Rh(I)/diene-catalyzed addition reactions of aryl/alkenylboronic acids with aldehydes

Article abstract of DOI:10.1016/j.tetlet.2009.06.074

[Rh(COD)Cl]₂-catalyzed addition reactions of arylboronic acids with aldehydes, with low Rh(I) catalyst loading, are described. We also found that the reaction of arylboronic acids with α,β-unsaturated aldehydes greatly depends on the solvent and the steric hindrance of the reagents/substrates.

Full text of DOI:10.1016/j.tetlet.2009.06.074

Tetrahedron Letters 50 (2009) 4953–4957
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Tetrahedron Letters
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Rh(I)/diene-catalyzed addition reactions of aryl/alkenylboronic acids
with aldehydes
*
Chun-Hui Xing, Tao-Ping Liu, Jin Rong Zheng, Jaclynn Ng, Michelle Esposito, Qiao-Sheng Hu
Department of Chemistry, College of Staten Island and the Graduate Center of the City University of New York, 2800 Victory Boulevard, Staten Island, NY 10314, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
[Rh(COD)Cl]2-catalyzed addition reactions of arylboronic acids with aldehydes, with low Rh(I) catalyst
Received 10 April 2009
Revised 20 May 2009
Accepted 1 June 2009
Available online 17 June 2009
loading, are described. We also found that the reaction of arylboronic acids with
aldehydes greatly depends on the solvent and the steric hindrance of the reagents/substrates.
a,b-unsaturated
Ó 2009 Elsevier Ltd. All rights reserved.
In 1998, Miyaura reported Rh(I)/bisphosphine-catalyzed addi-
tion reactions of aryl/alkenylboronic acids with aldehydes,1 which
marked an important step of transition metal-catalyzed such addi-
tion reactions.2–10 Subsequent study from the same group showed
that Rh(I)/t-Bu3P (1:1 ratio) possess much higher catalytic activity
than Rh(I)/bisphosphine catalysts,2 suggesting that bulky, mono-
dentate ligands would be superior ligands. Since then, a number
of Rh(I) catalysts derived from monodentate ligands have been
developed.3,4 In our laboratory, we are interested in developing
highly active/efficient catalysts for such addition reactions. We
have recently documented metalacycle-catalyzed addition reac-
tions of arylboronic acids with carbonyl-containing compounds.7
In our studies, we demonstrated that the catalytic activity of the
metalacycles could be tuned by varying the Lewis acidity of the
metal center, including employing less electron-donating ligands
and softer metal.7 We surmised that such Lewis acidity tuning
strategy might also be suitable to develop highly active Rh(I) cata-
lysts with unprecedented catalytic activities.
Our study began with the addition reaction of phenylboronic
acid with 4-nitrobenzaldehyde by using chloro(1,5-cyclooctadi-
ene)rhodium(I) dimer ([Rh(I)(COD)Cl]2) (1), chloronorbornadiene-
rhodium dimer ([Rh(I)(NBD)Cl]2) (2), and [Rh(I)(CH2CH2)2Cl]2 (3)
as catalysts (Table 1). We first tested KOH and KF, two bases that
have been previously used for this type of addition reactions with
other ligands for Rh(I).2,4k We found that with [Rh(COD)Cl]2 as cat-
alyst, a low conversion was observed for KF/toluene–H2O, and var-
ied conversions depending on the amount of the base used were
observed for KOH/dioxane, with 1 equiv of KOH affording the best
result (Table 1, entries 1–4). Screening other bases/solvents
showed that K3PO4/THF was an excellent solvent/base combination
(Table 1, entries 5–15). [Rh(I)(NBD)Cl]2 (2) and [Rh(I)(CH2CH2)2Cl]2
(3) exhibited less efficiency than 1 (Table 1, entries 16–20). Further
study revealed that the existence of water in the reaction system
can accelerate the reaction (Table 1, entries 21 and 22). We have
lowered the amount of [Rh(COD)Cl]2 to 0.1% for the addition reac-
tion. Once again, K3PO4 was observed as the best base.
Dienes have recently been reported as efficient ligands in Rh(I)-
With [Rh(COD)Cl]2 as catalyst and K3PO4 as base, we have
examined a number of aromatic aldehydes and arylboronic acids
for the addition reaction. We found that the reaction went
smoothly with 0.025–0.05% [Rh(COD)Cl]2 as catalyst (Table 2,
entries 1–10). Aliphatic aldehydes have been reported to be less
effective substrates in Rh(I)-catalyzed addition reaction of arylbo-
ronic acids with aldehydes due to the tendency of aliphatic alde-
hydes to undergo Aldol reaction under the reaction condition. It
was of interest to us to see whether the Rh(I)/diene system could
effect the reaction with this type of substrate. We were pleased
to find that the addition with aliphatic aldehydes as substrates pro-
ceeded well with high isolated yields (Table 2, entries 11–17). To
our knowledge, the 0.025% loading of 1 represented the lowest
Rh(I) loading in the addition reaction of arylboronic acids with
aldehydes. We have also tested vinylboronic acids as nucleophiles
for the addition and found that vinylboronic acids were less reac-
tive than arylboronic acids and higher catalyst loading was
required for the reaction (Table 2, entries 18 and 19).
catalyzed addition reaction of arylboronic acids with
a,b-unsatu-
rated ketones/esters/aldehydes.11,12 Importantly, Rh(I)/diene
catalysts exhibited higher catalytic activity than Rh(I)/phosphines
including Rh(I)/bisphosphine catalysts. We speculated that such
catalytic activity increase might in part be due to the less elec-
tron-donating ability of the dienes, which could make the Rh(I)
center more Lewis acidic. We thus envisioned that Rh(I)/diene cat-
alysts could be highly active catalyst systems for the addition of
arylboronic acids with aldehydes. In this Letter, we report on the
Rh(I)/diene-catalyzed addition reactions of arylboronic acids with
aldehydes, with low Rh(I) catalyst loading, and a highly efficient
tandem reaction sequence of arylboronic acids with
a,b-unsatu-
rated aldehydes.13
* Corresponding author. Tel.: +1 718 982 3901; fax: +1 718 982 3910.
E-mail address: qiaohu@mail.csi.cuny.edu (Q.-S. Hu).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.06.074

