A new BINOL-derived chiral bifunctional phosphine organocatalyst: Preparation and application in asymmetric (Aza)-morita-baylis-hillman reactions

Article abstract of DOI:10.1080/10426507.2012.761987

A new BINOL-derived chiral bifunctional phosphine has been designed and successfully prepared, which features a cyclic substructure of 1,3,5-diazaphosphinane. This chiral phosphine possesses good air stability in solid state, and it can be conveniently us

Full text of DOI:10.1080/10426507.2012.761987

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A New BINOL-Derived Chiral Bifunctional
Phosphine Organocatalyst: Preparation
and Application in Asymmetric (Aza)-
Morita-Baylis-Hillman Reactions
Chunzhang Wang a , Lijun Wang b , San Zeng b , Silong Xu b &
Zhengjie He b
a School of Chemistry and Chemical Engineering , Henan University ,
Kaifeng, P.R. China
b The State Key Laboratory of Elemento-Organic Chemistry and
Department of Chemistry , Nankai University , Tianjin , P.R. China
Accepted author version posted online: 25 Feb 2013.Published
online: 20 Sep 2013.
To cite this article: Chunzhang Wang , Lijun Wang , San Zeng , Silong Xu & Zhengjie He (2013) A
New BINOL-Derived Chiral Bifunctional Phosphine Organocatalyst: Preparation and Application in
Asymmetric (Aza)-Morita-Baylis-Hillman Reactions, Phosphorus, Sulfur, and Silicon and the Related
Elements, 188:11, 1548-1554, DOI: 10.1080/10426507.2012.761987
To link to this article: http://dx.doi.org/10.1080/10426507.2012.761987
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Phosphorus, Sulfur, and Silicon, 188:1548–1554, 2013
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.761987
A NEW BINOL-DERIVED CHIRAL BIFUNCTIONAL
PHOSPHINE ORGANOCATALYST: PREPARATION AND
APPLICATION IN ASYMMETRIC
(AZA)-MORITA-BAYLIS-HILLMAN REACTIONS
Chunzhang Wang,1 Lijun Wang,2 San Zeng,2 Silong Xu,2
and Zhengjie He2
1School of Chemistry and Chemical Engineering, Henan University, Kaifeng,
P.R. China
2The State Key Laboratory of Elemento-Organic Chemistry and Department
of Chemistry, Nankai University, Tianjin, P.R. China
GRAPHICAL ABSTRACT
OH
multistep synthesis
OH
OH
N
N
P
R-BINOL
a new chiral bifunctional phosphine
organocatalyst with good air-stability
Abstract A new BINOL-derived chiral bifunctional phosphine has been designed and suc-
cessfully prepared, which features a cyclic substructure of 1,3,5-diazaphosphinane. This chiral
phosphine possesses good air stability in solid state, and it can be conveniently used as a
relatively more nucleophilic phosphine organocatalyst. Preliminary investigations showed that
it could generally afford fair to excellent yields but only modest enantioselectivity in the (aza)-
Morita–Baylis–Hillman reactions of activated olefins such as ethyl acrylate and methyl vinyl
ketone with aldehydes or imines.
[Supplementary materials are available for this article. Go to the publisher’s online edition of
Phosphorus Sulfer and Silicon and the Related Elements for the following free supplemental
files: Additional text and figures.]
Keywords Chiral phosphine; bifunctional organocatalyst; Morita–Baylis–Hillman reaction;
asymmetric catalysis
Received 16 October 2012; accepted 20 December 2012.
Financial support from the National Natural Science Foundation of China (Grant Nos. 20672057, 21121002)
is gratefully acknowledged.
Address correspondence to Zhengjie He, The State Key Laboratory of Elemento-Organic Chemistry
and Department of Chemistry, Nankai University, 94 Weijin Road, Tianjin 300071, P.R. China. E-mail:
zhengjiehe@nankai.edu.cn
1548

