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An efficient and diastereoselective decarboxylative oxa-1,3-dipolar cycloaddition between 3-oxindoles and diverse amino acids is developed to access novel oxazolidine-dispirooxindole skeletons bearing vicinal quaternary carbon centers. This protocol features operational simplicity, a broad substrate scope, and good to excellent chemical yields and diastereoselectivities. In particular, minimal solvent (1 mL/10 mmol) and chromatography-free purification render this synthetic process more efficient and environmentally benign in the context of green chemistry. [ABSTRACT FROM AUTHOR]

The C70 δ-adducts with closed [5,6]-ring fusion are an important type of compound in classifying bond delocalization in the equatorial belt of C70. However, the formation of such compounds is severely restricted due to the low reactivity of the carbon atoms in the flat equatorial region. Such a restriction is lifted when reduced anionic C70 species are used, where the inert equatorial carbon atoms are activated. [ABSTRACT FROM AUTHOR]

C60 o-quinodimethane bisadducts [C60(QM)2] are promising electron acceptors for bulk heterojuction (BHJ) organic solar cells (OSCs). However, previous production of C60(QM)2 often resulted in excessive regioisomers, which were difficult to purify and might consequently obscure the structure-performance study of the organofullerene acceptors. Herein, the electrosynthesis of C60(QM)2 is reported. The reaction exhibits a strong regiocontrol with generation of fewer regioisomers. Pure regioisomers of cis-2, trans-3, and e C60(QM)2 are obtained, and the structures are solved with single-crystal X-ray diffraction. Interestingly, the cis-2 and trans-3 regioisomers exhibit better photovoltaic performance than the e regioisomer in the OSCs based on poly(3-hexylthiophene) (P3HT), which can be correlated with their structural difference. [ABSTRACT FROM AUTHOR]

Methoxylation of the singly bonded 1,4-1′,4′-BnC60-C60Bn dimer afforded 1,4-OMe(Bn)C60, a 1,4-C60 adduct with sterically less demanding addends, as the major adduct. The situation was different from that of direct functionalization of C60, where 1,2-OMe(Bn)C60 was obtained as the major product. The reaction was studied with in situ vis-NIR spectroscopy and computational calculations to obtain a better understanding of this unusual regioselectivity. The stability difference between 1,2- and 1,4-OMe(Bn)C60 was studied. [ABSTRACT FROM AUTHOR]

The base-promoted oxidative cycloaddition reaction of [60]fullerene with ethyl acetoacetate was investigated. The reaction resulted in C60 bis-2',3'-dihydrofuran derivatives, but only with the trans-1, trans-2, trans-3, and e configurations rather than any cis or trans-4 structures, demonstrating a new regioselectivity resulting from steric influence on C60 bisaddition. In addition, distribution of the bisadducts was complicated by the unsymmetrical nature of the addends, where each individual configuration may consist of several regioisomers. [ABSTRACT FROM AUTHOR]

C70 bis-heterocyclic derivative (1) bearing one oxazoline ring and one imidazoline ring with the 2 o'clock configuration is obtained with high chemio- and regioselectivity via the reaction of C70 with hydroxide and benzonitrile quenched with I2. Further study with benzylation experiment and theoretical calculations indicate that the oxazoline ring is the one first formed on the C70 cage, while the imidazoline ring is the one formed after the addition of I2 via a radical coupling reaction mechanism. [ABSTRACT FROM AUTHOR]

Upon reduction, singly bonded 1,2,4,15-C60 dimers with an oxazoline or imidazoline heterocycle dissociate into monoanionic 1,2,4-C60 intermediates, which surprisingly leads to the formation of 1,2,3,16-C60 rather than 1,2,4,15-C60 adducts of the original configuration by further benzylation, even though the analogue of dibenzylated C60 oxazoline with a 1,2,4,15-configuration is stable and has been obtained. These results are corroborated by computational calculations, which rationalize the reaction and clarify the structure of the 1,2,3,16-C60 adducts, providing new insights into the intrinsic reactivity of singly bonded C60 dimers. [ABSTRACT FROM AUTHOR]

