Syntheses of 2-silicon-substituted 1,3-dienes

Article abstract of DOI:10.1016/j.jorganchem.2013.12.046

A number of 2-silicon substituted 1,3-dienes have been prepared by one of three routes: 1) Reactions of 1,3-dienyl Grignard reagents with silyl electrophiles or silyl Grignard reagents with 1,3-dienyl electrophiles; 2) Hydrosilylation of enynes; 3) Enyne cross metathesis. The strengths and limitations of each preparative method are discussed.

Full text of DOI:10.1016/j.jorganchem.2013.12.046

Journal of Organometallic Chemistry 754 (2014) 88e93
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Syntheses of 2-silicon-substituted 1,3-dienes
*
Partha P. Choudhury, Christopher S. Junker, Ramakrishna R. Pidaparthi, Mark E. Welker
Department of Chemistry, Wake Forest University, P.O. Box 7486, Winston-Salem, NC 27109, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A number of 2-silicon substituted 1,3-dienes have been prepared by one of three routes: 1) Reactions of
1,3-dienyl Grignard reagents with silyl electrophiles or silyl Grignard reagents with 1,3-dienyl electro-
philes; 2) Hydrosilylation of enynes; 3) Enyne cross metathesis. The strengths and limitations of each
preparative method are discussed.
Received 25 October 2013
Received in revised form
23 December 2013
Accepted 24 December 2013
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
1,3-Dienes
Metal dienyls
Grignard reactions
Hydrosilylation
Enyne cross metathesis
1. Introduction
reagent and its addition to a dienyl electrophile (Scheme 1). In our
prior work, we have been successful in preparing Grignard reagents
We have been interested in the preparation and reaction
chemistry of metal substituted dienes for over 15 years. Initially, we
prepared a number of transition metal substituted dienes [1] for
these studies but more recently we have been interested in the
investigation of silicon and boron substituted dienes [2]. We have
reported the preparation of 2-silicon substituted 1,3-butadienes by
one of three different routes and demonstrated that they could be
used in sequential DielseAlder/cross coupling reactions but we
have never discussed the strengths and limitations of these
different silicon substituted diene preparative routes [3]. Here we
report the preparation of new 2-silicon substituted 1,3-dienes by
one of three different routes and focus our discussion on a com-
parison of those routes.
from simple halodienes like chloroprene (1) followed by treatment
of those reagents with boron substituted electrophiles [4] or alkoxy
silyl electrophiles [3a], but had always encountered some diffi-
culties in attempting to use Grignard reagents prepared from more
highly substituted 1,3-dienes [5]. We have found the same trends to
hold for silicon substituted diene synthesis with alkyl or aryl silyl
reagents. So while a Grignard reagent prepared from chloroprene
(1) reacts with dimethylphenylsilyl chloride or dichlor-
odimethylsilane (followed by hydrolysis) [6] to provide new dienes
(2 & 3), we found it most convenient to use trimethylsilylmagne-
sium chloride addition to the more highly substituted halodienes (4
and 6) to produce the trimethylsilyl substituted dienes 5 [7] and 7.
Attempts to prepare Grignard reagents from dienes 4 and 6 and
react them with TMSCl produced diene dimerization and decom-
position products rather than 5 and 7. Diene 2 participated in a
DielseAlder reaction cleanly with N-phenylmaleimide in high yield
to produce 8.
2. Results and discussion
2.1. Preparation of 2-silicon substituted 1,3-dienes via Grignard
chemistry
2.2. Preparation of 2-silicon substituted 1,3-dienes via
hydrosilylation of enynes
Preparation of 2-silicon substituted 1,3 dienes via Grignard
chemistry can be accomplished by one of two methods: i) prepa-
ration of a dienyl Grignard reagent and its addition to a silicon
electrophile or ii) preparation of a silicon containing Grignard
Our next attempts at the synthesis of 4-substituted 2-silyl di-
enes involved the cis-hydrosilylation of 1,3-enynes (Scheme 2). (E)-
4-Phenyl-3-buten-1-yne (9) was synthesized from trans-cinna-
maldehyde via the Colvin rearrangement [8]. Ruthenium-catalyzed
hydrosilylation of enyne (9) with triethoxysilane (10) was
* Corresponding author. Fax: þ1 336 758 4656.
