A newly-designed PE-supported arsine for efficient and practical catalytic Wittig olefination

Article abstract of DOI:10.1039/c1cc16747b

A newly designed PE-supported arsine has been developed as an excellent catalyst for catalytic Wittig-type olefination. Simple ketones, in particular inactive ketones prove to be suitable substrates for the first time. This reaction provides an easy access to di-, tri-, and tetra-substituted olefins in high yield.

Full text of DOI:10.1039/c1cc16747b

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COMMUNICATION
A newly-designed PE-supported arsine for efficient and practical catalytic
Wittig olefinationw
Peng Wang,a Chun-Rong Liu,a Xiu-Li Sun,*a Shuai-Shuai Chen,a Jun-Fang Li,a Zuowei Xieb
and Yong Tang*a
Received 31st October 2011, Accepted 8th November 2011
DOI: 10.1039/c1cc16747b
A newly designed PE-supported arsine has been developed as an
excellent catalyst for catalytic Wittig-type olefination. Simple
ketones, in particular inactive ketones prove to be suitable
substrates for the first time. This reaction provides an easy
access to di-, tri-, and tetra-substituted olefins in high yield.
(entry 10, Table 1). In particular, when polymethylhydrosiloxane
(PMHS), a much cheaper, more easy to handle and more
environmentally friendly reducing agent was used instead of
diphenylsilane, the reaction was promoted effectively, affording
the desired product in 98% isolated yield (entry 11). In contrast,
other catalysts such as AsBu3, AsPh3 and phosphine oxide could
not give satisfying results under current conditions (entries 12–14).
Under the optimized conditions, we investigated the sub-
strate scope of the catalytic Wittig olefination of ketones.
Wittig reaction1 and its variants2 are important synthetic tools
due to their unambiguous positioning and good stereo-
selectivity of the double bonds.3 The catalytic Wittig reaction
process, which provides an atom economic pathway by avoiding
the use of stoichiometric phosphines,4 has been paid much
attention.5–7 Recently, O’Brien and coworkers documented the
first catalytic Wittig olefination of aldehydes by using 3-methyl-
1-phenyl-phospholane-1-oxide catalyst.7 Although great progress
has been achieved on aldehydes5–7 and activated ketones,5a to
date, no catalytic Wittig olefination of inactive ketones has
been reported. In this communication, we present our original
breakthrough on developing a highly efficient and practical
catalytic Wittig olefination of general ketones and aldehydes,
employing newly designed recoverable and reusable PE-supported
arsine catalysts8 in low loading.
Table 1 Ylide olefination of ketones using different catalystsa
Entry
15b
25b
35a
45a
55a
66
Catalyst (mol%)
As(n-Bu)3 (20)
Substrates
Conv.b,c (%)
Trace
Trace
o5
31 (31)
0
As(n-Bu)3 (20)
AsPh3 (20)
AsPh3 (100)
AsPh3 (20)
Initially, we examined all of the documented catalyst systems
for catalytic Wittig-type reactions of both cyclohexanone and
benzophenone under the reported optimal conditions respectively
(entries 1–9, Table 1). Unfortunately, all of these catalysts gave no
reaction (entries 5, 7 and 9, Table 1) or trace amount of desired
products (entries 1, 2 and 8, Table 1) for both substrates except
for nBuTe-PEG-TeBun, which gave only 19% conversion for
cyclohexanone (entry 6, Table 1). Although AsPh3 was reported
as a catalyst for the Wittig olefination of trifluoromethyl
arylketone,5a only 31% yield was obtained for cyclohexanone
even when 100 mol% of triphenylarsine was employed (entry 4,
Table 1). To our delight, when a newly-designed PE-supported9,10
arsine (PE-1, Mn: 34 kg molÀ1, arsine incorporation ratio in
polyethylene: 5.2 mol%) was utilized, the catalytic olefination of
cyclohexanone could proceed smoothly with 100% conversion
nBuTe-PEG-TeBun (2.0)
nBuTe-PEG-TeBun (2.0)
19
76
0
87
97
Trace
0
10d
11e
12e
13e
PE-1 (2.0)
PE-1 (2.0)
AsBu3 (2.0)
AsPh3 (2.0)
100
100 (98)
41
53
14e
0
a State Key Laboratory of Organometallic Chemistry, Shanghai
Institute of Organic Chemistry, Chinese Academy of Sciences,
345 Lingling Lu, Shanghai 200032, China. E-mail: tangy@sioc.ac.cn
b Department of Chemistry, The Chinese University of Hong Kong,
Shatin, New Territories, Hong Kong, China
a
Under the optimal literature reaction conditions (for details, see ESI).
d
b
Determined by 1H NMR. c Isolated yields in brackets. Ketone
(3.0 mmol), EDA (2.0 equiv.), Fe(TCP)Cl (0.25 mol%), Ph2SiH2
(1.3 equiv.), 110 1C, toluene (3.0 mL), 12 h. e The same as footnote d
but using PMHS (Mn: 1700–3200 g molÀ1, 1.3 equiv.) instead of Ph2SiH2.
w Electronic supplementary information (ESI) available. See DOI:
10.1039/c1cc16747b
c
290 Chem. Commun., 2012, 48, 290–292
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Table 2 The PE-1 catalyzed Wittig reaction of ketonesa
