氯自由基介导的光催化芳基醚C(sp^(3))−H氧化生成酯

饱和的碳氢键氧化是合成化学和化学工业中一类重要的化学反应.然而,饱和C(sp^(3))−H键离解能(BDEs)较高、极性较弱,导致了底物难以活化和催化转化效率较低等问题.在过去的几十年,C(sp^(3))−H键的定向活化转化取得了重要的进展.其中,关于C(sp^(3))−H键催化氧化的研究主要涉及一些键能低的、预活化的C−H键,包括苄基型、亚甲基型、脂肪族X−CH_(2)(X=O,N)和甲苯等,含有未活化C(sp^(3))−H键的复杂化合物的选择性氧化仍具有挑战性.例如,芳基醚C(sp^(3))−H键功能化通常采用计量的过氧化物氧化剂,或者通过单电子氧化和碱促进的去质子化进一步构建C−C/C−N键,产物选择性较低,也带来了一些不利的环境影响.因此,有必要开发高效、温和的芳基醚C(sp^(3))−H键选择氧化方法,并将其应用于有机合成和药物开发.近年来,光催化C(sp^(3))−H键氧化因其操作简便、氧化还原中性等优点,已发展成为一种有用且多样的催化研究工具.本文发展了一种利用氧气作为氧化剂,在可见光驱动下选择性地将芳基醚C(sp^(3))−H键氧化成为甲酸苯酯类产物的新方法.使用Mes-10-phenyl-Acr^(+)−BF_(4)^(-)光催化剂,高效活化多种氯源(如盐酸、无机氯盐和有机氯化物)得到氯自由基,由于其具有较高的氧化能力(+2.03 V vs.SCE)和对氢原子的亲和力,能够通过氢原子转移过程活化芳基醚C(sp^(3))−键,攫取氢自由基得到相应的烷基碳自由基(•CH_(2)OPh)中间体,进一步被分子氧选择氧化得到酯类目标产物.研究结果表明,多种链状芳基醚和不同取代(如给电子基和吸电子基)芳基醚均可发生氧化反应,高收率地合成了一系列官能团丰富的甲酸苯酯类化合物.本文方法具有反应条件温和、操作简单、官能团耐受性好以及可规模化放大等优点,并且少量的水对反应没有明显影响.机理实验研究结果表明,芳基醚C(sp^(3))−H键的断裂是反应过程的决速步骤.紫外可见吸收光谱结果表明,氯离子与催化剂之间的相互作用强于底物,并且自由基捕获实验证实反应体系中存在氯自由基和烷基碳自由基物种,表明反应经历自由基路径.此外,电子顺磁共振测试结果表明,反应过程中存在单线态氧物种,可能是激发态的光催化剂直接与氧气发生能量转移得到;同位素实验(18O)揭示了甲酸苯酯类化合物氧的来源.综上,本文实现了温和条件下光催化芳基醚C(sp^(3))−H键选择氧化反应,高收率合成了一系列甲酸苯酯类化合物.该方法避免了化学计量的过氧化物和碱等添加剂的使用以及底物的过度氧化,阐明了催化反应机制,为其他醚类化合物的C(sp^(3))−H键氧化功能化提供了新思路,为后续化学合成和药物开发提供了参考和启示.

Simultaneously Enhanced Activity and Selectivity for C(sp^(3))-H Bond Oxidation Under Visible Light by Nitrogen Doping

Selective oxidation of saturated C(sp^(3))-H bonds in hydrocarbon to target chemicals under mild conditions remains a signifi-cant but challenging task because of the chemical inertness and high dissociation energy of C(sp^(3))-H bonds.Semiconductor photocatalysis can induce the generation of holes and oxidative radicals,off ering an alternative way toward selective oxidation of hydrocarbons under ambient conditions.Herein,we constructed N-doped TiO_(2) nanotubes(N-TNTs)that exhibited remark-able activity and selectivity for toluene oxidation under visible light,delivering the conversion of toluene and selectivity of benzaldehyde of 32% and>99%,respectively.Further mechanistic studies demonstrated that the incorporation of nitrogen induced the generation of N-doping level above the O 2p valance band,directly contributing to the visible-light response of TiO_(2).Furthermore,hydroxyl radicals generated by photogenerated holes at the orbit of O 2p were found to be unselective for the oxidation of toluene,aff ording both benzaldehyde and benzoic acid.The incorporation of nitrogen was able to inhibit the generation of hydroxyl radicals,terminating the formation of benzoic acid.

