Influence on the enantioselectivity in allylic alkylation of the spacer between the amido group of d-glucosamine and the diphenylphosphino group

Article abstract of DOI:10.1016/j.tetasy.2005.08.035

The synthesis of a new generation of chiral phosphine-amides derived from d-glucosamine is described. The palladium-catalyzed asymmetric allylic alkylation of racemic 1,3-diphenyl-2-propenyl acetate with dimethyl malonate has been investigated. The result

Full text of DOI:10.1016/j.tetasy.2005.08.035

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 16 (2005) 3183–3187
Influence on the enantioselectivity in allylic alkylation of the
spacer between the amido group of D-glucosamine and the
diphenylphosphino group
Anzhelika Konovets,a Katarzyna Glegoła,a,c Alexandra Penciu,a Eric Framery,a,*
Philippe Jubault,b Catherine Goux-Henry,a K. Michał Pietrusiewicz,c
Jean-Charles Quirionb and Denis Sinoua
a
`
´ ´
Laboratoire de Synthese Asymetrique, UMR UCBL/CNRS 5181, ESCPE Lyon, Universite Claude Bernard Lyon 1, 43 boulevard
du 11 novembre 1918, F-69622 Villeurbanne Cedex, France
b
`
Laboratoire dÕHe´te´rochimie Organique, UMR INSA/CNRS 6014, Universite´ de Rouen, 1 rue Tesniere,
F-76821 Mont-Saint-Aignan Cedex, France
cDepartment of Organic Chemistry, Maria Curie-Skłodowska University, ul. Gliniana 33, 20-614 Lublin, Poland
Received 7 July 2005; revised 23 August 2005; accepted 25 August 2005
Abstract—The synthesis of a new generation of chiral phosphine-amides derived from D-glucosamine is described. The palladium-
catalyzed asymmetric allylic alkylation of racemic 1,3-diphenyl-2-propenyl acetate with dimethyl malonate has been investigated.
The results obtained from these new ligands showed the importance of the rigidity of the complex and of the D-glucosamine skeleton
on the enantioselectivity of the reaction.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
carbohydrates have been used in a large number of cat-
alytic asymmetric reactions.4 With respect to the palla-
dium-catalyzed allylic substitution, several ligands
based on carbohydrates have already been described in
the literature. In addition to P–P, S–S, and S–X
(X = P or N) ligands derived from ferrocenylglucose,5
bis-thioglycosides6 and oxazoline-thioglucose,7 the P–
N ligands are amongst the most frequently described.
The P–N ligands based on oxazoline have been the first
efficient ones, with enantioselectivities up to 98% and
96% ee being obtained using a phosphinoaryloxazoline
ligand derived from a carbohydrate8 and a phosphi-
nite-oxazoline derived from D-glucosamine.9 A P–N
ligand derived from a carbohydrate has also been
described by Ruffo and co-workers,10 but gave very
low enantioselectivity. Finally, a P–N ligand derived
from the glucopyranose oxime-ether11 has also been pre-
pared, but gave no selectivity in the model allylic substi-
tution reactions. Two years ago, we reported on the
potential of the phosphine-amide ligand 1 derived from
D-glucosamine (Fig. 1).12 With this ligand, enantioselec-
tivities up to 97% were obtained in the palladium-cata-
lyzed allylic alkylation of 1,3-diphenyl-2-propenyl
acetate with various nucleophiles. We observed that
Over the last 15 years, palladium-catalyzed allylic sub-
stitution has been one of the most studied catalytic reac-
tions. The carbon–carbon and carbon–heteroatom bond
formation reactions have found many applications in
asymmetric synthesis. Since the first example described
by Trost and Strege in 1977,1 many asymmetric catalytic
systems have been described. Amongst the best ones are
TrostÕs P–P ligand2 and PfaltzÕs P–N ligand3 with
enantioselectivities up to 95% being obtained using these
ligands. In the main, the optimization of several experi-
mental parameters is often necessary in order to obtain
both the high activity and the high enantioselectivity,
and the ligand structure is one of the main factors.
