Aziridine-2-phosphonic acid,the valuable synthon for synthesis of 1-amino-2-functionalized ethanephosphonic acids

The ring-opening of aziridine-2-phosphonic acid with a series of nucleophiles was studied. This reaction was found to proceed regioselectively and to provide a good preparative method for the synthesis of phosphonic analogs of various 2-substituted 1-aminoethanecarboxylic acids.     

Synthesis and Applications of 3-Phenylthio-2-Sulfolenes

Treatment of 3-phenylthio-2-sulfolene ( 1 ) with an equimolar proportion of butyllithium at ?78 °C in THF followed by addition of an electrophile gave the 2-substituted 3-phenylthio-2-sulfolenes (2). The deprotonation was found to proceed only at the vinylic C-2 position. Some of the 2-sulfolenes 2 underwent desulfonylation upon heating with base. Of particular interest was the conversion of 3-phenylthio-2-trimethylsilyl-2-sulfolene ( 2h ) to its 3-sulfolene isomer 6 by sequential addition of butyllithium and salicylic acid at low temperatures. The 3-sulfolene 6 was desulfonylated by Kugelrohr distillation at 150° C under vacuum to give (Z)-2-phenylthio-l-trimethylsilyl-1,3-butadiene ( 8 ). The regiochemistry of the Diels Alder reaction of this highly reactive diene 8 was found to be controlled by the phenylthio group, and the stereochemistry is endo addition. Diene 8 was oxidized to its sulfone derivative 12 which also underwent a stereospecific Diels-Alder reaction.     

Secondary decomposition of C3H5 radicals formed by the photodissociation of 2-bromopropene

The photodissociation of 2-bromopropene at 193 nm produces C(3)H(5) radicals with a distribution of internal energies that spans the threshold for the secondary decomposition of the 2-propenyl radicals into C(3)H(4)+H. Just above this threshold, the decomposition rate is on the nanosecond time scale, and in the present study, time-resolved velocity-map ion imaging is used to gain insight into this process. The results provide information on the energy dependence of the secondary dissociation process. In addition, comparison of the results with theoretical predictions of the energy dependence of the dissociation rate provides information on the branching between fragment rotational and vibrational energies in the primary photodissociation process.     

1-Phenylthio-3-vinyl-3-cyclohexenol, a new reagent for bis-annelation of silyl enol ethers

1-Phenylthio-3-vinyl-cyclohex-1-en-3-ol (2) has been synthesized and investigated as a new bis-annelation reagent for silyl enol ethers. Reagent 2 can be synthesized by a Grignard reaction of vinyl magnesium bromide with 3-phenylthiocyclohexenone. The reaction with silyl enol ethers takes place under Lewis acid catalysis and generally proceeds in good yields. The resulting phenylthiodienes can be hydrolyzed to enones, which have been cyclized in a homologous aldol reaction to polycyclic compounds.     

Enhanced photoelectrochemical activity of magnetically modified TiO2 prepared by a simple ex-situ route

Journal of Solid State Electrochemistry - Modified TiO2 nanocomposites have been recognized as attractive photocatalytic materials in solar energy conversion. The aim of this study is to enhance...     

Metal-mediated DNA base pairing of easily prepared 2-oxo-imidazole-4-carboxylate nucleotides

