Remarkably high asymmetric amplification in the chiral lanthanide complex-catalyzed hetero-Diels - Alder reaction: First example of the nonlinear effect in ML3 system

Article abstract of DOI:10.1021/ol991189q

(formula presented) A remarkably high asymmetric amplification was realized in the Yb[(R)-BNP]₃-catalyzed hetero-Diels - Alder reaction as the first example in the metal/chiral ligand 1:3 system. The mechanism may be explained by the autogeneti

Full text of DOI:10.1021/ol991189q

ORGANIC
LETTERS
2000
Vol. 2, No. 1
49-52
Remarkably High Asymmetric
Amplification in the Chiral Lanthanide
Complex-Catalyzed Hetero-Diels−Alder
Reaction: First Example of the
Nonlinear Effect in ML3 System
Hiroshi Furuno, Takeshi Hanamoto,† Yuichi Sugimoto, and Junji Inanaga*
Institute for Fundamental Research of Organic Chemistry (IFOC), Kyushu UniVersity,
Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
inanaga@ms.ifoc.kyushu-u.ac.jp
Received October 27, 1999
ABSTRACT
A remarkably high asymmetric amplification was realized in the Yb[(R)-BNP]3-catalyzed hetero-Diels−Alder reaction as the first example in the
metal/chiral ligand 1:3 system. The mechanism may be explained by the autogenetic formation of the enantiopure complex as the most active
catalyst. The enantiomer-discriminative formation of homochiral ML3 complexes is quite general within the lanthanide metal ions with similar
ionic radii to that of the ytterbium ion.
Since the Kagan’s first report regarding the positive nonlinear
effect,1 such an asymmetric amplification2 has frequently
been observed in various catalytic asymmetric reactions using
chiral metal complexes.3-5 However, most of them are
limited within the range of Kagan’s ML2 (L ) chiral ligand)
model,4 and a high degree of asymmetric amplification
concerning the ML3 system has never been reported although
mathematical treatment allows one to expect considerable
nonlinear effects in this system.1,4c,d,6 We now report a
remarkably high asymmetric amplification realized in the
chiral lanthanide complex catalyzed hetero-Diels-Alder
†
Present address: Department of Chemistry, Saga University, Saga 840-
8502, Japan.
(1) Puchot, C.; Samuel, O.; Dun˜ach, E.; Zhao, S.; Agami, C.; Kagan, H.
B. J. Am. Chem. Soc. 1986, 108, 2353-2357.
(4) For recent mechanistic studies, see: (a) Blackmond, D. G. J. Am.
Chem. Soc. 1998, 120, 13349-13353. (b) Kitamura, M.; Suga, S.; Oka,
H.; Noyori, R. J. Am. Chem. Soc. 1998, 120, 9800-9809. (c) Brunel, J.-
M.; Luukas, T. O.; Kagan, H. B. Tetrahedron: Asymmetry 1998, 9, 1941-
1946. (d) Blackmond, D. G. J. Am. Chem. Soc. 1997, 119, 12934-12939.
(5) For recent examples on the asymmetric amplification, see: (a)
Kanemasa, S.; Oderaotoshi, Y.; Sakaguchi, S.; Yamamoto, H.; Tanaka, J.;
Wada, E.; Curran, D. P. J. Am. Chem. Soc. 1998, 120, 3074-3088. (b)
Dosa, P. I.; Fu, G. C. J. Am. Chem. Soc. 1998, 120, 445-446 and references
therein.
(6) Guillaneux, D.; Zhao, S.-H.; Samuel, O.; Rainford, D.; Kagan, H.
B. J. Am. Chem. Soc. 1994, 116, 9430-9439. The possibility of nonlinear
effect on the Danishefsky’s Eu(hfc)3-catalyzed hetero-Diels-Alder reaction
has been examined.
(2) For the term “asymmetric amplification”, see: Oguni, N.; Matsuda,
Y.; Kaneko, T. J. Am. Chem. Soc. 1988, 110, 7877-7878.
(3) For reviews, see: (a) Girard, C.; Kagan, H. B. Angew. Chem., Int.
Ed. Engl. 1998, 37, 2922-2959. (b) Kagan, H. B.; Girard, C.; Guillaneux,
D.; Rainford, D.; Samuel, O.; Zhang, S. Y.; Zhao, S. H. Acta Chem. Scand.
1996, 50, 345-352. (c) Avalos, M.; Babiano, R.; Cintas, P.; Jime´nez, J.
L.; Palacios, J. C. Tetrahedron: Asymmetry 1997, 8, 2997-3017. (d)
Reggelin, M. Nachr. Chem., Technol. Lab. 1997, 45, 622-627. (e) Reggelin,
M. Nachr. Chem., Technol. Lab. 1997, 45, 392-396. (f) Bolm, C. In
AdVanced Asymmetric Catalysis; Stephenson, G. R., Ed.; Blackie Academic
and Professional: New York, 1996; pp 9-26. (g) Noyori, R.; Kitamura,
M. Angew. Chem., Int. Ed. Engl. 1991, 30, 49-69.
10.1021/ol991189q CCC: $19.00 © 2000 American Chemical Society
Published on Web 12/14/1999

