Asymmetric allylation of aldehydes with chiral platinum phosphinite complexes

Article abstract of DOI:10.1016/j.tetasy.2007.09.027

Platinum phosphinite complexes made from chiral diols catalyze the enantioselective allylation of cinnamaldehyde. This reaction proceeds with better yields at shorter reaction times in the presence of acetic acid. Enantiomeric excesses were greater when r

Full text of DOI:10.1016/j.tetasy.2007.09.027

Available online at www.sciencedirect.com
Tetrahedron: Asymmetry 18 (2007) 2387–2393
Asymmetric allylation of aldehydes with chiral platinum
phosphinite complexes
Rakesh K. Sharma and Ashoka G. Samuelson*
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
Received 4 July 2007; accepted 27 September 2007
Available online 23 October 2007
Abstract—Platinum phosphinite complexes made from chiral diols catalyze the enantioselective allylation of cinnamaldehyde. This reac-
tion proceeds with better yields at shorter reaction times in the presence of acetic acid. Enantiomeric excesses were greater when reactions
were carried out with phosphinite ligands having hydrogen bond donors or acceptors.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
report a series of chiral platinum-phosphinite complexes
(Fig. 1), readily synthesized from chiral diols. The efficiency
of these catalysts is doubled in the presence of acetic acid.
The use of Lewis acids and bases to promote allylation has
been studied earlier,9 however Lewis acid catalysis often re-
quires anhydrous conditions while base catalysis is not
compatible with aliphatic aldehydes.
Enantioselective C–X (X = C, N, or O) bond formation is
a key step in the synthesis of many pharmaceuticals. The
development of chiral asymmetric catalysts for this step
has become a challenging task.1 The enantioselectivity
achieved in a reaction for a particular substrate is often
not transferable to a different substrate. Hartwig has ele-
gantly demonstrated that what is desirable is a set of cata-
lysts with similar reactivity, but editable stereochemical
elements to fine tune enantioselectivity.2 We wished to gen-
erate a set of ligands that could be readily modified for
achieving selectivity.
2. Results and discussion
Phosphinites have been shown to be excellent ligands in a
variety of reactions.10 Our complexes have been synthe-
sized by two different methods as outlined in Schemes 1
and 2. We refer to the procedure outlined in Scheme 1 as
a templated synthesis11 of the complex. The free ligands
are not readily accessible using the procedure outlined in
Scheme 2.
Asymmetric allylation of the aldehyde is particularly diffi-
cult. Available methods utilizing chiral (acyloxy)boranes,3
titanium,4 zirconium,5 indium,6 and silver7 complexes of
BINAP/BINOL are quite cumbersome. An exception to
this, is the report of Hall, which utilizes a diol–SnCl4 com-
plex at low temperatures with good selectivity.8 Herein, we
OH
OPPh2
Cl
Cl
cis-Pt (PPh2Cl)2Cl2
Pt
*
*
THF, RT
OPPh2
OPPh2
OH
OH
OH
Cl
Cl
OPPh2
Pt
Chiral Diols
*
*
Scheme 1. Synthesis of platinum bisphosphinite complexes (template
procedure).
Figure 1.
The choice of phosphinites was based on the presence of
hydrogen bond donors 8, 10–12, and 15 and hydrogen
bond acceptors 3, 4, and 9 in different stereochemical sites.
These were to be compared with chiral Pt complexes 1, 2, 5,
*
Corresponding author. Tel.: +91 80 22932663; fax: +91 80 23601552;
e-mail: ashoka@ipc.iisc.ernet.in
0957-4166/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2007.09.027

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R. K. Sharma, A. G. Samuelson / Tetrahedron: Asymmetry 18 (2007) 2387–2393
OPPh2
OPPh2
Cl
Cl
OH
OH
Pt(COD)Cl2
THF
Base
Pt
*
*
*
PPh2Cl
OPPh2
OPPh2
(6-9)
Scheme 2. Synthesis of platinum bisphosphinite complexes via the ligands L6–L9.
and 6 which did not have such functionalities. Pt complexes
based on isoascorbic acid 14–16 could also be synthesized
except when it was completely unfunctionalized. In this
case alone, the Pt-complex made from isoascorbic acid
decomposed during purification. Complexes 1, 2, 5, and 7
could be characterized by X-ray diffraction studies (Figs.
2–5).
O
Ph
OPPh2
OPPh2
Ph2PO
Ph
OPPh2
O
Ph
Ligand; L6
Ligand; L7
OPPh2
Ph2PO
OPPh2
OPPh2
CHCl2
O
O
N
O2N
H
O
O
Figure 3. X-ray crystal structure of complex 2. Ellipsoids set to 30%
probability. Hydrogen atoms are omitted for clarity.
