- Size-Exclusion Borane-Catalyzed Domino 1,3-Allylic/Reductive Ireland–Claisen Rearrangements: Impact of the Electronic and Structural Parameters on the 1,3-Allylic Shift Aptitude
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The reductive Ireland–Claisen rearrangement through borane-mediated hydrosilylation is reported. The method employs a borane catalyst with a special structural design and affords access to synthetically relevant products with high diastereoselectivity. Depending on electronic and structural parameters, the reaction can be coupled with a 1,3-allylic shift, thus the valence isomer of the Ireland–Claisen product is formed.
- Fegyverneki, Dániel,Kolozsvári, Natália,Molnár, Dániel,Egyed, Orsolya,Holczbauer, Tamás,Soós, Tibor
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supporting information
p. 2179 - 2183
(2019/01/04)
-
- Base-Free Dynamic Kinetic Resolution of Secondary Alcohols with a Ruthenium-Lipase Couple
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We report the dynamic kinetic resolution (DKR) of various secondary alcohols by the combination of a ruthenium catalyst and an anionic surfactant-activated lipoprotein lipase. The DKR reactions performed under totally base-free conditions at room temperature provided the products of excellent enantiopurities (91-99% ee or greater) in high yields (92-99%). More importantly, the DKR of α-arylallyl alcohols was achieved for the first time with high yields (87-91%).
- Yun, Inyeol,Park, Jin Yong,Park, Jaiwook,Kim, Mahn-Joo
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p. 16293 - 16298
(2019/12/27)
-
- Pseudomonas sp. Lipase Immobilized on Magnetic Porous Polymer Microspheres as an Effective and Recyclable Biocatalyst for Resolution of Allylic Alcohols
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Magnetic porous polymeric microspheres containing epoxy groups were prepared by suspension polymerization (denoted as magnetic Fe3O4@GEM microspheres). Fe3O4@GEM with a specific surface area of 30.41 m2/g, average pore diameter of 17.13 nm, and pore volume of 0.13 cm3/g exhibited superparamagnetic behavior with the saturation magnetization of 7.1 emu/g. The content of epoxy groups on Fe3O4@GEM was 0.22 mmol/g. Pseudomonas sp. lipase (PSL) was covalently immobilized onto the Fe3O4@GEM microspheres through the reaction between the amino groups of the enzyme and the epoxy groups on the microspheres. PSL/Fe3O4@GEM exhibited enhanced enantioselectivity for the resolution of allylic alcohol to the corresponding optically active (S)-allylic alcohol and (R)-allylic alcohol acetate compared to free PSL. The enantiomeric excess of (S)-l-pheny-2-propen-1-ol for the former (98.1%) was 81.7 times that of the latter (1.2%) when the immobilized PSL was used for transesterification resolution of (R,S)-l-pheny-2-propen-1-ol. Furthermore, the ees and eep values were still retained at 95.2% and 95.4% after PSL/Fe3O4@GEM was recycled 10 times, indicating that PSL/Fe3O4@GEM had very good reusability. In addition, the transesterification resolution of (R,S)-1-(4-methylphenyl)-2-propen-1-ol and (R,S)-1-(4-bromophenyl)-2-propen-1-ol was catalyzed by PSL/Fe3O4@GEM, affording ideal ees and eep values of 99.3%, 97.4% and 99.6%, 98.2%, respectively. Therefore, PSL/Fe3O4@GEM demonstrated its potential as a highly efficient enzymatic reactor and Fe3O4@GEM would be very promising carriers for immobilizing enzymes in industrial application.
- Gu, Yaohua,Xue, Ping
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p. 696 - 705
(2018/06/27)
-
- A Re2O7catalyzed cycloetherification of monoallylic diols
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A Re2O7catalyzed cycloetherification of monoallylic diols is described. The reaction features short reaction time, mild reaction conditions and exclusive E selectivity. A wide range of monoallylic alcohols with alkyl or aryl substituents on olefin smoothly undergo ring closure to deliver corresponding oxa-heterocycles. The reaction is also operationally simple and not sensitive to air and moisture.
