High‐Yield Diastereoselective Synthesis of Planar Chiral [2]‐ and [3]Rotaxanes Constructed from per‐Ethylated Pillar[5]arene and Pyridinium Derivatives

Planar chiral [2]‐ and [3]rotaxanes constructed from pillar[5]arenes as wheels and pyridinium derivatives as axles were obtained in high yield using click reactions. The process of rotaxane formation was diastereoselective; the obtained [2]rotaxane was a racemic mixture consisting of (pS, pS, pS, pS, pS) and (pR, pR, pR, pR, pR) forms of the per‐ethylated pillar[5]arene ( C2 ) wheel, and other possible types of the [2]rotaxane did not form. Isolation of the enantiopure [2]rotaxanes with one axle through (pS, pS, pS, pS, pS)‐ C2 or (pR, pR, pR, pR, pR)‐ C2 wheels was accomplished. Furthermore, pillar[5]arene‐based [3]rotaxane was successfully synthesized by attachment of two pseudo [2]rotaxanes onto a bifunctional linker. [3]Rotaxane formed in a 1:2:1 mixture with one axle threaded through two (pS, pS, pS, pS, pS)‐ C2 , one (pS, pS, pS, pS, pS)‐ C2 and one (pR, pR, pR, pR, pR)‐ C2 (meso form), or two (pR, pR, pR, pR, pR)‐ C2 wheels. The [3]rotaxane enantiomers and the meso form were successfully isolated using appropriate chiral HPLC column chromatography. The procedure developed in this study is the starting point for the creation of pillar[5]arene‐based interlocked molecules.     

Counterion distribution and many-body interaction in charged dendrimer solutions

Coarse-grained molecular dynamics simulations are performed to study the structural formation, counterion distribution and effective interaction on charged dendrimers in an aqueous solution. In particular, the many-body effects in triplet systems are clarified. The conformation of a dendrimer molecule depends on the size of counterions, and the counterion distribution can be scaled by the gyration radius of a dendrimer molecule. Two-body and three-body interactions have been numerically investigated, and the results indicate both similarities and differences between dendrimer solutions and other soft colloidal systems, such as star polymer solutions.     

Stereoselective coupling reaction of dimethylzinc and alkyne toward nickelacycles

Ni catalyst promotes the three-component coupling reaction of vinyloxacyclopropane, alkyne, and dimethylzinc to provide 2,5-heptadienyl alcohol in high yields. Vinylcyclopropane also participates in a similar three-component coupling reaction to afford dimethyl (α-heptadienyl)malonate with excellent E-stereoselectivity.     

The “Borrowing Hydrogen Strategy” by Supported Ruthenium Hydroxide Catalysts: Synthetic Scope of Symmetrically and Unsymmetrically Substituted Amines

The N‐alkylation of ammonia (or its surrogates, such as urea, NH₄HCO₃, and (NH₄)₂CO₃) and amines with alcohols, including primary and secondary alcohols, was efficiently promoted under anaerobic conditions by the easily prepared and inexpensive supported ruthenium hydroxide catalyst Ru(OH)_x/TiO₂. Various types of symmetrically and unsymmetrically substituted “tertiary” amines could be synthesized by the N‐alkylation of ammonia (or its surrogates) and amines with “primary” alcohols. On the other hand, the N‐alkylation of ammonia surrogates (i.e., urea and NH₄HCO₃) with “secondary” alcohols selectively produced the corresponding symmetrically substituted “secondary” amines, even in the presence of excess amounts of alcohols, which is likely due to the steric hindrance of the secondary alcohols and/or secondary amines produced. Under aerobic conditions, nitriles could be synthesized directly from alcohols and ammonia surrogates. The observed catalysis for the present N‐alkylation reactions was intrinsically heterogeneous, and the retrieved catalyst could be reused without any significant loss of catalytic performance. The present catalytic transformation would proceed through consecutive N‐alkylation reactions, in which alcohols act as alkylating reagents. On the basis of deuterium‐labeling experiments, the formation of the ruthenium dihydride species is suggested during the N‐alkylation reactions.     

