Development of a hemilabile P-P=O ligand based on the concept of conformational control

Article abstract of DOI:10.1055/s-2006-932458

Development of a new hemilabile P-P=O ligand based on the concept of conformational control is described. In Rh-catalyzed enantioselective phenylation of aromatic aldehydes with phenylboronic acid, MOD-DIOP monophosphine oxide is shown to function as a good ligand. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-932458

6
48
LETTER
Development of a Hemilabile P–P=O Ligand Based on the Concept of
Conformational Control
D
K
evelopment of
a
i
Hemila
y
bile P–P=O
oL igand to Suzuki, Satoru Ishii, Kazuhiro Kondo,* Toyohiko Aoyama*
Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan
Fax +81(52)8363439; E-mail: kazuk@phar.nagoya-cu.ac.jp; E-mail: aoyama@phar.nagoya-cu.ac.jp
Received 5 December 2005
9
optimize reaction conditions with MOD–DIOP, bis-
phosphine 4, as the precursor of hemilabile P–P=O ligand
Abstract: Development of a new hemilabile P–P=O ligand based
on the concept of conformational control is described. In Rh-cata-
lyzed enantioselective phenylation of aromatic aldehydes with
1
. Since hemilabile P–P=O ligand 1 was found to be very
phenylboronic acid, MOD-DIOP monophosphine oxide is shown to easily oxidized to bis-phosphineoxide 5 under air, it was
function as a good ligand.
decided that 1 was to be produced in situ with a Rh(III)
complex. After intensive screening of reaction conditions,
Key words: hemilabile chiral ligands, asymmetric arylation, opti-
cally active diarylmethanol, rhodium catalysts, boronic acid
10
the use of 2.0 equivalents of NaOt-Bu as base and
11
DME–H O (5:1) as solvent was found to be the most
2
effective combination, which gave 3 in 97% yield and
1
2
13
7
5% ee (Scheme 2). Charette’s bozphos 6 and BINAP
We have recently been developing a novel chiral phos-
phine ligand and an N-heterocyclic carbene ligand based
on the concept of conformational control. In order to ex-
14
monooxide 7 gave less-satisfactory results (6: 27%
yield, 21% ee; 7: no reaction).
1
pand the scope of our concept, we planned to develop
2
novel hemilabile P–P=O ligand 1 with both soft and hard
HO
Ph
CHO
*
coordinated centers within one molecule. Figure 1 shows
the possible design of a novel hemilabile ligand 1, such
that the soft Ar P group coordinates with a soft metal and
the hard Ar P=O group coordinates with a hard metal.
Rh(I)–MeO–MOP (cat)
PhB(OH)2
2
2
3: 41% ee
2
These two coordinations allow a fixed conformation of
the complex between hemilabile ligand 1 and metals (soft
and hard), leading to the creation of a favorable asym-
metric environment.
Scheme 1 Asymmetric phenylation by Miyaura
O
PAr2
PAr2
O
Ar2
O
O
PAr2
O
O
P
soft metal
hard metal
4: Ar =
OMe (3 mol%)
PAr2
O
PAr2
O
RhCl3·3H2O (3 mol%)
NaOt-Bu (2.0 mol equiv)
DME–H2O (5:1), 100 °C
1: Ar =
OMe
Figure 1 Possible design
O
O
PAr2
PAr2
O
1
We were interested in applying a novel hemilabile ligand
2
3
3
1
to Rh-catalyzed asymmetric phenylation of aromatic
PhB(OH)2 (2.0 mol equiv)
9
5% yield (75% ee)
aldehydes with phenylboronic acids, because no success-
ful example for this Rh-catalyzed asymmetric phenylation
O
Me
4
of aromatic aldehydes has been reported, although highly
O
O
PAr2
P
P
Me
PPh2
O
successful Rh-catalyzed asymmetric 1,4-conjugate addi-
PAr2
O
PPh2
Me
5
tion to electron-deficient alkenes and addition to tuned
5
Me
O
6
7
6
imines have been reported.
4
a
7
Scheme 2
Miyaura has reported Rh–MOP -catalyzed asymmetric
phenylation of 1-naphthaldehyde (2) with phenylboronic
acid, giving (1-naphthyl)phenylmethanol (3) in 41% ee Having established the best conditions, we examined the
8
1,5,16
(
Scheme 1). We first chose 2 as a substrate and began to reaction of several aromatic aldehydes 8.
The results
are shown in Table 1. The 4- and 3-substituted aromatic
aldehyde was found to be employable, giving the corre-
sponding products 9 in good enantioselectivities (up to
SYNLETT 2006, No. 4, pp 0648–0650
Advanced online publication: 20.02.2006
DOI: 10.1055/s-2006-932458; Art ID: U30805ST
0
3.
0
2.
2
0
0
6
8
5% ee). The results are, to the best of our knowledge, the
©
Georg Thieme Verlag Stuttgart · New York

