- METHODS OF BORYLATION AND USES THEREOF
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The present invention relates, in general terms, to methods of borylation and uses thereof. In particular, the present invention provides a method of borylating an alkene compound by contacting the compound with a boron compound, a Fe pre-catalyst and a protic additive. The borylation occurs at a vicinal (β) position to an electron donating or electron withdrawing moiety of the compound.
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Page/Page column 61-62
(2021/04/30)
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- Structural elucidation of a methylenation reagent of esters: Synthesis and reactivity of a dinuclear titanium(iii) methylene complex
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Transmetallation of a zinc methylene complex [ZnI(tmeda)]2(μ-CH2) with a titanium(iii) chloride [TiCl3(tmeda)(thf)] produced a titanium methylene complex. The X-ray diffraction study displayed a dinuclear methylene structure [TiCl(tmeda)]2(μ-CH2)(μ-Cl)2. Treatment of an ester with the titanium methylene complex resulted in methylenation of the ester carbonyl to form a vinyl ether. The titanium methylene complex also reacted with a terminal olefin, resulting in olefin-metathesis and olefin-homologation. Cyclopropanation by methylene transfer from the titanium methylene proceeded by use of a 1,3-diene. The mechanistic study of the cyclopropanation reaction by the density functional theory calculations was also reported.
- Kurogi, Takashi,Kuroki, Kaito,Moritani, Shunsuke,Takai, Kazuhiko
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p. 3509 - 3515
(2021/03/29)
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- Mild olefin formationviabio-inspired vitamin B12photocatalysis
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Dehydrohalogenation, or elimination of hydrogen-halide equivalents, remains one of the simplest methods for the installation of the biologically-important olefin functionality. However, this transformation often requires harsh, strongly-basic conditions, rare noble metals, or both, limiting its applicability in the synthesis of complex molecules. Nature has pursued a complementary approach in the novel vitamin B12-dependent photoreceptor CarH, where photolysis of a cobalt-carbon bond leads to selective olefin formation under mild, physiologically-relevant conditions. Herein we report a light-driven B12-based catalytic system that leverages this reactivity to convert alkyl electrophiles to olefins under incredibly mild conditions using only earth abundant elements. Further, this process exhibits a high level of regioselectivity, producing terminal olefins in moderate to excellent yield and exceptional selectivity. Finally, we are able to access a hitherto-unknown transformation, remote elimination, using two cobalt catalysts in tandem to produce subterminal olefins with excellent regioselectivity. Together, we show vitamin B12to be a powerful platform for developing mild olefin-forming reactions.
- Bam, Radha,Pollatos, Alexandros S.,Moser, Austin J.,West, Julian G.
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p. 1736 - 1744
(2021/02/22)
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- A Pd-Catalyzed Site-Controlled Isomerization of Terminal Olefins
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An effective Pd-catalyzed isomerization of olefins with 2-PyPPh2 as the ligand is described. A wide variety of trans-2-olefins bearing various functional groups can be obtained with high regio- A nd stereoselectivity under mild reaction conditions. The ligand is crucial for the reaction.
- Ren, Wenlong,Sun, Fei,Chu, Jianxiao,Shi, Yian
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supporting information
p. 1868 - 1873
(2020/03/03)
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- Iron-Catalyzed Tunable and Site-Selective Olefin Transposition
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The catalytic isomerization of C-C double bonds is an indispensable chemical transformation used to deliver higher-value analogues and has important utility in the chemical industry. Notwithstanding the advances reported in this field, there is compelling demand for a general catalytic solution that enables precise control of the C═C bond migration position, in both cyclic and acyclic systems, to furnish disubstituted and trisubstituted alkenes. Here, we show that catalytic amounts of an appropriate earth-abundant iron-based complex, a base and a boryl compound, promote efficient and controllable alkene transposition. Mechanistic investigations reveal that these processes likely involve in situ formation of an iron-hydride species which promotes olefin isomerization through sequential olefin insertion/β-hydride elimination. Through this strategy, regiodivergent access to different products from one substrate can be facilitated, isomeric olefin mixtures commonly found in petroleum-derived feedstock can be transformed to a single alkene product, and unsaturated moieties embedded within linear and heterocyclic biologically active entities can be obtained.