E-mail address: welker@wfu.edu (M.E. Welker).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.12.046

P.P. Choudhury et al. / Journal of Organometallic Chemistry 754 (2014) 88e93
89
Scheme 1. Preparation of silyl dienes via Grignard chemistry.
performed with Grubbs 1st generation catalyst and cyclo-
pentadienyl ruthenium salt (11). These reactions produced mix-
tures of 2- and 1-siloxy substituted dienes (12 and 13). We also
available 3-methyl-3-buten-1-yne (17 R1 ¼ H, R2 ¼ Me) the yield for
2 steps (condensation with diisopropylchlorosilane to yield 18a
followed by condensation with acetone to yield 19a) was an
acceptable 72%. Silylation of that same alkyne (17 R1 ¼ H, R2 ¼ Me)
with dimethylchlorosilane also yields an alkyne (18b) in good yield.
The crude product after condensation with acetone contains 19b
(by 1H NMR) but this compound did not survive chromatographic
purification on silica or alumina. 4-Phenyl-3-buten-1-yne (9) also
condenses with diisopropylchlorosilane to yield 18c in acceptable
yield and that alkyne condenses with formaldehyde to produce
another example of a siloxycyclopentene (19c) in good yield.
investigated
a
copper(I)-catalyzed hydrosilylation protocol
employing silyl boranes and this method also leads to a mixture of
2-silicon and 1-silicon substituted 1,3 diene products (15:16) [9].
The authors who first reported this method hypothesized a
mechanism involving transmetallation to a cupric silane species
and subsequent silylcupration of an alkyne. Under these conditions
we were able to effect hydrosilylation using (dimethylphenylsilyl)
boronic acid pinacol ester (14) to yield dienes (15 & 16) in moderate
yield and regioselectivity.
In addition to these enyne hydrosilylation reactions, we also
executed new examples of Lee’s protocol [10] which utilizes an
initial silylation of a terminal alkyne followed by a carbonyl
condensation (Scheme 3). The overall reaction is an example of an
unusual trans hydrosilylation of an alkyne. With commercially
2.3. Preparation of 2-silicon substituted-1,3-dienes via enyne
metathesis
In the past we had also reported the use of intermolecular enyne
cross metathesis to prepare 2-trialkoxysilyl substituted 1,3 dienes
Scheme 2. Enyne cis-hydrosilylation.

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P.P. Choudhury et al. / Journal of Organometallic Chemistry 754 (2014) 88e93
Scheme 3. Enyne trans-hydrosilylation.
[3d,e] but had not tried this method for triaryl or trialkylsilyl
substituted alkynes or for any intramolecular enyne cross metath-
esis. We first tried this reaction with triphenylsilylacetylene (20)
and styrene (21), however we only isolated 2-triphenylsilyl-1,3-
butadiene (23) in good yield (69%) along with trans-stilbene (24)
(Scheme 4). We hypothesized that the ethylene atmosphere typi-
cally used in these reactions contributed to the formation of 23
however, in the absence of ethylene the reaction still resulted in
formation of 23. Given that observation, it appears that ruthenium
benzylidene catalyst must react much faster with styrene (21) to
produce trans-stilbene (24) and methylidene catalyst (25) than it
reacts with triphenylsilylacetylene (20) so it is the methylidene
catalyst (25) that reacts with 20 and leads to the isolated silyl
substituted diene product (23).
We also tried enyne metathesis on a commercially available
internal alkyne (26) which bears a trialkylsilyl group on the alkyne
(Scheme 5) [11]. This reaction resulted in low yield and the use of
an internal alkyne changed the regiochemistry of the metathesis
reaction to yield 1,2,3-trisubstituted diene (27).
