the benzylic position and further investigations on the role of
these in asymmetric reactions in more detail are in progress.
Financial support from the National Natural Science Founda-
tion of China (Project 29790127 and 29872045), National
Outstanding Youth Fund, Chinese Academy of Sciences, and
Shanghai Committee of Science and Technology is gratefully
acknowledged.
Notes and references
† Crystal data for 5: M = 427.60, orthorhombic, space group P2,2,2, a =
3
14.633(2), b = 19.668(4), c = 7.749(2) Å, V = 2230.0(8) Å , Z = 4, Dc
=
1.274 g cm23, T = 293 K, l(Mo-Ka) = 0.7107 Å, m = 1.657 cm21, 2938
measured reflections, 2555 observed reflections, R = 0.0430, R1 = 0.0540,
S = 1.800, pmax, pmin = 0.431, 20.344 e Å23. CCDC 182/1650. See http:/
format.
Fig. 1 ORTEP drawing of 2-(R)-19-(S)-(Sp)-5 with the atomic number-
ing.
1 Catalytic Asymmetric Synthesis, ed. I. Ojima, VCH, New York, 1993;
R. Noyori, Asymmetric Catalysis In Organic Synthesis, Wiley, New
York, 1994.
2 For reviews, see: Ferrocenes, ed. A. Togni and T. Hayashi, VCH,
Weinheim, 1995; C. J. Richards and A. J. Locke, Tetrahedron:
Asymmetry, 1998, 9, 2377.
3 C. Bolm and K. Muniz, Chem. Soc. Rev., 1999, 28, 51.
4 (a) H. J. Reich and K. E. Yelm, J. Org. Chem., 1991, 56, 5672; (b) R.
Yanada, M. Higashikawa, Y. Miwa, T. Taga and F. Yoneda,
Tetrahedron: Asymmetry, 1992, 11, 1387; (c) D. Y. Antonov, Y. N.
Belokon, N. S. Ikonnikov, S. A. Orlova, A. P. Pisarevsky, N. I. Raevski,
V. I. Rozenberg, E. V. Sergeeva, Y. T. Struchkov, V. I. Tararov and
E. V. Vorontsov, J. Chem. Soc., Perkin Trans. 1, 1995, 1873;
(d) V. V. Sergeeva, V. I. Rozenberg, E. V. Vorontsov, T. D. Danilova,
Z. A. Starikova, A. I. Yanovsky, Y. N. Belokon and H. Hopf,
Tetrahedron: Asymmetry, 1996, 12, 3445; (e) Y. Belokon, M.
Moscalenko, N. Ionnikov, L. Yashkina, D. Antonov, E. Vorontsov and
V. Rozenberg, Tetrahedron: Asymmetry, 1997, 19, 3245; (f) P. J. Pye,
K. Rossen, R. A. Reamer, N. N. Tsou, R. P. Volante and P. J. Reider,
J. Am. Chem. Soc., 1997, 119, 6207; (g) K. Rossen, P. J. Pye, A.
Maliakal and R. P. Volante, J. Org. Chem., 1997, 62, 6462; (h) A. H.
Vetter and A. Berkessel, Tetrahedron Lett., 1998, 39, 1741; (i) P. J. Pye,
K. Rossen, R. A. Reamer, R. P. Volante and P. J. Reider, Tetrahedron
Lett., 1998, 39, 4441; (j) V. I. Rozenberg, N. V. Dubrovina, E. V.
Vorontsov, E. V. Sergeeva and Y. N. Belokon, Tetrahedron: Asym-
metry, 1999, 10, 511; (k) U. Wo¨rsdo¨rfer, F. Vögtle, M. Nieger, M.
Waletzke, S. Grimme, F. Glorius and A. Pfaltz, Synthesis, 1999, 4,
597.
Scheme 2
Table 1 The effect of different ligands on the enantioselective palladium-
catalyzed allylic substitution reaction using planar chiral N,S- and N,Se-
ligandsa
Yield
(%)b
Ee
Config-
Entry Ligand Solvent Salt
t/h
(%)c urationd
1
2
3
4
5
6
7
8
9
4a
4a
4a
4a
4b
5
8a
8b
9
PhMe
LiOAc
CH2Cl2 LiOAc
CH2Cl2 KOAc
40
24
36
32
21.5 98
1.5 98
20
30
2
98
98
98
98
54
50
53
54
63
94
57
73
93
R
R
R
R
S
S
R
S
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
98
98
98
S
a Molecular ratio: [Pd(h -C3H5)Cl]2+ligand+6+dimethyl malonate+BSA
+salt = 2+6+100+300+300+3. b Isolated yield after flash chromatography.
c Ee determined by HPLC (chiralel OJ column). d Absolute configuration of
the product 7 was assigned by comparison with the sign of specific rotation
according to literature data.14
3
5 R. S. Cahn, C. K. Ingold and V. Prelog, Experientia, 1956, 12, 81;
Angew. Chem., Int. Ed. Engl., 1966, 5, 385.
