Wittig reactions of stabilized phosphorus ylides with aldehydes in water

Article abstract of DOI:10.1081/SCC-200054816

The Wittig reactions of three stabilized phosphorus ylides with aldehydes in water were investigated. Most of the olefination reactions completed within 5-60 min in refluxing water in the presence of 1.2 M LiCl to afford the olefin products in 65-98% yields. It was found that the Wittig reactions of stabilized phosphorus ylides with aldehydes in water were faster than those carried out in organic solvents. Copyright Taylor & Francis, Inc.

Full text of DOI:10.1081/SCC-200054816

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Wittig Reactions of Stabilized
Phosphorus Ylides with
Aldehydes in Water
a
a
a
Jinlong Wu , Da Zhang & Shaoyong Wei
a
Laboratory of Asymmetric Catalysis and Synthesis,
Department of Chemistry, Zhejiang University,
Hangzhou, China
Version of record first published: 16 Aug 2006.
To cite this article: Jinlong Wu, Da Zhang & Shaoyong Wei (2005): Wittig Reactions of
Stabilized Phosphorus Ylides with Aldehydes in Water, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 35:9,
1213-1222
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Synthetic Communications , 35: 1213–1222, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200054816
Wittig Reactions of Stabilized Phosphorus
Ylides with Aldehydes in Water
Jinlong Wu, Da Zhang, and Shaoyong Wei
Laboratory of Asymmetric Catalysis and Synthesis, Department
of Chemistry, Zhejiang University, Hangzhou, China
Abstract: The Wittig reactions of three stabilized phosphorus ylides with aldehydes in
water were investigated. Most of the olefination reactions completed within 5–60 min
in refluxing water in the presence of 1.2 M LiCl to afford the olefin products in 65–98%
yields. It was found that the Wittig reactions of stabilized phosphorus ylides with
aldehydes in water were faster than those carried out in organic solvents.
Keywords: Aqueous reaction, aldehydes, phosphorus ylide, Wittig
INTRODUCTION
Organic reactions in water have attracted increasing attention in recent years
[1]
in developing environmentally benign chemical processes. Some reactions
involving organometallic species, which had previously been thought unlikely
to proceed in aqueous media, have been now successfully performed in water.
The Wittig reaction is one of the most versatile synthetic methods for
preparation of olefins from carbonyl compounds, and it is classically carried
out using a hydride or organometallic base in anhydrous aprotic solvents
[
2]
under an inert atmosphere. The reactions of semistabilized phosphorus
ylides (I) with water-soluble formaldehyde have been investigated in
[
3]
water in the absence of organic solvents. However, it was found that
other aldehydes did not successfully react with semistabilized phosphorus
Received in Japan November 10, 2004
Address correspondence to Jinlong Wu, Laboratory of Asymmetric Catalysis and
Synthesis, Department of Chemistry, Zhejiang University, Hangzhou 310027, China.
E-mail: wyz@zju.edu.cn

1214
J. Wu, D. Zhang, and S. Wei
ylides (I) to give the products. Industrial synthesis of vitamin A acetate is a
successful example of aqueous Wittig reaction involving a semistabilized
[
4]
phosphorus ylide (II).
[
5a,5b]
Recently, Russell and Warren
took a different approach and
reported the Wittig reactions of water-soluble semistabilized phosphorous
ylides (III) with aldehydes, but the scope of the aldehyde substrates was
[
5c]
quite limited. Sieber et al.
reported a water-soluble PEG-supported phos-
phonium salt in aqueous Wittig reactions via the in situ formed semistablized
phosphorous ylide (IV) in the presence of 1 N NaOH. Various 4-substituted
benzaldehydes were reacted to form the diaryl alkenes in 38–95% yields
and in ca. 1:1–3:1 E:Z ratios.
