Palladium catalysed regio- and stereoselective synthesis of (E)-4-aryl-1,3-bis(trimethylsilyl)but-3-en-1-ynes

Article abstract of DOI:10.1016/j.tet.2018.09.013

A practical and general synthetic approach to a series of 4-aryl-but-3-en-1-ynes is described. In the presence of palladium complexes a variety of aryl bromides (or iodides) undergo coupling with two equivalents of trimethylsilylacetylene with the formati

Full text of DOI:10.1016/j.tet.2018.09.013

Accepted Manuscript
Palladium catalyzed regio- and stereoselective synthesis of (E)-4-aryl-1,3-
bis(trimethylsilyl)but-3-en-1-ynes
Szymon Rogalski, Maciej Kubicki, Cezary Pietraszuk
PII:
S0040-4020(18)31068-8
10.1016/j.tet.2018.09.013
TET 29785
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 10 August 2018
Accepted Date: 4 September 2018
Please cite this article as: Rogalski S, Kubicki M, Pietraszuk C, Palladium catalyzed regio- and
stereoselective synthesis of (E)-4-aryl-1,3-bis(trimethylsilyl)but-3-en-1-ynes, Tetrahedron (2018), doi:
10.1016/j.tet.2018.09.013.
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Palladium Catalyzed Regio- and
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Stereoselective Synthesis of (E)-4-aryl-1,3-
bis(trimethylsilyl)but-3-en-1-ynes
Szymon Rogalskia, Maciej Kubickia and Cezary Pietraszuka,*
aAdam Mickiewicz University in Poznań, Faculty of Chemistry, Umultowska 89b, 61-614 Poznań, Poland

1
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Tetrahedron
journal homepage: www.elsevier.com
Palladium Catalyzed Regio- and Stereoselective Synthesis of (E)-4-aryl-1,3-
bis(trimethylsilyl)but-3-en-1-ynes
Szymon Rogalskia, Maciej Kubickia and Cezary Pietraszuka,*
aAdam Mickiewicz University in Poznań, Faculty of Chemistry, Umultowska 89b, 61-614 Poznań, Poland
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A practical and general synthetic approach to a series of 4-aryl-but-3-en-1-ynes is described. In
the presence of palladium complexes a variety of aryl bromides (or iodides) undergo coupling
with two equivalents of trimethylsilylacetylene with the formation of (E)-4-aryl-1,3-
bis(trimethylsilyl)but-3-en-1-ynes. The protocol is simple, efficient, and affords synthesis of
regio- and stereoselectively target products in good to high yields.
Available online
2009 Elsevier Ltd. All rights reserved
.
Keywords:
Enynes
Palladium
Homogeneous catalysis
1. Introduction
synthetic approaches include dimerization of terminal
arylacetylenes,1b,c,11 co-dimerization of aryl and silylacetylenes,12
Sonogashira coupling of corresponding Z-vinyl halides with
alkynes,13,14 cross-coupling of alkenyldialkylboranes with
trimethylsilylethynyl bromide,15 the sequence Wittig olefination
of heteroaryl aldehydes / Sonogashira coupling,16 sequence
Cu(I)-catalysed cross-coupling of α-diazo phosphonates and
alkynes / Horner−Wadsworth−Emmons (HWE) type reactions,17
and arylalkynylation of aryl iodides, internal alkynes, and
alkynylsilanes18 (Scheme 2).
Arylvinylacetylenes are valuable building blocks in organic
synthesis1 and are convenient starting materials in the
construction of aromatic and heteroaromatic rings.2,3,4 Moreover,
aromatic and aliphatic derivatives of conjugated enynes are
valuable precursors of a variety of functionalized compounds,
such as conjugated dienes,5 trienes,6 pyridines,7 pyrazolines,8
thiophenes,9 and others10 (Scheme 1).
Scheme 2. Catalytic methods of synthesis of arylvinylacetylenes.
Scheme 1. Selected synthetic applications of arylvinylacetylenes.
One example of arylvinylacetylene formation as the main product
in a reaction of 1,8-diiodonaphthalene with 2-methylbut-3-yn-2-
ol has been described by Echavarren.19 Recently Hu has
In recent years, significant advancements have been made in
the catalytic synthesis of arylvinylacetylenes with ethynyl and
aromatic groups in cis arrangement.1b,c The most important

2
Tetrahedron
described synthesis of a series of arylvinylacetylenes via the
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reaction
of
heteroaryl
iodide
with
aryl
and
trimethylsilylacetylenes in DMF, in the presence of [Pd(PPh3)4],
NBu3 and CuCl or ZnBr2 as co-catalysts.20 From amongst the
accessible
methods
of
arylvinylacetylene
synthesis,
homodimerization is efficient and atom-economical but usually
leads to a mixture of stereo- and regioisomers. On the other hand,
Sonogashira coupling, Suzuki coupling with alkynyl halides, and
metal carbene coupling methods exhibit high stereo- and
regioselectivity but suffer from limited accessibility of substrates.
