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1.
Synthesis of Highly Substituted γ‐Butyrolactones by a Gold‐Catalyzed Cascade Reaction of Benzyl Esters 下载免费PDF全文
Maria Camila Blanco Jaimes Alexander Ahrens Daniel Pflästerer Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):427-433
Easily accessible benzylic esters of 3‐butynoic acids in a gold‐catalyzed cyclization/rearrangement cascade reaction provided 3‐propargyl γ‐butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C?C bond is an intermolecular process. Initially propargylic–benzylic esters were used, but alkyl‐substituted benzylic esters worked equally well. In the case of the propargylic–benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl‐substituted γ‐butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one‐pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact. 相似文献
2.
A de novo tandem benzylic oxidative dihydroxylation of α‐vinyl‐ and α‐alkenylbenzyl alcohols has been developed to give α,β‐dihydroxypropiophenones (=2,3‐dihydroxy‐1‐phenylpropan‐1‐ones) and α,β‐dihydroxyalkyl phenones. This method was shown to be substrate‐selective and specific for the oxidation of benzylic alcohols. 相似文献
3.
Eiji Ihara Takao Wake Naoki Mokume Tomomichi Itoh Kenzo Inoue 《Journal of polymer science. Part A, Polymer chemistry》2006,44(19):5661-5671
α,α‐Dibromotoluene 1 was found to be polymerized by the reaction with excess Mg to give poly(phenylmethylene)s 2 , whose main chains were partially dehydrogenated to carbon–carbon double bonds (C?C). The C?Cs in 2 can be brominated by treatment with Br2. The polymerization mechanism was presumed to include the formation of Grignard reagents of various species with benzylic C? Br bonds and the nucleophilic attacks of the Grignard reagents to various compounds with benzylic C? Br bonds. Copolymerization of 1 with dichlorodimethylsilane successfully proceeded. Mg/Cu‐mediated copolycondensation of 1 with 1,6‐dibromohexane proceeded to give polymers that have similar compositions to those of random copolymers of ethylene and styrene. © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5661–5671, 2006 相似文献
4.
Metal‐ and Reagent‐Free Dehydrogenative Formal Benzyl–Aryl Cross‐Coupling by Anodic Activation in 1,1,1,3,3,3‐Hexafluoropropan‐2‐ol 下载免费PDF全文
Yasushi Imada Johannes L. Röckl Dr. Anton Wiebe Dr. Tile Gieshoff Dr. Dieter Schollmeyer Prof. Dr. Kazuhiro Chiba Prof. Dr. Robert Franke Prof. Dr. Siegfried R. Waldvogel 《Angewandte Chemie (International ed. in English)》2018,57(37):12136-12140
A selective dehydrogenative electrochemical functionalization of benzylic positions that employs 1,1,1,3,3,3‐hexafluoropropan‐2‐ol (HFIP) has been developed. The electrogenerated products are versatile intermediates for subsequent functionalizations as they act as masked benzylic cations that can be easily activated. Herein, we report a sustainable, scalable, and reagent‐ and metal‐free dehydrogenative formal benzyl–aryl cross‐coupling. Liberation of the benzylic cation was accomplished through the use of acid. Valuable diarylmethanes are accessible in the presence of aromatic nucleophiles. The direct application of electricity enables a safe and environmentally benign chemical transformation as oxidizers are replaced by electrons. A broad variety of different substrates and nucleophiles can be employed. 相似文献
5.
We have developed an effective organometallic‐based procedure allowing the employment of 2‐methylphenols as easily available starting materials in the synthesis of 3‐alkylbenzofuran‐2(3H)‐ones. The first step of this protocol, an anionic homologous Fries‐rearrangement, afforded 2‐(2‐ tert ‐butyldimethylsilyloxyaryl)acetamides, which were selectively metalated and monoalkylated at the benzylic position. Acidic work‐up of crude products afforded the desired heterocycles in satisfactory overall yields. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
6.
Palladium‐Catalyzed Asymmetric Benzylic Alkylation of Active Methylene Compounds with α‐Naphthylbenzyl Carbonates and Pivalates 下载免费PDF全文
Sho Tabuchi Prof. Dr. Koji Hirano Prof. Dr. Masahiro Miura 《Angewandte Chemie (International ed. in English)》2016,55(24):6973-6977
A Pd/(R)‐H8‐BINAP‐catalyzed asymmetric benzylic alkylation of active methylene compounds has been developed. The reaction proceeds without the use of an external base, and the starting racemic diarylmethyl carbonates are converted into the optically active coupling products which contain the benzylic chiral stereocenter by a dynamic kinetic asymmetric transformation (DYKAT). Additionally, with suitable carbonates bases, the same palladium catalysis allows the corresponding pivalates to be adopted in the same DYKAT process. 相似文献
7.
