- Oxygen Atom Transfer Mechanism for Vanadium-Oxo Porphyrin Complexes Mediated Aerobic Olefin Epoxidation
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The development of catalytic aerobic epoxidation by numerous metal complexes in the presence of aldehyde as a sacrificial reductant (Mukaiyama epoxidation) has been reported, however, comprehensive examination of oxygen atom transfer mechanism involving free radical and highly reactive intermediates has yet to be presented. Herein, meso-tetrakis(pentafluorophenyl) porphyrinatooxidovanadium(IV) (VOTPFPP) was prepared and proved to be efficient toward aerobic olefin epoxidation in the presence of isobutyraldehyde. In situ electron paramagnetic resonance spectroscopy (in situ EPR) showed the generation, transfer pathways and ascription of free radicals in the epoxidation. According to the spectral and computational studies, the side-on vanadium-peroxo complexes are considered as the active intermediate species in the reaction process. In the cyclohexene epoxidation catalyzed by VOTPFPP, the kinetic isotope effect value of 1.0 was obtained, indicating that epoxidation occurred via oxygen atom transfer mechanism. The mechanism was further elucidated using isotopically labeled dioxygen experiments and density functional theory (DFT) calculations.
- Han, Qi,Huang, Jia-Ying,Ji, Hong-Bing,Liu, Xiao-Hui,Tao, Lei-Ming,Xue, Can,Yu, Hai-Yang,Zhou, Xian-Tai,Zou, Wen
-
supporting information
p. 115 - 122
(2021/12/04)
-
- Asymmetric Hydrogenation of Racemic 6-Aryl 1,4-Dioxaspiro[4.5]decan-7-ones to Functionalized Chiral ?a'Aryl Cyclohexanols via a Dynamic Kinetic Resolution
-
A ruthenium-catalyzed asymmetric hydrogenation method for the synthesis of functionalized β-aryl cyclohexanols is described. With chiral spiro ruthenium catalyst (Ra,S,S)-5c, a series of racemic α-aryl cyclohexanones bearing a β-monoethylene ketal group were hydrogenated to the corresponding functionalized β-aryl cyclohexanols in high yields with enantioselectivity of up to 99% ee via a dynamic kinetic resolution. This protocol can be conducted on a decagram scale and provide potential approaches for the synthesis of optically active and densely functionalized aryl cyclohexanols.
- Yang, Dan,Yang, Ai-Jiao,Chen, Yong,Xie, Jian-Hua,Zhou, Qi-Lin
-
supporting information
p. 1616 - 1620
(2021/03/03)
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- Dynamic Kinetic Resolution of I-Substituted Cyclic β-Ketoesters via Asymmetric Hydrogenation: Constructing Chiral Cyclic β-Hydroxyesters with Three Contiguous Stereocenters
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An efficient asymmetric hydrogenation of racemic I-substituted cyclic β-ketoesters via dynamic kinetic resolution to provide chiral cyclic β-hydroxy esters with three contiguous stereocenters is reported. Using a chiral spiro iridium catalyst (R)-5 (Ir-SpiroSAP), a series of racemic I-Aryl/alkyl substituted cyclic β-ketoesters were hydrogenated to the corresponding chiral cyclic β-hydroxy esters in high yields (84-97%) with good to excellent enantioselectivities (69->99% ee) and cis,cis-selectivities (up to >99:1).
- Yang, Dan,Wu, Xiong,Zheng, Xiao-Jie,Xie, Jian-Hua,Zhou, Qi-Lin
-
supporting information
p. 5153 - 5157
(2021/07/20)
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- Polydopamine-Encapsulated Dendritic Organosilica Nanoparticles as Amphiphilic Platforms for Highly Efficient Heterogeneous Catalysis in Water
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Aqueous heterogeneous catalysis is a green, sustainable catalytic process that attracts increasing attention, but it often suffers from poor mass transfer, substrate adsorption and catalyst dispersion. Herein, we synthesized a type of amphiphilic core-shell catalysts with a hydrophilic polydopamine (PDA) shell and a hydrophobic dendritic organosilica nanoparticle (DON) core for heterogeneous catalysis in water. The hydrophilic shell allowed the catalyst dispersing well in water, and the hydrophobic core facilitated the absorption of organic reactants. The hierarchical core-shell structure facilitated rational arrangement of the location of catalytic species to match the reaction sequence. The obtained metal, enzyme and metal-enzyme amphiphilic catalysts demonstrated improved stability, selectivity and activity in aqueous reactions, including Pd-catalyzed cross-couplings (Suzuki, Liebeskind-Srogl, Heck and Sonogashira), enzymatic enantioselective reduction, chemoenzymatic cascade synthesis of chiral compounds and chemoenzymatic cascade degradation of organophosphates. The amphiphilic catalysts could be easily in situ recovered, and their high catalytic performance was sustained for five cycles.
- Gao, Jing,Guo, Na,Jiang, Yanjun,Liu, Guanhua,Liu, Pengbo,Liu, Yunting,Wang, Zihan,Zhang, Lei
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supporting information
p. 1975 - 1982
(2021/06/09)
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- Are bis(pyridine)iodine(i) complexes applicable for asymmetric halogenation?
