“…1 When the nitrogen atom within this heterocycle is not acylated or tosylated, the nucleophilic character, as well as the basicity, of the intracyclic amine is close to a linear amine, in contrast to aziridines where the basicity is considerably lower. Therefore, N-alkyl azetidines react with many electrophiles (eg chloroformates, 2 alkyl halides, 3 alkyl sulfonates, 4 triphosgene, 5 cyanogen bromide 6 ) to give a stable or transient azetidinium ion that can react further either by ring cleavage or by ring-expansion. 7 In this area, it was recently reported 8 (Scheme 1A) that C-3 substituted azetidiniums can be opened in an enantioselective manner in the presence of a catalytic amount of a SPINOL-derived phosphonate acting as a chiral counteranion for the azetidinium cation.…”