Organic Reactions Volume 4 - Sciencemadness Dot Org

84 ORGANIC REACTIONS
cyclopentadiene or cycloheptadiene derivative, isomeric with a-terpinene,
is also formed by dehydrating a-terpineol, for with ethyl acetylenedicarboxylate
a thermally stable adduct is formed. The perhydro acid
(LXVII) of the adduct (LXVI) of this l,5,6-trimethyH,3-cycloheptadiene
with ethyl acetylenedicarboxylate was identical with an acid
obtained from maleic anhydride and eucarvone by another route. The
reduction of the ketone and the ethene of LXVIII completes the proof
for the identity of this alicyclic diene.
Other dihydrobenzene systems with an ethano bridge result when
derivatives of the anthracene-methyl acetylenedicarboxylate adduct
(LIII) interact with conjugated dienes (butadiene, dimethylbutadienes,
1,1,3-trimetbylbutadiene, and cyclopentadiene). Dimethyl 9,10-dihydroanthracene-OjlO-^ndo-ai^-maleate
(LIII) has been transformed into
the corresponding acid, anhydride (anthracene-C^s), acid chloride,
amide, and nitrile. The anthracene»C403 adduct (LXIX) reacts vigorously
with a number of simple acyclic dienes (Table XI) at temperatures
below 100° to give the secondary adducts LXX. At temperatures above
LXIX
+
R-H, CH3 O
LXX
100°, pyrolytic extrusion of the 9,10-bridge system of LXX (R = CH3)
occurs with the formation of anthracene and dimethyldihydrophthalic
anhydride, whereas at the boiling point disproportionation also occurs
and the products of pyrolysis are 9,10-dihydroanthracene and phthalic
anhydride or an alkyl derivative.
This pyrolytic method was applied successfully to the synthesis of
the acid chloride of acetylenedicarboxylic acid, 63 after the usual methods
for the preparation of acid chlorides failed. Simple thermal dissociation
of the acid chloride of LIII failed to give the diacid chloride, for the
latter decomposed into carbon monoxide, carbon dioxide, and phosgene
at temperatures required for this reaction. The desired diacid chloride
was obtained by adding maleic anhydride. At moderately high temperatures
the more reactive maleic anhydride displaces the acetylenedicarboxylic
acid chloride from the equilibrium and the dichloride distils
from the reaction mixture. Attempts to prepare acetylenedicarboxylic
63 Diels and Thiele, Ber., 71, 1173 (1938).