Heck reaction of β-substituted acrylates in ionic liquids catalyzed by a Pd-benzothiazole carbene complex

Article abstract of DOI:10.1016/S0040-4020(01)00528-2

A Pd-catalyst with benzothiazole carbene as ligands allows, in tetrabutylammonium bromide melt as solvent, very fast and efficient reactions of haloaromatics with β-substituted acrylates.

Full text of DOI:10.1016/S0040-4020(01)00528-2

TETRAHEDRON
Pergamon
Tetrahedron 57 82001) 6071±6077
Heck reaction of b-substituted acrylates in ionic liquids catalyzed
by a Pd-benzothiazole carbene complex
p
Vincenzo Calo, Angelo Nacci, Antonio Monopoli, Luigi Lopez and Anna di Cosmo
Á
Á
Centro CNR `MISO', Dipartimento di Chimica, Universita di Bari, Via Amendola 173-70126 Bari, Italy
Received 16 February 2001; revised 24 April 2001; accepted 10 May 2001
AbstractÐA Pd-catalyst with benzothiazole carbene as ligands allows, in tetrabutylammonium bromide melt as solvent, very fast and
ef®cient reactions of haloaromatics with b-substituted acrylates. q 2001 Elsevier Science Ltd. All rights reserved.
The Heck reaction and related chemistry occupy a
special place among basic types of palladium-catalyzed
reactions.1±3 In most of the papers dedicated to the Heck
reaction, only a few examples of its use for the synthesis of
trisubstituted ole®ns have been reported.4±7 As some b,b-
diaryl acrylates are useful intermediates for the synthesis
of angiotensin II antagonist,8 platelet activating factors
antagonist,9 and SRS-A antagonists 8slow-reacting
substance of anaphylaxis),10 the development of an ef®cient
process for the Heck arylation of b-substituted acrylates
would be of signi®cant utility. Arylation of b-substituted,
a,b-unsaturated esters requires harsh reaction conditions,
cyclopalladated phosphanes5,6 or palladium acetate as
catalysts, sterically hindered tertiary amines as bases and
quaternary ammonium salts as phase-transfer agents in
DMF or DMA as solvents7 have been used.
In these reactions, TBAB proved to be an excellent solvent
for a fast and stereoselective synthesis of 8E)-cinnamates.
For example, bromobenzene reacted with butyl acrylate and
sodium carbonate as base to give 8E)-butyl cinnamate in
only ten minutes and 94% yield.
In spite of the increasing interest in the use of ionic liquids14
as environmentally benign solvents, different hypotheses on
their role in catalysis have been reported.2e This paper
reports our results on the synthesis of b-arylsubstituted
cinnamates catalyzed by 1 in TBAB as solvent and the
probable effects of this solvent in stabilizing the catalyst.
1. Results and discussion
Catalyst 1 ef®ciently allows the reaction of various p-substi-
tuted bromoaromatics with 8E)-ethyl cinnamate in TBAB
melt as solvent 8Scheme 1).
Recently we reported the synthesis11,12of a Pd catalyst 1
with benzothiazole carbenes as ligands and its application
to an ef®cient Heck synthesis13 of trans-cinnamates in tetra-
butylammonium bromide 8TBAB) as solvent.
As shown in Table 1, a procedure employing the catalyst 1
81.5%), sodium formate 83%) as reducing agent and sodium
bicarbonate as base in TBAB at 1308C, was very effective in
coupling trans-cinnamates with both electron-rich and
electron-poor aryl halides with 100% conversion. Even
p-nitrochlorobenzene was coupled with ethyl cinnamate as
the acceptor, albeit with a lower reaction rate, to give the
CH3
N
I
S
Pd
S
N
1
CH3
I
Ph
Ph
1 (1.5%)
CO2Et
CO2Et
Ar X
CO2Et
+
Ph
+
TBAB
Ar
Ar
2-7
(3÷5%)
Scheme 1. Arˆp-CH3C6H4, p-CH3OC6H4, p-CH3COC6H4, a-naphthyl, p-O2NC6H4, p-NCC6H4; XˆCl, Br.
Keywords: b-aryl cinnamates; ionic liquids; carbenes; Heck reaction.
Corresponding author. Tel.: 139-80-544-2071; fax: 139-80-544-2924; e-mail: calo@chimica.uniba.it
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020801)00528-2

Á
V. Calo et al. / Tetrahedron 57 02001) 6071±6077
6072
Table 1. Synthesis of b,b-diaryl acrylate in TBAB, catalyzed by Pd-benzothiazole carbene complex 1
Yield
[%]a
Entry
Aryl halide
Olefin
Product
E:Z Ratio Time [h]
CO2Et
Me
MeO
Ac
Br
1
59:41
61:39
60:40
8
17
7
91
84
97
CO2Et
2
Me
MeO
Ac
Br
2
3
" "
" "
CO2Et
3
Br
CO2Et
4
Br
4
" "
64:36
4
76
CO2Et
5
O2N
NC
Cl
Br
5
6
" "
" "
60:40
58:42
40
18
78
70
CO2Et
6
O2N
NC
CO2Et
7
Conditions: 1308C, TBAB 83 g), NaHCO2 3 mol%; ratio haloarene/ole®n/NaHCO3 1.5:1:2.5; 1.5 mol% of 1 with the exception of entry 5 82.5 mol% of 1).
