Chemistry Letters Vol.35, No.2 (2006)
173
PdCl2(MeCN)2
(1 equiv.)
Cl
O
O
Table 1. Catalytic asymmetric Diels–Alder reaction
N
Pd
N
N
7
CDCl3, rt, 24 h
97%
N
N
Pri
Pri
Pri
Cl
(2R)
Cl
cat. Pd(II) or Cu(II)
H
Cl
Cl
(3)
Pd
N
Pd
N
+
+
CHO
Cl
CH2Cl2, 0 °C
CHO
Pri
H
CHO
PdCl2(MeCN)2
(1 equiv.)
Cl
(5 equiv.)
H
8
N
Pd
CDCl3, rt, 24 h
>99%
Time Yield
/h /%
Endo ee/%
(config.)
O
O
Cl
Entry
Catalyst/mol %
Endo:exo
11
1
2
3
4
13 (5)
15 (5)
5
5
11
71
86:14
80:20
80:20
79:21
0
Cl(3)
6 (2R)
23 (2R)
38 (2R)
O(3)
O(4)
12 (10)/Cu(OTf)2 (10)
12 (20)/Cu(OTf)2 (10)
25 82
20 86
N(5)
N(7)
N(8)
Pd(2)
N(6)
Cl(7)
O
Pd(4)
Cl(8)
Cl(5)
/Cu(OTf)2 (10)
Cl(4)
Pd(3)
Cl(1)
Pri
N
5
20 46
80:20
0
N(4)
Cl(6)
16 (20)
N(2)
N(1)
N(3)
Pd(1)
Cl(2)
O(2)
In summary, we have provided simple synthesis of chiral
self-assembled macrocyclic complexes with n:n metal–bidentate
P,N- and N,N-ligands by intermolecular trans-chelation. Further
investigations toward asymmetric catalysis with trans-macrocy-
clic complexes are now underway.
O(1)
Figure 3. Preparation of macrocyclic trans 4:4 complex 11.
We next synthesized a new macrocyclic compound with the
essential structure of 11 to achieve asymmetric catalysis. New
bis(oxazolines) ligand 128 with PdCl2(MeCN)2 in CD3CN gave
the corresponding trans 2:2 complex 13 (Eq 4). The counter
anions in 13 could be changed from Cl to OCOCF3 to give 14.
trans 2:2 Cu(II) complex 15 also could be obtained by using
CuCl2 in CH2Cl2. Interestingly, 15 had a twisted structure with
References and Notes
1
For reviews: a) M. Fujita, Chem. Soc. Rev. 1998, 27, 417. b) S.
Leininger, B. Olenyuk, P. J. Stang, Chem. Rev. 2000, 100, 853.
c) B. J. Holliday, C. A. Mirkin, Angew. Chem., Int. Ed. 2001, 40,
2022. d) S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem., Int.
Ed. 2004, 43, 2334.
a) M. Fujita, J. Yazaki, K. Ogura, J. Am. Chem. Soc. 1990, 112,
5645. b) P. J. Stang, D. H. Cao, J. Am. Chem. Soc. 1994, 116,
4981. c) K. Uemura, S. Kitagawa, K. Fuku, K. Saito, J. Am. Chem.
Soc. 2004, 126, 3817.
Recent asymmetric catalysis with supramolecular complexes:
a) S. Joong, A. Hu, W. Lin, J. Am. Chem. Soc. 2002, 124,
12948. b) J. M. Takacs, D. S. Reddy, S. A. Moteki, D. Wu, H.
Palencia, J. Am. Chem. Soc. 2004, 126, 4494. c) Y. Liang, Q. Jing,
X. Li, L. Shi, K. Ding, J. Am. Chem. Soc. 2005, 127, 7694. d) C.-D.
Wu, A. Hu, L. Zhang, W. Lin, J. Am. Chem. Soc. 2005, 127, 8940.
e) T. Kano, T. Hashimoto, K. Maruoka, J. Am. Chem. Soc. 2005,
127, 11926.
Trans-chelating ligands in asymmetric catalysis: a) M. Sawamura,
H. Hamashima, Y. Ito, J. Am. Chem. Soc. 1992, 114, 8295. b) A.
Goeke, M. Sawamura, R. Kuwano, Y. Ito, Angew. Chem., Int.