6 D. J. Cram and N. Allinger, J. Am. Chem. Soc., 1955, 77, 6289.
7 H. J. Reich and D. J. Cram, J. Am. Chem. Soc., 1969, 91, 3517.
8 (a) X. D. Du, L. X. Dai, X. L. Hou, L. J. Xia and M. H. Tang, Chin. J.
Chem., 1998, 16, 90; (b) S. L. You, Y. G. Zhou, X. L. Hou and L. X. Dai,
Chem. Commun., 1998, 2765; (c) W. P. Deng, X. L. Hou and L. X. Dai,
Tetrahedron: Asymmetry 1999, 10, 4689; (d) L. X. Dai, X. L. Hou, W. P.
Deng, S. L. You and Y. G. Zhou, Pure Appl. Chem., 1999, 71, 1401;
(e) W. P. Deng, X. L. Hou, L. X. Dai, Y. H. Yu and W. Xia, Chem.
Commun., 2000, 285; (f) S. L. You, X. L. Hou and L. X. Dai,
Tetrahedron: Asymmetry, 2000, 11, 1495.
9 For reviews, see: B. M. Trost and D. L. Van Vranken, Chem. Rev., 1996,
96, 395; B. M. Trost, Acc. Chem. Res., 1996, 29, 355; G. J. Helmchen,
J. Organomet. Chem., 1999, 576, 203.
10 V. Rozenberg, N. Dubrovvina, E. Sergeeva, D. Antonov and Y. Belo-
kon, Tetrahedron: Asymmetry, 1998, 9, 653.
coordinating atoms at benzylic and benzene ring positions in
asymmetric synthesis. It can be seen that a higher ee value was
obtained for benzylic substituted ligand 9 relative to 8a and 8b
(entry 9 cf. entries 7,8 in Table 1). As for the N, S-ligand, the
reactivity of the benzylic derivative (9) as ligand is higher than
that using ring-substituted cyclophanes 8a and 8b as ligands.
These results clearly show that the ligand with the two
coordinating atoms at benzylic and benzene ring-positions is
more effective than that with both the coordinating atoms at
benzene ring-positions. This is presumably due to the increased
tether length between the donor atoms which coordinate
palladium in 5 and 9, bringing the asymmetric environment
closer to the allyl species during the reaction.15 Interestingly, 4a
and 8a with the same Sp planar chirality afforded 7 in (R)-
configuration, whereas 4b, 8b with Rp planar chirality gave rise
to 7 in (S)-configuration, even though all of these ligands
showed the same central chirality at the oxazoline. It seems that
the central chirality is not a decisive factor in controlling the
absolute configuration of the product in our reaction.8b,e
11 H. Vorbruggen and K. Krolikliewicz, Tetrahedron Lett., 1981, 22,
4471.
12 P. M. Keehn and S. M. Rosenfeld, Cyclophanes, Academic Press, New
York, 1983, p. 71.
13 A similar result was obtained in the diastereomeric deprotonation of
chiral ferrocenyl oxazolines: see: C. J. Richards, T. Damalidis, D. E.
Hibbs and M. B. Hursthouse, Synlett, 1995, 74; T. Sammakia and H. A.
Latham, J. Org. Chem., 1995, 60, 6002.
14 P. Wimmer and M. Widhalm, Tetrohedron: Asymmetry, 1995, 6, 657.
15 B. M. Trost and D. L. Van Vranken, Angew. Chem., Int. Ed. Engl., 1992,
31, 228; G. J. Dawson, C. G. Frost, C. J. Martin, J. M. J. Williams and
S. J. Coote, Tetrahedron Lett., 1993, 34, 7793; A. Chesney, M. R. Bryce,
R. W. J. Chubh, A. S. Batsancy and J. A. K. Howard, Tetrahedron:
Asymmetry, 1997, 8, 2337.
In summary, novel N,S- and N,Se-ligands bearing the two
coordinating atoms at benzylic and benzene ring positions
showed excellent enantioselectivity and reactivity in palladium-
catalyzed allylic alkylation reaction. The synthesis of further
similar ligands via introduction of other coordinating atoms at
1196
Chem. Commun., 2000, 1195–1196