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1.
《Tetrahedron: Asymmetry》2003,14(21):3415-3421
A series of novel ferrocenylphosphine-ketimine ligands 6 were prepared by reaction of (R,Sp)-PPFNH2-R or (S,Sp)-PPFNH2 with a variety of m-substituted acetophenones. A different catalytic activity was observed between ferrocenylphosphine-ketimine ligands and corresponding aldimine ligands. The efficiency and diastereomeric impact of these ferrocenylphosphine-ketimine ligands in Pd-catalyzed asymmetric allylic alkylation were first investigated, and higher enantioselectivity of over 98% e.e. with 95% yield was obtained by the use of ferrocenylphosphine-ketimine ligands. However, in Rh-catalyzed asymmetric hydrosilylation of aryl ketones, only 42% e.e. was obtained by the use of ferrocenylphosphine-ketimine ligands compared to 90% e.e. with the use of aldimine ligands.  相似文献   

2.
《Tetrahedron: Asymmetry》2003,14(14):2073-2080
Some novel ferrocenylphosphine-amidine ligands with central and planar chirality were prepared from (R,Sp)-PPFNH2-R 3 and its diastereomer (S,Sp)-PPFNH2 3a. The efficiency and diastereomeric impact of these ferrocenylphosphine-amidine ligands in the palladium-catalyzed asymmetric allylic substitution was examined, and up to 96% e.e. with 98% yield was achieved by the use of ligand (R,Sp)-4a with a methyl group in the amidino moiety. The results also indicated that (R)-central chirality and (Sp)-planar chirality in these ferrocenylphosphine-amidine ligands were matched for the palladium-catalyzed asymmetric allylic alkylation.  相似文献   

3.
《Tetrahedron: Asymmetry》2000,11(19):4009-4015
The asymmetric allylic alkylation of rac-1,3-diphenyl-2-propenyl acetate 1 with dimethyl malonate 2a proceeded smoothly in the presence of lithium acetate, BSA (N,O-bis(trimethylsilyl)acetamide), [Pd(η3-C3H5)Cl]2, and the chiral ligand (R)-i-Pr2N-PHEST (R)-5a to give the allylic alkylation product (R)-3a in 89% yield with 99% ee. Furthermore, the asymmetric allylic amination of 1 with potassium phthalimide 2c has been carried out using the same ligand to give the allylic amination product (S)-3c in 10% yield with 66% ee.  相似文献   

4.
《Tetrahedron: Asymmetry》1998,9(21):3797-3817
Palladium-catalyzed asymmetric allylic alkylations were studied by using chiral sulfoxide ligands bearing nitrogen atoms as coordinating elements, such as chiral α-sulfinylacetamides, β or γ-amino sulfoxides, and β-sulfinyl sulfonamides. The effects of the chiral sulfinyl functions on the asymmetric induction were demonstrated. Use of (S)-2-pyrrolidinophenyl p-tolyl sulfoxide or (S)-2-(N-butyl-N-methylaminomethyl)phenyl p-tolyl sulfoxide as chiral ligands in the palladium-catalyzed asymmetric allylic alkylations provided the highest enantioselectivity (50 or 58% e.e., respectively) among chiral sulfoxide ligands examined by us. The participation of the sulfinyl groups in these catalytic asymmetric reactions is rationalized, and the mechanism for the asymmetric induction is proposed on the basis of the stereochemical outcome obtained.  相似文献   

5.
We describe the synthesis of a new asymmetric P,N,N′-tridentate ligand (bis(pyrid-2-ylethyl) menthylphosphine, BPEMP), containing two pyridyl rings and (1S,2R,5S)-menthylphosphino group. The ligand is obtained in five steps from natural abundant l-menthol. The coordination behavior of the ligand toward cationic (allylic)Pd(II) moiety and its first application in palladium-catalyzed asymmetric allylic alkylation are presented. Crystallographic and spectroscopic analyses reveal that [(η3-allylic)Pd(BPEMP)]+ complex forms only one isomer in the solid state as well as in solution.  相似文献   

6.
The asymmetric allylic alkylation of racemic 1,3-diphenyl-2-propenyl acetate 3 with dimethyl malonate proceeded smoothly in the presence of lithium acetate, BSA (N,O-bis(trimethylsilyl)acetamide), [Pd(η3-C3H5)Cl]2, and chiral tert-butanesulfinylphosphine ligand 2c to give the allylic alkylation product in good yield and high enantiomeric excess (up to 93% ee), while the enantioselectivities of allylic amination of 3 with various amines were moderate (up to 76% ee).  相似文献   

