氯代卡宾与羰基化合物反应的研究——取代基的电子效应和底物的芳构化对脱氧反应的影响

氯溴卡宾与系列取代苯甲醛作用均产生CO(即羰基脱氧产物),取代基的电子效应直接影响CO的产率.捕获反应证实,该反应经历0°,0°型羰基叶立德中间体阶段.氟氯(溴)卡宾与四苯基环戊二烯酮(TPCP)反应除得到高产率的CO外,还生成偕氟卤环戊二烯(8)、双键加成物(9)及其重排产物(10).该类反应以脱CO途径为主,这可能是由于中间体羰基叶立德内部存在着"推-拉"稳定效应和不利于分子内电环化和分子间1,3-偶极加成的0°,90°型构象.本文讨论了这两类反应的微观作用机制.     

卤代羰基叶立德:“推-拉”稳定作用对四苯基环戊二烯酮与卡宾的脱氧反应的影响(英文)

研究了四苯基环戊二烯酮与三溴甲基苯基汞（二溴卡宾的前体化合物）的卡宾反应，发现该反应可给出比通常有立体障碍的酮要高得多的脱氧（以脱CO的形式）产率．本文从羰基叶立德中间体的“推-拉”稳定作用以及该中间体的构象和电子分布的角度出发，并结合产物分析对这一反常现象进行了讨论，发现在潜芳香结构的羰基化合物与二卤卡宾的反应中，有可能由于“推-拉”作用形成具有芳香结构的羰基是中间体，该中间体由于正负电荷及以较好的分散以及其接近0°／90°型的构象，有效地阻碍了分子间环加成和分子内电环化这两个竞争反应的进行，从而使脱氧途径成为该反应的主渠道．本项研究进一步揭示了一些尚未被人了解的反应规律，合理地解释了反应机理．     

无溶剂条件下简单、有效的合成多取代环己醇

取代苯乙酮与查尔酮在氢氧化钠存在下于70℃加热反应,取代苯乙酮与两分子查尔酮发生加成和环化反应,生成了多取代环己醇.本方法具有反应时间短、容易操作、产率高和环境友好等优点.产物的结构经过红外、核磁和元素分析确定,无溶剂方法是合成此类化合物的一条有效途径.     

2-[1-(1,2,4-三唑)甲基]-3-乙酰基-2,5-二取代芳基-1,3,4-噁二唑啉类化合物的合成

在冰醋酸存在下, 4-取代苯乙酮和溴素容易进行溴代反应, 得到α-溴-4-取代苯乙酮; 将其和1,2,4-三唑在丙酮中反应, 得到α-(1,2,4-三唑-1-基)-4-取代苯乙酮2; 在冰醋酸催化下, 2和4-取代苯甲酰肼1进行缩合, 得到相应酰腙衍生物3; 化合物3在乙酸酐的作用下环化生成一系列2-[1-(1,2,4-三唑)甲基]-3-乙酰基-2,5-二取代芳基-1,3,4-噁二唑啉4. 化合物4的结构经IR, 1H NMR, MS, 元素分析和单晶衍射确证.     

由α-氰基二硫缩烯酮制备多取代喹唑啉酮化合物

以α-氰基乙酸甲酯为起始原料,经与二硫化碳、碘甲烷反应先得到α-氰基二硫缩烯酮1,1与苯乙酮2反应得2H-吡喃-2-酮-3-腈化物3,碱诱导下3再与丙二腈经环转化得到多取代邻氨基芳香腈4,4与酮5在氢氧化钠催化下环化得到多取代喹唑啉酮目标物6.这组连续转化合成多取代喹唑啉酮的反应具有原料简便、反应温和等优点.     

氮杂环卡宾催化α,β-不饱和酰氯与亚硝基化合物的[4+2]环化反应

报道氮杂环卡宾催化的α,β-不饱和酰氯与亚硝基化合物的形式[4+2]环化反应合成氮杂-δ-内酯([1,2]嗪-6-酮)化合物.反应机理推测可能是卡宾进攻现场生成的烯基烯酮,得到烯基烯醇负离子,然后与取代的亚硝基苯发生[4+2]环合反应,从而得到的氮杂-δ-内酯产物.     

芳基高价碘盐诱导的亲电环化反应研究

亲电试剂诱导的环化反应是构建环状化合物的有效策略,而利用芳基高价碘盐作为亲电试剂诱导环化反应已经取得了诸多研究进展.在这些亲电环化反应中,高价碘盐不仅可以作为芳基化试剂诱导环化反应形成芳基取代环化物,还可以诱导苯并环化反应,形成苯并环状化合物.     