Herein, we report an efficient, regio- and stereoselective
synthesis of terminal arylvinylacetylene skeletons with cis
arrangement of aryl and acetylene moieties from easily accessible
and commercially available starting materials in the presence of
simple palladium complexes, without the use of Cu or Zn-based
co-catalyst.
Figure 2. Perspective view of the molecule 4m; ellipsoids are drawn at
the 50% probability level, hydrogen atoms are shown as spheres of arbitrary
radii. Only one set of the disordered atoms is shown.
selectivity of the reaction depends on the temperature. At 80 °C,
the formation of enyne is accompanied by significant amounts of
Sonogashira product (entries 1-3). Increasing the reaction
temperature to 110 °C resulted in a significant increase in the
yield of enyne (entry 4). Among different bases tested in the
process, triethylamine turned out to be the most efficient (entries
4 and 8-11).
2. Results and Discussion
We started our investigations with treatment of iodobenzene
with two equivalents of trimethylsilylacetylene in the presence of
[Pd(PPh3)4] and NH3 as a base. The reaction was performed in
toluene at 110 °C and led to the formation of Sonogashira
product 3a together with a major amount of an unknown
compound. On the basis of NMR and GC-MS analyses we
established the structure of the product 4a and we proposed the
equation for the reaction (Scheme 2).
Table 1. Optimization of the reaction conditions
entry
catalyst
base
Conv
yield of 4a
yield of 3a
[%]
[%]
[%]
1
PdCl2(PPh3)2
PdCl2(PhCN)2
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(OAc)2
NEt3
68
55
35b
26b
53b
92
75c
0
30
25
25
6
2
NEt3
3
NEt3
80
4
NEt3
100
85
5
NEt3
8
6
NEt3
30
30
28
20
21
28
12
Scheme 3. Coupling of iodobenzene with two equivalents of
trimethylsilylacetylene
7
PEPPSI-iPr
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
NEt3
30
0
8
K2CO3
Cs2CO3
KOtBu
HNiPr2
100
100
100
100
79
77
70
85
The geometry around the double bond in product 4a was
assigned through observation of through-space interactions of
hydrogens Ha, Hb, and Si(CH3)3 (Figure 1). NOESY spectrum
showed strong cross peaks between Ha and Hb at δ = 6.81 and
8.01 ppm, respectively, and a weak one between Ha and
hydrogens of the Si(CH3)3 group (δ=0.19 ppm), indicating E
configuration of the double bond (ESI, S13).
9
10
11
Reaction conditions: argon, closed system, toluene, 110 °C,
cat. 5 mol%, [ArX]:[C≡C] = 1:2; 5 h; a) GC yield, b) THF, 80
°C, 24 h, c) 2.5 mol% of [Pd];
In order to determine the scope of the reaction, a series of aryl
bromides and iodides were treated with trimethylsilylacetylene in
the optimized reaction conditions (Scheme 4 and Figure 3).
Me3Si
[Pd(PPh3)4]
Figure 1: Structure determination of compound 4a
(5 mol%)
SiMe3
Ar
SiMe3
+
+ 2
X
Ar
SiMe3
toluene
Rentgenostructural analysis of the coupling product of 9-
bromoanthracene with trimethylsilylacetylene (4m) (Figure 2)
provided additional confirmation of the proposed structure of the
synthesized enyne.
