Chiral bis-phosphoramidites based on linked-BINOL for rhodium-catalyzed 1,4-addition of arylboronic acids to α,β-unsaturated carbonyl compounds

Article abstract of DOI:10.1246/cl.2005.1224

Cationic rhodium(I) complex prepared from Shibasaki's linked-BINOL and [Rh(nbd)₂]BF₄ catalyzed asymmetric 1,4-addition of arylboronic acids to enones at room temperature with high enantioselectivities up to 99.8%ee. Copyright

Full text of DOI:10.1246/cl.2005.1224

1
224
Chemistry Letters Vol.34, No.9 (2005)
Chiral Bis-phosphoramidites Based on Linked-BINOL for Rhodium-catalyzed 1,4-Addition
of Arylboronic Acids to ꢀ,ꢁ-Unsaturated Carbonyl Compounds
Yasunori Yamamoto, Kazunori Kurihara, Noriyuki Sugishita, Kengo Oshita,
ꢀ
Dongguo Piao, and Norio Miyaura
Division of Chemical Process Engineering, Graduate School of Engineering, Hokkaido University,
Sapporo 060-8628
(Received June 24, 2005; CL-050815)
Cationic rhodium(I) complex prepared from Shibasaki’s
B(OH)2
R1
linked-BINOL and [Rh(nbd)2]BF4 catalyzed asymmetric 1,4-ad-
dition of arylboronic acids to enones at room temperature with
high enantioselectivities up to 99.8%ee.
FG
Rh(nbd)2]BF4/4a
FG
R1
R2
R3
R3
[
R2
O
3 2
Et N, dioxane–H O (6/1)
O
Scheme 2. Asymmetric 1,4-addition catalyzed by [Rh(I)/
a]BF4.
4
Metal-catalyzed conjugate addition reactions of carbon nu-
cleophiles to ꢀ,ꢁ-unsaturated compounds are the most widely
used method for asymmetric carbon–carbon bond formation.
A mixture of P(NMe2)3 or P(NEt2)3 and a (R,R)-O-linked-
1
BINOL13 was refluxed in toluene in the presence of a catalytic
amount of NH4Cl to give bisphosphoroamidite 4a (74%) and
2
3
4
The reactions catalyzed by copper, rhodium, and palladium
1
4
complexes are of great value for asymmetric syntheses because
of the availability of chiral ligands. Rhodium(I)–binap catalysts
were found to be excellent catalysts for 1,4-addition reactions of
4b (56%). N,N-Diisopropyl derivative (4c) was obtained in
11% yield by chlorophosphonylation–amidation of the linked-
1
2c
BINOL. The reaction of 4a with [Rh(nbd)2]BF4 in CD2Cl2
3
,5
31
aryl- and 1-alkenylboronic acids to electron-deficient alkenes.
Other catalysts that are effective for arylboronic acids are rho-
gave desired [Rh(4a)(nbd)]BF4 (5a). P NMR exhibited a single
signal at 142.4 ppm (d, JRh{P ¼ 248:9 Hz), thus suggesting the
intramolecular complexation of two phosphorous atoms to a rho-
dium metal center (Scheme 1). The formation of a 1:1 complex
was also confirmed by mass spectroscopy (FAB), which showed
6
dium(I) complexes of mono-phosphoramidites, chiral P–P li-
8
7
gands such as chiraphos and diphosphonites, P–N ligands of
9
amidomonophosphines, bis(alkene) ligands based on a norbor-
nadiene skeleton,10 and carbene ligands derived from biscyclo-
þ
a molecular weight of 955.1938 (M ꢁ BF4).
1
1
phane imidazolium salts. Among these chiral auxiliaries for
metal-catalyzed conjugate additions, phosphoramidites devel-
The performance of these ligands for asymmetric syntheses
was demonstrated by rhodium-catalyzed 1,4-addition of arylbor-
onic acids to unsaturated carbonyl compounds. The effects of
rhodium catalysts and bases in the reaction of 2-cyclohexenone
and phenylboronic acid in aqueous 1,4-dioxane are shown in
Table 1.
