Dibenzodehydro[12]annulene 1 has unique properties due to strained ring skeleton. However, 1 easily decomposes at ambient temperature and atmospheric pressure. As a thermally and chemically stable derivative of 1, we report herein the synthesis of silyl-substituted dibenzodehydro[12]annulene 2 and its unique properties due to the steric and the electronic effects of the silyl-substituents.
Compound 1 was reported to be obtained by the coupling reaction of o-diethynylbenzene with a copper reagent in a very low yield together with several cyclic oligomers. On the other hand, the coupling reaction of 2, 3-diethynyl-1, 4-bis(trimethylsilyl)benzene gave only 2 in a good yield. Compound 2 is thermally and photochemically stable and its structure was identified by X-ray analysis. UV-Vis absorption spectra showed significant electronic effects of the silyl-substituents.

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Silenes with a silicon-carbon double bond are known to be highly reactive and unstable species. We report herein synthetic studies of silene bearing hydrogen substituent on the silicon by taking advantage of efficient steric protection using a Tbt group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl group. Compounds 2 and 4, which are thought to be a good precursor for silene 1, was successfully synthesized and characterized. The attempted dehydrohalogenation of 2 and 4 will be described.

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The structure of 2-norbornyl cation (1) has attracted much attention for a long time, and recent study on 1 has confirmed its nonclassical nature. However, there have been reported few studies of silicon analogue of 2-norbornyl cation; recently Muller et al. has reported the nonclassical nature of a 2-sila-2-norbornyl cation. We wish to report a theoretical study of heptasila-2-norbornyl cation (2). The study revealed a classical cation nature of 2 at B3LYP/6-31G*. The positive charge in 2 resides mostly on the 2-Silicon atom and the cation is stabilized by hyperconjugation due to β-Si-Si bond. The nonclassical structure of 2 was calculated as a transition state during the skeletal rearrengement between the two classical cations. The structural difference between 1 and 2 may be assumed to the relative unstability of Si-Si double bond. Relative stability among regio isomers of 2, we will also be discussed.

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Recently, Wiberg and co-workers reported the preparation of TTF analogue with a disilane backbone, obtained from the reaction of the isolable disilene with carbon disulfide. They suggested that S-heterocyclic carbene intermediate plays the important role in the process of the generation of TTF analogue. Meanwhile, heterocyclic carbenes have attracted special attention as a spin source, ligand, catalyst and so forth, due to their unique coordination properties. Recently, we have reported the generation of a tetracyclosilene by the photolysis of the anti-dodecaalyltricyclo[4.2.0.0^2,5]octasilane. Herein we report the generation of S-heterocyclic carbene with a cyclotetrasilane backbone by [2+3] cycloaddition of tetracyclosilene with carbon disulfide. The carbene has been confirmed by trapping it with C₆₀ as a chemical probe. The structural determination of the obtained C₆₀ derivative has been performed by spectroscopic and X-ray crystallographic analysis.

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In this presentation, we report the photo-chemical reaction of C₆₀ with some silacyclopropanes. C₆₀ reacts with silacyclopropane upon photo-irradiation. In some case, the different major products were observed by the MALDI-TOF MASS spectra measurement. Under the condition of over 400 nm light irradiation, silacyclopropane adducts were obtained as major product. On the other hand, silylene adducts were observed as major product when the shorter wavelength light ( < 400 nm ) was applied for the reaction.

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Endohedral metallofullerene M₂@C₈₀ have attracted special attention for the dynamics of the encapsulated metal atoms because of their three-dimensional random motion inside the fullerene cage. It is proposed that such a dynamics are derived from the electrostatic potential inside the cage. If we can change the electrostatic potential, it may be possible to control the motion of encapsulated metal atoms. In this work, we synthesized and characterized the silylated M₂@C₈₀ by addition of the disilirane and the 1,3-dipolar cycloadduct of M₂@C₈₀ by addition of the azomethine ylide. It is revealed that the encapsulated metal atoms show two-dimensional circular motion inside the silylated M₂@C₈₀ and locate at the stable site on the mirror plane position inside the 1,3-dipolar cycloadduct.