In order to obtain chiral ligands, one methodology is the
use of chiral natural precursors, which can easily be
functionalized, and carbohydrates offer many advanta-
ges. During the last decade, many ligands derived from
*
Corresponding author. Tel.: +33 472 446 263; fax: +33 472 448
160; e-mail: framery@univ-lyon1.fr
0957-4166/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2005.08.035

3184
A. Konovets et al. / Tetrahedron: Asymmetry 16 (2005) 3183–3187
OAc OAc
O
O
AcO
AcO
AcO
AcO
OAc
OAc
HN
HN
O
O
Ph2P
Ph2P
1
2
OAc
O
AcO
OAc
AcO
HN
PPh2
O
R
(R)-3a: R = CH2CH3
(S)-3b: R = CH2CH3
3c: R = H
Figure 1. Phosphine-amide ligands 1–3 derived from D-glucosamine.
the enantioselectivity was higher with a ratio ligand/pal-
ladium of 1/1 ligand/palladium ratio, than with a ratio
of 2/1. This behavior was explained by two different
modes of chelation, P,O-chelation versus P,P-chelation,
respectively. The P,O-chelation gave higher enantiose-
lectivity, due to the rigidity of the formed complex, since
in the case of P,P-chelation, there is more freedom in the
complex.
already described,12 and the catalyst prepared also from
the new phosphine-amide ligands 2 and 3a–c based on
D-glucosamine (Fig. 1).
2. Results and discussion
The syntheses of D-glucosamine based diphenylaryl-
phosphine 2 and diphenylalkylphosphines 3a–c are
shown in Scheme 1. The phosphine-amide ligand 2
was obtained in 62% yield by the coupling of [2-
(diphenylphosphino)phenyl]acetic acid 4, prepared as
described in the literature,13 with 2-amino-1,3,4,6-
tetra-O-acetyl-2-deoxy-b-D-glucopyranose in CH2Cl2/
Herein, we report on the influence of the flexibility of the
spacer between the amido group of D-glucosamine and
the diphenylphosphino group in palladium-catalyzed
asymmetric allylic alkylations. We used the catalyst pre-
pared from palladium and phosphine-amide ligand 1
OAc
O
PPh2
AcO
OAc
AcO
(i)
HO
HN
O
O
Ph2P
4
2
OAc
O
BH3
PPh2
AcO
OAc
(i)
AcO
BH3
HN
HO
PPh2
O
R
O
R
(R)-6a, R = CH2CH3
(S)-6b, R = CH2CH3
6c, R = H
5a-c
(ii)
3a-c
Scheme 1. Synthesis of the D-glucosamine-based diphenylarylphosphine 2 and diphenylalkylphosphine 3a–c. Reagents and conditions: (i) 2-amino-
1,3,4,6-tetra-O-acetyl-2-deoxy-D-glucopyranose EDC, HOBT, CH2Cl2/THF, rt, 24 h; (ii) DABCO, toluene, rt, 48 h.

A. Konovets et al. / Tetrahedron: Asymmetry 16 (2005) 3183–3187
3185
Table 1. Palladium-catalyzed asymmetric allylic alkylation of racemic 1,3-diphenylprop-2-enyl acetate with dimethyl malonatea
OAc
Ph
CH(CO2Me)2
Ph
[Pd] / L*
+ CH2(CO2Me)2
Ph
Ph
BSA - LiOAc
Entry
Ligand L*
Conv. (%)b
Yield (%)c
ee (%)d (config.)e
1
2
3
4
5
1f
100
100
100
100
100
98
92
95
96
99
83 (R)
29 (R)
76 (R)
86 (R)
66 (R)
2
3a
3b
3c
a [Substrate]:[nucleophile]:[BSA]:[LiOAc]:[Pd]:[Ligand] = 25:75:75:1:1:1.
b Conversion determined by GC analysis.
c Isolated pure product.
d Determined by HPLC analysis (column Chiralpak AD 0.46 · 25 cm).
e Determined by comparison with an authentic sample.
f See Ref. 12.