- Wan, Xiaolong,Hu, Jiadong,Xu, Dongyang,Shang, Yang,Zhen, Yanxia,Hu, Chenchen,Xiao, Fan,He, Yu-Peng,Lai, Yisheng,Xie, Weiqing
-
supporting information
p. 1090 - 1093
(2017/03/02)
-
- Electrochemical properties and reactions of organoboronic acid esters containing unsaturated bonds at their α-position
-
Electrochemical analyses of 2-(cynnamyl)boronic acid pinacol ester and (3-phenyl-2-propynyl)boronic acid pinacol ester, and their trimethylsilyl analogues as well as their parent compounds were comparatively studied by cyclic voltammetry measurements. We
- Ohtsuka, Kazuhiro,Inagi, Shinsuke,Fuchigami, Toshio
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p. G23 - G28
(2017/12/26)
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- Kinetic Resolution of Racemic and Branched Monosubstituted Allylic Acetates by a Ruthenium-Catalyzed Regioselective Allylic Etherification
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We demonstrated the kinetic resolution of racemic and branched monosubstituted allylic acetates by a ruthenium-catalyzed regioselective allylic etherification. The reaction was effectively catalyzed by the chiral ruthenium catalyst, which was generated by [RuCl2(p-cymene)]2 and (S,S)-iPr-pybox and a catalytic amount of TFA, and both the allylic etherification product and recovered allylic acetate were obtained as an enantiomerically enriched form with up to a 103 s value.
- Shinozawa, Toru,Terasaki, Shou,Mizuno, Shota,Kawatsura, Motoi
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p. 5766 - 5774
(2016/07/14)
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- Organoselenium-catalyzed, hydroxy-controlled regio- and stereoselective amination of terminal alkenes: Efficient synthesis of 3-amino allylic alcohols
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An efficient route to prepare 3-amino allylic alcohols in excellent regio- and stereoselectivity in the presence of bases by orangoselenium catalysis has been developed. In the absence of bases α,β-unsaturated aldehydes were formed in up to 97% yield. Control experiments reveal that the hydroxy group is crucial for the direct amination.
- Deng, Zhimin,Wei, Jialiang,Liao, Lihao,Huang, Haiyan,Zhao, Xiaodan
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supporting information
p. 1834 - 1837
(2015/04/27)
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- Flow chemistry as a discovery tool to access sp2-sp3 cross-coupling reactions via diazo compounds
-
The work takes advantage of an important feature of flow chemistry, whereby the generation of a transient species (or reactive intermediate) can be followed by a transfer step into another chemical environment, before the intermediate is reacted with a coupling partner. This concept is successfully applied to achieve a room temperature sp2-sp3 cross coupling of boronic acids with diazo compounds, these latter species being generated from hydrazones under flow conditions using MnO2 as the oxidant.
- Tran, Duc N.,Battilocchio, Claudio,Lou, Shing-Bong,Hawkins, Joel M.,Ley, Steven V.
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p. 1120 - 1125
(2015/03/04)
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- Titanocene(III) chloride mediated radical-induced opening of monosubstituted epoxy acetates for the synthesis of primary allylic alcohols
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A simple and efficient method for the synthesis of primary allylic alcohols from monosubstituted epoxy acetates has been developed using titanocene(III) chloride mediated epoxide ring opening via acetate elimination.
- Chakraborty,Mandal,Roy
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p. 893 - 901
(2015/08/18)
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- Homogeneous Pd-catalyzed transformation of terminal alkenes into primary allylic alcohols and derivatives
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Synthesis of primary alcohols from terminal alkenes is an important process in both bulk and fine chemical syntheses. Herein, a homogeneous Pd-complex-catalyzed transformation of terminal alkenes into primary allylic alcohols, by using 5 mol % [Pd(PPh3)4] as a catalyst, and H2O, CO2, and quinone derivatives as reagents, is reported. When alcohols were used instead of H2O, allylic ethers were obtained. A proposed mechanism includes the addition of oxygen nucleophiles at the less-hindered terminal position of π-allyl Pd intermediates.
- Tomita, Ren,Mantani, Kohei,Hamasaki, Akiyuki,Ishida, Tamao,Tokunaga, Makoto
-
supporting information
p. 9914 - 9917
(2014/08/18)
-
- Silver acetate mediated acetoxylations of alkyl halides
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Silver acetate promotes the acetoxylation of alkyl halides under neutral reaction conditions. The reaction is applicable to primary and activated secondary alkyl halides, and 2,2-dibromoacetophenones for preparing the corresponding acetates in good yields. The presence of ester, amide, nitrile, hydroxy, and OTBDMS functions on the substrate is tolerated.
- Nolla-Saltiel, Roberto,Carrillo-Arcos, Ulises Alonso,Porcel, Susana
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p. 165 - 169
(2014/03/21)
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- 2: An efficient catalyst for highly regioselective allylic alkylations of chelated amino acid ester enolates
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Chelated amino acid ester enolates are excellent nucleophiles for ruthenium-catalyzed allylic alkylations. Although [Cp*Ru(MeCN) 3]PF6 was found to be the most reactive catalyst investigated, with the resulting allyl complexes reacting at temperatures as low as -78°C, unfortunately the process took place with only moderate regio- and diastereoselectivity. In contrast, [(p-cymene)RuCl2]2 allowed allylations to be performed with a high degree of regioretention. Secondary allyl carboxylates with a terminal double bond were found to be the most reactive substrates, giving rise to the branched amino acids with perfect regioretention and chirality transfer. In this case, no isomerization of the Ru-allyl complex formed in situ was observed, in contrast to the analogues palladium complexes. This isomerization-free protocol can also be used for the synthesis of (Z)-configured γ,δ-unsaturated amino acid derivatives, starting from (Z)-allylic substrates. Here, the more reactive phosphates were found to be superior to the carboxylates, providing the required amino acids in almost quantitative yield with perfect regio- and stereoretention. Therefore, the Ru-catalyzed allylation reactions are well positioned to overcome the drawbacks of Pd-catalyzed processes.
