Palladacycle-catalyzed asymmetric hydrophosphination of enones for synthesis of C*-and P*-chiral tertiary phosphines

Article abstract of DOI:10.1021/ic202472f

A highly reactive and stereoselective hydrophosphination of enones catalyzed by palladacycles for the synthesis of C^*-and P ^*-chiral tertiary phosphines has been developed. When Ph2PH was employed as the hydrophosphinating reagent, a

Full text of DOI:10.1021/ic202472f

Article
pubs.acs.org/IC
Palladacycle-Catalyzed Asymmetric Hydrophosphination of Enones
for Synthesis of C*- and P*-Chiral Tertiary Phosphines
Yinhua Huang, Sumod A. Pullarkat, Yongxin Li, and Pak-Hing Leung*
Division of Chemistry & Biological Chemistry, School of Physical & Mathematical Sciences, Nanyang Technological University,
Singapore 637371, Singapore
S
* Supporting Information
ABSTRACT: A highly reactive and stereoselective hydro-
phosphination of enones catalyzed by palladacycles for the
synthesis of C*- and P*-chiral tertiary phosphines has been
developed. When Ph2PH was employed as the hydrophos-
phinating reagent, a series of C*-chiral tertiary phosphines
were synthesized (C*−P bond formation) in high yields with
excellent enantioselectivities, and a single recrystallization pro-
vides access to their enantiomerically pure forms. When
racemic secondary phosphines rac-R3(R4)PH were utilized, a series of tertiary phosphines containing both C*- and P*-chiral
centers were generated (C*−P* bond formation) in high yields with good diastereo- and enantioselectivities. The
stereoelectronic factors involved in the catalytic cycle have been revealed.
boranes were obtained as the final products. Conversion of these
phosphine adducts to tertiary phosphines frequently involves
strong reaction conditions and low yields. Therefore, it is our
judgment that it is desirable to generate tertiary phosphines directly
from a catalytic process.
Among chiral phosphines, P*-chiral phosphines have
received increasing attention because they show great potential
in asymmetric catalysis, particularly, as organocatalysts.1c,4a
Catalytic approaches for the preparation of P*-chiral phos-
phines have been reported by the alkylation or arylation of
secondary phosphines via cross-coupling pathways.4a−j P*-
chiral phosphines have also been accessed by the hydro-
phosphination of activated olefins with rac-Ph(Me)PH, how-
ever, with low optical purity.5b
In a recent communication, we reported a C,N-palladacycle
(R)-A-catalyzed asymmetric hydrophosphination of enones
with Ph2PH to form several keto-substituted C*-chiral tertiary
phosphines.7b Herein, we report the evaluation of a series of
palladacycles A−F for this reaction. The C,P-palladacycle (R)-F
was found to be an improved catalyst, giving much enhanced
reactivities, enantioselectivities, and a wider substrate scope for
the asymmetric hydrophosphination reaction.
Furthermore, the same C,P-catalyst (R)-F can also be utilized
for the efficient activation of racemic secondary phosphine
(rac-3) to generate chiral tertiary phosphines with both C* and
P* stereocenters (eq 1). To date, catalytic formation of the
C*−P* bond with the simultaneous introduction of chirality at
both carbon and phosphorus centers has not been reported.
INTRODUCTION
■
Apart from their well-established contributions to classic
inorganic and organometallic chemistry, chiral phosphines
have also played critical roles as valuable ligands in metal-based
catalysis1 as well as in organocatalysis.2 Nevertheless, most of
the important chiral phosphines are prepared predominantly
either by the tedious resolution process or by use of the limited
chiral pool.3 Clearly, it is necessary to develop more efficient
and practical methodologies for these chiral ligands. For
obvious economic reasons, catalytic asymmetric transforma-
tions via C−P bond formation including cross-coupling4 and
hydrophosphination reactions for the efficient synthesis of
chiral phosphines have recently attracted great interest. Among
the catalytic methods, asymmetric hydrophosphination, the
stereocontrolled addition of a P−H bond to unsaturated C−C
bonds, is one of the most efficient and desired ways that
provide direct, atom-economic, and “green” access to the
targeted chiral phosphines.
Over the past decade, a few strategies for the synthesis of
tertiary C*-chiral phosphines via hydrophosphination employ-
ing secondary phosphines have been reported. These include
asymmetric hydrophosphination of Michael acceptors such as
α,β-unsaturated esters, ketones, aldehydes, nitriles, etc., via
transition-metal-catalyzed5 or organocatalytic6 processes.
Among the transition-metal catalysts, several cyclopalladated
complexes including pincer complexes have been demonstrated
recently as efficient catalysts for these kinds of transformations.7
In addition, tertiary C*-chiral phosphines have also been accessed
by efficient allylic phosphination (substitution).8 However, some of
the reported methods suffered from drawbacks such as low
stereoselectivity, low reactivity, and narrow substrate scope. More
importantly, phosphine oxides, phosphine sulfides, or phosphine
Received: November 16, 2011
Published: January 30, 2012
© 2012 American Chemical Society
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for catalysis. Complexes A−E are C,N-cyclopalladated com-
plexes, with similar electronic features originating from the
σ-donating nitrogen and the π-accepting aromatic carbon. On
the other hand, the C,P complex F is electronically designed to
exhibit higher oxophilicity toward substrates because of the
presence of both relatively soft carbon and phosporus donors.
As reported earlier,7b (R)-A is indeed an efficient catalyst in this
particular C−P bond formation reaction between Ph2PH and
the enone (entry 5). However, when complexes (R)-B−E were
employed, the reaction proceeded at significantly slower rates.
