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1.
The copper-catalysed aziridination of styrene derivatives using either Cu(OTf)2 as a homogeneous catalyst or copper-exchanged zeolite Y modified as a heterogeneous catalyst with bis(oxazoline) using [N-(p-nitrophenylsulfonyl)imino]phenyliodinane (PhI=NNs) as nitrene donor is described and discussed. For the homogeneously catalysed reaction virtually all the substituted derivatives gave lower yields of the aziridine with lower ee when compared with styrene, although 4-chlorostyrene did give enhanced ee. For the heterogeneous catalysed reaction the styrene derivatives often gave enhanced yield, particularly when the substituent was in the 4-position. Particularly high ee was observed for 2-chlorostyrene (95%) and 4-chlorostyrene (94%) and in general the ee observed for the heterogeneously catalysed reaction with the 2- and 4-substituted derivates was significantly higher than that for the equivalent homogeneously catalysed reaction. With copper-exchanged zeolite Y the leaching of Cu2+ into solution during reaction was much lower for the substituted styrene derivatives (0.4-7% of total Cu) than with styrene itself (10.3% of the total Cu). The effect of reaction time on aziridine yield reveals an S-shaped profile that is accentuated by the position of the substituent and this effect is observed for both the homogeneously catalysed pathway and the heterogeneously catalysed reaction. A series of competitive experiments in which styrene was co-reacted with equivalent quantities of 2-, 3- and 4-chlorostyrene revealed that the reaction of styrene enhanced by the other substrate, but the rate of reaction of the substituted styrene was decreased. Co-reaction of 2- and 4-chlorostyrene reveals interesting competitive effects, which are discussed in terms of the nature of the active site. 相似文献
2.
John Gullick Sophia Taylor Paul McMorn Donald Bethell Philip C Bulman Page Frederick E Hancock Frank King Graham Hutchings 《Journal of molecular catalysis. A, Chemical》2002,180(1-2):85-89
Chloramine-T and [N-(p-tolylsulfonyl)imino]phenyliodinane (PhI=NTs) are contrasted as nitrene donors for the aziridination of styrene using copper(II) triflate, and copper-exchanged zeolite Y (CuHY) as catalysts. For both catalysts, PhI=NTs is found to give significantly higher yields of the aziridine both in the presence and absence of a chiral bis(oxazoline) modifier. In addition, chloramine-T is found to induce leaching of most of the Cu from CuHY, and with this nitrene donor CuHY does not function as a heterogeneous catalyst. In contrast, PhI=NTs causes negligible leaching of Cu from CuHY and, consequently, for the heterogeneous CuHY catalyst, PhI=NTs is the preferred nitrene donor. With chloramine-T, the beneficial effects observed on addition of copper powder are shown to be due to the copper powder acting as a reservoir for Cu2+ in solution, since Cu2+ in solution is rapidly deactivated by toluenesulfonamide, a degradation product of the nitrene donor. 相似文献
3.
A new class of chiral pyrrolidine ligands have been successfully synthesized and their chiral induction abilities have been examined in the homogeneous catalytic enantioselective cyclo-propanation of styrene. 15-30% enantiomeric excess ( ee) has been achieved. 相似文献
4.
A novel chiral C(2)-symmetric 1,4-diamine with multistereogenic centers at the backbone of the ligand has been synthesized from cheap natural product D-mannitol through multistep transformations. Its diimine derivative (3 a) was found to be highly effective for the enantioselective control of the copper-catalyzed asymmetric aziridination of olefin derivatives with PhI==NTs as the nitrene source, affording the corresponding N-sulfonylated azirindine derivatives in good to excellent yields with up to 99 % ee (ee=enantiomeric excess). The catalyst system discovered in the present work was also extended to a one-pot enantioselective aziridination by using sulfonamide/iodobenzene diacetate as the nitrene source. In this case, most reactions proceeded smoothly to give the corresponding products in moderate yields with good to excellent enantiomeric excesses (75-96 % ee). 相似文献
5.
High enantioselectivity (80-92% enantiomeric excess (ee)) has been obtained for the epoxidation of various styrenes using an easily prepared ketone (4) catalyst. 相似文献
6.
