- CHEMICAL EVIDENCE FOR STABILIZATION OF ELECTRICALLY NEUTRAL DIVALENT CARBON BY POLAR SOLVENTS
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Benzylhalocarbene generated in non-polar solvent is trapped readily by alkene, but the intermolecular process comes to compete poorly with the intramolecular process as the solvent polarity is increased.
- Tomioka, Hideo,Hayashi, Norihiro,Izawa, Yasuji
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- Regio- and stereoselective synthesis of bromoalkenes by homolytic hydrobromination of alkynes with hydrogen bromide
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Homolytic hydrobromination of terminal and internal alkynes with a commercially available solution of hydrogen bromide in acetic acid has been investigated for regio- and stereoselective synthesis of bromoalkenes. Under an aerobic atmosphere at room temperature, the reaction of ethynylarenes with a small excess of HBr efficiently gave (2-bromoethenyl)arenes with good to high E-selectivity. (Alk-1-ynyl)arenes, or internal alkynes bearing both phenyl and alkyl groups at the sp-carbons also underwent the air-initiated hydrobromination to exhibit high Z-selectivity under kinetic conditions using a half equivalent of HBr.
- Kumaki, Wataru,Kinoshita, Hidenori,Miura, Katsukiyo
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- Nickel-Catalyzed, Regio- and Enantioselective Benzylic Alkenylation of Olefins with Alkenyl Bromide
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A NiH-catalyzed migratory hydroalkenylation reaction of olefins with alkenyl bromides has been developed, affording benzylic alkenylation products with high yields and excellent chemoselectivity. The mild conditions of the reaction preclude olefinic products from undergoing further isomerization or subsequent alkenylation. Catalytic enantioselective hydroalkenylation of styrenes was achieved by using a chiral bisoxazoline ligand.
- Liu, Jiandong,Gong, Hegui,Zhu, Shaolin
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supporting information
p. 4060 - 4064
(2020/12/25)
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- Selective Rhodium-Catalyzed Hydroformylation of Terminal Arylalkynes and Conjugated Enynes to (Poly)enals Enabled by a π-Acceptor Biphosphoramidite Ligand
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The hydroformylation of terminal arylalkynes and enynes offers a straightforward synthetic route to the valuable (poly)enals. However, the hydroformylation of terminal alkynes has remained a long-standing challenge. Herein, an efficient and selective Rh-catalyzed hydroformylation of terminal arylalkynes and conjugated enynes has been achieved by using a new stable biphosphoramidite ligand with strong π-acceptor capacity, which affords various important E-(poly)enals in good yields with excellent chemo- and regioselectivity at low temperatures and low syngas pressures.
- Zhao, Jiangui,Zheng, Xueli,Tao, Shaokun,Zhu, Yuxin,Yi, Jiwei,Tang, Songbai,Li, Ruixiang,Chen, Hua,Fu, Haiyan,Yuan, Maolin
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supporting information
p. 6067 - 6072
(2021/08/16)
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- The hydrodebromination of 1,1-dibromoalkenes via visible light catalysis
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Vinyl bromides are versatile synthetic intermediates and widely applied in organic synthesis and pharmaceuticals. Herein, a hydrodebromination reaction of 1,1-dibromoalkenes was established via visible light catalysis. A variety of structurally different vinyl bromides were obtained in moderate to excellent yields.
- Sun, Wencheng,Teng, Qiaoling,Cheng, Dongping,Li, Xiaonian,Xu, Xiaoliang
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supporting information
(2019/12/05)
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- Dual nickel- and photoredox-catalyzed reductive cross-coupling of aryl vinyl halides and unactivated tertiary alkyl bromides
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A novel reductive cross-coupling of aryl vinyl halides and unactivated tertiary alkyl bromides has been realized via photoredox/nickel dual catalysis to produce vinyl arene derivatives bearing all-carbon quaternary centers with excellent E-selectivity. A stoichiometric metal reductant could be avoided by employing commercially available N,N,N′,N′-tetramethylethylenediamine (TMEDA) as the terminal reductant.
- Yu, Weijie,Chen, Long,Tao, Jiasi,Wang, Tao,Fu, Junkai
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supporting information
p. 5918 - 5921
(2019/05/27)
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- Construction of Phenanthrenes and Chrysenes from β-Bromovinylarenes via Aryne Diels-Alder Reaction/Aromatization
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A highly efficient transition-metal-free general method for the synthesis of polycyclic aromatic hydrocarbons like phenanthrenes and chrysenes (and tetraphene) from β-bromovinylarenes and arynes has been developed. The reactions proceed via an aryne Diels-Alder (ADA) reaction, followed by a facile aromatization. This is the first report on direct construction of chrysenes (and tetraphene) using the ADA approach. Unlike the literature method which is limited to only 9/10-substituted derivatives, this method gives access to a wide variety of functionalized phenanthrenes.
