Undergo Diels-Alder Reactions Research Articles

Highly dispersed palladium supported on sulfuric acid-modified activated carbon for efficient dehydrogenation to produce novel aromatic monomer

Herein, a sustainable route to novel aromatic monomer, dimethyl 1,2,3,4-tetrahydro-1,4-methanonaphthalene-5,8-dicarboxylate, was developed, in which dimethyl muconate and norbornene used as the diene and dienophile undergo Diels-Alder reaction followed by dehydrogenation. The polycyclic cycloadduct, octahydro-1,4-methanonaphthalene-5,8-dicarboxylate, could be synthesized without catalyst. The activated carbon modified with sulfuric acid generated more oxygen-containing groups, stronger acidity and more acidic sites. Highly dispersed palladium metal particles with an average particle size of about 1.0 nm exhibited excellent activity in the dehydrogenation reaction and the yield of target product reached 73.8 %.

Anthriporphyrinoids: Design, Synthesis, and Reactivity towards Diels-Alder Reaction.

A series of non-aromatic anthripentaphyrins containing an anthracene unit, two thiophenes, and two pyrrole rings as a part of a macrocyclic framework connected via three meso-carbons were synthesized. The crystal structure of one of the anthripentaphyrins revealed that the two thiophene rings were in an inverted orientation, and the macrocycle adopts a nonplanar Z-like ruffled structure. These anthriporphyrinoids act as dienes and undergo Diels-Alder reaction with dienophiles to form stable non-aromatic Diels-Alder adducts.

Enantioselective fullerene functionalization through stereochemical information transfer from a self-assembled cage.

The regioselective functionalization of C60 remains challenging, while the enantioselective functionalization of C60 is difficult to explore due to the need for complex chiral tethers or arduous chromatography. Metal-organic cages have served as masks to effect the regioselective functionalization of C60. However, it is difficult to control the stereochemistry of the resulting fullerene adducts through this method. Here we report a means of defining up to six stereocentres on C60, achieving enantioselective fullerene functionalization. This method involves the use of a metal-organic cage built from a chiral formylpyridine. Fullerenes hosted within the cavity of the cage can be converted into a series of C60 adducts through chemo-, regio- and stereo-selective Diels-Alder reactions with the edges of the cage. The chiral formylpyridine ultimately dictates the stereochemistry of these chiral fullerene adducts without being incorporated into them. Such chiral fullerene adducts may become useful in devices requiring circularly polarized light manipulation.

Dienophilic reactivity of 2-phosphaindolizines: a conceptual DFT investigation.

The >C=P– or –N=P– functionality in 1,3-azaphospholo[1,5-a]pyridine, named as 2-phosphaindolizine and its 1- and 3-aza derivatives act as dienophiles and undergo Diels–Alder reactions with 1,3-dienes. However, the dienophilic reactivity is affected by the nature of the substituent groups on the two sides of the σ2,λ3-P atom and also by the presence of more nitrogen atom(s) in the five-membered ring. The conceptual density functional theory (DFT) calculations have been used in recent years to predict the reactivity of organic molecules in reactions. We calculated global hardness (η), global softness (S), electronic chemical potential (μ), electrophilicity (ω), and nucleophilicity (N) indices of four classes of 2-phosphaindolizines, on the basis of which their observed relative dienophilic reactivities could be rationalized. Besides, the Fukui functions of the carbon/nitrogen and phosphorus atoms of the >C=P– and –N=P– functionalities were also computed which revealed their hard electrophilic character and accorded well with the dienophilic reactivities observed experimentally. Furthermore, energies and symmetries of the lowest unoccupied molecular orbitals (LUMO) of 2-phosphaindolizines were found to be in conformity with their dienophilic reactivities.

Palladium-Catalyzed Aminomethylative Oppolzer-Type Cyclization of Enynes: Access to Aminomethylated Benzofulvenes

A novel palladium-catalyzed Oppolzer-type cyclization reaction aided by the aminomethyl cyclopalladated complex has been developed, which provides rapid access to functionalized benzofulvenes with excellent stereoselectivity. The corresponding products can undergo Diels-Alder reaction with maleimides, providing a series of complex polycyclic compounds with excellent regio- and stereoselectivities.

