Switching in molecular shapes: main chain length driven rod-circle transition of isolated helical polysilanes

Unique conformations such as rod, semicircle, and circle structures of isolated semi-flexible helical polysilanes were observed by atomic force microscopy (AFM); the chain topology was significantly related to the chain length (molecular weight) on the surfaces.     

Photooxygenation and photodimerization of 4-methoxystyrene in NaY. The role of co-adsorbed water and alkene–oxygen charge-transfer complex

On adsorption into NaY, 36% of 4-methoxystyrene (1) was consumed to yield its cis- and trans- chain dimers 2. Irradiation of the NaY sample under vacuum gave cyclic dimers 3, probably through the excimer of 1, and also caused trans-to-cis one-way isomerization of 2. When the NaY sample was irradiated under dry oxygen, 4-methoxybenzaldehyde (4) was given as the major product through photoinduced electron-transfer reaction on excitation of the contact charge-transfer complexes between the guest molecules and O₂. The effects of sodium ion and co-adsorbed water on the photodimerization and photooxygenation is also discussed.     

Convenient synthesis of 1,6,7,8-substituted 2-(3′,4′-substituted-phenyl)-4-quinolones via a 4-ethoxyflavylium salt

Condensation of 2-hydroxyacetophenone with benzaldehyde in the presence of 70% perchloric acid in ethyl orthoformate gave the corresponding 4-ethoxyflavylium perchlorate, which was treated with aqueous ammonia or methylamine solution to afford 1,6,7,8-substituted 2-(3′,4′-substituted-phenyl)-4-quinolone in fair to good yield.     

Novel Catalytic Hydrogenolysis of Trimethylsilyl Enol Ethers by the Use of an Acidic Ruthenium Dihydrogen Complex

The heterolytic cleavage of H ₂ is the key to the novel catalytic hydrogenolysis of trimethylsilyl enol ethers catalyzed by [RuCl(η²-H₂)(dppe)₂]OTf (dppe = 1,2-bis(diphenylphosphanyl)ethane, OTf = trifluoromethanesulfonate), which results in the formation of a ketone and Me₃SiH (see scheme). In addition, the stoichiometric, ruthenium-assisted protonation of a prochiral lithium enolate with H₂ gave a chiral ketone with high enantioselectivity (up to 75 % ee).     

Micropattern of GeO2/GeC lines prepared by UV irradiation and heat treatment of polygermane copolymers of methylphenylgermylene/phenylgermyne units

Upon ultraviolet irradiation of polygermane copolymers of methylphenylgermylene/phenylgermyne units (PhMeGe)_n(PhGe)_m in air, the germanium–germanium bond in the copolymer film changed into a digermoxane chain. Laser flash photolysis of the copolymer film showed the intermediacy of polygermyl radicals generated by Ge–Ge bond homolysis. The XPS showed the formation of germanium carbide (GeC) and germanium dioxide (GeO₂) upon heating the unirradiated and irradiated copolymer (PhMeGe)_n(PhGe)_m films, respectively. A relatively high-resolution micro- pattern of GeC/GeO₂ was obtained by combining the photochemical and thermal properties of the copolymers of methylphenylgermylene/phenylgermyne units. © 1997 John Wiley & Sons, Ltd.     

Synthesis of poly(tert-butoxycarbonyl-p-phenylene): precursor to poly(p-phenylene)

Poly[2-(tert-butoxycarbonyl)-1,4-phenylene] ( 2 ) was prepared by the Ni-catalyzed polymerization of tert-butyl 2,5-dichlorobenzoate ( 1 ). The microstructure of polymer 2 was probably alternating head-to-head and tail-to-tail. This polymer was soluble in dipolar aprotic solvents, chloroform, tetrahydrofuran, and dichloromethane. Polymer 2 was saponified easily by thermal or acid treatment to yield poly[2-carboxy-1,4-phenylene] ( 3 ). Decarboxylation of polymer 3 in quinoline in the presence of copper(II) oxide produced poly(p-phenylene) (PPP) ( 4 ).