Chiral ytterbium silylamide catalyzed enantioselective phospha-Michael addition of diethyl phosphite to chalcones

Article abstract of DOI:10.1016/j.tetasy.2014.06.008

An efficient and enantioselective phospha-Michael addition of diethyl phosphite to chalcones has been established. In the presence of a catalytic amount of chiral lanthanide silylamide generated from [(Me₃Si) ₂N]₃Yb(μ-Cl)Li(THF)₃ and salen, the reaction produced the target γ-oxophosphonates with high yields and enantioselectivity.

Full text of DOI:10.1016/j.tetasy.2014.06.008

Tetrahedron: Asymmetry 25 (2014) 989–996
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Chiral ytterbium silylamide catalyzed enantioselective
phospha-Michael addition of diethyl phosphite to chalcones
⇑
Guoyao Li, Lu Wang, Zhigang Yao, Fan Xu
Key Laboratory of Organic Synthesis, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 April 2014
Accepted 6 June 2014
An efficient and enantioselective phospha-Michael addition of diethyl phosphite to chalcones has been
established. In the presence of a catalytic amount of chiral lanthanide silylamide generated from
[(Me3Si)2N]3Yb(l-Cl)Li(THF)3 and salen, the reaction produced the target c-oxophosphonates with high
yields and enantioselectivity.
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
asymmetric reactions are scarce. Marks19 and Zi20 evaluated chiral
Ln catalysts generated from Ln[N(SiMe3)2]3 and different chiral
ligands, such as binaphthols and oxazolines, for the stereoselective
intramolecular hydroamination/cyclization of aminoalkenes,
respectively. Calter21 achieved an efficient asymmetric synthesis
1
Lanthanide silylamides, Ln[N(SiMe3)2]3 and their chloride-
bridged form [(Me3Si)2N]3Ln(
-Cl)Li(THF)3,2 are regarded as a
l
new type of catalyst that can function as a Lewis acid and a
Brønsted base at the same time. A series of intermolecular and
intramolecular reactions have been efficiently catalyzed by lantha-
nide silylamides and these include the Tishchenko reaction,3 ami-
dations,4 monoadditions of terminal alkynes to nitriles,5 coupling
of isocyanides with terminal alkynes,6 dimerization of terminal
alkynes,7 aldol condensations,8 aza-Henry reactions,9 guanylation
of amines,10 the Pudovik reaction,11 phospha-Brook rearrange-
ments,12 and phospha-Michael additions.13 Lanthanide silylamides
are also highly active catalysts in versatile hydroelementation pro-
cesses such as hydrosilylations,14 hydroborations,15 hydroamina-
tions,3b,16 hydrophosphinations,17 and hydroalkoxylations.18
The most characteristic feature of lanthanide silylamides is that
they can be used as precursors, because they easily react with
Brønsted acidic compounds such as alcohols, phenols, cyclopent-
adienes, acetylenes, phosphanes, and thiols (Scheme 1). The rapid
deprotonation of these substrates by HN(SiMe3)2 elimination
may readily result in the generation of new Ln-X (X = O, S, P, N,
C) bonds. It can therefore be assumed that if chiral Brønsted acidic
ligands react with lanthanide silylamides, chiral lanthanide com-
plexes can be prepared by the simple metathesis reaction between
Ln[N(SiMe3)2]3 and chiral ligands. To the best of our knowledge, a
few chiral lanthanide silylamides have been synthesized and stud-
ied, however their use in asymmetric organic synthesis has
received much less attention and reports concerning the develop-
ment and application of chiral lanthanide silylamide-catalyzed
of a-phenoxy-b-aryl-b-lactams in the presence of catalytic quanti-
ties of a silyl cinchona alkaloid and lanthanide silylamides. There-
fore, due to the high activity of lanthanide silylamides presented in
many reactions, the further development of chiral lanthanide
silylamides and relevant processes of high efficiency and stereose-
lectivity for the asymmetric synthesis of valuable small molecule is
a desirable and challenging goal.
Ln[N(SiMe3)2]3 + n HL
LnLn[N(SiMe3)2]3-n + n HN(SiMe3)2
HL: HOR, HSR, HNR2, HPR2, HCp, HC CR, etc
n: 1-3
Scheme 1. Metathesis reaction between lanthanide silylamides and Brønsted
acidic compounds.
The formation of CAP bonds is one of the most important trans-
formations in organic synthesis because of the tremendous impor-
tance of organophosphorus compounds in many different areas.
Phospha-Michael addition,22 the conjugate addition of P-nucleo-
philes to activated alkenes, is important in carbonAphosphorus
bond formation because of its step-economy and atom-economy,
and its catalysts, scope, and applications have been widely explored.
Recently, to meet the growing demand for enantiomerically pure
materials, the enantioselective phospha-Michael addition23 has
attracted considerable attention. Dialkyl phosphites,24–28 diaryl-
phosphines,29,30 and dialkyl phosphine oxides31–34 are used as
⇑
Corresponding author. Tel.: +86 512 65880331; fax: +86 512 65880305.
E-mail address: xufan@suda.edu.cn (F. Xu).
http://dx.doi.org/10.1016/j.tetasy.2014.06.008
0957-4166/Ó 2014 Elsevier Ltd. All rights reserved.

990
G. Li et al. / Tetrahedron: Asymmetry 25 (2014) 989–996
P-nucleophiles in this asymmetric addition. Considering the stabil-
ity and smell of phosphorus reagents, dialkyl phosphite is the
preferred choice and is also readily available. As for olefinic
indicates that the cyclohexanediamine-derived salens L7, L8 were
superior to the o-phenylenediamine-derived salens L9, L10, and
the ligands with bulkier substituent groups such as tert-butyl pro-
vided better results. Complex L7-Yb afforded the product with 41%
ee while L8-Yb afforded the product with the opposite configura-
tion in 51% ee. Therefore, the steric hindrance of the R group of
the salicylaldehyde moiety in the salen showed a complex effect
on the enantioselectivity of the reaction. Additionally, the salen-
like ligands L11 and L12 both afforded the product with no selec-
tivity (Table 1, entries 11 and 12).
