Enantioselective Epoxidation Of Olefins Research Articles

The Juliá-Colonna Reaction: A Phase-Transfer Catalyzed Enantioselective Olefin Epoxidation

Juliá and Colonna were one of the firsts chemists reporting examples of enantioselective organocatalyzed reactions, namely the Phase-Transfer Catalysis (PTC) olefin epoxidation. Although some reviews exist on the Juliá-Colonna reaction, none is devoted specifically to it. After an introduction reporting the main publications gathered in three tables, this review is organized into a) olefin epoxidation; b) other enantioselective catalysts; c) Juliá-Colonna papers; d, e) papers citing the "Juliá-Colonna" epoxidation with special stress on those by Stanley M. Roberts. This review summarizes the papers by these authors and reports the most relevant improvements.

Organoantimony Dihydroperoxides: Synthesis, Crystal Structures, and Hydrogen Bonding Networks.

Despite growing interest in the potential applications of p-block hydroperoxo complexes, the chemistry of inorganic hydroperoxides remains largely unexplored. For instance, single-crystal structures of antimony hydroperoxo complexes have not been reported to date. Herein, we present the synthesis of six triaryl and trialkylantimony dihydroperoxides [Me3Sb(OOH)2, Me3Sb(OOH)2·H2O, Ph3Sb(OOH)2·0.75(C4H8O), Ph3Sb(OOH)2·2CH3OH, pTol3Sb(OOH)2, pTol3Sb(OOH)2·2(C4H8O)], obtained by the reaction of the corresponding dibromide antimony(V) complexes with an excess of highly concentrated hydrogen peroxide in the presence of ammonia. The obtained compounds were characterized by single-crystal and powder X-ray diffraction, Fourier transform infrared and Raman spectroscopies, and thermal analysis. The crystal structures of all six compounds reveal hydrogen-bonded networks formed by hydroperoxo ligands. In addition to the previously reported double hydrogen bonding, new types of hydrogen-bonded motifs formed by hydroperoxo ligands were found, including infinite hydroperoxo chains. Solid-state density functional theory calculation of Me3Sb(OOH)2 revealed reasonably strong hydrogen bonding between OOH ligands with an energy of 35 kJ/mol. Additionally, the potential application of Ph3Sb(OOH)2·0.75(C4H8O) as a two-electron oxidant for the enantioselective epoxidation of olefins was investigated in comparison with Ph3SiOOH, Ph3PbOOH, t-BuOOH, and H2O2.

Mechanistic Studies on the Epoxidation of Alkenes by Macrocyclic Manganese Porphyrin Catalysts.

Macrocyclic metal porphyrin complexes can act as shape‐selective catalysts mimicking the action of enzymes. To achieve enzyme‐like reactivity, a mechanistic understanding of the reaction at the molecular level is needed. We report a mechanistic study of alkene epoxidation by the oxidant iodosylbenzene, mediated by an achiral and a chiral manganese(V)oxo porphyrin cage complex. Both complexes convert a great variety of alkenes into epoxides in yields varying between 20–88 %. We monitored the process of the formation of the manganese(V)oxo complexes by oxygen transfer from iodosylbenzene to manganese(III) complexes and their reactivity by ion mobility mass spectrometry. The results show that in the case of the achiral cage complex the initial iodosylbenzene adduct is formed on the inside of the cage and in the case of the chiral one on the outside of the cage. Its decomposition leads to a manganese complex with the oxo ligand on either the inside or outside of the cage. These experimental results are confirmed by DFT calculations. The oxo ligand on the outside of the cage reacts faster with a substrate molecule than the oxo ligand on the inside. The results indicate how the catalytic activity of the macrocyclic porphyrin complex can be tuned and explain why the chiral porphyrin complex does not catalyze the enantioselective epoxidation of alkenes.

Triphenyllead Hydroperoxide: A 1D Coordination Peroxo Polymer, Single-Crystal-to-Single-Crystal Disproportionation to a Superoxo/Hydroxo Complex, and Application in Catalysis.

