Stereochemistry of the nickel-catalyzed cross-coupling reaction of Grignard reagents with olefinic halides: stereospecific versus nonstereospecific-stereoselective reactions

The nickel-catalyzed cross-coupling reactions of Grignard reagents with monohalo-olefins proceed stereospecifically, while with 1,2-dihaloethylenes they proceed nonstereo-specifically to form cis-olefins stereoselectively in many cases.     

Preparation of certain chloromethyl- and dichloromethyl-substituted chlorodisilanes and their behavior toward aluminum halides

Four new (chloromethyl)disilanes, (ClCH₂)Cl₂SiSiCl₂Me (I), (Cl₂CH)Cl₂SiSiCl₂Me(II), (ClCH₂)MeClSiSiClMe₂(III) and (ClCH₂)Me₂SiSiCl₃(IV), have been prepared and studied as to their attitude toward intramolecular rearrangement with aluminum chloride. The reactivity decreases in the order: (III) > (IV) > (II) (I). Similar reactivity to rearrangement of Me₃SiSiMe₂(CH₂Br)(V), ClMe₂SiSiMe₂(CH₂Br) (VI) and Me₃SiSiMeCl(CH₂Br) (VII) in the presence of aluminum bromide has been found to decrease in the order: (V) > (VI) > (VII). The results are discussed in terms of a mechanism favoring initial rate-determining step of ionization of the carbon-halogen bond in which the migrating group plays a minor role, if any, followed by migration of a silyl group from silicon to carbon. Disilanes (I) and (II) enter into the Friedel-Crafts reaction with benzene to give, after methylation, PhCH₂SiMe₂SiMe₃ and Ph₂CHSiMe₂SiMe₃, respectively.     

Metal catalyzed cross-coupling reactions of carbanions α to silafunctional groups. New α-hydroxyalkyl anion equivalents

Carbanions α to (alkoxy)silyl or (amino)silyl groups act as nucleophilic α-hydroxy-alkylating agents for organic halides and epoxides via the metal catalyzed coupling reaction and the subsequent oxidative cleavage of the carbon-silicon bond.     

Fractionation of glycoprotein-derived oligosaccharides by affinity chromatography using immobilized lectin columns

Lectin affinity column chromatography is becoming a method of choice for the fractionation and purification of oligosaccharides, especially N-linked oligosaccharides. Using lectin affinity, it is easy to separate structural isomers and to isolate oligosaccharides based on specific features. Further, serial lectin column chromatography, when various lectin columns are used at the same time, can afford a very sensitive method for the fractionation and characterization of extremely small amounts of oligosaccharides. Thus, when used in conjunction with other separation techniques, lectin affinity chromatography can help to purify rapidly oligosaccharides and provide substantial information about their structural features.     

Skeletal rearrangement of a bicylic 1,3-diphenyltrisilane during acid-induced dephenylation reactions

Protic and Lewis acid-induced dephenylation reactions of bis(tetramethylene)-tethered bicyclic 1,3-diphenyltrisilane 1 have been found to be accompanied by a facile skeletal rearrangement that forms the ring-contracted silyl-substituted bicyclic disilanes. For the reaction with a protic acid (HX), such as HCl/AlCl₃ and trifluoromethanesulfonic acid (TfOH), the protonation of the ipso-carbon of the phenyl group would be followed by the nucleophilic attack of X⁻ on the central silicon atom that induces the skeletal rearrangement. In the case of the reaction with boron trichloride, the same rearranged product was obtained as well, although the reaction mechanism is not clear. Dedicated to Professor Mitsuo Kira on the occasion of being awarded the 2005 Wacker Award and in recognition of his outstanding contribution to silicon chemistry.     

Toward new materials for organic electroluminescent devices: synthesis, structures, and properties of a series of 2,5-diaryl-3,4-diphenylsiloles

A series of 2,5-diaryl-3,4-diphenylsiloles, with various mono-substituted phenyl groups, extended pi-conjugated groups, and heteroaryl groups as aryl groups at the 2,5-positions, has been prepared by a one-pot synthesis from bis(phenylethynyl)silanes based on the intramolecular reductive cyclization followed by the palladium-catalyzed cross-coupling with aryl halides. Crystal structures and chemical reactivities toward the alkaline desilylation reactions have been studied on the 2,5-bis(p-mono-substituted phenyl)silole derivatives to elucidate the effects of the p-substituents. The UV-visible absorption and fluorescence spectra, and cyclic voltammetry of the 2,5-diarylsiloles have been systematically evaluated. Their photophysical properties as well as their electronic structures significantly depend on the nature of the 2,5-aryl groups.     

Character and determinant formulae of quasifinite representation of theW 1+∞ algebra

We diagonalize the Hilbert space of some subclass of the quasifinite module of theW ₁₊ algebra. States are classified according to their eigenvalues for infinitely many commuting charges and the Young diagrams. The parameter dependence of their norms is explicitly derived. The full character formulae of the degenerate representations are given as summation of the bilinear combinations of the Schur polynomials.     

Heisenberg realization for U q (sl n ) on the flag manifold

We give the Heisenberg realization for the quantum algebra U _q (sl _n ), which is written by theq-difference operator on the flag manifold. We construct it from the action of U _q (sl _n ) on theq-symmetric algebraA _q (Mat _n ) by the Borel-Weil-like approach. Our realization is applicable to the construction of the free field realization for U _q [2].     

Free boson representation ofU_q (\widehat{sl}_3 )

A representation of the quantum affine algebra of an arbitrary levelk is constructed in the Fock module of eight boson fields. This realization reduces the Wakimoto representation in theq 1 limit. The analogues of the screening currents are also obtained. They commute with the action of modulo total differences of some fields.On leave from Department of Physics, University of Tokyo, Tokyo 113, Japan.