Next, a series of lanthanide silylamides were used to assess the
influence of the central metal on the activity and selectivity
(Table 2, entries 1–5). The results revealed that the lanthanide sily-
lamides tested, besides that of Yb, all gave slightly increased yields
with significantly diminished ee values. Considering the yield and
the enantioselectivity, the L8-Yb complex was chosen for subse-
quent investigation. A further optimization of the reaction condi-
tions, including catalyst loading and the molar ratio of lanthanide
metal to ligand, was carried out and we found that a 10 mol % load-
ing for both the catalyst and ligand was optimal (Table 2, entry 7).
The reaction temperature was decreased to 0 °C with essentially no
loss in yield; however, the enantioselectivity improved signifi-
cantly (Table 2, entry 11). A survey of various solvents (Table 2,
entries 11–17) revealed that toluene provided the product with
comparatively good reactivity and enantioselectivity. When the
chalcone/toluene solution was added slowly and evenly to the
mixture of phosphite and catalyst within 2 h, an obvious increase
in the enantiomeric excess from 73% to 89% was achieved and
the yield also improved to 94% (Table 2, entry 18). A further
decrease in temperature resulted in a reduction of the yield while
the enantioselectivity was retained (Table 2, entry 19). Therefore,
the optimal reaction conditions were identified as follows:
acceptors, reactions involving
challenge.28–32 To date only one report28 exists on the enantioselec-
tive phospha-Michael addition of a dialkyl phosphite to ,b-unsatu-
rated ketones. This reaction was carried out in the presence of a
dinuclear zinc catalyst to afford -oxophosphonates in high yields
a,b-unsaturated ketones remain a
a
c
and with excellent enantioselectivities. Therefore, the development
of efficient and catalytic processes to achieve this CAP bond-form-
ing transformation and enable the enantioselective and atom
economical synthesis of chiral phosphonates is still required.
Herein, we report our recent results into the application of chiral
lanthanide silylamides as catalysts for the asymmetric phospha-
Michael addition of dialkyl phosphites to chalcones.
2. Results and discussion
Initially, several chiral ligands (Scheme 2) were complexed
in situ with [(Me3Si)2N]3Yb(l-Cl)Li(THF)3, the tetracoordinate
ytterbium silylamide, to catalyze the model reaction between chal-
cone 1a and diethyl phosphite in dry toluene at room temperature;
the results are shown in Table 1. We found that when (R)-BINOL,
cinchonidine, quinine, and TADDOL L1–L4 were used, the products
were isolated in moderate yields but with no selectivity (Table 1,
entries 1–4). A remarkable enhancement in enantioselectivity
was achieved when the tridentate Schiff base L5, derived from L-
phenylglycinol and 3,5-di-tert-butylsalicylaldehyde, was used
(Table 1, entry 5). However, the hydrogenated Schiff base L6 affor-
ded a racemic product (Table 1, entry 6) although ligands L5 and L6
have the same absolute backbone configuration. Fortunately, the
salen–Yb complexes that were formed in situ from [(Me3Si)2N]3-
Yb(l-Cl)Li(THF)3 with different salens L7–L10 showed great poten-
tial in this reaction. Product 3a was thus obtained in moderate
yields and with enhanced ee values (Table 1, entries 7–10). Table 1
10 mol % [(Me3Si)2N]3Yb(l-Cl)Li(THF)3, 10 mol % L8, 0.6 mmol
diethyl phosphite, and 0.5 mmol chalcone in 2 mL toluene at 0 °C
for 24 h.
R
Ph
Ph
Ph
Ph
OH
O
O
OH
OH
OH
OH
Me
Me
N
N
L2
: R=H
L1
L4
L3: R=OMe
Ph
Ph
N
N
N
tBu
NH
OH
tBu
OH
R
OH HO
R
OH
OH
But
But
R
R
L7
: R=H
L5
L6
L8: R=But
Ph
N
Ph
N
N
N
N
N
R
OH HO
R
N
N
N
N
R
R
OH HO
L9
:
R=H
L10: R=But
L11
Scheme 2. Chiral ligands L1–L12.
L12

G. Li et al. / Tetrahedron: Asymmetry 25 (2014) 989–996
991
Table 1
Ligand screening for the asymmetric 1,4-addition of diethyl phosphite to chalconea
EtO
Ph
O
EtO
P
*
O
O
2 mol% [(Me3Si)2N]3Yb(µ-Cl)Li(THF)3
2 mol% Ligand
HOP(OEt)2
2
+
Ph
Ph
Ph
toluene, 24 h, r.t.
3a
1a
Entry
Ligand
Yieldb (%)
eec (%)
1
2
3
4
5
6
7
8
L1
L2
L3
L4
L5
L6
L7
L8
52
61
71
38
29
43
46
50
45
66
44
56
0
0
0
0
À23
0
À41
51
9
9
L9
10
11
12
L10
L11
L12
À37
0
0
a
The reactions were carried out under argon by reacting chalcone (0.5 mmol), diethyl phosphite
(0.6 mmol), 2 mol % [(Me3Si)2N]3Yb(
l-Cl)Li(THF)3, and 2 mol % ligand in 2 mL of toluene at 25 °C for 24 h.
b
Isolated yield.
c
Determined by HPLC analysis.
