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Enantioselective Catalytic Transfer-Hydrogenation of -Unsaturated Carboxylic Acids with Triethylammonium Formate.

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131 H. Paulsen, M. Schiiller, Liebigs Ann. Chem. 1987, 249: H. Paulsen, M.
Stiem, F. M. Unger, ibid. 2987, 273; M. Kiso, M. Fujita, E. Hayashi, A.
Hasegawa, F. M. Unger, J. Carbohydr. Chem. 6 (1987) 691, and references cited therein.
141 M. Imoto, N. Kusunose, Y. Matsuura, S . Kusumoto, T. Shiba, Terrahedron Lett. 28 (1987) 6277.
[51 R. R. Schmidt, M. Reichrath, U.Moering, J. Carbohydr. Chem. 3 (1984)
I61 R. R. Schmidt, M. Reichrath, Angew. Chem. 91 (1979) 497; Angew.
Chem. Int. Ed. Engl. 18 (1979) 466; R. R. Schmidt, ibid. 98 (1986) 213
and 25 (1986) 212, and references cited therein.
171 Favorable structural prerequisites for a-selective U-alkylation are found
for neuraminic acids.
IS] R. R. Schmidt, R. Betz, Angew. Chem. 96 (1984) 420; Angew. Chem. Int.
Ed. Engl. 23 (1984) 430.
191 A. Esswein, Dissertation, Universitat Konstanz 1988; A. Enhsen, Disserration, Universitat Konstanz 1988.
[lo] A corresponding conformation was also observed for a 4,5 :7,8-di-0isopropylidene-protected KDO derivative: see 141.
[111 H. Paulsen, Y. Hayauchi, F. M. Unger, Liebigs Ann. Chem. 1984. 1270,
1288: F. M. Unger, D. Stix, G. Schulz, Carbohydr. Res. 80 (1980) 191.
+ R*
d o
with those of compounds 4. To carry out a structural analysis, compound 7 was converted into the derivative 10 by
amide/ester conversion, azide reduction with hydrogen
sulfide/pyridine, acylation of the free amino group with
myristic acid, acid-catalyzed cleavage of the cyclohexylidene and terf-butyldimethylsilyl groups, 0-acetylation, hydrogenolytic debenzylation, and, once again, O-acetylation. The 'H NMR data for the KDO portion correspond
to those obtained for compound 9.
Enantioselective Catalytic Transfer-Hydrogenation
of a$-Unsaturated Carboxylic Acids with
Triethylammonium Formate**
By Henri Brunner, * and Walter Leitner
The hydrogenation of prochiral olefins in the presence
of optically active rhodium complexes is the most wellknown enantioselective catalysis by transition metal compounds."' The decomposition of formic acid to hydrogen
and carbon dioxide is also catalyzed by rhodium compounds.[21We have been able to combine these two processes to provide a simple, effective alternative to the dangerous and frequently impracticable use of gaseous hydrogen. Scheme 1 shows the enantioselective transfer-hydrogenation of (2)-a-acetylaminocinnamic acid l a and
itaconic acid l b to 2a and 2b, respectively.
General Experimental Procedure
4, 7, and 8 : 2 (2 mmol) was dissolved under N2 in 50 mL of dry dichloromethane (4) or tetrahydrofuran (7, 8) and the resulting solution was cooled
to - 30°C. Sodium hydride (4.2 mmol) was then added and, after 20 min, a
solution of the triflate (2.2 mmol; 3, 5 , and 6, respectively) in 30 mL of dry
dichloromethane, or tetrahydrofuran, was then slowly added dropwise. After
standing for 3 h at -3O"C, the solution was allowed to warm to - 10 to 0°C
and then stirred. The reaction was monitored by thin layer chromatography.
The reaction mixture was filtered through silica gel and concentrated under
vacuum, and the products were chromatographed on silica gel using petroleum ether (30-6O0C)/ethyl acetate as eluent.
R F (petroleum etherlethyl acetate). 4 ( l / l ) 0.41; 7 (2/1) 0.60; 8 (2/1) 0.48.