The stability of the anionic species of the ortho and para regioisomers of (MeO)BnC2n (Me = methyl, Bn = benzyl, n = 30 or 35) has been examined. The results show that the ortho adducts (electronically favored regioisomers) are stable upon receiving one or two electrons, while the para ones (sterically favored adducts) decompose by removing the methoxy group under similar conditions. Computational calculations indicate that the stability of the anionic species is significantly affected by the electronic structure, where the [5,6]-double bond is responsible for the instability of the reduced species of the para adducts. Further study with 1,15-(MeO)2-2,4-Bn2C60, an adduct with both the ortho and para positioned methoxy, shows that the reduced species is stable, indicating that the 1,2,4,15-configuration is an electronically preferential structure even though it has a [5,6]-double bond. [ABSTRACT FROM AUTHOR]

Reductive benzylation of C70 imidazolines bearing a bulky addend has been carried out under conditions similar to that reported for C60 analogues. However, different from the reaction of C60 analogues, the reaction of C70 imidazolines not only results in adducts with 1,2,3,16-configuration due to the steric effect, but also a considerable amount of dibenzylated and monobenzylated products with 1,2,3,4-configuration, demonstrating a reactivity difference between C60 and C70. Interestingly, the anions of the 1,2,3,16-C70 adduct are rather stable as shown by the electrochemical study, which is in contrast to the anions of 1,2,3,16-C60 counterparts, and can be rationalized by the electronic structure difference between C70 and C60 derivatives. [ABSTRACT FROM AUTHOR]

Oxazoline and imidazoline functionalization of a singly bonded C60 dimer is achieved via a one-pot reaction of C60HBn with OH- and aromatic nitriles, where the OH- not only functions as a Brønsted base that deprotonates C60HBn but also as a nucleophile that initiates the nucleophilic addition to the fullerene cage. The structures of the obtained oxazolinated and imidazolinated C60 dimeric compounds have been established by HRMS, UV--vis, and ¹H, 13C, and HMBC NMR characterizations and computational calculations. The reaction mechanism is studied with the in situ vis-near-IR spectra, which shows that the use of I2 is crucial for the functionalization of the C60 dimer, indicating that it is likely the dimeric molecule rather than the fragment of the dimer that is involved in the reaction. [ABSTRACT FROM AUTHOR]

The reactions of C702- with organic halides result in several isomeric products. However, the structures of the isomers have not been identified unambiguously and the reactions still remain elusive even though the first report of the reaction appeared more than ten years ago. Herein, the reactions of C702- with ArCH2Br (Ar = Ph, o-, m-, and p-BrC6H4) are revisited. Two types of isomeric para-adducts of 2,5- and 7,23-(ArCH2)2C70 are obtained and characterized with the X-ray single-crystal diffractions, HRMS, ¹H and 13C NMR, and UV-vis spectroscopies. An unusual singlet resonance instead of the typical AB quartet resonance is shown for the C2 diastereotopic methylene protons in ¹H NMR spectrum of 2,5-(PhCH2)2C70 recorded at ambient temperature. The unexpected magnetic equivalence is studied with the variable-temperature (VT) NMR and density functional theory (DFT) calculations. The results show that the greater local curvature in the C70 polar region is likely responsible for the unusual magnetic equivalence exhibited by the C2 diastereotopic methylene protons of 2,5-(PhCH2)2C70, indicating that under certain cases, it is improbable to elucidate the spectral data of fullerene derivatives with a less symmetrical carbon cage in analogy with those of the C60 derivatives. [ABSTRACT FROM AUTHOR]

The catalytic enantioselective fluorination of N--H-free 3-substituted oxindoles was accomplished by a Sc(III)/N,N'-dioxide complex. Under mild reaction conditions, a series of 3-aryl- and 3-alkyl-3-fluoro-2-oxin doles were obtained in excellent yields (up to 9896) and enantioselectivities (up to 99% ee) by using N-fluorobisbenzenesulfonimide (NFSI) as the fluorination agent MaxiPost was synthesized efficiently in 81% yield with 96% ee. [ABSTRACT FROM AUTHOR]

