Regioselective Suzuki-Miyaura cross-coupling reactions of the bis(triflate) of 4,7-dihydroxycoumarin

Article abstract of DOI:10.1016/j.tetlet.2014.01.148

Arylated coumarins were prepared by site-selective Suzuki-Miyaura cross-coupling reaction of the bis(triflate) of 4,7-dihydroxycoumarin. The reactions proceeded by initial attack to the sterically more hindered position, due to electronic reasons.

Full text of DOI:10.1016/j.tetlet.2014.01.148

Accepted Manuscript
Regioselective Suzuki-Miyaura Cross-Coupling Reactions of the Bis(triflate) of
4,7-Dihydroxycoumarin
Zien Khaddour, Omer A. Akrawi, Ali S. Suleiman, Tamás Patonay, Alexander
Villinger, Peter Langer
PII:
S0040-4039(14)00204-4
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.01.148
TETL 44181
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
8 November 2013
21 January 2014
28 January 2014
Please cite this article as: Khaddour, Z., Akrawi, O.A., Suleiman, A.S., Patonay, T., Villinger, A., Langer, P.,
Regioselective Suzuki-Miyaura Cross-Coupling Reactions of the Bis(triflate) of 4,7-Dihydroxycoumarin,
Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.2014.01.148
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Regioselective Suzuki-Miyaura Cross-Coupling
Reactions of the Bis(triflate) of 4,7-Dihydroxy-
coumarin
Leave this area blank for abstract info.
Zien Khaddour,a,b Omer A. Akrawi,a Ali S. Suleiman,a Tamás Patonay,c Alexander Villinger,a
Peter Langer* a,b
a Institut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany, Peter.langer@uni-
rostock.de
b Leibniz-Institut für Katalyse an der Universität Rostock e. V., Albert-Einstein-Str. 29a, 18059 Rostock, Germany
e Department of Organic Chemistry, University of Debrecen, H-4032 Debrecen, Egyetem tér 1, Hungary
Ar1
OTf
1) Ar1B(OH)2
2) Ar2B(OH)2
Ar2
O
O
[Pd]
TfO
O
O

Tetrahedron Letters
journal hom epage: www. elsevier. com
Regioselective Suzuki-Miyaura Cross-Coupling Reactions of the Bis(triflate) of 4,7-
Dihydroxycoumarin
Zien Khaddour,a,b Omer A. Akrawi,a Ali S. Suleiman,a Tamás Patonay,c Alexander Villinger,a Peter
Langer* a,b
a Institut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany, Peter.langer@uni-rostock.de
b Leibniz-Institut für Katalyse an der Universität Rostock e. V., Albert-Einstein-Str. 29a, 18059 Rostock, Germany
c Department of Organic Chemistry, University of Debrecen, H-4032 Debrecen, Egyetem tér 1, Hungary
ARTICLE INFO
ABSTRACT
Article history:
Received
Arylated coumarins were prepared by site-selective Suzuki-Miyaura cross-coupling
reaction of the bis(triflate) of 4,7-dihydroxycoumarin. The reactions proceeded by initial
attack to the sterically more hindered position, due to electronic reasons.