We had never attempted an intramolecular version of this enyne
cross metathesis reaction but we found that it could be effected for
a benzyldimethyl substituted heptenyne (29) to produce silyl
substituted diene (30) (Scheme 6). However, when we went to the
next higher homolog, i.e. an octenyne (32), we could prepare the
enyne (32) in good yield but we noted only enyne decomposition
with different ruthenium catalysts, catalyst loadings, and solvents
in attempts to produce 33 by enyne metathesis. The observed
product 30 is most easily rationalized through an yne then ene
cross metathesis mechanism rather than an ene then yne mecha-
nism [12].
3. Conclusions
In cases where 2-halo-1,3 dienes are commercially available or
synthetically accessed easily using Grignard chemistry to make 2-
silyl-1,3 dienes is the preferred method of synthesis. When the 2-
halo-1,3-dienes are not readily available, cis-hydrosilylation of
enynes containing terminal alkynes leads to mixtures of regioiso-
meric products. Compare, for instance, the preparation of diene 5
using Grignard chemistry to the preparation of structurally related
diene 15 by hydrosilylation to note the advantages of the Grignard
approach when feasible. Trans-hydrosilylation of enynes in
conjunction with carbonyl compound trapping is a viable synthetic
route to siloxy substituted alkenyl cyclopentenes (19). Intermo-
lecular enyne cross metathesis can be used to make 4-alkyl or 4-
aryl-2-silicon substituted dienes if the terminal alkynes used for
cross metathesis bear small substituents on silicon [3d]. The reac-
tion fails as a route to make 4-substituted-2-silicon dienes if the
terminal alkyne used bears silicon with large substituents such as
20. Intramolecular enyne cross metathesis can be used to make
additional silyl substituted alkenyl cyclopentenes such as 30, but
fails as a route to make a silyl substituted alkenyl cyclohexenes such
as 33.
4. Experimental
4.1. General procedures are part of the Supplementary material
4.1.1. Synthesis of (buta-1,3-dien-2-yl)dimethyl(phenyl)silane (2)
Chloroprene (4.58 g, 51.7 mmol) and phenyldimethylchlorosilane
(8.03 g, 47.1 mmol) were used according to the general procedure to
yield a light yellow colored crude product (14.4 g) as a mixture of
diene and xylenes. The crude product was subjected to fractional
distillation at reduced pressure (20 mm, 45 ꢀC) which resulted in a
brown colored liquid, which was further purified by flash chroma-
tography (100% pentanes) to yield the title compound (2) as a light
yellow liquid (8.36 g, 44.4 mmol, 97%): Rf 0.63 (100% pentanes); 1H
NMR (500 MHz, CDCl3) d 7.49e7.55 (m, 2H), 7.31e7.37 (m, 3H), 6.46
(dd, J ¼ 17.7, 10.9 Hz, 1H), 5.88 (d, J ¼ 3.2 Hz, 1H), 5.51 (d, J ¼ 3.2 Hz,
1H), 5.10 (d, J ¼ 17.7 Hz,1H), 5.00 (d, J ¼ 10.9 Hz,1H), 0.43 (s, 6H); 13
C
Scheme 4. Enyne metathesis of triphenylsilylacetylene.
Scheme 5. Enyne metathesis of an internal trimethylsilyl substituted alkyne.

P.P. Choudhury et al. / Journal of Organometallic Chemistry 754 (2014) 88e93
91
Scheme 6. Intramolecular silyl enyne cross metathesis.
NMR (75 MHz, CDCl3)
d
147.6, 141.1, 138.2, 133.9, 130.4, 129.0, 127.8,
4H), 1.54e1.60 (m, 4H), 1.41e1.50 (m, 2H), 0.07 (s, 9H); 13C NMR
(75 MHz, CDCl3) 150.3, 140.5, 125.1, 123.5, 37.4, 29.3, 29.0, 28.3,
116.7, ꢁ2.3; HRMS calcd for C12H16Si (Mþ) 188.1021, found 188.1020.
d
26.9, ꢁ1.95; HRMS calcd for
C
12H22Si (Mþ) 194.1491, found
194.1489.