'H NMR (400 MHz, CDCI3): 4 : 6=4.42 (ddd, J3,,,,4.=3.91, J3,ax,d,=4.46,
J4,,5,=7.33 Hz, 1 H, 4'-H), 4.30 (ddd, J6,.7,=6.59, J7.,8,a=6.34, J7.,8.b=4.88 Hz,
1 H, 7'-H), 4.17 (dd, J 5 , , c = 1.95 Hz, 1 H, S'-H), 4.05 (dd, J8,a,8,b=8.79 Hz, 1 H,
8%-H), 4.00 (dd, 1 H, 8'a-H), 3.75 (dd, 1 H, 6'-H), 2.76 (d, J=4.88 Hz, 3H,
15.38 Hz, I H, 3'ax-H), 1.90 (dd, 1 H, 3'eq-H).
NHCH,), 2.54 (dd, J31x.3.cq=
7: 6=4.43 (ddd, 1 H, 4'-H), 4.31 (ddd, J6,7,=6.34 Hz, I H, 7'-H), 4.16 (dd,
Js,.a,= 1.95, J4:5,=7.08 Hz, 1 H, 5'-H), 4.07 (dd, J8,a,8.b=8.55, J7:8+,=6.35 Hz,
1 H, 8'b-H), 3.94 (dd, J7:8.a=5.12 Hz, I H, 8'a-H), 3.74 (dd, 1 H, 6'-H), 2.75 (d,
J=5.13 Hz, 3H, NHCH,), 2.46 (dd, J3~,,,yeq=15.14, J3.,x,4.=5.12 Hz, l H ,
3'ax-H), 1.91 (dd, J3.eq.4.=3.91 Hz, 1 H, 3'eq-H).
8 : 6=4.30-4.27 (m. 2 H , 4"-, 7"-H), 4.06 (m, IH, 8"bH), 4.02 (dd,
J5..,6..=1.96 Hz, 1 H, 5"-H), 3.94 (dd, J8..a.8..b=8.55,J71..8..a=5.37Hz, I H, 8"aH), 3.75 (dd, J6..,-=5.61 Hz, 1 H, 6"-H), 2.71 (d, J=4.88 Hz,3H, NHCH,),
2.46 (dd, J3.,,,,,-,,=15.38, Hz, 1 H, 3"ax-H), 1.82 (dd,
J3.0q,4..=3.66Hz, I H, 3"eq-H).
'H NMR (400 MHz, C6Ds): 9 : 6=5.77 (s, br, 1 H, 5'-H), 5.68 (ddd,
J3,eq,4,=5.12,53~,,,4~=12.2,J4.,5,=2.93 Hz, 1 H, 4'-H), 5.54 (ddd, J ~ , p ~ = 4 . 3 9 ,
J,.,~,b=2.44,Ja,.7,=9.28 Hz, 1 H, 7'-H), 4.81 (dd, J8,a,8y,= 12.45 Hz, 1 H, 8%-H),
4.51 (dd, Js.,6.=0.98 Hz, 1 H, 6'-H), 4.23 (dd, I H, 8'a-H), 3.26 (s, 3H,
COOCH,), 2.40 (dd, J3h,.3Zq=
12.7 Hz, 1 H, 3'ax-H), 2.32 (dd, 1 H, 3'eq-H).
Ph2P (CH21, PPh,
Scheme 1. a, R'
Ph, R2= NHCOMe; b, R'
8 : [a]:&=+9.0° (c=0.7, CHCI,); 9 : [a]:&= + 105" (c=0.34, CHCl,); 10:
[a]:'&=+67.7" ( ~ = 0 . 7 ,CHCI,).
Received: May 4, 1988;
revised: June 28, 1988 [Z 2740 IE]
German version: Angew. Chem. 100 (1988) 1234
[ I 1 E. T. Rietschel, H. Brade, L. Brade, A. Biinsch, A. Tacker, U. Zahringer,
Forum Mikrobiol. 8 (1985) 286; F. M. Unger, Adu. Carbohydr. Chem. Biochem. 38 (1981) 323, and references cited therein.
[2] M. Imoto, S . Kusumoto, T. Shiba, H. Naoki, T. Iwashita, E. T. Rietschel,
H. W. Wollenweber, C. Galanos, 0. Luderitz, Tetrahedron Lett. 24
(1983)4017; H. Brade, E. T . Rietschel, Eur. J. Biochem. 14s (1984) 231;
H. Brade, U. Zahringer, E. T. Rietschel, Carbohydr Rex 134 (1984) 157;
R. Christian, G. Schulz, P. Waldstatten, F. M. Unger, Tetrahedron Lett.
25 (1984) 3433.
