Highly regioselective hydrosilylation of unsymmetric alkynes using a phenylthio directing group

Article abstract of DOI:10.1002/ejoc.201402577

Cobalt-assisted hydrosilylation of acetylenes is particularly interesting in organic synthesis since alkynyl group functionalization can give way to more useful substructures. This study aims to answer the general question of how to control hydrosilylatio

Full text of DOI:10.1002/ejoc.201402577

FULL PAPER
DOI: 10.1002/ejoc.201402577
Highly Regioselective Hydrosilylation of Unsymmetric Alkynes Using a
Phenylthio Directing Group
Kuan-Hsun Huang[a] and Minoru Isobe*[a]
Keywords: Synthetic methods / Hydrosilylation / Regioselectivity / Cobalt / Alkynes
Cobalt-assisted hydrosilylation of acetylenes is particularly
interesting in organic synthesis since alkynyl group function-
alization can give way to more useful substructures. This
study aims to answer the general question of how to control
hydrosilylation regioselectivity with unsymmetric alkynyl
reaction loses regioselectivity in cases involving substrates
with relatively small alkyl groups. The roles of the directing
group in this reaction are to (i) exert steric effects on the alkyl
group, and (ii) express stereoelectronic effects of the sulfur
or oxygen atom. The scope and limitation of the hydro-
groups. Cobalt-catalyzed hydrosilylation is highly regioselec- silylation as well as the role of such a directing group are
tive with alkyl-phenylthio-acetylenes affording correspond- discussed.
ing cis-α-silyl-α-thioaryl-substituted olefins. However, this
acetylene as shown in Scheme 1. This limitation arose due
to requirements imposed by the structures of specific target
Introduction
The dicobalthexacarbonyl complex of an acetylene[1] has
been recognized as a highly significant species in synthetic
organic chemistry for several decades, particularly given its
relevance to the Pauson–Khand reaction,[2] Nicholas reac-
tion,[3] cyclotrimerization reaction,[4] cross-coupling reac-
tions,[5] and others. Alkynyl cobalt complexes are often used
as key intermediates in many natural product syntheses as
a means by which to achieve stereoselective C–C or C–O
bond formation.[6] We have explored the application of sev-
eral reductive decomplexation methods for these acetylene-
dicobalt complexes. Among the approaches we have investi-
gated, heating with trialkyltin, trialkylsilane[7] or
compounds. We have, however, been successful in achieving
the regio- and stereoselective hydrosilylation in all cases;
100% cis-α selectivity of the phenylthioacetylenes was ac-
complished and the products then found to serve as partici-
pants in heteroatom-directed conjugate addition (HADCA)
methodology.[10]
[8]
NaH2PO2 have been applied to generate the correspond-
ing cis-olefins or cis-vinylsilanes. One of these methods in-
vokes hydrosilylation to convert the alkynyl group into the
corresponding cis-vinylsilane by treating with trialkylsilane
in either stoichiometric or catalytic amounts relative to the
cobalt reagent.[9] This hydrosilylation directly changes the
alkynyl group to cis-vinylsilane in the presence of a catalytic
amount of stable dicobalt complex from 2-methyl-3-butyne-
2-ol, for example.
In our previous work, this reaction was extensively em-
ployed to obtain hydrosilylation products from alkynes.
However, the practical application of this approach was
limited to cases of unsymmetric alkynes having a PhS- moi-
ety on one side and –CH(ORЈ)R on the other side of the
[a] Chemistry Department, National Tsing Hua University,
101, Sec. 2, Kuang-Fu Road, Hsinchu, Taiwan (ROC)
E-mail: minoru@mx.nthu.edu.tw
http://chem-en.web.nthu.edu.tw/files/13-1117-33471.php
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201402577.
Scheme 1. Hydrosilylation of assorted phenylthioacetylenes.
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4733
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K.-H. Huang, M. Isobe
FULL PAPER
Recently, we found examples of relatively low-selectivity
reactions involving alkynes. Attempted hydrosilylations of
12, 14 and 16 having the C- or H-substituted acetylene pro-
ceeded with variable regioselectivity (Scheme 2). These re-
sults suggested that the sulfur atom should have a signifi-
cant role in establishing regioselectivity due to neighboring
group participation during hydrosilylation. Herein we de-
scribe the importance of the sulfur atom or sulfonyl group
Results and Discussion
Simple phenylthio-propargyloxy substrates 17a–g were
subjected to hydrosilylation conditions as depicted in
Table 1. All cobalt-catalyzed hydrosilylation reactions
(Table 1, Entries 1–8) were completed in 2 h by heating at
80 °C with dimethylphenylsilane in dichloroethane solvent
to give vinylsilanes as the mixtures of regioisomers 18α (the
silyl group located at the α-position) and 18β in moderate
yields. For all cases, the silyl groups and hydrogen atoms
are in the cis-orientation. The regioselectivity of hydro-
silylation is not significantly influenced (4:1 to 3:2) by the
R groups although the major products are α-vinylsilanes;
the use of H, MOM, THP and tBu protective groups ren-
dered similar results (Table 1, Entries 1–4). Even the use of
bulkier silyl protective groups such as TBS or TBDPS failed
to significantly alter reaction selectivity (Table 1, Entries 5,
6). Consequently, the steric factor seems not to be signifi-
cant for setting selectivity in hydrosilylation using these
conditions. When the hydroxy group was protected by the
electron-withdrawing acetyl group, the ratio of regioisomers
remained as low as 3:2 (Table 1, Entry 7). The use of a more
hindered silane, Et3SiH, rendered only a little difference of
about 4:1 (Table 1, Entry 8). Instead of cobalt catalyst 2, a
platinum catalyst (Na2PtCl6) has been known to give a sin-
gle regioisomer α-18b, although the reaction is very slow;
even after heating at a higher temperature of 100 °C for
17 h to yield 18b was generated in only 33% yield (Table 1,
Entry 9).
as
a directing group during cobalt-catalyzed hydro-
silylations to induce regioselectivity.