Received in revised form
Accepted
Available online
Keywords:
Keyword_1 catalysis
Keyword_2 Suzuki-Miyaura reaction
Keyword_3 regioselectivity
Keyword_4 palladium
Keyword_5 heterocycles
Neoflavones (4-arylcoumarins) are of considerable
pharmacological relevance and occur in several natural
products and synthetic drugs.1 Natural and synthetic
neoflavones have been reported to exhibit various kinds of
pharmacological activities, such as anticancer,2 antimalarial,3
antibacterial,4 antiprotozoal,5 antivirus,6 antidiabetic,7
cytotoxic,8 and anti-inflammatory activity.9 Merck developed
a 7-substituted 4-arylcoumarin as a 5-lipoxygenase inhibitor
for the treatment of inflammatory diseases such as asthma,
chronic obstructive pulmonary disease and atherosclerosis
(Figure 1).10
assembly of the neoflavone framework: the first one involves
the formation of the pyrone ring by hydroarylation of
alkynes,12 or by reaction of the alkenyl C-H bond with carbon
dioxide.13 The second one relies on cross-coupling reactions
of position 4 of activated coumarins with organometallic
reagents.14
In recent years, site-selective cross coupling reactions of
bis(halides) or bis(triflates) have been developed as a
promising synthetic tool.15 In this context, palladium
catalyzed cross-coupling reactions of coumarin derivatives
have also been reported.16 Herein, we report what are, to the
best of our knowledge, the first Suzuki-Miyaura coupling
reaction of the bis(triflate) of 4,7-dihydroxycoumarin. The
reactions, which proceed with excellent regioselectivity in
favour of position 4, provide a convenient approach to various
arylated coumarin derivatives which are not readily available
by other methods.
As a result of the promising biological and pharmacological
activities of neoflavones, several strategies have been
developed for the construction of the 4-arylcoumarin
framework. Classically, neoflavones have been synthesized
using the Pechmann, Perkin, Ponndorf, Houben-Hösch and
Knoevenagel reactions.11 In recent years, transition metal
catalyzed reactions have emerged as vital synthetic tools for
the preparation of pharmacologically relevant heterocycles.
Two synthetic strategies have been developed for the

selectivity attack onto 4-position. During the optimization, it
proved to be important to carry out the reaction at lower
temperature (65 °C) as compared to the synthesis of the
diarylated coumarins. In addition, the employment of toluene
(instead of dioxane) proved to be important to optimize the
yield. This might be explained by the solubility of the starting
materials or change of the reactivity of the catalytic system by
the solvent. Again, both electron rich and poor arylboronic
acids gave good yields. The structure of 5d was independently
confirmed by X-ray crystal structure analyses (Figure 2).22
Ar
OTf
O
ArB(OH)2
Figure 1. A 5-lipoxygenase inhibitor developed by Merck
3a-d,g-j
i
TfO
O
O
TfO
O
The reaction of 4,7-dihydroxycoumarin (1) with triflic
anhydride gave bis(triflate) 2 (Scheme 1).17 The Suzuki–
Miyaura reaction of 2 with arylboronic acids 3a-f (2.4 equiv)
afforded 4,7-diarylcoumarins 4a-f in 65-81% yield (Scheme
2, Table 1).18,19 Both electron rich and poor arylboronic acids
were successfully employed.
5a-h
2
Scheme 3. Synthesis of 5a-h, Conditions: i, 2 (1.0 equiv.), 3a-d,g-j (1.0
equiv.), Pd(PPh3)4 (3 mol %), K2CO3 (2M), toluene, 65 °C, 6 h.
OTf
OH
Table 2. Synthesis of compounds 5a-h
i
3
a
5
a
Ar
% (5)a
TfO
O
O
HO
O
O
4-(MeO)C6H4
71
2
1
b
c
d
g
h
i
b
c
d
e
f
4-MeC6H4
4-(EtO)C6H4
3,5-Me2C6H5
4-EtC6H4
75
78
82
73
64
67
65
Scheme1. Synthesis of 2, Conditions; i, 1 (1.0 equiv.), pyridine (4.0 equiv.),
CH2Cl2, Tf2O (2.4 equiv.), 50°C, 4 h.
2-FC6H4
Ar
OTf
ArB(OH)2
g
h
3,4,5-(MeO)3C6H2
4-(F3CO)C6H4
3a-f
j
Ar
O
O
TfO
O
O
a Yield of isolated products
i
2
4a-f
Scheme 2. Synthesis of 4a-f, Conditions: i, 2 (1.0 equiv.), 3a-f (2.4 equiv.),
Pd(PPh3)4 (6 mol %), K2CO3 (2M), dioxane, 110 °C, 8 h.
