V
R
SYNTHETIC COMMUNICATIONS
5
derivative 2 with p-toluene sulphonohydrazide in refluxing pyridine. On the other hand,
treatment of ethyl formimidate 2 with ethyl carbazate in refluxing dioxane afforded
ethyl 2-f[(1-(2-chlorophenyl)-2-cyano-1H-benzo[f]chromen-3-yl)imino]methylg hydra-
zine-1-carboxylate (12) as a sole product. However, when the reaction was conducted in
pyridine, chromenotriazolo[1,5-c]pyrimidine derivative 13 was yielded as a sole product.
This behavior can be explained based on the basic nature of pyridine which is needed
to promote the 1,6-exo-dig cyclization, which involve proton transfer from –NH to CN
group, followed by 1,5-exo-trig cyclization to give 13.
The reaction of ethyl formimidate derivative with acid hydrazides was examined and
found to afford two ring annulations leading to the formation of fused triazolopyrimidine
[
39–41]
systems.
zolo[1,5-c] pyrimidin-2-yl)acetonitrile (14) was isolated via interaction of ethyl formimidate
with 2-cyanoacetohydrazide in refluxing dioxane (Scheme 3). The structure 14 was sub-
stantiated from studying analytical and spectroscopic data. Thus, the IR spectrum displayed
Thus, 2-(14-(2-chlorophenyl)-14H-benzo[5,6]chromeno[3,2-e][1,2,4]tria-
2
ꢁ
1
ꢁ1
m
CꢀN
at 2257cm (saturated nitrile) and m
4 was forthcoming from H NMR (CDCl ) spectrum which revealed the disappearance of
at 1634cm . Strong support of structure
C¼N
1
1
3
the triplet and quartet signals attributed to the ethyl protons of its precursor 2 and exhibited
the appearance of signals at (d, ppm): 4.08 (s, 2H, CH ), 6.74 (s, 1H, HC -pyran), 7.07–8.20
2
4
(m, 10H, Ar–H), 9.11 (s, 1H, pyrimidine moiety).
The presence of cyanomethyl functionality in 14 was utilized to insert and construct
new heterocyclic systems via reaction with different electrophilic reagents, namely, p-
nitrobenzaldehyde, salicylaldehyde, phenyl isothiocyanate, and carbon disulfide. It has
been reported that cyanomethyl derivatives underwent base-catalyzed condensation with
aromatic aldehydes to give Knoevenagel condensation product and reacted with salicy-
[
42]
laldehyde under basic condition to afford coumarin derivatives.
Similarly, cyano-
methyl derivative 14 was subjected to react with p-nitrobenzaldehyde and/or
salicylaldehyde in dioxane containing a catalytic amount of piperidine to afford aryli-
dene derivative 15 and iminochromene derivative 16, respectively. The IR spectrum of
ꢁ
1
compound 16 showed sharp stretching absorption bands at 3301 and 1648 cm charac-
teristic for NH and C¼N group frequencies and absence of absorption band of cyano-
1
group. Moreover, H-NMR spectrum of the product is devoid of methylene protons of
its precursor 14 and showed signals attributed to NH proton at d 10.18 ppm as singlet
exchanged with D O, singlet at d 9.66 ppm for HC -pyrimidine, singlet for HC -
2
2
4
chromene proton at d 8.99 ppm, multiplet for aromatic protons (14 H) at d
7
.79–8.21 ppm and singlet at d 6.57 ppm for HC -pyran.
4
Meanwhile, when compound 14 was allowed to react with phenyl isothiocyanate and
elemental sulfur in the presence of a catalytic amount of triethylamine, thiazole-2-thione
derivative 17 was obtained. IR spectrum exhibited group frequencies at 3446, 3298,
ꢁ
1
1
629 and 1240 cm representing the NH , C¼N together with C¼S groups, respect-
2
1
ively. H NMR spectrum displayed two singlet signals integrated for one proton at d
9
.51 and 6.49 ppm for HC -pyrimidine moiety and HC -pyran, respectively, in addition
2 4
to singlet signal at d 6.82 ppm integrated for two protons exchangeable with D O for
2
NH -group and multiplet for 15H at d 7.11–8.03 ppm.
2
Stirring cyanomethyl derivative 14 with carbon disulfide in ethanolic potassium
hydroxide and N,N-dimethylformamide afforded the dipotassium disulfide salt 18 which