Attempts to prepare aromatic O-acyl-hydroxylamines—II : Dehydrohalogenation of 1-bromo-4-acetyloxyimino-1,2,3,4-tetrahydrophenanthrene by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)

Dehydrohalogenation of 1-bromo-4-acetyloxyimino-1,2,3,4-tetrahydrophenanthrene by 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU) gave a mixture of products. Thirteen of these were identified and together account for 80 per cent of the total yield. The majority are considered to be formed via the labile O-acetylhydroxylamine (17); from which it may be concluded that 17 has the following properties under the basic conditions of the reaction. (a) It may rearrange to hydroxamic acid (which gives further products). (b) It may behave as an acetylating agent. (c) Possibly it may generate a nitrenium ion. A further indication that the nitrenium ion is involved, comes from the dehydrobromination reaction when performed in the presence of α-naphthol, α-naphthylamine, 4-hydroxydiphenylamine, and hydrazobenzene. Particular attention is given to the dehydrogenating property of the nitrenium ion.