Synthesis of optically active 2-aminotetraline derivatives via enantioselective ruthenium-catalyzed hydrogenation of ene carbamates

Article abstract of DOI:10.1016/S0957-4166(01)00153-7

The enantioselective hydrogenation of prochiral ene carbamates, directly derived from 2-tetralone, was completed using a catalytic ruthenium system generated from Ru(COD)(methallyl)², an optically pure diphosphine and a strong acid containing a non-coordinating counter anion.

Full text of DOI:10.1016/S0957-4166(01)00153-7

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 863–867
Synthesis of optically active 2-aminotetraline derivatives via
enantioselective ruthenium-catalyzed hydrogenation of ene
carbamates
Philippe Dupau, Anne-Emmanuelle Hay, Christian Bruneau* and Pierre H. Dixneuf
Institut de Chimie de Rennes, UMR 6509: CNRS-Universit e´ de Rennes 1, Organom e´ talliques et Catalyse, Campus de Beaulieu,
35042 Rennes Cedex, France
Received 8 February 2001; accepted 28 March 2001
Abstract—The enantioselective hydrogenation of prochiral ene carbamates, directly derived from 2-tetralone, was completed using
a catalytic ruthenium system generated from Ru(COD)(methallyl) , an optically pure diphosphine and a strong acid containing
2
a non-coordinating counter anion. © 2001 Elsevier Science Ltd. All rights reserved.
1
0
diphosphine complexes were used to reduce highly
functionalized ene carbamates. At the same time, we
reported the synthesis of optically active carbamates
through the hydrogenation of the endocyclic CꢀC bond
of ene carbamates in the presence of chiral ruthenium
1
. Introduction
Optically active amine derivatives represent an impor-
tant class of biologically active compounds and
homochiral amines are often used as resolving agents or
11
1
complexes. However, none of the previously reported
catalytic systems based on stable well-defined ruthe-
nium and rhodium catalyst precursors were able to
hydrogenate the ene carbamates derived from 2-tetra-
lone itself.
as auxiliaries in enantioselective synthesis. Therefore,
the development of practical methods to directly pro-
duce such derivatives is of great interest. Catalytic
enantioselective hydrogenation has become a competi-
2
tive route with respect to traditional methods such as
resolution or enzymatic processes. Many efforts have
been directed towards the enantioselective hydrogena-
We now report the transformation of 2-tetralone into
optically active amine derivatives via catalytic enan-
tioselective hydrogenation of ene carbamates using a
catalytic system based on Ru(COD)(methallyl)2
3
tion of enamides in the presence of ruthenium and
4
–6
rhodium
catalytic precursors. The highly enantiose-
lective syntheses of 2-aminotetraline derivatives which
are building blocks for biologically active compounds
and pharmaceutical intermediates via the hydrogena-
tion of enamides using ruthenium complexes have been
(
COD=1,5-cyclooctadiene), an optically pure diphos-
phine and HBF4.
7
reported.
2
. Preparation of ene carbamates from 2-tetralone and
primary carbamates
8
Although first described in 1975 by Kagan et al., the
enantioselective hydrogenation of ene carbamates is far
less documented in comparison with the equivalent
reaction of enamides; this is despite the advantageous
facile deprotection of carbamates under mild conditions
to yield amines. During the synthesis of alkaloid pre-
cursors, ruthenium catalysts were shown to be active
for the enantioselective hydrogenation of the exocyclic
Starting from 2-tetralone 1, the ene carbamates 2–7
were obtained in one step in the presence of an excess
of primary carbamate (2.5 equiv.) and a catalytic
amount of para-toluenesulfonic acid (PTSA) (0.1
equiv.) in refluxing toluene in a Dean–Stark apparatus
11
under inert atmosphere for 20 h. After purification by
flash chromatography over silica gel with an ether/pen-
tane mixture, the ene carbamates 2–7 were isolated in
9
CꢀC bond of ene carbamates, and recently, rhodium–
5
0–93% yield. Because of their low stability, they were
immediately hydrogenated or stored under an inert
atmosphere at 6°C (Scheme 1).
