Asymmetric hydrogenation of (E)-α, β-bis(N-acylamino)acrylates catalyzed by a rhodium complex with trans-chelating chiral diphosphine ligand

Article abstract of DOI:10.1016/S0957-4166(98)00297-3

The asymmetric hydrogenation of (E)-α,β-bis(N-acylamino)acrylates was promoted by a rhodium complex bearing a trans-chelating chiral diphosphine ligand (R,R)-(S,S)-PrTRAP, providing the corresponding optically active (2S,3R)-2,3-bis(N-acylamino)carboxylat

Full text of DOI:10.1016/S0957-4166(98)00297-3

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 9 (1998) 2773–2775
Asymmetric hydrogenation of (E)-α,β-bis(N-acylamino)acrylates
catalyzed by a rhodium complex with trans-chelating chiral
diphosphine ligand
Ryoichi Kuwano, Satoshi Okuda and Yoshihiko Ito ∗
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University,
Kyoto 606-8501, Japan
Received 23 June 1998; accepted 21 July 1998
Abstract
The asymmetric hydrogenation of (E)-α,β-bis(N-acylamino)acrylates was promoted by a rhodium complex
bearing a trans-chelating chiral diphosphine ligand (R,R)-(S,S)-PrTRAP, providing the corresponding optically
active (2S,3R)-2,3-bis(N-acylamino)carboxylates with 79–82% ee. The 2,3-bis(N-acylamino)carboxylates isolated
were readily hydrolyzed under acid to afford (2S,3R)-2,3-diaminocarboxylic acids in 95% yield without epimer-
ization. © 1998 Elsevier Science Ltd. All rights reserved.
Optically active α,β-diamino acids are important constituents of antibiotics, such as antrimycin1
and lavendomycin2 et al. Although some syntheses of optically active α,β-diamino acids have been
reported,3–5 they have not been accessible by catalytic asymmetric hydrogenation of the corresponding
olefinic precursor.
In a preceding paper, we reported that trans-chelating chiral diphosphines bearing linear
alkyl substituents on the phosphorus atoms, (S,S)-2,20-bis[(R)-1-(dialkylphosphino)ethyl]-1,10 -
biferrocenes, [abbreviated to (R,R)-(S,S)-alkylTRAPs]6 are effective for asymmetric hydrogenation
of β,β-disubstituted α-acetamidoacrylates catalyzed by rhodium complexes.7 The optically active
alkylTRAP–rhodium complex was also successfully applied for asymmetric hydrogenation of
both (Z)- and (E)-β-oxy-α-acetamidoacrylates, giving optically active β-hydroxy-α-amino acids.8
Herein, we wish to describe the asymmetric hydrogenation of (E)-α,β-bis(N-acylamino)acrylates by
TRAP–rhodium complex catalysts (Scheme 1), which provides an efficient synthesis of optically active
(2S,3R)-α,β-diamino acids after acid hydrolysis.
Several chiral diphosphine ligands were tested for the rhodium catalyzed asymmetric hydrogena-
tion of methyl (E)-2-(N-acetylamino)-3-(N-benzyloxycarbonylamino)-2-alkenoate 1, which was stereo-
∗
Corresponding author. Fax: +81-75-753-5668; e-mail: yoshi@sbchem.kyoto-u.ac.jp
0957-4166/98/$ - see front matter © 1998 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(98)00297-3

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R. Kuwano et al. / Tetrahedron: Asymmetry 9 (1998) 2773–2775
Scheme 1.
Table 1
Asymmetric hydrogenation of 1 catalyzed by TRAP–rhodium complexa
selectively prepared by dehydrative condensation of the corresponding methyl 2-(N-acetylamino)-
3-ketoalkanoate and benzyl carbamate with sulfuric acid catalyst. The results are summarized in Table 1.
Rhodium complexes coordinated with TRAP bearing linear alkyl P-substituents provided good catalytic
activity and enantioselectivity for the asymmetric hydrogenation of (E)-1a. PrTRAP was superior to
Et- and BuTRAP, giving 82% ee of (2S,3R)-(+)-2a without formation of its diastereomer (entries
1–3). The configuration of 2a at the α-carbon was the same as those of products obtained from
asymmetric hydrogenations of other β,β-disubstituted α-acetamidoacrylates catalyzed by an (R,R)-
(S,S)-alkylTRAP–rhodium complex, reported previously.7,8 It is notable that [Rh(COD){(R,R)-Me-
DuPHOS}]PF6,9 which is an effective catalyst for asymmetric hydrogenation of β,β-disubstituted α-
acetamidoacrylates,10,11 did not catalyze the hydrogenation of 1a. A significant decrease of the enantio-
meric excess of the product was observed by use of the substrate bearing the 3-N-phenoxycarbonyl
group (63% ee, EtTRAP), suggesting that the 3-N-substituent of 1 may significantly influence the
enantioselectivity of the asymmetric hydrogenation. α,β-Bis(N-acylamino)acrylates 1b–d were also
hydrogenated by a PrTRAP–rhodium catalyst, giving the corresponding optically active α,β-diamino
acids derivatives 2b–d with 79–81% ee (entries 4–6).
A typical procedure for the asymmetric hydrogenation of 1 is presented as follows. A mixture of (R,R)-
(S,S)-PrTRAP (3.6 mg, 5.0 µmol) and [Rh(COD)2]BF6 (2.0 mg, 5.5 µmol) in MeOH (1.0 ml) was stirred
for 10 min under an argon atmosphere, and then 1 (0.50 mmol) was added to the solution. Immediately,
the reaction vessel was cooled to −78°C, and successively evacuated and filled with hydrogen gas. After
stirring at 30°C for 24 h, the solution was condensed under reduced pressure. The residue was passed
through a short silica gel column to give 2.
As shown in Scheme 2, selective deprotection of the benzyloxycarbonyl group of 2a was accomplished

R. Kuwano et al. / Tetrahedron: Asymmetry 9 (1998) 2773–2775
2775
by hydrogenolysis (100 kg/cm2) with 5% palladium on an activated carbon catalyst in MeOH to give
1
3a. The absolute configuration of (+)-2a was assigned as (2S,3R) by H NMR analysis of the MTPA
amide 4a,12 which was prepared by reaction of 3a with MTPA chloride. In addition, optically active
(2S,3R)-(+)-2a was readily converted into (2S,3R)-2,3-diaminobutanoic acid dihydrochloride 5a without
epimerization by hydrolysis with 10% hydrochloric acid at 100°C for 6 h in 95% yield {[α]D25=+23.6
(c 1.00, H2O)}.
Scheme 2.
In summary, we succeeded in the first catalytic enantioselective hydrogenation of (E)-α,β-bis(N-
acylamino)acrylates 1 using cationic (R,R)-(S,S)-PrTRAP–rhodium complex, which gave 79–82% ee
of threo-α,β-diamino acid derivatives (2S,3R)-2 in high yield. The catalytic asymmetric hydrogenation
will provide an efficient synthetic route of various optically active α,β-diamino acids.
Acknowledgements
This work was financially supported by a Ciba-Geigy Japan Ltd Award in Synthetic Organic Chem-
istry, Japan.
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