A chemoselective and one-pot synthesis of 5-hydroxy and 7-hydroxy coumarin derivatives

Article abstract of DOI:10.1007/s00706-008-0078-2

An efficient one-pot reaction of dialkyl acetylenedicarboxylates with 2,4-dihydroxybenzo(or aceto)phenones in the presence of triphenylphosphine produces 5-hydroxy- and 7-hydroxycoumarin derivatives. The novel procedure features short reaction time, fairl

Full text of DOI:10.1007/s00706-008-0078-2

Monatsh Chem (2009) 140:489–493
DOI 10.1007/s00706-008-0078-2
ORIGINAL PAPER
A chemoselective and one-pot synthesis of 5-hydroxy
and 7-hydroxy coumarin derivatives
Robabeh Baharfar Æ Seyed M. Vahdat Æ
Fatemeh G. Hakimabadi
Received: 26 July 2008 / Accepted: 27 September 2008 / Published online: 28 October 2008
Ó Springer-Verlag 2008
Abstract An efficient one-pot reaction of dialkyl acety-
lenedicarboxylates with 2,4-dihydroxybenzo(or aceto)
phenones in the presence of triphenylphosphine produces
5-hydroxy- and 7-hydroxycoumarin derivatives. The novel
procedure features short reaction time, fairly good yields,
and simple workup.
reaction between the conjugate base of phenolic derivatives
1 and a vinyl triphenylphosphonium salt will be presented.
Thus, reaction of 2,4-dihydroxybenzo(or aceto)phenones 1
with dialkyl acetylenedicarboxylates 2a–2c in the presence
of triphenylphosphine leads to alkyl 6-benzoyl(or acetyl)-
5-hydroxy-2-oxo-2H-chromene-4-carboxylates 3a–3f and
alkyl 6-benzoyl(or acetyl)-7-hydroxy-2-oxo-2H-chromen-
4-carboxylates 4a–4f. Also, the by-products dimethyl
(E)-2-[6-benzoyl(or acetyl)-7-hydroxy-4-(methoxycar-
bonyl)-2-oxo-2H-chromen-5-yl]-2-butenedioates 5a and 5d
have been prepared from methyl acetylenic ester 2a
(Scheme 1).
Keywords Coumarin derivatives ꢀ Triphenylphosphine ꢀ
Tri-component reaction ꢀ One-pot synthesis ꢀ
Dialkyl acetylenedicarboxylates
Introduction
Coumarin and its derivatives have captured the attention of
organic synthesis chemists, and a large number of cou-
marin ring syntheses have been reported [1–8]. The
coumarin nucleus is incorporated in many biologically
active compounds and natural products [9–14].
Results and discussion
Compounds 3 and 4 result from the initial addition of tri-
phenylphosphine to the acetylenic ester and a subsequent
protonation of the reactive 1:1 adduct by the more acidic
free OH-group. Then, electrophilic attack of the vinyltri-
phenylphosphonium cation on the aromatic ring at the
ortho positions relative to the strong activating group forms
the phosphorus ylides 6 and 7, which via proton transfer
and removal of triphenylphosphine are recycled and lead to
the unsaturated diesters 8 and 9. However, we could only
isolate and identify the unsaturated diester intermediate 8c.
The final products 5-hydroxy- and 7-hydroxycoumarins 3
and 4 are presumably produced by intramolecular lacton-
ization of the unsaturated diesters 8 and 9 (Scheme 2).
Chemoselectivity of this reaction is explained by the
deactivation of the hydroxy group by an intramolecular
hydrogen bonding with the neighboring carbonyl group
[24]. Thus, in these cases, and others involving chelated
hydroxy groups, only the more acidic non-chelated
hydroxy groups are involved in chromenylation [25].
Classical routes to coumarins incorporate Pechmann,
Knoevenagel, Perkin, Reformastky, and Wittig condensa-
tion reactions [15–21]. To make these classical reactions
efficacious, several variations in terms of catalyst and
reaction conditions have been introduced [22, 23]. How-
ever, the classic methods suffer from expensive catalyst,
laborious multi-step procedures, long reaction time, high
reaction temperature, or waste problems. In this paper a
direct, efficient, and operationally convenient approach to
the synthesis of 5-hydroxy- and 7-hydroxycoumarin
derivatives based on the aromatic electrophilic substitution
R. Baharfar (&) ꢀ S. M. Vahdat ꢀ F. G. Hakimabadi
Department of Chemistry, University of Mazandaran,
47415 Babolsar, Iran
e-mail: baharfar@umz.ac.ir
123

490
R. Baharfar et al.
OH
O
/ CH2Cl2
r.t.
