A straightforward synthesis of symmetrical polyendiynes by dimerization reactions of silyl derivatives

Article abstract of DOI:10.1016/S0022-328X(98)00724-4

A straightforward synthesis of polyendiynes is described. The method is based upon a simple dimerization reaction of silylated enynes in the presence of copper salts. A variety of polyunsaturated compounds have been obtained in high yields and with high retention of configuration.

Full text of DOI:10.1016/S0022-328X(98)00724-4

Journal of Organometallic Chemistry 566 (1998) 251–257
A straightforward synthesis of symmetrical polyendiynes by
dimerization reactions of silyl derivatives
Francesco Babudri, Vito Fiandanese *, Giuseppe Marchese, Angela Punzi
Dipartimento di Chimica, Uni6ersita` di Bari, Centro CNR di Studio sulle Metodologie Inno6ati6e di Sintesi Organiche, 6ia Amendola 173,
70126 Bari, Italy
Received 16 April 1998
Abstract
A straightforward synthesis of polyendiynes is described. The method is based upon a simple dimerization reaction of silylated
enynes in the presence of copper salts. A variety of polyunsaturated compounds have been obtained in high yields and with high
retention of configuration. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Silicon and compounds; Dimerization; Diynes
1. Introduction
In connection with this type of synthetic work, we
considered of interest to investigate on the reactivity of
other bis-silylated system, presenting different type of
unsaturations, toward sulfur electrophiles.
In our previous studies dealing with the synthesis of
stereo-defined conjugated polyenes [1–13] we reported
a synthetic methodology based upon the chemoselective
acylation of dienyl and trienyl bis-silylated systems [2].
The procedure was successfully applied to the synthesis
of a series of natural compounds having a conjugated
polyene structure [3–7].
Furthermore, during our investigation, we employed
electrophiles different from acyl chlorides, in order to
obtain several polyfunctional polyenyl compounds. In
this respect, we found that (all E) 1,4-bis(trimethylsi-
lyl)-1,3-butadiene and 1,6-bis(trimethylsilyl)-1,3,5-hexa-
triene react with PhSCl and PhSCOCl [8] affording
conjugated dienyl and trienyl monosilylated sulfides
and thioesters, compounds presenting both silicon and
sulfur functionalities, which are synthetically useful.
Accordingly, we have reacted (E)-1,4-bis-(trimethylsi-
lyl)-3-buten-1-yne [11,14] 1 with PhSSPh in the presence
of CaCO3 and CuOTf, as described in a recent work
[15], with the aim of performing a chemoselective sub-
stitution, on the triple bond, of the trimethylsilyl group
with the phenylthio group. Surprisingly, as a result we
have not observed the formation of the expected
monosilylated sulfide, but the formation of a different
product, which, after appropriate analysis (GC/MS,
1H-NMR) revealed to be the dimeric product 2, accord-
ing to the Eq. 1. It seemed evident that this reaction
was not affected by the presence of PhSSPh. Indeed,
repeating the same reaction without PhSSPh, we have
obtained equally compound 2 in 64% yield.
* Corresponding author.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00724-4

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F. Babudri et al. / Journal of Organometallic Chemistry 566 (1998) 251–257
It is well known that symmetrical conjugated diynes
configuration. Indeed, for compounds 3,7–11 the ob-
served E/Z ratio was ]98%, as ascertained by GC
analysis, whereas only the bis-silylated hexadienyne 12
(entry 7) was obtained in low yield (36%) and with a
lower stereochemical purity (3E,5E/3Z,5E=80/20)
(1H-NMR analysis).
Due to the availability of these substrates, we carried
out the reactions of silylated enynes with CuOTf and in
the presence of an excess of CaCO3, in refluxing
THF:dioxane (1:1), obtaining the corresponding
polyendiynes in fair to good yields (Table 2). Indeed,
with this procedure, we have been able to synthesize
aryl polyenynes (entries 2–4, products 4, 13 and 14,
33–65% yields), alkyl derivatives (entries 5–7, products
15–17, 46–52% yields, with product 17 presenting six
are generally synthesized by oxidative dimerization of
terminal acetylenes in the presence of a tertiary amine
and copper salts, CuI [16], CuCl [17] or Cu(OAc)2 [18],
by self-coupling reactions of arylacetylenes in the pres-
ence of Pd(0)–CuI [19], or, more recently, by catalyzed
Pd(II)–CuI self-coupling of terminal aryl- and alky-
lacetylenes [20].
