1.3.4- Oxadiazolin-2-ones, tautomerism

A2-1,3,4-Oxadiazolin-5-ones acylation, 6, 439 alkylation, 6, 439 biological activity, 6, 445 melting point, 6, 430 synthesis, 6, 441, 442 tautomerism, 6, 430 A3- l,3,4-Oxadiazolin-2-ones 5,5-disubstituted IR spectra, 6, 429 PE spectra, 6, 430 A3-1,3,4-Oxadiazolin-5-ones ionization potential, 6, 428... 

Hydroxy- (8a), 2-mercapto- (8b) and 2-amino-l,3,4-oxadiazoles (8c) are in equilibrium with the tautomeric oxadiazolines (9a), (9b) and (9c) respectively. Evidence from UV (72CJC3079) and IR (Section 4.23.2.2.3) spectra supports structure (9a) for A2-l,3,4-oxadiazolin-5-ones and structure (9b) for A2-l,3,4-oxadiazoline-5-thiones. The UV and IR spectra, fluorescence and p/iT values of 2-amino-l,3,4-oxadiazoles indicate that the amine tautomer (8c or d) rather than the imine tautomer (9c or d) predominates (69BSF870, 874, 64CR(258)4579>. 

Because of the necessity of the tautomerizable group at C3 of the reactant, it was suggested that a tautomeric form 66 of the oxadiazole 65 or intermediate 67 (Scheme 21) might be involved in this phototransposition. The photoconversion of 2-methyl-5-phenyl-/ -l,2,4-oxadiazolin-3-one 69 to 3-methyl-5-phenyl-/ -l,3,4-oxadiazohn-2-one 70 is consistent with this suggestion. 

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