共查询到20条相似文献,搜索用时 31 毫秒
1.
Ming‐Zhong Wang Dr. Cong‐Ying Zhou Dr. Zhen Guo Dr. Ella Lai‐Ming Wong Dr. Man‐Kin Wong Prof. Chi‐Ming Che 《化学:亚洲杂志》2011,6(3):812-824
Chiral binuclear gold(I) phosphine complexes catalyze enantioselective intermolecular hydroarylation of allenes with indoles in high product yields (up to 90 %) and with moderate enantioselectivities (up to 63 % ee). Among the gold(I) complexes examined, better ee values were obtained with binuclear gold(I) complexes, which displayed intramolecular AuI AuI interactions. The binuclear gold(I) complex 4c [(AuCl)2( L3 )] with chiral biaryl phosphine ligand (S)‐(−)‐MeO‐biphep ( L3 ) is the most efficient catalyst and gives the best ee value of up to 63 %. Substituents on the allene reactants have a slight effect on the enantioselectivity of the reaction. Electron‐withdrawing groups on the indole substrates decrease the enantioselectivity of the reaction. The relative reaction rates of the hydroarylation of 4‐X‐substituted 1,3‐diarylallenes with N‐methylindole in the presence of catalyst 4c [(AuCl)2( L3 )] / AgOTf [ L3 =(S)‐(−)‐MeO‐biphep], determined through competition experiments, correlate (r2=0.996) with the substituent constants σ. The slope value is −2.30, revealing both the build‐up of positive charge at the allene and electrophilic nature of the reactive AuI species. Two plausible reaction pathways were investigated by density functional theory calculations, one pathway involving intermolecular nucleophilic addition of free indole to aurated allene intermediate and another pathway involving intramolecular nucleophilic addition of aurated indole to allene via diaurated intermediate E2 . Calculated results revealed that the reaction likely proceeds via the first pathway with a lower activation energy. The role of AuI AuI interactions in affecting the enantioselectivity is discussed. 相似文献
2.
Efficient Access to Bicyclo[4.3.0]nonanes: Copper‐Catalyzed Asymmetric Silylative Cyclization of Cyclohexadienone‐Tethered Allenes 下载免费PDF全文
Zhi‐Tao He Xiao‐Qi Tang Li‐Bo Xie Mian Cheng Ping Tian Prof. Guo‐Qiang Lin 《Angewandte Chemie (International ed. in English)》2015,54(49):14815-14818
The creation of three consecutive chiral carbon centers in one step is achieved using Cu‐catalyzed asymmetric silylative cyclization of cyclohexadienone‐tethered allenes. Through regioselective β‐silylation of the allene and subsequent enantioselective 1,4‐addition to cyclohexadienone, this tandem reaction could afford cis‐hydrobenzofuran, cis‐hydroindole, and cis‐hydroindene frameworks with excellent yields (80–98 %) and enantioselectivities (94–98 % ee) bearing vinylsilane and enone substructures. Meanwhile, this mild transformation is generally compatible with a wide range of functional groups, which allows further conversion of the bicyclic products to bridged and tricyclic ring structures. 相似文献
3.
从脯氨酸合成一种三齿手性配体及其在二乙基锌对醛的对映选择性加成中的应用 总被引:1,自引:0,他引:1
A new chiral tridentate ligand [1-(1-methyl-S-pyrrolidin-2-ylmethyl)-S-pyrrolidin-2-yl]-diphenylmethanol (1) has been successfully synthesized from S-proline. The structure of the ligand was characterized by NMR spectra and X-ray diffraction analysis. Its catalytic ability has also been examined in enantioselective addition of diethylzinc towards aldehydes with 15%-84% enantiomeric excesses (ee). 相似文献
4.
