The first total synthesis of gambierol, a marine polycyclic ether toxin, has been achieved. Highly efficient synthesis of the ABC and EFGH ring fragments allowed us to prepare those two advanced intermediates in multi-gram quantities. The key feature of the present total synthesis is the B-alkyl Suzuki-Miyaura coupling tactics, which culminated in the union of the advanced intermediates and convergent synthesis of the octacyclic polyether core. Introduction of the sensitive triene side chain via Pd (PPh₃) 4/CuCl/LiCl-promoted Stille coupling was conducted at the final step of the synthesis.
The present total synthesis supplied useful quantities of gambierol and its structural analogues for detailed biological studies : an interesting observation was gained through pathological studies. Also, preliminary structure-activity relationship studies revealed that the functionalities present in the H ring and unsaturated side chain are crucial for potent toxicity against mice.

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Vancomycin-resistance is one of the most important problems in public health. This review survey the recent studies of chemically modified vancomycin-related glycopeptide antibiotics with emphasis on multivalent effects.

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Silyltellurides react with carbonyl compounds and imines to generate α-silyloxy and α-silylaminoradicals, respectively. The radicals thus generated react with isonitriles and alkynes in a tellurium-group transfer manner to give the corresponding α-silyloxyimidoyltellurides, α-silyloxyvinyltellurides, and α-silylaminoimidoyltellurides, respectively. The coupling reaction proceeds under mild thermal and neutral conditions with the use of nearly an equivalent of each substrate. While the α-silyloxy and α-silylaminoradicals are deactivated by the tellurium-group transfer reaction to give α-silyloxytellrides and α-silylaminotellrides, respectively, they reversibly regenerate the same radical species under the reaction conditions. Therefore, all the starting substrates are eventually converted to the products. The carbon-tellurium bond in the products can be used for further synthetic transformations under radical and ionic conditions. Therefore, the coupling reaction and subsequent transformation provides a new synthetic method for combinatorial synthesis of synthetically important organic building blocks, such as α-alkoxy carbonyl compounds, α-amino acids, and allyl alcohols. Therefore, silyltellurides-mediated reaction opens a new possibility for the radical-mediated carbon-carbon bond formation involving carbon-hetero multiple bonds.

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Reagents containing carbon-tin-halogen inter-element linkages were found to be effective for palladium-catalyzed cross-coupling reaction with organic halides. It also enabled carbostannylation of norbornenes. Tetraorganotins were found to become quite efficient reagents for palladium-catalyzed cross-coupling reaction with organic halides, providing up to all four organic moieties on tin for the reaction upon addition of fluoride ion. Hydroxide ion was even more effective in utilizing plural number of organic groups on tin atom. In situ generated allylic tin trichlorides add to carbon-carbon double bonds of bicyclo [2.2.1] hept-2-ene (norbornene) and its derivatives, stereoselectively, under the catalysis of palladium (0) species in good yields. Aryltin trichlorides undergo palladium-catalyzed arylstannylation of norbornene, giving a mixture of products composed of that taking one norbornene and that incorporating two norbornenes. The product ratio is dependent on the electronic nature of the aromatic substituent. The reaction of vinyltin trichlorides is different, giving Heck-type product that does not contain tin moiety. The mechanistic study revealed that tin (IV) species oxidatively reacted with norbornene.

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[3_n] Cyclophanes ([3_n] CPs : n= 2-6) including the ultimate member of this series, [3₆] CP, and fluorinated [3₃] CPs were synthesized. The fundamental structural properties of these compounds both in solution and in the solid state are described. [3_n] CP shows strong electron-donating ability, which was evaluated by the λ_max of the charge transfer (CT) band of the [3_n] CP-TCNE complex and oxidation potential, and this is attributed to the effective hyperconjugation between the benzyl methylenes and the benzene ring. The solid state structural study of [3_n] CP-TCNQ-F₄ complexes provided the basic knowledge for understanding the CT interaction in the solid state. [3_n] CPs served as good ligands for Ru (II) and Os (II) metals. [3_n] CP (n=2, 4) reacted with dicyanoacetylene to give barrelenophane, which gave various valence isomers on photolysis. Our efforts to the synthesis of hexaprismane derivative via photolysis of [3_n] CP is described.

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Synthesis of ionic hydrocarbons by the combination of the tert-butyl-C₆₀ anion (t-BuC₆₀^-) and a tropylium or cyclopropenylium ion is described. The reactions of t-BuC₆₀^- and carbocations (R⁺) with pK_R⁺ values ranging from 3.88 to 10.0 resulted in regioselective carbon-carbon bond formation to form 1, 4-adducts, t-BuC₆₀-R. These covalent hydrocarbons underwent reversible heterolysis into t-BuC₆₀^- and R⁺ in polar solvents. Thermodynamic studies indicated that the heterolysis is promoted by the specific solvation of the produced ions. In contrast, t-BuC₆₀^- and tris (guaiazulenyl) cyclopropenylium ion gave a hydrocarbon salt. The ionic nature of this material was demonstrated by the vis/NIR and IR absorption spectra in the solid state. Electrical conductivity measurements indicated that this salt behaves as a strong electrolyte in DMSO. Single-electron reduction of C₆₀ with the crystal violet radical also gave a carbocation-carbanion salt, composed of the crystal violet cation and C₆₀^·-.

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[in Japanese]

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