Asymmetric Dihydroxylation Reaction Research Articles

Aggregation-Induced Catalysis: Asymmetric Catalysis with Chiral Aggregates.

So far, there have been 4 methods to control chirality including the use of chiral auxiliaries, reagents, solvents, and catalysts documented in literature and textbooks. Among them, asymmetric catalysts are normally divided into homogeneous and heterogeneous catalysis. In this report, we present a new type of asymmetric control-asymmetric catalysis via chiral aggregates that would not belong to the above categories. This new strategy is represented by catalytic asymmetric dihydroxylation reaction of olefins in which chiral ligands are aggregated by taking advantage of typical aggregation-induced emission systems containing tetrahydrofuran and H2O cosolvents. It was proven that the chiral induction can be enhanced from er of 78:22 to 97:3 simply by changing the ratios of these 2 cosolvents. The formation of chiral aggregates of asymmetric dihydroxylation ligands, (DHQD)2PHAL and (DHQ)2PHAL, has been proven by aggregation-induced emission and a new analytical tool-aggregation-induced polarization established by our laboratory. In the meanwhile, chiral aggregates were found to be formed either by adding NaCl into tetrahydrofuran/H2O systems or by increasing concentrations of chiral ligands. The present strategy also showed promising reverse control of enantioselectivity in the Diels-Alder reaction. This work is anticipated to be extended broadly to general catalysis, especially to asymmetric catalysis in the future.

A Stereocontrolled Total Synthesis of Lipoxin B4 and its Biological Activity as a Pro-Resolving Lipid Mediator of Neuroinflammation.

Two stereocontrolled, efficient, and modular syntheses of eicosanoid lipoxin B4 (LXB4 ) are reported. One features a stereoselective reduction followed by an asymmetric epoxidation sequence to set the vicinal diol stereocentres. The dienyne was installed via a one-pot Wittig olefination and base-mediated epoxide ring opening cascade. The other approach installed the diol through an asymmetric dihydroxylation reaction followed by a Horner-Wadsworth-Emmons olefination to afford the common dienyne intermediate. Finally, a Sonogashira coupling and an alkyne hydrosilylation/proto-desilylation protocol furnished LXB4 in 25 % overall yield in just 10 steps. For the first time, LXB4 has been fully characterized spectroscopically with its structure confirmed as previously reported. We have demonstrated that the synthesized LXB4 showed similar biological activity to commercial sources in a cellular neuroprotection model. This synthetic route can be employed to synthesize large quantities of LXB4 , enable synthesis of new analogs, and chemical probes for receptor and pathway characterization.

The Asymmetric Total Synthesis of (-)-Eurothiocin A and Its Enantiomer.

The first asymmetric total synthesis of (-)-eurothiocin A was achieved in 14 linear steps with 2% overall yield from the commercially available materials. A Sharpless asymmetric dihydroxylation reaction was utilized as the key step to construct the stereogenic center. Additionally, (+)- and (±)-eurothiocin A were also synthesized.

Dihydroxylation Studies of Isoquinolinones: Synthesis of the EF-Ring of Lysolipin I

AbstractInspired by the potent polycyclic xanthone antibiotic lysolipin I, a general study on asymmetric dihydroxylation reactions of variously substituted isoquinolinones was performed. Different isoquinolinones were efficiently prepared, either by a Pomeranz–Fritsch type condensation or a Curtius rearrangement. Under a broad variety of conventional oxygenation procedures, they proved very unreactive. However, either by suitable substitution of the appending aromatic ring or more forcing conditions a dihydroxylation could finally be performed, which allowed the synthesis of the EF-ring of lysolipin I.

Sequential iodine-mediated diallylsilane rearrangement/asymmetric dihydroxylation: Synthesis and reactions of enantioenriched oxasilacycles

Products from an iodine-mediated diallylsilane rearrangement were taken into an asymmetric dihydroxylation (AD) reaction resulting in the formation of diastereomeric 6-membered oxasilacycles. Removal of the epimeric stereocenter among this mixture of diastereomers by elimination of iodine produced a single enantioenriched cyclic allyl silyl ether. The resulting allyl silane was then successfully engaged in several further transformations, providing an alternative means to prepare useful polyoxygenated intermediates for enantioselective synthesis.