Furthermore, the resulting chemo- and stereoselectivities
became unacceptable (entries 10−13). In particular, (R)-B
gave numerous yet unidentified side products. These observa-
tions revealed that the catalytic properties of the C,N-
cyclopalladated complexes are highly sensitive to minor struc-
tural modifications. To our delight, the C,P complex (R)-F was
found to be an even better catalyst than (R)-A for this hydro-
phosphination reaction, with very high reactivity and excellent
enantioselectivity (entry 14). Under optimal conditions, the
reaction time was reduced noticeably from 24 to 2 h and the
enantiomeric excess (ee) was improved from 77% to 98%
(compared with that of entry 5). As expected, when the equally
accessible (S)-F was employed as the catalyst for the reaction,
the same enantioselectivity was achieved with reversal in the
configuration from S to R at the chiral center (entry 15).7b The
reaction was conveniently monitored by 31P{1H} NMR
spectroscopy. The ee was determined from 31P{1H} NMR
spectra of the derivatives, which resulted from treatment of the
tertiary phosphine product with an enantiopure palladacycle
(R)-G (Scheme 1).5e,f,7b The major diastereomer (RC,SC)-6a
RESULTS AND DISCUSSION
■
Selection of Catalysts. In our initial communication,7b we
observed that (R)-A is an efficient catalyst for the hydro-
phosphination of aromatic enones with Ph2PH. When (R)-A
was used to activate the chiral secondary phosphine R3R4PH,
however, unsatisfactory reactivity and enantioselectivity were
observed. In order to select a better hydrophosphination
catalyst for wider applications, we therefore screened a series of
palladacycles (R)-A−F as catalysts (Table 1). All complexes are
structurally similar with two coordination sites readily available
Scheme 1
Table 1. Catalyst, Solvent, Temperature, and Base Effects on
the Enantioselective Hydrophosphination of Enones with
a
Ph2PH
b
ee (S)
entry catalyst
solvent
T [°C]
−80
t [h]
base
[%]
1
(R)-A
(R)-A
(R)-A
(R)-A
(R)-A
(R)-A
(R)-A
(R)-A
(R)-A
(R)-B
(R)-C
(R)-D
(R)-E
(R)-F
(S)-F
DCM
acetone
toluene
CHCl3
THF
24
24
24
24
24
24
24
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
DBU
tBuOK
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
62
2
−80
−80
−40
−80
−40
68
68
3
4
49
5
77
6
THF
74
7
THF
20
51
c
and minor diastereomer (RC,RC)-6a were characterized by
X-ray crystallography. Thus, the absolute configuration of the
major and minor enantiomers of 4 could be determined to be
S and R by comparison, respectively.7b
8
THF
−80 to +20
−80
48
27
9
THF
2
16
10
11
12
13
14
15
THF
−80
24
messy
13
c
THF
−80 to +20
−80 to +20
−80 to +20
−80
48
c
d
THF
48
38
Substrate Scope for Hydrophosphination with Ph2PH.
In order to evaluate the catalytic versatility of the C,P complex,
a range of aromatic enones were screened for the asymmetric
hydrophosphination reaction catalyzed by (R)-F using the
established optimal conditions. The results are presented in
Table 2. All of the reactions proceeded to full conversion of
Ph2PH smoothly under the given conditions, allowing the
efficient transformation of a wide range of aromatic enones into
chiral tertiary phosphines in nearly quantitative yields and
excellent enantioselectivities. The process tolerates a broad
c
THF
48
15
98
THF
2
2
d
THF
−80
98
a
Conditions: 0.35 mmol of Ph2PH, 5 mol % catalyst, 1.0 equiv of
trans-chalcone, and 0.5 equiv of base were reacted at the given
temperature. The reaction was stopped after the indicated time with
b
full conversion of Ph2PH. The ee was determined by 31P{1H} NMR;
c
see the Supporting Information for details. The reaction was stirred at
−80 °C for 24 h and then gradually warmed to 20 °C for another 24 h.
d
The absolute configuration in this instance is R.
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a
Table 2. Substrate Scope of the (R)-F-Catalyzed Enantioselective Hydrophosphination of Enones with Ph2PH
a
Conditions: 0.30 mmol of Ph2PH, 5 mol % (R)-F, 5 mL of THF, 1.0 equiv of enone, and 0.5 equiv of Et3N were reacted at −80 °C, unless
b
c
otherwise noted. The yield was calculated from 31P{1H} NMR. In parentheses are the yields of isolated products after a single recrystallization. The
d
ee was determined by 31P{1H} NMR. In parentheses are the ee’s after a single recrystallization. See the Supporting Information for details. A total of
1.1 equiv of enone was used.
range of unprotected functional groups such as nitro and halo-
gens (F, Cl, Br). Both electron-withdrawing- and electron-
donating-group-substituted aromatic enones are suitable sub-
strates. However, those bearing electron-withdrawing groups
are more reactive than those bearing electron-donating groups.
As far as the substituent on R1 (R1 = NO2, for example) is
concerned, the para-substituted enone showed the best
reactivity and selectivity (entry 2, 98% ee) followed by the
meta-substituted enone (entry 3, 96% ee) and the ortho-
substituted enone (91% ee).9 Those with a substituent on R1
(entry 4) showed slightly better selectivities compared with
those with the same substituent on R2 (entry 14).
It is worth highlighting that all of these chiral tertiary
phosphine products described in Table 2 could be purified
efficiently to their enantiomerically pure forms (>99% ee) by a
single recrystallization from acetone under a nitrogen
atmosphere.
in the range of 30−35 kcal mol−1.4a,10 This configurational
stability makes it possible to synthesize P*-chiral tertiary
phosphines. Encouraged by the excellent yields and selectivities
achieved in Table 2, we explored the asymmetric hydro-
phosphination reaction employing the racemic secondary
phosphines rac-3 (R3 ≠ R4) as hydrophosphinating reagents
to stereoselectively generate tertiary phosphine products with
both C*- and P*-chiral centers (Table 3).
