Nickel-catalyzed cross-coupling reactions of 4-mesylcoumarins with aryl halides: Facile synthesis of 4-substituted coumarins

Article abstract of DOI:10.1055/s-2004-832818

A new and efficient nickel-catalyzed cross-coupling reaction between 4-mesylcoumarins and aryl halides was developed to give a number of 4-arylcoumarins in good yield under mild conditions. Unlike the previously reported coupling examples, this new method allows the direct cross-coupling of 4-mesylcoumarins with aryl- or vinyl halides in the NiCl₂(PPh ₃)2/PPh₃/Zn/toluene system. This has greatly facilitated the synthesis of biologically useful 4-substituted coumarins.

Full text of DOI:10.1055/s-2004-832818

2364
LETTER
Nickel-Catalyzed Cross-Coupling Reactions of 4-Mesylcoumarins with Aryl
Halides: Facile Synthesis of 4-Substituted Coumarins
N
i-Catalyz
i
ed Cro
a
ss-Couplin
n
g for
S
ynthe
-
sis of 4-
S
G
ubstituted
C
ouma
u
r
ins ang Lei, Ming-Hua Xu, Guo-Qiang Lin*
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Rd., Shanghai 200032, P. R. China
Fax +86(21)64166263; E-mail: lingq@mail.sioc.ac.cn
Received 22 June 2004
isofraxdin (2),11 by the homocoupling of its corresponding
Abstract: A new and efficient nickel-catalyzed cross-coupling re-
action between 4-mesylcoumarins and aryl halides was developed
to give a number of 4-arylcoumarins in good yield under mild con-
ditions. Unlike the previously reported coupling examples, this new
4-tosylcoumarin.12 In the continuation of our work, we
wish to prepare a number of different 4-substituted cou-
marins. Combining the above two successes, we envi-
method allows the direct cross-coupling of 4-mesylcoumarins with sioned the potential of nickel-catalyzed cross-coupling of
aryl- or vinyl halides in the NiCl2(PPh3)2/PPh3/Zn/toluene system.
4-sulphonylcoumarins with aryl halides to produce 4-aryl
This has greatly facilitated the synthesis of biologically useful 4-
substituted coumarins.
coumarins. It would be highly practical if these two readi-
ly available species could be directly coupled. Herein, we
report our preliminary results of the cross-coupling reac-
tion between 4-mesylcoumarins and aryl halides in the
Key words: coumarin, aryl halide, nickel-catalyzed, homocou-
pling, cross-coupling
presence of nickel catalyst.
In recent years, coumarins have attracted a lot of attention
OMe
because of their important physiological properties and
HO
O
O
O
their presence as important structural units in a large vari-
ety of biologically active natural products.1,2 Interest in
the synthesis of these compounds has stimulated the de-
velopment of numerous methods for the construction of
coumarin structures and their derivatives.3–8 Among the
various methods developed for the synthesis of 4-substi-
tuted coumarins, the cross-coupling approaches by using
transition metal such as palladium or nickel catalyst are
the most direct and attractive. Recently, remarkable
progress has been made in this area.4–8 For example, the
palladium-catalyzed Stille-type cross-coupling of 4-trifyl-
coumarin or 4-tosylcoumarin with organostannanes,5 and
Suzuki-type cross-coupling of 4-trifylcoumarins or 4-ha-
locoumarins with arylboronic acids6 are found efficient
for the preparation of 4-substituted coumarins. In addi-
tion, the nickel-catalyzed cross-coupling of 4-tosylcou-
marins with terminal acetylenes and organozinc reagents,7
OH
H
MeO
MeO
OMe
OMe
OH
H
OH
O
O
O
OMe
1 Bisbenzopyran-4-ol
2 4,4'-Biisofraxidin
Figure 1
To chose the best 4-coumarin sulfonates for cross-cou-
pling attempts, we first investigated the homocoupling re-
action of 4-tosylcoumarin, 4-trifylcoumarin and 4-
mesylcoumarin under our standard coupling conditions
[NiCl2(PPh3)2/PPh3/Zn/NaH/toluene, 90 °C].10 The ex-
perimental results are listed in Table 1. Among the three
substrates (3a–c) tested, the 4-trifylcoumarin (3b) should
have the highest reactivity in the coupling reaction, how-
ever, it only gave the homocoupling product in low yield
(41%) along with 40% of the reduced product (entry 2).