*
0
Corresponding author. E-mail: christian.bruneau@univ-rennes1.fr
957-4166/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(01)00153-7

8
64
P. Dupau et al. / Tetrahedron: Asymmetry 12 (2001) 863–867
Scheme 1.
Scheme 2.
3
. Enantioselective hydrogenation of ene carbamates
Me-Duphos. In comparison with other alkyl deriva-
tives, the tert-butyl carbamate 13 was still obtained
with lower selectivity (66% e.e.). Decreasing the reac-
tion temperature to 20°C did not significantly improve
the enantioselectivity in the hydrogenation of 5 (77%
e.e. at 20°C as compared to 76% e.e. at 50°C).
Whereas ene carbamates derived from functionalized
-tetralones were successfully hydrogenated in the pres-
ence of [(R)-Binap]Ru(O CCF ) , no conversion of the
ene carbamate 4 derived from the non-substituted tetra-
lone 1 was observed using the same catalyst precur-
sor. With this type of catalyst precursor, the presence
of another functional group on the molecule favoring
the coordination of the substrate to the ruthenium
center appeared to be essential for hydrogenation in
2
2
3 2
1
1
It is noteworthy that the use of the atropoisomeric
Binap and Biphemp ligands led to no activity for the
hydrogenation of these ene carbamates, which might be
explained by the transformation of these ligands into
monophosphines and the generation of new ruthenium
1
2
these conditions. The hydrogenation of the ene carba-
mates 2–7 was achieved using ruthenium catalyst pre-
cursors produced by treatment in dichloromethane of
an equimolar mixture of the ruthenium complex
Ru(COD)(methallyl)2 and an optically pure diphos-
phine: the BPE- or Duphos-type ligand, with 2 equiv.
of tetrafluoroboric acid. This catalytic system is
inspired from the ruthenium system recently developed
by Gen eˆ t, Rautenstrauch et al. for the hydrogenation of
a tetrasubstituted endocyclic CꢀC bond to produce
14
species in the presence of strong acids. Similarly,
hydrogenation did not occur in the presence of the
cationic [(Duphos)Rh(COD)]BF
(COD)]BF complexes.
and [(BPE)Rh-
4
4
13
methyl dihydrojasmonate, but differs by the use of 2
equiv. of acid and the absence of BF ·Et O as additive.
3
2
The catalytic hydrogenation reactions were performed
in methanol at 50°C under 100 bar pressure of hydro-
gen in the presence of 0.5 mol% of ruthenium and went
to completion within 20 h (non-optimized reaction
times) (Scheme 2).
Table 1. Enantioselective hydrogenation of ene carbamates
using BPE-type ligands
R
Diphosphine
Product Yielda (%) E.e.b (%)
(
substrate)
In the presence of BPE–ruthenium precursors, phenyl 8
and tert-butyl 13 carbamates were obtained with low
enantioselectivity (21–23% e.e.), probably as a result of
electronic and steric factors, respectively. Better results
were observed for carbamates bearing a linear alkyl
chain such as 10 (R=ethyl, 56% e.e.) and 11 (R=n-
butyl, 40 and 50% e.e.) (Table 1). The hydrogenation of
alkyl derivatives at 50°C under 100 bar hydrogen pres-
sure, using the more rigid Duphos bis-phosphine lig-
76c
Ph 2
Et 4
n-Bu 5
n-Bu 5
tert-Bu 7
tert-Bu 7
(S,S)-Me-BPE
(S,S)-Et-BPE
(S,S)-Me-BPE 11
(S,S)-Et-BPE 11
(S,S)-Me-BPE 13
(S,S)-Et-BPE 13
8
10
21 (+)
56 (+)
40 (+)
50 (+)
10 (+)
23 (+)
98
96
97
98
97
General conditions: [Ru*] cat.: (diphosphine)/Ru(COD)(methallyl)2/
2
5
HBF in molar ratio 1:1:2, 0.5 mol% of Ru, H (100 bar), MeOH,
0°C, 20 h, total conversion observed by H NMR.
