- Enantioselective Michael Addition of Photogenerated o-Quinodimethanes to Enones Catalyzed by Chiral Amino Acid Esters
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The first example of a photoexcitated amine-catalyzed process for asymmetric Michael addition of o-quinodimethanes to enones is described. In the presence of simple chiral amino acid esters, a variety of Michael adducts were generally obtained in good yie
- Yuan, Xiaoqian,Dong, Shupeng,Liu, Zhen,Wu, Guibing,Zou, Chuncheng,Ye, Jinxing
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- Heterogeneous Isomerization for Stereoselective Alkyne Hydrogenation to trans-Alkene Mediated by Frustrated Hydrogen Atoms
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Stereoselective production of alkenes from the alkyne hydrogenation plays a crucial role in the chemical industry. However, for heterogeneous metal catalysts, the olefins in cis-configuration are usually dominant in the products due to the most important and common Horiuti-Polanyi mechanism involved over the metal surface. In this work, through combined theoretical and experimental investigations, we demonstrate a novel isomerization mechanism mediated by the frustrated hydrogen atoms via the H2 dissociation at the defect on solid surface, which can lead to the switch in selectivity from the cis-configuration to trans-configuration without overhydrogenation. The defective Rh2S3 with exposing facet of (110) exhibits outstanding performance as a heterogeneous metal catalyst for stereoselective production of trans-olefins. With the frustrated hydrogen atoms at spatially separated high-valence Rh sites, the isolated hydrogen mediated cis-to-trans isomerization of olefins can be effectively conducted and the overhydrogenation can be completely inhibited. Furthermore, the bifunctional Rh-S/Pd nanosheets have been synthesized through the surface modification of Pd nanosheets with rhodium and sulfide. With the selective semihydrogenation of alkynes into cis-olefins catalyzed by the small surface PdSx ensembles, the bifunctional Rh-S/Pd nanosheets exhibit excellent activity and stereoselectivity in the one-pot alkyne hydrogenation into trans-olefin, which surpasses the most reported homogeneous and heterogeneous catalysts.
- Zhang, Weijie,Qin, Ruixuan,Fu, Gang,Zheng, Nanfeng
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supporting information
p. 15882 - 15890
(2021/10/02)
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- Z-Selective phosphine promoted 1,4-reduction of ynoates and propynoic amides in the presence of water
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Phosphine-mediated reductions of substituted propynoic esters and amides in the presence of water yield the partially reduced α,β-unsaturated esters and amides with highZ-selectivity. The competitivein situ ZtoE-isomerization of the product in some cases lowers theZtoEratios of the isolated α,β-unsaturated carbonyl products. Reaction time and the amounts of phosphine and water in the reaction mixture are the key experimental factors which control the selectivity by preventing or reducing the rates ofZ- toE-product isomerization. Close reaction monitoring enables isolation of theZ-alkenes with high selectivities. The computational results suggest that the reactions could be highlyZ-selective owing to the stereoselective formation of theE-P-hydroxyphosphorane intermediate.
- Drikermann, Denis,Kupfer, Stephan,Seifert, Fabian,Steinmetzer, Johannes,Vilotijevic, Ivan,Zi, You
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supporting information
p. 6092 - 6097
(2021/07/21)
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- Introducing the Dihydro-1,3-azaboroles: Convenient Entry by a Three-Component Reaction, Synthetic and Photophysical Application
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The (Fmes)BH2·SMe2 reagent (7) reacts sequentially with an acetylene and, e.g., xylylisonitrile in a convenient three-component reaction to give a series of unprecedented dihydro-1,3-azaborole derivatives 16. The tolane-derived example 16a was deprotonated and used as a ligand in organometallic chemistry. Compounds 16 served as the starting materials for the straightforward synthesis of various dihydro-1,3-azaborinine derivatives by treatment with an isonitrile. Several diaryldihydro-1,3-azaboroles showed interesting photophysical properties such as aggregation-induced emission and high fluorescence quantum yields.
