纳米多孔金催化有机反应研究进展

综述了金纳米多孔材料在催化CO和醇的氧化反应、含不饱和键化合物(炔烃、亚胺和α,β-不饱和醛)的加氢还原反应、炔基芳香醛与炔烃的成环反应、氧化脱氢偶联构筑新C—C键反应和C—X(X=B,Si)键形成反应中的应用研究结果.     

锰氧咔咯催化环己烷生成己二醛催化机理的理论研究

通过密度泛函理论计算,研究锰氧咔咯催化环己烷氧化成己二醛的反应,讨论该催化过程的多态反应活性.计算表明,该反应经历两步羟基化和一步C—C键断裂过程.两步羟基化都是由氢转移开始,形成碳自由基中间体,接着迅速发生的自由基反应形成二醇的中间体.C—C键断裂过程由氢转移开始,先形成氧自由基中间体,氧自由基单电子和邻近环C—C键存在强烈的相互作用,导致该C—C键活化断裂和第二个氢的协同转移.反应的速控步是第二步羟基化过程,因此碳自由基中间体的稳定性决定该反应的难易,这也解释了实验上观察到叔碳的活性大于仲碳的活性顺序.     

丙酮醇作用下3-亚烷基酮的区域选择性加氢还原反应

本文报道了一种室温、空气氛围下,以丙酮醇为还原剂的3-亚烷基氧化吲哚环外C=C双键选择性加氢还原反应合成3-取代氧化吲哚的方法。在碳酸钾存在下,丙酮醇与3-亚烷基氧化吲哚在甲醇中反应得到13个3-烷基取代氧化吲哚,其中6个为新化合物,其机理分析结果表明：该反应符合加成-消除机理。     

钯催化咖啡因C—H键直接烷氧基羰基化反应生成8-酯基咖啡因衍生物

咖啡因羰基衍生物在药物活性及生物荧光方面表现优异性能,其简便合成方法备受关注.从咖啡因C—H键直接出发,研究了过渡金属钯配合物催化咖啡因C—H键与醇的氧化羰基化反应.以Pd Cl_2(PPh_3)_2为催化剂,以醋酸铜为氧化剂的反应体系下,不同咖啡因衍生物与不同醇均能进行氧化羰基化反应,得到了一系列8-酯基咖啡因衍生物.反应所用CO为一个大气压,操作简便,溴、烯烃和苯环等官能团都与体系有很好的兼容性.     

环丁醇开环官能化反应:通过C—C键断裂区域选择性构建γ位取代脂肪酮的新策略

环丁醇开环官能化反应是制备γ位取代脂肪酮的重要策略之一。通过区域选择性的C—C键断裂和新化学键(例如:C—C、C—N、C—O、C—F键等)的构建,环丁醇开环反应可以高效地在羰基的γ位引入各种各样的取代基团。环丁醇的开环反应途径主要分为两种:1)通过过渡金属钯和铑催化的β-碳消除反应开环;2)自由基历程的环丁醇单电子氧化开环。本文依据不同的开环反应机理,对环丁醇的开环官能化反应进行了阐述和展望。     

利用碳-氢活化形成环钯络合物实现的“双烷基化”反应

正Angew.Chem.Int.Ed.2017,56,12288~12291近几十年来,过渡金属催化的C—H键活化一直是有机化学研究的热点.大多数C—H键活化反应需要利用导向基,这极大地限制了该类反应在有机合成中的应用.解决该问题的一个有效策略是发展"无痕"导向基.卤族元素是理想的"无痕"导向基;该类反应是由C—X键对过渡金属氧化加成开始,随后的分子内C—H键活化反应会形成含有两个C—Pd键环钯络合物.该类环钯络合物不仅有潜在的新颖反应活性,其中的两个C—Pd键还可以被官能团化,     

多取代烯丙基硅化合物的立体选择性合成研究

烯丙基硅化合物是一类重要的有机合成中间体,能参与多种类型的化学转化反应,被广泛应用于C—C键构建和复杂化合物的合成反应中,探索官能化烯丙基硅化合物的立体选择性合成对丰富有机合成方法学研究有重要意义.利用有机硅取代的环丙基三级醇化合物的Julia烯烃化反应,得到了一系列新型的烷氧甲基取代的高碘代烯丙基硅化合物.相对于烷基取代的三级醇底物,芳基取代的三级醇底物能得到立体选择性更好的产物.     