Enhancement of CH_(3)CO^(*) adsorption by editing d-orbital states of Pd to boost C–C bond cleavage of ethanol eletrooxidation

Improving the complete ethanol electrooxidation on Pd-based catalysts in alkaline media has drawn widely attention due to the high mass energy density.However,the weak adsorption energy of CH_(3)CO^(*) on Pd restricts the C–C bond cleavage.Inspired by the molecular orbital theory,we proposed the d-state-editing strategy to construct more unoccupied d-states of Pd for the enhanced interaction with CH_(3)CO^(*) to break C–C bonds.As expected,the reduced number of e_g electrons and more unoccupied d-states of Pd successfully formed on as-prepared porous Rh Au–Pd Cu nanosheets(PNSs).Theoretical calculations show that the optimized d-states of Rh Au–Pd Cu PNS can effectively improve the adsorption of CH_(3)CO^(*) and drastically reduce the energy barrier of C–C bond cleavage,thus boosting the complete oxidation of ethanol.The charge ratio of C_1 pathway on Rh Au–Pd Cu PNSs is 51.5%,more than 2 times higher than that of Pd NSs.Our finding provides an innovative perspective for the design of highly-efficient noble-based electrocatalysts.

Efficient Photolytic Halogenation and Oxidation of Unactivated Alkyl sp^(3) C—H Bonds with Iodine(III)

A metal-free,green,and sustainable functionalization of unactivated alkyl sp^(3) C—H bonds is reported using iodine(III)as a feasible dehydrogenation agent under visible light or KBr,and alkyl chlorides,bromides,alcohols,and ketones could be constructed by addition of different coupling reagents.Cheap and safe iodobenzene diacetate was used to form a radical to activate the alkyl sp^(3) C—H bond in a highly efficient manner,which can construct different alkylation products by adding corresponding coupling reagents.

甘氨酸衍生物C(sp^3)―H官能团化反应在喹啉类化合物合成中的应用

C(sp^3)―H键官能团化反应被认为是构建C―C键的最直接和高效的合成方法。近年来,通过甘氨酸衍生物C(sp^3)―H官能团化反应来合成喹啉类化合物的研究逐渐引起研究者的广泛关注。本文简要介绍了甘氨酸衍生物C(sp^3)―H官能团化反应研究现状,并总结了不同催化体系下此类反应在喹啉衍生物合成中的应用,目的在于通过对前沿科研内容的介绍,开拓大学生的知识视野,激发他们对于科学探索的兴趣。

电化学促进未活化C(sp^(3))—H官能团化研究进展

有机电合成以无痕电子代替传统的化学氧化剂或还原剂,具有绿色易放大等优势.未活化C(sp^(3))—H键的官能团化可以将目标官能团直接引入分子中进行修饰,避免预官能团化,兼具原子经济性和步骤经济性.随着有机电合成发展的日益成熟,电化学促进未活化C(sp^(3))—H官能团化成为了有机合成的研究热点之一.根据官能团类型对反应进行分类,总结了近年来涉及未活化C(sp^(3))—H官能化的研究成果,重点分析了反应优势、底物特点以及反应机理,最后展望了面临的挑战及未来的发展趋势.

