Concise Synthesis of Open‐Cage Fullerenes for Oxygen Delivery

Synthesis of spiro[indolenine]-methanofullerenes via Deoxofluor promoted deoxygenative cyclopropanation of 1,2-(3-indole)-fullerenols

Deoxofluor-promoted intramolecular cyclopropanation of 1,2-(3-indole)fullerenols has been developed as a straightforward and efficient protocol for the synthesis of various spiro[indolenine]-methanofullerenes. This approach exhibits low cost, operational simplicity, and convenient conditions, and thus has potential application value.

CH3 CN@open-C60 : An Effective Inner-Space Modification and Isotope Effect Inside a Nano-Sized Flask

Despite several small molecules being encapsulated inside cage-opened fullerene derivatives, such species have not considerably affected the structures and properties of the outer carbon cages. Herein, we achieved an effective inner-space modification for an open-cage C60 derivative by insertion of a neutral CH3 CN molecule into the cavity. The CH3 CN@open-C60 thus obtained showed an enhanced polarity, thus affording an easy separation from a mixture containing the empty cage by column chromatography on silica gel, without the preparative HPLC that was needed for previous cases. The less negative reduction potentials with respect to those of empty cage reflect the decreased energy level of the LUMO, which is supported by the DFT calculations. NMR spectroscopy, single-crystal X-ray analysis, and theoretical calculations revealed that both the presence of the encapsulated CH3 CN and cage deformation caused by the CH3 CN play an essential role in the change of the electronic properties. Furthermore, the favored binding affinity of deuterated acetonitrile CD3 CN with internal C60 surface is discussed.

Open-Cage Fullerene as a Selective Molecular Trap for LiF/[BeF]. Angew Chem Int Ed Engl 2023;62:e202300151. [PMID: 36718977 DOI: 10.1002/anie.202300151]

The insertion of ionic compounds into open-cage fullerenes is a challenging task due to the electropositive nature of the cavity. The present work reports the preparation of an open-cage C₆₀ derivative with a hydroxy group pointing towards the centre of the cavity, which can coordinate to a metal cation, thus acting as a bait/hook to trap the metal cation such as the lithium cation in neutral LiF and the beryllium cation in the cationic [BeF]⁺ species. Other metal salts could not be inserted under similar conditions. The structure of MF in the cage was unambiguously determined by single-crystal X-ray diffraction. Owing to its tendency to undergo polycoordination, Li⁺ monomer salts have not been isolated before, despite extensive research on Li bonds. The present results provide a unique example of a Li bond.

Open-Cage Fullerene as Molecular Container for F- , Cl- , Br- and I. Angew Chem Int Ed Engl 2022;61:e202212090. [PMID: 36316627 DOI: 10.1002/anie.202212090]

A 19-membered open-cage fullerene derivative was prepared from C₆₀ in 7 steps and 5.5 % yield through the peroxide-mediate pathway. There are four carbonyl groups, an ether oxygen and a quinoxaline moiety on the rim of the orifice. A chloride anion could be inserted into its cavity by heating with hydrochloric acid at 60 °C for 4 h. Encapsulation of fluoride, bromide and iodide anions was also achieved at slightly more forcing conditions, 90 °C for 14 h. Single crystal X-ray structures of the sodium salt of the chloride and the bromide encapsulated derivatives were obtained, which showed the halide anion in the center of the cavity and two sodium cations connecting two cages through coordination to the oxygen atoms on the rim of the orifices. The halide encapsulation ratio is quantitative in the isolated products.

Transition-Metal-Free Domino Reaction of [60]Fullerene, Indole, and DMSO/HCl: One-Pot Access to Diverse N-Substituted [60]Fulleroindole Derivatives

An unprecedented multicomponent domino reaction of [60]fullerene, indole, and DMSO/HCl has been developed for the one-pot efficient synthesis of diverse N-substituted [60]fulleroindole derivatives. This methodology features simple operation, low cost, and transition-metal-circumvented and good functional group tolerance in indole.