6
,12
oped by Feringa (1 and 2),
are the only ligands for which
monodentate form exhibit high enantioselectivity for a large
number of asymmetric transformations, including rhodium-cata-
lyzed 1,4-addition of organoboron compounds, though the effi-
1
2a
ciency of a bidentate ligand (3) was reported in copper-cata-
lyzed addition of diethylzinc to cyclic enones (Scheme 1).
Herein we report bidentate bisphosphoramidites 4 newly
The catalysts were prepared by mixing a rhodium precursor
and 10% excess of 4 since it resulted in yields and enantioselec-
tivities that were the same as those of isolated complexes. The
neutral complex thus prepared from [RhCl(coe)]2 and 4a did
not catalyze the reaction (Entry 1), but the reaction smoothly
took place in the presence of KOH, as was previously demon-
strated in analogous conjugated addition catalyzed by neutral
Rh(I)–phosphine complexes (Entries 2 and 3). A dramatic
rate-acceleration resulting in completion within 0.5 h at room
temperature was found when [Rh(nbd)2]BF4 and 4a were used
1
3
synthesized based on Shibasaki’s linked-BINOL. 4a was found
to be highly effective for the rhodium-catalyzed 1,4-addition of
arylboronic acids to ꢀ,ꢁ-unsaturated carbonyl compounds
(
Scheme 2). Both mono- and bisphosphoramidites resulted in ex-
cellent enantioselectivities for cyclic carbonyl compounds; how-
ever, the use of the rigid bidentate ligand was critical to achieve
high enantioselectivity for flexible acyclic substrates.
5
c
in the presence of Et3N (Entries 4 and 5). Use of the cationic
Table 1. Reaction Conditionsa
R1
R1
O
O
O
O
O
O
P N
P N
P N
N P
ꢂ
R2
R2
Entry
Rhodium complex
Base
C/h
Yield/%
%ee
O
R R
O
1
2
3
4
5
6
7
1/2[RhCl(coe)]2/4a none
1/2[RhCl(coe)] /4a Et N
50/16
50/16
0
46
—
1
2
3
97 (R)
98 (R)
99 (R)
99.6 (R)
83 (R)
—
2
3
1/2[RhCl(coe)]2/4a KOH 50/16
84
O
O
[Rh(nbd)2]BF4/4a
[Rh(nbd)2]BF4/4a
[Rh(nbd)2]BF4/4b
[Rh(nbd)2]BF4/4c
Et3N
Et3N
Et3N
Et3N
50/16
25/0.5
25/2
94
OH HO
OH HO
a or b
O
O
99
P
P
O
R R
O
N
N
62
R
R
25/2
trace
a) P(NMe2)3 or P(NEt2)3, NH4Cl, toluene (for 4a, 4b).
b) 1. PCl3, NEt3, toluene, –60 °C. 2. i-Pr2NH, n-BuLi,
40 °C (for 4c).
4a: R = Me
4b: R = Et
4c: R = i-Pr
aAll reactions were carried out in the presence of 2-cyclohexenone (1
–
mmol), phenylboronic acid (1.5 mmol), rhodium(I) catalyst (3 mol %),
ligand (3.3 mol %), and base (if used, 1 mmol) in dioxane–H2O (6/1).
Scheme 1. Phosphoramidites for asymmetric 1,4-addition.
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.9 (2005)
1225
1
Table 2. 1,4-Addition of arylboronic acid to ꢀ,ꢁ-unsaturated
carbonyl compounds
hindered substituent (R = isopropyl and phenyl) reduced the
3
a
selectivity by increasing the bulkiness of R groups (CH3 >
Ph > cyclohexyl) (Entries 13, 15, 16, 18, and 19).