U. Amrutha Beneesh P.Babu Sreedharan Prathapan 《Journal of heterocyclic chemistry》2019,56(12):3236-3243
In the cycloaddition reaction between fluorenone N‐aryl nitrones and 1,1‐disubstituted allenes, the initially formed cycloadduct underwent facile [1,3] shift to give 1′‐phenylspiro[fluorene‐9,2′‐pyrrolidin]‐4′‐ones. Although 1′‐phenylspiro[fluorene‐9,2′‐pyrrolidin]‐4′‐ones are stable in solid state, a few of them underwent facile aerial oxidation in solution to give the corresponding 1′‐phenylspiro[fluorene‐9,2′‐pyrrolidine]‐4′,5′‐diones in excellent overall yields. 相似文献
5.
Uranium Metalla‐Allenes with Carbene Imido R2C=UIV=NR′ Units (R=Ph2PNSiMe3; R′=CPh3): Alkali‐Metal‐Mediated Push–Pull Effects with an Amido Auxiliary 下载免费PDF全文
Dr. Erli Lu Dr. Floriana Tuna Dr. William Lewis Prof. Dr. Nikolas Kaltsoyannis Prof. Dr. Stephen T. Liddle 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11554-11558
We report uranium(IV)‐carbene‐imido‐amide metalla‐allene complexes [U(BIPMTMS)(NCPh3)(NHCPh3)(M)] (BIPMTMS=C(PPh2NSiMe3)2; M=Li or K) that can be described as R2C=U=NR′ push–pull metalla‐allene units, as organometallic counterparts of the well‐known push–pull organic allenes. The solid‐state structures reveal that the R2C=U=NR′ units adopt highly unusual cis‐arrangements, which are also reproduced by gas‐phase theoretical studies conducted without the alkali metals to remove their potential structure‐directing roles. Computational studies confirm the double‐bond nature of the U=NR′ and U=CR2 interactions, the latter increasingly attenuated by potassium then lithium when compared to the hypothetical alkali‐metal‐free anion. Combined experimental and theoretical data show that the push–pull effect induced by the alkali metal cations and amide auxiliary gives a fundamental and tunable structural influence over the C=UIV=N units. 相似文献
6.
Chun Ma Fei Jiang Feng‐Tao Sheng Yinchun Jiao Guang‐Jian Mei Feng Shi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(10):3046-3052
The first catalytic asymmetric construction of 3,3′‐bisindole skeletons bearing both axial and central chirality has been established by organocatalytic asymmetric addition reactions of 2‐substituted 3,3′‐bisindoles with 3‐indolylmethanols (up to 98 % yield, all >95:5 d.r., >99 % ee). This reaction also represents the first highly enantioselective construction of axially chiral 3,3′‐bisindole skeletons, and utilizes the strategy of introducing a bulky group to the ortho‐position of prochiral 3,3′‐bisindoles. This reaction not only provides a good example for simultaneously controlling axial and central chirality in one operation, but also serves as a new strategy for catalytic enantioselective construction of axially chiral 3,3′‐bisindole backbones from prochiral substrates. 相似文献
7.
Stereoselective Rhodium‐Catalysed [2+2+2] Cycloaddition of Linear Allene–Ene/Yne–Allene Substrates: Reactivity and Theoretical Mechanistic Studies 下载免费PDF全文
Ewelina Haraburda Òscar Torres Dr. Teodor Parella Prof. Dr. Miquel Solà Dr. Anna Pla‐Quintana 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):5034-5045
Allene–ene–allene ( 2 and 5 ) and allene–yne–allene ( 3 and 7 ) N‐tosyl and O‐linked substrates were satisfactorily synthesised. The [2+2+2] cycloaddition reaction catalysed by the Wilkinson catalyst [RhCl(PPh3)3] was evaluated. Substrates 2 and 5 , which bear a double bond in the central position, gave a tricyclic structure in a reaction in which four contiguous stereogenic centres were formed as a single diastereomer. The reaction of substrates 3 and 7 , which bear a triple bond in the central position, gave a tricyclic structure with a cyclohexenic ring core, again in a diastereoselective manner. All cycloadducts were formed by a regioselective reaction of the inner allene double bond and, therefore, feature an exocyclic diene motif. A Diels–Alder reaction on N‐tosyl linked cycloadducts 8 and 10 allowed pentacyclic scaffolds to be diastereoselectively constructed. The reactivity of the allenes on [2+2+2] cycloaddition reactions was studied for the first time by density functional theory calculations. This mechanistic study rationalizes the order in which the unsaturations take part in the catalytic cycle, the reactivity of the two double bonds of the allene towards the [2+2+2] cycloaddition reaction, and the diastereoselectivity of the reaction. 相似文献
8.
