Synthesis of 1,4-diaryl-2-naphthoates based on site-selective Suzuki-Miyaura reactions

Article abstract of DOI:10.1016/j.tetlet.2010.01.038

The palladium(0)-catalyzed Suzuki cross-coupling reaction of the bis(triflates) of phenyl 1,4-dihydroxy-2-naphthoate afforded various 1,4-diaryl-2-naphthoates. The reactions proceeded with very good site-selectivity. Due to electronic reasons, the first a

Full text of DOI:10.1016/j.tetlet.2010.01.038

Tetrahedron Letters 51 (2010) 1541–1544
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Synthesis of 1,4-diaryl-2-naphthoates based on site-selective Suzuki–Miyaura
reactions
Obaid-ur-Rahman Abid a,b, Muhammad Farooq Ibad a, Muhammad Nawaz a, Asad Ali a, Muhammad Sher c,
Nasim Hasan Rama b, Alexander Villinger a, Peter Langer a,d,
*
a Institut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany
b Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan
c Department of Chemistry, Allama Iqbal Open University, Islamabad, Pakistan
d Leibniz-Institut für Katalyse e. V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The palladium(0)-catalyzed Suzuki cross-coupling reaction of the bis(triflates) of phenyl 1,4-dihydroxy-
2-naphthoate afforded various 1,4-diaryl-2-naphthoates. The reactions proceeded with very good site-
selectivity. Due to electronic reasons, the first attack occurred at the sterically more hindered position
C-1.
Received 2 December 2009
Revised 7 January 2010
Accepted 8 January 2010
Available online 15 January 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Functionalized naphthalene derivatives are of considerable
pharmacological relevance and occur in a number of natural prod-
ucts. This includes, for example, 1,4-dihydroxy-2-naphthoates
(e.g., the antitumor agent rhinacanthin N),1 4-aryl-2-naphthoates
(e.g., eritrichin and globoidnan A),2 and naphthyl-tetrahydroiso-
quinolines (e.g., the dioncophyllines C and michellamines) which
show a very good activity against malaria or various cancer cell
lines.3
Site-selective palladium-catalyzed reactions of polyhalogenated
substrates are of considerable current interest.4 The site-selectivity
is influenced by electronic and steric parameters.5 Palladium-cata-
lyzed reactions of aromatic bis(triflates) have been previously re-
ported. In most reactions reported to date there was no issue of
site-selectivity.6 Hosokawa et al. reported a site-selective Sonogash-
ira reaction of a bis(triflate) prepared from a 1,3-dihydroxybenzene
derivative.7 Recently, we have observed that Suzuki–Miyaura (S–M)
reactions of the bis(triflate) of methyl 2,5-dihydroxybenzoate pro-
ceed with very good site-selectivity in favour of position 5 which
is presumably a result of steric effects.8 It occurred to us that the
site-selectivity might be different for benzoates and their naphtho-
ate analogues, due to electronic reasons. We chose phenyl 1,4-
dihydroxynaphthoate as a commercially available and inexpensive
starting material. The latter can be regarded as a benzo-annulated
analogue of methyl 2,5-dihydroxybenzoate. Transition metal-cata-
lyzed cross-coupling reactions of this or related naphthoate deriva-
tives (including the corresponding dihalides) have, to the best of our
knowledge, not been reported to date. We have found that indeed a
change of the site-selectivity is observed and the results of our stud-
ies are reported herein.
Phenyl 1,4-dihydroxynaphthoate (1) was transformed into the
novel bis(triflate) 2 in 83% yield (Scheme 1).9
The S-M reaction of 2 with boronic acids 3a–e (2.4 equiv) affor-
ded the novel 1,4-diaryl-2-naphthoates 4a–e in 61–85% yields
(Scheme 2, Table 1). The best yields were obtained when Pd(PPh3)4
(3 mol %) was used as the catalyst, when 2.4 equiv of the boronic
acid was employed, and when the reaction was carried out in
1,4-dioxane (110 °C, 8 h) using K3PO4 as the base.10,11 The use of
Pd(OAc)2 in the presence of XPhos12 or SPhos12 proved to be less
efficient in terms of yield. The yields of the products 4a,b, derived
from arylboronic acids containing electron-withdrawing substitu-
ents, were higher than the yields of 4d,e derived from electron-rich
boronic acids.