4 2
1
ands, generally led to
a
significant increase in
enantioselectivity (Table 2). Carbamates 9–13 were thus
obtained in 66–76% e.e. with Et-Duphos as a ligand,
which led to slightly better enantioselectivities than
a
b
c
Isolated yield.
Determined by HPLC (Chiralcel OD 25 column).
Partial conversion observed by H NMR.
1

P. Dupau et al. / Tetrahedron: Asymmetry 12 (2001) 863–867
865
Table 2. Enantioselective hydrogenation of ene carbamates
The activities of these precatalysts dramatically
depends on the nature of the diphosphine and the
acid used to generate the active catalytic species.
Hydrogenated carbamates were thus obtained with
e.e.s of up to 77%, depending on the ligand used and
also on the nature of the carbamate moiety. With the
objective of producing optically active amines, these
results are still less attractive than those obtained
using Duphos-type ligands
R
Diphosphine
Product Yielda (%) E.e. (%)d
(substrate)
60b
Ph 2
(R,R)-Me-Duphos
(R,R)-Me-Duphos
(S,S)-Et-Duphos
8
9
9
17 (−)
68 (−)
73 (+)
61 (−)
76 (+)
76 (+)
77 (+)
73 (+)
66 (+)
Me 3
Me 3
Et 4
Et 4
n-Bu 5
n-Bu 5
95
96
97
98
97
98
98
95
(R,R)-Me-Duphos 10
7c
from the corresponding amides, and thus provide
impetus for the search for more active catalytic sys-
tems.
(S,S)-Et-Duphos
(S,S)-Et-Duphos
(S,S)-Et-Duphos
(S,S)-Et-Duphos
(S,S)-Et-Duphos
10
11
11
12
13
c
iso-Bu 6
tert-Bu 7
5
. Experimental
General conditions: [Ru*] cat.: (diphosphine)/Ru(COD)(methallyl)2/
1
13
2
5
HBF in molar ratio 1:1:2, 0.5 mol% of Ru, H (100 bar), MeOH,
0°C, 20 h, total conversion observed by H NMR.
4 2
1
H NMR (200 MHz) and C NMR (50 MHz) spec-
tra were obtained using a Bruker AM 200 spectro-
meter with TMS as a reference. Silica gel column
chromatography was carried out using Si 60 Merck
silica gel. Analytical HPLC analyses were performed
using a Waters instrument equipped with UV detec-
tion and a Chiralcel OD 25 column.
a
b
c
Isolated yield.
Partial conversion observed by 1H NMR.
2
0°C, 20 h.
d
Determined by HPLC (Chiralcel OD 25 column).
The influence of the nature of the acid used to gener-
ate the ruthenium precursors was investigated in the
presence of (S,S)-Et-Duphos as a ligand in the hydro-
genation of 5 (Table 3). Similar results were obtained
with tetrafluoroboric and triflic acids (100% conver-
sion, 76 and 74% e.e.), but no conversion was
observed when hydrochloric and hydrobromic acids
5.1. Typical procedure for the preparation of a ruthe-
nium precatalyst
An equimolar mixture containing 0.33 mmol of
Ru(COD)(methallyl)2 and 0.33 mmol of the ligand
was dissolved in degassed CH Cl2 (6 mL) in a
2
1
5
were used. The strong coordinating properties of
halide anions are presumably responsible for the dra-
matic change in the catalytic activity of these ruthe-
nium systems, indicating that different organometallic
Schlenk tube under an inert atmosphere. The solution
was then cooled down to 0°C and 2 equiv. (0.66
mmol) of HBF (54 wt% in Et O) were slowly added.
4
2
After stirring at 0°C for 0.5 h the reaction mixture
was evaporated to dryness and afforded an orange
solid which was directly used for hydrogenation of
the ene carbamates.
