The behavior of 4-azidocoumarin-3-carboxaldehyde towards certain sulfur reagents and primary amines

Article abstract of DOI:10.1080/10426500902855133

The behavior of 4-azidocoumarin-3-carboxaldehyde (1) towards certain sulfur reagents such as isothiocyanates (2a-c), thionyl chloride, Lawesson's reagent (LR, 3), and phosphorus pentasulfide as well as towards primary amines such as glycine (4) and towards anthranilic acid (5) was investigated. The structures of the new products were attested by suitable analytical and spectroscopic measurements. Taylor & Francis Group, LLC.

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The Behavior of 4-
Azidocoumarin-3-
carboxaldehyde Towards
Certain Sulfur Reagents and
Primary Amines
a
a
Nabila M. Ibrahim , Hisham Abdallah A. Yosef , El-
b
a
Sayed M. A. Yakout & Mohamed Refat H. Mahran
a
Department of Organometallic and
Organometalloid Chemistry , National Research
Centre , Dokki, Cairo, Egypt
b
Department of Pesticide Chemistry , National
Research Centre , Dokki, Cairo, Egypt
Published online: 28 Apr 2009.
To cite this article: Nabila M. Ibrahim , Hisham Abdallah A. Yosef , El-Sayed M. A.
Yakout & Mohamed Refat H. Mahran (2009) The Behavior of 4-Azidocoumarin-3-
carboxaldehyde Towards Certain Sulfur Reagents and Primary Amines,
Phosphorus, Sulfur, and Silicon and the Related Elements, 184:5, 1124-1138, DOI:
10.1080/10426500902855133
To link to this article: http://dx.doi.org/10.1080/10426500902855133
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Phosphorus, Sulfur, and Silicon, 184:1124–1138, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902855133
The Behavior of 4-Azidocoumarin-3-carboxaldehyde
Towards Certain Sulfur Reagents and Primary Amines
1
1
Nabila M. Ibrahim, Hisham Abdallah A. Yosef, El-Sayed
2
1
M. A. Yakout, and Mohamed Refat H. Mahran
Department of Organometallic and Organometalloid Chemistry,
National Research Centre, Dokki, Cairo, Egypt
1
2
Department of Pesticide Chemistry, National Research Centre, Dokki,
Cairo, Egypt
The behavior of 4-azidocoumarin-3-carboxaldehyde (1) towards certain sulfur
reagents such as isothiocyanates (2a–c), thionyl chloride, Lawesson’s reagent (LR,
3), and phosphorus pentasulfide as well as towards primary amines such as glycine
(
4) and towards anthranilic acid (5) was investigated. The structures of the new
products were attested by suitable analytical and spectroscopic measurements.
Keywords 4-Azidocoumarin-3-carboxaldehyde; primary amines; reactions; structural
elucidations; sulfur reagents
INTRODUCTION
Azides are very important building blocks due to their industrial as
well as biological applications.1 They are also applied in synthesis,
–3
4
–7
particularly via 1,3-dipolar cycloaddition reactions.
Coumarins are
of great interest, since they display a broad range of biological activities
8
9
10–12
such as antimicrobial, coronary vasodilating, and anti-neoplastic
activity and can be also used for the treatment of retroviral infec-
tions against HIV-protease.1
3,14
In response to our growing interest
in the chemistry of coumarin derivatives,1
5–20
we have now studied
the behavior of 4-azidocoumarin-3-carboxaldehyde (1) towards a num-
ber of sulfur and nitrogen reagents: ethyl, cyclohexyl and ammonium
isothiocyanates (2a–c), thionyl chloride, Lawesson’s reagent (LR, 3),
Received 21 November 2007; accepted 25 February 2008.
Dedicated to Professor Marian Miko ꢀl ajczyk, CBMiM PAN in L
occasion of his 70th birthday.
ꢀ
o´ d z´ , Poland, on the
Address correspondence to Mohamed Refat H. Mahran, Department of Organometal-
lic and Organometalloid Chemistry, National Research Centre, Dokki, Cairo 12622,
Egypt. E-mail: mrh mahran@yahoo.com
1124

