Oxadiazole anions rearrangement

A theoretical study of degenerate Boulton-Katritzky rearrangements concerning the anions of the 3-hydroxyimi-nomethyl-l,2,5-oxadiazole has been carried out by using semi-empirical modified neglect of diatomic overlap (MNDO) and ab initio Hartree-Fock procedures. Different transition structures and reactive pathways were obtained in the two cases. Semi-empirical treatment shows asymmetrical transition states and nonconcerted processes via symmetrical intermediates. By contrast, ab initio procedures describe concerted and synchronous processes involving symmetrically located transition states <1998JMT(452)67>. 

A theoretical study of degenerate Boulton-Katritzky rearrangements concerning the anions of 3-formylamino-l,2,4-oxadiazole and 3-hydroxy-iminomethyl-1,2,5-oxadiazole has been carried out7 The treatment has shown the participation of asymmetric transition states and non-concerted processes via symmetrical intermediates. A detailed ab initio and density functional study of the Boulton-Katritzky rearrangement of 4-nitrobenzofuroxan has indicated a one-step mechanism for the process. 

The 5-substituted 3-amino-l,2,4-oxadiazole (76) condensed with -di-ketones and /Fketoesters, giving the corresponding 3-enaminones (91). These compounds did not rearrange on melting, but with sodium ethoxide in DMF (a dipolar aprotic solvent which increased the nucleophilic power of anion 93) at 110°C they were converted into the 4-substituted 2-acylamino-5-acylimidazoles (92).60,61... 

Ruccia et al.35 studied the degenerate rearrangement of the potassium salt of 3-acetylamino-5-methyl-l,2,4-oxadiazole (29). They suggested the possible formation of a symmetrical anion as transition state (115) or intermediate (116). 

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