Development of a Radical Silylzincation of (Het)Aryl-Substituted Alkynes and Computational Insights into the Origin of the trans-Stereoselectivity

Article abstract of DOI:10.1002/adsc.202001566

Aryl- and hetaryl-substituted acetylenes undergo regio- and stereoselective silylzincation by reaction with [(Me₃Si)₃Si]₂Zn in the presence of Et₂Zn (10–110 mol%) as additive. The distinctive feature of this addition across the C?C triple bond is its trans stereoselectivity. The radical nature of the silylzincation process is supported by diagnostic experiments and DFT calculations, which also corroborate the role played by steric effects to obtain that stereoselectivity. The procedure can be combined in one-pot with the copper(I)-mediated electrophilic substitution of the C(sp²)?Zn bond, with retention of the double bond geometry. This makes it valuable for the synthesis of stereodefined di- and trisubstituted vinylsilanes. (Figure presented.).

Full text of DOI:10.1002/adsc.202001566

UPDATES
DOI: 10.1002/adsc.202001566
Development of a Radical Silylzincation of (Het)Aryl-Substituted
Alkynes and Computational Insights into the Origin of the trans-
Stereoselectivity
Elise Romain,a Karen de la Vega-Hernández,a Frédéric Guégan,b
Juan Sanz García,b Carolin Fopp,c Fabrice Chemla,a Franck Ferreira,a
Hélène Gerard,b Olivier Jackowski,a Stéphanie Halbert,b,* Martin Oestreich,c,*
and Alejandro Perez-Lunaa,*
a
Sorbonne Université, CNRS, Institut Parisien de Chimie Moléculaire, IPCM, F-75005 Paris, France
E-mail: alejandro.perez_luna@sorbonne-universite.fr
Sorbonne Université, CNRS, Laboratoire de Chimie Théorique, LCT, F-75005 Paris, France
b
E-mail: stephanie.halbert@sorbonne-universite.fr
Technische Universität Berlin, Institut für Chemie, Straße des 17. Juni 115, D-10623 Berlin, Germany
c
E-mail: martin.oestreich@tu-berlin.de
Manuscript received: December 17, 2020; Revised manuscript received: March 1, 2021;
Version of record online: ■■■, ■■■■
Supporting information for this article is available on the WWW under https://doi.org/10.1002/adsc.202001566
substitution. Sequenced silylmetalation-electrophilic
Abstract: Aryl- and hetaryl-substituted acetylenes
undergo regio- and stereoselective silylzincation by
reaction with [(Me3Si)3Si]2Zn in the presence of
substitution of aryl- and alkyl-substituted alkynes was
reported with procedures involving silylcupration,[2]
Pt(II)- or Cu(I)-catalyzed silylmagnesiation,[3] and also
Et2Zn (10–110 mol%) as additive. The distinctive
direct[4] and Cu(I)-catalyzed[5,6] silylzincation. Also, the
feature of this addition across the CÀ C triple bond is
silylcupration-arylation of internal alkynes was dis-
its trans stereoselectivity. The radical nature of the
closed using a dual Cu(I)/Pd(0) catalytic system and
silylzincation process is supported by diagnostic
silylboranes as silicon source.[7] These protocols rely
experiments and DFT calculations, which also
on the transfer of anionic silicon, and involve syn-
corroborate the role played by steric effects to
obtain that stereoselectivity. The procedure can be
addition processes. Hence, the vinylsilanes accessible
are restricted to those having the geometry resulting
combined in one-pot with the copper(I)-mediated
electrophilic substitution of the C(sp2)À Zn bond,
from cis-stereoselectivity.
