Organic Reactions, Volume 2

SYNTHETIC APPLICATION 19
closure of 2-(Y,Y-dimethylallyl)-phenol gives only the chroman LXVIII,
irrespective of the presence or absence of peroxides. 29
Treatment of 2-allylphenols with mercuric salts gives mercurimethyl-
-CHCH2HgX
LXIX LXX
dihydrobenzofurans such as LXIX. 79 - 80 ' 81 The halomercuri group can
be replaced by iodine by treatment with potassium iodide, and this is a
method of preparing iodo compounds like LXX.
Another occasionally useful transformation of allylphenols is the
isomerization to propenylphenols by strong alkali, as in the well-known
isomerization of eugenol to isoeugenol. For example, 2-methoxy-6allylphenol
(LXXI) is changed to the propenyl compound LXXII by
OH
LXXI LXXII
heating 1 part of the phenol with 2 parts of powdered potassium hydroxide
and 1 of water for one hour at 170°.* This isomerization also can be
brought about by heating with soda lime without solvent/ but the
phenolic hydroxyl must be etherified. 64 A solution of sodium or potassium
hydroxide in diethylene glycol may be used for the isomerization.
81a The propenylphenols can be distinguished from the allylphenols
by their different behavior toward mercuric acetate. 82 The propenyl
compounds are oxidized to glycols, and mercurous acetate is precipitated;
the allyl compounds can add the elements of basic mercuric acetate,
giving a solid addition product from which the allyl compound can
be recovered by reduction with zinc and alkali. If a mixture of propenyl
and allyl compounds is present, and less than the necessary amount of
mercuric acetate is used, the allyl compound reacts preferentially and the
unchanged propenyl compound can be separated by extraction or steam
distillation. This makes possible a separation of the two isomers. However,
the 7,.7-dimethylallyl aromatic derivatives are oxidized by mer-
* See p. 52 of the article cited in reference 44.
79 Adams, Roman, and Sperry, J. Am. Chem. Soc., 44, 1781 (1922).
80 Mills and Adams, J. Am. Chem. Soc., 45, 1842 (1923).
81 Nesinejanow and Sarewitsch, Ber , 68, 1476 (1935).
810 Fletcher and Tarbell, J. Am. Chem. Soc, 66, 1431 (1943).
82 Balbiano, Ber., 48, 394 (1915), and previous papers.