Metal-mediated DNA base pairs, which consist of two ligand-type artificial nucleobases and a bridging metal ion, have attracted increasing attention in recent years as a different base pairing mode from natural base pairing. Metal-mediated base pairing has been extensively studied, not only for metal-dependent thermal stabilisation of duplexes, but also for metal assembly by DNA templates and construction of functional DNAs that can be controlled by metals. Here, we report the metal-mediated base paring properties of a novel 2-oxo-imidazole-4-carboxylate (Im^OC) nucleobase and a previously reported 2-oxo-imidazole-4-carboxamide (Im^OA) nucleobase, both of which can be easily derived from a commercially available uridine analogue. The Im^OC nucleobases were found to form stable Im^OC–Cu^II–Im^OC and Im^OC–Hg^II–Im^OC base pairs in the presence of the corresponding metal ions, leading to an increase in the duplex melting temperature by +20 °C and +11 °C, respectively. The Im^OC bases did not react with other divalent metal ions and showed superior metal selectivity compared to similar nucleobase design reported so far. The Im^OC–Cu^II–Im^OC base pair was much more stable than mismatch pairs with other natural nucleobases, confirming the base pair specificity in the presence of Cu^II. Furthermore, we demonstrated the quantitative assembly of three Cu^II ions inside a DNA duplex with three consecutive Im^OC–Im^OC pairs, showing great potential of DNA-template based Cu^II nanoarray construction. The study of easily-prepared Im^OC base pairs will provide a new design strategy for metal-responsive DNA materials.

A novel 2-oxo-imidazole-4-carboxylate (Im^OC) nucleobase, which can be easily derived from a commercially available uridine analogue, was found to form stable Cu^II- and Hg^II-mediated base pairs in DNA duplexes.     

2-Carbomethoxycyclopentenone as a synthon. synthesis of sarkomycin

The first regiospecific synthesis of sarkomycin (II), a compound active against ascites-type tumors, is reported. Treatment of 2-carbomythoxycyclopentenone (I) with Et₂AlCN generated the carbon skeleton; aelective functional group manipulations then gave the keto lactone X and the protected hydroxy acid XI; and mild acid treatment of these led to sarkomycin.     

Improved electrochemical performances of core-shell Cu2O/Cu composite prepared by a simple one-step method

Core-shell Cu₂O/Cu composites were successfully prepared by over-reduction of aqueous CuSO₄ with hydrazine hydrate as reductant. Field emission scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) clearly illuminate that the core is Cu₂O with 400 nm in diameter, and the shell is Cu with about 50 nm in thickness. The core-shell Cu₂O/Cu exhibited weaker polarization and higher coulombic efficiency than pure octahedral Cu₂O, especially in the initial stage of cycles. After 50 cycles, the reversible capacity of Cu₂O/Cu (360 mAh g^?1) was much higher than that of pure Cu₂O (160 mAh g^?1). The improvement of electrochemical properties is attributed to the core-shell structure of Cu₂O/Cu and the catalytic effect of Cu on the decomposition of Li₂O during the charging process.     

Synthesis of 2-hydroxy-3-indolinones and 3-hydroxy-2-indolinones by anionic cyclization, in situ oxidation and rearrangement

Lithiation with butyllithium of 2-(benzylamino)benzamides (N-benzyl anthranilamides) occurs at the benzylic position to give an α-amino-organolithium that cyclizes to the 3-indolinone (indoxyl) ring (similar to a Parham cyclization). Autoxidation in air gives 2-hydroxy-3-indolinones. In the absence of a proton source, rearrangement of the aryl group from C-2 to C-3 occurs to give the 3-hydroxy-2-indolinone (oxindole) ring.     

简单浸渍法制备纳米CuO/TiO2及其光催化剂活性

以Cu(NO₃)₂·3H₂O和P25为前躯体,通过简单浸渍法制备了CuO/TiO₂光催化剂,利用N₂物理吸附、XRD、TEM、UV-vis漫反射光谱分析了催化剂的结构特性。研究了Cu组分的负载量、催化剂在反应液中的分散量、催化剂焙烧温度、反应液中甲醇浓度对CuO/TiO₂光催化反应产氢活性的影响,并考察了催化剂的稳定性,提出了该体系光催化反应的机理。结果表明,Cu的适宜负载量为2.0%~7.5%(质量分数),在Cu质量分数2.0%、催化剂焙烧温度350℃、甲醇的体积浓度为10%、催化剂分散量为1.0 g/L时,产氢活性可达到1 022 μmol/(h·g),并且该催化剂具有较好的稳定性。     

Characterization of Bi2Se3 prepared by electrodeposition

Journal of Solid State Electrochemistry - Bi2Se3 compound was deposited catholically under potential control, from a mixture solution composed from equimolar SeO2 and BiCl3. The concentration of...     