Catalytic Asymmetric Construction of α‐Quaternary Cyclopentanones and Its Application to the Syntheses of (−)‐1,14‐Herbertenediol and (−)‐Aphanorphine 下载免费PDF全文
Dao‐Yong Zhu Ming‐Hui Xu Prof. Dr. Yong‐Qiang Tu Prof. Dr. Fu‐Min Zhang Prof. Dr. Shao‐Hua Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(44):15502-15505
A novel and efficient strategy to build α‐benzylic quaternary cyclopentanones with excellent enantioselectivities (up to 96 % ee) and high yields (up to 99 % yield) has been developed, and its application demonstrated by the first catalytic asymmetric total synthesis of (?)‐1,14‐herbertenediol and the formal synthesis of (?)‐aphanorphine. 相似文献
8.
Barry M. Trost Johnathan E. Schultz Yu Bai 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(34):11946-11951
We describe the development of a Pd‐catalyzed decarboxylative asymmetric allylic alkylation of α‐nitro allyl esters to afford acyclic tetrasubstituted nitroalkanes. Optimization of the reaction parameters revealed unique ligand and solvent combinations crucial for achieving chemo‐ and enantioselective C‐alkylation of electronically challenging benzylic nitronates and sterically encumbered 2‐allyl esters. Substrates were efficiently accessed in a combinatorial fashion by a cross‐Claisen/ α‐arylation sequence. The method provides functional group orthogonality that complements nucleophilic imine allylation strategies for α‐tertiary amine synthesis. 相似文献
9.
Yushuang Chen Yun Liu Zhaojing Li Shunxi Dong Xiaohua Liu Xiaoming Feng 《Angewandte Chemie (International ed. in English)》2020,59(21):8052-8056
An enantioselective synthesis of α‐aminoketone derivatives were readily available through a tandem insertion–[1,3] O‐to‐C rearrangement reaction. The rhodium salt and chiral N,N′‐dioxide‐indium(III) complex make up relay catalysis, which enables the O?H insertion of benzylic alcohols to N‐sulfonyl‐1,2,3‐triazoles, and asymmetric [1,3]‐rearrangement of amino enol ether intermediates, subsequently. Preliminary mechanistic studies suggested that the [1,3] O‐to‐C rearrangement step proceeded through an ion pair pathway. 相似文献
10.
3(2H)‐Furanones are efficiently generated from 3‐alkynyl oxireno[2,3‐b]chromenones by an Au/DDQ‐catalyzed domino reaction through a pathway composed of cyclization, C? C cleavage, nucleophilic addition, oxidation, and nucleophilic addition. It was found that stoichiometric AuCl3 or catalytic Au with stoichiometric DDQ can oxidize the benzylic sp3 C? H bond to facilitate nucleophilic addition. 相似文献
11.
Yueyue Ma Xiantong Yao Lei Zhang Pufan Ni Ruihua Cheng Jinxing Ye 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(46):16700-16704
A metal‐free convergent paired electrolysis strategy to synthesize benzylic amines through direct arylation of tertiary amines and benzonitrile derivatives at room temperature has been developed. This TEMPO‐mediated electrocatalytic reaction makes full use of both anodic oxidation and cathodic reduction without metals or stoichiometric oxidants, thus showing great potential and advantages for practical synthesis. This convergent paired electrolysis method provides a straightforward and powerful means to activate C?H bonds and realize cross‐coupling with cathodically generated species. 相似文献
12.
Direct synthesis of γ‐substituted phthalids from related ortho‐aryl benzoic acids with 48–85% yield are covered. The direct oxidation in the presence of peroxydisulphate‐copper (II) chloride in aqueous medium was applied. The reaction is highly regioselective and leads exclusively to γ‐butyrolactone, through very stable benzylic radical intermediate. 相似文献
13.
Synthesis and Application of Tetrahydro‐2H‐fluorenes by a Pd(0)‐Catalyzed Benzylic C(sp3)−H Functionalization 下载免费PDF全文
Satoshi Suetsugu Nobusuke Muto Misa Horinouchi Dr. Chihiro Tsukano Prof. Dr. Yoshiji Takemoto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(24):8059-8062
A new method has been developed for the synthesis of tetrahydro‐2H‐fluorenes based on a Pd(0)‐catalyzed benzylic C(sp3)?H functionalization. Importantly, the success of the cyclization step was dependent on there being substituents at the two positions ortho to the benzylic group to avoid an undesired C(sp2)?H functionalization. This method was subsequently used to prepare the right‐hand fragment of the hexacyclic triterpenoid benzohopanes, and therefore represents a powerful tool for the construction of the related compounds. 相似文献
14.
