Synthesis and study of trannulene derivatives of fullerenes

A series of trannulenes C₆₀F₁₅[CX(COOR)₂]₃ (X = COOMe, Br; R = Me, Et, Prⁿ, n-Hex, Bu^t, (CH₂)₃NHCOOBu^t) was synthesized. The first water-soluble trannulenes containing six carboxyl groups (C₆₀F₁₅[C(COOMe)(COOH)₂]₃) or six protonated amino groups (C₆₀F₁₅[C(COOMe)(COO(CH₂)₃NH₃ ⁺CF₃COO^?)₂]₃) were obtained. The compositions and structures of all compounds were proved by mass spectrometry, ¹H, ¹³C, and ¹⁹F NMR spectroscopy, and other physicochemical methods. The reactivity of trannulenes was studied for the first time. The unique isomerization of trannulenes to triumphenes accompanied by the migration of three organic addends from one hemisphere of the fullerene cage to another hemisphere was discovered. The structures of the isomerization products were proved using single-crystal X-ray diffraction analysis and ¹H, ¹³C, and ¹⁹F NMR spectroscopy. The concerted cascade of isomerization, elimination, and addition reactions was accomplished, which made it possible to obtain photoactive dyads C₆₀F₁₄R₂=A (R = C(X)(COOR)₂, A is a fragment of fullerenes C₆₀ or C₇₀, anthracene, or pentacene). These dyads contain the electron-deficient fluorofullerene core and electron-donor (with respect to the fluorofullerene core of the molecule) addend A. Photoinduced charge separation can occur in these systems, which makes them analogs of natural photosynthetic antennas.     

Carbon monoxide activation via O-bound CO using decamethylscandocinium-hydridoborate ion pairs

Ion pairs [Cp*(2)Sc](+)[HB(p-C(6)F(4)R)(3)](-) (R = F, 1-F; R = H, 1-H) were prepared and shown to be unreactive toward D(2) and α-olefins, leading to the conclusion that no back-transfer of hydride from boron to scandium occurs. Nevertheless, reaction with CO is observed to yield two products, both ion pairs of the [Cp*(2)Sc](+) cation with formylborate (2-R) and borataepoxide (3-R) counteranions. DFT calculations show that these products arise from the carbonyl adduct of the [Cp*(2)Sc](+) in which the CO is bonded to scandium through the oxygen atom, not the carbon atom. The formylborate 2-R is formed in a two-step process initiated by an abstraction of the hydride by the carbon end of an O-bound CO, which forms an η(2)-formyl intermediate that adds, in a second step, the borane at the carbon. The borataepoxide 3-R is suggested to result from an isomerization of 2-R. This unprecedented reaction represents a new way to activate CO via a reaction channel emanating from the ephemeral isocarbonyl isomer of the CO adduct.     

Nanofibers and nanospirals fabricated through the interfacial organization of a partially fluorinated compound

Nanostructures composed of fluorinated compounds are of great interest both for fundamental investigations and practical applications. In this paper, we have investigated the supramolecular assembly of two carbamate derivatives, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-henicosa fluorododecyl 1-naphthylcarbamate (F10C2Np) and 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-henicosa fluorododecyl phenylcarbamate (F10C2Ph), which bear partially fluorinated alkyl tails on their molecular skeletons, through the air/water interfacial organization. It has been found that F10C2Np could form nanofiber or nanospiral structure with a dimension of several micrometers, while F10C2Ph formed straight ribbon-like structures. More interestingly, when the multilayer films of both of the compounds were subjected to the circular dichroism (CD) measurements, distinct CD signals could be detected, although the compounds themselves are optically inactive. Based on a series of characterizations on the films and the structural features of the molecules, a size mismatching effect was suggested to explain the interesting phenomenon.     