The Horner–Wadsworth–Emmons (HWE) reactions of triethyl phospho-
noacetate and diethyl 2-oxoalkanephosphonates with aldehydes were reported
to take place in highly concentrated (6–10 M) aqueous solutions of potassium
[6]
carbonate or potassium hydrogen carbonate. However, decomposition of
phosphonium salts and phosphorus ylides caused by aqueous bases was
[
3b,7]
reported.
under heterogeneous conditions with inorganic bases, including liquid–
For this reason, the Wittig reactions have been carried out
[8]
[9]
liquid, solid–liquid, and solid–solid phases.
[10]
To the best of our
knowledge, aqueous Wittig reactions of stabilized phosphorus ylides have
not been reported. In connection with our efforts in developing the Wittig
[
11]
reactions under unconventional conditions using microwave irradiation
[
12]
and the asymmetric variations,
we systematically investigated the hetero-
geneous Wittig reactions in water without adding organic cosolvents. We
report here on the results of Wittig reactions of three stabilized phosphorus
ylides with aldehydes other than formaldehyde in water in the presence
of LiCl.
[
13]
First, we investigated the effect of LiCl on the Wittig reactions of (car-
bethoxymethylene)triphenylphosphorane (1a) in water under the refluxing
conditions (Table 1). With a reactive aldehyde, 4-nitrobenzaldehyde (2a),
the reactions completed in 5 min to give the olefin 3 in excellent yields and

Wittig Reactions of Phosphorus Ylides
1215
a
Table 1. Effect of LiCl on the Wittig reactions of 1a with aldehydes 2
c
Yield (%), E:Z
d
Entry
2: R
LiCl
t (min)
1
2
3
4
5
6
2a: 4-NO
2
C
6
H
4
—
1.2
6.0
—
5
5
98, 89:11
98, 89:11
97, 94:6
35, 91:9
77, 91:9
94, 91:9
2a
2a
5
2b: 4-MeOC
b
2b
2b
6
H
4
90
60
30
—
1.2
a
Carried out in refluxing H O with a 1.2:1 ratio of 1a and 2.
2
b
c
2
Carried out in refluxing H O with a 1.5:1 ratio of 1a and 2.
Isolated yield of both isomers.
d 1
Determined by H NMR.
in ꢀ89:11 isomeric ratios with or without the added LiCl (entries 1–3,
Table 1). However, a significant salt effect was observed for the reactions
of 4-anisaldehyde (2b). In the absence of LiCl, the reaction of 1a with 2b
for 90 min afforded the product in 35% yield whereas the yield of the
product increased to 77% by increasing the equivalents of 1a from 1.2 to
1
.5 (entries 4 and 5, Table 1). By adding 1.2 equivalents of LiCl, the
reaction of la with 2b, after refluxing for 30 min, furnished the olefin in
4% yield (entry 6, Table 1). These results clearly demonstrate that LiCl
accelerated the aqueous Wittig reactions because of increased hydrophobic
9
[13]
effect
and remarkably improved the chemical yields. In addition, the
isomeric ratios of the olefin products are almost not influenced by addition
of LiCl and a slight increase in E:Z ratio was observed at high concentration
of LiCl (entry 3, Table 1).
Next, we carried out aqueous Wittig reactions of three stabilized phosphorus
ylides 1a–c with a collection of representative aromatic and aliphatic aldehydes
2a–f. It is worth mentioning that all ylides and aldehydes used in this study have
a melting point or boiling point higher than 1008C. All reactions, except for
entries 12 and 14 in Table 2, were performed in refluxing H O in the presence
2
of 1.2 M LiCl, and the results are summarized in Table 2. In general, the
reactions of the ylide 1a with aromatic aldehydes 2a–e gave both good to
excellent yields and isomer ratios (entries 1–5, Table 2).