110 °C, NEt3
Ar
X = Br or I
1a-m 2 (2.2 equiv)
3a-m
4a-m
Scheme 4. Coupling of aryl halides with excess of trimethylsilylacetylene
Formation of enynes as by-products in the study of
Sonogashira coupling of aryl halides with arylacetylenes has
already been reported.21 We have made attempts to develop
procedures in order to use this reaction for an efficient synthesis
of enynes. For this purpose, the reaction conditions (temperature,
solvent, catalyst and base) were optimized (Table 1). It was
found that heating the reagents in boiling toluene, in the presence
of 5 mol% of [Pd(PPh3)4] results in product yield of up to 92%
within 5 hours. Lowering the catalyst loading leads to a
significant reduction in the reaction yield (entry 5). The
The reaction afforded a series of conjugated 1,3-enynes in good
yields and in a regio- and stereoselective manner. The reaction
proceeded efficiently in the presence of a variety of functional
groups including amine, chloro, methoxy, trifluoromethyl, and
vinyl. Moreover, highly conjugated aromatic groups such as
naphthyl, anthracenyl, and phenanthryl were also found to be
suitable reagents producing desirable 1,3-enynes with yields up
to 90%. Unfortunately, heteroaryl substrates such as pyridine and
pyrrole iodides and bromides did not result in the desired enynes,
reacting quantitatively with the formation of Sonogashira
products. The usefulness of the compounds obtained in the
synthesis is related to the ease of the silyl group removal from

3
acetylene moiety. The tests performed permitted determination of
conditions allowing a practically quantitative course of the
reaction. The desilylation tests performed for selected derivatives
in optimized conditions are summarized in Scheme 5.
In the hope of detecting the reaction intermediates, the
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complex [PdIPh(PPh3)2] was synthesized according to the
published method22,23 and reacted with an excess of
trimethylsilylacetylene. The reaction was performed in an NMR
tube in C6D6 and monitored by 1H NMR spectroscopy. The
spectra showed gradual
a disappearance of the signals
characteristic of the starting palladium complex (δ = 5.91 and
6.42 ppm) and formation of 1,3-enyne (4a) along with
Sonogashira product (3a) (Scheme 7). No reaction intermediates
were observed. Attempts to observe the relevant intermediates at
reduced temperatures also failed. This could be an indication that
carbometallation is a rate limiting step. The experiment also
indicates that oxidative addition of aryl iodide to palladium(0) is
involved in the catalytic cycle.
Scheme 7: Reaction of [PdIPh(PPh3)2] with excess of trimethylsilylacetylene
Based on the obtained results and mechanistic studies reported
by Woo21b and Mårtensson24 a reasonable reaction scheme
explaining catalytic formation of enynes (4) was proposed
(Scheme 8). The right cycle in Scheme 8 is consistent with the
copper-free Sonogashira coupling25 and includes a sequence of
oxidative addition of an aryl halide to palladium(0) complex,
formation of π-acetylene intermediate, deprotonation of acetylene
in the presence of a base leading to σ-acetylide complex D which
subsequently undergoes reductive elimination resulting in
formation of Sonogashira product, and regeneration of
palladium(0) complex. The deprotonation mechanism of copper-
free Sonogashira has recently been supported by DFT
calculations.24,26 π- Acetylene complex C may undergo two
competitive processes, i.e. deprotonation (right cycle) or regio-
and stereoselective carbopalladation, leading to complex E. The
regiochemistry of the carbopalladation step is controlled
primarily by steric effects so that the aryl group is transferred to
the less hindered position of the alkyne molecule. The observed
stereochemistry originates from syn addition of the organic
residue and the palladium moiety to the carbon–carbon triple
bond.27 Complex E subsequently may be transformed to σ-
acetylide complex F via a substitution/deprotonation sequence.
Finally, complex F undergoes reductive elimination, resulting in
the final product (4) and the regeneration of the catalytically
active species. Competition between deprotonation and
carbopalladation is crucial for the selectivity of the process. σ-
vinyl
Figure 3: The scope of the reaction. Reaction conditions: argon,
[Pd(PPh3)4] (5 mol%); toluene, 110 °C; NEt3; closed system, GC yields,
a)
b)
isolated yields in parentheses, obtained from aryl iodide, obtained from
aryl bromide
Scheme 5: Selective desilylation of 4 at acetylene moiety
In order acquire insight into the reaction mechanism, the
Sonogashira product (3a) was treated with silylacetylene (2) in
the presence of [Pd(PPh3)4]. The reaction did not lead to the
formation of any product, which permitted exclusion of the
formation of 4a by hydroethynylation of 3a (Scheme 6).
Scheme 8: Proposed reaction scheme explaining catalytic formation of 4
and competitive Sonogashira coupling.28
Scheme 6: Hydroalkynylation of 3a

4
Tetrahedron
mL of NEt3, (9.0 ×10-4 mol) of corresponding aryl iodide or
ACCEPTED MANUSCRIPT
bromide and 274 µL (1.98 ×10-3 mol) of trimethylsilylacetylene.
The reaction was carried out in a closed system at 110 °C for 24
h. After completion of the reaction, the resulting mixture was
filtered through a short pad of Celite, evaporated to dryness, and
the residue was purified using silica gel column chromatography.
