Hee-Gweon Woo

ENANTIOSELECTIVE RING OPENING OF EPOXIDES WITH 4-METHOXYPHENOL CATALYZED BY GALLIUM HETEROBIMETALLIC COMPLEXES : AN EFFICIENT METHOD FOR THE SYNTHESIS OF OPTICALLY ACTIVE 1,2-DIOL MONOETHERS

Useful chiral building blocks such as 1,2-diols can be obtained by the enantioselective ring opening of achiral epoxides with oxygen nucleophiles. The ring opening is carried out effectively (up to 94 % ee) with 4-methoxyphenol and catalytic amounts of gallium complexes. The novel complex GaSO 1 displays a particularly high catalytic activity.

One-pot synthesis of poly(alkoxysilane)s by SiSi/SiO dehydrocoupling of silanes with alcohols using Group IV and VIII metallocene complexes

Abstract SiSi/SiO dehydrocoupling reactions of silanes with alcohols (1:1.5 mole ratio), catalyzed by Cp 2 MCl 2 /Red-Al (M=Ti, Zr) and Cp 2 M′ (M′=Co, Ni), produced poly(alkoxysilane)s in one-pot in high yield. The silanes included p -XC 6 H 4 SiH 3 (X=H, CH 3 , OCH 3 , F), PhCH 2 SiH 3 , and (PhSiH 2 ) 2 . The alcohols were MeOH, EtOH, i PrOH, PhOH, and CF 3 (CF 2 ) 2 CH 2 OH. The weight average molecular weight of the poly(alkoxysilane)s ranged from 600 to 8000. The dehydrocoupling reactions of phenylsilane with ethanol (1:1.5 mole ratio) using Cp 2 HfCl 2 /Red-Al and phenylsilane with ethanol (1:3 mole ratio) using Cp 2 TiCl 2 /Red-Al gave only triethoxyphenylsilane as product.

A synthesis of (±)-sparteine

In a synthesis of racemic sparteine, Diels-Alder reaction between dimethyl bromomesaconate 14 and dicyclopentenyl 4, followed by cyclopropane formation, set up the stereochemistry at C-1 and C-5 as S and R, respectively, in a meso intermediate 8. The stereochemistry at C-2 and C-4 was then secured by a moderately diastereoselective protonation of the bis-enolate 17 derived from the diester 8 by reductive cleavage with lithium in liquid ammonia. The C=C in the racemic diester 19 was ozonolysed and the diketone converted by Beckmann rearrangement into the bis-lactam . Reduction of the bis-lactam with lithium aluminium hydride and intramolecular nucleophilic displacement gave racemic sparteine 1. Some ideas for making this synthesis amenable to a synthesis of enantiomerically enriched sparteine are presented.

Enantioselektive, durch Heterobimetall‐Galliumkomplexe katalysierte Ringöffnung von Epoxiden mit 4‐Methoxyphenol – eine leistungsfähige Methode zur Synthese optisch aktiver 1,2‐Diolmonoether

Praparativ nutzliche chirale Bausteine wie 1,2-Diole sind durch die enantioselektive Ringoffnung achiraler Epoxide mit Sauerstoff-Nucleophilen zuganglich. Die Ringoffnung kann effektiv mit 4-Methoxyphenol und Galliumkomplexen als Katalysatoren durchgefuhrt werden (bis zu 94% ee). Eine besonders hohe katalytische Aktivitat weist der neuartige Komplex GaSO 1 auf.

High Functional Inorganic Polymers Containing Main Group 13 – 16 Elements in the Polymer Backbone Chain

Polymers can be largely divided into two categories: organic polymers and inorganic polymers. Organic polymers tend to lose their advantageous material properties (e.g., light weight, flexibility, fabricability, elasticity, mechanical strength, conductivity, optoelectricity) in the presence of oxygen, ozone, corrosion, ultraviolet radiation or at extreme high/low temperatures. Nonetheless, most organic polymers used heavily and widely in modern daily life, hardly decompose in the natural environment and burn releasing toxic chemicals as well, creating serious environmental pollution.[1] Furthermore, the availability of raw materials for organic polymers, whose backbone chains mainly consist of carbon atoms linked together or separated by heteroatoms, such as oxygen or nitrogen, is limited by the anticipated shortage of natural petroleum/coal resources. Therefore, research on the design, synthesis, characterization and applications of inorganic polymers, inorganic-organic hybrid polymers or organometallic polymers is needed to avoid these problems.[2]