CHIRAL BIFUNCTIONAL PHOSPHINE ORGANOCATALYST
1549
INTRODUCTION
Asymmetric organocatalysis of chiral tertiary phosphines has recently attracted grow-
ing research interest.1 As a result, an array of chiral phosphines have been designed and
examined as organocatalysts.1 As a useful strategy in the development of highly effective
chiral catalysts, the bifunctionality design of the catalysts has been proven to be effective
and feasible. A delicate bifunctional catalyst, which possesses two functionalities to syner-
gistically facilitate the target transformation, often outperforms the conventional monofunc-
tional catalysts with regard to efficiency and selectivity.2 In the past two decades, a myriad
of highly efficient chiral bifunctional or multifunctional organocatalysts have been devel-
oped for a wide variety of reactions.3 A series of chiral bifunctional or even multifunctional
phosphine catalysts derived from chiral 1,1ꢀ-binaphthalenyl-2,2ꢀ-ols (BINOL) has also been
devised with great success in asymmetric (aza)-Morita–Baylis–Hillman (MBH) reactions.4
In 2003, Shi and coworkers5 reported that a BINOL-derived chiral phosphine 1 that bears
both a phosphine Lewis base and a phenolic hydroxyl Brønsted acid is an efficient bifunc-
tional catalyst in the aza-MBH reaction (Scheme 1). It was found that the phenolic OH of
the catalyst plays important roles in inducing high enantioselectivity, activating substrates,
and stabilizing enolate intermediates via hydrogen bonding interaction. Further evolution of
this bifunctional catalyst resulted in generation of several bifunctional and multifunctional
chiral phosphine catalysts 2–8 with different catalytic activity and scope in the asymmetric
(aza)-MBH reactions (Scheme 1).6,7
S
O
Ph
N
N
N
OH
OH
H
H
H
PPh2
PPh2
PPh2
PMe2
1
3
2
4
O
O
OH
OH
HO
PPh2
HO
HO
OH
PPh2
PPh2
OH
5
6
7
NH
OH
HO
N
P
PPh2
N
9
Me
8
Scheme 1
As a critical structural factor to affect the catalytic activity of a phosphine catalyst,
its nucleophilicity or electron-donating ability is predominantly influenced by the sub-
stituents at the phosphorus center: alkyl-substituted phosphines, namely, alkylphosphines,
have greater nucleophilicity than their arylphosphine analogs. As evidenced in previous

1550
C. WANG ET AL.
reports,8 tertiary alkylphosphines with strong nucleophilicity are often required for better
performance or distinct chemoselectivity in the phosphine-mediated synthetic reactions.
However, tertiary alkylphosphines are highly air sensitive and in some cases even py-
rophoric. This air sensitivity of tertiary alkylphosphines, to a substantial extent, restricts
their extensive use in both catalytic and stoichiometric reactions. To date, a few of precedent
attempts were reported to address the air sensitivity of tertiary alkylphosphines. Netherton
and Fu9 suggested converting air-sensitive alkylphosphines into their air-stable conjugate
acids such as tetrafluoroborate and then releasing them in situ by treatment with an appro-
priate base. This simple and practical approach has been proven effective in a diverse set
of reactions including the MBH reaction, although it carries some obvious drawbacks such
as involving extra manipulation. Another alternative solution to the air-sensitivity issue
is to develop structurally special tertiary alkylphosphines, which simultaneously possess
stability to air oxidation and high nucleophilicity.10 A couple of ferrocenyldialkylphos-
phines were reported to be air stable and strongly nucleophilic. Accordingly, they could be
conveniently used as effective catalysts in the MBH reaction of acrylates and aldehydes.10a
In our previous work,10b,10c we also demonstrated an air stable and highly nucleophilic
cage-like phosphine 1,3,5,-triaza-7-phosphaadamantane (PTA) could be conveniently used
as an alternative trialkylphosphine in the catalytic (aza)-MBH reactions and stoichiomet-
ric olefination reactions.10d As part of our continuous efforts to develop convenient and
efficient phosphine organocatalysts, we designed and synthesized a BINOL-derived chiral
phosphine 9 that features an acidic phenolic hydroxyl and a cyclic 1,3,5-diazaphosphinane
moiety (Scheme 1). On the basis of the above mentioned findings in the development of
both BINOL-derived chiral bifunctional or multifunctional phosphine catalysts and air-
stable nucleophilic tertiary alkylphosphines, we envisaged that compound 9 could possess
good air stability and strong nucleophilicity and acts as a chiral bifunctional phosphine
catalyst in asymmetric transformations including the (aza)-MBH reactions as well. Herein,
we report the results from such relevant investigations.
RESULTS AND DISCUSSION
Phosphine 9 is a new compound, which was readily prepared from (R)-BINOL
by a synthetic route shown in Scheme 2. According to the literature procedures,11 the
starting material (R)-BINOL was treated with Tf2O to give the corresponding triflu-
oromethanesulfonate 10 in a quantitative yield. The coupling reaction of 10 with di-
ethyl phosphonate was realized under the mediation of 10 mol% of Pd(OAc)2 and 1,2-
bis(diphenylphosphino)ethane (dppe) in DMSO at 100 ◦C to afford the intermediate 11 in
a modest yield (32%). Hydrolysis of 11 with sodium hydroxide in a mixed solvent of l,4-
dioxane and MeOH (2:1, V/V), followed by acidification with hydrochloric acid, produced
intermediate 12 in 89% yield. Reduction of phosphate 12 by a combination of LiAlH4 and
Me3SiCl in anhydrous THF readily afforded an air-stable primary phosphine 13 in 56%
yield. Finally, purified intermediate 13 was treated with formaldehyde and methylamine
under mild conditions to give the chiral phosphine 9 in 73% yield as a white solid. Product
9 was generated as a fine white precipitate in ethanol, and manipulation of centrifugation
was therefore needed in its isolation. The structure of phosphine 9 was confirmed by NMR
(1H, 13C, and 31P) and HRMS measurements. 1H and 13C NMR data together with COSY
and heteronuclear single quantum coherence (HSQC) analyses are well consistent with its
assigned structure. Its 31P NMR spectrum gave a single peak at δ −47.6 ppm, suggesting