通过苄醇与炔烃的环化反应快速高效构建茚及螺环茚

作为一类重要的碳环化合物,茚、螺环茚及其衍生物常见于各种天然产物骨架结构中,并作为合成中间体广泛地应用于材料、医药、有机不对称合成等领域.在路易斯酸TiCl_4或AlCl_3作用下,二苯甲醇或芳基取代环醇等苄醇通过生成碳正离子中间体,与炔烃进行环化反应高效合成多种茚及螺环茚.该反应仅需30 min,反应过程中完成了2个新C—C键的构建,对具有各种取代基的炔烃均有较好的适用性.芳基取代的环丁醇、环己醇、环庚醇、环辛醇以及环十二醇都可以适用于该方法,多样性地构建多种有合成价值的螺环骨架.该方法具有操作简便、反应时间短、条件温和等优点.     

大环二萜类化合物的研究(Ⅳ)——Isosarcophytol—A前体化合物的合成

Isosarcophytol-A(1)是1982年首次从澳大利亚软珊瑚(Nephthea brassica)中分离鉴定的西松烷型(Cembrane)大环二萜类化合物,其结构为6,10,14-三甲基-3-异丙基-3E,5E,9E,13E-环十四碳四烯-1-醇,是Sarcophytol—A(2)的异构体,但有关1的生物活性试验和全合成研究尚未见报道.我们在前文报道了以低价钛诱导的分子内二羰基偶联为环化方法,完成了天然大环二萜类化合物Cembrene—C的全合成和Sarcophytol—A(2)苄醚衍生物(3)的合成.本文报道以天然法呢醇4为起始原料,经区域选择性氧化、羟醛缩合等六步反应,合成了1的前体化合物11.合成路线如下:     

环己烯可控选择性催化氧化的最新进展（英文）

环己烯是一种价格低廉易得的大宗化工原料,通常由苯选择性加氢来合成.该化合物虽然分子结构简单,但却有两个不同的反应位点.随着反应所发生的位点与反应深度的不同,环己烯的氧化反应可生成一系列不同氧化程度与官能团的产物的混合物.环己烯双键的氧化反应,可生成环氧环己烷,而环氧环己烷进一步水解,则生成1,2-环己二醇,其中,随着使用不同催化剂导致的反应机理差异,产物可分别为顺式或反式结构.在强氧化剂作用下,环己烯双键充分氧化,可生成己二酸.环己烯烯丙基C-H键氧化,则可随着反应深度的不同分别生成2-环己烯醇与2-环己烯酮.上述环己烯氧化产物都是重要的有机化工中间体.其中,环氧环己烷是农药杀螨剂的主要原料,也用作合成表面活性剂、橡胶助剂等有用产品;1,2-环己二醇可用于合成化工中间体邻苯二酚;环己烯醇与环己烯酮是生产除草剂、香水、药物的原料;己二酸则是合成重要产品尼龙-6,6的原料.因此,随着市场需求的变化,对环己烯氧化反应进行选择性控制,提高其中某种产物的选择性,是重要的化工合成技术,有着巨大的应用潜力;从而控制反应历程与深度是有机化工合成工艺研究中最具有挑战性的研究课题之一,有很好的科学意义.目前,人们对环己烯的选择性控制氧化反应已进行了广泛的研究.该反应可使用金属催化剂,包括铁、钴、镍、锰、铬、钒、钨、铜、钛、金、银、铋、锇、钼、镉等;也可以使用无金属催化剂如磺酸、2,2,2-三氟苯乙酮、类石墨相碳化氮(g-C3N4)等.反应可使用化学氧化剂,如间氯过氧苯甲酸、醋酸碘苯、过氧叔丁醇等,也可使用更加清洁的过氧化氢、分子氧.研究表明,催化剂的种类、用量,以及反应溶剂、温度、氧化剂等一系列外在条件,可以影响环己烯氧化反应的选择性.本文以反应所使用的氧化剂归类,总结了该课题的最新研究进展,以期对从事环己烯可控选择性氧化的学术与工业研究人员有所帮助.     

Palladium-catalyzed aerobic oxidative amination of alkenes: development of intra- and intermolecular aza-Wacker reactions

Palladium-catalyzed methods for the aerobic oxidative coupling of alkenes and oxygen nucleophiles (e.g., water and carboxylic acids) have been known for nearly 50 years. The present account summarizes our development of analogous aerobic oxidative amination reactions, including the first intermolecular aza-Wacker reactions compatible with the use of unactivated alkenes. The reactions are initiated by intra- or intermolecular aminopalladation of the alkene. The resulting alkylpalladium(II) intermediate generally undergoes beta-hydride elimination to produce enamides or allylic amide products, but in certain cases, the Pd-C bond can be trapped to achieve 1,2-difunctionalization of the alkene, including carboamination and aminoacetoxylation. Mechanistic studies have provided a variety of fundamental insights into the reactions, including the effect of ancillary ligands on palladium catalysts, the origin of the Br?nsted-base-induced switch in regioselectivity in the oxidative amination of styrene, and evidence that both cis- and trans-aminopalladations of alkenes are possible. Overall, these reactions highlight the potential utility of an "organometallic oxidase" strategy for the selective aerobic oxidation of organic molecules.     

