The reaction of triphenylphosphonium or triphenylarsonium salts with aldehyde: Effect of the counteranion on their reactivity

Article abstract of DOI:10.1016/S0040-4020(00)00706-7

Some acetonyltriphenylphosphonium, methoxycarbonylmethyltriphenylphosphonium salts and their triphenylarsonium analogues could undergo Wittig reaction with aldehyde in good yields. Their reactivity was counteranion-dependent and was arranged in the following order: p-TsO^-, Br^-<3CO₂/^-<2CO₂/^-2/^-, HCO₂/^-, MeCO₂/^-. The proton-coupled ¹³C NMR splitting patterns of the α-methylene groups provided a valuable information to predict their reactivity with aldehyde. Only those onium salts without C-H coupling could undergo Wittig reaction. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00706-7

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 7893±7902
The Reaction of Triphenylphosphonium or Triphenylarsonium
Salts with Aldehyde: Effect of the Counteranion on
their Reactivity
*
Yung-Son Hon and Chia-Fu Lee
Department of Chemistry, National Chung Cheng University, Chia-Yi, Taiwan 621, ROC
Received 1 June 2000; accepted 9 August 2000
AbstractÐSome acetonyltriphenylphosphonium, methoxycarbonylmethyltriphenylphosphonium salts and their triphenylarsonium ana-
logues could undergo Wittig reaction with aldehyde in good yields. Their reactivity was counteranion-dependent and was arranged in
the following order: p-TsO2, Br2pCF3CO22pClCH2CO22,PhCO22, HCO22, MeCO22. The proton-coupled 13C NMR splitting patterns of the
a-methylene groups provided a valuable information to predict their reactivity with aldehyde. Only those onium salts without C±H coupling
could undergo Wittig reaction. q 2000 Elsevier Science Ltd. All rights reserved.
Introduction
with aldehyde to give the desired product (Fig. 1). To the
best of our knowledge, there is no precedent literature which
has reported the Wittig reaction from triphenylphosphonium
salts in the absence of base.1 The reaction rate of the stable
phosphonium ylide with ketone is facilitated by the presence
of a catalytic amount of benzoic acid. The role of benzoic
acid in the reaction has been postulated to result from the
protonation of the carbonyl oxygen, making it more
susceptible to be attacked by the ylide.4 In order to
demonstrate the possibility of our proposed mechanism in
Fig. 1, it is interesting to prepare compound B and
investigate its reaction with aldehyde. In this report, we
have prepared a variety of triphenylphosphonium and
The reaction of aldehyde with triphenylphosphonium ylide
is an important method of C±C double bond formation.1
Interestingly, we found that the mono-substituted ozonides
could react with stable triphenylphosphonium ylides
(1.3 mol equiv.) to give trans-a, b-unsaturated carbonyl
compounds in high yields (Fig. 1).2 The plausible mechan-
ism of this reaction is described as follows. The ozonide ring
proton is regioselectively deprotonated by triphenyl-
phosphonium ylide, followed by ring fragmentation to
give both aldehyde A and triphenylphosphonium formate
(B).3 The phosphonium formate B is proposed to react
Figure 1. Proposed mechanism for the reaction of ozonide and stable phosphonium ylide.
Keywords: triphenylphosphonium ylide; triphenylarsonium ylide; triphenylphosphonium salts; triphenylarsonium salts; counteranion; Wittig reaction;
ozonide.
* Corresponding author. Tel.: 1886-5-2720411 ext. 6262; fax: 1886-5-2721040; e-mail: cheysh@ccunix.ccu.edu.tw
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00706-7

7894
Y.-S. Hon, C.-F. Lee / Tetrahedron 56 (2000) 7893±7902
Scheme 1.
Scheme 2.
triphenylarsonium salts and disclose the fact that the
reactivity of these salts with aldehyde is counteranion-
dependent.
was the reaction of triphenylphosphonium bromides (2a and
4a) with silver salts via anion exchange in CH2Cl2 as shown
in Pathway II. The silver bromide precipitate was removed
by ®ltration (Scheme 1). Both methods afforded the corre-
sponding triphenylphosphonium salts in excellent yields.
However, we were unable to prepare compound 4f by either
method. Similarly, the triphenylarsonium salts with differ-
ent kinds of counteranions (6b±6f and 7b±7d) were also
prepared by Pathway I and II in excellent yields as shown in
Scheme 2. We were unable to prepare acetonyltriphenyl-
arsonium ylide (Ph3AsvCHCO2Me) so that arsonium
salts 6b±6f could only be prepared by Pathway II
(Scheme 2). All these onium salts were fully characterized
Results and Discussion
Preparation of triphenylphosphonium and triphenyl-
arsonium salts
The triphenylphosphonium salts with different kinds of
counteranions (2b±2g and 4b±4g) were prepared by the
following two methods (Scheme 1). One was the addition
of protic acid (1 mol equiv.) to the corresponding phospho-
nium ylides (i.e. 1 and 3) as shown in Pathway I. The other
1
by the H and 13C NMR, mass spectroscopy and elemental
analysis.
Table 1. The characteristic off-resonance decoupled splitting patterns for the a-carbon of the phosphonium salts and the results of their reactions with
aldehyde 8
b
Entry
Ph13 PC(a)H2Y X2a
13C of a-CH2
Reaction with aldehyde 8
pKa of HX
Yˆ
Xˆ
d (ppm)
Splitting pattern
1JH±C (Hz)
1JP±C (Hz)
Time (h)
Yieldc (%)
1
2
3
4
5
6
7
8
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
COMe
COMe
COMe
COMe
COMe
COMe
Br
2a
2b
2c
2d
2e
2f
2g
4a
4b
4c
4d
4e
4g
32.7
30.4
29.9
30.1
30.6
31.2
31.3
40.6
56.2
56.5
57.3
59.7
39.0
td
d
d
d
d
td
td
td
d
d
d
133.7
0
0
0
0
134.0
134.5
130.0
0
0
0
57.0
105.8
124.2
110.6
85.1
58.0
58.1
58.4
106.0
105.6
104.2
99.8
24
6
92
29
MeCO2
PhCO2
HCO2
ClCH2CO2
CF3CO2
p-TsO
Br
MeCO2
PhCO2
HCO2
ClCH2CO2
p-TSO
0.5
0.5
0.5
4
4.75
4.20
3.75
2.87
0.23
27
95
90
89
30d
0e
24
24
24
4
4
4
0f
29
9
90
90
81
85
0g
4.75
4.20
3.75
2.87
27
10
11
12
13
d
td
0
130.8
7
24
59.5
a All the phosphonium salts were characterized by 1H NMR, 13C NMR, IR, mass and elemental analysis.
b Ca was a carbon between phosphorus and carbonyl. The 13C NMR (50 MHz) spectra were taken in CDCl3 at rt.
c Only E-isomer was formed in each case.
d 49% of aldehyde was recovered.
e 71% of aldehyde was recovered.
f 73% of aldehyde was recovered and 6% yield of 2,4,6-tris(2-phenylethyl)-1,3,5-trioxane was isolated.
g 73% of aldehyde was recovered.