Scheme 2. Examples of low-selectivity hydrosilylation of various
acetylenes.
Table 1. Hydrosilylation of acetylenes 17a–g with cobalt catalyst 2 (A) or Pt catalyst (B).
1
[a] Determined by H NMR analysis of the crude product. [b] Yield of isolated product after column chromatography. [c] Yield of α and
β mixtures.
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Highly Regioselective Hydrosilylation of Unsymmetric Alkynes
These results suggest that steric factors might not have a
We next examined the reactivity of compounds having
bearing on regioselectivity with the cobalt-catalyzed hydro- different numbers of methylenes attached to the acetylene
silylation. For comparison with other hydrosilylation condi- at the other side of thiophenyl group as shown in Table 4.
tions, four similar phenylthioacetylenes 20a–d were pre- Starting materials 17a, 22a and 22b were prepared from
pared in two steps as shown in Table 2. Initial MnO2 oxi- commercially available hydroxyalkyl acetylenes through
dation of thiopropagylic alcohol 17a generated unstable sulfinylation of the corresponding dianions with diphenyl-
conjugated aldehyde 19. Given the lability of 19, this com- thiosulfonate (see Supporting Information). Each of the
pound was rapidly subjected to nucleophilic additions of phenylthio-hydroxyalkyl acetylenes was subjected to cata-
alkyl, vinyl or aryl groups. Addition of the four different lytic hydrosilylation to give mixtures of α-vinylsilane and β-
nucleophiles to 19 afforded secondary propargylic alcohols vinylsilane as summarized in Table 4. We found that as the
20a–d in good yields.
number of methylene groups distal from the thio moiety
increased, a higher ratio of α-silyl products resulted
(Table 4, Entries 1–3). Reflective of this, hydrosilylation of
propanol starting material 22b afforded α-23b exclusively in
70% yield (Table 4, Entry 3). Since the location of the hy-
droxy group away from the alkyne seemed to affect α-silyl
selectivity, we carried out the same reaction using pentyl
derivative 22c devoid of the hydroxy group. Pentane-con-
taining 22c was subjected to the same hydrosilylation condi-
tions previously applied to 17a, 22a and 22b and found to
be converted to single regioisomer α-23c in 69% yield
(Table 4, Entry 4). These results suggested that the hydroxy
group might influence regioselectivity through an electronic
factor.
Table 2. Preparation of the secondary propargyl alcohol 20a–d.
Table 4. Hydrosilylation of phenylthioacetylenes 17a, 22a–c.
[a] Two step yield of isolated product after column chromatagraphy.
Subjection of propargylic alcohols 20a–d to similar
hydrosilylation conditions in the presence of catalytic
amounts (0.1 equiv.) of stable cobalt-catalyst
2 and
1.5 equiv. of dimethylphenylsilane perfectly yielded all cor-
responding α-vinylsilanes α-21a–d in a 100%-regio- and
stereoselective manner without any traces of alternative re-
gioisomers (Table 3).
Table 3. Hydrosilylation of acetylenes 20a–d with stable cobalt cat-
alyst 2.
[a] Determined by 1H NMR spectroscopy of the crude product.
[b] Yield of isolated product after column chromatography.
We then directed our interests to studying the effect of
the sulfur moiety in phenylthioacetylene 17b. Oxidation of
17b with mCPBA afforded sulfone 24 (Table 5) which, when
subjected to the current hydrosilylation conditions (Table 5,
Entry 3), gave a mixture of α- and β-hydrosilylated 25. This
reaction required twice as much catalyst 2 (0.2 equiv.) to
ensure consumption of 24 (Table 5, Entry 3) compared to
analogous reactions with the sulfide congener (0.1 equiv. of
2, see Table 5, Entry 1). No reaction took place in the ab-
sence of cobalt-catalyst 2 (Table 5, Entry 2). The regioselec-
tivities noted for hydrosilylation reactions using sulfide and
sulfone groups were found to be similar in each case (ca. 3:1
preference for α-isomer generation). In short, little differ-
[a] Determined by 1H NMR spectroscopy of the crude product.
[b] Yield of isolated product after column chromatography.
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K.-H. Huang, M. Isobe
FULL PAPER
ence in hydrosilylation selectivity was noted; selectivities of 74% yield) or electron-withdrawing sulfonyl acetylene 24 as
product formation were similar regardless of whether one the hydrosilylation substrates (2.7:1, 85% yield).
used electron-donating phenylthio-acetylene 17b (3.4:1,
The hydrosilylation mechanism and origins of regioselec-
tivity enabled by acetylenedicobalt complex 2 have not yet
been clarified. However, Krafft et al. have reported that
intermolecular Pauson–Khand reactions (PKRs) can be ac-
celerated by cobalt as mediated by coordinating ligands.