We have developed a simple and practical process for the oxidation of alcohols to the corresponding carbonyl compounds by using a low catalytic amount of DDQ1 NaNO2 as a cocatalyst, and molecular oxygen as terminal oxidant Nitric oxide generated in situ by NaNO2 in the presence of AcOH is essential for the realization of the catalytic cycle at room temperature. The practical utility of this catalytic process has been demonstrated in the gram-scale oxidation of cinnamyl alcohol. [ABSTRACT FROM AUTHOR]

Singly bonded PhCH2C60-C60CH2Ph dimers are generated via controlled-potential bulk electroreduction and electrooxidation of 1,2-(PhCH2)HC60. The reaction mixture was purified by HPLC, and the isolated fraction was characterized with single-crystal X-ray diffractions, H and NMR, MS, elemental analysis, and cyclic voltammetry. It was shown that the fraction consists of two HPLC-inseparable PhCH2C60-C60CH2Ph regioisomers, which are assigned as the meso and racemic regioisomers. The bulk electrolysis processes for the formation of the dimers were followed by in situ cyclic voltammetry and were further corroborated with an in situ voltammetric titration of 1,2-(PhCH2)HC60 with tetra-n-butylammonium hydroxide (TBAOH), on the basis of which a reaction mechanism is proposed. [ABSTRACT FROM AUTHOR]

Isomerization of an oxazoline cycle from a [6,6]- to [5,6]-junction on the C60 sphere of dianionic [60]fullero-oxazoline (12-) during a 1,4-addition is studied by electrochemistry and a stepwise addition of PhCH2Br and PhCD2Br. Cyclic voltammerty of the in situ generated 12- shows a very unusual positive shift for the anodic peak corresponding to the oxidation of 12-, indicating that the C60 cage of dianionic 1 bears only one unit negative charge due to the heterolytic cleavage of the C60-O bond. Further study with a stepwise addition of PhCH2Br and PhCD2Br, which are used to differentiate the aryl groups added at each step onto dianionic 1, shows explicitly there is an exclusive selectivity of the C-O bond for the ring-opening and ring-closure during the isomerization of the heterocycle. A reaction mechanism is proposed on the basis of the experimental results and computational calculations. [ABSTRACT FROM AUTHOR]

The reactions of dianionic C60 with organic halides, which have been studied extensively in benzonitrile (PhCN), are revisited in a different solvent medium, N,N-dimethylformamide (DMF), by using ArCH2Br (Ar = Ph, C6H4CH3, C6H4Br). Interestingly, instead of the 1,4-R2C60 adducts, which are the typical products when the reactions are carried out in PhCN, the 1,2-dihydro[60]fullerenes (1,2-HRC60) have been obtained as the major products in DMF, except for the case of o-CH3C6H4CH2Br probably due to the steric effect. The obtained 1,2-dihydro[6Q]fullerenes have been characterized with single-crystal diffraction, 1H and 13C NMR, high-resolution mass spectrometry (HRMS), and UV-vis. Further examination with deuterated reagents including PhCD2Br, DMF-d7, and D2O has revealed that the fullerenyl hydrogen of 1,2-dihydrofullerenes originates from traces of water residue in DMF. When the reaction is re-examined in PhCN with the addition of an excessive amount of water, the yield of I ,2-dihydrofullerene increases significantly, but is still lower compared with that obtained in DMF, demonstrating a considerable solvent effect on the reactivity of C602-. A possible mechanism accounting for such a difference is proposed. The work has presented an alternative protocol for effective preparation of 1,2-dihydro[60]fullerenes, and may also provide clues toward a better understanding of the proton transfer process for anionic C60-mediated reducing reactions involving H2O. [ABSTRACT FROM AUTHOR]

