Design of high spin organic molecules is described in three categories ; use of strong exchange interaction in one-center diradicals, non-Kekule molecules, anti-aromatic annulenes including charged species. Magnetic behavior of metapoly-phenylmethylene (8) is discussed as a model of one-dimentional organic ferromagnet. Intermolecular interaction among triplet diphenyl carbenes generated in host crystals of a diazo precursor is interpreted in terms of the results in a model system of [2, 2] paracyclophanedicarbenes. An attempt to realize ferromagnetic material utilizing CT interaction is rewared with a success in the case of decamethylferrocene-TCNE complex. Finally the electronic requirement for realizing organic ferromagnet is discussed in reference to that for organic conductors.
High-pressure technique is a practical method for laboratory organic synthesis since simple equipment has become available in this decade. Pressure accelerates reactions if their values of 'the volume of activation' are negative, such as cycloaddition reactions and reactions through dipolar transition states. Especially, this technique is useful to drive reactions with steric hindrance. In this article are reviewed recent developments of substitution reactions, addition reactions to a carbonyl group, conjugated addition reactions, Deils-Alder reactions, 1, 4-cycloaddition reactions, other pericyclic reactions, and organometallic reactions since 1985.
Considerable attention has recently been directed towards the use of α-thiocarbocations to accomplish carbon-carbon bond forming reactions. In this article, our recent studies in this field are reviewed, dividing into four major topics : 1) electrophilic aromatic substitution, 2) ene reaction, 3) polar cycloaddition, and 4) olefin cyclization. Emphasis has been placed to the difference in reactivity between α-chlorosulfides and sulfoxides employed as precursors of the α-thiocarbocations. Applications of these methods to the natural products synthesis are also presented.
N-Acetylneuraminic acid (Neu5Ac), a typical sialic acid, located at the non-reducing ends of carbohydrate chains of glycoproteins and glycolipids plays an important role in biological phenomena. The synthesis of oligosaccharides which contain Neu5Ac has focused with clarification of their vital functions. In the synthesis of the sialylated oligosaccharides the most difficult problem remaining is the glycosidation of sialic acid, 3-deoxy-2-nonulopyranosonic acid, which has to be introduced into the oligosaccharide acceptor in the α-glycosidic linkage. This review article shows the enzymatic and synthetic approaches to the glycosidation of sialic acid, in particular, the methods involving an introduction of a substituent into 3-position of sialic acid.
Synthesis of optically active D-myo-inositol 1, 4, 5-trisphosphate (Ins (1, 4, 5) P3), and its metabolites, Ins (1, 3, 4) P3, Ins (1, 2-cyclic, 4, 5) P3, and Ins (1, 3, 4, 5) P4 which are involved in an intracellular signal transduction system were accomplished starting from myo-inositol. In the process of these synthesis, two phosphorylation methods of vicinal diols and sterically hindered alcohols were devised. That is, combination of tetrabenzyl pyrophosphate and butyllithium was found to be an efficient phosphorylation reagent. The other is the stepwise phosphorylation which employs phosphorus trichloride, benzyl alcohol, and t-butyl hydroperoxide successively. For the optical resolution, diastereomeric menthoxyacetic esters and chiral column were effectively employed.
Abnormal enolization reaction of naltrexone was found and the reactivity was applied to the syntheses of highly selective opioid receptor antagonists. Further, structure activity relationship of these antagonists was discussed.