The Suzuki reaction of 2 with boronic acids 3e–i (1.1 equiv), in
the presence of Pd(PPh3)4 (3 mol %), proceeded with very good site-
selectivity at carbon atom C-1 and afforded the 1-aryl-4-(trif-
luoromethylsulfonyloxy)-2-naphthoates 5a–e (Scheme 3, Table
2).10,13 The products were isolated in pure form after chromatogra-
phy. A small amount of the bis-coupled product could be detected
OH O
OTf O
i
OPh
OPh
OH
OTf
1
2 (83%)
* Corresponding author. Fax: +49 381 4986412.
E-mail address: peter.langer@uni-rostock.de (P. Langer).
Scheme 1. Synthesis of 2. Reagents and conditions: (i): 1) 1 (1.0 equiv), pyridine
(4.0 equiv), CH2Cl2, À78 °C, 10 min; 2) Tf2O (2.4 equiv), À78 to 0 °C, 4 h.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.01.038

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Obaid-ur-Rahman Abid et al. / Tetrahedron Letters 51 (2010) 1541–1544
Table 3
Synthesis of 6a–d
Ar
O
OTf O
ArB(OH)2
3a-e
OPh
OPh
a
6
3
Ar1
Ar2
% (6)
i
a
b
c
j,k
f,c
b,k
l,m
4-FC6H4
2,4-(MeO)2C6H3
4-(CF3)C6H4
3,4-(MeO)2C6H3
4-MeC6H4
3,4-(MeO)2C6H3
4-(MeO)C6H3
54
63
51
67
Ar
4a-e
OTf
2
d
4-(H2C@CH)C6H4
Scheme 2. Synthesis of 4a–e. Reagents and conditions: (i), 2 (1.0 equiv), 3a–e
(2.4 equiv), K3PO4 (3.0 equiv), Pd(PPh3)4 (3 mol %), 1,4-dioxane, 110 °C, 8 h.
a
Yields of isolated products.
first step of the one-pot protocol, to employ only a slight excess
of the arylboronic acid (1.1 equiv) and to carry out the reaction
at 95 °C instead of 110 °C.
Table 1
Synthesis of 4a–e
a
3,4
Ar
%
(4)
The structures of all products were proved by 2D NMR experi-
ments (NOESY, HMBC). The structures of 5c and 6c were indepen-
dently confirmed by X-ray crystal structure analyses (Figs. 1
and 2).16
a
b
c
d
e
3-FC6H4
85
80
76
65
61
4-(CF3)C6H4
4-MeC6H4
3-(MeO)C6H4
2-(EtO)C6H4
The S-M reaction of methyl 2,5-bis(trifluoromethylsulfonyl-
oxy)benzoate 7 occurs first at the sterically less hindered carbon
atom C-5. In contrast, naphthoate 2 is first attacked at the sterically
more hindered position C-1. This might be explained by electronic
effects (Scheme 5). The oxidative addition of the electron-rich pal-
ladium species usually occurs first at the most electron deficient
carbon atom.4 In case of 7, carbon atom C-2 is more electron defi-
cient than C-5, due to its location ortho to the ester group. For
naphthoate 2, carbon atom C-1 is also more electron deficient than
C-4, but this difference is more pronounced than for benzoate 7.
The nonsubstituted benzene moiety of naphthoate 2 represents a
a
Yields of isolated products.
Ar
O
OTf O
ArB(OH)2
OPh
OPh
3e-i
i
OTf
5a-e
OTf
2
Scheme 3. Synthesis of 5a–e. Reagents and conditions: (i): 2 (1.0 equiv), 3e–i
(1.1 equiv), K3PO4 (1.5 equiv), Pd(PPh3)4 (3 mol %), 1,4-dioxane, 95 °C, 8 h.
stable 6p aromatic system. In contrast, the aromaticity of the other
benzene moiety of 2 is considerably disturbed, because of the pres-
ence of the ester and the triflate groups. The aromaticity of the
substituted benzene moiety should be more disturbed than the
aromaticity of the benzene moiety of 7. The substituted benzene
moiety of 2 might thus be regarded as a cross-conjugated diene
Table 2
Synthesis of 5a–e
a
5
3
Ar
%
(5)
a
b
c
d
e
e
f
g
h
i
2-(EtO)C6H4
2,4-(MeO)2C6H3
2,6-(MeO)2C6H3
4-ClC6H4
59
66
33
73
71
4-tBuC6H4
a
Yields of isolated products.
by 1H NMR and GC–MS in the crude material before the purifica-
tion. All products were isolated in good yields (except for 5c which
is derived from the sterically hindered 2,6-disubstituted arylbo-
ronic acid 3g). During the optimization it proved to be important
to employ only a slight excess of the arylboronic acid (1.1 equiv)
and to carry out the reaction at 95 °C instead of 110 °C to avoid
double coupling.