3-芳基取代脯氨酸的合成

本文以脯氨酸为原料,通过在脯氨酸上引入导向基团和保护基团,实现脯氨酸3-位的碳氢键活化芳基化反应,从而制备3-芳基取代的脯氨酸衍生物。而后在碱和乙醇的作用下实现导向基团和保护基团的一步脱除,得到目标产物——3-芳基取代脯氨酸。整个合成路线只需要一次性合成脯氨酸底物即可得到一系列3-芳基取代脯氨酸衍生物,为3-芳基取代脯氨酸化合物的合成提供了一种简便快捷的有机合成新方法。此外,该合成路线的发现为进一步探索研究3-芳基取代脯氨酸的生物活性奠定了基础。

Transformations of N-arylpropiolamides to indoline-2,3-diones and acids via C≡C triple bond oxidative cleavage and C(sp^2)–H functionalization

A new palladium-catalyzed oxidative conversion of N-arylpropiolamides and H2O to various indoline-2,3-diones and acids through the C≡C triple bond cleavage and C(sp2)–H functionalization is described,which is promoted by a cooperative action of catalytic CuBr2,2,2,6,6-tetramethyl-1-piperidinyloxy(TEMPO)and O2.The method provides a practical tool for transformations of alkynes by means of a C–H functionalization strategy,which enables the formation of one C–C bond and multiple C–O bonds in a single reaction with high substrates compatibility and excellent functional group tolerance.

过渡金属参与C―H键切断模式的理论研究进展

过渡金属催化活化C―H键来构建新共价键因具有原子经济和合成简捷的特点,已成为合成化学中最为有效策略之一。本文中,我们总结了过渡金属参与的C―H键切断的理论研究进展,并系统性提出了C―H键切断的相关模式,包括:C―H键对金属的氧化加成、碱协助的去质子化、σ-复分解、Friedel-Crafts型亲电芳香取代、α-或β-氢消除以及夺氢活化等。理论计算表明,当使用还原性较强的零价金属催化剂时,反应可按照氧化加成模式进行。当使用金属羧酸盐作为催化剂时,通常以协同金属化-去质子化机理模式实现C―H键切断。当使用阳离子金属催化剂,富电子芳烃比缺电子芳烃优先反应时,C―H键切断则会经历碱协助的内部亲电取代模式。σ-复分解是协同金属化-去质子化机理的另一种模式。如果亲电体对芳烃进行加成时,则可按照Friedel-Crafts型亲电芳香取代方式活化C―H键。α-或β-氢消除也是比较常见的活化C―H键模式。此外,夺氢活化可通过自由基过程实现C―H键活化。本文通过对过渡金属参与的C―H键活化模式的论述旨在为实验提供理论指导。

Multipurpose sulfoximine-mediated radicalγ-heteroarylation of unactivated C(sp^(3))–H bonds

A conceptually novel,trifunctional sulfoximine-mediatedγ-functionalization of unactivated C(sp^(3))–H bonds has been achieved.The reaction is initiated by the photo-induced homolytic cleavage of an N–S bond in the absence of photosensitizer,and proceeds sequentially through a cascade of 1,5-hydrogen atom transfer,1,4-functional group migration,desulfoximination and a Minisci reaction.A major feature of this approach is the use of sulfoximine as a traceless directing group.Other positive properties include mild conditions,simple operation,exclusive site-selectivity,high product diversity and the avoidance of additional photosensitizers.The protocol provides a new reaction mode for HAT-induced C(sp^(3))–H functionalization,and allows a much broader chemical space for sulfoximine studies.

喹啉酮C-3位直接官能团化研究进展

C-3位取代的喹啉酮是一类重要的杂环化合物,在材料和医药等方面具有较为广泛的应用。通过C-H直接官能团化来构建3-喹啉酮衍生物是最为简便和有效的方法,引起了人们极大的关注。近年来,在金属或非金属催化下一系列高效、绿色的合成3-喹啉酮衍生物的方法已经被实现。本文按照不同的官能团化反应类型进行分类,综述了3-喹啉酮衍生物合成的研究进展。