4-diethylphosphonoxycoumarins
with
organozinc
reagents8 are also successfully developed to synthesize
various 4-substituted coumarins.
Interestingly, the mesylate 3c underwent homocoupling
reaction smoothly and afforded the best yield of 75% after
five hours (entry 3). Similar yield (76%) was achieved
when a substituted 4-mesylcoumarin (3d) was employed.
It seems likely that the 4-mesylcoumarin (3c) is an appro-
priate substrate for cross-coupling study. To our knowl-
edge, examples of using aryl mesylates in nickel-
catalyzed homocoupling and cross-coupling reactions has
been successfully reported in the pioneering work of
Percec.13
In our laboratory, we are interested in nickel-catalyzed
coupling reactions and their application in natural prod-
ucts synthesis. In the synthesis of bisbenzopyran-4-ol (1),
a natural product isolated from the root of Aloe barbaden-
sis,9 we have developed a new reagent system
[NiCl2(PPh3)2/PPh3/Zn/NaH/toluene] for the homocou-
pling of aryl halides or vinyl halides (Figure 1).10 Using
this modified Ullmann-type coupling reaction system, we
have also successfully accomplished the total synthesis of
a biologically active new biscoumarin compound, 4,4¢-bi-
To begin attempting the nickel-catalyzed cross-coupling
reaction of 4-mesylcoumarin (3c) with aryl halide, we
first sought to find a best reaction condition that would
minimize the homocoupling of both reactants. Thus, the
SYNLETT 2004, No. 13, pp 2364–2368
0
3
.1
1
.2
0
0
4
Advanced online publication: 24.09.2004
DOI: 10.1055/s-2004-832818; Art ID: U17804ST
© Georg Thieme Verlag Stuttgart · New York

LETTER
Ni-Catalyzed Cross-Coupling for Synthesis of 4-Substituted Coumarins
2365
the mixture of 3c and catalyst in toluene. The slow addi-
tion of 5a increased the yield of 7a to 42% (entry 5). In ad-
dition, we observed a higher yield (58%) in the absence of
Bu4NI and NaH (entry 6). The bidentate ligand dppe had
lower efficiency than the monodentate ligand PPh3 (entry
7 vs. 6). Surprisingly, the use of benzene as reaction
solvent caused a dramatic decrease in the yield of cross-
coupling product and led to the formation of both homo-
coupling by-products (entry 8). Based on these results, we
decided to choose the conditions in entry 6 as the best for
further study.14
Table 1 Homocoupling of 4-Coumarin Sulfonates under the
Standard Conditionsa
R
R2
R1
O
O
R1
R2
Ni-catalyst
toluene, 90 °C
R1
R2
O
O
3a: R=OTs, R1=H, R2=H
3b: R=OTf, R1=H, R2=H
3c: R=OMs, R1=H, R2=H
3d: R=OMs, R1=Me, R2=H
O
O
4
Entry
Substrate
Dimer
4a
Time (h)
Yield (%) b
Gratifyingly, the catalytic cross-coupling reactions of 3c
with a series of aryl halides were successful to afford the
corresponding 4-substituted coumarins in moderate to
good yields (Table 3). As shown in Table 3, the mesylate
3c reacted smoothly with both aryl bromide and iodide. In
most cases, the iodide and bromide show similar reactivi-
ty, the reaction usually could be done in two to five hours.
A little better yield was achieved by using the iodide.