- Bayer, Anton,Kazmaier, Uli
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p. 10484 - 10491
(2014/08/18)
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- Mechanistic investigation of palladium-catalyzed allylic C-H activation
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The mechanism for the palladium-catalyzed allylic C-H activation was investigated using a combination of experimental and theoretical methods. A Hammett study revealed a buildup of a partial negative charge in the rate-determining step, and determination of the kinetic isotope effect (KIE) indicated that the C-H bond is broken in the turnover-limiting transition state. These experimental findings were further substantiated by carrying out a detailed density functional theory (DFT)-based investigation of the entire catalytic cycle. The DFT modeling supports a mechanism in which a coordinated acetate acts as a base in an intramolecular fashion during the C-H activation step. The reoxidation of palladium was found to reach an energy level similar to that of the C-H activation. Calculations of turnover frequencies for the entire catalytic cycle for the C-H alkylation were used to acquire a better understanding of the experimental KIE value. The good correspondence between the experimental KIE and the computed KIE values allows discrimination between scenarios where the acetate is acting in an intramolecular fashion (C-H alkylation) and an intermolecular fashion (C-H acetoxylation and C-H amination).
- Engelin, Casper,Jensen, Thomas,Rodriguez-Rodriguez, Sergio,Fristrup, Peter
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p. 294 - 302
(2013/08/25)
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- Selective cross-coupling of organic halides with allylic acetates
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A general protocol for the coupling of haloarenes with a variety of allylic acetates is presented. Strengths of the method are a tolerance for electrophilic (ketone, aldehyde) and acidic (sulfonamide, trifluoroacetamide) substrates and the ability to couple with a variety of substituted allylic acetates. Secondary alkyl bromides can also be allylated under slightly modified conditions, demonstrating the generality of the approach. Finally, the coupling of a reactive vinyl halide could be achieved by the use of a very hindered ligand and more reactive, branched allylic acetates.
- Anka-Lufford, Lukiana L.,Prinsell, Michael R.,Weix, Daniel J.
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p. 9989 - 10000
(2013/01/15)
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- Study on the coupling of acyclic esters with alkenes - The synthesis of 2-(2-hydroxyalkyl)cyclopropanols via cascade cyclization using allylsamarium bromide
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The radical cyclization between aliphatic acyclic esters and alkenes was achieved unprecedentedly in the presence of allylsamarium bromide with HMPA and H2O as additives. The cascade radical cyclization-ring-opening- anionic cyclization allowed facile and efficient access to 2-(2-hydroxyalkyl) cyclopropanols from readily available materials.
- Tu, Yawei,Zhou, Liejin,Yin, Ruifeng,Lv, Xin,Flowers Ii, Robert A.,Choquette, Kimberly A.,Liu, Huili,Niu, Qingsheng,Wang, Xiaoxia
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supporting information
p. 11026 - 11028
(2013/01/15)
-
- Highly efficient kinetic resolution of allylic alcohols with terminal double bond
-
In this study, the lipase-catalyzed kinetic resolution (Novozyme 435) was employed to prepare chiral allylic alcohols and acetates with terminal double bonds in enantiomeric excesses ranging from 94 to >99 %.
- Marques, Francisco A.,Oliveira, Marcos A.,Frensch, Gustavo,Sales Maia, Beatriz Helena L. N.,Barison, Andersson,Lenz, Cesar A.,Guerrero Jr., Palimecio G.
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body text
p. 696 - 700
(2012/06/04)
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- Kinetic resolution of allylic alcohols via stereoselective acylation catalyzed by lipase PS-30
-
By using lipase PS-30 as catalyst, the kinetic resolution of a series of racemic allylic alcohols has been achieved via stereoselective acylation. The value of kinetic enantiomeric ratio (E) reached up to 968. Substituent effect is briefly discussed.
