大环轮烯的合成及其NMR谱特征

论述了大环轮烯、去氢轮烯、架桥轮烯及氮杂轮烯、氧杂轮烯、硫杂轮烯的合成方法;轮烯、去氧轮烯[4n+2]、[4n]体系以及杂原子轮烯[4n+1]、[4n-1]体系的NMR谱的特征;还介绍了近两年大环轮烯研究成果及发展趋势。     

N-对甲苯磺酰基-7-氮杂-双环[2.2.1]-2,5-庚二烯-2,3-二羧酸二甲酯光敏化电子转移异构反应研究

降冰片二烯及其衍生物是分子光化学贮存太阳能反应体系中研究较多的一类模型化合物^[1-4]。但是,从迄今报道的研究工作来看,大部分是关于7-位为碳原子的降冰片二烯衍生物。对于7-位为杂原子的衍生物的光异构化反应以及7-位杂原子对光异构化反应的影响还未见报道。     

烯亚砜化合物的制备及反应概述

烯亚砜作为一类重要的反应中间体在有机合成领域发挥着重要应用。常见的烯亚砜制备方法包括:硫羰基化合物氧化、亚磺酰衍生物β-消除反应、改进的Peterson反应、重氮甲基亚砜的杂原子-Wolff重排反应等。作为活性中间体的烯亚砜可以被亲核试剂进攻硫原子中心或者碳原子中心,分别得到亚砜化合物或者新的烯亚砜物种;而其自身亦可以作为亲核试剂,以氧原子作为亲核位点与其他亲电试剂反应。烯亚砜和酰基或者烯基烯亚砜可以分别作为亲双烯体或双烯体发生正常和逆电子需求的Diels-Alder反应。烯亚砜既可以作为亲偶极子,也可以作为偶极子发生偶极环加成反应。此外,烯亚砜自身还可以发生二聚、脱硫等反应。希望本文总结的内容能够对该研究领域感兴趣的化学工作者有所帮助,并促进烯亚砜化学的进一步发展。     

PdCl2催化炔酸烯丙酯环化反应的密度泛函研究

用密度泛函方法(DFT)研究了PdCl2催化炔酸烯丙酯环化反应的机理. 在B3LYP/6-311G**水平上优化了各反应中间体和过渡态的结构. 计算结果表明, 反应是放热的, 主要经历了炔键的卤钯化、烯烃对烯基钯的迁移插入以及β-杂原子消除等过程. 烯烃的迁移插入是反应的手性决定步骤, β-杂原子消除是反应的速率控制步骤. 理论预测的主要产物是与实验吻合的(Z,R)-α-亚烷基-γ-丁内酯.     

联烯的自由基反应

联烯是含有1,2-丙二烯官能团的重要化合物,具有很高的反应活性.概述了联烯及其衍生物的自由基反应,包括分子间自由基链加成和分子间-分子内自由基串联加成反应,及其在天然产物中的应用.联烯进行分子间自由基链加成反应时,自由基对联烯的加成既可发生在中间碳原子上,也可发生在末端碳原子上,主要取于所形成中间体的稳定性,空间效应、电负性和溶剂等因素也有影响.一般以碳为中心的自由基(如CH3·,CCl3·等)易进攻末端碳原子,而以杂原子为中心的自由基(如Br·,RS·,ArSO2·等)易进攻联烯的中心碳原子.联烯及其衍生物也易与烯烃、联烯、烯炔和乙烯酮进行[2 2]环加成反应,还可以与卡宾环丙烷化,这些反应都是通过自由基机理进行的.     

硅杂苯与亲二烯体的Diels-Alder反应

采用密度泛函理论(DFT)在B3LYP/6-311G(d,p)水平上研究了硅杂苯与一些亲二烯体的两类可能的Diels-Alder反应的微观机理、势能剖面、取代基效应和溶剂化效应. 计算结果表明, 所研究反应均以协同的方式进行. 亲二烯体分子碳原子上的苯基取代基对两个新键形成的非同步性和反应的活化能垒的影响取决于苯基在产物中的相对位置, 而硅杂苯分子中硅原子上的CCl3取代基有利于杂Diels-Alder反应的进行. 形成一个C—Si键的杂Diels-Alder反应在热力学和动力学上均远比相应的全碳Diels-Alder反应容易进行, 实验观察到的杂Diels-Alder反应中的区域选择性由动力学因素所控制. 硅杂苯与烯烃的反应比与相应炔烃的反应在动力学上容易进行一些, 但在热力学上后者远比前者容易进行. 苯溶剂对所研究反应的势能剖面影响较小.     