13,15
species are formed depending on the acid.
The tert-butyl carbamate 13 was deprotected without
racemization using a procedure based on the classical
method, which involved stirring the carbamate in
dichloromethane at 25°C for 1.5 hours in the pres-
ence of 10 equiv. of trifluoroacetic acid. The 2-
aminotetraline hydrochloride 14 was obtained in 90%
yield after treatment with 1N HCl (Scheme 3).
Table 3. Influence of the acid on the enantioselective
hydrogenation of ene carbamate 5
Conversiona (%)
E.e.b (%)
Acid
HBF4
HOTf
HCl
100
100
0
76 (+)
74 (+)
4. Conclusions
HBr
0
We have shown that the enantioselective hydrogena-
tion of 2-tetralone derived ene carbamates containing
an endocyclic CꢀC bond can be achieved using ruthe-
nium precursors generated upon protonation of
General
conditions:
[Ru*]
cat.:
(S,S)-Et-Duphos/
Ru(COD)(methallyl) /2HBF in molar ratio 1:1:2, 0.5 mol% of Ru,
2
4
H2 (100 bar), MeOH, 50°C, 20 h.
Ru(COD)(methallyl) with HBF or triflic acid in the
a
Conversion of the ene carbamate observed by 1H NMR.
2
4
b
presence of a BPE or Duphos ligand.
Determined by HPLC (Chiralcel OD 25 column).
Scheme 3.

8
66
P. Dupau et al. / Tetrahedron: Asymmetry 12 (2001) 863–867
5
.2. General procedure for the enantioselective hydro-
CH ), 3.80–4.20 (m, 3H, OCH +CHN), 4.91 (broad s,
2 2
13 1
genation of ene carbamate
1H, NH), 6.90–7.20 (m, 4H, H ar.). C NMR { H}
50.323 MHz, CDCl ), l 13.86 (CH ), 19.20 (CH ),
(
3
3
2
A solution of the ene carbamate (1 mmol) and the
ruthenium precatalyst (0.005 mmol based on the initial
27.32 (CH ), 29.11 (CH ), 31.20 (CH ), 36.06 (CH ),
2 2 2 2
46.75 (CHN), 64.68 (OCH ), 125.96 (CH ar.), 126.18
2
Ru(COD)(methallyl) complex) in degassed MeOH (8
(CH ar.), 128.86 (CH ar.), 129.50 (CH ar.), 134.25 (C
2
2
0
mL) was placed in a 125 mL autoclave under an inert
atmosphere. After removing the inert gas with hydro-
gen, a pressure of 100 bar of hydrogen was applied. The
autoclave was mechanically stirred at 50°C for 20 h and
quat. ar.), 135.54 (C quat. ar.), 156.32 (CO). [h] =
D
+25.0 (c 0.011, CH Cl ) (76% e.e.).
2
2
5.2.5. N-(1,2 3,4-Tetrahydronaphthalen-2-yl) isobutylcar-
1
1
the conversion was then determined by H NMR. The
bamate 12. H NMR (200.130 MHz, CDCl ), l 0.91 (d,
3
carbamates were purified by flash chromatography over
silica gel (ether/pentane (1:4) mixture used as eluent).
The enantiomeric excesses were determined by HPLC
using a Chiralcel OD 25 column (eluent: hexane/iso-
propanol, 85:15).