The one-pot reaction of 2 with two different arylboronic acids,
which were sequentially added, afforded the unsymmetrical 1,4-
diaryl-2-naphthoates 6a–d in 51–67% yields (Scheme 4, Table
3).14,15 During the optimization it proved to be important, for the
1) Ar1B(OH)2
3b,f,j,l
2) Ar2B(OH)2
3c,k,m
Ar1
O
OTf O
OTf
OPh
OPh
Ar2
i
2
6a-d
Scheme 4. Synthesis of 6a–d. Reagents and conditions: (1) 2 (1.0 equiv), 3b,f,j,l
(1.1 equiv), K3PO4 (1.5 equiv), Pd(PPh3)4 (3 mol %), 1,4-dioxane, 95 °C, 7 h; (2)
3c,k,m (1.3 equiv), K3PO4 (1.5 equiv), 110 °C, 8 h.
Figure 1. Crystal structure of 5c.

Obaid-ur-Rahman Abid et al. / Tetrahedron Letters 51 (2010) 1541–1544
1543
Acknowledgments
Financial support by the DAAD (scholarships for M.N., F.I., O.-U.-
R.A., and A.A.) and by the State of Pakistan (HEC stipend for M.S.) is
gratefully acknowledged.
References and notes
1. (a) Kongkathip, N.; Luangkamin, S.; Kongkathip, B.; Sangma, C.; Grigg, R.;
Kongsaeree, P.; Prabpai, S.; Pradidphol, N.; Piyaviriyagul, S.; Siripong, P. J. Med.
Chem. 2004, 47, 4427; (b) Jiang, Z.-H.; Tanaka, T.; Inutsuka, C.; Kouno, I. Chem.
Pharm. Bull. 2001, 49, 737.
2. (a) Cullmann, F.; Schmidt, A.; Schuld, F.; Trennheuser, M. L.; Becker, H.
Phytochemistry 1999, 52, 1647; (b) Fedoreyev, S. A.; Veselova, M. V.;
Krivoschekova, O. E.; Mischenko, N. P.; Denisenko, V. A.; Dmitrenok, P. S.;
Glazunov, V. P.; Bulgakov, V. P.; Tchernoded, G. K.; Zhuravlev, Y. N. Planta Med.
2005, 71, 446; (c) Ovenden, S. P. B.; Yu, J.; Wan, S. S.; Sberna, G.; Tait, R. M.;
Rhodes, D.; Cox, S.; Coates, J.; Walsh, N. G.; Meurer-Grimes, B. M.
Phytochemistry 2004, 65, 3255.
3. Bringmann, G.. In The Naphthyl Isoquinoline Alkaloids in the Alkaloids; Brossi, Ed.;
Academic Press: New York, 1986; Vol. 29,. pp 141–184.
4. For reviews of cross-coupling reactions of polyhalogenated heterocycles, 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.
5. For palladium-catalyzed reactions from our group, see for example: (a) Dang, T.
T.; Dang, T. T.; Ahmad, R.; Reinke, H.; Langer, P. Tetrahedron Lett. 2008, 49,
1698; (b) Dang, T. T.; Villinger, A.; Langer, P. Adv. Synth. Catal. 2008, 350, 2109;
(c) Hussain, M.; Nguyen, T. H.; Langer, P. Tetrahedron Lett. 2009, 50, 3929; (d)
Dang, T. T.; Dang, T. T.; Rasool, N.; Villinger, A.; Langer, P. Adv. Synth. Catal.
2009, 351, 1595.
6. (a) Takeuchi, M.; Tuihiji, T.; Nishimura, J. J. Org. Chem. 1993, 58, 7388; (b)
Sugiura, H.; Nigorikawa, Y.; Saiki, Y.; Nakamura, K.; Yamaguchi, M. J. Am. Chem.
Soc. 2004, 126, 14858; (c) Akimoto, K.; Suzuki, H.; Kondo, Y.; Endo, K.; Akiba, U.;
Aoyama, Y.; Hamada, F. Tetrahedron 2007, 63, 6887; (d) Akimoto, K.; Kondo, Y.;
Endo, K.; Yamada, M.; Aoyama, Y.; Hamada, F. Tetrahedron Lett. 2008, 49, 7361.