reaction6 and also some interesting insights into the mech-
anism.
Recently, we synthesized the 1:3 complexes of a series of
trivalent rare earth metal ions with chiral ligands, RE[(R)-
BNP]3 (RE ) rare earth; BNP ) 1,1′-binaphthyl-2,2′-diyl
phosphate), as isolable chiral Lewis acids which effectively
catalyze the hetero-Diels-Alder reaction of aldehydes with
the Danishefsky diene 27-10 (Scheme 1).
Scheme 1. Yb[(R)-BNP]3-Catalyzed Hetero-Diels-Alder
Reaction of Aldehydes with the Danishefsky’s Diene
Further investigation allowed us to find a remarkably high
positive nonlinear effect as the first example in ML3 system.
Thus, when solutions of enantiopure Yb[(R)-BNP]3 and Yb-
[(S)-BNP]3 complexes containing 2,6-lutidine were mixed
in different ratios (method I) and the resulting suspension
was used as a catalyst (A) for the reaction of 1a with 2, a
notable asymmetric amplification was observed (Figure 1).
Very interestingly, the catalysts (B) prepared from the chiral
ligands with various ees according to the method II further
promoted the amplification, e.g., by using only 20% ee of
the chiral ligand, the product 4a with a 90% ee was obtained.
The results strongly suggest that the active catalyst generated
from an enantiomerically impure ligand has the same
structure as that of the catalyst prepared from the enantiopure
ligand.
Figure 1. The asymmetric amplification observed in the hetero-
Diels-Alder reaction of 1a with 2 by the catalyst A or B.
Scheme 2. Correlation between Catalytic Activity and Optical
Purity of the Yb-BNP Complex
To gain an insight into the mechanism of the present highly
positive nonlinear effect, we carried out the reactions shown
in Scheme 2. The ytterbium complex (Yb-5) was prepared
from 50% ee of the ligand (R/S 75:25), and the once-isolated
complex was treated with 2,6-lutidine in dichloromethane.
Separation of the CH2Cl2-soluble part (complex 6) from the
insoluble part (complex 7) by centrifugation (6/7 41:59)
followed by LiAlH4 reduction of each part afforded the
corresponding BINOLs with 98 and 7% ee, respectively. In
addition, while the complex 6 did catalyze the reaction of
1a with 2 giving 4a (90% ee) in 98% yield, the complex 7
hardly promoted the reaction under the same reaction
(7) Inanaga, J.; Sugimoto, Y.; Hanamoto, T. New J. Chem. 1995, 19,
707-712.
(8) Hanamoto, T.; Furuno, H.; Sugimoto, Y.; Inanaga, J. Synlett 1997,
79-80.
50
Org. Lett., Vol. 2, No. 1, 2000