Evidence for the S(N)2' mechanism in hydrolysis of C60F48: origin of the stability of trannulenes

The products of hydrolysis of C60F48 (which contains six isolated double bonds) by either aq. acetone or aq. THF show that no more than twelve fluorines are replaced through nucleophilic substitution, as predicted by the recently identified S(N)2' mechanism. Subsequent HF elimination gives fragments containing a maximum of six epoxide oxygens. Calculated heats of formation of models for the possible initial hydroxy derivatives indicate that there is little energetic discrimination between them, so that a complex mixture is likely to be formed. Overall the data show that hydrolytic degradation of fluorofullerenes is less severe than believed previously, requires a specific motif, and explains the low susceptibility of C60F18 towards hydrolysis and the high stability of trannulenes.     

Catalytic Enantioselective and Diastereoselective Allylic Alkylation with Fluoroenolates: Efficient Access to C3‐Fluorinated and All‐Carbon Quaternary Oxindoles

Synthetically versatile 3,3‐disubstituted fluorooxindoles exhibiting vicinal chirality centers were obtained in high yields and with excellent enantio‐, diastereo‐, and regioselectivity through catalytic asymmetric fluoroenolate alkylation with allylic acetates. The reaction proceeds under mild conditions and can be scaled up without compromising the asymmetric induction. The unique synthetic usefulness of the products is highlighted by the incorporation of additional functionalities and the formation of 3‐fluorinated oxindoles exhibiting an array of four adjacent centers of chirality. A new C−F bond functionalization path that provides unprecedented possibilities for the stereoselective generation of a chiral quaternary carbon center in the alkaloid scaffold is introduced.     

Rhodium-catalyzed dehydrocoupling of fluorinated phosphine-borane adducts: synthesis, characterization, and properties of cyclic and polymeric phosphinoboranes with electron-withdrawing substituents at phosphorus

The dehydrocoupling of the fluorinated secondary phosphine-borane adduct R2PH.BH3 (R = p-CF3C6H4) at 60 degrees C is catalyzed by the rhodium complex [{Rh(mu-Cl)(1,5-cod)}2] to give the four-membered chain R2PH-BH2-R2P-BH3. A mixture of the cyclic trimer [R2P-BH2]3 and tetramer [R2P-BH2]4 was obtained from the same reaction at a more elevated temperature of 100 degrees C. The analogous rhodium-catalyzed dehydrocoupling of the primary phosphine-borane adduct RPH2.BH3 at 60 degrees C gave the high molecular weight polyphosphinoborane polymer [RPH-BH2]n (Mw = 56,170, PDI = 1.67). The molecular weight was investigated by gel permeation chromatography and the compound characterized by multinuclear NMR spectroscopy. Interestingly, the electron-withdrawing fluorinated aryl substituents have an important influence on the reactivity as the dehydrocoupling process occurred efficiently at the mildest temperatures observed for phosphine-borane adducts to date. Thin films of polymeric [RPH-BH2]n (R = p-CF3C6H4) have also been shown to function as effective negative-tone resists towards electron beam (e-beam) lithography (EBL). The resultant patterned bars were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS).     

Carbon-chain isomerization during the electrochemical fluorination in anhydrous hydrogen fluoride—a mechanistic study

The compounds i-C₄H₉SO₂F, i-C₃H₇SO₂F and cyclo-C₃H₇C(O)F have been subjected to electrochemical fluorination in anhydrous hydrogen fluoride. The resulting products were fully analyzed by NMR spectroscopy. From the reaction balances, literature data and quantum chemical calculations, a new mechanism for carbon-chain isomerization during the electrochemical fluorination (ECF) is proposed. The key step in the formation of isomeric products is believed to be a ring closure reaction involving carbo-cationic or biradical intermediates.     

