Chiral P*-monodentate phosphite ligand for Pd-catalysed asymmetric allylation reactions

Article abstract of DOI:10.1070/mc2003v013n03abeh001745

Monodentate diamidophosphite ligand 2 with stereogenic phosphorus and carbon atoms, which is easily available from (S)-2-phenylaminomethyl pyrrolidine, is an effective chiral inductor in Pd-catalysed asymmetric allylation reactions.

Full text of DOI:10.1070/mc2003v013n03abeh001745

, 2003, 13(3), 134–135
Chiral P*-monodentate phosphite ligand for Pd-catalysed asymmetric allylation
reactions
Konstantin N. Gavrilov,a Vasily N. Tsarev,*b Sergey E. Lyubimov,a Alexei A. Shyryaev,a Sergey V. Zheglov,a
Oleg G. Bondarev,b Vadim A. Davankov,b Anzhelika A. Kabro,b Sergey K. Moiseevb and Valery N. Kalininb
a Department of Chemistry, Ryazan State Pedagogic University, 390000 Ryazan, Russian Federation.
Fax: +7 0912 77 5498; e-mail: chem@ttc.ryazan.ru
b A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow, Russian Federation.
Fax: +7 095 135 6471; e-mail: tsarev@ineos.ac.ru
10.1070/MC2003v013n03ABEH001745
Monodentate diamidophosphite ligand 2 with stereogenic phosphorus and carbon atoms, which is easily available from
(S)-2-phenylaminomethyl pyrrolidine, is an effective chiral inductor in Pd-catalysed asymmetric allylation reactions.
Transition metal catalysed asymmetric allylation reactions are
one of the most powerful tools for the formation of carbon–
L
BF4
ligand , AgBF
2
4
carbon and carbon–heteroatom bonds. Palladium is usually a
metal of choice in these processes with P,N- and P,P-bidentate
ligands being the most common chiral inductors.1 Very few
examples of the application of P-monodentate ligands have
been reported. Namely, several amidophosphinites2 and phos-
phines3–5 were tested in Pd-catalysed asymmetric allylation
reactions resulting in the formation of C–C bonds, while amido-
phosphinites6 were used for C–C and C–N bond formation.
Note that all those ligands contained at least one P–C bond.
Therefore, to the best of our knowledge, no examples of chiral
monodentate phosphites applications to Pd-catalysed asymmetric
allylation have been reported so far. It is quite strange because
the presence of three P–N (or P–O) bonds in phosphite mole-
cules provides excellent opportunities for the fine tuning of
such important features as the π-acidity of ligands, their stability
and steric demands. Remarkably, the latest impressive achieve-
ments in the enantioselective hydrogenation, conjugate addition
and hydrosilylation/oxidation reactions are associated with mono-
dentate phosphite ligands.7 Moreover, the phosphite derivatives
of BINOL have shown good results in the asymmetric allylation
of cinnamyl acetate with dimethyl malonate, with [Ir(COD)Cl]2
being used as a pre-catalyst.8–10
[Pd(allyl)Cl]2
Pd
THF, 20 °C
L
3
Scheme 2
Both ligand 2 and its complex 3 were tested in the Pd-
catalysed asymmetric allylic sulfonylation reaction, as well as
in the direct asymmetric synthesis of a carborane derivative.
The sulfonylation of 1,3-diphenylpropen-2-yl acetate with
sodium p-toluenelsulfinate (Scheme 3) was carried out follow-
ing the method described earlier.14
The obtained results are summarized in Table 1. Complex 3
was found to be the most effective catalyst providing 97% ee
(entry 3). Remarkably, this is the highest enantioselectivity
achieved in the reaction up to date (v. 93% ee obtained in the
