Investigations of the Formation of Cyclic Acetal and Ketal Derivatives of D-Ribono-1,4-lactone and 2-Deoxy-D-ribono-1,4-lactone

Article abstract of DOI:10.1016/S0040-4020(01)80304-5

The reactions of D-ribono-1,4-lactone, and 2-deoxy-D-ribono-1,4-lactone with benzaldehyde and acetone in acidic media were investigated.The products obtained were isolated and characterized.The 1H NMR spectra of the 1,5-lactone product resulting from the thermodynamically controlled reaction of D-ribono-1,4-lactone with benzaldehyde were examined between 300 K and 200 K in a polar solvent.No conformational changes in the 1,5-lactone ring were observed within this temperature range.Detailed NMR studies showed that the acetalization of D-ribono-1,4-lactoneproceeded with the initial formation of the endo-2,3-acetal derivative, which in the presence of aqueous acids underwent ring expansion and isomerization to the 3,4-acetal of the 1,5-lactone.The endo preference of benzylidene acetals was explained by the transition state conformation of the reactants and the thermodynamic stability of the products, as calculated with molecular mechanics. Key words: D-ribono-1,4-lactone, 2-deoxy-D-ribono-1,4-lactone, acetal, ketal.