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The chemical reduction and oxidation of M@C82 (M = Y, La, and Ce) afford the corresponding anion and cation, respectively, which show unique and interesting chemical reactivities. It is found that the successful reversible gain or loss of electrons by ionization is useful for controlling the stability and reactivity of M@C82 towards both nucleophiles and electrophiles.

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Endohedral metallofullerenes are one of the most exciting topics in the fullerene science. Among these, La@C82 has been recognized as a prototype of endohedral metallofullerenes.Recently, we have verified that the carbon cages of the major (La@C82-A) and minor (La@C82-B) isomers of La@C82 have C2V and Cs symmetry, respectively. It indicates that the addition reaction of La@C82 would yield many regioisomers. Meanwhile, we recently found that the addiction reaction of La@C82-A with adamantanediazirine selectively proceeds. Since La@C82-B possesses 44 nonequivalent carbon atoms, it may produce more regioisomers than La@C82-A. In this context, we report here the first regioselective reaction of La@C82-B with adamantanediazirine.

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Although various borazines have been synthesized, there are few reports of borazine derivatives bearing sulfur atom. Sulfur-containing borazine derivatives would be mutual interaction between lone-pair electrons of the sulfur atom and the vacant orbital of the boron atom in the borazine ring. In this work, we tried the synthesis of novel borazine derivatives containing sulfur substituent on the boron atom. We will discuss the methodology for the formation of borazine with sulfur-boron bonding.

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Recently, we reported that the treatment of diphenylchloroborane with nucleophile such as pyridine in CD₂Cl₂ formed the 1:1 adduct, which gave the sp² cation in CD₃NO₂ by the addition of SbCl₅. On the other hand, the sp² cation in CD₃NO₂ is considered to be weakly coordinated with CD₃NO₂, which is indicated by its ¹¹B and ¹³C NMR specta. However, the structure of the sp² cation in CD₃NO₂ has not been confirmed yet. Accordingly, it is necessary to change leaving groups, nucleophiles, Lewis acids, and solvents in order to clarify the structure of the boron cation and to ascertain the condition of its formation. Furthermore, the structure of the boron cation in solution was estimated based on the optimized structure by ab initio calculation.

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Product-forming steps in SN1 solvolysis of substituted benzyl-X substrate systems, where X is 2-R1-6-R2-substituted 4-methylphenolate (R1=C(CF3)2OH; R2=CH2OH, SiMe3, H), have been established in various solvents on the basis of selective trapping of intimate ion-pair intermediate by the nucleofuge X through ortho-substitution of the phenolate ion by the counter carbocation.

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Solvolysis rates of 1-trifluoromethyl-1-(X-substitutedphenyl)-2-(dimethylphenylsilyl)ethyl esters were determined conductimetrically in 60% (v/v) aqueous ethanol. The effects of aryl substituents on the solvolysis rate at 25°C were correlated with Yukawa-Tsuno Eq. against σ parameter of r=1.25 which is characterization of β-silylated α-CF₃ cation system. This r value is identical to the value with α-H (r=-3.07). The results suggest that the silyl participation mechanism should remain the same in both α-CF₃ and α-H systems.

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The charge dispersion of erythro- and threo-3-(aryldimethylsilyl)-2-butyl 3,5-dinitrobenzoates was estimated in terms of the Tsuno-Fujio equation. The analysis shows different charge dispersion between erythro- and threo-isomer. An unexpected results that electron-withdrawing substituent (m-CF₃) has larger charge dispersion than electron-donating subsutituent (p-MeO) was obtained. In order to examine the cause of this results, ab initio calculation have been carried out to estimate charge between diastereomers and substituents.

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We reported that the beta-silicon participation in solvolyses was explained by a continuous spectrum of transition states from the kc mechanism to Si-bridged one based on the continuous change of the rho value with stability of reaction center. In order to confirm the continuous changes of Si-bridging mechanism, the solvolysis of beta,beta-dimethyl system is chosen in this study. The solvolysis rates of 2-(aryldimethylsilyl)-2-methylpropyl 3,5-dinitrobenzoates in 60% aq. EtOH at 50 ^oC were analyzed by the Y-T Eq. to give a rho value of -1.8 as high as that for the primary system, referable to the Si-bridged mechanism.