Y.-S. Hon, C.-F. Lee / Tetrahedron 56 (2000) 7893±7902
7895
Table 2. The characteristic off-resonance decoupled splitting patterns for the a-carbon of the arsonium salts and the results of their reactions with aldehyde 8
b
Entry
Ph13 AsC(a)H2Y X2a
13C of a-CH2
Reaction with aldehyde 8
pKa of HX
Yˆ
Xˆ
d (ppm)
Splitting pattern
1JH±C (Hz)
Time (h)
Yieldc (%)
1
2
3
4
5
6
7
8
9
CO2Me
CO2Me
CO2Me
CO2Me
COMe
COMe
COMe
COMe
COMe
Br
6a
6b
6c
6f
7a
7b
7c
7d
7f
33.8
32.1
29.7
32.2
40.2
57.0
55.5
56.0
42.2
t
141.1
0
0
141.2
136.5
0
24
0.5
0.5
24
24
2
2
2.5
24
0
93
92
16d
6
94
87
83
14e
29
MeCO2
PhCO2
CF3CO2
Br
MeCO2
PhCO2
HCO2
CF3CO2
s
s
t
4.75
4.20
0.23
29
4.75
4.20
3.75
0.23
t
s
s
s
t
0
0
137.3
a All the phosphonium salts were characterized by 1H NMR, 13C NMR, IR, mass and elemental analysis.
b Ca was a carbon between arsenic and carbonyl. The 13C NMR (50 MHz) spectra were taken in CDCl3 at rt.
c Only E-isomer was formed in each case.
d 75% of aldehyde was recovered.
e 71% of aldehyde was recovered.
Reactivity of the triphenylphosphonium and arsonium
salts with aldehyde
3-phenylpropanal (8) in dichloromethane was stirred at
room temperature and the results were shown in Table 1.
The triphenylphospnonium bromides (i.e. 2a and 4a) or
p-toluenesulfonates (i.e. 2g and 4g) almost did not react
with aldehyde at rt for 24 h, as expected (Entries 1, 7, 8
and 13, Table 1). However, when the counteranions were
The typical procedure to test the reactivity of the triphenyl-
phosphonium salts with aldehyde is described as follows. A
mixture of triphenylphosphonium salts (1.1 mol equiv.) and
Figure 2. The characteristic 13C NMR signals for the phosphonium salts 2a, 2c, 4a and 4c (Top: proton-decoupled; Bottom: proton-coupled).

7896
Y.-S. Hon, C.-F. Lee / Tetrahedron 56 (2000) 7893±7902
acetates (i.e. 2b and 4b), benzoates (i.e. 2c and 4c) or
formates (i.e. 2d and 4d), they underwent Wittig
reaction with aldehyde 8 within 0.5 h in excellent yields
(Entries 2±4; 9±11). Interestingly, the phosphonium chloro-
acetate (i.e. 2e and 4e) needed longer time (4.5±7 h) to give
a,b-unsaturated carbonyl compounds in good yields
(Entries 5 and 12). Furthermore, when the counteranion
was tri¯uoroacetate (i.e. 2f), its reactivity with aldehyde
was sluggish. It took 24 h at rt to give a,b-unsaturated
ester 9a in 30% yield and 49% of the aldehyde was
recovered (Entry 6). The results in Table 1 indicate that
the reactivity of the phosphonium salts in Wittig reaction
is counteranion-dependent.
faster than that from the corresponding phosphonium ylide
2a. It needs 1.5 h to complete the reaction with 3-phenyl-
propanal (8) for the ylide.4e Therefore, we have disclosed
the new possibility to carry out the Wittig reaction from the
phosphonium salts (or arsonium salts) instead of the corre-
sponding ylides. From the present study, we can arrange
the order of the reactivity for the onium salts according to
their counteranions as follows: p-TsO2, Br2pCF3CO22
pClCH2CO22 ,PhCO22, HCO22, MeCO22 .
The splitting patterns of the proton-coupled 13C NMR in
the phosphonium and arsonium salts
In order to correlate the structures of the triphenylphospho-
nium (or arsonium) salts to their reactivity with aldehyde as
described in Tables 1 and 2, their H NMR, broad band-
We then turned our interest to study the reactivity of the
triphenylarsonium analogues and their results are shown in
Table 2. The results also indicate that the structures of the
counteranion profoundly affect the reactivity of the
arsonium salts in Wittig reaction.
1
decoupled 13C NMR and off-resonance decoupled (i.e.
proton-coupled) 13C NMR spectra were taken in CDCl3 at
rt. We found that the proton-coupled splitting patterns of the
a-carbon (i.e. the carbon next to carbonyl group) signal
provided the most useful information as shown in Table 1.
The a-carbon splitting patterns for those poor reactive phos-
phonium salts consistently appeared as the triplet of doublet
where it was coupled with both of the adjacent proton and
phosphorus nuclei (Entries, 1, 5±8, 12, Table 1). For
In other words, the onium benzoates, formates, and acetates
show excellent reactivity with aldehyde, whereas the onium
bromides and tosylataes are not reactive for the same reac-
tion. It is worthy to mention that the Wittig reaction rate
from the phosphonium carboxylate (i.e. 2b, 2c, or 2d) is
Figure 3. The characteristic 13C NMR signals for the arsonium salts 6a, 6c, 7a and 7c (Top: Proton-decoupled; Bottom: proton-coupled).