Solvent‐Dependent Asymmetric Synthesis of Alkynyl and Monofluoroalkenyl Isoindolinones by CpRhIII‐Catalyzed C−H Activation 下载免费PDF全文
Teng Li Chao Zhou Xiaoqiang Yan Prof. Dr. Jun Wang 《Angewandte Chemie (International ed. in English)》2018,57(15):4048-4052
The asymmetric synthesis of alkynyl and monofluoroalkenyl isoindolinones from N‐methoxy benzamides and α,α‐difluoromethylene alkynes is enabled by C?H activation with a chiral CpRhIII catalyst. Remarkably, product formation is solvent‐dependent; alkynyl isoindolinones are afforded in MeOH (up to 86 % yield, 99.6 % ee) whereas monofluoroalkenyl isoindolinones are generated in iPrCN (up to 98:2 Z/E, 93 % yield, 86 % ee). Mechanistic studies revealed chiral allene and E‐configured alkenyl rhodium species as reaction intermediates. The latter is transformed into the corresponding Z‐configured monofluoroalkene upon protonation in the iPrCN system and into an alkyne by an unusual anti β‐F elimination in the MeOH system. Notably, kinetic resolution processes occur in this reaction. Despite the moderate enantiocontrol for the formation of the chiral allene, the Z‐monofluoroalkenyl isoindolinones and alkynyl isoindolinones were obtained in good enantiopurities by one or two sequential kinetic resolution processes. 相似文献
9.
Octahedral Chiral‐at‐Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions 下载免费PDF全文
Xiaodong Shen Haohua Huo Chuanyong Wang Bo Zhang Dr. Klaus Harms Prof. Dr. Eric Meggers 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9720-9726
Octahedral iridium(III) complexes containing two bidentate cyclometalating 5‐tert‐butyl‐2‐phenylbenzoxazole ( IrO ) or 5‐tert‐butyl‐2‐phenylbenzothiazole ( IrS ) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5–5.0 mol % catalyst loading) for a variety of reactions with α,β‐unsaturated carbonyl compounds, namely Friedel–Crafts alkylations (94–99 % ee), Michael additions with CH‐acidic compounds (81–97 % ee), and a variety of cycloadditions (92–99 % ee with high d.r.). Mechanistic investigations and crystal structures of an iridium‐coordinated substrates and iridium‐coordinated products are consistent with a mechanistic picture in which the α,β‐unsaturated carbonyl compounds are activated by two‐point binding (bidentate coordination) to the chiral Lewis acid. 相似文献
10.
Michael M. Yamano Rachel R. Knapp Aurapat Ngamnithiporn Melissa Ramirez Kendall N. Houk Brian M. Stoltz Neil K. Garg 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(17):5709-5713
The chemistry of strained cyclic alkynes has undergone a renaissance over the past two decades. However, a related species, strained cyclic allenes, especially heterocyclic derivatives, have only recently resurfaced and represent another class of valuable intermediates. We report a mild and facile means to generate the parent 3,4‐oxacyclic allene from a readily accessible silyl triflate precursor, and then trap it in (4+2), (3+2), and (2+2) reactions to provide a variety of cycloadducts. In addition, we describe a catalytic, decarboxylative asymmetric allylic alkylation performed on an α‐silylated substrate, to ultimately permit access to an enantioenriched allene. Generation and trapping of the enantioenriched cyclic allene occurs with complete transfer of stereochemical information in a Diels–Alder cycloaddition through a point‐chirality, axial‐chirality, point‐chirality transfer process. 相似文献
11.