Table 1. Synthesis of compounds 4a-f
3,4
a
Ar
% (4)a
4-(MeO)C6H4
68
b
c
d
e
f
4-MeC6H4
4-(EtO)C6H4
3,5-Me2C6H3
4-(F3C)C6H4
C6H5
79
66
81
65
79
a Yield of isolated products
Figure 2. Ortep plot for compound 5d
The Suzuki–Miyaura reaction of 2 with one equivalent of
arylboronic acids afforded the 4-aryl-7-
(trifluormethanesulfonyloxy)coumarins 5a-h in 64-82 % yield
(Scheme 3, Table 2).20,21 The reactions proceeded by site-
The one-pot reaction of 2 with two different arylboronic acids
(sequential addition) afforded the diarylated coumarin 6 in

65% yield (Scheme 4, Table 3).23,24 A fresh portion of the
catalyst and of solvent (dioxane) had to be added to the
reaction mixture in the second step in order to obtain a good
yield of diarylated coumarin 6.
3.
4.
5.
Argotte-Ramos, R.; Ramírez-Avila, G.; Rodriguez-Gutierrez, M.
C.; Ovilla-Munoz, M.; Lanz-Mendoza, H.M.; Rodriguez,
Gonzalez-Cortazar, M.; Alvarez, L. J. Nat. Prod. 2006, 69, 1442.
Verotta, L.; Lovaglio, E.; Vidari, G.; Finzi, P. V.; Neri, M. G.;
Raimondi, A.; Parapini, S.; Taramelli, D.; Riva, A.; Bombardelli,
E. Phytochemistry 2004, 65, 2867.
OMe
Pierson, J.-T.; Dumetre, A.; Hutter, S.; Delmas, F.; Laget, M.;
Finet, J.-P.; Azas, N.; Combes, S. Eur. J. Med. Chem. 2010, 45,
864.
OTf
Ar1B(OH)2
6.
7.
Marcal de Queiroz, P. Patent WO 98/25608, 1997.
Korec, R.; Sensch, K. H.; Zoukas, T. Arzneim. Forsch. 2000, 50,
122.
Ar2B(OH)2
i
O
O
TfO
O
O
84%
8.
9.
Combes, S. B.; Barbier, P.; Douillard, S.; McLeer-Florin, A.;
Bourgarel-Rey, V. R.; Pierson, J.-T.; Fedorov, A. Y.; Finet, J.-P.;
Boutonnat, J.; Peyrot, V. J. Med. Chem. 2011, 54, 3153.
Taechowisan, T.; Lu, C.; Shen, Y.; Lumyong, S. Food Agric.
Immunol. 2007, 18, 203.
2
6
Ar1 = 4-(MeO)C6H4
Ar2 = 4-MeC6H4
Scheme 4. Synthesis of 6. Conditions: i, 1)
2 (1.0 equiv.), (4-
10. Gosselin, F.; Britton, R. A.; Davies, I. W.; Dolman, S. J.;
Gauvreau, D.; Hoerrner, R.S.; Hughes, G.; Janey, J.; Lau, S.;
Molinaro, C.; Nadeau, C.; O’Shea, P. D.; Palucki, M.; Sidler, R. J.
Org. Chem. 2010, 75, 4154.
(MeO)C6H4)B(OH)2 (1.0 equiv.), Pd(PPh3)4 (3 mol %), K2CO3 (2M), toluene,
65 °C, 6 h; 2) (4-MeC6H4)B(OH)2 (1.2 equiv.), Pd(PPh3)4 (6 mol %), K2CO3
(2M), dioxane, 110 °C, 6 h.
11. (a) Garazd, M. M.; Garazd, Y. L.; Khilya, V. P. Chem. Nat.
Compd. 2005, 41, 245; (b) Crecente-Campo, J.; Vanzquez-Tato,
M.P.; Seijas, J. A. Eur. J. Org. Chem. 2010, 4130.