CHIRAL BIFUNCTIONAL PHOSPHINE ORGANOCATALYST
1551
it be a tertiary phosphine similar to dimethylphenylphosphine (31P NMR δ −44.1 ppm in
CDCl3)12 by phosphorus chemical shift.
(EtO)2POH
(CF3SO2)2O
OTf
OH
OH
OTf
OTf
pyridine
Pd(OAc)2 (10 mol %)
dppe (10 mol %)
32% yield
P(O)(OEt)2
100% yield
11
10
MeNH2
OH
OH
N
aq. NaOH
89% yield
OH
Me3SiCl
CH2O
73% yield
LiAlH4
P(O)(OEt)2
PH2
P
N
56% yield
Me
12
13
Scheme 2
9
Because the phosphorus atom of compound 9 bears two methylenes, it could be
expected that the chiral phosphine 9 possesses stronger nucleophilicity while compared with
that of triarylphosphines. Furthermore, our preliminary 31P NMR monitoring experiments
unveiled that phosphine 9 has a relatively good air stability; in its solid state, it can be stored
in the air for up to 1 week without any appreciable oxidation, although its CDCl3 solution
remains air sensitive.
To assess the catalytic performance of chiral phosphine 9 as a bifunctional organocata-
lyst in the asymmetric (aza)-MBH reactions, we first used the aza-MBH reaction of N-tosyl
p-chlorophenylimine and methylvinyl ketone (MVK) as a model reaction to search for
optimal reaction conditions (Table 1, entries 1–5). Under the catalysis of phosphine 9
(10 mol% relative to imine 14) and at room temperature, five common solvents were tested.
In a solvent like ethanol, THF or ether, the aza-MBH reaction afforded the correspond-
ing adduct 16a in good yields and modest ee values (entries 1–3). Solvents CH2Cl2 and
CH3CN were detrimental to the model reaction, giving a low yield or none of the product
16a (entries 4,5). Other selected arylimines like N-tosyl o-chlorophenylimine and N-tosyl
p-methylphenylimine could readily give their corresponding adducts with activated olefin
MVK, respectively, under the mediation of catalyst 9 but only in moderate yields and ee
values (entries 6,7). The catalyst 9 was also tested in the MBH reaction between aromatic
aldehydes and activated olefins like ethyl acrylate and MVK. It was found that catalyst
9 exhibited a good catalytic activity in the MBH reaction of reactive benzaldehydes with
both ethyl acrylate and MVK, giving the corresponding adducts 16 in moderate to excellent
yields (entries 8–15). However, in all cases, the MBH products were obtained in quite
disappointing ee values.
In conclusion, we have successfully synthesized a new BINOL-derived chiral bi-
functional phosphine that features a cyclic substructure of 1,3,5-diazaphosphinane. This
unique chiral phosphine possesses good air stability in its solid state while it could be still
used as an effective nucleophilic organocatalyst. In the studied asymmetric (aza)-MBH
reactions, this new bifunctional phosphine exhibited good to excellent catalytic activity but
somewhat disappointing enantioselectivity. Future efforts in our laboratory will be directed
toward exploring its application in other important nucleophilic phosphine catalyzed re-
actions like Lu-[3 + 2] cycloaddition reaction13 and [4 + 2] annulations of allenes14 and