When aryl iodide 5e was employed, the reaction was fast-
er and completed in one hour to give a moderate yield (en-
try 5).15 It is noteworthy that the reaction was not
hampered by ortho-substituents. Unlike most other cou-
pling reactions, it seems likely that the steric effect is not
the main problem here. Furthermore, the functional group
such as aldehyde is tolerated under the reaction condi-
tions. Other than the aryl halides, the vinyl halide 5j could
also react with 3c to produce the cross-coupling product
7f in good yield (83%, entry 10).16
1
2
3
4
3a
3b
3c
3d
30
13
5
62
41c
75
76
4a
4a
4b
18
a All reactions were performed using 0.2 equiv of NiCl2(PPh3)2, 0.4
equiv of PPh3, 0.1 equiv of NaI, 5 equiv of NaH, 3 equiv of Zn in
0.25 M of toluene at 90 °C.
b Isolated yield.
c Reduced product coumarin was observed in 40 % yield.
reaction of 3c with 5a was chosen and examined
(Table 2). We found that the cross-coupling product 7a
could be formed under our reaction system, however, the
yield was low (21%, entry 1). To avoid the homocoupling
of the corresponding substrates, we added the solution of
5a in toluene dropwise through a micro-syringe pump to
Table 2 Cross-Coupling between 4-Mesylcoumarin 3c and Aryl Iodide 5a under Different Reaction Conditionsa
OMe
OMe
OMe
OMs
O
Ni-catalyst
CHO
CHO
CHO
O
4a
+
+
+
toluene, 90 °C
CHO
O
I
O
OMe
6
3c
5a
7a
Entry
Bu4NI (equiv)
NaH (equiv)
Time1 (h)b
Time2c (h)
Yield of 6 (%)
Yield of 7a (%)
Yield of 4a (%)
1
0.1
0.1
0.1
0.1
0.1
6
6
6
5
6
0
4
7
34
21
40
14
0
21
36
11
22
42
58
20
27
18
0
2
0.5
1c
2
3d
4
6
14
0
11
9
5
3
0
6
3
4
18
74
13
0
7e
8f
3
5
0
3
5
13
a All reactions were performed using 0.2 equiv of NiCl2(PPh3)2, 0.4 equiv of PPh3, 3 equiv of Zn in toluene at 90 °C.
b Time of the addition of substrate 5a.
c Time after the addition of substrate 5a.
d Compound 3c was added slowly during 1 h.
e Instead of PPh3, dppe was used.
f Benzene was used as solvent instead of toluene.
Synlett 2004, No. 13, 2364–2368 © Thieme Stuttgart · New York

2366
J.-G. Lei et al.
LETTER
Table 3 Cross-Coupling of 3c with Aryl Halides 5a
Table 3 Cross-Coupling of 3c with Aryl Halides 5a (continued)
OMs
Aryl
OMs
Aryl
NiCl2(PPh3)2, PPh3 Zn
NiCl2(PPh3)2, PPh3 Zn
toluene, 90 °C
+
Aryl-X
+
Aryl-X
toluene, 90 °C
O
O
O
O
O
O
O
O
3c
5 X=I, Br
7
3c
5 X=I, Br
7
Yield (%)b Time (h)c
Entry
1
Aryl-X 5
Product
Yield (%)b Time (h)c
Entry
Aryl-X 5
Product
a Reaction conditions: a solution of 5 (0.6 mmol) in 3 mL of toluene
was added during 3 h into the solution of 3c (0.5 mmol), NiCl2(PPh3)2
(0.2 equiv), PPh3 (0.4 equiv), Zn (2–3 equiv) in 3 mL of toluene.
b Isolated yield based on mesylate 3c.
7a
58
85
71
2
2
2
OMe
CHO
c Reaction time after the addition of 5.