A highly stereoselective joint total synthesis of the potent polyketide macrolide antibiotics etnangien and etnangien methyl ester was accomplished by a convergent strategy and proceeds in 23 steps (longest linear sequence). Notable synthetic features include a sequence of highly stereoselective substrate-controlled aldol reactions to set the characteristic assembly of methyl- and hydroxyl-bearing stereogenic centers' of the propionate portions, an efficient diastereoselective Heck macrocyclization of a deliberately conformationally biased precursor, and a late-stage introduction of the labile side chain by means of a high-yielding Stille coupling of protective-group-free precursors. Along the way, an improved, reliable protocol for a Z-selective Stork—Zhao—Wittig olefination of aldehydes was developed, and an effective protocol for a I ,3-syn reduction of sterically particularly hindered β-hydroxy ketones was devised. Within the synthetic campaign, a more detailed understanding of the intrinsic isomerization pathways of these labile natural products was elaborated. The expedient and flexible strategy of the etnangiens should be amenable to designed analogues of these RNA-polymerase inhibitors, thus enabling further exploration of the promising biological potential of these macrolide antibiotics. [ABSTRACT FROM AUTHOR]

A highly efficient inter- and intramolecular addition of 1,3-diketone/β-ketoester to alkenes was developed by using silver catalysts. Silver triflate shows the highest catalytic activity. The reaction is reversible through the cleavage of a carbon-carbon bond by silver at an elevated temperature. [ABSTRACT FROM AUTHOR]

Oligo(ethylene glycols) 1a-h, which are incorporated with one to eight 2,3-naphthylene units, respectively, have been synthesized and characterized. The conformational changes of the new oligomers have been investigated in chloroform-acetonitrile binary solvents by the UV-vis, 1H NMR, and fluorescent spectroscopy. It has been revealed that the naphthalene units in hexamer If, heptamer lg, and octamer 1h are driven by solvophobic interaction to stack in polar solvents. As a result, compact helical conformations are formed that give rise to a cavity similar to that of 18-crown-6. Shorter oligomers lb-e exhibit weaker folding tendency. 1H NMR studies reveal that lf-h are able to complex ammonium or ethane-l,2-diaminium 19, but not secondary ammonium compounds. The association constants of complexes lf·19, lg·19, and 1h·19 in acetonitrile are determined to be 3.5(±0.4) × 103, 1.0(±0.12) × 104, and 2.5(±0.4) × 104 M-1, respectively, with the 1H NMR titration method. For comparison, hexamer 22, which incorporates six 1,5-naphthylene units, is also prepared. The UV-vis and fluorescent investigations show that 22 is also able to fold in polar solvents, but no helical structure can be produced due to mismatch of the stacking naphthalene units and consequently there is no obvious complexation between 22 with ethane- 1,2-diaminium ion. The structures of the longest foldamer 1h and its complex with 19 have been studied with molecular mechanics calculations. This work represents a new approach to building folding conformations from flexible linear molecules. [ABSTRACT FROM AUTHOR]

Examines the magnesium-mediated Barbier-Grignard type alkylation of aldehydes with alkyl halides in aqueous media. Reaction of aromatic aldehydes with allyl halides; Magnesium-mediated allylation of aldehydes with allyl bromide and iodide; Formation of the pinacol coupling products; Factor affecting the pinacol reaction.

Presents a study on the enantioselective total syntheses of (-)-6-epitrehazolin and (+)-trehazolin. Description of research materials and methods used; Role of inhibitors of glycosidases in major advances of modern glycobiology; Reference to the discovery of several aminocyclopentitol-containing natural products; Chemical and biological properties of trehazolin.

Studies the synthesis of azasugars via lanthanide-promoted aza Diels-Alder reactions in aqueous solution. Elucidation of the exo/endo selectivities and diastereoselectivities of the reaction by nuclear magnetic resonance, CD spectroscopy and X-ray crystallography; mechanism of action; Schematic outline of the reaction pathways.

Copper-catalyzed oxidative esterification of aldehydes with β-dicarbonyl compounds was developed using tert-butyl hydroperoxide as an oxidant. In general, the enol esters were synthesized in good yields (up to 87%) and high stereoselectivity under the optimized reaction conditions. [ABSTRACT FROM AUTHOR]

Examines the barbier-type reactions of cyclic tertiary alcohols. Role of Barbier reactions for synthesizing biological and abiological compounds; Utilization of [sup 13]C and [sup 1]H nuclear magnetic resonance spectroscopy; Effect of using methyl, ethyl, phenyl, propyl and butyl groups as side chains on the reaction process.