Yields refer to chromatographic isolated product.
a
trisubstituted ole®n 8entry 5). On the other hand, by
changing the ole®n acceptor with p-nitrocinnamate, the
reaction with bromobenzene did not afford the correspond-
ing trisubstituted ole®n. No palladium black deposition was
observed and a phosphane ligand was not necessary. This
result is important because a phosphane-free system is
desirable particularly for industrial applications. In every
case the coupling process was devoid of stereoselectivity.
This ®nding is of considerable interest since the generally
accepted mechanism for the Heck arylation of disubstituted
alkenes predicts that the trisubstituted alkene should be
formed in a stereospeci®c manner. The observed lack of
stereoselectivity was probably due, as found by
Buchwald et al.7 to equilibration of cinnamate esters
subsequent to the Heck arylation. Therefore, the stereo-
chemistry of these reactions is likely to be de®ned by
base-catalyzed isomerization of products leading to the
accumulation of the more thermodynamically favourable
isomer. This is not surprising as the ole®ns with such a
substitution pattern must be susceptible to base-catalyzed
E/Z-isomerization.
Due to the high catalytic activity of our system, we tried a
one-pot synthesis of b,b-diarylacrylates by reaction of butyl
acrylate with an excess of aryl bromides 8Scheme 2). This
procedure allows a fast and simple synthesis of trisubsti-
tuted ole®ns 8Table 2, entries 1±4). Interestingly, besides
the expected product, we observed, in all cases, the forma-
tion of very small quantities 83±5%) of 1,2-diaryl acrylates.
To verify the observation3,14±16 that ionic liquids bearing
coordinating halide anions are necessary for a bene®cial
solvent effect, we tested a different ammonium salt, as
butyl pyridinium tosylate 8entry 5). Reaction in this
solvent failed to give appreciable yield of coupling product.
Recycling of TBAB and catalyst was also attempted but,
after three cycles, the increase of NaBr rendered the reaction
medium more viscous and prevented further addition of the
reagents.
Ar
Ar
Ar
1 (1.5%)
CO2Bu
CO2Bu
CO2Bu
+
8-11
Ar Br
2
+
TBAB
Ar
3-5%
Scheme 2.

Á
V. Calo et al. / Tetrahedron 57 02001) 6071±6077
6073
Table 2. Synthesis of b,b-diaryl acrylate in TBAB, catalyzed by Pd-benzothiazole carbene complex 1
Yield
[%]a
Entry
Aryl halide
Olefin
Product
Time [h]
CO2Bu
Br
1
3
82
CO2Bu
8
Me
Me
Br
2
3
" "
" "
8
85
CO2Bu
9
Me
OMe
MeO
Br
12
86
CO Bu
2
10
MeO
Br
4
" "
" "
7.5
17
89
2
CO2Bu
11
5b
" "
" "
Conditions: 1308C, TBAB 83 g), NaHCO2 3 mol%; ratio haloarene/ole®n/NaHCO3 2.3:1:2.5; 1.5 mol% of 1.
Yields refer to chromatographic isolated product.
a
b Butylpyridinium tosylate as solvent 83 g), 1308C.
2. Discussion
16-electron anionic complex as [Pd8PPh3)2X]82). The
stabilization of catalytic systems by halide salts was also
demonstrated by extension of the lifetime of the Herrmann
palladacycle.23 To explain some ionic liquid effects, we
propose some considerations that could explain our results.
The addition of sodium formate does reduce24 1 to under-
ligated L2Pd80) complex, which, by reaction with TBAB,
would afford an anionic and catalytically active 16-electron
complex [L2Pd Br]82) 81)NR4. This would not be surprising,
since in TBAB the bromide ion, being poorly solvated,
should be a good nucleophile for palladium. On the
contrary, ionic liquids bearing different anions such as
tosylate or tetra¯uoroborate should not stabilize, the
14-electron complex L2Pd80) like halides can. Evidence
for this was provided by the inef®cacy of 1 in catalyzing
the reaction in butylpyridinium tosylate. Furthermore, the
same anion effect was observed19 in other ionic liquids such
as imidazolium tetra¯uoborate. The stabilizing effect was
exerted not only by the bromide ion, which is likely to enter
the co-ordination shell of underligated L2Pd80) to give the
anionic complex, but also by the large tetrabutylammonium
cation. Indeed, the formation of a large [L2Pd Br]82) 81)NR4
complex, by imposing a Coulombic barrier for collision,
should impede the formation of clusters growing further
into metal particles. Besides this effect, interaction of the
tetrabutylammonium cation with the bromide or iodide
ligated to the palladium center gives rise to the formation
of ion pairs with a naked L2Pd80)±Br82)±NR481) which does
afford a more reactive palladium80) complex.3,22 Further-
more, the ammonium cation could electrostatically assist
the polarization or decomplexation of the bromide ion
The results obtained in the TBAB melt were consistently
higher than those obtained by us11 with the same catalyst or
by Herrmann et al.15,16 in coupling styrene and unsubstituted
acrylates with aryl bromides in DMA or DMF solvents. The
catalyst 1 is very stable to high temperatures, air and
moisture. This was due, as also found for Pd-complexes
with imidazolidene carbene as ligands,17 to the high binding
energy of benzothiazolidene ligands to the Pd center which
renders carbene decomplexation highly improbable.