In conclusion, we have reported the first Suzuki–Miyaura
reactions of 4,7-bis(trifluoromethylsulfonyloxy)coumarin.
These reactions provide a convenient access to a variety of
arylated coumarins. The reactions proceeded with very good
site-selectivity in favour of 4-position. Palladium catalyzed
cross-coupling reactions of polyhalogenated substrates or of
bis(triflates) usually proceed in favour of the sterically less
hindered and electronically more deficient position.15 Position
4 is sterically more hindered than position 7, due to its
location next to the annulated benzene ring. The selectivity
can be explained by the highly electron deficient character of
the 4-position of the coumarin moiety (electron-withdrawing
effect of the carbonyl group).
12. (a) Kutubi, S.; Hashimoto, T.; Kitamura, T. Synthesis 2011, 1283;
(b) Yamamoto, Y.; Kirai, N. Org. Lett. 2008, 10, 5513.
13. Sasono, K.; Takaya, J.; Iwasawa, N. J. Am. Chem. Soc. 2013, 135,
10954.
14. (a) Zhang, L.; Meng, T.; Fan, R.; Wu, J. J. Org. Chem. 2007, 72,
7279; (b) Rao, M. L. N.; Venkatesh, V.; Jadhav, D. N. Eur. J. Org.
Chem. 2010, 3945; (c) Oh, S.; Jang, H. J.; Ko, S. K.; Ko, Y.; Park,
S. B. J. Comb. Chem. 2010, 12, 548; (d) Combes, S.; Pierson, J.-
T.; Finet, J.-P.; Barbier, P.; Douillard, S.; Bourgarel-Rey, V.;
Peyrot, V.; McLeer-Florin, A.; Boutonnat, J.; Fedorov, A. Y. J.
Med. Chem. 2011, 54, 3153; (e) Kuroda, J.-I.; Inamoto, K.;
Hiroya, K.; Doi, T.; Eur. J. Org. Chem. 2009, 2251; (f) Luo, Y.;
Wu, J. Tetrahedron Lett. 2009, 50, 2103; (g) Gao, W.; Luo, Y.;
Ding, Q.; Peng, Y.; Wu, J. Tetrahedron Lett. 2010, 51, 136; (h)
Wong, P. Y.; Chow, W. K.; Chung, K. H.; So, C. M.; Lau, C. P.;
Kwong, F. Y. Chem. Commun. 2011, 47, 8328; (i) Xing, C.-H.;
Lee, J.-R.; Tang, Z.-Y.; Zheng, J. R.; Hu, Q.-S. Adv. Synth. Catal.
2011, 353, 2051; (j) Wu, J.; Yang, Z. J. Org. Chem. 2001, 66,
7875; (k) Xu, L.; Li, B.-J.; Wu, Z.-H.; Lu, X.-Y.; Guan, B.-T.;
Wang, B.-Q.; Zhao, K.-Q. Org. Lett. 2010, 12, 884.
Acknowledgments. Financial support by the DAAD
(scholarship for O. A. A.) and by the Alexander von Humboldt
foundation (Institute Partnership Program Debrecen-Rostock)
is gratefully acknowledged. Financial support by the
European Social Fund (EFRE program) is also acknowledged.
15. For reviews of cross-coupling reactions of polyhalogenated
heterocycles and triflates, see: (a) Schröter, S.; Stock, C.; Bach, T.
Tetrahedron 2005, 61, 2245; (b) Schnürch, M.; Flasik, R.; Khan,
A. F.; Spina, M. Mihovilovic, M. D.; Stanetty, P. Eur. J. Org.
Chem. 2006, 3283; (c) Rossi, R.; Bellina, F.; Lessi, M. Adv. Synth.
Catal. 2012, 354, 1181; (d) Magano, J.; Dunetz, J. R. Chem. Rev.
