Asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated aldehydes catalyzed by a chiral diene-rhodium complex

Article abstract of DOI:10.1246/cl.2005.1480

Asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated aldehydes proceeded in the presence of a rhodium catalyst (3 mol %) coordinated with a chiral diene ligand ((R,R)-Bn-bod*) to give the corresponding β-arylaldehydes with perfect 1,4-selectivi

Full text of DOI:10.1246/cl.2005.1480

1480
Chemistry Letters Vol.34, No.11 (2005)
Asymmetric 1,4-Addition of Arylboronic Acids to ꢀ,ꢁ-Unsaturated Aldehydes
Catalyzed by a Chiral Diene–Rhodium Complex
Tamio Hayashi,ꢀ Norihito Tokunaga, Kazuhiro Okamoto, and Ryo Shintani
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502
(Received August 25, 2005; CL-051096)
Asymmetric 1,4-addition of arylboronic acids to ꢀ,ꢁ-unsat-
urated aldehydes proceeded in the presence of a rhodium catalyst
(3 mol %) coordinated with a chiral diene ligand ((R,R)-Bn-
bodꢀ) to give the corresponding ꢁ-arylaldehydes with perfect
1,4-selectivity and with 88–97% enantioselectivity.
Table 1. Rhodium-catalyzed addition of phenylboronic acid
(2m) to 2-heptenal (1a)a
[RhCl(C H ) ] /L
(3 mol% Rh)
2
4 2 2
H
H
+ PhB(OH)
2
KOH (10 mol%)
O
Ph O
1a
2m
3am
O
O
Chiral diene ligands have found wide applications in catalyt-
ic asymmetric reactions, especially in rhodium-catalyzed car-
bon–carbon bond forming reactions.1,2 The chiral diene–rhodi-
um catalysts have been demonstrated to possess advantages over
the chiral phosphine–rhodium catalysts in that they have higher
catalytic activity as well as higher enantioselectivity in asym-
metric arylation of imines with arylboronic acids3 and in asym-
metric 1,4-addition to some ꢀ,ꢁ-unsaturated carbonyl com-
pounds.4 In the rhodium-catalyzed asymmetric addition of aryl-
boronic acids to alkynals and alkyne-enoates, the diene ligand
showed unique chemoselectivity leading to preferential forma-
tion of arylative cyclization products.5 On the other hand,
Miyaura reported in 20006 that the selectivity in giving 1,4-addi-
tion product or 1,2-addition product can be switched by a proper
choice of reaction conditions in rhodium-catalyzed addition of
phenylboronic acid to cinnamaldehyde (Scheme 1).7 It is signif-
icant that an exclusive 1,4-addition was realized in the presence
of a cationic rhodium catalyst coordinated with cod in aqueous
methanol as a solvent. Based on this report, we have studied
rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids
to ꢀ,ꢁ-unsaturated aldehydes by use of the chiral diene ligands.
The asymmetric 1,4-addition to enals has been reported8 to be
catalyzed by [Rh((R)-binap)(nbd)]BF4, but the selectivity giving
the 1,4-addition products is not high. A recent communication
by Carreira9 prompted us to report our own results.
P NEt
2
Ph
Ph
Ph
Ph
(R,R)-Bn-bod*
(R,R)-Bn-nbd*
(S)-phosphoramidite
Ligand
on Rh
codd,e
codd,e
codd.e
codd
Temp Time Yieldb
Entry
Solvent
% eec
/ꢁC
/h
/%
1
2
3
4
5
6
7
8
9
MeOH/THF/H2Of 30
Dioxane/H2Og
30
MeOH/THF/H2Of 10
MeOH/THF/H2Of 10
1
1
1
1
1
1
6
1
1
88
35
64
91
—
—
—
—
(R,R)-Bn-bodꢀ MeOH/THF/H2Of 30
(R,R)-Bn-nbdꢀ MeOH/THF/H2Of 30
(R,R)-Bn-bodꢀ MeOH/THF/H2Of 10
Phosphoramiditeh MeOH/THF/H2Of 30
85 90 (S)
82 89 (S)
88 93 (S)
58 26 (R)
(R)-binap
MeOH/THF/H2Of 30
<3i
—
aThe reaction was carried out with enal 1a (0.20 mmol), arylboronic acid
2m (0.40 mmol), KOH (0.02 mmol), [RhCl(C2H4)2]2 (0.0060 mmol Rh),
and a ligand (0.0066 mmol) unless otherwise noted. bIsolated yield after
silica gel chromatography. cDetermined by HPLC analysis with a chiral
stationary phase column (Chiralpak AS) after reduction into 3-phenyl-
e
f
heptanol. d[Rh(OH)(cod)]2 was used. In the absence of KOH. The ratio
is 12/3/2. gThe ratio is 10/1. h0.0132 mmol. iStarting enone 1a was recov-
ered in a high yield.
