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61.
Yicong Luo Yuqi Ma Guanlin Li Xiaohong Huo Wanbin Zhang 《Angewandte Chemie (International ed. in English)》2023,62(47):e202313838
Fluorinated amino acids and related peptides/proteins have been found widespread applications in pharmaceutical and agricultural compounds. However, strategies for introducing a C−F bond into amino acids in an enantioselective manner are still limited and no such asymmetric catalysis strategy has been reported. Herein, we have successfully developed a Pd/Cu/Li ternary system for stereodivergent synthesis of chiral fluorinated amino acids. This method involves a sequential desymmetrization of geminal difluoromethylenes and allylic substitution with amino acid Schiff bases via Pd/Li and Pd/Cu dual activation, respectively. A series of non-natural amino acids bearing a chiral allylic/benzylic fluorine motif are easily synthesized in high yields with excellent regio-, diastereo-, and enantioselectivities (up to >20 : 1 dr and >99 % ee). A density functional theory (DFT) study revealed the F−Cu interaction of the allylic substrate and the Cu catalyst significantly influence the stereoselectivity. 相似文献
62.
Allylic thioethers of the general structure 1 underwent E/Z isomerization during both basic and acidic hydrolysis of the ester moiety at the remote end of the molecule. The isomerization was dependent on the substitution of the allylic moiety. The presence of a 5-membered heterocycle on the double bond supported the isomerization. However, analogous oxy-ethers were stable. 相似文献
63.
Christian Amatore Anny Jutand Laure Mensah 《Journal of organometallic chemistry》2007,692(7):1457-1464
Specific chiral ligands have been designed by Trost et al. to perform enantioselective Pd-catalyzed allylic alkylations. It is shown that the Pd(0) complex formed by addition of the Trost ligand (4) to Pd0(dba)2 is not stable in most solvents (acetone, DMF, CH2Cl2). Indeed, Pd0(dba)(4) leads to the formation of a stable PdII complex 5 (X-ray structure), likely by activation of the two N-H bonds of the ligand by the Pd0 centre. The formation of the PdII complex competes with the reaction of Pd0(4) with (E)-PhCHCH-CH(OAc)-Ph, excluding any investigation of the kinetics of the latter reaction. The ionization steps from intermediate (η2-PhCHCH-CH(OAc)-Ph)Pd0(4) were found to be very slow. The cationic P,P complex [(η3-Ph-CH-CH-CH-Ph)Pd(4)]+, expected to be generated by addition of 2 equiv. of 4 to the precursor [(η3-Ph-CH-CH-CH-Ph)Pd(μ-Cl)]2, in the presence of a chloride scavenger, leads to a complex mixture whereas addition of 1 equiv. of 4 affords a stable bis-cationic PdII complex {[(η3-Ph-CH-CH-CH-Ph)Pd]2(4)]}2+, (X-ray structure) via a P,O complexation of each allyl-Pd moieties. This dissymmetric P,O coordination will favour the enantioselectivity of Pd-catalyzed allylic alkylation of (E)-PhCHCH-CH(OAc)-Ph by the control of the regioselectivity of the nucleophilic attack onto the allylic ligand which is responsible of the enantioselectivity of the overall catalytic reaction. 相似文献
64.
Ana E. Platero-Prats Concepción López Xavier Solans Piet W.N.M. van Leeuwen Gino P.F. van Strijdonck 《Journal of organometallic chemistry》2007,692(20):4215-4226
A study of the reactivity of enantiopure ferrocenylimine (SC)-[FcCHN-CH(Me)(Ph)] {Fc = (η5-C5H5)Fe{(η5-C5H4)-} (1a) with palladium(II)-allyl complexes [Pd(η3-1R1,3R2-C3H3)(μ-Cl)]2 {R1 = H and R2 = H (2), Ph (3) or R1 = R2 = Ph (4)} is reported. Treatment of 1a with 2 or 3 {in a molar ratio Pd(II):1a = 1} in CH2Cl2 at 298 K produced [Pd(η3-3R2-C3H4){FcCHN-CH(Me)(Ph)}Cl] {R2 = H (5a) or Ph (6a)}. When the reaction was carried out under identical experimental conditions using complex 4 as starting material no evidence for the formation of [Pd(η3-1,3-Ph2-C3H3){FcCHN-CH(Me)(Ph)}Cl] (7a) was found. Additional studies on the reactivity of (SC)-[FcCHN-CH(R3)(CH2OH)] {R3 = Me (1b) or CHMe2 (1c)} with complex 4 showed the importance of the bulk of the substituents on the palladium(II) allyl-complex (2-4) or on the ferrocenylimines (1) in this type of reaction. The crystal structure of 5a showed that: (a) the ferrocenylimine adopts an anti-(E) conformation and behaves as an N-donor ligand, (b) the chloride is in acis-arrangement to the nitrogen and (c) the allyl group binds to the palladium(II) in a η3-fashion. Solution NMR studies of 5a and 6a and [Pd(η3-1,3-Ph2-C3H3){FcCHN-CH(Me)(CH2OH)}Cl] (7b) revealed the coexistence of several isomers in solution. The stoichiometric reaction between 6a and sodium diethyl 2-methylmalonate reveals that the formation of the achiral linear trans-(E) isomer of Ph-CHCH-CH2Nu (8) was preferred over the branched derivative (9). A comparative study of the potential utility of ligand 1a, complex 5a and the amine (SC)-H2N-CH(Me)(Ph) (11) as catalysts in the allylic alkylation of (E)-3-phenyl-2-propenyl (cinnamyl) acetate with the nucleophile diethyl 2-methylmalonate (Nu−) is reported. 相似文献
65.