O
Ligand; L8
Ligand; L9
The allylation of aldehydes by allyltributyltin was
attempted by using 1 as a catalyst. Complex 1 was found
to be significantly more effective than cis-Pt(PPh3)2Cl2 for
the test reaction12 (Scheme 3). Other aromatic aldehydes
such as benzaldehyde and anisaldehyde gave reasonable
Figure 4. X-ray crystal structure of complex 5. Ellipsoids set to 30%
probability. Hydrogen atoms are omitted for clarity.
chemical yields (62% and 68%) and moderate enantio-
selectivities (benzaldehyde; 55% and anisaldehyde; 54%)
with complex 8. The allylation of aliphatic aldehydes
however could not be carried out using the Pt complexes
reported here and continue to be a challenge. The recently
Figure 2. X-ray crystal structure of complex 1. Ellipsoids set to 30%
probability. Hydrogen atoms are omitted for clarity.

R. K. Sharma, A. G. Samuelson / Tetrahedron: Asymmetry 18 (2007) 2387–2393
2389
Table 2. Complexes made from ascorbic acids (AA) 10–13 and isoascorbic
acids (IAA) 14–16 using the template procedure
Cl
Pt
Cl
PPh2
O
Ph2P
O
*
O
O
R1
O
O
R2
complexes 10-16
Entry
R1
R2
Complex (LPtCl2)
1
2
3
4
5
6
7
H
Bn
H
Bn
Bn
H
H
H
10
11
12
13
14
15
16
Bn
Bn
H
Bn
Bn
Figure 5. X-ray crystal structure of complex 7. Ellipsoids set to 30%
probability. Hydrogen atoms are omitted for clarity.
Bn
OH
SnBu3
Table 3. Evaluation of the optimal reaction conditions for the allylation
reaction using complex 1
Ph
Ph
O
*
THF, CH3CN,
Yielda
(%)
17
18
Pt-L*,promoter
Entry
1
Solvent
T (h) Promoter
(mol %)
(1 equiv)
Scheme 3. Allylation of cinnamaldehyde by chiral platinum bisphosph-
inite complexes.
1
2
3
4
5
6
7
8
9b
10
1
1
1
1
1
1
0.1
1
THF
THF
THF
THF
18
22
30
31
29
None
None
Water
AcOH
AcOH
AcOH
Excess AcOH 29
AcOH
AcOH
84
48
62
90
90
90
reported Pd complex for the same reaction needs to be
heated to 50 ꢁC to achieve significant yields13 (see Tables
1 and 2).
CH3CN
CH3CN/THF; 1:1 14
CH3CN/THF; 1:1 50
CH3CN/THF; 1:1 45
CH3CN/THF; 1:1 72
63
0
Table 1. Complexes synthesized by the template procedure
a Isolated yield.
b No complex added.
R2
OPPh2
Cl
*
R1
R4
Pt
less than that achieved with acid. This effect is different
from what is observed in the Pd catalyzed allylation of imi-
nes where acid is detrimental and water was effective in
bringing about complete conversion.11
Cl
*
OPPh2
R3
complex 1-5
Entry
R1
R2
R3
R4
Complex (LPtCl2)
Complexes 1–16 were then scanned for enantioselective
catalysis using the best conditions achieved for the allyla-
tion of cinnamaldehyde. No attempts were made to opti-
mize the reaction further and the reported yields are the
average of three runs. These results are given in Table 4.
1
2
3
4
5
H
H
H
H
H
H
H
COOEt
COOEt
Ph
H
H
H
H
H
Ph
Ph
COOEt
COOEt
Ph
(R)-1
(S)-2
(2R,3R)-3
(2S,3S)-4
(1R,2R)-5
There are mechanistic studies by Zhao,15 Greeves,16 and
Denmark,17 on the Lewis acid promoted allylation reac-
tion. However, the mechanism of allylation catalyzed by
Pt is not well established. We carried out the activation
of allytributyltin18 as proposed by Yamamoto to generate
a Pt allyl species. Subsequently, the allyl group was added
to the protonated aldehyde. Examination of the observed
ee suggests that the presence of a hydrogen bond donor/
acceptor on the chiral ligand is essential for promoting
enantioselectivity. Complexes 1–6 did not show any ee. A
comparison of the crystal structures 1, 2, 5, and 7 suggests
In order to improve the reactivity, we tested the utility of
acetic acid as a promoter and the use of different solvent
mixtures. These results are summarized in Table 3.
Although very good chemical yields were obtained, no
enantioselectivity could be achieved under these conditions
with catalyst 1.
The enhancement achieved with the addition of acetic acid
is presumably due to the protonation of cinnamaldehyde.
The addition of water has a small effect but is significantly

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R. K. Sharma, A. G. Samuelson / Tetrahedron: Asymmetry 18 (2007) 2387–2393
Table 4. Allylation of cinnamaldehyde with various platinum bisphosph-
inite complexesa
4. Experimental
eeb (%)
4.1. General methods
Entry
Complex
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17c
1
2
14
17
09
11
06
30
12
22
22
13
10
19
18
28
32
23
72
90
82
85
92
97
64
91
88
81
90
89
77
84
81
70
83
59
Nil
Nil
Nil
Nil
Nil
Nil
28 (R)
88 (R)
12 (R)
73 (R)
83 (R)
15 (R)
Nil
70 (S)
47 (S)
Nil
All reactions and manipulations were routinely performed
under nitrogen atmosphere by using standard Schlenk
techniques in oven-dried glassware. Tetrahydrofuran and
diethyl ether were doubly distilled over sodium/benzo-
phenone and LiAlH4. Dichloromethane was purified by
distillation from P2O5. Triethylamine was distilled over
KOH followed by LiAlH4. Diphenylphosphine chloride
was purified by distillation under nitrogen prior to use.
