Über die Konvergenz des Verfahrens vonGrammel und seine mögliche Erweiterung

Summary The paper deals with the convergence ofR. Grammel's method for the solution of boundary-eigenvalue-problems. It is further shown thatGrammel's method can be extended to the case where it is difficult to find the exactGreen function. In this case one may use a different, relatedGreen function if one adds certain supplemental terms to the properGrammel equations.     

Note zur lokalen Struktur der Distributionen

Ohne Zusammenfassung     

Pyrazolylborate-zinc alkoxide complexes. 1. Basic properties, methylations, and heterocumulene insertions

While a solution of TpPh,MeZn-OH in methanol contains only traces of TpPh,MeZn-OMe, according to the equilibrium constant K = 5.8 x 10(-4), the reactions of TpPh,MeZn-OH with the electronegative alcohols trifluoroethanol and hexafluoro-2-propanol easily yield TpPh,MeZn-OCH2CF3 and TpPh,MeZn-OCH(CF3)2. The extremely hydrolytically sensitive TpPh,MeZn-OR complexes, with R = Me, Et, i-Pr, and CH2CH2F, as well as TpCum,MeZn-OR, with R = Me and i-Pr, are accessible from the Tp*Zn-hydride complexes and the corresponding alcohol. Alkylations with methyl iodide have revealed the high nucleophilicity of TpPh,MeZn-OMe by conversion to dimethyl ether and TpPh,MeZn-I. This conversion occurs rapidly not only with pure TpPh,MeZn-OMe but also with TpPh,MeZn-OH (as such or in the presence of methanol) and with TpPh,MeZn-OCOOMe. A relation of the Tp*Zn-alkoxides to the function of the zinc enzyme alcoholdehydrogenase exists in the reaction of TpPh,MeZn-OCH(CH3)2 with aromatic aldehydes, which yields acetone and the corresponding benzyl oxides TpPh,MeZn-OH2Ar. The heterocumulenes carbon dioxide, carbon disulfide, isothiocyanates, and one isocyanate are inserted into the Zn-OR bonds, yielding one alkyl carbonate complex (TpPh,MeZn-OC(O)OMe), two xanthogenate complexes (TpPh,MeZn-SC(S)OR), three iminothiocarbonate complexes (TpPh,MeZn-SC(NR')OR), and one alkyl carbamate complex (TpPh,MeZn-NR-COOMe). All insertion reactions can be described by a common mechanism involving a four-center intermediate in which the most basic heteroatom of the heterocumulene is attached to zinc.     

Crystal, molecular and electronic structure of N,N'-diphenyl-N,N'-bis(2,4-dimethylphenyl)-(1,1'-biphenyl)-4,4'-diamine and the corresponding radical cation

Oxidation of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD, 1 a) and N,N'-diphenyl-N,N'-bis(2,4-dimethylphenyl)-(1,1'-biphenyl)-4,4'-diamine (1 b) with SbCl(5) affords the corresponding radical cations quantitatively. The crystal and molecular structure of 1 b and [1 b]SbCl(6), the first tetraphenyl benzidene derivatives to be characterised crystallographically in both the neutral and radical cation states, reveal molecular parameters in agreement with the predictions made on the basis of DFT studies. Analysis of the NIR transition in the radical cations [1](+) (.) allows an estimate of the electronic coupling parameter V (1 a(+) (.) 3200 cm(-1); 1 b(+) (.) 3300 cm(-1)), the reorganisation energy lambda(1 a(+) (.) 7500 cm(-1); 1 b(+) (.) 7800 cm(-1)), and the linear coupling constant l (1 a(+) (.) 3100 cm(-1); 1 b(+) (.) 2700 cm(-1)) of the symmetric mode.     

Synthesis of a polymer-bound galactosylamine and its application as an immobilized chiral auxiliary in stereoselective syntheses of piperidine and amino acid derivatives

A 2,3,4-tri-O-pivaloylated beta-D-galactopyranosyl azide bearing a hydroxy-functionalized spacer unit at the C-6 position of the galactose was synthesized and immobilized on the solid phase by using a polymer-bound chlorosilane. The azide was reduced to the corresponding galactopyranosylamine, which served as a versatile chiral auxiliary in highly diastereoselective Ugi four-component condensation reactions at ambient temperature. Fluoride-induced cleavage from the polymeric support furnished N-glycosylated N-acylated alpha-amino acid amides. The reaction of the immobilized galactosylamine with aldehydes gave rise to the corresponding aldimines, which underwent a domino Mannich-Michael condensation reaction with Danishefsky's diene at ambient temperature to yield 2-substituted 5,6-didehydropiperidin-4-ones on the solid phase. Subsequent cleavage with tetra-n-butylammonium fluoride delivered the N-glycosylated products in high yields, purities, and diastereoselectivities. A chemoselective 1,4-hydride addition to the polymer-bound dehydropiperidinones was achieved in the presence of the bulky oxygenophilic Lewis acid methylaluminum [bis(2,6-di-tert-butyl-4-methylphenoxide)]. The conjugate addition of cyano-modified Gilman reagents to the immobilized dehydropiperidinones furnished 2,6-cis-substituted piperidine derivatives as the major diastereomers that were isolated after cleavage from the support.     

On a trigonometric sum of Vinogradov

The trigonometric sum

     

Isoserine-based biotinylated photoaffinity probes that interact with penicillin-binding protein 1b

The photolytic decomposition of trifunctional carbene generating photoaffinity probes in methanolic solution was studied, a cleavage reaction with butylamine in water, the conjugation with a ligand (moenomycin), and experiments that demonstrate that the fully armed probes interact with penicillin-binding protein 1b.     

Controlling the variation of axial water exchange rates in macrocyclic lanthanide(III) complexes

The rate of axial water exchange in well-defined series of lanthanide complexes depends on the extent of second sphere hydration which is determined by complex hydrophobicity and the nature of the lanthanide ion and its counter-ion.