Beckmann Rearrangement of 4,5,6-Trisubstituted 3-Acetylpyridin-2-one Oximes

Beckmann rearrangement of 4,5,6-trisubstituted 3-acetylpyridin-Bone oximes took place, involving equilibrium between the methyl-syn and -anti forms, to give exclusively 456-trisubstituted 3acetylaminopyridin-2-ones in satisfactory yields.There have been reported many methods concerning with syntheses of substituted aminopyridines.'including the Beckmann rearrangement of pyridyl ketoxime.Previously it was shown that 4.5.6-trisubstituted3-acetylpyridin-2-ones are readily accessible by simple ring transformation* of 2-substituted 6-methyl-l,3-oxazin-4-ones, which are prepared from diketene and appropriate imidates.3We wish to report the Beckmann rearrangement of 4.5,6-trisubstituted 3-acetylpyridin-2one oximes, providing a new method for preparation of 4,5,64risubstituted 3-amiopyridin-2-ones. 4,5,6-Trisubstituted 3-acetylpyridin-2-ones (3a-f) were synthesized by the ring transformation of 2substituted 6-methyl-l,3-oxazin-4-ones (1) with active methylene compounds such as ethyl acetoacetate (2a), ethyl benzoylacetate (2b), and diethyl acetonedicarboxylate (2c) according to the procedure previously reported.Pyridones (3a-f) were led almost quantitatively to the corresponding oximes (4a-f) by a general procedure4 using hydroxylamine hydrochloride and sodium acetate.The 1H-nmr spectral examination showed that each oxime consists of both methyl-syn and -anti isomers5 as expected.