Showing papers on "Double bond published in 2014"

Dual gold catalysis.

Abstract: For more than a decade the innovative field of homogeneous catalysis by gold was dominated by the interaction of the substrate molecule with one gold center, in most cases in mononuclear gold complexes. The initial interaction was typically a π-coordination of a carbon–carbon double bond to the gold, an activation of the unsaturated substrate molecule by a π-acidic metal center. Only recently clear evidence for reactions that involve the activation of organic substrates by two gold centers was obtained. In that new class of gold-catalyzed reactions the two gold centers interact with the substrate in a very different way. One gold complex is σ-bonded to a terminal alkynyl group in the substrate, the other one is π-coordinated. Only in a few cases, a combination π-coordination and σ-coordination to the same alkyne, which is the energetically preferred mode of interaction with two gold centers, initiates the reaction. In most of the cases, the reaction proceeds through an intermediate with one alkyne σ-bonde...

A new C–C bond formation model based on the quantum chemical topology of electron density

Abstract: ELF topological analyses of bonding changes in non-polar, polar and ionic organic reactions involving the participation of CC(X) double bonds make it possible to establish a unified model for C–C bond formation. This model is characterised by a C-to-C coupling of two pseudoradical centers generated at the most significant atoms of the reacting molecules. The global electron density transfer process that takes place along polar and ionic reactions favours the creation of these pseudoradical centers at the most nucleophilic/electrophilic centers of the reacting molecules, decreasing activation energies. The proposed reactivity model based on the topological analysis of the changes in electron density throughout a reaction makes it possible to reject the frontier molecular orbital reactivity model based on the analysis of molecular orbitals.

Direct observation of a borane–silane complex involved in frustrated Lewis-pair-mediated hydrosilylations

Abstract: Perfluorarylborane Lewis acids catalyse the addition of silicon-hydrogen bonds across C=C, C=N and C=O double bonds. This 'metal-free' hydrosilylation has been proposed to occur via borane activation of the silane Si-H bond, rather than through classical Lewis acid/base adducts with the substrate. However, the key borane/silane adduct had not been observed experimentally. Here it is shown that the strongly Lewis acidic, antiaromatic 1,2,3-tris(pentafluorophenyl)-4,5,6,7-tetrafluoro-1-boraindene forms an observable, isolable adduct with triethylsilane. The equilibrium for adduct formation was studied quantitatively through variable-temperature NMR spectroscopic investigations. The interaction of the silane with the borane occurs through the Si-H bond, as evidenced by trends in the Si-H coupling constant and the infrared stretching frequency of the Si-H bond, as well as by X-ray crystallography and theoretical calculations. The adduct's reactivity with nucleophiles demonstrates conclusively the role of this species in metal-free 'frustrated-Lewis-pair' hydrosilylation reactions.

Transition metal-catalyzed direct nucleophilic addition of C–H bonds to carbon–heteroatom double bonds

Abstract: Transition metal-catalyzed direct C–H functionalization has drawn great attention in the past several decades owing to its advantages compared to conventional organic transformations, including higher atom-, step- and cost-economy and the avoidance of tedious prefunctionalization and waste emission. At the current stage, to make the C–H functionalization more applicable, chemists have devoted themselves to expanding the substrate and reaction scope. In the past decade, we exerted ourselves to develop new transformations based on direct C–H functionalization. In this minireview we report on our recent achievements on the addition of C–H bonds to carbonyls and imines. The addition of organometallic reagents, such as Grignard reagents, toward carbon–heteroatom double bonds is one of the most powerful reactions in organic synthesis to produce secondary and tertiary alcohols and amines. This chemistry is broadly used in both laboratory and industry. However, this powerful transformation suffers from some drawbacks: (1) the preparation of initial organohalides from easily available fossil feedstocks is tedious and sluggish; (2) substantial amounts of metal halide salts are emitted as waste; (3) last but not least, the manipulation of organometallic reagents is complicated due to their sensitivity to air and moisture. In contrast, direct insertion of polar double bonds to C–H bonds via transition-metal catalysis is ideal from the viewpoint of atom-, step- and cost-economy and the avoidance of the waste emission, as well as of the complex manipulation of sensitive reagents. Starting from this point, we made a commitment to this project years ago and have made credible achievements in this field. We first carried out Ir-catalyzed addition of pyridinyl C–H bonds to aldehydes promoted by silane, showing an unusual C-3 selectivity. Later on, we developed Rh-catalyzed addition of aryl C–H bonds with aldimines in the absence of any additives with directing strategy with highest atom- and step-economy. The mechanism was investigated in depth by the isolation of key intermediates and systematic thermodynamic and kinetic studies. Such a concept was expanded to the coupling of aryl/alkenyl C–H bonds with aldehydes and imines. Notably, a tandem process of relayed C–H activation/alkyne insertion/cyclization between benzoates/benzimide and alkynes was developed, indicating the potential of the direct coupling of esters and amides with C–H bonds. Ideally, this strategy opens a new window to approach the ideal reactions to produce amines and alcohols from hydrocarbons.