Table 2
Condition screening for the asymmetric 1,4-addition of diethyl phosphite to chalconea
EtO
EtO
O
O
P
*
O
L8
[(Me3Si)2N]3Ln(µ-Cl)Li(THF)3 /
HOP(OEt)2
+
Ph
Ph
conditions
Ph
Ph
2
1a
3a
Entry
Ln
Catalyst loading (mol %)
Ligand loading (mol %)
Temp. (°C)
Solvent
Yieldb (%)
eec (%)
1
2
3
4
5
6
7
8
La
2
2
2
2
2
5
10
10
10
10
10
10
10
10
10
10
10
10
10
2
2
2
2
2
5
10
5
15
20
10
10
10
10
10
10
10
10
10
25
25
25
25
25
25
25
25
25
25
0
0
0
0
0
0
0
0
À10
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
THF
62
63
60
50
66
88
93
87
86
84
89
81
79
37
69
56
91
94
86
5
26
36
51
16
57
64
47
59
47
73
63
60
50
65
59
69
89
89
Nd
Sm
Yb
Y
Yb
Yb
Yb
Yb
Yb
Yb
Yb
Yb
Yb
Yb
Yb
Yb
Yb
Yb
9
10
11
12
13
14
15
16
17
18d
19d
CH3CN
Et2O
n-hexane
CH2Cl2
m-xylene
Toluene
Toluene
a
The reactions were carried out under argon by reacting chalcone (0.5 mmol) and diethyl phosphite (0.6 mmol) in 2 mL of
solvent for 24 h.
b
Isolated yield.
Determined by HPLC analysis.
The chalcone/toluene solution was added slowly and evenly to a mixture of phosphite and catalyst within 2 h.
c
d
A series of substituted chalcones were examined under the opti-
mized conditions, and the corresponding products were obtained in
high yields and with high enantioselectivities (Table 3). The
electronic properties of the aryls of chalcone had no obvious effect
on the enantioselectivities of the products, while the steric
hindrance was important with regard to the enantioselectivity.
Chalcones with an ortho-substituted phenyl at the 3-position affor-
ded the corresponding products with relatively higher ee values
(Table 3, entries 8, 11–17). 3-Naphthyl substituted and 3-heteroar-
omatic chalcones all reacted smoothly with diethyl phosphite to
give products with ee values higher than 90% (Table 3, entries 9
and 10). The absolute configuration of compound 3c (Table 3, entry
3) was determined to be (S) by comparison with the literature
data.28 The other products were tentatively assigned by analogy.
Although the detailed reaction process remains unclear, a plau-
sible mechanism is shown in Scheme 3. According to the properties
of [(Me3Si)2N]3Ln(l-Cl)Li(THF)3, the initial step of this reaction
involves an in situ protonolytic generation of the salen-Ln-
N(SiMe3)2 complex A. Complex A reacts with diethyl phosphite
to release the last HN(SiMe3)2 and forms intermediate B. As a

992
G. Li et al. / Tetrahedron: Asymmetry 25 (2014) 989–996
Table 3
Substrate scope for the asymmetric reactions of substituted chalcones with diethyl phosphitea
EtO
EtO
O
O
P
*
O
10 mol% [(Me3Si)2N]3Yb(µ-Cl)Li(THF)3
10 mol% L8
toluene, 24 h, 0oC
HOP(OEt)2
+
R1
R2
R1
R2
1
2
3
Entry
R1
R2
Product
Yieldb (%)
eec (%)
1
2
3
4
Ph
Ph
Ph
Ph
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
94
87
91
80
82
82
88
84
87
88
89
86
93
89
87
89
91
89
88
82(S)d
82
91
90
86
94
93
90
93
91
94
91
94
92
92
4-ClC6H4
4-MeOC6H4
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4-ClC6H4
4-MeOC6H4
4-MeC6H4
4-FC6H4
4-ClC6H4
4-BrC6H4
4-MeOC6H4
2-MeOC6H4
4-ClC6H4
4-BrC6H4
4-MeC6H4
2-MeC6H4
1-naphthyl
2-thienyl
2-MeC6H4
5e
6e
7
8
9
10
11
12
13
14
15
16
17
2-MeC6H4
2,6-(Me)2C6H3
2,6-(Me)2C6H3
2,6-(Me)2C6H3
2,6-(Me)2C6H3
2,6-(Me)2C6H3
a
The reactions were carried out under argon by reacting chalcone (0.5 mmol), diethyl phosphite
(0.6 mmol), 10 mol % [(Me3Si)2N]3Yb(
l
-Cl)Li(THF)3, 10 mol % L8 in 2 mL of toluene at 0 °C for 24 h.
b
Isolated yield.
Determined by HPLC analysis.
c
d
The absolute configuration was determined by chemical correlation with a known compound.
4 mL of toluene were used.
e
highly oxophilic Lewis acid, the central lanthanide atom of B can
coordinate with the carbonyl group of the chalcone. Such a coordi-
nation may both activate the chalcone and lead to a close contact
between the enone and the P-nucleophile. This simultaneously
leads to a further face selective reaction in a chiral environment.
temperature in THF. Evaporation of the resulting yellow solution
and crystallization from toluene and hexane gave a yellow powder,
which was characterized by 1H NMR spectroscopy. As expected, the
spectrum showed that the central Y atom bonds to two aryloxide
groups from salen and one silylamide, while one tetrahydrofuran
molecule is also coordinated to the central metal, as shown in
Scheme 4. Following the same procedure, the analogous L8–Yb
complex was prepared as a yellow powder and evaluated as a cata-
lyst for the model reaction between 1a and 2. A 93% yield and 85% ee
value were obtained, which were similar to the results obtained for
c-Oxophosphonate 3 is then released upon proton exchange
between C and another phosphite, and catalyst B is regenerated.
For further insight into the chiral active species for the reaction,
the L8-Y complex 4 was synthesized by treatment of L8 with
[(Me3Si)2N]3Y(
l
-Cl)Li(THF)3 in
a
molar ratio of 1:1 at room
Yb[N(SiMe3)2]3
N
O
N
O
N
N
Yb
N
But
But
But
OH HO
But
TMS TMS
2 HN(SiMe3)2
But
But
But
But
L* Yb N(TMS)2
HOP(OEt)2
L* Yb N(TMS)2
L
*
Yb
OP(OEt)2
A
B
HN(TMS)2
O
3
Ar
Ar
HOP(OEt)2
[Yb*]
O
O
P
[Yb*]
O
O
EtO
EtO
(EtO)2
Ar
P
*
Ar
Ar
Ar
C
Scheme 3. Proposed mechanism for the addition of diethyl phosphite to chalcone.