THF in the presence of 1-[3-dimethylaminopropyl]-3-
ethylcarbodiimide (EDC) and 1-hydroxybenzotriazole
(HOBT). The borane–phosphine-amide complexes
5a–c were obtained following the same procedure
from carboxylic acids 6a–c14 in 74%, 75%, and 61%
yields, respectively. The addition of 1,4-diazabicy-
clo[2.2.2]octane (DABCO) to a solution of 5a–c in tolu-
ene gave the corresponding D-glucosamine-based
diphenylalkylphosphine 3a–c in almost quantitative
yields.
Pd–C bonds have been measured. The length of the
˚
Pd–C bond trans to P is 2.20 A, and the Pd–C bond
˚
trans to O is 2.07 A, inducing in a P,O-chelated complex
the nucleophilic attack predominantly at the allyl termi-
nus trans to the Pd–P bond. Since the (R) alkylated
product was obtained as the major enantiomer in all
cases, the reaction most likely proceeds through com-
plex A rather than complex B as shown in Figure 2.
The difference in enantioselectivity between ligand 1
and ligand 2 could be due to the rigidity of the complex
of Pd with ligand 1 bearing a phenyl ring between the
amido group and the diphenylphosphino group. Effec-
tive chelation of palladium with the oxygen and phos-
phorus atoms gave a quite rigid six-member chelate
affording higher enantioselectivity (Fig. 2). In the case
of ligand 2, there is one methylene group between the
amido function and the phenyl ring thus affording a
more flexible seven-member chelate with palladium.
The conformation of this chelate is not favorable, and
ligand 2 gave a lower ee. Concerning ligands 3a–c, the
amido function and the diphenylphosphino group are
separated by two methylene units, affording a flexible
six-member chelate with palladium (Fig. 2). Ligand 3c
gave ees up to 66%, ligands 3a and 3b gave ees up to
76% and 86%, respectively, with the same (R)-configura-
tion being obtained. The model showed effectively that
for both ligands 3a and 3b (Fig. 2), the chelate is mainly
stabilized by the relative disposition of the carbohydrate
moiety and the ethyl group (R2 in Fig. 2). According to
the obtained results, the most important factor is the
asymmetric induction due to the carbohydrate moiety,
which directed the attack of the nucleophile. The posi-
tion of the ethyl group in the space [(R)- or (S)-configu-
ration] modified slightly the steric environment, and
consequently the ee.
Ligands 2 and 3a–c were examined in the palladium-cat-
alyzed asymmetric allylic alkylation of racemic 1,3-di-
phenyl-2-propenyl acetate with dimethyl malonate and
were compared to the results obtained using ligand 1
(Table 1). The conditions of this palladium-catalyzed
allylic substitution are the same as those described
previously.12 The reaction was performed in THF
(0.125 M) using 2 mol % of [Pd(g3-C3H5)Cl]2, 4 mol %
of ligand 2 or 3a–c, 3 equiv of dimethyl malonate and
a mixture of N,O-bis(trimethylsilyl)acetamide (BSA)
(3 equiv) and LiOAc (2 mol %) as base. The conversion
was quantitative for each ligand after 24 h at rt. The
results are summarized in Table 1.
The obtained enantioselectivities using ligands 3a–b
bearing a stereogenic center on the spacer are quite sim-
ilar to, or lower than, those previously reported for
amido-phosphine 1 (83% ee). Ligand 3b bearing an
(S)-stereogenic center gave a ee higher than ligand 1
(86% ee), while ligand 3a, bearing an (R)-stereogenic
center gave a lower ee (76% ee), with the same configu-
ration being obtained in all cases. Ligands 2 and 3a–c
gave the alkylation product with the same (R)-configu-
ration. Ligand 3c with no stereogenic center in the a-
position to the diphenylphosphino group gave ees up
66%. Finally, ligand 2 bearing a CH2C6H4PPh2 function
instead of a C6H4PPh2 gave the lowest enantioselectiv-
ity, with ees up to 29%.