- Yu, Xiaolong,Zhao, Haonan,Li, Ping,Koh, Ming Joo
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supporting information
p. 18223 - 18230
(2020/12/04)
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- Migratory Hydrogenation of Terminal Alkynes by Base/Cobalt Relay Catalysis
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Migratory functionalization of alkenes has emerged as a powerful strategy to achieve functionalization at a distal position to the original reactive site on a hydrocarbon chain. However, an analogous protocol for alkyne substrates is yet to be developed. Herein, a base and cobalt relay catalytic process for the selective synthesis of (Z)-2-alkenes and conjugated E alkenes by migratory hydrogenation of terminal alkynes is disclosed. Mechanistic studies support a relay catalytic process involving a sequential base-catalyzed isomerization of terminal alkynes and cobalt-catalyzed hydrogenation of either 2-alkynes or conjugated diene intermediates. Notably, this practical non-noble metal catalytic system enables efficient control of the chemo-, regio-, and stereoselectivity of this transformation.
- Liu, Bingxue,Liu, Qiang,Liu, Xufang
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supporting information
p. 6750 - 6755
(2020/03/13)
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- Controllable Isomerization of Alkenes by Dual Visible-Light-Cobalt Catalysis
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We report herein that thermodynamic and kinetic isomerization of alkenes can be accomplished by the combination of visible light with Co catalysis. Utilizing Xantphos as the ligand, the most stable isomers are obtained, while isomerizing terminal alkenes over one position can be selectively controlled by using DPEphos as the ligand. The presence of the donor–acceptor dye 4CzIPN accelerates the reaction further. Transformation of exocyclic alkenes into the corresponding endocyclic products could be efficiently realized by using 4CzIPN and Co(acac)2 in the absence of any additional ligands. Spectroscopic and spectroelectrochemical investigations indicate CoI being involved in the generation of a Co hydride, which subsequently adds to alkenes initiating the isomerization.
- Meng, Qing-Yuan,Schirmer, Tobias E.,Katou, Kousuke,K?nig, Burkhard
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p. 5723 - 5728
(2019/04/03)
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- Catalytic protodeboronation of pinacol boronic esters: Formal anti-Markovnikov hydromethylation of alkenes
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Pinacol boronic esters are highly valuable building blocks in organic synthesis. In contrast to the many protocols available on the functionalizing deboronation of alkyl boronic esters, protodeboronation is not well developed. Herein we report catalytic protodeboronation of 1°, 2° and 3° alkyl boronic esters utilizing a radical approach. Paired with a Matteson-CH2-homologation, our protocol allows for formal anti-Markovnikov alkene hydromethylation, a valuable but unknown transformation. The hydromethylation sequence was applied to methoxy protected (-)-Δ8-THC and cholesterol. The protodeboronation was further used in the formal total synthesis of δ-(R)-coniceine and indolizidine 209B.
- Clausen, Florian,Kischkewitz, Marvin,Bergander, Klaus,Studer, Armido
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p. 6210 - 6214
(2019/06/27)
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- Cobalt-Catalyzed Regioselective Olefin Isomerization under Kinetic Control
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Olefin isomerization is a significant transformation in organic synthesis, which provides a convenient synthetic route for internal olefins and remote functionalization processes. The selectivity of an olefin isomerization process is often thermodynamically controlled. Thus, to achieve selectivity under kinetic control is very challenging. Herein, we report a novel cobalt-catalyzed regioselective olefin isomerization reaction. By taking the advantage of fine-tunable NNP-pincer ligand structures, this catalytic system features high kinetic control of regioselectivity. This mild catalytic system enables the isomerization of 1,1-disubstituted olefins bearing a wide range of functional groups in excellent yields and regioselectivity. The synthetic utility of this transformation was highlighted by the highly selective preparation of a key intermediate for the total synthesis of minfiensine. Moreover, a new strategy was developed to realize the selective monoisomerization of 1-alkenes to 2-alkenes dictated by installing substituents on the γ-position of the double bonds. Mechanistic studies supported that the in situ generated Co-H species underwent migratory insertion of double bond/β-H elimination sequence to afford the isomerization product. The less hindered olefin products were always preferred in this cobalt-catalyzed olefin isomerization due to an effective ligand control of the regioselectivity for the β-H elimination step.
