Organic Reactions

32 ORGANIC REACTIONS
Anthrones do not undergo the normal Diels-Alder reaction but react
in the ketonic form to give anthronylsuccinic anhydrides. 257 Methyleneanthrone
and its substitution derivatives, however, react readily with
maleic anhydride, cinnamic acid, or quinones to give adducts which are
converted readily to benzanthrone derivatives. 258 Methyleneanthrone
(LXXVI), for example, combines with two molecules of maleic anhydride
in boiling acetic acid to give LXXVII. If the condensation is carried
out in boiling nitrobenzene or acetic anhydride, or by fusion of the components,
LXXVIII is produced instead, probably through intermediate
formation of LXXVIL
Lxxvr
LXXVIIX
2. Aromatic-acyclic and Aromatic-alicyclic Systems. An aromatic
double bond in conjugation with extranuclear unsaturation frequently
has been observed to produce an active diene system capable of undergoing
the Diels-Alder reaction. The essential features of this reaction
are exemplified in the addition of maleic anhydride to isosafrole. 101 ' 259
H2C'
""CHCH3
+
CHQO
OC—O
LXXIX
oc—6
LXXX
A normal adduct is probably the initial product and subsequently rearranges
to give the more stable aromatic isomer (LXXIX). Continued
heating of the reaction mixture results in dehydrogenation of LXXIX to
257 Baraett, Goodway, Higgins, and Lawrence, J. Chem. Soc.t 1934, 1224.
^Clar, Ber., 69, 1686 (1936).
259 Bruckner, Ber., 75, 2034 (1942) [C. A., 38, 1228 (1944)].