Unexpected product of the alkylation of perimidines by chalcones under Michael reaction conditions [5]

Full text of DOI:10.1023/A:1015368031946

Chemistry of Heterocyclic Compounds, Vol. 38, No. 2, 2002
UNEXPECTED PRODUCT OF THE
ALKYLATION OF PERIMIDINES
BY CHALCONES UNDER MICHAEL
REACTION CONDITIONS
I. V. Borovlev1, O. P. Demidov1, and A. F. Pozharskii2
Keywords: perimidine, alkylation, Michael reaction.
An attempt to effect the N-alkylation of perimidines 1a-c using α,β-unsaturated ketones (chalcones)
under Michael reaction conditions in a neutral medium similar to the reaction with acrylonitrile [1] and also in
basic medium in the system KOH–acetone was unsuccessful, perhaps due to steric hindrance. The reaction
proceeds under more vigorous conditions at 180-185°C with sodium glycolate in ethylene glycol. However, the
corresponding 1,3-diazapyrenes 8a-d proved somewhat unexpectedly to be the sole products of this reaction
along with considerable tar formation. Products 8a-d were obtained in our previous work from the same
reagents in polyphosphoric acid [2, 3]. While the result of this reaction would have been difficult to predict
a priori, this process undoubtedly occurs according to the mechanism below (Scheme 1).
The ambident nature of perimidine N-anion was also noted earlier in its reaction with allyl and benzyl
halides since C-alkylation products at C(4) and C(9) were isolated along with 1-allyl- and 1-benzylperimidines [4].
Anions 2 (R1 = H, Me, Ph) act as C(6)-nucleophiles in reactions with chalcones, i.e., in canonical structure 2b.
The product of the C-alkylation of compound 4 after deprotonation reacts as anion 5b, undergoing
intramolecular addition at the carbonyl group. Phenalene 7 is formed after dehydration. However, as in acid
media [2, 3], phenalene 7 readily undergoes aromatization, indicating high thermodynamic stability of the
1,3-diazapyrene molecule. Thus, the C-variant of the Michael reaction occurs in the first step taking account of
the likely reversibility of the N-alkylation of the perimidine anion under thermodynamic control conditions.
Despite the relatively low yield of compound 8, this transformation would appear to open new possibilities for
the synthesis of this heterocyclic system.
Thus, in the standard procedure, solution is prepared by adding metallic sodium (2.6 mmol) to ethylene
glycol (7 ml). Then, perimidine 1 (2 mmol) and benzalacetophenone or benzalacetone (4 mmol) are added and
heated to 180-185°C. The mixture is retained at this temperature for 4 h. After cooling, the solution was poured
into water (100 ml) and extracted with three 50-ml benzene portions. The combined extract was evaporated to
10 ml and passed through a silica gel column with benzene as the eluent for the first fraction and with ethyl
acetate for the second fraction. The first fraction containing a small amount of tarry products was discarded.
After distilling off the solvent, the second fraction gave products 8a-d. The yield of 6,8-diphenyl-1,3-
diazapyrene (8a) was 35%. The yield of 2-methyl-6,8-diphenyl-1,3-diazapyrene (8b) was 29%. The yield of
__________________________________________________________________________________________
1
2
Stavropol State University, 355009 Stavropol, Russia; e-mail: nauka@stavsu.ru.
Rostov State
University, 344090 Rostov-on-Don, Russia; e-mail: pozharsk@pozhar.rnd.runnet.ru. Translated from Khimiya
Geterotsiklicheskikh Soedinenii, No. 2, pp. 278-279, February, 2002. Original article submitted September 5, 2001.
0009-3122/02/3802-0257$27.00©2002 Plenum Publishing Corporation
257

Scheme 1
R1
R1
R1
_
N
NH
N
N
N
N
N
+
– H
_
2b
1
2a
R1
R1
NH
N
N
+
PhCH=CHCOR2
~ H
+
– H
O
O
H
Ph
R2
2
Ph
R
4
3
R1
R1
R1
_
N
N
N
_
N
N
N
+
+ H
O
O
H
HO
R2
Ph
Ph
Ph
R2
R2
5a
5b
6
R1
1
R
H
N
N
N
N
+
[O]
~H
– H2O
R2
R2
Ph
Ph
7
8
1 a R1 = H, b R1 = Me, c R1 = Ph; 8 a R1 = H, R2 = Ph, b R1 = Me, R2 = Ph, c R1 = R2 = Ph,
d R1 = H, R2 = Me
2,6,8-triphenyl-1,3-diazapyrene (8c) was 23%. The yield of 6-methyl-8-phenyl-1,3-diazapyrene (8d) was 22%.
Mixed probes of products 8a-d with previously obtained samples of the corresponding compounds [3] did not
give a melting point depression.
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Geterotsikl. Soedin., 973 (1981).
I. V. Borovlev, A. V. Aksenov, and A. F. Pozharskii, Khim. Geterotsikl. Soedin., 1523 (1997).
I. V. Borovlev, O. P. Demidov, and A. F. Pozharskii, Khim. Geterotsikl. Soedin., 796 (2001).
A. F. Pozharskii and A. A. Konstantinchenko, Khim. Geterotsikl. Soedin., 954 (1979).
2.
3.
4.
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