Organic Reactions, Volume 2

STRUCTURAL REQUIREMENTS FOR REARRANGEMENT 5
OCH,CH==CH2 O CH,CH=CHi!
I II I
C«HBC=NC6H6 -> C6H6C—NC6H6
VII f VIII
A further resemblance of this rearrangement to the Claisen type is to be
observed in the occurrence of inversion when the crotyl ether rearranges
(IX->X).
OCH2CH=CHCH3 0 CH(CH3)CH=CH,
1 " I
C6H66=NC6H5 -» C6H6C—NC6H6
IX x
Similar reactions are known of compounds in which the carbon-nitrogen
bond is part of a heterocyclic nucleus. 17 ' 18
The oxygen atom of the reactive system may be replaced by a sulfur
atom, with, however, some reduction in the tendency toward rearrangement.
Allyl p-tolyl sulfide rearranges (XI —> XII) to the extent of 27%
(50% based on sulfide not recovered) when subjected to refluxing at
228-264° for four hours. 19
SCH2CH=CH2
Allyl thiocyanate, CH2==CHCH2SC^N, on distillation rearranges
to allyl isothiocyanate, CH2==CHCH2N=C=S. 20 Cinnaniyl 21 and
crotyl 22 thiocyanates also rearrange: the rearrangement of the former
occurs without inversion, yielding cinnamyl isothiocyanate; that of the
latter is accompanied by inversion, yielding a-methylallyl isothiocyanate.
A reaction similar to the Claisen rearrangement but involving the
migration of an allyl group from one carbon atom to another has been
discovered recently; 23 for example, ethyl 1-cyclohexenylallylcyanoacetate
(XIII) rearranges quantitatively in ten hours at 170° to ethyl (2-allylcyclohexylidene)-cyanoacetate
(XIV).
17 Tschitschibabin and Jeletzsky, Ber., 57, 1158 (1924).
18 Bergmann and Heimhold, J. Chem. Soc., 1935, 1365.
»• Hurd and Greengard, J. Am. Chem. Soc., 52, 3356 (1930).
M BiUeter, Ber., 8, 462 (1875).
81 Bergmann, J. Chem. Soc., 1935, 1361.
11 Mumm and Richter, Ber., 73, 843 (1940).
28 Cope and Hardy, /. Am. Chem. Soc, 62, 441 (1940); Cope, Hoyle, and Heyl, ibid., 63,
1843 (1941); Cope, Hofmann, and Hardy, ibid., 63, 1852 (1941).