We recently addressed this limitation and developed
with retention of the double bond geometry. This
synthetic methods to achieve the β-regio and trans-
makes it valuable for the synthesis of stereodefined
di- and trisubstituted vinylsilanes.
stereoselective silylzincation of α-heteroatom-substi-
tuted alkynes (Scheme 1, top). Reaction with a mixture
of (Me3Si)3SiH and Et2Zn was suitable for terminal
ynamides,[8] while reaction with a combination of
Keywords: Radical reactions; Silylmetalation; Silyl-
[(Me3Si)3Si]2Zn and Et2Zn proved more general, and
zinc reagents; Vinylsilanes; Zinc
was also applicable to sulfur-, oxygen- and
phosphorus-substituted terminal alkynes (Scheme 1,
middle).[9] Both the stereochemical outcome of the
Vinylsilanes are popular synthetic building blocks, and additions across the CÀ C triple bonds, and the radical-
their regio- and stereoselective preparation continues stabilizing effect of the trimethylsilyl groups on the
to attract significant attention.[1] The silylmetalation of silicon-center were consistent with a radical mecha-
alkynes, i.e. the addition of a silicon-metal bond across nism involving a Zn-transfer process. For both
a CÀ C triple bond, represents a reliable tool for this procedures, it was possible to associate, in one-pot, the
purpose, as it creates a C(sp2)À Si bond and a C(sp2)- trans-silylzincation with subsequent copper(I)-medi-
metal bond in a single reaction, and the newly formed ated electrophilic substitution of the intermediate
reactive bond can be used, in one pot, as linchpin for C(sp2)À Zn bond, with retention of the double bond
subsequent CÀ C bond formation upon electrophilic geometry. Such reactions provide access to β,β-
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Table 1. Reaction of Aryl-substituted Acetylenes 1a and 1b
with (Me3Si)3SiH/Et2Zn.
Entry
Substrate
Vinylsilane:[a]
Ketone:
Yield (%)[b] [Z/E] [c]
Yield (%) [b]
1
1a
1a
1b
1b
1a
1b
2a:
61 [>98:2]
2a-d1 :
58 [>98 (22% D):2]
2b:
91 [>98:2]
2b-d1 :
82 [>98 (15% D):2]
2a:
81 [>98:2]
2b:
3a: <5[e]
3a: <5[e]
3b: <5[e]
3b: <5[e]
3a: 9
[d]
2
3
[d]
4
5[f]
6[f]
Scheme 1. Trans-stereoselective silylzincation of alkynes.
3b: 14
72 [>98:2]
disubstituted vinylsilanes that cannot be prepared using
hydrosilylation chemistry. We have now found that the
[(Me3Si)3Si]2Zn/Et2Zn system is also applicable to
terminal (het)aryl-substituted acetylenes (Scheme 1,
bottom). In this Update, we report these new advances,
including adjustments of the experimental conditions,
as well as computational evaluation of energetics and
geometrical features of the radical reaction mechanism
giving insights into the origin of the stereoselectivity.
Given that the radical hydrosilylation of terminal
aryl-substituted acetylenes can be achieved with
excellent β-regioselectivity by reaction with
[a] Only β-silylated regioisomers were detected (β:α>98:2).
[b] Determined by 1H NMR spectroscopy using butadiene
sulfone as internal standard.
[c] Determined by 1H NMR analysis of the crude reaction
mixture.
[d] The reaction was quenched with ND4Cl/D2O. The percentage
1
of deuterium incorporation estimated by H NMR spectro-
scopy is given in parenthesis.
[e] Not detected in the crude mixture (yield <5%).
[f] Air (15 mL) was introduced in the reaction medium.