4954
C.-H. Xing et al. / Tetrahedron Letters 50 (2009) 4953–4957
Table 1
a
Rh(I)/diene-catalyzed addition reactions of phenylboronic acid with 4-nitrobenzaldehyde
OH
Rh(I) Catalyst
PhB(OH)
+
O N
CHO
2
2
Base, Solvent, r. t.
NO
2
Entry
Rh(I) Cat.
Catalyst loading (%)
Solvent
Base
KF (2 equiv)
Time (h)
Conver.b (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
3
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
1
1
1
0.1
0.1
0.1
Toluene
Dioxane
Dioxane
Dioxane
Dioxane
THF
THF
Dioxane
THF
THF
THF
THF
THF
THF
THF
Dioxane
THF
Toluene
THF
THF
THF
THF
THF
0.5
0.5
0.5
0.5
0.5
0.5
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
1
18
66
87
12
99
99
91
85
41
43
16
34
10
<2
55
80
34
0
KOH (0.5 equiv)
KOH (1 equiv)
KOH (3 equiv)
K3PO4 (2 equiv)
K3PO4 (2 equiv)
K3PO4 (2 equiv)
K3PO4 (2 equiv)
KOH (2 equiv)
K2CO3
Na2CO3
KF
KOAc
NaOH
Cs2CO3
KOH (2 equiv)
KF (2 equiv)
KF (2 equiv)
K3PO4 (2 equiv)
K3PO4 (2 equiv)
K3PO4 (5.5 M, 2 equiv)
K3PO4 (5.5 M, 2 equiv)
K3PO4 (5.5 M, 3 equiv)
KOH (2 equiv)
91
0
0.25
1
0.5
0.5
0.5
99
92
81
42
25
THF/H2O (10:1)
Dioxane/H2O (10:1)
KOH (2 equiv)
a
Reaction conditions: aldehyde (0.5 mol), phenylboronic acid (0.75 mmol), THF (2 mL), base (0.5–3.0 equiv), rt.
Conversion based on 1H NMR.
b
Table 2
a
[Rh(COD)Cl]2-catalyzed addition reactions of aryl/alkenylboronic acids with aldehydes
OH
Ar
[Rh(COD)Cl]
2
RCHO
+
ArB(OH)
2
R
THF, K PO (5.0 M), r. t.
3
4
Entry
1
ArB(OH)2
RCHO
Cat. loading
0.025
Time (h)
Yieldb (%)
96
10
15
19
16
16
B(OH)
CHO
O N
2
2
2
3
4
5
0.025
0.05
0.05
0.05
97
82
83
90
CHO
MeO
B(OH)
O N
2
2
B(OH)
CHO
2
B(OH)
MeO
CHO
2
2
OMe
CHO
B(OH)
6
7
8
9
0.05
0.05
0.05
0.05
19
19
17
17
89
84
87
93
B(OH)
CHO
2
MeO
B(OH)
CHO
CHO
CHO
2
B(OH)
2
2
OMe
B(OH)