Pinpointing Double Bonds in Lipids by Paternò-Büchi Reactions and Mass Spectrometry

Abstract: The positions of double bonds in lipids play critical roles in their biochemical and biophysical properties. In this study, by coupling Paterno-Buchi (P-B) reaction with tandem mass spectrometry, we developed a novel method that can achieve confident, fast, and sensitive determination of double bond locations within various types of lipids. The P-B reaction is facilitated by UV irradiation of a nanoelectrospray plume entraining lipids and acetone. Tandem mass spectrometry of the on-line reaction products via collision activation leads to the rupture of oxetane rings and the formation of diagnostic ions specific to the double bond location.

Catalytic diamination of olefins via N-N bond activation.

Abstract: ConspectusVicinal diamines are important structural motifs present in various biologically and chemically significant molecules. Direct diamination of olefins provides an effective approach to this class of compounds. Unlike well-established oxidation processes such as epoxidation, dihydroxylation, and aminohydroxylation, direct diamination of olefins had remained a long-standing challenge and had been less well developed.In this Account, we summarize our recent studies on Pd(0)- and Cu(I)-catalyzed diaminations of olefins using di-tert-butyldiaziridinone and its related analogues as nitrogen sources via N–N bond activation. A wide variety of imidazolidinones, cyclic sulfamides, indolines, imidazolinones, and cyclic guanidines can be obtained from conjugated dienes and terminal olefins. For conjugated dienes, the diamination proceeds regioselectively at the internal double bond with the Pd(0) catalyst. Mechanistic studies show that the diamination likely involves a four-membered Pd(II) species resulting f...

Silicon-oxygen double bonds: a stable silanone with a trigonal-planar coordinated silicon center.

Abstract: SiO in a complex: The first silanone that is stable at room temperature (3) is reported. The two-step synthesis involves carbonylation of the silylidyne complex 1 to give the chromiosilylene 2, followed by oxidation of 2 with N2 O. Silanone 3 features a polar, short SiO bond (1.526(3) A) to a trigonal-planar-coordinated silicon center and reacts with water to give the dihydroxysilyl complex.

Iron-mediated intermolecular N-group transfer chemistry with olefinic substrates

Abstract: The dipyrrinato iron catalyst reacts with organic azides to generate a reactive, high-spin imido radical intermediate, distinct from nitrenoid or imido species commonly observed with low-spin transition metal complexes. The unique electronic structure of the putative group-transfer intermediate dictates the chemoselectivity for intermolecular nitrene transfer. The mechanism of nitrene group transfer was probed via amination and aziridination of para-substituted toluene and styrene substrates, respectively. The Hammett analysis of both catalytic amination and aziridination reactions indicate the rate of nitrene transfer is enhanced with functional groups capable of delocalizing spin. Intermolecular amination reactions with olefinic substrates bearing allylic C–H bonds give rise to exclusive allylic amination with no apparent aziridination products. Amination of substrates containing terminal olefins give rise exclusively to allylic C–H bond abstraction, C–N recombination occurring at the terminal C with transposition of the double bond. A similar reaction is observed with cis-β-methylstyrene where exclusive amination of the allylic position is observed with isomerization of the olefin to the trans-configuration. The high levels of chemoselectivity are attributed to the high-spin electronic configuration of the reactive imido radical intermediate, while the steric demands of the ligand enforce regioselective amination at the terminal position of linear α-olefins.