CF Activation in Perfluorinated Arenes with Isonitriles under UV‐Light Irradiation

Due to the great value of fluorinated arenes in agrochemistry, medicinal chemistry and materials science, development of methods for preparation of fluorinated arenes is of high importance. They can be either accessed by arene fluorination or by partial arene defluorination. However, the carbon?fluorine bond belongs to the strongest σ‐bonds, which renders C?F activation highly challenging. Here it is shown that aryl and alkyl isonitriles efficiently activate the strong C?F bond in perfluoroarenes by simple UV irradiation under mild conditions. Reactions proceed by formal direct insertion of the isonitrile into the C?F bond without any transition metal. Activation occurs at arene C?F bonds whereas aliphatic C?F bonds remain unreacted. For selected perfluoroarenes C?F activation occurs with high regioselectivity and resulting imidoyl fluorides are transformed into other valuable compounds. Theoretical studies give insights into the reaction mechanism.     

Directed Palladium Catalyzed C−H (Ethoxycarbonyl)difluoromethylthiolation Reactions

The unprecedented Pd-catalyzed (ethoxycarbonyl)difluoromethylthiolation reaction of various unsaturated derivatives was studied. In the presence of the (ethoxycarbonyl)difluoromethylsulfenamide reagent I and under mild reaction conditions (60 °C), both 2-(hetero)aryl and 2-(α-aryl-vinyl)pyridine derivatives were smoothly functionalized with this methodology (37 examples, up to 87 % yield). Moreover, the synthetic interest of this fluorinated moiety was further showcased by its conversion into various original fluorinated residues. Finally, a plausible mechanism for this transformation was suggested.     

(Fluoro)alkylation of alkenes promoted by photolysis of alkylzirconocenes

Difluoroalkylated compounds have important applications in pharmaceutical, agrochemical, and materials science. However, efficient methods to construct the alkylCF₂–alkyl bond are very limited, and the site-selective introduction of a difluoromethylene (CF₂) group into an aliphatic chain at the desired position remains challenging. Here, we report an unprecedented example of alkylzirconocene promoted difluoroalkylation of alkyl- and silyl-alkenes with a variety of unactivated difluoroalkyl iodides and bromides under the irradiation of visible light without a catalyst. The resulting difluoroalkylated compounds can serve as versatile synthons in organic synthesis. The reaction can also be applied to activated difluoroalkyl, trifluoromethyl, perfluoroalkyl, monofluoroalkyl, and nonfluorinated alkyl halides, providing a general method to controllably access fluorinated compounds. Preliminary mechanistic studies reveal that a single electron transfer (SET) pathway induced by a Zr(iii) species is involved in the reaction, in which the Zr(iii) species is generated by the photolysis of alkylzirconocene with blue light.

An unprecedented example of alkylzirconocene promoted difluoroalkylation of alkyl- and silyl-alkenes with a variety of fluoroalkyl and nonfluoroalkyl halides under the irradiation of visible light has been reported.     

Coupling-isomerization synthesis of chalcones

The Sonogashira coupling of electron-deficient (hetero)aryl halides 1 and (hetero)aryl or alkenyl 1-propargyl alcohols 2 does not terminate at the stage of the expected internal propargyl alcohols, but rather gives rise to the formation of alpha,beta-unsaturated ketones 3 with a variety of acceptor substituents. This new domino reaction, a coupling-isomerization reaction (CIR), can be rationalized as a sequence of rapid Pd/Cu-catalyzed alkynylation followed by a slow amine-base-catalyzed propargyl alcohol-enone isomerization. Performing the CIR in deuterated protic solvents or with a selectively deuterated propargyl alcohol revealed that the base-catalyzed isomerization step proceeds through a formal 1,3-H shift with minimal H/D exchange with the surrounding solvent. Additionally, 19F NMR kinetic measurements on the isomerization step with the fluorinated propargyl alcohol 4 r support the mechanistic rationale.     