Selective aerobic oxidation of hydroxy compounds catalyzed by photoactivated ruthenium-salen complexes (selective catalytic aerobic oxidation)

Selective oxidation of alcohols to the corresponding carbonyl compounds is one of the most fundamental reactions in organic synthesis. Traditional methods for this transformation generally rely on stoichiometric amount of oxidants represented by Cr(VI) or DMSO reagents, though their synthetic utility is encumbered by unpleasant waste materials. From ecological and atom-economic viewpoints, catalytic aerobic oxidation is much more advantageous because molecular oxygen is ubiquitous and the byproduct is basically non-toxic water or hydrogen peroxide. On the other hand, phenol derivatives undergo oxidative coupling, forming C-C or C-O bond, through radical intermediates coupled with an electron-transfer process. Molecular oxygen is also well known to serve as electron acceptor in this reaction. Thus, a variety of transition metal complexes have so far been examined for aerobic oxidations of alcohols and phenols, and high catalytic activities have been achieved in some cases. However, stereo- and chemo-selective aerobic oxidations are still limited in number and are of current interest. Presented in this paper is our recent studies on catalytic aerobic oxidations with photoactivated nitrosyl ruthenium-salen complexes, including asymmetric oxidation of secondary alcohols to ketones (kinetic resolution), enantioselective oxidative coupling of 2-naphthols to binaphthols and oxygen-radical bicyclization of 2,2'-dihydroxystilbene, chemoselective oxidation of primary alcohols to aldehydes and diols to lactols, and asymmetric desymmetrization of meso-diols to lactols.     

Copper-catalyzed aerobic oxidative C-H functionalizations: trends and mechanistic insights

The selective oxidation of C-H bonds and the use of O(2) as a stoichiometric oxidant represent two prominent challenges in organic chemistry. Copper(II) is a versatile oxidant, capable of promoting a wide range of oxidative coupling reactions initiated by single-electron transfer (SET) from electron-rich organic molecules. Many of these reactions can be rendered catalytic in Cu by employing molecular oxygen as a stoichiometric oxidant to regenerate the active copper(II) catalyst. Meanwhile, numerous other recently reported Cu-catalyzed C-H oxidation reactions feature substrates that are electron-deficient or appear unlikely to undergo single-electron transfer to copper(II). In some of these cases, evidence has been obtained for the involvement of organocopper(III) intermediates in the reaction mechanism. Organometallic C-H oxidation reactions of this type represent important new opportunities for the field of Cu-catalyzed aerobic oxidations.     

Reoxidation of Transition‐metal Catalysts with O2

Transition‐metal catalyzed oxidation reactions are central components of organic chemistry. On behalf of green and sustainable chemistry, molecular oxygen (O₂) has been considered as an ideal oxidant due to its natural, inexpensive, and environmentally friendly characters, and therefore offers attractive academic and industrial prospects. In recent years, some powerful organic oxidation methods have been continuously developed. Among them, the use of molecular oxygen (O₂) as a green and sustainable oxidant has attracted considerable attentions. However, the development of new transition metal‐catalyzed protocols using O₂ as an ideal oxidant is highly desirable but very challenging because of the low standard electrode potential of O₂ to reoxidize the transition‐metal catalysts. In this Account, we highlight some of our progress toward the use of transition‐metal catalyzed aerobic oxidation reactions. Through the careful selection of ligand and the acidic additives, we have successfully realized the reoxidation of Cu, Pd, Mn, Fe, Ru, Rh, and bimetallic catalysts under O₂ or air atmosphere (1 atm) for the oxidative coupling, oxygenation reactions, oxidative C‐H/C‐C bond cleavage, oxidative annulation, and olefins difunctionalization reactions. Most of the reactions can tolerate a range of functional groups. These methods provide new strategies for the green synthesis of alkynes, (α ‐keto)amides/esters, ketones/diones, O/N‐heterocycles, β ‐azido alcohols, and nitriles. The high efficiency, low cost, and simple operation under air make these methodologies very attractive and practical. We will also discuss the mechanisms of these reactions which might be useful to promote the new type of aerobic oxidative reaction design.     