Cinnamaldehyde was distilled before use. Analytical thin
layer chromatography (TLC) was performed using Merck
60 F254 precoated silica gel plate (0.2 mm thickness).
Subsequent to elution, plates were visualized using UV
radiation (254 nm). Further visualization was possible by
staining with iodine or a basic solution of potassium
permanganate, followed by heating on a hot plate. Column
chromatography was performed using Merck silica gel 60–
120 with freshly distilled solvents. Columns were typically
packed as a slurry and equilibrated with the appropriate
solvent system prior to use.
3
4
5
6
7
8
9
10
11
12
13
14
15
16
8
41 (R)
a The optimized reaction condition found in entry 6 of Table 3 was utilized
and the reaction was followed by TLC.
b Determined by chiral HPLC using Chiralcel OD column from Daicel.
c In the absence of acetic acid.
Nuclear magnetic resonance spectra (1H NMR) were
recorded on a Bruker AMX 400 spectrometer operating
that the complex showing moderate ee has a pronounced
asymmetry or a very bulky group at the asymmetric car-
bon, which bends over to the Pt–Cl side. Particularly inter-
esting examples are 6, 13, and 16, which all have bulky
substituents, but no hydrogen bond donors and exhibit
no enantioselectivity. Clearly, it is not only important to
have a bulky substituent on the asymmetric carbon, but
it is also important to have hydrogen bond donors/
acceptors.
1
at 400 MHz for H and 162.02 MHz for 31P (CDCl3 as
solvent). Chemical shifts for 1H NMR spectra are reported
as d in parts per million (ppm) downfield from SiMe4 (d
0.0) and relative to the signal of chloroform-d (d 7.26,
singlet). Multiplicities were given as: s (singlet); d (doublet);
t (triplet); q (quartet); dd (doublets of doublet); ddd
(doublets of doublets of doublet); dddd (doublets of
doublets of doublets of doublet); dt (doublets of triplet);
or m (multiplets). The number of protons (n) for a given
resonance is indicated by nH. Coupling constants are
reported in Hz. Phosphorus nuclear magnetic resonance
spectra (31P NMR) are reported as d in units of parts per
million (ppm) relative to external H3PO4 (d 0.0). HPLC-
analysis was performed using Chiralcel OD column.
Elemental analyses (C,H,N) were performed using Thermo
Finnigan FLASH EA 1112 analyzer.
Given the importance of the acetic acid in promoting the
reaction, it is not surprising that the hydrogen bond
donor/acceptor sites on the ligand play a role in enhancing
the enantioselectivity.14 Complexes 7 and 8 were generated
from readily available diols and tested for asymmetric
induction, although they are not similar to the ascorbic
acid complexes. Complex 8, which has hydrogen bond
donors and acceptors is exceptionally good in promoting
a re face attack, thus supporting our hypothesis. The
importance of acetic acid in achieving good enantio-
selectivity is evident from entry 17 in Table 4. Apart from
the drastic decrease in the chemical yield (59%), the enantio-
selectivity also suffers a setback without the addition of
acetic acid.
Literature methods were used for preparation of
[PtCl2(1,5-COD)],19 derivatives of ascorbic and isoascorbic
acid;
3-(benzyloxy)-5-(1,2-dihydroxyethyl)-4-hydroxy-
furan-2(5H)-one,20 4-(benzyloxy)-5-(1,2-dihydroxyethyl)-
3-hydroxyfuran-2(5H)-one,21
3,4-bis(benzyloxy)-5-(1,2-
dihydroxyethyl)furan-2(5H)-one,21 complexes 1 and 2.11
3. Conclusion
4.2. Synthesis of complexes 3–5, 10–1611
In conclusion, we have discovered new bisphosphinite
ligands from inexpensive starting materials and demon-
strated that Pt complexes of these ligands can be readily
synthesized. The ligands based on ascorbic acid provide
an opportunity for editing the stereochemical elements with
hydrogen bond donors and acceptors. They have excep-
tionally good potential for the catalytic enantioselective
allylation of carbonyl compounds. High selectivity and
turnover number are achieved in the presence of acetic acid
as a promoter.
4.2.1. [(2R,3R)-Diethyl 2,3-bis(diphenylphosphinooxy)succi-
nate PtCl2] 3. Colorless crystalline solid, yield 86%,
25
½aꢀD ¼ þ68:8 (c 2.0, CHCl3); 1H NMR d 7.77–7.69 (m,
8H, Harom) 7.50–7.46 (m, 4H, Harom) 7.37–7.31 (m, 8H,
Harom) 5.29 (dd, J = 12.4, 3.6 Hz, 2H, CHOP) 3.96 (m,
4H, CH2CH3) 1.13 (t, J = 14.4, 7.2 Hz, 6H, CH2CH3).