The synthesis, transformation, and application in catalysis of triphenyllead hydroperoxide, the first dioxygen lead complex, are described. Triphenyllead hydroperoxide is characterized by 207Pb nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and single-crystal X-ray diffraction, revealing the first one-dimensional (1D) coordination peroxo polymer. Photolytic isomorphous transformation of Ph3PbOOH yields a mixed hydroxo/superoxo crystalline structure, the first nonalkali superoxo crystalline metal salt, which is stable up to 100 °C. Upon further photolysis, another isomorphous transformation of the superoxide to hydroxide is observed. These are the first single-crystal-to-single-crystal hydroperoxide-to-superoxide and then to hydroxide transformations reported to date. Photolysis of triphenyllead hydroperoxide yields two forms of superoxide-doped crystalline structures that are distinguished by widely different characteristic relaxation times. The use of Ph3PbOOH as an easy-to-handle solid two-electron oxidant for the highly enantioselective epoxidation of olefins is described.

Theoretical and experimental investigations of the enantioselective epoxidation of olefins catalyzed by manganese complexes

The enantioselective epoxidation of olefin by MnII(R,R-PMCP)(OTf)2, H2O2 and H2SO4 was explored by DFT calculations and experiments. Theoretical results suggest that [MnV(O)(R,R-PMCP)(SO4)]+ species with a triplet ground spin state serves as the active species for the olefin epoxidation. It can be generated by the H2SO4 assisted O-O heterolysis of MnIII(OOH) species. MnIII-persulfate is also involved in this system, but it cannot promote the olefin epoxidation directly, preferring instead to transform into MnV(O). Actually, the asymmetric epoxidation reactions with H2O2/H2SO4 or Oxone provide similar enantioselectivity in the presence of manganese catalyst. These observations further support the transformation of MnIII-persulfate to MnV(O) species.

Two (Chemo)-Enzymatic Cascades for the Production of Opposite Enantiomers of Chiral Azidoalcohols

Multi-step cascade reactions have gained increasing attention in the biocatalysis field in recent years. In particular, multi-enzymatic cascades can achieve high molecular complexity without workup of reaction intermediates thanks to the enzymes’ intrinsic selectivity; and where enzymes fall short, organo- or metal catalysts can further expand the range of possible synthetic routes. Here, we present two enantiocomplementary (chemo)-enzymatic cascades composed of either a styrene monooxygenase (StyAB) or the Shi epoxidation catalyst for enantioselective alkene epoxidation in the first step, coupled with a halohydrin dehalogenase (HHDH)-catalysed regioselective epoxide ring opening in the second step for the synthesis of chiral aliphatic non-terminal azidoalcohols. Through the controlled formation of two new stereocenters, corresponding azidoalcohol products could be obtained with high regioselectivity and excellent enantioselectivity (99% ee) in the StyAB-HHDH cascade, while product enantiomeric excesses in the Shi-HHDH cascade ranged between 56 and 61%.

Enhanced enantioselectivity in heterogeneous manganese-catalyzed asymmetric epoxidation with nanosheets modified amino acid Schiff bases as ligands by modulating the orientation and the arrangement order

Catalytic enantioselective epoxidation of olefins plays an important role in the production of optically-active epoxy. Transition-metal complexes prove efficient for the catalytic epoxidation of un-functionalized olefins by employing privileged chiral ligands with rotational symmetry and bulky substituents, which usually require complicated multistep synthesis and are often very expensive. Here, this work proposes an efficient strategy to promote the enantioselectivity of Mn(III)-catalyzed indene epoxidation, which simply utilizes the nanosheets of layered double hydroxides (LDHs) to modify α-amino acid derivatives as chiral ligands, achieving an enantioselectivity of more than 91.0%, much higher than that (<35%) in the previous reports using chiral ligands without any rotational-symmetry. By virtue of “flexible” interlayer spaces of LDHs, intercalated L-tert-leucine, L-valine, L-leucine, and L-phenylalanine anions have further been derived in situ to L-tert-leucine, L-valine, L-leucine, and L-phenylalanine Schiff base anions. Over the Mn(III) coordinated with L-phenylalanine Schiff base anion intercalated LDHs, an indene conversion of 81.0 ± 1.0%, a chem-selectivity of 89.0 ± 1.0%, and an enantiomeric excesses (ee) value of 94.5 ± 0.5% for (1S,2R)-1,2-epoxyindane have been afforded. The spatial effects of LDH nanosheets on the enantioselectivity have been investigated, focusing on the interlayer orientation and arrangement order of intercalated amino acid derivative anions. The strategy has been proved valid for the epoxidation of functionalized olefins, which is more challenging, including allylic alcohols, chalcone, and chromene derivatives.