Sung Jae Na Nhat-Nguyen Bui Hye-Young Jang 《Journal of organometallic chemistry》2007,692(24):5523-5527
A new dirhodium tetraacetate II involving 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene I was synthesized and characterized by general spectroscopic tools in the solution state as well as single X-ray crystallographic analysis in the solid state. The catalytic activity of dirhodium tetraacetate carbenoid II was tested for the allylic oxidation, and the improved reactivity to the allylic oxidation was observed compared to that of Rh2(OAc)4. The different electrochemical properties of dirhodium tetraacetate carbenoid II and Rh2(OAc)4 were compared via cyclic voltammetry. 相似文献
66.
Huey-Wen Lin 《中国物理 C》2009,33(12):1238-1243
In this proceeding, I review the attempts to calculate the Nucleon resonance (including Roper as first radially excited state of nucleon and other excited states) using lattice quantum chromodynamics (QCD). The latest preliminary results from Hadron Spectrum Collaboration (HSC) with mπ≈ 380 MeV are reported. The Sachs electric form factor of the proton and neutron and their transition with the Roper at large Q2 are also updated in this work. 相似文献
67.
In the course of the ozonolysis of the bicyclo[2.2.1]heptene anhydride 1, the three bis-lactones 3-5 have been obtained (the structures were confirmed by X-ray crystallographic analysis). 相似文献
68.
The oxygen atom of oximes acts as a reactive nucleophile in the iridium-catalyzed allylic substitution of unsymmetrical substrates to give the branched oxime ethers. Among several chiral ligands evaluated, the iridium complex of pybox ligand having phenyl group catalyzed the allylic substitution of phosphates with high activity to form the branched oxime ethers with good enantioselectivities. 相似文献
69.
The reaction of [(NHC)AuCl] complexes (NHC = N-heterocyclic carbene) with a chloride abstractor of the type AgX, where X is a non-coordinating anion, led, in the presence of a neutral coordinating solvent S, to a series of cationic gold(I) complexes of formulae [(NHC)Au(S)]X. Hence, different cationic NHC-gold(I) species bound to acetonitrile, pyridine, 2-Br-pyridine, 3-Br-pyridine, norbornadiene, and THF could be synthesized and characterized by 1H and 13C NMR spectroscopies. Among these, the results of X-ray diffraction studies for [(IPr)Au(NCMe)]SbF6, [(IAd)Au(NCMe)]PF6, [(IPr)Au(pyr)]PF6, [(IPr)Au(2-Br-pyr)]PF6, [(IPr)Au(3-Br-pyr)]PF6 are discussed. As special feature, the structure of [(IPr)Au(2-Br-pyr)]PF6 presented a secondary interaction between the gold and bromine atoms. Additionally, while attempting to obtain crystals of [(IPr)Au(nbd)]PF6, we crystallized a decomposition product featuring a very rare anion as bridging ligand with formulae [(μ-PF4)((IPr)Au)2]PF4. The observation of a possible P-F bond activation has important implications for cationic Au-based homogeneous catalysis. Finally, we compared the catalytic activities of the different cationic [(NHC)Au(S)]X complexes in the allylic acetate rearrangement reaction and notably observed the inertness of pyridine-based catalysts. 相似文献
70.
The γ-selective allylation of catalytic and stoichiometric alkylzinc-cuprates have been kinetically studied. The reactivity profiles generated by allylation reactions of n-butylzinc chloride catalyzed by CuX compounds (X = I, Br, Cl, CN, SCN) and also catalyzed by n-butylzinc-copper reagents and di n-butylzinc-copper reagents were evaluated. Reactivity profiles for allylation of stoichiometric n-butylzinc-copper reagents and di n-butylzinc-copper reagents were also prepared. All CuX compounds have been screened for the preparation of Grignard reagent derived n-butylzinc-copper reagents and di n-butylzinc-copper reagents.The evaluation of the profiles indicates that the active catalyst might be RCu(X)ZnCl and also to some degree, R2CuZnCl · ZnClX, which both could favor formation of γ-product. All data supports the reductive elimination of σ-allyl Cu (III) complex formed at vinylic terminal to give γ-allylated product with a quite slow isomerization to σ-allyl Cu (III) complex formed at allylic terminal to give α-allylated product. In the allylation mechanism of zinc cuprates, the role of counter ion, ZnCl+ has been discussed. 相似文献