J 6.7 Hz, 6H, 2CH ), 1.60–1.95 (m, 2H, 1H CH +CH),
1.95–2.20 (m, 1H, CH ), 2.63 (dd, J 16.5 and 8.2 Hz,
3
2
2
1H, CH ), 2.87 (t, J 6.6 Hz, 2H, CH ), 3.11 (dd, J 16.5
2
2
and 5.0 Hz, 1H, CH ), 3.83 (d, J 6.7 Hz, 2H, OCH ),
2
2
3.87–4.15 (m, 1H, CHN), 4.73 (broad s, 1H, NH),
13
1
6
.90–7.20 (m, 4H, H ar.). C NMR { H} (50.323 MHz,
5
.2.1. N-(1,2,3,4-Tetrahydronaphthalen-2-yl) phenylcar-
CDCl ), l 19.16 (2CH ), 27.22 (CH ), 28.09 (CH),
29.05 (CH ), 36.08 (CH ), 46.72 (CHN), 70.99 (OCH ),
2 2 2
3
3
2
1
bamate 8. H NMR (200.130 MHz, CDCl ), l 1.70–
3
1
1
3
1
7
.97 (m, 1H, CH ), 2.01–2.25 (m, 1H, CH ), 2.73 (dd, J
6.3 and 8.0 Hz, 1H, CH ), 2.91 (t, J 6.6 Hz, 2H, CH ),
.19 (dd, J 16.3 and 5.0 Hz, 1H, CH ), 3.95–4.25 (m,
H, CHN), 5.07 (d, J 6.8 Hz, 1H, NH), 6.95–7.20 (m,
125.96 (CH ar.), 126.19 (CH ar.), 128.87 (CH ar.),
129.52 (CH ar.), 134.19 (C quat. ar.), 135.54 (C quat.
2
2
2
2
2
0
ar.), 156.31 (CO). [h] =+30.1 (c 0.011, CH Cl ) (73%
2
D 2 2
e.e.).
1
3
1
H, H ar.), 7.23–7.45 (m, 2H, H ar.). C NMR { H}
(
(
50.323 MHz, CDCl ), l 27.2 (CH ), 28.84 (CH ), 35.86
5.2.6. N-(1,2,3,4-Tetrahydronaphthalen-2-yl) tert-butyl-
3
2
2
1
CH ), 47.15 (CHN), 121.73 (2 CH ar.), 125.36 (CH
carbamate 13. H NMR (200.130 MHz, CDCl ), l 1.43
2
3
ar.), 126.08 (CH ar.), 126.33 (CH ar.), 128.94 (CH ar.),
(s, 9H), 1.60–1.85 (m, 1H, CH ), 1.90–2.15 (m, 1H,
2
1
1
29.37 (2CH ar.), 129.58 (CH ar.), 134.00 (C quat. ar.),
35.46 (C quat. ar.), 151.09 (C quat. ar.), 154.11 (CO).
CH ), 2.64 (dd, J 16.2 and 8.0 Hz, 1H, CH ), 2.86 (t, J
2
2
6.6 Hz, 2H, CH ), 3.11 (dd, J 16.2 and 5.0 Hz, 1H,
2
CH ), 3.85–4.15 (m, 1H, CHN), 4.72 (s broad, 1H,
2
5
.2.2. N-(1,2,3,4-Tetrahydronaphthalen-2-yl) methylcar-
NH), 6.90–7.20 (m, 4H, H ar.).
1
bamate 9. H NMR (200.130 MHz, CDCl ), l 1.60–
3
1
1
3
.85 (m, 1H, CH ), 1.90–2.15 (m, 1H, CH ), 2.63 (dd, J
5.3. General procedure for carbamate deprotection
2
2
6.1 and 8.0 Hz, 1H, CH ), 2.86 (t, J 6.6 Hz, 2H, CH ),
2
2
.10 (dd, J 16.1 and 5.0 Hz, 1H, CH ), 3.65 (s, 3H,
To a solution of tert-butylcarbamate 13 (1 equiv.) in
dichloromethane was slowly added trifluoroacetic acid
(10 equiv.) and the reaction mixture was stirred at room
temperature for 1.5 h. It was then evaporated to dry-
ness under vacuum. The residue was dissolved in
dichloromethane and 1N HCl was then added. The
biphasic mixture was vigorously stirred for 45 min. The
aqueous phase was then evaporated to dryness to
2
OCH ), 3.85–4.15 (m, 1H, CHN), 4.71 (broad s, 1H,
3
13
1
NH), 6.90–7.20 (m, 4H, H ar.). C NMR { H} (50.323
MHz, CDCl ), l 27.32 (CH ), 29.11 (CH ), 36.05
3
2
2
(CH ), 46.89 (CHN), 52.01 (OCH ), 125.97 (CH ar.),
2
3
1
1
26.20 (CH ar.), 128.85 (CH ar.), 129.49 (CH ar.),
34.20 (C quat. ar.), 135.51 (C quat. ar.), 156.59 (CO).