C.-H. Xing et al. / Tetrahedron Letters 50 (2009) 4953–4957
4955
Table 2 (continued)
Entry
ArB(OH)2
RCHO
Cat. loading
Time (h)
10
Yieldb (%)
91
10
11
12
13
14
15
16
17
18
0.05
B(OH)
CHO
CHO
Br
2
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.25
0.25
19
16
16
16
17
17
17
16
16
83
91
92
93
82
86
87
86
44
B(OH)
2
Ph
Ph
Ph
Ph
CHO
CHO
CHO
B(OH)
2
MeO
B(OH)
2
B(OH)
2
B(OH)
CHO
2
MeO
Ph
B(OH)
CHO
CHO
2
OMe
B(OH)
2
B(OH)
2
CHO
CHO
O2N
B(OH)
2
19
O2N
C H
6
13
a
Reaction conditions: aldehyde (1.0 equiv), boronic acid (1.5 equiv), THF (4 mL), K3PO4 (5.0 M, 3.0 equiv), rt.
Isolated yields.
b
The observation of aliphatic aldehydes as excellent substrates
found that the reaction of arylboronic acids with
a,b-unsaturated
for this reaction prompted us to carry out studies to understand
the reactivities of different aldehydes for this reaction. We tested
the addition reaction with phenylboronic acid as the nucleophile.
Our results are listed in Table 3. We found that p-nitrobenzalde-
hyde, which bears an electron-withdrawing substituent, exhib-
ited higher reactivity than p-methylbenzaldehyde, which bears
an electron-donating group (Table 3, entry 1). Aliphatic alde-
hydes such as hexanal and 3-methylbutanal showed a similar
reactivity as p-methylbenzaldehyde (Table 3, entries 1–5). Inter-
estingly, 3-phenylpropanal exhibited a higher reactivity than
hexanal, 3-methylbutanal, or p-methylbenzaldehyde (Table 3,
entries 2, 4, and 5). In addition, 3,3-diphenylpropanal showed
a higher reactivity than 3-phenylpropanal (Table 3, entry 6).
These results might suggest that the phenyl group participated
in the addition reaction.
aldehydes greatly depends on the solvent and the steric hindrance
of the reagents/substrates. Our future work will be directed to
determine the scope and limitation of Rh(I)/diene-catalyzed addi-
tion reactions and to develop the asymmetric version of these
processes.
Table 3
Competitive addition reaction of phenylboronic acid with aromatic aldehydes and
a
aliphatic aldehydes
OH
0.25% [Rh(COD)Cl]2
H
K3PO4, THF, r. t.
O
OH
O
PhB(OH)
+
+
H
+
2
R
R
R
1
R
1
Ph
2
2
Ph
(1 equiv.)
(1equiv.)
(1 equiv.)
A
B
Entry
1
Ratio of A:Bb
O
O
H
O
H
R1
R2
We have also employed [Rh(COD)Cl]2 as the catalyst for the
O
addition reaction of arylboronic acids with
a,b-unsaturated alde-
1:7.3
H
hydes.12,14 We found that the reaction outcome was dependent
on the solvent used and on the steric hindrance of substrates/re-
agents. With MeOH as solvent, the addition reaction occurred in
a 1,4-addition fashion and 3,3-diphenylpropanal was observed in
high yield (Table 4, entry 1), which was consistent with the previ-
ous observation.12 With THF as solvent, the 1,4-addition followed
by 1,2-addition occurred and alcohols were observed in good to
high yields (Table 4). With 2-substituted phenylboronic acids as
nucleophiles, we observed that crotonaldehyde gave tandem reac-
tion products in good yields, but cinnamaldehyde gave a mixture of
1,2-addition products and 1,4-addition followed by 1,2-addition
products, suggesting that the initial addition was dependent on
the steric hindrance of the substrates and reagents.
H
O2N
O
O
2
3
1:2.2
3.1:1
H
Ph
Ph
H
O
O
H
H
O N
2
O
O
O
O
4
5
1:2.4
1:2.5
1.2:1
H
Ph
Ph
Ph
H
H
H
O
H
H
Ph
O
6
Ph
a
In summary, we have demonstrated that [Rh(COD)Cl]2 was a
highly efficient catalyst for the addition reactions of arylboronic
acids with aldehydes, with low Rh(I) catalyst loading. We also
Reaction conditions: phenylboronic acid (1.0 equiv), aldehydes (1.0 equiv each).
THF (2 mL), K3PO4 (5 M, aqueous solution, 3.0 equiv), room temperature, 18 h.
b
Ratio based on 1H NMR.

