Organic Reactions, Volume 2

REARRANGEMENT IN OPEN-CHAIN COMPOUNDS 7
In the rearrangement of ethyl O-cinnamylacetoacetate (XVI), carried
out at 110° in the presence of ammonium chloride, the substituted
allyl group migrates with inversion to give XVII.
CH3C=CHCO2C2H6
I II I
OCH2CH=CHC«H6
CH3C-CHCO2C2H5
XVI XVII
CH3C—CHCO2C2HB
0 CH2CH=CHC6H6
XVIII
O CH(C6H6)CH=€H8
However, when the rearrangement is effected by heating at 260° for four
hours the product (XVIII) is formed by migration without inversion. 9
There is evidence that, when XVI is hydrolyzed with alcoholic alkali,
rearrangement takes place with inversion. 9 Apparently the occurrence
of inversion here depends on the experimental conditions.
The simplest compounds to undergo the Claisen rearrangement are
the vinyl allyl ethers. 10 Vinyl allyl ether itself rearranges cleanly at
255° in the gas phase (XIX -• XX).
CH2=CHOCH2CH=CH2 -» CH2=CHCH2CH2CHO
XIX XX
a-Methylvinyl allyl ether and a-phenylvinyl allyl ether behave similarly.
Inversion has been found to accompany the rearrangement of
vinyl 7-ethylallyl ether (XXI -»XXII).
CH2==CHOCH2CH=CHC2H6 -
XXI XXII
The rearrangement of ketene diallylacetal is of the Claisen type; it
occurs so readily that the ketene acetal cannot be isolated from the
products of reaction of diallylbromoacetal with potassium t-butoxide in
i-butyl alcohol. 26 "
BrCH2CH(OCH2CH==CH2)2 + KOC4H9(0
-* KBr +