由6-氨基取代富烯合成二茂锆配合物及其结构研究

富烯已被广泛应用于合成各种取代环戊二烯基、茚基和芴基金属配合物[1] .富烯的取代基对于它本身的反应性质以及由富烯所派生出的金属配合物的性质都起着重要的作用 .另外 ,富烯在手性配体及手性金属配合物的合成方面起着非常重要的作用 [2 ,3] ,仅就 6,6-二烷基富烯的加成反应而言 ,不但可以合成出多种烷基取代的手性金属配合物 [4 ] ,还可以引入杂原子而合成出手性配体 [5] .在研究 6-氨基富烯的加成反应时人们发现 ,由它不仅可以生成手性配体 ,而且其取代基上的氨基还可以与中心金属原子发生配位 [6 ] .最近 ,我们研究了 6-二甲氨基 - 6-…     

锗苯与亲二烯体的Diels-Alder反应的理论研究

采用密度泛函理论方法在B3LYP/6-311G(d,p)水平上研究了锗苯与一些亲二烯体的Diels-Alder反应的微观机理和势能剖面, 考察了取代基和苯溶剂对反应势能剖面的影响, 探讨了杂Diels-Alder反应中区域选择性的起源. 计算结果表明, 所研究反应均以协同的方式进行. 亲二烯体分子碳原子上的苯基取代基对杂Diels-Alder反应中2个新键形成的非同步性和活化能垒的影响与最终产物中苯基和锗原子间的相对位置有关, 锗苯分子中锗原子上的CCl3取代基在热力学和动力学上均有利于反应的进行. 苯溶剂对所研究反应的势能剖面影响较小. 实验观察到的杂Diels-Alder反应的区域选择性由动力学因素所控制.     

过渡金属催化氮杂二环烯烃不对称开环反应的研究进展

综述了近年来过渡金属催化氮杂二环烯烃的开环反应的研究进展,重点讨论了过渡金属催化剂的种类、亲核试剂的类型、配体、底物氮杂二环烯烃及其衍生物的结构、溶剂和添加剂等因素对开环反应的影响,并对开环反应的可能的机理进行了讨论.     

钯催化芳基乙炔对氧/氮杂苯并降冰片烯开环反应研究

过渡金属催化的碳亲核试剂对氧/氮杂苯并降冰片烯的开环反应是合成氢化萘衍生物的有效方法之一. 在该类反应中, 采用末端炔烃作为碳亲核试剂在反应操作、底物适用范围等多个方面都具有已报道的各种有机金属亲核试剂所不具备的优势. 目前, 对末端炔烃与氧/氮杂苯并降冰片烯的开环反应的研究进展有限, 只有Ni(dppe)Cl₂/ZnCl₂/Zn和手性的Rh两种催化体系被应用到该类反应当中, 但都面临一些不足. 为该类反应开发简单有效的新型催化体系仍然具有重要的意义和价值. 我们通过研究发现: PdCl₂与Xantphos的配合物是芳基乙炔对氧/氮杂苯并降冰片烯亲核开环反应的有效催化剂. 在优化后的反应条件下, 该Pd催化剂具有良好的催化活性和底物适应能力, 能够实现各种取代的芳基乙炔对氧/氮杂苯并降冰片烯的亲核加成, 并以较好的收率生成目标开环产物.     

