Efficient rearrangement of epoxides catalyzed by a mixed-valent iron trifluoroacetate [Fe3O(O2CCF3)6(H2O)3]

Styrene Oxide Isomerase-Catalyzed Meinwald Rearrangement in Cascade Biotransformations: Synthesis of Chiral and/or Natural Chemicals

Styrene oxide isomerase (SOI) catalyzes the Meinwald rearrangement of aryl epoxides to carbonyl compounds via a 1,2-trans-shift in a stereospecific manner. A number of cascade biotransformations with SOI-catalyzed epoxide isomerization as a key step have been developed to convert readily available substrates into valuable chiral chemicals. Cascade conversion of terminal or internal alkenes into chiral acids, alcohols or amines was achieved, which involved SOI-catalyzed enantio-retentive isomerization of terminal epoxides via 1,2-H shift, or internal epoxides via 1,2-methyl shift. SOI-involved cascades were also developed to convert racemic epoxides into chiral acids or amines via dynamic kinetic resolution. Additionally, combining SOI-catalyzed isomerization with enantioselective C-C bond forming enzymes enabled the synthesis of chiral amino acids or amino alcohols from racemic epoxides. Finally, integration of SOI-involved cascades with biosynthesis pathways allowed for the direct utilization of renewable substrates for the sustainable synthesis of high-value natural chemicals such as alcohols, acids, and esters.

Size-Tunable Magnetite Nanoparticles from Well-Defined Iron Oleate Precursors

The synthesis of iron oxide nanoparticles with control over size and shape has long been an area of research, with iron oleate being arguably the most successful precursor. Issues with reproducibility and versatility in iron oleate-based syntheses remain, however, in large part due to the mutable nature of its structure and stoichiometry. In this work, we characterize two new forms of iron oleate precursor that can be isolated in large quantities, show long-term stability, and have well-defined stoichiometry, leading to reproducible and predictable reactivity. Synthesis with these precursors is shown to produce iron oxide nanoparticles in a tunable size range of 4-16 nm with low size dispersity and properties consistent with magnetite in the superparamagnetic size regime.

Enzyme-Catalyzed Meinwald Rearrangement with an Unusual Regioselective and Stereospecific 1,2-Methyl Shift

The Meinwald rearrangement is a synthetically useful reaction but often lacks regioselectivity and stereocontrol. A significant challenge in the Meinwald rearrangement of internal epoxides is the non-regioselective migration of different substituents to give a mixture of products. Herein, an enzyme-catalyzed regioselective and stereospecific 1,2-methyl shift in the Meinwald rearrangement of internal epoxides is reported. Styrene oxide isomerase (SOI) catalyzed the unique isomerization of internal epoxides through 1,2-methyl shift without 1,2-hydride shift to give the corresponding aldehydes and a cyclic ketone as the sole product. SOI-catalyzed isomerization showed high stereospecificity, fully retaining the stereoconfiguration. The synthetic utility of this enzymatic Meinwald rearrangement was demonstrated by its incorporation into three new types of enantioselective cascades, to convert trans-β-methyl styrenes into the corresponding R-configured alcohols, acids, or amines in high ee and yield.

Synthesis of α-Alkylated Ketones via Selective Epoxide Opening/Alkylation Reactions with Primary Alcohols

A new method for converting terminal epoxides and primary alcohols into α-alkylated ketones under borrowing hydrogen conditions is reported. The procedure involves a one-pot epoxide ring opening and alkylation via primary alcohols in the presence of an N-heterocyclic carbene iridium(I) catalyst, under aerobic conditions, with water as the side product.

A Review: The Styrene Metabolizing Cascade of Side-Chain Oxygenation as Biotechnological Basis to Gain Various Valuable Compounds

Styrene is one of the most produced and processed chemicals worldwide and is released into the environment during widespread processing. But, it is also produced from plants and microorganisms. The natural occurrence of styrene led to several microbiological strategies to form and also to degrade styrene. One pathway designated as side-chain oxygenation has been reported as a specific route for the styrene degradation among microorganisms. It comprises the following enzymes: styrene monooxygenase (SMO; NADH-consuming and FAD-dependent, two-component system), styrene oxide isomerase (SOI; cofactor independent, membrane-bound protein) and phenylacetaldehyde dehydrogenase (PAD; NAD+-consuming) and allows an intrinsic cofactor regeneration. This specific way harbors a high potential for biotechnological use. Based on the enzymatic steps involved in this degradation route, important reactions can be realized from a large number of substrates which gain access to different interesting precursors for further applications. Furthermore, stereochemical transformations are possible, offering chiral products at high enantiomeric excess. This review provides an actual view on the microbiological styrene degradation followed by a detailed discussion on the enzymes of the side-chain oxygenation. Furthermore, the potential of the single enzyme reactions as well as the respective multi-step syntheses using the complete enzyme cascade are discussed in order to gain styrene oxides, phenylacetaldehydes, or phenylacetic acids (e.g., ibuprofen). Altered routes combining these putative biocatalysts with other enzymes are additionally described. Thus, the substrates spectrum can be enhanced and additional products as phenylethanols or phenylethylamines are reachable. Finally, additional enzymes with similar activities toward styrene and its metabolic intermediates are shown in order to modify the cascade described above or to use these enzyme independently for biotechnological application.