PPh3
R'O2C
C
C
CO2R'
R
HO
1
2
R'O2C
H
OH O
OH
O
R
R'O2C
OH O
R
R
R'O2C
O
O
O
O
O
O
CO2R'
CO2R'
3
5
4
3,4,5
R
R'
Me
Et
R
R'
Me
Et
3,4,5
a
b
c
Me
Me
Me
d
e
f
Ph
Ph
Ph
t-Bu
t-Bu
Fig. 1 Single crystal X-ray structure of compound 3f, with 50%
probability displacement ellipsoids
Scheme 1
R'O2C
OH O
H
Ph3P
R
H
R'O2C
O
O
6
HO
OH
R
Ph3P
C
C
H
CO2R'
O
R'O2C
O
R
HO
R'O2C
CO2R'
H
7
PPh3
R'O2C
OH
O
O
H
R
R
R'O2C
HO
8
- ROH
1) Proton shift
2) - PPh3
3 + 4
OH
HO
R'O2C
Fig. 2 Molecular structure of 5d, with 50% probability displacement
ellipsoids, H atoms with arbitrary radii
CO2R'
H
9
Scheme 2
aromatic protons, while compound 4 exhibited two single
lines at 6.85 and 8.95 ppm. The assignment of the (E)-
configuration of 5a is based on the chemical shift of the
Structures 3a–3f, 4a–4c, 4f, 5a, and 5d were assigned to
the isolated products on the basis of their IR, 1H, 13C NMR
and mass spectra. Unambiguous evidence for the structures
of 3f and 5d were obtained from single-crystal X-ray
analysis. ORTEP diagrams of 3f and 5d are shown in
Figs. 1 and 2.
1
vinylic proton [26]. Partial assignment of the H and 13C
NMR of compounds 3–5 is given in the experimental
section.
In conclusion, the reaction described herein represents a
simple entry into the synthesis of 5-hydroxy- and 7-hy-
droxycoumarin derivatives of potential interest. The
present coumarin synthesis complements the older estab-
lished methods and offers significant advantages for the
synthesis of coumarins having acid-sensitive functional
groups. In contrast, the well-known von Pechmann syn-
thesis [27] entails acidic conditions and frequently affords
low and erratic yields. In addition, the present procedure
affords advantages of short reaction time, moderate yields,
and simple workup. Further investigations of the present
method will be required to establish its utility and scope.
The IR spectrum of the compounds 3a and 4a shows a
strong OH stretching bond at bout 3,300–3,550 cm-1. The
1
regiochemistry of the cyclization was confirmed by the H
NMR analysis of 3 and 4, in which a singlet peak corre-
sponding to the remaining hydroxy proton was observed at
13.72 and 12.46 ppm. This proton has been deshielded
because of intramolecular hydrogen bonding with the
1
neighboring carbonyl group. The H NMR spectroscopy
was also applied to distinguish structure 3 from 4. Thus, the
1H NMR spectrum of 3 displayed an AX pattern for the
123

A chemoselective and one-pot synthesis of 5-hydroxy and 7-hydroxy coumarin derivatives
491
tert-Butyl 6-acetyl-5-hydroxy-2-oxo-2H-chromene-4-
carboxylate (3c, C17H16O6)
Experimental
Green powder, yield 15%, mp 143–145 °C; 1H NMR
(500 MHz, CDCl3): d = 1.59 (s, CMe3), 2.64 (s, CH3),
Dialkyl acetylenedicarboxylate, triphenylphosphine, and
2,4-dihydroxy benzo(or aceto)phenones were obtained
from Fluka (Buchs, Switzerland) and used without further
purification. Elemental analyses for C and H were per-
formed using a Heraeus CHN–O-Rapid analyzer and were
3
6.23 (s, CH), 6.85 (d, JHH = 8.9 Hz, CH), 7.88 (d,
3JHH = 8.9 Hz, CH), 13.83 (s, OH) ppm; 13C NMR
(125.7 MHz, CDCl3): d = 26.5 (CH3), 28.0 (CMe3), 84.4
(CMe3), 106.3 (C), 108.4 and 112.8 (2 CH), 115.5 (C), 134.1
(CH), 146.1, 159.1 and 159.5 (3 C), 161.1 and 164.4 (2 C=O,
1
found to be in accord with the calculated values. H and
13C NMR spectra were measured (CDCl3 solution) with a
Bruker DRX-500 AVANCE spectrometer at 500.1 and
125.8 MHz. IR spectra were recorded on a Shimadzu
IR-460 spectrometer.
