LongLarf

Synlett
DOI: 10.1055/s-0037-1610308

Ph3P/I–-promoted dichlorination and dibromination of epoxides by using XCH2CH2X (X = Cl or Br) as the halogen source and reaction solvent is described. All reagents are widely available and easy to handle, and mild conditions and operational simplicity make this protocol attractive.
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© Georg Thieme Verlag Stuttgart · New York

Article in Thieme eJournals:
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Make 5CCs from CO₂ : Renewable scaffolds and CO₂ are combined to produce five‐membered cyclic organic carbonates that serve as building blocks for the preparation of ubiquitous polymeric materials, including foams, adhesives, components of solid electrolytes in lithium batteries, and sensors. Recent advances are reviewed herein with a focus on the sustainable synthesis of monomers from renewable starting materials and on polymer applications.

Abstract

Given the large amount of anthropogenic CO₂ emissions, it is advantageous to use CO₂ as feedstock for the fabrication of everyday products, such as fuels and materials. An attractive way to use CO₂ in the synthesis of polymers is by the formation of five‐membered cyclic organic carbonate monomers (5CCs). The sustainability of this synthetic approach is increased by using scaffolds prepared from renewable resources. Indeed, recent years have seen the rise of various types of carbonate syntheses and applications. 5CC monomers are often polymerized with diamines to yield polyhydroxyurethanes (PHU). Foams are developed from this type of polymers; moreover, the additional hydroxyl groups in PHU, absent in classical polyurethanes, lead to coatings with excellent adhesive properties. Furthermore, carbonate groups in polymers offer the possibility of post‐functionalization, such as curing reactions under mild conditions. Finally, the polarity of carbonate groups is remarkably high, so polymers with carbonates side‐chains can be used as polymer electrolytes in batteries or as conductive membranes. The target of this Review is to highlight the multiple opportunities offered by polymers prepared from and/or containing 5CCs. Firstly, the preparation of several classes of 5CCs is discussed with special focus on the sustainability of the synthetic routes. Thereafter, specific classes of polymers are discussed for which the use and/or presence of carbonate moieties is crucial to impart the targeted properties (foams, adhesives, polymers for energy applications, and other functional materials).

C−N coupling: A new electrophilic amination of boronic acids with simple and inexpensive nitro compounds has been developed allowing the preparation of a variety of highly substituted and functionalized aromatic secondary amines. The process employs affordable PPh₃ as reducing agent, in the presence of an easily available and highly stable dioxomolybdenum(VI) complex as catalyst.

Abstract

The synthesis of aromatic amines is of utmost importance in a wide range of chemical contexts. We report a direct amination of boronic acids with nitro compounds to yield (hetero)aryl amines. The novel combination of a dioxomolybdenum(VI) catalyst and triphenylphosphine as inexpensive reductant has revealed to be decisive to achieve this new C−N coupling. Our methodology has proven to be scalable, air and moisture tolerant, highly chemoselective and engages both aliphatic and aromatic nitro compounds. Moreover, this general and step‐economical synthesis of aromatic secondary amines showcases orthogonality to other aromatic amine syntheses as it tolerates aryl halides and carbonyl compounds.

Chemoselective methylene oxidation in aromatic molecules

Chemoselective methylene oxidation in aromatic molecules, Published online: 17 December 2018; doi:10.1038/s41557-018-0175-8

A small-molecule manganese-based catalyst has been developed for the selective oxidation of strong methylene C–H bonds in the presence of more oxidatively labile aromatic functionality. This reaction enables the late-stage oxidative derivatization of medicinally relevant compound scaffolds and may also prove useful for diversifying aromatic drugs and natural products, as well as helping to quickly identify their metabolites.

Enzymatic assembly of carbon–carbon bonds via iron-catalysed sp³ C–H functionalization

Enzymatic assembly of carbon–carbon bonds via iron-catalysed <i>sp</i>³ C–H functionalization, Published online: 19 December 2018; doi:10.1038/s41586-018-0808-5

Evolved iron-containing enzymes based on cytochrome P450 achieve selective intermolecular alkylation of sp3 C–H bonds through a carbene C–H insertion strategy.

First hint of near-room-temperature superconductor tantalizes physicists

First hint of near-room-temperature superconductor tantalizes physicists, Published online: 19 December 2018; doi:10.1038/d41586-018-07831-x

High-pressure hydrogen materials could be a step towards a new era of superconductivity.

Desymmetrization of cyclohexanes by site- and stereoselective C–H functionalization

Desymmetrization of cyclohexanes by site- and stereoselective C–H functionalization, Published online: 19 December 2018; doi:10.1038/s41586-018-0799-2

Unactivated cyclohexane derivatives can be desymmetrized by site- and stereoselective C–H functionalization using carbene-insertion chemistry.

Catalytic deracemization of chiral allenes by sensitized excitation with visible light

Catalytic deracemization of chiral allenes by sensitized excitation with visible light, Published online: 12 December 2018; doi:10.1038/s41586-018-0755-1

Photochemical deracemization through irradiation with visible light in the presence of a chiral sensitizer enables the direct formation of single enantiomers from a racemic mixture of the same compound.

The development of visible‐light‐mediated allylation of unactivated sp³ C−H bonds is reported. The remote allylation was directed by the amidyl radical, which was generated by photocatalytic fragmentation of a pre‐functionalized amide precursor. Both aromatic and aliphatic amide derivatives could successfully deliver the remote C−H allylation products in good yields. A variety of electron deficient allyl sulfone systems could be used as δ‐carbon radical acceptor.

Abstract

The development of visible‐light‐mediated allylation of unactivated sp³ C−H bonds is reported. The remote allylation was directed by the amidyl radical, which was generated by photocatalytic fragmentation of a pre‐functionalized amide precursor. Both aromatic and aliphatic amide derivatives could successfully deliver the remote C−H allylation products in good yields. A variety of electron deficient allyl sulfone systems could be used as δ‐carbon radical acceptor.

Deciphering key intermediates in the transformation of carbon dioxide into heterocyclic products

Deciphering key intermediates in the transformation of carbon dioxide into heterocyclic products, Published online: 10 December 2018; doi:10.1038/s41929-018-0189-z

One of the major routes for the use of CO2 in chemical production is the formation of carbonates via cycloaddition of CO2 to epoxides. This work uses a range of experimental and computational techniques to map out the elusive key intermediates in this process.

Carbopalladation of C–C σ-bonds enabled by strained boronate complexes

Carbopalladation of C–C <i>σ</i>-bonds enabled by strained boronate complexes, Published online: 10 December 2018; doi:10.1038/s41557-018-0181-x

Widely used palladium-mediated cross-couplings typically operate via a handful of fundamental reaction steps. Now, the reactivity between palladium and C–C σ-bonds has been described. This carbopalladation enables the coupling of organoboronic esters and aryl triflates across a C–C σ-bond of a bicyclo[1.1.0]butane to form disastereomerically pure trisubstituted cyclobutanes.