- Singh, Vikram,Verma, Ram Subhawan,Khatana, Anil K.,Tiwari, Bhoopendra
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supporting information
p. 14161 - 14167
(2019/10/28)
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- Transition metal free large-scale synthesis of aromatic vinyl chlorides from aromatic vinyl carboxylic acids using bleach
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While continuing our research on Hunsdiecker reaction, we came across an interesting application of bleach, sodium hypochlorite (NaOCl) for decarboxylative chlorination reaction. The reaction is easily scaled up to 10 mmol. The reaction has good tolerance towards wide variety of functional groups. The reaction has mild conditions and gave relatively high chemical yield of the desired product.
- Hatvate, Navnath T.,Takale, Balaram S.,Ghodse, Shrikant M.,Telvekar, Vikas N.
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p. 3892 - 3894
(2018/10/02)
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- Organic electroluminescent material and organic light emitting device
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The invention provides an organic electroluminescent material and an organic light emitting device and belongs to the technical field of organic photoelectric materials. The structure of the organic electroluminescent material contains a structure similar to carbazole; and by linking more conjugated groups, a glass transition temperature of the organic electroluminescent material can be effectively raised, the possible crystallization in use is reduced, and the ability of transporting holes is stronger. Compared with the prior art, the organic electroluminescent material is applied to the organic light emitting device and has relatively high light emitting efficiency and longer service life when being particularly used as a light emitting material.
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Paragraph 0037-0038
(2018/03/25)
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- Nickel-Catalyzed Reductive Cross-Coupling of Vinyl Bromides with Unactivated Alkyl Halides
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The use of pyridine as the sole ligand for the reductive vinylation of unactivated secondary alkyl halides under Ni-catalyzed conditions has been developed. Both alkyl- and aryl-substituted vinyl bromides are suitable, in which alkyl-decorated α-alkenyl bromides resulted in the α-products in good results.
- Gu, Jun,Qiu, Canbin,Lu, Wenbin,Qian, Qun,Lin, Kunhua,Gong, Hegui
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supporting information
p. 1867 - 1873
(2017/04/06)
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- Piperidine-appended imidazolium ionic liquid as task-specific basic-IL for Suzuki and Heck reactions and for tandem Wittig-Suzuki, Wittig-Heck, Horner-Emmons-Suzuki, and Horner-Emmons-Heck protocols
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Facile, high yielding, one-pot methods for the synthesis of a library of diversely substituted bi-aryls, diarylethenes, and aryl-enoates, via Suzuki and Heck reactions, and by sequential Wittig-Suzuki, Wittig-Heck, Horner-Emmons-Suzuki, and Horner-Emmons-Heck reactions are reported. The reactions employ piperidine-appended imidazolium ionic liquid [PAIM][NTf2] as a task-specific basic-IL, butyl-methyl-imidazolium ionic liquid [BMIM][X] (X?=?PF6, BF4) as solvent, and catalytic amounts of Pd(OAc)2 with no other additives. Wittig and Horner-Emmons reactions are effected by reacting substituted benzaldehydes with 4-bromobenzyl-PPh3 (or bromomethyl-PPh3) phosphonium salts, or diethylphosphonate with bromobenzaldehydes respectively, to form the corresponding ethenes. Subsequent cross-coupling reactions are accomplished by addition of aryl-boronic acid or phenyl-ethenes along with Pd(OAc)2 to bring about the aforementioned hyphenated transformations. The feasibility to perform double-olefination via Wittig and Horner-Emmons reactions with dialdehydes to form highly conjugated bis-styryl and bis-enoate compounds is also shown. The [BMIM][X] solvent is recycled and reused.
- Savanur, Hemantkumar M.,Kalkhambkar, Rajesh G.,Laali, Kenneth K.
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p. 150 - 161
(2017/06/30)
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- ANTI-HIV COMPOUNDS
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This invention provides, among other things, tetrahydroisoquinolines useful for treating viral infections, pharmaceutical formulations containing such compounds, as well as methods of inhibiting the replication of a virus, such as HIV, or treating a disease, such as AIDS.
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Paragraph 0300; 0412
(2016/07/05)
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- Pd-Catalyzed C(sp3)-C(sp2) cross-coupling of Y(CH2SiMe3)3(THF)2 with vinyl bromides and triflates
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Pd-Catalyzed C(sp3)-C(sp2) cross-coupling of Y(CH2SiMe3)3(THF)2 with vinyl bromides and triflates has been developed for efficient synthesis of various allyltrimethylsilanes. The cross-coupling reaction was conducted at room temperature with low catalyst loading of either Pd(PPh3)4 or Pd(PPh3)2Cl2, and exhibited high efficiency and a broad substrate scope. In combination with the cross-coupling by the Lewis-acid catalyzed Hosomi-Sakurai reaction, a novel three-component one-pot cascade reaction was then accomplished to deliver homoallylic alcohols and ethers with high regioselectivity and diastereoselectivity. The three-component reaction defined the yttrium complex as a novel one-carbon synthon, which could either trigger bifunctionalization of alkenes or link two electrophiles and would find applications in organic synthesis.