The reaction time was found to be parallel to the intrinsic reactivity of
the aldehydes and follows the order of 4-nitrobenzaldehyde (2a) (5 min) ,
benzaldehyde (2c) ꢁ 4-hydroxybenzaldehyde (2d) ꢁ 2-furaldehyde (2e)

1216
J. Wu, D. Zhang, and S. Wei
a
Table 2. Aqueous Wittig reactions of ylides 1 with aldehydes 2
b
1: E
c
2: R
d
Yield (%), E:Z
e
Entry
t (min)
1
2
3
4
5
6
7
8
9
1a: CO Et
2
2a: 4-NO C H
2 6 4
5
30
10
10
8
98, 89:11
94, 91:9
78, 95:5
96, 85:15
83, 93:7
72, 66:34
92, 91:9
98, 95:5
89, 98:2
78, 96:4
81, 53:47
99, 57:43
65, 72:28
93, 79:21
96, 49:51
1a
1a
2b: 4-MeOC
2c: Ph
2d: 4-HOC
6 4
H
1a
1a
6 4
H
2e: 2-furanyl
2f: CH (CH
1a
1b: COMe
3
2
)
6
2
30
10
60
30
45
45
2a: 4-NO
2b: 4-MeOC H
2
C
6
H
4
1b
1b
6
4
2c: Ph
2e: 2-furanyl
1
1
1
1
1
1
0
1
2
3
4
5
1b
1b
2f: CH (CH )
3
2
2 6
f
1c: CN
1c
1c
2a: 4-NO
C
2 6
H
4
5
60
2b: 4-MeOC
2c: Ph
6
H
4
f
15
5
1c
2e: 2-furanyl
a
b
c
Carried out in refluxing H O with a 1.2:1 ratio of 1 and 2.
2
Mp: 128–1308C for 1a, 203–2058C for 1b, and 189–1958C for 1c.
Mp: 105–1088C for 2a, Bp: 2488C for 2b, 178–1798C for 2c, MP: 117–1198C
for 2d, Bp: 1628C for 2e, and 1718C for 2f.
d
Isolated yield of both isomers.
e
f
1
Determined by H NMR.
Carried out in H O at room temperature with a 1.2:1 ratio of 1 and 2.
2
(8–10 min) , 4-anisaldehyde (2b) (30 min). It is interesting to find that
the phenolic hydroxy group in 2d does not require protection (entry 4,
Table 2). The aliphatic aldehyde, octyl aldehyde (2f) reacted with 1a for
3
0 min to form 3 in 72% yield and in a decreased E:Z isomer ratio of 66:34
entry 6, Table 2). These results indicate that the Wittig reactions of 1a
(
are much more stereoselective with aromatic aldehydes than aliphatic
aldehydes. For the Wittig reactions of 1b with aromatic aldehydes, the
same results were obtained (78–98% yields, .91:9 E:Z ratios) as given in
entries 7–10 in Table 2. However, the reaction of 2f with 1b became nearly
nonstereoselective (entry 11, Table 2). Because of the higher reactivity of
the ylide 1a than 1b, slightly longer reaction times were required for the
olefination of 1b.
With less sterically demanding ylides 1c, the ratios of the product isomers
decreased significantly even for the aromatic aldehydes (entries 12–15,

Wittig Reactions of Phosphorus Ylides
1217
Table 2). For example, 1c reacted with 2a and 2e to afford the olefin 3 as the
7:43 and 49:51 mixture of E:Z isomers, respectively (entries 12 and 15,
Table 2). It is interesting to emphasize that the heterogeneous Wittig
5
reactions of 1c with 2a and 2c took place in H O even at room temperature
2
(
entries 12 and 14, Table 2), respectively, to give high yields of the olefin
. It represents a fast reaction (5 min) between two solid reagents 1c (mp
3
1
89–1958C) and 2a (mp 105–1088C), both suspended on a water surface at
room temperature, to form the olefin 3 in a quantitative yield. Our results
listed in Table 2 are superior to the previous reports on aqueous Wittig
reactions of semistabilized phosphorus ylides using water-soluble
[3,5]
reagents
and demonstrate that H O can be used to directly substitute the
2
organic solvents used in the Wittig olefination without extra structural modi-
fications on the substrates.