(Me3Si)3SiH under a variety of conditions and with alkyne leading to the loss of the C(sp2)À Zn function-
diverse radical initiators,[10] we reasoned that this ality, or 2) direct H-atom transfer from (Me3Si)3SiH to
substrate class would also be suitable for our radical vinyl radical I. The first process was reported to be
silylzincation procedures. Taking phenylacetylene (1a) only subsidiary in closely related radical carbozinca-
and 2-ethynylanisole (1b) as model substrates, we first tion reactions,[12] and we also arrived to a similar
considered the protocol involving reaction with conclusion for our system considering the reaction of
(Me3Si)3SiH (1.5 equiv.) and Et2Zn (3.0 equiv.) in n- 1b having deuterium attached to the terminal alkyne
hexane at 0 C (Table 1). Following work-up, vinyl- C-atom.[13] Thus, in the reaction of terminal aryl-
°
silanes 2a and 2b were obtained in, respectively, 61% substituted acetylenes and (Me3Si)3SiH/Et2Zn, hydro-
and 91% yield, in excellent β-regio- and Z-stereo- gen-atom transfer from the hydrosilane to vinyl radical
selectivity (entries 1 and 3).[11] However, when the I outcompetes ethylzinc-group transfer from Et2Zn
reactions were quenched with ND4Cl to evidence the (leading to II) and thus hydrosilylation prevails over
putative formation of vinylzinc species (intermediate silylzincation. This procedure is to be regarded rather
II, Scheme 1), 2a-d1 and 2b-d1 were recovered with as a radical hydrosilylation wherein Et2Zn acts chiefly
only 22% and 15% deuterium incorporation (entries 2 as radical initiator. It is noteworthy, that these hydro-
and 4). Two plausible explanations could account for silylation reactions can also be conducted in the
such low amounts of deuterium incorporation: 1) in- presence of deliberately added air (entries 5 and 6),
situ protonation of intermediate II by the starting with comparable yields and stereoselectivity. In this
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case however, aryl ketones (3a and 3b) are also sumed that the critical role played by Et2Zn was to
formed in ~10–15% yield. Similar side-products were allow for efficient radical chain initiation.[17] Close-to-
described in reports on the radical hydrogermylation of complete D-incorporation was observed upon quench-
alkynes, and their formation was attributed to the ing the reaction with ND4Cl (entry 3), thereby confirm-
reaction of intermediate vinylic radicals (similar to I) ing that in this reaction system, silylzincation is the
with oxygen.[14]
major pathway.
To prevent competitive hydrosilylation, we then
We then studied the scope of the conditions
turned our attention to the method relying on optimized for the silylzincation of 1b with other aryl-
[(Me3Si)3Si]2Zn as source of silyl radicals, and focused substituted acetylenes (Scheme 2). A large variety of
on ortho-anisyl derivative 1b, which seemed to afford monosubstituted phenylacetylenes afforded the corre-
better results (Table 2). The conditions previously sponding disubstituted Z-vinylsilanes in decent to good
developed for α-heteroatom-substituted alkynes were yields, with complete control of the stereoselectivity.
applied first; 1b was found to react with Suitable substrates included 1b–1e having electron-
[(Me3Si)3Si]2Zn[15,16] in the presence of Et2Zn donating substituents such as OMe and SMe, as well
°
(1.1 equiv.), in n-hexane at À 30 C, with full β- as 1f–1k having electron-withdrawing substituents
regioselectivity and excellent control of the double such as Cl, Br, CF3 and CO2Me, but not NO2-
bond geometry (entry 1). After reaction work-up, 2b substituted 1l for which only degradation was
was isolated in an encouraging 58% yield, as a single observed. With substrates 1c and 1d, the protocol
Z-stereoisomer. Here also, ketone 3b was recovered in involving 10 mol% Et2Zn gave poorly-reproducible
14% yield. It is however important to mention that this results, because conversion of the starting material was
amount was variable (and often higher) if the reactions not always complete. Increasing the amount of Et2Zn
were conducted at small scale (0.25 mmol or less), (1.1 equiv.) was beneficial in these cases and Z-vinyl-
likely because the relative amount of residual oxygen silanes 2c and 2d could be obtained with satisfactory
in the reaction media is higher in that case. To avoid yields.[18] Interestingly, no appreciable influence of the
this erratic behavior, we conducted routinely the substituent’s position (para-, meta- or ortho-) on the
reactions at 1 mmol scale.
reaction outcome was noted, as it can be seen by
It was possible to reduce the amount of Et2Zn to
10 mol%: a slight improvement in the yield (69%) was
obtained while keeping the same levels of regio- and
stereoselectivity (entry 2). Notwithstanding, the pres-
ence of Et2Zn as additive was necessary, because no
reaction occurred in its absence (entry 4). We pre-
Table 2. Optimization of the Trans-Stereoselective Silylzinca-
tion of 1b.