Furthermore, 1 is probably more stable and ef®cient, in
ionic liquids,18 than the Pd-complexes with imidazolidene
ligands, with the latter requiring the addition of phosphanes
to be ef®cient.6,16,20 This stability in TBAB makes the
recycling process feasible. Indeed, in only 3 g of TBAB,
after three cycles, 8 g of bromobenzene were processed
with a total TON of around 1720 thus making the whole
process economically viable. Despite the observed bene-
®cial effects exerted by quaternary ammonium salts on the
Heck reaction, the exact nature of this in¯uence cannot be
ascribed to a single effect such as the high polarity or phase-
transfer ability,2e but rather to a superposition of several
factors. For example, Reetz et al.21 found that reduction of
a Pd salt in THF and in the presence of tetrabutylammonium
acetate or formate gave Pd-nanoparticles stabilized by the
large ammonium cation. Furthermore, Neghishi et al.22 and
Amatore and Jutand,3 demonstrated that Pd80)8PPh3)2, the
proposed catalyst in the Heck reaction, was unstable in
the absence of halide or acetate ions which transform
this complex into a more stable and catalytically active

Á
V. Calo et al. / Tetrahedron 57 02001) 6071±6077
6074
from the anionic Pd8II) pentacoordinated complex
deriving from oxidative addition
0E)-Ethyl 3-phenyl-3-0p-tolyl)-propenoate. 1H NMR d 1.11
8t, Jˆ7.1 Hz, 3H, CH3 ethyl), 2.35 8s, 3H, CH3 tolyl), 4.04
8q, Jˆ7.1 Hz, 2H, CH2 ethyl), 6.35 8s, 1H, vinyl proton),
7.11±7.14 8m, 2H, aromatic protons), 7.17±7.22 8m, 5H,
aromatic protons), 7.36±7.39 8m, 2H, aromatic protons);
13C NMR d 13.76, 20.99, 59.66, 116.32, 127.57, 128.05,
128.36, 128.90, 129.03 137.74, 138.98, 140.95, 156.27,
165.91; MS 8EI) m/z 267 8M111, 18), 266 8M1, 100),
265 815), 237 818), 222 815), 221 897), 195 818), 194 883),
193 832), 191 821), 179 845), 178 871), 165 820), 152 812),
120 836), 115 847), 105 827), 95 820), 91 824), 89 823), 82
820), 77 817), 55 814), 51 824).
81)
[L2PdArBr2]82)NR4
with aryl bromides and this would render the Pd8II)-
complex more electrophilic for a fast ole®n insertion. This
is conceivable since it was calculated, for analogous Pd-
complexes with imidazolidene carbenes ligands, that the
removal of bromide from the oxidative addition complex
of aryl bromides was a strongly endothermic process.17
In conclusion, while some aspects of the catalytic cycle
involving Pd-carbene complexes in ionic liquids are not
well understood, our results show that ionic liquids cannot
be considered as simple high polarity solvents but their
ef®cacy is due to several factors which are studied by us.
1
0Z)-Ethyl 3-phenyl-3-0p-tolyl)-propenoate. H NMR d 1.16
8t, Jˆ7.1 Hz, 3H, CH3 ethyl), 2.40 8s, 3H, CH3 tolyl), 4.07
8q, Jˆ7.1 Hz, 2H, CH2 ethyl), 6.328s, 1H, vinyl proton),
7.09±7.12 8m, 2H, aromatic protons), 7.17±7.22 8m, 5H,
aromatic protons), 7.29±7.32 8m, 2H, aromatic protons);
13C NMR d 14.11, 21.15, 60.21, 116.92, 127.81, 128.09,
128.36, 128.63, 129.12; 135.77, 139.36, 144.34, 156.54,
166.67; MS 8EI) m/z 267 8M111, 20), 266 8M1, 98), 265
812), 237 820), 222 812), 221 8100), 195 815), 194 879), 193
835), 191 820), 179 842), 178 874), 165 817), 152 812), 120
838), 115 847), 105 826), 95 815), 91 829), 89 821), 82 821),
77 815), 55 817), 51 823).
3. Experimental
1H- and 13C NMR were recorded in CDCl3 on a Bruker AM
500 MHz spectrometer and chemical shifts were reported in
ppm 8d). IR and MS spectra were performed, respectively,
on a Perkin±Elmer FT-1710 and on a Shimadzu QP5000
instruments. GC analyses were carried out on HP 5890A
capillary gas-chromatograph 8ZB-1, 30 m, 0.25 mm i.d.).
Tetrabutylammonium bromide was purchased from Fluka
and used as received. Palladium catalyst 1 was prepared
as previous reported11 and puri®ed by ¯ash cromatography
on silica gel 8eluent dichloromethane). The stereochemistry
and the NMR signal assignment of all new compounds were
secured by NOE experiments.
