Enantiopure azetidinium salts presenting various and representative substitution patterns at C-2, C-3 and C-4 have been prepared by alkylation of the corresponding azetidine with methyl trifluoromethanesulfonate. These compounds were treated with an array of nitrogen (azide anion or benzylamine) and oxygen (acetate anion or alkoxides) nucleophiles which provided interesting insights into the regioselectivity of the ring-opening process. Nucleophilic opening occurred in most cases regioselectively at C-4 with azetidinium ions

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Series of enantiomerically pure 3-alkenylpyrrolidines, substituted azepanes and stereodefined aminoalkenes were synthesized from 2-alkenylazetidinium trifluoromethanesulfonate salts. The high chemoselectivity of these reactions was found to be strongly dependent both on the nature of the base involved in the process (PhLi or KHMDS) and on the relative cis or trans stereochemistry of the intermediate ammonium ylide. When the ylide and the adjacent alkene are

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