Y.-S. Hon, C.-F. Lee / Tetrahedron 56 (2000) 7893±7902
7897
Figure 4. The reactivity of the onium salts with aldehyde is counteranion-dependent (YˆMe, OMe; MˆP, As).
example, the triphenylphosphonium bromides were inert to
the aldehyde. Therefore, the a-carbon splitting pattern
for the methoxycarbonylmethyltriphenylphosphonium
bromide (2a) appeared as a triplet of doublet (d 32.7 ppm;
(1JH±Cˆ136.5 Hz), respectively. Both compounds had
1
distinct JH±C values so that they had no reactivity with
aldehyde (Entries 1 and 5, Table 2; Fig. 3). On the other
hand, the a-carbon splitting patterns for the triphenyl-
arsonium benzoates 6c and 7c appeared as singlets at d
29.7 ppm (1JH±Cˆ0 Hz) and d 55.5 ppm (1JH±Cˆ0 Hz),
respectively. They should have excellent reactivity with
aldehyde as expected (Entries 3 and 7, Table 2; Fig. 3).
Therefore, the empirical rule to predict the reactivity of
1
1JH±Cˆ133.7 Hz, JP±Cˆ57.0 Hz) and the acetonyltri-
phenylphosphonium bromide (4a) also appeared as a triplet
1
1
of doublet (d 40.6 ppm; JH±Cˆ130.0 Hz, JP±Cˆ58.4 Hz)
(Fig. 2).
1
On the other hand, the a-carbon splitting patterns for the
phosphonium salts having excellent reactivity in the Wittig
reaction appeared as a doublet only. It is because the
a-carbon is coupled with the adjacent phosphorus but not
with hydrogen nuclei (Entries 2±4, 9±11, Table 1). For
example, those phosphonium benzoates (2c) and (4c)
showed excellent reactivity with aldehyde and their
a-carbons appeared as a doublet (Entries 3 and 10, Table
1; Fig. 2). Therefore, the disappearance of the H±C coupling
(i.e. 1JH±Cˆ0 Hz) for the a-carbon is an important indication
to the high reactivity of the phosphonium salts in the Wittig
reaction. Oppositely, those phosphonium salts with distinct
the triphenylphosphonium salts based on the JH±C values
can also be applied to the corresponding triphenylarsonium
salts (Table 2 and Fig. 4). The reason for the absence of the
H±C coupling in the reactive phosphonium salts can be
rationalized by the example of triphenylphosphonium
acetates 2b as shown in Fig. 5. The a-methylene group of
compound 2b is quite acidic so that the intramolecular
proton exchange rate between the a-methylene group and
acetate is too fast to be differentiated by NMR. This
exchange process gives a transient intermediate (i.e. ylide
and acetic acid) which can subsequently undergo Wittig
reaction with aldehyde (Fig. 5). The acetic acid formed in
the transient intermediate will serve as a catalyst to
accelerate the Wittig reaction (Fig. 5).4e Therefore, the
reaction rate of the phosphonium acetate with aldehyde
should be faster than the reaction involving the phospho-
nium ylide only. We have reported that the a-methine
proton of the stable phosphonium ylide could be exchanged
rapidly with the trace amount of the proton source in the
reaction media.5f In Fig. 5, both the acetic acid and
phosphonium ylide are formed as transient intermediates.
Therefore, the acetic acid can exchange rapidly with the
a-methine proton of the phosphonium ylide (Fig. 5). This
1
H±C coupling (i.e. JH±C.0 Hz) will have poor reactivity
with the aldehyde.
Since the nuclear spin quantum number of arsine is zero, it
does not couple with the neighboring nuclei. Therefore, the
off-resonance decoupled splitting pattern for the triphenyl-
arsonium salts should be simpler than that of the triphenyl-
phosphonium analogues. For example, the a-carbon for the
methoxycarbonylmethyltriphenylarsonium bromide (6a)
and the acetonyltriphenylarsonium bromide (7a) appeared
as triplets at d 33.8 ppm (1JH±Cˆ141.1 Hz) and d 40.2 ppm
Figure 5. Proposed mechanism for the reaction of the phosphonium acetate with aldehyde.

7898
Y.-S. Hon, C.-F. Lee / Tetrahedron 56 (2000) 7893±7902
exchange process is responsible to the disappearance of the
C±H coupling in the 13C NMR. On the other hand, NMR did
not detect the intramolecular proton exchange between
a-methylene group and bromide of the triphenylphospho-
nium bromide 2a. Apparently, the exchange process is
determined by the Bronsted basicity of the counteranion.
Since the bromide is a weak Bronsted base, the intra-
molecular proton transfer in the phosphonium bromide is
not possible. Therefore, it is not reactive in the Wittig
reaction. The Bronsted basicity of the counteranion
decreases in the following order: CH3CO22 .PhCO22.H-
CO22 .ClCH2CO22 .CF3CO22.OTs2.Br2.6 The results in
Tables 1 and 2 indicate that the triphenylphosphonium (or
arsonium) salts are effective in the Wittig reaction only
when the basicities of their counteranions are ranged
between formate and chloroacetate. In other words, the
conjugated acid's pKa of the counteranion in triphenyl-
phosphonium (or arsonium) salts should not be lower than
4 in order to have good reactivity with aldehyde.
ꢀ3†
There are some important features for this anion exchange
approach. We are able to carry out the Wittig reaction by
mixing all of four reactants in the same ¯ask to give the
desired product in excellent yield as shown in Eq. (2). The
phosphonium bromide formation, the anion exchange
process and the reaction of the phosphonium acetate with
aldehyde occur sequentially in the same pot. We have
mentioned above that it is dif®cult for us to prepare
Ph3AsvCHCO2Me. Since our anion exchange process
avoids using ylide directly, we can easily get rid of the
above dif®culty by reaction of the triphenylarsonium
bromide 6a with aldehyde 8 in the presence of sodium
acetate as shown in Eq. (3). The reaction yield is excellent.
The disadvantage of this anion exchange approach are: (1) it
needs heating and longer reaction time; (2) both E- and
Z-isomers can be obtained from Eqs. (1)±(3) while only
E-isomer can be obtained from the corresponding phospho-
nium carboxylate as shown in Tables 1 and 2.
The pathway II in Scheme 1 is an effective but expensive
process to prepare the reactive phosphonium salts. There-
fore, to develop an economic process is needed. We carried
out the in situ anion exchange from the triphenylphospho-
nium bromide with NaOAc in acetonitrile although it was an
heterogeneous process. The Wittig reaction products were
isolated in high yield when triphenylphosphonium
bromides reacted with aldehyde in the presence of
1.2 mol equiv. of NaOAc in re¯uxing acetonitrile for 2 h.
