LongLarf

Bulky is best: The synthesis of well‐defined poly(thioester)s by the controlled alternating copolymerization of cyclic thioanhydrides and episulfides can be induced by simple organic ammonium salts. Both the cation and anion have strong effects, and a bulky cation was efficient in initiating the polymerization, resulting in poly(thioester)s with a completely alternating structure, controlled molecular weight, and narrow polydispersity.

Abstract

The precise synthesis of poly(thioester)s with diverse structures is still a significant challenge in the polymeric materials field. Herein, we report a novel approach to the synthesis of well‐defined poly(thioester)s by the controlled alternating copolymerization of cyclic thioanhydrides and episulfides induced by simple organic ammonium salts. Both the cation and anion have strong effects on the copolymerization. [PPN]OAc ([PPN]=bis(triphenylphosphine)iminium) with a bulky cation was proven to be efficient in initiating this polymerization, yielding poly(thioester)s with a completely alternating structure, controlled molecular weight, and narrow polydispersity. The poly(thioester) obtained from succinic thioanhydride and propylene sulfide is a typical semicrystalline material, possessing a high refractive index of up to 1.78. Because it uses readily available monomers, this method is expected to open up a new route to poly(thioester)s with diverse structures and properties.

Abstract

Among the attempts to consolidate the so‐called circular economy, the conversion of carbon dioxide (CO₂) into added‐value products has gained more and more attention during the last three decades. One of the feasible applications of CO₂ as a C₁ building block is its incorporation into cyclic organic carbonates (COCs) and aliphatic polycarbonates (APCs) by reaction with epoxides. A plethora of homogeneous catalytic systems has been reported to promote this reaction, based mainly on magnesium, aluminium, cobalt, chromium and zinc complexes. Despite the abundance and low toxicity of iron, only few examples of catalysts based on this metal had been reported until fifteen years ago, and relevant advances were made only during the last decade. This review seeks to cover this progress and to give a renewed impulse for further research into iron utilisation in this kind of catalysis.

Abstract

Carbon dioxide is a renewable C1‐feedstock that is exploited for the production of polymers. In this work, we report on the conversion of CO₂ into novel bis(oxo‐carbamate)s that are then exploited for the synthesis of degradable non‐isocyanate polyurethanes (NIPUs) bearing acid‐sensitive imine functions within the polymer backbone. Two CO₂‐sourced bis(oxo‐carbamate)s were first prepared by the facile catalyst‐free and regioselective aminolysis of an α‐alkylidene cyclic carbonate (prepared by carboxylative coupling of CO₂ with a propargylic alcohol) with two secondary diamines, piperazine and N,N’‐dimethyl‐1,6‐hexanediamine. A large diversity of poly(urethane‐co‐imine)s (PUIs) with molar masses ranging from 4500 to 8500 g/mol were then prepared by polycondensation of bis(oxo‐carbamate)s with various primary diamines, and by using Ti(OEt)₄ as catalyst and drying agent. Finally, the pH‐responsiveness of PUIs was demonstrated by immersing a representative polymer in aqueous solutions at different pH. This work illustrates that hydrolytically degradable NIPUs can be constructed by polycondensation of novel CO₂‐sourced monomers with diamines.

Abstract

Various CO₂ adducts of tetra‐hydropyrimidin‐2‐ylidene (THPE) derived from the commercially available 1, 5‐diazabicyclo[4.3.0]non‐5‐ene (DBN) were firstly synthesized. X‐ray single crystal analysis revealed the bent geometry of the binding CO₂ having an O−C−O angle of 127.50∼129.51° for THPE−CO₂ adducts. In situ FTIR experiments demonstrated that THPE−CO₂ adducts had unprecedented thermal stability in DMSO, even at 100 °C without decomposition. It was found that the THPE−CO₂ adducts were highly active in catalyzing the carboxylative cyclization of CO₂ with propargylic alcohols under mild conditions, significantly higher than the previously reported organocatalysts. Various internal and terminal functionalized propargylic alcohols were tolerated in these processes to afford the corresponding α‐alkylidene cyclic carbonates in moderate to good yields with complete (Z)‐stereoselectivity. Isotope labeling, in combination with in‐situ FTIR and stoichiometric experiments, reveal that the catalytic reaction tends to proceed via the THPE−CO₂‐mediated basic ionic pair mechanism.

