Synthesis of 2-substituted-5-methyl-pyridines and intermediates therefor
申请人:ICI AMERICAS INC.
公开号:EP0108483A2
公开(公告)日:1984-05-16
A process for the synthesis of compounds which are known intermediates for the pyridyloxyphenoxy herbicides as well as intermediates used in the process. Propionaldehyde and an acrylic compound, two readily available starting materials, are reacted to form a 2-formylpentanoic compound which is cyclized to a dihydro pyridone which is then oxidized to the 2-hydroxy pyridine. The hydroxypyridine may be halogenated to a 2-halopyridine.
A 2-oxo-5-methyl-5, 6-dihalopiperidine is contacted in a high boiling solvent, preferably trichlorobenzene, with a stoichiometric excess, up to 70 mole % excess, of a chlorinating agent, preferably phosphorus oxychloride or phosgene, at an elevated temperature between 80 and 130°C. The solution of 2-chloro-5-methylpyridine so obtained may be used directly for further chlorination to form 2-chloro-5-trichloromethylpyridine with, for example, chlorine gas in the presence of a free radical initiator. This chemical intermediate is useful in the synthesis of certain herbicidal compounds.
A 3- or 4-halo-2-pyridone compound of the formula:
in which X⁴ is halogen (preferably bromine or chlorine) is a useful chemical intermediate in the synthesis of 2-halo-5-methylpyridines themselves useful in the preparation of, for example, 4-(5-halomethyl-2-pyridyloxy)phenoxy herbicides.