NHC-Catalyzed Three-Component Hydroalkylation Reactions of [60]Fullerene: An Umpolung Approach to Diverse Monoalkylated Hydrofullerenes

A novel N-heterocyclic carbene-catalyzed three-component umpolung hydroalkylation of [60]fullerene with 4-(chloromethyl)-benzaldehydes/α,β-unsaturated aldehydes and alcohols/thioalcohols has been developed for the flexible and efficient preparation of diverse monoalkylated hydrofullerenes. Organic catalysis, broad substrate scope, excellent functional group tolerance, and products with high diversity and complexity levels are attractive features of this protocol.

Preparation of π-extended fullerene derivatives through addition of phenylenediamine to open-cage fullerene derivatives

Open-cage fullerenes with a quinoxaline moiety on the rim of the orifice showed evident π-system extension effect on the NMR and UV-Vis spectra.

Palladium-catalyzed decarboxylative [2 + 3] cyclocarbonylation reactions of [60]fullerene: selective synthesis of [60]fullerene-fused 3-vinylcyclopentan-4-ones and cyclopentane-4-carbaldehydes

A new palladium-catalyzed decarboxylative strategy has been developed toward direct cyclocarbonylation of [60]fullerene, selectively furnishing novel [60]fullerene-fused 3-vinylcyclopentan-4-ones and cyclopentane-4-carbaldehydes.

Reductive Decarbonylation of a Cage-Opened C60 Derivative

The decarbonylation of a cage-opened C₆₀ derivative was examined by employing single-electron reductants. During the reaction, an H₂O molecule was spontaneously encapsulated inside the cage (up to 78%) through the thus-formed 14-membered-ring orifice even though the H₂O encapsulation had long been considered to require an orifice consisting of at least 16 atoms. The crystallographic analysis revealed an orifice shape closer to a circle which significantly contributes to the decreased activation barrier for the H₂O encapsulation.

An H2 O2 Molecule Stabilized inside Open-Cage C60 Derivatives by a Hydroxy Stopper

An H₂ O₂ molecule was isolated inside hydroxylated open-cage fullerene derivatives by mixing an H₂ O₂ solution with a precursor molecule followed by reduction of one of carbonyl groups on its orifice. Depending on the reduction site, two structural isomers for H₂ O₂ @open-fullerenes were obtained. A high encapsulation ratio of 81 % was attained at low temperature. The structures of the peroxosolvate complexes thus obtained were studied by ¹ H NMR spectroscopy, X-ray analysis, and DFT calculations, showing strong hydrogen bonding between the encapsulated H₂ O₂ and the hydroxy group located at the center of the orifice. This OH group was found to act as a kinetic stopper, and the formation of the hydrogen bonding caused thermodynamic stabilization of the H₂ O₂ molecule, both of which prevent its escape from the cage. One of the peroxosolvates was isolated by HPLC, affording H₂ O₂ @open-fullerene with 100 % encapsulation ratio, likely due to the intramolecular hydrogen-bonding interaction.

Isocyanide-Induced Annulation Leading to Cyclopento-, Methano-, and Cyclopentano-[60]Fullerene Derivatives

The three-component annulation reactions of C₆₀, alkyl isocyanide, and dimethyl acetylenedicarboxylate (DMAD) or unsymmetric alkynes are investigated to afford cyclopent-2-en-1-imino- and ketenimine methano-[60]fullerene derivatives, which, upon hydration in the presence of acid, yield the corresponding fullerene amides. Dimethyl 2,3-pentadienedioate, the allene counterpart of DMAD, and ethyl buta-2,3-dienoate undergo four-component annulation with C₆₀, alkyl isocyanide, and water under similar conditions to yield cyclopentano-[60]fullerene derivatives with similar amide groups.