case of P,N-bidentate phosphinooxazoline ligands18).
The allylation reaction of methyl phenyl(2-phenyl-ortho-
carboran-1-yl)acetate 4 with methyl prop-2-enyl carbonate
(Scheme 4) is of interest as the first example of direct asym-
metric synthesis in the carborane series.19
On the other hand, many P,N-bidentate phosphite ligands,
including those prepared from (S)-2-phenylaminomethyl pyr-
rolidine,11–14 have been successfully used in Pd-catalysed
asymmetric allylation reactions.1,7,15 In this report, we demon-
strate that it is not necessary for the phosphite ligands to have
any nitrogen-containing functionality, for example, quinoline11
or oxazoline,14 to achieve high enantioselectivity.
O
NaSO2pTol, L*/[Pd], 2 mol% [Pd]
OAc
Ph
S
*
O
THF, 20 °C, 48 h
Ph
Ph
Ph
Scheme 3
Preparation of compound 2. A solution of ButOH (0.51 ml, 5.40 mmol)
†
in benzene (3 ml) was added dropwise to a vigorously stirred solution of
compound 1 (1.297 g, 5.40 mmol) and Et3N (0.73 ml, 5.40 mmol) in
benzene (8 ml) at 0 °C. The resulting mixture was warmed to 80 °C for a
short time, then cooled down to 20 °C. The Et3N·HCl solid was filtered
off, and the filtrate was evaporated in vacuo. The residue was distilled
in vacuo to obtain 2 as a colourless liquid (1.319 g, 88% yield).
Bp 70–72 °C/1 Torr. 13C NMR (101 MHz, CDCl3) d: 145.77–115.45
Ligand 2 was prepared from readily available (S)-2-phenyl-
aminomethyl pyrrolidine16 (Scheme 1).
PCl3, Et3N
NHPh
C6H6, 0 to 80 °C
N
H
2
(CAr), 74.29 (d, COP, 2JC,P 7.2 Hz), 62.46 [d, C(5), JC,P 8.0 Hz], 52.45
Cl
N
O
2
2
[d, C(4), JC,P 6.5 Hz], 47.83 [d, C(8), JC,P 35.5 Hz], 31.58 [s, C(6)],
1
30.73 (d, Me, JC,P 8.4 Hz), 25.95 [d, C(7), JC,P 4.6 Hz]. 31P NMR
(162 MHz, CDCl3) d: 128.43. MS (EI, 70 eV), m/z (I, %): 278 [M]+ (2),
221 [M – But]+ (25), 205 [M–ButO]+ (6). Found (%): C, 64.52; H, 8.42;
N, 10.28. Calc. for C15H23N2OP (%): C, 64.73; H, 8.33; N, 10.06.
3
3
ButOH, Et3N
P
P
2
8
6
N
N
7
3
Ph
Ph
N
5
C6H6, 0 to 80 °C
4
H
H
‡
Preparation of compound 3. A solution of ligand 2 (0.222 g, 0.8 mmol)
1
2
Scheme 1
in CHCl3 (15 ml) was added dropwise to a stirred solution of [Pd(Allyl)Cl]2
(0.073 g, 0.2 mmol) in the above solvent (15 ml) at 20 °C. The reaction
mixture was stirred at 20 °C for 1 h and then a solution of AgBF4
(0.078 g, 0.4 mmol) in THF (15 ml) was added. The solution was stirred
for another 1 h at 20 °C, filtered, concentrated to ~0.5 ml, and pre-
cipitated with diethyl ether. The obtained precipitate was separated by
centrifugation, washed with diethyl ether (2×10 ml) and dried in air and
in vacuo (1 Torr). Yellow solid (0.316 g, 93% yield). Mp 172–174 °C.
31P NMR (162 MHz, CDCl3) dP: 106.16. 19F NMR (188 MHz, CDCl3)
dF: –75.41. MS (FAB), m/z (I, %): 703 [M – BF4]+ (100), 662 [M –
BF4 – allyl]+ (13). Found (%): C, 49.92; H, 6.38; N, 6.85. Calc. for
C33H51BF4N4O2P2Pd (%): C, 50.11; H, 6.50; N, 7.08.
Intermediate (2R,5S)-2-chloro-3-phenyl-1,3-diaza-2-phospha-
bicyclo[3.3.0]octane 114 was isolated in good yield (71%) and
used for the synthesis of ligand 2 under mild conditions.† Both
compound 1 and ligand 2 are stable in a dry atmosphere and, if
needed, can be easily purified by distillation in vacuo. Ligand 2
has (R)-configuration of the P*-stereogenic centre, according
2
to the characteristic JC(8),P value in its 13C NMR spectra
(35.5 Hz).13,17 Starting from 2, cationic PdII complex 3 was
prepared (Scheme 2).‡
– 134 –

