Organic Reactions, Volume 2

INTRODUCTION
a 0 y
OCH2C&=CHCH3 OH y $ a
—CHCH==CH,
CHs
Allyl ethers of ortfto-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. 3 - 4 - 6 - 6 > 7 For example,
cinnamyl 2-carbomethoxy-6-methylphenyl ether (III) rearranges
without inversion 3 to yield the p-cinnamyl derivative (IV).
OCH2CH=CHC6HB
OH
CH2CH=CHC6H5
in iv
The crotyl ether of the same phenol also rearranges without inversion. 8
The only known example of para rearrangement accompanied by inversion
is the reaction of a-ethylallyl 2-carbomethoxy-6b-methy]phenyl
ether (V), which yields the p-(7-ethylallyl) derivative (VI). 6
OCH(C2HB)CH=CH2
CH2CH=CHC2H6
v vi
This is also the only known example of para rearrangement in which a
substituent is present on the a-carbon atom of the allyl group in the
ether. Although the number of known para rearrangements in which
inversion or non-inversion can be detected hardly justifies a generalization,
it does appear that a substituent on the 7-carbon atom of the allyl
group prevents inversion, whereas a substituent qn the a-carbon atom
favors inversion. In other werds, the para rearrangement appears to
operate in such a way that either an a- or 7-substituted allyl group leads
to a straight-chain substituent in the product.
The occurrence of inversion in the rearrangement of enol ethers appears
to be dependent upon, the experimental conditions, at least in
some instances. This question is discussed on p. 7.
* Mumm and Moller, Ber., 70, 2214 (1937).
4 Sp&th and Holzer, Ber., 66, 1137 (1933).
8 SpSth and Kuffner, Ber., 72, 1580 (1939).
' Mumm, Hornhardt, and Diederichsen, Ber., 72, 100 (1939).
7 Mumm and Diederichsen, Ber., 72, 1523 (1939).