The sulfur atom provided larger accelerations than the oxy-
gen atom in side-by-side comparisons of assorted sulfur- or
oxygen-substituted substrates.[11] Solà and co-workers also
have reported that dicobalt hexacarbonyl complexes of ter-
minal alkynes (with sulfide sulfoxide, sulfone, and amide
moieties) lead to different exo and endo stereoselectivities
in intermolecular PKRs. These observations may explain
electronic effects potentially at play in hydrosilylations as
well.[2b,12] Thus, we have proposed a plausible mechanism
to explain the noted regioselectivities of hydrosilylation in
accordance with above examples of PKRs. Notably, when
R is a simple primary alkyl group, the selectivity of hydro-
silylation was found to be α-silane dominant.
Table 5. Hydrosilylation of sulfinyl- and sulfonyl acetylenes.
The electronic effects of the sulfur atom and steric inter-
actions with the alkyl group are summarized in Scheme 3.
We found that when cobalt complex 2 is treated with a
silane, Co2(CO)6 B is generated in situ thus generating the
relevant catalyst. When the R group of C becomes as bulky
[a] Determined by 1H NMR spectroscopy of the crude product.
[b] Yield of isolated product after column chromatography.
Scheme 3. Plausible reaction mechanism for hydrosilylation.
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Highly Regioselective Hydrosilylation of Unsymmetric Alkynes
as the secondary alcohol, the regioselectivity of hydro-
silylation increases or even exclusive. When an alternative
functionality such as the oxygen atom, is located in the R
group at the γ or δ-position, higher regioselectivity to yield
α-silane dominant products can be observed. As suggested
in a plausible mechanism, dicobalthexacarbonyl complex D,
after heating at 80 °C in the presence of alkylsilane, loses
Experimental Section
General Procedure for Hydrosilylation: Cobalt complex 2 (0.5 m in
dichloromethane, 10 mol-%) was added to a mixture of alkyne
(1.0 mmol) and dimethylphenylsilane (1.5 mmol) in dry 1,2-di-
chloroethane (10 mL), then heated to 80 °C and stirred for 2 h.
After the reaction mixture was cooled to room temperature, the
solvent was removed in vacuo. The residue was washed with TBAF
one CO ligand from the apical position to give coordina- and brine, then purified by chromatography on silica gel with a
mixture of EtOAc and hexane as eluents to afford vinylsilane as a
colorless liquid.
tively unsaturated E, which is then stabilized by the sulfur
or oxygen atom as in F or G by intramolecular coordina-
tion. Metathesis calls for cleavage of the R3Si-Co–C(-SPh)
(Z)-3-[Dimethyl(phenyl)silyl]-3-(phenylthio)prop-2-en-1-ol (α-18a):
bond of H or Co–C(-CHROH) of K and attachment to H Rf = 0.16 (10% EtOAc/hex). 1H NMR (400 MHz, CDCl3): δ = 0.31
(s, 6 H), 4.37 (d, J = 5.2 Hz, 2 H), 6.59 (t, J = 5.2 Hz, 1 H), 7.09–
7.18 (m, 5 H), 7.29–7.36 (m, 3 H), 7.47–7.49 (m, 2 H) ppm. 13C
NMR (150 MHz, CDCl3): δ = –2.9 (CH3 ϫ2), 61.8 (CH2), 125.9
(CH), 127.8 (CHϫ2), 128.7 (CH ϫ2), 128.8 (CH ϫ2), 129.3 (CH),
134.0 (CH ϫ2), 134.5 (C), 136.4 (C), 136.8 (C), 151.1 (CH) ppm.
HRMS (ESI): calcd. for C17H20OSSiNa [M + Na]+ 323.0896;
found 323.0896.
and R3Si to afford I and L. Reaction selectivity might arise
from the different coordinative abilities of the sulfur atom
(F) or the oxygen atom (G). Following this migration, coor-
dination of the carbonyl ligand would quickly transfer I
and L through a reductive elimination to give J and M,
respectively. Intermediates J and M are then envisioned to
undergo reductive elimination to give major product α-si-
lanes and minor β-silanes, while also regenerating Co2-
(CO)6 B, which is used for the next cycle.
Despite the fact that the oxidized sulfone substrate
showed no significant difference in hydrosilylation reaction
selectivity relative to the thioether, we assume that the sulf-
one can act as the intramolecular coordinated ligand, stabi-
(E)-2-[Dimethyl(phenyl)silyl]-3-(phenylthio)prop-2-en-1-ol (β-18a):
Rf = 0.30 (10% EtOAc/hex). 1H NMR (400 MHz, CDCl3): δ = 0.43
(s, 6 H), 1.37 (t, J = 6.0 Hz, 1 H), 4.43 (dd, J = 1.2, 6.0 Hz, 2 H),
6.61 (t, J = 1.2 Hz, 1 H), 7.22–7.36 (m, 8 H), 7.53–7.55 (m, 2
H) ppm. 13C NMR (150 MHz, CDCl3): δ = –2.5 (CH3 ϫ2), 63.0
(CH2), 127.1 (CH), 127.9 (CH ϫ2), 129.16 (CH ϫ2), 129.20 (CH),
129.9 (CH ϫ2), 133.9 (CH ϫ2), 135.6 (C), 136.2 (CH), 138.0 (C),
lizing intermediate II (Scheme 4). The distorted intermedi- 139.7 (C) ppm. HRMS (ESI): calcd. for C17H20OSSiNa [M +
Na]+ 323.0896; found 323.0901.
ates II and III are proposed to afford the dominant α-silane
product (Scheme 4).
