The use of a new carboranylamidophosphite ligand in the asymmetric Pd-catalysed allylic alkylation in organic solvents and supercritical carbon dioxide

Article abstract of DOI:10.1016/j.jorganchem.2009.05.018

A novel P-monodentate ligand based on carboranyl alcohol and (S)-2-(anilinomethyl)pyrrolidine provides high enantioselectivities (ee's up to 95%) in the Pd-catalyzed allylic alkylation of (E)-1,3-diphenylallyl acetate. The first example of the Pd-catalysed allylic alkylation in supercritical carbon dioxide is also described.

Full text of DOI:10.1016/j.jorganchem.2009.05.018

Journal of Organometallic Chemistry 694 (2009) 3047–3049
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
The use of a new carboranylamidophosphite ligand in the asymmetric
Pd-catalysed allylic alkylation in organic solvents and supercritical carbon dioxide
a,*
b
b
a
Sergey E. Lyubimov , Ilya V. Kuchurov , Andrei A. Vasil’ev , Andrey A. Tyutyunov ,
a
a
b
Valery N. Kalinin , Vadim A. Davankov , Sergei G. Zlotin
a
A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov Street 28, 119991 Moscow, Russia
N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky Prosp. 47, 119991 Moscow, Russia
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel P-monodentate ligand based on carboranyl alcohol and (S)-2-(anilinomethyl)pyrrolidine provides
high enantioselectivities (ee’s up to 95%) in the Pd-catalyzed allylic alkylation of (E)-1,3-diphenylallyl
acetate. The first example of the Pd-catalysed allylic alkylation in supercritical carbon dioxide is also
described.
Received 15 April 2009
Accepted 18 May 2009
Available online 21 May 2009
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Asymmetric allylic alkylation
Palladium
Supercritical carbon dioxide
Carboranyldiamidophosphite
1
. Introduction
The development of novel optically active ligands remains one
enantioselectivities in the asymmetric hydrogenation processes
and motivated by our continuing efforts in the design of novel chi-
ral carboranylphosphite-type ligands, we have prepared a novel
sterically congested carborane-containing monodentate diam-
idophosphite ligand for application in other important asymmetric
catalytic transformations, namely Pd-catalyzed allylic substitution
of the most attractive areas in the field of transition metal-cata-
lyzed asymmetric reactions. To achieve the highest levels of reac-
tivity and selectivity in enantioselective catalytic reactions,
different reaction parameters must be explored and adjusted. In
this optimization process, not only a careful selection of the chiral
ligand but also reaction conditions, such as temperature, solvents
are always important. Recently, we designed a novel class of chiral
mono- and bidentate phosphite-type ligands containing sterically
congested carborane fragments and showed their high efficiency
for the Rh-catalyzed asymmetric hydrogenation of functionalized
olefins (up to 99.8% ee) [1]. Further examination of catalytic activ-
ity and selectivity of the ligands shows that monodentate ligands
are more effective compared to bidentate carboranylphosphite-
type ligands and electron-donating carboranyl substituents are
essential to obtain high levels of enantiodiscrimination and con-
version [2–4]. Along with the design of chiral ligands, another sig-
nificant challenge in metal complex asymmetric catalysis is the use
of alternative solvents often called as ‘‘green media” for catalytic
transformations [5]. Recently we showed that phosphite-type
ligands, including carborane-containing ones, are very effective
catalysts for asymmetric hydrogenation (up to 99% ee) in supercrit-
2
in organic solvents and scCO . The high synthetic utility of this
type of catalytic processes is now well established through numer-
ous efficient syntheses of enantiopure natural and unnatural prod-
ucts [8]. Our recent attempt to use bidentate carborane-containing
ligands in the Pd-catalyzed allylic substitution gave promising
results (up 83% ee) [9], but these results remained below the ee’s
of 99.8% which were achieved with monodentate carborane-con-
taining phosphites in the asymmetric hydrogenation processes.
2
. Results and discussion
The new monodentate diamidophosphite ligand 3 was synthe-
sized by a convenient one-step phosphorylation of the correspond-
ing ortho-9-hydroxy-1,2-dimethyldicarba-closo-dodecaborane (2,
3
1
13
11
Scheme 1). The ligand 3 was characterized by P, C, and
B
NMR spectroscopy and by elemental analysis (see Section 3). It is
a white solid and is air stable under ambient conditions.