A mixture of E- and Z-isomers was obtained and the
E-isomer was the major product under this reaction con-
dition. They were separable by silica gel column chromato-
graphy. This reaction condition was applied to prepare
several conjugated carbonyl compounds in high yields as
shown in Eq. (1).
Conclusion
In summary, the proton-coupled 13C NMR technique is an
important tool in the prediction of the reactivity of the
triphenylphosphonium (or arsonium) salts with aldehyde.
Only those salts with fast intramolecular proton exchange
process between the activated methylene group and the
1
counteranion (i.e. JC±Hˆ0 Hz) can react with aldehyde to
give a,b-unsaturated carbonyl compounds in good yields.
From the present study, we found that the pKa of the conju-
gated acid of the counteranion could not be lower than 2.87.
Experimental
ꢀ1†
All reactions were carried out under nitrogen. Unless other-
wise noted, materials were obtained from commercial
suppliers and used without further puri®cation. Melting
points were determined by using a Thomas±Hoover melting
point apparatus and were uncorrected. The 1H and 13C NMR
spectra were recorded on a Bruker Avance APX-400 and a
Varian Gemini-200 spectrometers, and chemical shifts were
given in ppm down®eld from tetramethylsilane (TMS). IR
spectra were taken with a Perkin±Elmer 682 spectrophoto-
meter and only noteworthy absorption was listed. Mass
spectra were measured on a VG-Trio-2000GC/MS spectro-
meter by electronic impact at 70 eV (unless otherwise
indicated). High Resolution Mass Spectroscopy (HRMS)
was measured on a JEOL JMS-HX 110 (National Hsing-
Hua University) or VG-11±250J (Academia Sinica) Mass
Spectrometer. The elemental analyses were measured on
Heraeus NCH-RAPID and Perkin-Elmer 2400 CHN
analyzer.
ꢀ2†

Y.-S. Hon, C.-F. Lee / Tetrahedron 56 (2000) 7893±7902
7899
General procedure to prepare the phosphonium salts by
the addition of protic acid to the phosphonium ylide
(Pathway I)
170.1 (d, Jˆ8.5 Hz); IR (KBr) 1742, 1613, 1438 cm21; MS
m/z (relative intensity): 334 (M12HCO2H, 25), 277 (57),
152 (100); Anal. Calcd for C22H21O4P: C, 69.47; H, 5.56.
Found: C, 69.49; H, 5.70.
To a stirring solution of the phosphonium ylide 1 (454.7 mg,
1.36 mmol) in 4 mL of anhydrous CH2Cl2 was added a
solution of acetic acid (81.7 mg, 1.36 mmol) in 1 mL of
anhydrous CH2Cl2 at rt under nitrogen. The reaction mixture
was stirred for 5 min and concentrated in vacuo to give
536 mg of phosphonium acetate 2b as white solid in
quantitative yield.
Methoxycarbonylmethyltriphenylphosphonium chloro-
acetate (2e). White solid; mp 103±1068C; 1H NMR
(CDCl3) d 3.52 (s, 3H, ±CH3), 3.92 (s, 2H, ±CH2±), 6.12
(br, 2H, ±CH2±), 7.53±7.73 (m, 15H, Ph); 13C NMR
1
(CDCl3) d 30.6 (d, JP±Cˆ84.6 Hz), 43.8, 51.8, 121.7 (d,
3
1JP±Cˆ89.8 Hz), 129.5 (d, JP±Cˆ12.7 Hz), 133.3 (d,
2JP±Cˆ10.3 Hz), 133.8, 167.8, 170.5; IR (KBr) 3050,
1738, 1618, 1436, 1346 cm21; MS m/z (relative intensity):
335 (M12ClCH2CO2, 100), 334 (M12ClCH2CO2H, 6),
277 (32), 183 (9); Anal. Calcd for C23H22O4ClP: C, 64.42;
H, 5.17. Found: C, 64.36; H, 5.20.
General procedure to prepare the phosphonium salts by
the reaction of the phosphonium bromide with silver salt
(Pathway II)
To a stirring solution of the phosphonium bromide 2a
(265.8 mg, 0.64 mmol) in 5 mL of anhydrous CH2Cl2 was
added silver acetate (111.8 mg, 0.67 mmol) in one portion at
rt under nitrogen. The reaction mixture was stirred for 5 min
and was centrifuged to precipitate the silver bromide. The
solution was ®ltered and concentrated to give 251 mg of
phosphonium acetate 2b as white solid in quantitative
yield.
Methoxycarbonylmethyltriphenylphosphonium tri¯uoro-
acatate (2f). White solid; mp 117±1198C; 1H NMR
(CDCl3) d 3.59 (s, 3H, ±CH3), 5.34 (d, Jˆ13.8 Hz, 2H,
±CH2±), 7.60±7.85 (m, 15H, Ph); 13C NMR (CDCl3) d
1
31.2 (d, JP±Cˆ58.0 Hz), 53.3, 117.9 (q, JC±Fˆ89.0 Hz),
3
1
130.2 (d, JP±Cˆ13.0 Hz), 133.0 (d, JP±Cˆ11.0 Hz), 133.7
(d, 2JP±Cˆ11.0 Hz), 135.1, 160.7 (q, JC±Fˆ33.0 Hz), 165.3;
IR (KBr) 1733, 1682, 1461, 1374 cm21; MS m/z (relative
intensity): 334 (M12CF3CO2H, 0.3), 277 (100), 183 (18);
Anal. Calcd for C23H20O4F3P: C, 61.61; H, 4.50. Found: C,
61.56; H, 4.59.
Methoxycarbonylmethyltriphenylphosphonium bromide
1
(2a).7 White solid; mp 161±1628C; H NMR (CDCl3) d
3.59 (s, 3H, ±CH3), 5.64 (d, Jˆ13.4 Hz, 2H, ±CH2±),
7.65±7.94 (m, 15H, Ph); 13C NMR (CDCl3) d 32.7 (d,
1
1JP±Cˆ57.0 Hz), 53.2, 117.5 (d, JP±Cˆ88.8 Hz), 130.0 (d,
Methoxycarbonylmethyltriphenylphosphonium p-toluene-
sulfonate (2g). White solid; mp 162±1648C; 1H NMR
(CDCl3) d 2.29 (s, 3H, ±CH3), 3.53 (s, 3H, ±CH3), 5.18
(d, Jˆ13.6 Hz, 2H, ±CH2±), 7.02 (d, Jˆ8 Hz, 2H, Ph),
7.61±7.85 (m, 17H, Ph); 13C NMR (CDCl3) d 21.1, 31.3
3JP±Cˆ13.1 Hz), 133.6 (d, 2JP±Cˆ10.9 Hz), 135.0, 164.7; IR
(KBr) 1724, 1586, 1429 cm21; MS m/z (relative intensity):
334 (M12HBr, 24), 277 (67), 183 (100).
