Unexpected formation of oxetanes from a geminal difluorinated δ-lactone

A perbenzylated 3,3-difluorinated hexono-1,5-lactone was prepared in several steps. Reaction of this lactone with MeOH/p-TsOH followed by a treatment with ion-exchange resin led to the formation of an exocyclic oxetane derived vinylether. Similar reaction with ammonia gave the corresponding carboxamido substituted oxetane in good yields.