Mark M. Maturi Matthias Wenninger Dr. Rafael Alonso Dr. Andreas Bauer Dr. Alexander Pöthig Prof. Dr. Eberhard Riedle Prof. Dr. Thorsten Bach 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7461-7472
The intramolecular [2+2] photocycloaddition of four 4‐(but‐3‐enyl)oxyquinolones (substitution pattern at the terminal alkene carbon atom: CH2, Z‐CHEt, E‐CHEt, CMe2) and two 3‐(but‐3‐enyl)oxyquinolones (substitution pattern: CH2, CMe2) was studied. Upon direct irradiation at λ=300 nm, the respective cyclobutane products were formed in high yields (83–95 %) and for symmetrically substituted substrates with complete diastereoselectivity. Substrates with a Z‐ or E‐substituted terminal double bond showed a stereoconvergent reaction course leading to mixtures of regio‐ and diastereomers with almost identical composition. The mechanistic course of the photocycloaddition was elucidated by transient absorption spectroscopy. A triplet intermediate was detected for the title compounds, which–in contrast to simple alkoxyquinolones such as 3‐butyloxyquinolone and 4‐methoxyquinolone–decayed rapidly (τ≈1 ns) through cyclization to a triplet 1,4‐diradical. The diradical can evolve through two reaction channels, one leading to the photoproduct and the other leading back to the starting material. When the photocycloaddition was performed in the presence of a chiral sensitizer (10 mol %) upon irradiation at λ=366 nm in trifluorotoluene as the solvent, moderate to high enantioselectivities were achieved. The two 3‐(but‐3‐enyl)oxyquinolones gave enantiomeric excesses (ees) of 60 and 64 % at ?25 °C, presumably because a significant racemic background reaction occurred. The 4‐substituted quinolones showed higher enantioselectivities (92–96 % ee at ?25 °C) and, for the terminally Z‐ and E‐substituted substrates, an improved regio‐ and diastereoselectivity. 相似文献
12.
Xiaowei Zhang Bonan Cao Yongjun Yan Dr. Shichao Yu Dr. Baoming Ji Dr. Xumu Zhang Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(3):871-877
A series of hybrid phosphine–phosphoramidite ligands has been designed and synthesized in moderate yields from chiral BINOL (1,1′‐bi‐2‐naphthol) or NOBIN (2‐amino‐2′‐hydroxy‐1,1′‐binaphthyl). They have achieved highly regio‐ and enantioselectivities in Rh‐catalyzed asymmetric hydroformylations of styrene derivatives (branched/linear ratio up to 56.6, ee up to 99 %), vinyl acetate derivatives (up to 98 % ee), and allyl cyanide (up to 96 % ee). Systematic variation of ligand structure showed that the steric factor on the phsophoramidite moiety determined the performance of the ligand. With the increased hindrance, the branched/linear ratio rose, while the ee value dropped in the hydroformylation of styrene. However, the N‐substituents did not influence the selectivities much. 相似文献
13.
Timothy J. Brown Dr. Atsushi Sugie Dr. Marina G. D. Leed Prof. Ross A. Widenhoefer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(22):6959-6971
A family of seven cationic gold complexes that contain both an alkyl substituted π‐allene ligand and an electron‐rich, sterically hindered supporting ligand was isolated in >90 % yield and characterized by spectroscopy and, in three cases, by X‐ray crystallography. Solution‐phase and solid‐state analysis of these complexes established preferential binding of gold to the less substituted C?C bond of the allene and to the allene π face trans to the substituent on the uncomplexed allenyl C?C bond. Kinetic analysis of intermolecular allene exchange established two‐term rate laws of the form rate=k1[complex]+k2[complex][allene] consistent with allene‐independent and allene‐dependent exchange pathways with energy barriers of ΔG≠1=17.4–18.8 and ΔG≠2=15.2–17.6 kcal mol?1, respectively. Variable temperature (VT) NMR analysis revealed fluxional behavior consistent with facile (ΔG≠=8.9–11.4 kcal mol?1) intramolecular exchange of the allene π faces through η1‐allene transition states and/or intermediates that retain a staggered arrangement of the allene substituents. VT NMR/spin saturation transfer analysis of [{P(tBu)2o‐binaphthyl}Au(η2‐4,5‐nonadiene) ]+SbF6? ( 5 ), which contains elements of chirality in both the phosphine and allene ligands, revealed no epimerization of the allene ligand below the threshold for intermolecular allene exchange (ΔG≠298K=17.4 kcal mol?1), which ruled out the participation of a η1‐allylic cation species in the low‐energy π‐face exchange process for this complex. 相似文献
14.