ꢀ
ester), 203.6 (C=O, ketone) ppm; IR (KBr): m ¼
3;320ꢁ3;500 (OH), 1,645–1,753 (C=O) cm-1; MS: m/z
(%) = 304 (M?,4), 303 (M?-1, 43), 215 (100), 187 (38),
43 (100).
General procedure
Methyl 6-benzoyl-5-hydroxy-2-oxo-2H-chromen-4-
carboxylate (3d, C18H12O6)
To a magnetically stirred solution of 2 mmol 2,4-di-
hydroxybenzo(or aceto)phenone and 0.52 g triphenyl-
phosphine (2 mmol) in 10 cm3 CH2Cl2 was added
dropwise at -10 °C over 10 min 2 mmol dialkyl acety-
lenedicarboxylates. The reaction mixture was then allowed
to warm up to room temperature and stand for 48 h. The
solvent was removed under reduced pressure, and the res-
idue was separated by silica gel column chromatography
(Merck 230–400 mesh) using n-hexane–ethyl acetate as
eluent.
Yellow crystal, yield 75%, mp 162 °C; 1H NMR
(500 MHz, CDCl3: d = 3.97 (s, OCH3), 6.32 (s, CH),
6.83 (d, JHH = 8.9 Hz, CH), 7.49–7.63 (m, CH, Aro-
3
3
matic), 7.79 (d, JHH = 8.9 Hz, CH), 13.72 (s, OH) ppm;
13C NMR (125.7 MHz, CDCl3: d = 53.3 (OCH3), 106.3
(C), 108.2, 132.5 (2 CH), 113.4 (C), 114.9, 128.7, 129.0
and 137.0 (4 CH), 137.1, 144.7 (2 C), 158.6, 159.2 (2
C–O), 161.7 and 166.0 (2 C=O, ester), 200.7 (C=O, ketone)
ꢀ
ppm; IR (KBr): m ¼ 3;400ꢁ3;550 (OH), 1,744–1,754
(C=O, ketone), 1,620–1,650 (C=O, ester), 1,410–1,415
(C=C) cm-1; MS: m/z (%) = 324 (6) (M?), 105 (12), 57
(95), 44 (100).
Methyl 6-acetyl-5-hydroxy-2-oxo-2H-chromene-4-
carboxylate (3a, C13H10O6)
White powder, yield 75%, mp 161–163 °C; 1H NMR
(500 MHz, CDCl3): d = 2.63 (s, CH3), 3.95 (s, OCH3),
Ethyl 6-benzoyl-5-hydroxy-2-oxo-2H-chromen-4-
carboxylate (3e, C19H14O6)
3
Yellow crystal, yield 75%, mp 132 °C; 1H NMR
6.30 (s, CH), 6.86 (d, JHH = 8.9 Hz, CH), 7.89 (d,
3JHH = 8.9 Hz, CH), 13.85 (s, OH) ppm; 13C NMR
(125.7 MHz, CDCl3): d = 26.5 (CH3), 53.3 (OCH3),
106.2 (C), 108.4 and 113.3 (2 CH), 115.5 (C), 134.3
(CH), 144.7, 158.6 and 159.3 (3 C), 160.7, and 166.0 (2
3
(500 MHz, CDCl3): d = 1.39 (t, JHH = 7.3 Hz, CH3),
4.44 (q, JHH = 7.3 Hz, CH2), 6.31 (s, CH), 6.82 (d,
3
3JHH = 9.1 Hz, CH), 7.49–7.63 (m, CH, Aromatic), 7.78
3
(d, JHH = 9.1 Hz, CH), 13.71 (s, OH) ppm; 13C NMR
ꢀ
C=O, ester), 203.7 (C=O, ketone) ppm; IR (KBr): m ¼
(125.7 MHz, CDCl3): d = 14.0 (CH3), 62.8 (CH2), 106.4
(C), 108.2, 132.5 (2 CH), 113.3 (C), 114.9, 128.6, 129.2
and 137.0 (4 CH), 137.1, 145.1 (2 C), 158.7, 159.3 (2 C-O),
161.8 and 165.6 (2 C=O, ester), 200.7 (C=O, ketone) ppm;
3;300ꢁ3;500 (OH), 1,650–1,750 (C=O) cm-1; MS: m/z
(%) = 263 (M?, 8), 262 (M?-1, 40), 215 (100), 187 (38),
43 (100).
