Sulfenamides as ligands in transition metal chemistry Pentacarbonyl(Sulfenamide)Chromium(0) Complexes

The complexes Cr(CO)₅(R′SNR₂) [R′ = CH₃; NR₂ = N(CH₃)₂, N(C₄H₈)O. R′ = C₆H₅; NR₂ = N(CH₃)₂, N(C₄H₄)O, N(CH₂? C₆H₅)₂, N(C₆H₁₁)₂] have been prepared by reaction of the sulfenamides with Cr(CO)₅ · THF and characterized by analytical and spectroscopic methods. The IR, ¹H-NMR, UV-VIS, and mass spectra of the complexes support the coordination of the sulfenamide via the sulfur atom. π-acceptor abilities of sulfenamides in the prepared coordination compounds, determined from IR and UV-VIS data, were compared with those of other divalent sulfur conpounds.     

Electronic delocalization contribution to the anomeric effect evaluated by computational methods

This study proposes the determination of the electronic delocalization contribution to the Anomeric Effect (EDCAE, Delta Delta E(deloc), eq 3) as a computational alternative in the evaluation of the excess of the axial preference shown by an electronegative substituent located at alpha position to the annular heteroatom of a heterocyclic compound (anomeric position) in both the presence and the absence of electronic delocalization retaining the same molecular geometry. The determination of the EDCAE is computationally accessible through the application of the natural bond orbital analysis (NBO). This type of analysis allows the comparison of hypothetical molecules lacking electronic delocalization (Lewis molecules, in which the electrons are strictly located in bonds and lone pairs) with the fully delocalized molecules retaining the same geometry and the evaluation of the anomeric effect in terms of eq 3. The role of the Lewis molecules is the same as the cyclohexane used experimentally to evaluate the anomeric effect. The advantage of doing this is that Lewis molecules are stereoelectronically inert. Applying this methology to cyclic and acyclic molecules at B3LYP/6-31G(d,p) and HF/6-31G(d,p)//B3LYP/6-31G(d,p) levels of theory, we found that the anomeric effect shown by Cl in 1,3-dioxane; F, Cl, SMe, PH(3), and CO(2)Me groups in 1,3-dithiane is of stereoelectronic nature while the preference of F, OMe, and NH(2) in 1,3-dioxane and the P(O)Me(2) group in 1,3-dithiane is not. Furthermore, this methodology shows that anomeric effects without stereoelectronic origin can modify the molecular geometry in agreement with the geometric pattern required by the double-bond no-bond model, as recently proposed by Perrin.     

Manifestation of stereoelectronic effects on the calculated carbon-hydrogen bond lengths and one bond (1)J(C-H) NMR coupling constants in cyclohexane,six-membered heterocycles,and cyclohexanone derivatives

Cyclohexane (1), oxygen-, sulfur-, and/or nitrogen-containing six-membered heterocycles 2-5, cyclohexanone (6), and cyclohexanone derivatives 7-16 were studied theoretically [B3LYP/6-31G(d,p) and PP/IGLO-III//B3LYP/6-31G(d,p) methods] to determine the structural (in particular C-H bond distances) and spectroscopic (specifically, one bond (1)J(C-H) NMR coupling constants) consequences of stereoelectronic hyperconjugative effects. The results confirm the importance of n(X) --> sigma*(C-H)(app) (where X = O, N), sigma(C-H)(ax) --> pi*(C=O), sigma(S-C) --> sigma*(C-H)(app), sigma(C-S)-->sigma*(C-H)(app), beta-n(O) --> sigma*(C-H), and sigma(C-H) --> sigma*(C-H)(app) hyperconjugation, as advanced in previous theoretical models. Calculated r(C-H) bond lengths and (1)J(C-H) coupling constants for C-H bonds participating in more than one hyperconjugative interaction show additivity of the effects.     

Total syntheses of variolin B and deoxyvariolin B

Two alternative synthetic routes have been developed for the preparation of variolin B and deoxyvariolin B. The strategy is based on the preparation of the core tricyclic ring common to all variolins, pyrido[3',2':4,5]pyrrolo[1,2-c]pyrimidine, followed by a palladium-catalyzed cross-coupling reaction to give the tetracyclic system.     

Almost Periodicity for a Nonautonomous Discrete Dispersive Population Model

In this article, study the almost periodic profile of solutions for nonautonomous difference equations in Banach spaces. We apply our results in population dynamics.     

Frequency‐Driven Self‐Organized Helical Superstructures Loaded with Mesogen‐Grafted Silica Nanoparticles

Adding colloidal nanoparticles into liquid‐crystal media has become a promising pathway either to enhance or to introduce novel properties for improved device performance. Here we designed and synthesized new colloidal hybrid silica nanoparticles passivated with a mesogenic monolayer on the surface to facilitate their organo‐solubility and compatibility in a liquid‐crystal host. The resulting nanoparticles were identified by ¹H NMR spectroscopy, TEM, TGA, and UV/Vis techniques, and the hybrid nanoparticles were doped into a dual‐frequency cholesteric liquid‐crystal host to appraise both their compatibility with the host and the effect of the doping concentration on their electro‐optical properties. Interestingly, the silica‐nanoparticle‐doped liquid‐crystalline nanocomposites were found to be able to dynamically self‐organize into a helical configuration and exhibit multi‐stability, that is, homeotropic (transparent), focal conic (opaque), and planar states (partially transparent), depending on the frequency applied at sustained low voltage. Significantly, a higher contrast ratio between the transparent state and scattering state was accomplished in the nanoparticle‐embedded liquid‐crystal systems.     

Thermal reactions of N‐alkyl‐2‐benzylaniline and N‐alkyl‐N′‐phenyl‐o‐phenylenediamine: An unusual route to 2‐phenylindole and 2‐phenylbenzimidazole

Thermal cyclization reactions of N‐alkyl‐2‐benzylaniline 1a‐d and N‐alkyl‐N′‐phenyl‐o‐phenylenediamine 2a‐b were carried out expecting to get seven‐membered heterocyclic compounds. However, the results show that aside from the formation of the normally expected six‐membered ring products of acridine 5 , anthracene 6 , and phenazine 8 , thermal cyclization of N‐alkyl‐2‐benzylaniline and N‐alkyl‐N′‐phenyl‐o‐phenylenediamine also resulted to the unexpected formation of 2‐phenylindole 3 and 2,3‐diphenylindole 4 , and 2‐phenylbenzimidazole 7 , respectively.     

Toward an artifical acetylcholinesterase

The methanolysis of choline p-nitrophenylcarbonate in chloroform containing 1% methanol is catalyzed with turnover by ditopic receptors 1 and 2, consisting of a calix[6]arene connected to a bicyclic guanidinium by means of a short spacer. The calix[6]arene subunit strongly binds to the trimethylammonium head group through cation-pi interactions, whereas the guanidinium moiety is deputed to stabilize through hydrogen bonding reinforced by electrostatic attraction the anionic tetrahedral intermediate resulting from methoxide addition to the ester carbonyl. The observed cholinesterase activity had been anticipated on the basis of the ability of the ditopic receptors 1 and 2 to bind strongly to the choline phosphate DOPC, which is a transition state analogue for the BAc2-type cleavage of choline esters.