Enantioselective Epoxidation Of Olefins Research Articles

Enantioselective epoxidation of alkenes catalyzed by 2-fluoro-N-carbethoxytropinone and related tropinone derivatives.

Several alpha-substituted N-carbethoxytropinones have been evaluated as catalysts for asymmetric epoxidation of alkenes with Oxone, via a dioxirane intermediate. alpha-Fluoro-N-carbethoxytropinone (2) has been studied in detail and is an efficient catalyst which does not suffer from Baeyer-Villiger decomposition and can be used in relatively low loadings. This ketone was prepared in enantiomerically pure form using chiral base desymmetrization of N-carbethoxytropinone. Asymmetric epoxidation catalyzed by 2 affords epoxides with up to 83% ee. Among other derivatives tested, the alpha-acetoxy derivative 7 affords the highest enantioselectivities.

Enantioselective epoxidation of olefins catalyzed by Mn (salen)/MCM-41 synthesized with a new anchoring method.

New immobilization of the chiral Mn(salen) complex through the complexation of managanese by oxygen atoms of the phenoxyl groups grafted on the surface of MCM-41 leads to a markedly higher ee than for the free complex.

Jacobsen’s Catalyst

Enantioselective epoxidation of olefins is a challenging and useful synthetic transformation. [1] Since its introduction in the early nineties, Jacobsen’s catalyst has proved reliable for highly enantioselective epoxidation of prochiral olefins. [2] Belonging to the salen-ligand class, [3] the catalyst has a manganese core in a square planar geo­metry, stabilised with a chlorine atom in the axial position. [2] Several stoichiometric oxidants have been used successfully, [4] with NaOCl the most frequently involved. [1a] [b] [5] Easy to prepare, the catalyst has become commercially available in both enantiomeric forms. [6] Applied also for the enantioselective oxidation of sulfides to sulf­oxides, [4e] and for the oxidation of hydrocarbons at the benzylic position, [4c] the catalyst has even been synthesised in a dimeric form for the epoxidation of olefins under heterogeneous conditions. [7] Recently, it has provided the first example of didehydrogenation of secondary hydroxyl­amines to the corresponding nitrones. [8]

Effect of Fifth Coordination in Catalytic Epoxidation by a Chiral Manganese Porphyrin

The effect of multifarious organic bases in chiral manganese porphyrin catalyzed enantioselective alkene epoxidation was investigated. For substituted pyridines, the enantioselectivity of cis-β-methylstyrene epoxidation follows a linear free energy relationship for pyridines bearing electron-donating groups. Compared to the case of no amine additive, a significant improvement in enantio­selectivity from 43% ee to 81% ee for epoxidation of cis-β-methylstyrene with a 86.5% stereospecificity were observed when DMAP and KHSO5 were employed as axial ligand and oxidant respectively.

Highly efficient asymmetric epoxidation of alkenes with a D(4)-symmetric chiral dichlororuthenium(IV) porphyrin catalyst.

