Shoko Yamazaki

A mild and efficient Si (111) surface modification via hydrosilylation of activated alkynes

A new Si surface modification with organic groups via hydrosilylation at room temperature is reported. A hydrogen-terminated Si (111) surface was reacted with activated alkynes such as propiolate esters, propiolic acid, but-3-yne-2-one, propiolonitrile and phenylacetylene at room temperature for 24–40 h to give modified surfaces. The coverage ratio was estimated to be 31–56% by XPS analysis. This surface modification method is mild, highly efficient and procedurally simple. The novel surfaces modified with various organic functional groups are expected to have interesting utilities.

Lewis Acid Promoted Reactions of Ethenetricarboxylates with Allenes: Synthesis of Indenes and γ-Lactones via Conjugate Addition/Cyclization Reaction

Indenes are important core structures in organic chemistry. Few simple arylallenes have been used to construct indene skeletons by Friedel-Crafts reaction. Lewis acid catalyzed reaction of ethenetricarboxylates 1 and arylallenes has been examined in this study. The reaction of arylallenes and ethenetricarboxylate triesters with SnCl(4) gave indene derivatives efficiently, via a conjugate addition/Friedel-Crafts cyclization reaction. On the other hand, the reactions of 1,1-diethyl 2-hydrogen ethenetricarboxylate and arylallenes or alkylallenes with SnCl(4) at -78 degrees C or room temperature and subsequent treatment with Et(3)N gave gamma-lactones. The reactions of triethyl ethenetricarboxylate and 1,1-dialkylallenes with SnCl(4) at room temperature also gave gamma-lactones.

Efficient Synthesis of Methylenetetrahydrofurans and Methylenepyrrolidines by Formal [3+2] Cycloadditions of Propargyl Substrates

Recent developments concerning the synthesis of methylenetetrahydrofurans and methylenepyrrolidines by one-pot formal [3+2] cycloadditions involving propargylic (and allylic) alcohols and amines with electrophilic alkenes are described. The synthetic methods provide powerful tools to prepare highly functionalized oxygen- and nitrogen-containing five-membered ring systems. The reactions can be effectively promoted by base, base/transition metals, and Lewis acids, depending on the substrates.

Microwave synthesis and electrospectrochemical study on ruthenium(II) polypyridine complexes

A microwave assisted simple method was developed to prepare various ruthenium(II) polypyridine complexes rapidly with a high yield. For example, [Ru(Hdpa)3](ClO4)2 was prepared from RuCl3·3H2O in a few minutes in more than 90% yield. The oxidation potentials were determined for over 50 Ru(II) polypyridine complexes in acetonitrile to estimate the electrochemical ligand (L) parameters, from which we calculated oxidation potentials of various polypyridine Ru complexes. A linear relation between calculated and observed values indicates the additivity of the ligand contribution to the Ru(III)/Ru(II) potential. Moreover, the linear relation between the average difference of 13C-NMR chemical shifts of 4,4′ carbon atoms of bipyridine ligands and oxidation potentials for the bis bipyridine complexes, [Ru(bpy)2L]2+, was found with respect to the π-donor/-acceptor properties of L. The relation can be explained by quantum mechanical calculation using gaussian-98.

Zn(OTf)2-Catalyzed Reactions of Ethenetricarboxylates with 2-Aminobenzaldehydes Leading to Tetrahydroquinoline Derivatives

Quinolines are an important class of compounds, and the development of new efficient synthetic strategies for the construction of quinolines is of considerable interest. Zinc triflate catalyzed cyclization of ethenetricarboxylate derivatives with 2-aminobenzaldehydes has been examined. The reaction of ethenetricarboxylate with 2-aminobenzaldehydes in the presence of zinc triflate (0.2 equiv) at 80 degrees C in ClCH(2)CH(2)Cl gave bridged tetrahydroquinoline derivatives in 15-95% yield. On the other hand, the reaction at room temperature in CH(2)Cl(2) gave hydroxy tetrahydroquinoline derivatives in 38-90% yield. Heating the hydroxy tetrahydroquinolines with zinc triflate (0.2 equiv) at 80 degrees C in ClCH(2)CH(2)Cl led to the bridged tetrahydroquinoline derivatives in 75-96% yield. Thermal reaction of the bridged tetrahydroquinolines (180 degrees C) gave indole derivatives regioselectively.