Round about NaOCP: The chemistry of the 2‐phosphaethynolate anion, a heavier phosphorus‐containing analogue of the cyanate anion, is comprehensively reviewed. This simple anion allows a wide breadth of chemical transformations leading to heterocycles, π‐conjugated molecules, and metal phosphides.

Abstract

In all likelihood the first synthesis of the phosphaethynolate anion, PCO⁻, was performed in 1894 when NaPH₂ was reacted with CO in an attempt to make Na(CP) accompanied by elimination of water. This reaction was repeated 117 years later when it was discovered that Na(OCP) and H₂ are the products of this remarkable transformation. Li(OCP) was synthesized and fully characterized in 1992 but this salt proved to be too unstable to allow for a detailed investigation of its chemistry. It was not until the heavier analogues of this lithium salt were isolated, Na(OCP) and K(OCP) (both of which are remarkably stable and can be even dissolved in water), that the chemistry of this new functional group could be explored. Here we review the chemistry of the 2‐phosphaethynolate anion, a heavier phosphorus‐containing analogue of the cyanate anion, and describe the wide breadth of chemical transformations for which it has been thus far employed. Its use as a ligand, in decarbonylative and deoxygenative processes, and as a building block for novel heterocycles is described. In the mere twenty‐six years since Becker first reported the isolation of this remarkable anion, it has become a fascinating reagent for the synthesis of a vast library of, often unprecedented, molecules and compounds.

OMEGA is not the end: A nanocrystalline ruthenium catalyst, embedded into a zeolite, catalyses the hydrogenolysis of cyclic carbonates into glycols and methane. The catalyst displays unprecedented selectivity towards methane, and the reaction may be considered as an extension of the OMEGA process, in which both a valuable liquid and gaseous product are formed.

Abstract

We report a ruthenium‐modified zeolite which efficiently transforms propylene carbonate to propylene glycol and methane, under solvent‐free conditions. The catalyst achieved high product selectivity and no significant ageing effect was observed after multiple cycles. The resulting liquid product (water‐containing glycol) can be directly used as anti‐freeze solution and the gas phase can directly be used as an energy carrier in the form of H₂‐enriched methane. This process efficiently bridges energy storage and an important chemical synthesis under sustainable (CO₂ consuming) conditions.

The chemistry provided herein details an efficient and flexible route toward architecturally distinctive 1-aminonorbornanes through the use of visible-light photoredox catalysis. The incorporation of readily diversifiable functional handles (e.g., -OH, -CO2Me, -NHBoc, -NHCbz) illustrates the potential utility of these 1-aminonorbornanes within drug-discovery programs. Additionally, these motifs offer improved metabolic stability relative to that of their aniline congeners (as demonstrated through microsomal stability assays and metabolite identification efforts), indicating applicability of 1-aminonorbornanes as aniline bioisosteres.

Au NPs and alkali dopants—an effective team: In situ FTIR spectroscopy and temporal analysis of products reveal the importance of the type of support and alkali‐metal dopant on the performance of Au NPs for CO₂ adsorption and its conversion with H₂ into C₃ or C₄ alcohols in the presence of C₂H₄ or C₃H₆. The active Au⁰ sites required for the activation of all feed components are generated by in situ reduction of Au ^δ+ during an activation process.