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Enantiopure halogenated molecules are of tremendous importance as synthetic intermediates in the construction of pharmaceuticals, fragrances, flavours, natural products, pesticides, and functional materials. Enantioselective halofunctionalizations remain
- Andreasson, M?ns,Erdelyi, Mate,Németh, Flóra Boróka,Pápai, Imre,Sethio, Daniel,von der Heiden, Daniel
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p. 8307 - 8323
(2021/10/12)
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- Aqueous chemoenzymatic one-pot enantioselective synthesis of tertiary α-aryl cycloketonesviaPd-catalyzed C-C formation and enzymatic C=C asymmetric hydrogenation
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An aqueous chemoenzymatic cascade reaction combining Pd-catalyzed C-C formation and enzymatic C=C asymmetric hydrogenation (AH) was developed for enantioselective synthesis of tertiary α-aryl cycloketones in good yields and excellent enantioselectivities. The stereopreference of the enzyme in AH of α-aryl cyclohexenones was studied. An enantiocomplementary enzyme was obtained by site-directed mutation.
- Luan, Pengqian,Liu, Yunting,Li, Yongxing,Chen, Ran,Huang, Chen,Gao, Jing,Hollmann, Frank,Jiang, Yanjun
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supporting information
p. 1960 - 1964
(2021/03/26)
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- Asymmetric Hydrogenation of Racemic α-Aryl-β-ethoxycarbonyl Cyclopentanones via Dynamic Kinetic Resolution and Its Application to the Synthesis of (+)-Burmaniol A
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An efficient asymmetric hydrogenation of racemic α-aryl-β-ethoxycarbonyl cyclopentanones via dynamic kinetic resolution is reported. Via catalysis by a chiral iridium Ir-SpiroPAP catalyst, a range of racemic α-aryl-β-ethoxycarbonyl cyclopentanones were hy
- Xiong, Ying,Lin, Han,Zhu, Chang-Liang,Chen, Yong-Hong,Ye, Rong,Hu, Guan-Wen,Xie, Jian-Hua,Zhou, Qi-Lin
-
supporting information
p. 8883 - 8887
(2021/11/17)
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- Selective C-H Allylic Oxygenation of Cycloalkenes and Terpenoids Photosensitized by [Cu(Xantphos)(neoc)]BF4
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We present herein for the first time the use of the [Cu(Xantphos)(neoc)]BF4 as a photocatalyst for the selective C-H allylic oxygenation of cycloalkenes into the corresponding allylic hydroperoxides or alcohols in the presence of molecular oxygen. The proposed methodology affords the products at good yields and has also been applied successfully to several bioactive terpenoids, such as geraniol, linalool, β-citronellol, and phytol. A mechanistic study involving also kinetic isotope effects (KIEs) supports the proposed singlet oxygen-mediated reaction. On the basis of the high chemoselectivity and yields and the fast and clean reaction processes observed, the present catalytic system, [Cu(Xantphos)(neoc)]BF4, has also been applied to the synthesis, at a laboratory scale, of the cis-Rose oxide, a well-known perfumery ingredient used in rose and geranium perfumes.
- Kallitsakis, Michael G.,Gioftsidou, Dimitra K.,Tzani, Marina A.,Angaridis, Panagiotis A.,Terzidis, Michael A.,Lykakis, Ioannis N.
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p. 13503 - 13513
(2021/09/13)
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- Electrochemically driven desaturation of carbonyl compounds
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Electrochemical techniques have long been heralded for their innate sustainability as efficient methods to achieve redox reactions. Carbonyl desaturation, as a fundamental organic oxidation, is an oft-employed transformation to unlock adjacent reactivity through the formal removal of two hydrogen atoms. To date, the most reliable methods to achieve this seemingly trivial reaction rely on transition metals (Pd or Cu) or stoichiometric reagents based on I, Br, Se or S. Here we report an operationally simple pathway to access such structures from enol silanes and phosphates using electrons as the primary reagent. This electrochemically driven desaturation exhibits a broad scope across an array of carbonyl derivatives, is easily scalable (1–100 g) and can be predictably implemented into synthetic pathways using experimentally or computationally derived NMR shifts. Systematic comparisons to state-of-the-art techniques reveal that this method can uniquely desaturate a wide array of carbonyl groups. Mechanistic interrogation suggests a radical-based reaction pathway. [Figure not available: see fulltext.]
- Gnaim, Samer,Takahira, Yusuke,Wilke, Henrik R.,Yao, Zhen,Li, Jinjun,Delbrayelle, Dominique,Echeverria, Pierre-Georges,Vantourout, Julien C.,Baran, Phil S.
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p. 367 - 372
(2021/03/31)
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- Iron-Catalyzed ?±,?-Dehydrogenation of Carbonyl Compounds
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An iron-catalyzed α,β-dehydrogenation of carbonyl compounds was developed. A broad spectrum of carbonyls or analogues, such as aldehyde, ketone, lactone, lactam, amine, and alcohol, could be converted to their α,β-unsaturated counterparts in a simple one-step reaction with high yields.
- Zhang, Xiao-Wei,Jiang, Guo-Qing,Lei, Shu-Hui,Shan, Xiang-Huan,Qu, Jian-Ping,Kang, Yan-Biao
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supporting information
p. 1611 - 1615
(2021/03/03)
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- Direct Synthesis of Enones by Visible-Light-Promoted Oxygenation of Trisubstituted Olefins Using Molecular Oxygen
-
A one-step synthesis of enones from olefins is described. The reaction was performed under visible-light irradiation in the presence of molecular oxygen and a photocatalyst. The reaction proceeded with various types of trisubstituted olefins to give enones in good yields with high regioselectivity. In particular, oxygen- and nitrogen-containing functional groups, heteroaromatic rings, and cyclopropanes were tolerated. Mechanistic studies and previous reports indicated that the active oxygen species generated in the reaction system is singlet oxygen.
