Iron-catalyzed electrochemical allylation of carbonyl compounds by allylic acetates

Homoallylic alcohols were synthesized from aldehydes or ketones and allylic acetates, using an electrochemical process catalyzed by iron complexes. We first studied the reactivity of allyl acetate, using N,N-dimethylformamide (DMF) or acetonitrile (AN) as solvent, FeBr(2) as catalyst, and Fe as the sacrificial anode. Then we tested the regioreactivity of crotyl acetate and other allylic derivatives.     

Efficient New Synthesis of N‐Arylbenzo[b]furo[3,2‐d]pyrimidin‐4‐amines and Their Benzo[b]thieno[3,2‐d]pyrimidin‐4‐amine Analogues via a Microwave‐Assisted Dimroth Rearrangement

A useful and rapid access to libraries of N‐arylbenzo[b]furo[3,2‐d]pyrimidin‐4‐amines ( 1 ) and their novel benzo[b]thieno[3,2‐d]pyrimidin‐4‐amine analogues ( 2 ) was investigated for the first time. Title compounds were obtained via microwave‐accelerated condensation and Dimroth rearrangement of suitable anilines with N′‐(2‐cyanaryl)‐N,N‐dimethylformimidamides obtained by reaction of benzo[b]furane and benzo[b]thiophene precursors with N,N‐dimethylformamide dimethyl acetal. This work also demonstrates that well‐controlled parameters offer comfortable use of microwave technology and are both safe and beneficial to the environment. Some products obtained in this article exhibit interesting in vitro antiproliferative effects.     

Potential cancer chemopreventive agents from Arbutus unedo

A phytochemical study of the petroleum ether and ethyl acetate extracts of the entire plant of Arbutus unedo led to the isolation of a new sterol, 7beta-hydroxystigmast-4-en-3-one (1), and nine known compounds of the flavan, steroid, and terpenoid types. The structure of 1 was determined by spectroscopic data interpretation in combination with molecular modeling calculations. The absolute stereochemistry of C-7 was assigned as S for compound 1 based on the obtained CD spectral data. Activity in the JB6 cell transformation assay was found for pomolic acid 3-acetate (4). All isolates obtained were evaluated in a cyclooxygenase-2 (COX-2) inhibition assay.     

NMR and theoretical calculations: a unified view of the cis/trans isomerization of 2-substituted thiazolidines containing peptides

The cis/trans isomerization of peptides containing the pseudoproline (4R)-thiazolidine-4-carboxylic acid Cys(Psi (R1,R2) pro) is investigated from both an experimental and a theoretical point of view by NMR and DFT calculations. A series of Ac-Cys(Psi(R1,R2) pro)-OCH3 and Ac-Cys(Psi(R1,R2) pro)-NHCH3 peptides were prepared to assess the influence of the substitution at the C2 position as well as of the amide following the thiazolidine residue. For each compound, the cis/trans ratio along with free energy, the puckering of the thiazolidine ring and the free rotational energy barrier are reported and discussed. We observe there is a pronounced effect of the C2 substituents and of the chirality upon the cis/trans ratio with the population of the cis content in the order (2R)-Cys(Psi(CH3,H) pro)<(2S)-Cys(Psi(H,CH3) pro)相似文献   

Self-broadening coefficients in the ν7 band of ethylene at room and low temperatures

Using a tunable diode-laser spectrometer, we have measured self-broadening coefficients for a few transitions in the ν₇ fundamental band of C₂H₄ at 298 and 174 K. The studied transitions J^′, K_a^′, K_c^′←J, K_a, K_c with 3?J?17, 1?K_a?4, and 1?K_c?14 are located in the spectral range 919-982 cm⁻¹. The collisional widths are measured by fitting each spectral line with Voigt, Rautian, and speed-dependent Rautian profiles. The latter model provides larger broadening coefficients than the Rautian profile and still larger coefficients than the Voigt profile. An approximate semiclassical calculation performed by considering only electrostatic interactions leads to reasonable agreement with the experimental data. By comparing the results obtained at room and low temperatures, the temperature dependence of the self-broadening has been determined both experimentally and theoretically.     

On a Plus-Construction for Algebras over an Operad

We prove a analogous to Quillen's plus-construction in the category of algebras over an operad. For that purpose we prove that this category is a closed model category and prove the existence of an obstruction theory. We apply further this plus-construction for the specific cases of Lie algebras and Leibniz algebras which are a noncommutative version of Lie algebras: let sl(A) be the kernel of the trace map gl(A)A/[A,A], where A is an associative algebra with unit and gl(A) is the Lie algebra of matrices over A. Then the homotopy of slA)⁺ in the category of Lie algebras is the cyclic homology of A whereas it is the Hochschild homology of A in the category of Leibniz algebras.     

Technique for multiplying the repetition rates of periodic trains of pulses by means of a temporal self-imaging effect in chirped fiber gratings

We show that a temporal effect that is equivalent to the spatial self-imaging (Talbot) effect applies to the reflection of periodic signals from linearly chirped fiber gratings. The effect can be used for multiplying the repetition frequency of a given periodic pulse train without distorting the individual pulse characteristics. The practical limit on the frequency-multiplication factor depends only on the temporal width of the individual pulse. Thus we demonstrate that a suitable combination of well-known techniques for short-pulse generation, such as pulse mode locking, and the technique proposed here allows us to obtain short-pulse trains with ultrahigh repetition rates (in the terahertz regime). Results from simulations show good agreement with those predicted by theory.     

Non-defluorinative electrochemical silylation of ethyl trifluoroacetate: a practical synthesis of trifluoroacetyltrimethylsilane via its ethyltrimethylsilyl ketal

An efficient method for the preparation of original trifluoroacetyltrimethylsilane, CF₃COSiMe₃ (3), in two steps from readily available ethyl trifluoroacetate is described. Electrochemical reduction of this ester using a sacrificial anode and performed on a semimolar scale afforded the unprecedented corresponding ketal, CF₃C(SiMe₃)(OSiMe₃)OEt (2) in 30-56% isolated yield. Treated with concentrated sulphuric acid at room temperature, the latter directly led to pure acylsilane 3 in 86% yield.