7.
Jun-Long Niu  Pei-Pei Kong 《Tetrahedron》2009,65(43):8869-7422
A series of new chiral heterobidentate sulfide-tertiary amine (sp3) ligands 3a-c, 6 were readily prepared from cheap and easily available (R)-cysteine and l-(+)-methionine. A Pd-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate was used as a model reaction to examine the catalytic efficiencies of these aziridine sulfide ligands, and ligand 3b afforded the enantioselectivity of up to 91% ee. The origin of enantioselectivity for heterobidentate sulfide-tertiary amine (sp3) ligands was first rationalized based on X-ray crystallographic data, and NMR spectroscopic data for relevant intermediate palladium allylic complexes. Our results demonstrated that the sulfur atom was a better π-allyl acceptor than the nitrogen atom for heterobidentate sulfide-tertiary amine (sp3) ligands, and the steric as well electronic properties of the palladium allylic complexes were crucial for the enantioselectivity.  相似文献   

8.
《Tetrahedron: Asymmetry》2000,11(5):1193-1198
Pyrrolidinyl- 2 and 2-azanorbornylphosphinooxazolidines 3, a new type of optically active ligands, were synthesized easily and their abilities as ligands were examined in Pd-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate. Enantiomeric excesses of up to 96% have been obtained using 1 mol% of [PdCl(η3-C3H5)]2 and 2.1 mol% of 2.  相似文献   

9.
《Tetrahedron: Asymmetry》2014,25(15):1116-1121
Diamidophosphite ligands based on 1,1′-bis(hydroxymethyl)ferrocene or N1,N2-bis((S)-1-hydroxy-3,3-dimethylbutan-2-yl)oxalamide and bearing 1,3,2-diazaphospholidine rings with stereogenic phosphorus atoms were obtained. The use of these ligands provides up to 96% ee in Pd-catalyzed asymmetric allylations of (E)-1,3-diphenylallyl acetate, up to 70% ee in Pd-catalyzed desymmetrizations of N,N′-ditosyl-meso-cyclopent-4-ene-1,3-diol bis-carbamate and up to 80% ee in Pd-catalyzed allylic alkylations of cinnamyl acetate with ethyl 2-oxocyclohexane-1-carboxylate. Results obtained with a diamidophosphite containing an oxalamide framework show the considerable potential of such ligands in enantioselective catalysis.  相似文献   

10.
《Tetrahedron: Asymmetry》2003,14(18):2821-2826
P-Stereogenic secondary phosphine oxides are configurationally stable in the presence of metal ions both in solution and in the solid state. They have the potential to serve as chiral monodentate phosphorus ligands for asymmetric catalysis. In the asymmetric allylic alkylation of 1,3-diphenylprop-2-enyl acetate, ca. 80% ee was achieved using (Rp)-tert-butylphenylphosphine oxide.  相似文献   

11.
New P,P-bidentate diastereomeric diphosphoramidite chiral ligands with mixed stereogenic elements and a C1 backbone symmetry have been prepared from (Sa)- and (Ra)-1,1′-binaphthyl-2,2′-diol (BINOL) and (S)-N-benzyl-1-(pyrrolidin-2-yl)methanamine and are fully characterized. The use of these ligands provides up to 84% ee in the Pd-catalyzed asymmetric allylic substitution of (E)-1,3-diphenylallyl acetate and up to 95% ee in the Rh-catalyzed asymmetric hydrogenation of α-dehydrocarboxylic acid esters. The results indicate that the catalytic performance is highly affected by the axial chirality of the binaphthyl moieties of the ligand and the nature of the solvent.  相似文献   

12.
A small family of P,P-bidentate C1-symmetric ligands containing 1,3,2-diazaphospholidine rings with stereogenic phosphorus atoms has been prepared. Palladium catalytic systems with these phosphine-diamidophosphites afforded 95% and 63% ees in asymmetric allylic substitution and desymmetrization processes, respectively. The influence of the nature of both the phosphine and diamidophosphite moieties of these compounds on the enantioselectivity is discussed. The ‘mixed-ligand approach’ in Pd-catalyzed asymmetric allylation with participation of some new P-monodentate diamidophosphites and PPh3 is also considered.  相似文献   

13.
Various chiral ligands bearing phosphorus or nitrogen donor atoms were obtained in a straightforward manner starting from trans-(2R,3R)-diphenylcyclopropane-1,1-dimethanol as a key structure. These chiral ligands were tested and compared in palladium(0)-catalyzed asymmetric allylic alkylation reactions (up to 71% ee) and rhodium(I)-catalyzed asymmetric hydrogenations (up to 88% ee). Moreover, in the asymmetric allylic alkylation, we observed excellent activity with a diphosphinite ligand (TOF = 600 mol 17 × [mol Pd × h)?1].  相似文献   