- Harada, Shinji,Matsuda, Daiki,Morikawa, Takahiro,Nishida, Atsushi
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supporting information
p. 1372 - 1377
(2020/10/02)
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- CeO2-Supported Pd(II)-on-Au Nanoparticle Catalyst for Aerobic Selective α,β-Desaturation of Carbonyl Compounds Applicable to Cyclohexanones
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Direct selective desaturation of carbonyl compounds to synthesize α,β-unsaturated carbonyl compounds represents an environmentally benign alternative to classical stepwise procedures. In this study, we designed an ideal CeO2-supported Pd(II)-on-Au nanoparticle catalyst (Pd/Au/CeO2) and successfully achieved heterogeneously catalyzed selective desaturation of cyclohexanones to cyclohexenones using O2 in air as the oxidant. Besides cyclohexenones, various bioactive enones can also be synthesized from the corresponding saturated ketones under open air conditions in the presence of Pd/Au/CeO2. Preliminary mechanistic studies revealed that α-C-H bond cleavage in the substrates is the turnover-limiting step of this desaturation reaction.
- Jin, Xiongjie,Mizuno, Noritaka,Takei, Daisuke,Yabe, Tomohiro,Yamaguchi, Kazuya,Yatabe, Takafumi
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p. 5057 - 5063
(2020/05/27)
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- 4-Methyltetrahydropyran (4-MeTHP): Application as an Organic Reaction Solvent
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4-Methyltetrahydropyran (4-MeTHP) is a hydrophobic cyclic ether with potential for industrial applications. We herein report, for the first time, a comprehensive study on the performance of 4-MeTHP as an organic reaction solvent. Its broad application to organic reactions includes radical, Grignard, Wittig, organometallic, halogen-metal exchange, reduction, oxidation, epoxidation, amidation, esterification, metathesis, and other miscellaneous organic reactions. This breadth suggests 4-MeTHP can serve as a substitute for conventional ethers and harmful halogenated solvents. However, 4-MeTHP was found incompatible with strong Lewis acids, and the C?O bond was readily cleaved by treatment with BBr3. Moreover, the radical-based degradation pathways of 4-MeTHP, THP and 2-MeTHF were elucidated on the basis of GC-MS analyses. The data reported herein is anticipated to be useful for a broad range of synthetic chemists, especially industrial process chemists, when selecting the reaction solvent with green chemistry perspectives.
- Kobayashi, Shoji,Tamura, Tomoki,Yoshimoto, Saki,Kawakami, Takashi,Masuyama, Araki
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p. 3921 - 3937
(2019/11/11)
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- Chemoselective Oxidation of Equatorial Alcohols with N-Ligated λ3-Iodanes
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The site-selective and chemoselective functionalization of alcohols in complex polyols remains a formidable synthetic challenge. Whereas significant advancements have been made in selective derivatization at the oxygen center, chemoselective oxidation to the corresponding carbonyls is less developed. In cyclic systems, whereas the selective oxidation of axial alcohols is well known, a complementary equatorial selective process has not yet been reported. Herein we report the utility of nitrogen-ligated (bis)cationic λ3-iodanes (N-HVIs) for alcohol oxidation and their unprecedented levels of selectivity for the oxidation of equatorial over axial alcohols. The conditions are mild, and the simple pyridine-ligated reagent (Py-HVI) is readily synthesized from commercial PhI(OAc)2 and can be either isolated or generated in situ. Conformational selectivity is demonstrated in both flexible 1,2-substituted cyclohexanols and rigid polyol scaffolds, providing chemists with a novel tool for chemoselective oxidation.
- Mikhael, Myriam,Adler, Sophia A.,Wengryniuk, Sarah E.
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supporting information
p. 5889 - 5893
(2019/08/26)
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- (Poly)cationic λ3-Iodane-Mediated Oxidative Ring Expansion of Secondary Alcohols
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Herein, a simplified approach to the synthesis of medium-ring ethers through the electrophilic activation of secondary alcohols with (poly)cationic λ3-iodanes (N-HVIs) is reported. Excellent levels of selectivity are achieved for C–O bond migration over established α-elimination pathways, enabled by the unique reactivity of a novel 2-OMe-pyridine-ligated N-HVI. The resulting hexafluoroisopropanol (HFIP) acetals are readily derivatized with a range of nucleophiles, providing a versatile functional handle for subsequent manipulations. The utility of this methodology for late-stage natural product derivatization was also demonstrated, providing a new tool for diversity-oriented synthesis and complexity-to-diversity (CTD) efforts. Preliminary mechanistic investigations reveal a strong effect of alcohol conformation on the reactive pathway, thus providing a predictive power in the application of this approach to complex molecule synthesis.
- Walters, Jennifer C.,Tierno, Anthony F.,Dubin, Aimee H.,Wengryniuk, Sarah E.