G. Li et al. / Tetrahedron: Asymmetry 25 (2014) 989–996
993
N
O
N
O
N
O
N
O
Y
Y
But
But
But
But
O
But
(TMS)2N
But
But
(EtO)2P
But
O
O
4
5
Scheme 4. Salen–Y complexes.
the in situ catalytic system. Next, complex 4 and diethyl phosphite
were mixed in a molar ratio of 1:1 on an NMR-tube scale using C6D6
as the solvent. The 1H NMR spectrum of the mixture showed that
complex 5 (Scheme 4) was formed. The silylamide group bonding
to the central metal in 4 was exchanged into a phosphite group,
which is consistent with the hypothesis on the transformation of
A to B in the proposed mechanism (Scheme 3). Bis(trimethyl-
silyl)amine [HN(SiMe3)2, 30 mol %], which is released in situ, was
also used to verify whether it could act independently as a catalyst.
No product was detected under the optimal reaction conditions.
Na2SO4, and concentrated in vacuo. The residue was purified by
column chromatography on silica gel (petroleum ether/ethyl
acetate 7:1 to 1:1) to give 3a as a colorless oil.
4.3. Synthesis of compound 4
A mixture of [(Me3Si)2N]3Y(l-Cl)Li(THF)3 (1.66 g, 2 mmol) and
L8 (1.09 g, 2 mmol) in THF (20 mL) was stirred at room tempera-
ture for 24 h. THF was then removed under reduced pressure,
and compound 4 was obtained as a yellow powder in toluene
and hexane mixed solvent at 0 °C. 1H NMR (400 MHz, C6D6) d
(ppm): 8.01 (s, 1H, N@CH), 7.77 (s, 1H, N@CH), 7.74 (d, J = 2.8 Hz,
1H, ArH), 7.73 (d, J = 2.8 Hz, 1H, ArH), 7.32 (d, J = 2.8 Hz, 1H, ArH),
7.05 (d, J = 2.8 Hz, 1H, ArH), 4.49–4.43 (m, 1H, NACH), 3.81 (m,
4H, 2 Â CH2 (THF)), 2.31–2.25 (m, 1H, NACH), 1.75 (s, 9H, t-Bu),
1.66 (s, 9H, t-Bu), 1.53–1.41 (m, 10H, 3 Â CH2 + 2 Â CH2 (THF)),
1.37 (s, 9H, t-Bu), 1.36 (s, 9H, t-Bu), 1.25–1.13 (m, 2H, CH2), 0.31
(s, 18H, 2 Â Si(CH3)3).
3. Conclusion
We have successfully developed an asymmetric phospha-
Michael addition of diethyl phosphite to chalcones. The chiral
lanthanide silylamide, formed in situ from [(Me3Si)2N]3Yb(
Li(THF)3 and salen, was found to be an efficient catalyst for the
reaction and provided the target -oxophosphonates in high yields
l-Cl)
c
and enantioselectivities. The further development of chiral lantha-
nide silylamide compounds and their application as catalysts for
asymmetric reactions are currently being investigated in our
laboratory.
4.4. Characterization of compound 5
The reaction of compound 4 (33.6 mg, 0.0388 mmol) with
HOP(OEt)2 (5 lL, 0.0388 mmol) was performed using C6D6
(0.8 mL) as the solvent in a Teflon valve-sealed J-Young tube and
the 1H NMR spectrum of 5 was obtained using C6D6 as an internal
reference. 1H NMR (400 MHz, C6D6) d (ppm): 7.84 (s, 1H, N@CH),
7.74 (d, J = 2.4 Hz, 1H, ArH), 7.70 (s, 1H, N@CH), 7.59 (d,
J = 2.4 Hz, 1H, ArH), 7.40 (d, J = 2.4 Hz, 1H, ArH), 7.06 (d,
J = 2.8 Hz, 1H, ArH), 4.75–4.70 (m, 1H, N-CH), 4.19–4.04 (m, 2H,
OCH2), 3.98–3.85 (m, 2H, OCH2), 3.59 (m, 4H, 2 Â CH2 (THF)),
2.25–2.19 (m, 1H, N-CH), 1.88 (s, 9H, t-Bu), 1.66 (s, 9H, t-Bu),
1.53 (s, 9H, t-Bu), 1.50–1.42 (m, 10H, 3 Â CH2 + 2 Â CH2 (THF)),
1.36 (s, 9H, t-Bu), 1.18–1.16 (m, 2H, CH2), 1.10 (t, J = 7.2 Hz, 3H,
CH2CH3), 0.89 (t, J = 7.2 Hz, 3H, CH2CH3).
4. Experimental
4.1. General information
All manipulations were conducted under an atmosphere of dry
argon with flame-dried glassware. [(Me3Si)2N]3Ln(l-Cl)Li(THF)3
2c-2e
were synthesized according to the literature method. Solvents were
distilled before use from calcium hydride or sodium/benzophenone.
1H, 13C, and 31P NMR spectra were obtained on a Bruker AVANCEIII
400 MHz spectrometer using tetramethylsilane (TMS) as an internal
reference. HRMS data were obtained on a Micromass GCT instru-
ment. IR spectra were obtained on a Varian Scimitar 1000 FT-IR
spectrometer. The enantiomeric excess data were determined on
an Agilent 1200 Series HPLC with Chiralpak AS-H, Chiralpak AD-H,
Chiralcel OJ-H, and Chiralpak IA columns.
5. Characterization of the products
5.1. (S)-Diethyl 3-oxo-1,3-diphenylpropylphosphonate13 3a
Colorless oil. 89% ee determined by HPLC on a Chiralpak AS-H
column (hexane/2-propanol = 90:10, flow rate = 1.0 mL/min,
4.2. Typical procedure for the asymmetric phospha-Michael
addition
tmajor = 10.0 min, tminor = 12.9 min). [
a]
29 = À33 (c 1.0, CHCl3). 1H
D
NMR (400 MHz, CDCl3) d (ppm): 7.94 (d, J = 7.6 Hz, 2H), 7.55 (t,
J = 7.2 Hz, 1H), 7.46–7.42 (m, 4H), 7.31–7.20 (m, 3H), 4.17–3.87
(m, 4H), 3.81–3.63 (m, 3H), 1.28 (t, J = 7.2 Hz, 3H), 1.08 (t,
J = 7.2 Hz, 3H).