Study of properties of 3-fluorinated cyclopropene derivatives

Treatment of 1-bromo-2,2-dichloro-3-trimethylsilylcyclopropane with 5 equiv of CsF resulted in the formation of a chlorocyclopropenyl cation, which, under different conditions, further reacted with fluoride ion selectively to generate 3,3-difluorocyclopropene or 1-chloro-3-fluorocyclopropene. The Diels-Alder reactions of fluorinated cyclopropene derivatives with DPIBF yielded only exo or exo-anti adducts. On treatment of fused tricyclic cis-1-chloro-3-fluorocyclopropane derivative with n-BuLi, 3-fluorocyclopropene derivative was formed, which underwent Diels-Alder reaction with DPIBF to give an endo-endo adduct. Additionally, fused tricyclic 3,3-difluorocyclopropane and cis-1-chloro-3-fluorocyclopropane derivatives were underwent ring-opening reaction of cyclopropane by BF3●Et2O, respectively, and 1,4-diphenylnaphthalene derivatives were obtained.

Incorporation of catechyl monomers into lignins: lignification from the non-phenolic endviaDiels–Alder cycloaddition?

Catechyl monomers 1-electron-oxidize and undergo radical coupling to produce benzodioxane units in lignin. Derivedo-quinones undergo Diels–Alder reactions giving oxatricyclo and new benzodioxane products, but does this occur in lignification?.

Conjugation between maleimide-containing Pt(IV) prodrugs and furan or furan-containing drug delivery vectors via Diels-Alder cycloaddition

Pt(IV) complexes are considered to act as antitumor prodrugs and their in vivo activity can be improved exploiting drug targeting and delivery strategies. With a view to such applications, the maleimide-containing ligand 2-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)acetic acid was used to produce the cisplatin-based Pt(IV) complexes (OC-6-44)-diamminedichlorido(ethanolato)(2-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)acetato)platinum(IV) and (OC-6-44)-acetatodiamminedichlorido(2-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)acetato)platinum(IV). These complexes underwent Diels-Alder reaction with furan, used as a model molecule to set up the experimental conditions, at ambient temperature up to 50 h, with limited decomposition. Finally, the reaction between the maleimide-containing Pt(IV) complexes and silica nanoparticles decorated with furan were successfully used as a proof-of-concept to demonstrate the clickability of functionalized vectors for drug delivery.

4 + 2] Cycloaddition of Vinylphosphine Oxides to α-Oxy-o-xylylene as a route to Phosphorylated Naphthyl and Biaryl Scaffolds

α-Oxy- o-xylylene, a highly reactive diene readily accessible from benzocyclobutenol, undergoes Diels-Alder reaction with vinylphosphine oxides, yielding the corresponding 2-phosphorylated 1-hydroxy-1,2,3,4-tetrahydronaphthalenes in excellent yields. Use of unsubstituted and trans-2-aryl-substituted vinylphosphine oxides leads to cycloadducts with complete regioselectivity and with cis/trans selectivity up to 19:1 in the most favorable case. In the case of P-stereogenic trans-2-aryl-substituted vinylphosphine oxides, a virtually complete chirality transfer from P to C can be achieved. Dehydration and aromatization of the obtained cycloadducts bearing the resolved P-stereogenic phosphinoyl groups can be carried out to afford the valuable P-stereogenic and axially chiral phosphorylated 1,2'-binaphthyl ring system. Cases of restricted rotation around Csp3-Csp2 single bond in some tetrahydronaphthalene cycloadducts have also been revealed.

Chelated Diborenes and Their Inverse-Electron-Demand Diels-Alder Reactions with Dienes.

A doubly base-stabilised diborane based on a benzylphosphine linker was prepared by a salt elimination reaction between 2-LiC6 H4 CH2 PCy2 ⋅Et2 O and B2 Br4 . This compound was reduced with KC8 to its corresponding diborene, with the benzylphosphine forming a five-membered chelate. The diborene reacts with butadiene, 2-trimethylsiloxy-1,3-butadiene, and isoprene to form 4,5-diboracyclohexenes, which interconvert between their 1,1- (geminal) and 1,2- (vicinal) chelated isomers. The 1,1-chelated diborene undergoes a halide-catalysed isomerisation into its thermodynamically favoured 1,2-isomer, which undergoes Diels-Alder reactions more slowly than the kinetic product.