RhCl(PPh3)3‐catalyzed [4+2] intramolecular cycloaddition of optically active axially chiral allene‐dienes afforded cis‐fused [3.4.0]‐bicyclic products with three chiral centers in good yields with an excellent chemo‐ and diastereoselectivity. A pair of enantiomers of such products was generated highly selectively from both enantiomers of starting allene‐dienes, indicating that the axial chirality dictated the absolute configurations of the three in situ generated chiral centers with a very high efficiency of chirality transfer. 相似文献
15.
Complementary Iron(II)‐Catalyzed Oxidative Transformations of Allenes with Different Oxidants 下载免费PDF全文
Venkata R. Sabbasani Hyunjin Lee Prof. Yuanzhi Xia Prof. Daesung Lee 《Angewandte Chemie (International ed. in English)》2016,55(3):1151-1155
Substituent‐ and oxidant‐dependent transformations of allenes are described. Given the profound influence of the substituent on the reactivity of allenes, the subtle differences in allene structures are manifested in the formation of diverse products when reacted with different electrophiles/oxidants. In general, reactions of nonsilylated allenes involve an allylic cation intermediate by forming a C?O bond, at the sp‐hybridized C2, with either DDQ (2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone) or TBHP (tert‐butyl hydroperoxide), along with FeCl2?4 H2O (10 mol %). In contrast, silylated allenes favor the formation of propargylic cation intermediates by transferring the allenic hydride to the oxidant, thus generating 1,3‐enynes (E1 product) or propargylic THBP ethers (SN1 product). The formation of these different putative cationic intermediates from nonsilylated and silylated allenes is strongly supported by DFT calculations. 相似文献
16.
Fjermestad T Pericàs MA Maseras F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(36):10050-10057
Density functional calculations were carried out to ascertain the origin of enantioselectivity in the brucine N‐oxide (BNO)‐assisted enantioselective Pauson–Khand reaction (PKR) of norbornene with 2‐methyl‐3‐butyn‐2‐ol. The computed ee value in acetone is 68 % (R), which compares well to the previously reported experimental value of 58 % (R). In DME the computed ee value of 76 % (R) is in excellent agreement with the experimentally determined value of 78 % (R). The mechanism of enantioselectivity consists of several steps. First, the dicobalt complex is activated by BNO with chirality transfer from enantiopure BNO to the dicobalt complex. Second, competition occurs between a racemization process and complexation with the olefin reagent, which leads to the products. The lower ee value in acetone is due to the lower energy barrier of the racemization process. Calculations show that replacement of BNO by a hypothetical more enantioselective chiral N‐oxide will hardly increase the ee value beyond 90 %. 相似文献
17.
Yoshiyuki Nagashima Keiji Sasaki Takahiro Suto Prof. Dr. Takaaki Sato Prof. Dr. Noritaka Chida 《化学:亚洲杂志》2018,13(8):1024-1028
Full details of a stereodivergent hydroboration of allenes are reported. While hydroboration of an allene with 9‐BBN provided a thermodynamically stable (E)‐allylic alcohol after oxidative work‐up, the reaction of an identical allene with HB(Sia)2 (disiamylborane) formed a (Z)‐allylic alcohol as the kinetic product. The developed conditions allowed for the synthesis of trisubstituted olefins in a highly stereoselective fashion, which is known to be challenging. The method was also applied to the stereodivergent synthesis of structural motifs such as skipped dienes and allylbenzenes, which are often embedded in biologically active natural products. 相似文献
18.