Nevertheless, this direct dimerization of terminal sily-
lated alkynes prompted us to investigate on the possi-
bility of employing other silylated enynes, with the aim
of synthesizing polyfunctional polyendiynes. Thus,
when we subjected compound 3 to the dimerization
reaction, we obtained the expected dimer 4 in 65% yield
(Eq. 2):
In order to extend the synthetic utility of this
methodology, we started to perform the synthesis of a
series of mono-silylated enynes and now we wish to
report their successfully utilization in the dimerization
reaction.
unsaturations) and also a bis-silylated conjugated di-
endiyne (entry 1, product 2, 64% yield), together with a
bis-silylated tetraendiyne (entry 8, product 18, 63%
yield). All these dimers, apart from compound 18, were
obtained with high retention of configuration (]95%,
as ascertained by 1H-NMR analysis). In the case of
compound 18, a predominant isomer was obtained,
with all E configuration, together with other isomers,
due to the low stereochemical purity of the starting
dienyne 12.
2. Results and discussion
There are a number of methods available for the
stereoselective synthesis of mono-silylated enynes, in-
cluding coupling reactions of trimethylsilylacetylene
with vinyl halides [21] in the presence of a Pd(II)
catalyst, coupling reactions of trimethylsilylethynyl zinc
halides [22,23], in the presence of a Pd(0) catalyst, with
the appropriate vinyl halides or the Wittig reaction [24].
However, we have developed a direct and general syn-
thethic approach to a wide range of silylated enynes.
Our methodology is based upon the coupling reac-
tion of the readily available (E)-1-chloro-2-phenylth-
ioethene 5 [25] with trimethylsilylacetylene in the
presence of Pd(0) [26] to afford (E)-4-phenylthio-1-
trimethylsilyl-3-buten-1-yne 6 in 89% yield [10]. This
compound represents the key intermediate for the syn-
thesis of enynes. Indeed it is sufficient to react com-
pound 6 with a series of Grignard reagents in the
presence of NiCl2(dppe) as a catalyst to obtain the
desired products (Scheme 1):
By inspection of the above results, it is clear that our
procedure could be applied, in principle, to any type of
functionalized silylated enyne, in spite of a few disap-
pointing yields.
However, while this work was in progress, a recent
study appeared [27] in which was realized the synthesis
of polyynes, starting from aryl ethynyl and butadiynyl
trimethylsilanes, by one-pot desilylation/dimerization
procedure. Thus, in order to compare the two methods,
we decided to repeat all the reactions in the conditions
reported in the cited study. These new conditions re-
quired a different copper salt, Cu(OAc)2, and K2CO3,
both present in a significant excess (30–40 equivalents),
and a different solvent (pyridine/methanol 1/1). We
found that in all cases examined, (Table 3), including
also the dimerization reaction of compound 6 (entry 3),
the dimers were obtained with the same stereochemical
purity and that there was an increase of the yields.
However, it is noteworthy that our procedure is opera-
tionally simpler than the reported method, due to very
mild reaction conditions. Indeed, it is not necessary a
The experimental results are reported in Table 1. The
mono-silylated enynes were obtained in high yields
(entries 1–6, 75–96% yields) and with high retention of
Scheme 1.

F. Babudri et al. / Journal of Organometallic Chemistry 566 (1998) 251–257
253
Table 1
Synthesis of silylated enynes and dienynes
a The stereochemical purity of compounds 3 and 7–11 was ]98% (E/Z ratio). For compounds 12 3E, 5E/3Z, 5E=80/20.
b Yields refer to products purified by flash chromatography; all compounds exhibited spectral data consistent with the assigned structure.
significant excess of reagent (only 0.6 equivalent of
(CuOTf).2benzene, instead of 40 equivalents of
Cu(OAc)2) and shorter reaction times (15 h, instead of
1–3 days) are required.
In conclusion, the procedure described here should
provide various stereodefined conjugated polyendiynes
with high stereospecificity. Moreover, the ready
availability of functionalized enynes, together with the
simplicity of the operations involved, are further attrac-
tive features of this methodology, which appears to be
superior or competitive with the existing methods.
