Aziridine ring, stability

Substituents in the aziridine ring stabilize (75JA4692) one of the nitrogen invertomers, as is expected from steric effects in derivative 86, the predominant form is the one with the acetyl group anti with respect to the phenyl group. 

The triazoline adducts from benzvalene (Scheme 21)162 and diphospha-benzvalene (Scheme 22) photolyze to yield novel tetracyclic aziridine ring systems165 that are valence isomers of azepines,162 whereas that from De-war thiophene (Scheme 20) gives a novel tricyclic aziridine that desulfurizes with triphenylphosphine to yield the trifluoromethylated Dewar pyrrole (Scheme 153).15 9,160 The stabilization of these strained molecules is attributed to the perfluoroalkyl effect.159... 

Noticeable is the absence of reaction when the aziridine ring does not bear at least one anion-stabilizing moiety. Noticeable also is the influence of the position of the trimethylsilyl group in the molecule as silyl group directly attached to the ring does not induce ring opening (see above). 

Another approach to aldehydes by partial reduction of acid derivatives involves introduction of groups that stabilize the partially reduced intermediate against elimination of water. The aziridine ring has this effect because of the I-strain that is introduced if elimination occurs. The partially reduced carbinolamine intermediates are stable to further reduction, and aldehydes are formed on subsequent... 

The most useful reactions combine carbanion nucleophiles with activated aziridines. For example, the ring expansion which occurs on treatment of aziridines (219) with malonate salts typifies the heterocyclic synthesis possible. The conversion is quite general since many analogous transformations have been observed in which different carbanion stabilizing substituents were employed (73S546). 

Florio et al. have employed heteroaromatic rings as organyl-stabilizing groups for metalated aziridines as well as for metalated epoxides. Regioselective deprotonation of aziridine 246 with n-BuLi, followed by addition of Mel, gave aziridine 247 (Scheme 5.62) [88]. 

Aziridine is the only one that has a serious instability risk according to CHETAH. It is due to the presence of a strained ring, which gives an endothermic character to the compound. As its stability should be more or less the same as ethylene oxide, so should be its propensity for polymerisation. 

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