2-芳基苯并噁唑的荧光猝灭和光诱导电子转移研究

本工作对两种不同的2-芳基苯并 唑化合物溶液荧光被四氯化碳所猝灭的机理进行了详细研究,通过多种途径研究表明该猝灭过程具有光诱导电子转移性质,工作还利用此电子转移所形成的活泼自由基来引发烯类单体的聚合,得到了有一定聚合度的聚甲基丙烯酸甲酯。     

光氧化反应的研究 II: 9-苯甲叉芴的电子转移光氧化反应

芳香族烯烃, 芳烃以及稠环芳烃是光氧化反应中的重要研究对象, 本文以9-苯甲叉芴(BF)作为底物, 发现它在9,11-二氰蒽(DCA)敏化作用下易发生电子转移反应, 反应生成芴酮和BF的相应环氧化物, 用紫外光谱测出BF的电荷转移配合物的络合物稳定常数,用循环伏安法测定BF的氧化电位. 由Rehm-Weller方程计算出DCA敏化的单电子转移过程的自由能变化, 并观察到BF对DCA有明显的荧光猝灭作用.     

痂囊腔菌素A与咔唑化合物间的光致电子转移

研究了咔唑、咔唑-9-乙酸、3-溴-咔唑-9-乙酸在缺氧条件下对天然苝醌化合物痂囊腔菌素A(简记为EA)的荧光猝灭行为;由竹红菌甲素(HA)和乙素(HB)的荧光寿命估算了EA在乙腈中的荧光寿命,并进而计算了三个咔唑化合物的双分子猝灭速度常数.结果表明,三个咔唑化合物在EA的可见光吸收区无光吸收,据此推测其对EA的荧光猝灭作用归因于咔唑化合物作为电子给体而EA作为电子受体的光致电子转移作用.三个咔唑化合物的Stern-Volmer猝灭常数分别为698、704和1 063L·mol-1;乙酸基对咔唑环的光致电子转移速率几乎没有影响,而溴原子取代能够增加咔唑化合物对EA的荧光猝灭程度和光致电子转移速率.此外,EA在乙腈中的荧光寿命为1.98ns,而三个咔唑化合物的双分子猝灭速率常数分别为3.52×1011,3.56×1011和5.37×1011 L·mol-1·s-1.     

异喹啉稠环吡咯化合物的合成研究进展

概述了异喹啉稠环吡咯化合物的合成方法,主要包括Tschitschibabin反应,Munchnone衍生物的1,3－偶极环加成反应,1,5－电环化反应和硝酮化合物的1,3－偶极环加成反应,参考文献20篇。     

新型exTTF衍生物的合成及其与四氯对苯醌的电子转移

以9,10-二蒽醌和1,3-二硫代环戊烯-2-硫酮(1和3)为原料,利用亚磷酸三乙酯为偶联剂的Wittig交叉偶合反应合成exTTF化合物9-(4,5-二氰乙基硫基-1,3-二硫代环戊烯-2-亚甲基)-10-[(4,5-亚乙基硫基)-1,3-二硫代环戊烯-2-亚甲基]-9,10-二氢蒽(4).在氢氧化铯存在下,化合物4与2-氯乙氧基乙醇反应得到exTTF化合物9-[4-氰乙基硫基-5-(2-(2-羟乙氧基)乙基硫基-1,3-二硫代环戊烯-2-亚甲基)]-10-[(4,5-亚乙基硫基)-1,3-二硫代环戊烯-2-亚甲基]-9,10-二氢蒽(5).利用Mitsunobu反应,在偶氮二甲酸二乙酯和三苯基膦催化下,化合物5与对硝基苯酚反应得到exTTF化合物9-{4-氰乙基硫基-5-[2-(2-对硝基苯氧乙氧基)乙基硫基]-1,3-二硫代环戊烯-2-亚甲基}-10-[(4,5-亚乙基硫基)-1,3-二硫代环戊烯-2-亚甲基]-9,10-二氢蒽(6).同时,X射线衍射分析了exTTF化合物4的晶体结构.循环伏安法研究表明化合物6呈现准可逆的两电子转移过程.利用紫外光谱法研究了exTTF化合物6与四氯对苯醌分子间的电子转移行为.结果表明,非氧化性金属阳离子Sc3+,Al3+和Pb2+可以有效促进电子供体6与电子接受体四氯对苯醌的分子间的电子转移行为.     

维生素B_6与牛血清白蛋白相互作用的液滴荧光法研究

利用荧光及紫外光谱法研究了生理pH条件下水溶液体系中维生素B6与牛血清白蛋白(BSA)的相互作用机制.维生素B6对牛血清白蛋白的荧光有较强的猝灭作用,其猝灭类型为静态猝灭.根据F(o)rster的偶极-偶极非辐射能量转移理论算出供体-受体的结合距离为2.72 nm.由Linewear-Burk方程求出不同温度下反应时复合物的形成常数KLB和结合位点数n及对应温度下结合反应的热力学参数,证明二者主要靠氢键和范德华力结合.同时采用同步荧光分析技术,对蛋白质与药物结合时构象的变化进行了探讨.     