Entry Et2Zn (equiv.) Vinylsilane:[a]
3b:
Yield (%)
Yield (%) [Z/E][b]
1
2
3
1.1
0.1
0.1
2b: 58 [>98:2]
14
12
2b: 69 [>98:2]
[c]
2b-d1
:
69 [>98 (84% D):2] 15
2b: <5% 10
4
0
[a] Only β-silylated regioisomers were detected (β:α>98:2).
1
[b] Determined by H NMR analysis prior to purification.
[c] The reaction was quenched with ND4Cl/D2O. The percentage
1
of deuterium incorporation estimated by H NMR spectro-
Scheme 2. Trans-stereoselective silylzincation of (het)aryl-sub-
scopy is given in parenthesis.
stituted acetylenes.
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comparing the yields in 2b vs 2c and 2d, 2f vs 2g, 16 h provided vinylsilane 5 with full β-regio- and very
and 2h vs 2i. 3-Naphtyl acetylene (1m), as well as di- high trans-stereoselectivity, albeit in low 20% yield
ortho-chloro-substituted phenyl acetylene 1n also because large amounts of starting material remained
afforded the desired Z-vinylsilanes in good yields and unreacted (entry 1). As for terminal aryl-substituted
excellent stereoselectivity. In view of the large scope acetylenes, adding 1.1 equiv. Et2Zn (entry 2) led to a
of the silylzincation reaction, the modest 47% yield in considerably better yield (45%) keeping the same
2a obtained from phenylacetylene (1a) is somewhat levels of regio- and stereoselectivity. An acceptable
intriguing.[19]
62% yield (49% isolated) was obtained using a larger
In most cases, the formation of aryl ketones 3 was excess (2.0 equiv.) of both [(Me3Si)3Si]2Zn and Et2Zn
°
not detected. However, along with 1b, phenyl (1a), (entry 3). Performing the reaction at 80 C was also
para-anisyl (1d), and naphtyl (1m) substituted alkynes beneficial in terms of yield, but detrimental for stereo-
were exceptions to this general trend. Small amounts control. At this temperature, the reaction with
(10–15%) of the corresponding ketones 3a, 3b and 3d [(Me3Si)3Si]2Zn for 16 h delivered vinylsilane 5 in
were recovered, as well as 20–25% of 3m. Seemingly, 55% yield as a Z/E=58:42 mixture (entry 4). More-
this side reaction is less favorable for substrates having over, an excellent 88% yield was obtained in the
electron-poor aromatic rings.
presence of 1.1 equiv. Et2Zn and radical initiator
Importantly, the silylzincation protocol was also AIBN, but again with no control of the double bond
suitable for hetaryl-substituted acetylenes. Thus, Z- geometry (entry 6). In fact, as evidenced in entry 5, the
vinylsilanes with 2-pyridyl (2o), 3-pyridyl (2p) and 5- stereoselectivity in favor of the Z diastereomer was
methyl-2-thienyl (2q) moieties β to the silicon atom found to be much better at early stages of the reaction,
were obtained with complete control of the regio- and strongly suggesting that trans-stereoselectivity is fa-
the stereoselectivity. The yields were decent for 2o vored kinetically but the alkenylzinc intermediate
(64%) and 2p (69%), but only modest for 2q (34%). undergoes isomerization.[20]
The latter was hampered by the formation of signifi-
cant amounts of oxidation product 3q.