is a solvent system often used for rhodium-catalyzed 1,4-addi-
tion reactions.10 The 1,4-addition catalyzed by [Rh(OH)(cod)]2
was found to be accelerated by addition of a catalytic amount
(10 mol %) of potassium hydroxide (Entries 3 and 4). Confirm-
ing that a rhodium/diene complex catalyzes the selective 1,4-
Ph
H
[Rh(cod)(MeCN)2]BF4 (3 mol%)
Ph
H
MeOH/H2O (6/1), 25 °C
Ph
1,4-addition
Ph Ph
O
O
+
1b
addition to enal, chiral diene ligands (R,R)-Bn-bodꢀ and Bn-
Rh(acac)(coe)2/t-Bu3P (3 mol%)
DME/H2O (3/2), 25 °C
PhB(OH)2
nbdꢀ1a were examined for their enantioselectivity. In the reaction
at 30 ꢁC, both of the two dienes gave (S)-3am with around 90%
ee (Entries 5 and 6). The best result was obtained in the reaction
with (R,R)-Bn-bodꢀ at 10 ꢁC, which gave 88% yield of (S)-3am
with 93% ee11,12 (Entry 7). Under otherwise the same reaction
conditions, the rhodium complexes of a phosphoramidite13 and
binap14 did not catalyze the asymmetric 1,4-addition efficiently
(Entries 8 and 9).
OH
1,2-addition
Scheme 1. 1,4-Addition vs 1,2-addition reported by Miyaura.
In the first set of experiment, addition of phenylboronic acid
(2m) to 2-heptenal (1a) was examined under several reaction
conditions (Table 1). The 1,4-addition giving 3-phenylheptanal
(3am) proceeded smoothly in the presence of 3 mol % of
[Rh(OH)(cod)]2 in a mixed solvent consisting of MeOH/THF/
H2O (12/3/2) at 30 ꢁC (Entry 1). This is in good agreement with
the Miyaura’s report6 that the 1,4-addition takes place in the
presence of a rhodium/diene catalyst in aqueous methanol. A
lower yield of the 1,4-addition product 3am was observed in
the reaction carried out in dioxane/H2O (10/1) (Entry 2), which
As illustrated in Table 2, the present asymmetric 1,4-addi-
tion is applicable to a broad range of arylboronic acids and
ꢀ,ꢁ-unsaturated aldehydes. In the presence of 3 mol % of the
rhodium/(R,R)-Bn-bodꢀ catalyst, 2-heptenal (1a) underwent
the addition of a variety of arylboronic acids (Entries 2–5).
Phenylboronic acids substituted with 4-methoxy, 4-chloro, and
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.11 (2005)
1481
Table 2. Asymmetric 1,4-addition of arylboronic acids 2 to
enals 1 catalyzed by Rh/(R,R)-Bn-bodꢀa
a 3,3-diarylpropanal ((R)-3cn and (S)-3dm) were readily ob-
tained by varying the combination for a single enantiomer of
the chiral diene ligand (R,R)-Bn-bodꢀ (see Entries 7 and 9).
In summary, we have shown that asymmetric 1,4-addition of
arylboronic acids to ꢀ,ꢁ-unsaturated aldehydes is efficiently
catalyzed by a rhodium complex coordinated with a chiral diene
ligand.