- Chen, Peiran,Xiang, Peng
-
supporting information; experimental part
p. 5758 - 5760
(2011/12/03)
-
- Synthesis of a platform to access bistramides and their analogues
-
The platform C14-C40, which can be used to prepare bistramide C and 39-oxobistramide K, was synthesized in 19 steps with an overall yield of 6.2%. Furthermore, the chemoselective reduction of the ketone at C-39 was performed giving an easy access to bistramides A, B, D, K, and L. Finally, the versatility of the synthesis of the C14-C40 fragment can allow the preparation of a large variety of stereoisomers to produce bistramide analogues.
- Commandeur, Malgorzata,Commandeur, Claude,Cossy, Janine
-
supporting information; experimental part
p. 6018 - 6021
(2011/12/16)
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- A new mathematical method for determining the enantiomeric ratio in lipase-catalyzed reactions
-
We present a new mathematical method for determining the enantiomeric ratio (E) during lipase-catalyzed kinetic resolutions. The method involves the fitting of a model to profiles of adimensionalized concentrations of the two enantiomers of the chiral substrate, plotted against degree of conversion. The model equations are presented for a reversible reaction involving bi-bi ping-pong kinetics in which the chiral substrate enters second and the chiral product leaves second. However, it is also shown that the method is easy to modify for analysis of resolutions involving other chiral substrate-product pairs and of resolutions in which the behavior of the system can be approximated by irreversible uni-uni kinetics. We show that our method retains several advantageous features of existing methods that help to ensure accuracy.
- Mitchell, David Alexander,Moure, Vivian Rotuno,Marques, Francisco de Assis,Krieger, Nadia
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experimental part
p. 23 - 28
(2010/11/02)
-
- REACTION SYSTEM
-
The invention provides a reaction system comprising: a first reaction promoter capable of converting a first substrate into a first substance; and a plurality of microcapsules, each of said microcapsules comprising a second reaction promoter encapsulated within an encapsulant, said second reaction promoter being capable of converting a second substrate into a second substance. The second substrate is capable of passing through the encapsulant to contact the second reaction promoter and the second substance is capable of passing out of the microcapsules through the encapsulant. In the reaction system, either (a) the first substance is, or is capable of being converted into, the second substrate and, in operation, the conversion of the second substrate by the second reaction promoter occurs to a greater extent than the conversion of the first substrate by the second reaction promoter and the conversion of the second substance by the first reaction promoter is low, or (b) the second substance is, or is capable of being converted into, the first substrate and, in operation, the conversion of the first substrate by the first reaction promoter occurs to a greater extent than the conversion of the second substrate by the first reaction promoter and the conversion of the first substance in the microcapsules is low.
- -
-
Page/Page column 17; 19
(2010/04/25)
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- Enzymatic kinetic resolution of primary allenic alcohols. Application to the total synthesis and stereochemical assignment of striatisporolide A
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Crude Porcine pancreatic lipase was successfully used for the kinetic resolution of axially chiral primary allenic alcohols providing very high enantioselectivities with E values above 200. This simple access to optically active allenes was applied to the total synthesis of the fungal metabolite (-)-striatisporolide A, allowing its unambiguous stereochemical assignment.
- Deska, Jan,Baeckvall, Jan-E.
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scheme or table
p. 3379 - 3381
(2010/01/06)
-
- Mechanistic investigations of bipyrimidine-promoted palladium-catalyzed allylic acetoxylation of olefins
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Several pyridine-like ligands were found to improve Pd(OAc) 2-catalyzed allylic oxidation of allylbenzene to cinnamyl acetate by p-benzoquinone in acetic acid. The best ligand examined, bipyrimidine, was used to identify the catalyst precursor for this system, (bipyrimidine)Pd(OAc) 2, which was fully characterized. Mechanistic studies suggest the reaction takes place through disproportionation of (bipyrimidine)Pd(OAc) 2 to form a bipyrimidine-bridged dimer, which reacts with olefin to form a PdII-olefin adduct, followed by allylic C-H activation to produce (η3-allyl)PdII species. The (η3-allyl)PdII intermediate undergoes a reversible acetate attack to generate a Pd0-(allyl acetate) adduct, which subsequently reacts with p-benzoquinone to release allyl acetate and regenerate (bipyrimidine)Pd(OAc)2. No KIE is observed for the competition experiment between allylbenzene-d0 and allylbenzene-d5 (CD2=CDCD2C6H5), suggesting that allylic C-H activation is not rate-determining. Catalytic allylic acetoxylations of other terminal olefins as well as cyclohexene were also effected by (bipyrimidine)Pd(OAc)2.
- Lin, Bo-Lin,Labinger, Jay A.,Bercaw, John E.