Metal-Free-Catalyzed Three-Component [2+2+2] Annulation Reaction of [60]Fullerene, Ketones, and Indoles: Access to Diverse [60]Fullerene-Fused 1,2-Tetrahydrocarbazoles

The first example of metal-free-catalyzed multicomponent annulation reaction of [60]fullerene has been developed for concise and efficient construction of novel [60]fullerene-fused 1,2-tetrahydrocarbazoles. Using inexpensive and readily available I₂ as a catalyst, [60]fullerene, ketones, and indoles undergo a formal [2+2+2] annulation process to conveniently assemble diverse 1,2-tetrahydrocarbazoles. Mechanistic studies indicate that this reaction proceeds through I₂-promoted generation of a 3-vinylindole structure with the characteristics of a conjugated diene followed by cycloaddition to [60]fullerene.

An "Umpolung Relay" Strategy: One-Pot, Twice Polarity Inversion Cascade Synthesis of Diversified [60]Fulleroindoles

An "umpolung relay" strategy, which includes an one-pot, twice polarity inversion cascade of C₆₀ via carbanion and carbocation polarity reversed relay pathway, has been developed for the synthesis of a diverse range of novel [60]fulleroindole derivatives.

Tumor cell-activated "Sustainable ROS Generator" with homogeneous intratumoral distribution property for improved anti-tumor therapy

Photodynamic therapy (PDT) holds a number of advantages for tumor therapy. However, its therapeutic efficiency is limited by non-sustainable reactive oxygen species (ROS) generation and heterogeneous distribution of photosensitizer (PS) in tumor. Herein, a "Sustainable ROS Generator" (SRG) is developed for efficient antitumor therapy. Methods: SRG was prepared by encapsulating small-sized Mn₃O₄-Ce6 nanoparticles (MC) into dendritic mesoporous silica nanoparticles (DMSNs) and then enveloped with hyaluronic acid (HA). Due to the high concentration of HAase in tumor tissue, the small-sized MC could be released from DMSNs and homogeneously distributed in whole tumor. Then, the released MC would be uptaken by tumor cells and degraded by high levels of intracellular glutathione (GSH), disrupting intracellular redox homeostasis. More importantly, the released Ce6 could efficiently generate singlet oxygen (¹O₂) under laser irradiation until the tissue oxygen was exhausted, and the manganese ion (Mn²⁺) generated by degraded MC would then convert the low toxic by-product (H₂O₂) of PDT to the most harmful ROS (·OH) for sustainable and recyclable ROS generation. Results: MC could be homogeneously distributed in whole tumor and significantly reduced the level of intracellular GSH. At 2 h after PDT, obvious intracellular ROS production was still observed. Moreover, during oxygen recovery in tumor tissue, ·OH could be continuously produced, and the nanosystem could induce 82% of cell death comparing with 30% of cell death induced by free Ce6. For in vivo PDT, SRG achieved a complete inhibition on tumor growth. Conclusion: Based on these findings, we conclude that the designed SRG could induce sustainable ROS generation, homogeneous intratumoral distribution and intracellular redox homeostasis disruption, presenting an efficient strategy for enhanced ROS-mediated anti-tumor therapy.

Palladium-catalyzed domino spirocyclization of [60]fullerene: synthesis of diverse [60]fullerene-fused spiro[4,5]/[5,5] derivatives

Herein a new, general and practical method for the spirocyclization of [60]fullerene through a palladium-catalyzed domino Heck/C-H activation reaction is presented. A wide range of novel [60]fullerene-fused spirocyclic derivatives can be easily and flexibly synthesized with a broad substrate scope and excellent functional-group tolerance. A plausible mechanism involving an alkyl Pd(ii) species as a key intermediate has been proposed.

Palladium-catalyzed synthesis of [60]fullerene-fused furochromenones and further electrochemical functionalization

The palladium-catalyzed heteroannulation of [60]fullerene with 4-hydroxycoumarins affords [60]fullerene-fused furochromenones, which can be further derivatized via an electrochemical method to synthesize 1,2,3,4-adducts.