蒈烯芳氰敏化光氧化反应的研究——Ⅰ.蒈烯对9,10-二腈基蒽荧光的猝灭特性

本文通过研究在不同溶剂中蒈烯对9,10-二腈基蒽(DCA)荧光猝灭的光物理特性及溶剂极性对猝灭速度的影响,温度效应的测定及其在乙腈中双分子猝灭速率常数k_q值与计算所得自由能的变化(△G)之间的关系符合 RehmWeller关系,证明了菇烯对DCA荧光的猝灭是一个电子转移的动态猝灭过程。     

光氧化反应的研究——Ⅲ.烷基取代的二苯乙烯的电子转移光氧化反应机理

本文研究了由9,10-二氰蒽(DCA)敏化的2-烷基-1,1-二苯乙烯1a—1b(Ph_2C=CHR,R=Me,Et,Pr)的光氧化反应及其机理。反应给出主要产物二苯酮,次要产物为环氧化物及其氢转移重排产物。产物分布特征、量子收率、氧化电位与热力学分析、荧光猝灭的Stern-Volmer关系等结果均表明该反应是通过DCA敏化循环链的电子转移进行的。自由基负离子中间体DCA的电子自旋共振谱的检测亦为上述电子转移反应机理提供了直接证据。因此,在1,1-二苯乙烯双键上引入烷基时,其光氧化反应仍按电子转移机理进行。     

咔唑及其衍生物对 9-氰基蒽的荧光猝灭机理的研究

本文研究咔唑及其衍生物对9-氰基蒽(9CNA)的荧光猝灭机理。结果表明, 猝灭过程有以下三种方式:(1)一系列N-烷基咔唑及1,4-二咔唑丁烷、反式1,2-二咔唑环丁烷、N-苄基咔唑等对9CNA的荧光猝灭是通过形成激基复合物。(2)咔唑对9CNA的荧光猝灭是通过形成氢键。(3)1,3-二咔唑丙烷及N-痖烯基咔唑对9CNA的荧光猝灭是属于一般碰撞猝灭过程。以上所有猝灭过程主要都是来自电荷转移相互作用。另外, 还讨论了空间位阻对形成激基复合物的影响。并由稳态和动态荧光实验结果,应用Ware关于激基复合物的形成和解离的动力学公式计算出一系列光物理速率常数。     

以聚醚链相连的9-氨基吖啶、苯甲酸酯二元体系的合成及分子内光诱导电子转移反应

本文用聚四乙二醇柔性链将9-氨基啶和不同取代基的苯甲酸酯连接起来,合成了一类新型二元分子体系。对各体系中9-氨基啶的电子转移荧光猝灭进行了研究,并根据稳态荧光猝灭计算了体系中的荧光猝灭效率和荧光猝灭速率常数。     

Concerted vs stepwise mechanism in 1,3-dipolar cycloaddition of nitrone to ethene, cyclobutadiene, and benzocyclobutadiene. A computational study

The problem of competition between concerted and stepwise diradical mechanisms in 1,3-dipolar cycloadditions was addressed by studying the reaction between nitrone and ethene with DFT (R(U)B3LYP/6-31G) and post HF methods. According to calculations this reaction should take place via the concerted cycloaddition path. The stepwise process is a viable but not competitive alternative. The R(U)B3LYP/6-31G study was extended to the reaction of the same 1, 3-dipole with cyclobutadiene and benzocyclobutadiene. The very reactive antiaromatic cyclobutadiene has an electronic structure that is particularly disposed to promote stepwise diradical pathways. Calculations suggest that its reaction with nitrone represents a borderline case in which the stepwise process can compete with the concerted one on similar footing. Attenuation of the antiaromatic character of the dipolarophile, i.e., on passing from cyclobutadiene to benzocyclobutadiene, causes the concerted 1,3-dipolar cycloaddition to become once again prevalent over the two-step path. Thus, our results suggest that, in 1,3-dipolar cycloadditions that involve normal dipolarophiles, the concerted path (Huisgen's mechanism) should clearly overwhelm its stepwise diradical (Firestone's mechanism) counterpart.     

Asymmetric synthesis of the spirocyclic core of the cylindricine-type alkaloids

Marine alkaloids from the cylindricine and lepadiformine families possess an interesting spirotricyclic skeleton. An intramolecular nitrone/olefin 1,3-dipolar cycloaddition has been used to form their spirocyclic 1-azaspiro[4.5]decane core in a regio- and stereoselective fashion. The cyclization precursor can be easily accessed using the asymmetric electrophilic hydroxyamination of enolate.     

A stereoselective method for the synthesis of enantiopure 3-substituted 4-hydroxyproline derivatives via 1,3-dipolar cycloadditions

The stereoselective 1,3-dipolar cycloaddition between (Z)-1,4-dichloro-2-butene and a menthone-derived nitrone led to the corresponding isoxazolidine. Regioselective azidation of a single chlorine atom followed by another Cu(I)-catalyzed azide–alkyne 1,3-dipolar cycloaddition (CuAAC) induced enantiopure 1,2,3-triazolyl-functionalized isoxazolidines. The subsequent acidic cleavage of the menthone chiral auxiliary and reductive cleavage of the isoxazolidine N–O bond triggered an intramolecular cyclization through the displacement of the second chlorine. This rapid and stereoselective synthetic strategy provided reliable access to a series of enantiopure 3-substituted 4-hydroxyproline derivatives.     