A dichlororuthenium(IV) complex of 5,10,15,20-tetrakis[(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,2:5,8-dimethanoanthrance-9-yl]porphyrin, [Ru(IV)(D(4)-Por)Cl(2)] (1), was prepared by heating [Ru(II)(D(4)-Por)(CO)(MeOH)] (2) in refluxing CCl(4). Complex 1 is characterized by (1)H NMR (paramagnetically shifted pyrrolic protons at delta(H) = -52.3 ppm), FAB-mass spectroscopies, and magnetic susceptibility measurement (mu(eff) = 3.1 mu(B)). The ruthenium complex exhibits remarkable catalytic activity toward enantioselective alkene epoxidation using 2,6-dichloropyridine N-oxide (Cl(2)pyNO) as terminal oxidant. The Ru(IV)-catalyzed styrene epoxidation is achieved within 2 h (versus 48 h for the 2-catalyzed reaction), and optically active styrene oxide was obtained in 69% ee and 84% yield (875 turnovers). Likewise, substituted styrenes and some conjugated cis-disubstituted alkenes (e.g., cis-beta-methylstyrene, cis-1-phenyl-3-penten-1-yne, 1,2-dihydronaphthalene, and 2,2-dimethylchromenes) are converted effectively to their organic epoxides in 50-80% ee under the Ru(IV)-catalyzed conditions, and more than 850 turnovers of epoxides have been attained. When subjecting 1 to four repetitive uses by recharging the reaction mixture with Cl(2)pyNO and styrene, styrene oxide was obtained in a total of 2190 turnovers and 69% ee. UV-vis and ESI-mass spectral analysis of the final reaction mixture revealed that a ruthenium-carbonyl species could have been formed during the catalytic reaction, leading to the apparent catalyst deactivation. We prepared a heterogeneous chiral ruthenium porphyrin catalyst by immobilizing 1 into sol-gel matrix. The heterogeneous catalyst is highly active toward asymmetric styrene epoxidation producing styrene oxide in 69% ee with up to 10,800 turnovers being achieved. The loss of activity of the Ru/sol-gel catalyst is ascribed to catalyst leaching and/or deactivation. On the basis of Hammett correlation (rho(+) = -1.62, R = 0.99) and product analysis, a dioxoruthenium(VI) porphyrin intermediate is not favored.

Synthesis and Spectral and Structural Characterization of a New Series of Bis-Strapped Chiral Porphyrins Derived from L-Proline

New chiral porphyrins were obtained in reasonable yields in three steps, starting from the aâaâ atropisomer of mesotetrakis(o-aminophenyl)porphyrin (TAPP). These potential catalysts for the enantioselective epoxidation of alkenes were obtained by the reaction of different linkers on the same Lprolinoyl-picket porphyrin. Their 1H NMR spectral characteristics, as well as the crystal structure of one of them, clearly indicate that the orientation of the proline cycle depends on the linker used to tether the two pickets on each side of the porphyrin. The same linker is employed for both sides of the porphyrin; hence the resulting D2-symmetric superstructure.

Synthesis and Use of Jacobsen's Catalyst: Enantioselective Epoxidation in the Introductory Organic Laboratory

Jacobsen's catalyst, N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride, is a popular reagent for the enantioselective epoxidation of alkenes. This reagent is suc...

Chiral dioxomolybdenum(VI) complexes for enantioselective alkene epoxidation

Chiral dioxomolybdenum(VI) complexes of the type MoO 2Cl 2(L*) (L*=oxime), MoO 2(THF) 2L* (L*= cis- p-menthane-3,8-diol) and MoO 2Cl(THF)L* (L*=8-phenylthioneomenthol and 8-phenylthioisoneomenthol) have been prepared in good yields by reacting MoO 2Cl 2(THF) 2 with the appropriate chiral organic bidentate O,O-, O,N- and O,S-ligands. The complexes were characterised by solution NMR ( 1H, 13C, 95Mo) and IR spectroscopy as well as elementary analysis, and were evaluated as catalysts in solution for the asymmetric epoxidation of cis-β-methylstyrene by tert-butylhydroperoxide (TBHP). The cis-diol complex shows high catalytic activity and enantiomeric excesses of up to 25%. An attempt was made to immobilise the complex MoO 2(THF)Cl[(−)-8-phenylthioneomenthol] within the channels of MCM-41 mesoporous silica by using a tethering ligand [L=NC(CH 2) 3Si(OEt) 3]. The material was characterised by powder X-ray diffraction (XRD), IR spectroscopy and magic-angle-spinning (MAS) NMR ( 13C, 29Si). Catalytic examinations demonstrated that it was active in the epoxidation of cyclooctene by TBHP.

Enantioselective epoxidation of olefins catalyzed by new sterically hindered salen–Mn(III) complexes

New, sterically hindered chiral salen–Mn(III) complexes, 5 and 6 , were prepared from an aldehyde derived from BINOL. These substances catalyze efficient, enantioselective NaOCl-promoted epoxidations of olefins and enantioselectivities as high as 96–99% ee are observed in epoxidations of cis-β-methylstyrene and 2,2-dimethylchromene.