The use of at least a twofold excess of silylacetylene in relation
to aryl halide is decisive for switching the selectivity of the
reaction towards the formation of enyne 4. The use of aryl
halides containing electron-donating groups promotes the
formation of enynes. In contrast, reaction of 1-bromo-4
nitrobenzene with trimethylsilylacetylene (2) leads to exclusive
formation of Sonogashira product.
4.4. Characterization of the products
4.4.1. (E)-1-phenyl-2,4-bis(trimethylsilyl)but-1-en-3-yne (4a).
The product was isolated by column chromatography over silica
gel and using n-hexane as an eluent. The product was obtained as
a yellow oil with a yield of 88%. Spectroscopic characterization:
1H NMR (CDCl3; ppm) δ: 8.03-8.01 (m, 2H, Ph), 7.39-7.30 (m,
3H Ph), 6.83 (s, 1H, =CH), 0.27 (s, 9H, SiMe3), 0.26 (s, 9H,
SiMe3); 13C NMR (CDCl3; ppm) δ: 145.0, 137.60, 128.80,
128.57, 128.08, 124.01, 107.23, 105.80, 0.03, -2.02; GC-MS
(EI): m/z (rel intensity): 73 (17), 241 (19), 257 (100), 258 (24),
272 (20, M+). HRMS (EI): calc: 272.1417; found: 272.1416.
3. Conclusions
Palladium-catalysed coupling of aryl halides with two
equivalents of trimethylsilylacetylene offers a new general, regio-
and stereoselective method for the synthesis of terminal
arylvinylacetylenes. This methodology is efficient for a series of
aryl iodides and bromides bearing a variety of functional groups.
The demonstrated selective desilylation of the acetylenic moiety
in synthesized enynes opens the potential for their further
functionalization.
4.4.2. (E)-2-(4-Chlorophenyl)-2,4-bis(trimethylsilyl)but-1-en-3-
yne (4b). The product was isolated by column chromatography
over silica gel and using n-hexane as an eluent. The product was
obtained as a yellow oil with a yield of 50%. Spectroscopic
4. Experimental section
4.1. General methods and chemicals:
1
characterization: H NMR (CDCl3; ppm) δ: 7.95-7.92 (m, 2H,
Unless written otherwise, all operations were performed by
using standard Schlenk techniques. H- and 13C-NMR spectra
1
C6H4), 7.32-7.29 (m, 2H, C6H4), 6.74 (s, 1H, =CH), 0.24 (s, 9H,
SiMe3), 0.23 (s, 9H, SiMe3); 13C NMR (CDCl3; ppm) δ: 143.36,
136.03, 133.95, 129.97, 128.22, 124.94, 108.11, 105.42, -0.08, -
2.09. GC-MS (EI): m/z (rel intensity): 45 (31), 73 (100), 74 (11),
75 (10), 97 (17), 147 (10), 155 (64), 156 (11), 163 (13), 218 (10),
255 (12), 275 (67), 276 (18), 277 (30), 291 (50), 292 (14), 293
(21), 306 (44, M+), 307 (15), 308 (18). HRMS (EI): calc:
306.1027; found: 306.1023.
were recorded on a Varian 400 operating at 402.6 and 101.2
MHz, respectively. NOE, COSY, HSQC and HMBC spectra
were recorded on a Bruker Avance DRX 600, operating at
frequency of 600.13 MHz (1H). All spectra were recorded at 298
K. GC analyses were carried out on a Bruker Scion 436-GC
(column: DB-5 30 m I.D. 0.53mm) equipped with TCD. The
GC/MS analyses were performed on a Varian Saturn 2100T
equipped with (DB-1, 30 m capillary column, I.D. 0.25 mm) and
Ion Trap Detector. The chemicals were obtained from the
4.4.3. (E)-1-(4-Methoxyphenyl)-2,4-bis(trimethylsilyl)but-1-en-3-
yne (4c). The product was isolated by column chromatography
over silica gel and using n-hexane/ethyl acetate (25:1) as an
eluent. The product was obtained as a yellow oil with a yield of
following
sources:
triethylamine,
4-methoxybromobenzene,
4-bromostyrene,
iodobenzene,
4-
2-
4-
chlorobromobenzene,
methoxybromobenzene,
trifluoromethylstyrene, 4-iodoaniline, 2-bromoaniline, 4-
iodobiphenyl, 1-iodonaphtalene, 9-bromoantracene, 3-
bromotiophene, Cs2CO3, AgNO3, CuI, KF, Pd(OAc)2, PEPPSI-
iPr, trimethylsilylacetylene and CDCl3 were purchased from
Sigma-Aldrich. Toluene, tetrahydrofuran and K2CO3 were
purchased from Chempur. Toluene was distilled prior to use from
sodium, tetrahydrofuran was distilled from Na/benzophenone and
the solvents were stored under argon over molecular sieves 4 Å.
