Imidazoles nitro-, isomeric

The reaction of 5-bromo-3-nitro-l,2,4-triazole and 3,5-dinitro-l,2,4-triazole with a variety of oxiranes yielded the expected 1-substituted imidazoles, and also resulted in the formation of 5,6-dihydrooxazolo[3,2-6]-s-triazoles upon treatment with base (75CHE612). The proposed pathway involves proton abstraction from the imidazole and subsequent attack of the oxirane on the N-anion followed by cyclization in a concerted fashion (equation 56). 2,4(5)-Dinitroimidazole reacts analogously with oxiranes to give isomeric nitro-imidazo[2,1 -f>]oxazoles in good overall yield (8UMC601). 

A number of attempts have been made to measure or calculate the relative stabilities of isomeric imidazoles, for example, fluoroimidazoles <88H(27)1803>, diazoimidazoles <87JMC357, 87JMC2222, 87JOC5538,90AHC(48)65>, nitro- and amino-imidazoles <89CJC1666,92JCS(Pl)2779>, 2-hydroxyimidazole, and 2-imidazolone <90JCS(P2)195>. 

The most common photochemical rearrangement in the azoles is the pyrazole imidazole isomerization (isomerization enthalpy 42 kJ mol" ). Any reverse reaction should be similar to the isomerization of oxazole to isoxazole (via an azirine intermediate) oxidation reactions (see Section 3.02.5.3.11), while rearrangements of A-nitro-, A-acyl-, and C- and A-alkenylimidazoles are discussed under reactions of the appropriate functional group (see Section 3.02.7). 

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