This article surveys recent developments in asymmetric epoxidation of olefins including i) epoxidations using chiral peracids and peroxides, and ii) metal catalyzed epoxidations, mainly Sharpless' asymmetric epoxidation. The scope and limitation of the epoxidation reaction using titanium tetraisopropoxide, dialkyl tartrate, and t-butyl hydroperoxide system will be discussed.
Reaction of optically active amino alcohol with 2 equiv. of BH3·THF gave the excellent asymmetric reducing agent, which reduced aromatic ketones, dialkylketones, and oxime ethers to yield chiral secondary alcohols and primary amines, respectively, with high optical yield (>90%ee). Optically active amino alcohols were easily prepared from amino acids. Cross-linked polystyrene supported chiral amino alcohols were also prepared. A polymeric asymmetric reducing agent could realize high enantioselectivity as same as monomeric one with quantitative recover and reuse. Catalytic use of the chiral amino alcohol-borane complex was also investigated on the basis of following behaviours. (1) The reduction with borane was accelerated by the presence of the complex. (2) Large amount of the product was obtained by the use of the small amount of the complex. (3) The product is optically active. (4) The product does not bind to the complex.
Various heterocycles are prepared from alkynylamines, alcohols, and carboxylic acids under catalytic action of Pd (II) species. The key reactions are intramolecular addition of NH, OH or COOH to acetylene moiety. Intermediary alkenylpalladium species are protonolyzed or coupled with allyl halides affording organic compounds under the recovery of pd (II) species. During the transformation, Pd (II) species are not reduced, therfore the catalyst can recycle without reoxidation of palladium catalyst which is often observed by the use of olefinic starting materials. Prepared heterocycles are : pyrroles, furans, 1-pyrolines, tetrahydropyridines, dihydrofurans, dihydropyrans, and intramolecular acetals. Syntheses of some insect pheromones bearing intramolecular acetal linkage are also described.
This article offers a brief description of the structures and an exposition of selected reactions of non - heme iron-sulfur protein sites and their synthetic analogs [Fe (SR) 4] 1-, 2-, [Fe2S2 (SR) 4] 2-, 3-, and [Fe4S4 (SR) 4] 2-, 3-. The properties of synthetic Fe -S complexes reveal them to be close representations of the redox centers of iron-sulfur proteins, and the analogs are useful as detailed structural models and as electron carries in some biomimetic reactions. Presented are also current observations pertinent to stabilizing the redox centers using 36-membered and cyclophane-type macrocyclic ligands as conducted in the author's laboratory.
Slow Reacting Substances of Anaphylaxis (SRS-A) which comprises of leukotrienes C4, D4 and E4 plays an important role in eliciting the symptoms of asthma. Since the discovery of the leukotrienes, many analogs have been synthesized in order to explore the relationships between the structure and biological activities. This review will focus on the leukotriene derivatives and the development of leukotriene antagonists.
Two series of 5-pyrazolone couplers, in which pyrazolyl and ο-alkoxyarylthio group are substituted at the dye forming position as anionic leaving groups, have been developed for photographic color negatives and color papers, respectively. Realization of these couplers afforded the following three advantages, 1) saving of the amount of couplers 2) reduction of yellow stain in the color paper on storage, 3) retention of color balance even in formalin atmosphere. Couplers with pyrazolyl group have been synthesized by the reaction of 4-bromopyrazolone only with neutral 2 molar excess pyrazole, which acted not only as a nucleophile but also as a trapping agent of hydrogen bromide. Couplers with ο-alkoxyarylthio group have been selectively synthesized by the reaction of 4-unsubstituted pyrazolones with an arylsulfenyl chloride in aprotic polar solvents.
Some of the microorganisms which assimilate hydrocarbons produce optically active epoxides from corresponding olefins. Although the substrates epoxidized by most of these microorganisms are restricted to aliphatic olefins, one of the gaseous olefin assimilating microorganisms, N.corallina, has been found to have a very wide substrate specificity in the epoxidation of olefins. This microorganism produces optically active epoxides from 1-alkenes (C3-C18), 2-alkenes, halogenated alkenes, styrene, phenyl allyl ether and their analogues. The rates of epoxidation of these substrates have been promoted by reducing the inhibitory effect of produced epoxides. In the epoxidation of moderate chain length 1-alkenes, the yield of (R) -1, 2-epoxides exceeded 80%. The optical purity of these 1, 2-epoxyalkanes ranges from 80 to 90% e.e.. These 1, 2-epoxyalkanes are now utilized as the intermediates in the syntheses of ferroelectric liquid crystals.