1
1
(d, JP±Cˆ58.1 Hz), 53.2, 117.9 (d, JP±Cˆ88.8 Hz), 126.0,
128.0, 130.1 (d, 3JP±Cˆ13.1 Hz), 133.7 (d, 2JP±Cˆ10.6 Hz),
135.0, 138.2, 144.3, 165.2; IR (KBr) 3059, 1719, 1603,
Methoxycarbonylmethyltriphenylphosphonium acetate
(2b). White solid; mp 128±1308C; H NMR (CDCl3) d
1
1.95 (s, 3H, ±CH3), 3.52 (s, 3H, ±CH3), 6.43 (s, 2H,
±CH2±), 7.50±7.74 (m, 15H, Ph); 13C NMR (CDCl3) d
1480, 1438 cm21
; MS m/z (relative intensity): 334
(M12CH3C6H4SO3H, 0.3), 277 (95), 154 (98), 78 (100);
Anal. Calcd for C28H27O5PS: C, 66.39; H, 5.37. Found: C,
66.30; H, 5.32.
1
22.2, 30.4 (d, JP±Cˆ105.8 Hz), 50.8, 124.8 (d,
3
1JP±Cˆ89.2 Hz), 129.1 (d, JP±Cˆ12.4 Hz), 132.8, 133.1
2
(d, JP±Cˆ10.3 Hz), 169.9, 175.4; IR (KBr) 1724, 1613,
1457 cm21
;
MS
m/z
(relative
intensity):
334
(M12CH3CO2H, 51), 333 (100), 152 (69); Anal. Calcd
for C23H23O4P: C, 70.04; H, 5.88. Found: C, 70.18; H,
5.89.
Acetonyltriphenylphosphonium bromide (4a). White
solid; mp 221±2238C; H NMR (CDCl3) d 2.48 (s, 3H,
1
±CH3), 5.96 (d, Jˆ11.3 Hz, 2H, ±CH2±), 7.53±7.81 (m,
3
15H, Ph); 13C NMR (CDCl3) d 32.5 (d, JP±Cˆ6.5 Hz),
1
1
40.6 (d, JP±Cˆ58.4 Hz), 118.4 (d, JP±Cˆ88.4 Hz), 129.9
Methoxycarbonylmethyltriphenylphosphonium benzo-
ate (2c). White solid; mp 155±1588C; H NMR (CDCl3)
d 3.53 (s, 3H, ±CH3), 4.54 (br, 2H, ±CH2±), 7.42±8.08
3
2
1
(d, JP±Cˆ12.9 Hz), 133.7 (d, JP±Cˆ10.7 Hz), 134.5,
200.6 (d, Jˆ6.9 Hz); IR (KBr) 3050, 1715, 1618,
1443 cm21; MS m/z (relative intensity): 319 (M12Br, 45),
318 (M12HBr, 100), 183 (23); Anal. Calcd for
C21H20OPBr: C, 63.17; H, 5.05. Found: C, 63.15; H, 5.10.
(m, 20H, ±CH2± and Ph); 13C NMR (CDCl3) d 29.9 (d,
1
1JP±Cˆ124.2 Hz), 49.9, 127.1 (d, JP±Cˆ54.6 Hz), 128.7
3
2
(d, JP±Cˆ12.4 Hz), 132.0, 133.0 (d, JP±Cˆ10.2 Hz),
169.8, 171.5; IR (KBr) 1726, 1631, 1442, 1347 cm21; MS
m/z (relative intensity): 334 (M12PhCO2H, 40), 333 (89),
183 (100); Anal. Calcd for C28H25O4P: C, 73.67; H, 5.52.
Found: C, 73.38; H, 5.53.
Acetonyltriphenylphosphonium acetate (4b). White
solid; mp 135±1388C; H NMR (CDCl3) d 1.84 (s, 3H,
1
±CH3), 2.11 (s, 3H, ±CH3), 7.46±7.65 (m, 17H, ±CH2±
and Ph); 13C NMR (CDCl3)
d
21.7, 26.8 (d,
1JP±Cˆ14.6 Hz), 56.2 (d, Jˆ106 Hz), 125.8 (d,
Methoxycarbonylmethyltriphenylphosphonium formate
(2d). White solid; mp 136±1388C; 1H NMR (CDCl3) d 3.51
(s, 3H, ±CH3), 5.18 (s, 2H, ±CH2±), 7.50±7.73 (m, 15H,
Ph), 8.51 (s, 1H, HCOO); 13C NMR (CDCl3) d 30.1 (d,
3
1JP±Cˆ90.5 Hz), 128.9 (d, JP±Cˆ12.3 Hz), 132.4, 133.0
2
(d, JP±Cˆ10.2 Hz), 174.4, 190.0; IR (KBr) 3059, 1696,
1484 cm21; MS m/z (relative intensity): 319 (M12OAc,
100), 318 (M12HOAc, 25), 185 (12); Anal. Calcd
for C23H23O3P: C, 73.00; H, 6.13. Found: C, 73.03; H, 6.07.
1
1JP±Cˆ110.6 Hz), 50.4, 125.4 (d, JP±Cˆ91.0 Hz), 128.9
3
2
(d, JP±Cˆ12.4 Hz), 132.5, 132.9 (d, JP±Cˆ9.9 Hz), 166.5,

7900
Y.-S. Hon, C.-F. Lee / Tetrahedron 56 (2000) 7893±7902
Acetonyltriphenylphosphonium benzoate (4c). White
solid; mp 136±1378C; H NMR (CDCl3) d 2.25 (s, 3H,
(relative intensity): 306 (17), 227 (20), 152 (100). Anal.
Calcd for C23H23O4As: C, 63.02; H, 5.29. Found: C,
63.39; H, 5.25.