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We have discussed the behavior of ion pair based on the products analysis for the solvolysis of 1-phenylethy thionobenzoates in 50/50 (v/v) TFE/H₂O (I = 0.5, NaClO₄) at 25^oC, and proposed the mechanism that the solvents attack to ion pair competes with the position change of leaving anion without the rotation of carbocation. In order to clarify the rotation of carbocation, we have examined the stereochemistry of 1-(4-fluorophenyl)ethyl alcohol obtained in this solvolsis. The product alcohol generated from (S)-enantiomer was isolated and the stereochemistry of this was determined by the ¹H NMR spectrum in the presence of (S)-(+)-2,2,2-trofluoro-1-(9-anthryl)ethanol. The ratio of (R)- and (S)-configuration was 1.2. This means that 91 % of product formation is accompanied with racemization. This value is much larger than that expected from the mechanism we proposed. The rotation of carbocation occurs in this solvolysis.

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The solvolysis of p-methoxyneophyl ester in ionic liquids was examined as the foundation that search for the useful organic reactions using the ionic liquids, and compared with the solvolysis in the standard molecular solvents. The reaction of p-fluorobenzensulfonate was followed by ¹⁹F-NMR and the rate of reaction was determined. The rate constants in [bmim][PF₆] and [emim][BF₄] are comparable to that in ethanol under buffer (2,6-dimethylpyridine) conditions, that is, the ionizing power is almost the same. The products and the thermodynamic parameter on rates indicate that the reaction mechanisms are S_N1 and E1. It was suggested that presence of hydrogen at imidazolium ring 2nd position has influenced the rate constants of phenonium ion formation. In the ionic liquid, it was also confirmed that there are the additive effects, such as halogen and water, and there is the large catalyst effect by acid.

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The gas-phase basicities (GBs) for a representative set of six formamidine ureas with variations in the imino substitutent (RN=CHN(Me)CONHMe) were determined in proton-transfer equilibria by ion cyclotron resonance (ICR) mass spectrometry and further explored with calculations at the B3LYP/6-31+G* level of theory. Relative GBs were linearly correlated to the inductive effect of the imine nitrogen substituents, giving a roh_I= -33. The magnitude of the roh_I value suggests that protonation occurs preferentially at the imino nitrogen. The calculated basicities for the imino N-protonated ones are in good agreement with the observed values. The GB values were also found to be similar to those previously reported for N¹,N¹-dimethyl-N²-substituted formamidines. These results indicate importance of intramolecular hydrogen-bonding interaction with the amide oxygen in the protonated ion.

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From the cold-spray ionization (CSI) mass spectra of ionic liquids (IL) it is found that ILs exist mostly as ion-pairs in acetonitrile while in methanol the specific interaction between ILs and methanol collapses weakly bound clusters. In addition, the CSI-MS spectra of a binary mixture of ILs showed that the relative amount of respective cluster ions is not agreement with the composition of ILs in the solution. The disagreement was attributed to the difference in strength of the binding interaction between M⁺ and X^-; a weakly bound ion-pair is easily collapsed to give ions detected in a mass spectrometer. This will provide quantitative information on the interaction between a cation and an anion of ILs.

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The molecular dynamics simulation about model PC solution of LiBF₄, LiPF₆, and LiB(CF₃,) ₄) are performed to obtain the self-diffusion coefficient, radial distribution function, and running integral with respect to the conductivity of the electrolyte solution. Analysis of MD results indicates that cation-anion direct contact pairs and various kinds of multiple ion complexes exist more in LiBF₄ solution than LiPF₆ solution.

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The interactions between solute ions and solvent molecules is an significant factor for the study of reactivity of reactant ions in solutions. However, solvation for organic ions has not been directly and thermodynamically studied. This time, we studied quantitatively the relative solvation energy for substituted tropylium ions and cyclopentadienide ions, as carbocations and carbanions, respectively. The solvation energy decreases for these ions by alkyl substituents. The decrease has a fairly good correlation with the total charge on the ring. Dispersion of charge by alkyl substituents is likely to cause the decrease in solvation.

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A fluorenyl cation was reported to be antiaromatic, since its solvolysis was faster than triphenylmethyl cation. However recently the cation was suggested to be a triplet cation or a simple conjugated carbocation on the base of results by flash photolysis, solvolysis, and theoretical calculations. Therefore we now report investigation of benzofluorenyl cations by NMR and DFT calculations.