We then verified that the C(sp2)À Zn bond created
during silylzincation remains available for subsequent
To finish our survey of substrates, we then stereoretentive functionalization and thus, that the
considered the silylzincation of 1-phenyl-1-propyne (4) procedure developed for the trans-silylzincation of
as model for internal aryl-substituted alkynes (Table 3). (het)aryl-substituted acetylenes is also suitable to
This substrate was much less reactive than terminal access 1,2,2-trisubstituted vinylsilanes. Cu(I)-mediated
alkynes, but was nevertheless amenable to silylzinca- electrophilic substitution with allyl bromide was taken
°
tion. The reaction with [(Me3Si)3Si]2Zn at 40 C for as model reaction. Allylation of α-(het)aryl-substituted
alkenylzinc intermediates II was readily achieved
using the THF-soluble salt CuCN·2LiCl, as previously
Table 3. Silylzincation of 1-Phenyl-1-Propyne (4).
for α-heteroatom-substituted alkenylzinc species
(Scheme 3). Importantly, introducing the copper salt
°
and the electrophile at À 30 C was critical to prevent
the loss of the double bond geometry. Trisubstituted
vinylsilanes 6b–c, 6e–j and 6m–p were prepared fully
stereoselectively as single Z-isomers[21] in comparable
yields to those of the silylzincation reactions.
The preparation of silylstannyl alkene 7 through
Entry
Si2Zn/Et2Zn
(equiv.)
Conditions
5:[a] Yield
sequential
trans-silylzincation-copper(I)-mediated
(%)[b] [Z/E][c]
stannylation demonstrates further that, similarly to α-
heteroatom-substituted alkynes, the electrophilic sub-
stitution step can be implemented with electrophiles
other than allyl bromide (Scheme 4). Note also that
this reaction represents a formal trans-selective alkyne
silylstannylation reaction, which is virtually
unknown.[22]
The final stage of our Update was focused on
gaining further evidence to assess for the radical
character of the silylzincation process. Towards this
end, we considered first the reaction of [(Me3Si)3Si]2Zn
and 1.1 equiv. Et2Zn with enoate 8 (Scheme 5), which
we had previously used as probe to discriminate
between radical and polar reaction pathways.[8,20] The
(predominant) formation of cyclized product 9-d1
°
1
2
3
4
5
6
1.1/0.0
1.1/1.1
2.0/2.0
1.1/0.0
0.7/0.0
1.1/1.1
40 C, 16 h
20 [>98:2]
45 [92:8]
°
40 C, 16 h
40 C, 16 h
62[d] [91:9]
55 [58:42]
24[e] [79:21]
88 [53:47]
°
°
80 C, 16 h
°
80 C, 30 min
°
80 C, 16 h
AIBN (10 mol%)
[a] Only β-silylated regioisomers were detected (β:α>98:2).
[b] Determined by 1H NMR spectroscopy using butadiene
sulfone as internal standard.
[c] Determined by 1H NMR analysis of the crude reaction
mixture.
[d] 49% isolated yield was obtained upon purification.
[e] Based on the disilylzinc reagent.
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Scheme 5. Reaction
[(Me3Si)3Si]2Zn /Et2Zn.
of
mechanistic
probe
8
with
Examination of the radical pathway was carried out
using DFT calculations. The reaction of the (Me3Si)3Si
radical with 2-ethynylanisole 1b leading to the β
silylzincation isomers is depicted in Figure 1.[26]
The activation energy for the addition of the
(Me3Si)3Si radical across the alkyne is only
2.3 kcalmolÀ 1 (corresponding to 14.5 kcalmolÀ 1 in
Gibbs free energy due to the associative nature of this
step).[27] The corresponding transition state TSA is
early, as demonstrated by the large SiÀ Cβ distance of
2.889 Å (compared to 1.919 Å in I), and the quasi-
°
linear geometry of the alkyne (HÀ CβÀ Cα angle of 159
°
in TSA compared to 178 in 1b). The formed vinylic
radical I is stable, with an energy of À 24.0 kcalmolÀ 1
below the free reactants (corresponding to ΔG=
À 10.5 kcalmolÀ 1 with respect to the separated reac-
tants), which suggests that the radical addition step is
irreversible. The obtained vinyl radical is linear[28]
Scheme 3. Tandem trans-stereoselective silylzincation-copper
(I)-mediated allylation of (het)aryl-substituted acetylenes.
