Ease of C-N Bond Cleavage in Four-membered Rings

The hydrolysis of an azetidin-2-ylideneammonium salt gives a β-lactam and an aminoamide by competitive endo- and exo-cyclic C-N bond cleavage, the product ratio being pH and buffer dependent; the rate law for hydrolysis shows a third order term which is first order in substrate, hydroxide, and carbonate ions, which is interpreted as kinetically equivalent to general acid catalysed breakdown of the ionised tetrahedral intermediate and as evidence for non-facile C-N bond cleavage in the four-membered ring.