Akira Tsubouchi

Bio: Akira Tsubouchi is an academic researcher from Tokyo University of Agriculture and Technology. The author has contributed to research in topics: Allylic rearrangement & Silylation. The author has an hindex of 19, co-authored 146 publications receiving 1280 citations. Previous affiliations of Akira Tsubouchi include University of California, Santa Barbara & University of Tokyo.

One- and Two-Metal Ion Catalysis of the Hydrolysis of Adenosine 3‘-Alkyl Phosphate Esters. Models for One- and Two-Metal Ion Catalysis of RNA Hydrolysis

Abstract: Adenosine 3‘-O(PO2-)OCH2R phosphate esters have been synthesized with R = 8-hydroxyquinol-2-yl (1a) and 8-(hydroxyquinolyl)-2-methylene (1b). The adenosine 3‘-O(PO2-)OCH2R structure has the essential features of an RNA dinucleotide. Equilibrium binding studies with metal ions Mg2+, Zn2+, Cu2+, and La3+ have been carried out with 1a, 1b, HOCH2R (7a and 7b), and 8-hydroxyquinoline (8), and equilibrium constants (Kas) have been determined for the formation of 1:1 (L)Mn+ complexes. The hydrolysis of 1a and 1b as well as (1a)Mn+ and (1b)Mn+ species are first order in HO-. The rate enhancement for hydrolysis of 1a by complexation with metal ions is as follows: ∼105 with Zn2+, ∼103 with Mg2+, ∼105 with Cu2+, and ∼109 with La3+. Molecular modeling indicates that metal ions ligated to the 8-hydroxyquinoline moiety in the complexes (1a)Mn+ and (1b)Mn+ catalyze 1a and 1b hydrolysis by interacting as Lewis acid catalysts with the negatively charged oxygen atom of the phosphate group. In the instance of La3+ complexe...

Copper(I) tert-Butoxide-Promoted 1,4 Csp2-to-O Silyl Migration: Generation of Vinyl Copper Equivalents and Their Stereospecific Cross-Coupling with Allylic, Aryl, and Vinylic Halides

Abstract: Successive treatment of the (Z)-γ-trimethylsilyl allylic alcohols with copper(I) tert-butoxide and allylic halides followed by the tetrabutylammonium fluoride-assisted hydrolysis produced the allylation products, 2,5-alkadien-1-ols, with complete retention of configuration. Similar treatment of the organometallic intermediates with aryl and vinylic halides in the presence of palladium(0) catalyst gave the corresponding cross-coupling products in good yields. The stereoselective preparation of the starting materials is also described.

Lanthanide-containing molecular and supramolecular polymetallic functional assemblies.

Abstract: As a result of the different degrees of stabilization experienced by the 4f, 5d, and 6s orbitals occurring upon ionization of the neutral metal, the lanthanides (La-Lu, Z ) 57-71) exist almost exclusively in their trivalent state Ln(III) ([Xe]4fn, n ) 0-14) in coordination complexes or supramolecular assemblies.1 Except for some arene compounds involving bulky substituted benzenes or cyclo-octatetraenes,2 covalence plays a minor role in Ln-ligand dative bonds and the nature of the coordination sphere is controlled by a subtle interplay between electrostatic interactions and interligand steric constraints.3 Variable coordination numbers (6 e CN e 12) and geometries are thus observed in lanthanide complexes, leading to limited success in the design of molecular architectures with predetermined structures.3,4 Although rigid or semirigid receptors may help to control the coordination sphere according to the lock-and-key and induced fit concepts,5 detailed studies of lanthanide solvates with water or acetonitrile suggest that trivalent lanthanides display a tendency to adopt nine-coordinate tricapped trigonal prismatic (TTP) arrangements around the metal ion in the solid state. In solution, the picture is a little more subtle:6 in water, for instance, large Ln(III) ions at the beginning of the series (Ln ) La-Nd) adopt TTP geometries, which are gradually transformed into eight-coordinate square antiprismatic (SAP) arrangements for small Ln(III) ions (Ln ) Tb-Lu), equilibria between CN ) 8 and CN ) 9 being observed for Ln ) Nd-Tb.7 The systematic contraction of the ionic radii observed when going from Ln ) La to Lu (often referred to as the lanthanide contraction)8 explains this trend and increases electrostatic bonding for heavier lanthanides, but this variation is so smooth and limited (15% contraction between La and Lu and ≈1% between two successive lanthanides) that selective recognition and incorporation into organized supramolecular architectures remains challenging.5 A rational access to extended polymetallic lanthanide-containing assemblies with predictable and controlled geometries is consequently very limited, and pioneer work in this field has focused on poorly characterized intricate mixtures of complexes in solution which are ‘transformed’ into well-defined solid-state clusters or networks through crystallization processes involving a rich palette of † Institute of Molecular and Biological Chemistry, Lausanne. E-mail: Jean-Claude.Bunzli@epfl.ch. ‡ Department of Inorganic, Analytical and Applied Chemistry, Geneva. E-mail: Claude.Piguet@chiam.unige.ch.

Silicon-based cross-coupling reaction: an environmentally benign version

Abstract: Much attention has been paid to the cross-coupling reaction of organosilicon compounds due to their stability, non-toxicity, and natural abundance of silicon. In addition, the silicon-based cross-coupling has many advantages over other cross-coupling protocols. Successful examples of the silicon-based cross-coupling reaction are reviewed, focusing especially on the advances made in the last decade. Having had a number of highly effective palladium catalysts developed mainly for other cross-coupling reactions, the development of the silicon-based protocol owes heavily to the design of organosilicon reagents which effectively undergo transmetalation, a key elemental step of the silicon-based cross-coupling reaction. This tutorial review thus classifies various organosilicon reagents depending on substituents on silicon and surveys their cross-coupling reactions with various electrophiles.