Showing papers in "Chemical Record in 2011"

Hydroarylation of alkynes catalyzed by nickel.

Abstract: Nickel catalysts derived from bis(1,5-cyclooctadiene)nickel [Ni(cod)2] and trialkylphosphines effect hydroarylation of alkynes through functionalization of C–H bonds of arenes including benzo-fused five-membered heteroarenes, pyridine-N-oxides, pyridines, 2-pyridones, and perfluoroarenes The reactions proceed with excellent stereo- and regioselectivity to give disubstituted arylethenes in good yields Use of Lewis acid (LA) co-catalysts is crucial for success in reactions of imidazoles, pyridines, and 2-pyridones; it is possible that coordination of the LA to the nitrogen or oxygen functionalities of such substrates increases the reactivity of their C–H bonds towards nickel(0) species DOI 101002/tcr201100023

Transition-metal-catalyzed aminations and aziridinations of C-H and C=C bonds with iminoiodinanes.

Abstract: Catalytic insertion or addition of a metal-imido/nitrene species, generated from reaction of a transition-metal catalyst with iminoiodanes, to CH and CC bonds offers a convenient and atom economical method for the synthesis of nitrogen-containing compounds. Following this groundbreaking discovery during the second half of the last century, the field has received an immense amount of attention with a myriad of impressive metal-mediated methods for the synthesis of amines and aziridines having been developed. This review will cover the significant progress made in improving the efficiency, versatility and stereocontrol of this important reaction. This will include the various iminoiodanes, their in situ formation, and metal catalysts that could be employed and new ligands, both chiral and non-chiral, which have been designed, as well as the application of this functional group transformation to natural product synthesis and the preparation of bioactive compounds of current therapeutic interest. DOI 10.1002/tcr.201100018

Nanoscale polyoxometalate‐based inorganic/organic hybrids

Abstract: The latest advances in the area of polyoxometalate (POM)-based inorganic/organic hybrid materials prepared by self-assembly, covalent modification, and supramolecular interactions are presented. This Review is composed of five sections and documents the effect of organic cations on the formation of novel POMs, surfactant encapsulated POM-based hybrids, polymeric POM/organic hybrid materials, POMs-containing ionic crystals, and covalently functionalized POMs. In addition to their role in the charge-balancing, of anionic POMs, the crucial role of organic cations in the formation and functionalization of POM-based hybrid materials is discussed.

Molecular catalysis for fullerene functionalization.

Abstract: This account highlights elements of our efforts to explore new functionalization chemistry of fullerenes using molecular catalysts since 2006. These endeavors have led to the development of new reactions such as (i) organoboron addition to fullerenes, (ii) CH bond allylation and arylation of organo(hydro)fullerenes, (iii) CH/CC bond cleavage of alkynyl(hydro)fullerenes, (iv) regioselective tetraallylation of fullerenes, (v) double nucleophilic substitution of aziridinofullerene, and (vi) [2 + 2] cycloaddition of aziridinofullerene with alkynes. These works not only highlight the potential of molecular catalysis for fullerene functionalization, but also unlock opportunities for markedly different strategies in nanocarbon synthesis. DOI 10.1002/tcr.201100022

Allenyl-β-lactams: versatile scaffolds for the synthesis of heterocycles

Abstract: The hybrid allenic β-lactam moiety represents an excellent building block for carbo- and heterocyclization reactions, affording a large number of cyclic structures containing different sized skeletons in a single step. This strategy has been studied under thermal and radical-induced conditions. More recently, the use of transition-metal catalysis has been introduced as an alternative that relies on the activation of the allenic component. On the other hand, the intramolecular version has attracted much attention as a strategy for the synthesis of bi- and tricyclic compounds in a regio- and stereoselective manner. This overview focuses on the most recently developed cyclizations on 2-azetidinone-tethered allenes along with remarkable early works accounting for the mechanism, as well as for the regio- and diastereoselectivities of the cyclizations.