2011, 111, 2177; (e) Hassan, Z.; Patonay, T.; Langer, P. Synlett
2013, 24, 412.
References
1.
(a) Murray, R. D. H. Nat. Prod. Rep. 1995, 12, 477; (b) Estevez-
Braun, A.; Gonzalez, A. G. Nat. Prod. Rep. 1997, 14, 465; (c)
Malikov, V. M.; Saidkhodzhaev, A. I. Khim. Prir. Soedin. 1998,
34, 250.
2.
(a) Bailly, C.; Bal, C.; Barbier, P.; Combes, S.; Finet, J.-P.;
Hildebrand, M.-P.; Peyrot, V.; Wattez, N. J. Med. Chem. 2003, 46,
5437; (b) Rappl, C.; Barbier, P.; Bourgarel-Rey, V.; Gregoire, C.;
Gilli, R.; Carre, M.; Combes, S.; Finet, J.-P.; Peyrot, V.
Biochemistry 2006, 45, 9210.
16. (a) Zhang, L.; Meng, T.; Fan, R.; Wu, J. J. Org. Chem. 2007, 72,
7279; (b) Wang, L.; Xia, J.; Tian, H.; Qian, C.; Ma, Y. Indian J.
Chem., Sect. B 2003, 42, 2097; (c) Akrawi, O. A.; Nagy, G.;
Patonay, T.; Villinger, A.; Langer, P. Tetrahedron Lett. 2012, 53,
3206; (d) Eleya, N.; Khaddour, Z.; Patonay, T.; Langer, P. Synlett
2012, 223; (e) Hamdy, A.; Eleya, N.; Mohammed, M.; Khaddour,

Z.; Patonay, T.; Villinger, A.; Langer, P. Tetrahedron Lett. 2013,
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mmole), 3a (7 mg, 0.045 mmole), Pd(PPh3)4 (1.5 mg, 3 mole%),
K2CO3 (2M, 2ml), and toluene (3 ml), 5a was isolated as a white
solid (13 mg, 71 %), mp: 86-88 °C. 1H NMR (300 MHz, CDCl3):
δ = 3.83 (s, 3H, OCH3), 6.33 (s, 1H, C=CH), 6.95 (d, 2H, J = 8.7
Hz, ArH), 7.10 (dd, 1H, J = 8.9, 2.3 Hz, ArH), 7.24 (d, 1H, J =
2.3 Hz, ArH), 7.33 (d, 2H, J = 8.7 Hz, ArH), 7,59 (d, 1H, J= 8.9
Hz, ArH). 13C NMR (62.9 MHz, CDCl3): δ = 55.5 (OCH3), 110.8,
114.6, 114.3, 117.3 (CH), 118.3 (q, JF,C = 320.0 Hz, CF3), 119.3,
126.6 (C), 128.9, 129.9 (CH), 150.8, 154.8, 159.7 (C), 161.2
(C=O). 19F NMR (282.4, MHz): δ = -72.5. IR (KBr, cm-1): v =
3039, 2967, 2929 (w), 1756, 1699 (s), 1651, 1645, 1596 (s), 1577,
1538, 1519, 1503, 1474, 1453 (w). GC-MS (EI, 70 eV): m/z (%) =
400 ([M]+, 67), 240 (15), 211 (100), 183 (23), 240 (11), 168 (19).
HRMS (EI, 70 eV) calcd. for C17H11O6F3S1 [M]+: 400.02197;
found: 400.02229.
17. Synthesis
of
2-oxo-2H-chromene-4,7-diyl bis(trifluoro-
methanesulfonate) (2). To a CH2Cl2 solution (50 ml) of 1 (1.0 g,
5.6 mmole) was added pyridine (1.8 ml, 22.4 mmole) and the
solution was stirred at 20°C for 10 min. under argon atmosphere.
