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71.
72.
E. H. Riesenfeld H. E. Wohlers Lockyer Beckmann und Rupp 《Fresenius' Journal of Analytical Chemistry》1907,46(2-3):167-169
Ohne Zusammenfassung 相似文献
73.
74.
The synthesis of five natural products (3, 6, 7, 10, and 14), isolated from the Indian neem tree Azadirachta indica, is reported from a common intermediate (2). The judicious choice of transacetalization conditions allows efficient access to both the azadirachtinin (9 and 10) and the azadirachtin (3, 6, 7, and 14) skeletons. 相似文献
75.
Arno Behr Thomas Beckmann Pierre Schwach 《Journal of organometallic chemistry》2008,693(18):3097-3102
Two different routes to acetoxyoctadiene are presented. The first one uses the well-known telomerisation of butadiene with acetic acid operating in a multiphase semi-batch mode. The second reaction involves the cleavage of acetic anhydride, hydrogen transfer via ketene formation and thus a telomerisation as well. 相似文献
76.
Eva A. Gallardo-Gutié rrez Marí a J. Gonzá lez Artur Nicolau 《Transactions of the American Mathematical Society》2008,360(1):395-410
For any simply connected domain , we prove that a Littlewood type inequality is necessary for boundedness of composition operators on , , whenever the symbols are finitely-valent. Moreover, the corresponding ``little-oh' condition is also necessary for the compactness. Nevertheless, it is shown that such an inequality is not sufficient for characterizing bounded composition operators even induced by univalent symbols. Furthermore, such inequality is no longer necessary if we drop the extra assumption on the symbol of being finitely-valent. In particular, this solves a question posed by Shapiro and Smith (2003). Finally, we show a striking link between the geometry of the underlying domain and the symbol inducing the composition operator in , and in this sense, we relate both facts characterizing bounded and compact composition operators whenever is a Lavrentiev domain.
77.
Heinze K Beckmann M Hempel K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(31):9468-9480
This overview highlights recent progress in the field of selective construction of linear, oligonuclear transition-metal complexes by using solid-phase synthesis procedures. Two general protocols have been identified: formation of coordinative bonds between metal centres and bridging ligands and formation of covalent bonds between preformed kinetically inert transition-metal-containing building blocks in the chain growth step. Currently available suitable building blocks for the second approach are based on ferrocene units, bis(terpyridine)-ruthenium(II) moieties or metal porphyrins. 相似文献
78.
Ley SV Abad-Somovilla A Anderson JC Ayats C Bänteli R Beckmann E Boyer A Brasca MG Brice A Broughton HB Burke BJ Cleator E Craig D Denholm AA Denton RM Durand-Reville T Gobbi LB Göbel M Gray BL Grossmann RB Gutteridge CE Hahn N Harding SL Jennens DC Jennens L Lovell PJ Lovell HJ de la Puente ML Kolb HC Koot WJ Maslen SL McCusker CF Mattes A Pape AR Pinto A Santafianos D Scott JS Smith SC Somers AQ Spilling CD Stelzer F Toogood PL Turner RM Veitch GE Wood A Zumbrunn C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(34):10683-10704
We describe in full the first synthesis of the potent insect antifeedant azadirachtin through a highly convergent approach. An O-alkylation reaction is used to unite decalin ketone and propargylic mesylate fragments, after which a Claisen rearrangement constructs the central C8-C14 bond in a stereoselective fashion. The allene which results from this sequence then enables a second critical carbon-carbon bond forming event whereby the [3.2.1] bicyclic system, present in the natural product, is generated via a 5-exo-radical cyclisation process. Finally, using knowledge gained through our early studies into the reactivity of the natural product, a series of carefully designed steps completes the synthesis of this challenging molecule. 相似文献
79.
80.
Hydrogen bonding of the type SiO-H...A (A = O, N) has been studied in the gas phase for simple H3SiOH.acceptor complexes with the acceptor molecules being O(H)SiH3, OH2, O(H)CH3, O(CH3)2, O(CH3)SiH3, O(SiH3)2, NH3, N(CH3)H2, N(CH3)2H, N(CH3)3, N(CH3)2C6H5, and NC5H5, respectively, at the B3LYP/6-311+(2d,p) level of theory, using Bader's atoms in molecules (AIM) and Weinhold's natural bond orbital (NBO) methodology. For all complexes (except H3SiOH.N(CH3)2C6H5) the complex energy Eadd. is a good estimate for the hydrogen bond energy EHB, which is generally higher in N-acceptor complexes (-5.52 to -7.17 kcal mol-1) than in O-acceptor complexes (-2.09 to -5.06 kcal mol-1). In case of H3SiOH.N(CH3)2C6H5, EHB and Eadd. differ by the energy associated with the loss of n(N)-->pi conjugation in N(CH3)2C6H5 upon complex formation. EHB shows no correlation with O...A distances and the red shifts Deltanu(OH) of the OH-stretching vibrations when different acceptors are compared, although both parameters are commonly used to estimate the strength of the hydrogen bond from spectroscopic and diffraction data. A good linear correlation of the hydrogen bond energy EHB has been established with parameters derived from the AIM and NBO analyses, namely, the electron densities rho(HA) and rho(OH) at the H...A and O-H bond critical points (BCPs) and the NLMO bond orders BONLMO(HA) of the H...A bonds of the H3SiOH.acceptor complexes as well as the change of natural charges DeltaqNPA(O) at the O-donor atom upon H3SiOH.acceptor complex formation. Hydrogen bonding of the type SiO-H...A (A = O, N) has been also studied in the related cyclic multiple H3SiOH.acceptor complexes (H3SiOH)3, (H3SiOH)2.NC5H5, and (H3SiOH)4, respectively, at the same level of theory. Cooperative hydrogen bonding is evident for all cyclic multiple H3SiOH.acceptor complexes, whereby the strongest concomitant strengthening of the hydrogen bonds is observed for (H3SiOH)4 and (H3SiOH)2.NC5H5. 相似文献