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81.
82.
Stereodivergent Synthesis and Stereochemical Reassignment of the C79–C104 Fragment of Symbiodinolide
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Prof. Dr. Hiroyoshi Takamura Takayuki Fujiwara Yohei Kawakubo Prof. Dr. Isao Kadota Prof. Dr. Daisuke Uemura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(6):1984-1996
We have synthesized eight possible diastereoisomers 3 a – h of the C79–C97 fragment of symbiodinolide ( 1 ) in a stereodivergent manner by utilizing a dithiane addition to the aldehyde as a key step. Comparison of the 13C NMR chemical shifts of the natural product 1 and the synthetic products 3 a – h indicated that the relative stereostructure of this fragment in symbiodinolide ( 1 ) is that represented in 3 a or f . We have stereodivergently synthesized eight possible diastereoisomers of the C94–C104 fragment 4 a – h , and we have compared their 13C NMR chemical shifts with those of the natural product, which established the relative stereochemistry of this fragment to be that described in diastereoisomers 4 a or e . By combining the stereostructural outcomes of the C79–C97 and C94–C104 fragments, we have proposed four candidate compounds of the C79–C104 fragment 2 a – d . We also synthesized diastereoisomers 2 a and b ( 2 a in the preceding article; Chem. Eur. J. 2015 , DOI: 10.1002/chem.201503880) by a Julia–Kocienski olefination and diastereoisomers 2 c and d by a Wittig reaction. By comparing the 13C NMR chemical shifts of natural symbiodinolide ( 1 ) with those of the synthetic products 2 a – d , we have reassigned the stereostructure of the C79–C104 fragment of natural product 1 to be that depicted in diastereoisomer 2 b . 相似文献
83.
Yoshihiro Abe Hideo Hosono Takayuki Kamae Kouichi Kawashima 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):113-116
Abstract Protons in alkaline-earth phosphate glasses give much higher mobility than those in silicate glasses. This is caused by the difference in O-H bonding state. Protons in P-OH form a strong hydrogen bonding with oxygen anion, resulting in formation of weak O-H bond. The electrical conductivity of the glasses is proportional to the square of the proton concentration. The activation energy for the conduction is related to νOH, peak wavenumber of infrared absorption band (around~3000 cm?1), due to fundamental O-H stretching vibration. The mobility of protons increases with decreasing νOH, which depends on the species of ions included in the phosphate glasses. 相似文献
84.
Tsuneyuki Sato Toshio Kadowaki Hiroshi Takeda Takayuki Otsu 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):1225-1239
(S)-4-Methyl-2-N,N-dimethylaminopentyl methacrylate (DMAPM) was synthesized from the reaction of N,N-dimethyl-L-leucinol with methacryl chloride, and its radical polymerization was investigated. It was found that DMAPM readily polymerized by α,α1-azobisisobutyronitrile (AIBN) as an initiator to give poly-DMAPM. The copolymerization of DMAPM(M1) with styrene(Mz) was also studied in various solvents with AIBN as an initiator at 60°C. From the result obtained in benzene, Q and e values of DMAPM were determined to be 0.64 and -0.04, respectively. Specific rotations of the copolymers of DMAPM with styrene were not proportional to the weight percent of the DMAPM unit incorporated, but the observed relation gave a downward curve. The copolymerizations DMAPM with α, β-disubstituted monomers such as maleic acid, maleimide, and N-phenylmaleimide were carried out in order to induce asymmetric center in the polymer chain. After hydrolysis of the copolymers obtained, the hydrolyzed polymers were found to be optically active, suggesting an induction of asymmetric center into the polymer chain. 相似文献
85.
A kinetic study of radical polymerization of vinyl mercaptobenzothiazole (VMBT) with α,α′-azobisisobutyonitrile (AIBN) at 60°C was carried out. The rate of polymerization (Rp) was found to be expressed by the rate equation: Rp = k[AIBN]0.5 [VMBT]1.0, indicating that the polymerization of this monomer proceeds via an ordinary radical mechanism. The apparent activation energy for overall polymerization was calculated to be 20.9 kcal/mole. Moreover, this monomer was copolymerized with methyl methacrylate, acrylonitrile, vinyl acetate, phenyl vinyl sulfide, maleic anhydride, and fumaronitrile at 60°C. From the results obtained, the copolymerization parameters were determined and discussed. 相似文献
86.
