Organic Reactions, Volume 2

EFFECT OF SUBSTITUENTS IN THE ALLYL GROUP 9
meta position. 26 - 34 The para rearrangement usually is as satisfactory as
the ortho rearrangement, with yields sometimes in excess of 85%.
Effect of Substituents in the Allyl Group. Ethers with the allyl group
substituted by alkyl groups in the a- or 7-position, ArOCH(R)CH=CH2
or ArOCH2CH=CHR, rearrange to give products in which the, 7-carbon
atom of the allyl group is attached at the ortho position of the ring. This
phenomenon of inversion (see p. 2) was first noted 35 in the rearrangement
of cinnamyl phenyl ether (XXV) to 2-(a-phenylallyl)-phenol
(XXVI).
OCH2CH=CHC6H6
XXV XXVI
^ !H(C6HB)CH=CH2
The structure of XXVI was deduced from the fact that it was different
from the 2-cinnamylphenol obtained by direct C-cinnamylation of
phenol. 16 Later investigators showed that XXVI is the sole product;
ozonization yielded formaldehyde but not benzaldehyde. 7-Methylallyl
phenyl ether also rearranges with inversion, yielding 2-(a-methylallyl)-phenol;
36 the structure of the rearrangement product has been
definitely established 87> 38 by a combination of degradative and synthetic
procedures.
Study of many substituted allyl ethers has shown that in no case in
rearrangement to the ortho position is the substituted allyl group attached
to the nucleus after rearrangement by the same carbon which
was attached to the oxygen; usually the attachment is by the 7-carbon
(inversion). The first example of the abnormal rearrangement (attachment
by other than the 7-carbon atom) was found in the rearrangement
of 7-ethylallyl phenyl ether (XXVII). 39 ' 40 The product is 2-
(a,7-dimethylallyl)-phenol (XXVIII), which must be formed as a result
of attachment of the 5- (or /3-) carbon to the nucleus.
OCH2CH=CHCH2CH3
OH
XXVII XXVIII
" Hurd and Yamall, J. Am. Chem. Soc., 59, 16S6 (1937).
36 Claisen and Tietze, Ber., 68, 275 (1925).
•* Claisen and Tietze, Ber., 59, 2344 (1926).
8T Lauer and Ungnade, J. Am. Chem. Soc., 68, 1392 (1936).
88 Lauer and Hansen, /. Am. Chem. Soc, 61, 3039 (1939).
a » Hurd and Pollack, /. Org. Chem., 3, 550 (1939).
40 Ljiuer and Filbert, J. Am. Chem. Soc., 58, 1388 (1936).