Sulfurization of 4-Azidocoumarin-3-carboxaldehyde
1125
phosphorus pentasulfide, glycine (4), and anthranilic acid (5) (Scheme
).
1
The azido-function in ortho-activated aryl azides is known to
suffer attack by stabilized carbanions to produce interesting new
heterocyclic systems.1
9,21,22
Compound 1 is essentially prepared by
2
3
reacting 4-hydroxycoumarin with DMF/POCl3 (Vilsemeier) followed
by condensation of the resulting 4-chlorocoumarin-3-carboxaldehyde
with sodium azide.23
SCHEME 1
RESULTS AND DISCUSSION
When a mixture of 4-azidocoumarin-3-carboxaldehyde (known also
as 4-azido-2-oxo-2H-chromene-3-carbaldehyde) (1) and ethyl isoth-
iocyanate (2a) in THF was stirred at ambient temperature, a
colorless crystalline substance was obtained and identified as 2-oxo-
4-(thioxoamino)-2H-chromene-3-carbaldehyde (8) (Scheme 2) for the
following reasons:
a. Correct elemental analysis and molecular weight determination
(MS) for compound 8 corresponded to C10H5NO3S.
b. The strong absorption band for the azido group present in the IR
−
1
spectrum of 1 at 2176 cm was absent in the spectrum of compound

1126
N. M. Ibrahim et al.
SCHEME 2
8
. Strong absorption bands were observed at 3150 (CH, aromatic),
1
760 (C O, lactone), 1730 (C O, aldehyde), 1600 (C C, aromatic),
−
1
and at 1380 (C O, stretching) cm
.
1
c. The H NMR spectrum of compound 8 (in d6-DMSO) showed the
signal of the proton of the CHO group at δ = 10.20 (not exchangeable
with D2O). The aromatic protons gave signals at δ = 8.08 (d, JHH =
7
.8 Hz, 1H), 7.70 (dd, JHH = 8.4, 8.7 Hz, 1H) and at 7.48 (m, 2H).
These data exclude an alternative structure like 8A for the product
of the reaction of 1 with 2a (or 2b).
d. The mass spectrum of 8 showed the molecular ion peak at m/z 219
+
(
100%). Loss of sulfur radical from M yields cation a at m/z 187
(
70%), which suffers further loss of two neutral CO molecules to
afford cations b and c at m/z 159 (23%) and 131 (8%), respectively
(Scheme 3).

Sulfurization of 4-Azidocoumarin-3-carboxaldehyde
1127
SCHEME 3
Under similar conditions, compound 1 reacted with cyclohexyl isothio-
cyanate (2b) to give a colorless crystalline product proved to be 8 (mp,
mmp, and IR data). Formation of 8 may be explained in terms of the
initial formation of a nitrene species like 6 under the current reaction
conditions. Attack by 6 on the isothiocyanate sulfur atom would pro-
duce a transient species like 7, which undergoes molecular rearrange-
ment via elimination of the corresponding alkyl isocyanide to give 8
(
Scheme 2).
Upon reacting azide 1 with ammonium isothiocyanate (2c) in THF,
a yellow crystalline material was obtained and identified as bis(3-
carbonyl-4-azido-2-oxo-2H-chromeno)sulfide (9) for the following rea-
sons (Figure 1):
FIGURE 1

1128
N. M. Ibrahim et al.
a. Correct elemental analysis and molecular weight determination
+
(
MS) for 9 corresponded to C20H8N6O6S (m/z 460, M , 5%).
b. Strong absorption bands appeared in the IR spectrum of 9 (KBr)
at 3112 (CH, aromatic), 2373 (N3), 1731 (C O, lactone and thioan-
hydride), 1609, 1557 (C C, aromatic) and 1362 (C O, stretching)
−
1
cm
.
1
c. The H NMR spectrum of compound 9 (DMSO) showed the absence
of signals around δ = 10 (CHO). The aromatic protons (10 H) ap-
peared as a multiplet in the region 8.35–7.24 ppm.
d. The mass spectrum of compound 9 showed the base peak d at m/z
+
2
30 (100%), which is expected from the cleavage of M (Scheme 4).
SCHEME 4
Cleavage at the same position also produces ion e at m/z 198 (32%).
Loss of a sulfur radical from ion d can also produce ion e.
On the other hand, refluxing of 1 with thionyl chloride yielded a yel-
+
low material that is isomeric [C10H5NO3S, MS: m/z 219, (M , 5%)] but
not identical to compound 8. It was identified as 4-nitroso-2-oxo-2H-
chromeno-3-carbthialdehyde (10) (Figure 2). Its IR spectrum (KBr) re-
vealed the presence of strong absorption bands at 3102 (CH, aromatic),
1
766 (C O, lactone), 1613 (C C, aromatic), 1559 (C-NO, monomer),
−
1
1
and 1407 (C O, stretching) cm . The H NMR spectrum of compound
0 revealed the presence of signals at 10.26 (s, 1H, CHS) and 8.09–7.26
m, 4H, arom-H).
1
(

