APPROACH TO OXETANE AND FURAN NUCLEOSIDES WITH AN ANOMERIC CARBON SUBSTITUENT - NUCLEOPHILIC-SUBSTITUTION AT HIGHLY HINDERED ALPHA-BROMO-OXETANE-CARBOXYLATES AND ALPHA-TETRAHYDROFURAN-CARBOXYLATES

Treatment of oxetane-2-carboxylic esters with lithium hexamethyldisilazide generates anions which can be trapped with carbon tetrabromide to give epimeric 2-bromo-oxetane-2-carboxylic esters which undergo rapid displacement of bromide by azide with clean inversion of configuration. This may provide an approach to the synthesis of oxetane nucleosides possessing a carbon substituent at the anomeric position. An example of similar chemistry applied to tetrahydrofuran-2-carboxylic ester is also reported.