7. Hosokawa, S.; Fumiyama, H.; Fukuda, H.; Fukuda, T.; Seki, M.; Tatsuta, K.
Tetrahedron Lett. 2007, 48, 7305.
Figure 2. Crystal structure of 6c.
8. Nawaz, M.; Farooq Ibad, M.; Obaid-Ur-Rahman, A.; Khera, R. A.; Villinger, A.;
Langer, P. Synlett 2010, 150.
carbon C-1
more sterically hindered
more electron-deficient
9. Phenyl 1,4-bis(trifluoromethylsulfonyloxy)-2-naphthoate (2): To a solution of 1
(1.0 equiv) in CH2Cl2 (10 mL per 1 mmol of 1), was added pyridine (4.0 equiv)
at À78 °C under an argon atmosphere. After stirring for 10 min, Tf2O (2.4 equiv)
was added at À78 °C. The mixture was allowed to warm up to 0 °C and stirred
for 4 h. The reaction mixture was filtered and the filtrate was concentrated in
vacuo. The products of the reaction mixture were isolated by rapid column
chromatography (flash silica gel, heptanes/EtOAc). Starting with 1 (2.800 g,
10.0 mmol), pyridine (3.2 mL, 40.0 mmol), 2 was isolated as a white solid
(4.515 g, 83%); mp = 100–101 °C; 1H NMR (300 MHz, CDCl3): d = 7.20–7.27 (m,
3H, ArH), 7.36–7.41 (m, 2H, ArH), 7.75–7.85 (m, 2H, ArH), 8.08 (s, 1H, ArH), 8.12
(dd, J = 7.1, 1.8 Hz, 1H, ArH), 8.24 (d, J = 7.9 Hz, 1H, ArH); 13C NMR (62.90 MHz,
CDCl3): d = 118.5 (CH), 118.6 (q, 1JCF = 321 Hz, CF3), 118.7 (q, 1JCF = 321 Hz, CF3),
121.2 (C), 121.4 (2CH), 121.5 (CH), 123.1 (CH), 126.6 (CH), 127.9 (C), 129.6 (C),
129.7 (2CH), 129.9 (CH), 131.4 (CH), 144.0 (C), 144.2 (C), 150.2 (C), 161.9
(C@O); 19F NMR (282.4 MHz. CDCl3): d = À72.27 (3F, CF3), À72.96 (3F, CF3); IR
~
carbon C-2
more sterically hindered
2
1
O
OTf
OTf
O
2
1
OMe
OPh
1
2
3
4
3
5
4
OTf
OTf
2
2
7
(ATR, cmÀ1):
m = 3068 (w), 1733(m), 1589 (w), 1482 (w), 1427 (s), 1358 (m),
1
carbon C-4
less sterically hindered
less electron deficient
1347 (m), 1247 (m), 1203 (s), 1130 (s), 1045 (m), 1018 (m), 936 (m), 873 (s),
761 (s), 641 (s), 597 (s); MS (EI, 70 eV): m/z (%): 544 (M+, 10), 453 (16), 452
(22), 451 (100), 318 (64), 234 (3), 186 (19), 185 (97), 157 (47), 129 (16), 101
(18), 75 (5), 69 (8), 64 (9), 51 (3); HRMS (EI) calcd for C19H10O8F6S2 [M+]:
543.97158; found 543.97051.
carbon C-5
less sterically hindered
Scheme 5. Possible explanation for the site-selective reactions of 2.
10. General procedure for Suzuki–Miyaura reactions: A 1,4-dioxane solution (4 mL
per 0.5 mmol of 2) of 2, K3PO4, Pd(PPh3)4 and arylboronic acid 3 was stirred at
110 or 95 °C for 8 or 7 h. After cooling to 20 °C, a saturated aqueous solution of
NH4Cl was added. The organic and the aqueous layer were separated and the
latter was extracted with CH2Cl2. The combined organic layers were dried
(Na2SO4), filtered and the filtrate was concentrated in vacuo. The residue was
purified by column chromatography.
