Exhaustive and partial alkoxylation of polymethylhydrosiloxane by copper‐catalyzed dehydrocoupling with alcohols: Synthesis,crosslinking behavior,and thermal properties of the products

Polymethylhydrosiloxane (PMHS) reacts with aliphatic and aromatic alcohols at room temperature in the presence of [CuH(PPh₃)]₆ complex catalyst to give poly[(methyl) (alkoxy)siloxane]s in high yields. Reactivity of alcohols decreases in the order of p‐methoxyphenol > p‐cresol > phenol > benzyl alcohol > allyl alcohol > ethanol > isopropanol > tert‐butyl alcohol. Partially p‐cresylated polymers, which still retain unreacted Si? H bonds, react further with ethylene glycol or water to form cross‐linked polymers, which, depending on the extent of cross linking, gelate during the cross‐linking process. Propargyl alcohol reacts with PMHS very rapidly to give exhaustively and partially propargyloxylated PMHS. Resulting polymers, upon heating, undergo crosslinking. Partially propargyloxylated polymers display high thermal stability [T_d5 (temperature of 5% weight loss) > 500 °C] as compared with starting PMHS (243 °C) and exhaustively propargyloxylated one (414 °C). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Stereoselective Cross-Coupling of Baylis–Hillman Acetates with Diphenyl Disulfides and Diselenides Using Palladium Acetate

An efficient method is described for the stereoselective synthesis of diorganyl chalcogenides from a variety of Baylis–Hillman acetates and diaryl chalcogens using palladium catalyst. This reaction is a convenient new method to produce unsymmetrical sulfides and selenides in good yields.     

Oxidative bromination of ketones using ammonium bromide and oxone®

A highly efficient, environmentally safe and economic method for selective α-monobromination of aralkyl, cyclic, acyclic, 1,3-diketones and β-keto esters and α,α-dibromination of 1,3-diketones and β-keto esters without catalyst is reported using ammonium bromide as a bromine source and oxone® as an oxidant. The reaction proceeds at ambient temperature and yields range from moderate to excellent. Bromination of unsymmetrical ketones takes place at the less substituted α-position predominantly. Aromatisation of tetralones is also carried out with this reagent system.     

Stereoselective total synthesis of xyolide

A stereoselective total synthesis of xyolide is described employing MacMillan α-hydroxylation, Steglich esterification, and ring closing metathesis as key steps. The use of organocatalytic MacMillan α-hydroxylation to construct two of the chiral centers of the xyolide makes this approach attractive.     

Total Synthesis of a Mevinic Acid Analog

Total synthesis of mevinic acid analog 1 has been achieved efficiently starting from chiral 2,3‐O‐isopropylidene‐D ‐glyceraldehyde ( 2 ). The synthesis involves Mitsunobu reaction and Evans' intramolecular oxa‐Michael syn‐addition reactions as key steps.     

Silver-Mediated Mild Oxidation of Nitrogen-Containing Heteroaryl-2-methanols to Esters

Oxidation of nitrogen-containing heteroaryl-2-methanols to esters with Ag₂O and isopropyl iodide is reported. This methodology is very mild and can tolerate many functional groups.     

Intermolecular Dipole–Dipole Relaxation of Xe Dissolved in Water

Intermolecular ¹²⁹Xe–¹H nuclear Overhauser effects and ¹²⁹Xe longitudinal relaxation time measurements were used to demonstrate that the dipole–dipole coupling is the dominant relaxation mechanism for ¹²⁹Xe in water, at room temperature. ¹²⁹Xe–¹H cross-relaxation rates were derived to be ς_XeH 3.2 ± 0.3 × 10⁻³ s⁻¹, independent of xenon pressure (in the range of 1–10 bar) and of the presence of oxygen. Corresponding xenon–proton internuclear distances were calculated to be 2.69 ± 0.12 Å. Using the magnitude of the dipole–dipole coupling and the spin density ratio between dissolved xenon and bulk water, it is estimated that ¹²⁹Xe–¹H spin polarization-induced nuclear Overhauser effects would yield little net proton signal enhancement in water.     

Chemoselective Reduction of Carbonyl Compounds with PMHS - ZnCl2

An inexpensive and safer reagent system comprising of PMHS and ZnCl₂ has been developed for the selective reduction of carbonyl compounds to corresponding alcohols.

     

Synthesis and Spectral Characterization of Related Substances of Lacidipine,an Antihypertensive Drug

Five related substances (impurities) were detected in lacidipine bulk drug substance by a simple high-performance liquid chromatographic method (HPLC) and were identified by liquid chromatography–mass spectrometry (LC-MS). These related substances were independently synthesized, characterized, and co-injected with the sample containing impurities.