- Cai, Guilong,Zhou, Zhibing,Wu, Wenchao,Yao, Bo,Zhang, Shaowen,Li, Xiaofang
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supporting information
p. 8702 - 8706
(2016/10/03)
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- Ultrasonically Assisted Decarboxylative Bromination of α,β-Unsaturated Carboxylic Acids under Vilsmeier-Haack Conditions
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An efficient method for decarboxylative bromination of cinnamic acids (α,β-unsaturated carboxylic acids or 3-arylpropenoic acids) was achieved under relatively mild conditions using Vilsmeier-Haack reagent and KBr in acetonitrile media. Vilsmeier-Haack reagent is prepared by using 1:1 ratio of oxychloride (SOCl2 or POCl3) and DMF under chilled condition. Ultrasonically assisted reactions underwent smoothly with highly significant rate enhancements and afforded bromostyrenes as products in very good yields even though the reactions were too sluggish.
- Kumar, M. Satish,Rajanna,Venkanna,Venkateswarlu,Sudhakar Chary
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p. 642 - 646
(2015/12/26)
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- Experimental and theoretical studies on nickel-zinc-catalyzed cross-coupling of gem-dibromoalkenes with P(O)-H compounds
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A new stereoselective one-pot protocol for the preparation of E-alkenyl-phosphorus compounds under catalysis of an inexpensive nickel-zinc catalyst system has been developed, which provides a potential useful method for C-P bond formation. 31P NMR spectrum and density functional theory calculations were performed to study the reaction mechanism.
- Liu, Liu,Lv, Ye,Wu, Yile,Gao, Xiang,Zeng, Zhiping,Gao, Yuxing,Tang, Guo,Zhao, Yufen
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p. 2322 - 2326
(2014/01/06)
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- Transition-metal free synthesis of diaryl vinyl selenides: A simple synthetic approach with high selectivity
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A simple, highly efficient synthetic protocol is developed for the synthesis of unsymmetrical diaryl vinyl selenides from diaryldiselenide and β-bromo styrene under transition-metal free conditions in N,N′-dimethyl propylene urea and 130 °C to afford high yields and excellent selectivities. This method provides a new strategy to fabricate a wide variety of important substituted molecular skeletons and an alternative to conventionally used metal salts, additives, and ligands.
- Mohan, Balaji,Hwang, Sori,Woo, Hyunje,Park, Kang Hyun
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supporting information
p. 2699 - 2702
(2014/04/17)
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- Palladium(0)-catalyzed cross-coupling of 1,1-diboronates with vinyl bromides and 1,1-dibromoalkenes
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Palladium-catalyzed cross-coupling reactions of 1,1-diboronates with vinyl bromides and dibromoalkenes were found to afford 1,4-dienes and allenes, respectively. These reactions utilize the high reactivities of both 1,1-diboronates and allylboron intermediates generated in the initial coupling.
- Li, Huan,Zhang, Zhikun,Shangguan, Xianghang,Huang, Shan,Chen, Jun,Zhang, Yan,Wang, Jianbo
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supporting information
p. 11921 - 11925
(2015/01/09)
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- A green hunsdiecker reaction of cinnamic acids
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Tribromo- and trichloroisocyanuric acids react with cinnamic acids in NaOH/H2O/Et2O at room temperature to produce (E)-2-halostyrenes regioselectively in 25-95percent yield. Mechanism studies using Hammett correlations and DFT (density functional theory) calculations have shown that this reaction has as rate determining step the electrophilic addition of chlorine atom to the double bond.
- Sodre?, Leonardo R.,Esteves, Pierre M.,De Mattos, Marcio C. S.
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p. 212 - 218
(2013/05/08)
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- Formation of quaternary stereogenic centers by copper-catalyzed asymmetric conjugate addition reactions of alkenylaluminums to trisubstituted enones
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Alkenylaluminums undergo asymmetric copper-catalyzed conjugate addition (ACA) to β-substituted enones allowing the formation of stereogenic all-carbon quaternary centers. Phosphinamine-copper complexes proved to be particularly active and selective compared with phosphoramidite ligands. After extensive optimization, high enantioselectivities (up to 96 % ee) were obtained for the addition of alkenylalanes to β-substituted enones. Two strategies for the generation of the requisite alkenylaluminums were explored allowing for the introduction of aryl- and alkyl-substituted alkenyl nucleophiles. Moreover, alkyl-substituted phosphinamine (SimplePhos) ligands were identified for the first time as highly efficient ligands for the Cu-catalyzed ACA. Chiral synthesis made easy: The copper-catalyzed conjugate addition of alkenylaluminum reagents to 3-substituted cyclic enones allows for the formation of all-carbon chiral quaternary centers (see scheme; CuTC=copper(I) thiophene-2-carboxylate). Chiral phosphinamine (SimplePhos) ligands were found to be highly efficient for this transformation.