Fabrication and properties of thermal insulating glass fiber reinforced composites from low temperature curable polyphosphate inorganic polymers

Glass fiber reinforced polymetalphosphate matrix composites prepared by a simple process displayed excellent thermal insulating and mechanical properties. Low-viscous Al 3 Cr(H 2 PO 4 ) x=9,12 binders were prepared by dissolving Al(OH) 3 and Cr(OH) 3 or CrO 3 in 85% phosphoric acid, and mixed with Al 2 O 3 and Cr 2 O 3 fillers. The glass fiber pre-pregs impregnated by the binder solution were laid-up and cured at 150-200 °C for 12 h under pressure, which are similar conditions to those used for carbon fiber/phenolic resin matrix composites. The composites cured using the hot-press or autoclave showed outstanding hygroscopic resistance even after standing in air for 30 days, due to the chemical stability of the cured network. Hot-press cured composites with higher density exhibited maximum flexural strengths of 155 MPa and thermal conductivity in the range 1.12-3.45 W/mK, while the porous autoclave cured composites displayed 60-77 MPa and 0.4-0.6 W/mK, respectively.

Photonic polymer replicas from distributed Bragg reflectors structured porous silicon.

Well defined 1-dimentional (1-D) photonic crystals of polymer replicas have been successfully obtained. DBR porous silicon containing nanometer-scale pores are prepared by an anodic electrochemical etch of p(++)-type silicon wafer. The resulting DBR porous silicon film removed from the substrate by applying an electropolishing current has been thermally oxidized in the furnace at 400 degrees C for 3 h. Oxidized DBR PSi/polystyrene composite films are prepared by casting of polymer solution onto a free-standing porous silicon photonic crystal layer. Flexible photonic polymer replicas have been prepared after the removal of oxidized DBR PSi matrix in HF/H2O mixture solution. Polymer replicas exhibit a sharp resonance in the reflectivity spectrum. Optical characteristics of photonic polymer replica indicate that the surface of polymer film has a negative structure of DBR PSi. This replica is stable in aqueous solutions for several days without any degradation.

Dehydrocoupling Synthesis and Optoelectronic Properties of Polysilole

Abstract Dehydrocoupling of 2,3,4,5-tetraphenylsilole dihydride 1 with various inorganic hydrides (such as Red-Al, N-Selectride, and super-hydride) produces polysiloles 2 in high yields. The polysiloles emit green light at 520 nm and are electroluminescent at 520 nm.

Synthesis and structural characterization of a silacycloheptadiene

The dilithium salt of tetraphenylbutadiene (1) reacts normally with phenylethynyltrichlorosilane to give 1-chloro-1-phenylethynyl-2,3,4,5-tetraphenylsilole (3), but with vinyltrichlorosilane the unexpected product is the silacycloheptadiene 2, and X-ray crystal structures were obtained for 2 and 3; the seven-membered ring in 2 adopts a boat conformation, and a possible mechanism for the formation of 2 is suggested.

Fabrication and optical characterization of multi-encoded rugate porous silicon/polymer composite.

Multi-encoded rugate porous silicon (MRPS)/polystyrene composite films were fabricated by using a free-standing multi-encoded rugate PS and polystyrene. MRPS exhibiting three reflection resonances was generated by an electrochemical etching of silicon wafer using a composite waveform summed three computer-generated pseudo-sinusoidal current waveforms, which were corresponded to the each of the sine components varied from 0.40, 0.38, to 0.36 Hz, with a spacing of 0.02 Hz between each sine component. They displayed three sharp photonic reflection resonances in the optical reflectivity spectrum. MRPS/polymer composite films obtained by casting of polystyrene polymer solution exhibited excellent photonic characteristics and robust structure upon flexing. For a possible application as VOCs sensor, these films were served for the detection of organic vapors such hexane and methanol.