The ring contraction of δ-lactones with leaving group α-substituents: a strategy for the synthesis of 2,5-disubstituted highly functionalised homochiral tetrahydrofurans
Approach to oxetane and furan nucleosides with an anomeric carbon substituent: Nucleophilic substitution at highly hindered α-bromo-oxetane- and -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.