The reaction mechanisms of Pd(OAc)2-catalyzed dehydrogenative alkylation of 2-phenylpyridine with oxirane were investigated using DFT calculations. The most plausible reaction pathway was confirmed as a PdII/IV/II catalytic cycle consisting of four processes: C-H activation, ring-opening oxidative addition of oxirane, reductive elimination, and recovery of the catalyst. According to the B2PLYP/DGDZVP computational data, the oxidative addition of oxirane for converting PdII to PdIVwas assigned to be the rate-determining step with a free-energy barrier of 28.1 kcal•mol-1. For comparison, we also studied the alternative PdII-only pathway without a change of oxidation state and found that it was hindered kinetically by a high free-energy barrier of 75.1 kcal•mol-1 occurring for the ring-opening migratory insertion of oxirane. In addition, the small-ring strain of oxirane should be responsible for the feasible C-O bond-cleavage and subsequent PdII → PdIVconversion, because the designed four-, five-, and six-membered-ring reagents did not display such an oxidative addition reactivity. Lastly, an extended reactivity order among oxirane, PhI, PhBr, and PhCl toward oxidative addition onto PdII to form PdIV was proposed in this article based on the computed kinetic parameters. [ABSTRACT FROM AUTHOR]

Oxazolination of C70 has been achieved via the aerobic oxidation of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. in the presence of PhCN. Only one C70 oxazoline regioisomer (1) is obtained, indicating that the oxazolination of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. occurs with an unusual regioselectivity. Further benzylation of 12- with benzyl bromide leads to the formation of the first cis-1 C70 derivative with respect to the apical pentagon (2), as shown by the X-ray single-crystal structure and various spectral characterizations. The structure of the obtained C70 oxazoline (1) is resolved with H/D labeling benzylation and HMBC (heteronuclear multiple bond coherence) NMR on the basis of the structure of 2. The result shows that for compound 1, the O atom is selectively bonded to the C1, while the N atom is bonded to the C2 of C70. The exhibited regioselectivity for the orientation of oxazolino group on C70 is further rationalized with computational calculations, and a reaction mechanism for the oxazolination of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. is proposed. [ABSTRACT FROM AUTHOR]

Investigates the synthesis of polysubstituted tetrahydropyrans and thiacyclohexanes through indium trichloride mediated cyclizations. Stereochemistry of tetrahydropyran products; Correlation between tetrahydropyrans and homoallyl alcohols; Production of pentasubstituted tetrahydopyran derivatives.

Presents a study on the preparation of a mixture of alpha-L-taluronamide and beta-D-alluronamide nucleoside derivatives. Methods used to conduct the study; Identification of two typical families of nucleoside antibiotics; Results and discussion on the study.

Studies the lanthanide-promoted reactions of aldehydes and amine hydrochlorides in aqueous solution. Synthesis of 2,3-dihydropyridinium and pyridinium derivatives; Versatile intermediates in the synthesis of alkaloids; Lanthanide-promoted condensation.

Hydrogen-bonding organocatalysts L-pyroglutamic sulphonamides were readily synthesized for the first time by fully exploiting the potentials of L-pyroglutamic acid. The newly designed catalyst was successfully applied in catalyzing asymmetric Diels-Alder cyclization of methyleneindolinones with 2-vinyl-1H-indoles to efficiently assemble carbazolespirooxindoles in excellent stereoselectivity (up to 99% ee, >20:1 dr) and yields (up to 99%). Mechanistic studies disclosed that the well-designed hydrogen-bonding modes between L-pyroglutamic sulphonamide and substrates were crucial for stereocontrol in the cyclization. [ABSTRACT FROM AUTHOR]

A novel and efficient PhI(OAc)2-promoted one-pot reaction of aromatic hydroxylamines, aldehydes, and TMSCN in the presence of BF3·Et2O is described. A wide variety of N-substituted benzimidazolones are obtained with satisfactory yields under mild reaction conditions. The method was proven to be efficient for the synthesis of benzimidazolone derivatives from readily available starting materials. [ABSTRACT FROM AUTHOR]