- Li, Jun,Daniliuc, Constantin G.,Kartha, Kalathil K.,Fernández, Gustavo,Kehr, Gerald,Erker, Gerhard
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supporting information
p. 2059 - 2067
(2021/02/06)
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- Synthetic Entry to Polyfunctionalized Molecules through the [3+2]-Cycloaddition of Thiocarbonyl Ylides
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Here we present a comprehensive study on the [3+2]-cycloaddition of thiocarbonyl ylides with a wide variety of alkenes and alkynes. The obtained dihydro- and tetrahydrothiophene products serve as exceptionally versatile intermediates providing access to thiophenes, dienes, dendralenes, and vic-quarternary carbon centers. The use of high-pressure conditions enables thermally unstable, sterically encumbered or moderately reactive substrates to undergo the cycloaddition under mild conditions, thereby increasing the yield by up to 58percent. In addition, we showcase its utility by the formal syntheses of the pharmaceuticals NGB 4420 and tenilapine.
- Habiger, Christoph,Haut, Franz-Lucas,Korber, Johannes Nepomuk,Müller, Thomas,Magauer, Thomas,Mayer, Peter,Speck, Klaus,Wurst, Klaus
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supporting information
(2019/09/06)
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- Z- and E-selective Horner–Wadsworth–Emmons reactions
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In the present work, we determined and evaluated the stereochemical outcome of the Horner–Wadsworth–Emmons (HWE) reaction of 2-oxoalkylphosphonates with different ester functions (bis(2,2,2-trifluoroethyl), 2,2,2-trifluoroethyl methyl, dimethyl) and side chains (aliphatic, aromatic) with three different aldehydes (benzaldehyde, THP- and PPB-protected Corey aldehydes) under two reaction conditions. The “trans” protocol is generally used in the E-selective HWE reactions, while “cis” protocol promotes the Z-selectivity.
- Molnár, Katalin,Takács, László,Kádár, Mihály,Faigl, Ferenc,Kardos, Zsuzsanna
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p. 1214 - 1224
(2017/07/06)
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- Stereospecific Decarboxylative Nazarov Cyclization Mediated by Carbon Dioxide for the Preparation of Highly Substituted 2-Cyclopentenones
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Highly substituted 2-cyclopentenones were stereospecifically and regioselectively constructed with high catalytic efficiency through Lewis-acid catalyzed decarboxylative Nazarov cyclization of the cyclic carbonate derivative, which is prepared by reacting the propargyl alcohol with carbon dioxide in the presence of a silver catalyst. The stereochemistry of the 2-cyclopentenone is strictly controlled by the geometry of the alkene in the starting material. This method is applicable for various substrates.
- Komatsuki, Keiichi,Sadamitsu, Yuta,Sekine, Kohei,Saito, Kodai,Yamada, Tohru
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supporting information
p. 11594 - 11598
(2017/09/11)
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- Application of Pd Nanoparticles Supported on Mesoporous Hollow Silica Nanospheres for the Efficient and Selective Semihydrogenation of Alkynes
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Herein, the preparation of a heterogeneous catalyst consisting of 1-2 nm sized Pd nanoparticles supported on amino-functionalized mesoporous hollow silica nanospheres and its use for the semihydrogenation of mono- And disubstituted alkynes is reported. By utilizing this Pd nanocatalyst together with the green poisoning agent DMSO, high yields of the desired alkenes could be achieved, while suppressing the degree of over-reduction to alkanes. To our delight, the Pd nanocatalyst displayed remarkable chemoselectivity towards the alkyne moiety, allowing the transformation to be carried out in the presence of other reducible functionalities, such as halogens, carbonyl, and nitro groups.
- Verho, Oscar,Zheng, Haoquan,Gustafson, Karl P. J.,Nagendiran, Anuja,Zou, Xiaodong,B?ckvall, Jan-E.
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p. 773 - 778
(2016/03/05)
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- Selective Hydrogenation of Functionalized Alkynes to (E)-Alkenes, Using Ordered Alloys as Catalysts
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Intermetallic Pd3Pb acts as a highly selective alkyne semihydrogenation catalyst that is greatly superior to the conventional Lindlar catalyst. Density functional theory (DFT) calculations demonstrate an ideal adsorption property of Pd3Pb, where the surface holds alkynes while releasing alkenes. A tandem catalytic system that is comprised of Pd3Pb/SiO2 for alkyne semihydrogenation and RhSb/SiO2 for alkene isomerization allows one-pot (E)-alkene synthesis from a functionalized alkyne, which is the first success using heterogeneous catalysts. A variety of functionalized alkynes with aldehyde, ketone, carboxylic acid, and ester moieties are hydrogenated into the corresponding (E)-alkene in good to excellent yields under 1 atm H2 at room temperature.