In the presence of 10 mol % (R)-F, rac-Ph(Me)PH reacted
with trans-chalcone quantitatively after 14 h at −80 °C,
resulting in 87:13 dr (diastereomeric excess) and 71% ee. The
ee was determined by the same method via derivatization with
the enantiopure palladacycle (R)-G (Scheme 1). The major
derivative (RC,SC,RP)-7a was characterized by X-ray crystallog-
raphy (Figure 1 and Table 4). Thus, the absolute configurations
of the corresponding free phosphine product 5 at both phos-
phorus and carbon chiral centers could be determined to be S
by comparison. It needs to be noted that the configuration at
phosphorus in complex (RC,SC,RP)-7a is R, and this apparent
inversion of the configuration that occurs when the phosphine
Selection of Secondary Phosphines. P*-chiral tertiary
phosphines are configurationally stable at room temperature.
The energy required to invert tertiary aryldialkylphosphines is
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phosphorus atom is exclusively coordinated with palladium
trans to the σ-donating nitrogen. The five-membered ring is
locked into a δ configuration, with the methyl group occupying
an axial position at the chiral carbon center.
Table 3. Optimization of the Hydrophosphination Reaction
between trans-Chalcone and rac-3
a
By a comparison of the respective reaction rates, Ph(Me)PH
showed a lower reactivity than Ph2PH for the hydrophos-
phination reaction, which indicates that an aromatic substituent
at phosphorus facilitates the hydrophosphination process. At
higher reaction temperatures, lower stereoselectivities were
obtained. The reaction rate was significantly slower when the
methyl group of the secondary phosphine was replaced by
other sterically demanding substituents (entries 6 and 7).
Substrate Scope for Hydrophosphination with rac-
Ph(Me)PH. On the basis of the reactivity and selectivity
considerations, rac-Ph(Me)PH was selected as the hydrophos-
phinating agent for screening various substrates toward the
asymmetric hydrophosphination reaction to be catalyzed by
(R)-F (Table 5).
The results showed that the reaction proceeded smoothly,
allowing the transformation of a range of aromatic enones and
rac-Ph(Me)PH into functionalized tertiary phosphines with
chiral centers at both phosphorus and carbon. The electronic
properties of the substituents show a significant impact on the
reactivity and selectivity. In general, those bearing election-
withdrawing groups reacted much faster with lower selectivity,
while those bearing electron-donating groups reacted slower
with better selectivity.
b
c
d
entry R3
R4
time [h] T [°C] yield [%]
dr
ee [%]
1
2
3
4
5
6
7
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Me
Me
Me
Me
Me
tBu
Mes
14
12
5
−80
−40
−10
0
96
87:13
85:15
79:21
77:23
70:30
-
71
68
63
62
52
-
97
97
5
97
4
20
95
24
20
trace
e
60
20
95
59:41
79
a
Conditions: 0.36 mmol of rac-R3(R4)PH, 10 mol % (R)-F, 5 mL of
THF, 1.2 equiv of trans-chalcone, and 1.0 equiv of Et3N were reacted
b
at the given temperature, unless otherwise noted. The yield was
c
calculated from 31P{1H} NMR. dr was determined from 31P{1H}
d
NMR of the crude products. The ee (of the major diastereomer) was
determined by 31P{1H} NMR; see the Supporting Information for
details. For entries 1−5, the absolute configuration at phosphorus is S,
and for entries 6 and 7, the absolute configuration at phosphorus is R
e
according to the CIP rules. Mes = 2,4,6-trimethylphenyl.
Mechanism. On the basis of the experimental observations,
a mechanism was proposed for the (R)-F-catalyzed asymmetric
hydrophosphination of enones with secondary phosphines
(Scheme 2). Free PR3(R4)H having a high affinity to palladium
gives the bis(phosphine) complex by displacement of the
relatively weakly coordinated solvent (NCMe) on the original
(R)-F. However, because of the strong π-accepting properties
of the aromatic carbon donor, the P−Pd bond in the trans P−
Pd−C moiety of the intermediate is weak and labile and readily
undergoes the ligand redistribution process.
On the other hand, this readily available coordination posi-
tion has shown significant oxophilicity. A number of stable
complexes containing various trans O−Pd−C moieties, includ-
ing some keto O−Pd−C species, have been isolated.13 In com-
parison, the trans P−Pd−P moiety in the catalytic intermediate
is more stable.14 This renders acidification of the P−H bond in
the reacting PR3(R4)H facile. In the presence of Et3N as the
external base, the secondary phosphine on palladium is thus
readily converted to the corresponding phosphido species
[Pd]P(R3)(R4), which rapidly undergoes inversion. The
reactive phosphido intermediates then proceed to undergo
the desired intramolecular 1,4-addition reaction with the acti-
vated enone at −80 °C to form the expected tertiary phos-
phines. The high stereoselectivity observed is attributed to
the efficient control offered by the two projecting prochiral
P-phenyl rings of the C,P-cyclopalladated catalyst. It should be
noted that the significantly faster reaction rate observed with
the C,P catalyst (R)-F compared to its C,N analogue (R)-A is,
as designed, an electronic phenomenon. The phosphine
product elimination process is clearly faster in a system
involving the P−Pd−P species than those involving N−Pd−P
bonds.
Figure 1. Molecular structure and absolute stereochemistry of the
complex (RC,SC,RP)-7a with 50% probability thermal ellipsoids shown.