Furan-functionalised melamine-formaldehyde particles performing Diels-Alder reactions

Functionalised particles are highly requested in materials research, as they can be used as vital components in many advanced applications such as smart materials, functional coatings, drug carrier systems or adsorption materials. In this study, furan-functionalised melamine-formaldehyde (MF) particles were successfully prepared for the first time using an organic sol-gel process. Commercially available 2-Aminomethylfuran (AMF) and 2-Aminomethyl-5-methylfuran (AMMF) were used as modifying agents. In the isolated polymer particles, a melamine (M) to modifying agent ratio of M:AMF mol/mol 2.04:1 and M:AMMF ratio of mol/mol 1.25:1 was used. The obtained particles were isolated in various centrifugation and re-dispersion cycles and analysed using ATR-FT-IR, Raman and solid state 13C NMR spectroscopy, TGA, SEM and DSC measurements. Upon functionalisation the size of the MF particles increased (MF 1.59 µm, 27% CV (coefficient of variation); MF-AMF 2.56 µm, 25% CV; MF-AMMF 2.20 µm, 35% CV). DSC measurements showed that another type of exothermic residual reactivity besides condensation-based curing takes place with the furan-modified particles that is not related to the liberation of volatile compounds. The newly obtained particles are able to undergo Diels-Alder reactions with maleimide groups. The characteristic IR and Raman absorbance bands of the reaction products after the particles were reacted with 4,4′-Diphenylmethanebismaleimide reagent confirm the formation of a Diels-Alder adduct.

Azacyclic allenes harnessed

The allene motif—in which two double bonds join three carbons together—tends to be an oddball among functional groups. Squeeze an allene into a ring system, and it becomes even more unusual. A team at the University of California, Los Angeles, led by Neil K. Garg and Kendall N. Houk, hopes to change the allene’s reputation with a report that azacyclic allenes can be useful synthetic tools (Nat. Chem. 2018, DOI: 10.1038/s41557-018-0080-1). The researchers developed silyl triflate precursors that readily generate azacyclic allenes by adding CsF under mild conditions—an advance over past syntheses that required harsh conditions and gave poor yields. These azacyclic allenes undergo Diels-Alder reactions with dienes (example shown). Computational studies of the transition states of these reactions show how substituents are able to control which double bond reacts. The methodology provides access to substituted piperidines—which are often skeletons in drug molecules—by forming two new bonds and three stereocenters

Controlling the Substitution Pattern of Hexasubstituted Naphthalenes by Aryne/Siloxyfuran Diels–Alder Additions: Regio‐ and Stereocontrolled Synthesis of Arizonin C1 Analogs

3,4‐Dimethoxybenz‐1‐yne and 2‐siloxylated furans without or with a bromine atom at C‐3 undergo Diels–Alder reactions with orientational selectivity. Hydrolysis furnished a bromine‐free or a bromine‐containing naphthalene, respectively. Bromination of the former provided a regioisomer of the latter. Either of the two compounds was processed to give a variety of unnatural naphthoquinonopyrano‐γ‐lactones. This occurred by a succession of (1) Heck coupling, (2) asymmetric dihydroxylation, (3) oxa‐Pictet–Spengler cyclization, and (4) oxidation. The fifteen monomeric naphthoquinonopyrano‐γ‐lactone structures that we prepared resemble the natural product (–)‐arizonin C1 or its C‐5 epimer. Accordingly, they represent hexasubstituted naphthalenes likewise. The sixteenth naphthoquinonopyrano‐γ‐lactone that we synthesized is a kind of dimer. Its moieties are bridged differently than those in naturally occurring naphthoquinonopyrano‐γ‐lactone dimers.

Iodobenzene and m-chloroperbenzoic acid mediated oxidative dearomatization of phenols

Oxidative dearomatization of 2- and 4-substituted phenols to their corresponding benzoquinone monoketals by catalytic amount of iodobenzene, and m-CPBA as a co-oxidant has been achieved via in situ generation of PhIO2, a hypervalent iodine(V) species. The transiently generated orthobenzoquinone monoketals further underwent Diels–Alder reaction with various dienophiles to furnish densely substituted bicyclo[2.2.2]octenones in high selectivities and yields. This methodology features ready availability of reagents, cost effectiveness, safety, brevity, selectivity, diversity and excellent yields.