-
body text
p. 264 - 271
(2009/10/23)
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- Enantioselective hydrolysis of 1-arylallyl acetates catalyzed by Candida antarctica lipase
-
(R)-1-Arylallyl alcohols were obtained with excellent enantioselectivities via kinetic resolution of the corresponding acetates using immobilized Candida antarctica lipase. The scope and limitations of this reaction were investigated. The best results are obtained using the water/acetonitrile solvent system, and the reaction tolerates a variety of aryl and heteroaryl substituents.
- Kadnikova, Ekaterina N.,Thakor, Vikalp A.
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p. 1053 - 1058
(2008/09/19)
-
- A convenient and versatile method for the preparation of α-hydroxymethyl ketone derivatives from the corresponding allyl silyl ethers or allyl carboxylates
-
The ozonolysis of 1-substituted allyl silyl ethers or 1-substituted allyl carboxylates followed by treatment with bases gave the corresponding α-silyloxymethyl- or α-acyloxymethyl-ketones in good yields. It is proposed to proceed via the corresponding α-silyloxy- or α-acyloxyaldehydes intermediates followed by 1,4-group migration. The results of theoretical calculations are applicable to explain the experimental results.
- Hon, Yung-Son,Wong, Ying-Chieh,Wu, Kuo-Jui
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experimental part
p. 896 - 914
(2009/12/06)
-
- Synthesis of enantiopure 1-arylprop-2-en-1-ols and their tert-butyl carbonates
-
(Chemical Equation Presented) Enantiomerically pure 1-arylpropenols 8 have been prepared by resolution of the corresponding racemates, using the lipase formulation Novozyme 435. Deprotonation of the latter alcohols with n-BuLi, followed by derivatization with (t- BuO)2CO, afforded the corresponding carbonates 5. Optimization of the process is presented.
- Stambasky, Jan,Malkov, Andrei V.,Kocovsky, Pavel
-
body text
p. 9148 - 9150
(2009/04/11)
-
- [(NHC)Au1]-catalyzed rearrangement of allylic acetates
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Equation Presented [(NHC)AuCl] complexes (NHC = N-heterocyclic carbene), in conjunction with a silver salt, were found to efficiently catalyze the rearrangement of allylic acetates under both conventional and microwave-assisted heating. The optimization of several reaction parameters (solvent, silver salt, and ligand) as well as a study of the reaction scope are reported. The steric hindrance of the ligand bound to gold was found crucial for the outcome of the reaction as only extremely bulky ligands permitted the isomerization.
- Marion, Nicolas,Gealageas, Ronan,Nolan, Steven P.
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p. 2653 - 2656
(2008/02/09)
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- Iridium(I)-catalyzed stereospecific decarboxylative allylic amidation of chiral branched benzyl allyl imidodicarboxylates
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(Chemical Equation Presented) Ir(I)-catalyzed decarboxylase allylic amidation of chiral branched benzyl allyl imidodicarboxylates has been shown to proceed with complete retention of enantiomeric purity and configuration. The transformation is stereospecific and appears to be quite general, accommodating a wide range of R groups.
- Singh, Om V.,Han, Hyunsoo
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p. 4801 - 4804
(2008/03/15)
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- The photochemistry of ring-substituted cinnamyl acetates
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The photochemistry of the (E)-cinnamyl acetates ((E)-1-aryl-3-propenyl acetates, 8a-8e) with substituents H, 4-CH3O, 3-CH3O, 4-CF3, and 3-CF3, respectively, was examined in both cyclohexane and methanol solvents. Alkene isomerization (E to Z) occurred more efficiently than other reactions and evidence is presented that this process occurs from the excited triplet state. In a slower process, 1,3-migration of the acetoxy group led to the rearranged 3-aryl-3-propenyl acetate isomers (9a-9e) as the major pathway, particularly in cylohexane. In methanol, the isomeric ethers 3-aryl-3-methoxypropene (14) and 1-aryl-3-methoxypropene (15) were formed by reaction of methanol with the photochemically generated cation. The combined yield of 14 and 15 (95% and 5%, respectively) was quantitative for the 4-methoxyphenyl compound (8b). Independent irradiations of the isomers 9a-9c demonstrated that the ethers 14 and 15 were primary photoproducts from 8 and not secondary photoproducts from 9. Fluorescence quantum yields and excited singlet state lifetimes indicated that the reactions, other than the E to Z isomerization, are from the excited singlet state.
- Fleming,Renault,Grundy,Pincock
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p. 1146 - 1154
(2007/10/03)
-
- Convenient and efficient Pd-catalyzed regioselective oxyfunctionalization of terminal olefins by using molecular oxygen as sole reoxidant
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(Chemical Equation Presented) Just the one: The combination of palladium dichloride and N,N-dimethylacetamide (DMA) constitutes a highly efficient and reusable catalytic system, which uses molecular oxygen as the sole reoxidant for liquid-phase Wacker oxidation and acetoxylation of terminal olefins to the corresponding methyl ketones and linear allylic acetates, respectively (see scheme). 2006 Wiley-VCH Verlag GmbH Co. KGaA.