An unusual photo‐oxidation pathway for a poly(2,6‐dimethyl‐1,4‐phenylene oxide) model compound 下载免费PDF全文
James E. Pickett 《Journal of polymer science. Part A, Polymer chemistry》2017,55(13):2221-2226
The long wavelength UV photochemistry was investigated of a model compound for poly(2,6‐dimethyl‐1,4‐phenylene oxide). Irradiation of the phenyl‐capped dimer of 2,6‐dimethyl phenol at wavelengths >290 nm with UVA‐340 fluorescent lamps in the absence of oxygen gave no detectable products after 27 days. Very low conversion to oxidation products was found in the presence of oxygen, but about 20% conversion to products in which solvent had added to the benzylic methyl groups occurred under aerobic conditions when the solvents had readily abstractable hydrogen atoms. A mechanism is proposed involving the facile, reversible abstraction of a benzylic hydrogen by oxygen as a first step in the oxidation. The hydroperoxyl radical that is formed can abstract hydrogen atoms from 2° and 3° carbons of the solvent, and these radicals can combine with the benzylic radicals to give the solvent adducts. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2221–2226 相似文献
15.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(52):16872-16876
A rhodium(II)‐catalyzed reaction of newly prepared 4‐acyl‐1‐sulfonyl‐1,2,3‐triazoles with benzene, and its derivatives, is investigated. Acceptor/acceptor carbenoids generated from 4‐acyltriazoles undergo selective insertion at aromatic C(sp2)−H bonds in the presence of benzylic C(sp3)−H bonds to produce N ‐sulfonylenaminones. 相似文献
16.
Manganese‐Catalyzed Dehydrogenative Alkylation or α‐Olefination of Alkyl‐Substituted N‐Heteroarenes with Alcohols 下载免费PDF全文
Dr. Guoying Zhang Dr. Torsten Irrgang Thomas Dietel Fabian Kallmeier Prof. Dr. Rhett Kempe 《Angewandte Chemie (International ed. in English)》2018,57(29):9131-9135
Catalysis with earth‐abundant transition metals is an option to help save our rare noble‐metal resources and is especially interesting when novel reactivity or selectivity patterns are observed. We report here on a novel reaction, namely the dehydrogenative alkylation or α‐olefination of alkyl‐substituted N‐heteroarenes with alcohols. Manganese complexes developed in our laboratory catalyze the reaction with high efficiency whereas iron and cobalt complexes stabilized by the same ligands are essentially inactive. Hydrogen is liberated during the reaction, and bromine and iodine functional groups as well as olefins are tolerated. A variety of alkyl‐substituted N‐heteroarenes can be functionalized, and benzylic and aliphatic alcohols undergo the reaction. 相似文献
17.
José Luis García Ruano Prof. Ana M. Martín‐Castro Prof. Francisco Tato Dr. Esther Torrente Ana M. Poveda Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(21):6317-6325
Enantiomerically enriched α,α‐disubstituted phenylacetonitriles have been readily prepared by stereoselective quaternization of 2‐alkyl‐2‐[2‐(p‐tolylsulfinyl)phenyl]acetonitriles with different alkylating electrophiles in the presence of bases. The use of potassium hexamethyldisilazane (KHMDS)/[18]crown‐6 ether and NHMDS with alkyl halides afforded S,SS and R,SS diastereoisomers, respectively, in high enantiomeric purities, thus providing stereodivergent processes for synthesizing both isomers. The dependence of the stereochemical course of the reactions on the experimental conditions (mainly on the counterion) has been rationalized by assuming a planar or pyramidal structure for the benzylic carbanions. This hypothesis has been supported by NMR spectroscopic studies, which permit one to assign a chelated pyramidal structure to the sodium benzylic carbanions and an almost planar naked carbanionic structure to the potassium benzylic carbanions generated in the presence of [18]crown‐6 ether. 相似文献
18.
Synthesis of Chiral β‐Lactams by Pd‐Catalyzed Enantioselective Amidation of Methylene C(sp3)–H Bonds
Tao Zhou Meng‐Xue Jiang Xu Yang Qiang Yue Ye‐Qiang Han Yi Ding Bing‐Feng Shi 《中国化学》2020,38(3):242-246
A Pd(II)‐catalyzed enantioselective intramolecular amidation of both benzylic and unbiased methylene C(sp3)?H bonds for the straightforward synthesis of chiral β‐lactams from aliphatic carboxamides is reported. The combination of 2‐pyridinylisopropyl (PIP) auxiliary with 3,3’‐substituted BINOL ligands is crucial for the enhancement of both reactivity and enantiocontrol of differentiating unbiased methylene C(sp3)?H bonds. The desired chemoselective C—N reductive elimination was achieved by employing 2‐fluoro‐1‐iodo‐4‐nitrobenzene as oxidant. 相似文献
19.
A highly ef?cient synthesis of novel pyrido[2,3‐d]pyrimidin‐4‐ols was developed via an iodine‐catalyzed tandem oxidative cyclization under focused microwave irradiation. Pyrido[2,3‐d]pyrimidin‐4‐ols were obtained from easily available 2‐amino‐4‐aryl‐6‐arylnicotinamides and benzylic amines with good to excellent yields. 相似文献
20.
Prof. Dr. Barry M. Trost Dr. Lara C. Czabaniuk 《Angewandte Chemie (International ed. in English)》2014,53(11):2826-2851
The coordination of transition metals to organic fragments can yield complexes with fascinating and unexpected binding patterns. The study of metal‐benzyl complexes has demonstrated the feasibility of η3‐coordination, which results in a dearomatized ring. These complexes also offer insight into reaction mechanisms as proposed intermediates in catalytic cycles. In this Review we discuss the synthesis and characterization of these complexes with late transition metals and the subsequent development of catalytic benzylic functionalization methods, including asymmetric variants. 相似文献