3.1.2. %E) and %Z) ethyl 3-phenyl-3-%p-methoxyphenyl)-
propenoate %3). This product was isolated as an oily
mixture of the two E/Z stereoisomers. IR 8liquid ®lm) n
3050, 2980, 2935, 1719, 1604, 1574, 1511, 1484, 1464,
1445, 1421, 1373, 1354, 1252, 1151, 1096, 1035, 875,
834, 796, 775, 700 cm21. The NMR signal assignment of
the two isomers was made by comparison of the mixture
spectral data with those reported in the literature.25
3.1. General procedure for the synthesis of bis-arylated
acrylates
0E)-Ethyl 3-phenyl-3-0p-methoxyphenyl)-propenoate. 1H
NMR d 1.128t, Jˆ7.1 Hz, 3H, CH3 ethyl), 3.79 8s, 3H,
OCH3), 4.05 8q, Jˆ7.1 Hz, 2H, CH2 ethyl), 6.34 8s, 1H,
vinyl proton), 6.84 8d, Jˆ8.9 Hz, 2H, aromatic protons),
7.20±7.24 8m, 1H, aromatic proton), 7.26 8d, Jˆ8.9 Hz,
2H, aromatic protons), 7.30±7.33 8m, 2H, aromatic
protons), 7.38±7.41 8m, 2H, aromatic protons); 13C NMR
d 13.65, 55.12, 59.68, 113.61, 115.21, 127.66, 128.92,
129.15, 129.57, 130.77, 139.12, 156.08, 160.62, 166.07;
MS 8EI) m/z 283 8M111, 18), 282 8M1, 100), 253 810),
238 814), 237 870), 211 818), 210 895), 209 821), 195 832),
194 821), 178 817), 166 824), 165 874), 152 811), 139 811),
135 855), 119 88), 105 827), 91 817), 89 815), 82 817), 77
818), 63 817), 51 820).
A pyrex reaction ¯ask was charged with tetrabutylammo-
nium bromide 83 g) and heated at 1308C. To the stirred
molten salt were added in strict order the catalyst
80.11 mmol), sodium formate 80.22 mmol), haloarene
817.5 mmol), sodium bicarbonate 819 mmol) and butyl
acrylate 87.6 mmol). The reaction was stirred at 1308C and
monitored by GLC until the disappearance of the mono-
arylated intermediate. When the ethyl cinnamate
85.7 mmol) was used as ole®n, the amounts of reagents
were: catalyst 80.09 mmol), sodium formate 80.18 mmol),
sodium bicarbonate 814.3 mmol), haloarene 88.6 mmol). In
this case, the reaction was stopped when ethyl cinnamate
had completely disappeared. After completion of the
reaction, the mixture was treated with aqueous HCl
830 ml) and extracted with 3£30 ml portions of diethyl
ether. The organic layer was dried on Na2SO4 and the
solvent evaporated under vacuum. The oily residue was
chromatographed on silica gel 8eluent petroleum ether/
ethyl acetate) to give the following puri®ed products:
0Z)-Ethyl 3-phenyl-3-0p-methoxyphenyl)-propenoate. 1H
NMR d 1.18 8t, Jˆ7.1 Hz, 3H, CH3 ethyl), 3.84 8s, 3H,
OCH3), 4.11 8q, Jˆ7.1 Hz, 2H, CH2 ethyl), 6.30 8s, 1H,
vinyl proton), 6.928d, Jˆ8.8 Hz, 2H, aromatic protons),
7.18 8d, Jˆ8.8 Hz, 2H, aromatic protons), 7.30±7.33 8m,
2H, aromatic protons), 7.34±7.37 8m, 1H, aromatic proton),
7.38±7.41 8m, 2H, aromatic protons); 13C NMR d 13.97,
55.01, 59.80, 113.06, 116.73, 127.81, 128.14, 128.38,
130.97, 132.93, 141.38, 156.38, 159.59, 166.07; MS 8EI)
m/z 283 8M111, 20), 282 8M1, 100), 253 811), 238 811),
237 873), 211 817), 210 894), 209 820), 195 829), 194 821),
178 815), 166 821), 165 874), 152 811), 139 811), 135 850),
105 833), 91 815), 89 817), 82810), 77 817), 63 818), 51 821).
3.1.1. %E) and %Z) ethyl 3-phenyl-3-%p-tolyl)-propenoate
%2). This product was isolated as an oily mixture of the two
E/Z stereoisomers. IR 8liquid ®lm) n 3058, 3047, 2959,
2972, 1723, 1639, 1610, 1522, 1511, 1447, 1370, 1310,
1288, 1163, 1114, 1095, 1041, 988, 878, 822, 772,
699 cm21. The NMR signal assignment of the two isomers
was made by comparison of the mixture spectral data with
those reported in the literature.25

Á
V. Calo et al. / Tetrahedron 57 02001) 6071±6077
6075
3.1.3. %E) and %Z) ethyl 3-phenyl-3-%p-acetylphenyl)-
propenoate %4). This product was isolated as a yellow,
oily mixture of the two E/Z stereoisomers.
3.1.5. %E) and %Z) ethyl 3-phenyl-3-%p-nitrophenyl)-
propenoate %6). This product was isolated as a yellow,
oily mixture of the two E/Z stereoisomers.
1
0E)-Ethyl 3-phenyl-3-0p-nitrophenyl)-propenoate. H NMR
0E)-Ethyl 3-phenyl-3-0p-acetylphenyl)-propenoate. 1H
NMR d 1.10 8t, Jˆ7.1 Hz, 3H, CH3 ethyl), 2.59 8s, 3H,
CH3CO), 4.05 8q, Jˆ7.1 Hz, 2H, CH2 ethyl), 6.40 8s, 1H,
vinyl proton), 7.15±7.20 8m, 2H, aromatic protons), 7.35±
7.40 8m, 5H, aromatic protons), 7.86±7.90 8m, 2H, aromatic
protons); 13C NMR d 13.89, 26.63, 60.23, 119.26, 127.99,
128.30, 128.36, 128.41, 129.00, 137.30, 138.23, 146.21,
154.87, 165.71, 197.43; IR 8liquid ®lm) n 3058, 2981,
2931, 2873, 1723, 1688, 1605, 1576, 1562, 1446, 1406,
1370, 1266, 1168, 1115, 1097, 1076, 1042, 958, 878, 839,
774, 701 cm21; MS 8EI) m/z 294 8M1, 27), 279 824), 265
82), 249 815), 223 86), 222 85), 207 822), 178 810), 152 85),
125 85), 117 82), 102 82), 89 85), 76 87), 63 82), 51 85), 43
8100).
