SPECTROSCOPIC, CRYSTALLOGRAPHIC AND COMPUTATIONAL STUDIES OF THE FORMATION AND ISOMERIZATION OF CYCLIC ACETALS AND KETALS OF PENTONOLACTONES

The different reactivities of D-ribonolactone, L-arabinonolactone, D-xylonolactone, D-lyxonolactone and 2-deoxy-D-ribonolactone toward benzaldehyde and acetone in acidic media, were examined. The reactions involved complex equilibria and were investigated with extensive C-13 NMR studies as well as X-ray crystallographic analysis of selected products. Molecular mechanics (MM2) and semiempirical (PM3 and AMI) calculations of some derivatives were carried out in order to facilitate structural and conformational assignments. The differences in reactivity observed for the reactions of D-pentono-1,4-lactones with benzaldehyde and acetone are rationalized in terms of their structural and conformational features.