(Z)-[3-(Methoxymethoxy)-1-(phenylthio)prop-1-en-1-yl]dimethyl-
(phenyl)silane (α-18b). Rf = 0.16 (2.5 % EtOAc/hex). 1H NMR
(400 MHz, CDCl3): δ = 0.29 (s, 6 H), 3.30 (s, 3 H), 4.34 (d, J =
5.2 Hz, 2 H), 4.59 (s, 2 H), 6.58 (t, J = 5.2 Hz, 1 H), 7.07–7.17
(m, 5 H), 7.28–7.34 (m, 3 H), 7.46–7.48 (m, 2 H) ppm. 13C NMR
(150 MHz, CDCl3): δ = –2.9 (CH3 ϫ2), 55.2 (CH3), 66.5 (CH2),
96.3 (CH2), 125.7 (CH), 127.6 (CH ϫ2), 128.6 (CH ϫ2), 128.8
(CH ϫ2), 129.1 (CH), 133.9 (CH ϫ2), 134.9 (C), 136.2 (C), 136.8
(C), 149.1 (CH) ppm. HRMS (ESI): calcd. C19H24O2SSiNa for [M
+ Na]+ 367.1158; found 267.1157.
(E)-[3-(Methoxymethoxy)-1-(phenylthio)prop-1-en-2-yl]dimethyl-
(phenyl)silane (β-18b): Rf = 0.24 (2.5 % EtOAc/hex). 1H NMR
(400 MHz, CDCl3): δ = 0.42 (s, 6 H), 3.28 (s, 3 H), 4.30 (d, J =
1.2 Hz, 2 H), 4.53 (s, 2 H), 6.64 (d, J = 1.2 Hz, 1 H), 7.27–7.34 (m,
8 H), 7.51–7.54 (m, 2 H) ppm. 13C NMR (150 MHz, CDCl3): δ =
–2.5 (CH3 ϫ2), 55.3 (CH3), 67.3 (CH2), 96.0 (CH2), 127.0 (CH),
127.7 (CH), 129.0 (CH), 129.1 (CH ϫ2), 130.0 (CH ϫ2), 134.0
(CH ϫ2), 135.9 (C), 136.6 (C), 137.6 (CH ϫ2), 137.8 (C) ppm.
HRMS (ESI): calcd. for C19H24O2SSiNa [M + Na]+ 367.1158;
found 367.1161.
Scheme 4. Acetylenesulfone stabilizes the empty orbital.
Conclusions
(Z) Dimethyl(phenyl){1-(phenylthio)-3-[(tetrahydro-2H-pyran-2-
yl)oxy]prop-1-en-1-yl}silane (α-18c). Rf = 0.06 (2.5% EtOAc/hex).
1H NMR (400 MHz, CDCl3): δ = 0.34 (s, 6 H), 1.48–1.61 (m, 4
H), 1.64–1.74 (m, 1 H), 1.79–1.85 (m, 1 H), 3.43–3.48 (m, 1 H),
3.79–3.84 (m, 1 H), 4.36 (ddd, J = 14.4, 5.6, 1.6 Hz, 1 H), 4.52
(ddd, J = 14.4, 5.6, 1.6 Hz, 1 H), 4.57 (br, 1 H), 6.68 (ddd, J = 5.6,
5.6, 1.2 Hz, 1 H), 7.07–7.18 (m, 5 H), 7.29–7.35 (m, 3 H), 7.48–
7.50 (m, 2 H) ppm. 13C NMR (150 MHz, CDCl3): δ = –2.8
(CH3 ϫ2), 19.5 (CH2), 25.3 (CH2), 30.6 (CH2), 62.3 (CH2), 66.5
(CH2), 98.8 (CH), 125.6 (CH), 127.7 (CH ϫ2), 128.6 (CH ϫ2),
128.7 (CH ϫ2), 129.1 (CH), 133.9 (CH ϫ2), 134.1 (C), 136.4 (C),
137.0 (C), 150.0 (C) ppm. HRMS (ESI): calcd. for C22H28O2SSiNa
[M + Na]+ 407.1471; found 407.1471.
In conclusion, we have disclosed the first systematic stud-
ies to determine the factors responsible for regioselectivity
in the Co-catalyzed hydrosilylation of phenylthioacetylenes.
Substrate-borne heteroatoms such as sulfur and oxygen can
act as directing groups for regioselective hydrosilylation af-
fording the corresponding α-vinylsilane. This logic helps to
explain not only examples discussed in this paper but also
those of previous publications. These results and ensuing
rationale are currently being applied to a new total synthe-
sis of natural products.
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K.-H. Huang, M. Isobe
(E)-Dimethyl(phenyl){1-(phenylthio)-3-[(tetrahydro-2H-pyran-2-yl)- 126.7, 127.58, 127.62, 127.67, 127.71, 128.5, 128.9, 129.0, 129.2,
FULL PAPER
methoxy]prop-1-en-2-yl}silane (β-18c). Rf = 0.12 (2.5% EtOAc/hex).
1H NMR (400 MHz, CDCl3): δ = 0.43 (s, 6 H), 1.42–1.64 (m, 6
H), 1.67–1.177 (m, 1 H), 3.41–3.47 (m, 1 H), 3.65–3.72 (m, 1 H),
4.22 (dd, J = 12.8, 1.6 Hz, 1 H), 4.53–4.57 (m, 2 H), 6.59 (dd, J =
1.6, 1.6 Hz, 1 H), 7.21–7.36 (m, 8 H), 7.53–7.56 (m, 2 H) ppm. 13C
NMR (150 MHz, CDCl3): δ = –2.2 (CH3 ϫ2), 18.9 (CH2), 25.4
(CH2), 30.2 (CH2), 61.4 (CH2), 67.8 (CH2), 98.2 (CH), 126.9 (CH),
127.6 (CH ϫ2), 128.9 (CH), 129.1 (CH ϫ2), 129.8 (CH ϫ2), 134.0
(CH ϫ2), 136.0 (C), 136.1 (CH ϫ1), 137.3 (C), 138.2 (C) ppm.
