Conformational analyses of six-membered ring oxocarbenium ion intermediates and kinetic resolution of tertiary hydroperoxides

The three-dimensional structures of dioxocarbenium ions related to glycosyl cations were examined by an analysis of spectroscopic, computational, and reactivity data. Hypothetical low-energy structures of the dioxocarbenium ions were correlated with both experimentally determined 1H NMR coupling constants and diastereoselectivity results from nucleophilic substitution reactions. This method confirmed the pseudoaxial preference of C-3 alkoxy-substituted systems and revealed the conformational preference of the C-5 alkoxymethyl group. The preferred diaxial conformer of the trans-4,5-disubstituted tetrahydropyranyl system underscored the importance of electrostatic effects in dictating conformational equilibria. In the 2-deoxymannose system, although steric effects influenced the orientation of the C-5 alkoxymethyl substituent, the all-axial conformer was favored because of electrostatic stabilization.;The conformations of C-2 alkoxymethyl and C-3 alkoxymethyl exocyclic oxocarbenium ions were also investigated by product analyses. The product ratio obtained for the C-2 alkoxymethyl system suggested either a lack of electrostatic influence or the presence of a Curtin-Hammett scenario. Interpretation of the diastereoselectivity results for the C-3 alkoxymethyl system was hindered by difficulties associated with determining the relative stereochemistries of the products. The use of iminium ions as exocyclic oxocarbenium ion surrogates was also investigated.;A methodology for the kinetic resolution of tertiary hydroperoxides was developed using the Sharpless epoxidation system. A geminally substituted enantiopure allylic alcohol was employed along with dicyclododecyl tartrate to provide a selectivity factor of 4.1, the highest selectivity observed for the catalytic kinetic resolution to date. A model that accounts for the observed selectivities has been proposed.