N-杂环卡宾催化合成取代γ-丁内酯研究进展

取代γ-丁内酯是一类非常重要的精细化学品。N-杂环卡宾(NHC)催化α,β-不饱和醛发生共轭极性反转后,与芳香醛、三氟甲基酮、酮酸酯或邻二酮等发生环化反应可一步生成不同取代的γ-丁内酯化合物。该方法具有原子经济性高、路径简捷、反应条件温和等明显的优势。本文主要结合笔者课题组的研究方向,从不同催化剂前体和不同反应底物两方面进行分类,介绍近年来NHC催化合成取代γ-丁内酯的方法及其研究进展,归纳总结了不同催化体系的优缺点,并在此基础上展望了NHC催化合成取代γ-丁内酯反应的发展趋势和应用前景。     

相转移催化反应研究 V: 利用^1^4C标记法研究取代苯乙烯及α-芳代苯乙烯与二溴卡宾反应动力学

本文应用放射性计数进行反应物及产物的定量测定, 比较了一些冠醚类相转移催化剂的性能. 发现新型氮杂冠醚在催化二溴卡宾与1,1-二苯乙烯加成反应时有最好的催化性能. 本文还测定了取代苯乙烯、α-芳代苯乙烯类化合物与二溴卡宾反应的相对速率常数, 并通过线性相关分析, 比较了两类化合物与二溴卡宾反应特性常数的差别, 对α-取代苯乙烯中取代基R的性质和相对速率常数作了比较.     

二氯卡宾与四苯基环戊二烯酮反应机理的研究

二氯卡宾与四苯基环戊二烯酮（１）反应放出ＣＯ，并生成偕二卤化物（３）、二氯环氧乙烯（４）以及双键加成物（５）。羰基叶立德的芳香性结构及其“中介型”爸象决定了该应以脱ＣＯ为主电环化途径次之。     

二卤卡宾与羰基化合物反应的研究进展

对近年来二卤卡宾与羰基化合物的反应机理研究进行了总结，指出二卤羰基Ｙｉｌｄｅ为反应的中间体，并对影响二卤羰基Ｙｌｉｄｅ的稳定性及后续反应的因素如底物的立体效应，取代基的电子效应，Ｃａｐｔｏｄａｔｉｖｅ效应以卤原子半径大小进行了讨论。     

Substituent effect on photochromism of indolinospirooxazines

The photochromic reactions of five indolinospirooxazine derivatives ( II, III, V and VII) were examined using nanosecond laser flash photolysis techniques. Photolysis of II–V leads to the formation of long-lived photomerocyanines (PMCs), whereas the only detectable product in the photolysis of CII is a short-lived, charge-separated, twisted species (CT intermediate). The results show that the substituent in the 2′ position of the oxazine ring has a decisive role on the photochromic reaction products and all of the substituents influence the absorption maxima of the photoproducts of indolinospirooxazines. A proposed potential energy surface model has been established to explain these phenomena. Moreover, the characteristics of the absorption spectra of the PMCs and CT intermediate are discussed.     

Theoretical study of silylene substituent effects on the abstraction reactions with oxirane and thiirane

The potential energy surfaces for the abstraction reactions of silylenes with oxirane and thiirane have been characterized in detail using density functional theory (B3LYP) as well as the ab initio method (QCISD), including zero-point corrections. Five silylene species including SiH(2), Si(CH(3))(2), Si(NH(2))(2), Si(OH)(2), and SiF(2) have been chosen in this work as model reactants. All the interactions involve the initial formation of a donor-acceptor ylide-like complex followed by a heteroatom shift via a two-center transition state. The complexation energies, activation barriers, and enthalpies of the reactions were used comparatively to determine the relative silylenic reactivity, as well as the influence of substituents on the reaction potential energy surface. As a result, our theoretical investigations suggest that, irrespective of deoxygenation and desulfurization, the alkyl-substituted silylene abstractions are much more favorable than those of the pi donor-substituted silylenes. Moreover, for a given silylene, while both deoxygenation and desulfurization are facile processes, the deoxygenation reaction is more exothermic as well as more kinetically favorable. Furthermore, a configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results. The results obtained allow a number of predictions to be made.     