- Mitsudome, Takato,Umetani, Takuya,Nosaka, Naoya,Mori, Kohsuke,Mizugaki, Tomoo,Ebitani, Kohki,Kaneda, Kiyotomi
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p. 481 - 485
(2007/10/03)
-
- Practical synthesis of allylic silanes from allylic esters and carbamates by stereoselective copper-catalyzed allylic substitution reactions
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The first copper-catalyzed allylic substitution reactions of allylic acetates and carbamates employing a bis(triorganosilyl)zinc reagent are reported. This novel procedure avoids the use of stoichiometric amounts of copper salts which are usually mandatory with this chemistry. Application of this methodology to standard model substrates substantiates a high diastereoselectivity for the double bond geometry (E:Z) as well as the relative configuration (syn:anti).
- Oestreich, Martin,Auer, Gertrud
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p. 637 - 640
(2007/10/03)
-
- Aminocyclopentadienyl Ruthenium Complexes as Racemization Catalysts for Dynamic Kinetic Resolution of Secondary Alcohols at Ambient Temperature
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Aminocyclopentadienyl ruthenium complexes, which can be used as room-temperature racemization catalysts with lipases in the dynamic kinetic resolution (DKR) of secondary alcohols, were synthesized from cyclopenta-2,4-dienimines, Ru3(CO)12, and CHCl 3: [2,3,4,5-Ph4(η5-C 4CNHR)]Ru-(CO)2Cl (4: R = i-Pr; 5: R = n-Pr; 6: R = t-Bu), [2,5-Me2-3,4-Ph2(η5-C 4CNHR)]Ru(CO)2Cl (7: R = i-Pr; 8: R = Ph), and [2,3,4,5-Ph4(η5-C4CNHAr)]Ru(CO) 2Cl (9: Ar =p-NO2C6H4; 10: Ar = p-ClC6H4; 11: Ar = Ph; 12: Ar = p-OMeC6H 4; 13: Ar = p-NMe2C6H4). The tests in the racemization of (S)-4-phenyl-2-butanol showed that 7 is the most active catalyst, although the difference decreased in the DKR. Complex 4 was used in the DKR of various alcohols; at room temperature, not only simple alcohols but also functionalized ones such as allylic alcohols, alkynyl alcohols, diols, hydroxyl esters, and chlorohydrins were successfully transformed to chiral acetates. In mechanistic studies for the catalytic racemization, ruthenium hydride 14 appeared to be a key species. It was the major organometallic species in the racemization of (S)-1-phenylethanol with 4 and potassium tert-butoxide. In a separate experiment, (S)-1-phenylethanol was racemized catalytically by 14 in the presence of acetophenone.
- Choi, Jun Ho,Choi, Yoon Kyung,Kim, Yu Hwan,Park, Eun Sil,Kim, Eun Jung,Kim, Mahn-Joo,Park, Jaiwook
-
p. 1972 - 1977
(2007/10/03)
-
- Solvent-dependent dynamic kinetic asymmetric transformation/kinetic resolution in molybdenum-catalyzed asymmetric allylic alkylations
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Catalytic asymmetric alkylation reactions of branched racemic carbonates 1a and 1b with sodium dimethyl malonate, promoted by molybdenum and ligand 5, proceed by a kinetic resolution in toluene, THF, tetrahydropyran, i-PrOAc, 1,2-dichloroethane, and MeCN with krel of 7-16. In THF, MeCN, tetrahydropyran, and i-PrOAc using the (S,S)-5 ligand, the fast reacting (S)-carbonate enantiomer provides the branched product with high ee (97-99.5%) and branched/linear selectivity, but the ee erodes as the reaction of the slow-reacting (R)-enantiomer takes place. This implies that the rate of equilibration of the oxidative addition complexes in these solvents is competitive with the subsequent malonate displacement step. In toluene and dichloroethane, the ee and branched/linear ratios diminish during the reaction of the slow-reacting (R)-isomer, but not nearly as much as in the other solvents. This is most likely due to either an increase in the rate of equilibration of the oxidative addition complexes relative to the malonate displacement step, or vice versa. Because of the minimal stereochemical memory effect in toluene and 1,2-dichloroethane, the reactions in these solvents can be carried to completion (dynamic kinetic asymmetric transformation) and still provide product with excellent ee (>95%). The anion of dimethyl methylmalonate also reacts via a kinetic resolution, although the ee's, rates, and krel values differ from those of the reactions with dimethyl malonate.
- Hughes, David L.,Palucki, Michael,Yasuda, Nobuyoshi,Reamer, Robert A.,Reider, Paul J.
