MgBr2·OEt2 mediated protection of alcohols with hexamethyldisilazane: An efficient catalytic route for the preparation of silyl ethers under solvent-free conditions

Various types of alcohols and phenols were rapidly protected by hexamethyldisilazane in good to excellent yields at room temperature in the presence of catalytic amount of magnesium bromide ethyl etherate under solvent-free conditions. Good to excellent chemoselectivity was demonstrated for competitive protection of primary hydroxyls in the presence of secondary and tertiary alcohols. Highly selective protection of phenols in the presence of aromatic amines was also demonstrated successfully.     

Solvent-Free Acetylation of Thiols Under Catalysis of MgBr2·OEt2

Solvent-free protection of aromatic and aliphatic thiols with acetic anhydride was performed at room temperature under trace quantities of magnesium bromide ethyl etherate, affording rapid formation of various thiol esters in excellent yields.     

Convenient Synthesis of 2-Aminothiophene Derivatives by Acceleration of Gewald Reaction Under Ultrasonic Aqueous Conditions

Under ultrasound irradiation and in the presence of H₂O/Et₂NH, ethyl cyanoacetate or malononitrile can combine with α-methylene carbonyl compounds and elemental sulfur to efficiently yield 2-aminothiophene derivatives within a few minutes. Products are easily obtained by simple filtration because of their spontaneous precipitation in the reaction mixtures.     

Superparamagnetic iron oxide as an efficient and recoverable catalyst for rapid and selective trimethylsilyl protection of hydroxyl groups

At room temperature and under solvent‐free conditions, various types of alcohols and phenols were efficiently protected within a few minutes using hexamethyldisilazane and magnetically recoverable Fe₃O₄. Preferential protection of primary alcohols was observed when they competed with secondary or tertiary alcohols. Highly selective protection of phenols in the presence of aromatic amines or thiophenol was also observed. Copyright © 2008 John Wiley & Sons, Ltd.     

Two new eudesmane derivatives from Verbesina virginica

<正>Two new eudesmane derivatives were isolated from the leaves and flowers of Verbesina virginica,along with the known 6-O-β-E -p-coumaroyl-4α-hydroxyeudesmane(1).Their structures were determined as 6-O-β-Z-p-coumaroyl-4α-hydroxyeudesmane(2) and 6-O-α-E-p-coumaroyl-1β-4α-dihydroxyeudesmane(3) by spectroscopic methods.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

PRESSURE-VELOCITY EQUILIBRIUM HYDRODYNAMIC MODELS

This article describes mathematical models for phase separated mixtures of materials that are in pressure and velocity equilibrium but not necessarily temperature equilibrium. General conditions for constitutive models for such mixtures that exhibit a single mixture sound speed are discussed and specific examples are described.     

Ultrasound promoted aminolysis of epoxides in aqueous media: a rapid procedure with no pH adjustment for additive-free synthesis of beta-aminoalcohols

An efficient and environmentally friendly procedure promoted by ultrasound irradiation is developed for stereoselective ring opening of various epoxides with aromatic and aliphatic amines under aqueous conditions in the presence of no catalyst or additive. Chemoselectivity of the protocol is shown by competition of piperidine and aniline to react with different epoxides resulting in exclusive formation of the respective products of piperidine.     

Facile solvent-free synthesis and structural elucidation of styrylcyclohex-2-enone derivatives

A remarkably efficient procedure for the synthesis of styrylcyclohex-2-enone derivatives at room temperature is described using a mild reaction medium consisting of lithium perchlorate and N-(trimethylsilyl)diethylamine. Several compounds of this class are synthesized conveniently and rapidly. Spectroscopic and X-ray diffraction experiments confirm the proposed structures. Correspondence: Mohammad M. Mojtahedi and Mohammad Saeed Abaee, Organic Chemistry Laboratory, Chemistry and Chemical Engineering Research Center of Iran, P.O. Box 14335-186, Tehran, Iran.