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A new synthetic method for p-conjugated fused oligosiloles has been developed by combining a rhodium-catalyzed stitching reaction and subsequent remote conjugate elimination. Aromatization-driven 1,8-, 1,10-, or 1,12-dehydration was successfully utilized and up to 3 silole units were consecutively fused in a p-conjugated manner. The structural change upon conjugate elimination was confirmed by using X-ray crystallographic analysis, and the optical and electrochemical properties of a series of newly synthesized fused oligosiloles were also examined. [ABSTRACT FROM AUTHOR]

An efficient synthesis of 7H-benzo[e]naphtho[1,8-bc]silines has been developed by a rhodium-catalyzed [2 + 2 + 2] cycloaddition of alkynyl(8-alkynyl-1-naphthyl)silanes with internal alkynes. High chemoselectivity can be realized by employing P(2-MeOC6H4)3 as the ligand for rhodium. Preliminary investigation of its asymmetric variant has also been described to create a silicon stereogenic center with relatively high enantioselectivity. [ABSTRACT FROM AUTHOR]

It is highly important to develop efficient synthetic methods for various enantioenriched chiral compounds due to their high significance in our life. In this regard, asymmetric catalysis is one of the most attractive ways of synthesizing such compounds from achiral precursors. Although various methods have been developed for the enantioselective preparation of carbon-stereogenic compounds, the corresponding methods for silicon-stereogenic compounds are much less established. In particular, little progress has been made on catalytic enantioselective synthesis using prochiral organosilanes until recently. This account focuses on the recent progress in the catalytic enantioselective preparation of silicon-stereogenic organosilanes through desymmetrization of prochiral organosilanes. 1 Introduction 2 Desymmetrization of Diorganodihydrosilanes 3 Desymmetrization of Tetraorganosilanes 3.1 Desymmetrization through Cleavage of Silicon-Carbon Bonds 3.2 Desymmetrization without Cleavage of Silicon-Carbon Bonds 4 Conclusion [ABSTRACT FROM AUTHOR]

The study describes that the addition/cyclization of arylboronic acids to alkynals proceeds smoothly by the use of a rhodium/ diene catalyst, leading to cyclic allylic alcohols with a tetrasubstituted olefin and effective asymmetric catalysis is achieved by the use of chiral diene ligands. A range of arylboronic acids is efficiently coupled by employing a chiral bicyclo-[2.2.2]octadiene ligands with these substrates in very good enantiomeric excess.

Diindenosilole Si1, a silicon-bridged fulvalene derivative, was successfully reduced to its dianions using various alkali metals, and the structures were characterized by X-ray crystallographic analysis. Radical anions of Si1 as well as dianions of π-extended Si3 could also be synthesized, and the structural and physical properties were systematically compared. It was also found that the NMR spectra of dianions Si12– and Si32– show countercation and temperature dependency for their signal broadness, indicating the possible existence of thermal interconversion between closed-shell singlet states and open-shell triplet states. [ABSTRACT FROM AUTHOR]

New quinoidal fused oligosiloles containing an even number of silole units have been synthesized by a rhodium-catalyzed stitching reaction. Employing [RhCl(tfb)]2 as the catalyst significantly improved the stitching efficiency, and up to six siloles could be fused in quinoidal form. A systematic comparison of the physical properties of Si1-Si6' confirmed the unique trend in their LUMO levels, which become higher with longer π conjugation. To understand the origin of this unusual trend, theoretical calculations were also carried out using various model compounds, and the results indicated that the terminal indenylidene (cyclopentadienylidene) moieties in Si1-Si6 (Si1a-Si6a) are primarily responsible for this phenomenon through their frontier orbital correlations with the HOMO of the central polyene unit, which becomes higher in energy with longer π conjugation. [ABSTRACT FROM AUTHOR]

An intermolecular three-component arylsilylation of alkynes has been developed under mild palladium/copper cooperative catalysis. The reaction proceeds through syn-addition of an aryl group and a silyl group across the carbon-carbon triple bond of an alkyne. This represents the first transition-metal-catalyzed fully intermolecular arylsilylation of alkynes, and transformations of the resulting products have also been demonstrated. [ABSTRACT FROM AUTHOR]

Recent progress in copper-catalyzed asymmetric allylic substitution reactions with organoboron nucleophiles is reviewed. Wide availability, high functional group compatibility, and mild reaction conditions are the main advantages over conventional highly reactive organometallic nucleophiles. The use of diboron and silylboron reagents for the synthesis of enantioenriched allylboronates and allylsilanes is also included. 1 Introduction 2 Chirality Transfer of Enantioenriched Allylic Substrates with Organoboron Nucleophiles 3 Enantioselective Allylic Substitution of Achiral Substrates with Organoboron Nucleophiles 4 Enantioselective Allylic Substitution of Achiral Substrates with Other Boron-Based Nucleophiles 5 Conclusions. [ABSTRACT FROM AUTHOR]

A rhodium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles has been developed through a [2+ 2+2] cycloaddition of silicon-containing prochiral triynes with internal alkynes. High yields and enantioselectivities have been achieved by employing an axially chiral monophosphine ligand, and the present catalysis is also applicable to the asymmetric synthesis of a germaniumstereogenic dibenzogermole. Preliminary studies on the optical properties of these compounds are also described. [ABSTRACT FROM AUTHOR]