31P NMR d 93.3 (s) JPPt = 4014.8. Anal. Calcd for
C32H32P2O6PtCl2: C, 45.73; H, 3.84. Found: C, 45.98; H,
4.40.

R. K. Sharma, A. G. Samuelson / Tetrahedron: Asymmetry 18 (2007) 2387–2393
2391
4.2.2. [(2S,3S)-Diethyl 2,3-bis(diphenylphosphinooxy)succi-
nate PtCl2] 4. Colorless crystalline solid, yield 75%,
4.4.3. (R)-4-((1S,2R)-2-((S)-2,2-Dimethyl-1,3-dioxolan-4-yl)-
1,2-bis(diphenylphosphinooxy)ethyl)-2,2-dimethyl-1,3-dioxo-
lane L9. Colorless semisolid, yield 52%. 1H NMR; d 7.22–
7.57 (m, 20H, Harom) 4.14 (dd, 2H, J = 12.0, 11.6 Hz,
CH2C) 3.97 (dd, 1H, J = 8.8, 8.4 Hz, CHOC) 3.75 (d,
1H, J = 6.0 Hz, CHOP) 1.41 (s, 3H, CH3) 1.35 (s, 3H,
CH3) 31P NMR; d 117.6 (s) and 116.7 (s).
25
1
½aꢀD ¼ ꢁ61:1 (c 2.0, CHCl3); H NMR; d 7.79–7.69 (m,
10H, Harom) 7.50–7.35 (m, 10H, Harom) 5.28 (s, 2H, CHOP)
3.97 (m, 4H, CH2CH3) 1.14 (t, J = 14.4, 7.2 Hz, 6H,
CH2CH3). 31P NMR; d 93.3 (s). Anal. Calcd for
C32H32P2O6PtCl2: C, 45.73; H, 3.84. Found: C, 45.90; H,
4.30.
4.5. General procedure for the synthesis of bisphosphinite
complexes (6–9)
4.2.3. [(1R,2R)-1,2-Bis(diphenylphosphinooxy)-1,2-diphenyl-
ethane PtCl2] 5. Colorless crystalline solid, yield 88%,
25
1
½aꢀD ¼ ꢁ12:3 (c 1.2, CHCl3); H NMR; d 8.01–6.62 (m,
30H, Harom) 5.09 (t, J = 12.0, 5.2 Hz, 1H, CHOP) 31P
NMR; d 96.1 (s) JPPt = 4236.8 Hz. Anal. Calcd for
C38H32P2O6PtCl2ÆCHCl3: C, 48.39; H, 3.44. Found: C,
48.39; H, 3.59.
4.5.1. [(S)-1,2-Bis(diphenylphosphinooxy)-1,1,2-triphenyl-
ethane PtCl2] 6. Bisphosphinite ligand L6 (0.157 mmol)
was dissolved in 1 ml dry THF and added to a solution
of Pt(COD)Cl2 (0.157 mmol) in THF (5 ml) under a dry
nitrogen atmosphere. The solution was stirred until it be-
came a clear yellow solution (5 h). After 2 h a yellow pre-
cipitate appeared that was filtered and washed with cold
4.3. Synthesis of (S)-1,2-bis(diphenylphosphinooxy)-1,1,2-
triphenylethane L6
THF (5 ml) and diethyl ether (5 ml) to give a light yellow
25
powder 6, 77% yield, ½aꢀD ¼ þ9:6 (c 0.5, CHCl3); 1H
(S)-1,1,2-Triphenylethane-1,2-diol (0.1 g, 0.344 mmol) was
dissolved in THF (10 ml) and cooled to ꢁ40 ꢁC, and n-
butyllithium in hexane (0.98 M, 0.575 mmol) was added.
Freshly distilled PPh2Cl (0.575 mmol) was added to this
cooled solution, and the reaction mixture was allowed to
warm up to room temperature and stirred for 14 h. The
solvent and other volatile components were removed under
a reduced pressure. The colorless residue was dissolved in
dry degassed toluene and passed through activated basic
alumina under nitrogen. The toluene solution was washed
with degassed water and dried over anhydrous K2CO3,
filtered, and toluene was removed in vacuum. Compound
L6 was obtained as a white semisolid (0.148 g, 65% yield).
1H NMR; d 7.11–6.45 (m, 35H, Ph) 5.99 (s, 1H, CHOP).
31P NMR; d 114.8 (s) and 111.1 (s).
NMR; d 7.74–6.33 (m, 35H, Ph) 6.33 (d, J = 15.6 Hz,
1H, CHOP). 31P NMR; d 134.9 (d) JPP = 38.8 Hz and
108.1 (d) JPP = 40.5 Hz. Anal. Calcd for C44H36P2O2PtCl2:
C, 57.15; H, 3.92. Found: C, 57.33; H, 3.83.