_
O
O
1
+
R
2
R
11. Phenyl 1,4-di(p-tolyl)-2-naphthoate (4c): Starting with 2 (272 mg, 0.5 mmol),
K3PO4 (318 mg, 1.5 mmol), Pd(PPh3)4 (3 mol %), 3c (163 mg, 1.2 mmol) and 1,4-
dioxane (4 mL), 4c was isolated as a colourless solid (163 mg, 76%), mp = 120–
122 °C. 1H NMR (300 MHz, CDCl3): d = 2.37 (s, 3H, CH3), 2.38 (s, 3H, CH3), 6.70–
6.74(m, 2H, ArH), 7.02–7.08 (m, 1H, ArH), 7.15–7.26 (m, 8H, ArH), 7.31–7.43
(m, 4H, ArH), 7.65 (dd, J = 8.1, 1.2 Hz, 1H, ArH), 7.89 (s, 1H, ArH), 7.91 (dd,
J = 7.6, 1.2 Hz, 1H, ArH). 13C NMR (75.46 MHz, CDCl3): d = 21.3 (CH3), 21.4
(CH3), 121.5 (2CH), 125.7 (CH), 126.3 (2CH), 126.5 (CH), 127.5 (C), 127.6 (CH),
128.3 (CH), 128.9 (2CH), 129.2 (2CH), 129.3 (2CH), 129.9 (2CH), 130.0 (2CH),
133.2 (C), 133.4 (C), 135.9 (C), 137.0 (C), 137.2 (C), 137.5 (C), 140.2 (C), 141.0
~
3
4
Scheme 6. Diene character of 2.
system (Scheme 6). Due to the p-acceptor effect of the ester group,
the nucleophilic attack occurs at carbon atom C-1 of the diene sys-
(C), 150.8 (C), 167.1 (C@O). IR (ATR, cmÀ1):
m = 3022 (w), 2921 (w), 2865 (w),
tem (conjugate addition).
1711(s), 1591 (w), 1511 (w), 1485 (m), 1378 (m), 1367 (m), 1241 (s), 1220 (s),
1192 (s), 1099 (m), 1020 (m), 926 (m), 814 (s), 746 (s), 687 (m), 595 (m). MS
(EI, 70 eV): m/z (%): 428 (M+, 3), 336 (27), 335 (100), 292 (7), 289 (6), 276 (6),
145 (3), 65 (2). HRMS (EI): calcd for C31H24O2 [M+]: 428.17708; found
428.17783.
In conclusion, we have reported site-selective Suzuki–Miyaura
reactions of the bis(triflate) of phenyl 1,4-dihydroxynaphthoate.
The first attack occurred at the sterically more hindered position
C-1.

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Obaid-ur-Rahman Abid et al. / Tetrahedron Letters 51 (2010) 1541–1544
12. Billingsley, K.; Buchwald, S. L. J. Am. Chem. Soc. 2007, 129, 3358. and references
water and extracted with CH2Cl2 (3 Â 25 mL). The combined organic layers
were dried (Na2SO4), filtered and the filtrate was concentrated in vacuo. The
residue was purified by flash chromatography (silica gel, EtOAc/heptanes).
15. Phenyl 4-(3,4-dimethoxyphenyl)-1-(4-(trifluoromethyl)phenyl)-2-naphthoate (6c):
Starting with 2 (272 mg, 0.5 mmol), K3PO4 (318 mg, 1.5 mmol), Pd(PPh3)4
(3 mol %), 3b (104 mg, 0.55 mmol), 1,4-dioxane (4 mL), and 3k (118 mg,
0.65 mmol), 6c was isolated as colourless crystals (134 mg, 51%), mp = 163–
165 °C; 1H NMR (250 MHz, CDCl3): d = 3.85 (s, 3H, OCH3), 3.90 (s, 3H, OCH3),
6.70–6.73(m, 2H, ArH), 6.96 (d, J = 8.2 Hz, 1H, ArH), 7.01–7.11 (m, 3H, ArH),
7.17–7.24 (m, 2H, ArH), 7.40 (dd, J = 7.3, 2.4 Hz, 1H, ArH), 7.44–7.50 (m, 4H,
ArH), 7.68–7.71 (m, 2H, ArH), 7.95–7.99 (m, 1H, ArH), 8.0 (s, 1H, ArH). 13C NMR
(75.46 MHz, CDCl3): d = 56.0 (OCH3), 56.1 (OCH3), 111.3 (CH), 113.3 (CH), 121.2
cited therein.
