A carbon-heteroatom bond has the hard-soft dissymmetry as well as the charge dissymmetry. Thus, a pertinent combination of a hard acid and a soft nucleophile can cleave the carbon-heteroatom bond. This article describes a number of combination systems of a hard Lewis acid and a soft nucleophile which have been developed for the cleavage of C-O, C=C, C-NO2, and C-X bonds.
Shape selectivity has been an important and valid concept in heterogeneous catalysis since the discovery of methanol to gasoline (MTG) conversion by Mobil Oil Co. The most popular shapeselective catalyst is zeolite, of which the pore size is comparable with the dimension of many simple molecules. The reactions of such molecules are often controlled in selectivity by the use of zeolite as a catalyst. Clay intercalation compounds have also been given attention as the shapeselective catalyst. The interlayers of several kinds of clay can be cross-linked by the “pillar” which controlls the interlayer spacing. This review describes the synthetic method of clay intercalation compounds and their application to shape-selective catalysts.
The progress of electrically conducting polymers is reviwed. Synthesis and properties of mainchain conjugated polymers are described in the first section, among which are polyacetylene, polypyrrole given by anodic oxidation of pyrrole, poly (p-phenylene sulfide) and pyropolymers. They show high electrical conductivities through doping with electron acceptors or electron donors. The mechanism of doping and the nature of electrical carrier are discussed. The second section is devoted to the description of characteristics of amorphous conducting polymers given by the modification of side chains, and “molecularlydoped polymers” in which electrically active molecules are dispersed in an inert polymer matrix. A molecular localized state prevails and the hopping mechanism is accepted for electrical conduction in these materials. Finally, organic photoconductive polymers are dealt with from the standpoint of the preparation, photogeneration and carrier transport properties. Also is explained the design of carrier transport compounds based on the perturbation molecular orbital theory.
N-α, β-Unsaturated acylenamines and N-α, β-unsaturated acylanilides, which form a common conjugated six π electron system, are two major types of enamides capable of undergoing smooth cyclization under both photochemical and thermal conditions according to the Woodward-Hoffmann rule. These cyclizations of enamides are found to occur under various conditions, such as nonoxidative (in the absence of oxygen), oxidative (in the presence of oxidizing agent), reductive (in the presence of hydride reagent), and even under asymmetric conditions (under asymmetric circumstance), thus established the enamide cyclization as a useful synthetic weapon widely applicable to the construction of nitrogen-containing heterocyclic compounds, particularly related to alkaloids. Usefulness of this enamide cyclization is proved by the establishment of stereochemical and regiochemical controls of the cyclization by the use of substituent and solvent effects. This review covers rather quick look at the outline of this enamide cyclization and its application to the synthesis of heterocycles.