Table 3 The PE-1 catalyzed Wittig reaction of aldehydesa
Yieldb
(%)
Yieldb
(%)
PE-1
(mol%)
Yield
(%)
Entry
R
Entry
R
Entry
1
1
2 (equiv.)
2a (2.0)
E/Zb
1
2
3
4
5
6
7
1-Naphthyl 4a
2-NO2C6H4 4b
99
95
17
18
19
20
21
22
23
2-Furyl 4q
PhCH|CH 4r
PhCH2CH2 4s
98
96
97
2.0
97
499/1
2,6-Cl2C6H3 4c 98
2,4-Cl2C6H3 4d 99
C6H5(CH3)CH 4t 98
2
2a (2.0)
2a (2.0)
2a (2.5)
2.0
2.0
3.0
98
95
93
—
—
—
4-ClC6H4 4e
4-BrC6H4 4f
4-CF3C6H4 4g
99
99
96
Cyclohexyl 4u
CH3(CH2)6 4v
BnO(CH2)3 4w
98
94
93
3
8
9
4-NO2C6H4 4h
4-CNC6H4 4i
99
99
24c
87
99
4c
10
11
3-NO2C6H4 4j
3-ClC6H4 4k
98
99
5d
2a (3.0)
4.0
81
60/40
25d
12
13
14
15
16
2-ClC6H4 4l
4-MeC6H4 4m
4-MeOC6H4 4n 97
3,4-Me2C6H3 4o 94
98
99
26e
27f
4-ClC6H4 4e
4-ClC6H4 4e
CH3(CH2)6 4v
CH3(CH2)6 4v
1-Naphthyl 4a
98
94
95
94
87
6d
7d
2a (3.0)
2a (3.0)
4.0
4.0
83
81
63/37
83/17
28e
29f,g
30h
Ph 4p
99
a
b
8e
2a (4.0)
2b (2.5)
2c (3.0)
8.0
4.0
4.0
64
98
94
—
Aldehyde (3.0 mmol), EDA (1.6 equiv.), toluene (3 mL). E/Z 4
99/1. 100% ee. 94% ee. With 1.5 equiv. of 2b and 1.0 mol% of
c
d
e
f
PE-1. With 2.0 equiv. of 2c and 1.0 mol% of PE-1, 15 h. E/Z =
h
79 : 21. 4a (24 mmol), EDA (3.0 equiv.), PE-1 (0.05 mol%),
g
9f
95/5
93/7
10g
Fe(TCP)Cl (0.03 mol%), toluene (6 mL), 98 h.
11g
2c (3.0)
2c (3.0)
4.0
4.0
84
85
—
—
very high yields (entries 18–25, Table 3). The reaction condi-
tions were mild enough and no racemization was observed
when optically active aldehydes such as 4x and 4y were
employed (entries 24 and 25, Table 3). Diazo acetophenone
and ethyl 2-diazopropanoate proved to react with aldehydes
smoothly under the reaction conditions (entries 26–29,
Table 3). In all cases described above, the stereoselectivity is
excellent and the E/Z ratio is 499/1 except for the reaction of
capryl aldehyde with 2c (entry 29, Table 3). Thus, it provides a
facile way for the synthesis of di-, tri-a,b-unsaturated carbonyl
compounds with excellent E-selectivity. Remarkably, the
loading of PE-1 could be further reduced down to 0.05 mol%
when the reaction was scaled up (entry 30, Table 3).
12g
a
b
Ketone (3.0 mmol), toluene (3 mL). Determined by 1H NMR.
d
15 h. 18 h. 48 h. 38 h. 36 h.
c
e
f
g
As summarized in Table 2, PE-1 could catalyze the olefination
of simple ketones with diazoacetate (EDA)11 very well, affording
the desired 1,1,2-trisubstituted alkenes in excellent yields. For
example, trifluoromethyl phenyl ketone gave (E)-ethyl 4,4,
4-trifluoro-3-phenylbut-2-enoate in 97% yield with 499/1
E-selectivity (entry 1, Table 2). Both cyclic and acyclic aliphatic
ketones were suitable substrates in the presence of a catalytic
amount of PE-1. For instance, cyclohexanone, cyclopentanone,
and hex-5-en-2-one reacted with EDA, giving the corresponding
olefins in high yields (entries 2, 4 and 6, Table 2). Even for
benzophenone, inert in the reported catalytic systems, 64% yield
was obtained when 8 mol% of PE-1 was employed (entry 8,
Table 2). Other diazo compounds, such as diazo acetophenone
and ethyl 2-diazopropanoate, were also suitable substrates for
the current Wittig-type olefination, providing an efficient access
to tri- and tetra-substituted alkenes (entries 9–12, Table 2).
PE-1 can promote the catalytic Wittig olefination of simple
ketones very well, suggesting that the reduction of the PE-1
loading for the reaction of aldehydes is possible. As expected,
with only 0.8 mol% of PE-1 as the catalyst, both electron-
withdrawing and -donating aromatic aldehydes worked well,
giving 1,2-disubstituted alkenes in higher than 94% yields
(entries 1–16, Table 3). Furan-2-carbaldehyde gave 98% yield
(entry 17, Table 3). Aliphatic aldehydes were also favorable
substrates affording the corresponding unsaturated esters in
The influence of the arsine content in the PE chain on the
catalytic efficiency is nearly negligible. As shown in Table 4,
for example, PE-2 with 0.39 mol% incorporation ratio of
arsine was very efficient as well. Moreover, the PE-supported
arsine proves to be a temperature-controlled recoverable and
reusable catalyst. In the PE-2 catalyzed reaction between
4-chlorobenzaldehyde and EDA, the desired olefin could
be obtained in 98% yield and 499 : 1 E/Z selectivity even
after 5 runs (entry 5, Table 4).
The current reaction is practically useful. For instance, (E)-
heptan-3-yl 3-(4-methoxyphenyl) acrylate 7,12 which is useful
as the UV-light absorbing ingredient in commercially available
sunscreens, could be readily synthesized from p-methoxybenz-
aldehyde in 98% yield in the presence of 0.25 mol% of
Fe(TCP)Cl and 1.0 mol% of PE-1 (Scheme 1).
In summary, a new catalyst has been developed for highly
efficient catalytic Wittig-type reactions. The substrate scope is
universal and the catalytic olefination of inactive ketones was
c
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Chem. Commun., 2012, 48, 290–292 291