Complexation of the novel diamidophosphite 3 with [Pd(al-
ical carbon dioxide (scCO
2
) [1,2,6,7]. Encouraged by the excellent
lyl)Cl]
(Scheme 2).
To study the potential of the carboranylphosphite ligand 3 and
its Pd complex 4, we tested them in the Pd-catalyzed allylic
2 4
(in the presence of AgBF ) produced cationic Pd(II) complex
4
*
Corresponding author. Tel.: +7 499 1352548; fax: +7 499 1356471.
E-mail address: lssp452@mail.ru (S.E. Lyubimov).
0
022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.05.018

3
048
S.E. Lyubimov et al. / Journal of Organometallic Chemistry 694 (2009) 3047–3049
HO
+
Me
N
N
N
2.
N
P
Me
Et N, C H
3 6 6
P
1.
Cl
3.
-
Et NxHCl
O
3
Me
Me
Scheme 1. Synthesis of chiral carborane-containing diamidophosphite ligand.
+
2 3
to Cs CO strongly increased the enantioselectivity from 64% to
81% ee and moreover the reaction proceeded without addition of
the crown ether.
Cl
Cl
4
L, 2 AgBF4
L
L
BF4
Pd
Pd
2
Pd
-
2 AgCl
4
.
Scheme 2. Synthesis of Pd complex 4.
3. Conclusions
In conclusion, we have prepared a novel carborane-containing
diamidophosphite ligand for the use in asymmetric catalysis. The
ligand proved to be efficient in the Pd-catalysed allylic alkylation
of (E)-1,3-diphenylallyl acetate with dimethyl malonate (up to
+
CH (CO Me) ,
MeO C
CO Me
2
2
2
2
2
OAc
Ph
base, cat*
Ph
* Ph
Ph
9
5% ee). We have shown also that the ligand can catalyze actively
the allylic alkylation process in the presence of a simple base –
CO under phase-transfer conditions with a complete conversion
5.
6.
Scheme 3. Pd-catalyzed allylic alkylation of (E)-1,3-diphenylallyl acetate.
K
2
3
and high enantioselectivity (91% ee). No less important, the ligand
has provided for the first time a very good enantioselectivity (up to
substitution of (E)-1,3-diphenylallyl acetate 5 (which is widely
used as a model substrate) with dimethyl malonate (Scheme 3
and Table 1).
8
2
1% ee) in scCO with the use of inorganic bases.
The use of CH
2
Cl
2
or THF as standard solvents for the reaction
4. Experimental
and BSA (N,O-bis(trimethylsilyl)acetamide) as base showed excel-
lent enantioselectivities (90–95% ee) and complete conversion in
all cases, independent of the L/Pd ratio (Table 1, entries 1–6). Test-
ing the pre-formed complex 4 and a simple and inexpensive base,
4.1. General
31P, 13C, and 11B spectra were recorded with a Bruker AMX 400
3
1
13
such as K
2
CO
3
4
under phase-transfer conditions (Bu NBr) developed
instrument (162.0 MHz for P, 100.6 MHz for C and 128.4 MHz
1
1
1
by us earlier for achiral allylic substrates [10], gave complete con-
version of 5 in 16 h compared to 36 h with the liquid base – BSA
for B). Chemical shifts (ppm) are given relative to Me
4
Si ( H
1
3
31
*
11
and C), 85% H
3
PO
4
(
P NMR) and BF
3
2
Et O ( B). Elemental
and the same level of enantioselectivity (91% ee) in CH
, entries 5 and 7). In the case of THF as solvent, the use of BSA
or K CO (under phase-transfer conditions) showed the same level
of enantioselectivity (90% ee, Table 1, entries 6 and 8), but only 56%
conversion of 5 was observed in 18 h, compared to the reaction in
2
Cl
2
(Table
analyses were performed at the Laboratory of Microanalysis (Insti-
tute of Organoelement Compounds, Moscow). Conversion of sub-
strate 5 and optical purity of product 6 were determined using
HPLC (Daicel Chiralcel OD-H column) as described previously
[11]. Phosphorylating reagent 1 – (2R,5S)-2-chloro-3-phenyl-1,3-
diaza-2-phosphabicyclo[3.3.0]octane [12] and 9-hydroxy-1,2-dim-
ethylcarborane 2 [13] were prepared as published. Cationic
palladium complex 4 was synthesised analogously to the known
procedure [12].