- Furukawa, Shinya,Komatsu, Takayuki
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p. 2121 - 2125
(2016/03/15)
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- Green semi-hydrogenation of alkynes by Pd@borate monolith catalysts under continuous flow
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Palladium nanoparticles were immobilized onto an unconventional polymeric borate macroporous monolith and the resulting mesoreactor (i.d. 3 mm, length 25 mm) used in liquid-phase catalytic semi-hydrogenation reaction of substituted alkynes under continuous flow. The catalytic system showed excellent efficiency, both in terms of activity and selectivity, and long-term stability under mild reaction conditions (methanol, room temperature, 1.5 bar H2 max), with no need of additives. Particularly, the leaf alcohol cis-3-hexen-1-ol was for the first time obtained with selectivity comparable to that of the industrial batch process. The performance of the catalyst is discussed and compared with those of the analogous batch and industrial processes.
- Liguori, Francesca,Barbaro, Pierluigi
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p. 212 - 220
(2014/01/17)
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- Iridium(I)-catalyzed regioselective C-H activation and hydrogen-isotope exchange of non-aromatic unsaturated functionality
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Isotopic labelling is a key technology of increasing importance for the investigation of new C-H activation and functionalization techniques, as well as in the construction of labelled molecules for use within both organic synthesis and drug discovery. Herein, we report for the first time selective iridium-catalyzed C-H activation and hydrogen-isotope exchange at the β-position of unsaturated organic compounds. The use of our highly active [Ir(cod)(IMes)(PPh3)][PF6] (cod = 1, 5-cyclooctadiene) catalyst, under mild reaction conditions, allows the regioselective β-activation and labelling of a range of α, β-unsaturated compounds with differing steric and electronic properties. This new process delivers high levels of isotope incorporation over short reaction times by using low levels of catalyst loading.
- Kerr, William J.,Mudd, Richard J.,Paterson, Laura C.,Brown, Jack A.
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p. 14604 - 14607
(2015/03/04)
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- Efficient and exceptionally selective semireduction of alkynes using a supported gold catalyst under a CO atmosphere
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A new efficient method for chemo- and regio-selective semireduction of alkynes using CO/H2O as the hydrogen source catalyzed by gold supported on high surface area TiO2 was developed. A facile and practical synthesis of 1,2-dideuterioalkenes was also realized by using CO/D2O as the reducing agent. the Partner Organisations 2014.
- Li, Shu-Shuang,Liu, Xiang,Liu, Yong-Mei,He, He-Yong,Fan, Kang-Nian,Cao, Yong
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supporting information
p. 5626 - 5628
(2014/05/20)
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- Synthesis of β-sulfanyl ketones via a tandem rearrangement-conjugate addition reaction catalyzed by a Re(V)-oxo complex
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A method for synthesizing β-sulfanyl ketones via a tandem rearrangement and conjugate addition reaction has been developed. This methodology provides access to a range of β-sulfanyl ketones through the rearrangement of propargyl alcohols to the corresponding enones followed by the conjugate addition of unactivated thiols. The one-pot, tandem transformation is catalyzed by ReOCl3(OPPh3)(S(CH3)2) affording aryl and alkyl β-sulfanyl ketones in good to excellent yield.
- Garst, Alyson E.,Badiceanu, Alexandra D.,Nolin, Kristine A.
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p. 459 - 461
(2013/02/23)
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- Anomalous Z-isomer content in Wittig reaction products from keto-stabilised ylides with ortho-heteroatom substituted benzaldehydes
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Wittig reaction products of keto-stabilised ylides with ortho-substituted benzaldehydes are found to show significantly higher than expected Z-alkene content (up to 50%) compared to analogous reactions of the same ylides with benzaldehyde itself. A cooperative effect is seen whereby the unusual Z-content is further augmented if the ylide bears greater steric bulk in the α′-position. These results are consistent with our previous observations on reactions of all ylide types with aldehydes bearing a β-heteroatom. Significantly, the cooperative effect, previously seen only with semi-stabilised ylides, has now been extended to stabilised ylides. Both the anomalous increase in Z-content and the cooperative effect can be rationalised within the [2+2] cycloaddition mechanism of the Wittig reaction.