d 1.10 8t, Jˆ7.1 Hz, 3H, CH3 ethyl), 4.06 8q, Jˆ7.1 Hz, 2H,
CH2 ethyl), 6.41 8s, 1H, vinyl proton), 7.15±7.20 8m, 2H,
aromatic protons), 7.36±7.41 8m, 3H, aromatic protons),
7.44 8d, Jˆ9.2Hz, 2H, aromatic protons), 8.16 8d,
Jˆ9.2Hz, 2H, aromatic protons); 13C NMR d 13.85,
60.41, 120.61, 123.55, 123.77, 128.17, 128.68, 128.95,
137.63, 147.03, 148.03, 153.49, 165.35; IR 8liquid ®lm) n
3110, 3065, 2989, 2935, 2968, 1719, 1630, 1590, 1530,
1475, 1440, 1411, 1342, 1263, 1174, 1110, 1077, 1032,
910, 855, 778, 760, 737, 698 cm21; MS 8EI) m/z 298
8M111, 12), 297 8M1, 67), 296 819), 280 84), 269 817),
268 827), 253 819), 252 8100), 236 82), 225 839), 224 819),
207 87), 206 812), 179 812), 178 858), 177 827), 176 834), 165
829), 152 824), 151 814), 115 84), 105 814), 102 816), 88 810),
76 827), 63 813), 51 824).
0Z)-Ethyl 3-phenyl-3-0p-acetylphenyl)-propenoate. 1H
NMR d 1.11 8t, Jˆ7.1 Hz, 3H, CH3 ethyl), 2.64 8s, 3H,
CH3CO), 4.06 8q, Jˆ7.1 Hz, 2H, CH2 ethyl), 6.428s, 1H,
vinyl proton), 7.23±7.27 8m, 2H, aromatic protons), 7.29±
7.38 8m, 5H, aromatic protons), 7.96±8.00 8m, 2H, aromatic
protons); 13C NMR d 13.97, 26.60, 60.20, 117.94, 127.95,
128.05, 128.50, 129.27, 129.68, 136.46, 139.81, 144.10,
155.48, 165.65, 197.65; IR 8liquid ®lm) n 3070, 2981,
2925, 2870, 1723, 1688, 1612, 1570, 1562, 1446, 1370,
1263, 1168, 1115, 1089, 1076, 1042, 960, 878, 839, 770,
703 cm21; MS 8EI) m/z 294 8M1, 29), 279 829), 265 82), 249
815), 223 87), 222 87), 207 824), 178 811), 152 85), 125 85),
117 82), 102 82), 89 85), 76 88), 63 82), 51 85), 43 8100).
0Z)-Ethyl 3-phenyl-3-0p-nitrophenyl)-propenoate. Yellow
1
oil, H NMR d 1.15 8t, Jˆ7.1 Hz, 3H, CH3 ethyl), 3.89 8q,
Jˆ7.1 Hz, 2H, CH2 ethyl), 6.46 8s, 1H, vinyl proton), 7.24
8d, Jˆ7.2, Hz, 2H, aromatic protons), 7.33±7.39 8m, 5H,
aromatic protons), 8.24 8d, Jˆ9.0 Hz, 2H, aromatic
protons); 13C NMR d 13.94, 60.37, 118.52, 123.16,
127.93, 128.65, 128.95, 129.96, 139.12, 145.97, 147.36,
154.31, 165.32; IR 8liquid ®lm) n 3107, 3080, 2992, 2937,
2972, 1719, 1631, 1598, 1530, 1492, 1477, 1445, 1411,
1343, 1263, 1173, 1110, 1077, 1036, 912, 856, 777, 760,
737, 700 cm21; MS 8EI) m/z 298 8M111, 13), 297 8M1, 67),
296 822), 280 82), 269 814), 268 825), 253 818), 252 8100),
236 84), 225 839), 224 822), 207 87), 206 812), 179 814), 178
863), 177 827), 176 834), 165 827), 152 823), 151 817), 115
85), 105 812), 102 817), 88 810), 76 824), 63 812), 51 824).
3.1.4. %E) and %Z) ethyl 3-phenyl-3-%1-naphthyl)-
propenoate %5). This product was isolated as an oily
mixture of the two E/Z stereoisomers. IR 8liquid ®lm) n
3057, 2979, 1723, 1615, 1592, 1576, 1506, 1463, 1445,
1368, 1271, 1254, 1197, 1164, 1065, 1046, 1027, 973,
3.2. Ethyl 3-phenyl-3-%p-cyanophenyl)-propenoate %7)
957, 878, 797, 778 cm21
.
This product was isolated as a yellow, oily mixture of the
two E/Z stereoisomers.
