The behavior of certain coumarins and furocoumarins toward sulfur reagents

Article abstract of DOI:10.1080/10426500500536523

The behavior of 4-hydroxycoumarin (1), 7-hydroxycoumarin (2), 4-hydroxy-bergapten (3), and 4-hydroxyisopimpinellin (4) toward sulfur reagents, namely, thionyl chloride, phosphorus pentasulfide, thiolacetic acid, and Lawesson's reagent (5), was studied. The nature of products in each case depended upon the type of reactants and reaction conditions. Possible reaction mechanisms were considered, and structural elucidations of the new products were based upon compatible elementary and spectroscopic evidences. Copyright Taylor & Francis Group, LLC.

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The Behavior of Certain
Coumarins and Furocoumarins
Toward Sulfur Reagents
a
Nabila M. Ibrahim
a
Department of Organometallic and
Organometalloid Chemistry, National Research
Centre, Dokki, Cairo, Egypt
Published online: 01 Feb 2007.
To cite this article: Nabila M. Ibrahim (2006): The Behavior of Certain Coumarins
and Furocoumarins Toward Sulfur Reagents, Phosphorus, Sulfur, and Silicon and the
Related Elements, 181:8, 1773-1784
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Phosphorus, Sulfur, and Silicon, 181:1773–1784, 2006
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500500536523
The Behavior of Certain Coumarins and Furocoumarins
Toward Sulfur Reagents
Nabila M. Ibrahim
Department of Organometallic and Organometalloid Chemistry,
National Research Centre, Dokki, Cairo, Egypt
The behavior of 4-hydroxycoumarin (1), 7-hydroxycoumarin (2), 4-hydroxy-
bergapten (3), and 4-hydroxyisopimpinellin (4) toward sulfur reagents, namely,
thionyl chloride, phosphorus pentasulfide, thiolacetic acid, and Lawesson’s reagent
(
5), was studied. The nature of products in each case depended upon the type of reac-
tants and reaction conditions. Possible reaction mechanisms were considered, and
structural elucidations of the new products were based upon compatible elementary
and spectroscopic evidences.
Keywords Coumarins; furocoumarins; sulfur reagents; thiation, chlorination
INTRODUCTION
Coumarins and furocoumarins constitute two important classes of com-
1
−7
10,11
pounds, many of which exhibit useful drug activity.
They act as
hepatoprotective,8 antiinflammtory and antiallergic,
,9
antimicro-
agents. They
also act as effective photoreactive cross-linkage reagents for nucleic
bial and anti-HIV,1
2,13
and antimitotic and anticancer
14−16
1
7
acids. The chemistry of coumarins and furocoumarins has received
considerable interest.3
,18−20
Relatively limited attention, however, was
2
1
paid for studying their behavior toward sulfur reagents. This together
with our growing interest in this area2
behavior of 4-hydroxycoumarin (1), 7-hydroxycoumarin (Umbelliferone,
), 4-hydroxybergapten (3), and 4-hydroxyisopimpinellin (4) toward a
2−25
has prompted us to study the
2
number of sulfur reagents, namely, thionyl chloride, phosphorus pen-
tasulfide, thiolacetic acid, and 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithia-
phosphetane-2,4-disulfide(Lawesson’s Reagent, LR, 5) (Schemes 1,
2).
Received September 5, 2005; accepted December 2, 2005.
Address correspondence to Nabila M. Ibrahim, National Research Center, Depart-
ment of Organometallic and Organometalloid Chemistry, Dokki, Cairo, Egypt. E-mail:
n motafa@yahoo.com
1773