4.1.2. Synthesis of (buta-1,3-dien-2-yl) dimethylsilanol (3)
Chloroprene in 50% xylenes (1.0 mL, 5.15 mmol) and dichlor-
odimethylsilane (0.645 g, 5 mmol) were used according to the
general procedure above (1 M acetate buffer of pH 5 was used
instead of 0.5 M HCl for the quench) to yield a light yellow colored
liquid. 1H NMR of the crude product (1.1 g) showed a mixture of
xylenes, diene and the corresponding disiloxane dimer. Kugelrohr
distillation at 60 ꢀC (4 mm Hg) of the crude product yielded the
target compound (3) (0.300 g, 2.3 mmol, 46%). 1H NMR (300 MHz
4.2. DielseAlder reactions
4.2.1. Synthesis of 3a,4,7,7a-tetrahydro-5-[dimethyl(phenyl)silyl]-
2-phenyl-2H-isoindole-1,3-dione (8)
Diene (2) (0.302 g, 1.60 mmol) and N-phenylmaleimide (0.103 g,
0.595 mmol) were dissolved in THF (5 mL) and degassed in a sealed
tube. After heating for 4 h at 90 ꢀC, the reaction mixture was filtered
through a cotton plug and volatiles were removed by rotary evap-
oration. The resulting yellow colored residue was purified by flash
chromatography with the excess diene (2) eluting (0.151 g,
0.802 mmol, 78% recovery: Rf 0.84, pentane/diethyl ether, 1:1)
followed by the cycloadduct 8 as a colorless, clear viscous liquid
(0.204 g, 0.564 mmol, 98%): Rf 0.29 (pentane/diethyl ether, 1:1); 1H
CDCl3)
d
6.46 (dd, J ¼ 17.8, 10.8 Hz, 1H), 5.77 (d, J ¼ 3.0 Hz, 1H), 5.56
(d, J ¼ 2.9 Hz, 1H), 5.37 (d, J ¼ 18.2 Hz, 1H), 5.12 (d, J ¼ 10.8 Hz, 1H),
2.25 (bs, 1H), 0.30 (s, 6H); 13C NMR (75 MHz, CDCl3)
d 148.65,
140.88, 129.58, 116.56, 0.32; EIMS calcd for C6H13OSi (M þ H)þ
129.06, found 129.0.
NMR (500 MHz, CDCl3)
d 7.41e7.54 (m, 4H), 7.29e7.41 (m, 4H),
4.1.3. Synthesis of trimethyl[(E)-4-phenyl-1,3-butadien-2-yl]silane
(5)
7.09e7.20 (m, 2H), 6.34 (m, 1H), 3.18e3.30 (m, 2H), 2.71e2.88 (m,
2H), 2.22e2.36 (m, 2H), 0.36 (s, 3H), 0.35 (s, 3H); 13C NMR (75 MHz,
1-[(E)-3-Bromobuta-1,3-dienyl]benzene [13] (4) (1.99 g,
9.49 mmol) and trimethylsilylchloride (1.37 g, 12.6 mmol) were
used according to the general method, producing the crude com-
pound as a dark brown liquid. Purification by flash chromatography
(hexanes/Et2O, 9:1) yielded compound 5 as a brown-yellow oil
(1.56 g, 7.73 mmol, 85%). This compound has been reported pre-
viously by a different route but no characterization data were
provided [7]: Rf 0.15 (hexanes/Et2O, 9:1); 1H NMR (500 MHz, CDCl3)
CDCl3)
d 179.1, 178.7, 140.7, 138.4, 137.0, 133.9, 132.0, 129.2, 129.0,
128.4, 127.8, 126.3, 39.3, 39.2, 26.4, 25.0, ꢁ3.88, ꢁ3.89; HRMS calcd
for C22H23NO2Si (Mþ) 361.1498, found 361.1490. Anal. calcd for
C22H23NO2Si: C, 73.10; H, 6.42. Found: C, 72.63; H, 6.38.