Enantioselective epoxidation of electron-deficient olefins: an organocatalytic approach.

Abstract: Versatile synthetic intermediates—α,β-epoxyketones and α,β-epoxyaldehydes—can be obtained through asymmetric organocatalytic epoxidation of α,β-unsaturated ketones and aldehydes. This Review focuses on some recent advances in these epoxidation reactions with respect to scope and limitations with polyamino acids, phase-transfer catalysts (PTCs), amines, and guanidines as chiral organocatalysts. Furthermore, recent results obtained with chiral peroxides are discussed. © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.201000006

The smallest man-made jet engine.

Abstract: The design of catalytic engines powered by chemical fuels is an exciting and emerging field in multidisciplinary scientific communities Recent progress in nanotechnology has enabled scientists to shrink the size of macroengines down to microscopic, but yet powerful, engines Since a couple of years ago, we have reported our progress towards the control and application of catalytic microtubular engines powered by the breakdown of hydrogen peroxide fuel which produces a thrust of oxygen bubbles Efforts were undertaken in our group to prove whether the fabrication of nanoscale jets is possible Indeed, the smallest jet engine (600 nm in diameter and 1 picogram of weight) was synthesized based on heteroepitaxially grown layers These nanojets are able to self-propel in hydrogen peroxide solutions and are promising for the realisation of multiple tasks DOI 101002/tcr201100010

Toward rational design of complex nanostructured liquid crystals.

Abstract: An analogy of block copolymer micro-segregation as a low-molecular weight nanostructured liquid crystal (LC) was tested with recently found columnar and cubic phase-forming LC molecules, to clarify the broader applicability of the analogy as a molecular design principle. We found that the copolymer analogy principle also works well for new micellar cubic phase-forming molecules. For bicontinuous cubic phase-forming 1,2-bis(4'-n-alkoxybenzoyl)hydrazines (BABH-n) compounds that cover a much broader core fraction range than that predicted by the copolymer analogy, we propose hierarchical preferential orientation as an additional mechanism for their cubic range broadening. For azo-dichiral molecules that also do not fit with the above principle, we propose chiral segregation as an alternative origin for their cubic phase formation.

Monolayers at air-water interfaces: from origins-of-life to nanotechnology.

Abstract: The air-water interface presents several interesting features, namely a) a molecularly flat environment, b) a boundary region between two phases with different dielectric constants, c) permits or promotes dynamic interactions within the interface region, and d) a point of interaction between hydrophobic compounds and aqueous molecules. Accordingly, Langmuir monolayers at the air-water interface have several unique characteristics and properties, which require investigation. In this review-type personal account, typical examples of molecular recognition and molecular patterning at air-water interfaces are first introduced, followed by descriptions of specific and unusual properties of monolayers on water. In addition, two examples of our own results concerning Langmuir monolayers are explained. We have selected examples from two apparently unrelated research areas, these being the origin of life and future nanotechnology, in order to emphasize the diverse scientific contribution of research on monolayers at the air-water interface.

π-Conjugated molecules covered by permethylated cyclodextrins.

Abstract: Insulated π-conjugated molecules, in which the π-conjugated compounds are covered by a cyclic protective sheath, have attracted considerable attention because of their potential applicability in next-generation mono-molecular electronic devices. We have developed new methods of synthesizing insulated π-conjugated molecules involving the self-inclusion of rotaxane precursors linking π-conjugated units as a guest and permethylated cyclodextrin (PMCD) as a macrocyclic host. The insulated π-conjugated molecules thus formed are highly soluble in organic solvents and display photoluminescence efficiency. This paper also highlights a new method for synthesizing insulated molecular wire (IMW) through the polymerization of insulated π-conjugated molecules as monomers. The IMWs thus formed have a high covering ratio, rigidity, and showed high charge mobility in the solid state; further, they are readily soluble in a variety of organic solvents. In this account, the synthetic methodologies and characteristic of insulated π-conjugated molecules and IMWs are discussed. DOI 10.1002/tcr.201100009

Ruthenium-catalyzed cyclizations of enynes via a ruthenacyclopentene intermediate: development of three novel cyclizations controlled by a substituent on alkyne of enyne.