3. Conclusion
In conclusion, new chiral phosphine-amides derived from
D-glucosamine were easily prepared, and used in the pal-
ladium-catalyzed asymmetric allylic alkylation with ees
In the case of the P,O-chelated complex obtained from
diamidocyclohexane-phosphine,15 the lengths of the

3186
A. Konovets et al. / Tetrahedron: Asymmetry 16 (2005) 3183–3187
OAc OAc
O
O
OAc
OAc
R1
AcO
AcO
AcO
AcO
R1
HN
HN
R2
R2
*
*
O
O
PPh2
PPh2
Ph
Pd
Pd
Ph
Ph
Ph
Nu
Nu
complex B
complex A
CHR1-CHR2 =
, R1 = H / R2 = Et, H
Figure 2. A plausible scheme in the allylic alkylation using six-member chelates 1 and 3a–c.
up to 86%. The influence of the D-glucosamine moiety
seems to be the most important factor in this asymmet-
ric allylic alkylation. The synthesis of new carbohydrate-
based ligands is currently in progress, in order to have a
deeper insight on the factors influencing this asymmet-
ric-catalyzed reaction.
Rf = 0.60 (petroleum ether/ethyl acetate 1/2);
25
½aꢀD ¼ þ25:3 (c 0.6, CHCl3); 1H NMR (CDCl3): d
7.63–7.52 (m, 1H, Harom), 7.45–7.26 (m, 11H, Harom),
7.24–7.16 (m, 1H, Harom), 6.92–6.85 (m, 1H, Harom),
5.68 (br d J = 8.7 Hz, 1H, NH), 5.50 (d, J = 8.9 Hz,
1H, H-1), 5.07 (dd, J = 9.4, 9.2 Hz, 1H, H-3), 5.03
(dd, J = 9.6, 9.4 Hz, 1H, H-4), 4.28 (dd, J = 12.4,
4.5 Hz, 1H, H-6), 4.20 (dd, J = 8.9, 9.2 Hz, 1H, H-2),
4.10 (dd, J = 12.4, 2.2 Hz, 1H, H-60), 3.75 (ddd,
J = 9.6, 4.5, 2.2 Hz, 1H, H-5), 3.70 (br s, 2H, CH2),
2.10 (s, 3H, CH3), 2.06 (s, 3H, CH3), 1.94 (s, 3H,
CH3), 1.86 (s, 3H, CH3); 31P NMR (CDCl3): d ꢁ12.9;
HRMS [M+H]+ C34H36NO10P: calcd 650.2155, found
650.2152.
4. Experimental
4.1. General
Solvents were purified by standard methods and dried if
necessary. All commercially available reagents were used
as received. All reactions were monitored by TLC (TLC
plates GF254 Merck). Air and moisture sensitive reac-
tions were performed under the usual inert atmosphere
techniques. Reactions involving organometallic catalysis
were carried out in a Schlenk tube under an inert atmo-
sphere. Column chromatography was performed on sil-
ica gel 60 (230–240 mesh, Merck). Optical rotations
were recorded using a Perkin–Elmer 241 polarimeter.
NMR spectra were recorded with a Bruker AMX 300
4.3. General procedure for the synthesis of 3a–c
2-Amino-1,3,4,6-tetra-O-acetyl-2-deoxy-b-D-glucopyra-
nose (500 mg, 1.44 mmol), carboxylic acid 6a–c
(1.51 mmol), EDC (326 mg, 1.70 mmol), and HOBT
(230 mg, 1.70 mmol) were dissolved in a mixture of
CH2Cl2 (10 mL) and THF (20 mL) in a Schlenk tube.
After being stirred for 48 h at rt, the solvents were evap-
orated. The residue was purified by chromatography on
silica gel to give borane–phosphine-amide complexes
5a–c. Complexes 5a–c and DABCO (4.53 mmol) were
dissolved in toluene (10 mL) in a Schlenk tube under
argon. After being stirred for 48 h at rt, the solvent was
evaporated. The crude powder was purified by flash-
chromatography on silica gel using petroleum ether/
ethyl acetate (10/15) as the eluent to give ligand 3a–c.