1
±CH3), 7.35±7.69 (m, 20H, ±CH2± and Ph), 8.04±8.06
(m, 2H, Ph); 13C NMR (CDCl3)
d
26.8 (d,
1JP±Cˆ14.4 Hz), 56.5 (d, Jˆ105.6 Hz), 125.5 (d,
Methoxycarbonylmethyltriphenylarsonium
benzoate
3
1
1JP±Cˆ90.0 Hz), 127.7, 128.9 (d, JP±Cˆ12.2 Hz), 129.6,
(6c). White solid; mp 104±1078C; H NMR (CDCl3) d
3.46 (s, 3H, ±CH3), 7.22±7.98 (m, 22H, ±CH2± and Ph);
13C NMR (CDCl3) d 29.7, 52.2, 123.4, 127.0, 129.4, 129.6,
130.1, 132.2, 133.2, 136.7, 169.3, 171.2; IR (KBr) 3050,
1728, 1595, 1443, 1374 cm21; MS m/z (relative intensity):
378 (M12PhCO2H, 5), 306 (14), 152 (100). HRMS Calcd
for (M12PhCO2H) C21H19O2As: 378.0602. Found:
378.0601.
2
131.4, 132.4, 133.1 (d, JP±Cˆ10.0 Hz), 169.4, 190.1; IR
(KBr) 3050, 1701, 1521, 1263 cm21; MS m/z (relative
intensity): 319 (M12PhCO2, 5), 318 (M12PhCO2H, 24),
303 (100); Anal. Calcd for C28H25O3P: C, 76.35; H, 5.72.
Found: C, 76.26; H, 5.78.
Acetonyltriphenylphosphonium formate (4d). White
solid; mp 152±1548C; H NMR (CDCl3) d 2.15 (s, 3H,
CH3), 7.49±7.66 (m, 17H, ±CH2± and Ph), 8.17 (s, 1H,
1
Methoxycarbonylmethyltriphenylarsonium tri¯uoro-
acetate (6f). White solid; mp 117±1208C; 1H NMR
(CDCl3) d 3.61 (s, 3H, ±CH3), 5.28 (s, 2H, ±CH2±),
7.65±7.78 (m, 15H, Ph); 13C NMR (CDCl3) d 32.2, 53.4,
121.2, 130.6, 132.7, 134.1, 160.6 (q, JC±Fˆ32.6 Hz), 166.4;
IR (KBr) 1738, 1687, 1447, 1263 cm21; MS m/z (relative
intensity): 379 (M12CF3COO, 0.03), 306 (34), 152 (100);
Anal. Calcd for C23H20O4F3As: C, 56.11; H, 4.09. Found: C,
56.11; H, 4.15.
1
HCOO); 13C NMR (CDCl3) d 26.5 (d, JP±Cˆ14.2 Hz),
1
57.3 (d, Jˆ104.2 Hz), 125.2 (d, JP±Cˆ90.6 Hz), 129.0 (d,
2
3JP±Cˆ12.5 Hz), 132.6, 133.0 (d, JP±Cˆ10.0 Hz), 165.3,
189.1; IR (KBr) 1724, 1609, 1438, 1351 cm21; MS m/z
(relative intensity): 319 (M12HCO2, 4), 318
(M12HCO2H, 19), 303 (100); Anal. Calcd for
C22H21O3P: C, 72.52; H, 5.81. Found: C, 72.57; H, 5.92.
Acetonyltriphenylphosphonium chloroacetate (4e).
White solid; mp 94±968C; H NMR (CDCl3) d 2.34 (s,
1
Acetonyltriphenylarsonium bromide (7a).8 White solid;
1
3H, ±CH3), 3.93 (s, 2H, ±CH2±), 6.92 (br, 2H, ±CH2±),
7.53±7.68 (m, 15H, Ph); 13C NMR (CDCl3) d 25.1 (dd,
mp 169±1708C; H NMR (CDCl3) d 2.47 (s, 3H, ±CH3),
6.01 (s, 2H, ±CH2±), 7.51±7.75 (m, 15H, Ph); 13C NMR
(CDCl3) d 31.3, 43.8, 121.6, 130.2, 132.6, 133.4, 201.6; IR
(KBr) 3032, 2820. 1710, 1438, 1355 cm21; MS m/z (relative
intensity): 364 (100), 362 (M12HBr, 12), 229 (21), 152
(24).
1
Jˆ13.3 Hz, Jˆ28.1 Hz), 40.3, 59.7 (d, JP±Cˆ99.8 Hz),
1
3
122.9 (d, JP±Cˆ91.3 Hz), 128.9 (d, JP±Cˆ12.6 Hz), 132.6
2
(d, JP±Cˆ10.5 Hz), 132.8, 169.9, 187.1; IR (KBr) 3059,
1715, 1609, 1438 cm21; MS m/z (relative intensity): 319
(M12ClCH2CO2, 100), 318 (M12ClCH2CO2H, 14), 303
(13), 183 (10); Anal. Calcd for C23H22O3ClP: C, 66.91; H,
5.37. Found: C, 66.99; H, 5.39.
Acetonyltriphenylarsonium acetate (7b). White solid; mp
104±1068C; H NMR (CDCl3) d 1.87 (s, 3H, ±CH3), 2.19
1
(s, 3H, ±CH3), 6.83 (s, 2H, ±CH2±), 7.51±7.67 (m, 15H,
Ph); 13C NMR (CDCl3) d 22.3, 26.1, 57.0, 126.9, 129.6,
132.2, 132.4, 175.1, 189.0; IR (KBr) 3050, 1710, 1516,
Acetonyltriphenylphosphonium p-toluenesulfonate (4g).
White solid; mp 163±1658C; H NMR (CDCl3) d 2.30 (s,
1
3H, ±CH3), 2.50 (s, 3H, ±CH3), 5.59 (d, Jˆ11.5 Hz, 2H,
±CH2±), 7.06 (d, Jˆ3.9 Hz, 2H, Ph), 7.54±7.79 (m, 17H,
Ph); 13C NMR (CDCl3) d 21.1, 31.9 (d, 3JP±Cˆ6.5 Hz), 39.0
(d, 1JP±Cˆ59.5 Hz), 118.5 (d, 1JP±Cˆ88.6 Hz), 125.8, 128.2,
129.5, 129.9 (d, 3JP±Cˆ13.2 Hz), 133.6 (d, 2JP±Cˆ10.7 Hz),
134.4, 138.7, 143.6, 201.1 (d, Jˆ6.7 Hz); IR (KBr) 1719,
1438, 1268 cm21
; MS m/z (relative intensity): 363
(M12OAc, 100), 362 (M12HOAc, 11), 229 (17), 152
(23); Anal. Calcd for C23H23O3As: C, 65.41; H, 5.49.