ꢀ
IR (KBr): m ¼ 3;350ꢁ3;480 (OH), 1,745–1,755 (C=O,
Ethyl 6-acetyl-5-hydroxy-2-oxo-2H-chromene-4-
carboxylate (3b, C14H12O6)
ketone), 1,615–1,645 (C=O, ester), 1,425–1,432 (C=C)
cm-1, MS: m/z (%) = 338 (7) (M?), 293 (48), 105 (100),
77 (100), 44 (46).
White powder, yield 60%, mp 150–152 °C; 1H NMR
(500 MHz, CDCl3): d = 1.38 (t, 3JHH = 7.2 Hz, CH3), 2.64
3
(s, CH3), 4.42 (q, JHH = 7.2 Hz, OCH2), 6.30 (s, CH),
tert-Butyl 6-benzoyl-5-hydroxy-2-oxo-2H-chromen-4-
carboxylate (3f, C21H18O6)
Yellow oil, yield 75%; 1H NMR (500 MHz, CDCl3):
6.87 (d, 3JHH = 8.9 Hz, CH), 7.89 (d, 3JHH = 8.9 Hz, CH),
13.84 (s, OH) ppm; 13C NMR (125.7 MHz, CDCl3):
d = 13.9 (CH3), 26.5 (CH3), 62.7 (OCH2), 106.2 (C), 108.4
and 113.3 (2 CH), 115.5 (C), 134.2 (CH), 145.1, 158.7 and
159.4 (3 C), 160.9 and 165.5 (2 C=O, ester), 203.6 (C=O,
3
d = 1.62 (s, CMe3), 6.27 (s, CH), 6.83 (d, JHH = 8.9 Hz,
CH), 7.51–7.70 (m, CH, Aromatic), 7.79 (d,
3JHH = 8.9 Hz, CH), 13.72 (s, OH) ppm; 13C NMR
(125.7 MHz, CDCl3): d = 28.0 (CMe3), 84.5 (CMe3),
106.4 (CH), 108.2 (C), 112.9, 114.8 (2 CH), 128.7, 129.1
and 132.5 (3 CH), 136.9, 137.1 and 146.1 (3 C), 159.1,
ꢀ
ketone) ppm; IR (KBr): m ¼ 3;311ꢁ3;526 (OH), 1,640–
1,748 (C=O) cm-1; MS: m/z (%) = 276 (M?, 5), 275
(M?-1, 42), 215 (100), 187 (38), 43 (100).
123

492
R. Baharfar et al.
159.5 (2 C-O), 162.0 and 164.5 (2 C=O, ester), 200.8
(C=O, ketone) ppm; selected X-ray crystallographic data:
˚
monoclinic, space group = C2/c, a = 22.1263 (12) A,
116.1, 116.9 (2 CH), 128.6, 129.3 and 132.5 (3 CH), 134.2,
137.3 and 143.9 (3 C), 159.3, 159.6 (2 C–O), 162.7 and
166.2 (2 C=O, ester), 200.7 (C=O, ketone) ppm; IR (KBr):
ꢀm ¼ 3;300ꢁ3;550 (OH), 1,730–1,740 (C=O, ketone),
1,620–1,640 (C=O, ester), 1,400–1,410 (C=C) cm-1; MS:
m/z (%) = 366 (5) (M?), 105 (36), 44 (100).