1
0E)-Ethyl 3-phenyl-3-01-naphtyl)-propenoate. H NMR d
0.87 8t, Jˆ7.1 Hz, 3H, CH3 ethyl), 3.90 8q, Jˆ7.1 Hz, 2H,
CH2 ethyl), 6.79 8s, 1H, vinyl proton), 7.26±8.02 8m, 12H,
aromatic protons); 13C NMR d 13.50, 59.73, 119.22,
125.02, 125.61, 125.87, 126.06, 127.35, 127.70, 128.15,
128.44, 128.83, 129.38, 131.47, 133.29, 136.81, 139.79,
154.42, 165.54; MS 8EI) m/z 3028M 1, 14), 273 83), 257
86), 255 85), 239 82), 230 818), 229 8100), 228 873), 227 814),
226 815), 215 82), 202 88), 189 82), 167 82), 152 86), 151 82),
127 85), 114 812), 113 815), 101 88), 88 83), 77 85), 63 82), 51
86).
1
0E)-Ethyl 3-phenyl-3-0p-cyanophenyl)-propenoate. Oil. H
NMR d 1.10 8t, Jˆ7.1 Hz, 3H, CH3 ethyl), 4.06 8q,
Jˆ7.1 Hz, 2H, CH2 ethyl), 6.39 8s, 1H, vinyl proton),
7.15±719 8m, 2H, aromatic protons), 7.36±7.40 8m, 5H,
aromatic protons), 7.59 8d, Jˆ8.2Hz, 2H, aromatic
protons); 13C NMR d 13.88, 60.38, 112.74, 118.39,
120.12, 128.15, 128.61, 128.77, 128.00, 132.14, 137.69,
145.18, 153.95, 165.46; IR 8liquid ®lm) n 3058, 2980,
2934, 2873, 2228, 1719, 1621, 1575, 1556, 1504, 1492,
1465, 1446, 1409, 1392, 1370, 1266, 1170, 1117, 1096,
1075, 1035, 1001, 973, 925, 891, 840, 776, 701 cm21; MS
8EI) m/z 278 8M111, 12), 277 8M1, 55), 276 812), 248 822),
233 819), 232 8100), 218 82), 205 841), 204 864), 203 846),
190 810), 177 819), 176 824), 151 810), 125 87), 110 814), 105
814), 88 816), 77 819), 63 85), 51 836).
1
0Z)-Ethyl 3-phenyl-3-01-naphtyl)-propenoate. H NMR d
1.23 8t, Jˆ7.1 Hz, 3H, CH3 ethyl), 4.20 8q, Jˆ7.1 Hz, 2H,
CH2 ethyl), 6.27 8s, 1H, vinyl proton), 7.26±8.02 8m, 12H,
aromatic protons); 13C NMR d 13.91, 60.16, 121.31,
124.94, 125.32, 125.77, 126.27, 127.06, 127.92, 128.22,
128.38, 128.78, 129.38, 131.03, 133.70, 139.27, 139.74,
155.04, 166.15; MS 8EI) m/z 3028M 1, 12), 273 83), 257
86), 255 85), 239 82), 230 817), 229 8100), 228 876), 227 812),
226 817), 215 82), 202 89), 189 82), 167 82), 152 88), 151 88),
127 83), 114 812), 113 812), 101 89), 88 82), 77 85), 63 82), 51
86).
1
0Z)-Ethyl 3-phenyl-3-0p-cyanophenyl)-propenoate. Oil. H
NMR d 1.13 8t, Jˆ7.1 Hz, 3H, CH3 ethyl), 4.04 8q,
Jˆ7.1 Hz, 2H, CH2 ethyl), 6.43 8s, 1H, vinyl proton),
7.20±724 8m, 2H, aromatic protons), 7.29±7.38 8m, 5H,
aromatic protons), 7.67 8d, Jˆ8.1 Hz, 2H, aromatic

Á
V. Calo et al. / Tetrahedron 57 02001) 6071±6077
6076
protons); 13C NMR d 13.97, 60.33, 111.80, 118.40, 118.69,
128.00, 128.65, 129.82, 129.92, 131.70, 139.31, 143.99,
154.60, 165.40; IR 8liquid ®lm) n 3060, 2981, 2936, 2873,
2228, 1719, 1619, 1575, 1556, 1503, 1492, 1465, 1448,
1409, 1392, 1370, 1266, 1173, 1118, 1096, 1076, 1032,
1003, 972, 926, 893, 841, 774, 702 cm21; MS 8EI) m/z
278 8M111, 13), 277 8M1, 56), 276 812), 248 824), 233
818), 232 8100), 218 84), 205 840), 204 864), 203 846), 190
811), 177 822), 176 823), 151 811), 125 88), 110 812), 105
812), 88 815), 77 819), 63 85), 51 840).
Jˆ6.4 Hz, 2H, CH2 butyl), 6.58 8s, 1H, vinyl proton),
7.29±7.55 8m, 8H, aromatic protons), 7.77±7.90 8m, 4H,
aromatic protons), 8.04 8d, Jˆ8.8 Hz, 1H, aromatic
protons), 8.47 8d, Jˆ8.8 Hz, 1H, aromatic protons); 13C
NMR d 13.52, 18.75, 30.11, 64.11, 125.01, 125.16,
125.23, 125.68, 125.89, 126.13, 126.40, 126.77, 127.04,
127.26, 127.80, 128.26, 128.41, 128.65, 128.96, 129.84,
130.69, 131.35, 134.11, 138.51, 139.48, 152.43, 165.99;
IR 8liquid ®lm) n 3056, 2959, 2872, 1724, 1613, 1591,
1562, 1507, 1464, 1379, 1278, 1217, 1187, 1163, 1061,
1023, 957, 866, 779, 738 cm21; MS 8EI) m/z 380 8M1,
15), 341 89), 323 88), 306 89), 305 829), 289 811), 281
811), 280 818), 279 885), 278 889), 277 862), 276 845), 274
89), 265 88), 264 811), 263 812), 252 815), 196 815), 152 815),
138 824), 128 833), 112 83), 96 85), 73 839), 57 818), 41
8100). Anal. Calcd for C27H24O2: C, 85.23; H, 6.36.