Sulfurization of 4-Azidocoumarin-3-carboxaldehyde
1129
FIGURE 2
The reaction of 1 with Lawesson’s reagent (LR, 3) proceeded in dry
toluene to give a mixture of two products. The first (major, 60%) was
identified as 4-nitroso-2-oxo-2H-chromeno-3-carbaldehyde (11) (Figure
3) for the following reasons:
a. Correct elemental analysis and molecular weight determination
+
(
MS) for 11 corresponded to C10H5NO4(m/z 203, M , 100%).
b. The IR spectrum (KBr) showed the presence of absorption bands at
3
1
098 (CH, aromatic), 1763 (C O, lactone), 1717 (C O, aldehyde),
611 (C C, aromatic), 1533 (C-NO, monomer), and 1186 (C O,
−
1
stretching) cm
.
1
c. The H NMR spectrum of compound 11 (DMSO, δ ppm) showed the
signal of the CHO proton at δ = 10.22. The aromatic protons gave
signals at 8.18 (t, JHH = 7.02 Hz, 1H) and 7.75–7.38 (m, 3H).
d. The mass spectrum of compound 11 showed the molecular ion peak
+
at m/z 203 (100%). Loss of an oxygen radical from M as expected
for N-oxides24 yields cation a at m/z 187 (42.5%). The latter ion
suffers loss of two CO molecules to yield cations b and c at m/z 159
(
22%) and 131 (12%), respectively, as in the fragmentation pattern
+
of compound 8 vide supra. Loss of a neutral CO molecule from M
yields radical cation f at m/z 175 (32.5%) (Scheme 5).
FIGURE 3

1130
N. M. Ibrahim et al.
SCHEME 5
The second product (minor, 10%) resulting from the reaction of
with LR was proved to be 2-oxo-4-(thioxoamino)-2H-chromene-3-
1
carbaldehyde (8) (mp, mmp, and IR and mass spectra).
The reaction of 1 with purified phosphorus pentasulfide proceeded
in refluxing toluene to give two isomeric but not identical substances,
which were separated by column chromatography. The first (ma-
jor product, 55%) was identified as 2H-chromeno[4,3-b]azete-2,3(1H)-
dithione (12) (Figure 4) for the following reasons:
a. Correct elemental analysis and molecular weight determination
+
(
MS) for 12 corresponded to C10H5NOS2 (MS: m/z 219, M , 95%;
175, M C S, 100%).
b. The IR spectrum (KBr) revealed the presence of strong bands at
−
1
3
428 (NH), 1597, 1517 (C C, aromatic), and 1134 (C S) cm . The

Sulfurization of 4-Azidocoumarin-3-carboxaldehyde
1131
FIGURE 4
strong lactone–carbonyl band present in the spectrum of 1 at 1722
−
1
cm was absent in the spectrum of 12.
1
c. The H NMR spectrum of 12 (d6-DMSO) showed the signal of the
NH proton as a singlet at 10.35 (exchangeable with D2O). Signals
were also observed at 8.05 (d, JHH = 7.8 Hz, 1H, H-8), 7.75 (t, 1H, H-
7
), 7.65 (d, JHH = 8.2 Hz, 1H, H-5), and 7.50 (t, 1H, H-6). According
to the aforementioned spectral data, an alternative isothioxolene
structure like 13, can be excluded.
The second substance (minor product, 10%) was proved to be compound
8
(mp, mmp, and IR and mass spectra).
The presence of the formyl function in 1 prompted us to examine
its behavior towards certain primary aminated aliphatic and aromatic
carboxylic acids, namely, glycine (4), and anthranilic acid (5). Thus
heating a mixture of 1 and 4 in dry toluene under reflux yielded a pale
yellow crystalline product identified as 2-hydroxy-6H-chromeno[3,4-
f ][1,4]oxazepine-6-one (16) according to the following evidence: (a) Cor-
rect elemental analysis and molecular weight determination (MS) for
1
6 corresponded to a composition C12H7NO4; (b) the IR spectrum of 16
(
1
KBr) showed strong absorption bands at 3326 (OH), 1710 (C O), 1594,
555 (C C aromatic, C N) and 1230 (C O, stretching) cm ; and (c)
−
1
1
3
the C NMR spectrum of compound 16 (DMSO-d6) showed the pres-
ence of the following 12 signals caused by its carbon skeleton: δ = 189.6
(
1
6
C-2), 169.3 (C-6), 162.9 (C-14), 157.0 (C-5), 155.1 (C-13), 134.9 (C-9),
29.4 (C-11), 124.4 (C-10), 118.3 (C-8), 114.8 (C-12), 95.6 (C-15), and
9.1 (C-3).
It is evident that formation of 16 proceeds via initial
1
9
19
deazidofication of 1 through elimination of HN3 to yield the interme-
diate 14. Intramolecular cyclization of 14 via elimination of H2O yields
15, which is enolized to 16 (Scheme 6).