Practical synthesis of aromatic bisabolanes: Synthesis of 1,3,5-bisabolatrien-7-ol, peniciaculin A and B, and hydroxysydonic acid

The enantioselective synthesis of aromatic bisabolanes, such as 1,3,5-bisabolatrien-7-ol, peniciaculin A and B, and hydroxysydonic acid, has been described. Our methodology for the total synthesis of aromatic bisabolanes involves the stereoselective construction of the C-7 stereogenic center via a Sharpless asymmetric dihydroxylation reaction, followed by a SmI 2 -mediated Julia olefination. Preliminary results obtained for the odor evaluation of 1,3,5-bisabolatrien-7-ol and the confirmation of the absolute configurations of peniciaculin A and B are also described.

Recent Advancements in the Development of Osmium Catalysts for Various Oxidation Reactions: A New Era?

ABSTRACT Symmetric and asymmetric dihydroxylation reactions catalyzed by osmium have emerged as the most efficient route in the one-step synthesis of diols. This is because on an industrial scale 1,2-diols are prepared via a two-step procedure. Still, it is a challenge to prepare and apply osmium catalysts in dihydroxylation catalysis because of their safety and environmental implications; e.g., volatile, highly toxic, product contamination, etc. To date, few efforts were reported to comprehensively overcome these drawbacks with great success by heterogenizing to an insoluble matrix, including diminishment in catalytic performance. Hence, the need for efficacious solid-supported osmium catalysts to subdue these difficulties is a topic of great importance. This mini review provides a concise overview of some of the most encouraging solid-supported osmium catalysts reported over the last few years, which proved to be more efficient under mild conditions as opposed to other immobilized osmium catalytic systems. The summary discusses the latest developments in the synthetic heterogenizing and homogenization strategies, structure analysis and investigation toward symmetric and asymmetric dihydroxylation for diol production. Specific emphasis is focused on their mechanistic considerations, their reusability and improvement in their safety, and environmental implications.

The modulatory role of sulfated and non-sulfated small molecule heparan sulfate-glycomimetics in endothelial dysfunction: absolute structural clarification, molecular docking and simulated dynamics, SAR analyses and ADMET studies.

The conceptual technology of small molecule glycomimetics, exemplified by compounds C1–4, has shown promising protective effects against lipid-induced endothelial dysfunction, restorative effects on diabetic endothelial colony forming cells, and preventative effects on downstream vascular calcification amongst other important in vitro and ex vivo studies. We report the optimised synthesis of an array of 17 small molecule glycomimetics, including the regio-, enantio- and diastereo-meric sulfated scaffolds of a hit structure along with novel desulfated examples. For the first time, the absolute stereochemical configurations of C1–4 have been clarified based on an identified and consistent anomaly with the Sharpless asymmetric dihydroxylation reaction. We have investigated the role and importance of sulfation pattern, location, regioisomers, and spatial orientation of distal sulfate groups on the modulation of endothelial dysfunction through their interaction with hepatocyte growth factor (HGF). In silico studies demonstrated the key interactions the persulfated glycomimetics make with HGF and revealed the importance of both sulfate density and positioning (both point chirality and vector) to biological activity. In vitro biological data of the most efficient binding motifs, along with desulfated comparators, support the modulatory effects of sulfated small molecule glycomimetics in the downstream signaling cascade of endothelial dysfunction. In vitro absorption, distribution, metabolism, elimination and toxicity (ADMET) data demonstrate the glycomimetic approach to be a promising approach for hit-to-lead studies.

Iron-Catalyzed Highly Enantioselective cis-Dihydroxylation of Trisubstituted Alkenes with Aqueous H2 O2.

Reliable methods for enantioselective cis-dihydroxylation of trisubstituted alkenes are scarce. The iron(II) complex cis-α-[FeII (2-Me2 -BQPN)(OTf)2 ], which bears a tetradentate N4 ligand (Me2 -BQPN=(R,R)-N,N'-dimethyl-N,N'-bis(2-methylquinolin-8-yl)-1,2-diphenylethane-1,2-diamine), was prepared and characterized. With this complex as the catalyst, a broad range of trisubstituted electron-deficient alkenes were efficiently oxidized to chiral cis-diols in yields of up to 98 % and up to 99.9 % ee when using hydrogen peroxide (H2 O2 ) as oxidant under mild conditions. Experimental studies (including 18 O-labeling, ESI-MS, NMR, EPR, and UV/Vis analyses) and DFT calculations were performed to gain mechanistic insight, which suggested possible involvement of a chiral cis-FeV (O)2 reaction intermediate as an active oxidant. This cis-[FeII (chiral N4 ligand)]2+ /H2 O2 method could be a viable green alternative/complement to the existing OsO4 -based methods for asymmetric alkene dihydroxylation reactions.

