Synthesis and stereoelectronic properties of sugar-shaped polyhydroxylated hexahydropyrimidine-2-thiones

Article abstract of DOI:10.1016/S0040-4020(98)00872-2

The reactivity and conformations in water solution of polyhydroxylated hexahydropyrimidine-2-thiones structurally related to biologically active nonulosonic acids and azaoctitols, obtained by intramolecular cyclization of sugar-derived μ-oxothioureas, have been investigated. The total preference for the axial orientation of the pseudoanomeric C - O bond and the high tendency to undergo acid-promoted intramolecular glycosylation are interpreted in terms of stabilizing hyperconjugative interactions in both the aminoketalic derivatives and the reactive azacarbenium cations. Moreover, repulsion between lone pairs and vicinal C - H bonds leads to a preference for structures bearing axial α-carbon substituents. The present results provide strong experimental evidence for the predominance of molecular orbital over electrostatic interactions in the stereoelectronic properties of these systems.