1
86%. Spectroscopic characterization: H NMR (CDCl3; ppm) δ:
8.00-7.96 (m, 2H, C6H4), 6.89-6.85 (m, 2H, C6H4), 6.74 (s, 1H,
=CH), 3.83 (s, 3H, OCH3), 0.25 (s, 9H, SiMe3), 0.23 (s, 9H,
SiMe3); 13C NMR (CDCl3; ppm) δ: 159.73, 144.49, 130.89,
130.37, 129.83, 120.59, 113.36, 106.21, 55.26, 0.01, -2.00. GC-
MS (EI): m/z (rel intensity): 73 (20), 271 (47), 272 (24), 287
(23), 302 (100, M+), 303 (30); HRMS (EI): calc: 302.1522;
found: 302.1528.
4.4.4. (E)-1-(2-Methoxyphenyl)-2,4-bis(trimethylsilyl)but-1-en-3-
yne (4d). The product was isolated by column chromatography
over silica gel and using n-hexane/ethyl acetate (25:1) as an
eluent. The product was obtained as a yellow oil with a yield of
Complexes
[PdIPh(PPh3)2],
[Pd(PPh3)4],
[PdCl2(PPh3)4],
[PdCl2(PhCN)2] were synthesized according to literature data.20,21
4.2. Procedure for the optimization tests
1
86%. Spectroscopic characterization: H NMR (CDCl3; ppm) δ:
An oven dried 20 mL Schlenk flask closed with a Rotaflo valve,
equipped with a magnetic stirring bar was charged under argon
with 0.026 g (2.25 ×10-5 mol) of [Pd(PPh3)4], 3 mL of toluene or
THF, 0.5 mL of NEt3 and 0.25 mL of dodecane (internal
standard). Then 48 µL (4.5 ×10-4 mol) of iodobenzene was added
to the reaction mixture followed by 137 µL (9.9 ×10-4 mol) of
trimethylsilylacetylene. The mixture was heated at 110 °C in a
closed system in an oil bath for 5h. Reaction course was
monitored by gas chromatography.
8.63 (dd, J = 7.8, 1.7 Hz, 1H, C6H4), 7.30 (s, 1H, =CH), 7.29-
7.25 (m, 1H, C6H4), 6.96-6.92 (m, 1H, C6H4), 6.87 (dd, J = 8.3,
1.0 Hz, 1H, C6H4), 3.84 (s, 3H, OCH3), 0.25 (s, 9H, SiMe3), 0.22
(s, 9H, SiMe3). 13C NMR (CDCl3; ppm) δ: 156.78, 138.98,
129.75, 128.65, 126.42, 123.12, 119.82, 110.37, 106.31, 55.51, -
0.03, -1.96. GC-MS (EI): m/z (rel intensity): 119 (15), 257 (16),
287 (100), 288 (30), 302 (95, M+), 303 (24). HRMS (EI): calc:
302.1522; found: 302.1525.
4.4.5. (E)-1-(4-Vinylphenyl)-2,4-bis(trimethylsilyl)but-1-en-3-yne
(4e). Compound is unstable. GC-MS (EI): m/z (rel intensity): 45
(37), 73 (100), 74 (11), 75 (11), 97 (18), 131 (11), 147 (12), 155
(48), 195 (21), 209 (30), 210 (18), 267 (95), 267 (30), 269 (11),
283 (56), 284 (15), 298 (80, M+), 299 (23).
4.3. Representative synthesis of (E)-1-Aryl-2,4-(bis)tri-
methylsilyl-1,3-enynes
All operations were performed by using standard Schlenk
techniques. The synthesis was carried out in a Schlenk flask with
a capacity of 20 mL, equipped with a magnetic stirring bar and
closed with a Rotaflo valve. The flask was charged under argon
with 0.052 g (4.5 ×10-5 mol) of [Pd(PPh3)4], 6 mL of toluene, 1
4.4.6. (E)-1-(4-trifluoromethyl)-2,4-bis(trimethylsilyl)but-1-en-3-
yne (4f). The product was isolated as a yellow oil by column

5
chromatography over silica gel and using n-hexane/ethyl acetate
(53), 292 (19), 307 (25), 322 (31, M+), 323 (11); HRMS (EI):
calc: 322.1573; found: 322.1576.