Then Tf2O (2.3 ml, 13.44 mmole) was added at 20°C and the
reaction mixture was heated at 50 °C for 20 min. The reaction
mixture was cooled to room temperature and filtered, the filtrate
was concentrated in vacuo. The product 2 was isolated by column
chromatography (flash silica gel, heptane/EtOAc) as a colorless
solid (2.10 g, 85%); Mp: 79 -77 oC. 1H NMR (300 MHz. CDCl3):
δ = 6.51 (s, 1H, C=CH), 7.27-7.32 (m, 2H, ArH), 7.74 (d, 1H, J =
8.7 Hz, ArH). 13C NMR (62.9 MHz, CDCl3): δ = 105.6, 110.1,
111.6 (CH), 112.9 (C), 118.3 (q, JF,C = 320.1 Hz, CF3), 118.6 (q,
JF,C = 320.0 Hz, CF3), 123.6 (CH), 151.4, 152.0, 154.9 (C), 157.3
(C=O). 19F NMR (282.4, MHz): δ = -72.5, -72.4. IR (KBr, cm-1): v
= 3171, 2988 (w), 1755 (s), 1698, 1643 (w), 1577 (m), 1550,
1499, 1475, 1433 (w). GC-MS (EI, 70 eV): m/z (%) = 442 ([M]+,
88), 426 (100), 356 (15), 276 (33), 234 (23), 195 (16), HRMS (EI,
70 eV) calcd. for C11H4O8F6S2 [M]+: 441.93145; found:
441.93087.
22. CCDC-xxx contains all crystallographic details of this publication
and
is
available
free
of
charge
at
www.ccdc.cam.ac.uk/conts/retrieving.html or can be ordered from
the following address: Cambridge Crystallographic Data Centre,
12 Union Road, GB-Cambridge CB21EZ; Fax: (+44)1223-336-
033; or deposit@ccdc.cam.ac.uk.
23. General procedure C for the synthesis of 6. A solution of 2
(0.045 mmole), K2CO3 (2M, 2mL), Pd(PPh3)4 (3 mole%) and
arylboronic acid (1.0 equiv.) in toluene (3 ml) was stirred at 65
°C. for 6 h. under argon atmosphere. After cooling to 20 °C, Ar2
B(OH)2 (1.2 equiv.), K2CO3 (2M, 2ml), Pd(PPh3)4 (6 mole %) and
1,4-dioxane (2 ml) were added and reaction mixture was heated at
110 °C for further 6 h. to the reaction mixture H2O (20 ml) and
CH2Cl2 (25 ml) were added. The organic and the aqueous layers
were separated and the latter was extracted with CH2Cl2 (2 x 20
ml). The combined organic layers were dried over (Na2SO4),
filtered and the filtrate was concentrated in vacuo. The residue was
purified by column chromatography (silica gel, heptane/EtOAc).
18. General Procedure A for the synthesis of 4a-f. A solution of 2
(0.045 mmol), K2CO3 (2M, 2 ml), Pd(PPh3)4 (6 mol %) and
arylboronic acid (2.4 equiv.) in 1,4-dioxane (3 ml) was stirred at
110 °C for 6 h under argon atmosphere. To the reaction mixture
H2O (20 ml) and CH2Cl2 (25 ml) were added. The organic and the
aqueous layers were separated and the latter was extracted with
CH2Cl2 (2 x 20 ml). The combined organic layers were dried over
(Na2SO4), filtered and the filtrate was concentrated in vacuo. The
residue was purified by column chromatography (silica gel,
heptane/EtOAc).
