Masaya Sawamura

Reversible Mechanochromic Luminescence of [(C6F5Au)2(μ-1,4-Diisocyanobenzene)]

Reversible mechanochromic luminescence of [(C6F5Au)2(mu-1,4-diisocyanobenzene)] is reported. Grinding of the complex induced a photoluminescent color change, which was restored by exposure to a solvent. This cycle was repeated 20 times with no color degradation in the emissions. Their optical properties, X-ray crystallographic analysis, IR, and XRD measurements strongly suggested that the change in the molecular arrangement is responsible for this mechanochromic property. Intermolecular aurophilic bondings presumably play a key role in the altered emission.

Stacking of conical molecules with a fullerene apex into polar columns in crystals and liquid crystals

Polar liquid crystalline materials can be used in optical and electronic applications, and recent interest has turned to formation strategies that exploit the shape of polar molecules and their interactions to direct molecular alignment. For example, banana-shaped molecules align their molecular bent within smectic layers, whereas conical molecules should form polar columnar assemblies. However, the flatness of the conical molecules used until now and their ability to flip have limited the success of this approach to making polar liquid crystalline materials. Here we show that the attachment of five aromatic groups to one pentagon of a C60 fullerene molecule yields deeply conical molecules that stack into polar columnar assemblies. The stacking is driven by attractive interactions between the spherical fullerene moiety and the hollow cone formed by the five aromatic side groups of a neighbouring molecule in the same column. This packing pattern is maintained when we extend the aromatic groups by attaching flexible aliphatic chains, which yields compounds with thermotropic and lyotropic liquid crystalline properties. In contrast, the previously reported fullerene-containing liquid crystals all exhibit thermotropic properties only, and none of them contains the fullerene moiety as a functional part of its mesogen units. Our design strategy should be applicable to other molecules and yield a range of new polar liquid crystalline materials.

Directed Ortho Borylation of Functionalized Arenes Catalyzed by a Silica-Supported Compact Phosphine−Iridium System

An immobilized monophosphine-Ir system, which was prepared in situ from [Ir(OMe)(cod)](2) and a silica-supported, compact phosphine, showed high activities and selectivities for the borylation of aromatic C-H bonds with bis(pinacolato)diboron. This system was effective not only for the borylation of benzene but also for the ortho borylation of arenes with directing groups, such as ester, amide, sulfonate, acetal, alkoxymethyl, and chloro groups, under mild reaction conditions.

Asymmetric synthesis of β-hydroxy-α-alkylamino acids by asymmetric aldol reaction of α-isocyanocarboxylates catalyzed by chiral ferrocenylphosphine-gold(I) complexes

Abstract Aldol reaction of methyl α-isocyanocarboxylates (CNCH(R)COOMe: R = H, Me, Et, i -Pr) with benzaldehyde or acetaldehyde in the presence of 0.5–1.0 mol% of a chiral (aminoalkyl)ferrocenylphosphine-gold(I) complex gave optically active 4-methoxycarbonyl-4,5-dialkyl-2-oxazolines with high enantioselectivity in a quantitative yield. The oxazolines were converted into optically active β-hydroxy-α-alkylamino acid methyl esters.

Palladium-Catalyzed γ-Selective and Stereospecific Allyl−Aryl Coupling between Acyclic Allylic Esters and Arylboronic Acids

Reactions between acyclic (E)-allylic acetates and arylboronic acids in the presence of a palladium catalyst prepared from Pd(OAc)(2), phenanthroline (or bipyridine), and AgSbF(6) (1:1.2:1) proceeded with excellent gamma-selectivity to afford allyl-aryl coupling products with E-configuration. The reactions of alpha-chiral allylic acetates took place with excellent alpha-to-gamma chirality transfer with syn stereochemistry to give allylated arenes with a stereogenic center at the benzylic position. The reaction tolerated a broad range of functional groups in both the allylic acetates and the arylboronic acids. Furthermore, gamma-arylation of cinnamyl alcohol derivatives afforded gem-diarylalkane derivatives containing an unconjugated alkenic substituent. The synthetic utility of this method was demonstrated by its utilization in an efficient synthesis of (+)-sertraline, an antidepressant agent. The observed gamma-regioselectivity and E-1,3-syn stereochemistry were rationalized based on a Pd(II) mechanism involving transmetalation between a cationic mono(acyloxo)palladium(II) complex and arylboronic acid, and directed carbopalladation followed by syn-beta-acyloxy elimination. The results of stoichiometric reactions of palladium complexes related to possible intermediates were fully consistent with the proposed mechanism.