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The synthetic applications of tris(t-butylthio)cyclopropenyl cation (1) and 2,3-bis(t-butylthio)cyclopropenethione (7) which have highly strained three-membered rings have been examined. A one-pot reaction of 1 with lithium 2-methylpiperidinide at -78°C gave N-heterocyclic compound 6. The reaction of 1 with substituted ethynyl anions gave ethynylallene derivatives 3a-c in good yields. Furthermore, the reaction of 7 with thionylchloride at 0°C, followed by treatment with ethynyl anions, afforded the diethynylallene derivative 9. The structures of 3c and 6, were determined by X-ray analyses. Features of the above synthetic reactions and properties of products are presented.

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The rates of the reaction of BH3 and benzaldehyde in THF were measured with stopped-flow photometer and UV spectrophotometer. The curves of the decrease of benzaldehyde concentration with a large excess of BH3 did not show a simple monoexponential decay. By the simulation of the experimental curve, the reaction scheme could be separated into two steps (complex formation step and reduction step). From the dependence of the rate on the concentration of BH3 in each step, the reaction order of BH3 was calculated. In the presentation, the results of substitution effects will be discussed.

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It has been known that alfa-haloketone shows remarkably enhanced reactivity in SN2 reaction. To clarify the origin of this effect, reaction pathways and transit states for the reactions of RCOCH2Cl (R=Me, Ar) and various nucleophiles (OH-, Cl-, CH3- and H2O) were calculated. It was found that the reaction pathway varied with a nucleophile, and that a strong nucleophile formed the carbonyl-carbon adduct, which then gave the substituted product through an intramolecular reaction. The experimental results for the reaction of PhCOCH2Cl and nucleophiles will also be discussed at the presentation.

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The origin of anomalous relation between rates and equilibria for the proton-transfer reactions of nitroalkanes, known as nitroalkane anomaly, was investigated by kinetic experiments. The present study gave the Hammett rho value of 1.35 for the deprotonations reactions of substituted phenylnitromethane and hydroxide. Comparison of the rho value with that for the equilibrium constant (1.23) gave the Bronsted alfa value of 1.1. The larger-than-unity alfa value is consistent with the well-know behavior of nitroalkane anomaly. However, the acid-catalyzed protonation (reverse process) of phenylnitronate anion gave the Hammett rho value of 1.54. The large positive rho value clearly indicated that the acid-base equilibrium is not a single step process, but is complicated by an intervention of some kind of intermediate.

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For relatively large molecules such as 1,8-anthracene diol, a proton transfer takes place by the mediation of a solvent water molecule, whereas an intramolecular proton transfer for small molecules occurs without solvent molecule intervention. Analyses of these mechanisms using theoretical calculations will contribute to understanding of fundamental themes of organic reactions, such as processes of a hydrogen-bond and electron transfer, and concomitant solvation-desolvation dynamics. In this meeting, we will discuss the mechanism of a water mediated proton shift of 1,8-anthracene diol and the substituent effect on the process, and compared the mechanism with that of an intramolecular proton transfer.

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When many solvent molecules are around the solute molecules, it is necessary to take account of the free energy difference along the reaction. To evaluate how solvent molecules affect the reaction profile, we calculated the free energy maps for X^-+CR₃X+100H₂O (X=F or Cl, R=H or CH₃) using QM/MM method together with Monte Carlo method. We found a reaction path in aqueous solution is close to the IRC path in gas phase in the reaction of Cl^-+CH₃Cl, while it is different in the reaction of Cl^-+C(CH₃)₃Cl.

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A chemical reaction in solution takes place with a concomitant solvation-desolvation event. In order to understand the mode of solvation and its effect on chemical reactivity, we took a hydride transfer reaction of acyloin anion, and calculated the react pathway with quantum mechanical methods. It was found that the reaction has about 10 kcal/mol of activity energy or lower for the reactions of RC(=O)CH(-O)R' anion in a water cluster. In the presentation, we will discuss the effect of R,R' and solvation structure on the reaction pathway.