Dr. Xiao‐Qiang Yu Tomohiko Shirai Dr. Yasunori Yamamoto Prof. Dr. Norio Miyaura 《化学:亚洲杂志》2011,6(3):932-937
Rhodium‐catalyzed 1,4‐addition of lithium 5‐methyl‐2‐furyltriolborate ([ArB(OCH2)3CCH3]Li, Ar=5‐methyl‐2‐furyl) to unsaturated ketones to give β‐furyl ketones was followed by ozonolysis of the furyl ring for enantioselective synthesis of γ‐oxo‐carboxylic acids. [Rh(nbd)2]BF4 (nbd=2,5‐norbornadiene) chelated with 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (binap) or 2,3‐bis(diphenylphosphino)butane (chiraphos) gave high yields and high selectivities in a range of 91–99 % ee at 30 °C in a basic dioxane/water solution. The corresponding reaction of unsaturated esters, such as methyl crotonate, had strong resistance under analogous conditions, but the 1,4‐adduct was obtained in 70 % yield and with 94 % ee when more electron‐deficient phenyl crotonate was used as the substrate. 相似文献
19.
Dr. Haibo Wu Dr. Zhiyao Zheng Dr. Kaiheng Zhang Dr. Johan Kajanus Dr. Magnus J. Johansson Prof. Dr. Armando Córdova Prof. Dr. Jan-E. Bäckvall 《Angewandte Chemie (International ed. in English)》2023,62(50):e202314512
Classical Crabbé type SN2' substitutions of propargylic substrates has served as one of the standard methods for the synthesis of allenes. However, the stereospecific version of this transformation often requires either stoichiometric amounts of organocopper reagents or special functional groups on the substrates, and the chirality transfer efficiency is also capricious. Herein, we report a sustainable methodology for the synthesis of diverse 1,3-di and tri-substituted allenes by using a simple and cheap cellulose supported heterogeneous nanocopper catalyst (MCC-Amp-Cu(I/II)). This approach represents the first example of heterogeneous catalysis for the synthesis of chiral allenes. High yields and excellent enantiospecificity (up to 97 % yield, 99 % ee) were achieved for a wide range of di- and tri-substituted allenes bearing various functional groups. It is worth noting that the applied heterogeneous catalyst could be recycled at least 5 times without any reduced reactivity. To demonstrate the synthetic utility of the developed protocol, we have applied it to the total synthesis of several chiral allenic natural products. 相似文献
20.
Desimoni G Faita G Toscanini M Boiocchi M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(12):3630-3636
The asymmetric Friedel–Crafts reaction between a series of substituted indoles 2 a – l and methyl (E)‐2‐oxo‐4‐aryl‐3‐butenoates 3 a – c has been efficiently catalyzed by the scandium(III) triflate complex of (4′S,5′S)‐2,6‐bis[4′‐(triisopropylsilyl)oxymethyl‐5′‐phenyl‐1′,3′‐oxazolin‐2′‐yl]pyridine (pybox; 1 ). Substituted 4‐(indol‐3‐yl)‐2‐oxo‐4‐arylbutyric acid methyl esters 4 a – n were usually formed in excellent yields and the enantioselectivity was up to 99 % ee, irrespective of the electronic character of the substituent and its location on the indole ring, albeit with the exclusion of position 2. The adducts could be obtained as stable enol tautomers and the equilibrium with the keto structure is discussed. The X‐ray crystal structure determination of 4 m indicated the 4R absolute configuration, thus confirming the proposal of Jørgensen for 4 i . The sense of the stereoinduction can be rationalized by the same octahedral complex 5 between 3 , pybox 1 , and scandium triflate already proposed for the Diels–Alder/hetero‐Diels–Alder and the Mukaiyama–aldol reactions of pyruvates. 相似文献