1
774
N. M. Ibrahim
SCHEME 1
SCHEME 2
RESULTS AND DISCUSSION
Reactions With Thionyl Chloride
Upon heating compound 1 with thionyl chloride in the absence of a
solvent, a light orange crystalline substance was obtained and assigned
structure 7 for the following reasons: (a) Correct elementary analyses
and molecular weight determination (MS) corresponded to C18H8O6S.
(
3
7
b) The strong OH absorption band present in the IR spectrum of 1 at
−1
360 cm was absent in the spectrum of 7. (c) The mass spectrum of
+
showed the molecular ion peak at m/z 352 (M , 55%).
Apparently, the reaction of 1 with SOCl2 proceeds via initial dehy-
drochlorination involving the hydroxyl group in 1 to give the intermedi-
ate bis-product 6. The tendency of 1 to form bis-compounds is noticed in
2
0
its reaction with many reagents, e.g., aldehydes. The intramolecular
dehydration of 6 yields 7 (Scheme 3).
2
1
On this basis, structure 8, formerly proposed by Klosa for the same
reaction product of 1 with SOCl2, can be dismissed (Scheme 4).
On the other hand, when 4-hydroxybergapten (3) was allowed to
react with SOCl2 in the absence of a solvent, it yielded a colorless

Coumarins and Furocoumarins
1775
SCHEME 3
SCHEME 4
crystalline material formulated as 6-chloro-5-hydroxy-4-methoxy-7H-
furo[3,2-g][1]benzopyran-7-one (9) (Scheme 5) for the following reasons:
(
9
a) Elementary analyses and molecular weight determination (MS) for
corresponded to C12H7ClO5.
SCHEME 5
(
(
1
b) Its IR spectrum (KBr, cm−1) showed strong absorption bands at 3237
OH), 1718 (C O, lactone), 1637, 1576, 1551 (C C, aromatic and furan),
1
162 (C O, stretching), and 751 (Cl−C). (c) The H NMR spectrum of 9
(
DMSO/D2O, δ ppm) revealed the presence of two singlets at 4.34 (3H,

1
776
N. M. Ibrahim
OCH3) and 7.48 (1H, HC-9) and two doublets (each with JHH = 2.5Hz)
due to the furan ring protons at 8.10 and 7.40. Moreover, the HC-3
proton present in the spectrum of 3 at δ 6.5 was absent in the spectrum
of 9. The mass spectrum of 9 showed the molecular ion peak at m/z
266 (268).
In the same sense, 4-hydroxyisopimpinellin (4) yielded the respec-
tive 3-chloro-derivative (10) upon heating with SOCl2 in the absence
of a solvent (Scheme 6). Structure 10 was supported with compatible
elementary and spectroscopic measurements (Tables I and II).
Reactions With Phosphorus Pentasulfide
When a mixture of 4-hydroxycoumarin (l) and (P2S5)x in dry toluene
was boiled under reflux, it yielded an orange-red crystalline sub-
ꢀ
stance formulated as 3,3 -bis-(4-thiohydroxycoumarin) [4-mercapto-
3-(4-mercapto-2-oxo-2H-chromen-3-yl)-2H-chromen-2-one] (11) for the
following reasons: (a) The correct elementary and molecular weight de-
termination (MS) for 11 corresponded to C18H10O4S2. (b) Its mass spec-
+
trum (m/z, %) showed ion peaks at 354 (M , 100%) and at 321 (M-SH
radical, 95%).
SCHEME 6
Under similar conditions, 7-hydroxycoumarin (2) reacted with (P2S5)x
to give a golden yellow crystalline product formulated as 7-hydroxy-
2H-chromene-2-thione (12) (Scheme 7). Its elementary analyses and
molecular weight determination (MS) confirmed a molecular formula
of C9H6O2S. The mass spectrum of 12 showed the molecular ion peak
+
at m/z 178 (100%). A loss of 44 mass units (CS) from M yielded the
peak at m/z 134 (92.1%). The IR spectrum of 12 revealed the presence
−
1
of hydroxyl group absorption around 3250 cm and the absence of the
−1
lactone carbonyl band around 1700 cm
.
1
The H NMR spectrum of 12 (DMSO, δ ppm) disclosed 3 sets of dou-
blets (each with JHH = 15 Hz) at 7.75 (HC-3), 7.60 (HC-4), and 7.00
(
HC-5), as well as a multiplet centered at 6.85 (2H) due to (HC-6) and
1
its m-coupling with (HC-8). The H NMR spectrum also disclosed a sin-
glet at 11.00 due to OH group (D2O exchangeable). On this basis, the
other alternative structure 13 can be overlooked (Scheme 8).