1132
N. M. Ibrahim et al.
SCHEME 6
The alternative mechanism (Scheme 7) involving deazidofication19
of 1 by 4 followed by dehydration of the resulting intermediate such as
17 to give 18 or 19 is thus overlooked.
SCHEME 7

Sulfurization of 4-Azidocoumarin-3-carboxaldehyde
1133
FIGURE 5
In the same sense, the reaction of 1 with anthranilic acid (5)
proceeded in boiling toluene to yield a pale brown product identi-
fied as (5Z)-2H,7H-chromeno[4,3-b][5,1]benzoxazocine-2,9-dione (20)
(
Figure 5).
Correct elemental analysis and molecular weight determination
+
for 20 (MS) corresponded to C17H9NO4 [m/z 291 (M , 1.4%), m/z 262
(
M-HCN, 5.02%), m/z 247 (M-CO2, 100%)]. The IR spectrum (KBr,
−
1
cm ) showed bands at 3124 (CH, aromatic), 1749 (C O, lactone), 1611
C N), 1567, 1513, 1467 (C C, aromatic), and 1152 (C O, stretching)
(
−
1
1
cm . The H NMR spectrum (d6-DMSO) showed the signal of the
azomethine proton as a singlet at δ = 9.40. The aromatic protons (8H)
gave signals at δ = 8.60 (d, JHH = 6.48, 1H), 8.30 (d, JHH = 6.48, 1H),
8
7
.07 (t, 1H), 7.75 (m, 1H), 7.55 (m, 1H), 7.10 (t, 1H), 6.65 (d, JHH =
.29, 1H), and 6.45 (t, 1H).
Based on these data, an alternative structure such as 22 for the
reaction product of 1 with 5 can be excluded (Scheme 8).
SCHEME 8

1134
N. M. Ibrahim et al.
CONCLUSION
Apparently, the azido-function in 1 seems to be the most vulnerable
site for attack by alkyl isothiocyanates (2a,b), LR 3, thionyl chloride,
and phosphorus pentasulfide. The formyl function in 1, on the other
hand, is the only site for attack by ammonium isothiocyanate (2c).
Both functions, however, are involved in the reaction of 1 with aminated
derivatives of carboxylic acids (4 and 5) leading to polycyclic systems
of types 16 and 20, respectively. Although thionitroso compounds are
known to be mostly unstable,2
5,26
compound 8, on the other hand, shows
marked stability, and its spectral data are reproducible and concordant
with the proposed structure. To the best of our knowledge, the results of
the present study show new synthetic potentials for the azido function,
either as such or coupled with a vicinal formyl group.
EXPERIMENTAL
Melting points were determined with an electrothermal digital melt-
ing point apparatus and are uncorrected. Elemental analytical data
(
in accord with the calculated values) were obtained at the analyti-
cal laboratory of the National Research Centre, Cairo, Egypt. The IR
spectra were recorded in KBr disks on a Jasco Fourier Transform In-
frared spectrophotometer model FT/IR-3000E. The H NMR spectra
1
were recorded in deuterated dimethylsulfoxide (d6-DMSO) with a Var-
ian Mercury VX-300 spectrometer (300 MHz), using tetramethylsilane
(
TMS) as internal reference. Mass spectra (EI-MS) were obtained at 70
eV with a Finnigan MAT SSQ 7000 spectrometer.
Reaction of 4-Azidocoumarin-3-carboxaldehyde (1) with Ethyl
Isothiocyanate (2a) or Cyclohexyl Isothiocyanate (2b)
A mixture of 0.22 g 1 (1 mmol) and 0.09 g or 0.14 g of the isothiocyanate
2
a or 2b (1 mmol), respectively, in 20 mL of dry THF was stirred at room
temperature for 5–8 h (the progress of the reaction was controlled by
TLC). The volatile materials were evaporated under reduced pressure,
and the residue was chromatographed on silica gel using petroleum
◦
ether (bp 60–80 C) and acetone as eluent. Compound 8 could be isolated
from both reactions (mp, mmp, and comparative IR spectra). Physical,
analytical, and spectral data of compound 8 are presented in Tables I
and II.