Abstract: Three novel ruthenium-catalyzed cyclizations of enynes were developed. In each cyclization, a ruthenacyclopentene derived from enyne and Cp*RuCl(cod) is a common intermediate. When an enyne having an alkyl, an ester, or a formyl group on an alkyne was reacted with Cp*RuCl(cod) under ethylene gas, ethylene was inserted into the ruthenium-sp2 carbon bond of ruthenacyclopentene to afford ruthenacycloheptene, and β-hydrogen elimination followed by reductive elimination occurred to give a cyclic compound having a 1,3-diene moiety. When an acyl group was placed on the alkyne, the carbonyl oxygen coordinated to the ruthenium metal of ruthenacyclopentene to produce a ruthenium carbene complex, which reacted with ethylene to give a cyclic compound having a cyclopropane ring on the substituent. On the other hand, when the substituent on the alkyne was pent-4-enyl, insertion of an alkene part into ruthenacyclopentene followed by reductive elimination gave a tricyclic compound by a ruthenium-catalyzed [2 + 2 + 2] cyclization of diene and an alkyne. DOI 10.1002/tcr.201100003

The longest quinoidal oligothiophene: a Raman story.

Abstract: The main research on the family of aromatic and quinoidal oligothiophenes is described, with a focus on their longest members. We have described how the comprehensive understanding of the vibrational Raman spectra of oligothiophenes in a variety of situations permitted the elucidation of properties of fundamental importance, not only for basic research in molecular physics and in physical chemistry, but also for applications. We have written the Raman story that brought us to the elucidation of the biradicaloid nature of the longest quinoidal oligothiophene. DOI 10.1002/tcr.201000022

Transition-State Spectroscopy Using Ultrashort Laser Pulses

Abstract: To gain a complete understanding of a chemical reaction, it is necessary to determine the structural changes that occur to the reacting molecules during the reaction. Chemists have long dreamed of being able to determine the molecular structure changes that occur during a chemical reaction, including the structures of transition states (TSs). The use of ultrafast spectroscopy to gain a detailed knowledge of chemical reactions (including their TSs) promises to be a revolutionary way to increase reaction efficiencies and enhance the reaction products, which is difficult to do using conventional methods that are based on trial and error. To confirm the molecular structures of TSs predicted by theoretical analysis, chemists have long desired to directly observe the TSs of chemical reactions. Direct observations have been realized by ultrafast spectroscopy using ultrashort laser pulses. Our group has been able to stably generate visible to near-infrared sub-5-fs laser pulses using a noncollinear optical parametric amplifier (NOPA). We used these sub-5-fs pulses to study reaction processes (including their TSs) by detecting structural changes. We determine reaction mechanisms by observing the TSs in a chemical reaction and by performing density-functional theory calculations. DOI 10.1002/tcr.201000018

Construction of contiguous tetrasubstituted chiral carbon stereocenters via direct catalytic asymmetric aldol and mannich‐type reactions

Abstract: Catalytic asymmetric synthesis of unnatural amino acids with vicinal tetrasubstituted chiral carbon stereocenters is described. In the first part, direct catalytic asymmetric aldol reaction of simple non-activated ketone electrophiles with α-substituted α-isothiocyanato ester donors was realized. A Mg/Schiff base catalyst promoted the aldol reaction, and α-amino-β-hydroxy esters were obtained in up to 98% ee and 98:2 d.r. In the second part, the Mg/Schiff base catalyst and a Sr/Schiff base catalyst were utilized for stereodivergent direct asymmetric Mannich-type reaction of ketimines. The Mg/Schiff base catalyst gave syn-α,β-diamino esters, while the Sr/Schiff base catalyst produced anti-α,β-diamino esters in good to high enantioselectivity, up to 97% ee.

