A diastereodivergent direct catalytic asymmetric inverse electron demand Diels–Alder reaction between ketenes and 3-alkylenyloxindoles was accomplished by using chiral N,N′-dioxide/gadolinium ...complexes. By adjusting only the substituents of the ligand and retaining other catalysis conditions, both syn- and anti-indole-fused dihydropyranones bearing two vicinal stereogenic centers were obtained in high yields with excellent ee values. Thus, by changing the configuration of the chiral ligands, all stereoisomers could be obtained from the same set of starting materials.
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IJS, KILJ, NUK, PNG, UL, UM
Retro: Cyclo8isoindole, which has a saddle‐shaped geometry (see picture, 2), was synthesized by oxidative coupling of a bicyclo2.2.2octadiene(BCOD)‐fused 2,2′‐bipyrrole followed by a ...retro‐Diels–Alder reaction of BCOD‐fused cyclo8pyrrole (1). Key trends in the optical spectra of ring‐annelated cyclo8pyrroles are identified based on magnetic circular dichroism spectra and theorectical calculations.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Targeted delivery and specific activation of photosensitizers can greatly improve the treatment outcome of photodynamic therapy. To this end, we report herein a novel dual receptor‐mediated ...bioorthogonal activation approach to enhance the tumor specificity of the photodynamic action. It involves the targeted delivery of a biotinylated boron dipyrromethene (BODIPY)‐based photosensitizer, which is quenched in the native form by the attached 1,2,4,5‐tetrazine unit, and an epidermal growth factor receptor (EGFR)‐targeting cyclic peptide conjugated with a bicycle6.1.0non‐4‐yne moiety. Only for cancer cells that overexpress both the biotin receptor and EGFR, the two components can be internalized preferentially where they undergo an inverse electron‐demand Diels–Alder reaction, leading to restoration of the photodynamic activity of the BODIPY core. By using a range of cell lines with different expression levels of these two receptors, we have demonstrated that this stepwise “deliver‐and‐click” approach can confine the photodynamic action on a specific type of cancer cells.
The internalization of two bioorthogonal components mediated by the corresponding receptors, followed by inverse electron‐demand Diels–Alder reaction leads to specific activation of the photodynamic action inside the target cells. This dual receptor‐mediated bioorthogonal activation approach works as an AND logic device that can greatly enhance the precision of antitumoral photodynamic therapy.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The Diels–Alder reaction of maldoxin with an isopropenylallene at 60–75
°C afforded an adduct closely related to chloropestolide A (24%) and a second adduct (0–11%) that underwent an ene reaction to ...generate the chloropupukeanolide D (11–22%) skeleton. The Diels–Alder reaction occurred with good selectively (>5:1) from a single face of maldoxin under much milder conditions than previously reported for the analogous dimethoxycyclohexadienone. Furthermore, the ene reaction took place under mild conditions, whereas the analogous Diels–Alder adduct from the dimethoxycyclohexadienone did not undergo an ene reaction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Fiber reinforced thermoset composites (FRPCs) have received tremendous attention because of their merits of light weight, high modulus and high strength. However, the efficient recycling of the waste ...during the manufacturing and service life of FRPCs is still great challenge. This paper reports a newly designed dynamic crosslinked network based on Diels-Alder chemistry as matrix for fully recyclable aramid fabric reinforced composites. The DA network shows good thermomechanical properties owing to the incorporated aromatic amide bonds, and the overall performance can be readily tailored by adjusting the ratio of amide-containing component and flexible aliphatic component. The good reversibility of the DA network and highly efficient recovery of mechanical properties of recycled sample are confirmed. With optimized composition, the DA network exhibits good interfacial strength with aramid fiber that is comparable to that of widely used epoxy resin due to the interfacial hydrogen bonds among amide bonds between fiber and matrix. Moreover, the closed-loop recycling of both matrix and reinforced fabric without any other additive is also demonstrated. This paper presents the first report on recyclable aramid fiber reinforced composites and is expected to provide hints for future development of fully recyclable and high-performance FRPCs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We report herein the first examples of chiral phosphoric acid‐catalyzed enantioselective Diels–Alder reactions between 2‐trifluoroacetamido‐1,3‐dienes 1 and α,β‐unsaturated carbonyl compounds 2. ...Polysubstituted 1‐acetamido cyclohexenes 3 were formed in high yields with excellent diastereo‐ and enantioselectivities. The reaction proceeds through a stepwise process as shown by deuterium labelling experiments. A catalytic enantioselective three‐component reaction of 1, 2 and ortho‐hydroxybenzhydryl alcohols 4 was subsequently developed furnishing the densely functionalized hexahydroxanthenes 5 in a highly stereoselective manner. This multicomponent reaction generates four chemical bonds with concurrent creation of five contiguous stereocenters.