1135

1136
N. M. Ibrahim et al.
TABLE II 1H NMR Spectral Data for Compounds 8–12 and 20
1
H NMR (DMSO-d , δ ppm)
6
8
7.48 (m, 2H, arom-H), 7.70 (dd, JHH = 8.4, 8.7 Hz, 1H, arom-H), 8.08 (d, JHH =
7
.8 Hz, 1H, arom-H), 10.20 (s, 1H, CHO)
9
0
1
2
7.24-8.35 (m, 8H, arom-H)
7.26-8.09 (m, 4H, arom-H), 10.26 (s, 1H, CHS)
1
1
1
7.38-7.75 (m, 3H, arom-H), 8.18 (t, JHH = 7.0 Hz, 1H, arom-H), 10.22 (s, 1H, CHO)
7.50 (t, 1H, H-6), 7.65 (d, JHH = 8.2 Hz, 1H, H-5), 7.75 (t, 1H, H-7), 8.05 (d, JHH =
7.8 Hz, 1H, H-8), 10.35 (s, 1H, NH exchangeable with D2O)
20
6.45 (t, 1H, arom-H), 6.65 (d, JHH = 7.3 Hz, 1H, arom-H), 7.10 (t, 1H, arom-H),
7
.55 (m, 1H, arom-H), 7.75 (m, 1H, arom-H), 8.07 (t, 1H, arom-H), 8.30 (d,
JHH = 6.5 Hz, 1H, arom-H), 8.60 (d, JHH = 6.5 Hz, 1H, arom-H), 9.40 (s, 1H,
azomethine proton)
Reaction of 4-Azidocoumarin-3-carboxaldehyde (1) with
Ammonium Isothiocyanate (2c)
A mixture of 1 (0.22 g, 1 mmol) and ammonium isothiocyanate (0.08 g,
1
7
mmol) in 20 mL of dry THF was stirred at ambient temperature for
h. The volatile materials were evaporated under reduced pressure,
and the residue was crystallized from DMF/H2O to give compound 9.
Physical, analytical, and spectral data of compound 9 are presented in
Tables I and II.
Reaction of 4-Azidocoumarin-3-carboxaldehyde (1) with
Thionyl Chloride
A solution of 1 (0.44 g, 2 mmol) in 10 mL of thionyl chloride was refluxed
in the absence of solvent on a steam bath for 8 h. After evaporation of the
volatile materials under reduced pressure, the remaining solid material
was collected and recrystallized from DMF/H2O to give compound 10.
Physical, analytical, and spectral data of compound 10 are presented
in Tables I and II.
Reaction of 4-Azidocoumarin-3-carboxaldehyde (1) with
Lawesson’s Reagent (3)
A mixture of 1 (0.44 g, 2 mmol) and 3 (0.61 g, 1.5 mmol) in 20 mL of dry
toluene was refluxed for 7 h. The volatile materials were evaporated
under reduced pressure, and the residue was chromatographed on silica
◦
gel using petroleum ether (bp 60–80 C) and acetone as eluent to give
compounds 8 (mp, mmp, and comparative IR spectra) and 11. Physical,

Sulfurization of 4-Azidocoumarin-3-carboxaldehyde
1137
analytical, and spectral data of compound 11 are presented in Tables I
and II.
Reaction of 4-Azidocoumarin-3-carboxaldehyde (1) with
Phosphorus Pentasulfide (P S5)x
2
1
(0.44 g, 2 mmol) and (P2S5)x (1.0 g) purified by cautious extraction
with CS2 (Soxhlet) were mixed in 20 mL of dry toluene and refluxed for
0 h (TLC). The reaction mixture was filtered while hot, and the volatile
1
materials were evaporated under reduced pressure. The residue was
◦
chromatographed on silica gel using petroleum ether (bp 60–80 C) and
acetone as eluent to give compounds 8 (mp, mmp, and comparative IR
spectra) and 12. Physical, analytical, and spectral data of compound 12
are presented in Tables I and II.
Reaction of 4-Azidocoumarin-3-carboxaldehyde (1) with
Glycine (4)
A mixture of 1 (0.44 g, 2 mmol), 4 (0.27 g, 2 mmol), and a few drops of
piperidine was refluxed in 20 mL of dry toluene for 10 h. After evapo-
ration of the volatile materials under reduced pressure, the remaining
solid material was collected and recrystallized from DMF/H2O to give
compound 16. Physical, analytical, and spectral data of compound 16
are presented in Tables I and II.
Reaction of 4-Azidocoumarin-3-carboxaldehyde (1) with
Anthranilic acid (5)
A mixture of 1 (0.44 g, 2 mmol) and 5 (0.15 g, 2 mmol) in 20 mL of dry
toluene was refluxed for 4 h. After evaporation of the volatile materials
in vacuo, the remaining solid material was collected and recrystallized
from DMF/H2O to give compound 20. Physical, analytical, and spectral
data of compound 20 are presented in Tables I and II.
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