Proton-assisted ring opening of a 2,3-dialkyl-4-alkylimino-1,2-oxazetidine

4-Cyclohexylimino-2-methyl-3-t-butyl-1,2-oxazetidine (Ib) prepared by BF3-catalysed [3 + 1] cycloaddition of N-2,2-dimethylpropylidenemethylamine N-oxide (C-t-butyl-N-methyl nitrone) with cyclohexyl isocyanide is shown to give reactions of the hypothetical Schiff base from formaldehyde and the α-aminocarboxamide (V) when handled in acidic media.