4.5.2. [(3S,6S)-3,6-Bis(diphenylphosphinooxy)-hexahydro-
furo[3,2-b]furan PtCl2] 7. Colorless crystalline solid, yield
25
1
85%, ½aꢀD ¼ þ16:2 (c 0.5, CH2Cl2); H NMR; d 7.89–7.22
(m, 20H, Harom) 5.30 (d, J = 11.6 Hz, 2H, CHOP) 4.58 (s,
2H, CHOC) 4.07 (s, 2H, CHHO) 3.95 (d, J = 12 Hz, 2H,
CHHO). 31P NMR;d 76.9 (s) JPtP = 4280.5 Hz. Anal.
Calcd for C30H28P2O4PtCl2: C, 46.17; H, 3.62. Found: C,
45.79; H, 3.82.
4.5.3. [N-((1R,2R)-1,3-Bis(benzhydryloxy)-1-(4-nitrophenyl)-
propan-2-yl)-2,2-dichloroacetamide PtCl2] 8. Colorless
25
4.4. General procedure for the synthesis of bisphosphinite
ligands L7–L9
crystalline solid, yield 82%, ½aꢀD ¼ þ49:4 (c 1.0, CH2Cl2);
1H NMR; d 7.98–7.03 (m, 24H, Harom) 6.01 (s, 1H, CHCl2)
5.59 (d, J = 14 Hz, 1H, CHOP) 4.53 (t, J = 24.8, 12.4 Hz,
1H, CHHOP) 4.32 (d, J = 8.0 Hz, 1H, CHHOP) 3.78 (m,
1H, CHN) 31P NMR (162.02 MHz, CDCl3) d 94.0 (d)
and 92.7 (d) JPP = 6.4, 8.1 Hz. JPtP = 4144.4, 4099 Hz.
Anal. Calcd for C35H30P2N2O5PtCl4: C, 43.91; H, 3.16;
N, 2.93. Found: C, 43.86; H, 3.67; N, 3.55.
4.4.1.
(3S,6S)-3,6-Bis(diphenylphosphinooxy)-hexahydro-
furo[3,2-b]furan L7. Isomannide (0.342 mmol) was dried
azeotropically and dissolved in a dried and degassed mix-
ture of dichloromethane (1 ml), triethylamine (5 ml), and
4-dimethylaminopyridine (0.342 mmol). This solution was
cooled to 0 ꢁC and PPh2Cl was added dropwise. When
the addition was complete, the ice bath was removed and
stirring was continued for 15 h. The solvent was removed
under reduced pressure, and the residue dissolved in dry
toluene and passed through a basic alumina column under
nitrogen. Toluene was removed under reduced pressure. Li-
gand L6 was obtained as a light yellow oil and, was used
for complexation without further purification, yield 68%.
1H NMR; d 6.90–6.84 (m, 9H, Harom) 6.83–6.69 (m, 11H,
Harom) 4.65 (dd, J = 12.0, 9.6 Hz, 1H, CHOP). 31P
NMR; d 114.4 (s).
4.5.4. [(R)-4-((1S,2R)-2-((S)-2,2-Dimethyl-1,3-dioxolan-4-yl)-
1,2-bis(diphenylphosphinooxy)ethyl)-2,2-dimethyl-1,3-dioxo-
lane PtCl2] 9. Colorless crystalline solid, yield 86%;
25
1
½aꢀD ¼ þ23:1 (c 0.2, CHCl3); H NMR; d 8.11–7.45 (m,
20H, Harom) 4.17 (d, J = 9.2 Hz, 1H, CHHC) 4.05 (d,
J = 4.8 Hz, 1H, CHHC) 3.70 (dd, 1H, J = 7.2, 8.8 Hz,
2H, CHOC) 3.57 (dd, 1H, J = 5.6, 8.4 Hz, CHOP) 1.19
(s, 3H, CH3) 1.05 (s, 3H, CH3) 31P NMR; d 95.4 (s),
JPPt = 4180 Hz. Anal. Calcd for C36H40P2O6PtCl2: C,
48.22; H, 4.50. Found: C, 47.32; H, 4.89.
4.4.2. N-((1R,2R)-1,3-Bis(benzhydryloxy)-1-(4-nitrophenyl)
propan-2-yl)-2,2-dichloroacetamide L8. Yellow semisolid,
yield 51%, H NMR; d 6.98–8.10 (m, 24H, Harom) 6.26
4.6. Synthesis of bisphosphinite complexes, derived from
ascorbic and isoascorbic acid
1
(s, 1H, CHCl2) 5.63 (d, 1H, J = 6.4 Hz, CHOP) 5.25 (m,
2H, CHHOP) 4.93 (m, 1H, CHN) 31P NMR; d 117.6 (s)
and 116.5 (s).