Finally, we examined the solvent effect on the Wittig reactions of the
ylide 1b with both aromatic and aliphatic aldehydes and the results are
given in Table 3. Reactions in three organic solvents, PhMe, DMF, and
a
Table 3. Effect of solvent on the Wittig reactions of 1b with aldehydes 2
d
Yield (%), E:Z
e
Entry
2: R
Solvent
t (min)
b
1
2
3
4
5
6
7
8
9
2a: p-NO C H
2
H O
2
10
20
92, 91:9
90, 97:3
6
4
2a
2a
2a
PhMe
DMF
THF
c
10
35
90, . 99:1
95, .99:1
98, 95:5
b
2b: p-MeOC
6
H
4
H
PhMe
2
O
60
2b
2b
1440
1800
4320
30
85, .99:1
91, .99:1
92, .99:1
89, 98:2
c
DMF
THF
2b
b
2c: Ph
2c
2c
2
H O
1
1
1
1
1
0
1
2
3
4
PhMe
DMF
THF
120
120
1200
45
88, .99:1
87, .99:1
92, .99:1
81, 53:47
80, 78:22
c
2c
2f: CH
b
3
(CH
2
)
6
2
2
H O
2f
PhMe
90
a
b
c
Carried out at refluxing temperature, except for DMF, with a 1.2:1 ratio of lb and 2.
In the presence of 1.2 M LiCl.
Carried out at 1108C.
Isolated yield of both isomers.
d
e 1
Determined by H NMR.

1218
J. Wu, D. Zhang, and S. Wei
THF, were compared with that done in H O. The reaction temperatures were
2
set closely for PhMe (1108C), DMF (1108C), and H O (1008C) but it was
2
quite lower for THF (678C). The data for aqueous Wittig reactions of 1b
(entries 1, 5, 9, and 13, Table 3) are taken from Table 2. In general, the
yields of the olefin 3 formed from the reactive aldehyde 2a in all four
media are nearly the same (entries 1–4, Table 3), whereas extremely slow
reactions of 1b with 2b were observed in PhMe and DMF even at higher
temperature (entries 6 and 7 vs. entry 8, Table 3). Also, the Wittig
reactions of 2c and 2f in organic solvents took longer time to complete.
Therefore, it is clearly demonstrated that the heterogeneous Wittig reactions
of stabilized ylides in refluxing H O are faster than the same reactions
2
carried out in homogeneous organic solvents at similar reaction temperatures.
This is an interesting finding that may shed light on developing “greener”
chemical processes by using H O as the reaction medium. A weak point is
2
that the stereoselectivity of the Wittig reactions in H O decreases notably
2
for aliphatic aldehydes, but the difference is minimal for the reactions of
aromatic aldehydes.
In summary, we have established a general protocol for aqueous Wittig
reactions of stabilized phosphorus ylides with both aromatic and aliphatic
aldehydes in the presence of 1.2 M LiCl at refluxing temperature for 5–
6
0 min to afford the olefin products in 65–98% isolated yields. Moreover,
we have demonstrated that the aqueous Wittig reactions are faster than the
same reactions carried out in homogeneous organic solvents at similar
reaction temperatures. Our study suggests that H O may be used to directly
2
substitute for organic solvents in other types of organic reactions without
structural modification on the substrates.
EXPERIMENTAL
Representative Procedure
A suspension of the ylide 1 (1.2 mmol) and the aldehyde 2 (1.0 mmol) in H O
2
.
(5 mL) containing LiCl H O (362.5 mg, 6.0 mmol) was refluxing in air for the
2
indicated time. After cooling to room temperature, the reaction mixture was
extracted with EtOAc (10 mL Â 3) and the combined organic layer was
washed with brine, dried over Na SO , filtered, and condensed under
2
4
reduced pressure. The residue was then purified by column chromatography
over silica gel (10–30% EtOAc in hexane) to give the olefin product 3. The
results are found in Table 2.