3. Experimental details
Merck silica gel (60, particle size 0.040–0.063 mm)
for flash column chromatography and Merck plastic
sheets with silica gel 60 F254 for TLC were used. GC
analysis was performed on a Hewlett-Packard 5890
series II gas chromatograph equipped with a SE-30
(methylsilicone, 30 m×0.25 mm id) capillary column.
GC/mass-spectrometry analysis was performed on a
Hewlett-Packard 5970A equipped with an HP-1 capil-
lary column, 25 m, and HP MSD 5970B. 1H-NMR

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F. Babudri et al. / Journal of Organometallic Chemistry 566 (1998) 251–257
Table 2
Synthesis of polyendiynes by dimerization reactions with CuOTf
a Yields refer to products purified by flash chromatography; all compounds exhibited spectral data consistent with the assigned structure.
b Product 18 was obtained as a mixture of isomers (all E isomer was predominant).
spectra were recorded in deuterochloroform on a Bruker
AM 500 spectrometer at 500 MHz and on a Bruker AM
300 spectrometer at 300 MHz. Elemental analyses were
recorded on a Carlo Erba EA1108 elemental analyzer.
The products were purified by flash chromatography, by
distillation with a Kugelrohr apparatus Bu¨chi GKR-51
or by crystallization. Petroleum ether 40–70°C was used
as eluent for chromatography. Melting points (uncor-
rected) were determined on a Reichert microscope.
ture, under nitrogen, to a stirred mixture of (E)-1-
bromo-2-trimethylsilylethene (3.32 g, 18.53 mmol),
n-butylamine (2.03 g, 27.80 mmol), CuI (0.177 g, 0.93
mmol) and Pd(PPh3)4 (0.323 g, 0.28 mmol) in benzene
(30 ml). The reaction mixture was stirred for 1 h,
quenched with saturated aqueous NH4Cl and extracted
with ethyl acetate. The organic extracts were dried over
anhydrous Na2SO4 and concentrated under vacuum.
The residue was purified by distillation (Kugelrohr oven
temperature 70°C/1 mmHg) affording 2.91 g (80% yield)
of 1 as a colorless oil [11]. 1H-NMR (500 MHz, CDCl3):
l 0.05 (s, 9H), 0.16 (s, 9H), 5.94 (d, J=19.3 Hz, 1H),
6.49 (d, J=19.3 Hz, 1H) ppm. MS m/e 196 (M+, 17),
181 (100), 155 (67), 141 (10), 123 (16), 122 (15), 97 (21),
83 (13), 73 (53), 70 (9).
3.1. Preparation of products 1 and 6
3.1.1. (3E)-1,4-Bis(trimethylsilyl)-3-buten-1-yne (1)
A solution of ethynyltrimethylsilane (1.82 g, 18.53
mmol) in benzene (25 ml) was added at room tempera-

F. Babudri et al. / Journal of Organometallic Chemistry 566 (1998) 251–257
255
Table 3
Synthesis of polyendiynes by dimerization reactions with Cu(OAc)2
a Yields refer to products purified by flash chromatography.
3.1.2. (3E)-4-Phenylthio-1-trimethylsilyl-3-buten-1-yne
(6)
3.2. General procedure for the synthesis of
mono-silylated enynes
A solution of ethynyltrimethylsilane (1.42 g, 14.47
mmol) in benzene (20 ml) was added at room tempera-
ture, under nitrogen, to a mixture of (E)-1-phenylthio-
2-chloroethene 5 (2.47 g, 14.47 mmol), n-butylamine
(1.59 g, 21.70 mmol), CuI (0.137 g, 0.72 mmol) and
Pd(PPh3)4 (0.254 g, 0.22 mmol) in benzene (30 ml). The
reaction mixture was stirred for 3 h (reaction comple-
tion), quenched with saturated aqueous NH4Cl and
extracted with ethyl acetate. The organic extracts were
dried over anhydrous Na2SO4 and concentrated under
vacuum. The residue was purified by distillation
(Kugelrohr oven temperature 175°C/1 mmHg) leading
to compound 6 as a yellow oil (2.99 g, 89%). The
spectral data are in according with those reported [10].