Unexpectedly Simple Synthesis of Benzazoles by tBuONa‐Catalyzed Direct Aerobic Oxidative Cyclocondensation of o‐Thio/Hydroxy/Aminoanilines with Alcohols under Air

tBuONa‐catalyzed direct aerobic oxidative cyclocondensation reactions of readily available alcohols and o‐thio/hydroxy/aminoanilines under air have been developed and provide an efficient, practical, and green method for the synthesis of benzazoles. Mechanistic studies revealed that o‐substituted anilines promote the initial aerobic alcohol‐oxidation step, which explains the high reactivity and success of this unexpectedly simple and practical cyclocondensation method.     

Palladium-assisted multicomponent cyclization of aromatic aldehydes, arylamines and terminal olefins under molecular oxygen: an assembly of 1,4-dihydropyridines

The palladium-assisted one-pot three-component reactions of aldehydes, amines and olefins proceeded smoothly to give 2,6-unsubstituted 1,4-dihydropyridines (1,4-DHPs) using molecular oxygen as a sole oxidant. It also provides efficient Pd-catalyzed aerobic oxidation access to the anti-Markovnikov oxidative amination products of olefins from primary aromatic amines and alkenes. The method is atom-efficient, using cheap and easily available starting materials and an environmentally benign oxidant.     

Palladium oxidase catalysis: selective oxidation of organic chemicals by direct dioxygen-coupled turnover

Selective aerobic oxidation of organic molecules is a fundamental and practical challenge in modern chemistry. Effective solutions to this problem must overcome the intrinsic reactivity and selectivity challenges posed by the chemistry of molecular oxygen, and they must find application in diverse classes of oxidation reactions. Palladium oxidase catalysis combines the versatility of Pd(II)-mediated oxidation of organic substrates with dioxygen-coupled oxidation of the reduced palladium catalyst to enable a broad range of selective aerobic oxidation reactions. Recent developments revealed that cocatalysts (e.g. Cu(II), polyoxometalates, and benzoquinone) are not essential for efficient oxidation of Pd(0) by molecular oxygen. Oxidatively stable ligands play an important role in these reactions by minimizing catalyst decomposition, promoting the direct reaction between palladium and dioxygen, modulating organic substrate reactivity and permitting asymmetric catalysis.     

Cs2CO3‐Catalyzed Aerobic Oxidative Cross‐Dehydrogenative Coupling of Thiols with Phosphonates and Arenes

An efficient Cs₂CO₃‐catalyzed oxidative coupling of thiols with phosphonates and arenes that uses molecular oxygen as the oxidant is described. These reactions provide not only a novel alkali metal salt catalyzed aerobic oxidation, but also an efficient approach to thiophosphates and sulfenylarenes, which are ubiquitously found in pharmaceuticals and pesticides. The reaction proceeds under simple and mild reaction conditions, tolerates a wide range of functional groups, and is applicable to the late‐stage synthesis and modification of bioactive molecules.     

Mechanistic insights into copper-catalyzed aerobic oxidative coupling of N–N bonds

Catalytic N–N coupling is a valuable transformation for chemical synthesis and energy conversion. Here, mechanistic studies are presented for two related copper-catalyzed oxidative aerobic N–N coupling reactions, one involving the synthesis of a pharmaceutically relevant triazole and the other relevant to the oxidative conversion of ammonia to hydrazine. Analysis of catalytic and stoichiometric N–N coupling reactions support an “oxidase”-type catalytic mechanism with two redox half-reactions: (1) aerobic oxidation of a Cu^I catalyst and (2) Cu^II-promoted N–N coupling. Both reactions feature turnover-limiting oxidation of Cu^I by O₂, and this step is inhibited by the N–H substrate(s). The results highlight the unexpected facility of the N–N coupling step and establish a foundation for development of improved catalysts for these transformations.

Mechanistic studies provide valuable insights into Cu-catalyzed N–N coupling reactions relevant to energy conversion and pharmaceutical synthesis.     

Detection of Palladium(I) in Aerobic Oxidation Catalysis

Palladium(II)‐catalyzed oxidation reactions exhibit broad utility in organic synthesis; however, they often feature high catalyst loading and low turnover numbers relative to non‐oxidative cross‐coupling reactions. Insights into the fate of the Pd catalyst during turnover could help to address this limitation. Herein, we report the identification and characterization of a dimeric Pd^I species in two prototypical Pd‐catalyzed aerobic oxidation reactions: allylic C−H acetoxylation of terminal alkenes and intramolecular aza‐Wacker cyclization. Both reactions employ 4,5‐diazafluoren‐9‐one (DAF) as an ancillary ligand. The dimeric Pd^I complex, [Pd^I(μ‐DAF)(OAc)]₂, which features two bridging DAF ligands and two terminal acetate ligands, has been characterized by several spectroscopic methods, as well as single‐crystal X‐ray crystallography. The origin of this Pd^I complex and its implications for catalytic reactivity are discussed.