- Liu, Xufang,Zhang, Wei,Wang, Yujie,Zhang, Ze-Xin,Jiao, Lei,Liu, Qiang
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supporting information
p. 6873 - 6882
(2018/05/30)
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- Umpolung of Carbonyl Groups as Alkyl Organometallic Reagent Surrogates for Palladium-Catalyzed Allylic Alkylation
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Palladium-catalyzed allylic alkylation of nonstabilized carbon nucleophiles is difficult and remains a major challenge. Reported here is a highly chemo- and regioselective direct palladium-catalyzed C-allylation of hydrazones, generated from carbonyls, as a source of umpolung unstabilized alkyl carbanions and surrogates of alkyl organometallic reagents. Contrary to classical allylation techniques, this umpolung reaction utilizes hydrazones prepared not only from aryl aldehydes but also from alkyl aldehydes and ketones as renewable feedstocks. This strategy complements the palladium-catalyzed coupling of unstabilized nucleophiles with allylic electrophiles by providing an efficient and selective catalytic alternative to the traditional use of highly reactive alkyl organometallic reagents.
- Zhu, Dianhu,Lv, Leiyang,Li, Chen-Chen,Ung, Sosthene,Gao, Jian,Li, Chao-Jun
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supporting information
p. 16520 - 16524
(2018/11/23)
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- Stereodivergent Olefination of Enantioenriched Boronic Esters
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A stereodivergent coupling reaction between vinyl halides and boronic esters is described. This coupling process proceeds without a transition-metal catalyst, instead proceeding by electrophilic selenation or iodination of a vinyl boronate complex followed by stereospecific syn or anti elimination. Chiral, nonracemic boronic esters could be coupled with complete enantiospecificity. The process enables the highly stereoselective synthesis of either the E or Z alkene from a single isomer of a vinyl coupling partner.
- Armstrong, Roly J.,García-Ruiz, Cristina,Myers, Eddie L.,Aggarwal, Varinder K.
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p. 786 - 790
(2017/01/14)
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- An Agostic Iridium Pincer Complex as a Highly Efficient and Selective Catalyst for Monoisomerization of 1-Alkenes to trans-2-Alkenes
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A unique Ir complex (tBuNCCP)Ir with the pyridine–phosphine pincer as the sole ligand, featuring a dual agostic interaction between the Ir and two σ C?H bonds from a tBu substituent, has been prepared. This complex exhibits exceptionally high activity and excellent regio- and stereoselectivity for monoisomerization of 1-alkenes to trans-2-alkenes with wide functional-group tolerance. Reactions can be performed in neat reactant on a more than 100 gram scale using 0.005 mol % catalyst loadings with turnover numbers up to 19000.
- Wang, Yulei,Qin, Chuan,Jia, Xiangqing,Leng, Xuebing,Huang, Zheng
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supporting information
p. 1614 - 1618
(2017/02/05)
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- Chemo- and regioselective reductive transposition of allylic alcohol derivatives via iridium or rhodium catalysis
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We report highly chemo- and regioselective reductive transpositions of methyl carbonates to furnish olefin products with complementary regioselectivity to that of established Pd-catalysis. These Rh- and Ir-catalysed transformations proceed under mild conditions and enable selective deoxygenation in the presence of functional groups that are susceptible to reduction by metal hydrides.
- Lundgren, Rylan J.,Thomas, Bryce N.
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supporting information
p. 958 - 961
(2016/01/20)
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- An alternative mechanism for the cobalt-catalyzed isomerization of terminal alkenes to (Z)-2-alkenes
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The cobalt-catalyzed selective isomerization of terminal alkenes to the thermodynamically less-stable (Z)-2-alkenes at ambient temperatures takes place by a new mechanism involving the transfer of a hydrogen atom from a Ph2PH ligand to the starting material and the formation of a phosphenium complex, which recycles the Ph2PH complex through a 1,2-H shift.