A
mixture
of
[(Me3Si)2N]3Yb(
l
-Cl)Li(THF)3
(45.5 mg,
0.05 mmol) and L8 (27.3 mg, 0.05 mmol) in toluene (0.5 mL) was
stirred at room temperature for 20 min. Next, a solution of diethyl
phosphite (77 lL, 0.6 mmol) in toluene (0.5 mL) was added and
stirred for 20 min. The mixture was then cooled to 0 °C, which
was followed by the addition of a solution of chalcone 1a
(104.1 mg, 0.5 mmol) in toluene (1 mL) slowly and evenly within
2 h at 0 °C. The mixture was then stirred at this temperature for
24 h. Water was added, and the mixture was extracted with ethyl
acetate. The combined organic layer was dried over anhydrous
5.2. (S)-Diethyl 3-(4-chlorophenyl)-3-oxo-1-phenylpropylphos
phonate13 3b
Colorless oil. 88% ee determined by HPLC on a Chiralpak AD-H
column (hexane/2-propanol = 90:10, flow rate = 1.0 mL/min,

994
G. Li et al. / Tetrahedron: Asymmetry 25 (2014) 989–996
tminor = 19.8 min, tmajor = 23.5 min). [
a
]
27 = À41 (c 1.0, CHCl3). 1H
5.9. (S)-Diethyl 1-(naphthalen-1-yl)-3-oxo-3-phenylpropylphos
phonate13 3i
D
NMR (400 MHz, CDCl3) d (ppm): 7.88 (d, J = 8.0 Hz, 2H), 7.42–
7.40 (m, 4H), 7.32–7.21 (m, 3H), 4.10–3.85 (m, 4H), 3.76–3.60
(m, 3H), 1.28 (t, J = 7.2 Hz, 3H), 1.07 (t, J = 7.2 Hz, 3H).
Colorless oil. 93% ee determined by HPLC on a Chiralpak AD-H
column (hexane/2-propanol = 90:10, flow rate = 1.0 mL/min,
5.3. (S)-Diethyl 3-(4-methoxyphenyl)-3-oxo-1-phenylpropyl-
tmajor = 18.0 min, tminor = 22.1 min). [
a
]
28 = À81 (c 1.0, CHCl3). 1H
D
phosphonate13 3c
NMR (400 MHz, CDCl3) d (ppm): 8.40 (d, J = 8.0 Hz, 1H), 7.95 (d,
J = 7.6 Hz, 2H), 7.83 (d, J = 8.0 Hz, 1H), 7.75–7.43 (m, 8H), 4.94 (d,
J = 22.4 Hz, 1H), 4.12–4.06 (m, 2H), 3.91 (dd, J = 10.4, 6.8 Hz, 2H),
3.78–3.68 (m, 1H), 3.42–3.36 (m, 1H), 1.26 (t, J = 7.2 Hz, 3H), 0.79
(t, J = 7.2 Hz, 3H).
Colorless oil. 82% ee determined by HPLC on a Chiralcel OJ-H
column (hexane/2-propanol = 92/8, flow rate = 1.0 mL/min,
tminor = 19.7 min, tmajor = 24.5 min). [
NMR (400 MHz, CDCl3) d (ppm): 7.93 (d, J = 8.4 Hz, 2H), 7.44 (d,
J = 7.2 Hz, 2H), 7.31–7.21 (m, 3H), 6.90 (d, J = 8.8 Hz, 2H), 4.10–
3.89 (m, 4H), 3.84 (s, 3H), 3.76–3.58 (m, 3H), 1.28 (t, J = 7.2 Hz,
3H), 1.07 (t, J = 7.2 Hz, 3H).
a]
29 = À44 (c 1.0, CHCl3). 1H
D
5.10. (S)-Diethyl 3-oxo-3-phenyl-1-(thiophen-2-yl)propylphos-
phonate 3j
Colorless oil. 90% ee determined by HPLC on a Chiralpak AS-H
column (hexane/2-propanol = 90:10, flow rate = 1.0 mL/min,
5.4. (S)-Diethyl 1-(2-methoxyphenyl)-3-oxo-3-phenylpropyl-
phosphonate13 3d
tmajor = 9.9 min, tminor = 11.3 min). [
a]
D
28 = À25 (c 1.0, CHCl3). 1H
NMR (400 MHz, CDCl3) d (ppm): 7.96–7.94 (m, 2H), 7.58–7.54
(m, 1H), 7.47–7.43 (m, 2H), 7.16–7.15 (m, 1H), 7.09 (t, J = 3.2 Hz,
1H), 6.93–6.91 (m, 1H), 4.35–4.26 (m, 1H), 4.14–3.83 (m, 4H),
3.76–3.61 (m, 2H), 1.29 (t, J = 7.2 Hz, 3H), 1.18 (t, J = 7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3) d (ppm): 196.0 (d, J = 14.3 Hz), 138.1
(d, J = 8.3 Hz), 136.5, 133.5, 128.7, 128.2, 126.9, 126.8, 124.7 (d,
J = 3.4 Hz), 63.2 (d, J = 6.8 Hz), 62.5 (d, J = 7.2 Hz), 40.4, 34.3 (d,
J = 144.8 Hz), 16.4 (d, J = 5.9 Hz), 16.3 (d, J = 5.9 Hz). 31P NMR
Colorless oil. 82% ee determined by HPLC on a Chiralpak AS-H
column (hexane/2-propanol = 90:10, flow rate = 1.0 mL/min,
tmajor = 9.2 min, tminor = 12.9 min). [
a
]
29 = À40 (c 1.0, CHCl3). 1H
D
NMR (400 MHz, CDCl3) d (ppm): 7.94 (d, J = 7.6 Hz, 2H), 7.53 (t,
J = 7.2 Hz, 1H), 7.45–7.41 (m, 3H), 7.19 (t, J = 7.6 Hz, 1H), 6.90–
6.86 (m, 2H), 4.66–4.57 (m, 1H), 4.11–4.08 (m, 2H), 3.95–3.69
(m, 4H), 3.87 (s, 3H), 1.27 (t, J = 7.2 Hz, 3H), 1.09 (t, J = 7.2 Hz, 3H).