1552
C. WANG ET AL.
Table 1 (Aza)-MBH reactions under the catalysis of 9
XH
X
9 (10 mol %)
EWG
+
CH
EWG
Ar
solvent, rt
Y
16
14
15
Entry
X
Y
EWG
Solvent
16
Time[h]
Yield[%]a
ee[%] b
1
2
3
4
5
6
7
8c
9c
10c
11c
12c
13
14
15
N-Ts
N-Ts
N-Ts
N-Ts
N-Ts
N-Ts
N-Ts
O
O
O
O
O
p-Cl
p-Cl
p-Cl
p-Cl
p-Cl
o-Cl
p-Me
p-NO2
o-NO2
m-NO2
p-CF3
o-Cl
p-NO2
m-NO2
o-NO2
COMe
COMe
COMe
COMe
COMe
COMe
COMe
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
COMe
COMe
COMe
EtOH
THF
Et2O
CH2Cl2
CH3CN
Et2O
Et2O
neat
neat
neat
neat
neat
16a
16a
16a
16a
16a
16b
16c
16d
16e
16f
16g
16h
16i
16j
16k
24
48
48
24
48
48
48
48
48
48
48
48
24
24
24
67
56
61
17
/
44
43
87
89
71
62
38
98
88
99
29
45
30
42
/
40
38
8
<5
15
16
20
<5
12
9
O
O
O
THF
THF
THF
aIsolated yield based on imine or aldehyde.
bDetermined by HPLC analysis on Chiralpak AD-H column.
cAn excess of ethyl acrylate (5.0 mL) was used.
modifying its structure to improve its catalytic performance with regard to the efficiency
and enantioselectivity.
EXPERIMENTAL
Unless otherwise noted, all reactions were carried out in a nitrogen atmosphere.
Commercially available chemicals were used as received. Nuclear magnetic resonances
(1H, 13C, 31P, COSY, and HSQC) were recorded on Bruker 300 MHz and Variant 400 MHz
NMR spectrometers using TMS as internal standard and CDCl3 as solvent.
Synthesis of Bifunctional Phosphine 9
Following a multistep route shown in Scheme 2, the phosphine 9 was readily synthe-
sized from (R)-BINOL. The intermediates 10–13 were prepared according to the reported
procedures (for details, see Supplemental Materials).11
(R)-2ꢀ-(1,3-Dimethyl-1,3,5-diazaphosphinan-5-yl)-1,1ꢀ-binaphthalenyl-2-ol (9):
To a stirred mixture of 37% aqueous formaldehyde (0.936 g, 11.5 mmol) and 25%
aqueous methylamine (0.476 g, 3.8 mmol) was dropwise added a solution of 13 (0.594 g,
1.9 mmol) in degassed EtOH (12 mL) over a period of 20 min. A white precipitate was
formed immediately. The reaction was stirred at room temperature for 10 h and was then
diluted with a 2:1 mixture of EtOH/H2O (20 mL). The white precipitate was collected by
centrifugation, washed with water (2 mL × 2), and dried under vacuum. Thus, phosphine
9 was obtained as a white solid (0.559 g, 73% yield), mp 200–203 ◦C. 1H NMR (CDCl3,

CHIRAL BIFUNCTIONAL PHOSPHINE ORGANOCATALYST
1553
400 MHz) δ: 8.16 (m, 1 H), 8.03 (d, J = 8.6 Hz, 1H), 7.92 (m, 2H), 7.86 (d, J = 7.8 Hz,
1H), 7.48 (m, 1H), 7.26 (m, 5H), 7.02 (d, J = 8.38 Hz, 1H), 3.46 (d, J = 10.0 Hz, 1H),
3.18 (d, J = 14.1 Hz, 1H), 2.96 (d, J = 14.1 Hz, 1H), 2.76 (d, J = 10.1 Hz, 1H), 2.59 (m,
1H), 2.43 (m, 1H), 2.28 (s, 3H), 2.20 (s, 3H); 13C NMR δ: 152.1, 137.5 (d, J = 19.2 Hz),
136.8 (d, J = 24.7 Hz), 134.7, 133.8, 133.4 (d, J = 4.7 Hz), 130.6 (d, J = 13.0 Hz), 129.2,
129.0, 128.4, 128.3, 127.0, 127.0, 126.8, 125.5, 125.2, 123.7, 118.2 (d, J = 10.0 Hz), 79.4,
51.6 (d, J = 21.3 Hz), 51.3 (d, J = 21.3 Hz), 45.2 (d, J = 4.0 Hz), 45.1 (d, J = 3.1 Hz); 31P
NMR (CDCl3, 160 MHz) δ: −47.6 ppm; HRMS(ESI): calcd for C25H25N2OPNa [M +
Na]+ 423.1602, found 423.1598; [α]20D = +68.4 (c = 0.01 g/mL, CH2Cl2).
General Procedure for Asymmetric (aza)-MBH Reactions (Table 1)
To a solution of aldehyde or imine 14 (0.5 mmol) and chiral phosphine catalyst 9
(0.05 mmol) in a specific solvent (5 mL) was added activated alkene 15 (0.5 mmol). The
resulting mixture was stirred at room temperature for a specified time listed in Table 1. After
removal of volatile components on a rotary evaporator, the crude product was subjected
to column chromatographic isolation on silica gel (eluent: petroleum ether/ethyl acetate
10:1) to give the (aza)-MBH product 16 as an enantiomeric mixture. The ee values of 16
were measured on HP 1100 HPLC instrument equipped with a Chiralpak AD-H column
(mobile phase: hexane/2-propanol 95:5–98:2; flow rate: 1.0 mL/min; wavelength: 220 nm).
Products 16 are all known compounds that were reported in our previous work.10b
Supplemental Materials: Experimental details for preparation of the intermediates
10–13; copies of NMR spectra (1H, 13C, and 31P) of 9. This material is available in the
Supplemental Materials.
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