- Byrne, Peter A.,Higham, Lee J.,McGovern, Pádraic,Gilheany, Declan G.
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p. 6701 - 6704
(2013/01/15)
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- Heteropoly compound catalyzed synthesis of both z- and e-α,β- unsaturated carbonyl compounds
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An EZ switch: The cationic species of the heteropoly compounds has a critical impact on the Z/E selectivity of the Meyer-Schuster rearrangement of propargyl alcohols (see scheme). The isolation of the thermodynamically unfavorable Z-α,β-unsaturated carbonyl compounds is notable. The high Z selectivities were obtained at a reaction temperature as high as 50°C.
- Egi, Masahiro,Umemura, Megumi,Kawai, Takuya,Akai, Shuji
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supporting information; experimental part
p. 12197 - 12200
(2012/01/19)
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- Enantioselective reduction of ketones and imines catalyzed by (CN-Box)ReV-oxo complexes
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The development and application of chiral, non-racemic ReV-oxo complexes to the enantioselective reduction of prochiral ketones is described. In addition to the enantioselective reduction of prochiral ketones, we report the application of these complexes to 1) a tandem Meyer-Schuster rearrangement/reduction to access enantioenriched allylic alcohols and 2) the enantioselective reduction of imines.
- Nolin, Kristine A.,Ahn, Richard W.,Kobayashi, Yusuke,Kennedy-Smith, Joshua J.,Toste, F. Dean
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scheme or table
p. 9555 - 9562
(2010/10/03)
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- Chromatography-free wittig reactions using a bifunctional polymeric reagent
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The first example of a polystyrene bearing two distinct reagent groups has been prepared. This phosphine and amine functionalized material was used in one-pot Wittig reactions with an aldehyde and either an α-halo-ester, -ketone, or -amide. Due to the heterogeneous nature of the polymer, the desired alkene product of these reactions could be isolated in excellent yield in essentially pure form after only filtration and solvent removal.
- Leung, Peter Shu-Wai,Teng, Yan,Toy, Patrick H.
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supporting information; experimental part
p. 4996 - 4999
(2010/12/25)
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- Morpholinium trifluoroacetate-catalyzed aldol condensation of acetone with both aromatic and aliphatic aldehydes
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We report a highly efficient, general and practical method for the aldol condensation of acetone with aromatic and aliphatic aldehydes, using morpholinium trifluoroacetate as a catalyst.
- Zumbansen, Kristina,Doehring, Arno,List, Benjamin
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experimental part
p. 1135 - 1136
(2010/09/05)
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- Partial hydrogenation of alkynes to cis-olefins by using a novel Pd 0-polyethyleneimine catalyst
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The creation and application of a new Pd0-polyethyleneimine complex catalyst (Pd0-PEI) was investigated. The 55 Pd 0-PEI catalyst was prepared by introduction of Pd(OAc)2 directly in the MeOH solution of deaerated PEI under Ar atmosphere. Reactions were carried out using 10 weight % versus substrate of 5% Pd0-PEI in 2mL solvent under H2 atmosphere at room temperature. The generality of the process was shown by disubstituting alkynes. Even for the substrate bearing a conjugated ketone on the alkyne, the serious over-reduction was not observed while significant cistrans isomerization of methyl styryl ketone accompanied the partial hydrogenation on the basis of keto-enol tautomerism. Pd0-PEI catalyst is also applicable to the partial hydrogenation of monosubstituted alkynes to monosubstituted olefins.