4.3. Cis-hydrosilylation reactions
d
7.43 (d, J ¼ 7.7 Hz, 2H), 7.34 (t, J ¼ 7.7 Hz, 2H), 7.24 (t, J ¼ 7.4 Hz,
4.3.1. Copper-catalyzed hydrosilylation of (E)-4-phenyl-3-buten-1-
yne (9)
To a 5-mL sealable microwave tube equipped with a stir bar,
copper(I) chloride (0.031 g, 0.31 mmol), JohnPhos (0.037 g,
0.12 mmol), and sodium tert-butoxide (0.015 g, 0.16 mmol) were
suspended in THF (2.6 mL) and degassed with argon. (Dimethyl-
1H), 6.94 (d, J ¼ 16.5 Hz, 1H), 6.64 (d, J ¼ 16.5 Hz, 1H), 5.89 (d,
J ¼ 3.0 Hz, 1H), 5.53 (d, J ¼ 3.0 Hz, 1H), 0.27 (s, 9H); 13C NMR
(75 MHz, CDCl3)
0.8.
d 148.9,137.7,134.0,130.5,128.6,128.5,127.3,126.3,
4.1.4. Synthesis of (1-cyclohexylideneprop-2-en-2-yl)
phenylsilyl)boronic acid pinacol ester (14) (234 mL, 0.86 mmol) was
trimethylsilane (7)
added to the reaction vessel, the tube was sealed with a crimp cap,
Chlorotrimethylsilane (0.685 g, 6.30 mmol) and (2-
bromoallylidene)cyclohexene [14] (6) (0.929 g, 4.64 mmol) were
used according to the general procedure. The resulting dark brown
crude residue after purification by flash chromatography (hexanes/
Et2O, 15:1 / 9:1) yielded compound 7 as a browneyellow oil
(0.483 g, 2.49 mmol, 47%): Rf 0.84 (hexanes/Et2O, 15:1); 1H NMR
and placed in a circulating chiller at 0 ꢀC. After 30 min (E)-4-phenyl-
3-buten-1-yne (9) (0.108 g, 0.84 mmol) and MeOH (65
mL,
1.61 mmol) were injected into the reaction vessel. After 24 h at 0 ꢀC
the reaction mixture was filtered through a plug of celite with DCM
(100 mL). The organic solution was then condensed by rotary
evaporation and dried under reduced pressure to yield a greenish
brown liquid (0.386 g). The crude product was purified on silica gel
(500 MHz, CDCl3)
d 5.71 (s, 1H), 5.40e5.49 (m, 2H), 2.10e2.23 (m,

92
P.P. Choudhury et al. / Journal of Organometallic Chemistry 754 (2014) 88e93
with 20:1 hexanes/ethyl acetate resulting in dienes 15:16 as a
yellow liquid (0.091 g, 0.34 mmol, 41%): Rf 0.5 (hexanes/ethyl ac-
which was purified by preparative silica gel chromatography and
eluted with (3:3:96) triethylamine:diethyl ether:pentane mixture
(Rf 0.4). An orange colored liquid (19c) was isolated (0.030 g,
etate 20:1); 15 (major product): 1H NMR (300 MHz, CDCl3)
d 7.59e
7.14 (m, 10H), 6.92 (d, J ¼ 16.4 Hz, 1H), 6.48 (d, J ¼ 16.2 Hz, 1H), 6.00
0.11 mmol, 53%). 1H NMR (300 MHz, CDCl3)
d
7.23e7.43 (m, 5H),
7.13 (d, J ¼ 15.98 Hz, 1H), 6.85 (bs, 1H), 6.40 (d, J ¼ 15.98 Hz, 1H),
1.06e1.12 (m, 14H); 13C NMR (75 MHz, CDCl3)
146.44, 137.45,
(d, J ¼ 2.9 Hz, 1H), 5.57 (d, J ¼ 2.9 Hz, 1H), 0.49 (s, 6H). 13C NMR
(75.5 MHz, CDCl3)
d
146.8 (C), 138.1 (C), 137.5 (C), 133.9 (CH), 133.5
d
(CH), 131.5 (CH), 130.5 (CH2), 129.1 (CH), 128.5 (CH), 127.9 (CH),
127.3 (CH), 126.2 (CH), ꢁ2.1 (CH3). GC/MS: m/z (relative, %): 265.2
(2) [M þ 1], 264.1 (8) [Mþ], 204.1 (2), 173.1 (3), 171.0 (3), 145.0 (4),
137.1 (4), 136.1 (14), 135.1 (100), 128.1 (27), 121.0 (4), 107.0 (6), 105.0
137.40, 132.71, 128.61, 127.48, 126.24, 72.63, 17. 36, 16.96, 13.27.