Hydrogen atoms except those on the chiral centers are omitted for
clarity.
Table 4. Selected Bond Lengths (Å) and Angles (deg) of
Complex (RC,SC,RP)-7a
Pd1−C1
Pd1−P1
C15−P1
C18−O1
2.019(3)
2.274(1)
1.835(3)
1.209(3)
Pd1−N1
Pd1−Cl1
C16−P1
C31−P1
2.142(2)
2.371(1)
1.869(3)
1.816(3)
C1−Pd1−N1
N1−Pd1−P1
N1−Pd1−Cl1
C25−C16−P1
C15−P1−C16
C31−P1−Pd1
81.3(1)
C1−Pd1−P1
C1−Pd1−Cl1
P1−Pd1−Cl1
C17−C16−P1
C16−P1−Pd1
C15−P1−Pd1
97.8(1)
178.6(1)
89.6(1)
170.6(1)
91.2(1)
115.8(2)
101.7(2)
110.7(1)
106.1(2)
109.4(1)
121.8(1)
CONCLUSION
In summary, we have evaluated a series of palladacycles and
found that the phosphapalladacycle (R)-F is a much improved
product is coordinated with the metal is merely a consequence
of the Cahn−Ingold−Prelog (CIP) sequence rules.11 The Pd−Cl
bond is thermodynamically and kinetically stable,12 and the
■
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a
Table 5. Substrate Scope of the (R)-F-Catalyzed Stereoselective Hydrophosphination of Enones with rac-Ph(Me)PH
a
Conditions: 0.36 mmol of rac-Ph(Me)PH, 10 mol % (R)-F, 5 mL of THF, 1.2 equiv of enones, and 1.0 equiv of Et3N were reacted at −80 °C,
b
c
d
unless otherwise noted. The yield was calculated from 31P{1H} NMR. dr was determined from 31P{1H} NMR of the crude products. The ee (of
the major diastereomer) was determined by 31P{1H} NMR; see the Supporting Information for details.
catalyst for the powerful palladium(II)-catalyzed asymmetric
hydrophosphination protocol. Furthermore, we also extended
this reaction to allow the stereochemically challenging simul-
taneous formation of chirality at both carbon and phosphorus
stereogenic centers. The resulting tertiary phosphine ligands
can be coordinated directly onto other metal ions without the
need for any tedious protection−deprotection sequence. This
method should be applicable to the synthesis of a large range of
functionalized chiral phosphine ligands containing carbon or
phosphorus stereogenic centers, or both.
Scheme 2. Proposed Catalytic Cycle
EXPERIMENTAL SECTION
■
All air-sensitive manipulations were performed under a positive
pressure of nitrogen or argon using a standard Schlenk line. Solvents
were degassed prior to use when necessary. Tetrahydrofuran (THF)
was purchased from Tedia Co. (AR, stabilized with 0.02−0.03% BHT)
and freshly distilled before use. A Low Temp PAIRSTIRRER PSL-
1800 machine was used for controlling low temperatures for reactions.
Column chromatography was conducted on silica gel 60 (Merck).
NMR spectra were recorded on Bruker ACF 300, 400, and 500
spectrometers. Chemical shifts are reported in δ (ppm) referenced to
an internal SiMe4 standard (δ = 0 ppm) for 1H NMR and chloroform-
d (δ = 77.23 ppm) for 13C NMR. The reaction was monitored by
31P{1H} NMR at room temperature immediately upon removal of an
aliquot from the reaction mixture under inert conditions. Optical
rotations were measured on the specified solution in a 0.1 dm cell at
20 °C with a Perkin-Elmer 341 polarimeter. Chiral palladacycles,15,7e
enones16 and racemic unsymmetrical phosphines17 were prepared
according to the literature.
Caution! Perchlorate salts of metal complexes are potentially explosive
compounds and should be handled with care.
General Experimental Procedure for the Synthesis of C*-
Chiral Phosphines. To a solution of Ph2PH 2 (55.9 mg, 0.30 mmol,
1.0 equiv) in THF (5 mL) was added (R)-F (9.4 mg, 0.015 mmol,
5 mol %), and the solution was cooled to −80 °C. Subsequently,
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1
2
aromatic enone 1 (0.30 mmol, 1.0 equiv) was added. Et3N (15.2 mg,
0.15 mmol, 0.5 equiv) in THF (0.5 mL) was added dropwise. The
solution was subsequently stirred at −80 °C. The reaction was moni-
tored by 31P{1H} NMR. After the reaction was completed, the mixture
was warmed to room temperature and the solution was evaporated by
a vacuum pump to give the crude phosphine product 4 (air-sensitive)
as a solid. The crude 4 was dissolved in 10 mL of dichloromethane
(DCM) and filtered through a short silica gel column using a pipet
fixed on a two-necked Schlenk flask protected by nitrogen or argon.
The solvent was removed by a vacuum pump to give the product as a
solid. A single recrystallization from acetone gave the enantiopure
product 4.
General Experimental Procedure for the Synthesis of C*-
and P*-Chiral Phosphines. To a solution of rac-Ph(Me)PH 3a
(44.7 mg, 0.36 mmol, 1.0 equiv) in THF (5 mL) was added (R)-F
(22.6 mg, 0.036 mmol, 10 mol %), and the solution was cooled to
−80 °C. Subsequently, aromatic enone 1 (0.43 mmol, 1.2 equiv) was
added. Et3N (36.4 mg, 0.36 mmol, 1.0 equiv) in THF (0.5 mL) was
added dropwise. The solution was subsequently stirred at −80 °C. The
reaction was monitored by 31P{1H} NMR. After the reaction was
completed, the mixture was warmed to room temperature, and the
solution was evaporated by a vacuum pump to give the crude
phosphine product 5 (air-sensitive).