BMS-911543 is a complex pyrrolopyridine investigated as a potential treatment for myeloproliferative disorders. The development of a short and efficient synthesis of this molecule is described. During the course of our studies, a Ni-mediated C-N bond formation was invented, which enabled the rapid construction of the highly substituted 2-aminopyridine core. The synthesis of this complex, nitrogen-rich heterocycle was accomplished in only eight steps starting from readily available materials. [ABSTRACT FROM AUTHOR]

A new kind of imide dyes based on dihydroindeno[2,1-c]fluorene have been developed. Consequently, a series of the organic dyes were conveniently and efficiently synthesized. The single crystal structure showed the dihydroindeno[2,1-c]fluorene core was almost planar, and the dye molecule could pack into herringbone-like structure in the solid state. It was found that the imide dyes all showed strong fluorescence emissions in tetrahydrofuran, and they also exhibited obvious red shifts with the increase of the π-conjugation system and the enhancement of the electronic-donating effect. Moreover, the electrochemical cyclic voltammograms of the imide dyes displayed irreversible redoxes in the film state. The electronic structures of aryl substituted imide dyes were also studied by the density functional theory (DFT), which gave a further explanation for their electrochemical behaviors. [ABSTRACT FROM AUTHOR]

The reaction of Morita-Baylis-Hillman (MBH) alcohols with Me2PhSiBpin under the catalysis of Cu(OTf)2/pyridine in methanol has been developed. The direct silylation of allylic alcohols via dual activation of the Si-B bond and the hydroxyl group of the MBH alcohol provides an efficient and convenient method for the synthesis of functionalized allylsilanes. [ABSTRACT FROM AUTHOR]

Dendrodolides A-M (1-13), 13 new 12-membered macrolides, were isolated from Dendrodochium sp., a fungus associated with the sea cucumber Holothuria nobilis Selenka, which was collected from the South China Sea. The structures of the dendrodolides were elucidated by means of detailed spectroscopic analysis and X-ray single-crystal diffraction. The absolute configurations were assigned using the modified Mosher method, exciton-coupled circular dichroism (ECCD), electronic solution and solid-state circular dichroism (ECD) supported by time-dependent density functional theory (TDDFT) ECD calculations, and X-ray analysis. A detailed conformational analysis of the 13 derivatives indicated that the conformation of the flexible macrolide ring plays a decisive role in their chiroptical properties. Thus, it is highly recommended to apply advanced levels of theory and to avoid simple comparison of ECD spectra to determine the absolute configurations of these derivatives. In an in vitro bioassay, compounds 1-5, 7-9, 11, and 12 exhibited different levels of growth inhibitory activity against SMMC-7721 and HCT116 cells. This is the first report of 12-membered macrolides from the fungus of the genus Dendrodochium. The coisolation of four pairs of epimers is extremely interesting and indicates the complexity of β-ketoreductase stereospecificity in the biosynthesis of enigmatic iterative fungal polyketides. [ABSTRACT FROM AUTHOR]

We combined Monte Carlo simulations and density functional theory calculations to study the mechanism of the Diels-Alder reaction of p-quinone and cyclohexadiene catalyzed by a self-assembled molecular capsule. Our calculations show that the encapsulation of the reactants into the cage is driven by hydrogen-bonding interactions and π-π stacking interactions between two reactants and the capsule. The encapsulated Diels-Alder reaction at different locations inside the capsule may have quite different reactivity due to different guest-host interactions. A comparison of the free energy profiles of the Diels-Alder reaction in the capsule and in the bulk solution reveals that the Diels-Alder reaction in the capsule is accelerated because the host-guest interaction leads to a relatively smaller barrier for the cycloaddition step. [ABSTRACT FROM AUTHOR]

A metal-free method for the direct regioselective fluorination of anilides has been developed. In the presence of bis(tert-butylcarbonyloxy)iodobenzene (PhI(OPiv)2) and hydrogen fluoride-pyridine, the para-fluorination products of anilides were obtained in moderate to good yields. Because of its operational safety and the use of readily available reagents, this new procedure provides facile access to a variety of para-fluorinated anilides. [ABSTRACT FROM AUTHOR]