HRMS (ESI): C22H28O2SSiNa [M + Na]+ 407.1471; found
407.1468.
129.5, 129.59, 129.64, 132.3, 133.2, 133.5, 133.9, 134.1, 135.0,
135.4, 135.5, 135.7, 136.4, 137.2, 138.3, 139.7, 152.6 ppm HRMS
(ESI): calcd. for C33H38OSSi2Na [M + Na]+ 561.2074; found
561.2076.
(Z)-3-[Dimethyl(phenyl)silyl]-3-(phenylthio)allyl acetate (α-18g) and
(E)-2-[Dimethyl(phenyl)silyl]-3-(phenylthio)allyl Acetate (β-18g): Rf
= 0.3 (10% EtOAc/hexane). 1H NMR (400 MHz, CDCl3): δ = 0.28
(s, 6 H, α-18g), 0.41 (s, 6 H, β-18g), 1.88 (s, 3 H, β-18g), 2.04 (s, 3
H, α-18g), 4.83–4.85 (m, 4 H, α, β-18g), 6.45 (t, 1 H, J = 5.6 Hz,
α-18g), 6.68 (t, 1 H, J = 1.2, β-18g), 7.10–7.18 (m, 5 H, α, β-18g),
7.25–7.37 (m, 10 H, α, β-18g), 7.45–7.51 (m, 5 H, α, β-18g) ppm.
13C NMR (150 MHz, CDCl3): δ = –2.8, –2.6, 20.6, 20.9, 63.2, 64.3,
126.1, 127.2, 127.7, 127.8, 129.2, 129.25, 129.28, 130.0, 133.8,
133.9, 134.2, 135.3, 135.8, 136.6, 137.1, 137.4, 138.6, 145.7, 170.5,
170.6 ppm. HRMS (ESI): calcd. for C19H22O2SSiNa [M + Na]+
365.1007; found 365.1004.
(Z)-[3-(tert-Butoxy)-1-(phenylthio)prop-1-en-1-yl]dimethyl(phenyl)-
silane (α-18d). Rf = 0.16 (2.5 % EtOAc/hexane). 1H NMR
(400 MHz, CDCl3): δ = 0.29 (s, 6 H), 1.13 (s, 9 H), 4.17 (d, J =
4.8 Hz, 2 H), 6.59 (d, J = 4.8 Hz, 1 H), 7.05–7.16 (m, 5 H), 7.26–
7.33 (m, 3 H), 7.46–7.48 (m, 2 H) ppm. 13C NMR (150 MHz,
CDCl3): δ = –2.8 (CH3 ϫ2), 27.5 (CH3 ϫ3), 61.6 (CH2), 73.4 (C),
125.6 (CH), 127.6 (CH ϫ2), 128.6 (CH ϫ2), 128.8 (CH ϫ2), 129.1
(CH), 132.5 (CH), 133.9 (CH ϫ 2), 136.5 (C), 137.1 (C), 151.7
(CH) ppm. HRMS (ESI): calcd. for C21H28OSSiNa [M + Na]+
379.1522; found 379.1520.
(Z)-Triethyl[3-(methoxymethoxy)-1-(phenylthio)prop-1-en-1-yl]-
silane (α-18h): Rf = 0.12 (2.5 % EtOAc/hexane). 1H NMR
(400 MHz, CDCl3): δ = 0.55 (q, 6 H, J = 7.6 Hz), 0.88 (t, 9 H, J
= 7.6 Hz), 3.38 (s, 3 H), 4.34 (d, 2 H, J = 5.2 Hz), 4.61 (s, 2 H),
6.60 (t, 1 H, J = 5.2 Hz), 7.09–7.14 (m, 1 H), 7.20–7.23 (m, 4
H) ppm. 13C NMR (150 MHz, CDCl3): δ = 2.9 (CH3 ϫ 3), 7.2
(CH2 ϫ3), 55.2 (CH3), 66.5 (CH2), 96.3 (CH2), 125.5 (CH), 128.3
(CH ϫ2), 128.6 (CH ϫ2), 133.3 (C), 136.7 (C), 149.1 (CH) ppm.
HRMS (ESI): calcd. for C17H28O2SSiNa [M + Na]+ 347.1477;
found 347.1472.
(E)-[3-(tert-Butoxy)-1-(phenylthio)prop-1-en-2-yl]dimethyl(phenyl)-
silane (β-18d). Rf = 0.20(2.5 % EtOAc/hexane). 1H NMR
(400 MHz, CDCl3): δ = 0.41 (s, 6 H), 1.11 (s, 9 H), 4.14 (d, J =
1.6 Hz, 2 H), 6.47 (t, J = 1.6 Hz, 1 H), 7.18–7.22 (m, 1 H), 7.26–
7.32 (m, 7 H), 7.52–7.53 (m, 2 H) ppm. 13C NMR (150 MHz,
CDCl3): δ = –1.9 (CH3 ϫ2), 27.2 (CH3 ϫ3), 62.5 (CH2), 73.1 (C),
126.8 (CH), 127.5 (CH ϫ2), 128.8 (CH), 129.0 (CH ϫ2), 129.7
(CH ϫ2), 134.1 (CH ϫ2), 134.5 (CH), 136.2 (C), 138.6 (C), 138.9
(C) ppm. HRMS (ESI): calcd. for C21H28OSSiNa [M + Na]+
379.1522; found 379.1520.