14.
A dramatic improvement of the catalytic activity was observed when a phosphine was added in allylic alkylation reactions catalyzed by (NHC)Pd(η3-C3H5)Cl complexes. Consequently, several palladium complexes, generated in situ from different NHC-silver complexes, [Pd(η3-C3H5)Cl]2 and PPh3, were tested in this reaction to evaluate their potential. High reaction rates and conversions could be obtained with this catalytic system in the alkylation of allylic acetates with dimethylmalonate, particularly under biphasic conditions using water/dichloromethane and KOH 1 M as the base. These conditions are experimentally more convenient and gave higher reaction rates than the classical anhydrous conditions (NaH/THF). In this system, the phosphine is essential since no conversion was obtained when it is not present. The steric hindrance of the carbene ligand has a great influence on the activity and the stability of the catalytic system. The best NHC ligands for this reaction are either 1-mesityl-3-methyl-imidazol-2-ylidene or 1-(2,6-diisopropylphenyl)-3-methyl-imidazol-2-ylidene which are less bulky among the NHC tested. These two ligands led in 5 min to a complete conversion at 20 °C. The Pd-catalyzed allylic amination reaction using (E)-1,3-diphenylprop-3-en-yl acetate and benzylamine was also tested with (NHC)(PPh3)Pd complexes and under the biphasic conditions. This reaction was found to be slower than the alkylation with dimethylmalonate but a complete conversion could be reached in 6 h at 20 °C using K2CO3 1 M as the base. NMR experiments indicated that mixed (NHC)(PPh3)Pd complexes are formed in situ but their structure could not be established exactly.  相似文献   

15.
A small family of readily available phosphoramidite ligands, including compounds with P-stereocenters, has been prepared from phenyl-substituted 1,2-diols as simple and cheap starting materials. Using these ligands, up to 84% ee was achieved in Pd-catalyzed asymmetric allylic substitution. The influence of structural modules such as asymmetric atoms and steric demand on the enantioselectivity is discussed.  相似文献   

16.
Reaction between a chiral imidazole–amine precursor derived from (1R,2R)-trans-diaminocyclohexane and P1Cl (where P1 = PPh2, P(1,3,5-Me3C6H3)2, P(2,2′-O,O′-(1,1′-biphenyl), P((R)-(2,2′-O,O′-(1,1′-binaphthyl))) and P((S)-(2,2′-O,O′-(1,1′-binaphthyl)))) followed by RX (where R = nPr, iPr, CHPh2, X = Br; R = iPr, X = I), respectively, gives a selection of chiral imidazolium–phosphine compounds. Deprotonation of the imidazolium salt gives the corresponding NHC–P ligands that can be used in metal-mediated asymmetric catalytic applications. Catalytic reactions show that NHC–P ligands give a significantly greater rate of reaction for a palladium catalysed allylic substitution reaction in comparison to analogous di-NHC or NHC–imine ligands and that NHC–P hybrids are also effective for iridium catalysed transfer hydrogenation.  相似文献   

17.
《Tetrahedron: Asymmetry》2005,16(17):2965-2972
Two new chiral fluorous bis(oxazolines) with a fluorous content of 56.9% and 59.3%, respectively, have been prepared starting from (S)-serine and (S)-tyrosine. Applications of these compounds as fluorous box ligands in asymmetric alkylations gave ees up to 92%, and in allylic oxidations ees up to 50%. Recycling and reuse of the ligands in asymmetric alkylation and of the catalytic system in allylic oxidation gave the same enantioselectivities.  相似文献   

18.
The synthesis of a third generation phosphorus-containing dendrimer possessing 24 chiral iminophosphine end groups derived from (2S)-2-amino-1-(diphenylphosphinyl)-3-methylbutane is described. In situ complexation of this dendrimer by [Pd(η3-C3H5)Cl]2 affords a catalyst, which is used in asymmetric allylic alkylations of rac-(E)-diphenyl-2-propenyl acetate and pivalate. The percentage of conversion, the yield of isolated 2-(1,3-diphenylallyl)-malonic acid dimethyl ester, and its enantiomeric excess have been measured in each case, and were found to be good to very good (ee from 90% to 95%). Furthermore, the dendritic catalyst can be recovered and reused at least two times, with almost the same efficiency.  相似文献   

19.
Two novel P1-stereogenic bisdiamidophosphites derived from (3R,4R)-N-benzyltartarimide as a chiral 1,2-diol have been prepared from readily available starting materials. Palladium and rhodium catalytic systems containing these new P1,P1-bidentate ligands afforded 96%, 83% and 65% ee in asymmetric allylic substitution, hydrogenation and addition processes, respectively. These diastereomeric diamidophosphites were found to be complementary stereoselectors.  相似文献   

20.
《Tetrahedron: Asymmetry》2007,18(1):131-136
Enantiomeric pyrrolidine alcohols and Cinchona alkaloids reacted with PhSeCN/Bu3P in toluene at 0–25 °C to give the corresponding phenyl selenides with complete inversion of configuration at the substitution centers. Thus, the chiral selenoethers obtained were tested in the Pd-catalyzed allylic alkylation of dimethyl malonate with rac-1,3-diphenyl-2-propenyl acetate. When chiral selenium pyrrolidine derivatives were applied, the enantioselectivity observed was improved versus the respective sulfur pyrrolidine derivatives up to over 98% ee. The results suggest that the pyrrolidine selenoethers served as the effective N(sp3), Se-donating chiral ligands. The selenoethers obtained from Cinchona alkaloids also gave the allylic alkylation product with a higher ee over those for the corresponding thioethers. The results are in agreement with nucleophilic attack directed at the allylic carbon located trans to the chalcogen atom in the intermediate η3-allylpalladium complex.  相似文献   

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