Coumarins and Furocoumarins
1777

1
778
N. M. Ibrahim
TABLE II 1H NMR Spectral Data for Compounds 7, 9, 10, 11, 12, 14, 17,
8, 19, and 20
1
Compound
1H NMR (DMSO-d6 or CDCl3, δ ppm) Values
7a
9
7–8.05(m, 8H, aromatics)
a
4.34(s, 3H, OCH3); 7.4, 8.1(2d, each with JHH = 2.5Hz, 2H, furan);
∗
7.48(s,1H, aromatic); 11(bs, 1H, OH )
1
0a
4.05, 4.20(2s, 6H, 2 OCH3); 7.40, 8.15(2d, each with JHH = 2.5Hz, 2H,
∗
furan); 11.15(bs, 1H, OH )
a
∗
11
7.37–7.95(m, 10H, 8 aromatics & 2 SH )
a
12
6.85(m, 2H, HC-6 & HC-8); 7.00, 7.60, 7.75(3d, each with JHH = 15Hz, 3H,
∗
HC-5 & HC-4 & HC-3); 11(bs, 1H, OH )
4a
7b
4.22(s, 3H,OCH3); 4.48(bs, 1H, SH ); 7.40(m, 2H, furan & pyran); 7.62(s,
∗
1
1
H, aromatic); 8.15(d, JHH = 2.5Hz, 1H, furan)
∗
1
4.00(s,1H, SH ); 4.25(s, 3H, OCH3); 7.171–7.179(d, 1H, JHH = 2.1Hz,
furan); 7.80(s, 1H, vinyl proton); 7.82–7.81(d, JHH = 2.1Hz, 1H, furan)
a
∗
18
7.05(s, 1H, HC-3); 7.15–7.85(m, 5H, aromatics & SH )
a
∗
19
3.96(bs, 1H, SH ); 4.11, 4.22(2s, 6H, 2 OCH3); 6.96, 6.97(d, JHH = 2.5Hz,
1
H, furan); 7.12(s, 1H, vinyl proton); 7.67, 7.68(d, JHH = 2.5Hz, 1H, furan).
2
0a
3.25(s, 3H, CH3COO); 6.50(d, JHH = 9.3Hz, HC-3); 7.18(d, JHH = 10.5Hz,
HC-6); 7.30(d, JHH = 2.4Hz, HC-8); 7.80(d, JHH = 8.4Hz, HC-4); 8.50(d,
JHH = 9.9Hz, HC-5).
a
DMSO-d6.
b
CDCl3.
∗
Exchangeable with D2O.
SCHEME 7
SCHEME 8
4
-hydroxybergapten (3) reacted with (P2S5)x in boiling toluene to give
a yellow product formulated as 5-mercapto-4-methoxy-7H-furo[3,2-
g][1]benzopyran-7-thione (14) (Scheme 9) for the following reasons: (a)
Correct elementary analyses and molecular weight determination (MS)

