Catalyzed Asymmetric Arylation Reactions

Addition and substitution reactions with carbon nucleophiles are fundamental processes in organic synthesis, and the development of general catalytic asymmetric variants thereof is still a major challenge today. In contrast to enantioselective alkyl transfer reactions, the corresponding arylations have not yet reached a high level of maturity. The existing protocols are either of no general applicability or are limited in terms of selectivity. This article summarizes established routes for catalytic asymmetric aryl transfer together with the latest developments in this area. The scope and limitations of this reaction are discussed.     

Radical Arylation of Phenols,Phenyl Ethers,and Furans

Radical arylations of para‐substituted phenols and phenyl ethers proceeded with good regioselectivity at the ortho position with respect to the hydroxy or alkoxy group. The reactions were conducted with arenediazonium salts as the aryl radical source, titanium(III) chloride as the reductant, and diluted hydrochloric acid as the solvent. Substituted biaryls were obtained from hydroxy‐ and alkoxy‐substituted benzylamines, phenethylamines, and aromatic amino acids. The methodology described offers a fast, efficient, and cost‐effective new access to diversely functionalized biphenyl alcohols and ethers. Free phenolic hydroxy groups, aromatic and aliphatic amines, as well as amino acid substructures, are well tolerated. Two examples for the applicability of the methodology are the partial synthesis of a β‐secretase inhibitor and the synthesis of a calcium‐channel modulator.     

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.     

Catalysis of Radical Reactions: A Radical Chemistry Perspective

The area of catalysis of radical reactions has recently flourished. Various reaction conditions have been discovered and explained in terms of catalytic cycles. These cycles rarely stand alone as unique paths from substrates to products. Instead, most radical reactions have innate chains which form products without any catalyst. How do we know if a species added in “catalytic amounts” is a catalyst, an initiator, or something else? Herein we critically address both catalyst‐free and catalytic radical reactions through the lens of radical chemistry. Basic principles of kinetics and thermodynamics are used to address problems of initiation, propagation, and inhibition of radical chains. The catalysis of radical reactions differs from other areas of catalysis. Whereas efficient innate chain reactions are difficult to catalyze because individual steps are fast, both inefficient chain processes and non‐chain processes afford diverse opportunities for catalysis, as illustrated with selected examples.     

Copper in Cross-Coupling Reactions: II. Arylation of Thiols

Russian Journal of Organic Chemistry - The review presents an analysis of the recent literature on the use of copper catalysis in the formation of a C-S bond between aryl halides and thiols. The...     

Copper in Cross-Coupling Reactions: III. Arylation of Azoles

Russian Journal of Organic Chemistry - The review discusses recently published data on copper-catalyzed arylation of azoles with aryl halides with the formation of new C–N bonds. Ligand-free...     

Radical Addition and Substitution Reactions of (η6-Arene)-tricarbonylmetal Complexes

We report here the first alkyl radical additions of (η6-arene)tricarbonylmanganese complexes in the presence of alkylmercury chloride and NaI (Eq. 1). The mechanism was postulated to be the alkyl radical addition to ArMn- (CO)+3 cation to form the corresponding 17 valence electron intermediate, which was then reduced by alkylmercury chloride via a single electron transfer process to afford the product and regenerate an alkyl radical. [1]     

Merging Regiodivergent Catalysis with Atom‐Economical Radical Arylation

A titanocene‐catalyzed regiodivergent radical arylation is described that allows access to either enantiomerically pure tetrahydroquinolines or indolines from a common starting material. The regioselectivity of epoxide opening that results in the high selectivity of heterocycle formation is controlled by two factors, the absolute configuration of the enantiopure ligands of the (C₅H₄R)₂TiX₂ catalyst and the inorganic ligand X (X=Cl, OTs). The overall reaction is atom‐economical and constitutes a radical Friedel–Crafts alkylation.     

Arylation of 2,5-dimethyl-4-phenylpyridine

The position of the pyridine ring is arylated by reaction of 2,5-dimethyl-4-phenylpyridine with phenyllithium and p-tolyllithium. Destructive oxidation of the diaryl-substituted pyridines primarily affects the pyridine ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1359–1361, October, 1970.     

