Many plants close their leaves in the evening like sleeping and open early in the morning. Such a circadian rhythm has been known to be controlled by their internal clock. Moreover, rapid seismonastic movement was also observed in Mimosa pudica L.
Since Ricca's ingenious experiments suggested that some chemicals play an important role in leaf-movement of Mimosa pudica, many biologists and chemists have attempted to search for leaf-closing substances, and a number of compounds have been obtained, particularly, by Schildknecht et al
. But, we have now demonstrated that the genuine leaf-movement factor of Mimosa is the mixture of three chemical substances, two of the three were identified as potassium L-malate and magnesium transaconitate. The mixture of these substances was effective at 10^-8-10^-9 M.
On the other hand, we have isolated chemical substances that control the nyctinastic leaf-movement from several nyctinastic plants. Each substance was effective at 10^-6-10^-7 M only for the original plant, but not for other nyctinastic species. Thus, different leaf-movement factors exist in every nyctinastic plants. This is contrary to the old theory established by Schildknecht. This movement is controlled by the change in the balance of two inversely effective factors, leaf-closing and opening factor. Me0H-extracts of a nyctinastic plant, Lespedeza cuneata G. Don. collected in the daytime and at night showed inverse bioactivity. Thus, the balance of concentration between two leaf-movement factors in this plant which is controlled by biological clock was really inversed through a day. This mechanism for the control of nyctinastic movement is common among all nyctinastic plants.

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In order to develop a practical method for the construction of chiral molecules, efficient chiral systems have been designed by the control of the coordination environment to metals. First, the stereodifferentiation in the addition of metallic reagents to chiral ketones or imine derivatives with a few heteroatoms was investigated. Second, a novel chiral system possessing two metal centers utilizing tartaric acid esters was designed and efficient asymmetric Simmons-Smith reaction, asymmetric 1, 3- dipolar cycloaddition, and asymmetric nucleophilic addition were realized.

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An overview of the recent studies on the asymmetric syntheses, stereochemical studies, reactions and applications of chiral chalcogenuranes is described. Chiral chalcogenuranes, including halooxachalcogenuranes and spirochalcogenuranes, have been synthesized by highly diastereoselective oxidation of the 2-exo-hydroxy-10-bornyl chalcogenides. The stereochemistry of chalcogenuranes have been confirmed to be trigonal bipyramid (TBP). Nucleophilic reactions of these compounds provided a good method to prepare the chiral chalcogenonium (IV) compounds with excellent diastereoselectivity. Hydrolysis of the chiral spirosulfurane gave optically pure sulfoxides with different stereochemistry at the sulfur atom under various conditions, which indicated that the reactivity of the axial bonds plays an important role in the control of the stereochemistry of the reactions. Mechanistic and stereochemical studies on the nucleophilic reactions have revealed that two kinds of pathways, dissociative and associative routes, seem to exist. The application of the reactions through the [2, 3] sigmatropic rearrangement and enantioselective protonation with optically active selenonium compounds have been investigated to give good selectivities of the reactions.

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Asymmetric acylation of alcohols is very important in synthetic organic chemistry and holds great potential for the preparation of small chiral compounds which are suited for further manipulation in the synthesis of biologically active natural products. Although enzymatic acylation has been extensively studied and established as a promising method for the preparation of chiral alcohol variants, development of nonenzymatic alternatives in this field has been scattered. From this viewpoint, we wish to demonstrate highly efficient and practical methods for the catalytic asymmetric acylation of racemic secondary alcohols and various meso-diols by the reaction with achiral benzoyl chloride in the presence of a chiral 1, 2-diamine derived from (S) -proline.

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The following reactions catalyzed by rhodium and iridium complexes are described. 1) Complete reversal of stereoselectivity in neutral rhodium complex-catalyzed hydrosilylation of 1-alkynes. 2) Selective synthesis of (E) -vinylsilanes by cationic rhodium complex-catalyzed hydrosilylation of 1alkynes; synthesis of (E) -γ-silyl allylic alcohols and N- [(E) -γ-silyl allylic] sulfonamides. 3) Isomerization of (E) -γ-silyl allylic alcohols to β-silyl ketones. Tandem hydrosilylation/isomerization of propargylic alcohols to β-silyl ketones. 4) Iridium complex-catalyzed allylic alkylation of allylic esters with a stabilized carbon nucleophile at the substituted allylic terminus. 5) Rhodium complex-catalyzed allylic alkylation of allylic esters with a stabilized carbon nucleophile.

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Studies on transition metal complexes supported by the hydrotris (pyrazolyl) borate ligands (Tp^R) are reviewed with the emphasis on (i) the synthesis and characteristic properties of the Tp^R ligands and their metal complexes and (ii) the chemistry of transition metal-dioxygen complexes with the Tp^R ligand. The mononegative 6e-donating Tp^Rligands are versatile in the following aspects : (1) They are isoelectronic with the cyclopentadienyl ligands (η⁵5-C₅R₅), the very popular organometallic ligands. (2) They work as facially coordinating tripodal N₃-ligands. (3) The coordination environment provided by the Tp^R ligand can mimic those created by the facially arranged three imidazolyl groups from the His residues and are frequently found in the metal coordination sites of metalloproteins. The latter half part of the review is devoted to the studies on the dioxygen complexes based on the third concept in hope of comprehensive understanding of the mechanisms of oxygenation reactions.

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Some series of novel nematic liquid crystalline tolans having high birefringence and low viscosity with a high NA (Nematic-to-Isotropic) transition temperature were developed in order to improve the response time of Supertwisted Nematic-Liquid Crystal Display (STN-LCD). Some nematic liquid crystalline mixtures of the tolans and other familiar series of nematic mixtures were prepared and their physical properties were compared. The drastic advantages of the tolans, which are useful for laptop computers and word processors, are demonstrated. Moreover, the details of industrialization of the tolans are described.

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