Coumarins and Furocoumarins
1779
SCHEME 9
corresponded to C12H8O3S2. (b) Its IR spectrum (KBr, cm−1) disclosed
the absence of carbonyl absorption in the 1750–1650 region.
On the other hand, the spectrum showed a medium band at 2472
(
SH) and a strong band at 1154 (C S).26 Strong bands were also present
1
in the 1627–1500 region (C C, furan and aromatic). (c) The H NMR
of 14 (DMSO, δ ppm) showed signals at 4.22 (s, 3H, OCH3), 8.15 (d,
JHH = 2.5 Hz, lH, furan), 7.62 (s, lH, aromatic), and 7.40 (m, 2H, furan
and pyran). The SH proton appeared as a broad singlet at 4.48 ppm. The
reaction of 4-hydroxyisopimpinellin (4) with (P2S5)x proceeded in boil-
ing toluene to give a yellow crystalline substance for which structure
1
7 is assigned. Structural reasonings for 17 are as follows; (a) Elemen-
tary analyses and molecular weight determination (MS) agreed with
the molecular formula, C12H7O3PS5. (b) The IR spectrum of 17 (KBr,
−
1
cm ) revealed the absence of carbonyl group absorption in the 1750–
1
−1
1
650 cm region. (c) The H NMR spectrum of 17 (DMSO or CDCl3
δ ppm) showed one singlet due to the OCH3 protons at 4.25. Signals
were also found at 7.80 (s, 1H, HC-3), 7.82–7.81 (d, JHH = 2.1 Hz, 1H,
HC-6, furan), 7.179–7.171 (d, JHH = 2.1 Hz, 1H, HC-7, furan), and 4.00
(
SH, D2O-exchangeable).
A mechanism for the formation of 17 is depicted in Scheme 10. It
involves the initial partial demethylation of 4 under the influence of the
2
7
thiating agent to give 15. Intermediate 15 then undergoes thiation
with the same reagent to afford 16, which reacts with an additional
molecule of (P2S5)x to afford the final product 17.
Reactions With Lawesson’s Reagents (LR, 5)
4-hydroxycoumarin (1) reacted with LR 5 in boiling toluene to give
a golden yellow crystalline product formulated as 4-thiohydr-oxycou-
marin-2-thione (4-mercapto-2H-chromene-2-thione) (18) (Scheme 11)
for the following reasons: (a) Elementary analyses and molecular
weight determination (MS) for 18 corresponded to C9H6OS2. (b) Its IR
−1
spectrum (KBr, cm ) revealed the absence of OH absorption around

1
780
N. M. Ibrahim
SCHEME 10
SCHEME 11
3400 and the absence of the lactone-carbonyl around 1750, while the
SH absorption band appeared at 2373.
1
(
c) Its H NMR spectrum (DMSO, δ ppm) showed the HC-3 proton
as a singlet at 7.05 and the aromatic protons (4H) as a multiplet in the
region 7.85–7.15 ppm. The mass spectrum of 18 showed the molecular
ion peak at m/z 194 (100%). Prominent ion peaks were also observed in
the spectrum at m/z 161 (M-SH radical, 16.2%) and m/z 150 (M C S,
47.9%).
The reaction of 7-hydroxycoumarin (2) with LR, 5 also proceeded in
boiling toluene to give a golden yellow crystalline product proved to be
-hydroxy-2H-chromene-2-thion (12) based upon compatible elemen-
7
1
tary and spectoscopic analyses (comparative IR, H NMR, and mass
spectra).

Coumarins and Furocoumarins
1781
LR, 5 induced thiation of both the hydroxyl group and the lactone-
carbonyl group in 4-hydroxybergapten (3) upon refluxing together in
toluene to give a yellow product formulated as 5-mercapto-7H-furo[3,2-
1
g][1]benzopyran-7-thione (14) (comparative IR, H NMR, and mass
spectra).
In the same sense, the thiation of 4-hydroxyisopimpinellin (4) with
LR, 5 yielded a compound formulated as 4,9-dimethoxy-5-mercapto-7H-
furo[3,2-g][1]benzopyran-7-thione (19) almost exclusively (Scheme 12).
SCHEME 12
The reaction of 7-hydroxycoumarin with thiolacetic acid proceeded in
boiling toluene to give a white crystalline material formulated as 7-
acetoxycoumarin (20) (Scheme 13) for the following reasons: (a) Correct
elementary and molecular weight determination (MS) corresponded to
−1
C11H8O4. (b) Its IR spectrum (KBr, cm ) revealed the absence of OH
group absorption around 3400, while strong bands were recorded in the
spectrum at 1780 (C O, lactone), 1620, 1565 (C C, aromatic), and 1204
(
C O, stretching).
SCHEME 13
1
(
c) Its H NMR spectrum (DMSO, δ ppm) showed 5 sets of doublets
at 8.50 (HC-5, JHH = 9.9 Hz), 7.80 (HC-4, JHH = 8.4 Hz), 7.30 (HC-8,
JHH = 2.4 Hz due to m-coupling with HC-6), 7.18 (HC-6, JHH = 10.5 Hz),
and 6.50 (HC-3, JHH = 9.3 Hz). Protons of the CH3COO group appeared
as a singlet (3H) at δ = 3.25 ppm. (d) The mass spectrum of 20 showed
+
prominent ion peaks at m/z 204 (M , 25.5%), m/z 162 (M COCH2, ion