A freshly prepared THF solution of Grignard
reagent (three equivalents) was added at room tempera-
ture, under nitrogen, to a stirred THF solution of 6
(one equivalent) and NiCl2 (dppe) (0.09 equivalents).
After reaction completion (15 h), the mixture was
quenched with saturated aqueous NH4Cl and extracted
with ethyl acetate. The organic extracts were dried
(Na2SO4) and concentrated. The crude material was
purified by flash chromatography leading to com-
pounds 3 [22], 7 [22], 8 [21], 9 [24], 10 [23], 11 and 12.
The spectral and physical data of unknown compounds
are as follows.

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F. Babudri et al. / Journal of Organometallic Chemistry 566 (1998) 251–257
3.2.1. (3E)-1-Trimethylsilyl-3,7-octadien-1-yne (11).
Compound 11 was prepared from 6 (0.5 g, 2.16
mmol) in accordance with general procedure. Purifica-
tion by flash chromatography (petroleum ether) gave 11
3.4.1. (1E, 7E)-1,8-Bis(trimethylsilyl)-1,7-octadien-3,5-
diyne (2)
Product 2 was obtained from 1 (0.2 g, 1.02 mmol) as
a pale yellow oil, after purification by flash chromatog-
1
1
(0.288 g, 75% yield) as a colorless oil. H-NMR (500
raphy (petroleum ether) (0.108 g, 86% yield). H-NMR
MHz, CDCl3): l 0.16 (s, 9H), 2.10–2.22 (m, 4H),
4.95–5.04 (m, 2H), 5.51 (dt, J=15.9, 1.6 Hz, 1H), 5.77
(ddt, J=17.0, 10.3, 6.4 Hz, 1H), 6.19 (dt, J=15.9, 6.7
Hz, 1H) ppm. MS m/e 178 (M+, 8), 164 (17), 163
(100), 137 (11), 135 (11), 122 (26), 109 (32), 107 (20), 95
(16), 83 (25), 73 (38), 59 (98).
(500 MHz, CDCl3): l 0.07 (s, 18H), 5.98 (d, J=19.0
Hz, 2H), 6.61 (d, J=19.0 Hz, 2H) ppm. MS m/e 246
(M+, 22), 231 (51), 205 (51), 179 (19), 173 (10), 147
(12), 145 (10), 131 (17), 123 (18), 83 (10), 73 (100), 59
(49). Elemental analysis: Found C, 67.98; H, 8.87.
Calculated for C14H22Si2: C, 68.21; H, 9.00.
3.2.2. 1,6-Bis(trimethylsilyl)-3,5-hexadien-1-yne (12)
Compound 12, as a mixture of two isomers, (3E,
5E/3Z, 5E=80/20), was prepared from 6 (0.5 g, 2.15
mmol), in accordance with general procedure, and ob-
tained as a colorless oil in 36% yield (0.172 g) after flash
chromatography (petroleum ether).
3.4.2. (1E, 7E)-1,8-Diphenyl-1,7-octadien-3,5-diyne (4)
Product 4 was prepared from 3 (0.1 g, 0.5 mmol).
Purification by flash chromatography (petroleum ether/
AcOEt 9.5/0.5) afforded 4 as a pale yellow solid (m.p.
135–136°C; lit. 135–135.5°C) [28] (0.052 g, 82% yield).
1H-NMR (500 MHz, CDCl3): l 6.26 (d, J=16.0 Hz,
2H), 7.09 (d, J=16.0 Hz, 2H), 7.27–7.42 (m, 10H)
ppm. MS m/e 254 (M+, 59), 253 (67), 252 (100), 250
(24), 239 (8), 226 (9), 151 (8), 150 (11), 139 (31), 126
(27), 125 (11), 115 (21), 113 (15). Elemental analysis:
Found C, 94.37; H, 5.48; calculated for C20H14: C,
94.45; H, 5.55.
(3E, 5E)-isomer-1H-NMR data (500 MHz, CDCl3): l
0.06 (s, 9H), 0.17 (s, 9H), 5.60 (d, J=15.5 Hz, 1H),
5.97 (dd, J=18.1, 0.7 Hz, 1H), 6.48 (dd, J=18.1, 10.4
Hz, 1H), 6.59 (ddd, J=15.5, 10.4, 0.7 Hz, 1H) ppm.