Heterogeneously catalyzed efficient hydration of alkynes to ketones by tin-tungsten mixed oxides

The Sn–W mixed oxide prepared by calcination of the Sn–W mixed hydroxide precursor with a Sn/W molar ratio of 2:1 at 800 °C (SnW2‐800) acts as an efficient heterogeneous catalyst for the hydration of alkynes. Structurally diverse terminal and internal alkynes, including aromatic, aliphatic, and double‐bond‐containing ones, can be converted into the corresponding ketones in moderate to high yields. The catalytic activity of SnW2‐800 is much higher than those of previously reported heterogeneous catalysts and commonly utilized acid catalysts. The observed catalysis was truly heterogeneous, and the retrieved catalyst can be reused at least three times with retention of its high catalytic performance. The reaction rate for the SnW2‐800‐catalyzed hydration was decreased by addition of 2,6‐lutidine and the hydration hardly proceeded in the presence of an equimolar amount of this compound with respect to that of the Brønsted acid sites in SnW2‐800. Therefore, the present hydration is mainly promoted by the Brønsted acid sites in SnW2‐800.     

On-line microfluidic sensor integrated with a micro array electrode and enzyme-modified pre-reactor for the real-time monitoring of blood catecholamine

We developed an on-line microfluidic sensing device with an interdigitated array (IDA) electrode and a micro pre-reactor for the real-time monitoring of blood catecholamine (CA) and succeeded in the highly sensitive detection of dopamine (DA) in the presence of L-ascorbic acid (AA). Our device exhibits the lowest detection limit (110 ± 10 pM (S/N=3)), of reported catecholamine sensors. The improvement in sensitivity results from the high redox cycling of DA and the increase in the mass transfer rate per unit time onto the IDA electrode achieved by the flow measurement. The pre-reactor was integrated upstream in the micro flow channel to eliminate AA. A large number of rectangular shaped micropillars, which were modified with ascorbate oxidase, were formed in the pre-reactor to increase the surface area. The flow was disturbed by the two dimensional micropillar arrangement. This structure enables us to increase the elimination efficiency for AA. As a result, we achieved both the continuous and highly selective detection of 1 nM DA with complete elimination of 10 μM AA in the sample solution without employing any selective membrane such as Nafion, whose use reduces sensitivity due to the low diffusion coefficient of DA inside the membrane.     

Emulsion and dispersion polymerization of styrene in the presence of PEO macromonomers with p-vinylphenylalkyl end groups

Poly(ethylene oxide) (PEO) macromonomers with α-p-vinylphenylalkyl (propyl, pentyl, and hexyl) and ω-hydroxy end groups were applied to emulsion and dispersion polymerization of styrene as reactive emulsifiers and dispersants in water and in methanol-water mixture (9:1 v/v), respectively. Nearly monodisperse microspheres of submicron to micron size were obtained. Particle size in the emulsion system was one or half order of magnitude smaller than that in the dispersion system, while in both systems the size decreased approximately according to minus one half power of the macromonomer concentration in weight. The particle size was substantially independent on the PEO chain length and also on the spacer alkyl chain length of the α-polymerizing end group. The total weight of the PEO chains incorporated by copolymerization into the particle surfaces (shells), relative to that of styrene polymerized into the particle cores, appears to be a key factor for controlling the particle size. To cite this article: K. Landfester et al., C. R. Chimie 6 (2003).     

Efficient and Selective Formation of Unsaturated Carboxylic and Phenylacetic Acids from Diketene

A nickel catalyst promotes the multicomponent coupling reaction of diketene, an alkyne, and Me₂Zn to provide 3‐methylene‐4‐hexenoic acids in excellent yields. Under similar conditions, the combination of the nickel catalyst and Et₂Al(OEt) promotes a cycloaddition reaction involving dimerization of an alkyne to furnish phenylacetic acids. In the presence of PPh₃, a formal [2+2+1+1] cycloaddition reaction proceeds to afford regioisomeric phenylacetic acids via cleavage of the C?C bond.     

Palladium-catalyzed asymmetric alkylation of 2-azaallyl acetates for the synthesis of β-carboxyaspartic acid derivatives

Palladium-catalyzed asymmetric alkylation of 2-azaallyl acetate, N-(diphenylmethylene)acetoxyglycine ester with a sodium salt of malonate ester was successfully carried out. High enantioselectivities were achieved using sodium dimethyl methylmalonate (98%ee) or sodium dimethyl malonate (93%ee) as a nucleophile with t-butyl ester of 2-azaallyl acetate in the presence of (S)-BINAP in acetonitrile.