[
14]
(
CO Et, as a 89:11 mixture of E:Z isomers) (500 MHz, CDCl ) d 8.25
E)-Ethyl 3-(4-Nitrophenyl)-2-propenoate:
(R ¼ 4-NO C H , E ¼
3
2
6 4
2
(
d, J ¼ 8.7 Hz, 2H), 7.70 (d, J ¼ 16.0 Hz, 1H), 7.67 (d, J ¼ 8.7 Hz, 2H),
6
.56 (d, J ¼ 16.0 Hz, 1H), 4.29 (q, J ¼ 7.1 Hz, 2H), 1.35 (t, J ¼ 7.1 Hz, 3H).

Wittig Reactions of Phosphorus Ylides
E)-Ethyl 3-(4-Methoxyphenyl)-2-propenoate:
1219
[
15]
(
(R ¼ 4-MeOC H ,
6
4
E ¼ CO Et, as a 91:9 mixture of E:Z isomers) (500 MHz, CDCl ) d 7.64
2
3
(
d, J ¼ 16.0 Hz, 1H), 7.47 (d, J ¼ 8.7 Hz, 2H), 6.90 (d, J ¼ 8.7 Hz, 2H),
.31 (d, J ¼ 16.0 Hz, lH), 4.25 (q, J ¼ 7.1 Hz, 2H), 3.83 (s, 3H), 1.33
t, J ¼ 7.1 Hz, 3H).
E)-Ethyl 3-Phenyl-2-propenoate:
6
(
[
14,15]
(
(R ¼ C H , E ¼ CO Et, as a 95:5
6
5
2
mixture of E:Z isomers) (500 MHz, CDCl ) d 7.68 (d, J ¼ 16.0 Hz, 1H), 7.51–
3
7
.52 (m, 2H), 7.36–7.38 (m, 3H), 6.44 (d, J ¼ 16.0 Hz, 1H), 4.26
(
q, J ¼ 7.1 Hz, 2H), 1.33 (t, J ¼ 7.1 Hz, 3H).
E)-Ethyl 3-(4-Hydroxyphenyl)-2-propenoate:
E ¼ CO Et, as a 85:15 mixture of E:Z isomers) (500 MHz, CDCl ) d 7.64
[15]
(
(R ¼ 4-HOC H ,
3
6
4
2
(
d, J ¼ 16.0 Hz, 1H), 7.42 (d, J ¼ 8.5 Hz, 2H), 6.86 (d, J ¼ 8.5 Hz, 2H),
.30 (d, J ¼ 16.0 Hz, 1H), 6.10 (bs, lH), 4.26 (q, J ¼ 7.1 Hz, 2H), 1.34
6
(
t, J ¼ 7.1 Hz, 3H.
[
16]
(
E)-Ethyl 3-(2-Furanyl)-2-propenoate:
(R ¼ 2-furanyl, E ¼ C0 Et, as
2
a 93:7 mixture of E:Z isomers) (500 MHz, CDCl ) d 7.47 (d, J ¼ 0.9 Hz, 1H),
3
7
.43 (d, J ¼ 15.7 Hz, 1H), 6.60 (d, J ¼ 3.3 Hz, 1H), 6.46 (dd, J ¼ 3.3 Hz,
.9 Hz, 1H), 6.31 (d, J ¼ 15.7 Hz, lH), 4.24 (q, J ¼ 7.1 Hz, 2H), 1.32
0
(
t, J ¼ 7.1 Hz, 3H).