The kinetics of the cationic polymerization of 1-β-cyanoethyl aziridine initiated 3-hydroxy- 1-propane sulfonic acid sultone and methyl tosylate have been studied. The course of polymerization involved the propagation stage and termination reaction due to the reaction between the growing chain and imino groups in the polymer chain. The propagation constants and termination constants were obtained. The enthalpies of activation for the propagation and termination reactions are ΔHp? = 12.9 kcal/mol and ΔHt? = 12.4 kcal/mol, and the entropies of activation are ΔSp? = -31 cal/deg·mol and ΔSt? = -39 cal/deg·mol. Otherwise, the polymerization initiated with methyl tosylate involved an early stage which was initiated very quickly. 相似文献
87.
Abstract Oligomerization of butadiene with the catalyst system of nickel(II)chloride, electron donor, and lithium aluminum hydride or sodium borohydride has been studied. Most oligomers obtained with this catalyst were linear, and dihydrogenated dimers, trimers, and tetramers. They were n-octa-1,6-diene, n-octa-1,7-diene, n-dodeca-1,6,10-triene, and n-hexadeca-1,6,10,14-tetraene, which were identified by means of infrared, nuclear magnetic resonance, and mass spectrometry. Yields of each oligomer were strongly affected by the nature of the electron donors used. The hydrogen required for the formation of the hydrooligomers was assumed to originate from the lithium aluminum hydride or sodium borohydride used as a reducing agent. A proposed mechanism for the hydrooligomerization is that butadiene is oligomerized on the nickel atom, and the produced oligoolefins, bonded to the nickel by two terminal π-allylic bonds, are dihydrogenated to linear hydrooligomers. 相似文献
88.
Abstract Polymers of bis(trimethylsilyl) fumarate, di-tert-amyl fumarate, and methyl tert-amyl fumarate were prepared by radical polymerization at 60 or 120°C. The polymers were converted into poly(dimethyl fumarate) via thermolysis or hydrolysis and subsequent methylation to determine the tacticity using 13C-NMR spectroscopy. The probabilities of meso addition (P m) were revealed to be 0.66 (60°C) for the bis(trimethylsilyl) ester, 0.60 (60°C) and 0.52 (120°C) for the di-tert-amyl ester, and 0.54 (60 and 120°C) for the methyl tert-amyl ester. From the temperature dependence of the P m values, the differences in activation enthalpies and entropies for the meso and racemo additions were evaluated. The microstructure of poly(dimethyl fumarate) derived from poly(maleic anhydride) was also examined. The opening and addition modes in propagation of the fumaric and maleic derivatives were discussed based on the results obtained in the present and previous work. 相似文献
89.
Polystyrene sulfonic acid resin (Amberlyst 15) was found to initiate the cationic polymerization of 1,3-dioxolane easily in bulk at 0 to 50° C, and polymers with a reduced viscosity of 0.1 were obtained. However, this resin showed only low initiator activity for the polymerizations of 2-methyl-1, 3-dioxolane and trioxane. 相似文献
90.
The conductance through single 7,7,8,8‐tetracyanoquinodimethane (TCNQ) connected to gold electrodes is studied with the nonequilibrium Green’s function method combined with density functional theory. The aim of the study is to derive the effect of a dicyano anchor group, ?C(CN)2, on energy level alignment between the electrode Fermi level and a molecular energy level. The strong electron‐withdrawing nature of the dicyano anchor group lowers the LUMO level of TCNQ, resulting in an extremely small energy barrier for electron injection. At zero bias, electron transfer from electrodes easily occurs and, as a consequence, the anion radical state of TCNQ with a magnetic moment is formed. The unpaired electron in the TCNQ anion radical causes an exchange splitting between the spin‐α and spin‐β transmission spectra, allowing the single TCNQ junction to act as a spin‐filtering device. 相似文献