9510
F. Jafarpour et al. / Tetrahedron 66 (2010) 9508e9511
O
O
O
H
Ag
O
Ag
O
H
O
O
R
R
R
R
O
O
O
O
O
AgX
HX
HX AgX
CO2
Scheme 1. A plausible mechanism for the Ag-catalyzed protiodecarboxylation of coumarin-3-carboxylic acids.
3. Conclusion
(1H, d, J 8.90 Hz, ]CH); dC (75 MHz, CDCl3) 160.8, 154.1, 143.5, 131.9,
127.9, 124.5, 118.9, 116.7, 116.6.
In summary, we have developed a mild and efficient protocol for
silver-catalyzed decarboxylations of coumarin-3-carboxylic acids.
This procedure proved to be generally applicable for smooth pro-
tiodecarboxylation of diversely functionalized coumarin-3-car-
boxylic acids and a variety of substituents were tolerated under the
reaction conditions. Operational simplicity, the lower toxicity of Ag
(I) salts and reduced reaction temperatures and therefore wide
substrate compatibility are the advantages of this method.
4.2.4. 8-Methoxy-2H-chromen-2-one (2d)17. Operation as above
with 8-methoxy-2-oxo-2H-chromene-3-carboxylic acid 1d (0.044 g,
0.2 mmol) compound 2d (0.017 g, 47%) was obtained as colorless
needles, mp 86e87 ꢀC; Rf (20% EtOAc/hexane) 0.26; dH (300 MHz,
CDCl3) 7.60 (1H, d, J 10.1 Hz, CH]), 7.03 (1H, d, J 8.0 Hz, Ph), 6.92 (1H,
d, J 8.0 Hz, Ph), 6.90 (1H, dd, J 8.0,1.2 Hz, Ph), 6.27 (1H, d, J 10.1 Hz, ]
CH), 3.89 (3H, s, OMe); dC (75 MHz, CDCl3) 160.5, 147.2, 144.1, 143.6,
124.5, 119.5, 119.4, 116.8, 113.9, 56.3.
4. Experimental section
4.1. General
4.2.5. 8-Hydroxy-2H-chromen-2-one (2e)18. Operation as above
with 8-hydroxy-2-oxo-2H-chromene-3-carboxylic acid 1e (0.041 g,
0.2 mmol) compound 2e (0.021 g, 65%) was obtained as colorless
needles, mp 159e161 ꢀC; Rf (20% EtOAc/hexane) 0.15; dH (300 MHz,
acetone-d6) 7.92 (1H, d, J 9.6 Hz, CH]), 7.11e7.15 (3H, m, Ph), 6.39
(1H, d, J 9.6 Hz, ]CH), 6.13 (1H, s, OH); dC (75 MHz, acetone-d6)
160.1, 145.2, 144.8, 143.2, 125.1, 120.5, 119.4, 119.0, 116.9.
Anhydrous solvents were used. Metal catalysts were commer-
cially available and used as received. The protiodecarboxylation
reactions were carried out in an oil bath using Microwave vials
(2e5 mL). 1H and 13C NMR spectra were recorded at room tem-
perature on 300 and 75 MHz spectrometers, respectively, using
CDCl3 and acetone-d6 as the NMR solvents. 1H NMR spectra are
referenced to tetramethylsilane (0.00 ppm) and 13C NMR spectra
are referenced from the solvent central peak. Chemical shifts are
given in parts per million. Melting points were determined using
a Gallenkamp melting point apparatus and are uncorrected.
4.2.6. 5-Bromo-2H-chromen-2-one (2f)16. Operation as above with
5-bromo-2-oxo-2H-chromene-3-carboxylic acid 1f (0.054 g, 0.2
mmol) compound 2f (0.026 g, 58%) was obtained as colorless needles,
mp 93e95 ꢀC; Rf (20% EtOAc/hexane) 0.52; dH (300 MHz, CDCl3) 7.90
(1H, d, J 9.1 Hz, CH]), 7.71 (1H, dd, J 7.1, 1.34 Hz, Ph), 7.34 (1H, dd, J 7.1,
1.34 Hz, Ph), 7.25e7.27 (1H, m, Ph), 6.67 (1H, d, J 9.1 Hz, ]CH); dC
(75 MHz, CDCl3) 160.1, 154.2, 150.0, 142.5, 135.0, 130.6, 119.1, 118.3,
117.4.
