Novel norcassane-type diterpene from the seed kernels of Caesalpinia crista

Three novel norcassane-type diterpenes were isolated from a CH₂Cl₂ extract of the seed kernels of Caesalpinia crista together with four known cassane-type diterpenes. All the new compounds represent unprecedented carbon framework. Norcaesalpinin A (1) and B (2) had 17-norcassane skeleton, while norcaesalpinin C (3) had 16-norcassane skeleton. Their structures were elucidated on the basis of spectral analysis.     

Synthesis of a novel naphthalene-based poly(arylene ether-ketone) by polycondensation of 1,5-bis(4-fluorobenzoyl)-2,6-dimethylnaphthalene with bisphenol a

Synthesis of 1,5-bis(4-fluorobenzoyl)-2,6-dimethylnaphthalene ( 1 ), polycondensation of 1 with Bisphenol A, and properties of the obtained polymer were studied. Friedel–Crafts acylation of 2,6-dimethylnaphthalene with 4-fluorobenzoyl chloride in nitrobenzene selectivity afforded 1 in 82% yield. X-ray single crystal structural analysis of 1 confirmed that the dibenzoylation proceeded regioselectively and two methyl groups sterically inhibited the coplanarity of the two aromatic planes. The polycondensation of 1 with Bisphenol A in toluene/N-methyl-2-pyrrolidone (NMP) mixed solvent in the presence of excess potassium carbonate as a condensation reagent was carried out at 180°C for 4 h to quantitatively afford the corresponding poly(arylene ether-ketone) (PEK) 3 with high molecular weight (M?_n～30,000) as a slightly yellow powder. As the reaction time was prolonged, both M?_n and MWD of 3 increased and the solubility of 3 in chloroform clearly decreased. By GPC-LALLS, M?_n of 3 obtained by the polycondensation for 16 h, was 85,000. The PEK 3 with high molecular weight was produced in a quantitative yield in a variety of solvents such as sulfolane. Water formed during the polycondensation hardly affected the yield and molecular weight of 3 , although a small molecular weight decrease took place. To evaluate the special effect of the methyl groups of 3 , polycondensation of 2,6-bis(4-fluorobenzoyl)naphthalene 2 with bisphenol A was carried out for comparison and the corresponding PEK 4 was quantitatively obtained. Whereas 3 was soluble in ordinary organic solvents such as tet-rahydrofuran (THF), chloroform, and NMP at room temperature, 4 was insoluble in most solvents except for strong acids such as conc. sulfonic acid. The polymer 3 showed high glass transition temperature (238°C) and 5% weight loss temperature (457°C). Casting of the polymer from THF solution gave a transparent, tough, flexible, and amorphous film. © 1995 John Wiley & Sons, Inc.     

Chemical conversion of humulene to dactylol. Biomimetic,apparent 1,2-shift of a methyl group

Africanol, which had been previously derived from humulene, was converted to dactylol through a formal 1,2-shift of a methyl group, which involved a cyclopropane sliding reaction and subsequent cyclopropane ring opening.     

Generalized doubly symbolic formulation for integral-driven direct configuration interaction method

Summary A direct configuration interaction (CI) scheme using the generalized double symbolism both for the external space and for the internal space is proposed in an integral-driven context. The reason why the double symbolism is used in the present formulation is that the main target is in investigating large molecular systems. The integrals, configuration state functions, and energy expressions are systematically classified in terms of the orbital labels and their mutual relations. Various types of CI wavefunctions can be set up flexibly. The resulting structure of integral processings in the sigma vector construction is complicated. The number of unique loop types for two-electron integrals is 1325. Because the parallel architecture is gaining importance in the recent computational platforms, the parallelism is also addressed.     