1
2
3
CH
The use of scCO
the presence of 18-crown-6 gave moderate enantioselectivity
64% ee) and conversion 75%. A simple change of the inorganic base
2
Cl
2
under phase-transfer conditions (Table 1, entries 7 and 8).
2
as solvent and the inorganic base – K CO in
2
3
(
Table 1
Pd-catalyzed enantioselective allylic alkylation of 5 with dimethyl malonate.
Entry
Catalyst
L/Pd
Solvent
Base
T (h)
Conversion (%)
ee (%)
1
2
3
4
5
6
7
8
9
[Pd(allyl)Cl]
[Pd(allyl)Cl]
[Pd(allyl)Cl]
[Pd(allyl)Cl]
4
4
4
4
4
4
2
/3
2
/3
2
/3
2
/3
1/1
1/1
2/1
2/1
2/1
2/1
2/1
2/1
2/1
2/1
CH
THF
CH Cl
THF
CH Cl
THF
CH Cl
2
Cl
2
2
2
2
BSA
BSA
BSA
BSA
BSA
BSA
36
36
36
36
36
36
18
18
18
18
100
100
100
100
100
100
100
56
93 (S)
91 (S)
95 (S)
92 (S)
92 (S)
90 (S)
91 (S)
90 (S)
64 (S)
81 (S)
2
2
a
a
b
2
K
K
K
2
CO
2
CO
2
CO
3
3
3
THF
scCO
scCO
2
2
75
60
1
0
Cs
2
CO
3
a
Phase-transfer conditions – Bu
Phase-transfer conditions – 18-crown-6.
4
NBr.
b

S.E. Lyubimov et al. / Journal of Organometallic Chemistry 694 (2009) 3047–3049
3049
4.2. Synthesis of (2R,5S)-2-(1,2-dimethyl-ortho-carboran-9-yloxy)-3-
10 min, then dimethyl malonate (0.1 mL, 0.87 mmol), K
2 3
CO
phenyl-1,3-diaza-2-phosphabicyclo[3.3.0]-octane (3)
(87 mg, 0.75 mmol) and Bu NBr were added and the reaction mix-
4
ture stirred for a further 18 h. The resulting solution was diluted
with water (5 mL), three times extracted with benzene (3 mL),
The corresponding hydroxycarborane 2 (0.188 g, 1.0 mmol) was
added to a vigorously stirred solution of the phosphorylating agent
the organic solvents were separated, dried with CaCl
vents removed under vacuum.
2
and the sol-
1
(0.240 g, 1.0 mmol) and NEt
3
(0.135 mL, 1.0 mmol) in benzene
(
25 mL). The mixture was stirred for 10 min. The reaction mixture
Method C: The pre-formed catalysts 4 (0.02 mmol), dimethyl
malonate (0.07 mL, 0.6 mmol), substrate 5 (0.1 mL, 0.5 mmol),
was then heated at reflux for 10 min, cooled, and filtered. The
resulting solution was passed through a short silica gel plug and
the solvent was evaporated at reduced pressure. Yield – 0.275 g
K
2
CO
of K CO
sel was filled with scCO
2
3
or Cs
) were placed open to air into a 10 mL autoclave. The ves-
by means of a syringe-press to a total
2 3
CO (0.75 mmol) and 18-crown-6 (25 mg, in the case
2
3
3
1
(
70%), colourless oil. P{H} NMR (CDCl
3
): = 130.01 (q, JP,B = 74 Hz).
): À13.55–9.68 (m, 8B), À6.42 (d, J = 148.4 Hz, 1B),
3
1
1
B NMR (CDCl
3
pressure of 170 atm. The mixture was allowed to equilibrate to
the reaction temperature of 70 °C (20 min) and stirred for 18 h.