4.5. Enyne cross metathesis
(8), 91.1 (4), 78,1 (7), 51.1 (3). 2:1 ratio of
a:b regioisomers was
determined by the integrations of vinyl resonances in the 1H NMR
spectrum.
4.5.1. (Z)-3-Methylene-5-phenyl-4-(trimethylsilyl)pent-4-en-2-one
(27)
To a dried 50-mL round bottom flask equipped with a stir bar,
HoveydaeGrubbs 2nd generation catalyst (0.165 g, 0.26 mmol) was
added, dissolved in DCM (36.5 mL), and degassed with argon. 4-
4.4. Trans-hydrosilylation reactions
(Trimethylsilyl)-3-butyn-2-one (26) (292 mL, 1.78 mmol) and sty-
4.4.1. Trans-hydrosilylation/carbonyl condensation of enynes to
prepare siloxycyclopentenes (19)
rene (21) (1.0 mL, 8.7 mmol) were then added successively to the
reaction flask. The flask was then fitted with a condenser and
heated to 40 ꢀC. After 24 h the reaction was cooled to room tem-
perature, condensed by rotary evaporation, and dried under
reduced pressure to yield a brown liquid (0.42 g). The crude product
was then purified on silica gel with 5:1 hexanes/ethyl acetate as
eluent resulting in a yellow oil 27 (0.041 g, 0.17 mmol, 9%): Rf 0.3
In a 100 mL flame dried flask equipped with a magnetic stir bar,
3-methyl-3-buten-1-yne (1.39 g, 20.9 mmol) was added followed
by anhydrous THF (20 mL). The solution was cooled to ꢁ78 ꢀC and
nBuLi (15.0 mL of a 1.6 M soln in hexanes, 23.0 mmol) was added
slowly and stirred for 20 min. Chlorodiisopropylsilane (3.44 g,
23.0 mmol) in THF (10 mL) was added drop wise to the above re-
action mixture. After stirring for 30 min at ꢁ78 ꢀC it was allowed to
warm and stirred 12 h at RT. The milky white reaction mixture was
diluted with diethyl ether (100 mL) and washed with half saturated
NH4Cl solution (100 mL). The organic layer was dried over MgSO4
and the solvent was evaporated under reduced pressure to give a
light yellow colored liquid (18a) (3.279 g, 18.18 mmol, 87%): 1H
(hexanes/ethyl acetate, 5:1); 1H NMR (300 MHz, CDCl3)
d 7.30 (m,
5H), 7.16 (s, 1H), 5.94 (d, J ¼ 0.9 Hz, 1H), 5.75 (d, J ¼ 0.9 Hz, 1H), 2.39
(s, 3H), ꢁ0.05 (s, 9H). 13C NMR (75.5 MHz, CDCl3)
d 200.0 (C]O),
155.7 (C), 144.8 (C), 144.5 (CH), 139.4 (C), 128.5 (CH), 127.8 (CH),
127.3 (CH), 123.0 (CH2), 26.4 (CH3), 0.48 (CH3); HRMS [M þ Na]þ
calcd for C15H20NaOSi, 267.1181; found, 267.1194. Regiochemistry
supported by HMBC spectroscopy. Double bond isomer supported
by NOE spectroscopy.