- Sajiki, Hironao,Mori, Shigeki,Ohkubo, Tomoyuki,Ikawa, Takashi,Kume, Akira,Maegawa, Tomohiro,Monguchi, Yasunari
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supporting information; experimental part
p. 5109 - 5111
(2009/05/07)
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- Influence of the double-bond geometry of the Michael acceptor on copper-catalyzed asymmetric conjugate addition
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Focusing on mechanistic aspects, a study of the influence of the (E)/(Z) double-bond geometry of the Michael acceptor on the enantioselectivity of copper-catalyzed asymmetric conjugate addition reactions has been realized. In spite of numerous articles co
- Vuagnoux-D'Augustin, Magali,Alexakis, Alexandre
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p. 5852 - 5860
(2008/04/13)
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- Application of organocerium reagents for the efficient conversion of Z-α,β-unsaturated Weinreb amides to Z-α,β-unsaturated ketones
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The reactions of Z-rich unsaturated Weinreb amides with organolithium and organocerium reagents were examined. Taking in consideration both the extent of geometry retention and cleanness of the reaction, organocerium reagents were more effective for the conversion to Z-α,β-unsaturated ketones. Copyright
- Kojima, Satoshi,Hidaka, Tsugihiko,Yamakawa, Atsushi
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p. 470 - 471
(2007/10/03)
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- Stereoselective Synthesis of Stannyl Enones via Palladium-Catalyzed and Free Radical Hydrostannation of Alkynyl Ketones with Trineophyltin Hydride
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A study on the addition of trineophyltin hydride (1) to alkynones under free radical (AIBN and Et3B) and palladium-catalyzed [(PPh3) 2PdCl2] conditions is reported. The results obtained indicate that the addition of 1 to eight ynones catalyzed by bis(triphenylphosphine)palladium(II) chloride led in all cases to addition products in very high yields (80-96%). These additions take place with excellent regio- and stereochemistry, leading to the α adducts as major products in seven out of the eight cases studied. Also the E adducts, resulting from a syn attack, were the only (seven cases) or the predominant (one case) products. The radical hydrostannations initiated by AIBN of ynones 2-5 with 1 led to addition products in good yields (60-88%); with the more hindered ketones 6 and 7-9 the yields obtained were lower. The radical additions initiated by triethylboron to ynones 2-6 follow a similar pattern but with lower yields; no addition products in the hydrostannation of ynones 7-9 were detected. The new acyl-substituted vinylstannanes, owing to their greater stability compared with that of their tributyl- and trimethylstannyl analogues, can be purified by column chromatography using neutral alumina (in all cases) or silica gel 60 (in most cases) as adsorbents. Full 1H, 13C, and 119Sn NMR data are given.
- Dodero, Veronica I.,Koll, Liliana C.,Faraoni, M. Belen,Mitchell, Terence N.,Podesta, Julio C.
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p. 10087 - 10091
(2007/10/03)
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- Palladium on pumice: New catalysts for the stereoselective semihydrogenation of alkynes to (Z)-alkenes
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High selectivities (93-99%) and excellent stereoselectivities (>99%) in the semihydrogenation of C-C triple bonds were achieved using palladium on pumice with a metal loading of 0.5, 1.5 or 3.0% wt as catalyst. The reactions were carried out in ethanol or tetrahydrofuran with only 2.5% of ethylenediamine allowing a self-terminating semihydrogenation independently on the C-C triple bond.
- Gruttadauria, Michelangelo,Liotta, Leonarda F.,Noto, Renato,Deganello, Giulio
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p. 2015 - 2017
(2007/10/03)
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- Triphenylphosphine-mediated olefination of aldehydes with (Z)-(2- acetoxyalk-1-enyl)phenyl-λ3-iodanes: Generation and reaction of (2- oxoalkyl)phenyl-λ3-iodanes
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(Z)-(2-Acetoxyalk-1-enyl)phenyl-λ3-iodanes, on treatment with triethylamine in methanol in the presence of triphenylphosphine, undergo Wittig olefination with aldehydes, which involves the intermediacy of α- iodanyl ketones generated by in situ
- Ochiai, Masahito,Nishi, Yoshio,Nishitani, Junichi,Chen, Da-Wei,Hashimoto, Sakiko,Tsuchimoto, Yoshimi
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p. 1157 - 1158
(2007/10/03)
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- Wittig reactions in the ionic solvent [bmim][BF4]
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The ionic salt [bmim][BF4] is an attractive solvent for Wittig reactions, allowing both easier separation of alkenes from Ph3PO together with eficient reuse to the solvent.