ACCEPTED MANUSCRIPT
(25:1) as an eluent. Isolated yield = 50%; 1H NMR (CDCl3; ppm)
δ: 8.10-8.08 (m, 2H, C6H4), 7.61-7.58 (m, 2H, C6H4), 6.82 (s, 1H,
=CH), 0.26 (s, 9H, SiMe3), 0.25 (s, 9H, SiMe3); 13C NMR
(CDCl3; ppm) δ: 142.93, 140.66, 128.79, 128.59, 127.78, 125.02
(m), 122.75, 109.04, 105.15, 0.12, -2.12. GC-MS (EI): m/z (rel
intensity): 73 (65), 77 (15), 97 (17), 155 (11), 165 (12), 233 (12),
309 (22), 321 (29), 325 (100), 326 (28), 340 (12, M+); HRMS
(EI): calc: 340.1290; found: 340.1280.
4.4.12. (E)-1-(9-Anthracenyl)-2,4-bis(trimethylsilyl)but-1-en-3-
yne (4l). The product was isolated by column chromatography
over silica gel and using n-hexane/ethyl acetate (25:1) as an
eluent. The product was obtained after recrystallization from n-
hexane as an orange microcrystalline solid with a yield of 85%.
1
Spectroscopic characterisation: H NMR (CDCl3; ppm) δ: 8.47
(s, 1H, Ar), 8.28 (dq, J = 8.6, 1.0 Hz, 1H, Ar), 8.10 (ddd, J = 8.6,
1.2, 0.7 Hz, 1H, Ar), 8.00 (d, J = 8.4 Hz, 1H, Ar), 7.81 (d, J = 6.6
Hz, 1H, Ar), 7.62-7.57 (m, 3H, Ar, =CH), 7.49-7-43 (m, 1H, Ar),
7.15 (dd, J = 5.2, 0.6 Hz, 1H, Ar), 0.17 (s, 9H, SiMe3), 0.08 (s,
9H, SiMe3); 13C NMR (CDCl3; ppm) δ: 140.25, 134.32, 130.28,
128.07, 128.00, 127.72, 127.53, 127.35, 126.83, 125.76, 124.72,
124.18, 1.94; GC-MS (EI): m/z (rel intensity): 73 (87), 97 (11),
202 (100), 203 (22), 269 (25), 283 (51), 284 (54), 285 (17), 298
(26), 299 (20), 372 (48), 373 (22); HRMS (EI): calc: 372.1730.;
found: 372.1738.
4.4.7. (E)-1-(4-aminophenyl)-2,4-bis(trimethylsilyl)but-1-en-3-
yne (4g). The product was isolated by column chromatography
over silica gel and using n-hexane/ethyl acetate (25:1) as an
eluent. The product was obtained as an orange oil with a yield of
1
60%. Spectroscopic characterization: H NMR (CDCl3; ppm) δ:
7.88-7.86 (m, 2H, C6H4), 6.68 (s, 1H, =CH), 6.65-6.62 (m, 2H,
C6H4), 3.79 (brs, 2H, NH2), 0.23 (s, 9H, SiMe3), 0.21 (s, 9H,
SiMe3); 13C NMR (CDCl3; ppm) δ: 146.85, 145.12, 130.47,
128.96, 118.29, 114.26, 106.69, 105.52, 0.05, -1.95. GC-MS
(EI): m/z (rel intensity): 256 (34), 257 (11), 272 (20), 287 (100),
288 (30); HRMS (EI): calc: 287.1526; found: 287.1520.
4.4.13. (E)-1-(9-Phenanthryl)-2,4-bis(trimethylsilyl)but-1-en-3-
yne (4m). The product was isolated by column chromatography
over silica gel and using n-hexane/ethyl acetate (25:1) as an
eluent. The product was obtained after recrystallization from n-
hexane as a yellow crystalline solid with a yield of 77%.