VO_3/CeO_2(111)催化剂上丙烷氧化脱氢反应活性和选择性的密度泛函理论研究（英文）

低碳烯烃一直以来都是化工行业非常重要的基础原料,一般采用烷烃直接热裂解制得,但该方法耗能很大,经济价值有限.近年来,人们开始尝试利用氧化脱氢反应(ODH)方法制备低碳烯烃,并取得了巨大的研究进展,其中稀土氧化物负载钒氧化物催化剂具有良好的低碳烷烃氧化脱氢性能.本文分析了前人对于钒氧化物负载在CeO_2表面的计算研究结果,并选取了最具代表性的VO_3/CeO_2(111)作为烷烃ODH制烯烃的模型催化剂,详细研究了丙烷在该催化剂体系中发生ODH反应机理.通过使用密度泛函理论,对丙烷在VO_3/CeO_2(111)催化剂上断裂第一根和第二根碳氢键的反应过程进行了理论模拟,并对比了丙烷制丙烯中碳氢键断裂先后的活化能及VO_3/CeO_2(111)催化剂材料自身的电子性质.结果表明该催化剂的电子结构在丙烷氧化脱氢反应中扮演关键角色.在丙烷分子断裂第一根碳氢键的反应过程中,会产生两个自由电子,对其电子结构分析发现,其中的一个自由电子会局域在由VO_3/CeO_2(111)催化剂中五个相关氧原子的2p轨道所形成的新发生局域空轨道(NELS)上,这个独特的新发生局域空轨道只能接受一个电子,另一个电子则会通过丙基在CeO_2表面发生吸附将电子传递到CeO_2表面的Ce原子上;当丙烷分子进一步发生第二根碳氢键断裂反应时,同样会产生两个新的局域电子,其中一个电子局域在Ce的4f轨道上,此时CeO_2表面存在两个局域电子,相互排斥,导致该催化剂上丙烷断裂第二根碳氢键所需的活化能远高于第一根碳氢键.综上,本文对VO_3/CeO_2(111)催化剂上低碳烷烃ODH反应独特的催化活性和选择性给出了较为细致的分析和解释.

烃类C—H键催化断裂活性受相邻基团的影响规律

采用密度泛函理论研究了烃类C—H键在醋酸铜催化作用下断裂活性受其相邻基团的影响规律。计算结果表明,与不同基团相连的甲基和次甲基C—H键的催化断裂活性顺序:苯基>正己基>环己基;而亚甲基C—H键的催化断裂活性顺序:苯基>环己基>正己基。通过对C—H键催化断裂活性的理论分析,发现相邻基团对所连C—H键催化断裂活性的影响与相邻基团在催化剂发生吸附前后的电荷变化量以及空间位阻大小有关。

CeCl_(3)-Promoted Simultaneous Photocatalytic Cleavage and Amination of C_(α)–C_(β)Bond in Lignin Model Compounds and Native Lignin

It remains challenging to achievevaluableplatformchemicals from lignin because of itscomplicated polymeric structure and inherent inert chemical activities.So far,only a fewexamples have been reported for the selective cleavage of C–C bonds in lignin due to their intrinsic inertness and ubiquity.Here,we present a simple and commercially available cerium(Ⅲ)chloride(CeCl_(3))-promoted photocatalytic depolymerization strategy to realize the simultaneous cleavage and amination ofC_(α)–C_(β)bond in a variety of lignin model compounds at room temperature.This procedure does not require any pretreatments and breakdown of C–O bonds or loss ofγ-CH_(2)OHgroup to generate aldehydes(up to 97%)and N-containing products(up to 95%)in good to excellent yields.Additionally,this CeCl_(3)-based photocatalyst system could maintain excellent catalytic performance even after 10 sequential cycles with newstarting materials.Moreover,this approach realizes the precise control over the reaction via switching the external light stimuli on/off.Further,this method is effective for the depolymerization of real lignin,thus affording the corresponding cleavage and amination products of C_(α)–C_(β)bonds.

