Synthetic polymers are usually the mixture of molecules of different molecular weights. Since molecular weight and its distribution affect the fundamental properties of polymer materials, one of the most important subjects in synthetic chemistry is to establish facile and versatile procedures for the synthesis of polymers with regulated molecular weight, in view of the great demand for the design of polymer materials of elaborate functions. Up to now, however, the successful examples are limited. This paper describes our recent findings that some metalloporphyrins of aluminum are excellent catalyst of much wider applicability than the reported examples for the synthesis of polymers with regulated molecular weight. The polymer of epoxide or β-lactone, the copolymer of phthalic anhydride-epoxide or CO2-epoxide and their block copolymers are synthesized in the form of regulated molecular weight. The polymer formation takes place on the faces of metalloporphyrin.
Recent developments of triphase catalysis are reviewed. First, applications of ion-exchange resins to organic synthesis as reagents and catalysts are described in connection with polymeric phase transfer catalysts. Subsequently, polymeric phase transfer catalysts are classified into three typical groups, namely, onium salts type, crown ethers and cryptands type, and cosolvents type. Their specific features in triphase catalysis are demonstrated. Activity-determining factors and mechanistic aspects of triphase catalysis are also discussed.
Preparations and characterizations of ultrafine colloidal catalyst particles such as colloidal platinum and gold are reviewed, and the applications for organic syntheses are summarized. Stable, monodisperse, and ultrafine colloidal metals are formed by the reduction of the corresponding metal ions in the presence of protective reagents like synthetic polymers, or in the internal aqueous phases of microemulsions and artificial liposomes. Methods for characterization of ultrafine colloidal catalysts and properties of the colloids are summarized. Several examples of the application of the colloids to organic reactions are described. Colloidal platinum with hydrogen is especially important as reductase models to activate dioxygen or to carry out clean reductions by avoiding any inorganic contaminant.
In optical disk memory system, recording medium is an important element. Organic dyes which were originally used as heat-mode recording media, have also been applied to the optical memory systems. In order to improve the recording characteristics, multilayer structure consisting of dyes and metals have been developed. Recently, the dyes which can be utilized as monolayer structure have been found. In this paper, the designing method of optical characteristics which are important factors for the recording media for optical disk memory and also the recent trend of developing dye materials are described.
Reactions of carbenes generated photolytically in rigid organic solid at low temperature are reviewed mainly from the synthetic point of view. In the case of carbenes with triplet ground states there are profound differences between the chemistry observed in fluid solution at ambient temperature and that obtained in matrix at -196°C. For example, the arylcarbene generated in alcoholic solution at ambient temperature gives O-H insertion products almost exclusively, whereas the arylcarbene generated in alcoholic matrices at -196°C results in a dramatic increase in C-H insertion products at the expense of the ether. Similar dependence of the product distributions has been observed in the reaction of the arylcarbene with alkene, amine, halide, ether and acetone. These C-H insertion products are explained to be formed via H atom tunneling from organic solid to the triplet state of arylcarbene, followed by an efficient recombination of the resulting radical pairs. Reactions of arylcarbene with organic compounds with no active C-H bonds, e.g., styrene and t-butyl alcohol are also reviewed.
One of the major ongoing objectives in synthetic organic chemistry today has been the discovery and development of highly stereoselective carbon-carbon bond forming reaction. Since Cram proposed the general rules of the diastereotopic face selection of chiral aldehyde, stereoselective aldol and aldol addition reactions have been widely used in organic synthesis. Particularly during the past half decade, a number of stereo-controlled synthetic methods were devised and used as the key reactions for construction of the complex molecules. This review describes recent highly stereo-controlled reactions of chiral aldehydes, which are classfied into Cram, Anti-Cram, chelation and dipolar models. The first part presents fundamental concepts of aldol and aldol addition reactions. In the second part is discussed the reaction stereochemistry of chiral aldehydes involving α-alkoxy, α-alkyl and other aldehydes, and in the final part a double stereo-differentiation and a mutual kinetic resolution are outlined.
An explosive increase of significance of fluorinated compounds, e. g., coolant, artificial blood, insecticides, antipsychotics, anti-cancer drugs, etc., has drawn our attention to study the chemistry of fluorides. 19F NMR spectroscopy has shown its high usefulness for investigating the physical character or environment of fluorides, which may be interacting with biological substances. In this manuscript, we briefly review characteristics and analyses of data of 19F NMR spectroscopy. Furthermore, biochemical, pharmaceutical, analytical and medical applications and prospect of 19F NMR spectroscopy are summarized.