Some New Radical Reactions of Xanthates

Xanthates are convenient precursors of a variety of radicals that can be captured in an inter- or intramolecular fashion. Overall, the process involves rupture of the sulfide C-S bond and addition of the elements of the xanthate to the olefinic trap. The xanthate in the product can be used in another radical sequence or ionically modified in a great variety of ways. S-Propargyl xanthates exhibit a special but interesting behaviour which involves a sigmatropic rearrangement to the corresponding allene and ring closure to a novel betaine.     

Arylation of aromatic hydrocarbons by thermal decomposition of 2, 6-di-tert-butyl-p-benzoquinonediazide

Conclusions A new method of arylation has been developed, permitting the preparation of 4-aryl-2,6-di-tert-butylphenols by the thermal decomposition of 2,6-di-tert-butyl-p-benzoquinonediazide in a medium of aromatic hydrocarbons and their derivatives.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 204–206, January, 1968.The authors thank N. M. Émanuel for his continuing interest during the progress of this work.     

Sodium p-Toluenesulfinate in Free Radical Reactions

A sulfonyl radical induced addition reaction of p-tolyl p-toluenethiosulfonate with olefins by using sodium p-toluenesulfinate as sulfonyl radical precursor is described.     

水介质中的有机自由基反应

化学反应溶剂的绿色化是绿色化学发展的必然趋势,利用储量丰富、廉价易得、无毒性、无污染的水替代传统有机溶剂作为反应介质是化学家们追求的目标。自由基反应由于反应活性高、反应条件温和,逐渐成为有机合成的一种重要策略。本文依据所构建化学键类型的不同,对近5年来水介质中的有机自由基反应研究进展进行了综述。     

自由基三氟甲基化反应进展

近年来,三氟甲基化反应得到了快速的发展和广泛的关注,由于三氟甲基本身的一些特殊化学和物理性质,使得其在医药、农药和材料等领域发挥着越来越重要的作用。 随着有机氟化学的发展,对于自由基三氟甲基化反应也有了新的认识。 本文通过对不同的三氟甲基试剂作为三氟甲基自由基的前体,综述了近年来自由基三氟甲基化反应的研究进展,并予以展望。     

催化不对称光诱导自由基反应

自由基反应的立体选择性调控一直是不对称催化领域的挑战性难题.近年来,光化学过程特别是可见光化学过程在有机合成中越来越受到研究人员的重视,光诱导自由基化学也再次进入人们的视野.相对传统的自由基化学,光诱导自由基化学反应条件温和,易于调控,为实现高效催化不对称自由基反应带来了新的契机,展示了蓬勃的发展潜力.本文根据光诱导产生自由基种类的不同,简要介绍最近该方向的研究进展.     

基于自由基机理的有机硼酯化反应

有机硼酸和硼酸酯化合物是以Suzuki-Miyaura偶联为代表的多种重要化学反应的底物.发展有机硼化合物的高效合成方法具有重要意义.近十年来,基于自由基机理的有机硼酯化反应得以发展,并迅速成为高效构建碳硼键的一类重要方法.自由基硼酯化反应的一般策略为:利用不同反应条件产生的碳自由基活泼中间体与联硼化合物反应,生成相应的有机硼酸或硼酸酯.本文根据反应产生的碳自由基种类的不同,将硼酯化反应分为基于芳基自由基和基于烷基自由基两大部分.各部分依据自由基前体种类的不同,又具体分为基于碳氮、碳氧、碳卤等化学键的硼酯化反应以及羧酸脱羧硼酯化反应.最后,我们进一步总结分析了未来自由基硼酯化反应的研究趋势.     

5-氨基异噁唑的4-位芳基化

在温和、简单条件下实现了5-氨基异噁唑C4位芳基化的反应,以中等到优秀的产率（最高达99%）合成了一系列4-芳基-5-氨基异噁唑类衍生物,产物结构经核磁与高分辨质谱确证。