Photopolymerization of thiol‐ene systems based on oligomeric thiols

Thiol oligomers were copolymerized with a triallyl ether by a photoinduced polymerization process. These oligomeric thiol‐ene systems comprise the same components as a photopolymerized thiol‐ene‐acrylate ternary system, yet the photopolymerized networks have much lower glass transition temperatures. An investigation into the effect of oligomeric thiol design on network formation was conducted by analyzing the reaction kinetics and thermal/mechanical properties of the thiol‐ene networks. Real‐time FTIR analysis shows that total conversion is >90% for all thiols investigated. Photo‐DSC analysis shows that the maximum exotherm rate is roughly equivalent for all of the thiols when the equivalent weight of the thiol is taken into account. As would be expected, the glass transition temperature and tensile strength increase with thiol functionality and lower thiol equivalent weight for thiols with functionality from 2 to 4. Films made using the oligomeric thiols have essentially the same glass transition temperatures and tensile modulus values regardless of thiol design. These results distinguish the method for generation of networks consisting of an initial Michael reaction of thiols and acrylates followed by a photoinitiated copolymerization with a multifunctional ene from the traditional photolysis of the corresponding thiol‐ene‐acrylate ternary systems with no Michael reaction. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 14–24, 2009     

Electronic effects in the regioselectivity of the singlet oxygen and 4-methyl-1,2,4-triazoline-3,5-dione ene reactions with isobutenylarenes

The regioselectivity of the ene pathway in the photooxidation of several 1-aryl-2-methylpropenes, as probed by stereoselective deuterium-labeling, depends on the electronic nature of the para phenyl-substituents. The reaction of the same array of alkenylarenes with 4-methyl-1,2,4-triazoline-3,5-dione (MTAD) gives ene products with an impressive >97% allylic hydrogen abstraction from the more substituted side of the alkene.     

Effect of hetero atom on the conformational stability of the forming ring in the transition structures of Type-II ene cyclization: a theoretical study

The chair conformation of the forming ring in the transition structure, for its high stability, is usually considered for the determination of the overall stereoselectivity in a type-II ene cyclization reaction. However, present theoretical investigation reveals that the presence of a heteroatom like oxygen or nitrogen in the tether of type-II carbonyl ene cyclization stabilizes the transition structure, in which the forming ring adopts a boat conformation. Due to such stability of the boat conformer the overall stereoselectivity of some type-II reactions may differ from the expected one.     

Lewis Acid‐Assisted Ene Cyclization of 2‐Azetidinone‐Tethered Enals: Synthesis of Enantiopure Carbacepham Derivatives

Diastereocontrolled Lewis acid‐catalyzed preparation of enantiopure carbacepham derivatives have been developed starting from 2‐azetidinone‐tethered enals. The BF₃?Et₂O‐promoted reaction of alkenylaldehydes 1 and 16 is effective as carbocyclization protocol to afford 4‐substituted 5‐hydroxycarbacephams or 3‐substituted 4,5‐dihydroxycarbacephams, respectively, by a type I carbonyl‐ene reaction, while the BF₃?Et₂O or SnCl₄‐mediated type II carbonyl‐ene cyclization of alkenylaldehydes 2 furnishes 3‐methylene 5‐hydroxycarbacephams along with the corresponding 3‐halo 5‐hydroxycarbacepham. The stereochemical outcome of these carbonyl‐ene cyclizations leading to carbacepham derivatives can be explained in terms of six‐membered, cyclic chair‐like transition‐state models. The formation of halocarbacepham derivatives is proposed to proceed by a stepwise mechanism.     

Facial Synthesis of o‐Carborane‐Substituted Alkenes and Allenes by a Regioselective Ene Reaction of 1,3‐Dehydro‐o‐carborane

1,3‐Dehydro‐o‐carborane is a useful synthon for selective cage boron functionalization of o‐carboranes. It reacts readily with alkenes or alkynes to give a variety of cage B(3)‐alkenyl/allenyl o‐carboranes by ene reactions in very high yields and excellent regioselectivity. This can be ascribed to the highly polarized cage C?B multiple bond, which lowers the activation barriers of the ene reaction.     

