Diazines 57N-Oxides(see also page 49)
Nucleophilic displacement of nitro at C-3 in pyridazine N-oxides (i.e. to an N-oxide function), occurs about as readily
as that of a -nitro group and faster than for the corresponding base.
Nucleophilic substitutions by halide, cyanide and carbon nucleophiles such as enamines and acetate (by reaction with
acetic anhydride), with concomitant loss of the oxide function, occur smoothly in all three systems, though the site of
introduction of the nucleophile is not always that ( to the N-oxide) predicted by analogy with pyridine chemistry.
Amine substtuents (see also pages 48 and 164)
Aminodiazines show a strong analogy to aminopyridines and similarly exist in the amino tautomeric form. They are
stronger bases than the parent heterocycles, protonation and quaternisation occurring on the ring nitrogen.
The alkali-promoted rearrangement of quaternary salts derived from 2-aminopyrimidine is an example of the Dimroth
rearrangement – where the ring nitrogen and the side-chain nitrogen swap places (another ANRORC sequence). The
larger the substituent on the positively charged ring nitrogen, the more rapidly the rearrangement proceeds, as a result
of the consequent relief in strain between the substituent and the adjacent amino group.