- Schmidt, Anastasia,N??dling, Alexander R.,Hilt, Gerhard
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supporting information
p. 801 - 804
(2015/03/04)
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- Z -selective alkene isomerization by high-spin cobalt(II) complexes
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The isomerization of simple terminal alkenes to internal isomers with Z-stereochemistry is rare, because the more stable E-isomers are typically formed. We show here that cobalt(II) catalysts supported by bulky β-diketiminate ligands have the appropriate kinetic selectivity to catalyze the isomerization of some simple 1-alkenes specifically to the 2-alkene as the less stable Z-isomer. The catalysis proceeds via an "alkyl" mechanism, with a three-coordinate cobalt(II) alkyl complex as the resting state. β-Hydride elimination and [1,2]-insertion steps are both rapid, as shown by isotopic labeling experiments. A steric model explains the selectivity through a square-planar geometry at cobalt(II) in the transition state for β-hydride elimination. The catalyst works not only with simple alkenes, but also with homoallyl silanes, ketals, and silyl ethers. Isolation of cobalt(I) or cobalt(II) products from reactions with poor substrates suggests that the key catalyst decomposition pathways are bimolecular, and lowering the catalyst concentration often improves the selectivity. In addition to a potentially useful, selective transformation, these studies provide a mechanistic understanding for catalytic alkene isomerization by high-spin cobalt complexes, and demonstrate the effectiveness of steric bulk in controlling the stereoselectivity of alkene formation.
- Chen, Chi,Dugan, Thomas R.,Brennessel, William W.,Weix, Daniel J.,Holland, Patrick L.
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supporting information
p. 945 - 955
(2014/02/14)
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- Simple protocol for enhanced (E)-selectivity in Julia-Kocienski reaction
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A short and efficient Julia-Kocienski olefination protocol, based upon the use of chelating agents (18-crown-6 or TDA-1 for K+; 12-crown-4 or HMPA for Li+), was developed. This protocol enhances the (E)-selectivity of the reaction an
- Pospí?il, Ji?í
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supporting information; experimental part
p. 2348 - 2352
(2011/05/16)
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- Gold-catalyzed intramolecular hydroarylation of olefins. Scope evaluation and preliminary mechanistic studies
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We report a gold-catalyzed intramolecular hydroarylation of unactivated olefins using a combination of AuCl3/AgOTf as the catalytic system affording dihydrobenzopyrans, tetralins and tetrahydroquinolines in good yields. For our preliminary mechanistic studies, we have investigated the kinetic isotope effects with deuterated arene compounds and found that this catalytic hydroarylation is consistent with an electrophilic aromatic substitution process.
- Jean, Mickael,Van De Weghe, Pierre
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supporting information; experimental part
p. 3509 - 3513
(2011/07/09)
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- A stereospecific palladium-catalyzed route to monoalkyl diazenes for mild allylic reduction
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(Chemical Equation Presented) One step beyond: The first single-step stereospecific transition-metal-catalyzed conversion of allylic electrophiles into monoalkyl diazenes is described. This synthesis of allylic monoalkyl diazenes offers a new strategy for asymmetric synthesis by the reduction of optically active substrates or the use of chiral catalyst systems. Sensitive substrates are reduced in a highly selective manner. Ar = 2-NO2C 6H2.
- Movassaghi, Mohammad,Ahmad, Omar K.
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body text
p. 8909 - 8912
(2009/05/26)
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- Copper catalyzed magnesium-Barbier reaction for γ-selective alkyl-allyl coupling
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CuCN catalyzed alkyl-allyl coupling under magnesium-Barbier conditions occurs regioselectively and affords predominantly the γ-products in good to high yields. This one-pot CuCN catalyzed reaction utilising Mg, an alkyl halide and an allylic substrate in THF at room temperature provides an easy alternative to the classical CuCN catalyzed γ-allylation of alkyl Grignard reagents.
- Erdik, Ender,Ko?o?lu, Melike
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p. 4211 - 4214
(2008/02/08)
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- Superbase-promoted rearrangement of oxiranes to cyclopropanes
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Aryl- and alkenyl substituted oxiranes, when submitted to treatment with superbasic reagents, undergo a highly regio- and stereoselective rearrangement leading to cyclopropylmethanol derivatives. The process can also be applied to mono- and dihydroxy subs
- Mordini, Alessandro,Peruzzi, Daniela,Russo, Francesco,Valacchi, Michela,Reginato, Gianna,Brandi, Alberto
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p. 3349 - 3360
(2007/10/03)
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- From vinyl sulfides, sulfoxides and sulfones to vinyl zirconocene derivatives
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An easy and straightforward new method for the preparation of sp 2 zirconocene derivatives from a wide range of heterosubstituted alkenes such as vinyl sulfides, sulfoxides and sulfones is described. In all cases, a complete isomerization of the stereochemistry is observed and only the E-isomer is obtained. The reactivity of the resulting vinylic organometallic can be increased by a transmetalation reaction into organocopper, organozinc or organopalladium species and, therefore, several carbon-carbon formation were easily realized.