I
5a
OMe
2
3
7a
7b
We also investigated the possibility of the cross-coupling
of diverse 4-mesylcoumarins 3d–g with a variety of aryl
or vinyl halides (Table 4). Substitution groups (such as
methyl, fluoro, methoxy and so on) on the coumarin
scaffold did not affect the coupling efficiency. Iodo- or
bromo-substituted benzaldehydes were treated with those
CHO
OMe
Br
5b
MeO
MeO
CHO
Table 4 Cross-Coupling of Diverse 4-Mesylcoumarins with a
I
Variety of Aryl or Vinyl Halidesa
5c
Aryl
O
OMs
4
7b
70
3
R2
R1
OMe
R2
R1
NiCl2(PPh3)2, PPh3,
Zn, toluene, 90 °C
MeO
MeO
Aryl
X
+
O
O
O
CHO
CHO
CHO
3d: R1=H, R2=Me
3e: R1=H, R2=F
3f: R1=H, R2=OMe
7
5 X=I, Br
Br
5d
MeO
5
6
7
7c
7c
7d
72
67
67
1
4
2
Entry 3
Aryl-X 5
7
Yield Time
(%)b
(h)c
MeO
I
1
2
3
4
3d
3d
3d
3e
5c
7g
7h
7i
69
4
5e
MeO
5k
5a
83
2
MeO
53
5
Br
7j18
90
2
5f
O
I
O
OMe
CHO
MeO
CHO
CHO
I
5m
5h
5g
5
6
3f
3f
7k
7l
90
55
5
5
8
7d
52
5
OMe
I
MeO
Br
CHO
5h
5n
5n
9
7e
7f
63
83
5
3
7
7m19
63
19
OMs
O
CHO
I
O
5i
10
O
O
MeO
I
3g
a Reaction conditions are the same as in Table 3.
b Isolated yield based on 4-mesylcoumarin s 3.
c Reaction time after the addition of 5.
5j
Synlett 2004, No. 13, 2364–2368 © Thieme Stuttgart · New York

LETTER
Ni-Catalyzed Cross-Coupling for Synthesis of 4-Substituted Coumarins
2367
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4-mesylcoumarins to obtain the corresponding coupling
products in moderate to high yields (entries 1, 3–7). 3-
Iodo-6-methoxy-benzopyran-4-one (5k) also reacted with
mesylate 3d to give 83% yield of the corresponding prod-
uct 7h (entry 2).17
In summary, we have demonstrated a new nickel-cata-
lyzed cross-coupling of 4-mesylcoumarins with aryl or vi-
nyl halides in the NiCl2(PPh3)2/PPh3/Zn/toluene reaction
system. A number of useful 4-arylcoumarin compounds
were obtained in good yields under mild conditions. Un-
like the previously reported coupling examples, this new
coupling method avoids the use of toxic organostannanes,
sensitive organozinc reagents and expensive arylboronic
acids; on the contrary, it allows the direct cross-coupling
of easily accessible 4-mesylcoumarins with aryl or vinyl
halides. Furthermore, the functional group such as alde-
hyde is tolerated under the reaction conditions. This has
greatly facilitated the synthesis of a variety of biologically
important 4-substituted coumarins. Application of this
coupling method to construct a library of 4-coumarins is
currently underway.
(4) Kadnikov, D. V.; Larock, R. C. Org. Lett. 2000, 2, 3643.
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J. Chem. Soc., Perkin Trans. 1 1996, 2591.
(6) Yao, M.-L.; Deng, M.-Z. Heteroat. Chem. 2000, 11, 380.
(7) Wu, J.; Liao, Y.; Yang, Z. J. Org. Chem. 2001, 66, 3642.
(8) Wu, J.; Yang, Z. J. Org. Chem. 2001, 66, 7875.
(9) Saleem, R.; Faizi, S.; Deeba, F.; Siddiqui, B. S.; Qazi, M. H.
Planta Med. 1997, 63, 454.
(10) Lin, G.-Q.; Hong, R. J. Org. Chem. 2001, 66, 2877.