Boron Radical Cations from the Facile Oxidation of Electron‐Rich Diborenes

Abstract: The realization of a phosphine-stabilized diborene, Et3P⋅(Mes)B=B(Mes)⋅PEt3 (4), by KC8 reduction of Et3P⋅B2Mes2Br2 in benzene enabled the evaluation and comparison of its electronic structure to the previously described NHC-stabilized diborene IMe⋅(Dur)B=B(Dur)⋅IMe (1). Importantly, both species feature unusual electron-rich boron centers. However, cyclic voltammetry, UV/Vis spectroscopy, and DFT calculations revealed a significant influence of the Lewis base on the reduction potential and absorption behavior of the B-B double bond system. Thus, the stronger σ-donor strength and larger electronegativity of the NHC ligand results in an energetically higher-lying HOMO, making 1 a stronger neutral reductant as 4 (1: E1/2=−1.55 V; 4: −1.05 V), and a smaller HOMO–LUMO gap of 1 accompanied by a noticeable red-shift of its lowest-energy absorption band with respect to 4. Owing to the highly negative reduction potentials, 1 and 4 were easily oxidized to afford rare boron-centered radical cations (5 and 6).

Enantioselective synthesis of highly functionalized dihydrofurans through copper-catalyzed asymmetric formal [3+2] cycloaddition of β-ketoesters with propargylic esters.

Abstract: An enantioselective synthesis of highly functionalized dihydrofurans through a copper-catalyzed asymmetric [3+2] cycloaddition of β-ketoesters with propargylic esters has been developed. With a combination of Cu(OTf)2 and a chiral tridentate P,N,N ligand as the catalyst, a variety of 2,3-dihydrofurans bearing an exocyclic double bond at the 2 position were obtained in good chemical yields and with good to high enantioselectivities. The exocyclic double bond can be hydrogenated in a highly diastereoselective fashion to give unusual cis-2,3-dihydrofuran derivatives, thus further enhancing the scope of this transformation.

Triamidoamine-uranium(IV)-stabilized terminal parent phosphide and phosphinidene complexes

Abstract: Reaction of [U(TrenTIPS)(THF)][BPh4] (1; TrenTIPS=N{CH2CH2NSi(iPr)3}3) with NaPH2 afforded the novel f-block terminal parent phosphide complex [U(TrenTIPS)(PH2)] (2; U–P=2.883(2) A). Treatment of 2 with one equivalent of KCH2C6H5 and two equivalents of benzo-15-crown-5 ether (B15C5) afforded the unprecedented metal-stabilized terminal parent phosphinidene complex [U(TrenTIPS)(PH)][K(B15C5)2] (4; U[DOUBLE BOND]P=2.613(2) A). DFT calculations reveal a polarized-covalent U[DOUBLE BOND]P bond with a Mayer bond order of 1.92.

A Concerted Transfer Hydrogenolysis: 1,3,2‐Diazaphospholene‐Catalyzed Hydrogenation of NN Bond with Ammonia–Borane

Abstract: 1,3,2-diazaphospholenes catalyze metal-free transfer hydrogenation of a NN double bond using ammonia–borane under mild reaction conditions, thus allowing access to various hydrazine derivatives. Kinetic and computational studies revealed that the rate-determining step involves simultaneous breakage of the BH and NH bonds of ammonia–borane. The reaction is therefore viewed as a concerted type of hydrogenolysis.

Cyclization Reactions of Anode-Generated Amidyl Radicals

Abstract: Amidyl radicals have been generated from amides under mild conditions electro-oxidatively. Their reactivity toward electron-rich double bonds to form five- and six-membered rings has been demonstrated experimentally and explored with density functional theory (DFT) calculations (UB3LYP/6-31G(d,p)).

General Catalyst Control of the Monoisomerization of 1-Alkenes to trans-2-Alkenes

Abstract: After searching for the proper catalyst, the dual challenges of controlling the position of the double bond, and cis/trans-selectivity in isomerization of terminal alkenes to their 2-isomers are finally met in a general sense by mixtures of (C5Me5)Ru complexes 1 and 3 featuring a bifunctional phosphine. Typically, catalyst loadings of 1 mol % of 1 and 3 can be employed for the production of (E)-2-alkenes at 40–70 °C. Catalyst comprising 1 and 3 avoids more than any other known example the thermodynamic equilibration of alkene isomers, as the trans-2-alkenes of both nonfunctionalized and functionalized alkenes are generated.

