Rearrangements in Six-Membered Heteroaromatic Rings

The Claisen rearrangement of 2-allylthiopyridine to l-allyl-2-pyri-dinethione is also catalyzed by transition metals. The role of the catalyst, PdCl2(PhCN)2, is particularly important in this case since the reaction is thermodynamically unfavorable, and presumably the product is stabilized by complex formation. When the product is freed from the metal by addition of excess pyridine, it readily reverts to starting material on heating (80JOC5221). 

The Claisen rearrangement of 2- and 4-alIyloxypyridine N-oxides has also been studied. Heating the 2-allyloxypyridine N-oxides 86 (R = H, Me  

Thermolysis of 4-allylthioquinolines also leads to cyclized products. The thienoquinolines 94 formed by cyclization of the initial product of Claisen rearrangement 95. Again, when the rearrangement was carried out in the presence of butyric anhydride, the initial product was intercepted as its butyrate (96) hydrolysis of the butyrate gave 95, which cyclized on warming (66TL6399 69TL1971). 

Claisen rearrangements have also been observed in 1,3,5-triazines, and 2,4,6-tris(allyloxy)-I,3,5-triazine is reported to give l,3,5-triallyltriazine-2,4,6-trione on heating to 30-70°C in the presence of a copper catalyst 

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