20
D 2 2
[
h] =+37.0 (c 0.010, CH Cl ) (73% e.e.).
afford
(1,2,3,4-tetrahydronaphthalen-2-yl)-amine
5
.2.3. N-(1,2,3,4-Tetrahydronaphthalen-2-yl) ethylcarba-
chlorhydrate 14 as a white solid in 90% yield.
1
mate 10. H NMR (200.130 MHz, CDCl ), l 1.22 (t, J
3
7
.1 Hz, 3H, CH ), 1.60–1.90 (m, 1H, CH ), 1.90–2.20
5.3.1. (1,2,3,4-Tetrahydronaphthalen-2-yl)-amine chlor-
3
2
1
(m, 1H, CH ), 2.63 (dd, J 16.3 and 8.2 Hz, 1H, CH ),
hydrate 14. H NMR (200.130 MHz, D O), l 1.60–1.90
2
2
2
2
1
.86 (t, J 6.6 Hz, 2H, CH ), 3.10 (dd, J 16.3 and 5.2 Hz,
(m, 1H, CH ), 1.95–2.15 (m, 1H, CH ), 2.60–2.90 (m,
2
2
2
H, CH ), 3.80–4.30 (m, 3H, OCH +CHN), 4.75 (broad
3H, 1H CH +CH ), 3.09 (dd, J 16.1 and 5.2 Hz, 1H,
2 2
13
2
2
1
3
1
s, 1H, NH), 6.90–7.20 (m, 4H, H ar.). C NMR { H}
CH ), 3.40–3.65 (m, 1H, CHN), 7.10 (s, 4H, H ar.).
C
2
1
(
50.323 MHz, CDCl ), l 14.70 (CH ), 27.17 (CH ),
NMR { H} (50.323 MHz, D O), l 26.42 (CH ), 26.63
3
3
2
2 2
2
1
1
9.03 (CH ), 36.08 (CH ), 46.66 (CHN), 60.73 (OCH ),
(CH ), 32.79 (CH ), 47.44 (CHN), 126.30 (CH ar.),
2 2
126.74 (CH ar.), 128.80 (CH ar.), 129.26 (CH ar.),
132.25 (C quat. ar.), 134.95 (C quat. ar.).
2
2
2
25.96 (CH ar.), 126.19 (CH ar.), 128.86 (CH ar.),
29.52 (CH ar.), 134.16 (C quat. ar.), 135.52 (C quat.
2
0
ar.), 156.12 (CO). [h] =+49.4 (c 0.011, CH Cl ) (76%
D
2
2
e.e.).
.2.4. N-(1,2,3,4-Tetrahydronaphthalen-2-yl) butylcarba-
Acknowledgements
5
1
mate 11. H NMR (200.130 MHz, CDCl ), l 0.93 (t, J
3
.1 Hz, 3H, CH ), 1.20–1.47 (m, 2H, CH ), 1.47–1.65
The authors are very grateful to ORIL Industry Com-
pany for fruitful discussions and financial support to
P.D., and Ascot Fine Chemicals-Chirotech Technology
Ltd. for the loan of chiral diphosphines.
3
2
2
2
1
H, CH ), 2.64 (dd, J 16.3 and 8.3 Hz, 1H, CH ), 2.87
2
2
(
t, J 6.6 Hz, 2H, CH ), 3.10 (dd, J 16.3 and 5.1 Hz, 1H,
2

P. Dupau et al. / Tetrahedron: Asymmetry 12 (2001) 863–867
867
References
1832.