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supporting information
p. 1460 - 1464
(2018/04/06)
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- Bronsted Acid Mediated Direct α-Hydroxylation of Cyclic α-Branched Ketones
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We report a Bronsted acid mediated direct α-hydroxylation of cyclic α-branched ketones via a tandem aminoxylation/N-O bond-cleavage process. Nitrosobenzene is used as the oxidant and subsequently promotes the liberation of the free alcohol. The desired pr
- Shevchenko, Grigory A.,Dehn, Stefanie,List, Benjamin
-
supporting information
p. 2298 - 2300
(2018/10/20)
-
- Stereoselective and Regioselective Pinacol-Type Rearrangement of a Fused Bicyclic Oxetanol Scaffold
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The Paternò-Büchi reaction between benzaldehyde and trimethylsilyloxycyclopentene gave access to an unprecedented silyl ether derivative of 6-oxabicyclo[3.2.0]heptan-1-ol. The bicyclic structure underwent selective reductive ring opening and acid-catalyzed pinacol-type rearrangement reactions with complete regioselectivity, accompanied by moderate to excellent mechanism-dependent diastereoselectivity.
- Melis, Nicola,Luridiana, Alberto,Guillot, Régis,Secci, Francesco,Frongia, Angelo,Boddaert, Thomas,Aitken, David J.
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p. 5896 - 5902
(2017/10/31)
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- A highly efficient metal-free approach to: Meta - And multiple-substituted phenols via a simple oxidation of cyclohexenones
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A novel and efficient metal-free approach to substituted phenols has been disclosed from simple and readily available cyclohexenones and cyclohexenone equivalents. Dimethyl sulfoxide (DMSO), a simple and common organic reagent, was employed as a mild oxidant in this I2-catalysis, which significantly tolerates various substituents including some easily oxidizable or reducible functionalities. The challenging meta- and multiple-substituted phenols could be well prepared by this method. The metal-free and mild oxidation make this protocol very simple, practical, and easy to handle.
- Liang, Yu-Feng,Song, Song,Ai, Lingsheng,Li, Xinwei,Jiao, Ning
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supporting information
p. 6462 - 6467
(2018/06/08)
-
- Formation of contiguous quaternary and tertiary stereocenters by sequential asymmetric conjugate addition of grignard reagents to 2-substituted enones and mg-enolate trapping
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Herein a comprehensive study is provided on the asymmetric conjugate addition (ACA) of Grignard reagents to α-substituted cyclic enones. After the elucidation of the optimal experimental conditions, the scope of Grignard reagents and Michael acceptors was examined. Whereas secondary Grignards gave better enantioselectivities with 2-cyclopentenones, both linear and branched Grignard reagents were tolerated for the ACA to 2-methylcyclohexenone. The sequential ACA-enolate trapping, which leads to quaternary stereocenters, was then studied. Thus, many electrophiles have been tested, thereby giving rise to highly functionalized cyclic ketones with contiguous α-quaternary and β-tertiary centers. The present technique is believed to bring a new approach to versatile terpenoid-like skeletons of bioactive natural products. Straightforward derivatizations of enantioenriched saturated cyclic ketones further support the potential of the present methodology in synthesis.
- Germain, Nicolas,Alexakis, Alexandre
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supporting information
p. 8597 - 8606
(2015/06/02)
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- Synthesis of 2-Arylphenol Derivatives through a One-Pot Suzuki-Miyaura Coupling/Dehydrogenative Aromatization Sequence with Pd/C Catalysis
-
One-pot synthesis of 2-arylphenols starting from 2-iodo-2-cyclohexen-1-one and arylboronic acids through sequential Suzuki-Miyaura coupling/dehydrogenative aromatization with Pd/C catalysis has been developed. A range of arylboronic acids serve as substrates, including those containing electron-donating or electron-withdrawing groups. Additionally, one-pot synthesis of di- or trisubstituted phenols bearing a phenyl group at the ortho position are also generated by using 2-iodo-2-cyclohexen-1-one derivatives as substrate. In the present method, commercially available and easily removable Pd/C was employed as a catalyst without any ligands. The operationally simple procedure and accessible conditions were used to provide modified phenols as the sole product in moderate to high yields.
- Kikushima, Kotaro,Nishina, Yuta
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supporting information
p. 5864 - 5868
(2015/09/15)
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- Oxygen-promoted coupling of arylboronic acids with olefins catalyzed by [CA]2[PdX4] complexes without a base
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Abstract An efficient method was developed for the oxidative Heck reaction between arylboronic acids and olefins catalyzed by anionic palladium complexes of the type [CA]x[PdCl4] (x = 1,2) and [CA]2[Pd2Cl6] (CA = imidazolium or pyridinium cation). Molecular oxygen was employed as an environmentally benign oxidant to regenerate Pd(II) species during the reaction. The elaborated protocol could be applied to the coupling of different arylboronic acids with both electron-rich and electron-poor olefins. The catalyst system was further employed for the one-pot oxidative Heck reaction followed by the Heck coupling to build conjugated compounds in good yield. Mass spectrometry (ESI-MS) and UV-vis spectroscopy was used to identify palladium-containing complexes in the reactions. A plausible reaction mechanism of the oxidative Heck reaction was proposed.
- Silarska,Trzeciak
-
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- Versatile CuI/Pd0 dual catalysis for the synthesis of quaternary α-allylated carbonyl compounds: Development, mechanistic investigations and scope
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We report herein a versatile cooperative dual catalysis reaction based on a CuI/Pd0 system. Mechanistic investigation shows that every component plays a crucial role in determining the reaction outcome. The reaction is successfully extended to various substrates; such as α,β-unsaturated ketones, malonates and coumarins. The strategy tolerates different substitution patterns and affords good yields for each family of substrates.