Direct enantio-convergent transformation of racemic substrates without racemization or symmetrization

Asymmetric reactions that transform racemic mixtures into enantio-enriched products are in high demand, but classical kinetic resolution produces enantiopure compounds in <50% yield even in an ideal case. Many deracemization processes have thus been developed including dynamic kinetic resolution and dynamic kinetic asymmetric transformation, which can provide enantio-enriched products even after complete conversion of the racemic starting materials. However, these dynamic processes require racemization or symmetrization of the substrates or intermediates. We demonstrate a direct chemical enantio-convergent transformation without a racemization or symmetrization process. Copper(I)-catalysed asymmetric allylic substitution of a racemic allylic ether afforded a single enantiomer of an α-chiral allylboronate with complete conversion and high enantioselectivity (up to 98% enantiomeric excess). One enantiomer of the substrate undergoes an anti-SN2′-type reaction whereas the other enantiomer reacts via a syn-SN2′ pathway. The products, which cannot be prepared by dynamic procedures, have been used to construct all-carbon quaternary stereocentres. Processes that convert racemic chiral compounds into enantioenriched chiral products are highly sought after. Here, in a copper-catalysed borylation reaction one enantiomer of a cyclic allylic ether reacts with anti-stereoselectivity and the other reacts with syn-stereoselectivity. The starting material is not easily racemized and this new process is dubbed an enantioconvergent reaction.

Copper(I)-Catalyzed Asymmetric Monoborylation of 1,3-Dienes: Synthesis of Enantioenriched Cyclic Homoallyl- and Allylboronates

Copper(I)-catalyzed asymmetric monoborylation of 1,3-dienes has been developed. We describe the production of either optically active homoallyl- or allylboronates with high regio- and enantioselectivity (88-97% ee) through monoborylation of 1,3-dienes. The reaction with 1,3-cyclohexadiene derivatives afforded the corresponding enantioenriched homoallyboronates. By simply changing the reaction conditions, a drastic change of product preference between homoallyl- and allylboronates was found in the reaction of 1,3-cyclopentadiene and 1,3-cycloheptadiene.

Functionalized Fullerene as an Artificial Vector for Transfection

Materials. Dulbecco modified Eagle medium (DMEM) was purchased from Sigma, fetal bovine serum (FBS) from Equitech-Bio. The green fluorescent protein (GFP) vector plasmid (pGreen LANTERN-1) was purchased from Life Technologies and was propagated by the lysozyme-Triton procedure. Vector DNA was purified by the CsCl equilibrium density gradient centrifugation and phenol extractions in the presence of 1% sodium dodecyl sulfate (SDS). Final concentration of plasmid was determined by absorbance at 260 nm. Organic solvents were distilled and, when necessary, dried over molecular sieves 4Å before use.

Asymmetric synthesis catalyzed by chiral ferrocenylphosphine transition metal complexes. 10 gold(i)-catalyzed asymmetric aldol reaction of isocyanoacetate☆

Abstract Optically active ferrocenylbisphosphine ligands containing 2-(dialkylamino)ethylamino group on the ferrocenylmethyl position have been prepared and used for the gold(I)-catalyzed asymmetric aldol reaction of isocyanoacetate with aldehydes. Six-membered ring amines, such as morpholino or piperidino group, at the terminal of the side chain were most stereoselective to give optically active trans-4- methoxycarbonyl-5-alkyl-2-oxazolines (up to 97% ee) with high enantio- and diastereoselectivity in a quantitative yield.

Copper(I)-Catalyzed Substitution of Propargylic Carbonates with Diboron: Selective Synthesis of Multisubstituted Allenylboronates

A versatile synthetic method for the preparation of the allenylboronates, Cu(I)-catalyzed reaction of propargylic carbonates with a diboron, is described. A Cu(O-t-Bu)-Xantphos catalyst system was effective for the preparation of various allenylboron compounds, allenylboronates with different substitution patterns, those with functional groups, and an axially chiral one. The Lewis acid promoted stereoselective addition to aldehydes leading to homopropargylic alcohols showed the usefulness of the new allenylboronates.