-
p. 2762 - 2768
(2007/10/03)
-
- Kinetic resolution in Pd-catalyzed allylic substitution using the helical PHelix ligand
-
The chiral helical diphosphine 2,15-bis(diphenylphosphino)-hexahelicene (PHelix) is an excellent ligand in palladium catalyzed kinetic resolution involving allylic substitution. Depending upon the substrate, enantioselectivities (ee) of up to 99% are observed. Although formally a diphosphine, PHelix appears not to undergo chelation, which means that it behaves as a chiral monophosphine.
- Reetz, Manfred T.,Sostmann, Stefan
-
p. 105 - 109
(2007/10/03)
-
- Microscale determination of the absolute configuration of α-aryl- substituted alcohols by the CD exciton chirality method
-
The absolute configurations of a broad spectrum of aryl alcohols 1 have been determined for the first time by the CD exciton chirality method. The configurational assignment is additionally verified by computer modeling and lipase-catalyzed acetylation of the racemic alcohols. The CD-spectroscopic data have revealed that the S enantiomers of the benzoate derivatives 2 display a positive first Cotton effect and the R enantiomers a negative one at around 228 nm. Thus, the sense of the first Cotton effect of the benzoate derivative 2 allows a reliable assignment of the absolute configuration of the corresponding alcohol 1.
- Adam, Waldemar,Lukacs, Zoltan,Viebach, Kirsten,Humpf, Hans-Ulrich,Saha-Moeller, Chantu R.,Schreier, Peter
-
p. 186 - 190
(2007/10/03)
-
- Deamination of trans-2-Methyl- And trans-2-Phenylcyclopropylamines
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The deaminations of trans-2-methyl- and 2-phenylcyclopropylamine hydrochlorides in acetic acid solution have been examined. A major product in each case was an allylic chloride, and the amount of chlorides increased when the chloride ion concentration was increased. With the methyl-substituted amine, increasing the chloride ion concentration changed the major chloride product from crotyl chloride to methallyl chloride. The addition of lithium perchlorate led to a reduction in the amount of chlorides formed. These results indicate that an ion pair is involved in the reaction. The deamination of the related open chain amines gave only small amounts of chlorides. B3LYP/ 6-31G* calculations found cyclopropyldiazonium chloride to prefer to have the chloride ion over the cyclopropyl ring. The transition state was located, and when followed down to products, allyl chloride was found. Similar calculations for the methyl-substituted series led to crotyl chloride from the ion pair with one chloride ion and to methallyl chloride from the ion-triplet with two chloride ions. The deaminations of the corresponding nitrosoureas in basic methanol also were studied. The products were the expected ethers. The addition of azide ion led to azides that were largely formed by initial reaction with the diazonium ion to give a pentazene that lost nitrogen to give the azide. However, some of the azide was formed by an SN2 displacement.
- Wiberg, Kenneth B.,Oesterle, Carmen G.
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p. 7756 - 7762
(2007/10/03)
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- Chirale Phosphanodihydrooxazole in der asymmetrischen Katalyse: Wolfram-katalysierte allylische Substitution
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Stichworte: Alkylierungen * Asymmetrische Synthesen * Dihydrooxazole * Katalyse * Wolframverbindungen
- Lloyd-Jones, Guy C.,Pfaltz, Andreas
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p. 534 - 536
(2007/10/02)
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- Acetoxyselenenylation of Olefins for the Preparation of Vinylic and Allylic Acetates
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Terminal and 1,2-disubstituted olefins were irreversibly acetoxyselenenylated by treatment with PhSeBr in an acetate buffer solution.Styrene derivatives yielded only Markovnikov adducts whereas simple terminal olefins and olefins containing an allylic oxygen substituent (acyloxy or aryloxy group) afforded significant amounts (50-85percent) of the anti-Markovnikov isomer.The product mixtures were isomerized to contain 90-97percent of the Markovnikov products by treatment with a catalytic amount (6-41percent) of BF3*OEt2 in chloroform.Oxidation (SO2Cl2/hydrolysis or MCPBA) of the isomerized products and selenoxide elimination at elevated temperature toward the acetoxy group afforded enol acetates in fair yields.The selenoxides of the anti-Markovnikov isomers (unisomerized mixtures) spontaneously eliminated, in the presence of the selenoxides of the Markovnikov isomer, to give allylic acetates in good yields at ambient temperature.