4956
C.-H. Xing et al. / Tetrahedron Letters 50 (2009) 4953–4957
Table 4
References and notes
a
Tandem reactions catalyzed by [Rh(COD)Cl]2
1. Aakai, M.; Ueda, M.; Miyaura, N. Angew. Chem., Int. Ed. 1998, 37, 3279–3281.
2. Ueda, M.; Miyaura, N. J. Org. Chem. 2000, 65, 4450–4452.
0.5%[Rh(COD)Cl]
K3PO4, solvent
O
2
Ar
OH
Ar
ArB(OH)
+
2
R
H
3. For recent review on Rh-catalyzed addition reactions of arylboronic acids with
carbonyl-containing compounds: (a) Glorius, F. Angew. Chem., Int. Ed. 2004, 43,
3364–3366; (b) Hayashi, T.; Yamasaki, K. Chem. Rev. 2003, 103, 2829–2844; (c)
Fagnou, K.; Lautens, M. Chem. Rev. 2003, 103, 169–196. and references cited
therein.
R
room temperature, 48 h
Entry
ArB(OH)2
Solvent
Yieldb (%)
O
R
H
4. Selected examples of Rh(I)-catalyzed 1,2-addition of arylboronic acids with
aldehydes: (a) Trindade, A. F.; Gois, P. M. P.; Veiros, L. F.; Andre, V.; Duarte, M.
T.; Afonso, C. A. M.; Caddick, S.; Cloke, F. G. N. J. Org. Chem. 2008, 73, 4076–
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Organomet. Chem. 2008, 693, 425–434; (c) Gois, P. M. P.; Trindade, A. F.; Veiros,
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Chem., Int. Ed. 2007, 46, 5750–5753; (d) Jagt, R. B. C.; Toullec, P. Y.; Schudde, E.
P.; De Vries, J. G.; Feringa, B. L.; Minnaard, A. J. J. Comb. Chem. 2007, 9, 407–414;
(e) Kilincarslan, R.; Yigit, M.; Ozdemir, I.; Cetinkaya, E.; Cetinkaya, B. J.
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Cetinkaya, B. Transition Metal Chem. 2007, 32, 536–540; (g) Arao, T.; Suzuki, K.;
Kondo, K.; Aoyama, T. Synthesis 2006, 3809–3814; (h) Yan, C.; Zeng, X.; Zhang,
W.; Luo, M. J. Organomet. Chem. 2006, 691, 3391–3396; (i) Suzuki, K.; Ishii, S.;
Kondo, K.; Aoyama, T. Synlett 2006, 648–650; (j) Ozdemir, I.; Yigit, M.;
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W.-J.; Zhang, Q.; Zhou, Q.-L. Org. Lett. 2006, 8, 1479–1481; (m) Jagt, R. B. C.;
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O
1
2
MeOH
THF
98c
86
B(OH)2
B(OH)2
Ph
Ph
H
H
O
O
O
O
O
3
4
THF
THF
THF
THF
THF
THF
THF
THF
THF
73
B(OH)2
Ph
Ph
Ph
Ph
H
H
H
H
80
MeO
B(OH)2
d
5
B(OH)2
OMe
e
6
B(OH)2
O
O
O
O
O
7
80
86
78
55
81f
B(OH)2
H
H
H
H
H
8
B(OH)2
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J.-P. J. Am. Chem. Soc. 2004, 126, 15356–15357.
9
MeO
B(OH)2
10
B(OH)2
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OMe
B(OH)2
11
a
Reaction conditions: aldehyde (1.0 equiv), arylboronic acid (3.0 equiv), solvent
(6 mL), K3PO4 (5 M aqueous solution, 6.0 equiv), room temperature.
b
Isolated yields.
c
Conversion based on 1H NMR.
d
A mixture of 1,2-addition allylic alcohol and 1,4-addition followed by 1,2-adi-
ition was observed, in a ratio of 0.67:1.
e
A mixture of 1,2-addition allylic alcohol and 1,4-addition followed by 1,2-
addition was observed, in a ratio of 4.6:1.
f
0.25% [Rh(COD)Cl]2 was used.
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Acknowledgments
We gratefully thank the NSF (CHE0719311) for funding. Partial
support from PSC-CUNY Research Award Program is also gratefully
acknowledged. We also thank Frontier Scientific, Inc. for its gener-
ous gifts of arylboronic acids.
10. For iron-catalyzed 1,2-addition of arylboronic acids with aldehydes: Zou, T.; Pi,
S.-S.; Li, J.-H. Org. Lett. 2009, 11, 453–456.
11. For recent examples of Rh(I)/diene-catalyzed Michael addition reactions of
Supplementary data
arylbornic acids with
a, b-unsaturated ketones/esters: (a) Soergel, S.;
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General procedure of Rh(I)/diene-catalyzed addition reactions
and characterizations of the reaction products are available. Sup-
plementary data associated with this article can be found, in the
online version, at doi:10.1016/j.tetlet.2009.06.074.

C.-H. Xing et al. / Tetrahedron Letters 50 (2009) 4953–4957
4957
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