Ed. Engl. 1996, 35, 662. c) J. R. Krumper, M. Gerisch, J. M.
Suh, R. G. Bergmann, T. D. Tilley, J. Org. Chem. 2003, 68, 9705.
ortho-P,N-Ligands: a) P. von Matt, A. Pfaltz, Angew. Chem., Int.
Ed. Engl. 1993, 32, 566. b) J. Sprinz, G. Helmchen, Tetrahedron
Lett. 1993, 34, 1769. c) G. J. Dawson, C. G. Frost, J. M. J.
Williams, S. J. Coote, Tetrahedron Lett. 1993, 34, 3149.
ortho-N,N-Ligands: H. Nishiyama, H. Sakaguchi, T. Nakamura,
M. Horihata, M. Kondo, K. Itoh, Organometallics 1989, 8, 846.
Crystallographic data reported in this manuscript have been depos-
ited with Cambridge Crystallographic Data Centre as supplementa-
ry publication Nos. CCDC-273441 for 11, CCDC-273442 for 13,
and CCDC-273444 for 15. Copies of the data can be obtained free
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge, CB2 1EZ, UK; fax: +44 1223 336033; or deposit@
ccdc.cam.ac.uk). See Supporting Information in detail.
ortho- and meta-Bisoxazolines: a) C. Bolm, K. Weickhardt, M.
Zehnder, T. Ranff, Chem. Ber. 1991, 124, 1173. b) M. A. Stark,
C. J. Richards, Tetrahedron Lett. 1997, 38, 5881. c) Y. Motoyama,
N. Makihara, Y. Mikami, K. Aoki, H. Nishiyama, Chem. Lett.
1997, 951.
unambiguous ꢀ–ꢀ stacking between two benzene rings at
3.441 A by X-ray analysis (Figure 4). Taking advantage of
7
2
3
ꢀ
the Lewis-acidity of bis(oxazolines)–Cu(II) catalysts,9 we exam-
ined the asymmetric Diels–Alder reaction of acrolein with cyclo-
pentadiene in the presence of 5 mol % of 15 (Table 1, Entry 2).
The major endo product was obtained in 71% yield but with only
6% ee by macrocyclic Cu(II) catalyst 15, while Pd(II) complex
13 was quite ineffective (Entry 1). Cu(II) catalyst which was
prepared in situ from 12 (10 mol %) and Cu(OTf)2 (10 mol %)
showed better enantioselectivity than 15 (Entry 3). Moreover,
Cu(II) catalyst prepared from 20 mol % of 12 gave the product
in 86% yield and 38% ee (Entry 4). Decompositions in dinuclear
complexes as seen in X-ray analyses can not be excluded com-
pletely under catalysis conditions. However, the results also sug-
gest the possibility of asymmetric catalysis by the self-assem-
bled complexes, since monooxazoline ligand 16 which can not
chelate to Cu(OTf)2 gave racemic product with lower reactivity
than macrocyclic complexes (Entry 5).
4
5
O
O
O
O
6
7
N
M
N
N
M
N
N
N
Pri
Pri
Pri
Pri
Pri
Pri
X
X
(4)
12
X
X
MXn (1 equiv.)
CD3CN or CH2Cl2, rt
O
O
13 (M = Pd, X = Cl) >99%
14 (M = Pd, X = OCOCF3) 95%
15 (M = Cu, X = Cl) 94%
AgOCOCF3
(4 equiv.)
O(9)
O(1)
8
9
O(8)
O(4)
Cl(3)
N(9)
Cl(8)
N(6)
Cl(6) N(8)
Pd(4)
Cl(7)
N(1)
Cu(1)
N(3)
N(2)
Cu(2)
N(4)
Cl(1)
Cl(2)
Pd(3)
Cl(5)
N(5)
Cl(4)
O(6)
O(2)
a) D. A. Evans, J. A. Murry, P. von Matt, R. D. Norcross, S. J.
Miller, Angew. Chem., Int. Ed. Engl. 1995, 34, 798. b) A. K.
Ghosh, H. Cho, J. Cappiello, Tetrahedron: Asymmetry 1998, 9,
3687.
O(3)
O(5)
13
15
Figure 4. Preparation of trans 2:2 Pd complex 13 and Cu complex 15.