- Engman, Lars
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p. 884 - 890
(2007/10/02)
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- Oxidation by Cobalt(III) Acetate. Part 10. Effects of Ring Substituents on the Product Distributions in the Oxidation of β-Methylstyrenes by Cobalt(III) Acetate in Acetic Acid
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The oxidation of ring-substituted β-methylstyrenes by cobalt(III) acetate in acetic acid has been studied by product analysis and the relative rates were measured by a competition method.Electron-releasing groups (p-MeO, pMe and p-But) accelerated both the reaction rate and the formation of glycol monoacetates, while electron-withdrawing groups (p-Cl and m-Cl) not only retarded the reaction but also favoured the formation of allylic acetate instead of glycol monoacetate.The good relationship of relative rates with ?+ in the Hammett plot showed that both products were derived from the same intermediate.The reaction mechanism is discussed in connection with the stabilities of radical cations formed by a one-electron transfer from the olefins to cobalt(III) acetate.
- Morimoto, Takashi,Hirano, Masao,Echigoya, Kohki,Sato, Takafumi
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p. 1205 - 1210
(2007/10/02)
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- Oxidation of Styrene Derivatives by S2O82--CuII in Acetic Acid and Acetonitrile. Reaction Paths in Oxidations via Radical Cations
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β-Aryl carbonyl compounds are major products in the oxidation of a variety of styrene derivatives by S2O82--CuII.Evidence is presented that they arise via oxidation to a radical cation, nucleophilic addition of water to give a β-hydroxyalkyl radical, CuII oxidation to epoxide, and finally acid-catalyzed rearrangement.Data on oxidation of alkyl aromatics with additional functional groups are presented.With ether and amino groups, oxidation occurs at the functional group even when it is remote from the aryl nucleus.These and previous data are summarized to give a coherent picture of the various paths by which aryl side chains may be degraded via initial radical cation intermediates.
- Walling, Cheves,El-Taliawi, Gamil M.,Amarnath, Kalyani
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p. 7573 - 7578
(2007/10/02)
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- Photosensitized (Electron-Transfer) Rearrangements of Cinnamyl Alcohol Derivatives
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Specific electron-donor compounds are capable of photosensitizing the rearrangement and solvolysis of several cinnamyl alcohol derivatives.Under suitable conditions, the formation of rearranged α-phenylallyl derivatives occurs in synthetically useful yields.The intermediates in this process have ionic character and have been trapped by methanol as methyl ether derivatives.The ability of the photosensitizers to effect these electron-transfer-initiated reactions correlates well with the enthalpy of reaction calculated by the Weller equation.
- Lee, George A.,Israel, Samuel H.
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p. 4557 - 4563
(2007/10/02)
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- SECONDARY TRITIUM ISOTOPE EFFECTS, A USEFUL MECHANISTIC PROBE FOR THE STUDY OF ACETOXYL PARTICIPATION AND TRANSFER
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Tritium labelling on the acetoxyl methyl group has been used to probe the mode of incorporation of acetate into cinnamyl acetate in the solvolyses of cinnamyl chloride and cinnamylmercuric acetate, and in the allylic oxidation of allylbenzene with mercuric acetate.
- Wolfe, Saul,Campbell, Peter G. C.
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p. 1227 - 1230
(2007/10/02)
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- Mechanistic Features of Allylic Hydrogen Abstraction by Alkoxy Radicals
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A TS(excit) of angular H abstraction from allylbenzene in the course of the allylic acetoxylation reaction was previously invoked to explain a temperature-independent primary KIE; kH/kD = 2.90.This reaction geometry is now fully supported by the finding of inverse α-secondary deuterium isotope effects at both ends of the double bond in allylbenzene; (kH/kD)αC1 = 0.977 and (kH/kD)αC2 = 0.985.In keeping with these results an unsymmetrically structured, bridged radical intermediate, formed by the interaction of t-BuO with the allylic double bond, steers the reaction course.Such a complex is recognized to be unusual since most of the verified cases of radical bridging involve heteroatom centers capable of octet expansion.A discussion is also given of the factors determining the relative influence of benzene and double bond participation in the H-abstraction reactions of allylbenzene, which possesses both of these activating functions.
- Kwart, H.,Brechbiel, M.,Miles, W.,Kwart, L.D.
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p. 4524 - 4528
(2007/10/02)
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- Oxidation by Cobalt(III) Acetate. Part 3. Allylic Oxidation of Various Olefins in Acetic Acid
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Allylic oxidation of various olefins with cobalt(III) acetate in acetic acid under nitrogen has been investigated.The substrates studied include allylbenzene, oct-1-and -trans-4-ene, cycloalkenes (C5-C8), and 1-and 4-methyl-cyclohexene.The reaction gave exclusively the allylic acetate as the primary product; no 1,2-addition or skeletal rearrangement product was formed in significant amount.Some mechanistic aspects of allylic oxidation are discussed.
- Hirano, Masao,Nakamura, Kouji,Morimoto, Takashi
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p. 817 - 820
(2007/10/02)
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