0 VCH VerlagsgesellschaJi mbH, 0-6940 Weinheim, 1988
In situ systems of [Rh(cod)CI], (cod = 1,5-cyclooctadiene) and phosphane ligands serve as catalysts, as are
also used in the hydrogenation with molecular hydrogen.
[*I Prof. Dr. H. Brunner, DipLChem.
W. Leitner
Institut fur Anorganische Chemie der Universitat
Universitatsstrasse 3 1 , D-8400 Regensburg (FRG)
[**I Enantioselective Catalysis, Part 43. This work was supported by the
Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, the Stiftung Volkswagenwerk, and BASF AG, Ludwigshafen.-Part
42: H. Brunner, A. Sicheneder, Angew. Chem. 100 (1988) 730; Angew.
Chem. In[. Ed. Engl. 27 (1988) 718.
0570-0833/88/0909-1180 $ 02.50/0
Angew. Chem. Int. Ed. Engl. 27 (1988) No. 9
Triethylammonium formate (TEAF)[31has proven to be a
useful source of hydrogen. TEAF is a commercially available azeotrope of formic acid and triethylamine (molar ratio
5 :2).'"] Owing to its solubility in organic solvents, TEAF, in
contrast to other formates, furnishes homogeneous reaction mixtures. On using dipolar aprotic solvents, under
mild conditions, results are obtained which approach or
even surpass those achieved with hydrogen. Even in boiling acetone or ethanol the transfer-hydrogenation leads to
complete reduction of the CC double bond, albeit with optical yields of less than 10%. The highest enantiomeric excesses are achieved in DMSO (Table 1).
Table 1. Enantioselective transfer-hydrogenation of (2)-a-acetylaminocinnamic acid l a and itaconic acid l b with triethylammonium formate (TEAF).
The substrates were quantitatively hydrogenated [a].
MPY [d]
ee [Yo][b]
50.0k2.1 (R)
20.5 (R)
49.1k1.6 (S)
83.851.2 (S)
Fig. 1. 'H-NMR spectroscopic monitoring of the transfer-hydrogenation of
Ib with [Rh(cod)Cll2 in the presence of the ligand 8 as catalyst (see text).
Number of ee [Yo]
experiments [c]
81 [7]
93 191
45 IS]
94 191
[a] Determined 'H-NMR spectroscopically. [b] Determined polanmetrically.
Rotations of the pure hydrogenation products: (9-N-acetylphenylalanine:
[a]g=46.5" ( c = I , EtOH) [51, (R)-methylsuccinic acid: [ a ] g = 15.5" (c=2.82,
EtOH) 161. [c] For comparison: rhodium-catalyzed hydrogenation with H2.
The data refer only to substrate and ligand, not to solvent and temperature!
[d] MPY = N-methylpyrrolidone.
In the case of l a the transfer-hydrogenation affords
somewhat lower values, in the case of l b , however, similar
values as the rhodium-catalyzed hydrogenation with molecular hydrogen. With the ligand 3, the optical induction
in the transfer-hydrogenation of l b is even higher than in
the hydrogenation with molecular hydrogen. In all the
cases investigated so far the preferred configuration is the
same in both types of reaction. The employment of TEAF
in DMSO as source of hydrogen is a substantial improvement compared to the transfer-hydrogenation with 80% aqueous formic acid recently described by us.['o1
High enantioselectivities and high reaction rates are
achieved in the transfer-hydrogenation with TEAF only
when ligands such as 3 or 4 are used which can form seven-membered chelate rings. With the ligands norphos["] or
prophos,['21which form five-membered chelate rings and
have proven useful in hydrogenation, only small enantiomeric excesses, usually with incomplete hydrogenation, are
obtained in the transfer-hydrogenation described here.
This influence of the chelate ring size is also reflected in
the relative rates of reaction for the ligands 5 - 8 . When the
decrease in concentration of l b during the catalysis is
monitored via the decrease in intensity of the peaks of the
methylene protons in the 'H-NMR spectrum (6=6.39 and
5.90) relative to the internal standard mesitylene ( S = 6.69)
curves like those shown in Figure 1 for 8 are obtained. A
short induction phase is followed by a linear decrease in
the substrate concentration.
