“…In triflic acid or in HF-SbF 5 , ethyl 2-nitroacetate (1) undergoes protonation and the loss of a molecule of water to afford a transient reactive hydroxynitrilium ion (protonated nitrile oxide) able to react with aromatics to form, for instance, ethyl (2E)-2-hydroxyimmino-2-phenylacetate (2, Ar = Ph; Scheme 1). 4 The configuration of the oxime is indirect evidence of the existence of a reactive transient species with a CN triple bond. 5 The protonation/dehydration of N,S-or S,S-nitroketene aminals 3 in triflic acid initially affords cations 4, then the stable hydroxyiminium cations 5 that have been characterized by 1 H NMR and 13 C NMR spectroscopy at low temperature.…”