Iron‐Catalyzed Highly Enantioselective cis‐Dihydroxylation of Trisubstituted Alkenes with Aqueous H2O2

AbstractReliable methods for enantioselective cis‐dihydroxylation of trisubstituted alkenes are scarce. The iron(II) complex cis‐α‐[FeII(2‐Me2‐BQPN)(OTf)2], which bears a tetradentate N4 ligand (Me2‐BQPN=(R,R)‐N,N′‐dimethyl‐N,N′‐bis(2‐methylquinolin‐8‐yl)‐1,2‐diphenylethane‐1,2‐diamine), was prepared and characterized. With this complex as the catalyst, a broad range of trisubstituted electron‐deficient alkenes were efficiently oxidized to chiral cis‐diols in yields of up to 98 % and up to 99.9 % ee when using hydrogen peroxide (H2O2) as oxidant under mild conditions. Experimental studies (including 18O‐labeling, ESI‐MS, NMR, EPR, and UV/Vis analyses) and DFT calculations were performed to gain mechanistic insight, which suggested possible involvement of a chiral cis‐FeV(O)2 reaction intermediate as an active oxidant. This cis‐[FeII(chiral N4 ligand)]2+/H2O2 method could be a viable green alternative/complement to the existing OsO4‐based methods for asymmetric alkene dihydroxylation reactions.

Stitching alkynes into bryostatin 3

Organic Chemistry The bryostatin family of marine natural products has been explored for a wide variety of pharmaceutical applications but remains challenging to source. The general structure comprises a macrocycle that contains three smaller, six-membered rings. Bryostatin 3 is distinguished by the added complexity of a fourth, fused lactone ring. Trost et al. report a convergent synthesis of this complex molecule, taking advantage of alkyne coupling reactions to stitch together three main fragments and asymmetric dihydroxylation and propargylation reactions to set stereochemistry. Science , this issue p. [1007][1] [1]: /lookup/doi/10.1126/science.abb7271

Catalytic Asymmetric Synthesis of α,α-Difluoromethylated and α-Fluoromethylated Tertiary Alcohols.

The catalytic asymmetric synthesis of α,α-difluoromethylated tertiary alcohols is described, using an asymmetric dihydroxylation reaction. This protocol using either the AD-mix-α or AD-mix-β allowed an easy access to these valuable fluorinated chiral building blocks, which have been obtained with excellent yields and er. In addition, the reaction was extended to the α-fluoromethylated analogues.

Stereoselective Synthesis of the C1-C22 Carbon Framework of (-)-Amphidinolide K.

Two stereoselective routes to the C7-C22 subunit of amphidinolide K are disclosed. Jacobsen's hydrolytic kinetic resolution and Sharpless' asymmetric dihydroxylation reactions have been employed for the construction of the tetrahydrofuran ring. The C10-C11, C16-C17, C9-O, and C18-O bonds have been created using α-chloro sulfide intermediates and [2,3] sigmatropic rearrangement. Marshall's propargylation protocol is utilized to create the C4 stereogenic center, and regioselective hydrozirconation/iodine quench afforded an alkenyl iodide which is employed in the NHK coupling with the C7-C22 subunit. Oxonia-Cope rearrangement resulted in the creation of the C18 carbinol stereogenic center and chain elongation.

Total Synthesis of Originally Proposed and Revised Structure of Hetiamacin A.

The first total synthesis of the originally proposed and correct structures of hetiamacin A has been accomplished via Wittig olefination and Sharpless asymmetric dihydroxylation reaction. These total syntheses culminated in the stereostructural confirmation of the reassignment of hetiamacin A.

Synthesis and Antimalarial Activity of New Enantiopure Aminoalcoholpyrrolo[ 1,2-a]quinoxalines.