Direct kinetic measurements of reactions between the simplest Criegee intermediate CH2OO and alkenes.

Abstract: The simplest Criegee Intermediate (CH2OO), a well-known biradical formed in alkene ozonolysis, is known to add across double bonds. Here we report direct experimental rate measurements of the simplest Criegee Intermediate reacting with C2–C4 alkenes obtained using the laser flash photolysis technique probing the recently measured B1A′ ← X1A′ transition in CH2OO. The measured activation energy (298–494 K) for CH2OO + alkenes is Ea ≈ 3500 ± 1000 J mol–1 for all alkyl substituted alkenes and Ea = 7000 ± 900 J mol–1 for ethene. The measured Arrhenius pre-exponential factors (A) vary between (2 ± 1) × 10–15 and (11 ± 3) × 10–15 cm3 molecule–1 s–1. Quantum chemical calculations of the corresponding rate coefficients reproduce qualitative reactivity trends but overestimate the absolute rate coefficients. Despite the small Ea’s, the CH2OO + alkene rate coefficients are almost 2 orders of magnitude smaller than those of similar reactions between CH2OO and carbonyl compounds. Using the rate constants measured here,...

Controlled Divinyl Monomer Polymerization Mediated by Lewis Pairs: A Powerful Synthetic Strategy for Functional Polymers

Abstract: Lewis pair cooperation provides a facile approach for polymerizing dissymmetric divinyl polar monomers such as 4-vinylbenzyl methacrylate in excellent regioselectivity and high reactivity at mild conditions, affording soluble polymers bearing pendant active vinyl groups with high molecular weight (up to 6.4 × 105 g/mol) and narrow polydispersity (PDI < 1.5). ESI-TOF MS study demonstrated that the polymerization process only concerned the methacrylic double bond and selectively remained the pendant allylic or styrene C═C bond.

Acylsilanes in Rhodium(III)‐Catalyzed Directed Aromatic C–H Alkenylations and Siloxycarbene Reactions with C ? C Double Bonds

Abstract: Acylsilanes are known to undergo a 1,2-silicon-to-oxygen migration under thermal or photochemical conditions to form siloxycarbenes. However, there are few reports regarding the application of siloxycarbenes in organic synthesis and surprisingly, their reaction with CC double or triple bonds remains virtually unexplored. To facilitate such a study, previously inaccessible aromatic acylsilanes containing an ortho-tethered CC double bond were identified as suitable substrates. To access these key intermediates, we developed a new synthetic method utilizing a rhodium-catalyzed oxidative Heck-type olefination involving the application of an acylsilane moiety as a directing group. When exposed to visible-light irradiation, the ortho-olefinated acylsilanes underwent a smooth intramolecular cyclization process to afford valuable indanone derivatives in quantitative yields. This result paves the way for the development of new transformations involving siloxycarbene intermediates.

Catalytic, enantioselective sulfenylation of ketone-derived enoxysilanes.

Abstract: A catalytic, enantioselective, Lewis base-catalyzed α-sulfenylation of silyl enol ethers has been developed. To avoid acidic hydrolysis of the silyl enol ether substrates, a sulfenylating agent that did not require additional Bronsted acid activation, namely N-phenylthiosaccharin, was developed. Three classes of Lewis bases—tertiary amines, sulfides, and selenophosphoramides—were identified as active catalysts for the α-sulfenylation reaction. Among a wide variety of chiral Lewis bases in all three classes, only chiral selenophosphoramides afforded α-phenylthio ketones in generally high yield and with good enantioselectivity. The selectivity of the reaction does not depend on the size of the silyl group but is highly sensitive to the double bond geometry and the bulk of the substituents on the double bond. The most selective substrates are those containing a geminal bulky substituent on the enoxysilane. Computational analysis revealed that the enantioselectivity arises from an intriguing interplay among s...

Fabrication of cuprous nanoparticles in MIL-101: an efficient adsorbent for the separation of olefin–paraffin mixtures

Abstract: Various amounts of Cu+ nanoparticles were successfully deposited to the pores of metal–organic frameworks MIL-101 with a double-solvent method. An optimized, cuprous-loaded MIL-101 was shown to have an enhanced ethylene adsorption capacity and higher ethylene–ethane selectivity (14.0), compared to pure MIL-101 (1.6). The great improvement in selectivity can be attributed to the newly generated nano-sized cuprous chloride particles that can selectively interact with the carbon–carbon double bond in ethylene through π-complexation.

