The stereospecific cis-hydroxylation of 1-(2,3-dideoxy-P-~-glyceropent-2-enofuranosy1)thymine (1) into 1 -P-D-ribofuranosylthymine (2) by osmium tetroxide is described. Treatment of 2', 3'-0,O-isopropylidene-5-methyl-2,5'-anhydrouridine (8) with hydrogen sulfide or methanolic ammonia afforded 5'-deoxy-2', 3'-0, O-isopropylidene-5'-mercapto-5-methyluridine (9) and 2',3'-0,O-isopropylidene-5-methyl-isocytidine (lo), respectively. The action of ethanolic potassium hydroxide on 5'-deoxy-5'-iodo-2', 3'-0,O-isopropylidene-5-methyluridine (7) gave rise to the corresponding l-(~-deoxy-~-~-erythropent-4-enofuranosyl)5-methyluracil (13) and 2-0-ethyl-5 -methyluridine (14).The hydrogenation of 2 and its 2', 3'-0,O-isopropylidene derivative 4 over 5% Rh/A120, as catalyst generated diastereoisomers of the corresponding 5-methyl-5,6dihydrouridine (17 and 18).