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Previously we proposed an approximated equation which, based on the general perturbation theory, provides a simple theoretical method to evaluate the linear free energy relationship of the substituent effects. An parameter d was introduced to this equation in order to estimate the extent of localization of the eigenvectors on the reaction sites of the asymmetric component at the transition state. Since this method should be generally applicable to concerted cycloaddition reactions provided that one of the reactants has a symmetrical structure, this time we have applied this method to the substituent effects of Diels-Alder reactions using kinetic data on literatures. Satisfactory results were obtained not only with aromatic dienes (e.g. ArCH=CH-CH=CH₂ + maleic anhydride) or dienophiles (e.g. methyl propiolates + tetraphenylcyclopentadienone) but also with nonaromatic alkenes (e.g. trans-XCH=CH-Y + 9,10-dimethylanthracene).

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We succeeded to construct a reaction system mimicking the function of the pyruvate dehydrogenase complex and obtained thiolesters in good yields from benzaldehydes in dichloromethane. The key step of the formation was the attack of the thiazolium carbene to the formyl group. On the basis of the above findings, we have set up a reaction system in which thiolester is formed within a vesicular membrane composed of dimethyldimyristylammonium bromide, 3-dodecyl-4-methyl-thiazolium bromide (catalyst), and N¹-dodecylnicotinamide bromide (oxidant) in a ratio of 0.8 mM : 0.6 mM : 0.3 mM, in a triethanolamine-HCl buffer (30 mM, pH ~ 7.7) solution. In the vesicle, 4-methoxycarbonylbenzaldehyde was converted to the corresponding thiolester in about 70% yield. As the yield depends on the amount of the catalyst and pH, the reaction efficiency may be influenced by the competitive nucleophilic attack to the formyl group by hydroxide anion.

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An optically active, axially chiral NAD model compound (1) with a quinoline ring system was reduced by the chiral NADH model compound (Me₂PNPH) and achiral NADH model compound (PNAH), affording a mixture of 1,2- and 1,4-dihydroquinolines. The 1,2-/1,4-isomer ratio (2/3) and enantiomer ratio in 2((R)-2/(S)-2) and 3((R)-3/(S)-3) reveal that the carbonyl orientation governs the molecular arrangement in the transition state of the reaction and determines the regio- and enantioselectivity of the product.

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We have recently reported that in the asymmetric cyclopropanation reaction between pyridinium ylides and substituted methylidenemalononitriles, the stereochemistry between reactions involving the ylide bearing an 8-phenylmenthyl ester and that with an 8-phenylmenthyl amide (N-H amide) was opposite. We have carried out an examination of the N-Me amide and have found that diastereochemistry was generally higher for reactions of the N-Me amide compared with those of the N-H amide. This result implied that steric factors govern the stereochemical outcome. In order to gain further insight to the mechanism of the reaction, the N-iBu amide has been synthesized and it is now under investigated. In addition, PM3 calculations are also being carried out. For the N-H amide, under certain reaction conditions, the cyclopropane product underwent further cyclization to give bicyclic compounds.

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We have examined the [2+2] cycloaddition of cycloalkenes of 5- to 8-membered rings and ketene generated from diazoester by photolysis in the liquid phase and by FVP in the gas phase to show that the high stereoselectivity was maintained over the wide range of temperature when the alkene and the diazoester was linked with 2,4-pentanediol or the related tethers. The product ratio, 8/9, in the photolysis did not depend on the conversion, and the product ratios obtained are considered to be the diastereoselctivity of the addition reaction. Although the repeated FVP at high temperature (350 oC) induced isomerization of 8 to 9, no change of the product ratio was observed at lower temperature of 250 oC. Thus, the product ratios of FVP are no better than the stereoselectivity of the main reaction. It was found that the diastereoselectivity was not much dependent on the temperature over - 60 to 300 oC , and mainly controlled by the differential activation entropy irrespective of the ring size.

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Alkylideneallyl cation intermediate can be readily generated by the ring-opening reaction of alkylidenecyclopropanone silyl acetal in the presence of Lewis acid. The ring-opening reaction in the presence of carbon nucleophiles gave trapping products. Reaction with allyl stannane gave allylic adducts, and silyl enol ether gave a 3 + 2 adduct. A 3 + 4 adduct was also obtained by the reaction with furan. The reaction mechanism of the cycloadditions will be discussed in addition to the reagioselectivity of nucleohilic addition to the alkylideneallyl cation intermediate.