δ 39.4 (d, 1C, JPC = 11.8 Hz, PCH), 42.4 (d, 1C, JPC = 22.0 Hz,
CH2COPh), 128.1−139.6 (m, 24C, Ar), 197.8 (d, 1C, 3JPC = 12.6 Hz,
COPh).
Synthesis of (S)-4f. Crude (S)-4f was synthesized according to a
general procedure (99% yield, 99% ee). Pure (S)-4f was obtained after
20
purification as a solid (91% yield, >99% ee; air-sensitive). [α]D
=
−145.0 (c = 1.0, CH2Cl2). 31P NMR (CDCl3, 162 MHz): δ−0.9. H
NMR (CDCl3, 400 MHz): δ 3.06 (ddd, 1H, J = 17.6, 8.0, and 2.8 Hz,
CHHCOPh), 3.54−3.62 (m, 1H, CHHCOPh), 4.21−4.26 (m, 1H,
PCHCH2), 6.71−7.68 (m, 19H, Ar). 13C NMR (CDCl3, 100 MHz):
1
1
2
δ 39.3 (d, 1C, JPC = 11.4 Hz, PCH), 42.5 (d, 1C, JPC = 22.3 Hz,
CH2COPh), 115.2−162.7 (m, 24C, Ar), 198.0 (d, 1C, 3JPC = 13.0 Hz,
COPh). 19F NMR (CDCl3, 376.5 MHz): δ −116.4.
Synthesis of (S)-4g. Crude (S)-4g was synthesized according to a
general procedure (99% yield, 96% ee). Pure (S)-4g was obtained after
20
purification as a solid (91% yield, >99% ee; air-sensitive). [α]D
=
−156.4 (c = 1.1, CH2Cl2). 31P NMR (CDCl3, 162 MHz): δ 0.2. H
NMR (CDCl3, 400 MHz): δ 3.14 (ddd, 1H, J = 17.6, 8.0, and 2.8 Hz,
CHHCOPh), 3.60−3.69 (m, 1H, CHHCOPh), 4.30−4.35 (m, 1H,
PCHCH2), 7.05−7.70 (m, 19H, Ar). 13C NMR (CDCl3, 100 MHz):
1
1
2
δ 40.0 (d, 1C, JPC = 12.7 Hz, PCH), 42.2 (d, 1C, JPC = 21.4 Hz,
CH2COPh), 123.0−145.5 (m, 25C, Ar), 197.6 (d, 1C, 3JPC = 12.3 Hz,
COPh). 19F NMR (CDCl3, 376.5 MHz): δ −62.4.
Synthesis of (S)-4a. Crude (S)-4a was synthesized according to a
general procedure (99% yield, 98% ee). Pure (S)-4a was obtained after
Synthesis of (S)-4h. Crude (S)-4h was synthesized according to a
general procedure (99% yield, 99% ee). Pure (S)-4h was obtained after
20
20
purification as a solid (90% yield, >99% ee; air-sensitive). [α]D
=
purification as a solid (90% yield, >99% ee; air-sensitive). [α]D
=
1
−152.5 (c = 1.2, CH2Cl2). 31P NMR (CDCl3, 121 MHz): δ 0.1. H
NMR (CDCl3, 300 MHz): δ 3.07 (ddd, 1H, J = 17.3, 8.3, and 2.8 Hz,
CHHCOPh), 3.58−3.69 (m, 1H, CHHCOPh), 4.23−4.29 (m, 1H,
PCHCH2), 6.98−7.68 (m, 20H, Ar). 13C NMR (CDCl3, 75 MHz):
−169.3 (c = 1.1, CH2Cl2). 31P NMR (CDCl3, 121 MHz): δ −0.3. H
NMR (CDCl3, 300 MHz): δ 2.13 (s, 3H, CH3O), 3.03 (ddd, 1H, J =
17.4, 8.4, and 3.0 Hz, CHHCOPh), 3.52−3.63 (m, 1H, CHHCOPh),
4.20−4.26 (m, 1H, PCHCH2), 6.85−7.67 (m, 19H, Ar). 13C NMR
(CDCl3, 75 MHz): δ 21.2 (s, 1C, CH3O), 39.5 (d, 1C, 1JPC = 11.3 Hz,
1
1
2
δ 40.0 (d, 1C, JPC = 11.4 Hz, PCH), 42.6 (d, 1C, JPC = 22.1 Hz,
CH2COPh), 126.5−141.0 (m, 24C, Ar), 198.1 (d, 1C, 3JPC = 12.8 Hz,
COPh).
2
PCH), 42.5 (d, 1C, JPC = 22.1 Hz, CH2COPh), 128.1−137.8 (m,
24C, Ar), 198.2 (d, 1C, JPC = 12.7 Hz, COPh).