- Farhat, Shahera,Zouev, Irena,Marek, Ilan
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p. 1329 - 1337
(2007/10/03)
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- Enantioface-selective palladium-catalyzed silaboration of allenes via double asymmetric induction
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Enantioenriched β-borylallylsilanes were synthesized by palladium-catalyzed enantioface-selective addition of the silicon-boron bond to terminal allenes using a palladium catalyst possessing a chiral monodentate phosphine ligand. Use of a silylborane bear
- Suginome, Michinori,Ohmura, Toshimichi,Miyake, Yoshihiro,Mitani, Shin'ichirou,Ito, Yoshihiko,Murakami, Masahiro
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p. 11174 - 11175
(2007/10/03)
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- Stereochemistry of Carbenic 1,2-Vinyl Shifts
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Various 1-phenylbut-3-enylidenes, (Ph)CCR2CH=CHR', were generated thermally and photolytically from tosylhydrazone (diazo) precursors. 1,2-Vinyl shifts, leading to 1,3-dienes, R′CH=CHC(Ph)=CR2, were found to predominate over γ-C-H insertion (R = Me) and to compete with 1,2-H shifts (R = H). Intramolecular addition to the double bond was detected in the case of R = R′ = Me. The resulting bicyclobutane is thermally stable and does not mediate the vinyl shift. Stereospecific migration of 1-propenyl groups (R′ = Me), with retention of configuration, was observed on thermolysis and direct photolysis of appropriate substrates. These data exclude the intervention of a triplet diradical and point to vinyl migration in the singlet manifold. Benzophenone-sensitized generation of the carbenes led to partial stereomutation but did not provide conclusive evidence for a triplet rearrangement (isomerization of the diene products could not be avoided under these conditions).
- Kirmse, Wolfgang,Kopannia, Siegfried
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p. 1178 - 1184
(2007/10/03)
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- Integrated chemical process. One-pot preparation of olefins by alkylation and desulfonylation
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Integration of alkylation of allylic sulfone and reductive desulfonylation under basic conditions effects one-pot synthesis of various olefins.
- Orita, Akihiro,Watanabe, Akihiro,Otera, Junzo
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p. 1025 - 1026
(2007/10/03)
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- An efficient method for the reductive transposition of allylic alcohols
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The Mitsunobu reaction of allylic alcohols with o- nitrobenzenesulfonylhydrazine (NBSH) as nucleophile proceeds at -30 °C with invertive displacement; warming the resultant N-allylic sulfonylhydrazine derivative to 23 °C then leads to allylic diazene formation followed by sigmatropic elimination of dinitrogen. This one-step method for reductive 1,3-transposition is shown to be efficient and highly regio- and stereocontrolled within a wide range of allylic alcohol substrates.
- Myers, Andrew G.,Zheng, Bin
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p. 4841 - 4844
(2007/10/03)
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- A Bridged Tetrahydrophosphole Ylide Derived from 9-Phenylphosphabicyclononane: A Reagent for E-Selective Wittig Reactions
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The bicyclic ylide 4 reacts with aldehydes to afford the E-alkenes.Selectivity is 94 - 6percent E for unbranched aldehydes, but the selectivity decreases with increasing α-branching.Ylide 4 is the first E-selective, nonstabilized ylide that allows efficient utilization of the P-alkyl substituent.
- Vedejs, E.,Peterson, M. J.
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p. 1985 - 1986
(2007/10/02)
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- Mechanism of the Wittig Reaction: The Role of Substituents at Phosphorus
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The variation in Wittig reaction stereochemistry is attributed to a dominant kinetic control in nearly all cases.Formation of cis or trans oxaphosphetanes is the decisive step, and this occurs by an asynchronous cycloaddition.An interplay of 1, 2 and 1, 3
- Vedejs, E.,Marth, C. F.