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1998, 64, 774.
(12) Lei, J.-G.; Lin, G.-Q. Chin. J. Chem. 2002, 20, 1263.
(13) (a) Percec, V.; Bae, J.-Y.; Zhao, M.; Hill, D. H. J. Org.
Chem. 1995, 60, 176. (b) Percec, V.; Bae, J.-Y.; Hill, D. H.
J. Org. Chem. 1995, 60, 1060. (c) Percec, V.; Bae, J.-Y.;
Zhao, M.; Hill, D. H. J. Org. Chem. 1995, 60, 1066.
(d) Percec, V.; Golding, G. M.; Smidrkal, J.; Weichold, O. J.
Org. Chem. 2004, 69, 3447.
(14) General Procedure for the Synthesis of 7: To an oven-
dried Schlenk flask (25 mL) was charged 4-coumarin
compound 3 (0.5 mmol), NiCl2 (PPh3)2 (0.2 equiv), PPh3 (0.4
equiv), zinc dust (2.2 mmol) and dry toluene (3 mL) under
argon. The resulting mixture was heated to 90 °C. The aryl
halide 5 (0.6 mmol) was then added dropwise through
micro-syringe pump over 3 h. After the addition, the reaction
mixture was stirred at the same temperature until
completion. The reaction mixture was cooled down to r.t.,
quenched with 5% HCl and diluted by CH2Cl2. The mixture
was stirred vigorously at r.t. until the solution was clear. The
organic layer was separated and the water layer was
extracted with CH2Cl2 (3 × 10 mL). The combined organic
layer was washed with sat. aq NaHCO3, brine, and dried over
Na2SO4. The solution was concentrated under vacuum; the
obtained residue was purified by silica column chromato-
graphy to give the corresponding cross-coupling product 7
(selected characterization data of 7 are listed as follows).
(15) Compound 7c. 1H NMR (300 MHz, CDCl3): d = 9.69 (s, 1
H), 7.86 (m, 1 H), 7.54 (m, 1 H), 7.45 (m, 1 H), 7.22–7.16
(m, 2 H), 7.01 (m, 1 H), 6.40 (s, 1 H), 4.05 (s, 3 H), 3.70 (s,
3 H). MS (EI): m/z (%) = 310 (71) [M+], 295 (100). IR (KBr):
3088, 2947, 2837, 2733, 1729, 1695, 1683, 1604, 1584, 1566
cm–1. Anal. Calcd for C18H14O5: C, 69.67; H, 4.55. Found: C,
69.86; H, 4.57.
Acknowledgment
Financial support from the National Natural Science Foundation of
China (20172063 and 203900506), the Major State Basic Research
Development Program (G2000077506), and the Shanghai Munici-
pal Committee of Science and Technology is acknowledged.
References
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Beley, M.; Kirsch, G. Tetrahedron Lett. 2000, 41, 1175.
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Cox, D.; Prosser, E.; Thornes, R. D. Drug Metab. Rev. 1990,
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263. (c) Murray, R. D. H. Nat. Prod. Rep. 1995, 12, 477.
(d) Trivedi, K. N.; Rao, S. S. M.; Mistry, S. V.; Desai, S. M.
J. Indian Chem. Soc. 2001, 78, 579.
(3) (a) Awasthi, A. K.; Tewari, R. S. Synthesis 1986, 1061.
(b) Sato, K.; Inour, S.; Kobayashi, T.; Ota, T.; Tazaki, M. J.
Chem. Soc., Perkin Trans. 1 1987, 1753. (c) Desouza, M.
D.; Joshi, V. Indian J. Heterocycl. Chem. 1993, 3, 93.