- Mueller, Daniel,Alexakis, Alexandre
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supporting information
p. 15226 - 15239
(2013/11/06)
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- Nickel(II)-magnesium-catalyzed cross-coupling of 1,1-dibromo-1-alkenes with diphenylphosphine oxide: One-pot synthesis of (E)-1-alkenylphosphine oxides or bisphosphine oxides
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A novel nickel(II)-magnesium-mediated cross-coupling of diphenylphosphine oxide with a variety of 1,1-dibromo-1-alkenes has been developed, which provides a powerful and general methodology for the stereoselective synthesis of various (E)-1-alkenylphosphine oxides or bisphosphine oxides, with operational simplicity of the procedure, good to high yields and broad substrate applicability. Mechanistic studies reveal that the reaction might involve a Hirao reduction, cross-coupling and Michael addition. Copyright
- Liu, Liu,Wang, Yulei,Zeng, Zhiping,Xu, Pengxiang,Gao, Yuxing,Yin, Yingwu,Zhao, Yufen
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p. 659 - 666
(2013/04/10)
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- Bromoform activation. TiCl4-Mg-promoted CHBr2 - and CBr3- transfer to a variety of aldehydes and ketones
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TiCl4-Mg can mediate addition of CHBr3 to a variety of aldehydes and ketones to form dibromomethyl carbinols and also be used to effect CBr3 transfer to carbonyl groups to form tribromomethyl carbinols. The successful application of TiCl4-Mg-promoted coupling of CHBr3 with various carbonyl compounds, especially in the case of highly enolizable ketones such as 2-indanone and β-tetralone, highlights the extraordinary reactivity and selectivity and the weakly basic nature of this system.
- Yan, Tu-Hsin,Chang, Su-Haur,Chang, Cheng-Ta,Lin, Chia-Kuan,Liu, Chien-Yu
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supporting information
p. 5802 - 5805
(2013/12/04)
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- Synthesis of acetylenes via dehydrobromination using solid anhydrous potassium phosphate as the base under phase-transfer conditions
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Phase-transfer catalyzed preparation of acetylenes from the corresponding vicinal dibromo compounds via double dehydrobromination using the mild solid base, anhydrous potassium phosphate, under very mild conditions is reported.
- Shenawi-Khalil, Sanaa,Sonavane, Sachin U.,Sasson, Yoel
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experimental part
p. 2295 - 2297
(2012/07/27)
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- Regioselective copper(I)-catalyzed C-H hydroxylation/C-S coupling: Expedient construction of 2-(styrylthio)phenols
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Regioselective copper(I)-catalyzed C-H hydroxylation/C-S coupling of aryl thiols with vinyl halides was developed. Starting from substituted aryl thiols and vinyl halides, various 2-(styrylthio)phenol derivatives were efficiently prepared. The application of the synthetic methodology to generate the bioactive organic intermediate was also exemplified.
- Xu, Run-Sheng,Yue, Lei,Pan, Yuan-Jiang
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experimental part
p. 5046 - 5052
(2012/08/07)
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- Synthesis of 2,3,4-trisubstituted pyrroles via a facile reaction of vinyl azides and tosylmethyl isocyanide
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A facile synthesis of polysubstituted pyrroles from tosylmethyl isocyanide (TOSMIC) and readily synthesized vinyl azides was developed. The reaction proceeded under mild conditions in the presence of base. 2-Tosyl-substituted pyrroles were obtained in moderate to good isolated yields. Additionally, a base-initiated one-pot pyrrole synthesis also was developed using carboxaldehydes, ethyl 2-azidoacetate, and TOSMIC.
- Chen, Wenteng,Shao, Jiaan,Li, Zhi,Giulianotti, Marc A.,Yu, Yongping
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body text
p. 214 - 221
(2012/03/07)
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- A simple microwave-assisted preparation of 2-bromo-1-alkenes from 1-alkynes using the LiBr-TMSCl-TEAB reagent system
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2-Bromo-1-alkenes are cleanly and conveniently generated in good yields and selectivities via microwave-assisted hydrobromination of 1-alkynes using a combination of lithium bromide (LiBr), chlorotrimethylsilane (TMSCl), and tetraethylammonium bromide (TEAB) in acetonitrile (MeCN).