4.4.8. (E)-1-(2-methylphenyl)-2,4-bis(trimethylsilyl)but-1-en-3-
yne (4h). The product was isolated by column chromatography
over silica gel and using n-hexane/ethyl acetate (25:1) as an
eluent. The product was obtained as a yellow oil with a yield of
1
Spectroscopic characterisation: H NMR (CDCl3; ppm) δ: 8.75-
1
86%. H NMR (CDCl3; ppm) δ: 8.43-8.38 (m, 1H, C6H4), 7.21-
8.73 (m, 1H, Ar), 8.68-8.66 (m, 1H, Ar), 8.67 (s, 1H, Ar), 8.11
(dd, J = 8.1, 1.4 Hz, 1H, Ar), 7.88 (dd, J = 7.7, 1.6 Hz, 1H, Ar),
7.69-7.58 (m, 5H, Ar and =CH), 0.36 (s, 9H, SiMe3), 0.18 (s, 9H,
SiMe3); 13C NMR (CDCl3; ppm) δ: 142.56, 132.02, 131.40,
130.57, 130.37, 128.91, 127.74, 126.96, 126.85, 126.70, 126.55,
126.27, 124.00, 123.07, 122.46, 106.17, 105.41, 0.06, -1.85. GC-
MS (EI): m/z (rel intensity): 73 (11), 269 (13), 283 (16), 357
(23), 371 (14), 372 (100, M+), 373 (35); HRMS (EI): calc:
372.1730; found: 372.1742.
7.17 (m, 3H, C6H4), 7.07 (s, 1H, 1H, =CH), 2.90 (s, 3H, CH3),
0.26 (s, 9H, SiMe3), 0.21 (s, 9H, SiMe3); 13C NMR (CDCl3; ppm)
δ: 13C NMR (75 MHz, cdcl3) δ 143.02, 136.14, 136.06, 130.04,
128.32, 128.05, 125.31, 124.68, 105.94, 105.61, 19.71, -0.05, -
1.95; GC-MS (EI): m/z (rel intensity): 45 (38), 73 (100), 182
(30), 196 (20), 197 (58), 198 (18), 212 (75), 253 (75), 254 (19),
270 (32), 286 (10); HRMS (EI): calc: 286.1573; found: 286.1580
4.4.9. (E)-1-(3-thiophenyl)-2,4-bis(trimethylsilyl)but-1-en-3-yne
(4i). Compound is unstable. It decomposes during isolation. GC-
MS (EI): m/z (rel intensity): 263 (100), 264 (27), 265 (14), 278
(24, M+).
4.5. Representative procedure for selective protodesilylation
A 10 mL two neck round bottom flask, equipped with a
condenser and a magnetic stirring bar was charged with 0.1 g
(3.68 ×10-4 mol) of (E)-1-phenyl-2,4-bis(trimethylsilyl)but-1-en-
3-yne, 0.21 g (3.68 ×10-3 mol) of KF and 5 mL of methanol. The
mixture was heated at 65 °C for 3 h. After this time the solvent
was evaporated under vacuum and the product was purified by
column chromatography over silica gel and using n-hexane/ethyl
acetate (25:1) as an eluent.
4.4.10. (E)-1-Biphenyl-2,4-bis(trimethylsilyl)but-1-en-3-yne (4j).
The product was isolated by column chromatography over silica
gel and using n-hexane/ethyl acetate (25:1) as an eluent. The
product was obtained as a yellow microcrystalline solid with a
1
yield of 82%. Spectroscopic characterization: H NMR (CDCl3;
ppm) δ: 8.09 (d, J = 8.2 Hz, 2H, Ph), 7.65-7.58 (m, 3H Ph), 7.55
(s, 1H, Ph), 7.47-7.43 (m, 2H, Ph), 7.38-7.34 (m, 1H, Ph), 7.26
(s, 1H, =CH), 0.27 (s, 9H, SiMe3), 0.26 (s, 9H, SiMe3); 13C NMR
(CDCl3; ppm) δ: 144.42, 141.11, 140.64, 136.68, 132.37, 129.24,
128.76, 127.41, 127.00, 126.70, 124.10, 107.56, 105.95, -0.01, -
2.01. GC-MS (EI): m/z (rel intensity): 259 (10), 317 (22), 333
(65), 334 (27), 348 (100, M+), 349 (40); HRMS (EI): calc:
348.1730; found: 348.1717.
4.5.1. (E)-1-Phenyl-2-trimethylsilylbut-1-en-3-yne (5a). The
product was isolated by column chromatography over silica gel
and using n-hexane/ethyl acetate (25:1) as an eluent. The product
was obtained as a yellow oil with a yield of 88%. Spectroscopic
1
characterisation: H NMR (CDCl3; ppm) δ: 7.97 (d, J = 7.6 Hz,
2H, Ph), 7.38-7.29 (m, 3H, Ph), 6.90 (s, 1H, =CH), 3.69 (s, 1H,
≡C-H), 0.26 (s, 9H, SiMe3); 13C NMR (CDCl3; ppm) δ: 146.14,
137.38, 128.76, 128.65, 128.18, 122.93, 88.90, 84.01, 76.98, -
2.09. GC-MS (EI): m/z (rel intensity): 45 (27), 59 (15), 73 (88),
83 (27), 159 (14), 169 (20), 172 (29), 183 (59), 185 (100), 186
(18), 199 (12, M+); HRMS (EI): calc: 200.1021; found:
200.1019.
