Facile selective synthesis of 2-methyl-5-amino-1,2,4-oxadiazolium bromides as further targets for nucleophilic additions

Abstract

The reaction of aminonitrones R¹C(NH₂) = N⁺(Me)O⁻ (R¹ = Alk, Ar) with isocyanides R²NC (R² = Alk, Ar; 1.2 equiv.) and Br₂ (1 equiv.) conducted in CHCl₃ (RT, 5 min) gives 2-methyl-5-amino-1,2,4-oxadiazolium bromides in good to excellent yields (65–95%; 16 examples). These species are highly electrophilically activated and 5-cyclohexylamino-2-methyl-3-phenyl-1,2,4-oxadiazolium bromide, taken as a model compound for the reactivity study, reacts rapidly under mild conditions with hydroxylamine, hydrazine, or benzamidine, to give 5-cyclohexylamino-3-phenyl-1,2,4-oxadiazole (88%), 5-cyclohexylamino-3-phenyl-1,2,4-triazole (95%), and 2-cyclohexylamino-4,6-diphenyl-1,3,5-triazine (64%), respectively. Treatment of the oxadiazolium salt with excess water provides N-benzoyl-N′-cyclohexylurea (95%).