- Nahra, Fady,Mace, Yohan,Boreux, Arnaud,Billard, Francois,Riant, Olivier
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supporting information
p. 10970 - 10981
(2014/09/17)
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- Asymmetric hydrogenation of α,α′-disubstituted cycloketones through dynamic kinetic resolution: An efficient construction of chiral diols with three contiguous stereocenters
-
Chiral diols with three contiguous stereocenters were synthesized by a highly enantioselective ruthenium-catalyzed asymmetric hydrogenation of racemic α,α′-disubstituted cycloketones involving dynamic kinetic resolution. This new catalytic asymmetric method provides a concise route to the alkaloid (+)-γ-lycorane. Copyright
- Liu, Chong,Xie, Jian-Hua,Li, Ya-Li,Chen, Ji-Qiang,Zhou, Qi-Lin
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supporting information
p. 593 - 596
(2013/02/23)
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- Copper/palladium-catalyzed 1,4 reduction and asymmetric allylic alkylation of α,β-unsaturated ketones: Enantioselective dual catalysis
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Cooperative efforts: The catalytic coupling of the two organometallic intermediates is possible through a Cu/Pd-based dual catalysis (see scheme; LG=leaving group), in which the CuI catalytic cycle generates catalytically the starting material
- Nahra, Fady,Mace, Yohan,Lambin, Dominique,Riant, Olivier
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supporting information
p. 3208 - 3212
(2013/04/23)
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- CuCl-catalyzed aerobic oxidation of allylic and propargylic alcohols to aldehydes or ketones with 1:1 combination of phenanthroline and bipyridine as the ligands
-
We developed a modified protocol for the oxidation of 2,3-allenyl alcohols using CuCl with 1:1 combination of phenanthroline and bipyridine as the catalyst. To further investigate the applicability of this system, other types of alcohols such as allylic and propargylic alcohols have been tested: we found that both allylic and propargylic alcohols may be oxidized to the corresponding aldehydes or ketones using molecular oxygen in air as the oxidant with moderate to excellent yields. Copyright
- Liu, Yu,Ma, Shengming
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experimental part
p. 29 - 34
(2012/03/11)
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- Oxidative conversion of silyl enol ethers to α,β-unsaturated ketones employing oxoammonium salts
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The oxidative conversion of silyl enol ethers to α,β-unsaturated ketones using a less-hindered class of oxoammonium salts (AZADO +BF4-) is described. The reaction proceeds via the ene-like addition of oxoammonium salts to silyl enol ethers.
- Hayashi, Masaki,Shibuya, Masatoshi,Iwabuchi, Yoshiharu
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supporting information; experimental part
p. 154 - 157
(2012/02/16)
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- Development of a general and practical iron nitrate/TEMPO-catalyzed aerobic oxidation of alcohols to aldehydes/ketones: Catalysis with table salt
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Oxidation of alcohols is a fundamental transformation related to our daily life. Traditional approaches with at least one stoichiometric amount of oxidants are expensive and cause serious environmental burdens. There are many reports on the aerobic oxidation of simple alcohols such as alkyl or phenyl carbinols and allylic alcohols, which used oxygen or air as the environmentally benign oxidant forming water as the only by-product. However, no such protocol has been reported for allenols and propargylic alcohols. Thus, it still highly desirable to develop efficient room temperature oxidations of alcohols with a wide scope including allenols and propargylic alcohols. In this paper, an efficient and clean aerobic oxidation of so far the widest spectrum of alcohols using 1 atm of oxygen or air, producing aldehydes/ketones at room temperature in fairly high isolated yields mostly within a couple of hours is described. It is interesting to observe that the reaction has been efficiently expedited by a catalytic amount of sodium chloride in easily recoverable 1,2-dichloroethane. A mechanism involving NO and NO2 has been proposed based on the results of the control experiments and GC-MS studies of the in-situ formed gas phase of the reaction mixture.
- Ma, Shengming,Liu, Jinxian,Li, Suhua,Chen, Bo,Cheng, Jiajia,Kuang, Jinqiang,Liu, Yu,Wan, Baoqiang,Wang, Yuli,Ye, Juntao,Yu, Qiong,Yuan, Weiming,Yu, Shichao
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experimental part
p. 1005 - 1017
(2011/06/17)
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- Synthesis of cyclic enones via direct palladium-catalyzed aerobic dehydrogenation of ketones
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α,β-Unsaturated carbonyl compounds are versatile intermediates in the synthesis of pharmaceuticals and biologically active compounds. Here, we report the discovery and application of Pd(DMSO)2(TFA)2 as a catalyst for direct dehydrogenation of cyclohexanones and other cyclic ketones to the corresponding enones, using O2 as the oxidant. The substrate scope includes heterocyclic ketones and several natural-product precursors.
- Diao, Tianning,Stahl, Shannon S.