[RhCl(C H ) ] (3 mol% Rh)
(R,R)-Bn-bod* (3.3 mol%)
2
4 2 2
R
H
R
H
+ ArB(OH)
2
KOH (10 mol%)
O
Ar
O
MeOH/THF/H O (12/3/2)
2
1
2
3
10 °C, 6 h
1a: R = n-Bu
1b: R = i-Pr
1c: R = Ph
1d: R = 4-MeOC H 2p: Ar = 2-MeC H
1e: R = 2-MeOC H 2q: Ar = 2-naphthyl
2m: Ar = Ph
2n: Ar = 4-MeOC H
6
4
4
This work was partially supported by a Grant-in-Aid for
Scientific Research, the Ministry of Education, Culture, Sports,
Science and Technology, Japan. N. T. thanks the Japan Society
for the Promotion of Science for the award of a fellowship for
graduate students.
2o: Ar = 4-ClC H
6
4
6
4
6
4
6
4
1f: R = 4-NO C H
2r: Ar = 4-FC H
2
6
4
6 4
(R,R)-Bn-bod*
2q: Ar = 2-MeOC H
6
References and Notes
H
H
O
H
H
1
2
3
a) T. Hayashi, K. Ueyama, N. Tokunaga, and K. Yoshida,
J. Am. Chem. Soc., 125, 11508 (2003). b) Y. Otomaru, K.
Okamoto, R. Shintani, and T. Hayashi, J. Org. Chem., 70,
2503 (2005). c) Y. Otomaru, A. Kina, R. Shintani, and T.
Hayashi, Tetrahedron: Asymmetry, 16, 1673 (2005).
a) C. Fischer, C. Defieber, T. Suzuki, and E. M. Carreira,
J. Am. Chem. Soc., 126, 1628 (2004). b) C. Defieber, J.-F.
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(2004). c) F. Lang, F. Breher, D. Stein, and H. Grutzmacher,
¨
Organometallics, 24, 2997 (2005).
a) N. Tokunaga, Y. Otomaru, K. Okamoto, K. Ueyama, R.
Shintani, and T. Hayashi, J. Am. Chem. Soc., 126, 13584
(2004). b) Y. Otomaru, N. Tokunaga, R. Shintani, and T.
Hayashi, Org. Lett., 7, 307 (2005).
Ar
O
O
O
(S)-3am-3aq
(R)-3bm
(R)-3cn
(R)-3cr
F
OMe
MeO
O N
2
H
H
H
O
MeO
O
O
¨
(S)-3dm
R in
Enal 1
n-Bu (1a)
(S)-3em
(S)-3fm
Ar in
ArB(OH)2
Yieldb
/%
Entry
% eec
2
1
2
Ph (2m)
88 (3am) 93 (S)
94 (3an) 88 (S)
88 (3ao) 97 (S)
95 (3ap) 90 (S)
90 (3aq) 88 (S)
83 (3bm) 92 (R)
88 (3cn) 90 (R)
84 (3cr) 90 (R)
86 (3dm)e 90 (S)
93 (3em) 90 (S)
92 (3fm) 91 (S)
4
5
a) R. Shintani, K. Ueyama, I. Yamada, and T. Hayashi, Org.
Lett., 6, 3425 (2004). b) R. Shintani, T. Kimura, and T.
Hayashi, Chem. Commun., 2005, 3213.
a) R. Shintani, K. Okamoto, Y. Otomaru, K. Ueyama, and T.
Hayashi, J. Am. Chem. Soc., 127, 54 (2005). b) R. Shintani, A.
Tsurusaki, K. Okamoto, and T. Hayashi, Angew. Chem., Int.
