9
382 J . Org. Chem., Vol. 64, No. 26, 1999
Yonehara et al.
and their esters in an aqueous/organic biphasic medium
reported similar effects of the SDS in the hydrogenation
of enamides in water using rhodium catalysts 3 and 4.
Then we applied the combination of the catalyst 2 and
SDS to the hydrogenation of several enamides in water.
The results are summarized in Table 1. The hydrogena-
3
e,f,h
using water-soluble rhodium complexes 1 and 2 prepared
4
from R,R- and â,â-trehalose as ligand sources, respec-
tively (Figure 1).5 In a previous study, we also found that
sodium dodecyl sulfate (SDS) works as a surfactant to
enhance the enantioselectivity up to 99.9% ee in the
hydrogenation of methyl (Z)-R-acetamidocinnamate in
water.5 This success stimulated us to investigate the
asymmetric hydrogenation of other substrates in the
presence of a water-soluble rhodium catalyst and a
surfactant in water. In this paper we report the scope
and limitations of water-soluble rhodium complexes as
catalysts in the hydrogenation of various enamides and
itaconic acid under micellar conditions.
a
2
tion of enamides was carried out under H pressure (5
atm) at room temperature using 1 mol % of 2 in the
presence of SDS. (Z)-R-N-Acetamidocinnamic acid was
a
-
3
hydrogenated in the presence of SDS (7.5 × 10 M) to
give the N-acetylphenylalanine in >99% ee (entry 1). The
reaction of methyl (Z)-R-N-benzamidocinnamate required
-
2
a higher concentration of SDS (1.5 × 10
M), its
selectivity being 93% ee (entry 2). The introduction of
chloro and nitro groups on the phenyl ring caused the
decrease of solubility of substrates in water, and there-
-
2
fore, a higher concentration of SDS (9.0 × 10 M) was
required to attain the good selectivities (94% ee) and
shorter reaction times (entries 3-6). The hydrogenation
of methyl (Z)-R-acetamido-â-(1-naphthyl)acrylate and
methyl (Z)-R-acetamido-â-(2-naphthyl)acrylate required
Resu lts a n d Discu ssion
We previously reported the hydrogenation of methyl
(
(
(
2
Z)-R-acetamidocinnamate in water under H pressure
5 atm) using water-soluble rhodium catalysts 1 and 2
Figure 1), where the enantioselectivities of the product
-1
much higher concentration of SDS (1.0 × 10 M) to give
5
a
were in 55% and 88% ee, respectively (eq 1). On the
an almost complete selectivity (entries 7 and 8). The use
-
3
of a lesser amount of SDS (7.5 × 10 M) frustrated the
conversion of the substrate at most to 20%, possibly due
to poor solubility of the substrate in water. Methoxy
groups on a phenyl ring decreased the amount of SDS
-3
required to 7.5 × 10 M, the induction of chirality being
over 99% ee (entries 9 and 10). The addition of SDS (7.5
-
3
×
10 M) also affected the enantioselectivity in the
hydrogenation of methyl R-N-acetamidoacrylate, leading
to 96% ee (entry 11). We also attempted the hydrogena-
tion of simple enamides, resulting in the formation of
chiral amines, because, despite their potential impor-
6
tance, few successful results have so far been reported.
A highly enantioselective hydrogenation (83% ee) pro-
other hand, the reactions in the presence of sodium
ceeded with N-acetyl-R-phenylethenamine in water in the
-3
dodecyl sulfate (SDS) (7.5 × 10 M) as a surfactant gave
higher selectivity of 90% and 99.9% ee, respectively. The
use of SDS also accelerated each reaction to be complete
within 1 h. Oehme, Selke, and co-workers have already
-3
presence of the catalyst 2 and SDS (7.5 × 10 M) (entry
1
2). To the best of our knowledge, this is the most
successful result in the hydrogenation of this substrate
in water. This catalytic system, however, is only margin-
ally effective in the hydrogenation of R-(N-acetylamido)-
indene to give 33% ee (entry 13). Itaconic acid was also
hydrogenated under the same condition to give the
corresponding product with moderate selectivity (71% ee)
(4) The derivatization of monosaccharide and R,R-trehalose for the
synthesis of chiral ligands and their application to asymmetric
reactions have been reported. For examples, see: (a) RajanBabu, T.
V.; Radetich, B.; You, K. K.; Ayers, T. A.; Casalnuovo, A. L.; Calabrese,
J . C. J . Org. Chem. 1999, 64, 3429. (b) Yonehara, K.; Hashizume, T.;
Ohe, K.; Uemura, S. Bull. Chem. Soc. J pn. 1998, 71, 1967. (c) Boog-
Wick, K.; Pregosin, P. S.; W o¨ rle, M.; Albinati, A. Helv. Chim. Acta 1998,
(entry 14).