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supporting information; experimental part
p. 14566 - 14569
(2011/10/17)
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- Palladium-catalyzed coupling reaction of -diazocarbonyl compounds with aromatic boronic acids or halides
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Efficient palladium-catalyzed cross-coupling reactions of -diazocarbonyl compounds and arylboronic acids or aryl halides have been developed. The reaction proceeds smoothly for a range of diazo compounds, boronic acids, and halides. The coupling reaction conditions tolerate various substituents on the aromatic rings of the substrates, such as chloro, fluoro, acyl, oxo, ester, and nitro groups. This coupling reaction constitutes a novel access to -aryl-substituted ,-unsaturated carbonyl compounds. Mechanistically, palladium-carbene is supposed to be the key intermediate; its formation is followed by migratory insertion of an aryl group to the carbenic carbon of the palladium-carbene complex and subsequent -hydride elimination. Kinetic isotope effect (KIE) data measured for intra- and intermolecular competition experiments suggest that -hydride elimination is not involved in the rate-determining step
- Peng, Cheng,Yan, Guobin,Wang, Yan,Jiang, Yubo,Zhang, Yan,Wang, Jianbo
-
experimental part
p. 4154 - 4168
(2011/02/25)
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- α-Arylation and alkynylation of cyclic -iodoenones using palladium-catalyzed cross-coupling reactions with trifluoroborate salts
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An expeditious synthesis of -aryl- and -alkynylcyclohexenones is described and illustrated by palladium-catalyzed cross-coupling reaction of cyclic -iodoenones with potassium aryltrifluoroborate salts. This procedure offers easy access to -arylated and al
- Gueogjian, Kemilla,Singh, Fateh V.,Pena, Jesus M.,Amaral, Monica F. Z. J.,Stefani, Hélio A.
-
experimental part
p. 427 - 432
(2010/04/26)
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- Addition of hypobromous acid to 1-phenylcycloalkenes
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Reaction of 1-phenylcyclooctene and 1-phenylcycloheptene with N-bromosuccinimide (NBS) in aqueous DMSO gives the corresponding 3-bromo-2-phenylcycloalkenes and 2-phenylcycloalk-2-enols in a ratio of 3: 1. Unlike them, 1-phenylcyclohexene gives a mixture of 3-bromo-2-phenylcyclohexene and 2-bromo-1-phenylcyclohexanol. The oxidation of allylic alcohols with pyridinium chlorochromate afforded the corresponding α,β-unsaturated ketones.
- Ceylan,Findik,Sahin,Kazaz
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p. 2299 - 2303
(2014/05/06)
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- The palladium-catalyzed aerobic kinetic resolution of secondary alcohols: Reaction development, scope, and applications
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The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23°C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-toexcellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones.
- Ebner, David C.,Bagdanoff, Jeffrey T.,Ferreira, Eric M.,McFadden, Ryan M.,Caspi, Daniel D.,Trend, Raissa M.,Stoltz, Brian M.
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supporting information; experimental part
p. 12978 - 12992
(2010/06/19)
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- Palladium-catalyzed enantioselective oxidation of chiral secondary alcohols: Access to both enantiomeric series
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(Chemical Equation Presented) Rapid resolution: A new catalyst system for the oxidative kinetic resolution of secondary alcohols leads to dramatic rate increases. This system allows the use of a diamine to provide access to either enantiomer of a range of alcohols with good selectivity factors (see scheme). This method has been applied to the formal total synthesis of (-)-amurensinine.
- Ebner, David C.,Trend, Raissa M.,Genet, Cedric,McGrath, Matthew J.,O'Brien, Peter,Stoltz, Brian M.
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scheme or table
p. 6367 - 6370
(2009/03/11)
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- Palladium-catalyzed cross-coupling of α-diazocarbonyl compounds with arylboronic acids
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Pd(PPh3)4-catalyzed reaction between α-diazocarbonyl compounds and arylboronic acids leads to the formation of cross-coupling products in good yields. Copyright
- Peng, Cheng,Wang, Yan,Wang, Jianbo
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p. 1566 - 1567
(2008/09/17)
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- Cationic P(OPh)3- or PPh3-rhodium(I) complex-catalyzed isomerizations of 5-alkynals to δ-alkynyl ketones, cyclopent-1-enyl ketones, and cyclohexenones
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We have developed catalytic isomerizations of 5-alkynals to γ-alkynyl ketones and cyclopent-1-enyl ketones using [Rh{P(OPh)3} 2]BF4 as a catalyst. Cu(OTf)2 and AgBF 4 are also effective catalysts for
- Tanaka, Ken,Sasaki, Kaori,Takeishi, Kenzo,Hirano, Masao
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p. 5675 - 5685
(2008/09/17)
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- The search for tolerant Lewis acid catalysts. Part 2: Enantiopure cycloalkyldialkylsilyl triflimide catalysts
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A series of 2-aryl- and arylmethyl-3-dialkylphenylsilyl cycloalkanones have been prepared and resolved. The pure enantiomers were reduced to the corresponding cycloalkane derivatives. These were used for the in situ generation of enantiopure cycloalkylsil
- Tang, Zilong,Mathieu, Benoit,Tinant, Bernard,Dive, Georges,Ghosez, Léon
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p. 8449 - 8462
(2008/02/09)
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- The α-arylation of α-bromo- and α-chloroenones using palladium-catalysed cross-coupling
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The palladium-catalysed cross-coupling reaction of various arylboronic acids with α-bromoenones and α-chloroenones offers an operationally simple approach to the synthesis of both cyclic and acyclic α-arylenones.
- Banks, James C.,Mele, David Van,Frost, Christopher G.
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p. 2863 - 2866
(2007/10/03)
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- Practical and efficient Suzuki-Miyaura cross-coupling of 2-iodocycloenones with arylboronic acids catalyzed by recyclable Pd(0)/C
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The first Suzuki-Miyaura cross-coupling of 2-iodocycloenones with arylboronic acids catalyzed by 10% Pd(0)/C is described as an interesting alternative to classical homogeneous conditions. Most of the substrate reacted under mild condition at 25 °C under air in aqueous DME. The conditions described tolerate a wide range of iodoenones and boronic acids. Notably, the procedure features inexpensive reagents and solvents with low toxicity rendering the method environmentally benign. Additionally 10% Pd(0)/C could be recovered and efficiently reused at least five times without significant alteration of the yields of the cross-coupled product.