LETTER
Development of a Hemilabile P–P=O Ligand
649
Table 1 Substrate Generalitya
References and Notes
4
(1) (a) Kondo, K.; Kazuta, K.; Fujita, H.; Sakamoto, Y.;
RhCl3·3H2O (3 mol%)
NaOt-Bu (2.0 mol equiv)
DME–H2O (5:1), 100 °C
Murakami, Y. Tetrahedron 2002, 58, 5209. (b) Horibe, H.;
Kazuta, K.; Kotoku, M.; Kondo, K.; Okuno, H.; Murakami,
Y.; Aoyama, T. Synlett 2003, 2047. (c) Horibe, H.; Fukuda,
Y.; Kondo, K.; Okuno, H.; Murakami, Y.; Aoyama, T.
Tetrahedron 2004, 60, 10701. (d) Arao, T.; Kondo, K.;
Aoyama, T. Tetrahedron Lett. 2006, 47, 1417.
O
O
PAr2
PAr2
OH
Ph
O
1
(2) For a review of hemilabile ligands, see: Grushin, V. V.
Chem. Rev. 2004, 104, 1629.
(3) Successful examples for asymmetric arylation of aromatic
aldehyde with other metal catalysts: (a) Bolm, C.; Rudolph,
J. J. Am. Chem. Soc. 2002, 124, 14850. (b) Tomita, D.;
Wada, R.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc. 2005,
Ar'–CHO
PhB(OH)2 (2.0 mol equiv)
Ar'
8
9
Entry
Ar¢
Yield of 9 ee of 9
Absolute
configuration
b
(
%)
(%)
67
79
85
76
70
127, 4138. (c) Qin, Y.-C.; Pu, L. Angew. Chem. Int. Ed.
1
2
3
4
2-Naphthyl
4-Me-C H -
94
95
90
97
90
R
2006, 45, 273.
(
(
4) (a) Sakai, M.; Ueda, M.; Miyaura, N. Angew. Chem. Int. Ed.
998, 37, 3279. (b) Moreau, C.; Hague, C.; Weller, A. S.;
R
6
4
1
4-MeO-C H -
R
Frost, C. G. Tetrahedron Lett. 2001, 42, 6957. (c) Focken,
T.; Rudolph, J.; Bolm, C. Synthesis 2005, 429. (d) Suzuki,
K.; Kondo, K.; Aoyama, T. Synthesis in press.
6
4
4-F-C H -
R
6
4
5) (a) Takaya, Y.; Ogasawara, M.; Hayashi, T.; Sakai, M.;
Miyaura, N. J. Am. Chem. Soc. 1998, 120, 5579.
5
3-MeO-C H -
Ndc
6
4
a
(b) Hayashi, T.; Senda, T.; Ogasawara, M. J. Am. Chem. Soc.
The reactions were performed using aromatic aldehydes 8, 3 mol%
of RhCl ·3H O and (R,R)-MOD–DIOP, and 2 equiv of PhB(OH) and
2000, 122, 10716. (c) Kuriyama, M.; Tomioka, K.
3
2
2
Tetrahedron Lett. 2001, 42, 921. (d) Reetz, M. T.; Moulin,
D.; Gosberg, A. Org. Lett. 2001, 3, 4083. (e)Amengual, R.;
Michelet, V.; Genêt, J.-P. Synlett 2002, 1791. (f) Yoshida,
K.; Ogasawara, M.; Hayashi, T. J. Am. Chem. Soc. 2002,
NaOt-Bu in DME–H O (5:1) at 100 °C for 72 h.
2
b
Determined by HPLC.
c
Not determined.
1
24, 10984. (g) Ma, Y.; Song, C.; Ma, C.; Sun, Z.; Chai, Q.;
Andrus, M. B. Angew. Chem. Int. Ed. 2003, 42, 5871.
h) Hayashi, T.; Ueyama, K.; Tokunaga, N.; Yoshida, K. J.
Am. Chem. Soc. 2003, 125, 11508. (i) Mauleón, P.;
Carretero, J. C. Org. Lett. 2004, 6, 3195. (j) Shintani, R.;
Ueyama, K.; Yamada, I.; Hayashi, T. Org. Lett. 2004, 6,
3425.
best enantioselectivity in the reported literature for Rh-
catalyzed phenylation of aromatic aldehydes. Based on
the working model depicted in Figure 1, the transition
state of transmetalation in the present system can be
(
1
7,18
assumed as shown in Figure 2.
(
6) (a) Kuriyama, M.; Soeta, T.; Hao, X.; Chen, Q.; Tomioka, K.
J. Am. Chem. Soc. 2004, 126, 8128. (b) Tokunaga, N.;
Otomaru, Y.; Okamoto, K.; Ueyama, K.; Shintani, R.;
Hayahshi, T. J. Am. Chem. Soc. 2004, 126, 13584.
H
Ar
Ar
P
Rh
O
Ar′
O
H
X
(7) Uozumi, Y.; Hayashi, T. J. Am. Chem. Soc. 1991, 94, 6429.
O
H
–
(8) Miyaura has reported that DIOP and BINAP were not
B
Na+ (OH)3
effective ligands (0% enantioselectivity) in this arylation.
4a
P
O
Ar
(
9) Morimoto, T.; Chiba, M.; Achiwa, K. Tetrahedron Lett.
Ar
1989, 30, 735.
Figure 2 Plausible transition state of transmetalation
(10) Other bases such as NaOH, KOH, NaOMe, CsOH, KOt-Bu,
Na CO , Cs CO , LiOH and RbOH gave less-satisfactory
2
3
2
3
results.
In summary, we have reported development of a new
hemilabile P–P=O ligand based on the concept of confor-
mational control, which opens the possibility of synthe-
sizing a new class of asymmetric catalysis. Further
application to other catalytic asymmetric reactions is now
in progress.
(
11) Other solvents such as toluene, PrOH and dioxane gave less-
satisfactory results.
+
(12) Only a fragment of mono-phosphineoxide Na 10 in the
reaction mixture was observed by ESI-MS (Figure 3).
HRMS: m/z calcd for C H O P Na: 769.3393; found:
43 56
7 2
769.3433.
O
O
PAr2
Na+
Acknowledgment
PAr2
O
We thank the Ministry of Education, Culture, Sports, Science and
Technology, Japan for support. K.K. was financially supported by
Astellas Foundation for Research on Medicinal Resources. For the
ESI-MS measurement, thanks are due to Prof. Akito Nagatsu
10: Ar =
OMe
Figure 3
(
Kinjyo Gakuin University).
Synlett 2006, No. 4, 648–650 © Thieme Stuttgart · New York