As mentioned above, the combination of the water-
8
1, 1622. (d) RajanBabu, T. V.; Ayers, T. A.; Halliday, G. A.; You, K.
soluble chiral catalyst 2 and SDS is most effective in the
enantioselective hydrogenation of enamides and itaconic
acid in water. More interestingly, the catalyst 2 showed
amphiphilic nature in solubility; i.e., it was soluble in
less polar solvent such as 1,2-dichloroethane as well as
in water.5 Therefore, the hydrogenation of methyl (Z)-
R-acetamidocinnamate in 1,2-dichloroethane using the
catalyst 2 smoothly occurred to give the product with high
enantioselectivity (94% ee) (eq 2). On the contrary, the
K.; Calabrese, J . C. J . Org. Chem. 1997, 62, 6012. (e) RajanBabu, T.
V.; Casalnuovo, A. L.; Ayers, T. A. Adv. Catal. Proc. 1997, 2, 1. (f)
Berens, U.; Selke, R. Tetrahedron: Asymmetry 1996, 7, 2055. (g)
Gilbertson, S. R.; Chang, C.-W. T. J . Org. Chem. 1995, 60, 6226. (h)
Casalnuovo, A. L.; RajanBabu, T. V.; Ayers, T. A.; Warren, T. H. J .
Am. Chem. Soc. 1994, 116, 9869. (i) Selke, R.; Facklam, C.; Foken, H.;
Heller, D. Tetrahedron: Asymmetry 1993, 4, 369. (j) RajanBabu, T.
V.; Casalnuovo, A. L. J . Am. Chem. Soc. 1992, 114, 6265. (k) Selke, R.
J . Organomet. Chem. 1989, 370, 249. (l) Brown, J . M.; Cook, S. J .;
Khan, R. Tetrahedron 1986, 42, 5105. (m) Selke, R.; Pracejus, H. J .
Mol. Catal. 1986, 37, 213. (n) J ackson, R.; Thompson, D. J . J .
Organomet. Chem. 1978, 159, C29. (o) Cullen, W. R.; Sugi, Y.
Tetrahedron Lett. 1978, 1635.
a
7
complex 5 with cyclohexylidene protections of hydroxy
groups at 4,6:2′,3′:4′,6′ positions of 2 was fairly soluble
in 1,2-dichloroethane, but less in water. Thus, the
hydrogenation of methyl (Z)-R-acetamidocinnamate using
the catalyst 5 took place in 1,2-dichloroethane with high
enantioselectivity of 95% ee, while the same reaction
scarcely occurred in water. However, the addition of SDS
(
5) (a) Yonehara, K.; Hashizume, T.; Mori, K.; Ohe, K.; Uemura, S.
J . Org. Chem. 1999, 64, 5593. (b) Recently, RajanBabu and co-worker
have independently reported the synthesis of water-soluble chiral Rh
complex from R,R-trehalose. See: Shin, S.; RajanBabu, T. V. Org. Lett.
999, 1, 1229.
(
Chem. 1999, 64, 1774. (b) Hu, W.; Yan, M.; Lau, C.-P.; Yang, S. M.;
Chan, A. S. C.; J iang, Y.; Mi, A. Tetrahedron Lett. 1999, 40, 973. (c)
Zhu, G.; Zhang, X. J . Org. Chem. 1998, 63, 9590. (d) Burk, M. J .; Casy,
G.; J ohnson, N. B. J . Org. Chem. 1998, 63, 6084. (e) Zhang, F.-Y.; Pai,
C.-C.; Chan, A. S. C. J . Am. Chem. Soc. 1998, 120, 5808. (f) Burk, M.
J .; Wang, Y. M.; Lee, J . R. J . Am. Chem. Soc. 1996, 118, 5142. (g) Sinou,
D.; Kagan, H. B. J . Organomet. Chem. 1976, 114, 325.
1
6) (a) Zhang, Z.; Zhu, G.; J iang, Q.; Xiao, D.; Zhang, X. J . Org.
(7) The rhodium complex 5 was synthesized from 2,3:4,6-di-O-
cyclohexylidene-â-D-glucopyranosyl-(1,1)-4,6-O-cyclohexylidene-2,3-di-
5
a
2 4
O-(diphenylphosphino)-â-D-glucopyranoside) and [Rh(cod) ]BF in
degassed THF under Ar at room temperature for 1 h.