Dinér P Kjaersgaard A Lie MA Jørgensen KA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(1):122-127
The origin of the enantioselectivity in the TMS-protected (TMS=trimethylsilyl) prolinol-catalysed alpha-heteroatom functionalisation of aldehydes has been investigated by using density functional theory calculations. Eight different reaction paths have been considered which are based on four different conformers of the TMS-protected prolinol-enamine intermediate. Optimisation of the enamine structures gave two intermediates with nearly the same energy. These intermediates both have an E configuration at the C==C bond and the double bond is positioned anti or syn, relative to the 2-substituent in the pyrrolidine ring. For the four intermediates, the chiral TMS-protected-diaryl substituent effectively shields one of the faces of the reacting C==C bond in the enamine intermediate. A number of transition states have been calculated for the enantioselective fluorination by N-fluorobenzenesulfonimide (NFSI) and based on the transition-state energies it has been found that the enantioselectivity depends on the orientation of the C==C bond, being anti or syn, relative to the 2-substituent on the pyrrolidine ring, rather than the approach of the electrophilic fluorine to the face of the reacting carbon atom in the enamine which is less shielded relative to the face with the highest shielding. The calculated enantiomeric excess of 96 % ee (ee=enantiomeric excess) for the fluorination reaction corresponds well with the experimentally found enantiomeric excess-97 % ee. The transition state for the alpha-amination reaction with the same type of intermediate has also been calculated by using diethyl azodicarboxylate as the amination reagent. The implication of the intermediate structures on the stereoselection of alpha-functionalisation of aldehydes is discussed. 相似文献
7.
8.
Liang JL Huang JS Yu XQ Zhu N Che CM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(7):1563-1572
Chiral metalloporphyrins [Mn(Por*)(OH)(MeOH)] (1) and [Ru(Por*)(CO)(EtOH)] (2) catalyze asymmetric aziridination of aromatic alkenes and asymmetric amidation of benzylic hydrocarbons to give moderate enantiomeric excesses. The mass balance in these nitrogen-atom-transfer processes has been examined. With PhI=NTs as the nitrogen source, the aziridination of styrenes, trans-stilbene, 2-vinylnaphthalene, indene, and 2,2-dimethylchromene catalyzed by complex 1 or 2 resulted in up to 99 % substrate conversions and up to 94 % aziridine selectivities, whereas the amidation of ethylbenzenes, indan, tetralin, 1-, and 2-ethylnaphthalene catalyzed by complex 2 led to substrate conversions of up to 32 % and amide selectivities of up to 91 %. Complex 1 or 2 can also catalyze the asymmetric amidation of 4-methoxyethylbenzene, tetralin, and 2-ethylnaphthalene with "PhI(OAc)(2) + NH(2)SO(2)Me", affording the N-substituted methanesulfonamides in up to 56 % ee with substrate conversions of up to 34 % and amide selectivities of up to 92 %. Extension of the "complex 1 + PhI=NTs" or "complex 1 + PhI(OAc)(2) + NH(2)R (R=Ts, Ns)" amidation protocol to a steroid resulted in diastereoselective amidation of cholesteryl acetate at the allylic C-H bonds at C-7 with substrate conversions of up to 49 % and amide selectivities of up to 90 % (alpha:beta ratio: up to 4.2:1). An aziridination- and amidation-active chiral bis(tosylimido)ruthenium(VI) porphyrin, [Ru(Por*)(NTs)(2)] (3), and a ruthenium porphyrin aziridine adduct, [Ru(Por*)(CO)(TsAz)] (4, TsAz=N-tosyl-2- (4-chlorophenyl)aziridine), have been isolated from the reaction of 2 with PhI=NTs and N-tosyl-2-(4-chlorophenyl)aziridine, respectively. The imidoruthenium porphyrin 3 could be an active species in the aziridination or amidation catalyzed by complex 2 described above. The second-order rate constants for the reactions of 3 with styrenes, 2-vinylnaphthalene, indene, ethylbenzenes, and 2-ethylnaphthalene range from 3.7-42.5x10(-3) dm(3) mol(-1) s(-1). An X-ray structure determination of complex 4 reveals an O- rather than N-coordination of the aziridine axial ligand. The fact that the N-tosylaziridine in 4 does not adopt an N-coordination mode disfavors a concerted pathway in the aziridination by a tosylimido ruthenium porphyrin active species. 相似文献
9.
Sandee AJ Petra DG Reek JN Kamer PC van Leeuwen PW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(6):1202-1208
The solid-phase synthesis of new asymmetric transfer hydrogenation catalysts as well as the use of these silica supported systems in batch and flow reactors is reported. The ruthenium complex of NH-benzyl-(1R,2S)-(-)-norephedrine covalently tethered to silica showed a high activity and enantioselectivity in the reduction of acetophenone. In three consecutive batchwise catalytic runs, we obtained ee values of 88%. In a continuous flow reactor, a very constant catalytic activity was observed; no catalyst deactivation occurred over a period of one week. This has been ascribed to successful site isolation. Using optimized conditions in this flow reactor, the ee was as high as 90% at 95% conversion. The supported catalysts generally show the same trend in catalyst performance as in solution. The viability of our approach was further shown in one example, the ruthenium(II) complex of (1S,2R)-(+)-2-amino-1,2-diphenylethanol, for which an enantiomeric excess of 58% was observed, which is nearly three times higher than its homogeneous analogue. 相似文献
10.
