2-Pyrrolidones azetidines

In the thermolysis of oxaziridines there is competitive formation of two acid amides, since in principle either substituent can migrate to nitrogen. In one case the dependence of the competing reactions on temperature was observed. At 150°C the bicyclic oxaziridine undergoes ring contraction with formation of the acylated azetidine, whereas methyl migration with formation of the pyrrolidone 15 predominates at 300°C. ... 

All lower lactams have strained rings but with some differences among them aziridin-2-one and azetidin-2-one are highly strained, while 2-pyrrolidone and 2-piperidone have weakly strained rings. The stability of the highly strained lactams maybe increased by substitution in fact, aziridin-2-one is known only in the substituted form. 

In the case of 3,3-dialkyl-substituted azetidin-2-ones (a,a-disubstituted p iactams), other factors must be taken into account to explain, in some reaction conditions, the favorable effect of bulky substituents. Indeed, contrary to previously published data, ° the propagation rate constant in the anionic polymerization of 3-alkyl-3-methyl-azetidin-2-one, conducted in dimethyl sulfoxide (DMSO) at 22 °C using potassium (or tetramethylammonium) 2-oxopyrrolidin-l-ide and N-acetyl-2-pyrrolidone, has been found to be approximately twofold enhanced by inaeasing the length of R from methyl to (following the order shown in Scheme 2 and being in any case much lower than that for the 4,4-dimethyl derivative). 

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