(E)-Triethyl[3-(methoxymethoxy)-1-(phenylthio)prop-1-en-2-yl]-
silane (β-18h): Rf = 0.18 (2.5 % EtOAc/hexane). 1H NMR
(400 MHz, CDCl3): δ = 0.65 (q, 6 H, J = 8.0 Hz), 0.93 (t, 9 H, J
= 8.0 Hz), 3.41 (s, 3 H), 4.29 (s, 2 H), 4.66 (s, 2 H), 7.22–7.25 (m,
1 H), 7.30–7.38 (m, 4 H) ppm. 13C NMR (150 MHz, CDCl3): δ =
3.2 (CH3 ϫ 3), 7.4 (CH2 ϫ 3), 55.5 (CH3 ϫ 1), 67.5 (CH2), 96.1
(CH2), 126.9 (CH), 129.1 (CH ϫ 2), 129.9 (CH ϫ 2), 135.9
(C), 136.3 (C), 136.7 (CH) ppm. HRMS (ESI): calcd. for
C17H28O2SSiNa [M + Na]+ 347.1477; found 347.1470.
(Z)-tert-Butyl({3-[dimethyl(phenyl)silyl]-3-(phenylthio)allyl}oxy)-
dimethylsilane (α-18e). Rf = 0.08 (1% EtOAc/hexane). 1H NMR
(400 MHz, CDCl3): δ = 0.00 (s, 6 H), 0.29 (s, 6 H), 0.84 (s, 9 H),
4.39 (d, J = 4.8 Hz, 2 H), 6.53 (t, J = 4.8 Hz, 1 H), 7.07–7.16
(m, 5 H), 7.27–7.33 (m, 3 H), 7.46–7.48 (m, 2 H) ppm. 13C NMR
(150 MHz, CDCl3): δ = –5.2 (CH3 ϫ2), –2.83 (CH3), –2.82 (CH3),
18.3 (C), 25.9 (CH3 ϫ3), 62.7 (CH2), 125.7 (CH), 127.7 (CH ϫ2),
128.6 (CH ϫ2), 128.9 (CH ϫ2), 129.2 (CH), 132.1 (C), 133.9 (CH
ϫ2), 135.2 (C), 137.0 (C), 152.9 (CH) ppm. HRMS (ESI): calcd.
for C23H34OSSi2Na [M + Na]+ 437.1761; found 437.1764.
(Z)-4-[Dimethyl(phenyl)silyl]-4-(phenylthio)but-3-en-2-ol (α-21a): Rf
= 0.3 (20% EtOAc/hexane). 1H NMR (400 MHz, CDCl3): δ = 0.28
(s, 3 H), 0.29 (s, 3 H), 1.25 (d, 3 H, J = 6.4 Hz), 4.99 (qd, 1 H, J
= 6.4, 7.2 Hz), 6.49 (d, 1 H, J = 7.2), 7.09–7.19 (m, 5 H), 7.29–7.37
(m, 3 H), 7.45–7.48 (m, 2 H) ppm. 13C NMR (150 MHz, CDCl3):
δ = –2.7 (CH3 ϫ2), 22.6 (CH3), 66.2 (CH), 125.9 (CH), 127.7 (CH
ϫ2), 128.6 (CH ϫ2), 129.1 (CH ϫ2), 129.2 (CH), 133.3 (C), 133.9
(CH ϫ2), 136.4 (C), 136.9 (C), 155.8 (CH) ppm. HRMS (ESI):
calcd. for C18H22OSSiNa [M + Na]+ 337.1053; found 337.1057.
(E)-tert-Butyl({2-[dimethyl(phenyl)silyl]-3-(phenylthio)allyl}oxy)-
dimethylsilane (β-18e). Rf = 0.20 (1% EtOAc/hexane). 1H NMR
(400 MHz, CDCl3): δ = –0.02 (s, 6 H), 0.40 (s, 6 H), 0.83 (s, 9 H),
4.44 (d, J = 1.6 Hz, 2 H), 6.42 (t, J = 1.6 Hz, 1 H), 7.18–7.23
(m, 1 H), 7.28–7.32 (m, 7 H), 7.51–7.53 (m, 2 H) ppm. 13C NMR
(150 MHz, CDCl3): δ = –5.6 (CH3 ϫ2), –1.9 (CH3 ϫ2) 18.4 (C),
25.9 (CH3 ϫ 3), 64.1 (CH2), 126.8 (CH), 127.6 (CH ϫ 2), 128.8
(CH), 129.1 (CH ϫ2), 129.6 (CH ϫ2), 133.5 (CH), 134.0 (CH
ϫ2), 136.2 (C), 138.5 (C), 140.7 (C) ppm. HRMS (ESI): calcd. for
C23H34OSSi2Na [M + Na]+ 437.1761; found 437.1765.
(Z)-1-[Dimethyl(phenyl)silyl]-1-(phenylthio)penta-1,4-dien-3-ol (α-
21b): Rf = 0.2 (10% EtOAc/hexane). 1H NMR (400 MHz, CDCl3):
δ = 0.23 (s, 3 H), 0.24 (s, 3 H), 1.86 (d, 9 H, J = 4.0 Hz), 5.12 (ddd,
1 H, J = 10.4, 1.2, 1.2 Hz), 5.23 (ddd, 1 H, J = 17.2, 1.2, 1.2 Hz),
5.39 (m, 1 H), 5.84 (ddd, 1 H, J = 17.2, 10.4, 5.6 Hz), 6.39 (d, 1
H, J = 7.6 Hz), 7.08–7.15 (m, 4 H), 7.26–7.34 (m, 4 H), 7.41–7.43
(m, 2 H) ppm. 13C NMR (150 MHz, CDCl3): δ = –2.59 (CH3),
–2.55 (CH3), 71.1 (CH), 115.4 (CH2), 126.1 (CH), 127.7(CH ϫ2),
128.6 (CH), 129.2 (CH), 129.5 (CH ϫ2), 133.9 (CH ϫ2), 135.3
(C), 136.1 (C), 136.9 (C), 138.0 (CH), 151.7 (CH) ppm. HRMS
(ESI): calcd. for C19H22OSSiNa [M + Na]+ 349.1053; found
349.1054.