Tricyclic-isoxazolidine analogues via intramolecular 1,3-dipolar cycloaddition reactions of nitrones

The tricyclic-isoxazolidine analogues tetrahydrothiochromenoisoxazoles, hexahydroisoxazolequinolines and tetrahydroisoxazolepyranopyridines were prepared by an intramolecular 1,3-dipolar cycloaddition reaction of a nitrone with an alkene. For N-alkylated hexahydroisoxazolequinolines, reduction of the reaction time from two days to 40 min was achieved using microwave heating. The cyclization to form tetrahydroisoxazolepyranopyridines only proceeded when the alkene was substituted with an electron withdrawing group.     

Diastereoselective synthesis of some carbocyclic 2′-oxa-3′-aza-nucleosides

Two strategies for the synthesis of isoxazolidinyl nucleosides as potential antiviral agents are reported: a one-step approach based on 1,3-dipolar cycloaddition of D-lyxosyl nitrone with N,N-dibenzyl-9-vinyl adenine, and a two-step methodology based on the Vorbrüggen nucleosidation of the 5-acetoxyisoxazolidine. The chiral D-lyxosyl nitrone undergoes regioselective 1,3-dipolar cycloadditions with N,N-dibenzyl-9-vinyl adenine and vinyl acetate giving 5-substituted isoxazolidines as a mixture of four diastereoisomers in good yields. The condensation of 5-acetoxyisoxazolidine with silylated uracil, thymine, and N-acetylcytosine proceeded with moderate to good stereoselectivity with the formation of the expected isoxazolidinyl β-and α-nucleosides. Dedicated to Prof. Dr. E. Lukevics on the occasion of his 70th birthday __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 01, pp. 14–21, Januvary, 2007.     

Reaction of nitrones with silyl ketene acetals: a DFT study

Theoretical calculations at the DFT level indicate that the reaction of a nitrone with a silyl ketene acetal proceeds, contrary to previous suggestions, through a classical 1,3-dipolar cycloaddition, followed by a silyl group transfer step to give the open-chain product. Introduction of a diffuse basis set is necessary to describe properly nitrones. The influence of a Lewis acid has been studied.     

A new bicyclic dipeptide isostere with pyrrolizidinone skeleton

The synthesis of a new conformationally constrained Gly-(s-cis)Pro Turn Mimetic (GPTM) in both racemic and enantiomerically pure forms and their incorporation into peptides 18, 21, and 24 are reported. The synthetic strategy adopted to assemble the bicyclic pyrrolizidinone skeleton is based on the 1,3-dipolar cycloaddition of the cyclic nitrone 4a derived from proline and acrylamide, followed by a reductive cleavage/cyclization domino process. The enantiomerically pure GPTMs are obtained by synthesis and separation of diastereomeric intermediates containing (1R)-1-phenylethylamine as chiral auxiliary. Analysis of pseudotripeptides 18, 21, and 22 by FT-IR and NMR shows that the amide proton of GPTM derivatives 21 is intramolecularly hydrogen bonded in CDCl(3), while DMSO was shown to disrupt this hydrogen bond.     

Assessment of non-standard reaction conditions for asymmetric 1,3-dipolar organocatalytic cycloaddition of nitrone with <Emphasis Type="Italic">α,β</Emphasis>-unsaturated aldehydes

Non-standard experimental conditions can often enhance organocatalytic reactions considerably. The current study explores the effectiveness of a range of non-standard reaction conditions for the asymmetric organocatalytic 1,3-dipolar cycloaddition of a nitrone with α,β-unsaturated aldehydes. The influence of ionic liquids, high-pressure conditions, ultrasound, microwave irradiation and ball-milling was tested as well as the flow process. Because of the low reactivity of the nitrone and unsaturated aldehydes in the 1,3-dipolar cycloaddition, cycloadducts were isolated in only moderate yields from the majority of experiments. However, high diastereo- and enantioselectivities were observed in ionic liquids under solvent-free conditions and in the flow reactor.     

1,3-偶极环加成反应在有机合成方面的新进展

1,3-偶极环加成是新近被用于杂环和天然产物合成的重要反应。本文主要综述1,3-偶极环加成反应在有机合成方面的研究现状和发展趋势,着重介绍基于硝酮,腈氧化物等偶极体系的合成策略和实例。     

Aroylnitrile oxide cyclizations. 2. Synthesis of (3-aroylisoxazol-5-yl)alkanoic acids

Intermolecular cyclization of 1,3-dipolar aroylnitrile oxides to terminal alkynols followed by phase transfer catalyzed oxidation provided a short, convenient route to several novel (3-aroylisoxazol-5-yl)alkanoic acids.