Total synthesis and functional analysis of non-ribosomal peptides

Abstract: Antillatoxin and polytheonamide B are cytotoxic non-ribosomal peptides, both isolated from marine sources. These molecules possess unique biological activities that relate to ion channel proteins. Antillatoxin binds and activates voltage-gated sodium channels, while polytheonamide mimics functions of an ion channel protein. The goal of this research program is to control the function and behavior of ion channels in a desired fashion by exploiting structural motifs of these natural products. In the opening phase of this program, we first developed general and efficient synthetic routes to antillatoxin and polytheonamide B. The strategies for the total syntheses were then applied to the preparation of structurally varied derivatives for studies of structure-function relationships, which resulted in deciphering important structural elements for the potent biological activities of these natural products.

Exohedral functionalization of fullerenes and supramolecular chemistry.

Abstract: We have investigated the exohedral functionalization of [60]fullerene, especially bisaddition; we have revealed the regioselectivity of bisaddition and the properties of obtained bisadducts. The bisaddition without any restriction generally shows low regioselectivity. The electronic and photophysical properties of bisadducts mainly depend on the addition patterns and are almost independent of the nature of addends. We have also attained the regioselective synthesis of bisadducts by controlling the distance and orientation between two reactive species with suitable covalent templates and their application into some functional materials. The synthesis of fullerene-containing interlocked molecules, such as catenanes and rotaxanes, was accomplished by using a noncovalent interaction, mainly a donor-acceptor interaction, in addition to the covalent functionalization. The bistable rotaxanes, which can serve as a molecular shuttle or switch, were also successfully prepared.

Catalytic migratory oxidative coupling of nitrones through an outer‐sphere C(sp3)‐H activation process

Abstract: Outer-sphere redox catalysis is key to efficient C-H activation, which has attracted increased interest in organic chemistry. In this account, we describe a CuI-catalyzed oxidative coupling between nitrones and various ethers or amines as an example. Predictable site-selective C-C bond formation was achieved through activation of the C-H bonds in each coupling partner and the migration of a C-N double bond. Mechanistic studies strongly suggested that the reaction proceeded via an oxonium/iminium cation species as the key intermediate. The mechanistic information allows for future extension of outer-sphere redox catalysis. DOI 10.1002/tcr.201100024

Synthetic challenge to ubiquitous natural products from plant origin: flavan-derived polyphenols.

Abstract: Flavan-derived polyphenols (catechin derivatives), widely destributed in the plant kingdom, have been given much considerable attention owing to their significant bioactivitites coupled with their extreme structural diversity. However, biochemical functions of this class of molecules are still not well understood because of the limited availavility of natural samples in sufficient quantity and quality. Here we report our synthetic challenges toward flavan-derived polyphenols, based on the flavonoid-sugar analogy. The key for success was the C(4)-elaboration of the flavan skeleton, which posed an important relevance to their structure diversification both in terms of the biogenetic origin of flavan derivatives as well as chemical synthesis of this class of compounds. Various nucleophilic units could be introduced to the C(4) position via the SN1-type substitution, and orthogonal activation of two distinct flavan units enabled block assembly of linear catechin oligomers. These methodologies would serve as a reliable way to supply valuable, homogeneuous samples for biological testing. DOI 10.1002/tcr.201100026

Nanostructure control in polymer solar cells by self-organization.