ArB(OH)2, Temp Yield
Entry
Carbonyl compound
%eec
X=
3-Cl
/h
%b
References
1
1
2
3
4
5
6
7
8
9
2-Cyclopentenone
25/2
99 96
a) N. Krause and A. Hoffmann-R o¨ der, Synthesis, 2001, 171.
b) K. Tomioka and Y. Nagaoka, in ‘‘Comprehensive Asym-
metric Catalysis,’’ ed. by E. N. Jacobsen, A. Pfalts, and
H. Yamamoto, Springer-Verlag, Berlin (1999), Chap. 31.1.
a) A. Alexakis and C. Benhaim, Eur. J. Org. Chem., 2002,
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Rev., 103, 169 (2003). c) T. Hayashi, Pure Appl. Chem., 76,
2-Cyclohexenone
H
25/0.5 99 99.6 (R)
2-Cyclohexenone
3-MeO
4-MeO
3-Cl
H
25/2
25/2
25/2
25/2
25/2
90 99.5 (R)
99 99.8
86 99.8
90 98
2-Cyclohexenone
2-Cyclohexenone
2-Cycloheptenone
2
3
(E)-C5H11CH=CHCOCH3
(E)-C5H11CH=CHCOCH3
(E)-C5H11CH=CHCOCH3
(E)-C5H11CH=CHCOCH3
(E)-C5H11CH=CHCOPh
(E)-(CH3)2CHCH=CHCOCH3
H
87 74
H
5/48 42 84
3-MeO
3-F
25/2
25/2
25/2
25/6
98 80
1
1
1
1
1
1
1
1
1
1
2
2
2
2
0
1
2
3
4
5
6
97 81
3-MeO
H
91 85
4
65 (2004).
80 92 (R)
4
a) T. Nishikata, Y. Yamamoto, and N. Miyaura, Angew.
Chem., Int. Ed., 42, 2768 (2003). b) T. Nishikata, Y.
Yamamoto, and N. Miyaura, Chem. Lett., 32, 752 (2003).
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mun., 2004, 1822. d) T. Nishikata, Y. Yamamoto, and N.
Miyaura, Organometallics, 23, 4317 (2004). e) T. Nishikata,
Y. Yamamoto, and N. Miyaura, Chem. Lett., 34, 721 (2005).
a) Y. Takaya, M. Ogasawara, T. Hayashi, M. Sakai, and
N. Miyaura, J. Am. Chem. Soc., 120, 5579 (1998). b) T.
Hayashi, M. Takahashi, Y. Tkaya, and M. Ogasawara,
J. Am. Chem. Soc., 124, 5052 (2002). c) R. Itooka, Y. Iguchi,
and N. Miyaura, J. Org. Chem., 68, 6000 (2003).
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Org. Lett., 5, 681 (2003). c) A. Duursma, R. Hoen, J.
Schuppan, R. Hulst, A. J. Minnard, and B. L. Feringa, Org.
Lett., 5, 3111 (2003). d) J.-G. Boiteau, A. J. Minnard,
and B. L. Feringa, J. Org. Chem., 68, 9481 (2003). e) A.
Duursma, J.-G. Boiteau, L. Lefort, J. A. F. Boorgers,
A. H. M. de Vries, J. G. de Vries, A. J. Minnard, and B. L.
Feringa, J. Org. Chem., 69, 8045 (2004).
(E)-(CH3)2CHCH=CHCOCH3 3-MeO
(E)-(CH3)2CHCH=CHCOCH3 3-F
(E)-(CH3)2CHCH=CHCOC6H11 3-MeO
25/16 78 94
25/16 71 90
25/2
25/6
62 81
98 85
(E)-(CH3)2CHCH=CHCOPh
3-MeO
7d (E)-cyclo-C6H11CH=CHCOCH3 3-MeO
25/10 81 86
8
9
0
1
2
3
(E)-PhCH=CHCOCH3
(E)-PhCH=CHCOPh
3-MeO
3-MeO
25/2
25/6
25/3
99 78
98 66
93 89
5
6
(E)-2-NaphthylCH=CHCOCH3 3-MeO
(E)-CH3CH=CHCO2CH3
5H-Furan-2-one
3-MeO
3-MeO
3-MeO
25/24 57 75
25/6 68 77
25/12 61 91
5,6-Dihydro-2H-pyran-2-one
aAll reactions were carried out in the presence of enone (1 mmol), arylboron-
ic acid (1.5 mmol), [Rh(nbd)2]BF4 (0.03 mmol, 3 mol %), 4a (0.033 mmol)
b
and Et3N (1 mmol) in dioxane (2.6 mL) and H2O (0.43 mL). Isolated yields.