Metal-Free Preparation of Cycloalkyl Aryl Sulfides via Di-tert-butyl Peroxide-Promoted Oxidative C(sp3)[BOND]H Bond Thiolation of Cycloalkanes.

Abstract: The formation of C–S bonds represents an active research area in general organic chemistry, material science as well as biological and pharmaceutical chemistry.[1] In the past decade, a number of methodologies have been developed in this field. In particular, transition-metal-catalyzed cross-coupling reactions of thiols with aryl halides provided the most general strategies for constructing C–S bonds.[2] Recently, metal-catalyzed C–S bonds formation through C(sp2)–H bond activation has become an alternative and intriguing methods for preparation of sulfides due to its high atom-economy and efficiency.[3] However, the cleavage of C(sp3)–H bond leading to the C–S bond formation is less studied. Very recently, Xiang and co-workers reported a novel thiolation of C(sp3)–H bond adjacent to a nitrogen or oxygen atom (Scheme 1a and 1b).[4] To date, the thiolation of C(sp3)–H bond of unactivated alkanes still have not been developed. Scheme 1 C(sp3)–H bond functionalization. Direct C(sp3)–H transformation of alkanes, which is a great challenge due to their low reactivity and the lack of a coordination site for the metal catalyst, has attracted many generations of organic chemists in recent years.[5] However, C(sp3)–H bond activation of cycloalkanes to form C–C,[6] C–O,[7] C–N[8] bonds still has not been well reported because C(sp3)–H bond activation of cycloalkanes is more difficult than C(sp3)–H bond activation adjacent to heteroatoms, double bonds, phenyl or electron withdrawing groups. Li and others have done elegant work in this field using a transition-metal catalyst (such as Ru, Sc, Fe, etc.) both for activating the C(sp3)–H bond of cycloalkanes and subsequent coupling to form C–Y (Y = O, N, C) bonds.[9] Recently, our group also developed a Fe-catalyzed decarboxylative alkenylation of cycloalkanes via a radical process.[10] The metal-free C(sp3)–H bond functionalization progress for C(sp2)–C(sp3) bond formation of heteroaromatics and cycloalkanes promoted by DTBP have also been reported (Scheme 1c).[11,12] To the best of our knowledge, no reports for the construction of C–S bond through C(sp3)–H bond functionalization of cycloalkanes are described. Herein, we would report the first realization on the thiolation of C(sp3)–H bond of cycloalkanes through DTBP-mediated oxidative C(sp3)–H bond functionalization without the aid of transition-metal catalyst (Scheme 1d). Initially, we conducted our investigation by reacting 1,2-diphenyldisulfane 1 (0.5 mmol) with cyclohexane 2a (2 mL) in the presence 4.0 equiv of tert-butylhydroperoxide (TBHP) at 120 °C for 24 h. The reaction could happen, and afforded the expected product of cyclohexyl(phenyl)sulfane 3a in a poor yield (23%, Table 1, entry 1). Replacing TBHP with DTBP, the yield dramatically increased to 88% without the aid of any metal catalyst or other additives (Table 1, entry 2). The use of other oxidants such as DDQ, K2S2O8, H2O2 (30% aqueous solution) or TBPB did not provide better results (Table 1, entries 3–6). A decreased loading of DTBP to 2.0 equiv or a lower temperature to 100 °C, the lower yield would be obtained in 75% and 69%, respectively (Table 1, entries 7 and 8). No significant effect in yield of 3a was found with 6.0 equiv of DTBP or a higher temperature (Table 1, entries 9 and 10). Furthermore, the addition of metal-catalyst, Cu(OAc)2 (10 mol %), did not result any improvement on the yield (79%, Table 1, entry 11). Further optimization of the conditions showed that the reaction could not proceed without the use of oxidant DTBP (Table 1, entry 12). Table 1 Optimization of reaction condition [a] With the optimized reaction conditions in hand, this approach was then applied to the coupling of cyclohexane to a variety of diaryl disulfides (Scheme 2). As shown in Scheme 2, the process has a broad scope and high compatibility with functional groups, such as methyl, methoxy, halo and nitro substituent groups. Ortho-, meta- and para-substituted diaryl disulfides were well tolerated, and the reactions gave the corresponding products with good to excellent yields of 71–92% (3a-h). The lower yields observed in the case of ortho-substituted diaryl disulfides compared to its para- or meta- analogues, is possibly due to the steric hindrance (3d-f). The reaction with p-methyl and p-methoxy substituted diaryl disulfides afforded the expected product with excellent yields (3b and 3c). However, when p-fluoro and p-nitro substituted diaryl disulfides were used