(Z)-tert-Butyl({3-[dimethyl(phenyl)silyl]-3-(phenylthio)allyl}oxy)-
diphenylsilane (α-18f) and (E)-tert-Butyl({2-[dimethyl(phenyl)silyl]-
3-(phenylthio)allyl}oxy)diphenylsilane (β-18f). Rf = 0.1 (1% EtOAc/
hexane). 1H NMR (400 MHz, CDCl3): δ = 0.25 (s, 6 H, α-18f),
0.46 (s, 6 H, β-18f), 0.99 (s, 9 H, β-18f), 1.02 (s, 9 H, α-18f), 4.45
(d, 2 H, J = 1.2 Hz, β-18f), 4.49 (d, 2 H, J = 4.8 Hz, α-18f), 6.53
(t, 1 H, J = 1.2 Hz, β-18f), 6.61 (t, 1 H, J = 4.8 Hz, α-18f), 6.96–
9.97 (m, 3 H, α, β-18f), 7.03–7.09 (m, 4 H, α, β-18f), 7.27–7.44
(Z)-3-[Dimethyl(phenyl)silyl]-1-phenyl-3-(phenylthio)prop-2-en-1-ol
(α-21c): Rf = 0.3 (10 % EtOAc/hexane). 1H NMR (400 MHz,
(m, 25 H, α, β-18f), 7.59–7.61 (m, 8 H, α, β-18f) ppm. 13C NMR CDCl3): δ = 0.24 (s, 3 H), 0.25 (s, 3 H), 2.19 (1 H, br), 5.99 (d, 1
(150 MHz, CDCl3): δ = –2.8, –1.8, 1.0, 19.1, 26.8, 63.5, 64.7, 125.6,
H, J = 7.6 Hz), 6.67 (d, 1 H, J = 7.6 Hz), 7.11–7.15 (m, 5 H),
4738
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Eur. J. Org. Chem. 2014, 4733–4740

Highly Regioselective Hydrosilylation of Unsymmetric Alkynes
7.24–7.36 (m, 8 H), 7.39–7.41 (m, 2 H) ppm. 13C NMR (150 MHz,
(m, 5 H), 7.46–7.54 (m, 5 H) ppm. 13C NMR (150 MHz, CDCl3):
CDCl3): δ = –2.57 (CH3), –2.53 (CH3), 71.8 (CH), 126.1 (CH), δ = –2.2 (CH3 ϫ2), 55.4 (CH3), 66.4 (CH2), 96.6 (CH2 ϫ2), 127.0
126.3 (CH ϫ2), 127.65 (CH), 127.68 (CH ϫ2), 128.58 (CH ϫ2),
128.65 (CH ϫ2), 129.2 (CH), 129.5 (CH ϫ2), 133.9 (CH ϫ2),
134.7 (C), 136.1 (C), 136.9 (C), 142.4 (C), 152.9 (CH) ppm. HRMS
(ESI): calcd. for C23H24OSSiNa [M + Na]+ 399.1209; found
399.1206.
(CH ϫ2), 128.0 (CH ϫ2), 128.8 (CH ϫ2), 129.7 (CH), 132.9 (CH),
134.4 (CH), 135.2 (C), 141.8 (C), 144.9 (C), 156.6 (CH) ppm.
HRMS (ESI): calcd. for C19H24O4SSiNa [M + Na]+ 399.1057;
found 399.1058.
(E)-[3-(Methoxymethoxy)-1-(phenylsulfonyl)prop-1-en-2-yl]di-
methyl(p-yl)dimethyl(phenyl)silane (β-25): Rf = 0.26 (20% EtOAc/
(Z)-tert-Butyl 5-[dimethyl(phenyl)silyl]-3-hydroxy-5-(phenylthio)-
pent-4-enoate (α-21d): Rf = 0.2 (10% EtOAc/hexane). 1H NMR
(400 MHz, CDCl3): δ = 0.21 (s, 3 H), 0.24 (s, 3 H), 1.42 (s, 9 H),
2.44 (d, 1 H, J = 7.6 Hz), 2.45 (d, 1 H, J = 4.4 Hz), 3.41 (d, 1 H,
J = 4.4 Hz), 5.13 (1 H, dddd, J = 7.6, 6.8, 4.4, 4.4 Hz), 6.47 (d, 1
H, J = 6.8 Hz), 7.09–7.17 (m, 3 H), 7.26–7.36 (m, 3 H), 7.40–7.42
(m, 2 H) ppm. 13C NMR (150 MHz, CDCl3): δ = –2.6 (CH3), –2.5
(CH3), 28.1 (CH3 ϫ3), 41.2 (CH2), 66.9 (CH), 81.6 (C), 126.2 (CH),
127.7 (CH ϫ2), 128.7 (CH ϫ2), 129.2 (CH), 129.7 (CH ϫ2), 133.9
(CH ϫ 2), 134.9 (C), 135.8 (C), 136.9 (C), 152.3 (CH), 171.7
(C) ppm. HRMS (ESI): calcd. for C23H30O3SSiNa [M + Na]+
437.1577; found 437.1578.