A practical mass spectrometry-based enantioselectivity assay is presented which makes use of enantiomerically enriched, but not enantiomerically pure, probe molecules readily obtained from esterase hydrolysis of prochiral malonates. The technique presented here allows us to recycle materials obtained from esterase hydrolysis which give substantial, but synthetically insufficient, enantiomeric excess as probe molecules in an enantioselectivity assay. The enantiomerically enriched products are esterified using deuterium-labelled alcohol. The enantiomeric excess is measured using mass spectrometry (LC–MS and LDI) by measuring the D5/H5 ratio in the resulting products obtained from an enzymatic hydrolysis. The D5/H5 ratio is corrected to account for the enantiomeric purity of the probe. Herein we report the results obtained from Pig Liver Esterase hydrolyses of prochiral malonate esters and outline the strengths and limitations of this approach to enantioselectivity determinations. This assay strategy was able to identify reaction conditions that led to an improvement in ee from 70% ee to >97% ee in the PLE-catalyzed hydrolysis of a prochiral malonate used to prepare unnatural serine analogues. 相似文献
11.
Graham E. O'Mahony Kevin S. Eccles Robin E. Morrison Alan Ford Simon E. Lawrence Anita R. Maguire 《Tetrahedron》2013
Steric and electronic effects in the copper-catalysed asymmetric oxidation of aryl benzyl, aryl alkyl and alkyl benzyl sulfides have been investigated. The presence of an aryl group directly attached to the sulfur is essential to afford sulfoxides with high enantioselectivities, with up to 97% ee for 2-naphthyl benzyl sulfoxide, the highest enantioselectivity achieved to date for copper-catalysed asymmetric sulfoxidation. In contrast, the benzyl substituent can be replaced by sterically comparable groups with no effect on enantioselectivity. Copper-mediated oxidation of substituted aryl benzyl sulfides display modest steric and electronic effects resulting in comparable or lower enantioselectivities to those obtained with the unsubstituted benzyl phenyl sulfide. 相似文献
12.
Raquel Almansa Juan F. Collados David Guijarro Miguel Yus 《Tetrahedron: Asymmetry》2013,24(2-3):116-120
l-Prolinol-based ligands anchored to Merrifield or Wang-type resins have been shown to form efficient catalysts for the enantioselective addition of dialkylzinc reagents to N-(diphenylphosphinyl)imines. The enantioselectivity achieved with the polymeric catalyst (ee up to 88%) is slightly lower than the one obtained with the homogeneous ligand N-benzyl-l-prolinol, but the polymer-supported ligand presents the advantage of its recyclability: it can be recovered and used in up to six consecutive catalytic cycles with only a slight decrease in the enantiomeric excess. The phosphinamides obtained as addition products can be transformed into the corresponding enantiomerically enriched α-branched primary amines under mild acidic conditions. 相似文献
13.
M. Merced Montero‐Campillo M. Natália D. S. Cordeiro 《International journal of quantum chemistry》2013,113(16):2002-2011
Experimental studies show that copper complexes can be effectively anchored onto the pores of mesoporous solids, having a good catalytic performance in several reactions, among them the aziridination of olefins and in particular, styrene. In this work, the mechanism of the aziridination of styrene catalyzed by a bis(oxazoline) copper(I) complex was studied in detail by means of density functional theory (DFT) calculations. For such reactions in the homogeneous phase, our calculations revealed a wide diversity of reaction‐pathways, which have not been considered in previous studies, and should be taken into account due to the small energy differences between them. What is more, our results show that there is a strong dependence on the chosen DFT functional. This has profound implications on the way the heterogeneous reaction is studied. © 2013 Wiley Periodicals, Inc. 相似文献
14.
Gullick J Taylor S Ryan D McMorn P Coogan M Bethell D Bulman Page PC Hancock FE King F Hutchings GJ 《Chemical communications (Cambridge, England)》2003,(22):2808-2809
During the aziridination of styrene using copper bis(oxazoline) complexes the ee increases with conversion due to further reactions of the product. 相似文献
15.
Highly enantioselective aziridination of chalcones catalyzed by a novel backbone 1,8-bisoxazolidinylanthracene (AnBOX) and CuOTf with up to >99% ee and the opposite enantioselectivity compared with the ligands of Evans are described. 相似文献
16.