, 2003, 13(3), 134–135
References
Table 1 Enantioselective Pd-catalysed allylic sulfonylation of 1,3-di-
phenylpropen-2-yl acetate.
1
2
3
4
5
6
B. M. Trost and C. Lee, in Catalytic Asymmetric Synthesis, ed. I. Ojima,
Wiley–VCH, New York, 2000, p. 593.
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Isolated
yield (%)
Entry
Catalyst precursor
[Pd(allyl)Cl]2
L*/[Pd]
1/1
eea (%)
1
2
3
32
16
44
94(S)
80(S)
97(S)
[Pd2(dba)3·CHCl3] 1/1
2/1
3
a ee measured by HPLC [(R,R)-Whelk-01].
Ph
PhC CCHCOOMe
7
8
OCO2Me
B10H10
4
9
10 B. Bartels, C. Garcia-Yebra, F. Rominrer and G. Helmchen, Eur. J.
Inorg. Chem., 2002, 2569.
L*/[Pd], 2 mol% [Pd]
20 °C, 96 h, BSA, KOAc
*
PhC CC(Ph)COOMe
11 T. Constantieux, J.-M. Brunel, A. Labande and G. Buono, Synlett,
1998, 49.
12 G. Delapierre, J.-M. Brunel, T. Constantieux and G. Buono, Tetrahedron:
Asymmetry, 2001, 12, 1345.
B
10H10
5
Scheme 4
In addition, this is a relatively rare type of Pd-catalysed
asymmetric allylation that produces a chiral centre not at the
allyl moiety, but at the attacking nucleophile. The stereoselec-
tivity of this allylation is difficult to control since the nucleo-
13 O. G. Bondarev, K. N. Gavrilov, V. N. Tsarev, V. A. Davankov, R. V.
Lebedev, S. K. Moiseev and V. N. Kalinin, Izv. Akad. Nauk, Ser. Khim.,
2002, 484 (Russ. Chem. Bull., Int. Ed., 2002, 51, 521).
14 K. N. Gavrilov, O. G. Bondarev, V. N. Tsarev, A. A. Shyryaev, S. E.
Lyubimov, A. S. Kucherenko and V. A. Davankov, Izv. Akad. Nauk,
Ser. Khim., 2003, 116 (Russ. Chem. Bull., Int. Ed., 2003, 52, 122).
15 K. N. Gavrilov and A. I. Polosukhin, Usp. Khim., 2000, 69, 721 (Russ.
Chem. Rev., 2000, 69, 661).
16 S. Iriuchijima, Synthesis, 1978, 684.
17 J.-M. Brunel, T. Constantieux and G. Buono, J. Org. Chem., 1999, 64,
8940.
18 H. Eichelmann and H.-J. Gais, Tetrahedron: Asymmetry, 1995, 6, 643.
19 R. V. Lebedev, S. K. Moiseev, O. G. Bondarev, M. M. Il’in, K. N. Gavrilov
and V. N. Kalinin, Izv. Akad. Nauk, Ser. Khim., 2002, 476 (Russ. Chem.
Bull., Int. Ed., 2002, 51, 513).
3
phile approaches the allyl ligand of the intermediate η -allyl-
palladium complex from the side opposite to the transition
metal atom and hence the chiral ligand.19 The asymmetric
reaction shown in Scheme 4 had been effected earlier using
P,N-bidentate ligands,13,19 the highest ee obtained up to date
being 48%.13 Our results obtained with ligand 2 and complex 3
are listed in Table 2. Note that in the case of complex 3 the
enantioselectivity (about 70% ee) does not depend on whether
THF or CH2Cl2 were used as the solvent. Furthermore, the same
result was obtained when the catalyst was prepared from ligand
2 and [Pd(allyl)Cl]2 in situ. The achieved enantioselectivity is
rather high for the allylation reactions giving rise to the chiral
centre at the attacking nucleophile.19 Unfortunately, the reac-
tion is very slow (the conversion of starting compound 4 was
about 10% after 96 h in all cases),§ but it is typical of such
processes.19
We are grateful to Dr. A. V. Korostylev (Institut für
Organische Katalyse, Rostock, Germany) for his assistance in
preparation of the manuscript. The receipt of a chiral HPLC
column (R,R)-Whelk-01 as a gift from Regis Technologies Inc.
(USA) is gratefully acknowledged. This work was supported in
part by the Russian Foundation for Basic Research (grant nos.
00-15-97427 and 03-03-32181).
Table 2 Enantioselective Pd-catalysed allylation of carborane derivative 4.
Entry
Catalyst precursor
L*/[Pd]
Solvent
eea (%)
1
2
3
[Pd(allyl)Cl]2
3
3
2/1
2/1
2/1
CH2Cl2
CH2Cl2
THF
70
73
68
a ee measured by HPLC [(R,R)-Whelk-01].
§
General procedure for the Pd-catalysed allylation of carborane
derivative 4: To a solution of 3 (0.02 mmol) in 4 ml THF or CH2Cl2
{or to solution of [Pd(allyl)Cl]2 (3.7 mg, 0.01 mmol) and ligand 2
(0.04 mmol) in 4 ml CH2Cl2 stirred for 20 min} ester 4 (185 mg,
0.5 mmol), methyl prop-2-enyl carbonate (0.12 ml, 1 mmol), BSA [N,O-
bis(trimethylsilyl)acetamide, 0.15 ml, 0.6 mmol), and anhydrous KOAc
(3 mg, 0.03 mmol) were added. The resulting homogeneous solution
was kept at 20 °C for 96 h. The solvent was then removed in vacuo; the
residue was dissolved in 30 ml of ether and washed with 5% HCl
(2×20 ml), a saturated solution of NaHCO3 (20 ml), and water. The
organic layer was dried over Na2SO4, and the solvent was removed at a
reduced pressure. The products were separated by column chromato-
graphy on silica gel [200×25 mm, eluent: petroleum ether–EtOAc (7:1)].
After removing the solvent, the obtained mixture of 5 and starting ester 4
was analysed by 1H NMR spectroscopy.
Received: 31st March 2003; Com. 03/2071
– 135 –