3
Synthesis of (S)-4b. Crude (S)-4b was synthesized according to a
general procedure (99% yield, 98% ee). Pure (S)-4b was obtained after
Synthesis of (S)-4i. Crude (S)-4i was synthesized according to a
general procedure (99% yield, 99% ee). Pure (S)-4i was obtained after
20
20
purification as a solid (89% yield, >99% ee; air-sensitive). [α]D
=
purification as a solid (92% yield, >99% ee; air-sensitive): [α]D
=
1
1
−248.0 (c = 1.3, CH2Cl2).31P NMR (CDCl3, 121 MHz): δ 1.5. H
NMR (CDCl3, 300 MHz): δ 3.19 (ddd, 1H, J = 17.8, 7.7, and 2.8 Hz,
CHHCOPh), 3.60−3.71 (m, 1H, CHHCOPh), 4.34−4.40 (m, 1H,
PCHCH2), 7.07−7.91 (m, 19H, Ar). 13C NMR (CDCl3, 75 MHz):
−178.5 (c = 1.3, CH2Cl2). 31P NMR (CDCl3, 161 MHz): δ −1.4. H
NMR (CDCl3, 400 MHz): δ 3.03 (ddd, 1H, J = 17.1, 7.9, and 2.6 Hz,
CHHCOPh), 3.53−3.62 (m, 1H, CHHCOPh), 3.63 (s, 3H, CH3O),
4.18−4.23 (m, 1H, PCHCH2), 6.60−7.68 (m, 19H, Ar). 13C NMR
(CDCl3, 100 MHz): δ 39.1 (d, 1C, 1JPC = 11.0 Hz, PCH), 42.7 (d, 1C,
2JPC = 22.4 Hz, CH2COPh), 55.3 (s, 1C, CH3O), 113.9−158.2 (m,
1
2
δ 39.4 (d, 1C, JPC = 11.8 Hz, PCH), 42.4 (d, 1C, JPC = 22.0 Hz,
CH2COPh), 123.6−149.4 (m, 24C, Ar), 197.3 (d, 1C, 3JPC = 12.6 Hz,
COPh).
3
24C, Ar), 198.3 (d, 1C, JPC = 13.0 Hz, COPh).
Synthesis of (S)-4c. Crude (S)-4c was synthesized according to a
general procedure (99% yield, 96% ee). Pure (S)-4c was obtained after
Synthesis of (S)-4j. Crude (S)-4j was synthesized according to a
general procedure (99% yield, 98% ee). Pure (S)-4j was obtained after
20
20
purification as a solid (85% yield, >99% ee; air-sensitive). [α]D
=
purification as a solid (90% yield, >99% ee; air-sensitive): [α]D
=
1
−230.3 (c = 1.0, CH2Cl2). 31P NMR (CDCl3, 161 MHz): δ 0.3. H
NMR (CDCl3, 400 MHz): δ 3.20 (ddd, 1H, J = 17.8, 7.8, and 2.7 Hz,
CHHCOPh), 3.63−3.71 (m, 1H, CHHCOPh), 4.35−4.39 (m, 1H,
PCHCH2), 7.07−7.97 (m, 19H, Ar). 13C NMR (CDCl3, 125 MHz): δ
1
−195.6 (c = 0.9, CH2Cl2). 31P NMR (CDCl3, 121 MHz): δ −0.7. H
NMR (CDCl3, 300 MHz): δ 3.00 (ddd, 1H, J = 17.1, 7.8, and 2.7 Hz,
CHHCOPh), 3.48−3.59 (m, 1H, CHHCOPh), 4.15−4.21 (m, 1H,
PCHCH2), 5.74 (dd, 2H, J = 5.4 and 1.5 Hz, CH2O2), 6.45−7.68 (m,
18H, Ar). 13C NMR (CDCl3, 75 MHz): δ 39.8 (d, 1C, 1JPC = 11.2 Hz,
PCH), 42.8 (d, 1C, 2JPC = 22.7 Hz, CH2COPh), 100.9 (s, 1C, CH2O2),
1
2
39.8 (d, 1C, JPC = 13.0 Hz, PCH), 41.9 (d, 1C, JPC = 21.8 Hz,
CH2COPh), 121.6−148.2 (m, 24C, Ar), 197.3 (d, 1C, 3JPC = 12.6 Hz,
COPh).
3
108.3−147.6 (m, 24C, Ar), 198.1 (d, 1C, JPC = 12.8 Hz, COPh).
Synthesis of (S)-4k. Crude (S)-4k was synthesized according to a
Synthesis of (S)-4d. Crude (S)-4d was synthesized according to a
general procedure (99% yield, 98% ee). Pure (S)-4d was obtained after
general procedure (99% yield, 99% ee). Pure (S)-4k was obtained after
20
20
purification as a solid (89% yield, >99% ee; air-sensitive). [α]D
=
purification as a solid (91% yield, >99% ee; air-sensitive): [α]D
=
1
−164.2 (c = 1.7, CH2Cl2). 31P NMR (CDCl3, 161 MHz): δ−0.7. H
NMR (CDCl3, 400 MHz): δ 3.07 (ddd, 1H, J = 17.2, 7.6, and 2.4 Hz,
CHHCOPh), 3.53−3.61 (m, 1H, CHHCOPh), 4.20−4.25 (m, 1H,
PCHCH2), 7.00−7.68 (m, 19H, Ar). 13C NMR (CDCl3, 100 MHz):
1
−229.0 (c = 1.1, CH2Cl2). 31P NMR (CDCl3, 161 MHz): δ −0.7. H
NMR (CDCl3, 400 MHz): δ 3.15 (ddd, 1H, J = 17.4, 8.2, and 2.7 Hz,
CHHCOPh), 3.70−3.78 (m, 1H, CHHCOPh), 4.42−4.47 (m, 1H,
PCHCH2), 6.99−7.68 (m, 22H, Ar). 13C NMR (CDCl3, 75 MHz):
1
2
1
2
δ 39.4 (d, 1C, JPC = 11.8 Hz, PCH), 42.3 (d, 1C, JPC = 21.2 Hz,
CH2COPh), 120.3−140.2 (m, 24C, Ar), 197.8 (d, 1C, 3JPC = 12.6 Hz,
COPh).
δ 40.0 (d, 1C, JPC = 11.7 Hz, PCH), 42.6 (d, 1C, JPC = 22.4 Hz,
CH2COPh), 125.5−138.7 (m, 28C, Ar), 197.9 (d, 1C, 3JPC = 12.3 Hz,
COPh).