°
(CβÀ CαÀ Caryl angle equal to 178 in I), due to the
delocalization of the radical over the aryl π system (the
spin density is represented in Figure S1 of the
Supporting Information).
The second part of the mechanism involves the
reaction of radical I with [(Me3Si)3Si]2Zn. It occurs in
a single step through homolytic substitution (SH2) at
the zinc atom. Indeed, the coordination of the
diorganosilylzinc reagent to vinyl radical I is associ-
ated in the same step with the concerted cleavage of
one of the ZnÀ Si bonds, thus leading to the regener-
ation of the (Me3Si)3Si radical, and the formation of
the silylzincation products PZ and PE. The trans
Scheme 4. Formal trans-stereoselective silylstannylation of 1c.
(71%) provided evidence for a silyl radical 1,4- product PZ is kinetically favored by 14.4 kcalmolÀ 1
addition (delivering an intermediate β-alkoxy radical and thermodynamically favored by 3 kcalmolÀ 1 over
that undergoes 5-exo-dig cyclization).[23] Conversely, the cis addition product PE.
alcohol 10 arising from the fragmentation of an
Two transition states TSE and TSZ were identified
intermediate β-alkoxy anion[24] that could arise from a (Figure 2) with significantly different geometrical
polar conjugate addition of [(Me3Si)3Si]2Zn was only features. In the structure of TSE, the zinc center is in a
formed in 18% yield.[25] These results lend clear distorted tetrahedral geometry (see Table S1). The
evidence that [(Me3Si)3Si]2Zn has the potential to ZnÀ Cα bonding (2.585 Å) is well advanced (compared
engage in radical reactions that override its anionic to 1.954 Å in PE) and the two ZnÀ Si bonds are
reactivity.
equivalent (2.492 and 2.520 Å vs. 2.336 Å in free
[(Me3Si)3Si]2Zn). We note the presence of a secondary
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Figure 1. Energy profiles for the cis- and trans- radical silylzincation of 2-methoxyphenylacetylene (1b). Energies (in kcal molÀ 1)
are given relative to the separated reactants (see Table S1).
Figure 2. Structures of the stereodivergent transition states TSE (left, cis-silylzincation, 30.3 kcalmolÀ 1 energy barrier) and TSZ
(right, trans-silylzincation, 15.8 kcalmolÀ 1 energy barrier). Angles are given in degrees, distances in Å.; most methyl groups are
omitted for clarity.
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interaction between the oxygen atom of the methoxy within I, and disfavor the pathway leading to the E-
group and the zinc center, as indicated by a ZnÀ O isomer (PE).
distance of 2.269 Å. In addition, the angle at Cα of the
In conclusion, using [(Me3Si)3Si]2Zn as silicon
°
°
vinyl motif (CβÀ CαÀ Caryl angle of 124 close to 118 in donor in the presence of Et2Zn, the silylzincation of
PE) and the SiÀ ZnÀ Si angle in the diorganosilylzinc terminal (het)aryl-substituted acetylenes was achieved
°
°
unit (136
in comparison to 179
in free with excellent β-regio and trans-stereoselectivity,
[(Me3Si)3Si]2Zn) are clearly bent. By contrast, TSZ is a which is unprecedented. Owing to the possibility to
more early-like TS, as indicated by the rather linear use the C(sp2)À Zn bond to introduce, with retention of
°
geometry of zinc unit (154 ), the long ZnÀ Cα distance the double bond geometry, an additional substituent by
of 3.775 Å (compared to 1.945 Å in PZ) and the copper(I)-mediated electrophilic substitution, the pro-
°
scantily bent configuration at the Cα center (148 vs. tocol offers a versatile access to stereodefined di- and
125 in PZ). The arrangement around the zinc center is trisubstituted vinylsilanes. In many cases, 10 mol% of
°
tricoordinated with similar ZnÀ Si distances (2.395 and Et2Zn suffice to obtain optimal results for the
2.414 Å) and a longer ZnÀ O distance of 2.686 Å.
