Organic Reactions Volume 4 - Sciencemadness Dot Org

ORGANIC REACTIONS
In the absence of a catalyst, N~methylpyrrole + acetylenedicarboxylic
acid, 2-methylpyrrole and 4-methylimidazole + methyl acetylenedicarboxylate
react similarly (Table X). These substituted maleic acids
LaJ-" H *" LTJ~CC02H
^r ^y" Il
CH3 + HO2CC^CCO2H CH8 CHC ° 2H
can react with a second mole of the heterocyclic diene, e.g., 2,4-dimethylpyrrole,
N-methylindole, and 1-methylimidazole + methyl acetylenedicarboxylate.
Dependence of the course of the reaction upon the
CO2CH8
I—| CH8 + S ^ i—| CH * ac o—i
2H3C^ A H3Cl^AnH CHANJCH3
H CQ2CH8 H I (H
CO2CH8 CO2CH1
reagent is clearly illustrated by the formation of methyl l-methyl-8,9dihydroindole-4,5,6,7~tetracarboxylate
(LXXIX) from N-methylpyrrole
and methyl acetylenedicarboxylate. 1,2-Dimethylimidazole, pyridine,
a-picoline, 2-stilbazole, quinoline, isoquinoline, and phenanthridine [see
Norton, Chem. Revs., 31, 319 (1942)] react in an analogous manner with
a +
•w
CH8
CO2CH3
i
CO2CH,
CH8
CO2CH8
t^NcOiCH,
L^JcO2CH8
CO2CH8
LXXIX
methyl acetylenedicarboxylate. The reaction mixture from the pyridines
and their benzologs contains, as well as the stable adduct (LXXXI), a
labile isomer (LXXX) which is isomerized to the stable form by heat
or solution in ethanol, acetic acid, or sulfuric acid.
CO2CH3
(-)A
/^J-CO2CH3
CO2CH3
f^Y^C02CH3
N^ ^--CO2CHs
(+)
T
VzN^JcO2CH8
CO2CH8
CO3CH8
LXXX VSXU.