We prepared a novel series of enantiopure mefloquine analogues with pyrrolo[ 1,2-a]quinoxaline core in order to fight Plasmodium falciparum resistant strain. To observe the influence of pyrrolo[1,2-a]quinoxaline core versus quinoline core on the antimalarial activity. Four enantiopure aminoalcoholpyrrolo[1,2-a]quinoxalines 2 were synthetized via Sharpless asymmetric dihydroxylation reaction in eight steps. Their antimalarial activity was evaluated on two Plasmodium falciparum strains 3D7 and W2 with a SYBR Green I fluorescence-based method and their cytotoxicity was measured on four cell lines HepG2, THP-1, CHO and HFF. IC50 values of the four compounds 2 were close to the micromolar against the two P. falciparum strains. They were more active against P. falciparum strain W2 vs. P. falciparum strain 3D7. (R)- enantiomers were always more active than their (S)-counterpart whatever the strain. Selectivity indexes of compounds 2 were lower than 100. A novel series of enantiopure aminoalcohols with pyrrolo[1,2-a]quinoxaline core were synthesized in eight steps. They displayed IC50 values close to the micromolar against two P. falciparum strains 3D7 and W2. Although, In this series, 2,8-bistrifluoromethylquinoline was a best core than pyrrolo[1,2-a]quinoxaline for an optimal antimalarial activity, the pyrroloquinoxaline 2b showed an interesting antimalarial activity.

Ferrocenyl GNA Nucleosides: A Bridge between Organic and Organometallic Xeno-nucleic Acids.

The enantioselective synthesis and electrochemistry of the first ferrocenyl GNA nucleosides is reported. These compounds were obtained by a Sharpless asymmetric dihydroxylation reaction of [3-(N1-thyminyl)-1-(ferrocenyl)]propene as S,R and R,S enantiomers in about 70 % yield with enantiomeric excesses of >99 % and 71 %, respectively. The absolute configurations of the chiral carbon atoms in the nucleosides were assigned by single-crystal X-ray diffraction analysis of the methyl derivatives in the solid state. The compounds were also studied with circular dichroism (CD) spectroscopy in solution. The enantiomeric relationship between the S,R and R,S isomers was confirmed by the near-mirror-image CD spectra. The redox properties of the nucleosides and their methylated derivatives were investigated using cyclic voltammetry. The cyclic voltammograms revealed reversible redox processes for the entire series of compounds at potentials of -25 mV (for nonmethylated derivatives) and 75 mV (for methylated derivatives) versus the ferrocene/ferrocenium reference redox couple.

Gram-Scale, Stereoselective Synthesis and Biological Evaluation of (+)-Armillariol C.

Natural products with heteroaromatic cores are ample and widespread in nature, with many compounds exhibiting promising therapeutic properties. (+)-Armillariol C (1a) is a furan-based natural product isolated from Armillaria species. Herein, we report the first enantioselective synthesis of (+)-armillariol C (1a, 79% overall yield), its enantiomer (1b), and four other analogues, on a gram-scale, using microwave-mediated, Suzuki-Miyaura cross-coupling and Sharpless asymmetric dihydroxylation reactions. Compounds were tested for plant- and mycelia-growth regulatory activity, with 1b, 7a, and 7b showing the strongest inhibitory properties in a lettuce assay and 7b and 9b inhibiting Flammulina velutipes.

Ionophilic Imidazolium-Tagged Cinchona Ligand on LDH-Immobilized Osmium: Recyclable and Recoverable Catalytic System for Asymmetric Dihydroxylation Reaction of Olefins

A catalytic system for the asymmetric dihydroxylation of olefins was developed by using an ionic-tagged biscinchona alkaloid ligand immobilized onto OsO4-exchanged layered double hydroxide (LDH) as a robust recyclable homogenous–heterogeneous catalytic system. The desired products were obtained in high yield and enantioselectivity.

ChemInform Abstract: Total Synthesis of (‐)‐Heliespirone A and (+)‐Heliespirone C.

Total syntheses of the spiro-epimeric natural products (–)-heliespirone A and (+)-heliespirone C are described. The successful strategy involved an aromatic Claisen rearrangement, a diastereoselective Sharpless asymmetric dihydroxylation (AD) reaction, and an intramolecular oxa-Michael addition.

ChemInform Abstract: A Ring‐Closing Enyne Metathesis Approach to Functionalized Semicyclic Dienes: The Total Synthesis of (‐)‐Tetrangomycin.

The angucycline antibiotic (–)-tetrangomycin was synthesized in 13 steps (11 % overall yield) by using a stereoselective Diels–Alder reaction between a naphthoquinone and a semicyclic diene to construct the benz[a]anthraquinone ring system. The diene intermediates were synthesized through a ring-closing enyne metathesis reaction. The tertiary alcohol at C-3 was installed by an asymmetric dihydroxylation reaction. The relative stereochemistry of the dienes was verified by the NMR analyses of the cycloadducts that were obtained from their reaction with N-phenylmaleimide. Selective aromatization of the B ring was achieved under oxidative conditions.