- Bunrit, Anon,Ruchirawat, Somsak,Thongsornkleeb, Charnsak
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supporting information; experimental part
p. 3124 - 3127
(2011/06/26)
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- α-Selective Ni-catalyzed hydroalumination of aryl- and alkyl-substituted terminal alkynes: Practical syntheses of internal vinyl aluminums, halides, or boronates
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A method for Ni-catalyzed hydroalumination of terminal alkynes, leading to the formation of α-vinylaluminum isomers efficiently (>98% conv in 2-12 h) and with high selectivity (95% to >98% α), is described. Catalytic α-selective hydroalumination reactions proceed in the presence of a reagent (diisobutylaluminum hydride; dibal-H) and 3.0 mol % metal complex (Ni(dppp)Cl2) that are commercially available and inexpensive. Under the same conditions, but with Ni(PPh3)2Cl2, hydroalumination becomes highly β-selective, and, unlike uncatalyzed transformations with dibal-H, generates little or no alkynylaluminum byproducts. All hydrometalation reactions are reliable, operationally simple, and practical and afford an assortment of vinylaluminums that are otherwise not easily accessible. The derived α-vinyl halides and boronates can be synthesized through direct treatment with the appropriate electrophiles [e.g., Br 2 and methoxy(pinacolato)boron, respectively]. Ni-catalyzed hydroaluminations can be performed with as little as 0.1 mol % catalyst and on gram scale with equally high efficiency and selectivity.
- Gao, Fang,Hoveyda, Amir H.
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supporting information; experimental part
p. 10961 - 10963
(2010/09/17)
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- Copper-catalyzed intermolecular oxidative [3 + 2] cycloaddition between alkenes and anhydrides: A new synthetic approach to γ-lactones
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A new copper-catalyzed oxidative [3 + 2] cycloaddition of alkenes with anhydrides using oxygen as the sole oxidant to afford γ-lactones has been developed. This catalyzed cyclization process has a broad substrate scope and affords γ-lactones in good to excellent yields.
- Huang, Liangbin,Jiang, Huanfeng,Qi, Chaorong,Liu, Xiaohang
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supporting information; experimental part
p. 17652 - 17654
(2011/03/16)
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- Novel system for decarboxylative bromination of α,β-unsaturated carboxylic acids with diacetoxyiodobenzene
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A simple and mild method for the conversion of varieties of α,β-unsaturated carboxylic acids to the corresponding bromoalkenes using diacetoxyiodobenzene (IBD) in combination with tetraethyl-ammonium bromide (TEAB) at room temperature is discussed. Advantages of this system are short reaction time, easy work up and gave good to excellent yields.
- Fursule, Ravindra Abhykumar,Patil, Pravin Onkar,Shewale, Bharti Devaji,Kosalge, Satish Bhaskar,Deshmukh, Prashant Krishnarao,Patil, Dilip Ashok
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experimental part
p. 1243 - 1245
(2010/08/06)
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- Preparation of (Z)-1-halo-1-alkenes and (Z)-1-halo-2-alkoxy-1-alkenes using Cr(II/III) and Fe(0)
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Reduction of 1,1,1-trihaloalkanes by Cr(II) or Cr(III) regenerated by Fe(0) in moist tetrahydrofuran at room temperature stereoselectively generates (Z)-1-halo-1-alkenes and (Z)-1-halo-2-alkoxy-1-alkenes in good to excellent yields. Georg Thieme Verlag Stuttgart.
- Falck,He, Anyu,Bejot, Romain,Mioskowski, Charles
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p. 2652 - 2654
(2008/09/16)
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- Stereoselective synthesis of (E)-β-arylvinyl bromides by microwave-induced reaction of anti-3-aryl-2,3-dibromopropanoic acids using an AgOAc-AcOH system
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(E)-β-Arylvinyl bromides were stereoselectively prepared in high yields by microwave irradiation of the corresponding anti-3-aryl-2,3- dibromopropanoic acids in AcOH in the presence of AgOAc for 0.5-3.0 min. (E)-β-Arylvinyl bromides were stereoselectively prepared in high yields by microwave irradiation of the corresponding anti-3-aryl-2,3-dibromo-propanoic acids in AcOH in the presence of AgOAc for 0.5-3.0 min.
- Kuang, Chunxiang,Senboku, Hisanori,Tokuda, Masao
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p. 637 - 642
(2007/10/03)
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- Mild regioselective monobromination of activated aromatics and heteroaromatics with N-bromosuccinimide in tetrabutylammonium bromide
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Highly regioselective nuclear bromination of activated aromatic and heteroaromatic compounds has been accomplished using N-bromosuccinimide in tetrabutylammonium bromide. Pre-dominant para-selective monobromination of activated aromatics such as phenols and anilines, rate acceleration of bromination for moderately activated and less reactive substrates on addition of acidic montmorillonite K-10 clay, with or without microwave assistance, are the notable features of this protocol.
