Vitamin-C- and isovitamin-C-derived chemistry, Part I. : synthesis of 2,3-dideoxy derivatives of the ascorbic acids

5,6-O-Isopropylidene-L-gulono- and -D-mannono-1,4-lactones are converted into 2-(dimethylamino)-1,3-dioxolane derivatives on treatment with N,N-dimethylformamide dimethyl acetal in chloroform with azeotropic removal of the methanol thus formed. Quaternisation of the products with iodomethane, followed by thermal decomposition yields the corresponding C(4)-substituted enantiomeric butenolides. Some aspects of the reactions, the characterisation of the products, and further transformations are described.