Condensation of 5-O-tert-butyldimethylsilyl-1, 2-O-isopropylidene-α-D-erythro-3-pentulo-furanose (4) with 2, 4-dimethoxypyrimidin-6-ylmethyllithium (5) afforded a 3-pyrimidinylmethyl-ribose derivative (6). The protecting groups of 6 were changed to give the 5-O-benzoyl-1, 2-di-O-acetyl derivative (8). The intramolecular glycosylation of 8 by treatment with stannic chloride furnished the 6, 3'-methanol-O4-methyluridine derivative (9), which was further converted to 6, 3'-methanouridine (10) and 6, 3'-methanocytidine (11). The 2'-deoxygenation of 9 by way of the 2'-imidazolylthiocarbonyl dericative gave, after appropriate derivatization, 2'-deoxy-6, 3'-methanocytidine (16) and -uridine (17).