c
d
Enantiomer excess determined by a chiral stationary column. Arylboronic
acid (2.5 mmol) was used.
catalyst [Rh(nbd)2]BF4/4a resulted in higher enantioselectivi-
ties than [RhCl(coe)]2/4a. The mildness of Et3N to common
functional groups is also advantageous over the former combina-
tion using KOH. On the other hand, N,N-diethyl and N,N-diiso-
propyl derivatives (4b and 4c) were not effective (Entries 6 and
7
8
P. Mauleon and J. C. Carretero, Org. Lett., 6, 3195 (2004).
M. T. Reetz, D. Moulin, and A. Gosberg, Org. Lett., 3, 4083
(2001).
M. Kuriyama, K. Nagai, K. Yamada, Y. Miwa, T. Taga, and
K. Tomioka, J. Am. Chem. Soc., 124, 8932 (2002).
31
7
). P NMR spectrum of a mixture of [Rh(nbd)2]BF4 and 4b
gave a single signal (142.3 ppm, d, JRh{P ¼ 248:9 Hz) analogous
31
to 5a, but 4c did not provide a single complex. P NMR exhib-
ited several signals at 24.8, 111.0, and 134.1 ppm, presumably
due to intra- and intermolecular coordination of two phosphine
atoms.
9
10 a) T. Hayashi, K. Ueyama, N. Tokunaga, and K. Yoshida,
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Lett., 6, 3873 (2004).
With these optimized conditions, the scope of the catalyst
[
Rh(nbd)2]BF4/4a was investigated using representative aryl-
boronic acids and ꢀ,ꢁ-unsaturated carbonyl compounds (Table
). There was no difficulty in obtaining high chemical yields
2
and high enantioselectivities for cyclic enones within 2 h at room
temperature (Entries 1–6). These selectivities were comparable
to or even higher than those of previously reported mono-phos-
11 Y. Ma, C. Song, C. Ma, Z. Sun, Q. Chai, and M. B. Andrus,
Angew. Chem., Int. Ed., 42, 5871 (2003).
12 a) A. H. M. de Vries, A. Meetsma, and B. L. Feringa, Angw.
Chem., Int. Ed., 35, 2374 (1996). b) B. L. Feringa, M.
Pineschi, L. A. Arnold, R. Imbos, and A. H. M. de Vries,
Angew. Chem., Int. Ed., 36, 2620 (1997). c) L. A. Arnold,
R. Imbos, A. Mandoli, A. H. M. de Vries, R. Naasz, and
B. L. Feringa, Tetrahedron, 56, 2865 (2000).
13 S. Matsunaga, J. Das, J. Roels, E. M. Vogl, N. Yamamoto,
T. Iida, K. Yamaguchi, and M. Shibasaki, J. Am. Chem.
Soc., 122, 2252 (2000).
5
–11
phoramidites 1 or bisphosphine ligands.
The enantioselectivities for acyclic (E)-enones were de-
1
pendent on the ꢁ-substituent (R ) and a substituent on ketone
3
1
carbonyls (R ). The effect of R increased in the order of
Ph < n-C5H11 < cyclohexyl ꢃ 2-naphthyl < isopropyl for a
series of methyl ketones (Entries 9, 13, 17, 18, and 20). Steric
1
3
balance between R and R also can be an important factor af-
fecting on the selectivity. The selectivities were improved by
3
increasing the bulkiness of R for enones having a primary alkyl
group at the ꢁ-carbon (Entries 9 and 11), but those possessing a
14 R. Hulst, N. K. de Vries, and B. L. Feringa, Tetrahedron:
Asymmetry, 5, 699 (1996).
Published on the web (Advance View) July 30, 2005; DOI 10.1246/cl.2005.1224