Rearrangements and Mechanistic Features

The earliest report on the Claisen rearrangement of allyl ethers in the pyridine series was by Saltzer et ai.4 Reaction of 2,6-dimethyl-4-pyridone with allyl bromide and crotyl bromide was assumed to give 

Takahashi and H. Kano, Chem. Pharm. Bull. (Tokyo) 12, 282 (1964). 

In a more recent investigation11 Moffett prepared 4-allyloxypyri-dine by reacting 4-bromopyridine with sodium allyloxide. Attempts to rearrange this compound led largely to polymeric products. No characterizable rearrangement product could be isolated. 

3-Allyloxypyridine was difficult to prepare. Treatment of the sodium salt of 3-hydroxypyridine with allyl bromide resulted in attack mostly on the nitrogen. No rearrangement could therefore be attempted on this derivative. 

In a more extensive study devoted to the mechanistic aspects of these rearrangements, Dinan and Tieckelmann5 investigated the behaviour of three different allyl ethers by heating them in dimethyl-aniline solution in a sealed tube at 255°. Their results are summarized in Eq. (2). The starting materials and products are shown in Table I. 

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