MS; m/e 222 (M+, 14), 207 (34), 192 (8), 191 (39), 175
(6), 163 (6), 149 (53), 135 (19), 133 (18), 119 (10), 83
(16), 73 (100), 59 (38).
(3Z, 5E)-isomer-1H-NMR data (500 MHz, CDCl3): l
0.09 (s, 9H), 0.20 (s, 9H), 5.44 (d, J=10.6 Hz, 1H),
6.07 (d, J=18.5 Hz, 1H), 6.39 (dt, J=10.6, 0.9 Hz,
1H), 7.06 (ddd, J=18.5, 10.6, 0.9 Hz, 1H). MS m/e 222
(M+, 5), 207 (16), 192 (17), 191 (84), 175 (7), 163 (5),
149 (45), 135 (23), 133 (18), 119 (17), 83 (13), 73 (100),
59 (28).
3.4.3. (1E, 7E)-1,8-Bis(2-thienyl)-1,7-octadien-3,5-
diyne (13)
Product 13 was prepared from 7 (0.1 g, 0.485 mmol)
and purified by flash chromatography (petroleum ether/
AcOEt 9.5/0.5) (0.063 g, 97% yield). The residual solid
was washed with ethyl acetate giving yellow crystals of
1
13 (m.p. 150–151°C). H-NMR (500 MHz, CDCl3): l
6.04 (d, J=15.7 Hz, 2H), 6.96–7.08 (m, 4H), 7.16 (d,
J=15.7 Hz, 2H), 7.20–7.25 (m, 2H) ppm. MS m/e 266
(M+, 100), 265 (54), 264 (78), 232 (22), 221 (54), 208
(10), 189 (15), 132 (12), 114 (12), 110 (12), 108 (10), 69
(16). Elemental analysis: Found C, 71.83; H, 3.94; S,
23.80; calculated for C16H10S2: C, 72.14; H, 3.79; S,
24.07.
3.3. Dimerization reactions of enynes with CuOTf:
general procedure
A solution of the complex (CF3SO2Cu).2benzene (0.6
equivalents) in THF/1,4-dioxane (1:1 v:v) was added at
70°C, under nitrogen, to a stirred suspension of CaCO3
(four equivalents) and enynes in THF/1,4-dioxane (1:1
v/v). The mixture was reacted at the same temperature
for 15 h, then quenched with NH4Cl, extracted with
ethyl acetate and dried (Na2SO4). After removal of the
solvent, the residue was purified by flash chromatogra-
phy leading to products 2,4 and 13–18.
3.4.4. (1E, 7E)-1,8-Bis(p-methoxyphenyl)-1,7-octadien-
3,5-diyne (14)
Product 14 was prepared from 8 (0.1 g, 0.43 mmol)
and purified by flash chromatography (petroleum ether/
AcOEt 7/3) (0.046 g, 67% yield). The residual solid was
washed with ethyl acetate giving yellow crystals of 14
(m.p. 164–165°C). 1H-NMR (500 MHz, CDCl3): l 3.80
(s, 6H), 6.09 (d, J=15.9 Hz, 2H), 6.85 (br d, J=8.7
Hz, 4H), 7.02 (d, J=15.9 Hz, 2H), 7.32 (br d, J=8.7
Hz, 4H) ppm. MS m/e 314 (M+, 100), 299 (39), 284
(11), 283 (16), 271 (21), 268 (15), 256 (20), 255 (22), 240
(20), 239 (44), 228 (25), 227 (29), 226 (39), 169 (11), 145
(21), 119 (15), 113 (23), 101 (14). Elemental analysis:
Found C, 83.89; H, 5.71; calculated for C22H18O2: C,
84.05; H, 5.78.
3.4. Dimerization reactions of enynes with Cu(OAc)2:
general procedure
A methanol solution of enynes was added to a stirred
suspension of Cu(OAc).2H2O (40 equivalents) and
K2CO3 (30 equivalents) in pyridine/methanol (1:1 v/v)
and the resulting mixture warmed at 50°C. After reac-
tion completion (1–3 days), the usual workup afforded
a residue which was purified by flash chromatography
and led to compounds 2, 4 and 13–19.