5.5. (S)-Diethyl 1-(4-chlorophenyl)-3-oxo-3-phenylpropylphos-
(121 MHz, CDCl3) d (ppm): 26.5. IR mmax: 2982, 1689, 1597, 1393,
phonate13 3e
1249, 1028, 852, 789, 757, 692 cmÀ1. HRMS (ESI): calcd for C17H21-
NaO4PS [M+Na]+ 375.0790, found 375.0788.
Colorless oil. 91% ee determined by HPLC on a Chiralpak AS-H
column (hexane/2-propanol = 90/10, flow rate = 1.0 mL/min,
5.11. (S)-Diethyl 3-(4-chlorophenyl)-3-oxo-1-o-tolylpropylphos
phonate 3k
tmajor = 7.0 min, tminor = 9.0 min). [
a
]
29 = À46 (c 1.0, CHCl3). 1H
D
NMR (400 MHz, CDCl3) d (ppm): 7.93 (d, J = 8.0 Hz, 2H), 7.56 (t,
J = 7.2 Hz, 1H), 7.47–7.26 (m, 6H), 4.14–4.05 (m, 2H), 3.99–3.89
(m, 2H), 3.83–3.61 (m, 3H), 1.29 (t, J = 7.2 Hz, 3H), 1.13 (t,
J = 7.2 Hz, 3H).
Colorless oil. 93% ee determined by HPLC on a Chiralpak AS-H
column (hexane/2-propanol = 90:10, flow rate = 1.0 mL/min,
tmajor = 6.7 min, tminor = 9.0 min). [
a]
D
29 = À64 (c 1.0, CHCl3). 1H
NMR (400 MHz, CDCl3) d (ppm): 7.87 (d, J = 8.4 Hz, 2H), 7.42–
7.40 (m, 3H), 7.17–7.10 (m, 3H), 4.24–4.15 (m, 1H), 4.12–4.04
(m, 2H), 3.89–3.73 (m, 2H), 3.68–3.56 (m, 2H), 2.54 (s, 3H), 1.29
(t, J = 7.2 Hz, 3H), 1.03 (t, J = 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3)
d (ppm): 194.8 (d, J = 15.6 Hz), 139.2, 137.4 (d, J = 7.5 Hz), 134.4,
133.9 (d, J = 6.6 Hz), 130.1, 129.1, 128.5, 127.1 (d, J = 3.7 Hz),
126.7, 125.8, 62.6 (d, J = 6.8 Hz), 61.5 (d, J = 7.2 Hz), 39.2, 33.6 (d,
J = 140.0 Hz), 19.8, 16.1 (d, J = 5.8 Hz), 15.8 (d, J = 5.4 Hz). 31P
5.6. (S)-Diethyl 1-(4-bromophenyl)-3-oxo-3-phenylpropylphos-
phonate13 3f
Colorless oil. 90% ee determined by HPLC on a Chiralpak AD-H
column (hexane/2-propanol = 90:10, flow rate = 1.0 mL/min,
tmajor = 19.9 min, tminor = 25.1 min). [
a
]
26 = À43 (c 1.0, CHCl3). 1H
D
NMR (400 MHz, CDCl3) d (ppm): 7.93 (d, J = 7.6 Hz, 2H), 7.57 (t,
J = 7.2 Hz, 1H), 7.47–7.27 (m, 6H), 4.15–3.87 (m, 4H), 3.84–3.60
(m, 3H), 1.29 (t, J = 7.2 Hz, 3H), 1.13 (t, J = 7.2 Hz, 3H).
NMR (121 MHz, CDCl3) d (ppm): 29.0. IR mmax: 2982, 1689, 1592,
1496, 1243, 1045, 1020, 860, 781, 740 cmÀ1. HRMS (ESI): calcd
for C20H24ClNaO4P [M+Na]+ 417.0993, found 417.0991.
5.7. (S)-Diethyl 3-oxo-3-phenyl-1-p-tolylpropylphosphonate13 3g
Colorless oil. 86% ee determined by HPLC on a Chiralpak AS-H
column (hexane/2-propanol = 90/10, flow rate = 1.0 mL/min,
5.12. (S)-Diethyl 3-(4-methoxyphenyl)-3-oxo-1-o-tolylpropylph
osphonate 3l
tmajor = 10.5 min, tminor = 14.9 min). [
a]
29 = À34 (c 1.0, CHCl3). 1H
D
NMR (400 MHz, CDCl3) d (ppm): 7.94 (d, J = 7.2 Hz, 2H), 7.54 (t,
J = 7.2 Hz, 1H), 7.43 (t, J = 7.6 Hz, 2H), 7.32 (dd, J = 8.0, 2.0 Hz,
2H), 7.09 (d, J = 7.6 Hz, 2H), 4.12–4.02 (m, 2H), 3.98–3.87 (m,
2H), 3.78–3.61 (m, 3H), 2.28 (s, 3H), 1.28 (t, J = 7.2 Hz, 3H), 1.10
(t, J = 7.2 Hz, 3H).