Abstract

Au/TiO₂ and Au/SiO₂ catalysts containing 2 wt % Au and different amounts of K or Cs were tested for alcohol synthesis from CO₂, H₂, and C₂H₄/C₃H₆. 1‐Propanol or 1‐butanol/isobutanol were obtained in the presence of C₂H₄ or C₃H₆. Higher yields of the corresponding alcohols were obtained over TiO₂‐based catalysts in comparison with their SiO₂‐based counterparts. This is caused by an enhanced ability of the TiO₂‐based catalysts for CO₂ activation, as concluded from in situ fourier‐transform infrared (FTIR) spectroscopy and temporal analysis of products (TAP) studies. The synthesized carbonate and formate species adsorbed on the support do not hamper CO₂ conversion into CO and the hydroformylation reaction. The transformation of Au ^δ+ to active Au⁰ sites proceeds during an activation procedure. As reflected by CO adsorption and scanning transmission electron microscopy, the accessible Au⁰ sites are influenced by the amount of alkali dopants and the support. FTIR data and TAP tests reveal a very weak interaction of C₂H₄ with the catalyst, suggesting its quick reaction with CO and H₂ after activation on Au⁰ sites to form propanol and propane.

Synlett
DOI: 10.1055/s-0037-1609656

The sulfoximine group has been reported as a versatile and beneficial functionality for pharmaceutical or agrochemical entities. Herein, we report the Csp2–H sulfoximidation of electron-rich arenes ­under the irradiation of blue light using an organic acridinium photocatalyst and molecular oxygen or peroxodisulfates as terminal oxidants. The method allows for the late-stage introduction of various sulfoximines onto complex bioactive compounds showing high functional group compatibility without the need for prefunctionalization.
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© Georg Thieme Verlag Stuttgart · New York

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Enantioselective α-functionalizations of ketones via allylic substitution of silyl enol ethers

Enantioselective α-functionalizations of ketones via allylic substitution of silyl enol ethers, Published online: 19 November 2018; doi:10.1038/s41557-018-0165-x

Typical methods for the enantioselective α-functionalizations of ketones join ketone enolate nucleophiles with carbon or heteroatom electrophiles. We report an umpolung strategy to achieve this transformation with masked ketone electrophiles and a wide range of conventional heteroatom and carbon nucleophiles catalysed by a metallacyclic iridium catalyst in high yield and enantioselectivity.

Abstract

Carbon dioxide (CO₂) is an attractive building block for organic synthesis that is environmentally friendly. Continuous flow technologies have enabled C−O and C−C bond forming reactions with CO₂ that previously were either low‐yielding or impossible in batch to afford value‐added chemicals. This review describes recent advances in continuous flow as an enabling strategy in utilizing CO₂ as a C₁ building block in chemical synthesis.

Abstract

Improved molecularly‐defined cobalt catalysts for the hydrogenation of carbon dioxide to methanol have been developed. A key factor for increased productivity (up to twofold compared to previous state‐of‐the‐art‐system) is the specific nature of substituents on the triphos ligand. In addition, the effect of metal precursors, and variations of additives have been investigated.

Heterobiaryls composed of pyridine and diazine rings are key components of pharmaceuticals and are often central to pharmacological function. We present an alternative approach to metal-catalyzed cross-coupling to make heterobiaryls using contractive phosphorus C–C couplings, also termed phosphorus ligand coupling reactions. The process starts by regioselective phosphorus substitution of the C–H bonds para to nitrogen in two successive heterocycles; ligand coupling is then triggered via acidic alcohol solutions to form the heterobiaryl bond. Mechanistic studies imply that ligand coupling is an asynchronous process involving migration of one heterocycle to the ipso position of the other around a central pentacoordinate P(V) atom. The strategy can be applied to complex drug-like molecules containing multiple reactive sites and polar functional groups, and also enables convergent coupling of drug fragments and late-stage heteroarylation of pharmaceuticals.

We demonstrate that the chemical-feature model described in our original paper is distinguishable from the nongeneralizable models introduced by Chuang and Keiser. Furthermore, the chemical-feature model significantly outperforms these models in out-of-sample predictions, justifying the use of chemical featurization from which machine learning models can extract meaningful patterns in the dataset, as originally described.