1
782
N. M. Ibrahim
a, 99.7%), and m/z 134 (ion a-CO, 100%). Moreover, compound 20 was
1
also unequivocally prepared and identified (comparative IR, H NMR,
and mass spectra) by the acetylation of 7-hydroxycoumarin (2) with
boiling acetic anhydride.28
EXPERIMENTAL
All melting points were determined on an electro-thermal melting point
apparatus and were uncorrected. The infrared spectra were carried out
in KBr on a Philips Infracord. Microanalyses were carried out at the
Micro-Analytical laboratory at the National Research Centre, Dokki,
1
Cairo, Egypt. H NMR spectra were measured with a Jeol-GLM 270
MHz (superconducting magnet) in DMSO or CDCl3, and chemical shifts
were recorded in δ-scale ppm relative to TMS as an internal standard.
Mass spectra were run at 70 eV with a Finnigan SSQ GC/MS spectrom-
eter using the electron Ionization Technique.
The Reaction of 4-Hydroxycoumarin (I), 4-Hydroxybergapten
(
3), and 4-Hydroxyisopimpinellin (4) With Thionyl Chloride
General procedure
A solution of the coumarin derivative (0.005 mol) in 10 mL of thionyl
chloride was refluxed in the absence of a solvent on a steam bath for
10–15 h. After the evaporation of the volatile materials in vacuo, the
remaining solid material was collected and recrystallized from the ap-
propriate solvent to give compounds 7, 9, and 10. Physical, analytical,
and spectral data of compounds 7, 9, and 10 are presented in Tables I
and II.
The Reaction of Compounds 1, 2, 3, and 4
with Phosphorous Pentasulfide
General procedure
The coumarin derivative (0.005 mol) and 1 g (P2S5)x purified by cau-
tious extraction with CS2 (Soxhlet) were mixed in 20 mL of toluene
and refluxed for 8 10 h (TLC). The reaction mixture was filtered while
hot, and the volatile materials were evaporated from the filtrate in
vacuo on a small amount of silica gel until dryness. Then the mixture
was separated by column chromatography using acetone/pet. ether (b.p.
◦
6
0–80 C) as the eluent to give compounds 11, 12, 14, and 17. Physical,
analytical, and spectral data of compounds 11, 12, 14, and 17 are pre-
sented in Tables I and II.

Coumarins and Furocoumarins
1783
The Reaction of Compounds 1, 2, 3, and 4 with Lawesson’s
Reagent (LR, 5)
General procedure
A mixture of the coumarin derivative (0.005 mol) and 0.005 mol of
Lawesson’s reagent in 20 mL of acetonitrile (or toluene) was refluxed for
8–10 h (the reaction was controlled with TLC). The volatile materials
were then evaporated in vacuo on a small amount of silica gel until
dryness, and the mixture was separated with column chromatography
◦
using acetone/pet. ether (b.p. 60–80 C) as the eluent. Compounds 18,
1
2, 14, and 19 were separated and purified.
Their physical, analytical, and spectral data are presented in Tables I
and II.
The Reaction of 7-Hydroxycoumarin (2) With Thiolacetic Acid
A mixture of 7-hydroxycoumarin (0.81 g, 0.005 mol) and 1 mL of thio-
lacetic acid in 20 mL of toluene was refluxed for 6 h. After evaporating
the volatile materials in vacuo, the remaining solid was collected and
recrystallized from acetone to give 20 as a white powder, m.p. and mixed
◦
28
m.p. 140 C.
The Acetylation of 2
-hydroxycoumarin (2) (0.81 g, 0.005 mol) was refluxed with acetic an-
7
hydride for ca 5 h; then the reaction mixture was cooled, poured onto ice,
and left overnight. The formed precipitate was filtered, dried, and re-
crystallized from acetone to give 20 (m.p.; mixed m.p; and comparative
1
IR, H NMR, and mass spectra).
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