A new mode of metal-catalyzed polymerization reaction has been developed by exploiting the ability of 1,4-rhodium migration of an organorhodium(I) species. Specifically, it has been demonstrated that 3,3-diarylcyclopropenes undergo polymerization through an insertion-1,4- rhodium migration sequence by using an arylrhodium(I) initiator/catalyst to give poly(cyclopropylene-o-phenylene)s, which are difficult to synthesize by conventional polymerization methods. [ABSTRACT FROM AUTHOR]

A copper/N-heterocycliccarbene catalyzed hydroboration of carbondioxide has been developed to give a formic acid derivative selectivelyunder mild conditions. Investigations directed toward understandingthe catalytic cycle of this process have been carried out, and thehydroboration product can be directly used as a formylation reagentfor various amines. [ABSTRACT FROM AUTHOR]

A palladium-catalyzed decarboxylative [4 + 3] cyclization of γ-methylidene-δ-valerolactones with 1,1-dicyanocyclopropanes has been developed to produce cycloheptane derivatives in a convergent manner. This method can be applied to the synthesis of azepanes by reacting with aziridines, and their asymmetric variants have also been described. In addition, selective ring-expansion reactions can be achieved for certain γ-methylidene-δ-valerolactones to give nondecarboxylated nine-membered lactones. [ABSTRACT FROM AUTHOR]

Paper based on a presentation at the 14th International Symposium on Organometallic Chemistry Directed Towards Organic Synthesis (OMCOS-14), 2-6 August 2007, Nara, Japan. Other presentations are published in this issue, pp. 807-1194A new type of reagent, γ-methylidene-δ-valerolactones, has been devised, which acts as a four-carbon unit in a Pd-catalyzed cycloaddition reaction through the formation of a 1,4-zwitterionic species. The utility has been demonstrated in the context of stereoselective [4+3] cycloaddition with nitrones to provide highly functionalized 1,2-oxazepines, including the asymmetric variant with high enantioselectivity. [ABSTRACT FROM AUTHOR]

Addition of arylmagnesium bromides to aryl(alkyl)acetylenes proceeded in the presence of an iron catalyst and a N-heterocyclic carbene ligand to give high yields of the corresponding alkenylmagnesium reagents, which were transformed into tetrasubstituted alkenes by subsequent treatment with electrophiles. [ABSTRACT FROM AUTHOR]

A rhodium-catalyzed asymmetric addition of readily available potassium organotrifluoroborates to both N-tosyl and N-nosyl ketimines has been developed. High enantioselectivity has been achieved by using a chiral diene ligand, and the nosyl group of the addition products can be easily removed while retaining the enantiomeric purity. [ABSTRACT FROM AUTHOR]

A rhodium-catalyzed 1,4-addition of sodium tetraarylborates to β,β-disubstituted α,β-unsaturated esters has been developed. Highly efficient asymmetric catalysis has also been described to create quaternary carbon stereocenters at the β-position of esters by tuning the ester group of substrates and employing a readily available chiral diene ligand. [ABSTRACT FROM AUTHOR]

A new synthetic method of spirooxindole derivatives has been developed by way of a palladium-catalyzed decarboxylative cyclization of γ-methylidene-δ-valerolactones with isatins. By employing a newly prepared phosphoramidite ligand, the reaction proceeds smoothly with excellent diastereoselectivity. Preliminary results of its application to asymmetric catalysis using a chiral phosphoramidite ligand are also described. [ABSTRACT FROM AUTHOR]

A new synthetic method of multisubstituted nipecotic acid (piperidine-3-carboxylic acid) derivatives has been developed by way of palladium-catalyzed decarboxylative cyclization of γ-methylidene-δ-valerolactones with imines. By employing the diethoxyphosphinoyl group as the N-protecting group for imines, the reaction proceeds smoothly with high diastereoselectivity. The products thus obtained can be further derivatized with high efficiency under simple reaction conditions. [ABSTRACT FROM AUTHOR]

A nonenzymatic kinetic resolution of tertiary homoallyl alcohols has been developed through a rhodium-catalyzed retro-allylation reaction under simple conditions. Selectivity factors of up to 12 have been achieved by employing (R)-H8-binap as the ligand, and the reaction can be conducted on a preparative scale. [ABSTRACT FROM AUTHOR]

A new synthetic method of chiral allylsilanes has been developed through a rhodium-catalyzed asymmetric 1,4-addition of alkenyl2-(hydroxymethyl)phenyldimethylsilanes to -silyl ,-unsaturated ketones. By employing (S,S)-Ph-bod as a ligand, a range of alkenyl nucleophiles have been installed to these substrates in high yield and enantiomeric excess. The resulting allylsilanes can be used for stereoselective intramolecular allylation reactions to control two contiguous tertiary and quaternary stereocenters. [ABSTRACT FROM AUTHOR]

A single-molecule single-electron transistor (SM-SET) consisting of a π-conjugated quinoidal-fused oligosilole derivative, Si-2, of radius 0.75 nm and heteroepitaxial spherical (HS) Au/Pt nanogap electrodes is demonstrated. Si-2 with two inner silicon atoms and two ethylenethiol groups at both ends is chemisorbed by an S–Au bond between HS-Au/Pt nanogap electrodes fabricated by combining electron-beam lithography and electroless Au plating. An ideal Coulomb staircase, Coulomb oscillation, and Coulomb diamond were observed using the 1.5 nm Si-2 SM-SET, which were supported by theoretical results based on the orthodox model. [ABSTRACT FROM AUTHOR]

A palladium-catalyzed decarboxylative cyclization of γ-methylidene-δ-valerolactones with isocyanides has been developed to afford conjugated cyclopentenimines under mild conditions. Some preliminary results toward the development of an asymmetric variant have also been described. [ABSTRACT FROM AUTHOR]