˚
˚
b = 7.3012 (4) A, c = 22.5428 (12) A, a = 90°, b =
3
˚
103.118 (5)°, c = 90°, V = 3546.7 (3) A , T = 120 (2)
K, Z = 8, dx = 1.372 Mg m-3, l = 0.10 mm-1; CCDC
679,388 contains the supplementary crystallographic data
for this paper.
(E)-dimethyl-2-[6-acetyl-7-hydroxy-4-(methoxycarbonyl)-
2-oxo-2H-chromen-8-yl]-2-butenedioate
Methyl 6-acetyl-7-hydroxy-2-oxo-2H-chromene-4-
carboxylate (4a, C13H10O6)
(5a, C19H16O10)
White powder, yield 5%, mp 134–136 °C; 1H NMR
(500 MHz, CDCl3): d = 2.70 (s, CH3), 3.63, 3.78 and
4.00 (3 s, 3 OCH3), 6.86, 7.23 and 9.02 (3 s, 3 CH), 12.97
(s, OH) ppm; 13C NMR (125.7 MHz, CDCl3): d = 26.6
(CH3), 52.0, 53.0 and 53.2 (3 OCH3), 108.3, 112.1 and
117.0 (3 C), 117.4, 131.2 and 132.1 (3 CH), 135.2, 140.9,
156.1 and 158.8 (4 C), 162.5, 164.0, 164.6 and 165.1 (4
White powder, yield 17%, mp 143–145 °C; 1H NMR
(500 MHz, CDCl3): d = 2.68 (s, CH3), 3.99 (s, OCH3),
6.84 (s, CH), 6.85 and 8.95 (2 s, 2CH), 12.66 (s, OH) ppm;
13C NMR (125.7 MHz, CDCl3): d = 26.6 (CH3), 53.3
(OCH3), 105.5 (CH), 108.6 (C), 117.5 (CH), 117.7 (C),
131.4 (CH), 140.7 (C), 159.2 and 159.3 (2 C), 164.1 and
165.5 (2 C=O, ester), 203.9 (C=O, ketone) ppm; IR (KBr):
ꢀ
C=O, ester), 204.1 (C=O, ketone) ppm; IR (KBr): m ¼
m ¼ 3;379ꢁ3;529 (OH), 1,648–1,755 (C=O) cm-1; MS:
ꢀ
3; 420 ꢁ 3; 680 (OH), 1,648–1,760 (C=O) cm-1
.
m/z (%) = 263 (M?, 6), 262 (M?-1, 26), 247 (79), 43
(100).
(E)-dimethyl-2-[6-benzoyl-7-hydroxy-4-
(methoxycarbonyl)-2-oxo-2H-chromen-5-yl]-2-
butenedioate (5d, C24H18O10)
Ethyl 6-acetyl-7-hydroxy-2-oxo-2H-chromene-4-
carboxylate (4b, C14H12O6)
Yellow crystal, yield 75%, mp 184 °C; 1H NMR (500 MHz,
CDCl3): d = 3.66, 3.82 and 3.86 (3 s, 3 OCH3), 6.82, 7.27
and 8.85 (3 s, 3 CH), 7.54 –7.76 (m, CH, Aromatic), 12.90
(s, OH) ppm; 13C NMR (125.7 MHz, CDCl3): d = 52.1,
53.1 and 53.2 (3 OCH3), 108.1 (CH), 112.3, 116.2, 117.2 (3
C), 128.6, 129.5, 132.1 and 132.7 (4 CH), 134.2, 135.3 and
137.1 (3 C), 141.6 (CH), 156.1 and 158.8 (2 C–O), 163.4,
163.9, 164.7 and 165.3 (4 C=O, ester), 200.7 (C=O, ketone)
Yellow powder, yield 35%, mp 133–135 °C; 1H NMR
(500 MHz, CDCl3): d = 1.43 (t, 3JHH = 7.1 Hz, CH3), 2.68
3
(s, CH3), 4.45 (q, JHH = 7.1 Hz, OCH2), 6.86 (s, CH),
6.87 and 8.96 (2 s, 2 CH), 12.65 (s, OH) ppm; 13C NMR
(125.7 MHz, CDCl3): d = 14.1 (CH3), 26.6 (CH3), 62.6
(OCH2), 105.5 (CH), 108.7 (C), 117.4 (CH), 117.6 (C),
131.4 (CH), 141.1, 159.3 and 159.4 (3 C), 163.6 and 165.5
ꢀ
(2 C=O, ester), 203.9 (C=O, ketone) ppm; IR (KBr): m ¼
3;400ꢁ3;530 (OH), 1,650–1,737 (C=O) cm-1; MS: m/z
(%) = 276 (M?, 4), 275 (M?-1, 28), 258 (80), 43 (100).
