A 2-substituted amino-6-methylpyridine-N-oxide derivative is useful as an intermediate for the synthesis of chemical substances for pharmaceuticals and agrochemicals such as the tetrazolyloxime derivative disclosed in Patent Document 1 since the halogenation or the like of a methyl group at position 6 is easy.
In general, pyridine-N-oxide derivatives can be obtained by the oxidation of pyridine derivatives. For example, in Patent Document 2, a method for producing 2-chloro-pyridine-N-oxide by the oxidation of 2-chloro-pyridine using hydrogen peroxide in the presence of a catalyst represented by Y[PW2O13(OH)] (in which Y represents a hydrogen atom, alkyl or ammonium) has been disclosed.
In addition, with respect to the reaction of pyridine-N-oxide derivatives, as a method for introducing a halogen into the methyl group of 2-picoline derivatives, for example, it has been reported in Non-Patent Document 1 that 6-chloro-2-chloromethyl pyridine can be produced by rearranging 6-chloro-2-methylpyridine-N-oxide with acetic anhydride to introduce oxygen to the methyl group, followed by the action of thionyl chloride thereon.
In Non-Patent Document 2, a halogenation method by reacting triphosgene or diphosgene with 2-picoline-N-oxide in the presence of di-1-propylamine or triethylamine has been reported.
In addition, in Patent Document 3, a method to synthesize 2-chloro-5-methylpyridine from 3-methylpyridine-1-oxide has been shown. According to Patent Document 3, it has been reported that a desired product can be obtained by the method through a rearrangement reaction using trimethylamine and phosgene to convert the 2nd position of the pyridine ring to trimethylammonium, followed by chlorination thereof.
USPTO Backgrounds
USPTO Backgrounds