Chirality organization of ferrocenes bearing dipeptide chains of heterochiral sequence

[structures: see text] The symmetrical introduction of two dipeptide chains of heterochiral sequence (-L-Ala-D-Pro-NHPy) into the ferrocene scaffold as a central reverse-turn unit was demonstrated to induce both antiparallel beta-sheet-like and type II beta-turn-like structures simultaneously, affording the chirality-organized structure. The ferrocene bearing only one dipeptide chain (-L-Ala-D-Pro-NHPy) exhibited a left-handed helically ordered molecular assembly through a network of intermolecular hydrogen bonds instead of intramolecular hydrogen bonds.     

Reactions of cyclic disulfides with carbenes; desulfurization and insertion

Reactions of several cyclic disulfides with carbenes generated by catalytic and photochemical decompositions of diazo compounds have been studied. Carbenes reacted with cyclic disulfides yielding 1,3-dithiane quantitatively as S-S insertion reaction, while the selective desulfurization results in the reaction of disulfides with bulky substituents. The carbene reaction is sensitive to bulkiness of disulfides.     

Spectrophotometric determination of vanadium in natural waters and rocks after selective adsorption on sephadex gel

Vanadium(V) ions are strongly adsorbed on Sephadex G-25 gel at pH 4.2, and are desorbed reversibly into 0.1 M acids. Vanadium present in rocks and in natural waters at μg l⁻¹ levels can be separated and concentrated by means of a gel column at pH 6 (in order to avoid the interference of molybdenum(VI)) and determined spectrophotometrically with 4-(2-pyridylazo)resorcinol. Interference by iron(III) can be suppressed by adding copper(II)—CyDTA. Large amounts of sodium chloride and potassium nitrate have little effect on the adsorption.     

Electron-transfer-induced substitution of alkylated C60 chlorides with proton sponge

A series of alkylated C(60) chlorides 1,4-RC(60)Cl (1) were found to undergo nucleophilic substitution with 1,8-bis(dimethylamino)naphthalene (2), affording 1,4-RC(60)Ar [3, Ar = 4,5-bis(dimethylamino)-1-naphthyl] in good yields. An S(RN)1 mechanism, initiated by a single-electron transfer from 2 to 1, is proposed on the basis of the enhanced rates compared with the rate of the S(N)1 reaction of 1 with anisole. The involvement of free radicals in the reaction is supported by the formation of a small amount of dimer RC(60)-C(60)R (4) as a byproduct. The enhanced ability of C(60) chlorides 1 to accept an electron, attributable to the inductive effect of the directly attached chlorine atom, was demonstrated by its reduction potential and calculated LUMO energy.     

An investigation of the decomposition of the common intermediate ions produced by electron impact. IV—[C6H5CO]+ ions from several alkyl benzoates

The decomposition of the [C₆H₅CO]⁺ ions produced from eight alkyl benzoates by electron impact has been studied. By calculating the heat of formation of [C₆H₅CO]⁺ ions from the appearance potential value, it is shown that the ions from C₆H₅COOR when R?H, CH₃, C₂H₅ have some excess energy, and those where R = n-C₃H₇, iso-C₃H₇, n-C₄H₉, iso-C₄H₉, iso-C₅H₁₁ are produced with more excess energy. It is also shown that by taking this excess energy into account, there is a linear relationship between the heat of formation of the activated complex produced in the reaction [C₆H₅CO]⁺→[C₆H₅]⁺ + CO and the vibrational degree of freedom of the neutral fragment ? OR.     

An investigation of the mechanism of single and double hydrogen atom transfer reactions in alkyl benzoates by the ortho effect

Single and double hydrogen atom transfers in reactions (1) and (2) in the mass spectra of ethyl benzoate, isopropyl benzoate, and isobutyl benzoate have been investigated with reference to the ortho effect: (1) [C₆H₅CO₂R]⁺? → [C₆H₅CO₂H]⁺? (m/z 122) + (R-H); (2) [C₆H₅CO₂R]⁺? → [C₆H₅CO₂H₂]⁺ (m/z 123) + · (R-2H). It is demonstrated that the intermediate ion [C₆H₅CO₂H₂]⁺ has the protonated benzoic acid structure with the hydrogen atom on the carbonyl group.