[
17]
(
E)-Ethyl 2-Decenoate:
(R ¼ n-CH (CH ) , E ¼ CO Et, as a 66:34
3
2 6
2
mixture of E:Z isomers) (500 MHz, CDCl ) d 6.96 (dt, J ¼ 15.7, 7.1 Hz,
3
1
H), 5.80 (d, J ¼ 15.7 Hz, 1H), 4.18 (q, J ¼ 7.1 Hz, 2H), 2.17–2.21
(
Ethyl 2-Decenoate:
m, 2H), 1.42–1.46 (m, 2H), 1.27–1.30 (bm, 8H), 0.87–0.89 (m, 6H); (Z)-
(R ¼ n-CH (CH ) , E ¼ CO Et, as a 66:34 mixture
[
17]
3
2 6
2
of E:Z isomers) (500 MHz, CDCl .) d 6.76 (dd, J ¼ 15.7, 6.0 Hz, 1H), 5.85
3
(
d, J ¼ 15.7 Hz, 1H), 4.18 (q, J ¼ 7.2 Hz, 3H), 1.62–1.73 (m, 2H), 1.44 (bs,
2
H), 1.27–1.32 (bm, 10H), 0.87–0.88 (m, 3H).
(
[
18]
E)-4-(4-Nitrophenyl)-3-buten-2-one:
as a 91:9 mixture of E:Z isomers) (500 MHz, CDCl ) d 8.26 (d, J ¼ 8.7 Hz,
(R ¼ 4-NO C H , E ¼ COMe,
2
6 4
3
2
H), 7.70 (d, J ¼ 8.7 Hz, 2H), 7.54 (d, J ¼ 16.2 Hz, 1H), 6.82
(
d, J ¼ 16.2 Hz, 1H), 2.43 (s, 3H).
[15]
E)-4-(4-Methoxyphenyl)-3-buten-2-one:
(
(R ¼ 4-MeOC H , E ¼ COMe,
6
4
as a 95:5 mixture of E:Z isomers) (500 MHz, CDCl ) d 7.49 (d, J ¼ 8.7 Hz,
3
2
H), 7.47 (d, J ¼ 16.2 Hz, 1H), 91 (d, J ¼ 8.7 Hz, 2H), 6.60
(
d, J ¼ 16.2 Hz, 1H), 3.84 (s, 3H), 2.37 (s, 3H).
6 5
[
19,20]
(
mixture of E:Z isomers) (500 MHz, CDCl ) d 7.49–7.54 (m, 3H), 7.39–
E)-4-Phenyl-3-buten-2-one:
(R ¼ C H , E ¼ COMe, as a 98:2
3
7
.40 (m, 3H), 6.71 (d, J ¼ 16.2 Hz, 1H), 2.38 (s, 3H).
[
21,22]
(
6:4 mixture of E:Z isomers) (500 MHz, CDCl ) d 7.51 (s, 1H), 7.28
E)-4-(2-Furanyl)-3-buten-2-one:
(R ¼ 2-furanyl, E ¼ COMe, as a
3
9
(
d, J ¼ 16.0 Hz, 1H), 6.67 (d, J ¼ 3.3 Hz, 1H), 6.62 (d, J ¼ 16.0 Hz, 1H),
.49 (dd, J ¼ 3.3 Hz, 1.7 Hz, 1H), 2.33 (s, 3H).
6
[
17]
(
E)-3-Undecen-2-one:
(R ¼ CH (CH ) , E ¼ COMe, as a 53:47
3
2 6
mixture of E:Z isomers) (500 MHz, CDCl ) d 6.80 (dt, J ¼ 16.0, 7.0 Hz,
3

1220
J. Wu, D. Zhang, and S. Wei
1
H), 6.07 (d, 1H, J ¼ 16.0 Hz), 2.24 (s, 3H), 2.20–2.27 (m, 2H), 1.44–1.48
(
m, 2H), 1.27–1.30 (bm, 8H), 0.89 (t, J ¼ 7.0 Hz, 3H); (Z) -3-Undecen-2-
[17]
one:
(R ¼ CH (CH ) , E ¼ COMe, as a 53:47 mixture of E:Z isomers)
3 2 6
(
500 MHz, CDCl ) d 6.65 (dd, J ¼ 16.0, 6.5 Hz, 1H), 6.10 (d, J ¼ 16.0 Hz,
3
1
0
H), 2.27 (s, 3H), 1.62–1.72 (m, 2H), 1.47–1.49 (m, 24H), 1.27 (bm, 8H),
.86–0.89 (m, 3H).
