Critical importance of leaving group ‘softness’ in nucleophilic ring closure reactions of ambident anions to 1,2-diazetidines

Highly strained, four-membered 1,2-diazetidine rings are produced in good yields (50–98%) in nucleophilic ring closure reactions provided ‘soft’ leaving groups such as iodide are used, a finding that can be rationalised in terms of the Hard Soft Acids and Bases principle.