- Boulaire, Virginie Le,Gree, Rene
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p. 2195 - 2196
(2007/10/03)
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- A highly chemoselective oxidation of alcohols to carbonyl products with iodosobenzene diacetate mediated by chromium(III)(salen) complexes: Synthetic and mechanistic aspects
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The catalytic oxidation of the allylic alcohols 1d-n with iodosobenzene diacetate, mediated by the [CrIII(salen)]X complex, affords the respective enones in excellent chemoselectivity for Cl- as counterion [complex A(Cl)], while for the counterions TfO- [complex A(TfO)] and PF6- [complex A(PF6)] nearly equal amounts of enone and epoxide are observed. This counterion-dependent oxidation of allylic alcohols by CrIII(salen) complexes is rationalized in terms of Lewis acid catalysis by the complex A(Cl) and redox catalysis for A(TfO) and A(PF6).
- Adam, Waldemar,Hajra, Saumen,Herderich, Markus,Saha-M?ller, Chantu R.
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p. 2773 - 2776
(2007/10/03)
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- A highly selective synthesis of (Z)-α,β-unsaturated ketones
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New Wadsworth-Emmons reagents, bis(2,2,2-trifluoroethyl)-(2-oxopropyl)phosphonate 6 and bis(2,2,2-trifluoroethyl)-(1-methyl-2-oxopropyl)-phosphonate 7 were prepared and their reactions with aldehydes yielded disubstituted and trisubstituted (Z)-α,β-unsaturated ketones.
- Yu, Wensheng,Su, Mei,Jin, Zhendong
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p. 6725 - 6728
(2007/10/03)
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- Characterization of the Main Radical and Products Resulting from a Reductive Activation of the Antimalarial Arteflene (Ro 42-1611)
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The peroxide-containing antimalarial drug arteflene (Ro 42-1611) generates an alkyl radical after the reductive homolytic cleavage of the peroxide bond in the presence of a heme model MnII(TPP). This alkyl radical has been trapped by TEMPO, and the different products of the reduction activation of arteflene have been characterized. These data suggest that, in these experimental conditions, arteflene is not a significant alkylating agent compared to artemisinin, a trioxane-containing antimalarial drug.
- Cazelles, Jerome,Robert, Anne,Meunier, Bernard
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p. 6776 - 6781
(2007/10/03)
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- Chemoselectivity in Catalytic Transfer Hydrogenation - Reduction of Alkenes and Alkynes with the H2PO2-NH4+*H2O/Pd-C System
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The H2PO2-*H2O/Pd-C system acts as an unusually powerful reducing agent, which is able to reduce cyclooctene to cyclooctane, Δ9,10-octalin to decalins, α- and β-pinenes to pinanes at room temperature in high yield without the formation of byproducts.This system reduces each of these compounds or partly (alkynes to alkenes), depending on the competition between the transfer hydrogenation to give alkanes and the protonolysis to give hydrogen gas on the palladium catalyst. - Key Words: Chemoselectivity/ Protonolysis/ Transfer hydrogenation/ Alkenes, reduction of/ Alkynes, reduction of
- Khai, Bui The,Arcelli, Antionio
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p. 2265 - 2268
(2007/10/02)
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- A Simple and Highly Stereoselective Route to E-α,β-Unsaturated Aldehydes
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Zinc bromide mediated reaction of α,α-bis(trimethylsilyl)-tert-butylacetaldimine (3) with a wide range of aldehydes takes place under mild conditions and affords the corresponding α,β-unsaturated aldehydes in good yields and with high E stereoselectivity (>98percent).This procedure is successfully applied to the preparation of intermediates for retinoid and natural product synthesis.