1
spectrometer and referenced as follows: H (300 MHz),
internal SiMe4 at d 0.00 ppm and 31P (121 MHz),
external 85% H3PO4 at d 0.00 ppm. Conversion was
determined by GC using a Quadrex OV1 column
(30 m · 0.25 mm), and enantiomeric excess was deter-
mined by HPLC with
a
ChiralpakAD column
(25 cm · 4.6 mm) using a ratio of hexane/i-propanol as
eluent.
4.2. Synthesis of 1,3,4,6-tetra-O-acetyl-2-deoxy-2-({[2-
diphenylphosphino)phenyl]acetyl}amino-b-D-glucopyra-
nose, 2
4.3.1. 1,3,4,6-Tetra-O-acetyl-2-deoxy-2-{[(3R)-3-(diphen-
ylphosphino)pentanoyl]amino}-b-D-glucopyranose,
3a.
Rf = 0.60 (petroleum ether/ethyl acetate 10/15);
25
½aꢀD ¼ þ8:5 (c 0.2, CHCl3); 1H NMR (CDCl3): d
2-Amino-1,3,4,6-tetra-O-acetyl-2-deoxy-b-D-glucopyra-
nose (500 mg, 1.44 mmol), carboxylic acid 4 (484 mg,
1.51 mmol), EDC (326 mg, 1.70 mmol), and HOBT
(230 mg, 1.70 mmol) were dissolved in a mixture of
CH2Cl2 (10 mL) and THF (20 mL) in a Schlenk tube.
After being stirred for 48 h at rt, the solvents were evap-
orated. The residue was purified by chromatography on
silica gel to give phosphine-amide 2 (yield 62%).
7.92–7.82 (m, 2H, Harom), 7.80–7.69 (m, 2H, Harom),
7.52–7.32 (m, 6H, Harom), 5.80 (br d J = 8.7 Hz, 1H,
NH), 5.69 (d, J = 8.9 Hz, 1H, H-1), 5.30 (dd, J = 9.4,
9.2 Hz, 1H, H-3), 5.10 (dd, J = 9.8, 9.4 Hz, 1H, H-4),
4.29 (dd, J = 12.4, 4.5 Hz, 1H, H-6), 4.26 (dd, J = 9.2,
8.9 Hz, 1H, H-2), 4.11 (dd, J = 12.4, 1.9 Hz, 1H, H-
60), 3.88 (ddd, J = 9.8, 4.5, 1.9 Hz, 1H, H-5), 3.39–3.24
(m, 1H, CH), 2.40–2.20 (m, 2H, CH2CO), 2.09 (s, 3H,

A. Konovets et al. / Tetrahedron: Asymmetry 16 (2005) 3183–3187
3187
COCH3), 2.04 (s, 3H, COCH3), 2.00 (s, 3H, COCH3),
1.93 (s, 3H, COCH3), 1.58–1.39 (m, 2H, CH2CH3),
0.78 (t, J = 7.2 Hz, 3H, CH2CH3); 31P NMR (CDCl3):
diethyl ether (15 mL) and water (5 mL). The organic
phase was washed with brine and dried over MgSO4.
Evaporation of the solvent gave a residue, which was
purified by chromatography (petroleum ether/ethyl ace-
tate 10/1). The enantiomeric excesses were determined
by HPLC analysis.
d
ꢁ4.5; HRMS [M+H]+ C31H39NO10P: calcd
616.2312, found 616.2317.
4.3.2. 1,3,4,6-Tetra-O-acetyl-2-deoxy-2-{[(3S)-3-(diphen-
ylphosphino)pentanoyl]amino}-b-D-glucopyranose,
3b.
