I. Catalyst development in asymmetric phase transfer catalysis employing QSAR methods II. Computational investigations on the stereochemical course of the addition of allylsilanes to aldehydes

Part I of this dissertation describes the investigation in APTC employing a chemoinformatic analysis of the alkylation of a protected glycine imine with libraries of enantiomerically enriched quaternary ammonium ions. The synthesis of the quaternary ammonium ions follows a diversity oriented approach wherein the tandem inter[4+2]/intra[3+2] cycloaddition of nitroalkenes serves as the key transformation.. Catalyst activity and selectivity are rationalized in a qualitative way based on the effective positive potential of the ammonium ion. The next stage involved the development of quantitative structure -selectivity relationships (QSSR) for the alkylation of a protected glycine imine with libraries of quaternary ammonium ion catalysts. The variation in the observed enantioselectivity was rationalized employing a comparative molecular field analysis (CoMFA) using both the steric and electrostatic fields of the catalysts. A qualitative analysis of the developed model reveals preferred regions for catalyst binding to afford both configurations of the alkylated product.;In Part II, the diastereoselectivity of the addition allylsilanes to aldehydes is investigated using density functional theory. The interaction-distortion/activation-strain model of reactivity is used to rationalize the origin of the selectivity. Consistent with experimental model systems, the synclinal transition states are determined to be preferred over the antiperiplanar transition states in the electrophilic-activated manifolds and vice versa for the fluoride-activated manifold. The selectivity for the syn diastereomer in the electrophilic activation manifolds is accounted for by increased electrostatic and orbital interactions for a particular synclinal transition state at the expense of increased steric interactions relative to antiperiplanar transition states. The selectivity for the anti diastereomer in the nucleophilic manifold is explained by the lesser electrostatic repulsion in the antiperiplanar transition states which are favored relative to the synclinal transition states. Comparison of the transition states at constant distortion also reveals the origin of the variation in distortion in the transition states in terms of components of the interaction energy.