Popcorn-Shaped Fe x O (Wüstite) Nanoparticles from a Single-Source Precursor: Colloidal Synthesis and Magnetic Properties

Colloidal nanoparticles (NPs) with myriads of compositions and morphologies have been synthesized and characterized in recent years. For wüstite Fe _x O, however, obtaining phase-pure NPs with homogeneous morphologies have remained challenging. Herein, we report the colloidal synthesis of phase-pure Fe _x O (x ≈ 0.94) popcorn-shaped NPs by decomposition of a single-source precursor, [Fe₃(μ₃-O)(CF₃COO)(μ-CF₃COO)₆(H₂O)₂]·CF₃COOH. The popcorn shape and multigrain structure had been reconstructed using high-angle annular dark-field scanning transmission electron micrograph (HAADF-STEM) tomography. This morphology offers a large surface area and internal channels and prevents further agglomeration and thermal tumbling of the subparticles. [Fe₃(μ₃-O)(CF₃COO)(μ-CF₃COO)₆(H₂O)₂]·CF₃COOH behaves as an antiferromagnetic triangle whose magnetic frustration is mitigated by the low symmetry of the complex. The popcorn-shaped Fe _x O NPs show the typical wüstite antiferromagnetic transition at approximately 200 K, but behave very differently to their bulk counterpart below 200 K. The magnetization curves show a clear, unsymmetrical hysteresis, which arises from a combined effect of the superparamagnetic behavior and exchange bias.

Efficient epoxide isomerization within a self-assembled hexameric organic capsule

The supramolecular organic nano-capsule formed by the self-assembly of six resorcin[4]arene units efficiently promotes the isomerization of epoxides (Meinwald isomerization) to the corresponding carbonyl compounds.

Steam treatment of a hollow lithium phosphate catalyst: enhancing carbon deposition resistance and improving the catalytic performance of propylene oxide rearrangement

The reaction mechanism of propylene oxide rearrangement on a hollow lithium phosphate catalyst in the presence of steam.

Meinwald-type rearrangement of monosubstituted epoxides to methyl ketones using an [Al porphyrin]+[Co(CO)4]−catalyst

A Meinwald-type rearrangement of monosubstituted epoxides to methyl ketones using a well-defined aluminum porphyrin catalyst is reported.

An air-stable cationic iridium hydride as a highly active and general catalyst for the isomerization of terminal epoxides

We describe the use of an air-stable iridium hydride catalyst for the isomerization of terminal epoxides into aldehydes with perfect regioselectivity.

A synthetic strategy for a new series of oxo-centered tricobalt complexes with mixed bridging ligands of acetate and pyrazolate anions

A new series of oxo-centered tricobalt(III, III, III) complexes, containing mixed bridges of acetate and pyrazolate anions, has been synthesized based on a strategy consisting of two stages. In the first stage, the reaction of cobalt(II) acetate tetrahydrate with pyrazole in the presence of oxidants, followed by purification with silica-gel column chromatography, afforded six tricobalt complexes: [Co(3)O(μ-OAc)(5)(μ-pz)(Hpz)(3)](PF(6)) (mono), two isomers of [Co(3)O(μ-OAc)(4)(μ-pz)(2)(Hpz)(3)](PF(6)) (bis-1 and bis-2), two isomers of [Co(3)O(μ-OAc)(3)(μ-pz)(3)(Hpz)(3)](PF(6)) (tris-2 and tris-3), and one isomer of [Co(3)O(μ-OAc)(2)(μ-pz)(4)(Hpz)(3)](PF(6)) (tetra-1). In the second stage, substitution reactions have been examined for the complexes obtained in the first stage. As a result, one acetate bridge in bis-1, bis-2, and tris-3 could be substituted with one pyrazolate site-selectively. Bis-1, bis-2, and tris-3 were converted to another isomer of [Co(3)O(μ-OAc)(3)(μ-pz)(3)(Hpz)(3)](PF(6)) (tris-1), tris-2, and tetra-1, respectively. Single-crystal X-ray diffraction studies found that in every complex acetato and pyrazolato work as bridging ligands, while pyrazole (Hpz) acts as a terminal ligand. Moreover, the electrochemical properties of the seven new tricobalt complexes (mono, bis-1, bis-2, tris-1, tris-2, tris-3, and tetra-1) were investigated by cyclic voltammetry and it was found that (1) each complex shows reversible redox behaviour corresponding to the Co(III)Co(III)Co(III)/Co(III)Co(III)Co(IV) couple and (2) the redox potential decreases from 1.21 V vs. Fc/Fc(+) in mono to 1.09 V vs. Fc/Fc(+) in tetra-1, as the number of pyrazolate bridges increases.

Silicon-(thio)urea Lewis acid catalysis

We present a new class of catalysts based on the combination of N,N'-diaryl(thio)ureas and weak silicon Lewis acids (e.g., SiCl(4)). Such silicon-(thio)urea catalysts effectively catalyze the stereospecific rearrangement of epoxides to quaternary carbaldehydes.