An improved method for the synthesis of large and complex oligosaccharides on ionic liquid (LL) support was developed. A strategy to attach the acceptor on IL using a more stable ether linker was used to prevent undesirable decomposition and side products. A "dissolution--evaporation--precipitation" purification procedure was also developed by combining the advantages of precipitation and solid--liquid extraction to reduce mechanical loss and purification time. This approach was successfully used for the rapid assembly of ionic liquid supported homolinear α(1→2)-linked nonamannoside in 25.2% overall yield within 28.5 h. [ABSTRACT FROM AUTHOR]

An interesting aldehyde- and ketone-induced intermolecular tandem decarboxylation-coupling (Csp3Csp) catalyzed by copper with usc of natural α-amino acids as starting materials is developed under neutral conditions with the production of CO2 and H2O as the only byproducts. Various functionalized nitrogen-containing compounds were obtained by this method. In these processes, interesting regioselecsivites of the alkylation were observed, which has been rationalized by the relative stability of proposed resonance structures based on computation methods. [ABSTRACT FROM AUTHOR]

We report a structural motif based on a C3-symmetric bowl-shaped core, on which three substituted amino acids on the periphery adopt either a folded or a spread-out conformation. This class of chiral folded structures is achieved by controlling the reactivity of the stereogenic protons on the nonplanar aromatic rings of trioxatricornan to afford predominantly C3- symmetric isomers. Bromination of trioxatricornan afforded a C1-symmetric and a C3-symmetric trisubstituted isomer, with the former being the major product as a statistical consequence during the reaction cascade. To obtain the C3 symmetric isomer as the major product, C-H activation by means of ortho-lithiation with the bulky tert-butyl lithium and tetramethyl-ethylenediamine was followed by a nucleophilic substitution that successfully reversed the statistically controlled regioselectivity. Further derivatization of the trioxatricornan with amino acids or menthol afforded diastereomers that were resolved by preparative chromatography. The absolute configurations of the diastereomers were determined by vibrational circular dichroism (VCD) in combination with density functional theory (DFT) and electronic circular dichroism (ECD). The folding structure of cysteine-derivatized trioxatricornan diastereomers was determined by two-dimensional NMR spectroscopy and molecular dynamics calculation, which revealed that one diastereomer has the amino acids folded toward the cavity of trioxatricornan and the other has a "spread-out" structure. [ABSTRACT FROM AUTHOR]

A highly efficient alkynylation-cyclization of terminal alkynes with salicylaldehydes leading to substituted 2,3-dihydrobenzofuran-3-ol derivatives was developed by using Cy3P-silver complex as catalyst in water. Counter anions in the silver complex proved to be the key factor to Z/E stereoselectivity control. Aurones can also be obtained effectively from the cascade reaction followed by oxidation without further purification. [ABSTRACT FROM AUTHOR]

This paper describes the self-assembly of a new class of three-component dynamic [2]catenanes, which are driven or stabilized by intramolecular hydrogen bonding, coordination, and electrostatic interaction. One of the component molecules 2, consisting of an aromatic oligoamide spacer and two peripheral zinc porphyrin units, was designed to adopt a folded preorganized conformation, which is stabilized by consecutive intramolecular three-centered hydrogen bonds. Component molecule 3 is a linear secondary ammonium bearing two peripheral pyridine units, which was designed to form a 1:1 complex with 24- crown-8 (5). The ¹H NMR and UV-vis experiments in CDCI3-CD3CN (4:1 v/v) revealed that, due to the preorganized U-shaped feature, 2 could efficiently bind 3 through the cooperative zinc-pyridine coordination to generate highly stable 1:1 complex 23. Adding 5 to the 1:1 solution of 2 and 3 led to the formation of dynamic three-component [2]catenane 2·3·5 as a result of the threading of 3 through 5. ¹H NMR studies indicated that in the 1:1:1 solution (3 mM) [2]catenane 2·3·5 was generated in 55% yield at 25 °C. The yield was increased with the reduction of the temperature and [2]catenane could be produced quantitatively in a 1:1:2 solution ([2] = 3 mM) at -13 °C. Replacing 3 with 1,2-bis(4,4′- bipyridinium)ethane (4) in the three-component solution could also give rise to similar dynamic [2]-catenane 245 albeit in slightly lower yield. [ABSTRACT FROM AUTHOR]