CPA‐catalyzed annulation of 2‐trifluoroacetamido‐1,3‐dienes with α,β‐unsaturated carbonyl compounds affords highly functionalized 1‐trifluoroacetamido cyclohex‐1‐ene derivatives 3 in high yields with excellent diastereo‐ and enantioselectivities. An asymmetric three‐component reaction of 1, 2 and ortho‐hydroxybenzhydryl alcohols 4 provides the densely functionalized hexahydroxanthenes with concurrent creation of five contiguous stereocenters.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A microwave-promoted solvent- and catalyst-free aza-Diels–Alder reaction is described. 6-2-(dimethylamino)vinyl-1,3-dimethyluracil reacts with aldehyde and amine inside a microwave reactor to produce ...dihydropyrido4,3-dpyrimidine derivatives in excellent yield and within a very short time.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In this study, gellan gum (Gel) derivatives were allowed to interact via aqueous Diels-Alder chemistry without the need for initiators, producing a crosslinked hydrogel network that exhibited good ...potential as a drug carrier using tramadol as a drug model. Hydrogel conjugation was achieved by the synthesis of a maleimide and furan-functionalized Gel, and the pre- and post-gelation chemical structure of the resulting hydrogel precursors was fully investigated. Potential uses of the developed hydrogel in the pharmaceutical industry were also evaluated by looking at its gelation duration, temperature, morphologies, swelling, biodegradation, and mechanical characteristics. The Gel-FM hydrogels were safe, showed good antimicrobial activity, and had a low storage modulus, which meant that they could be used in many biochemical fields. The encapsulation and release of tramadol from the hydrogel system in phosphate-buffered saline (PBS) at 37 °C were investigated under acidic and slightly alkaline conditions, replicating the stomach and intestinal tracts, respectively. The in-vitro release profile showed promising results for drug encapsulation, revealing that the drug could safely be well-encapsulated in acidic stomach environments and released more quickly in slightly alkaline intestinal environments. This implies that the hydrogels produced could work well as polymers for specifically delivering medication to the colon.
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•Gellan gum was chemically modified through incorporation of both furyl and maleimide units.•Both the functionalized biopolymers were cross-linked via click Diels-Alder reaction.•The crosslinking was monitored to optimize the gelation conditions.•The morphology and swelling properties were examined.•The developed hydrogel utilized as drug carrier using tramadol as a drug model.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Remending properties of a network polymer with reversible reactivity are described. The network structure is constructed by a Diels–Alder (DA) reaction between furyl-telechelic poly(ethylene adipate) ...(PEAF
2) and a tris-maleimide, M
3. When a film sample was cut into two pieces and the cut surfaces were kept in contact with each other at 60
°C, rejoining of the cut pieces was observed. This mending was induced by the reversible cross-linking reaction bridging the cut surfaces. At the cut front, the “weak” DA adducts are selectively dissociated sacrificially to release the stress so as to protect the chemical structure of the prepolymer and the linker against the scission or degradation. The dissociated furan and maleimide readily reconnect by forward DA reaction to mend the material. The remending was also observed for the samples kept at room temperature after melting at 60
°C. So, the PEAF
2 network polymer is a thermo-responsive mendable material in which crack healing is induced by a prompt thermal stimulus.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Epoxy resins containing Diels-Alder (DA) furan and maleimide moieties are presented with the capability to self-heal after exposure to an external heat source. A conventional epoxy amine system has ...been combined with furfuryl and maleimide functional groups in a two-step process, to avoid major side-reactions, and the concentration of a thermo-reversibly binding cross-linker was considered to balance thermoset and thermoplastic behaviours, and the subsequent self-healing performance. In the context of self-repair technologies an inbuilt 'intrinsic' self-healing system is deemed favourable as the healing agent can be placed in known 'hot spot' regions (i.e. skin-stringer run outs, ply drops and around drilled holes) where operational damage predominately occurs in load bearing aerospace structures. In this study, the mechanical and self-healing performance of furan functionalised epoxy resins containing varying amounts (10, 20, 30 or 40 pph) of bismaleimide were investigated using a bulk epoxy polymer tapered double cantilever beam test specimen geometry. Two forms, a thin film and a bulk material, were evaluated to account for future integration methods into fibre reinforced polymer (FRP) composites. The highest healing efficiency, with respect to the obtained initial load value, was observed from the 20 pph bulk material derivative. The polymers were successful in achieving consistent multiple (three) healing cycles when heated at 150 °C for 5 min. This novel investigated DA material exhibits favourable processing characteristics for FRP composites as preliminary studies have shown successful coextrution with reinforcing fibres to form free standing films and dry fibre impregnation.
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