Studies on the Synthesis of the C-Glycosidic Part of Nogalamycin, Part 1

Studies aimed at the construction of the C-glycosidic part of nogalamycin (1) and menogarol (2) are described. The stereochemistry of the addition of aryl lithiums to 4-acetyl-1,3-dioxolane 16, prepared from D-glucose via 10a-15, was studied. The major isomers were the (S)-isomers 17a and 17b as shown by X-ray analysis of 17a with the unnatural configuration. The adduct 17a was further converted to the anomeric naphthoquinones 22a and 22b by acetal cleavage, ozonolysis, acetalization and Diels-Alder reaction with 1-methoxybutadiene.