Organic Reactions Volume 4 - Sciencemadness Dot Org

DIENE SYNTHESIS I 41
anhydride. In boiling benzene, for example, the equilibrium mixture
obtained from equimolecular proportions of 20-methylcholanthrene and
maleic anhydride contained 94% of the adduct, compared with 22%
present in boiling xylene. By the use of thirty moles of maleic anhydride
in boiling xylene, on the other hand, the following yields of adducts were
obtained: 123 from 9-phenylanthracene, 97%; 9,10-diphenylanthracene,
78%; 1,2-benzanthracene, 99%; 1,2,5,6-dibenzanthracene, 91%; 20methylcholanthrene,
83%.
The nature of the product obtained from a Diels-Alder reaction is
dependent in some instances upon the solvent employed. Such variations,
however, are generally due to secondary changes in the adduct
initially formed. When fused with maleic anhydride, 1,6-diphenylhexatriene,
for example, yields an adduct which is diJBferent from that
obtained when the reaction is effected in boiling xylene. The adducts
are isomers, and the difference is attributed to migration of one double
bond. 1,8-Diphenyloctatetraene exhibits a similar phenomenon in its
reaction with maleic anhydride. 108 ' 151 When a Diels-Alder reaction is
effected in boiling nitrobenzene, dehydrogenation of the primary hydroaromatic
adduct frequently occurs with simultaneous reduction of
nitrobenzene to aniline. 29 ' 260 ' 258 ' 321 ' 322 This transformation generally
occurs when maleic anhydride or a quinone is employed as the dienophile.*
Reaction of Maleic Anhydride with Butadiene. 323 A mixture of 50 g.
of maleic anhydride and 80 ml. of benzene in a soda bottle is chilled to
0°. The bottle is tared, charged with 32 g. of butadiene by distillation,
capped, and placed in an autoclave along with 100 ml. of benzene (to
equalize the pressure on both sides of the reaction bottle). The reaction
mixture is allowed to stand at room temperature for twelve hours and
is then heated at 100° for five hours. Crystallization of the 1,2,3,6tetrahydrophthalic
anhydride from benzene-ligroin yields 69.9 g. (90%)
of long, colorless needles, m.p. 101-103°.
Reaction of Maleic Anhydride with l-Phenyl-l,3-butadiene. 151 Maleic
anhydride (7.5 g.) and l-phenyU,3~butadiene (10 g.) are carefully
heated on a water bath until vigorous boiling indicates that reaction has
started. Heating is then discontinued. When the vigorous reaction
has subsided, a small amount of benzene is added and the mixture is
* See, however, Weidlich, Ber., 71, 1203 (1938); Bergmann and Weizman, J, Org.
Chem., 9,415 (1944).
321 Bergmann, Haskelberg, and Bergmann, J. Org. Chem., 7, 303 (1942).
822 Bergmann, J. Am Chem. Soc, 64, 176 (1942).
s23 Heser and Novello, J. Am. Chem. Soc, 64, 802 (1942).