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11.
The reactions of organolithium reagents and Grignard reagents with optically active alkoxygermanes R3GeOR′ have been studied [R3GeOR′ = ()-i-PrPhNpGeOCH3, ()-i-PrPhNPGeOMen and ()-MePhNpGeOMen]. Saturated reagents (e.g. butyllithium) give retention of configuration at germanium whilst unsaturated reagents (e.g. allyl- or benzyllithium) lead to inversion. 相似文献
12.
Francis Pochat 《Tetrahedron letters》1981,22(37):3595-3596
Ar-C(CN)=NN=C(CN)-Ar and Ar-C(CN)=NNHCO-Ar′, easily prepared from the bromoderivatives Ar-CBr(SEt)-CN, afford in good yields, by heating in a basic medium, 3,6-diaryl-5 hydroxy-1,2,4-triazines. 相似文献
13.
The reaction of PhSeCl and N-PSP with homogeranic acid () or homoneric acid () affords butanolides in a stereospecific way. Despite the large number of cyclic cases studied in the literature such acyclic systems were remained largely unexplored. PhSe+ was unable to realize polycyclization. 相似文献
14.
Hydrogen-aarbonyl chelation and magnesium-arene π coordination are proposed to aooount for enhanced enantioselectivïty in 1,4-addition reactions of chiral cuprates. 相似文献
15.
Francis Choucroun 《Geometriae Dedicata》1994,53(1):69-74
Résumé On décrit une bijection canonique qui associe à un bon espace ultramétrique, localement compact, non compact, un arbre pointé par un bout: cet espace s'identifie à l'ensemble des autres bouts.
We describe a canonical bijection, which associates a tree with a chosen end to a nice ultrametric, locally compact, non-compact space: this space is identified with the set of other ends.相似文献
16.
17.
An activated D-residue of a protected dipeptide when coupled racemizes twice as much as an activated L-residue, which is contrary to the case for couplings of acylamino acids. 相似文献
18.
Yoshim Tokura Richard L. Edelson Francis P. Gasparro 《Photochemistry and photobiology》1993,58(6):822-826
Abstract The effects of cell differentiation and mitogen and phorbol ester stimulation on the formation of 8-methoxypsoralen (8-MOP)-DNA photoadducts in murine T lymphocytes were examined using 3 H-8-MOP. While there were no significant differences in 8-MOP photoadduct formation among BALB/c thymocytes, splenocytes, splenic T cells and MRL/1pr lymph node cells, BALB/c bone marrow cells showed fewer photoadducts than did the lymphocytes. This suggested that proliferating progenitor cells may be resistant to 8-MOP photoadduct formation. Incubation of purified splenic T cells with lectin mitogens for 2 h or with phorbol 12-myristate 13-acetate (PMA) for 2–43 h resulted in reduction of 8-MOP photoadduct formation in the DNA, whereas 64 h cultivation with these agents augmented the photoadduct formation. The reduction of photoadduct formation induced by phytohemagglutinin was restored by the further addition of a protein kinase C (PKC) inhibitor, H-7, to the culture. Thus, it is assumed that the reduction of adduct formation evoked by mitogens and PMA is mediated in part by the activation of PKC in the cells. On the other hand, the augmentation of the adduct formation induced by the longer-period cultures with mitogens and PMA appeared to be caused by down-regulation of PKC. The present study showed that the stimulatory signals in which PKC is presumably involved affect the ability of cells to form 8-MOP-DNA photoadducts. 相似文献
19.
Optically detected magnetic resonance (ODMR) techniques are used to determine the orbital assignment of the phosphorescent triplet state of p-bezonquinone in the condensed phase. The principal spin—orbit coupling routes are discussed in terms of the observed spin—vibronic activity. 相似文献
20.
Koren AB Curtis MD Francis AH Kampf JW 《Journal of the American Chemical Society》2003,125(17):5040-5050
Syntheses are reported of new 4,4'-dialkyl-2,2'-bithiazole oligomers that have alkenoxy side chains that are capable of easy conversion to oligomers with functionalized side chains, e.g., terminally substituted hydroxy chains. The crystal structures of two representative oligomers (4,4',4' ',4' "-tetra-(2-propenoxymethyl)-2,2',5',5' ',2' ',2' "-quaterthiazole (3P2) and 4,4',4' ',4' "-tetra-(3-hydroxypropyloxymethyl)-2,2',5',5' ',2' ',2' "-quaterthiazole (3H2)) were determined; 3P2 crystallizes in a pi-stacked motif with two molecules per unit cell, whereas 3H2 forms pi-stacks that are linked with hydrogen bonds to form infinite two-dimensional sheets with one molecule per unit cell. A comparison of the UV-vis spectra of the compounds in solution and in the solid state provides unequivocal evidence for the presence of a Davydov splitting, W(D) approximately 0.2 eV, in solid 3P2. The spectra are interpreted in the framework of molecular exciton theory to extract a value of the intermolecular transfer integral, J approximately 0.2 eV, for a total exciton bandwidth of ca. 0.8 eV. Monte Carlo calculations were used to determine the density of states of the exciton band and the absorption and emission line shapes of the 0 <-- 0 transition. It is suggested that the "three-humped" absorption profile typical of partially crystalline, regioregular polymers is the "optical signature" of pi-stacking. 相似文献