Para-allyl phenol

Q 2. Thermal reaction of allyl phenyl ether generates a mixture of ortho- and para-allyl phenols. The para-allyl phenol is formed via ... 

If both ortho positions bear substituents other than hydrogen, the allyl group will further migrate to the para position. This reaction is called the para-Claisen rearrangement. The formation of the para-substituted phenol can be explained by an initial Claisen rearrangement to an ortho-2l y intermediate which cannot tautomerize to an aromatic o-allylphenol, followed by a Cope rearrangement to the p-allyl intermediate which can tautomerize to the p-allylphenol e.g. 6 ... 

In unsubstituted phenyl ethers, the enolisation is faster than the Cope reaction. This is why the product is predominantly ortho isomer. When both the ortho positions are substituted, the allyl group undergoes a second migration via a concerted sigmatropic mechanism giving a para substituted phenol. This is called para Claisen condensation. 

Rearrangement of allyl phenyl ethers with 1 results mainly in para-substituted phenols rather than the ort/io-substituted phenols formed by thermal rearrangements.2... 

Claisen rearrangement The thermal rearrangement of allylarylethers to ortho-allyl-phenols. If both ortho positions are occupied, then the allyl group migrates to the para position. 

If both ortho positions are substituted, the allyl group undergoes a second migration, giving the para-substituted phenol ... 

Allyl ethers of orf/io-disubstituted phenols rearrange to the corresponding p-allylphenols. It is noteworthy that the para rearrangement is not usually accompanied by inversion of the allyl group.8-4-6-6-7 For example, cinnamyl 2-carbomethoxy-6-methylphenyl ether (III) rearranges without inversion8 to yield the p-cinnamyl derivative (IV). 

From the molecular beam MS of the pyrolysis products of the P/N fractions, a number of phenolic compounds were detected guaiacol (2-methoxyphenol) (m/z 124), catechols (m/z 110), isomers of substituted 2-methoxyphenols with alkyl groups such as methyl (m/z 138), vinyl (m/z 150), 3-hydroxy-propen(l)-yl (m/z 180), allyl (m/z 164), hydroxyethyl (m/z 168), and ethyl (152), most likely in the para position. In addition, a few carbohydrate-derived components are also present in this fraction such as furfuryl alcohol and other furfural derivatives. 

A unique rearrangement of 2-bromophenyl allyl ethers 196 proceeds as a completely regio- and stereospecific process without any migration to the para-position and with conservation of the regiochemistry in the allyl substiments of the phenolic products 198. It was assumed that the reaction occurs via the 7r-allyl complexes 197 (equation 91) . ... 

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