonate and triethylamine. The reaction proceeds with complete regioselectivity and high stereoselectivity following a stepwise mechanism. Spiro-fused bicyclo[2.2.2]octane derivatives can be constructed with high stereoselectivity by the intromolecular double Michael reaction by using the first method. Enantiomerically pure atisine and the enantiomer of atisirene were synthesized stereoselectively by application of this methodology. The syntheses of steroids and angular triquinane-type sesquiterpenoids were possible with the second method. Heterocyclic compounds with a bridgehead nitrogen atom were obtained by the reaction of α, β-unsaturated amides following the second and third methods. The asymmetric synthesis of tylophorine with diastereofacial control was achieved by the intramolecular reaction according to the third method. The sulfur-mediated intramolecular double Michael reaction utilizing the third method produced trans-hydroindane derivatives. Furthermore, the intramolecular Michael-aldol reaction can be employed in synthesizing polycyclic systems with cyclobutane units by treatment with tert-butyldimethylsilyl trifluoromethanesulfonate in the presence of triethylamine. The intermolecular double Michael reaction and related reactions will also be described.     

Ugi反应在环肽生物碱和小肽衍生物抗生素及细胞毒素类等天然产物合成中的应用

Ugi反应是由1分子醛或酮、1分子胺、1分子异腈和1分子羧酸4个组分通过缩聚反应生成α- 酰氨基酰胺类化合物的反应。 具有反应条件温和、产率高和原子经济性好等特点。 该反应还可与Suzuki、Heck和Smiles等经典反应偶联,使得其在天然产物合成方面得到越来越多的关注。 本文概括总结了近几十年来Ugi反应在一些天然产物合成中的应用。     

Epoxidation reaction of perfluoroalkenes with tert-amine N-oxide

Straight-chain aliphatic terr-amine N-oxides were found to be useful oxidizing agent for epoxidation of tri- and tetra-substituted perfluoroalkenes under mild conditions in high yields.The process for epoxidation by employing tri-n-butylamine N-oxide gave the best result in the reagent survey.     

Epoxidation of phosphinoyl alkenes with hydrogen peroxide

The epoxidation of alkenylphosphorus compounds with hydrogen peroxide was systematically studied, revealing that while alkenylphosphine oxides failed to produce the corresponding epoxides, alkenylphosphonates, or phosphinates having a phenyl group at α-position reacted with H₂O₂/K₂CO₃ or alkenylphosphonic acids or phosphinic acids having an aliphatic group at α- or β-positions reacted with H₂O₂/Na₂WO₄/Et₃N to produce high yields of the corresponding epoxides.