13. Phenyl
1-(2,6-dimethoxyphenyl)-4-(trifluoromethylsulfonyloxy)-2-naphthoate
(5c): Starting with
2
(272 mg, 0.5 mmol), K3PO4 (160 mg, 0.75 mmol),
Pd(PPh3)4 (3 mol %), 3g (100 mg, 0.55 mmol) and 1,4-dioxane (4 mL), 5c was
isolated as colourless crystals (88 mg, 33%), mp = 162–164 °C; 1H NMR
(300 MHz, CDCl3): d = 3.53 (s, 6H, OCH3), 6.62 (d, J = 8.4 Hz, 2H, ArH), 6.79–
6.84(m, 2H, ArH), 7.06–7.12 (m, 1H, ArH), 7.20–7.26 (m, 2H, ArH), 7.33 (t,
J = 8.26, 1H, ArH), 7.41–7.48 (m, 1H, ArH), 7.55 (d, J = 8.1 Hz, 1H, ArH), 7.64 (dt,
J = 7.8, 1.3 Hz, 1H, ArH), 8.07 (d, J = 8.3 Hz, 1H, ArH), 8.08 (s, 1H, ArH); 13C NMR
(62.90 MHz, CDCl3): d = 55.9 (2OCH3), 104.1 (2CH), 114.8 (C), 118.3 (CH), 118.8
1
(q, JCF = 321 Hz, CF3), 120.9 (CH), 121.3 (2CH), 125.7 (CH), 127.7 (C), 127.9
1
3
(CH), 128.0 (CH), 128.2 (C), 129.3 (2CH), 129.5 (CH), 130.1 (CH), 134.3 (C),
(2CH), 122.4 (CH), 124.3 (q, JCF = 272 Hz, CF3), 125.2 (q, JCF = 3.8 Hz, 2CH),
125.9 (CH), 126.4 (CH), 126.5 (CH), 126.8 (C), 126.9 (CH), 127.8 (CH), 128.1
(CH), 129.4 (2CH), 129.9 (d, 2JCF = 32.5 Hz, C), 130.3 (2CH), 132.3 (C), 132.8 (C),
133.7 (C), 139.7 (C), 140.9 (C), 143.1 (C), 148.9 (C), 149.0 (C), 150.5 (C), 166.2
(C@O). 19F NMR (282.4 MHz. CDCl3): d = À62.38 (3F, CF3). IR (ATR, cmÀ1):
~
137.0 (C), 144.9 (C), 150.7 (C), 157.8 (2C), 164.7 (C@O); IR (ATR, cmÀ1):
~
m
= 3014 (w), 2937 (w), 2839 (w), 1723 (m), 1589 (w), 1510 (w), 1470 (m),
1413 (m), 1336 (m), 1247 (m), 1192 (s), 1109 (s), 1011 (m), 956 (m), 828 (m),
747 (m), 687 (m), 599 (m). MS (EI, 70 eV): m/z (%): 532 (M+, 4), 441 (7), 440
(21), 439 (100), 306 (17), 275 (25), 263 (20), 248 (4), 220 (6) 176 (2), 94 (3), 69
(4), 43 (5). HRMS (EI) calcd for C26H19O7F3S [M+]: 532.07981; found 532.08011.
14. General procedure for the synthesis of 6a–d: The reaction was carried out in a
m
= 3065 (w), 2966 (w), 2838 (w), 1712 (m), 1597 (w), 1515 (m), 1406 (w),
1320 (m), 1239 (m), 1212 (m), 1159 (s), 1101 (s), 1023 (m), 923 (w), 775 (m),
744 (m), 685 (m), 623 (m), 549 (w). MS (EI, 70 eV): m/z (%): 528 (M+, 18), 436
(27), 435 (100), 376 (4), 333 (4), 252 (3), 207 (3), 153 (3), 94 (18), 69 (13), 60
(25), 43 (29). HRMS (EI) calcd for C32H23O4F3 [M+]: 528.15430; found
528.15443.
pressure tube. To
a dioxane suspension (4 mL) of 2 (272 mg, 0.5 mmol),
Pd(PPh3)4 (3 mol %) and K3PO4 (159 mg, 0.75 mmol) was added Ar1B(OH)2
(0.55 mmol)and the solution was degassed by bubbling argon through the
solution for 10 min. The reaction mixture was heated at 95 °C under argon
atmosphere for 7 h. The reaction mixture was cooled to 20 °C and Ar2B(OH)2
(0.65 mmol) and K3PO4 (159 mg, 0.75 mmol) were added. The reaction mixture
was heated under Argon atmosphere for 8 h at 110 °C. They were diluted with
16. CCDC 760147 and 760148 contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.