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p. 3948 - 3958
(2007/10/02)
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- DBP YLDES: WITTIG REAGENTS FOR SYNTHESIS OF E-ALKENES FROM ALDEHYDES
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Phosphorus yldes based on the dibenzophosphole (DPP) ring system convert aldehydes into trans-disubstituted oxaphosphetanes with good to excellent selectivity.Decomposition at 70-110 deg C affords alkenes with E:Z rations from 6:1 to > 100:1.
- Vedejs, E.,Marth, C.
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p. 3445 - 3448
(2007/10/02)
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- The Stereocontrolled Horner-Wittig Reaction: Synthesis of Disubstituted Alkenes
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Addition of the lithium derivatives of phosphine oxides Ph2P(O)CH2R1 to aldehydes gives erythro adducts (11) with good stereoselectivity.Reduction of α-diphenylphosphinoyl ketones (12) gives threo adducts (11) with even better stereoselectivity.Purification by flash chromatography and/or crystallisation followed by elimination of Ph2PO2 gives pure Z- or E-alkenes with high material conversion.Explanations are offered for the stereoselectivities, conditions defined for full stereochemical control, and guidelines suggested for approaches to a given alkene.
- Buss, Antony D.,Warren, Stuart
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p. 2307 - 2326
(2007/10/02)
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- Gas-Phase Elimination Kinetics of ω-Phenylalkyl Chlorides. Participation of the Phenyl Ring
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The kinetics of the gas-phase dehydrochlorination of several phenylalkyl chlorides were determined in a static system, seasoned with allyl bromide, and in the presence of the free radical inhibitor propene.The working temperature and pressure ranges were 398.8-480.6 deg C and 66-202 torr, respectively.The reactions are homogeneous, unimolecular, and follow a first-order rate law.The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for 3-chloro-1-phenylpropane, log k1 (s-1) = (13.99 +/- 0.26) - (238.4 +/- 3.5) kJ*mol-1; for 4-chloro-1-phenylbutane, log k1 (s-1) = (13.07 +/- 0.43) - (220.5 +/- 5.8) kJ*mol-1 (2.303RT)-1; and for 5-chloro-1-phenylpentane, log k1 (s-1) = (13.75 +/- 0.36) - (231.2 +/- 4.9) kJ*mol-1 (2.303RT)-1.When the rates of HCl elimination among each of the phenylalkyl chlorides are compared with those for the coresponding unsubstituted alkyl chloride, participation of the C6H5 group at the 3 position is more favored, while that at the 5 and 6 positions is rather weak.Participation of C6H5 group at the 4 position is apparently absent.
- Chuchani, Gabriel,Rotinov, Alexandra,Martin, Ignacio
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p. 551 - 552
(2007/10/02)
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- Low-temperature characterization of the intermediates in the Wittig reaction
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Nonstabilized salt-free ylides react with aldehydes and nonhindered or strained ketones at -78°C to give oxaphosphetanes. The Wittig intermediates can be observed by 31P and 1H NMR techniques. In the presence of LiBr, betaine-lithium bromide adducts often precipitate from solution. The oxaphosphetane from PhCHO + CH2=PPh3 reacts rapidly with LiBr to give a betaine·LiBr adduct, and the corresponding salt Ph3P+CH2CHOHPh Br- reacts with KH at -40°C to form the oxaphosphetane. No salt-free betaine has been detected. Lithium bromide is shown to decrease cis selectivity (CH3CH=PPh3 + PhCH2CH2CHO) in the condensation step and not by oxaphosphetane equilibration. Oxaphosphetane reversal to ylide + aldehyde is confirmed for aryl aldehydes but not for aliphatic aldehydes or ketones according to three types of crossover experiments. Rationales for cis selectivity of aldehyde-ylide reactions are discussed. A "crisscrossed" cycloaddition rationale is proposed, aldehyde and ylide planes tilted toward an orthogonal arrangement to minimize steric interactions, to explain cis-alkene formation. Other transition-state geometries having carbonyl and ylide planes roughly parallel are considered more likely for trans-olefin formation or for Wittig reactions of ketones.
- Vedejs,Meier,Snoble
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p. 2823 - 2831
(2007/10/02)
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