Tion, molecular model

The high levels of enantioselectivity obtained in the asymmetric catalytic carbomagnesa-tion reactions (Tables 6.1 and 6.2) imply an organized (ebthi)Zr—alkene complex interaction with the heterocyclic alkene substrates. When chiral unsaturated pyrans or furans are employed, the resident center of asymmetry may induce differential rates of reaction, such that after -50 % conversion one enantiomer of the chiral alkene can be recovered in high enantiomeric purity. As an example, molecular models indicate that with a 2-substituted pyran, as shown in Fig. 6.2, the mode of addition labeled as I should be significantly favored over II or III, where unfavorable steric interactions between the (ebthi)Zr complex and the olefmic substrate would lead to significant catalyst—substrate complex destabilization. 

Fig. 38a-f. One-electron level °u pictures and self-energy diagrams for fluctuation and relaxa- °g tion of hole levels within a molecular model-level structure oj, (for explanation of (a) to (f) see text)... 

Fig. 27. Molecular model for the etching of Si in strong bases. In NaOH two routes are possible for the hydrolysis step. The chemical one (top route) dominates at the rest potential. The H-termina-tion persists despite dissolution because the initial steps are rate-determining. HSi(OH)j is further oxidized to Si(OH)4 which liberates another H2 molecule (after [122]).

Self-organization of ligands in multi-component titanium catalysts [69] with conformationally flexible biphenols [52] is also found in the enantioselective glyoxylate-ene reaction [60] to give the significantly high enantioselectivity (Eq. (7.25)) [70]. Some molecular modeling was reported that the hexacoordina-tion of the titanium atom would make the central titanium atom a center of chirality and that the A isomer is more favorable than the A isomer (Fig. 7-15). 

The benzylamino residue in 25 is immersed into the CD cavity prior to complexa-tion of the phenyl ring, as evident from NMR analyses. Complexation with a peptide then requires that this intramolecular association must be given up, which explains why the affinity is not increased by possible lipophilic interactions of aromatic peptide side chains and the benzyl group outside the cavity. The conformational switching triggered by complexation with a peptide was followed by suitable NMR experiments, and is supported by computer-aided molecular modeling (see our website). 

Teppen, B.J., C.-H. Yu, D.M. Miller, and L. Schafer. 1998c. Molecular modeling studies of TCE sorp-tion/desorption on clays, p. 39. In Molecular modeling of clays and clay surface properties. Meet. Progr. Abstracts, 35th Annu. Meet., Cleveland, OH. 6-10 June. Clay Miner. Soc., Boulder, CO. 

Carvone was used as a precursor for the synthesis of the cyclohexene 159, and this was used to make the cyclohexenyl nucleoside analogue 160. The same chiral precursor was also manipulated to give the enantiomers of 159 and 160. Both enantiomers of 160 showed potent antiherpetic activity. Molecular modelling of the binding of both compounds to the active site of HSV-1 thymidine kinase was carried out, and a model for the binding of both enantiomers was proposed.An analogue of carbocyclic 2 -deoxyuridine, conforma-tionally-restricted due to a 6,6 -oxido-link (Vol. 32, p. 278), has now been reported in optically-active form, in the L-series. ... 

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