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Table 4 PE-2 as a recoverable and reusable catalyst for Wittig
reaction
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Run
Yield (%)
E/Z
Run
Yield (%)
E/Z
1
2
3
99
99
94
499 : 1
499 : 1
499 : 1
4
5
96
98
499 : 1
499 : 1
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Scheme 1 Synthesis of UV-light absorbing reagent 7.
realized for the first time. Even for diphenylketone and
hex-5-en-2-one, high yields were obtained. Both aromatic alde-
hydes and aliphatic aldehydes work well for such an olefination
with excellent yields and stereoselectivities. EDA, diazo aceto-
phenone, and ethyl 2-diazopropanoate are good reagents for the
olefination. Thus it provides an easy access to 1,2-disubstituted
alkenes, 1,1,2-trisubstituted alkenes, and 1,1,2,2-tetrasubstituted
alkenes with high stereoselectivity. The loading of PE-supported
catalyst could be reduced down to 0.05 mol% in the presence of the
cheap reducing agent PHMS and the PE-supported arsine was
recoverable and reusable, making the current reaction atom-
economic and potentially practically useful in organic synthesis.
We are grateful for the financial support from the National
Natural Science Foundation of China (No. 20821002 and
20932008), the Major State Basic Research Development
Program (Grant No. 2009CB825300), NSFC/RGC Joint
Research Scheme (Grant No. 21061160493 to YT and
N_CUHK470/10 to ZX) and Chinese Academy of Sciences.
P. Wang and C.-R. Liu have equal contribution to this paper.
9 Selected examples for polyethylene as
a catalyst carrier, see:
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c
292 Chem. Commun., 2012, 48, 290–292
This journal is The Royal Society of Chemistry 2012