Rf = 0.60 (petroleum ether/ethyl acetate 10/15);
Acknowledgements
25
½aꢀD ¼ þ17:2 (c 0.25, CHCl3); 1H NMR (CDCl3): d
7.92–7.83 (m, 2H, Harom), 7.82–7.73 (m, 2H, Harom),
7.52–7.32 (m, 6H, Harom), 5.73 (d, J = 8.8 Hz, 1H, H-
1), 5.68 (br d J = 8.7 Hz, 1H, NH), 5.16 (dd, J = 9.4,
9.2 Hz, 1H, H-3), 5.11 (dd, J = 9.4, 9.4 Hz, 1H, H-4),
4.30 (dd, J = 12.5, 4.5 Hz, 1H, H-6), 4.25 (dd, J = 9.4,
8.8 Hz, 1H, H-2), 4.13 (dd, J = 12.5, 2.2 Hz, 1H, H-
60), 3.83 (ddd, J = 9.4, 4.5, 2.2Hz, 1H, H-5), 3.39–3.24
(m, 1H, CH), 2.40–2.20 (m, 2H, CH2CO), 2.10 (s, 3H,
COCH3), 2.06 (s, 3H, COCH3), 2.04 (s, 3H, COCH3),
1.83 (s, 3H, COCH3), 1.60–1.41 (m, 2H, CH2CH3),
0.80 (t, J = 7.2 Hz, 3H, CH2CH3); 31P NMR (CDCl3):
A.K. thanks the CNRS, and A.P. and K.G. thank the
MENSR for fellowships.
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ꢁ4.5; HRMS [M+H]+ C31H39NO10P: calcd
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4.3.3.
1,3,4,6-Tetra-O-acetyl-2-deoxy-2-({[2-(diphen-
ylphosphino)phenyl]acetyl}amino)-b-D-glucopyranose, 3c.
Rf = 0.55 (petroleum ether/ethyl acetate 10/15);
25
½aꢀD ¼ þ14:5 (c 0.2, CHCl3); 1H NMR (CDCl3): d
7.80–7.60 (m, 4H, Harom), 7.52–7.38 (m, 6H, Harom),
6.03 (br d J = 8.1 Hz, 1H, NH), 5.75 (d, J = 8.7 Hz,
1H, H-1), 5.24 (dd, J = 9.8, 9.4 Hz, 1H, H-3), 5.10
(dd, J = 9.8, 9.4 Hz, 1H, H-4), 4.28 (dd, J = 12.4,
4.2 Hz, 1H, H-6), 4.21 (dd, J = 9.4, 8.7 Hz, 1H, H-2),
4.12 (dd, J = 12.4, 1.9 Hz, 1H, H-60), 3.86 (ddd,
J = 9.8, 4.2, 1.9 Hz, 1H, H-5), 2.58–2.49 (m, 2H,
CH2), 2.36–2.30 (m, 2H, CH2CO), 2.08 (s, 3H, COCH3),
2.07 (s, 3H, COCH3), 2.04 (s, 3H, COCH3), 1.98 (s, 3H,
COCH3); 31P NMR (CDCl3):
d
ꢁ15.2; HRMS
[M+Na]+ C29H34NO10NaP: calcd 610.1818, found
610.1815.
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4.4. General procedure for the allylic alkylation
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In a Schlenk tube, [Pd(g3-C3H5)Cl]2 (8.8 mg, 24 lmol)
and the ligand (48 lmol) were dissolved in THF
(1 mL). After being stirred for 1 h at rt, a solution of
racemic 1,3-diphenyl-2-propenyl acetate (302 mg,
1.2 mmol) in THF (1 mL) was added. After 30 min, this
solution was transferred to a Schlenk tube containing
dimethyl malonate (475 mg, 3.6 mmol), BSA (732 mg,
3.6 mmol), and LiOAc (2.5 mg, 24 lmol) in THF
(2 mL). The reaction mixture was stirred at the desired
temperature for 24 h. The conversion was determined
by GC analysis. The mixture was then diluted with
´
14. Leautey, M.; Jubault, P.; Pannecoucke, X.; Quirion, J.-C.
Eur. J. Org. Chem. 2003, 3761–3768.
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