4.6.1. [(R)-5-((S)-1,2-Bis(diphenylphosphinooxy)ethyl)-3,4-
dihydroxyfuran-2(5H)-one PtCl2] 10. L-Ascorbic acid
(0.009 g, 0.053 mmol) was dissolved in dry degassed THF

2392
R. K. Sharma, A. G. Samuelson / Tetrahedron: Asymmetry 18 (2007) 2387–2393
(2 ml), DMF (0.1 ml), and HMPA (0.1 ml) and added
dropwise to stirred solution of [Pt(PPh2Cl)2Cl2]
1H, CHHOP) 5.28 (d, 1H, J = 11.8 Hz, CHHOP) 4.88
(m, 1H, CHOP) 4.66 (d, J = 4.0 Hz, 1H, CHOC) 4.14
(m, 1H, CHHOP) 4.00 (m, 1H, CHHOP) 31P NMR; d
94.9 (s) JPPt = 4064.7 Hz and 90.3 (s) JPPt = 3965.4 Hz.
Anal. Calcd for C37H32P2O6PtCl2: C, 49.34; H, 3.58.
Found: C, 50.75; H, 3.69. (HRMS in CH3CN,
sens = 4.37e4): found 865.1082 [MꢁCl]+ (C37H32P2O6PtCl
requires 865.0962).
a
(0.053 mmol) under nitrogen for 13 h at room temperature.
The solvent was removed under vacuum and ether (10 ml)
was added to the residue, which resulted in a gummy solid.
Addition of warm toluene gave a hazy solution that grad-
ually precipitated complex 10, which was filtered and
washed with cold toluene and diethyl ether to give a white
25
powder 0.018 g, yield 43%; ½aꢀD ¼ þ29:6 (c 1.1, DMSO);
1H NMR; d 7.85–7.28 (m, 20H, Harom) 5.58 (br s, 1H,
CHOP) 4.68 (s, 1H, CHOC) 4.40 (m, 1H, CHHOP) 3.91
(m, 1H, CHHOP) 31P NMR; d 93.7 (s) and 82.2 (s)
JPPt = 4183.3 Hz. Anal. Calcd for C30H26P2O6PtCl2: C,
44.46; H, 3.23. Found: C, 45.41; H, 3.12.
4.6.7. [(R)-5-((R)-1,2-Bis(diphenylphosphinooxy)ethyl)-3,4-
bis(benzyloxy)furan-2(5H)-one PtCl2] 16. White powder,
25
87% yield; ½aꢀD ¼ þ27:7 (c 2.0, CHCl3); 1H NMR; d
7.79–7.03 (m, 30H, Harom) 5.11–4.86 (m, 4H, 2CH2OPh)
4.63 (d, J = 3.2 Hz, 1H, CHOP) 4.09 (m, 1H, CHHOP)
3.70 (m, 1H, CHHOP) 31P NMR; d 96.3 (d), JPPt = 4081.2,
J = 11.3 Hz and 87.5 (d) JPtP = 4081.2, JPP = 9.7 Hz. Anal.
Calcd for C44H38P2O6PtCl2: C, 53.34; H, 3.86. Found: C,
53.18; H, 3.74. (HRMS in CH3CN, sens = 7.21e3): found
955.1322 [MꢁCl]+ (C44H38P2O6PtCl requires 955.1431).
4.6.2.
[(R)-5-((S)-1,2-Bis(diphenylphosphinooxy)ethyl)-3-
(benzyloxy)-4-hydroxyfuran-2(5H)-one PtCl2] 11. White
25
powder, yield 61%; ½aꢀD ¼ þ18:1 (c 1.7, CHCl3); 1H
NMR; d 7.80–7.11 (m, 25H, Harom) 5.47 (br s, 1H, CHOP)
4.90 (d, J = 10.8 Hz, 1H, CHOC) 4.72 (d, J = 10.8 Hz, 1H,
CHHPh) 4.63 (s, 1H, CHHPh) 4.38 (m, 1H, CHHOP) 3.86
(m, 1H, CHHOP) 31P NMR; d 95.45 (s) and 84.19 (s)
JPPt = 4102.2 Hz. Anal. Calcd for C37H32P2O6PtCl2: C,
49.34; H, 3.58. Found: C, 49.32; H, 4.10.
4.7. 1-Phenylhexa-1,5-dien-3-ol 18
Optimized method for the asymmetric allylation of
cinammaldehyde (Tables 3 and 4, entry 6). To an oven-
dried 5 ml round-bottom side arm flask equipped with a
magnetic stirring bar, was added 1 (570 lg, 0.756 lmol)
and cinnamaldehyde 17 (9.5 ll, 75.6 lmol) in 0.5 ml aceto-
nitrile. Allyltributyl stannane (28 ll, 90.7 lmol) was dis-
solved in 0.5 ml THF and added to the resulting mixture,
which was then stirred for 10 min, followed by addition
of the promotor AcOH (4.5 ll, 75.6 lmol). The reaction
mixture was stirred for the required time at room temper-
ature and then extracted with ether (5 · 10 ml). The com-
bined organic extracts were washed with brine, dried over
anhydrous sodium sulfate, filtered, and concentrated in va-
cuo. The residual crude product was purified via silica gel
chromatography to afford homoallylic alcohol 18 (phenyl-
hexa-1,5-dien-3-ol) as a colorless oil. 1H NMR; d 7.40–7.21
(m, 5Harom), 6.60 (d, J = 15.9 Hz, 1H, PhCH@CH), 6.25
(dd, J = 15.9, 6.3 Hz, 1H, PhCH@CH), 5.93–5.79 (m,
1H, CH2CH@CH2), 5.21–5.15 (m, 2H, CH2CH@CH2),
4.37–4.35 (m, 1H, CH2CHOH), 2.48–2.33 (m, 2H,
CH2CH@CH2). The enantiomeric excess was determined
by HPLC analysis employing a Chiralcel OD column from
Daicel [hexane/i-propanol 90:10, 1.0 ml/min, k = 220 nm,
t1 = 7.79 min for the (R)-enantiomer, t2 = 11.44 min for
the (S)-enantiomer]. It has been established that the (R)-
enantiomer elutes first.22
4.6.3.
