4242
J. Am. Chem. Soc. 1998, 120, 4242-4243
Catalytic Asymmetric Allylation of Imines via Chiral
Bis-π-allylpalladium Complexes
Hiroyuki Nakamura, Kaori Nakamura, and
Yoshinori Yamamoto*
Department of Chemistry, Graduate School of Science
Tohoku UniVersity, Sendai 980-77, Japan
ReceiVed October 9, 1997
Enantioselective formation of carbon-carbon bonds between
achiral substrates using catalytic amounts of chiral sources is a
main goal in asymmetric synthesis. Recently, various Lewis acid
catalysts have been synthesized and applied to asymmetric
reactions of carbonyl compounds.1 However, very few examples
have been reported on catalytic asymmetric reactions of imines
so far,2 since the amines produced from the imines coordinate to
Lewis acids strongly, making the catalysts inert. We recently
found that imines underwent allylation reaction in the presence
of palladium catalysts to afford the corresponding homoally-
lamines in high yields.3 The mechanistic studies reveal that bis-
π-allylpalladium complex is a reactive intermediate for this
allylation3b,4 and reacts with imines as a nucleophile, although
ordinary π-allylpalladium complexes such as π-allylPdX (X )
OAc and halides) act as an electrophile.5 Furthermore, we have
quite recently reported that bis-π-allylpalladium complex has an
amphiphilic character.6 It occurred to us that, by proper choice
of the two allyl groups of bis-π-allylpalladium complexes, one
of the allyl groups could react with imines as a nucleophile and
the other could stay on the palladium atom. If a chiral π-allyl
group is introduced as the nontransferable π-allyl ligand, the
allylation may proceed enantioselectively with catalytic amounts
of the chiral reagent. Herein, we report the first catalytic
asymmetric allylation of imines 1 with allyltributylstannane in
the presence of chiral π-allylpalladium complex 3e (eq 1).
Chiral BINAP-palladium 3a and π-allylpalladium catalysts
3b-f were prepared according to the literature procedures.7 The
reaction of imine 1a (1 equiv) with allyltributylstannane (1.2
equiv) in DMF was carried out in the presence of various
palladium catalysts 3 (5 mol %) at 0 °C under Ar atmosphere.
The use of chiral BINAP-palladium 3a gave the corresponding
homoallylamine 2a in 39% yield and the enantiomeric excess of
the product was 0%. Although the reactions using the chiral
π-allylpalladium chloride complexes (3b,c), which were prepared
from (1R)-(+)-camphor, resulted in very low enantiomeric excess
(ee), the use of the chiral catalyst 3d which was derived from
(1S)-â-(-)-pinene gave 2a in 62% yield with the enantiomeric
excess of 50%. The exomethylene of â-(-)-pinene was converted
to exoethylidene, and the corresponding π-allylpalladium chloride
3e was prepared.7 The allylation of 1a using this catalyst 3e
afforded 2a in 62% yield with the enantiomeric excess of 81%
(entry 1 in Table 1). The catalyst 3f, which was prepared from
(1S)-(+)-3-carene, was not effective for this asymmetric allylation.
THF was also an effective solvent in this asymmetric allylation.
The reaction of 1a in THF proceeded smoothly in the presence
of 3e, giving 2a in 72% yield with the same high level of ee
(entry 1 vs 2).
We next examined the various imines using the complex 3e
as a catalyst. The imine 1b underwent this allylation reaction
with 80% ee in DMF (entry 3) and 82% ee in THF (entry 4).
The allylation of imine 1c derived from aniline resulted in ∼0%
ee (entry 5). Perhaps, sterically bulky phenyl group would prevent
efficient coordination of nitrogen atom of the imine to palladium
atom, diminishing the influence of the chiral ligand on the
asymmetric induction. The imine 1d derived from benzaldehyde
and propylamine gave 2d in 70% ee (entry 6). These results
suggest that a sterically less bulky group should be attached to
the nitrogen atom in order to obtain high ee values. Not only
the imines derived from benzaldehyde but also those from
p-methoxybenzaldehyde and 2-naphthylaldehyde (1e and 1f)
underwent the allylation with enantiomeric excesses of 78% and
(1) Catalytic asymmetric allylation: (a) Costa, A. L.; Piazza, M. G.;
Tagiavini, E.; Trombini, C.; Umani-Ronchi, A. J. Am. Chem. Soc. 1993, 115,
7001. (b) Keck, G. E.; Tarbet, K. H.; Geraci, L. S. J. Am. Chem. Soc. 1993,
115, 8467. (c) Yanagisawa, A.; Nakashima, H.; Ishiba, A.; Yamamoto, H. J.