conditions (<1% yield). These results clearly indicate that
the active catalyst 6 is composed entirely of the enantiopure
ligands, whereas the inactive 7 is made up with almost a
1:1 mixture of enantiomers.
The experiments shown in Scheme 3 indicate how easily
the ligands of the complex 3 can be exchanged by sodium
salt of the opposite enantiomer, giving the heterochiral
complex, whereas the complex 8 prepared from racemic
BNPH hardly gives rise to such a ligand exchange reaction
under similar conditions. These results demonstrate the
remarkable thermodynamic stability of the heterochiral
complex.
This phenomenon (autogenetic formation of the enantio-
pure ytterbium complex) was also confirmed by use of THF
instead of 2,6-lutidine/dichloromethane and turned out to be
quite general within the lanthanide metal ions with similar
ionic radii to that of the ytterbium ion, e.g., Nd, Gd, and Ho
(Table 1).
Table 1. Correlation between the THF-Soluble Complex RE-9
and Optical Purity of the Liganda
Scheme 3. Attempted Ligand Exchange Reactions of 3 and 8
ee of
entry
RE
La
RE-9:RE-10
(R)-BINOL, %b
1
2
3
4
5
6
7
3:97
3:97
Ce
Nd
Gd
Ho
Ybc,d
Sc
36:64
37:63
41:59
46:54e
54:46
99
98
97
98
64
a RE-5 prepared from 50% ee (R)-ligands was used. b BINOL derived
from RE-9. Determined by HPLC using DAICEL CHIRALPAK AD.
c Elementary analyses of Yb-9 and Yb-10 were carried out. Yb-9. Calcd
for C64H46O14P3Yb [)Yb(BNP)3‚H2O‚THF]: C, 58.90; H, 3.55. Found:
C, 58.62; H, 3.63. Yb-10. Calcd for C60H38O13P3Yb [)Yb(BNP)3‚H2O]:
C, 58.45; H, 3.11. Found: C, 58.67; H, 3.02. d The hetero-Diels-Alder
reaction of 1a with 2 catalyzed by Yb-9 or Yb-10 in the presence of 2,6-
lutidine in dichloromethane afforded 4a with 88% ee (94% chemical yield)
or 1% ee (8%), respectively. e Yb-10 was reduced by LiAlH4 and the
corresponding (R)-BINOL was obtained in 5% ee.
Taking all these facts into consideration, we propose the
origin of the present asymmetric amplification as shown in
Figure 2. For the formation of YbL3, there are four
In conclusion, an extremely high asymmetric amplification
was observed in the Yb[(R)-BNP]3-catalyzed hetero-Diels-
Alder reaction and the unique enantiomer-discriminative
process in the formation of homochiral ML3 complex was
revealed. These findings would lead to a new phase in the
area of asymmetric catalysis with chiral metal complexes,
especially lanthanide ones.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research on Priority Areas from the
(9) For recent works using other chiral catalysts, see: (a) Mihara, J.;
Hamada, T.; Takeda, T.; Irie, R.; Katsuki, T. Synlett 1999, 1160-1162.
(b) Schaus, S. E.; Brånalt, J.; Jacobsen, E. N. J. Org. Chem. 1998, 63,
403-405. (c) Ghosh, A. K.; Mathivanan, P.; Cappiello, J. Tetrahedron Lett.
1997, 38, 2427-2430. (d) Matsukawa, S.; Mikami, K. Tetrahedron:
Asymmetry 1997, 8, 815-816. (e) Ghosh, A. K.; Mathivanan, P.; Cappiello,
J.; Krishnan, K. Tetrahedron: Asymmetry 1996, 7, 2165-2168. (f) Keck,
G. E.; Li, X.-Y.; Krishnamurthy, D. J. Org. Chem. 1995, 60, 5998-5999.
(g) Mikami, K.; Kotera, O.; Motoyama, Y.; Sakaguchi, H. Synlett 1995,
975-977. (h) Motoyama, Y.; Mikami, K. J. Chem. Soc., Chem. Commun.
1994, 1563-1564. (i) Gao, Q.; Ishihara, K.; Maruyama, T.; Mouri, M.;
Yamamoto, H. Tetrahedron 1994, 50, 979-988. (j) Corey, E. J.; Cywin,
C. L.; Roper, T. D. Tetrahedron Lett. 1992, 33, 6907-6910. (k) Togni, A.
Organometallics 1990, 9, 3106-3113.
Figure 2. A possible chirality-discrimination process for the
formation of the ytterbium complex.
possibilities in choosing three chiral ligands: (LR)3, (LR)2LS,
LR(LS)2, and (LS)3. From these four complexes, the hetero-
chiral pairs such as Yb(LR)3 and Yb(LS)3 and/or Yb[(LR)2LS]
and Yb[LR(LS)2] seem to irreversibly assemble, forming the
thermodynamically very stable complexes which have almost
no catalytic activity for the hetero-Diels-Alder reaction. As
a result, the enantiopure Yb complex based on excess amount
of the enantiomer, Yb(LR)3, would remain in solution as the
real catalyst.11
(10) For the first catalytic enantioselective reaction, see: Bednarski, M.;
Maring C.; Danishefsky, S. Tetrahedron Lett. 1983, 24, 3451-3454.
(11) Because of the difficulty in making a good crystalline of the Yb
complex suitable for X-ray analysis, we cannot discuss here in detail about
the possible chirality (∆ or Λ) of the metal center of the complex.
Org. Lett., Vol. 2, No. 1, 2000
51

Ministry of Education, Science, Sports and Culture and also
by the Nagase Science and Technology Foundation.
mination of the optical purity of the component ligand of
the complex Yb-9 (see Table 1). This material is available
free of charge via the Internet at http://pubs.acs.org.
Supporting Information Available: A typical experi-
mental procedure for the asymmetric amplification of the
enantioselective hetero-Diels-Alder reaction and the deter-
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