[(R)-5-((S)-1,2-Bis(diphenylphosphinooxy)ethyl)-4-
(benzyloxy)-4-hydroxyfuran-2(5H)-one PtCl2] 12. White
25
powder, yield 82%. ½aꢀD ¼ þ26:7 (c 1.3, CHCl3); 1H
NMR; d 7.89–7.42 (m, 25H, Harom) 5.43 (d, J = 11.6 Hz,
1H, CHHOPh) 5.28 (d, J = 11.2 Hz, 1H, CHHOPh) 4.86
(m, 1H, CHOP) 4.50 (s, 1H, CHOC) 4.29 (m, 1H,
CHHOP) 4.24 (m, 1H, CHHOP) 31P NMR; d 93.9 (d)
and 90.2 (d) JPP = 11.3, JPtP = 4082.9 Hz. Anal. Calcd
for C37H32P2O6PtCl2: C, 49.34; H, 3.58. Found: C, 49.75;
H, 4.09.
4.6.4. [(R)-5-((S)-1,2-Bis(diphenylphosphinooxy)ethyl)-3,4-
bis(benzyloxy)furan-2(5H)-one PtCl2] 13. White powder,
25
83% yield; ½aꢀD ¼ þ31:5 (c 1.0, CHCl3); 1H NMR; d
7.80–7.18 (m, 30H, Harom) 5.23 (d, J = 11.6 Hz, 2H,
CH2OPh) 5.14 (d, J = 11.6 Hz, 1H, CHHOPh) 5.04 (br s,
1H, CHHOPh) 4.72 (d, J = 11.2 Hz, 1H, CHOP) 4.48 (s,
1H, CHOC) 4.18 (m, 1H, CHHOP) 4.08 (m, 1H, CHHOP)
31P NMR;
d 94.3 (s) J = 4084.5 Hz and 90.3 (s)
JPPt = 3917.6 Hz. Anal. Calcd for C44H38P2O6PtCl2: C,
53.34; H, 3.86. Found: C, 53.21; H, 4.22.
4.6.5.
[(R)-5-((R)-1,2-Bis(diphenylphosphinooxy)ethyl)-3-
(benzyloxy)-4-hydroxyfuran-2(5H)-one PtCl2] 14. White
25
powder, yield 64%; ½aꢀD ¼ ꢁ20:1 (c 1.0, CHCl3); 1H
4.8. Crystal data
NMR; d 7.72–6.95 (m, 25H, Harom) 5.86 (br s, 1H, CHOP)
5.27 (s, 1H, CHOC) 5.03 (d, J = 10.0 Hz, 1H, CHHPh)
4.92 (d, J = 11.6 Hz, 1H, CHHPh) 3.92 (m, 1H, CHHOP)
3.11 (d, J = 10.4 Hz, 1H, CHHOP) 31P NMR; d 98.3 (s)
JPPt = 3870.6 Hz and 83.5 (s) JPPt = 4113.6 Hz. Anal.
Calcd for C37H32P2O6PtCl2: C, 49.34; H, 3.58. Found: C,
49.29; H, 4.06.
Suitable single crystals were mounted and X-ray diffraction
data were collected on a SMART APEX CCD diffractom-
eter (graphite-monochromated Mo-Ka radiation, P–x-
˚
scan technique, k = 0.71073 A). The intensity data were
integrated by means of the SAINT program.23 SADABS
24
was used to perform area-detector scaling and absorption
corrections. The structures were solved by direct methods
and were refined against F2 using all reflections with the
aid of the SHELXTL package.25 All non-hydrogen atoms
were refined anisotropically. The H atoms were included
in calculated positions with isotropic thermal parameters
4.6.6.
[(R)-5-((R)-1,2-Bis(diphenylphosphinooxy)ethyl)-4-
(benzyloxy)-4-hydroxyfuran-2(5H)-one PtCl2] 15. White
25
powder, yield 69%; ½aꢀD ¼ ꢁ16:2 (c 1.0, CHCl3); 1H
NMR; d 7.85–7.12 (m, 25H, Harom) 5.30 (d, J = 11.6 Hz,

R. K. Sharma, A. G. Samuelson / Tetrahedron: Asymmetry 18 (2007) 2387–2393
2393
3. Marshall, J. A.; Palovich, M. R. J. Org. Chem. 1998, 63,
4381.
4. (a) Hanawa, H.; Hashimoto, T.; Maruoka, K. J. Am. Chem.