Reactions and rearrangement of 2,4-quinazolinediones. An efficient simple synthesis of 3-amino-1H,3H-quinazolinedione

An efficient synthesis of 3-amino-1H,3H-quinazolinedione by the action of hydrazine on the readily accessible 3-phenyl-2,4(1H,3H)-quinazolinedione and 2-anilino-4H-3,1-benzoxazin-4-one are described.     

Thiophene backbone amide linkers, a new class of easily prepared and highly acid-labile linkers for solid-phase synthesis

Solid-phase synthesis is of tremendous importance for small-molecule and biopolymer synthesis. Linkers (handles) that release amide-containing products after completion of solid-phase synthesis are widely used. Here we present a new class of highly acid-labile backbone amide linkers (BAL handles) based on 3,4-ethylenedioxythiophene (EDOT), which we have termed T-BAL. These thiophene linkers are synthesized in three convenient steps from commercially available EDOT. In the linker design, the spacer was introduced to the EDOT core either via a carbon-carbon bond or via a thioether linkage. Introduction of the spacer via a C-C bond was performed by a chemoselective Negishi coupling without transient protection of the aldehyde group to provide the T-BAL1 handle. Introduction via a thioether linkage was performed by a facile nucleophilic aromatic substitution between the brominated EDOT aldehyde and unprotected mercapto acids to provide T-BAL2 and T-BAL3 handles. The minimal use of protecting groups gave the corresponding linker molecules in few synthetic steps and in good yields. After anchoring of the linker to a polymeric support, introduction of the first amino acid was achieved by reductive amination, giving a secondary amine. A following acylation of the secondary amine with a symmetrical amino acid anhydride resulted in a backbone amide linkage between the handle and the growing substrate (e.g., peptide chain). After solid-phase synthesis, the substrates could be released from the resin by either low acid conditions using 1% TFA in CH2Cl2 or high acid conditions such as 50% TFA in CH2Cl2. Peptide thioesters could be released from the T-BAL1 handle under very mild conditions using aqueous acetic acid. Tert-butyl based protecting groups, tert-butyl esters, tert-butyl ethers, and Boc groups, as well as dimethyl acetals were relatively stable to these mild conditions for release of the peptides.     

Acyclic stereoselection. 21. Synthesis of an ionophore synthon having four asymmetric carbons by sequential aldol addition,claisen rearrangement and hydroboration

Allylic alcohol 7, obtained by a synthesis involving stereoselective aldol addition to an unsaturated aldehyde, is transformed by the Ireland variant of the Claisen rearrangement into unsaturated acid 9. Subsequent elaboration of this material gives homoallylic alcohols 13 and 14, which are hydroborated to obtain primarily 3 and 4. It is shown that the hydroboration is intermolecular, rather than intramolecular.     

Ring-degenerate rearrangement of 5-amino-4-iminomethyl-1, 2, 3-triazoles

5-Amino-4-(substituted)iminomethyl-1-phenyl-1, 2, 3-triazoles 5 rearrange thermally to 4-amidino-substituted triazoles 6 instead of undergoing the Dimroth rearrangement to 5-anilinotriazoles 3 .     

3-Diazopyrazolo[3,4-b] pyridine,a versatile synthon for new heterocyclic systems

3-Diazopyrazolo[3,4-b] pyridine was synthesized and its transformations were investigated. With reactive methylene compounds the corresponding hydrazones are formed and they can be cyclized into condensed 1,2,4-triazine derivatives. With amines of thiols the diazo compound forms triazenes or diazosulfides. From hydrazines tetrazenes are formed first and they give upon fragmentation a mixture of N-N or C-N bond fission products. The diazo compound undergoes cycloaddition, reacting as a 1,2-dipole. 3-Azidopyrazolo [3,4-b] pyridine was prepared and converted into the tetrazolo isomer, whereas the 3-amino compound was used for the synthesis of some pyridopyrazolopyrimidines.