Diazepines. Part XIV. Reactivities of positions 5 and 6 in 2,3-dihydro-1,4-diazepines towards quasi-aromatic substitution by bromine

Abstract

Simple theory predicts that in a 2,3-dihydro-1,4-diazepine or its mono-cation a proton at position 6 should be much more reactive towards electrophilic substitution than protons at positions 5 and 7. The measured rate of bromination at position 6 of the 5-methyl-7-phenyl derivative in dilute aqueous acid solution was 2·4 × 10⁶ l mol^–1 s^–1 and that of the 1,4,5,7-tetramethyl derivative was approximately similar, in concordance with an earlier value for the 5,7-dimethyl derivative. The 6-methyl and 1,4,6-trimethyl derivatives, though unsubstituted at positions 5 and 7, reacted rapidly in a different way at position 6, giving non-conjugated products which were hydrolysed. 2-lmidazoline, used as an alternative model compound, failed to react with bromine or chlorine, in agreement with expectation.