Ed., 44, 3909 (2005).
n-Bu (1a)
n-Bu (1a)
n-Bu (1a)
n-Bu (1a)
i-Pr (1b)
Ph (1c)
4-MeOC6H4 (2n)
4-ClC6H4 (2o)
2-MeC6H4 (2p)
2-naphthyl (2q)
Ph (2m)
3
4
5
6d
7
4-MeOC6H4 (2n)
4-FC6H4 (2r)
Ph (2m)
8
Ph (1c)
9
4-MeOC6H4 (1d)
2-MeOC6H4 (1e)
4-NO2C6H4 (1f)
6
7
M. Ueda and N. Miyaura, J. Org. Chem., 65, 4450 (2000).
Rhodium-catalyzed 1,4-addition to enals has been also
reported with organotin reagents: S. Oi, M. Moro, H. Ito,
Y. Honma, S. Miyano, and Y. Inoue, Tetrahedron, 58, 91
(2002).
10
11f
Ph (2m)
Ph (2m)
aThe reaction was carried out at 10 ꢁC for 6 h with enal 1 (0.20 mmol),
arylboronic acid 2 (0.40 mmol), KOH (0.02 mmol), [RhCl(C2H4)2]2
(0.0060 mmol Rh), and (R,R)-Bn-bodꢀ (0.0066 mmol) in a mixed
solvent consisting of MeOH (0.60 mL), THF (0.15 mL), and H2O
(0.10 mL). bIsolated yield after silica gel chromatography. cDetermined
by HPLC analysis with a chiral stationary phase column after reduction
into alcohols (See Supporting Information). dReaction with 0.80 mmol
of PhB(OH)2. eEnantiomer of 3cn. fFor 3 h.
8
9
R. Itooka, Y. Iguchi, and N. Miyaura, J. Org. Chem., 68, 6000
(2003).
J.-F. Paquin, C. Defieber, C. R. J. Stephenson, and E. M.
Carreira, J. Am. Chem. Soc., 127, 10850 (2005).
10 T. Hayashi and K. Yamasaki, Chem. Rev., 103, 2829 (2003).
20
20
11 ½ꢀꢂ D þ10:7 (c 2.2, benzene). Meyers reported ½ꢀꢂ D þ10:7
(c 2.0, benzene) for (S)-3am of 97% ee: A. I. Meyers and M.
Shipman, J. Org. Chem., 56, 7098 (1991).
2-methyl, all gave high yields of the corresponding (S)-3-aryl-
heptanals with high enantioselectivity. Asymmetric addition to
4-methyl-2-pentenal (1b) proceeded as well, giving (R)-3bm15
of 92% ee (Entry 6). Asymmetric synthesis of 3,3-diarylpropa-
nals is also possible by the rhodium-catalyzed 1,4-addition of
arylboronic acids to 3-arylpropenals (1c–1f). Thus, the reaction
of cinnamaldehyde (1c) with both electron-rich boronic acid
[4-MeOC6H4B(OH)2 2n] and electron-poor boronic acid [4-
FC6H4B(OH)2 2r] proceeded smoothly to give the correspond-
ing 3-phenyl-3-(substituted phenyl)propanals with 90% ee
(Entries 7 and 8). The chiral 3,3-diarylpropanals of around
90% ee were also obtained by the other combination, that is,
the addition of phenylboronic acid (2m) to 3-(substituted
phenyl)propenals (1d–1f) (Entries 9–11). Both enantiomers of
12 The enantiomeric excess was determined by HPLC analysis
with a chiral stationary phase column (Chiralpak AS,
hexane/2-propanol ¼ 98=2) after reduction with NaBH4 into
3-phenylheptanol.
13 J.-G. Boiteau, A. J. Minnaard, and B. L. Feringa, J. Org.
Chem., 68, 9481 (2003).
14 H. Takaya, K. Mashima, K. Koyano, M. Yagi, H.
Kumobayashi, T. Taketomi, S. Akutagawa, and R. Noyori,
J. Org. Chem., 51, 629 (1986).
20
20
15 ½ꢀꢂ
ꢃ14:2 (c 1.4, dichloromethane). Fu reported ½ꢀꢂ
D
D
ꢃ17:3 (c 1.38, dichloromethane) for (R)-3bm of 93% ee:
K. Tanaka and G. C. Fu, J. Org. Chem., 66, 8177 (2001).
Published on the web (Advance View) September 28, 2005; DOI 10.1246/cl.2005.1480