Asymmetric conjugate addition reaction of 2-trimethylsilylbenzenethiol with enoates and enones is catalyzed by a chiral amino ether-lithium thiolate complex and affords adducts with high enantioselectivity. Both the s-cis conformation and a steric wall at one side of the carbonyl group are structural requirements in substrates yielding adducts with high enantioselectivity. Reactions with tert-butyl enones gave addition products with high enantioselectivity. Construction of two contiguous chiral centers was possible by this addition-protonation sequence. Methyl tiglate was stereoselectively converted to a single syn-adduct of 95% enantiomeric excess (ee) bearing two contiguous chiral centers. Methyl 2-phenyl-2-butenoate was converted to a single syn-adduct of 95% ee, which was desulfurized to methyl 2-phenylbutanoate of 95% ee. These additions generate a transient lithium enolate that is protonated by a thiol anti to the C-S bond, giving the corresponding product having two adjacent stereocenters. 相似文献
17.
水-离子液和水-有机溶剂体系中萘普生酶法拆分的比较研究 总被引:6,自引:1,他引:6
在水—有机溶剂和水—离子液两相体系中研究了脂肪酶催化的萘普生甲酯的立体选择性水解反应。考察了转化率,对映体过量值(eep);(ees)与时间的关系。据此构建了一种可以进行萘普生甲酯立体选择性水解的水—离子液两相体系,在该水—离子液两相体系中酶的活性与传统的水—有机相两相体系相比没有明显的变化,但是酶的立体选择性却明显提高,同时也对水—离子液两相体系中水含量对萘普生甲酯立体选择性水解反应的影响进行了研究,发现在水:离子液(v/v)为1:1时酶的活性和立体选择性最好。 相似文献
18.
Vijaya Bhaskara Reddy Iska Shashi Kant Tiwari Gadamsetti Surendra Babu Adeline Adrien 《Tetrahedron letters》2007,48(40):7102-7107
Chiral cyclic and acyclic allyl aminosulfoxonium ylides have been generated from aminosulfoxonium-substituted β,γ-unsaturated α-amino acids (method A) and 1-alkenyl aminosulfoxonium salts (method B) upon treatment with DBU. Their application to the asymmetric aziridination of N-tert-butyl-sulfonyl imino ester, generated either in situ (method A) or externally added (method B), gave the corresponding alkenyl aziridine carboxylates with medium to high diastereoselectivity and enantioselectivity. A highly stereoselective Pd(0)-catalyzed isomerization of an E,trans-configured alkenyl aziridine methanol derivative to its E-cis-isomer is described, which proceeded with retention of the double bond configuration. 相似文献
19.
《Tetrahedron: Asymmetry》2005,16(22):3718-3734
A series of rigid backbone 1,8-anthracene-linked bis-oxazolines (AnBOXes) have been designed, synthesized, and evaluated in the catalytic asymmetric aziridination with [N-(p-toluenesulfonyl)imino]phenyliodinane (PhINTs) as a nitrene source. The results indicate that highly enantioselective aziridination of chalcones catalyzed by an AnBOX and CuOTf complex with up to >99% ee and the opposite enantioselectivity, compared with the ligands of Evans et al., can be achieved. The enantioselectivity is substituent dependent with respect to chalcones. Chalcones with electron-donating substituents show higher enantioselectivities due to the stronger Lewis basicity of the oxygen of their carbonyl groups than those with electron-withdrawing substituents. The results also indicate that the coordination between the oxygen of the carbonyl group in chalcones and the ether group in alkenes with the copper in the catalyst is essential for high enantioselectivity, while the π–π stacking interaction between two reactants plays an importantly additional role for high enantioselectivity in asymmetric aziridination. An excellent backbone-controlled stereoselectivity was observed for the AnBOX ligands in asymmetric aziridination, as this will provide very important information for designing novel ligands. 相似文献
20.
The activity and enantiomeric excess (ee) (in some cases >85%) obtained for the asymmetric addition of trimethylsilyl cyanide to aldehydes using different heterogeneous chiral catalysts are compared. A library of recoverable catalysts was developed by immobilization of a chiral vanadyl salen complex having a terminal carbon-carbon double bond onto a series of scaffolds including silica, single-wall carbon nanotubes, activated carbon and room-temperature ionic liquids. The covalent linkage has been achieved by radical initiated addition of mercapto groups to CC. The highest enantiomeric excesses, similar to those obtained in the homogeneous phase, were achieved using silica as support or with the homogeneous tetra-tert-butyl salen catalyst dissolved in an imidazolium ionic liquid. The use of silica as support permits an easier separation and reuse of the catalyst from the reaction media. 相似文献