- Bellassoued, Moncef,Majidi, Assieh
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p. 2517 - 2522
(2007/10/02)
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- A New Protocol for Regio- and Stereocontrolled Aldol Reactions through the Conjugate Addition of Dialkylboranes to α,β-Unsaturated Ketones
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A one-pot, two-step procedure, consisting of the 1,4-addition of dialkylboranes to β-substituted (E)-α,β-unsaturated ketones followed by the reaction of the resulting configurationally pure (Z)-(vinyloxy)boranes with aldehydes, is reported.The overall process corresponds to a regio- and stereocontrolled aldol addition of an unsymmetrical ketone to an aldehyde.A concerted 1,4-addition mechanism accounts for the stereochemical outcome of the hydroboration reaction; cyclic enones do not undergo conjugate addition, while (Z)-β-substituted or β,β-disubstituted α,β-unsaturated ketones still react in a 1,4-fashion, but with a slower rate and a lower degree of chemoselectivity with respect to β-substituted (E)-α,β-unsaturated ketones.In the cases of α,β-disubstituted α,β-unsaturated ketones and (E)-(S-phenylthio)cinnamate, which react with dicyclohexylborane to give a mixture of E and Z enolates, an alternative mechanism is proposed.
- Boldrini, Gian Paolo,Bortolotti, Michele,Mancini, Fabrizio,Tagliavini, Emilio,Trombini, Claudio,Umani-Ronchi, Achille
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p. 5820 - 5826
(2007/10/02)
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- Photoreactions of trans-Benzalacetone in Solution and Organised Media
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Direct photolysis of trans-benzalacetone (1) in diethyl ether results in the formation of a mixture of photoproducts containing trans- and cis-benzalacetones (2) in approximately 1:1 ratio.Irradation of 1 in n-butyl stearate medium affords a photostationa
- Singh, Anil K.,Lalitha, S.
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p. 935 - 938
(2007/10/02)
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- Photochemistry of the Carbon-Nitrogen Double Bond. Part 1. Carbon-Nitrogen vs. Carbon-Carbon Double Bond Isomerisation in the Photochemistry of α,β-Unsaturated Oxime Ethers: The Benzylideneacetone Oxime O-Methyl Ether System
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The syntheses of the four benzylideneacetone oxime O-methyl ether isomers (2)-(5) are described.Direct or sensitised irradiation of the E,E-isomer (2) or Z,E-isomer (3) leads to equilibration of all four isomers by a combination of rapid carbon-nitrogen double bond isomerisation and slower carbon-carbon double bond isomerisation.A previous investigation of the photochemistry of the E,E-isomer (2) had reported only carbon-carbon double bond isomerisation.
- Pratt, Albert C.,Abdul-Majid, Qais
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p. 1691 - 1694
(2007/10/02)
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- Surface Photochemistry: CdS Photoinduced Cis-Trans Isomerization of Olefins
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The CdS powder photomediated cis-trans isomerization of six styrene derivatives has been demonstrated.The reaction with cis-stilbene is quenched by electron donors (methoxybenzenes and pyrene) and is affected by the amount of CdS used, light intensity, and the temperature.A minimal simple scheme involving the radical cation is proposed, as a basis for further work, to which Langmuir-Hinshelwood and Freundlich kinetic treatments are applied, the latter somewhat more successfully.The presence of oxygen inhibits the reaction.
- Al-Ekabi, Hussain,Mayo, Paul de
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p. 5815 - 5821
(2007/10/02)
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- EVIDENCE FOR A REVERSIBLE d,?*-COMPLEXATION, β-CUPRATION SEQUENCE IN THE CONJUGATE ADDITION REACTION OF GILMAN REAGENTS WITH α,β-ENONES.
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In situ trapping of reaction intermediates combined with stereochemical studies of the reaction of lithium dimethylcuprate with enones provides evidence for a pathway involving d,?*-cuprate-enone and copper(III) β-adducts as important intermediates in cuprate-mediated conjugate addition of carbon.
- Corey, E. J.,Boaz, Neil W.
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p. 6015 - 6018
(2007/10/02)
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- Palladium-Catalyzed Acylation of Unsaturated Halides by Anions of Enol Ethers
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Zinc salts of enol ether anions are coupled to aryl and alkenyl halides by using palladium catalysts, effecting a direct acetylation of aryl and alkenyl halides.Zinc salts of allenic ethers are coupled with aryl and alkenyl halides under similar conditions to give α,β-unsaturated ketones, the allenic ether serving as a source of the acryloyl group.Allenic ethers were γ arylated in a palladium-catalyzed coupling with aryl halides to give β,β-diaryl-α,β-unsaturated aldehydes.
- Russell, Charles E.,Hegedus, Louis S.
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p. 943 - 949
(2007/10/02)
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