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21.
[reaction: see text] The gas-phase thermal isomerization of cis,anti,cis-tricyclo[6.3.0.0(2,7)]undec-3-ene (1) to endo-tricyclo[5.2.2.0(2,6)]undec-8-ene (2) at 315 degrees C occurs cleanly through a symmetry-forbidden [1,3] suprafacial,retention (sr) pathway. 相似文献
22.
The structures of the [M? OH]+ ions of m- and pethylnitrobenzene have been compared by measurements of metastable ion spectra, collisional activation spectra, kinetic energy releases and critical energies for the formation of these ions and their subsequent decomposition. Normalized rates of fragmentation of metastable molecular ions and metastable [M? OH]+ ions have been compared for ion lifetimes up to 30 μs. The energy measurements fail to distinguish between the structures of the [M? OH]+ ions, but the normalized fragmentation rates and the collisional activation spectra show their structures to be different. 相似文献
23.
Yang Nan Subhash P. Upadhyaya Wei Xu Kathrine E. Hughes William J. Dunn Ludwig Bauer Hemendra N. Bhargava George A. Doss 《Journal of heterocyclic chemistry》1996,33(2):399-407
A number of (E)-7-arylidenenaltrexones were synthesized by azeotropic distillation of water from a benzene solution of naltrexone and an aromatic aldehyde (benzaldehyde, 4-chloro- and 4-fluorobenzaldehyde, 3-and 4-pyridinecarboxaldehyde and 1-methyl-2-imidazolecarboxaldehyde) using piperidine as a catalyst. In addition, (E)-7-benzylidenenaloxone was prepared by the previously published Claisen-Schmidt condensation using sodium hydroxide in methanol. The stereochemistry of these arylidene derivatives 3–9 was determined to be (E) by means of nuclear Overhauser enhancement experiments. The 13C nmr spectra of (E)- 3–9 are recorded in deuteriochloroform and those of the hydrochlorides in deuteriodimethyl sulfoxide. 相似文献
24.
[reaction: see text] A study toward a possible biomimetic hetero Diels-Alder reaction is reported between humulene and a novel tropolone ortho-quinone methide. A suitable tropolone ortho-quinone methide precursor has been prepared from 3-methyl-2-furoate. Heating the ortho-quinone methide precursor gave a tropolone ortho-quinone methide, which in the presence of humulene underwent a hetero Diels-Alder reaction to give a deoxy analogue of epolone B. 相似文献
25.
Hydroxyapatite-poly(d,l-lactide) Nanografts. Synthesis and Characterization as Bone Cement Additives
Kristina L. Goranova Anne Kathrine Kattenhj Sloth Overgaard Ivan Gitsov 《Molecules (Basel, Switzerland)》2021,26(2)
This paper reports the creation of hydroxyapatite/polyester nanografts by “graft-from” polymerization of d,l-lactide with [Ca5(OH)(PO4)3]2 as the initiator and tin(II)-2-ethylhexanoate as the catalyst. Model polymerizations were performed with cyclooctanol as initiator to confirm the grafting on the surface of the hydroxyapatite nanocrystals. Polymers with the highest molecular mass (Mn) between 4250 Da (cyclooctanol) and 6100 Da (hydroxyapatite) were produced. In both cases the molecular mass distributions of the polymers formed were monomodal. The materials obtained were characterized by size-exclusion chromatography, NMR and FT-IR spectroscopy, and thermal methods. Their suitability as additives for commercial bone cement (Simplex P Speedset, Stryker Orthopaedics) has been confirmed by thermal analysis techniques and mechanical testing. The results obtained show that addition of the hydroxyapatite/ polyester nanografts improved both thermal and mechanical properties of the bone cement. 相似文献
26.
Jack E. Baldwin Robert M. Adlington Bernard J. Rawlings Richard H. Jones 《Tetrahedron letters》1985,26(4):485-488
Practical procedures for the resolution of racemic modification of (1, 2)-and (1, 2)-1-amino-2-ethylcyclopropane-1-carboxylic acid ,,(1, 2)- and (1, 2)-1-amino-2-methylcyclopropane-1-carboxylic acid ,, and (1, 2)- and (1, 2)-1-amino-2-methylcyclopropane-1-carboxylic acid , are described; the structures as ,, and were confirmed by X-ray-crystallographic methods. 相似文献
27.
28.
[structures: see text] The total syntheses of the amaryllidaceae alkaloids haemanthidine, pretazettine, and tazettine as optically pure enantiomers are reported. Using D-mannose as the starting material, the critical relative stereochemical relationships are established with an intramolecular nitrone-alkene cycloaddition reaction. The synthetic route leads successively to (-)-haemanthidine and then to (+)-pretazettine and (+)-tazettine, taking advantage of the well-established complex relationships among these three alkaloids. 相似文献
29.
Mass-selected beams of N+ and N2+ in the energy range 5–50 eV react with molybdenum to produce a surface nitride. The relative reaction cross section for N+ reaction is higher than that of N2+ in the range 5–25 eV and N2+ exhibits a reaction threshold near 7 eV. The N2+ threshold suggests collisional dissociation prior to reaction. 相似文献
30.
Sylvain Celanire Frederic Marlin Jack E. Baldwin Robert M. Adlington 《Tetrahedron》2005,61(12):3025-3032
The synthesis of 3,11-dioxatricyclo[5.3.1.01,5]undeca-5,9-dien-8-ones is reported from suitable 5-substituted furfuryl alcohols bearing an acetylenic side-chain. Successive peracid-mediated oxidative rearrangement of furan carbinols and base-assisted intramolecular 1,3-dipolar cycloaddition afforded oxygen-bridged tricyclo-undecane derivatives. Stereoselective transformations of cycloadducts are also discussed. 相似文献