- Ganguly, Nemai C.,De, Prithwiraj,Dutta, Sanjoy
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p. 1103 - 1108
(2007/10/03)
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- Unexpected chemoselective debromination and reduction of 1,1-dibromo-1-alkenes mediated by samarium metal in methanol
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An unexpected samarium metal mediated chemoselective debromination and reduction of 1,1-dibromo-1-alkenes in methanol has been developed, which generates vinyl monobromides, alkenes, and alkanes respectively with appropriate molar ratio of samarium to 1,1-dibromo-1-alkene.
- Wang, Lei,Li, Pinhua,Xie, Yuanyuan,Ding, Yanbin
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p. 1137 - 1140
(2007/10/03)
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- Versatile Transformations of α,β-Dibromoesters and Ketones in Basic Media under Microwave Irradiation
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Depending on the reaction medium, α,β-dibromoesters under microwave irradiation may selectively lead to α-bromoalk-enes, to alkenes or to (E)-β-bromostyrenes. The corresponding ketones give selectively the α-bromoketones.
- Hamelin, Jack,Saoudi, Aicha,Benhaoua, Hadj
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p. 2185 - 2188
(2007/10/03)
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- Study of the mechanism of base induced dehydrobromination of trans-β-bromostyrene
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Observation that rates of dehydrobromination of trans-β-bromostyrene (1) and the Hofmann degradation of tetrabutyl ammonium cation depend on strength of base in different ways and that treatment of 1 with base results in fast abstraction of the β-proton imply the possibility that the dehydrobromination of 1 could proceed via α-elimination and Ph migration. In order to clarify this question, β-13C-labeled 1 was obtained and subjected to PTC dehydrobromination which proceeds without migration of Ph. The obtained results are consistent with an irreversible E1cB mechanism.
- Ma?kosza, Mieczys?aw,Chesnokov, Alexey A.
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p. 1995 - 2000
(2007/10/03)
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- Mechanism of dehydrobromination of 1,2-dibromo-1-phenylethane under conditions of phase-transfer catalysis
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Selective dehydrobromination of 1,2-dibromo-1-phenylethane to α-bromostyrene was effected under conditions of phase-transfer catalysis in systems containing KOH, toluene, and tetraalkylammonium bromides. The high selectivity of the catalytic systems originates from stabilization by lipophilic cation of the phase-transfer catalyst of a E1cb-like transition state in the E2 mechanism. In the presence of a catalytic amount of lipophilic alcohols, phenylacetylene was obtained. Substrate activation by alcohol molecules is explained by enhancement of the acceptor power of halogen atoms due to solvation and by increased mobility of hydrogen atoms.
- Suvorova,Panicheva,Mamontova,Belyatskii
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p. 957 - 962
(2007/10/03)
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- Photochemical generation of a primary vinyl cation from (E)-bromostyrene: Mechanisms of formation and reaction
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The photochemistry of (E)-bromostyrene was investigated to determine the nature of the product-forming intermediates and to clarify the mechanism of formation of vinylic cations and vinylic radicals. Both a cation- and a radical-derived product are formed, and the ionic origin of the former product is demonstrated by significant scrambling of the label, starting from specifically deuterated (E)-bromostyrene. MO calculations show that the isolated incipient primary vinyl cation is not a metastable species, but that specific interaction with a counterion in combination with a polar environment makes it metastable. The effects of variation of the wavelength of irradiation, solvent polarity, temperature, and isotopic substitution all agree with a mechanism of direct heterolytic C-Br bond cleavage producing an ion pair followed by formation of a radical pair via electron transfer. The vinylic cation is proposed to stem directly from the indirectly populated lowest excited singlet state of bromostyrene with an energy of activation of 6.7 kcal/mol. Branching between proton loss and electron transfer in the resulting ion pair determines the ratio of cation- to radical-derived product. The E/Z-isomerization occurs in a separate process and does not involve C-Br bond cleavage.
- Gronheid, Roel,Zuilhof, Han,Hellings, Mark G.,Cornelisse, Jan,Lodder, Gerrit
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p. 3205 - 3215
(2007/10/03)
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- The concerted addition of HBr to aryl alkynes; orthogonal pi bond selectivity
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In a weakly acidic solution, the addition of HBr to 1-phenylprop-1-yne produces predominantly the anti-Markovnikov product. In this paper, we consider five possible explanations for this behavior and conclude that the concerted addition is occurring on the acetylenic π bond orthogonal to the extended aromatic π system. The electronic effect of the distal methyl group and the steric hindrance of the coplanar phenyl ring combine to promote bromide attack at the β carbon. Attack on this π bond is insensitive to the electronic effect of meta and para substituents on the ring but is very (sterically) sensitive toward all ortho substituents.
