Azomethine imines open-chain

Heterocyclic N-imines contain a quaternary azomethine group which can be attacked by hydroxyl ions, leading to ring-opening. Such reactivity is strongly dependent on the heterocycle. For instance, pyridine N-imines are rather stable to bases17 69 whereas the 1,2,4-triazole 4-imines react very easily.80 82-90 137 In this reaction, the open-chain formamide 96 is... 

It is possible to compare the reactivity of some 1,3-dipoles inserted in cyclic structures with that of the same dipoles in open chains. This comparison, recalling that between cyclic and open-chain dienes (Section 4.1.3), is limited to two classes of 1,3-dipoles without a double bond , namely azomethine imines and oxides. For the former, there are data in Table 12 for the reaction with dimethyl acetylene dicarboxylate (iii) the cyclic azomethine imine (sydnone) is about 300 times less reactive than the open-chain cyanoazo-methine imine. In the case of nitrones, a typical comparison is. for reaction with ethyl crotonate in toluene at 100°C "... 

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