as the coupling partner the product yields dropped (85% for 3d and 75% for 3h). These results imply that the electronegativity of the substituents in the diaryl disulfides has an obvious effect on the chemical yields. In addition, the disubstituted diaryl disulfide is also well tolerated in this reaction to give the target product with a slightly lower yield of 80% (3i). Notably, the heterocyclic disulfides thienyl or pyridinyl disulfide can work well in the reaction to provide the corresponding alkyl heteroaryl sulfide (3j-k). It is worth to note that the reaction with complex heterocyclic disulfides 2,2’-dithiobis(benzothiazole) and 5,5’-dithiobis(1-phenyl-1H-tetrazole) also proceed successfully under the optimized condition (3l-m). Disappointingly, 1,2-dibenzyldisulfane was not a suitable substrate for the current thiolation system (3n). Scheme 2 Thiolation of cyclohexane with disulfides. Reaction conditions: 1 (0.5 mmol), cyclohexane (2 mL), DTBP (4.0 equiv), 120 °C, 24 h. Isolated yields based on 1. Subsequently, other cycloalkanes, including cyclopentane, cycloheptane and cyclooctane were employed as substrates for this reaction to further examination of the reaction scope (Scheme 3). Fortunately, they work well in the system under the optimized conditions, and can react with different diaryl disulfides 1, giving the corresponding products 4a–j in 67–89% chemical yield. Comparing with the results shown in Scheme 2 for cyclohexane as a substrate, the reaction with cyclopentane showed a lower efficiency, and obvious lower yields were found (67–82%, 4a–g). However, for the cases of larger cycloalkanes, such as cycloheptane and cyclooctane, comparative chemical yields were obtained (4h–j). Scheme 3 Thiolation of cyclopentane with disulfides. Reaction conditions: 1 (0.5 mmol), cycloalkanes (2 mL), DTBP (4.0 equiv), 120 °C, 24 h. Isolated yields based on 1. Then intramolecular and intermolecular competition experiments were carried out. Firstly, heteroaryl aryl disulfide 1o was used for the investigation of the intramolecular competition reaction (Scheme 4). We found both of these two ArS• could react with cyclohexane well, giving the cross-coupling products 3l and 3b in 85% and 86% chemical yields respectively. Scheme 4 Investigation of the intramolecular competition reaction. Reaction conditions: 1o (0.5 mmol), cyclohexane (2 mL), DTBP (4.0 equiv), 120 °C, 24 h. Then, the examination of the intramolecular competition reaction was performed with the using of disulfides 1l and 1b as substrates at the same time (Scheme 5). The reaction with both of these two disulfides proceeded very well, and good chemical yields were obtained (3l and 3b in 82% and 84% respectively). Scheme 5 Investigation of the intermolecular competition reaction. Reaction conditions: 1l (0.25 mmol), 1b (0.25 mol), cyclohexane (2 mL), DTBP (8.0 equiv), 120 °C, 24 h. To gain insight into the reaction mechanism, several control experiments were carried out (Scheme 6). Addition of the radical-trapping reagents 2,2,6,6 tetramethylpiperidine N-oxide (TEMPO) or azobisisobutyronitrile (AIBN) can completely inhibit the reaction and almost no desired product was observed. These results indicate that the transformation may proceed via a radical course. Scheme 6 Insights into the mechanism. Based on the above results and literature reports,[4, 10, 13] a possible mechanism for the cycloalkane thiolation reaction is illustrated in Scheme 7, which includes a key radical oxidative coupling step. At the beginning, homolysis of DTBP give tert-butoxy radical intermediate A under the condition of heating. Then, cyclohexane radical intermediate B is generated via reaction of intermediate A and cyclohexane 2a through a C–H bond cleavage. The following step is the reaction between intermediate B and 1,2-diphenyldisulfane 1, affording the final target product 3a, along with the formation of PhS• free radical intermediate C. Finally, the free radical C couples with cyclohexane readical B, giving another molecular of product 3a. Scheme 7 A possible reaction mechanism. In conclusion, we have presented a novel and highly efficient method for C–S cross-coupling through direct C(sp3)–H bond functionalization of cycloalkanes with diaryl sulfides using DTBP as the oxidant without use of any metal catalyst. Varieties of substituted diphenyl disulfides and heterocyclic disulfides could be tolerated and coupled with cycloalkanes, giving the cycloalkyl aryl sulfides in good to excellent yields. Moreover, this synthetic strategy for direct C–S bond formation might be very valuable and attractive in radical chemistry.

