Study of the O-glycidylation of natural phenolic compounds. The relationship between the phenolic structure and the reaction mechanism

The O-alkylation reaction by epichlorohydrin of some natural phenolic compounds such as 4-methylcatechol, gallic acid, protocatechuic acid, pyrogallol and resorcinol was investigated. Phenolic compounds reacted first with epichlorohydrin in the presence of benzyltriethylammonium chloride as phase transfer catalyst. Then, an aqueous solution of sodium hydroxide was added.It was demonstrated that the two competitive mechanisms involved in the O-alkylation reaction were highly dependent of the starting material. The O-alkylated products obtained in this reaction could be further used as bisphenol A substitutes in the synthesis of epoxy resins pre-polymers.     

Stereoselective Cascade Cyclizations with Samarium Diiodide to Tetracyclic Indolines: Precursors of Fluorostrychnines and Brucine

A series of γ-indolylketones with fluorine, cyano or alkoxy substituents at the benzene moiety was prepared and subjected to samarium diiodide-promoted cyclization reactions. The desired dearomatizing ketyl cascade reaction forming two new rings proceeded in all cases with high diastereoselectivity, but with differing product distribution. In most cases, the desired annulated tetracyclic compounds were obtained in moderate to good yields, but as second product tetracyclic spirolactones were isolated in up to 29 % yield. The reaction rate was influenced by the substituents at the benzene moiety of the substrate as expected, with electron-accepting groups accelerating and electron-donating groups decelerating the cyclization process. In case of a difluoro-substituted γ-indolylketone a partial defluorination was observed. The intermediate samarium enolate of the tetracyclic products could be trapped by adding reactive alkylating agents as electrophiles delivering products with quarternary carbons. In the case of a dimethoxy-substituted tetracyclic cyclization product a subsequent reductive amination stereoselectively provided a pentacyclic compound that was subsequently N-protected and subjected to a regioselective elimination. The obtained functionalized pentacyclic product should be convertible into the alkaloid brucine by four well-established steps. Overall, the presented report shows that functionalized tetracyclic compounds with different substituents are rapidly available with the samarium diiodide cascade cyclization as crucial step. Hence, analogues of the landmark alkaloid strychnine, for example, with specific fluorine substitutions, should be easily accessible.     

Determination of phenolic compounds by MALDI–TOF and essential oil composition by GC–MS during three development stages of Origanum majorana L.

This study aimed to investigate the effect of the maturation process of sweet marjoram (Origanum majorana L.) on essential oil composition, the phenolic profile of ethanolic extract and their antioxidant capacities. The essential oil composition was studied at three stages of maturity by GC–MS. Thirty compounds were detected representing 100% of the total essential oil. p‐Menth‐1‐en‐4‐ol was the major compound (37.15–76.94%) followed by cyclohexanol‐3,3,5 trimethyl (5.41–15.99%) and α‐terpineol (0.94–11.34%). During the maturation process, an accumulation of oxygenated monoterpenes was observed. The phenolic composition was studied using matrix‐assisted laser desorption/ionization time of flight. The analysis showed the presence of short flavonoid monomers at all stages of maturation. The antioxidant capacity of ethanolic extracts and essential oils was evaluated using the DPPH assay, iron chelating power and reducing power assay. The highest phenolic content and antioxidant capacity were found at flowering stage. These findings on essential oil composition, phenolic profile and antioxidant capacity of O. majorana at three different stages of development provide more information on how these secondary metabolites are accumulated.     

Stabilizing torsion-free periodic orbits using method of harmonic oscillators

Nonlinear Dynamics - An odd number of real Floquet multipliers greater than unity prevents the classical time delayed feedback control from stabilizing torsion-free orbits of nonautonomous systems....     

Room temperature suzuki cross‐coupling polymerizations of aryl dihalides and aryldiboronic acid/acid esters with t‐Bu3P‐coordinated 2‐phenylaniline‐based palladacycle complex as the precatalyst

Room temperature Suzuki cross‐coupling polymerization of aryl dibromides/diiodides with aryldiboronic acids/acid esters with t‐Bu₃P‐coordinated 2‐phenylaniline‐based palladacycle complex, [2′‐(amino‐kN)[1,1′‐biphenyl]‐2‐yl‐kC]chloro(tri‐t‐butylphosphine)palladium, as a general precatalyst is described. Such room temperature Suzuki cross‐coupling polymerization is achieved by employing six equivalents or more of the base and affords polymers within an hour, with the yields and the molecular weights in general comparable to or higher than reported results that required higher reaction temperature and/or longer polymerization time. Our study provides a general catalyst system for the room temperature Suzuki cross‐coupling polymerization of aryl dibromides/diiodides with aryldiboronic acids/acid esters and paves the road for the investigation of employing other monodentate ligand‐coordinated palladacycle complexes including other electron‐rich monophosphine‐coordinated ones for room temperature cross‐coupling polymerizations. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1606–1611     

Versatile functional poly(3‐hexylthiophene) for hybrid particles synthesis by the grafting onto technique: Core@shell ZnO nanorods

We demonstrate an efficient strategy to anchor poly(3‐hexylthiophene) (P3HT) onto zinc oxide (ZnO) surfaces. Synthesis of a novel triethoxysilane‐terminated regioregular P3HT is herein reported and supported by thorough characterization. Three triethoxysilane‐terminated P3HTs of different molar masses were prepared via a hydrosilylation reaction from allyl‐terminated P3HT. MALDI‐TOF and ¹H NMR were performed to characterize the polymer and show that around 80% of the chains are end‐functionalized. These polymers were then grafted onto the ZnO nanorods to create a macromolecular self‐assembled monolayer. This versatile technique could be subsequently applied to different metal oxide surfaces, such as silicon, titanium, or indium‐tin oxide, and represents a new one‐pot strategy based on triethoxysilane coupling reaction. Importantly, the influence of the molar mass on the grafting density and the polymer shell thickness was studied via thermo gravimetric analysis and transmission electron microscopy. The optical properties of the hybrid materials were determined by UV–visible absorption and photoluminescence to show a quenching effect of P3HT fluorescence by ZnO when grafted. This electronic transfer associated with an improved miscibility of the ZnO@P3HT, makes these hybrid materials suitable candidates for photovoltaic applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 30–38