High‐Spin and Low‐Spin Perferryl Intermediates in Fe(PDP)‐Catalyzed Epoxidations

AbstractTwo bioinspired hydroxo‐bridged diferric complexes 6 and 7 with N4‐donor ligands of the PDP type (PDP=N,N′‐bis(pyridin‐2‐ylmethyl)‐2,2′‐bipyrrolidine), differing by substituents at the pyridine rings (4‐NMe2 in 7 vs. 3,5‐Me2‐4‐OMe in 6), efficiently catalyze the enantioselective alkene epoxidation with H2O2 and peracetic acid in the presence of a carboxylic acid additive (up to 99 catalyst turnover numbers, TON, toward epoxide, up to 94 % ee). Catalyst systems based on complex 7 display the high‐spin perferryl intermediate 7 aAA (S=3/2, g1, g2=3.69, g3=1.96), whereas catalyst systems based on complex 6 exhibit the low‐spin perferryl intermediate 6 aAA (S=1/2, g1=2.07, g2=2.01, g3=1.96). The S=3/2 and the S=1/2 intermediates directly react with cyclohexene and cyclohexane at low temperatures (−40 °C and −85 °C, respectively). The catalyst systems, exhibiting less reactive intermediate 7 aAA, demonstrate higher enantioselectivity (% ee) in the epoxidation of chalcone. The origin of the unprecedented high‐spin state of the perferryl intermediate is discussed.

Covalently functionalized carbon nanoparticles with a chiral Mn-Salen: a new nanocatalyst for enantioselective epoxidation of alkenes.

A new protocol to obtain carbon nanoparticles (CNPs) covalently functionalized with a chiral Mn-Salen catalyst is described here. The new nanocatalyst (CNPs-Mn-Salen) was tested in the enantioselective epoxidation of some representative alkenes (CN-chromene, 1,2-dihydronaphthalene and cis-β-ethyl styrene), obtaining better enantiomeric excess values than that of the catalyst single molecule, highlighting the role of the nanostructure in the enantioselectivity.

Highly enantioselective epoxidation of olefins by H2O2 catalyzed by a non-heme Fe(ii) catalyst of a chiral tetradentate ligand.

The chiral tetradentate N4-donor ligand, 1-methyl-2-({(S)-2-[(S)-1-(1-methylbenzimidazol-2-yl methyl)pyrrolidin-2-yl]pyrrolidin-1-yl}methyl) benzimidazole (S,S-PDBzL), based on a chiral dipyrrolidine backbone, has been synthesized and its corresponding Fe(ii) complex has been prepared and characterized. The X-ray structure of the complex reveals that the Fe(ii) ion is in a distorted octahedral coordination environment with two cis-oriented coordination sites occupied by (labile) triflate anions. The ability of the iron complex to catalyze asymmetric epoxidation reactions of olefins with H2O2 was investigated, using 2-cyclohexen-1-one, 2-cyclopenten-1-one, cis-β-methylstyrene, isophorone, chalcones and tetralones as substrates. Different carboxylic acids were used as additives to enhance yields and enantioselectivities, and 2-ethylhexanoic acid was found to give the best results. The catalysis results indicate that the Fe(ii) complex is capable of effecting comparatively high enantioselectivities (>80%) in the epoxidation reactions.

Enantioselective epoxidation of olefins with hydrogen peroxide catalyzed by bioinspired aminopyridine manganese complexes derived from L-proline

Three chiral aminopyridine ligands derived from L-proline were prepared. Careful evaluation of the corresponding aminopyridine manganese complexes in asymmetric epoxidation of olefins revealed a broad substrate scope in the presence of 0.2 mol% manganese complex and 0.5 equiv. 2,2-dimethylbutyric acid, with aqueous hydrogen peroxide as an oxidant. A variety of olefins including styrenes, chromenes, and cinnamamides were transformed successfully into the target epoxides with moderate to excellent enantioselectivity (yield up to 95%, ee up to 99%).