Colorless oil. 91% ee determined by HPLC on a Chiralpak AS-H
column (hexane/2-propanol = 90:10, flow rate = 1.0 mL/min,
tmajor = 7.5 min, tminor = 8.6 min). [
a]
D
29 = À63 (c 1.0, CHCl3). 1H
NMR (400 MHz, CDCl3) d (ppm): 7.93 (d, J = 8.8 Hz, 2H), 7.43 (d,
J = 6.4 Hz, 1H), 7.16–7.07 (m, 3H), 6.90 (d, J = 8.4 Hz, 2H), 4.27–
4.18 (m, 1H), 4.10–4.02 (m, 2H), 3.85–3.74 (m, 5H), 3.65–3.57
(m, 2H), 2.55 (s, 3H), 1.29 (t, J = 7.2 Hz, 3H), 1.03 (t, J = 7.2 Hz,
3H). 13C NMR (100 MHz, CDCl3) d (ppm): 194.9 (d, J = 15.5 Hz),
163.5, 137.7 (d, J = 7.0 Hz), 134.4 (d, J = 5.9 Hz), 130.3, 129.5,
127.5, 127.4, 126.9, 126.0, 113.6, 62.9 (d, J = 6.5 Hz), 61.8 (d,
J = 6.8 Hz), 55.3, 39.1, 33.9 (d, J = 139.7 Hz), 20.1, 16.3 (d,
5.8. (S)-Diethyl 3-oxo-3-phenyl-1-o-tolylpropylphosphonate13 3h
Colorless oil. 94% ee determined by HPLC on a Chiralpak AS-H
column (hexane/2-propanol = 90:10, flow rate = 1.0 mL/min,
tmajor = 5.3 min, tminor = 7.6 min). [
a
]
29 = À48 (c 1.0, CHCl3). 1H
D
J = 5.6 Hz), 16.1 (d, J = 5.3 Hz). 31P NMR (121 MHz, CDCl3)
d
NMR (400 MHz, CDCl3) d (ppm): 7.94 (d, J = 7.6 Hz, 2H), 7.55 (t,
J = 7.2 Hz, 1H), 7.46–7.42 (m, 3H), 7.17–7.08 (m, 3H), 4.27–4.18
(m, 1H), 4.12–4.02 (m, 2H), 3.88–3.79 (m, 2H), 3.72–3.58 (m,
2H), 2.55 (s, 3H), 1.29 (t, J = 7.2 Hz, 3H), 1.04 (t, J = 7.2 Hz, 3H).
(ppm): 29.6. IR mmax: 2981, 1681, 1601, 1512, 1243, 1058, 1028,
838, 788, 769 cmÀ1. HRMS (ESI): calcd for C21H27NaO5P [M+Na]+
413.1488, found 413.1490.

G. Li et al. / Tetrahedron: Asymmetry 25 (2014) 989–996
995
5.13. (S)-Diethyl 1-(2,6-dimethylphenyl)-3-oxo-3-p-tolylpropyl-
phosphonate 3m
3H), 2.55 (s, 3H), 1.26 (t, J = 7.2 Hz, 3H), 0.99 (t, J = 7.2 Hz, 3H). 13C
NMR (100 MHz, CDCl3) d (ppm): 195.8 (d, J = 10.9 Hz), 138.8 (d,
J = 7.7 Hz), 137.7 (d, J = 4.4 Hz), 135.2, 132.9 (d, J = 5.7 Hz), 132.0,
130.3 (d, J = 2.8 Hz), 129.6, 128.5, 128.4, 127.1, 63.0 (d, J = 6.8 Hz),
61.7 (d, J = 7.2 Hz), 38.3, 34.0 (d, J = 140.3 Hz), 21.9, 21.8, 16.4 (d,
J = 6.0 Hz), 16.1 (d, J = 5.8 Hz). 31P NMR (121 MHz, CDCl3) d (ppm):
Colorless oil. 94% ee determined by HPLC on a Chiralpak IA col-
umn
(hexane/2-propanol = 90:10,
flow
rate = 1.0 mL/min,
tminor = 4.6 min, tmajor = 5.2 min). [
a]
28 = À58 (c 1.0, CHCl3). 1H
D
NMR (400 MHz,CDCl3) d (ppm): 7.86 (d, J = 8.4 Hz, 2H), 7.24 (d,
J = 8.0 Hz, 2H), 7.02–6.96 (m, 3H), 4.70 (dt, J = 28.4, 6.0 Hz, 1H),
4.14–4.02 (m, 2H), 3.92–3.79 (m, 2H), 3.76–3.54 (m, 2H), 2.66 (s,
3H), 2.56 (s, 3H), 2.39 (s, 3H), 1.25 (t, J = 7.2 Hz, 3H), 0.99 (t,
J = 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3) d (ppm): 196.1 (d,
J = 10.7 Hz), 144.0, 138.7 (d, J = 7.5 Hz), 137.7 (d, J = 4.4 Hz),
133.9, 133.0 (d, J = 5.6 Hz), 130.2, 129.3, 128.3, 128.1, 126.9, 62.8
(d, J = 6.9 Hz), 61.5 (d, J = 7.2 Hz), 38.0, 34.8 (d, J = 139.1 Hz), 21.8,
21.7, 21.6, 16.3 (d, J = 6.1 Hz), 16.0 (d, J = 5.6 Hz). 31P NMR
29.3. IR
m
.
max: 2979, 1690, 1585, 1474, 1244, 1053, 1030, 799,
770 cmÀ1
HRMS (ESI): calcd for C21H26BrNaO4P [M+Na]+
475.0644, found 475.0644.
5.17. (S)-Diethyl 1-(2,6-dimethylphenyl)-3-(4-methoxyphenyl)-
3-oxopropylphosphonate 3q
Colorless oil. 92% ee determined by HPLC on a Chiralpak IA col-
umn (hexane/2-propanol = 90:10, flow rate = 1.0 mL/min, tminor
=
(121 MHz, CDCl3) d (ppm): 29.7. IR
m
max: 2980, 1689, 1608, 1242,
6.6 min, tmajor = 7.8 min). [
a]
29 = À59 (c 1.0, CHCl3). 1H NMR
D
1029, 798, 770 cmÀ1. HRMS (ESI): calcd for C22H29NaO4P [M+Na]+
411.1696, found 411.1694.