8
. Kagan, H. B.; Langlois, N.; Dang, T. P. J. Organomet.
1
. (a) Burk, M. J.; Martinez, J. P.; Feaster, J. E.; Cosford,
N. Tetrahedron 1994, 50, 4399; (b) Lucet, D.; Le Gall, T.;
Mioskowski, C. Angew. Chem., Int. Ed. Engl. 1998, 37,
Chem. 1975, 90, 363.
9. Couture, A.; Deniau, E.; Lebrun, S.; Grandclaudon, P.;
Carpentier, J.-F. J. Chem. Soc., Perkin Trans. 1 1998,
2
580; (c) Blaser, H.-U.; Spindler, F. Top. Catal. 1997, 4,
1403.
2
75.
1
0. (a) Burk, M. J.; Johnson, N. B.; Lee, J. R. Tetrahedron
Lett. 1999, 40, 6685; (b) Li, X.; Yeung, C.-H.; Chan, A.
S. C.; Lee, D.-S.; Yang, T.-K. Tetrahedron: Asymmetry
2
. (a) Noyori, R. Asymmetric Catalysis In Organic Chem-
istry; Wiley: New York, 1994; (b) Akutagawa, S. Appl.
Catal. A: Gen. 1995, 128, 171; (c) Ohkuma, T.; Kitamura,
M.; Noyori, R. In Catalytic Asymmetric Synthesis;
Ojima, I., Ed.; John Wiley: New York, 2000; pp. 1–110.
. Noyori, R.; Ohta, M.; Hsiao, Y.; Kitamura, M. J. Am.
Chem. Soc. 1986, 108, 7117.
1999, 10, 3863.
1
1. Dupau, P.; Bruneau, C.; Dixneuf, P. H. Tetrahedron:
Asymmetry 1999, 10, 3467.
2. Hydrogenation of ene carbamates with
3
4
5
6
7
1
a methyl
propanoate group in position 5 also occurred using ((R)-
. Kagan, H. B.; Dang, T. P. J. Am. Chem. Soc. 1972, 18,
Binap)Ru(O CCF ) as a catalyst (unpublished results).
2
3 2
6
429.
. Burk, M. J.; Casy, G.; Johnson, N. B. J. Org. Chem.
998, 63, 6084.
1
3. Dobbs, D. A.; Vanhessche, K. P. M.; Brazi, E.; Rauten-
strauch, V.; Lenoir, J.-Y.; Gen eˆ t, J.-P.; Wiles, J.; Bergens,
S. H. Angew. Chem., Int. Ed. 2000, 39, 1992.
4. den Reijer, C. J.; W o¨ rle, M.; Pregosin, P. S.
Organometallics 2000, 19, 309.
5. (a) Gen eˆ t, J. P.; Mallard, S.; Pinel, C.; Jug e´ , S. Tetra-
hedron: Asymmetry 1991, 2, 43; (b) Gen eˆ t, J. P.; Pinel, C.;
Ratovelomanana-Vidal, V.; Mallard, S.; Pfister, X.; Cano
de Andrade, M. C.; Laffite, J. A. Tetrahedron: Asymm-
etry 1994, 5, 665.
1
. Zhang, Z.; Zhu, G.; Jiang, Q.; Xiao, D.; Zhang, X. J.
1
Org. Chem. 1999, 64, 1774.
. (a) Tschaen, D. M.; Ambranson, L.; Cai, D.; Desmond,
R.; Dolling, V. H.; Frey, L.; Karady, S.; Shi, Y. J.;
Verhoeven, T. R. J. Org. Chem. 1995, 60, 4324; (b)
Devocelle, M.; Morteux, A.; Agbossou, F.; Dormoy,
J.-R. Tetrahedron Lett. 1999, 40, 4551; (c) Dupau, P.; Le
Gendre, P.; Bruneau, C.; Dixneuf, P. H. Synlett 1999,
1
.