- Felpin, Francois-Xavier
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p. 8575 - 8578
(2007/10/03)
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- Phosphine Catalyzed α-Arylation of Enones and Enals Using Hypervalent Bismuth Reagents: Regiospecific Enolate Arylation via Nucleophilic Catalysis
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Exposure of enones and enals to 20 mol % tributylphosphine in the presence of triarylbismuth(V) dichlorides results in regiospecific aryl transfer to the α-position of the enone or enal pronucleophile. These results represent the first examples of enolate
- Koech, Phillip K.,Krische, Michael J.
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p. 5350 - 5351
(2007/10/03)
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- Catalytic allylic oxidation with a recyclable, fluorous seleninic acid
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In conjunction with iodoxybenzene as reoxidant perfluorooctylseleninic acid catalyzes the allylic oxidation of alkenes to enones in trifluoromethylbenzene at reflux in moderate to good yield. After a reductive workup with sodium metabisulfite, the catalyst is recovered by fluorous extraction in the form of bis(perfluorooctyl) diselenide, which, itself, serves as a convenient catalyst precursor.
- Crich, David,Zou, Yekui
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p. 775 - 777
(2007/10/03)
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- Organic synthesis in ionic liquids: The stille coupling
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equation presented The Stille coupling reaction has been performed in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM BF4), a room-temperature ionic liquid (RTIL). Use of this solvent system allows for facile recycling of the solvent and catalyst system, which can be used at least five times with little loss in activity. An interesting preference in starting catalyst oxidation state for use with aryl bromides and aryl iodides was observed.
- Handy, Scott T.,Zhang, Xiaolei
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p. 233 - 236
(2007/10/03)
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- Mimicking the reaction of phenylalanine ammonia lyase by a synthetic model
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Phenylalanine and histidine ammonia lyases (PAL and HAL) catalyze the reversible conversion of α-amino acids to the corresponding acrylic acids by elimination of ammonia. The prosthetic group 3,5-dihydro-5-methylidene-4H-imidazol-4-one (MIO) at the active site of both enzymes supposedly undergoes an electrophilic attack at the aromatic nucleus in the first step of the mechanism of action. Since no chemical analogy existed for such an electrophile-assisted elimination, we synthesized model compounds, some portion of which mimicked the essentials of the substrate phenylalanine and another portion the electrophilic Michael acceptor in a sterically appropriate distance. The first model, (±)-rel-(1R,2S,3S)-3-[1-methylidene-2-oxo-2-(pyrrolidin-1-yl)ethyl]-2-phenyl cyclohexanamine (7) did not react under Friedel-Crafts conditions in the expected way (Scheme 2). The second model compound (±)-2-rel-(1R,2S,3S)-3-(dimethylamino)-2-(3-methoxyphenyl)cyclohexyl]prop-2- enal (12) with a more nucleophilic methoxyphenyl and a more electrophilic α,β-unsaturated carbonyl moiety, underwent an intramolecular Friedel-Crafts-type substitution, but no elimination of the dimethylamino group (Scheme 4). The third model compound, (±)-γ-[(dimethylamino)methyl]-3-methoxy-2,4,6-trimethyl-α-methylidenebenze nebutanal (25) eliminated dimethylamine upon treatment with Lewis acids and subsequent hydrolysis of the intermediate (Scheme 6). When the 3-methoxy-2,4,6-trimethylphenyl moiety of 25 was replaced by the 2,4,6-trimethyl-3-nitrophenyl group, no elimination product could be observed (Scheme 7).
- Rettig, Martin,Sigrist, Andreas,Retey, Janos
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p. 2246 - 2265
(2007/10/03)
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- Oxidation of 2-substituted cycloalkanones with cerium(IV) sulfate tetrahydrate in alcohols and acetic acid
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The reaction of 2-substituted cycloalkanones with cerium(IV) sulfate tetrahydrate (CS) in alcohols and acetic acid gave the corresponding alkyl esters of oxo acids (80-96%) and oxo acids (78-96%), respectively, by oxidative cleavage of the C(R).C=O bond. In the case of 2-iodocycloalkanones in methanol, the dimethyl ester was obtained in good yield. A treatment of 5α-cholestan-3-one with CS in methanol produced 2-acetal 3-ester of 2,3-seco derivative in good yield. The effects of cerium(IV) and copper(II) salts are also discussed.
- He, Liangyou,Horiuchi, C. Akira
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p. 2515 - 2521
(2007/10/03)
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- Synthesis of 2-phenyl-2-cycloalkenones via palladium-catalyzed tandem epoxide isomerization-intramolecular aldol condensation
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We have extended the scope of our palladium-catalyzed tandem epoxide isomerization/aldol condensation reaction to encompass intramolecular condensations, which provide facile access to conjugated cycloalkenones from epoxy aldehydes or diepoxides. For example, reaction of 5,6-epoxy-6- phenylhexanal with Pd(OAc)2-PBu3 catalyst in the presence of NaHCO3 and 3A molecular sieves forms 2-phenyl-2-cyclopentenone (80%). Similarly, 1,2;5,6-diepoxy-1-phenylhexane affords 3-methyl-2-phenyl-2-cyclopentenone (72%). The observation of dicarbonyl intermediates (e.g., 1-phenyl-2,5- hexanedione in the latter case) demonstrates that the reaction proceeds via Pd-catalyzed isomerization of the diepoxide to the diketone, followed by base-catalyzed aldol condensation.