Found: C, 65.20; H, 5.60.
Acetonyltriphenylarsonium benzoate (7c). White solid;
1
1443, 1263 cm21
;
MS m/z (relative intensity): 319
mp 108±1108C; H NMR (CDCl3) d 2.29 (s, 3H, ±CH3),
(M12OTs, 5), 318 (M12TsOH, 23), 303 (100); Anal.
Calcd for C27H27O4PS: C, 68.56; H, 5.55. Found: C,
68.51; H, 5.60.
7.29±8.03 (m, 20H, ±CH2± and Ph), 8.50 (s, 2H, Ph); 13C
NMR (CDCl3) d 26.5, 55.5, 126.0, 127.4, 129.2, 129.5,
129.6, 130.5, 132.3, 170.3, 190.5; IR (KBr) 3059, 1710,
1599, 1438, 1369 cm21; MS m/z (relative intensity): 362
(M12PhCO2H, 1.1), 306 (27), 152 (100); Anal. Calcd
for C28H25O3As: C, 69.42; H, 5.20. Found: C, 69.35; H,
5.33.
Methoxycarbonylmethyltriphenylarsonium
bromide
1
(6a). White solid; mp 179±1808C; H NMR (CDCl3) d
3.51 (s, 3H, ±CH3), 5.41 (s, 2H, ±CH2±), 7.56±7.76 (m,
15H, Ph); 13C NMR (CDCl3) d 34.2, 53.5, 121.2, 130.7,
133.0, 134.1, 166.2; IR (KBr) 1721, 1437, 1317 cm21; MS
m/z (relative intensity): 378 (M12HBr, 0.13), 306 (21), 152
(100). Anal. Calcd for C21H20O2AsBr: C, 54.93; H, 4.39.
Found: C, 54.89; H, 4.34.
Acetonyltriphenylarsonium formate (7d). White solid;
mp 118±1208C; H NMR (CDCl3) d 2.21 (s, 3H, ±CH3),
1
7.49±7.68 (m, 17H, ±CH2± and Ph), 8.42 (1H, HCO2); 13
C
NMR (CDCl3) d 26.5, 56.0, 126.2, 129.8, 132.4, 166.5,
189.6; IR (KBr) 3050, 1710, 1599, 1512, 1438 cm21; MS
m/z (relative intensity): 363 (M12HCO22, 100), 362
(M12HCO2H, 9), 347 (11), 229 (13), 152 (18); Anal.
Calcd for C22H21O3As: C, 64.71; H, 5.18. Found: C,
64.69; H, 5.18.
Methoxycarbonylmethyltriphenylarsonium acetate (6b).
White solid; mp 136±1388C; H NMR (CDCl3) d 1.83 (s,
1
3H, ±CH3), 3.53 (s, 3H, ±OCH3), 6.81 (s, 2H, ±CH2±),
7.53±7.70 (m, 15H, Ph); 13C NMR (CDCl3) d 23.1, 32.1,
51.9, 124.4, 130.0, 132.4, 132.5, 133.0, 168.8, 175.9; IR
(KBr) 3059, 1728, 1599, 1484, 1434 cm21; MS m/z
Acetonyltriphenylarsonium tri¯uoroacetate (7f). White

Y.-S. Hon, C.-F. Lee / Tetrahedron 56 (2000) 7893±7902
7901
1
1
solid; mp 138±1398C; H NMR (CDCl3) d 2.45 (s, 3H,
(Z)-5-phenyl-2-pentenoic acid methyl ester (9a-Z). H
NMR (CDCl3) d 2.74±2.78 (m, 2H, ±CH2±), 2.95±2.99
(m, 2H, ±CH2±), 3.68 (s, 3H, ±CH3), 5.79±5.85 (m, 1H,
±CHvCH±), 6.21±6.28 (m, 1H, ±CHvCH±), 7.15±7.29
(m, 5H, Ph); 13C NMR (CDCl3) d 30.4, 35.0, 51.0, 119.9,
126.0, 128.3, 128.4, 141.1, 149.2, 166.7; IR (KBr) 2957,
1731, 1451, 1422 cm21; HRMS Calcd for C12H14O2:
190.0944. Found: 190.0991.
±CH3), 5.67 (s, 2H, ±CH2±), 7.60±7.74 (m, 15H, Ph); 13C
NMR (CDCl3) d 30.5, 42.2, 121.8, 130.4, 132.6, 133.6,
160.8, 201.9; IR (KBr) 1682, 1466, 1374 cm21; MS m/z
(relative intensity): 362 (M12CF3CO2H, 3.3), 227 (38),
152 (100); Anal. Calcd for C23H20O3F3As: C, 58.00; H,
4.23. Found: C, 58.22; H, 4.45.
General procedure of the Wittig reaction from the
triphenylphosphonium carboxylate with aldehyde
(E)-2,2-dimethyl-7-phenyl-4-hepten-3-one (9h-E). 1H
NMR (CDCl3) d 1.48 (s, 9H, ±(CH3)3), 2.48±2.52 (m,
2H, ±CH2±), 2.75±2.78 (m, 2H, ±CH2±), 5.76±5.81 (m,
1H, ±CHvCH±), 6.89±6.93 (m, 1H, ±CHvCH±), 7.18±
7.31 (m, 5H, Ph); 13C NMR (CDCl3) d 28.1, 33.8, 34.4,
80.1, 123.5, 126.1, 128.3, 128.4, 141.0, 146.8, 166.0; IR
(KBr) 2967, 1715, 1655, 1457, 1369 cm21; MS m/z (relative
intensity): 217 (M111, 10), 159 (26), 130 (18), 91 (100);
Anal. Calcd for C15H20O: C, 77.55; H, 8.68. Found: C,
77.56; H, 8.64.
The solution of phosphonium acetate 2b (394.4 mg,
1.0 mmol) and 3-phenylpropanal (8) (134.1 mg, 1.0 mmol)
in 5 mL of anhydrous CH2Cl2 was stirred at rt for 30 min.
The solution was concentrated and chromatographed to give
174.9 mg of Wittig reaction product 9a±E (0.92 mmol) as
colorless oil in 92% yield.