Am. Chem. Soc. 1996, 118, 4723. (d) Yu, C.-M.; Choi, H.-S.; Jung, W.-H.;
Lee, S.-S. Tetrahedron Lett. 1996, 37, 7095. Catalytic asymmetric Aldol
reaction: (e) Sodeoka, M.; Ohrai, K.; Shibasaki, M. J. Org. Chem. 1995, 60,
2648. (f) Evans, D.; Murry, J. A.; Kozlowski, M. C. J. Am. Chem. Soc. 1996,
118, 5814. (g) Evans, D.; Kozlowski, M. C.; Burgey, C. S.; MacMillan, D.
W. C. J. Am. Chem. Soc. 1997, 119, 7893.
(2) Asymmetric addition of organolithium reagents to imines in the presence
of chiral ligands has been reported, although one equivalent amount (or more
than 1 equiv in certain cases) of the ligands is needed in most cases. (a) Shindo,
M.; Koga, K.; Tomioka, K. J. Am. Chem. Soc. 1992, 114, 8732. Fujieda, H.;
Kanai, M.; Kambara, T.; Iida, A.; Tomioka, K. J. Am. Chem. Soc. 1997, 119,
2060 (two examples for catalytic use of the ligand are reported). (b) Demmark,
S. E.; Nakajima, N.; Nicaise, O. J.-C. J. Am. Chem. Soc. 1994, 116, 8797.
Demmark, S. E.; Nicaise, O. J.-C. J. Chem. Soc., Chem. Commun. 1996, 999
(four examples of substrates are reported for catalytic asymmetric addition).
More recently, catalytic asymmetric Mannich-type reactions using chiral
zirconium catalyst has been reported: (c) Ishitani, H.; Ueno, M.; Kobayashi,
S. J. Am. Chem. Soc. 1997, 119, 7153.
(3) (a) Nakamura, H.; Iwama, H.; Yamamoto, Y. J. Chem. Soc., Chem.
Commun. 1996, 1459. (b) Nakamura, H.; Iwama, H.; Yamamoto, Y. J. Am.
Chem. Soc. 1996, 118, 6641.
(4) Nakamura, H.; Asao, N.; Yamamoto, Y. J. Chem. Soc., Chem. Commun.
1995, 1273.
(5) (a) Tsuji, J. In Palladium Reagents and Catalysts; John Wiley and
Sons: Chichester, 1995; p 61. (b) Codleski, S. A. In ComprehensiVe Organic
Synthesis; Semmelhack, M. F., Ed.; Pergamon Press: Oxford, 1991; Vol. 4,
p 585. (c) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. In
Principles and Applications of Organotransition Metal Chemistry; University
Science Books: Mill Valley, CA, 1987; p 417.
(7) For the synthesis of chiral π-allylapalladium complexes, see: (a) Heck,
R. F. In Palladium Reagents in Organic Syntheses; Academic Press: London,
1985; pp 1-18. (b) Trost, B. M.; Strege, P. E.; Weber, L.; Fullerton, T. J.;
Dietsche, T. J. J. Am. Chem. Soc. 1978, 100, 3407. For the reactions using
chiral π-allylapalladium catalysts, see: (c) Hosokawa, T.; Uno, T.; Inui, S.;
Murahashi, S.-I. J. Am. Chem. Soc. 1981, 103, 2318. Hosokawa, T.; Okuda,
C.; Murahashi, S.-I. J. Org. Chem. 1985, 50, 1282.
(6) Nakamura, H.; Shim, J.-G.; Yamamoto, Y. J. Am. Chem. Soc. 1997,
119, 8113.
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Published on Web 04/18/1998