A Lewis acid-promoted cyclization of ethenetricarboxylate derivative aromatic compounds. Novel syntheses of oxindoles and benzofuranones via Friedel–Crafts intramolecular Michael addition

A novel cyclization reaction of ethenetricarboxylate derivative aromatic compounds in the presence of various Lewis acids gave benzo-annulated cyclic compounds such as oxindole and benzofuran derivatives via Friedel-Crafts intramolecular Michael addition in high yields. For example, the reaction of diethyl 2-[(N-methyl-N-phenylcarbamoyl)methylene]malonate (1a) in the presence of ZnCl2 at room temperature gave diethyl 2-(1-methyl-2-oxoindolin-3-yl)malonate (2a) in 98% yield. The reactions also proceeded with a catalytic amount of a Lewis acid such as AlCl3, ZnCl2, ZnBr2, Sc(OTf)3, or InBr3.

Lewis acid-promoted cyclization of heteroatom-substituted enynes

Lewis acid-promoted cyclizations of heteroatom-substituted enynes have been examined. The reaction of enynes and bearing silicon substituents on an alkyne afforded the halogenated five-membered gamma-lactones and gamma-lactams as the main products. The reaction of substrates and having 2-phosphonoacrylate instead of malonate also gave halogenated five-membered cyclic compounds and as the major products. The cyclized products are highly substituted and potentially useful for further synthetic transformations.

Active Role of Hydrogen Bonds in Rupe and Meyer-Schuster Rearrangements.

Rupe and Meyer-Schuster rearrangements for the R2C(OH) [Formula: see text] C⋮C [Formula: see text] H + H3O(+) and (H2O)9 model (R = methyl and phenyl groups) have been investigated by the use of density functional theory calculations. In the substrate R2C(OH) [Formula: see text] C⋮CH catalyzed by H3O(+)(H2O), three reaction channels, the two rearrangements and SN (nucleophilic substitution), were predicted by the frontier molecular orbital theory. The SN (the OH-group exchange) path was found to have a large activation energy. For 2-methylbut-3-yn-2-ol (R = Me), the Rupe rearrangement has been found to be much more favorable than the Meyer-Schuster rearrangement. For 1,1-diphenylprop-2-yn-1-ol (R = Ph), the occurrence of Meyer-Schuster rearrangement is very likely with the small activation energy. Both rearrangements do not involve the carbonium ion intermediates. However, the calculated geometries of the first transition state are carbonium-ion-like. Dehydration and hydration may occur via the intermolecular proton relay along the hydrogen-bond chains. Minimal models were proposed to represent reaction mechanisms of both rearrangements.

Lewis acid-promoted cyclization reactions of alkenyl ethenetricarboxylates: stereoselective synthesis of 2-oxotetrahydrofurans and 2-oxopyrrolidines.

Lewis acid-promoted intramolecular reactions of alkenyl ethenetricarboxylates and the corresponding amides have been examined. Reaction of allyl ethenetricarboxylates and the amides with Lewis acids (1-2 equiv) such as TiCl4, TiBr4, AlCl3, and AlBr3 gave 3,4-trans-halogenomethyl 2-oxotetrahydrofuran and pyrrolidine derivatives stereoselectively in high yields. The stereochemistries were determined by NOE experiments. Reaction of alkyl-substituted allylic ethenetricarboxylates with Lewis acids gave chloro 2-oxotetrahydrofurans and pyrans. For some alkyl-substituted substrates, cationic intermediates may be formed under the reaction conditions, and rearranged products have been obtained.

Solid-state thiotropolone: an extremely rapid intramolecular proton transfer.

Through variable-temperature solution-state NMR and molten- and solid-state CP/MAS (13)C NMR spectra, thiotropolone is found to exist as two rapidly equilibrated tautomeric structures, thione and enethiol, even in the solid state far below the melting point. The crystal structure shows an almost perpendicular packing, suggesting that the intramolecular hydrogen bond is dominant.