Synthesis of (S)-4e. Crude (S)-4e was synthesized according to a
Synthesis of (S)-4l. Crude (S)-4l was synthesized according to a
general procedure (99% yield, 98% ee). Pure (S)-4e was obtained after
general procedure (99% yield, 97% ee). Pure (S)-4l was obtained after
20
20
purification as a solid (90% yield, >99% ee; air-sensitive). [α]D
=
purification as a solid (89% yield, >99% ee; air-sensitive): [α]D
=
1
1
−208.7 (c = 1.2, CH2Cl2). 31P NMR (CDCl3, 121 MHz): δ 0.0. H
NMR (CDCl3, 300 MHz): δ 3.07 (ddd, 1H, J = 17.4, 7.9, and 2.8 Hz,
CHHCOPh), 3.52−3.63 (m, 1H, CHHCOPh), 4.20−4.27 (m, 1H,
PCHCH2), 7.02−7.68 (m, 19H, Ar). 13C NMR (CDCl3, 75 MHz):
−153.3 (c = 0.8, CH2Cl2). 31P NMR (CDCl3, 162 MHz): δ −0.8. H
NMR (CDCl3, 400 MHz): δ 3.11 (ddd, 1H, J = 17.2, 8.0, and 2.8 Hz,
CHHCOPh), 3.64−3.72 (m, 1H, CHHCOPh), 4.39−4.43 (m, 1H,
PCHCH2), 6.90−7.70 (m, 21H, Ar). 13C NMR (CDCl3, 100 MHz):
2538
dx.doi.org/10.1021/ic202472f | Inorg. Chem. 2012, 51, 2533−2540

Inorganic Chemistry
Article
1
2
1
2
δ 41.2 (d, 1C, JPC = 12.8 Hz, PCH), 46.5 (d, 1C, JPC = 21.7 Hz,
CH2COPh), 115.6−138.6 (m, 28C, Ar), 196.5 (d, 1C, 3JPC = 12.4 Hz,
COPh). 19F NMR (CDCl3, 376.5 MHz): δ −105.2.
δ 39.4 (d, 1C, JPC = 11.7 Hz, PCH), 42.5 (d, 1C, JPC = 22.6 Hz,
CH2COPh), 115.2−162.8 (m, 24C, Ar), 196.9 (d, 1C, 3JPC = 12.8 Hz,
COPh). 19F NMR (CDCl3, 282.4 MHz): δ −116.3.
Synthesis of (S)-4m. Crude (S)-4m was synthesized according to
Synthesis of (S)-4t. Crude (S)-4t was synthesized according to a
20
20
general procedure (99% yield, 96% ee). Pure (S)-4n was obtained after
ASSOCIATED CONTENT
* Supporting Information
X-ray crystallographic data in CIF format, general information,
experimental section, NMR spectra, and X-ray data. This
material is available free of charge via the Internet at http://
pubs.acs.org.
■
20
purification as a solid (88% yield, >99% ee; air-sensitive). [α]D
=
S
1
−120.6 (c = 1.0, CH2Cl2). 31P NMR (CDCl3, 121 MHz): δ 0.1. H
NMR (CDCl3, 300 MHz): δ 3.02 (ddd, 1H, J = 17.1, 8.4, and 3.0 Hz,
CHHCOPh), 3.49−3.60 (m, 1H, CHHCOPh), 4.18−4.25 (m, 1H,
PCHCH2), 6.98−7.63 (m, 19H, Ar). 13C NMR (CDCl3, 75 MHz):
1
2
δ 40.2 (d, 1C, JPC = 11.6 Hz, PCH), 42.6 (d, 1C, JPC = 22.2 Hz,
CH2COPh), 126.6−140.8 (m, 24C, Ar), 197.2 (d, 1C, 3JPC = 12.8 Hz,
COPh).
AUTHOR INFORMATION
Corresponding Author
*E-mail: pakhing@ntu.edu.sg.
■
Synthesis of (S)-4o. Crude (S)-4o was synthesized according to a
general procedure (99% yield, 97% ee). Pure (S)-4o was obtained after
20
purification as a solid (89% yield, >99% ee; air-sensitive): [α]D
=
1
−144.0 (c = 1.0, CH2Cl2). 31P NMR (CDCl3, 121 MHz): δ 0.0. H
NMR (CDCl3, 300 MHz): δ 3.02 (ddd, 1H, J = 17.1, 8.6, and 2.9 Hz,
CHHCOPh), 3.50−3.61 (m, 1H, CHHCOPh), 4.18−4.25 (m, 1H,
PCHCH2), 6.97−7.60 (m, 19H, Ar). 13C NMR (CDCl3, 75 MHz):
ACKNOWLEDGMENTS
We thank Nanyang Technological University for supporting
this research and for a Ph.D. scholarship to Y.H.
■
1
2
δ 40.1 (d, 1C, JPC = 11.7 Hz, PCH), 42.4 (d, 1C, JPC = 22.3 Hz,
CH2COPh), 126.6−140.8 (m, 24C, Ar), 196.9 (d, 1C, 3JPC = 12.7 Hz,
COPh).
REFERENCES
■
(1) (a) Crabtree, R. H., Mingos, M., Eds. Comprehensive Organo-
metallic Chemistry III; Elsevier: London, 2007. (b) Ojima, I., Ed.
Catalytic Asymmetric Synthesis, 3rd ed.; Wiley-VCH: New York, 2010.
(c) Tang, W.; Zhang, X. Chem. Rev. 2003, 103, 3029.