Found: C, 85.28; H, 6.35.
1
3.2.1. Butyl 3,3-diphenyl-propenoate %8). Yellow oil. H
NMR d 0.85 8t, Jˆ7.4 Hz, 3H, CH3 butyl), 1.21 8sextet,
Jˆ7.4 Hz, 2H, CH2 butyl), 1.40±1.48 8m, 2H, CH2 butyl),
3.99 8t, Jˆ6.6 Hz, 2H, CH2 butyl), 6.36 8s, 1H, vinyl
proton), 7.18±7.25 8m, 2H, aromatic protons), 7.26±7.39
8m, 8H, aromatic protons);13C NMR d 13.61, 19.01,
30.44, 63.99, 117.51, 127.80, 127.99, 128.19, 128.29,
129.05, 129.29, 131.47, 140.78, 156.22, 166.23; IR 8liquid
®lm) n 3058, 3026, 2959, 2976, 1723, 1617, 1576, 1493,
1446, 1265, 1164, 1064, 1032, 772, 698 cm21; MS 8EI) m/z
280 8M1, 19), 224 848), 223 852), 207 884), 180 838), 179
876), 178 8100), 167 840), 152821), 105 831), 89 819), 77
817), 51 835), 41 841). Anal. Calcd for C19H20O2: C, 81.39;
H, 7.19. Found: C, 81.45; H, 7.22.
Acknowledgements
This work was in part ®nancially supported by
Á
Ministero dell'Universita e della Ricerca Scienti®ca e
Tecnologica, Rome, and the University of Bari 8National
Project: `Stereoselezione in Sintesi Organica: Metodologie
ed Applicazioni').
3.2.2. Butyl 3,3-di-p-tolyl-propenoate %9). Oil. 1H NMR d
0.85 8t, Jˆ7.3 Hz, 3H, CH3 butyl), 1.18±1.27 8m, 2H, CH2
butyl), 1.41±1.50 8m, 2H, CH2 butyl), 2.34 8s, 3H, CH3
tolyl), 2.38 8s, 3H, CH3 tolyl), 3.99 8t, Jˆ6.6 Hz, 2H, CH2
butyl), 6.29 8s, 1H, vinyl proton), 7.06±7.38 8m, 8H,
aromatic protons); 13C NMR d 13.64, 19.04, 21.16, 21.28,
30.50, 63.87, 116.21, 128.22, 128.47, 128.96, 129.08,
130.71, 137.78, 138.24, 139.45, 156.59, 166.41; IR 8liquid
®lm) n 3025, 2959, 2872, 1723, 1606, 1568, 1510, 1456,
1265, 1162, 1069, 1013, 821, 804, 730, cm21; MS 8EI) m/z
308 8M1, 65), 252 873), 251 848), 235 8100), 208 887), 193
848), 191 846), 190 843), 189 843), 165 816), 119 863), 115
840), 91 824), 65 814), 41 843). Anal. Calcd for C21H24O2: C,
81.78; H, 7.84. Found: C, 81.82; H, 7.86.
References
1. Heck, R. F. J. Am. Chem. Soc. 1968, 90, 5518±5526.
2. 8a) de Meijer, A.; Meyer, F. E. Angew. Chem. 1994, 106,
2473±2506 Angew. Chem., Int. Ed. Engl. 1994, 33, 2379±
2411. 8b) Cabri, W.; Candiani, I. Acc. Chem. Res. 1995, 28,
2±7. 8c) Crisp, G. T. Chem. Soc. Rev. 1998, 27, 427±436.
8d) Genet, J. P.; Savignac, M. J. Organomet. Chem. 1999,
576, 305±317. 8e) Beletskaya, I. P.; Cheprakov, A. V.
Chem. Rev. 2000, 100, 3009±3066.
3. For a recent mechanistic study on Heck reaction see: Amatore,
C.; Jutand, A. J. Organomet. Chem. 1999, 576, 254±278.
4. Arcadi, A.; Cacchi, S.; Fabrizi, G.; Pace, P. Tetrahedron 1996,
52, 6983±6996.
3.2.3. Butyl 3,3-di-%4-methoxyphenyl)-propenoate %10).
1
Yellow oil, H NMR d 0.86 8t, Jˆ7.4 Hz, 3H, CH3 butyl),
1.20±1.29 8m, 2H, CH2 butyl), 1.45±1.528m, 2H, CH
butyl), 3.79 8s, 3H, OCH3), 3.828s, 3H, OCH ), 4.00 8t,
5. Beller, M.; Riermeier, T. H. Tetrahedron Lett. 1996, 37,
6535±6538.