Deoxygenation and desulfurization of oxiranes and thiiranes by carbenes: a theoretical study

The potential-energy surfaces for the abstraction reactions of carbenes with oxirane and thiirane have been characterized in detail by using density functional theory (B3LYP/6-31G*), which include zero-point corrections. Six carbene species: dimethylcarbene, cyclobutylidene, cyclohexylidene, phenylchlorocarbene, methoxyphenylcarbene, and dimethoxycarbene have been chosen in this work is model reactants. All the interactions involve the initial formation of a loose donor-acceptor complex followed by a heteroatom shift via a two-center transition state. The complexation energies, activation barriers, and enthalpies of the reactions were used comparatively to determine the relative carbenic reactivity, as well as the influence of substituents on the reaction potential-energy surface. As a result, our theoretical investigations indicate that, irrespective of deoxygenation and desulfurization, the relative carbenic reactivity decreases in the order: cyclobutylidene > dimethylcarbene approximately equals cyclohexylidene > phenylchlorocarbene > methoxyphenylcarbene > dimethoxycarbene. Namely, the alkyl-substituted carbene abstractions are much more favorable than those of the pi-donor-substituted carbenes. Moreover, for a given carbene, while both deoxygenation and desulfurization are facile processes, the deoxygenation reaction is more exothermic but less kinetically favorable. Furthermore, a configuration-mixing model based on the work of Pross and Shaik is used to rationalize the computational results. The results obtained are in good agreement with available experimental observations, and allow a number of predictions to be made.     

Theoretical study of benzotriazole UV photostability: ultrafast deactivation through coupled proton and electron transfer triggered by a charge-transfer state

A theoretical CASSCF study of the reaction path for excited-state intramolecular proton transfer (ESIPT) for a model system derived from the UV absorber 2-(2'-hydroxyphenyl) benzotriazole without the fused benzo ring on the triazole has been carried out. A planar reaction path can be optimized but is shown to have no physical significance. The true reaction path involves twisted geometries. Adiabatic proton transfer is triggered by a charge-transfer from the phenol to the triazole group, and is followed by radiationless decay at the keto form. Along the nonplanar reaction path, there is a coupled proton and electron transfer in a manner similar to tryptophan. This rationalizes unexpected experimental results on the effect of electron withdrawing substituent groups on the photostability. The coupled proton and electron transfer is followed by a barrierless relaxation in the ground state to recover the enol form. An alternative photostabilization pathway from a phenyl localized state has also been documented and is similar to the channel 3 decay pathway in benzene photochemistry. Additionally, a long-lived intermediate for a twisted intramolecular charge-transfer (TICT) state has been identified as the species potentially responsible for the increase of blue fluorescence in strongly polar media.     

Structure and isomerization of cyclotrimetallenes

The substituent migration on the X₂Y rings (X, Y=C, Si, Ge) was studied by theoretical method with silyl and hydrogen substituents and it was found that all the reactions (with the exception of cyclopropene) proceed in a two-step mechanism via a stable intermediate. The rate determining step of the reaction is the first step. The barrier of the second step is small and the energy of the intermediate is close to that of the reactant. Both the first transition state (T1) and the intermediate (I) are of monobridge structures of different types. Since the intermediate bridge structure is almost as stable as the product, it may be observed in the substituent migration reactions.     

A Theoretical and Experimental Study of the Effects of Silyl Substituents in Enantioselective Reactions Catalyzed by Diphenylprolinol Silyl Ether

The effect of silyl substituents in diphenylprolinol silyl ether catalysts was investigated. Mechanistically, reactions catalyzed by diphenylprolinol silyl ether can be categorized into three types: two that involve an iminium ion intermediate, such as for the Michael‐type reaction (type A) and the cycloaddition reaction (type B), and one that proceeds via an enamine intermediate (type C). In the Michael‐type reaction via iminium ions (type A), excellent enantioselectivity is realized when the catalyst with a bulky silyl moiety is employed, in which efficient shielding of a diastereotopic face of the iminium ion is directed by the bulky silyl moiety. In the cycloaddition reaction of iminium ions (type B) and reactions via enamines (type C), excellent enantioselectivity is obtained even when the silyl group is less bulky and, in this case, too much bulk reduces the reaction rate. In other cases, the yield increases when diphenylprolinol silyl ethers with bulky substituents are employed, presumably by suppressing side reactions between the nucleophilic catalyst and the reagent. The conformational behaviors of the iminium and enamine species have been determined by theoretical calculations. These data explain the effect of the bulkiness of the silyl substituent on the enantioselectivity and reactivity of the catalysts.     

烯酮及取代烯酮与环戊二烯环加成反应机理的理论研究

利用半经验分子轨道理论AM1方法,研究了烯酮及取代烯酮与环戊二烯环加成反应机理。采用Berny梯度法优化得到各反应的过渡态和中间体,并进行了振动分析确认。计算结果表明,该环加成反应是按照协同的非同步途径进行的,经过一个四元环发生扭曲的过渡态,并有部分电荷从环戊二烯迁移到烯酮或取代烯酮上,前线轨道分析表明反应机理为“2×[1+1]”机理;而氯甲基取代的烯酮与环戊二烯的环加成反应是按照分步途径发生的。计算结果可以很好地说明实验所观察到的立体选择性,并根据烯酮上取代基的电子效应和位阻效应对反应机理的影响进行了分析。