STUDIES ON THE SYNTHESIS OF THE C-GLYCOSIDIC PART OF NOGALAMYCIN, PART 3

The addition of the metalated 1,4-dimethoxybenzenes 17a-c to the methy l ketone 14 was investigated in connection with the construction of th e C-glycosidic part of nogalamycin. In most reactions, a selectivity t owards the undesired Q-isomer 16a was observed, However, the reaction of the lithiated aromate 17c with 14 at low temperatures in THF favore d the formation of the desired (R)-alcohol 15a (15a:16a = 4.8:1) in ac cordance with the chelate model A. The selectivity was considerably en hanced in the addition of the more hindered lithiated naphthalene 18 y ielding the (R)-isomer 15b exclusively. Reduction of 15b afforded the dimethylamino compound 19b, a direct precursor of the CDEF-ring system of nogalamycin.