- Weiss, Hilton M.,Touchette, Kim M.,Angell, Sarah,Khan, Jihan
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p. 2152 - 2156
(2007/10/03)
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- Cocatalysis in phase-transfer catalyzed base induced β-elimination. Part 2: Model studies of dehydrobromination of trans-β-bromostyrene
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Phase-transfer catalyzed β-elimination of HBr from trans-β-bromostyrene proceeds as a cocatalytic process when cocatalysts of low acidity such as n-butanol and highly concentrated aqueous NaOH at elevated temperatures are used. Without added cocatalyst the reaction is autocatalyzed because the produced phenylacetylene forms lipophilic acetylenide anion acting as a base in the organic phase. Competition between the β-elimination of HBr from trans-β-bromostyrene and the Hofmann degradation of tetrabutylammonium cation as a function of base was studied.
- Ma?kosza, Mieczys?aw,Chesnokov, Alexey A.
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p. 7295 - 7301
(2007/10/03)
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- A mild procedure for the stereospecific transformation of trans cinnamic acid derivatives to cis β-bromostyrenes
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A new mild procedure has been developed for the synthesis of cis β- bromostyrene analogs with complete Z/E selectivity and good to excellent yields (58.4 - 90.9 %). The process involves carboxyl-halo-elimination of cinnamic acid dibromides by using triethylamine in N,N-dimethylformamide at room temperature. A one-pot procedure has also been described for the direct transformation of cinnamic acids to β-bromostyrenes.
- Kim, Sun Hee,Wei, Han-Xun,Willis, Steven,Li, Guigen
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p. 4179 - 4185
(2007/10/03)
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- Reactions of Phenyl(styryl)iodonium Tetrafluoroborate with Halide Ions
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Reactions of (E)-phenyl(styryl)iodonium tetrafluoroborate with chloride, bromide, and iodide ions are examined under various conditions. The products are those of substitution and elimination, involving (Z)-1-halo-2-phenylethene (2), phenylacetylene (3), and iodobenzene as main products as well as minor products of (E)-2 and 1-halo-1-phenylethene. Results of product analysis, UV absorption spectroscopy, and kinetic measurements are consistent with major pathways involving pre-equilibrium formation of halo-λ3-iodane and iodate intermediates, leading to the in-plane vinylic SN2 substitution to (Z)-2 and the intramolecular β-elimination to 3. The minor retained product (E)-2 is concluded to be formed through the vinylenebenzenium ion intermediate in 2,2,2-trifluoroethanol through the ligand coupling within the λ3iodane intermediate in acetonitrile. 1-Bromo-1-phenylethene is considered to be derived from 3 by reaction with HBr formed during the reaction.
- Okuyama, Tadashi,Oka, Hsjime,Ochiai, Masahito
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p. 1915 - 1921
(2007/10/03)
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- Study of Oxidation of Terminal Unsaturated Compounds by Reagents Based on Dimethylsulfoxide
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The products of reactions of styrene, phenylacelylene, and 1-bromo-1-phenylethane with HBr and Br2 in DMSO were studied for the first time by high-performance liquid chromatography and gas chromatography-mass spectrometry. Phenylglyoxal is the main product in the reactions with styrene and bromophenylethane, while dibromostyrenes are formed as the main products in the reaction with phenylacetylene. Schemes of the reactions of these substrates with the reagents are proposed. The reactions of nucleophilic addition and decomposition of the dimethylsulfoxonium salts formed are the key stages of the processes considered.
- Krasnokutskaya,Habicher,Yusubov,Filimonov
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p. 153 - 157
(2007/10/03)
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- Brominative Deoxygenation of Some Aldehydes and Ethers
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Three aldehydes (4a-c) are transformed into 1,1-dibromides (6a-c) by 2,2,2-tribromo-2,2-dihydro-1,3,2-benzodioxaphosphole (2).This reagent (2) is also very active in the cleavage of ethers; its reactions may show some features of carbonium as well as of SN2 character.
- Roman, Ulrich von,Knorr, Rudolf,Behringer, Claudia,Ruhdorfer, Jakob
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p. 260 - 262
(2007/10/02)
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- Reactions of 1,1-Dihaloalkenes with Triorganozincates: A Novel Method for the Preparation of Alkenylzinc Species Associated with Carbon-Carbon Bond Formation
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Lithium trialkylzincates react with 1,1-dibromoalkenes 1 and 1-bromo-1-chloroalkenes 2 at -85 deg C in THF to give 1-bromoalkenes 5 and 1-chloroalkenes 7, respectively, upon hydrolysis.The intermediate (1-haloalkenyl)zincates 4 and 6 are stable at low temperature but, when allowed to warm to 0 deg C, they undergo a 1,2-alkyl migration reaction to afford alkenylzinc species 10.A variety of alkylation products 11 are obtained by the hydrolysis of 10.In the presence of (Ph3P)2Pd (5 molpercent), alkenylzinc species 10 react smoothly with organic halides (AcCl, EtOCOCl, CH2=CH(Me)Br, PhBr) to yield the corresponding coupling products 13-16.