Competitive thermal ene reaction and Diels-Alder reactions of 2-[N-(alk-2-enyl)benzylamino]-3-vinylpyrido[1,2-a]pyrimidin-4(4H)-ones

Thermal reaction of 2-[N-(alk-2-enyl)benzylamino]-3-(2-substituted and 2,2-disubstituted)vinylpyrido[1,2-a]pyrimidin-4(4H)-ones gave azepine, the desired ene products, and/or pyran derivatives. The formation of the latter was responsible for the [4+2] cycloaddition reaction between the α,β-unsaturated ester carbonyl moiety as a diene part and the alkenylamino moiety as an ene one. The reaction features depended upon the kinds of substituents both on the vinyl and alkenyl counterparts; strongly electron-withdrawing substituents on the vinyl moiety or an electron-donating substituent on the alkenyl one changed the reaction feature from the ene reaction to the hetero Diels-Alder reaction.     

A Nazarov-Ene Tandem Reaction for the Stereoselective Construction of Spiro Compounds

The different reactivity of trienones under Lewis and Brønsted acids catalysis was investigated, resulting in distinct cyclization products and carbon backbones that originated either from a conjugate Prins cyclization or an interrupted Nazarov cyclization. In particular, an unprecedented Nazarov cyclization tandem reaction is presented, terminating the oxyallyl cation by an ene-type reaction, and leading stereoselectively to bicyclic spiro compounds. The terminal olefin of this motif represents a useful handle for further functionalization, making it a strategic intermediate in total syntheses. The tandem Nazarov/ene cyclization was shown to be preferred over a Nazarov/[3+2] tandem reaction for all our substrates, independent of chain length. Deuteration studies further support the mechanistic hypothesis of the terminating ene reaction.     

Evaluation of thiol‐ene click chemistry in functionalized polysiloxanes

Polysiloxanes are commonly used in a myriad of applications, and the “click” nature of the thiol‐ene reaction is well suited for introducing alternative functionalities or for crosslinking these ubiquitous polymers. As such, understanding of the thiol‐ene reaction in the presence of silicones is valuable and would lead to enhanced methodologies for modification and crosslinking. Here, the thiol‐ene reaction kinetics were investigated in functionalized oligosiloxanes having varying degrees of thiol functionalization (SH), π–π interactions (from diphenyls, DP), and ene types (C?C). In the ene‐functionalized oligomers, π–π interactions were controlled through the use of dioctyl repeats (DO). The polymerization rate and rate‐limiting steps were determined for all systems containing an allyl‐functionalized oligomer, and rates ranging from 0.10 to 0.54 mol L^?1 min^?1 were seen. The rate‐limiting step varied with the oligomer composition; examples of rate‐limited propagation (5:3:2 C?C:DP:DO/1:1 SH:DP) or chain transfer (5:3:2 C?C:DP:DO/3:1 SH:DP) were found in addition to cases with similar reaction rate constants (5:2:3 C?C:DP:DO/1:1 SH:DP). None of the siloxanes were found to exhibit autoacceleration despite their relatively high viscosities. Instead, the allyl‐, vinyl‐, and acrylate‐functionalized siloxanes were all found to undergo unimolecular termination based on their high α scaling values (0.98, 0.95, and 0.82, respectively) in the relation R_p ∝ R_i^α. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Phytochemicals from Echinacea and Hypericum: A Direct Synthesis of Isoligularone

Reaction of trienes with α,β‐unsaturated aldehydes produces bicyclic products via a tandem Diels–Alder/ene reaction. The adduct from tiglic aldehyde was converted into isoligularone by conversion to a furan followed by benzylic oxidation.     

Preparation of Reactive Three‐Dimensional Microstructures via Direct Laser Writing and Thiol‐ene Chemistry

Three‐dimensional microstructures are fabricated employing the direct laser writing process and radical thiol‐ene polymerization. The resin system consists of a two‐photon photoinitiator and multifunctional thiols and olefins. Woodpile photonic crystals with 22 layers and a rod distance of 2 μm are fabricated. The structures are characterized via scanning electron microscopy and focused ion beam milling. The thiol‐ene polymerization during fabrication is verified via infrared spectroscopy. The structures are grafted in a subsequent thiol‐Michael addition reaction with different functional maleimides. The success of the grafting reaction is evaluated via laser scanning microscopy and X‐ray photoelectron spectroscopy. The grafting density is calculated to be close to 200 molecules μm⁻².