(400 MHz, CDCl3) d (ppm): 7.94 (d, J = 9.2 Hz, 2H), 7.01–6.96 (m,
3H), 6.91 (d, J = 8.8 Hz, 2H), 4.70 (dt, J = 28.4, 6.0 Hz, 1H), 4.12–
4.02 (m, 2H), 3.90–3.80 (m, 5H), 3.73–3.56 (m, 2H), 2.67 (d,
J = 1.6 Hz, 3H), 2.57 (s, 3H), 1.25 (t, J = 7.2 Hz, 3H), 0.98 (t,
J = 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3) d (ppm): 195.1 (d,
J = 10.7 Hz), 163.6, 138.8 (d, J = 7.5 Hz), 137.8 (d, J = 4.5 Hz), 133.2
(d, J = 5.5 Hz), 130.3, 130.2, 129.5, 128.3, 126.9, 113.8, 62.8 (d,
J = 6.9 Hz), 61.6 (d, J = 7.2 Hz), 55.4, 37.9, 34.0 (d, J = 138.9 Hz),
21.9, 21.8, 16.3 (d, J = 6.0 Hz), 16.1 (d, J = 5.6 Hz). 31P NMR
5.14. (S)-Diethyl 1-(2,6-dimethylphenyl)-3-(4-fluorophenyl)-3-
oxopropylphosphonate 3n
Colorless oil. 91% ee determined by HPLC on a Chiralpak IA col-
umn (hexane/2-propanol = 90:10, flow rate = 1.0 mL/min, tminor
=
4.6 min, tmajor = 5.1 min). [
a
]
D
29 = À46 (c 1.0, CHCl3). 1H NMR
(400 MHz, CDCl3) d (ppm): 7.99 (dd, J = 8.0, 5.6 Hz, 2H), 7.12
(t, J = 8.4 Hz, 2H), 7.03–6.98 (m, 3H), 4.67 (dt, J = 28.8, 6.0 Hz,
1H), 4.12–4.02 (m, 2H), 3.93–3.79 (m, 2H), 3.74–3.54 (m, 2H),
2.66 (s, 3H), 2.56 (s, 3H), 1.26 (t, J = 7.2 Hz, 3H), 0.99 (t, J = 7.2 Hz,
3H). 13C NMR (100 MHz, CDCl3) d (ppm): 195.3 (d, J = 10.3 Hz),
165. 9 (d, J = 253.7 Hz), 138.9 (d, J = 7.7 Hz), 137.8 (d, J = 4.3 Hz),
133.1, 133.0, 130.8 (d, J = 9.2 Hz), 130.4, 128.5, 127.1, 115.9
(d, J = 21.7 Hz), 63.0 (d, J = 6.8 Hz), 61.7 (d, J = 7.2 Hz), 38.3, 34.1
(d, J = 139.2 Hz), 21.9, 21.8, 16.4 (d, J = 6.1 Hz), 16.1 (d, J = 5.9 Hz).
(121 MHz, CDCl3) d (ppm): 29.8. IR
1242, 1054, 1030, 838, 798, 772 cmÀ1. HRMS (ESI): calcd for
22H29NaO5P [M+Na]+ 427.1645, found 427.1640.
mmax: 2980, 1681, 1602, 1512,
C
Acknowledgements
The authors would like to thank the financial support received
from the National Natural Science Foundation of China
(21272168, 20872106).
31P NMR (121 MHz, CDCl3) d (ppm): 29.4. IR
mmax: 2981, 1690,
1598, 1506, 1234, 1158, 1027, 841, 797, 769 cmÀ1. HRMS (ESI):
calcd for C21H27FO4P [M+H]+ 393.1626, found 393.1626.
References
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5.15. (S)-Diethyl 3-(4-chlorophenyl)-1-(2,6-dimethylphenyl)-3-
oxopropylphosphonate 3o
Colorless oil. 94% ee determined by HPLC on a Chiralpak IA col-
umn
(hexane/2-propanol = 90:10,
flow
rate = 1.0 mL/min,
tminor = 5.1 min, tmajor = 5.9 min). [
a]
29 = À43 (c 1.0, CHCl3). 1H
D
NMR (400 MHz, CDCl3) d (ppm): 7.89 (d, J = 8.8 Hz, 2H), 7.42 (d,
J = 8.4 Hz, 2H), 7.03–6.98 (m, 3H), 4.66 (dt, J = 28.8, 6.0 Hz, 1H),
4.12–4.03 (m, 2H), 3.92–3.81 (m, 2H), 3.73–3.56 (m, 2H), 2.65 (s,
3H), 2.55 (s, 3H), 1.26 (t, J = 7.2 Hz, 3H), 0.99 (t, J = 7.2 Hz, 3H). 13C
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(d, J = 7.5 Hz), 137.7 (d, J = 4.4 Hz), 134.7, 132.8 (d, J = 5.5 Hz),
130.3, 129.5, 129.0, 128.4, 127.1, 63.0 (d, J = 6.9 Hz), 61.7 (d,
J = 7.3 Hz), 38.3, 33.9 (d, J = 139.2 Hz), 21.9, 21.8, 16.4 (d,
J = 6.0 Hz), 16.1 (d, J = 5.7 Hz). 31P NMR (121 MHz, CDCl3) d (ppm):
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29.3. IR
m
.
max: 2980, 1690, 1590, 1475, 1242, 1093, 1029, 801,
771 cmÀ1
HRMS (ESI): calcd for C21H26ClNaO4P [M+Na]+
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431.1149, found 431.1150.
5.16. (S)-Diethyl 3-(4-bromophenyl)-1-(2,6-dimethylphenyl)-3-
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Colorless oil. 92% ee determined by HPLC on a Chiralpak IA col-
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5.3 min, tmajor = 6.2 min). [
(400 MHz, CDCl3) d (ppm): 7.82 (d, J = 8.4 Hz, 2H), 7.59 (d,
J = 8.4 Hz, 2H), 7.03–6.98 (m, 3H), 4.65 (dt, J = 28.4, 6.0 Hz, 1H),
4.12–4.02 (m, 2H), 3.91–3.79 (m, 2H), 3.73–3.54 (m, 2H), 2.65 (s,
=
a
]
D
27 = -49 (c 1.0, CHCl3). 1H NMR

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