铜催化环状烯烃烯丙位C(sp^(3))—H磺酰化反应研究

发展了一种温和的铜催化烯丙位C(sp^(3))—H直接高效磺酰化方法,以简单环状烯烃和亚磺酸钠为反应原料,以中等至良好的收率合成了一系列烯丙基砜衍生物.机理研究表明,该反应可能经历了自由基中间体.

导向基辅助的过渡金属催化C(sp^(3))—H键氮宾插入反应研究进展

过渡金属催化C(sp^(3))—H键活化形成碳-氮键的反应一直是具有挑战性且热门的研究领域.过渡金属催化的C(sp^(3))—H胺化策略为形成C—N键提供了更为直接高效的方式.随着碳-氢键活化领域的蓬勃发展,人们发展出了丰富多样的导向基和过渡金属催化体系,为通过内轨机制实现C(sp^(3))—H胺化提供了有效工具.近年来,导向基辅助的C(sp^(3))—H键胺化反应取得了重要进展,许多基于不同过渡金属的催化体系和廉价高效的胺化试剂得以开发.综述了近十年来在导向基团辅助下,过渡金属催化C(sp^(3))—H氮宾插入反应的研究进展.

基于羧酸衍生物远程γ-C(sp^(3))–H键官能团化研究进展

碳氢键选择性活化是化学领域中最基本和最具挑战性的问题之一,在合成各种生物活性物质中具有重要的作用.羧酸及其衍生物是最易获得的原料之一.通常羧酸的α-和β-C(sp^(3))–H键官能化较为容易,而γ-和δ-C(sp^(3))–H因距离较远则难以官能化.因此,发展简便、高效的方法实现羧酸及其衍生物远程C(sp^(3))–H键官能团化成为近年研究热点之一.本文根据不同的反应分类,综述了近些年在不同催化条件下基于羧酸衍生物的远程γ-C(sp^(3))–H键官能团化反应研究进展,详细讨论了反应底物普适性、反应机理和应用,并对该领域的发展前景和局限性进行了总结.

Radical Functionalization of Remote C(sp^(3))-H Bonds Mediated by Unprotected Alcohols and Amides

Aliphatic alcohols and amides are highly valued,ubiquitous chemicals in synthetic chemistry.Radical-promoted regioselective functionalization of unactivated C(sp^(3))–H bonds offers an atom and step economic manner for direct transformation of aliphatic alcohols and amides,especially structural elaboration of complex natural products and bioactive molecules without de novo synthesis.Despite the rapid growth of hydrogen atom transfer(HAT)processes mediated by O-or N-centered radicals generated from prefunctionalized precursors of alcohols and amides in the past few years,exploration of remote C(sp^(3))–H functionalization via HAT mediated by unprotected alcohols or amides lags behind,due to the difficult homolysis of O–H and N–H bonds with high bond-dissociation energies(BDEs).In this minireview,the recent advances in regioselective C(sp^(3))–H functionalization mediated by unprotected alcohols and amides are summarized.

C(sp^3)–H bond functionalization of non-cyclic ethers by decarboxylative oxidative coupling with α,β-unsaturated carboxylic acids

A copper-catalyzed decarboxylative oxidative coupling of α,β-unsaturated carboxylic acids with non-cyclic ethers is developed.This method provides a new approach for C(sp^3)–H bond functionalization of non-cyclic ethers. Mechanism study shows the reaction involves a radical process.

Recent advances in sulfenylation of C(sp^3)-H bond under transition metal-free conditions

In recent years,the transition metal-free sulfenylation of C-H bond for C-S formation has been rapidly advanced and has become an eco-friendly synthetic tool for pharmacists and organic chemists.Various natural or bioactive molecules such as(hetero)arenes,olefins,carbonyl compounds,alkanes,have been employed for sulfenylating reactions.This review will focus on the recent five-year advances in C-S bond formation via direct sulfenylation of C(sp^3)-H bonds under metal-free conditions and elaborate their mechanisms from a new perspective.