A novel nine-membered enediyne antibiotic N 1999-A 2 was chemically synthesized and its absolute stereochemistry was determined. Chemical evidence of the thiol-triggered activation as well as the DNA cleavage profiles of N 1999-A 2 and its stereoisomers proved that the configuration of the C 11-naphthoate moiety played a dominant role in governing not only the orientation of the thiol attack but also the specificity of DNA cleavage.

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Tandem Claisen rearrangement of various kinds of isobutenyl bis (aryl) ether derivatives can give rearranged-products which have plural hydroxy groups. Bis (benzaldehyde) - and bis (benzoyl chloride) derivatives of them prepared in high yields can react with amine compounds to give diimines and diamides, respectively. The reactions with diamines gave selectively either 1 : 1 or 2 : 2 macrocycles with self-assembly in high yields without high-dilution conditions. Furthermore, bis (benzaldehyde) derivatives react with tris (2-aminoethyl) amine in the presence of metal ions such as lanthanides to give a 3 : 2 three dimensional macrobicycle as a self-organized product in moderate yield. On the other hand, the reaction of bis (benzoyl chloride) derivative with p-phenylenediamine gives a 2 : 2 macrocycle predominantly, where hydrogen bond formation in the reaction process plays an important role. Thus, the self-assembled combination of bis (benzaldehyde) -and bis (benzoyl chloride) derivatives with diamines either in the presence or in the absence of metal ions could result in forming specific macrocycles, spontaneously.

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We have been interested in diastereoface-discrimination reactions using a variety of TiX4, and have found that differences in the reactivities of the tetrahalides can enable distinct reaction pathways through selection of an appropriate tetrahalide derivative to promote the specific reaction. Titanium tetraiodide is an excellent reagent for the reductive formation of enolate species form α-halo carbonyl or imino compounds, and the subsequent reactions with carbonyl compounds give aldol products in good yields. Regarding chemoselective reductions using titanium tetraiodide, α-dicarbonyl or α-imino carbonyl compounds were chemoselectively reduced with titanium tetraiodide to give α-hydroxy or α-amino carbonyl compounds, respectively, in good to excellent yields. Subsequent reactions with aldehydes or imines realize the selective formation of amino alcohol or diamine derivatives in good yields. Pinacol coupling of aromatic and α-halo-α, β-unsaturated aldehydes was efficiently promoted by titanium tetraiodide in propionitrile to give the 1, 2-diol derivatives with high dl-selectivities in high yields. Chemoselective deoxygenation of sulfoxides was also carried out successfully using TiI₄ as a reducing agent to give sulfides in good to excellent yields

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The chemistry of the molybdenum and tungsten complexes containing bis (η-cyclopentadienyl) M (Cp₂M) fragment is described. Protonation of Cp₂MH₂ with p-toluenesulfonic acid (TsOH) afforded isolable trihydrido cationic complexes, [Cp₂MH₃]⁺TsO^-. When the reaction was carried out in the presence of ketones, aldehydes, or imines, their reductions to yield the corresponding alcohols or amines took place : the reactions with high diastereo- and moderate enantio-selectivity were achieved. The reactions of Cp₂MoH₂ with allylic alcohols in the presence of protonic acids yielded the cationic η-allyl complexes accompanied with cyclic γ-hydorxypropyl complexes. The first molybdenocene derivatives with the stable carbene, imidazole-2-ylidene or imidazolin-2-ylidene, were successfully synthesized starting from Cp₂Mo (H) OTs or [Cp2Mo (H) Li]₄. Cp₂W (H) Ph, which was prepared by irradiating Cp₂WH₂ in benzene, was reacted with RCOOH to yield either carboxylato (hydrido) -or dicarboxylato-tungsten complexes, and with CO₂ in the presence of water to give carbonato derivative. Cp₂M(OTs)₂ was converted to the di-μ-hydroxy dinuclear complex by treating it with water in acetone in the presence of Cp₂MH₂. Finally, the corresponding chemistries involving the bis (MeCp) complex in the place of Cp₂ are described.

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Cyclic enediyne antibiotics such as calicheamicin and dynemicin A exhibit extraordinary potent antitumor activities through DNA cleavage by phenylene diradical, which is generated by Bergman reaction of the 10-membered enediyne moiety. To mimic this action mechanism of dynemicin A, we designed the two simplified compounds model A and model B having epoxide and 10-membered enediyne ring, and synthesized these molecules. The model A did not undergo the Bergman reaction under acidic conditions, while the model B exhibited DNA cleavage and in vitro cytotoxicity. Both enantiomers of the model B were also synthesized. In the synthesis of a model compound of calicheamicin, we examined cyclization conditions of an enediyne aldehyde to find out NHK reaction was the most reliable. During these studies, several new reactions were developed, such as reaction of N-acyliminium cation with silyl- and tin-acetylene, palladium catalyzed coupling reaction of allyl derivatives and tinacetylene, remote asymmetric induction in acetylide addition to quinoline nucleus, and one pot synthesis of haloacetylene from silylacetylene.

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