Enantioselective epoxidation of olefins catalyzed by two novel chiral poly-salen–Mn(III) complexes

Two novel chiral poly-salen–Mn(III) complexes 1 and 2, derived from ( R, R)-1,2-diaminocyclohexane and the disalicylaldehydes 5 and 6 were synthesized and employed in the enantioselective epoxidation of olefins. A range of 30–92% ee and 75–97% yield was achieved in NaClO/4-PPNO and m-CPBA/NMO oxidant systems when substituted styrenes and substituted 2,2-dimethylchromenes were used as substrates. Furthermore, the poly-salen–Mn(III) complexes could be recovered easily and recycled efficiently several times by a simple catalysis/separation method. After five reactions, an 82% ee and 78% yield of epoxide were obtained using 2,2-dimethylchromene as substrate.

Second-generation fluorous chiral (salen) manganese complexes

Sterically hindered chiral (salen)manganese complexes bearing long perfluoroalkyl substituents are synthesized and successfully employed as catalysts in the enantioselective (ee = 50–87%) epoxidation of alkenes under fluorous biphasic conditions.

The Development of Chiral, Nonracemic Dioxiranes for the Catalytic, Enantioselective Epoxidation of Alkenes

The catalytic, enantioselective epoxidation of unfunctionalized alkenes is a long-standing objective in organic synthesis. With the advent of dioxiranes as powerful oxygen atom transfer reagents that operate under neutral conditions, much attention has been directed to the development of chiral ketone precursors that can catalytically, differentiate the enantiotopic faces of simple alkenes. Advances in the design of various catalyst structures and the understanding of factors that influence high catalytic activity and stereoselectivity are presented.

Ruthenium-oxo and -tosylimido porphyrin complexes for epoxidation and aziridination of alkenes

Abstract

ChemInform Abstract: Catalytic Enantioselective Epoxidation of Alkenes with a Tropinone‐Derived Chiral Ketone.

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Catalytic enantioselective epoxidation of alkenes with a tropinone-derived chiral ketone

α-Fluoro-N-ethoxycarbonyltropinone is an efficient catalyst for the epoxidation of alkenes by Oxone® with good enantioselectivity.

Stoichiometric enantioselective alkene epoxidation with a chiral dioxoruthenium(VI) D4-porphyrinato complex

A dioxoruthenium(VI) complex containing a D4-porphyrinato ligand por* {H2por* = 5,10,15,20-tetrakis[(1S,4R,5R,8S)-1,2,3,4,5,6,7,8-octahydro-1,4∶5,8-dimethanoanthracen-9-yl]porphyrin} has been prepared by oxidation of its ruthenium(II) carbonyl precursor with m-chloroperoxybenzoic acid and characterised by spectroscopic methods. The [RuVI(por*)O2] complex undergoes enantioselective epoxidation of alkenes and the highest enantiomeric excess (ee) attainable is 77%. In the presence of pyrazole the complex transforms to [RuIV(por*)(pz)2] when reacting with alkenes. The kinetics of the epoxidation of para-substituted styrenes has been studied. The experimental rate law is –d[RuVI]/dt = k2[RuVI][alkene]. The second order rate constants k2 at 25 °C fall in a narrow range, 2.1 × 10–3–9.7 × 10–3 dm3 mol–1 s–1. Comparison of the Hammett plot (log krelvs. σ˙) with those for achiral analogues [RuVI(tpp)O2] (H2tpp = 5,10,15,20-tetraphenylporphyrin) and [RuVI(oep)O2] (H2oep = 2,3,7,8,12,13,17,18-octaethylporphyrin) suggests the formation of a radical intermediate for the alkene epoxidations. Both [RuII(por*)(CO)(EtOH)] and [RuVI(por*)O2] were examined for enantioselective catalysis. Enantioselectivities of the stoichiometric and catalytic reactions showed good correlation. There is no solvent dependence on enantioselectivity when changing the solvent from dichloromethane to benzene.