19. Synthesis of 4,7-diphenyl-2H-chromen-2-one (4f). Starting with
2 (20 mg, 0.045 mmol), 3f (13 mg, 0.11 mmole), Pd(PPh3)4 (3 mg,
6 mole%), K2CO3 (2M, 2ml) and 1,4-dioxane (3 ml), 4f was
isolated as a white solid (10 mg, 79%), mp: 131-133 °C. 1H NMR
(300 MHz, CDCl3): δ = 6.31 (s, 1H, C=CH), 7.34-7.37 (m, 1H,
ArH), 7.39-7.44 (m, 5H, ArH), 7.47-7.49 (m, 4H, ArH), 7.56 -
7.58 (m, 3H, ArH). 13C NMR (62.9 MHz, CDCl3): δ = 113.8,
114.4 (CH), 116.8 (C), 121.9, 126.2, 126.3 (CH), 126.5 (C), 127.4,
127.6, 127.9, 128.1, 128,7 (CH), 134.3, 138.0, 144.1, 153.6 (C),
162.1(C=O). v = 3133, 2788, 2729 (w), 1856, 1799, 1775 1633
(s), 1599, 1528, 1517, 1502, 1444, 1432 (w).GC-MS (EI, 70 eV):
m/z (%) = 298 ([M]+, 89), 297 (17), 271 (100), 241(28), 240 (11),
239 (32). HRMS (EI, 70 eV) calcd. for C21H14O2 [M]+: 298.09803;
found: 298.09883.
24. 4-(4-Methoxyphenyl)-7-(p-tolyl)-2H-chromen-2-one
(6).
Starting with 2 (20 mg, 0.045 mmol), 3a (7 mg, 0.045 mmole),
Pd(PPh3)4 (1.5 mg, 3 mole%), K2CO3 (2M, 2ml) and toluene (3
ml), and 3b (7 mg, 0.054 mmol), Pd(PPh3)4 (3 mg, 6 mole%),
K2CO3 (2M, 2ml) and 1,4-dioxane (2 ml), 6 was isolated as a
white solid (13 mg, 84%), mp: 133-135 °C. 1H NMR (300 MHz,
CDCl3): δ = 2.38 (s, 3H, CH3), 3.84 (s, 3H, OCH3), 6.28 (s, 1H,
C=CH), 7.01 (d, 2H, J = 8.7 Hz, ArH), 7.28 -7.33 (m, 1H, ArH),
7.37-7.41 (m, 6H, ArH), 7.53 (d, 2H, J = 8.00 Hz, ArH). 13C
NMR (62.9 MHz, CDCl3): δ = 21.3 (CH3), 55.5 (OCH3), 114.2
(C), 114.4, 115.5 (CH), 118.0 (C), 122.9, 124.4 (CH), 127.6 (C),
127.9, 129.0, 129.3, 129.9 (CH), 138.8, 145.2, 152.5, 154.7, 155.2
(C), 161.2 (C=O). IR (KBr, cm-1): v = 3012, 2878, 2822 (w), 1966,
1844 (s), 1744, 1696 (m), 1601, 1578, 1522, 1504 (w), 1487,
1454, 1412 (m). ).GC-MS (EI, 70 eV): m/z (%) = 342 ([M]+, 100),
318 (23), 280 (16), 234 (10), 187 (19). HRMS (EI, 70 eV) calcd.
for C23H18O3 [M]+: 342.12505; found: 342.12459.
20. General procedure B for the synthesis of (5a-h). A solution of 2
(0.045 mmole), K2CO3 (2M, 2ml), Pd(PPh3)4 (3 mole%) and
arylboronic acid (1.0 equiv.) in toluene (3 ml) was stirred at 65
°C. for 6 h. under argon atmosphere. To the reaction mixture H2O
(20 ml) and CH2Cl2 (25 ml) were added. The organic and the
aqueous layers were separated and the latter was extracted with
CH2Cl2 (2 x 20 ml). The combined organic layers were dried over
(Na2SO4), filtered and the filtrate was concentrated in vacuo. The
residue was purified by column chromatography (silica gel,
heptane/EtOAc).
21. 4-(4-Methoxyphenyl)-2-oxo-2H-chromen-7-yl
trifluoromethanesulfonate (5a). Starting with 2 (20 mg, 0.045