Chemo-, regio-, and stereoselective silver-catalyzed aziridination of dienes: scope, mechanistic studies, and ring-opening reactions.

Abstract: Silver complexes bearing trispyrazolylborate ligands (Tpx) catalyze the aziridination of 2,4-diene-1-ols in a chemo-, regio-, and stereoselective manner to give vinylaziridines in high yields by means of the metal-mediated transfer of NTs (Ts = p-toluensulfonyl) units from PhI═NTs. The preferential aziridination occurs at the double bond neighboring to the hydroxyl end in ca. 9:1 ratios that assessed a very high degree of regioselectivity. The reaction with the silver-based catalysts proceeds in a stereospecific manner, i.e., the initial configuration of the C═C bond is maintained in the aziridine product (cis or trans). The degree of regioselectivity was explained with the aid of DFT studies, where the directing effect of the OH group of 2,4-diene-1-ols plays a key role. Effective strategies for ring-opening of the new aziridines, deprotection of the Ts group, and subsequent formation of β-amino alcohols have also been developed.

Endohedral fullerene with μ3-carbido ligand and titanium-carbon double bond stabilized inside a carbon cage.

Abstract: In all metallofullerenes known before this work, metal atoms form single highly polar bonds with non-metal atoms in endohedral cluster. This is rather surprising for titanium taking into account the diversity of organotitanium compounds. Here we show that the arc-discharge synthesis of mixed titanium-lutetium metallofullerenes in the presence of ammonia, melamine or methane unexpectedly results in the formation of TiLu2C@Ih-C80 with an icosahedral Ih(7) carbon cage. Single-crystal X-ray diffraction and spectroscopic studies of the compound reveal an unprecedented endohedral cluster with a μ3-carbido ligand and Ti-C double bond. The Ti(IV) in TiLu2C@Ih-C80 can be reversibly reduced to the Ti(III) state. The Ti=C bonding and Ti-localized lowest unoccupied molecular orbital in TiLu2C@Ih-C80 bear a certain resemblance to titanium alkylidenes. TiLu2C@Ih-C80 is the first metallofullerene with a multiple bond between a metal and the central, non-metal atom of the endohedral cluster. Metallofullerenes typically have polar single bonds between metals and non-metals. Here, through arc-discharge experiments, the authors observe the formation of an endohedral fullerene with an encapsulated tri-coordinate μ3-carbon centre and a stable titanium-carbon double bond.

Aerobic Carbon–Carbon Bond Cleavage of Alkenes to Aldehydes Catalyzed by First-Row Transition-Metal-Substituted Polyoxometalates in the Presence of Nitrogen Dioxide

Abstract: A new aerobic carbon–carbon bond cleavage reaction of linear di-substituted alkenes, to yield the corresponding aldehydes/ketones in high selectivity under mild reaction conditions, is described using copper(II)-substituted polyoxometalates, such as {α2-Cu(L)P2W17O61}8– or {[(Cu(L)]2WZn(ZnW9O34)2}12–, as catalysts, where L = NO2. A biorenewable-based substrate, methyl oleate, gave methyl 8-formyloctanoate and nonanal in >90% yield. Interestingly, cylcoalkenes yield the corresponding epoxides as products. These catalysts either can be prepared by pretreatment of the aqua-coordinated polyoxometalates (L = H2O) with NO2 or are formed in situ when the reactions are carried with nitroalkanes (for example, nitroethane) as solvents or cosolvents. Nitroethane was shown to release NO2 under reaction conditions. 31P NMR shows that the Cu-NO2-substituted polyoxometalates act as oxygen donors to the C–C double bond, yielding a Cu-NO product that is reoxidized to Cu-NO2 under reaction conditions to complete a catalyti...