Aerobic enantioselective alkene epoxidation by a chiral trans-dioxo(D4-porphyrinato)ruthenium(VI) complex

Download options Please wait... Article information DOI https://doi.org/10.1039/A802009D Article type Paper Download Citation Chem. Commun., 1998, 1583-1584 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Aerobic enantioselective alkene epoxidation by a chiral trans-dioxo(D4-porphyrinato)ruthenium(VI) complex T. Lai, R. Zhang, K. Cheung, C. Che, T. Lai and H. Kwong, Chem. Commun., 1998, 1583 DOI: 10.1039/A802009D To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Tat-Shing Lai Rui Zhang Kung-Kai Cheung Chi-Ming Che Tat-Shing Lai Hoi-Lun Kwong

Polymeric catalysts for chemo- and enantioselective epoxidation of olefins: New crosslinked chiral transition metal complexing polymers

Polymeric analogs of well-known chiral Mn(III)-salen complexes were synthesized and were used as recyclable catalysts for asymmetric epoxidation of olefins. For this purpose two different monomers, 2 and 3, bearing chiral Mn(III)-salen moieties were synthesized. The monomer 3 carries a bulky substituent closer to the Schiff base moiety, while monomer 2 lacks such a substituent. These metal complexed chiral monomers were subsequently copolymerized with ethylene glycol dimethacrylate producing insoluble crosslinked functional matrices that possess macroporous morphology. Chemo- and enantioselective catalytic activities of these two polymers were evaluated for epoxidation of olefins. Both polymers catalyzed the epoxidation of a variety of olefins at room temperature in the presence of iodosylbenzene (PhIO) as the terminal oxidant with yields comparable to the homogenous system. In terms of their enantioselective catalytic activity, polymer P-2 (obtained from 3) performed better than polymer P-1 (obtained from 2). Unfortunately, while the homogeneous systems are reported to offer over 80% enantioselectivity, with the present polymeric catalysts, enantioselectivity to a maximum of 30% were observed. Unlike the homogeneous system, use of an external nitrogenous donor played a very insignificant role in influencing enantioselectivity.

Polymeric catalysts for chemo‐ and enantioselective epoxidation of olefins: New crosslinked chiral transition metal complexing polymers

Polymeric analogs of well-known chiral Mn(III)-salen complexes were synthesized and were used as recyclable catalysts for asymmetric epoxidation of olefins. For this purpose two different monomers, 2 and 3, bearing chiral Mn(III)-salen moieties were synthesized. The monomer 3 carries a bulky substituent closer to the Schiff base moiety, while monomer 2 lacks such a substituent. These metal complexed chiral monomers were subsequently copolymerized with ethylene glycol dimethacrylate producing insoluble crosslinked functional matrices that possess macroporous morphology. Chemo- and enantioselective catalytic activities of these two polymers were evaluated for epoxidation of olefins. Both polymers catalyzed the epoxidation of a variety of olefins at room temperature in the presence of iodosylbenzene (PhIO) as the terminal oxidant with yields comparable to the homogenous system. In terms of their enantioselective catalytic activity, polymer P-2 (obtained from 3) performed better than polymer P-1 (obtained from 2). Unfortunately, while the homogeneous systems are reported to offer over 80% enantioselectivity, with the present polymeric catalysts, enantioselectivity to a maximum of 30% were observed. Unlike the homogeneous system, use of an external nitrogenous donor played a very insignificant role in influencing enantioselectivity. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1809–1818, 1997

Enantioselective epoxidation of olefins by single-oxygen atom donors catalyzed by managanese-glycoconjugated porphyrins

New chiral porphyrins bearing glycosyl substituents (glucose, maltose or lactose) at ortho or meta positions of the meso-phenyl groups have been synthesized. Their manganese complexes, associated with hydrogen monopersulfate, lithium hypochlorite, hydrogen peroxide, or iodosylbenzene, have been used as enantioselective catalysts for the epoxidation of 4-chlorostyrene and 1,2-dihydronaphthalene.