New and efficient syntheses of alpha-iodo-alpha,alpha-difluoro- and beta-iodo-alpha,alpha,beta,beta-tetrafluorocarboxylic acid derivatives as useful building blocks for making functional fluoro compounds

Perfluoroolefins reacted with I-Cl and ClSO(3)H under mild conditions to give R(F)CFICF(2)OSO(2)Cl, which could be readily converted into various alpha-iodo-perfluorocarboxylic acid derivatives or telomerized with tetrafluoroethylene to I(CF(2)CF(2))(n)()OSO(2)Cl. Ring-opening reaction of perfluoroalkoxypentafluorocyclopropane with iodine at 240 degrees C produced ICF(2)CF(2)COF, which was quenched by alcohol, water, or NH(3) to give beta-iodo-alpha,alpha,beta,beta-tetrafluorocarboxylic acid derivatives. These functional fluorinated iodides can be used as building blocks for making selectively fluorinated compounds.     

(S)-2-[(R)-fluoro(phenyl)methyl]oxirane: a general reagent for determining the ee of alpha-chiral amines

(S)-2-[(R)-Fluoro(phenyl)methyl]oxirane is a new, synthetic, yet enantiopure, chiral resolution reagent, readily obtained from enantiopure (2S,3S)-phenylglycidol, that reacts with a variety of alpha-chiral primary and secondary amines in a straightforward manner through a regioselective ring-opening. Diastereomeric products are easily identified and quantified by (19)F, (1)H, and (13)C NMR and by HPLC, which makes this fluorinated compound a most versatile reagent for the analysis of scalemic mixtures of amines. [reaction: see text]     

Isomerizing Olefin Metathesis

Isomerizing olefin metathesis is currently undergoing a transformation from laboratory curiosity to powerful synthetic concept at the heart of orthogonal tandem catalysis. In this process, an isomerization catalyst continuously moves double bonds along carbon chains, while a metathesis catalyst scrambles the residues at the C−C double bonds. This cooperative action of two catalysts can be used to access single, defined products from a complex mixture of compounds. Alternatively, it enables the transformation of uniform starting materials into complex product blends with defined, tunable properties. This concept article highlights recent developments and potential applications of this fascinating reaction concept.     

Synthesis and Characterization of Some New Triorganophosphorus, -Arsenic and -Antimony(V) Amido Derivatives

A number of triorganophosphorus, -arsenic, and -antimony(V) amido derivatives of the general formula R 2 R'ML 2 [where R = C 6 F 5 , C 6 H 5 ; R' = C 6 F 5 , C 6 H 4 CH 3 - p ; M = P, As or Sb and L = imidazole, benzimidazole, 2-methyl benzimidazole, indazole, and 1,2,3,4-tetrahydrocarbazole] have been synthesized by the metathetical reaction of triorganophosphorus, -arsenic, and -antimony(V) halides and the corresponding imidazoles in the presence of triethyl amine. These compounds have been characterized by elemental analysis, IR and NMR ( 1 H and 19 F) spectroscopy, conductance, and molecular weight data. The Van't Hoff factor "i" and molar conductance data of the compounds revealed them to be monomeric and nonionic in nature. On the basis of spectroscopic studies, a tentative trigonal bipyramidal structure has been assigned for these amido derivatives.     

Selectivity of biohydroxylation with Beauveria bassiana of trans-2-fluorocycloalkyl N-phenylcarbamates

