Yuya Hu

Cycloaddition of CO₂ : 1,2,3‐Triazole‐bridged bisphenol was developed as organocatalyst for cycloaddition of CO₂ and epoxides, which is among the most efficient organocatalysts that are active in the absence of both metal and halide. The bisphenol was recycled 14 times in the presence of halide, and 5 times in the absence of halide.

Abstract

1,2,3‐triazole‐bridged bisphenol has been developed as organocatalyst in the coupling of CO₂ and epoxides. In the absence of halide co‐catalyst, halomethyl‐substituted epoxides reacted with 1 bar CO₂, while a series of aryl‐substituted epoxides were transformed into cyclic carbonates in 57–95 % yields at 120 °C and 10 bar pressure. 1,2,3‐triazole‐bridged bisphenol is thus among the most efficient organocatalysts that are active in the absence of both metal and halide. For alkyl‐substituted epoxides, good yields of 80–95 % were obtained under 1 bar CO₂ in the presence of halide. The bisphenol was recycled 14 times in the presence of halide, and 5 times in the absence of halide. The two hydroxyl groups of bisphenol are proposed to work synergistically in the catalytic cycle.

Blown away: Microcellular self‐blown non‐isocyanate polyurethane foams were constructed from reactive formulations by guiding the chemo‐ and regioselective ring‐opening and decarboxylation of cyclic carbonates by amines and thiols. This novel concept is versatile, easily accessible, and scalable.

Abstract

Polyurethane (PU) foams are indisputably daily essential materials found in many applications, notably for comfort (for example, matrasses) or energy saving (for example, thermal insulation). Today, greener routes for their production are intensively searched for to avoid the use of toxic isocyanates. An easily scalable process for the simple construction of self‐blown isocyanate‐free PU foams by exploiting the organocatalyzed chemo‐ and regioselective additions of amines and thiols to easily accessible cyclic carbonates is described. These reactions are first validated on model compounds and rationalized by DFT calculations. Various foams are then prepared and characterized in terms of morphology and mechanical properties, and the scope of the process is illustrated by modulating the composition of the reactive formulation. With impressive diversity and accessibility of the main components of the formulations, this new robust and solvent‐free process could open avenues for construction of more sustainable PU foams, and offers the first realistic alternative to the traditional isocyanate route.

Cycling with polymers: This Review discusses the recent advances made in the cycloaddition reaction of captured CO₂ with epoxides over a variety of imidazolium‐functionalized organic cationic polymers as a class of eminent heterogeneous catalysts.

Abstract

The cycloaddition reaction of CO₂ with various epoxides to generate cyclic carbonates is one of the most promising and efficient approaches for CO₂ fixation. Typical imidazolium‐based ionic liquids possessing electrophilic cations and nucleophilic halogen anions have been identified as excellent and environmentally friendly candidates for synergistically activating epoxides to convert CO₂. Therefore, the feasible construction of a series of imidazolium‐functionalized organic cationic polymers can bridge the gap between homogeneous and heterogeneous catalysis, thereby obtaining highly selective CO₂ adsorption and simultaneous conversion ability. This Review describes the recent advancements made with regard to the design and synthesis of this type of polymeric networks having imidazolium functionality. They are considered as an outstanding heterogeneous catalyst for the cycloaddition of CO₂ to epoxides. Based on the perspective from the design of building blocks to the synthesis of cationic polymers, the focus mainly lies on how to introduce imidazole units into the material backbone via a covalent linking approach and how to incorporate other active sites capable of activating CO₂ and/or epoxides into such polymeric materials.

Nature Chemistry, Published online: 30 March 2020; doi:10.1038/s41557-020-0439-y

Inverting the order of nature’s two-phase biosynthesis of terpenes offers a strategy by which the synthesis of these compounds can be simplified. The key reaction is a palladium-catalysed polyenyne cycloisomerization that not only tolerates the presence of all of the oxygen functionalities but also is facilitated by them.

Nature Chemistry, Published online: 27 March 2020; doi:10.1038/s41557-020-0450-3

The copolymerization of CO2 with epoxides is an attractive approach for valorizing waste products and improving sustainability in polymer manufacturing. Now, a heterodinuclear Mg(ii)Co(ii) complex has been shown to act as a highly active and selective catalyst for this reaction at low CO2 pressure. The synergy between the two metals was investigated using polymerization kinetics.