silylzincation, strongly suggesting that its role is
The energetic consequences of the geometrical mainly to ensure radical initiation. DFT calculations
differences between TSZ and TSE was then explored provide support for the radical character of the
using the activation strain model.[29] In this approach, mechanism and insight into the origin of the diaster-
the transition state is described as two distorted eoselection which is mostly related to steric effects
reactants in weak interaction which allows to decom- associated with the large size of the (Me3Si)3Si group.
pose the activation energy into distortion and inter- As part of this work, we have also demonstrated that
action energies (Table 4).[30]
this trans-silylzincation reaction is not fundamentally
The obtained results confirm the late nature of TSE, restricted to terminal alkynes. Even though further
for which the interaction term is much more stabilizing research is still necessary to obtain satisfactory
(À 15.6 kcalmolÀ 1) than for TSZ (À 1.3 kcalmolÀ 1). procedures for synthetic purposes, this approach could
Nevertheless, this difference is largely overridden by offer a valuable solution for the stereodefined prepara-
the larger distortion energy evaluated at 45.9 kcalmolÀ 1 tion of tetrasubstituted vinylsilanes, which remains an
in TSE (vs. 17.1 kcalmolÀ 1 in TSZ). In TSE, this large unsolved problem.[31]
distortion term is associated with about 12 kcalmolÀ 1
for SiÀ ZnÀ Si bending and 8 kcalmolÀ 1 for CβÀ CαÀ Caryl
Experimental Section
bending (vs. 3 and 3 kcalmolÀ 1, respectively for TSZ,
Tables S2 and S3). In the case of TSZ, distortion is the General Procedure A for Silylzincation of Terminal
main contribution while interaction remains small. (Het)Aryl-Substituted Acetylenes
This transition state is thus well described as two
A Schlenk tube was charged with the appropriate (het)aryl-
fragments: a vinyl radical I and a diorganosilylzinc
substituted acetylene (1.00 mmol) and
[(Me3Si)3Si]2Zn (620 mg, 1.11 mmol) in n-hexane (8 mL) was
a suspension of
unit. In contrast, for TSE, the interaction energy is
much larger and cannot be considered as a weak
interaction. This TS is thus viewed as a single metal
complex in which ZnÀ O intramolecular interaction
plays a role, probably by facilitating the addition of the
vinylic radical to the Zn atom. Whereas the interaction
energy is significantly higher in TSE, a closer look at
the geometrical data also highlights that the bulky
(Me3Si)3Si group significantly thwarts the approach of
[(Me3Si)3Si]2Zn to I. In contrast, the major steric
hinderance in TSZ is localized within I, as the bulky
(Me3Si)3Si group tilts the o-methoxy aryl group from a
planar geometry leading to an earlier TSZ. Considering
the relative energies of the two TS, we can assume that
inter-fragment steric effects predominate over those
°
added at À 30 C, followed by Et2Zn (1.0 M in hexane, 0.10 mL,
0.10 mmol). The turbid mixture was stirred at this temperature
for 3 h. The mixture was then diluted with CH2Cl2 (60 mL) and
quenched with aqueous NH4Cl/NH3 (2:1) (8 mL). The layers
were separated and the aqueous one was extracted with CH2Cl2
(2×60 mL). The combined organics were washed with brine
(20 mL), dried (Na2SO4), filtered and concentrated under
reduced pressure. The crude product was purified by flash
column chromatography on silica gel.
General Procedure B for Tandem Silylzincation/
Cu(I)-Mediated Allylation
A Schlenk tube was charged with the appropriate (het)aryl-
substituted acetylene (0.25 mmol) and
a suspension of
[(Me3Si)3Si]2Zn (155 mg, 0.27 mmol) in n-hexane (2 mL) was
°
added at À 30 C, followed by Et2Zn (1.0 M in hexane,
Table 4. Distortion and Interaction Energies (in kcal molÀ 1) for
TSZ and TSE transition states using the activation strain model.