Biohydroxylation with Beauveria bassiana of racemates and the pure enantiomers of trans-2-fluorocyclohexyl- 3 and trans-2-fluorocycloheptyl N-phenylcarbamates 6 were investigated and compared with results found for the corresponding nonfluorinated parent compounds. In all cases, mixtures of diastereomeric products hydroxylated in the 4-position were isolated, besides products of p-hydroxylation of the aromatic ring and succeeding compounds derived from these primary reaction products. The regioselectivity of hydroxylation by this fungus is not changed by a single fluorine substituent attached closely to the electron-rich anchoring group in the trans-2-position. There is a different influence on the diastereoselectivity of hydroxylation depending on the absolute configuration of the fluorinated substrates. While the transformation of the (S,S)-2-fluorocycloalkyl N-phenylcarbamates is not diastereoselective giving almost 1:1 mixtures of cis- and trans-4-hydroxyl compounds, the corresponding reactions of the (R,R)-isomers led preferentially to the products trans-hydroxylated in the 4-position. The transformation of the racemic fluorinated six-membered N-phenylcarbamate 3 led to products having a very small enantiomeric excess. The fluorine substituent slightly increased the enantioselectivity of transformation of the racemic seven-membered substrate 6 compared to the C(s)()-symmetric nonfluorinated carbamate. Thus, the fluorine substituent in the trans-2-position in these examples did not change the regioselectivity but rather influenced the stereochemistry of biotransformation, depending on the absolute configuration of the substrate and ring size.     

Iron(II)‐Catalyzed Hydrophosphination of Isocyanates

The first transition metal catalyzed hydrophosphination of isocyanates is presented. The use of low‐coordinate iron(II) precatalysts leads to an unprecedented catalytic double insertion of isocyanates into the P−H bond of diphenylphosphine to yield phosphinodicarboxamides [Ph₂PC(=O)N(R)C(=O)N(H)R], a new family of derivatized organophosphorus compounds. This remarkable result can be attributed to the low‐coordinate nature of the iron(II) centers whose inherent electron deficiency enables a Lewis‐acid mechanism in which a combination of the steric pocket of the metal center and substrate size determines the reaction products and regioselectivity.     

Incompletely condensed fluoroalkyl silsesquioxanes and derivatives: precursors for low surface energy materials

A novel synthetic method was developed for the controlled functionalization of fluorinated polyhedral oligomeric silsesquioxanes (F-POSS), which are useful as low surface energy materials for superhydrophobic and superoleophobic materials. Utilizing triflic acid, open-cage compounds were created and then reacted with a variety of dichlorosilanes to produce functional F-POSS structures possessing alkyl-, aryl-, and acrylate-based moieties. The crystal structure for an endo,endo-disilanol F-POSS compound was determined by single-crystal X-ray diffraction. The chemical structures were confirmed using multinuclear NMR spectroscopy ((1)H, (13)C, (19)F, and (29)Si), FT-IR, and combustion analysis. Dynamic contact angle measurements of these compounds were taken with water and hexadecane. These novel structures were found to possess excellent wetting-resistant behavior, similar to that of the parent F-POSS compound. They are the first well-defined fluorinated nano-building blocks with a controlled level of reactive functionality for the development of new superhydrophobic and superoleophobic materials.     

Adamantyl-containing fluorinated 1,3-diketones

A convenient one-step procedure has been developed for the synthesis of fluorine-containing 2-(adamant-l-yl)-1,3-diketones by reaction of fluorinated 1,3-diketones with 1,3-dehydroadamantane. The products can be used as starting compounds for the preparation of new fluorinated adamantyl-containing heterocyclic compounds.     

Design and synthesis of multi-component 18 pi annulenic fluorofullerene ensembles suitable for donor-acceptor applications

A series of trannulene (all-trans annulene) derivatives of [60]fullerene have been prepared by reacting C(60)F(18) with methanetricarboxylate esters that incorporate a range of photoactive functions. All the compounds have the intense emerald-green colour of fullerene trannulenes, characterised by strong bands at ca. 612 and 667 nm. Single crystal X-ray studies show that the packing varies with the nature of the addend, attributable to differing steric effects. UV/vis absorption spectra display transitions of the respective fullerene and addend models, indicating absence of electronic interactions between them in the ground state. These now provide an extensive series for testing photoactive (light-harvesting) properties, with the exceptional properties of having strong visible light absorption. Their exceptional stability is attributed to the 18[small pi] aromatic circuit, inability to undergo nucleophilic substitution without disrupting this circuit, and a curved cage region that is shielded to reagents by the three bulky addends.