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The [1,2]-Stevens rearrangement is a useful transformation in organic synthesis since it can convert a readily obtainable C-N bond into a new C-C bond. However, the utility of its asymmetric versions has been severely limited because the [1,2]-Stevens rearrangement proceeds via a radical cleavage-recombination mechanism, thus leading to a decreased stereoselectivity. Recently West et al. have reported that the asymmetric [1,2]-Stevens rearrangement of N-benzyl-N-methylproline esters provides only 77 % of the asymmetric transmission. Herein we wish to report that the stereoselectivity of this [1,2]-Stevens rearrangement can be improved dramatically by proper choice of the base and solvent used. The best result was obtained under a phase-transfer conditions (CsOH in dichlorometane): the corresponding α-benzylated proline tert-butyl ester was obtained in 58 % yield with high stereoselectivity (94 % er).

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Anions of allyl silyl ethers might undergo an intramolecular migration of the silyl group from oxygen to carbon which is called as the [1,n]-retro-Brook rearrangement. While [1,2]-retro-Brook rearrangement of allyl silyl ethers has been well studied and applied for organic synthesis, the [1,4]-retro-Brook rearrangement has been quite rare. Only a few examples have been reported by Still and Nakazaki, but its details are still unclear. Herein we report that the [1,4]-retro-Brook rearrangement of allyl trialkylsilyl ethers can be brought about exclusively without any [1,2]-retro-Brook rearrangement by addition of t-BuOK or HMPA to give the γ-silylated (Z)-silyl enol ethers by trapping with trimethylsilyl chloride. The effect of t-BuOK or HMPA, and the mechanism of the [1,4]-retro-Brook rearrangement will be discussed in terms of the silicate intermediacy.

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Domino Michael reaction of 2,6,6-trimethyl-cyclohex-2-ene-1,4-dione and its derivatives with Michael partners have been effected to give bicyclo[2.2.2]octane-2,5-dione derivatives by a catalytic amount of Bronsted base generated from silica-gel and n-BuLi.

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We have attempted the construction of variously substituted 2-cyclohexenone derivatives with acrylates via successive Michael reactions.
The annulation precursors were prepared by the intermolecular Michael reaction of cyclohexenone derivatives with acrylates. The intramolecular Michael reaction of the annulation precursors was performed in the presence of K₂CO₃ as the base and n-Bu₄NBr as the phase transfer catalyst. The annulation proceeded to give a mixture of α, α'-annulation products obtained from annulation at the α' position of the carbonyl group with accompanied migration of the double bond and α, γ-annulation products obtainednfrom annulation at the γ-position of the carbonyl group. The one-pot reaction also gave annulation products with a tendency similar to that of the stepwise reaction.

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15-crown-5-ether preferentially captures Na⁺, which ion size fits the crown ring size, among Na⁺, Li⁺ and Mg²⁺. But N-aryl-monoaza-15-crown-5-ehters (ArN15C) preferentially captures Li⁺ and Mg²⁺ than Na⁺. It is considered four oxygens of ArN15C coordinates Li⁺ and Mg²⁺ because the nitrogen coordinating ability is reduced by electron-withdrawing aryl group. The ArN15C ring is probably twisted so that Li⁺ and Mg²⁺ may pull the four oxygens. So we synthesized N-aryl-dibenzo-monoaza 15-crown-5-ethers (DBArN15C) having two benzene rings in crown ring. Crown ring of DBArN15C is less flexible crown ring than ArN15C. We investigated the stability constants of DBArN15C-metal ion complexes. The stability constants was the order of Li⁺ > Na⁺ > Mg²⁺, and the selectivity of Na⁺ inclusion was improved.

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The main goal of this research was to compute activation energy barrier for the allowed by orbital symmetry rules simultaneous, conrotatory process of cyclobutene ring closure for a series of compounds that differ in position of substitution and number of fluorine atoms in the system, taking torquoselectivity theory into consideration.
We have made an attempt at evaluating the influence of vinylic fluorine substituent on geometrical parameters and thermodynamic stability of 3-vinylcoumarin and its fluorinated analogues.
It was find that fluorine influences the shape of transition state and perfluorination in vinyl group yields the lowest activation barrier and the most thermodynamically stable product.

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