Showing papers by "Chizuko Kabuto published in 1994"
95 citations
TL;DR: The s-cis/s-trans preference of acyclic α, β-unsaturated esters has been studied by their reactions to elucidate the preference in the transition state and by supersonic jet spectroscopy, NOE experiments, and X-ray analysis to clarify the preference as discussed by the authors.
Abstract: The s-cis/s-trans preference of acyclic α,β-unsaturated esters has been studied by their reactions to elucidate the preference in the transition state and by supersonic jet spectroscopy, NOE experiments, and X-ray analysis to clarify the preference in the ground state. It has been rudely accepted that enoate-Lewis acid complexes prefer the s-trans conformation not only in the ground state but also in the transition state of the reactions involving those complexes. The conjugate addition of metal amides to uncomplexed enoates proceeds predominantly through the s-cis conformation, and most organocopper conjugate additions in the absence of Lewis acids or related metal salts take place preferentially in the s-cis conformation
41 citations
34 citations
23 citations
TL;DR: In this article, the 1,3-diselenetane rings of the products caused cycloreversion by heating to generate 2-methylene-3-cyclobutene-1-selones and the selones were trapped with diene to give [4+2] cycloadducts.
Abstract: Heating of alkynyl propargyl selenides afforded a stereoisomeric mixture of 5,10-diselenadispiro[3.1.3.1]deca-1,7-dienes. The 1,3-diselenetane rings of the products caused cycloreversion by heating to generate 2-methylene-3-cyclobutene-1-selones and the selones were trapped with diene to give [4+2] cycloadducts.
14 citations
TL;DR: The bis[tris(bicyclo[2.2]octeno)cycloheptatrienyl]acetylene dication 3 as mentioned in this paper, which is the first example of the acetylene having two tropylium ion units at both ends, has been synthesized by stepwise introduction of the tris[cyclo[ 2.2.
Abstract: The titled dication, bis[tris(bicyclo[2.2.2]octeno)tropyliumyl]acetylene dication 3, which is the first example of the acetylene having two tropylium ion units at both ends, has been synthesized by stepwise introduction of the tris(bicyclo[2.2.2]octeno)cycloheptatrienyl unit to acetylene followed by hydride abstraction. The results of X-ray crystallography indicated that the two tropylium rings are twisted with each other by the angle of 44 o and the tropylium rig is slightly bent into a boat form. The dication 3 was neutralized in 50% aqueous acetonitrile via two steps at the pH values of 7.0 and 11.5, which correspond to the pK R+ values of the dication and the half-neutralized monocation, respectively. Thus, the dication 3 is 6 pK R + units destabilized compared with the corresponding monocation due to the intramolecular electrostatic repulsion of the positive charge. The cyclic voltammetry indicated that the dication 3 undergoes two reversible one-electron reductions consecutively in dichloromethane. The electrochemical reduction of 3 as well as chemical reduction with zinc powder in dichloromethane-acetonitrile afforded a blue solution of the corresponding cation radical 3 .+ , but not the diradical, as shown by ESR experiments
12 citations
TL;DR: In this article, three new benzocycloheptenone derivatives, favelol, isofavelol and favelone, were isolated from the bark of Cnidoscolus phyllacanthus.
8 citations
TL;DR: In this paper, T4rans(t4r)ans, t4r-anss-(t4 r)anss,THF中,金属ナトリウムで縮合させると4,8-ジクロロオクタ-t-ブチルテトラシクロテト-ラゲルマン(7)が生成した.
Abstract: 1,2,3,4-テトラ-t-ブチル-1,2,3,4-テトラフェニルシクロテトラゲルマン(3)をベンゼン中,塩化アルミニウム触媒存在下,塩化水素の作用で四官能性の1,2,3,4-テトラ-t-ブチル-1,2,3,4-テトラクロロシクロテトラゲルマン(4)に変換しだ.化合物4は4種の可能な立体異性体中,熱力学的に安定なtrans-の配置であることをX線結晶構造解析によって明らかにした.シクロテトラゲルtマranンs-(t4r)ansをTHF中,金属ナトリウムで縮合させると4,8-ジクロロオクタ-t-ブチルテトラシクロ[3.3.0.02,7.03,6]オクタゲルマン(6)と3,4,7,8-テトラクロロオクタ-t-ブチルトリシクロ[4.2.0.02.5]オクタゲルマン(7)が生成した.ポリゲルマン(7)は2個の四員環がアンチ形に連結したはしご形ポリゲルマンであることをX線結晶構造解析によって明らかにした.
3 citations
TL;DR: In this article, three new benzocycloheptenone derivatives, favelol, isofavelol and favelone, were isolated from the bark of Cnidoscolus phyllacanthus.
Abstract: Three new benzocycloheptenone derivatives, favelol (1), isofavelol (2), and favelone (3), were isolated from the bark of Cnidoscolus phyllacanthus. Their structures were elucidated on the basis of the spectroscopic analysis. Application of the CD exciton chirality method to 4-methoxybenzoates of 1 and 2 led to determination of the R absolute configuration at C-9, which was confirmed by X-ray crystallographic analysis of the 4-bromobenzoyl derivative of 2.
2 citations
TL;DR: In this article, the treatment of α,β-unsaturated esters having a ketone function at an appropriate position with either TBDMSOTf in the presence of Et 3 N or TMSI (TMS) 2 NH provided, via a tandem intramolecular Michael-aldol reaction sequence, several different types of cyclobutane derivatives.
Abstract: The treatment of α,β-unsaturated esters having a ketone function at an appropriate position with either TBDMSOTf in the presence of Et 3 N or TMSI in the presence of (TMS) 2 NH provided, via a tandem intramolecular Michael-aldol reaction sequence, several different types of cyclobutane derivatives. The two reaction conditions were complementary. Tricyclo[4.2.1.03-8]nonanes 34 and 35, tricyclo[5.1.1.0 3,8 ]nonane 40, tricyclo[5.4.0.0 3,7 ]undecane 51, tetracyclo[5.4.0.0 3,7 .0 9,11 ]undecane 45, and the bicyclo[3.2.0]heptanes 36, 57, and 38, which have structures either partially or completely similar to those of endiandric acids A (1a), B (1b), and C (2), trihydroxydecipiadiene (3), lintenone (4), italicene (3), and filifolone (6), were stereoselectively synthesized by the tandem reaction
1 citations