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7. (a) Wang, C. J.; Shi, M. Eur. J. Org. Chem. 2003, 2823; (b)
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Yamamoto, H. Bull. Chem. Soc. Jpn. 2001, 74, 1129; (c) Shi,
M.; Sui, W. S. Tetrahedron: Asymmetry 2000, 11, 773.
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2426.
9. For reviews, see: (a) Yanagisawa, A. In Comprehensive
Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamam-
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S.; Sugiura, M.; Ogawa, C. Adv. Synth. Catal. 2004, 346,
1023.
related to those of the supporting carbon atoms but were
not included in the refinement. All non-hydrogen atoms
were found from the difference Fourier syntheses. All cal-
culations were performed using the BRUKER SMART
program.
4.8.1. Complex 1. (CCDC 648572): PtCl2(C32H28O2P2)Æ
CHCl3, M = 891.84; monoclinic, space group P21, a =
˚
9.472(6), b = 17.526(10), c = 11.041(7) A, b = 110.225(8)ꢁ,
3
˚
V = 1719.92(57) A , T = 293(2) K, Z = 2, l = 4.590
mmꢁ1, Rint = 0.0290 (for 12,358 measured reflections),
R1 = 0.0339 [for 5837 unique reflections with I > 2r(I)],
wR2 = 0.0908 (for all 6029 unique reflections).
4.8.2. Complex 2. (CCDC 648573): PtCl2(C32H28O2P2)Æ
CHCl3, M = 891.84, monoclinic, space group P21, a =
˚
9.470(5), b = 17.555(5), c = 11.046(5) A, b = 110.041(5)ꢁ,
3
ꢁ1
˚
V = 1725.2(13) A , T = 293(2) K, Z = 2, l = 4.576 mm
,
Rint = 0.0207 (for 12,587 measured reflections), R1 =
0.0209 [for 5852 unique reflections with I > 2r(I)],
wR2 = 0.0493 (for all 6228 unique reflections).
4.8.3. Complex 5. (CCDC 648574): PtCl2(C38H32O2P2)Æ
CHCl3, M = 967.93; monoclinic, space group P21, a =
˚
9.891(3), b = 17.537(5), c = 11.225(3) A, b = 92.302(4)ꢁ,
10. (a) Shin, S.; RajanBabu, T. V. Org. Lett. 1999, 8, 1229; (b)
Park, H.; Kumareswaran, R.; RajanBabu, T. V. Tetrahedron
2005, 61, 6352.
11. Sharma, R. K.; Samuelson, A. G. J. Chem. Sci. 2006, 118,
569.
3
ꢁ1
˚
V = 1945.6(9) A , T = 293(2) K, Z = 2; l = 4.056 mm
,
Rint = 0.1711 (for 22,406 measured reflections), R1 =
0.0613 [for 7656 unique reflections with I > 2r(I)],
wR2 = 0.1469 (for all 8967 unique reflections).
12. Nakamura, H.; Asao, N.; Yamamoto, Y. J. Chem. Soc.,
Chem. Commun. 1993, 1273.
13. Piechaczyk, O.; Cantat, T.; Mezailles, N.; Floch, P. L. J. Org.
Chem. 2007, 72, 4228.
14. (a) Corey, E. J.; Lee, T. W. Chem. Commun. 2001, 1321; (b)
Pihko, P. M. Angew. Chem., Int. Ed. 2004, 43, 2062.
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16. Aspinall, H. C. A.; Bissett, J. S.; Greeves, N.; Levin, D.
Tetrahedron Lett. 2002, 43, 319.
4.8.4. Complex 7. (CCDC 648575): PtCl2(C30H28O4P2),
M = 780.45; monoclinic, space group P21, a = 9.659(5),
˚
b = 16.265(5), c = 9.863(5) A, b = 111.761(5)ꢁ, V =
3
1435.2(11) A , T = 293(2) K, Z = 2, l = 5.222 mmꢁ1
,
˚
Rint = 0.0299 (for 12,480 measured reflections), R1 =
0.0274 [for 5787 unique reflections with I > 2r(I)]
wR2 = 0.0586 (for all 6361 unique reflections).
17. Denmark, S. E.; Fu, J.; Lawler, M. J. J. Org. Chem. 2006, 71,
1523.
18. Nakmura, H.; Iwama, H.; Yamamoto, Y. J. Am. Chem. Soc.
1996, 118, 6641.
Acknowledgement
19. Drew, D.; Doyle, J. R. Inorg. Synth. 1990, 28, 346.
20. Tahir, H.; Hindsgaul, O. J. Org. Chem. 2000, 65, 911.
21. Kulkarni, M. G.; Thopate, S. R. Tetrahedron 1996, 52,
1293.
We acknowledge the Department of Science and Techno-
logy, New Delhi, for financial support.
22. (a) Nakajima, M.; Saito, M.; Shiro, M.; Hashimoto, S. J. Am.
Chem. Soc. 1998, 120, 6419; (b) Lee, C. H. A.; Loh, T. P.
Tetrahedron Lett. 2004, 45, 5819.
References
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