General procedure of the Wittig reaction from the
triphenylphosphonium bromide with aldehyde in the
presence of sodium acetate
(E)-5-phenyl-2-pentenonitrile (9i-E). 1H NMR (CDCl3) d
2.49±2.60 (m, 2H, ±CH2±), 2.73±2.80 (m, 2H, ±CH2±),
5.31(dd, Jˆ16.2, 1.6 Hz, 1H, ±CHvCH±), 6.65±6.80 (m,
1H, ±CHvCH±), 7.13±7.35 (m, 5H, Ph); 13C NMR
(CDCl3) d 33.9, 34.9, 100.4, 126.5, 128.1, 128.3, 154.7;
IR (KBr) 3032, 2212, 1627, 1493 cm21; MS m/z (relative
intensity): 157 (M1, 18), 30 (4), 91 (100); Anal. Calcd for
C11H11N: C, 84.04; H, 7.05. Found: C, 84.00; H, 7.04.
A mixture of the phosphonium bromide 2a (415.3 mg,
1.0 mmol), 3-phenylpropanal (8) (134.2 mg, 1.0 mmol)
and sodium acetate (98.4 mg, 1.2 mmol) in 5 mL of
anhydrous acetonitrile was re¯uxed under nitrogen for 2 h.
The solution was concentrated and chromatographed to give
152.1 mg of 9a-E (0.80 mmol) and 20.9 mg of 9a-Z
(0.11 mmol) in 91% yield.
1
(Z)-5-phenyl-2-pentenonitrile (9i-Z). H NMR (CDCl3) d
2.49±2.60 (m, 2H, ±CH2±), 2.73±2.80 (m, 2H, ±CH2±),
5.27±5.36 (m, 1H, ±CHvCH±), 6.45±6.50 (m, 1H,
±CHvCH±) 7.13±7.35 (m, 5H, Ph); 13C NMR (CDCl3) d
33.2, 34.3, 100.2, 117.3, 126.5, 128.1, 128.3, 128.6, 153.8.
General procedure of the Wittig reaction from tri-
phenylphosphine, methyl bromoacetate, 3-phenyl-
propanal (8) in the presence of sodium acetate
A mixture of triphenylphosphine (262.3 mg, 1.0 mmol),
methyl bromoacetate (153.0 mg, 1 mmol), 3-phenylpropa-
nal (8) (134.1 mg, 1 mmol) and sodium acetate (98.4 mg,
1.2 mmol) in 5 mL of anhydrous acetonitrile was re¯uxed
under nitrogen for 16 h. The reaction mixture was concen-
trated and chromatographed to give 154.0 mg of 9a-E
(0.81 mmol) and 15.2 mg of 9a-Z (0.08 mmol) in 89%
yield.
1
(E)-6-phenyl-3-hexen-2-one (9a0-E). H NMR (CDCl3) d
2.23 (m, 3H, ±CH3), 2.49±2.60 (m, 2H, ±CH2±), 2.76±2.83
(m, 2H, ±CH2±), 6.04±6.13 (m, 1H, ±CHvCH±), 6.75±
6.89 (m, 1H, ±CHvCH±), 7.16±7.35 (m, 5H, Ph); 13C
NMR (CDCl3) d 27.0, 34.1, 34.4, 126.2, 128.1, 128.3,
128.5, 131.7, 198.5; IR (KBr) 3026, 1676, 1626, 1497,
1362 cm21; MS m/z (relative intensity): 174 (M1, 5), 131
(13), 116 (46), 91(100); Anal. Calcd for C12H14O: C, 82.72;
H, 8.10. Found: C, 82.69; H, 8.17.
Wittig reaction from the triphenylarsonium bromide
with aldehyde in the presence of sodium acetate
1
(Z)-6-phenyl-3-hexen-2-one (9a0-Z). H NMR (CDCl3) d
2.18 (m, 3H, ±CH3), 2.74±2.76 (m, 2H, ±CH2±), 2.91±2.97
(m, 2H, ±CH2±), 6.06±6.16 (m, 2H, ±CHvCH±), 7.19±
7.30 (m, 5H, Ph); 13C NMR (CDCl3) d 30.7, 31.5, 35.1,
126.0, 127.6, 128.3, 128.5, 141.1, 146.9, 199.1; IR (KBr)
2927, 1701, 1621, 1467, 1367 cm21; MS m/z (relative inten-
sity): 174 (M1, 12), 131 (40), 104 (21), 91 (100).
To a stirring solution of the arsonium bromide 6a
(459.2 mg, 1.0 mmol), 3-phenylpropanal (8) (134.2 mg,
1.0 mmol) in 5 mL of anhydrous acetonitrile was added
sodium acetate (98.4 mg, 1.2 mmol). The mixture was
re¯uxed under nitrogen for 4 h. The solution was concen-
trated and chromatographed to give 159.7 mg of 9a-E
(0.84 mmol) and 5.7 mg of 9a-Z (0.03 mmol) in 87% yield.
1
(E)-5-phenyl-2-pentenoic acid methyl ester (9a-E). H
Acknowledgements
NMR (CDCl3) d 2.49±2.55 (m, 2H, ±CH2±), 2.75±2.79
(m, 2H, ±CH2±), 3.71 (s, 3H, ±CH3), 5.84 (d, Jˆ7.8 Hz,
1H, ±CHvCH±), 6.97±7.04 (m, 1H, ±CHvCH±), 7.16±
7.31 (m, 5H, Ph); 13C NMR (CDCl3) d 33.8, 34.3, 51.4,
121.4, 126.1, 128.3, 128.4, 140.7, 148.3, 166.9; IR (KBr)
2940, 1733, 1659, 1438, 1318 cm21; MS m/z (relative inten-
sity): 190 (M1, 2.0), 130 (15), 91 (100); Anal. Calcd for
C12H14O2: C, 75.76; H, 7.42. Found: C, 75.71; H, 7.55.
We are grateful to the National Science Council and
National Chung Cheng University for the ®nancial support.
References
1. Reviews of the Wittig reaction from triphenylphosphonium

7902
Y.-S. Hon, C.-F. Lee / Tetrahedron 56 (2000) 7893±7902
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2. (a) Hon, Y. S.; Lu, L.; Li, S. Y. J. Chem. Soc., Chem. Commun.
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Chemist's Companion, A handbook of Practical Data Techniques
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4. (a) Ruchardt, C.; Eichler, S.; Panse, P. Angew. Chem. 1963, 2,
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1963, 46, 1580. (c) Ruchardt, C.; Panse, P.; Eichler, S. Chem. Ber.
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5. (a) Randall, F. J.; Johnson, A. W. Tetrahedron Lett. 1968, 24,
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