- Harada, Toshiro,Katsuhira, Takeshi,Hara, Daiji,Kotani, Yasuo,Maejima, Keiji,et al.
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p. 4897 - 4907
(2007/10/02)
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- SYNTHESIS OF ARYL SUBSTITUTED EPIHALOHYDRIN DERIVATIVES
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Aryl substituted epihalohydrin derivatives were synthesized by the dehydrohalogenation of 2,3-dihalo-3-arylpropanol derivatives in the two phase solvent system of aqueous alkali solution and benzene with a phase transfer reagent such as benzyltrimethylammonium chloride.
- Yoshida, Masaaki,Hide, Tetsuro,Ohshima, Masabumi,Sasaki, Haruko,Toda, Takashi
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p. 507 - 510
(2007/10/02)
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- STEREOSELECTIVE SYNTHESIS OF (+/-)-threo-2-AMINO-1-(4-NITROPHENYL)-1,3-PROPANEDIOL
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Addition of hypobromic acid to styrene afforded styrene bromohydrin (I) which was dehydrated to ω-bromostyrene (II).Prince reaction of II with aqueous formaldehyde gave 5-bromo-4-phenyl-1,3-dioxane (III).The bromine atom in III was replaced with amino group by treatment with methanolic ammonia at 150 deg C and 6 - 8 MPa and the obtained threo-5-amino-4-phenyl-1,3-dioxane (IVa) was hydrolyzed to give (+/-)-threo-2-amino-1-phenyl-1,3-propanediol (V).Suitably chosen method of nitration converted the free base IVa or its N-acetyl derivative IVb into 5-amino-4-(4-nitrophe nyl)-1,3-dioxane (VIa) or its N-acetyl derivative VIb which without isolation were hydrolyzed to threo-2-amino-1-(4-nitrophenyl)-1,3-propanediol (VII), isolated as hydrochloride.The liberated base was resolved into enantiomers and dichloroacetylated in the known manner to give D-(-)-threo-2-dichloroacetylamino-1-(4-nitrophenyl)-1,3-propanediol (chloramphenicol).
- Cervinka, Otakar,Dudek, Vaclav,Fabryova, Anna,Kolar, Jiri,Lukac, Juraj,et al.
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p. 2748 - 2752
(2007/10/02)
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- An Examination of the β-Effect in an Addition Reaction with Different Ligands on Silicon
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The degree of cis-addition of bromine to a series of β-silylstyrenes may be used to compare the ability of silicon atoms bearing a variety of different ligands to stabilize a β-carbocation.
- Brook, Michael A.,Hadi, Mahmud A.,Neuy, Axel
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p. 957 - 959
(2007/10/02)
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- A convenient preparation of mono- or gem-di-halogenoalkanes from α-sulfonyl carbanions and halogenolithiocarbenoids.
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Various α-sulfonyl carbanions have been shown to react at low temperature with di- or tri-halogenolithiocarbenoids, to give 1-mono- or 1,1-di-halogenoalkanes.Bromocarbenoids gave better results than their chloro-analogues.Reaction of dibromolithiomethane with α-lithiated sulfones gives a high yield of vinylic bromides, the stereochemistry of which is cleanly E.Evidence is presented that the carbenoid itself is responsible for the reaction, and is not first converted into the corresponding carbene.
- Charreau, Philippe,Julia, Marc,Verpeaux, Jean-Noel
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p. 201 - 210
(2007/10/02)
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- Benzylbromocarbene: Absolute Rate Constant for 1,2-Hydrogen Migration and Ambiphilicity
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Laser flash photolysis studies of the reaction of benzylbromocarbene with pyridine enables the determination of the absolute rate constant for the 1,2-hydrogen migration in benzybromocarbene.Thus, k= 5.6E7/s-1 at 25 deg C.Relative reactivities of benzylbromocarbene toward electron-poor and electron-rich alkenes indicate that the carbene is ambiphilic.The present results are consistent with a mechanism involving a carbene-alkene intermediate.
- Bonneau, Roland,Liu, Michael T. H.,Suresh, R. V.
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p. 4802 - 4806
(2007/10/02)
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- Vinylic Organoboranes. 13. A Convenient Stereospecific Synthesis of (Z)-1-Halo-1-alkenes from 1-Alkynes via (E)-1-Alkenylborane Derivatives with Halogens
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The reaction of (E)-1-alkenylborane derivatives with bromine under various conditions was investigated, and a simple stereospecific synthesis of (Z)-1-bromo-1-alkenes has been developed.Addition of bromine to (E)-1-alkenyldisiamylborane, derived from the
- Brown, Herbert C.,Subrahmanyam, Chitti,Hamaoka, Tsutomu,Ravindran, Nair,Bowman, Donald H.,et al.
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p. 6068 - 6075
(2007/10/02)
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