After this, the vessel was slowly depressurised. The resulting solu-
tion was diluted with water (5 mL), three times extracted with
benzene (3 mL), the organic solvents was separated, dried with
1
1
1.48 (s, 1B). C {H}NMR (CDCl
s, Ar), 118.1 (s, Ar), 115.5 (d, J = 12.6 Hz), 68.0 (s, carb), 62.3 (d,
J = 8.4 Hz, C ), 57.7 (s, carb), 53.2 (d, J = 6.8 Hz, C ), 47.5 (d,
J = 35.9 Hz, C ), 31.4 68.0 (s, C ), 26.1 (d, J = 4.2 Hz, C ), 23.6 (s,
CH ), 20.6 (s, CH ). Anal. Calc. for C15 OP: C, 45.90; H,
.45; N, 7.14. Found: C, 46.07; H, 7.56; N, 7.10%.
3
): 145.7 (d, J = 15.5 Hz, Ar), 128.5
(
5
4
8
6
7
3
3
29
H B
10
N
2
2
CaCl and concentrated under reduced pressure.
7
References
4.3. Palladium complex 4 [Pd(allyl)(3)
2 4
]BF
[
[
[
[
1] S.E. Lyubimov, A.A. Tyutyunov, V.N. Kalinin, E.E. Said-Galiev, A.R. Khokhlov,
P.V. Petrovskii, V.A. Davankov, Tetrahedron Lett. 48 (2007) 8217–
Yield: 92%, white solid; m.p.: 152 (dec.). 31P{H} NMR
8219.
(
CDCl ): = 105.10. Anal. Calc. for C33 Pd: C, 38.89;
3
63 21 4 4 2 2
H B F N O P
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H, 6.23; N, 5.50. Found: C, 38.95; H, 6.35; N, 5.68%.
(
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4
.4. Pd-catalysed allylic alkylation of 1,3-diphenyl-2-propenyl acetate
with dimethyl malonate
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Petrovskii, V.A. Davankov, J. Supercrit. Fluid. 45 (2008) 70–73.
2
Method A: A solution of [Pd(allyl)Cl] (0.0037 g, 0.01 mmol) and
ligand 3 (0.02 or 0.04 mmol, depending on desired Pd/L ratio) in
mL of the appropriate solvent was stirred for 10 min [alterna-
[
[
3
tively, the pre-synthesised complex 4 (0.02 mmol) was dissolved
in the appropriate solvent (3 mL)]. (E)-1,3-diphenylallyl acetate
[7] S.E. Lyubimov, V.A. Davankov, E.E. Said-Galiev, A.R. Khokhlov, Catal. Commun.
(2008) 1851–1852.
9
[
[
8] Z. Lu, S. Ma, Angew. Chem., Int. Ed. 47 (2008) 258–297.
9] S.E. Lyubimov, A.A. Tyutyunov, P.A. Vologzhanin, A.S. Safronov, P.V. Petrovskii,
V.N. Kalinin, K.N. Gavrilov, V.A. Davankov, J. Organomet. Chem. 693 (2008)
(
1
(
0.1 mL, 0.5 mmol) was added and the solution stirred for
0 min, then dimethyl malonate (0.1 mL, 0.87 mmol), BSA
0.22 mL, 0.87 mmol) were added and the reaction mixture stirred
3321–3323.
[
10] A.A. Vasil’ev, S.E. Lyubimov, E.P. Serebryakov, V.A. Davankov, S.G. Zlotin,
Mendeleev Commun. 19 (2009) 103–105.
for further 36 h. The resulting solution was filtered through silica
gel. The solvent was removed under vacuum to give dimethyl
[11] H. Kodama, T. Taiji, T. Ohta, I. Furukawa, Tetrahedron: Asymmetr. 11 (2000)
009–4015.
4
[
(E)-1,3-diphenyl-prop-2-en-1-yl]malonate (6) as a yellow oil
[
12] V.N. Tsarev, S.E. Lyubimov, A.A. Shiryaev, S.V. Zheglov, O.G. Bondarev, V.A.
Davankov, A.A. Kabro, S.K. Moiseev, V.N. Kalinin, K.N. Gavrilov, Eur. J. Org.
Chem. (2004) 2214–2222.
slowly crystallizing on storage.
Method B: A solution of complex 4 (0.02 mmol) was dissolved in
the appropriate solvent (5 mL). (E)-1,3-diphenylallyl acetate
[
13] L.I. Zakharkin, V.N. Kalinin, L.S. Podvisotskaya, Zh. Obshch. Khim. 36 (1966)
1786–1789.
(
0.1 mL, 0.5 mmol) was added and the solution stirred for