APPROACH TO OXETANE AND FURAN NUCLEOSIDES WITH AN ANOMERIC CARBON SUBSTITUENT - NUCLEOPHILIC-SUBSTITUTION AT HIGHLY HINDERED ALPHA-BROMO-OXETANE-CARBOXYLATES AND ALPHA-TETRAHYDROFURAN-CARBOXYLATES - Choi, S; Witty, D; Fleet, G; Myers, P; Storer, R; Wallis, C; Watkin, D; Pearce, L (1991)