4.4.11. (E)-1-(1-Naphthyl)-2,4-bis(trimethylsilyl)but-1-en-3-yne
(4k). The product was isolated by column chromatography over
silica gel and using n-hexane as an eluent. The product was
recrystallized from n-hexane and obtained as a yellow crystalline
1
solid with a yield of 70%. Spectroscopic characterisation: H
NMR (CDCl3; ppm) δ: 8.46 (d, J = 7.3 Hz, 1H, Ar), 8.09-8.06
(m, 1H, Ar), 7.87-7.81 (m, 2H, Ar), 7.63 (s, 1H, =CH), 7.55-7.47
(m, 3H, Ar), 0.34 (s, 9H, SiMe3), 0.19 (s, 9H, SiMe3); 13C NMR
(CDCl3; ppm) δ: 150.36, 142.25, 133.61, 133.55, 131.29, 128.75,
128.63, 126.53, 126.03, 125.55, 125.02, 123.31, 105.81, 105.61, -
0.05, -1.87; GC-MS (EI): m/z (rel intensity): 45 (35), 73 (100),
74 (12), 75 (10), 97 (14), 152 (64), 153 (11), 155 (11), 219 (33),
233 (55), 234 (45), 235 (15), 247 (20), 248 (21), 249 (19), 291
4.5.2. (E)-1-(1-Naphthyl)-2-trimethylsilylbut-1-en-3-yne (5b).
The product was isolated by column chromatography over silica
gel and using n-hexane as an eluent. The product was obtained as
a yellow oil with a yield of 92%. Spectroscopic characterisation:
1H NMR (CDCl3; ppm) δ: 8.26 (dt, J = 7.3, 0.9 Hz, 1H, Ar),
8.04-8.02 (m, 1H, Ar), 7.87-7.81 (m, 2H, Ar), 7.67 (s, 1H, =CH),
7.55-7.48 (m, 3H, Ar), 3.45 (s, 1H, ≡C-H), 0.34 (s, 9H, SiMe3);
13C NMR (CDCl3; ppm) δ: 144.08, 133.80, 133.52, 131.22,
128.77, 128.63, 126.42, 126.11, 125.87, 125.68, 125.17, 123.45,

6
Tetrahedron
ACCEPTED MANUSCRIPT
Y, Liu T-L, Zheng Y, Li S, Ma J-A. Eur. J. Org. Chem. 2015;
18:3905–3912; (f) Hoshi M, Okimoto M, Nakamura S, Takahashi S.
Synthesis 2011; 23:3839–3847; (g) Cao J, Huang X. Org. Lett. 2010;
12:5048–5051.
87.19, 83.71, -1.94; HRMS (EI): calc: 250.1178; found:
250.1178.
4.5.3. (E)-1-Biphenyl-2-trimethylsilylbut-1-en-3-yne (5c). The
product was isolated by column chromatography over silica gel
and using n-hexane as an eluent. The product was obtained as a
yellow oil with a yield of 90%. Spectroscopic characterisation:
1H NMR (CDCl3; ppm) δ: 8.05 (d, J = 9.1 Hz, 2H, Ar), 7.65-7.60
(m, 5H, Ar), 7.47-7.33 (m, 4H, Ar), 6.93 (s, 1H, =CH), 3.74 (s,
1H, ≡C-H), 0.28 (s, 9H, SiMe3); 13C NMR (CDCl3; ppm) δ:
145.62, 141.22, 140.60, 136.45, 129.17, 128.77, 127.43, 126.99,
126.83, 123.02, 89.21, 84.17, -2.06; HRMS (EI): calc: 276.1334;
found: 276.1330.
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1
4.6. H NMR spectroscopic study of equimolar reaction of
[PdIPh(PPh3)2] with 2.
An NMR tube equipped with a rotaflo valve was charged
under argon with 0.01g (1.2×10-5 mol) complex, 0.65 mL of C6D6
and anthracene as an internal standard. After this, the starting
NMR spectrum was recorded. Then 3.0 ꢀL (2.4×10-5 mol) of
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1
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Acknowledgments
This work was supported by the National Centre for Research
and Development (NCBR) [Project ORGANOMET No:
PBS2/A5/40/2014].
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