F. Babudri et al. / Journal of Organometallic Chemistry 566 (1998) 251–257
257
3.4.5. (3E, 9E)-1,12-Diphenyl-3,9-dodecadien-5,7-diyne
(15)
(petroleum ether/AcOEt 9/1) gave 19 as a yellow solid
(0.27 g, 71% yield). Further crystallization from
petroleum ether/ethyl acetate afforded yellow crystals
of 19 (m.p. 73–74 °C). H-NMR (300 MHz, CDCl3): l
5.55 (d, J=15.8 Hz, 2H), 6.97 (d, J=15.8 Hz, 2H),
Product 15 was prepared from 9 (0.1 g, 0.438 mmol).
Purification by flash chromatography (petroleum ether/
AcOEt 9.5/0.5) afforded 0.067 g of 15 (98% yield).
Washing with petroleum ether gave white crystals of 15
1
7.28–7.45 (m, 10H) ppm.
1
(m.p. 90–91°C). H-NMR (500 MHz, CDCl3): l 2.41–
2.49 (m, 4H), 2.71 (t, J=7.7 Hz, 4H), 5.56 (d, J=15.6
Hz, 2H), 6.31 (dt, J=15.6, 7.1 Hz, 2H), 7.12–7.25 (m,
10H) ppm. MS m/e 310 (M+, 10), 219 (9), 204 (18),
203 (27), 202 (10), 191 (15), 178 (15), 141 (13), 117 (13),
115 (14), 91 (100), 65 (16). Elemental analysis: Found
C, 92.53; H, 6.98; calculated for C24H22: C, 92.85; H,
7.15.
Acknowledgements
This work was financially supported in part by the
Ministero dell’Universita` e della Ricerca Scientifica e
Tecnologica, Rome, and the University of Bari (Na-
tional Project ‘Stereoselezione in Sintesi Organica.
Metodologie ed Applicazioni’).
3.4.6. (7E, 13E)-7,13-eicosadien-9,11-diyne (16)
Product 16 was prepared from 10 (0.1 g, 0.48 mmol).
Purification by flash chromatography (petroleum ether)
gave 0.048 g of 16 as a pale yellow oil (74% yield).1H-
NMR (500 MHz, CDCl3): l 0.86 (t, J=6.9 Hz, 6H),
1.19–1.31 (m, 12H), 1.32–1.41 (m, 4H), 2.06–2.15 (m,
4H), 5.52 (d, J=15.6 Hz, 2H), 6.27 (dt, J=15.6, 7.2
Hz, 2H) ppm. MS m/e 270 (M+, 98), 213 (11), 199
(21), 186 (22), 157 (24), 143 (49), 141 (27), 129 (89), 128
(78), 127 (30), 117 (29), 115 (100), 105 (19), 102 (76), 91
(48), 79 (23), 77 (23), 67 (22), 55 (30).
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cation by flash chromatography (petroleum ether).1H-
NMR (500 MHz, CDCl3): l 2.10–2.17 (m, 4H),
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Hz, 2H), 5.76 (ddt, J=17.0, 10.3, 6.4 Hz, 2H), 6.27 (dt,
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(41), 89 (30), 77 (26), 76 (21), 75 (31), 65 (23), 63 (34).
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47 (1991) 1677.
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Siegmann, Tetrahedron 34 (1978) 1323.
Product 18, as a mixture of isomers, was prepared
from 12 (0.15 g, 0.68 mmol). Purification by flash
chromatography (petroleum ether) gave 18 as an or-
1
ange oil (0.095 g, 94% yield). All E-isomer H-NMR
(500 MHz, CDCl3): l 0.08 (s, 18H), 5.68 (d, J=15.2
Hz, 2H), 6.05 (d, J=18.2 Hz, 2H), 6.52 (dd, J=18.2,
10.5 Hz, 2H), 6.67 (dd, J=15.2, 10.5 Hz, 2H) ppm. MS
m/e 298 (M+, 15), 210 (3), 209 (4), 195 (20), 165 (4), 73
(100), 59 (7), 45 (11).
3.4.9. (1E, 7E)-1,8-Bis(phenylthio)-1,7-octadien-3,5-
diyne (19)
Product 19 was prepared from 6 (0.551 g, 2.37
mmol). Purification by flash chromatography