NMR (300 MHz, CDCl3)
d
5.37e5.38 (m,1H), 5.27 (p, J ¼ 1.66 Hz,1H),
3.75 (bs, 1H), 1.90 (t, J ¼ 1.14 Hz, 3H), 1.06 (m, 14H); 13C NMR
(75 MHz, CDCl3)
d 126.79, 123.04, 109.17, 86.68, 23.88, 18.49, 18.24,
10.86; HRMS calcd for C11H20Si (Mþ) 180.1333, found 180.1333.
In a 20 mL flame dried flask, anhydrous THF (5 mL) was added
followed by acetone (0.269 g, 4.64 mmol). To that solution, the
silylation product (18a) (0.92 g, 5.11 mmol) was added followed by
95% KOtBu (0.052 g, 0.464 mmol). The solution was stirred for
40 min at RT and then washed with half saturated NH4Cl solution
(20 mL) and diethyl ether (20 mL), and the organics dried over
MgSO4. Upon removal of the solvent under reduced pressure and
flash chromatography with 4% diethyl ether in pentane (Rf 0.44),
the target compound (19a) was isolated as a clear liquid, (0.918 g,
4.5.2. Intramolecular enyne cross metathesis
6-Hept-1-yne (28) was synthesized from 5-bromo-1-pentene as
described previously [15]. The enyne (28) (0.6 g, 6.37 mmol) was
treated with nBu-Li (4.5 mL of a 1.6 M soln in hexanes, 7 mmol) and
benzylchlorodimethylsilane (1.404 g, 7.5 mmol) as described above
for 18aec. A light yellow colored liquid (29) was obtained (1.377 g,
5.68 mmol, 89%). 1H NMR (500 MHz, CDCl3)
d
7.22 (t, J ¼ 8.04 Hz,
2H), 7.09 (m, 3H), 5.8 (ddt, J ¼ 17, 10.25, 6.7 Hz, 1H), 5.045 (dd,
J ¼ 17.1,1.72 Hz,1H), 5.00 (m,1H), 2.24 (t, J ¼ 7.1 Hz, 2H), 2.19 (s, 2H),
2.14 (q, J ¼ 7.44 Hz, 2H), 1.61 (p, J ¼ 8.04 Hz, 2H), 0.11 (s, 6H); 13C
3.85 mmol, 83%): 1H NMR (300 MHz, CDCl3)
1H), 4.79 (bs, 1H), 1.91 (s, 3H), 1.35 (s, 6H), 0.98 (m, 14H); 13C NMR
d 6.51 (s, 1H), 4.98 (bs,
NMR (75 MHz, CDCl3) d 139.22,137.74,128.33,128.06,124.21,115.19,
108.55, 83.10, 32.68, 27.68, 26.51, 19.23, ꢁ1.91; HRMS calcd for
C
16H22Si (Mþ) 242.1491, found 242.1492.
(75 MHz, CDCl3)
d 151.04, 142.12, 137.93, 116.31, 82.43, 29.73, 20.7,
17.84, 17.4, 13.19; HRMS calcd for C14H26OSi (Mþ) 238.1753, found
238.1755.