Non‐noble‐metal catalysis : The cobalt‐catalyzed hydrogenation of epoxides for the synthesis of anti‐Markovnikov alcohols is reported. This method is suitable for internal, as well as terminal, epoxides and works smoothly even with multi‐substituted derivatives under mild conditions.

Abstract

A straightforward methodology for the synthesis of anti‐Markovnikov‐type alcohols is presented. By using a specific cobalt triphos complex in the presence of Zn(OTf)₂ as an additive, the hydrogenation of epoxides proceeds with high yields and selectivities. The described protocol shows a broad substrate scope, including multi‐substituted internal and terminal epoxides, as well as a good functional‐group tolerance. Various natural‐product derivatives, including steroids, terpenoids, and sesquiterpenoids, gave access to the corresponding alcohols in moderate‐to‐excellent yields.

To show the synthetic utility of the Rh‐catalyzed C−C/C−H activation cascade of 3‐arylcyclopentanones, described are the collective concise and asymmetric syntheses of the terpenoids (−)‐microthecaline A, (−)‐leubehanol, (+)‐pseudopteroxazole, (+)‐seco‐pseudopteroxazole, pseudopterosin A–F and G–J aglycones, and (+)‐heritonin in four to nine steps.

Abstract

To show the synthetic utility of the catalytic C−C activation of less strained substrates, described here are the collective and concise syntheses of the natural products (−)‐microthecaline A, (−)‐leubehanol, (+)‐pseudopteroxazole, (+)‐seco‐pseudopteroxazole, pseudopterosin A–F and G—J aglycones, and (+)‐heritonin. The key step in these syntheses involve a Rh‐catalyzed C−C/C−H activation cascade of 3‐arylcyclopentanones, which provides a rapid and enantioselective route to access the polysubstituted tetrahydronaphthalene cores presented in these natural products. Other important features include 1) the direct C−H amination of the tetralone substrate in the synthesis of (−)‐microthecaline A, 2) the use of phosphoric acid to enhance efficiency and regioselectivity for problematic cyclopentanone substrates in the C−C activation reactions, and 3) the direct conversion of serrulatane into amphilectane diterpenes by an allylic cyclodehydrogenation coupling.

Biopolymers : The selective catalytic synthesis of limonene‐derived monofunctional cyclic carbonates and their subsequent functionalisation via thiol–ene addition and amine ring‐opening is reported. The selective catalytic route to monofunctional limonene carbonates gives straightforward access to monomers for novel bio‐based polymers.

Abstract

The selective catalytic synthesis of limonene‐derived monofunctional cyclic carbonates and their subsequent functionalisation via thiol–ene addition and amine ring‐opening is reported. A phosphotungstate polyoxometalate catalyst used for limonene epoxidation in the 1,2‐position is shown to also be active in cyclic carbonate synthesis, allowing a two‐step, one‐pot synthesis without intermittent epoxide isolation. When used in conjunction with a classical halide catalyst, the polyoxometalate increased the rate of carbonation in a synergistic double‐activation of both substrates. The cis isomer is shown to be responsible for incomplete conversion and by‐product formation in commercial mixtures of 1,2‐limomene oxide. Carbonation of 8,9‐limonene epoxide furnished the 8,9‐limonene carbonate for the first time. Both cyclic carbonates underwent thiol–ene addition reactions to yield linked di‐monocarbonates, which can be used in linear non‐isocyanate polyurethanes synthesis, as shown by their facile ring‐opening with N ‐hexylamine. Thus, the selective catalytic route to monofunctional limonene carbonates gives straightforward access to monomers for novel bio‐based polymers.

Abstract

An imidazolium catalyst supported on thermomorphic polyethylene (PE) was prepared from 1‐methylimidazole and polyethylene iodide (PE−I). The catalyst was characterized by ¹H and ¹³C NMR, SEC and MALDI‐ToF mass spectrometry. Its catalytic activity was evaluated in the ring‐opening of epoxides with carbon dioxide to give cyclic carbonates under solvent‐free conditions. The catalyst proved to be active at low catalyst loading (down to 0.1 mol%) and allows the reaction to occur at low CO₂ pressure (1–5 bar) and moderate temperature (100 °C). A range of terminal and internal epoxides was converted to the corresponding cyclic carbonates with high yields and selectivities. The recyclability of the catalyst was studied and no significant loss of activity was observed after 5 runs.