Zoltán Kovári

Synthesis and Conformational Analysis of Dicationic N,N′‐Bridged Bis(benzimidazolium) and Bis(imidazolium) Macrocycles

Two-step alkylations of benzimidazole, 2-methylbenzimidazole, and imidazole at their nitrogen atoms with various bifunctional alkylating agents have afforded a series of 16-membered quaternary azacyclophanes. Of these macrocycles, those bearing methyl or methoxy groups on the azole or at the aromatic bridges have been found to exist as mixtures of conformers. In some cases, the structures of the conformers have been determined by NMR methods and X-ray crystallography, and have been correlated with the results of a computer-aided conformational search.

Theoretical studies on long-range substituent effects in the reduction of 7-norbornanones

The energetics of the stereoselective reduction of norbornan-7-one derivatives have been studied by semiempirical AM1 molecular orbital calculations. It was found that the reaction is kinetically controlled; correct prediction of the selectivity is possible only on the basis of the relative energies of the transition states of the reaction. Theoretically calculated and experimental anti–syn product ratios are in semiquantitative agreement, in contrast to results obtained from molecular electrostatic potentials. Geometry relaxation of the transition state is essential in obtaining reliable isomer ratios.

Steric vs. electrostatic effects in the nucleophilic addition to a hindered cyclohexanone

The relative importance of steric vs. electrostatic effects in the nucleophilic addition to (4R,6S)-4-(tert-butyldimethylsiloxy)-2,2,6-trimethylcyclohexanone (1), a well-known chiral building block, is investigated.