4.5.3. Preparation of diene 30
4.4.2. Preparation of 19c
HoveydaeGrubbs second generation catalyst (0.045 g,
0.053 mmol) was added to a flame dried flask equipped with stir
bar and 4 A molecular sieves (40% w/w). DCM (3 mL) was added
and the solution was degassed. Silyl enyne (29) (0.080 g,
0.353 mmol) was added and refluxed for 12 h under Ar. The reac-
tion was monitored by 1H NMR spectroscopy. Upon completion of
the reaction, solvent was removed under vacuum and the crude
product was purified by preparative silica gel TLC (Rf 0.66 (trie-
thylamine/Et2O/pentane, 1:1:50)) to yield 30 (0.034 g, 0.140 mmol,
(E)-4-Phenyl-3-buten-1-yne (9) was synthesized from trans-
cinnamaldehyde as described previously [8]. Enyne 9 (1.361 g,
10.61 mmol), nBu-Li (7.3 mL of a 1.6 M soln in hexanes, 11.7 mmol),
and chlorodiisopropylsilane (1.76 g, 11.7 mmol) were combined and
worked up as described above to yield crude 18c (2.343 g) as a dark
brown liquid. Flash chromatography using 3% triethylamine in
pentane (Rf 0.6) produced 18c as a light yellow colored oil (1.906 g,
ꢀ
7.86 mmol, 74%). 1H NMR (300 MHz, CDCl3)
7.03 (d, J ¼ 16.3 Hz, 1H), 6.20 (dd, J ¼ 16.3, 1.04 Hz), 3.80 (bs, 1H),
1.08e1.12 (m, 14H). 13C NMR (75 MHz, CDCl3)
142.75, 136.05,
128.82, 128.71, 126.31, 107.96, 107.93, 99.56, 18.53, 18.30, 10.93;
HRMS calcd for C16H12Si (Mþ) 242.1490, found 242.1486. Com-
pound 18c (0.05 g, 0.206 mmol), paraformaldehyde, (0.0051 g,
0.17 mmol), and 95% KOtBu (0.002 g, 0.17 mmol)) were combined
and worked up as described above for 19a to yield a crude product
d 7.28e7.40 (m, 5H),
40%). 1H NMR (500 MHz, CDCl3)
d
7.19 (t, J ¼ 7.54 Hz, 2H), 7.06 (t,
d
J ¼ 7.38 Hz, 1H), 6.98 (d, J ¼ 8.1 Hz, 2H), 5.8 (bs, 1H), 5.66 (d,
J ¼ 2.66 Hz, 1H), 5.36 (d, J ¼ 2.65 Hz, 1H), 2.48e2.51 (m, 4H), 2.26 (s,
2H), 1.9 (p, J ¼ 7.64 Hz, 2H), 0.133 (s, 6H); 13C NMR (75 MHz, CDCl3)
d
145.15, 144.19, 140.11, 129.40, 128.27, 128.00, 125.66, 123.96, 33.68,
33.07, 29.7, 25.96, 22.44; HRMS calcd for C16H22Si (Mþ) 242.1491,
found 242.1494.

P.P. Choudhury et al. / Journal of Organometallic Chemistry 754 (2014) 88e93
93
[3] (a) R.R. Pidaparthi, M.E. Welker, C.S. Day, M.W. Wright, Org. Lett. 9 (2007)
1623;
Acknowledgments
(b) R.R. Pidaparthi, M.E. Welker, Tetrahedron Lett. 48 (2007) 7853;
(c) R.R. Pidaparthi, C.S. Junker, M.E. Welker, C.S. Day, M.W. Wright, J. Org.
Chem. 74 (2009) 8290;
We thank the National Science Foundation for their support of
this work (CHE-0749759) and the NMR and X-ray instrumentation
used to characterize the compounds reported here. The UNC Mass
Spectrometry facility and Mass Spectrometry Lab, School of
Chemical Sciences, University of Illinois at Urbana-Champaign
performed high resolution mass spectral analyses.
(d) C.S. Junker, M.E. Welker, C.S. Day, J. Org. Chem. 75 (2010) 8155;
(e) C.S. Junker, M.E. Welker, Tetrahedron 68 (2012) 5341.
[4] S. De, M.E. Welker, Org. Lett. 7 (2005) 2481.
[5] S. De, C. Day, M.E. Welker, Tetrahedron 63 (2007) 10939.
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Appendix A. Supplementary data
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Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.12.046.
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