Synthesis of 1,3-azaphospholo[1,5-f]phenanthridines through 1,5-electrocyclization

GRAPHICAL ABSTRACT

Polymer Functional Nanodiamonds by Light-Induced Ligation

A light-triggered strategy to functionalize nanodiamonds (NDs) with well-defined functional polymers is presented. The employed grafting approach is based on o-methylbenzaldehydes, which upon UV irradiation form o-quinodimethanes that undergo Diels–Alder reactions with dienophiles. A series of well-defined maleimide end-group functional polymers, i.e., poly(styrene) (Mn = 5800 g mol–1; Đ = 1.2), poly(N-isopropylacrylamide) (Mn = 5800 g mol–1, Đ = 1.2), and poly(2-(2′,3′,4′,6′-tetra-O-acetyl-α-d-mannosyloxy)ethyl methacrylate) (Mn = 24 300, 39 000, and 58 800 g mol–1, Đ ≤ 1.3), were prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization of protected maleimide functional RAFT agents. After deprotection of the furan-protected maleimide end groups, the polymers were photografted to o-methylbenzaldehyde functional NDs and characterized in detail via infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The grafting density decreas...

ChemInform Abstract: Total Synthesis of the Galbulimima Alkaloids Himandravine and GB17 Using Biomimetic Diels—Alder Reactions of Double Diene Precursors.

The enantioselective total syntheses of himandravine and GB17 were completed through a common biomimetic strategy involving Diels–Alder reactions of unusual double diene containing linear precursors. The double diene precursors, containing or lacking a C12 substituent as required to produce GB17 or himandravine, respectively, were found to undergo Diels–Alder reactions to afford mixtures of regioisomeric cycloadducts that map onto the alternative carbocyclic frameworks of both himandravine and GB17. Computational investigations revealed that these Diels–Alder reactions proceed via transition state structures of similar energy that have a high degree of bispericyclic character and that the low levels of regioselectivity observed in the reactions are a consequence of competing orbital interaction and distortion energies. The combined experimental and computational results provide valuable insights into the biosynthesis of the Galbulimima alkaloids.

ChemInform Abstract: Amine‐Promoted Asymmetric [4 + 2] Cycloadditions of α‐Acetoxymethyl Allenoate and Dual Activated Alkenes: Stereoselective Synthesis of Poly‐Substituted Cyclohexenes.

AbstractThe allenic ester (I) reacts with (S)‐benzylmorpholine (BMP) to generate a chiral diene intermediate which readily undergoes Diels—Alder reactions with acrylic nitriles (II) to offer functionalized cyclohexenes (III) after hydrolytic cleavage of the chiral secondary amine auxiliary.

Total Synthesis of the Galbulimima Alkaloids Himandravine and GB17 Using Biomimetic Diels-Alder Reactions of Double Diene Precursors.

The enantioselective total syntheses of himandravine and GB17 were completed through a common biomimetic strategy involving Diels-Alder reactions of unusual double diene containing linear precursors. The double diene precursors, containing or lacking a C12 substituent as required to produce GB17 or himandravine, respectively, were found to undergo Diels-Alder reactions to afford mixtures of regioisomeric cycloadducts that map onto the alternative carbocyclic frameworks of both himandravine and GB17. Computational investigations revealed that these Diels-Alder reactions proceed via transition state structures of similar energy that have a high degree of bispericyclic character and that the low levels of regioselectivity observed in the reactions are a consequence of competing orbital interaction and distortion energies. The combined experimental and computational results provide valuable insights into the biosynthesis of the Galbulimima alkaloids.

Preparation and Diels–Alder reactions of 1′-heterosubsituted vinylimidazoles

A Diels–Alder/rearrangement sequence has been pursued in our lab en route to a number of oroidin dimers. In order to access the fully substituted core of these molecules, 1′,2′-disubstituted 4-vinylimidazoles were required as dienes. The preparation of a series of 4-vinylimidazoles containing substituents on the vinyl moiety via hydroalumination/electrophilic trapping or hydrosilylation is described. These derivatives undergo Diels–Alder reactions with N-phenylmaleimide to provide the tetrahydrobenzimidazole derivatives. The cycloadducts derived from halosubstituted systems can undergo elimination, leading to the corresponding dihydrobenzimidazole, whereas the silyl and stannyl derivatives provide the corresponding 4-substituted tetrahydrobenzimidazole.