ꢀ
ppm; IR (KBr): m ¼ 3;320ꢁ3;550 (OH), 1735–1750 (C=O,
ketone), 1,615–1,632 (C=O, ester), 1,400–1,435 (C=C)
cm-1; MS: m/z (%) = 466 (9) (M?), 105 (25), 44 (98);
selected X-ray crystallographic data: monoclinic, space
tert-butyl 6-acetyl-7-hydroxy-2-oxo-2H-chromene-4-
carboxylate (4c, C16H16O6)
˚
group = P 21 21 21, a = 9.2661 (17) A, b =
White powder, yield 75%, mp 160–162 °C; 1H NMR
(500 MHz, CDCl3): d = 1.69 (s, CMe3), 2.69 (s, CH3), 6.78
˚
˚
11.508 (2) A, c = 19.661 (4) A, a = 90°, b = 90°,
3
˚
c = 90°, V = 2096.5 (7) A , T = 120 K, Z = 4, dx =
1.478 g cm-3, l = 0.117 mm-1; CCDC 679387 contains
the supplementary crystallographic data for this paper.
(s, CH), 6.85 and 8.93 (2 s, 2 CH), 12.63 (s, OH) ppm; 13
C
NMR (125.7 MHz, CDCl3): d = 26.6 (CH3), 28.1 (CMe3),
84.5 (CMe3), 105.4 (CH), 108.9 (C), 116.9 (CH), 117.6
(C), 131.4 (CH), 142.6, 159.3 and 159.7 (3 C), 162.7 and
165.3 (2 C=O, ester), 203.9 (C=O, ketone) ppm; IR (KBr):
Di(tert-butyl)(E)-2-(3-acetyl-2,6-dihydroxyphenyl)-2-
butenedioate (8c, C20H26O7)
White powder, mp 160–161 °C; 1H NMR (500 MHz,
CDCl3): d = 1.31 and 1.45 (2 s, 2 CMe3), 2.53 (s, CH3),
m ¼ 3;500ꢁ3;700 (OH), 1655–1750 (C=O) cm-1; MS: m/z
ꢀ
(%) = 304 (M?, 3), 303 (M?-1, 27), 286 (82), 43 (100).
3
6.12 (s, OH), 6.46 (d, JHH = 8.9 Hz, CH), 6.94 (s, CH),
7.60 (d, 3JHH = 8.9 Hz, CH), 13.04 (s, OH) ppm; 13C NMR
(125.7 MHz, CDCl3): d = 26.2 (CH3), 27.7 and 27.8 (2
CMe3), 82.3 and 82.9 (2 CMe3), 108.8 (CH), 111.4 (C),
113.6 (CH), 129.1 (C), 132.6 (CH), 136.4, 160.5 and 162.6
(3 C), 165.2 and 166.1 (2 C=O, ester), 202.7 (C=O, ketone)
tert-Butyl 6-benzoyl-7-hydroxy-2-oxo-2H-chromen-4-
carboxylate (4f, C21H18O6)
Yellow crystal, yield 75%, mp 163 °C; 1H NMR
(500 MHz, CDCl3): d = 1.41 (s, CMe3), 6.69 (s, CH),
6.95 (s, CH), 7.52–7.70 (m, CH, Aromatic), 8.60 (s, CH),
12.46 (s, OH) ppm; 13C NMR (125.7 MHz, CDCl3):
d = 27.8 (CMe3), 84.5 (CMe3), 105.7 (CH), 108.7 (C),
ꢀ
ppm; IR (KBr): m ¼ 3;190ꢁ3;730 (2 OH), 1640–1728
(C=O) cm-1
.
123

A chemoselective and one-pot synthesis of 5-hydroxy and 7-hydroxy coumarin derivatives
493
Acknowledgment We are grateful for the financial support of
Mazandaran University of the Islamic Republic of Iran.
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