Abstract: Recently, polymer solar cells (PSCs) based on "bulk heterojunctions" using a simple mixture of electron donor and acceptor materials in thin fi lms have been extensively studied. Although relatively high power conversion effi ciencies have been achieved by using this approach, further improvement is necessary to precisely construct stable, reproducible nanostructures that are suitable for both effi cient charge separation and transport inside such fi lms. For this purpose, it is highly desirable to utilize a bottom-up approach, such as the self-organized formation of inorganic and organic nanostructures. In this review, an overview of our recent studies on the control of nanostructures in PSCs is presented. DOI 10.1002/tcr.201000015

Fabrication of the smallest organic nanocolloids by a top-down method based on laser ablation

Abstract: Stable aqueous colloids of 10-nm sized organic nanoparticles were tailored by laser ablation of microcrystalline quinacridone in water. The nanocolloids were flaky in shape and had the dimension of a width of 13 (±5) nm and a height of 1.4 (±0.5) nm. The formation mechanism is discussed in terms of laser-induced fragmentation of organic solids and the potential application of aqueous organic nanocolloids free from any additives and chemicals is considered.

Vital significance of addition of "shape similarity" between solutes to shape complementarity for more precise molecular recognition in aqueous binary solvents.

Abstract: Precise and specific molecular recognition is vital to living systems. Discrimination has mainly been studied by using particular host molecules (e.g., crown ethers, cyclodextrin and urea derivatives). Several studies in various fields have pointed out that the famous “lock-and-key theory” (the concept of shape complementarity) is, at present, insufficient for understanding precise discrimination. This seems to come from the fact that various types of intermolecular interactions are decisive in such discrimination. This Review intends to describe the novel concept that “shape similarity” between interacting solutes should be added to “shape complementarity” for more precise discrimination to be achieved. Further, the role of shape similarity between solvent and solute molecules is also described. In relation to precise molecular recognition, weak interactions, which depend on the three-dimensional shape of substituents (shape-specific weak interactions), are described. Possibility of alterations in solvent structures is discussed in aqueous binary solvents. DOI 10.1002/tcr.201100001

Ushering in a new era

Abstract: highlights” journal, publishing critical overviews of topical areas of chemistry that are written from a personal perspective. It is this personalized quality that makes the journal unique from other review journals and brings authors and readers together in approaching a pair of all-encompassing questions: What areas are of the most imminent relevance to researchers’ endeavors across multiple disciplines, and what challenges do researchers face in reaching the next level of discovery? While The Chemical Record has undergone a number of positive developments over the past few years, its position as an international and interdisciplinary forum for addressing these big-picture questions has only gotten stronger. During this year, fittingly within the International Year of Chemistry 2011, The Chemical Record has been able to celebrate a series of editorial highlights of its own. There have been several recent developments in and around The Chemical Record that have been truly inspiring. After the publishing responsibility for The Chemical Record was transferred two years ago to the offices of Wiley-VCH, society publishers of Angewandte Chemie and Chemistry-An Asian Journal, the cooperation between the publisher and the owner societies of The Chemical Record was intensified toward mapping the editorial progress of the journal. During these two years, and even starting well before that, the journal was set on a new path forward, with the Chemical Society of Japan (CSJ) taking the leading society role. The Chemical Record is now an official journal of the Chemical Society of Japan. To top it all off, the Chemical Society of Japan and Wiley-VCH have recently strengthened their collaboration on The Chemical Record through the signing of a new publishing agreement during the recent Angewandte Symposium in June 2011 in Tokyo (Figure 1). This signing came just days before it was announced that TCR had received its highest Impact Factor ever: 4.604 for 2010, which is an eye-catching 19% increase over its 2009 Impact Factor of 3.862. This increase represents the journal’s third in a row. The recent trend of a sharply rising Impact Factor for The Chemical Record is the culmination of several years of dedicated effort from the scientists behind the journal, not least of which through the tireless commitment of immediate past Editor-inChief Koji Nakanishi and current Editor-in-Chief Hisashi Yamamoto, who succeeded Professor Nakanishi in 2010 and has already made outstanding and creative contributions. To expand the horizons of the journal even further, an infusion of extremely talented scientists joined the Editorial Board and the International Advisory Board at the beginning of 2011. The members of the Editorial Board (Figure 2) are active in each of