- Kim, Ji-Hyun,Kulawiec, Robert J.
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p. 3107 - 3110
(2007/10/03)
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- Applications of the β-azidonation reaction to organic synthesis. α,β- Enones, conjugate addition, and γ-lactam annulation
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The β-azido functionalization reaction provides a mechanistically different enone synthesis that involves treatment of 2 with fluoride anion to effect desilylation and concomitant β-elimination to give 3. Table 1 lists a number of examples of the direct conversion of a TIPS enol ether into the corresponding α,β-enone via a β-azido TIPS enol ether. The β-azido group can be ionized with Me3Al or Me2AlCl and the intermediate enonium ion trapped by a variety of nucleophiles such as an allylstannane, electron-rich aromatics, TMS enol ethers, Et2AlCN, Me2AlCCR, Me4AlLi, and vinylaluminum reagents to give the products listed in Table 2. The diastereoselectivity of the reaction of a 4-substituted enonium ion with indole shows an unusual increase of selectivity with increasing temperature. Reduction of the azide 2 provides access to β-amino TIPS enol ethers 5, which, for example, can be converted into a cinnamide derivative and cyclized via a putative 'ene' process into a γ-lactam.
- Magnus, Philip
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p. 12486 - 12499
(2007/10/03)
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- Use of conjugated dienones in cyclialkylations: Total syntheses of arucadiol, 1,2-didehydromiltirone, (±)-hinokione, (±)-nimbidiol, sageone, and miltirone
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Functionalized hydrophenanthrenes can be prepared using a cyclialkylation-based strategy. These annulations are highly dependent on the directing effects of the arene substitutents and on conformational considerations. The utility of this methodology was featured in the syntheses of six diterpenoids.
- Majetich, George,Liu, Shuang,Fang, Jing,Siesel, David,Zhang, Yong
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p. 6928 - 6951
(2007/10/03)
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- Photoinduced electron transfer from enol silyl ethers to quinone. Part 1. Pronounced effects of solvent polarity and added salt on the formation of α-enones
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The enol silyl ethers (ESE) of various ketones are efficiently oxidized to the corresponding α, β-unsaturated enones (E) when a dichloromethane solution containing equimolar amounts of chloranil is irradiated with filtered light (λexc > 380 nm). The 1:1 adduct (A) of enol silyl ether and quinone is a byproduct, the structure of which is established by X-ray crystallography. Solvent polarity and added salts play a major role in establishing the product distribution between E and A. Such a medium effect, coupled with the ready isomerization of the kinetic-thermodynamic isomers derived from the silylation of 2-methylcyclohexanone, points to the cation radical of the enol silyl ether (ESE.+) as the reactive intermediate. A radical-ion pair mechanism involving the rapid one-electron oxidation of enol silyl ethers by photoactivated chloranil is discussed.
- Bockman, T. Michael,Shukla,Kochi, Jay K.
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p. 1623 - 1632
(2007/10/03)
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- Photoinduced electron transfer from enol silyl ethers to quinone. Part 2. Direct observation of ion-pair dynamics by time-resolved spectroscopy
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Time-resolved spectroscopy in two time domains (encompassing picoseconds and nanoseconds/microseconds) allows all the reactive intermediates involved in the photooxidation of enol silyl ethers (ESE) by chloranil (CA) to be identified, and each step in their temporal evolution to α-enone (E) and adduct (A) to be delineated.Thus, the radical-ion pair is the common intermediate formed in unit quantum yield via the highly efficient quenching of triplet chloranil by enol silyl ethers in both dichloromethane and acetonitrile.In the context of the Fuoss-Winstein formulation, the first-formed is a contact ion-pair, which in a non-polar solvent, such as dichloro-methane, predominantly suffers an initial ion-pair collapse (internal return) by β-proton transfer, and the resultant radical pair ultimately leads to α-enone (E).The contact ion-pair formed in the polar solvent undergoes diffusive separation, and the free ion ESE cation radical suffers desilylation by acetonitrile and ultimately leads to adduct (A).Added electrolyte to dichloromethane solutions modulates the ion-pair behaviour via the 'special salt effect' to divert the enone pathway to adduct formation.
- Bockman, T. Michael,Kochi, Jay K.
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p. 1633 - 1644
(2007/10/03)
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- Synthesis of dioxochromium(VI) complexes, potential oxidation catalysts
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Some new chromium(VI) complexes have been synthesised using a number of tridentate and tetradentate ligands.Catalytic behaviour of one representative dioxochromium complex has been investigated in various oxidation reactions using 70percent t-butylhydroperoxide as oxidant.
- Agarwal, D. D.,Raina, Daisy,Agarwal, S. C.,Kaul, Anju
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p. 288 - 291
(2007/10/03)
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- Cetyltrimethylammonium chlorochromate (CTACC)-t-butyl hydroperoxide (TBHP): A convenient oxidation reagent
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An efficient chromium (VI) catalyst cetyltrimethylammonium chlorochromate (CTACC) in combination with t-butyl hydroperoxide (TBHP) effects excellently the epoxidation of olefins, oxidation of secondary alcohols to carbonyl compounds and various allylic and benzylic oxidations.Some successful stoichiometric oxidations of olefins have been studied.
- Agarwal, D. D.,Kaul, Anju,Raina, Daisy
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p. 158 - 160
(2007/10/02)
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