Synthesis of (S)-4p. Crude (S)-4p was synthesized according to a
general procedure (99% yield, 97% ee). Pure (S)-4p was obtained after
20
purification as a solid (90% yield, >99% ee; air-sensitive). [α]D
=
1
−138.9 (c = 0.9, CH2Cl2). 31P NMR (CDCl3, 121 MHz): δ 0.1. H
NMR (CDCl3, 300 MHz): δ 3.02 (ddd, 1H, J = 17.1, 8.1, and 3.0 Hz,
CHHCOPh), 3.52−3.63 (m, 1H, CHHCOPh), 4.20−4.26 (m, 1H,
PCHCH2), 6.89−7.70 (m, 19H, Ar). 13C NMR (CDCl3, 75 MHz):
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Z.; Jiang, Q.; Xiao, D.; Cao, P.; Zhang, X. J. Am. Chem. Soc. 1997, 119,
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Glueck, D. S. J. Am. Chem. Soc. 2002, 124, 13356. (j) Julienne, D.;
Delacroix, O.; Lohier, J.; Oliveira-Santos, J. S.; Gaumont, A. Eur. J.
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1
2
δ 40.1 (d, 1C, JPC = 11.6 Hz, PCH), 42.5 (d, 1C, JPC = 22.3 Hz,
CH2COPh), 115.6−167.5 (m, 24C, Ar), 196.5 (d, 1C, 3JPC = 12.9 Hz,
COPh). 19F NMR (CDCl3, 282.4 MHz): δ −105.3.
Synthesis of (S)-4q. Crude (S)-4q was synthesized according to a
general procedure (99% yield, 92% ee). Pure (S)-4q was obtained after
20
purification as a solid (71% yield, >99% ee; air-sensitive). [α]D
=
1
−133.0 (c = 1.0, CH2Cl2). 31P NMR (CDCl3, 162 MHz): δ 0.6. H
NMR (CDCl3, 400 MHz): δ 3.30 (ddd, 1H, J = 17.6, 7.7, and 3.2 Hz,
CHHCOPh), 3.98−4.06 (m, 1H, CHHCOPh), 4.27−4.32 (m, 1H,
PCHCH2), 6.96−8.55 (m, 19H, Ar). 13C NMR (CDCl3, 100 MHz):
1
2
δ 40.1 (d, 1C, JPC = 17.6 Hz, PCH), 41.6 (d, 1C, JPC = 22.0 Hz,
CH2COPh), 122.0−153.4 (m, 24C, Ar), 199.9 (d, 1C, 3JPC = 12.7 Hz,
COPh).
Synthesis of (S)-4r. Crude (S)-4r was synthesized according to a
general procedure (98% yield, 98% ee). Pure (S)-4r was obtained after
20
purification as a solid (88% yield, >99% ee; air-sensitive). [α]D
=
1
−150.6 (c = 0.9, CH2Cl2). 31P NMR(CDCl3, 161 MHz): δ −0.5. H
NMR (CDCl3, 400 MHz): δ 3.01 (ddd, 1H, J = 17.2, 8.4, and 2.8 Hz,
CHHCOPh), 3.55−3.63 (m, 1H, CHHCOPh), 3.73 (s, 3H, CH3O),
4.23−4.28 (m, 1H, PCHCH2), 6.73−7.68 (m, 19H, Ar). 13C NMR
(CDCl3, 100 MHz): δ 40.1 (d, 1C, 1JPC = 11.4 Hz, PCH), 42.5 (d, 1C,
2JPC = 22.0 Hz, CH2COPh), 55.6 (s, 1C, CH3O), 113.8−163.6 (m,
3
(5) For selected examples of transition-metal-catalyzed asymmetric
hydrophosphination, see: (a) Scriban, C.; Kovacik, I.; Glueck, D. S.
Organometallics 2005, 24, 4871. (b) Kovacik, I. D.; Wicht, K.; Grewal,
N. S.; Glueck, D. S.; Incarvito, C. D.; Guzei, I. A.; Rheingold, A. L.
Organometallics 2000, 19, 950. (c) Wicht, D. K.; Kourkine, I. V.;
Kovacik, I.; Nthenge, J. M.; Glueck, D. S. Organometallics 1999, 18,
5381. (d) Wicht, D. K.; Kourkine, I. V.; Lew, B. M.; Nthenge, J. M.;
Glueck, D. S. J. Am. Chem. Soc. 1997, 119, 5039. (e) Sadow, A. D.;
24C, Ar), 196.6 (d, 1C, JPC = 12.8 Hz, COPh).
Synthesis of (S)-4s. Crude (S)-4s was synthesized according to a
general procedure (99% yield, 97% ee). Pure (S)-4s was obtained after
20
purification as a solid (90% yield, >99% ee; air-sensitive). [α]D
=
1
−133.9 (c = 0.6, CH2Cl2). 31P NMR (CDCl3, 121 MHz): δ −0.2. H
NMR (CDCl3, 400 MHz): δ 3.03 (ddd, 1H, J = 17.2, 8.0, and 2.8 Hz,
CHHCOPh), 3.47−3.55 (m, 1H, CHHCOPh), 4.18−4.22 (m, 1H,
PCHCH2), 6.72−7.60 (m, 18H, Ar). 13C NMR (CDCl3, 100 MHz):
2539
dx.doi.org/10.1021/ic202472f | Inorg. Chem. 2012, 51, 2533−2540

Inorganic Chemistry
Article
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(5 mL), Et3N (0.5 equiv), and 2-nitrochalcone (1.1 equiv) were
reacted at −80 °C for 2 days and then at −10 °C for another 2 days.
The product cannot be purified by recrystallization.
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