Mechanistic Insights into the Enantioselective Epoxidation of Olefins by Bioinspired Manganese Complexes: Role of Carboxylic Acid and Nature of Active Oxidant

Bioinspired manganese and iron complexes bearing nonporphyrinic tetradentate N4 ligands are highly efficient catalysts in asymmetric oxidation reactions by hydrogen peroxide (H2O2), in which carboxylic acid is employed as an essential additive to improve product yields and stereo-, regio-, and enantioselectivities. The metal catalysts should possess two cis-binding sites for oxidant (e.g., H2O2) and carboxylic acid to generate high-valent metal-oxo species as active oxidants via a “carboxylic acid-assisted” mechanism. In the present study, we have investigated the role(s) of carboxylic acid and the nature of reactive intermediate(s) in the manganese complex-catalyzed enantioselective epoxidation of olefins, by employing non-heme manganese catalysts, such as 1 bearing a tetradentate N4 ligand (LN4) and 2 bearing a pentadentate N5 ligand (LN5), and using various oxidants, such as H2O2, alkyl hydroperoxides, and iodosylbenzene (PhIO). As expected, 1 possessing two cis-binding sites is an effective catalyst i...

A New Mn–Salen Micellar Nanoreactor for Enantioselective Epoxidation of Alkenes in Water

A new chiral Mn–salen catalyst, functionalized with a long aliphatic chain and a choline group, able to act as surfactant catalyst for green epoxidation in water, is here described. This catalyst was employed with a commercial surfactant (CTABr) leading to a nanoreactor for the enantioselective epoxidation of some selected alkenes in water, using NaClO as oxidant. This is the first example of a nanoreactor for enantioselective epoxidation of non-functionalized alkenes in water.

Collaborative effect of Mn-porphyrin and mesoporous SBA-15 in the enantioselective epoxidation of olefins with oxygen

The rational design of heterogeneous, low cost transition metal complexes that can catalyze olefin with high enantioselectivity and activity has been a challenging goal for the synthetic chemist. In this study a chiral ion pair strategy was used for the synthesis of a biomimetic efficient manganese-tetrapyridylporphyrin (H2TPyP) catalyst for the asymmetric epoxidation of olefins with O2. Complex Mn-TPyP was covalently linked to mesoporous SBA-15 in heme-type environments and its counter ion was replaced by l-tartrate anion (SBA15-[Mn(TPyP)TA]). Chiral and achiral homogeneous analogous of Mn-TPyP were also prepared. The Mn-porphyrin confined in nanoreactors of SBA-15 exhibited enhanced activity (TOF = 652 h−1) and enantiomeric excess (ee 93%) compared with the value obtained when the same chiral catalyst functioned in homogeneous solution (TOF 97 h−1 and ee 83%) in the oxidation of 1-decene with O2/isobutyraldehyde. The high specific surface area, uniformly sized pore channels and site isolated active centers of the catalyst may contribute to the high activity and enantioselectivity. SBA15-[Mn(TPyP)TA] was structurally stable and could be recycled for repeated use. Total turnover number in the oxidation of styrene after five cycles was 47,400 with 86% epoxide selectivity and ee 86%.

Chiral Manganese Aminopyridine Complexes: the Versatile Catalysts of Chemo- and Stereoselective Oxidations with H2 O2.

In the last decade, manganese(II) complexes with N-donor tetradentate aminopyridine ligands emerged as efficient catalysts of enantioselective epoxidation of olefins and direct selective oxidation of C-H groups in complex organic molecules, with environmentally benign oxidant hydrogen peroxide. In this personal account, we summarize the progress of these catalysts with regard to ligands design, structure-reactivity correlations, evaluation of the substrate scope, as well as mechanistic studies, shedding light on the nature of active sites and the mechanisms of selective oxygenations. Several practically promising catalytic syntheses with the aid of Mn aminopyridine catalysts are exemplified.