1
hexane). H NMR (400 MHz, CDCl3): δ = 0.43 (s, 6 H), 3.14 (s, 3
H), 4.40 (s, 2 H), 4.79 (d, 2 H, J = 2.0 Hz), 6.32 (t, 1 H, J = 2.0 Hz),
7.28–7.34 (m, 3 H), 7.40–7.42 (m, 2 H), 7.51–7.54 (m, 2 H), 7.57–
7.63 (m, 1 H), 7.85–7.88 (m, 2 H) ppm. 13C NMR (150 MHz,
CDCl3): δ = –2.3 (CH3 ϫ2), 55.4 (CH3), 66.6 (CH2), 96.2 (CH2),
127.3 (CH ϫ2), 127.9 (CH ϫ2), 129.3 (CH ϫ2), 129.5 (CH), 133.0
(C), 133.5 (CH), 133.9 (CH ϫ2), 135.7 (CH), 136.0 (C), 159.3
(CH) ppm. HRMS (ESI): calcd. for C19H24O4SSiNa [M + Na]+
399.1057; found 399.1057.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures, copies of the 1H and 13C NMR
spectra for all new compounds.
(Z)-4-[Dimethyl(phenyl)silyl]-4-(phenylthio)but-3-en-1-ol (α-23a): Rf
= 0.2 (20% EtOAc/hexane). 1H NMR (400 MHz, CDCl3): δ = 0.29
(s, 6 H), 2.64 (td, 2 H, J = 6.4, 6.4 Hz), 3.67 (t, 2 H, J = 6.4 Hz),
6.60 (t, 1 H, J = 6.4 Hz), 7.05–7.17 (m, 5 H), 7.28–7.36 (m, 3 H),
7.47–7.49 (m, 2 H) ppm. 13C NMR (150 MHz, CDCl3): δ = –2.8
(CH3 ϫ2), 34.5 (CH2), 61.6 (CH2), 125.3 (CH), 127.7 (CH ϫ2),
128.1 (CH ϫ2), 128.6 (CH ϫ2), 129.1 (CH), 134.0 (CH ϫ2), 135.1
(C), 137.1 (C), 137.3 (C), 150.2 (CH) ppm. HRMS (ESI): calcd. for
C18H22OSSiNa [M + Na]+ 337.1053; found 337.1052.
Acknowledgments
The authors acknowledge the National Science Council and
National Tsing Hua University, Taiwan for financial support.
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(E)-3-[Dimethyl(phenyl)silyl]-4-(phenylthio)but-3-en-1-ol (β-23a): Rf
= 0.3 (20% EtOAc/hexane). 1H NMR (400 MHz, CDCl3): δ = 0.41
(s, 6 H), 1.33 (t, 1 H, J = 5.6 Hz), 2.62 (t, 2 H, J = 7.2 Hz), 3.58
(td, 2 H, J = 7.2, 5.6 Hz), 6.69 (s, 1 H), 7.23–7.25 (m, 1 H), 7.31–
7.36 (m, 7 H), 7.50–7.53 (2 H,m) ppm. 13C NMR (150 MHz,
CDCl3): δ = –2.9 (CH3 ϫ2), 35.8 (CH2), 61.5 (CH2), 126.8 (CH),
128.0 (CH ϫ2), 129.1 (CH ϫ2), 129.3 (CH), 129.8 (CH ϫ2), 133.9
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(ESI): calcd. for C18H22OSSiNa [M + Na]+ 337.1053; found
377.1055.
(Z)-5-[Dimethyl(phenyl)silyl]-5-(phenylthio)pent-4-en-1-ol (α-23b):
Rf = 0.16 (20% EtOAc/hexane). 1H NMR (400 MHz, CDCl3): δ =
0.28 (s, 6 H), 1.40 (1 H, br), 1.63 (dd, 2 H, J = 7.2, 6.8 Hz), 2.45
(td, 2 H, J = 7.2, 6.8 Hz), 3.57 (2 H, br), 6.53 (t, 1 H, J = 6.8 Hz),
7.05–7.17 (m, 5 H), 7.28–7.36 (m, 3 H), 7.46–7.48 (m, 2 H) ppm.
13C NMR (150 MHz, CDCl3): δ = –2.8 (CH3 ϫ2), 27.2 (CH2), 31.4
(CH2), 62.0 (CH2), 125.2 (CH), 127.7 (CH ϫ2), 128.0 (CH ϫ2),
128.5 (CH ϫ2), 129.1 (CH), 132.8 (CH), 133.9 (CH ϫ2), 137.1
(C), 137.3 (C), 153.7 (CH) ppm. HRMS (ESI): calcd. for
C19H24OSSiNa [M + Na]+ 351.1209; found 351.1206.
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0.84 (t, 3 H, J = 6.8 Hz), 1.19–1.27 (m, 6 H), 1.32–1.37 (m, 2 H),
2.36 (td, 2 H, J = 6.8, 6.8 Hz), 6.55 (t, 1 H, J = 6.8 Hz) ppm. 13C
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(CH2), 28.7 (CH2), 29.0 (CH2), 31.0 (CH2), 31.6 (CH2), 125.0 (CH),
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Eur. J. Org. Chem. 2014, 4733–4740
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Received: May 14, 2014
Published Online: June 17, 2014
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Eur. J. Org. Chem. 2014, 4733–4740