Á
6. Moreno-ManÄas, M.; Perez, M.; Pleixats, R. Tetrahedron Lett.
2
3
Jˆ6.6 Hz, 2H, CH2 butyl), 6.22 8s, 1H, vinyl proton), 6.82
8d, Jˆ9.0 Hz, 2H, aromatic protons), 6.89 8d, Jˆ8.8 Hz, 2H,
aromatic protons), 7.13 8d, Jˆ8.8 Hz, 2H, aromatic
protons), 7.23 8d, Jˆ9.0 Hz, 2H, aromatic protons); 13C
NMR d 13.64, 19.07, 30.56, 55.09, 55.25, 63.78, 113.15,
113.61, 114.94, 115.64, 129.90, 130.75, 131.26, 132.14,
156.10, 160.65, 166.54; IR 8liquid ®lm) n 3037, 3001,
2958, 2873, 2837, 1718, 1600, 1510, 1490, 1462, 1420,
1248, 1149, 1034, 871, 833, 781, 749 cm21; MS 8EI) m/z
340 8M1, 37), 284 819), 267 832), 240 865), 225 833), 209
816), 181 89), 190 843), 165 813), 153 814), 152821), 135
8100), 121 89), 107 87), 89 87), 77 88), 55 87), 41 840). Anal.
Calcd for C21H24O4: C, 74.09; H, 7.11. Found: C, 74.16; H,
7.13.
1996, 37, 7449±7452.
7. GuÈrtler, C.; Buchwald, S. L. Chem. Eur. J. 1999, 5, 3107±
3112.
8. Almansa, C.; Gomez, L. A.; Cavalcanti, F. L.; de Arriba, A. F.;
 Â
Rodrõguez, R.; Carceller, E.; Garcõa-Rafanell, J.; Forn, J.
Â
J. Med. Chem. 1996, 39, 2197±2206.
9. For example: Himmelsback, F.; Pieper, H.; Austel, V.; Linz,
G.; Guth, B.; Mueller, T.; Weisemberger, J. 8Dr Karl Thomae
Gmbh), Eur. Pat. EP 612,741, 1994. Chem. Abstr. 1995, 122,
314547p.
10. Kadin, S. B. 8P®zer Inc.) US Pat. US 4, 342,781 1982; Chem.
Abstr. 1982, 97, 215790w.
Á
11. Calo, V.; Del Sole, R.; Nacci, A.; Schingaro, E.; Scordari, F.
Eur. J. Org. Chem. 2000, 869±871.
1
3.2.4. Butyl 3,3-di-%1-naphtyl)-propenoate %11). Oil, H
12. For the ®rst palladium complex with benzothiazolidene
ligands see: Cardin, D. J.; Cetinkaya, D.; Cetinkaya, E.;
Lappert, M. F. J. Chem. Soc., Dalton Trans. 1973, 514±522.
NMR d 0.70 8t, Jˆ7.3 Hz, 3H, CH3 butyl), 0.86±0.96 8m,
2H, CH2 butyl), 1.06±1.14 8m, 2H, CH2 butyl), 3.828t,

Á
V. Calo et al. / Tetrahedron 57 02001) 6071±6077
6077
Á
13. Calo, V.; Nacci, A.; Lopez, L.; Mannarini, N. Tetrahedron
Lett. 2000, 41, 8973±8976.
19. Xu, L.; Chen, W.; Xiao, J. Organometallics 2000, 19, 1123±
1127.
14. For a review on ionic liquids as solvents see: Welton, T. Chem.
Rev. 1999, 99, 2071±2083; Seddon, K. R. Ionic Liquid Rev.
8WWW version:http://www.ch.qub.ac.uk/krs/krs.html).
20. Carmaichael, A. J.; Earle, M. J.; Holbrey, J. D.; Seddon, K. R.
Org. Lett. 1999, 1, 997±1000.
21. 8a) Reetz, M. T.; Maase, M. Adv. Mater. 1999, 11, 773±777.
8b) Reetz, M. T.; Westermann, E. Angew. Chem., Int. Ed.
Engl. 2000, 39, 165±168.
È
15. Herrmann, W. H.; Elison, M.; Fisher, J.; Kocher, K.; Artus,
G. R. J. Angew. Chem. 1995, 107, 2602 Angew. Chem., Int. Ed.
Engl. 1995, 34, 2371±2374.
22. Neghishi, E.-I.; Takahashi, T.; Akiyoshi, K. J. Chem. Soc.,
Chem. Commun. 1986, 1338±1339.
È
23. Herrmann, W. H.; Brossmer, C.; Ofele, K.; Reisinger, C.-P.;
È
16. 8a) Weskamp, T.; Bohm, V. P. W.; Herrmann, W. A.
J. Organomet. Chem. 1999, 585, 348. 8b) Bohm, V. P. W.;
È
Priermeier, T.; Beller, M.; Fisher, H. Angew. Chem., Int. Ed.
Engl. 1995, 34, 1844±1448.
Herrmann, W. A. Chem. Eur. J. 2000, 6, 1017±1025.
È
17. Albert, K.; Gisdakis, P.; Rosch, N. Organometallics 1998, 17,
1608±1616.
24. Yu, J.; Spencer, J. B. Chem. Eur. J. 1999, 5, 2237±2240.
25. Kamigata, N.; Satoh, A.; Yoshida, M. Phosphorus Sulfur
Silicon 1989, 46, 121±129.
18. McGuinnes, D. S.; Cavell, K. J.; Skelton, B. W.; White, A. H.
Organometallics 1999, 18, 1596±1605.