A comparison of the slopes of the linear portions of the
curves shows that the rate of hydrogenation is lowest with
6.With 5 it increases by a factor of 4, with 7 by a factor of
77, and with 8 by even a factor of 128. The reason for this
behavior could lie in the lack of readiness of five-membered ring forming ligands to act as so-called "dangling
I i g a n d ~ " , ~and
' ~ ] thus to make coordination sites free at the
metal atom.
Angew. Chem. lnt. Ed. Engl. 27 (1988) No. 9
t [rninl
500 mg of substrate, 0.7 mol-Yo of [Rh(cod)CI], and 1.8 mol-% of ligand were
dissolved in 3.75 mL of anhydrous DMSO under an atmosphere of nitrogen.
After 30 mins' stirring at the given reaction temperature (Table 1) the mixture
was treated with sufficient TEAF (Merck; dried over MgSO, and distilled
under NZ) to make the substrate/formic acid ratio 1 :5. Shortly thereafter a
vigorous evolution of gas was observed in the orange solution. The mixture
was then stirred for 20 h, rendered alkaline with 10 mL of 2 N NaOH, and
filtered. The filtrate was washed with 4 x 30 mL of ether, acidified with 6 mL
of 10% HCI, and the product extracted with 4 x 50 mL of ether. After drying
over MgS04 the solvent was removed and the product dried for 5 h at 40°C
under vacuum. The yields were quantitative. To avoid the tedious drying necessary for the removal of DMSO residues, the ether extracts of the acid sohtion can be washed with 3 x 5 mL of 5% HCI. The yields are then about
Received: May 1 1 , 1988 [Z 2756 IE]
German version: Angew. Chem. I00 (1988) 1231
[I] J. D. Morrison (Ed.): Asymmetric Synthesis. Vol. 5, Academic Press, Orlando 1985; H. Brunner, Top. Stereochem. 18 (1988) 129.
[2] S. H. Strauss, K. H. Whitmire, D. F. Shriver, J. Organomef. Chem. 174
(1979) C59.
[3] L. F. Fieser, M. Fieser (Eds.): Reagenfs for Organic Synthesis. Vol. 3.
Wiley, New York 1972, p. 300.
[4] K. Narita, M. Sekiya, Chem. Pharm. Bull. 25 (1977) 135.
[5] E. J. Eisenbrunn, S . M. McElvain, J. Am. Chem. SOC.77 (1955) 3383.
161 R. Glaser, M. Twaik, S. Geresh, J. Blumenfeld, Tetrahedron Lert. 1977,
[7] T. P. Dang, J . C. Poulin, H. B. Kagan, J. Organomef. Chem. 91 (1975)
181 S . Saito, Y. Nakamura, Y. Morita, Chem. Pharm. Bull. 33 (1985) 5284.
[9] I. Ojima, T. Kogure, N. Yoda, J. Org. Chem. 45 (1980) 4728.
[lo] H. Brunner, M. Kunz, Chem. Ber. 119 (1986) 2868.
[ l l ] H. Brunner, W. Pieronczyk, B. Schonhammer, K. Streng, I. Bernal, J.
Korp, Chem. Ber. 114 (1981) 1137.
1121 M. D. Fryzuk, B. Bosnich, J. Am. Chem. Soc. 100 (1978) 5491.
(131 B. R. James, D. Mahajan, J. Organornet. Chem. 279 (1985) 31.
Synthesis and Structure of
a Dimeric Material
Containing a Novel Phenoxide Bridge**
By Loren D. Durfee, Phillip E. Fanwick, and
Ian P. RothweN*
The last few years has seen a resurgence of interest in
both the structure and bonding of main group element
compounds."] In the case of the alkali metal compounds
[*I Prof. 1. P. Rothwell, Dr. L. D. Durfee, Dr. P. E. Fanwick
Department of Chemistry, Purdue University
West Lafayette, Indiana 47907 (USA)
This work was supported by the US National Science Foundation.
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acid, formate, triethylammonium, transfer, catalytic, carboxylic, unsaturated, enantioselectivity, hydrogenation
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