Highly efficient asymmetric epoxidation of olefins with a chiral manganese-porphyrin covalently bound to mesoporous SBA-15: Support effect

A chiral MnIII-porphyrin complex covalently bonded with mesoporous SBA-15 (SBA15-[Mn(TCPP-R∗)Cl]) was synthesized and fully characterized. The heterogeneous SBA15-[Mn(TCPP-R∗)Cl] exhibited remarkable catalytic activity toward enantioselective olefin epoxidation using O2 as terminal oxidant in the presence of isobutyraldehyde. The catalyst showed higher enantioselectivity than its homogeneous counterpart in the oxidation of α-methylstyrene. SBA15-[Mn(TCPP-R∗)Cl] catalyzed epoxidation of styrene was achieved within 8h and optically active styrene oxide was obtained in 89% ee and 90% yield. Likewise, styrene derivatives (trans-β-methylstyrene, indene), conjugated cis- and trans-disubstituted olefins (e.g. cis- and tans-stilbene) and terminal olefins were converted effectively to their corresponding epoxides in 63–99%ee under the Mn(III)-catalyzed conditions. The catalyst could be recycled five times without any significant loss in activity.

Aerobic enantioselective epoxidation of olefins mediated by an easy-to-prepare recyclable manganese-porphyrin

Asymmetric catalysis is limited by using complex catalyst synthesis and enantioselectivity of the catalyst. Here, we report a simple and an easy to synthesis recyclable chiral manganese-porphyrin (Fe3O4-[Mn(TPyP)tart]) for enantioselective aerobic epoxidation of olefins. With magnetite nanoparticles as support, the immobilized cationic manganese–porphyrin system showed high activity and selectivity for the oxidation of olefins (cis- and trans-stilbene, styrene, 1-decene, 1-phenyl-1-cyclohexene) by RCHO/O2 to give optically active epoxides (enantiomeric excess up to 97%). The effects of solvent and reaction time and the performance of the recovered catalysts were studied.

Bioinspired Manganese Complexes and Graphene Oxide Synergistically Catalyzed Asymmetric Epoxidation of Olefins with Aqueous Hydrogen Peroxide

AbstractBioinspired manganese complexes of N4ligands and graphene oxide (GO) synergistically catalyze the highly enantioselective epoxidation of olefins (up to 99%ee), which is a rare example with GO as a co‐catalyst in asymmetric catalysis. GO as a new and key additive not only successfully functions in catalytic amounts, but also has a positive effect for improving the enantioselectivity of the asymmetric epoxidation compared with the traditional stoichiometric organic carboxylic acid method [e.g., chalcone, 95%ee(3.5 mg GO)vs. 84%ee(5 equiv., 75 mg acetic acid), ethyl cinnamate, 84%ee(3.5 mg GO)vs. 19%ee(5 equiv., 75 mg acetic acid)]. The X‐ray photoelectron spectroscopy (XPS) spectra of GO before and after the reaction indicate that the intensities of C–O become stronger after the reaction, which may have a certain relationship with hydrogen peroxide (H2O2) and gives a reasonable rationale for the large consumption of H2O2. Also, part of the hydrogen peroxide was used for the oxidation of GO.magnified image

ChemInform Abstract: Enantioselective Epoxidation of Olefins with H2O2 Catalyzed by Bioinspired Aminopyridine Manganese Complexes.

A novel family of bioinspired manganese(II) complexes bearing chiral aminopyridine ligands that possessed additional aromatic groups and strong donating dimethylamino groups were synthesized and characterized. These manganese complexes exhibited efficient and improved activities in the asymmetric epoxidation of various olefins, such as styrene derivatives (up to 93% ee) with H2O2 as the oxidant, even with a catalytic amount of carboxylic acid as the additive.

Enantioselective Epoxidation of Olefins with H2O2 Catalyzed by Bioinspired Aminopyridine Manganese Complexes.

A novel family of bioinspired manganese(II) complexes bearing chiral aminopyridine ligands that possessed additional aromatic groups and strong donating dimethylamino groups were synthesized and characterized. These manganese complexes exhibited efficient and improved activities in the asymmetric epoxidation of various olefins, such as styrene derivatives (up to 93% ee) with H2O2 as the oxidant, even with a catalytic amount of carboxylic acid as the additive.