[
19,23]
(
as a 57:43 mixture of E:Z isomers) (500 MHz, CDCl ) d 8.28
E)-3-(4-Nitrophenyl)-2-propenentrile:
(R ¼ 4-NO C H , E ¼ CN,
3
2
6 4
(
d, J ¼ 8.7 Hz, 2H), 7.63 (d, J ¼ 8.7 Hz, 2H), 7.47 (d, J ¼ 16.6 Hz, 1H),
[19,23]
6
.05 (d, J ¼ 16.6 Hz, 1H); (Z)-3-(4-Nitrophenyl)-2-propenentrile:
2 6 4
(
R ¼ 4-NO C H , E ¼ CN, as a 57:43 mixture of E:Z isomers) (500 MHz,
CDCl ) d 8.31 (d, J ¼ 8.7 Hz, 2H), 7.96 (d, J ¼ 8.7 Hz, 2H), 7.24
3
(
d, J ¼ 12.1 Hz, 1H), 5.71 (d, J ¼ 12.1 Hz, 1H).
[
19]
(
E)-3-(4-Methoxyphenyl)-2-propenentrile: (R ¼ 4-MeOC H , E ¼ CN,
6
4
as a 72:28 mixture of E:Z isomers) (500MHz, CDCl ) d 7.39 (d, J ¼ 8.7 Hz,
3
2
H), 7.33 (d, J ¼ 16.6Hz, 1H), 6.91 (d, J ¼ 8.7 Hz, 2H), 5.71
(
d, J ¼ 16.6Hz, 1H), 3.84 (s, 3H); (Z)-3-(4-Methoxyphenyl)-2-propenen-
[19]
trile:
(R ¼ 4-MeOC H , E ¼ CN, as a 72:28 mixture of E:Z isomers)
6 4
(
500MHz, CDCl ) d 7.79 (d, J ¼ 8.7 Hz, 2H), 7.04 (d, J ¼ 12.1Hz, 1H),
3
6
.94 (d, J ¼ 8.7 Hz, 2H), 5.29 (d, J ¼ 12.1Hz, 1H), 3.85 (s, 3H).
[
19,23]
(
mixture of E:Z isomers) (500 MHz, CDCl.) d 7.37–7.45 (m, 6H), 5.87
E)-3-Phenyl-2-propenentrile:
(R ¼ C H , E ¼ CN, as a 79:21
6
5
[19,23]
(
d, J ¼ 16.6 Hz, 1H); (Z)-3-Phenyl-2-propenentrile:
(R ¼ C H ,
6
5
E ¼ CN, as a 79:21 mixture of E:Z isomers) (500 MHz, CDCl ) d 7.38–
3
7
4
.45 (m, 5H) 7.12 (d, J ¼ 12.1 Hz, 1H), 5.44 (d, J ¼ 12.1 Hz, 1H).
[
16,23]
(
9:51 mixture of E:Z isomers) (500 MHz, CDCl ) d 7.49 (s, 1H), 7.11
E)-3-(2-Furanyl)-2-propenentrile:
(R ¼ 2-furanyl, E ¼ CN, as a
3
(
d, J ¼ 16.2 Hz, 1H), 6.62 (d, J ¼ 3.3 Hz, 1H), 6.50 (dd, J ¼ 3.3, 1.7 Hz,
[16,23]
1
H), 5.76 (d, J ¼ 16.2 Hz, 1H); (Z)-3-(2-Furanyl)-2-propenentrile:
(
R ¼ 2-furanyl, E ¼ CN, as a 49:51 mixture of E:Z isomers) (500 MHz,
CDCl ) d 7.57 (s, 1H, 7.03 (d, J ¼ 3.3 Hz, 1H), 6.95 (d, J ¼ 12.5 Hz, 1H),
3
6
.53 (dd, J ¼ 3.3, 1.7 Hz, 1H), 5. 23 (d, J ¼ 12.5 Hz, 1H).
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