Conformational restriction of nucleosides by spirocyclic annulation at C4' including synthesis of the complementary dideoxy and didehydrodideoxy analogues.

The concept of spirocyclic restriction, when generically applied to nucleoside mimics, allows for the preparation of diastereomeric pairs carrying either a syn- or anti-oriented hydroxyl at C-5'. Reported herein are convenient synthetic routes to enantiomerically pure 1-oxaspiro[4.4]nonanes featuring fully dihydroxylated end products as well as congeners having dideoxy and didehydrodideoxy substitution patterns. Notable use is made of the capacity for introducing unsaturation in the furanose sector via phenylsulfenylation and the incorporation of uracil and thymine by way of their silylated derivatives under catalysis with stannic chloride.