6
50
K. Suzuki et al.
LETTER
(
(
(
13) Côté, A.; Boezio, A. A.; Charette, A. B. Angew. Chem. Int.
Ed. 2004, 43, 6525.
14) Faller, J. W.; Grimmond, B. J.; D’Alliessi, D. G. J. Am.
Chem. Soc. 2001, 123, 2525.
(17) As shown in Figure 4, a linear correlation between the ee of
the ligand and that of the product 3 was observed, indicating
that a 1:1 ratio of ligand to Rh is present in the catalytic
complex.
15) Representative Procedure for Asymmetric Phenylation.
To a stirred solution of RhCl ·3H O (3.95 mg, 0.0150 mmol)
3
2
in DME–H O (5:1, 2.4 mL) were added (R,R)-MOD-DIOP
2
(
4, 11.0 mg, 0.0150 mmol), NaOt-Bu (96.1 mg, 1.00 mmol),
PhB(OH) (122 mg, 1.00 mmol) and 1-naphthaldehyde (2) at
2
r.t. The reaction mixture was stirred at 100 °C for 72 h under
argon atmosphere, allowed to cool, diluted with H O and
2
extracted with EtOAc. The combined extracts were washed
with brine, dried (Na SO ) and concentrated. The residue
2
4
was purified by silica gel column (EtOAc–hexane = 19:1 to
9
9
:1) to give (R)-(1-naphthyl)phenylmethanol (3, 114 mg,
7% yield, 75% ee) as a colorless oil. The spectral data of 3
4
a
were comparable to those reported. The ee of 3 was
determined by HPLC analysis (Daicel chiralcel OD-H).
16) The reaction of 1-naphthaldehyde with 4-methoxy- and 4-
chloro-phenylboronic acids did not proceed. The reaction of
cyclohexylaldehyde with phenylboronic acid gave low
enantioselectivity (44% yield, 25% ee).
(
Figure 4
(18) For a bifunctional asymmetric catalysis, see: Shibasaki, M.;
Kanai, M.; Funabashi, K. Chem. Commun. 2002, 1989; and
references cited therein.
Synlett 2006, No. 4, 648–650 © Thieme Stuttgart · New York