(d) Ivanova, D. I.; Eremin, S. V.; Shvets, V. I. Tetrahedron
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Tetrahedron 1998, 54, 12215. (f) De la Hoz, A.; Moreno,
A.; Vazquez, E. Synlett 1999, 608. (g) Yavari, I.; Adib, M.;
Hojabri, L. Tetrahedron 2001, 57, 7537. (h) Gonzalez-
Gomez, J. C.; Santana, L.; Uriarte, E. Synthesis 2002, 43.
(i) Bose, D. S.; Rudradas, A. P.; Babu, M. H. Tetrahedron
(16) Compound 7f. 1H NMR (300 MHz, CDCl3): d = 8.08 (d,
J = 2.1 Hz, 1 H), 7.64 (s, 1 H), 7.54 (d, J = 7.5 Hz, 1 H), 7.51
(d, J = 7.5 Hz, 1 H), 7.42–7.21 (m, 4 H), 6.45 (d, J = 2.1 Hz,
1 H), 3.93 (s, 3 H). 13C NMR (75.5 MHz, CDCl3): d =
175.12, 160.67, 157.84, 154.08, 153.90, 151.45, 148.05,
132.41, 127.02, 124.91, 124.52, 120.90, 120.03, 118.95,
117.70, 117.45, 105.45, 56.28. MS (EI): m/z (%) = 320 (4)
[M+], 292 (10.00). IR (KBr): 3078, 2963, 1720, 1649, 1610,
1488, 1446, 1334, 1271 cm–1. HRMS: m/z calcd for
C19H12O5: 320.0685; found: 320.0734.
(17) Compound 7h. 1H NMR (300 MHz, CDCl3): d = 8.05 (s, 1
H), 7.65 (s, 1 H), 7.55–7.30 (m, 4 H), 7.11 (s, 1 H), 6.42 (s,
1 H), 3.94 (s, 3 H), 2.34 (s, 3 H). 13C NMR (75.5 MHz,
CDCl3): d = 174.84, 160.58, 157.73, 153.66, 151.79, 151.20,
147.65, 133.95, 133.21, 126.31, 124.64, 120.69, 119.76,
118.46, 117.47, 116.90, 105.26, 59.01, 20.91. MS (EI):
Synlett 2004, No. 13, 2364–2368 © Thieme Stuttgart · New York

2368
J.-G. Lei et al.
LETTER
m/z (%) = 335 (18) [M+ + 1], 334 (78) [M+], 333 (21) [M+ –
1], 306 (100). IR (KBr): 3078, 2959, 2929, 2498, 1719,
1698, 1646, 1618, 1568, 1488, 821 cm–1. HRMS: m/z calcd
for C20H14O5: 334.0841; found: 334.0874.
(19) Compound 7m. 1H NMR (300 MHz, CDCl3): d = 10.16 (s, 1
H), 8.09 (d, J = 9.0 Hz, 2 H), 7.89 (d, J = 9.0 Hz, 2 H), 7.74–
7.58 (m, 4 H), 7.37 (d, J = 9.3 Hz, 1 H), 7.16 (d, J = 8.7 Hz,
1 H), 6.51 (s, CH, 1 H). MS (EI): m/z (%) = 301 (20) [M+ +
1], 300 (91) [M+], 272 (100). IR (KBr): 1733, 1631, 1601,
1549, 1500, 1470, 1375, 1209 cm–1. HRMS: m/z calcd for
C20H12O3: 300.0786; found: 300.0809.
(18) Compound 7j. 1H NMR (300 MHz, CDCl3): d = 9.70 (s, 1
H), 7.54–7.30 (m, 5 H), 6.80 (s, 1 H), 6.39 (d, J = 15 Hz, 2
H). MS (EI): m/z (%) = 312 (71) [M+], 269 (100). IR (KBr):
3075, 2913, 2861, 1725, 1682, 1610, 1571, 1504, 1482,
1440, 1369, 1268, 1253 cm–1. HRMS: m/z calcd for
C17H9FO5: 312.0434; found: 312.0385.
Synlett 2004, No. 13, 2364–2368 © Thieme Stuttgart · New York