1.2- Diazetidin-3-ones, structure

Carbonyl-substituted isocyanates have been reported to add [2 + 2] to carbodiimides, although in one case the reported 4-imino-l,3-diazetidin-2-one (64AP623) was reassigned an oxadiazine structure (72BCJ1534). It is clear that the initially formed [2 + 2] kinetically favored adducts are thermally unstable and ultimately form more stable [4 + 2] products, oxadiazines (Scheme 13) (79BSF(2)499). 

Desiraju et at. have prepared some mono and bicyclic-l,3-diazetidine-2-ones with a view to study them as aza analogues of /3-lactams and to evaluate their biological activities. The X-ray structure of azacarbapenam 35 and azacarbacepham 36 suggests is that the structural requirement for the biological activities of /3-lactams is met. Aza-/3-lactam analogue 37 was also crystallized and an X-ray analysis was carried out <1998J(P1)2597>. Only limited X-ray studies have been reported for aza-/3-lactams. 

Diazetidin-3-ones substituted at N-1 dimerized on standing to give materials with the suggested structures (104) (mp 149-151 °C) and (105) (mp 310-315°C) (Equation (24)) <84JOC44l5>. 

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