4.2. Synthesis of 2H-chromen-2-ones 2ae2g via
protiodecarboxylation of coumarin-3-carboxylic acids
4.2.7. 2H-Benzo[g]chromen-2-one (2g)19. Operation as above with
2H-benzo[g]chromen-2-one-3-carboxylic acid 1g (0.048 g, 0.2 mmol)
compound 2g (0.026 g, 67%) was obtained as yellowish solid, mp
124e125 ꢀC; Rf (20% EtOAc/hexane) 0.40; dH (300 MHz, CDCl3) 8.27
(1H, m, Ph), 8.12 (1H, m, Ph), 8.03 (1H, d, J 8.6 Hz, Ph), 8.00 (1H, m,
Ph), 7.65 (2H, m, Ph), 7.55 (1H, d, J 7.3 Hz, Ph), 6.47 (1H, d, J 9.5 Hz, ]
CH); dC (75 MHz, CDCl3) 160.1, 151.4, 143.1, 132.1, 131.0, 130.0, 127.0,
125.1, 124.4, 115.8, 113.6.
4.2.1. 7-(Diethylamino)-2H-chromen-2-one (2a)15. A vial equipped
with a stir bar was charged with 7-(diethylamino)-2-oxo-2H-
chromene-3-carboxylic acid 1a (0.052 g, 0.2 mmol), Ag2CO3
(10 mol %), and ACOH (5 mol %) and DMA (0.5 M) was added and the
vial was capped. The resulting mixture was heated in an oil bath at
100 ꢀC for 16 h, cooled then filtered through a short plug of silica
and the solvent was removed under vacuo. Purification of the
crude product by flash column chromatography (20% EtOAc/hex-
ane) afforded the corresponding product 2a (0.036 g, 84%) as an
orange solid, mp 87e89 ꢀC; Rf (20% EtOAc/hexane) 0.40; dH
(300 MHz, CDCl3) 7.50 (1H, d, J 10.6 Hz, CH]), 7.24 (1H, d, J 8.8 Hz,
Ph), 6.55 (1H, dd, J 8.8, 2.5 Hz, Ph), 6.48 (1H, d, J 2.5 Hz, Ph), 6.00
(1H, d, J 10.6 Hz, ]CH), 3.38 (4H, q, J 7.1 Hz, CH2CH3), 1.22 (6H, t, J
7.1 Hz, Me); dC (75 MHz, CDCl3) 162.6,157.1,151.1,144.1,129.2,109.4,
109.1, 108.6, 97.8, 45.2, 12.8.
Acknowledgements
We thank the Research Council of the University of Tehran for
financial support for this project.
Supplementary data
Supplementary data associated with this article can be found in
4.2.2. 6-Nitro-2H-chromen-2-one (2b)16. Operationasabovewith6-
nitro-2-oxo-2H-chromene-3-carboxylic acid 1b (0.047 g, 0.2 mmol)
compound 2b (0.034 g, 90%) was obtained as yellowish solid, mp
181e182 ꢀC; Rf (20% EtOAc/hexane) 0.33; dH (300 MHz, CDCl3) 8.04
(1H, dd, J 7.35, 1.35 Hz, Ph), 7.93 (1H, d, J 1.35 Hz, Ph), 7.78 (1H, d, J
9.12 Hz, CH]), 7.25 (1H, d, J 7.35 Hz, ph), 6.40 (1H, d, J 9.12 Hz, ]CH);
dC (75 MHz, CDCl3) 163.3,159.2,150.5,148.6,129.0,113.4,112.0,111.5.
References and notes
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MA, 2000.
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4.2.3. 2H-Chromen-2-one (2c)16. Operation as above with 2-oxo-
2H-chromene-3-carboxylic acid 1c (0.038 g, 0.2 mmol) compound
2c (0.018 g, 63%) was obtained as colorless needles, mp 68e70 ꢀC; Rf
(20% EtOAc/hexane) 0.43; dH (300 MHz, CDCl3) 7.85 (1H, d, J
8.90 Hz, CH]), 7.44e7.58 (2H, m, Ph), 7.38e7.22 (2H, m, Ph), 6.70