0.025 mL, 0.025 mmol). The turbid mixture was stirred at this
temperature for 3 h and then CuCN·2LiCl (1.0 M in THF,
0.30 mL, 0.30 mmol) was added, followed by allyl bromide
(0.11 mL, 1.27 mmol). The mixture was stirred overnight at
ΔE�
ΔE�
ΔE�
distortion
interaction
TSZ
TSE
15.8
30.3
17.1
45.9
À 1.3
°
À 30 C and then diluted with CH2Cl2 (15 mL) and quenched
À 15.6
with aqueous NH4Cl/NH3 (2:1) (2 mL). The layers were
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separated and the aqueous one was extracted with CH2Cl2 (2×
15 mL). The combined organics were washed with brine (2×
5 mL), dried (Na2SO4), filtered and concentrated under reduced
pressure. The crude product was purified by flash column
chromatography on silica gel.
(Z)-2-(4-methoxystyryl)-1,1,1,3,3,3-hexamethyl-
2-(trimethylsilyl)trisilane (2d)
Prepared according to the general procedure A from 4-
ethynylanisole (1d) (33 mg, 0.25 mmol) using a larger amount
of Et2Zn (0.27 mL, 1.0 M in hexane, 0.27 mmol). Purification
of the crude product (Z/E >98:2) by flash chromatography on
silica gel (pentane/Et2O 100:0 then 98:2) afforded analytically
pure 2d (62 mg, 65%, Z/E >98:2) as a colorless oil.
(Z)-1,1,1,3,3,3-hexamethyl-2-styryl-2-(trimethylsilyl)
trisilane (2a)
1H NMR (C6D6, 400 MHz) δ 7.44 (d, J=14.4 Hz, 1H), 7.37–
7.34 (m, 2H), 6.84–6.81 (m, 2H), 5.92 (d, J=14.4 Hz, 1H),
3.30 (s, 3H), 0.25 (s, 27H). 13C NMR (C6D6, 100 MHz) δ
159.8, 147.0, 133.6, 129.8, 121.5, 114.2, 54.8, 1.6. IR (neat) ν
2948, 2893, 1608, 1506, 1243, 1036, 824, 684, 617 cmÀ 1.
HRMS (ESI) calcd for [C18H36OSi4 +Na]+ 403.1735 found
403.1742.
Prepared according to the general procedure A from phenyl-
acetylene (1a) (110 μL, 1.00 mmol). Purification of the crude
product (Z/E >98:2) by flash chromatography on silica gel
(cyclohexane) afforded analytically pure 2a (165 mg, 47%, Z/E
>98:2) as a colorless oil. The spectral data was in good
agreement with that previously reported.[10l]
1H NMR (C6D6, 400 MHz) δ 7.44 (d, J=14.5 Hz, 1H), 7.35 (d,
J=7.6 Hz, 2H), 7.18–7.14 (m, 2H), 7.06–7.02 (m, 1H), 5.99
(dd, J=14.5, 1.5 Hz, 1H), 0.22 (s, 27H). 13C NMR (C6D6,
100 MHz) δ 147.4, 141.0, 128.7, 128.4, 127.7, 124.3, 1.5.
(Z)-1,1,1,3,3,3-hexamethyl-2-[4-(methylthio)styryl]-
2-(trimethylsilyl)trisilane (2e)
Prepared according to the general procedure A from 1-ethynyl-
4-(methylthio)benzene (1e) (148 mg, 1.00 mmol). Purification
of the crude product (Z/E >98:2) by flash chromatography on
silica gel (pentane) afforded analytically pure 2e (273 mg, 69%,
Z/E >98:2) as a white gum.
(Z)-2-(2-methoxystyryl)-1,1,1,3,3,3-hexamethyl-
2-(trimethylsilyl)trisilane (2b)
Prepared according to the general procedure A from 2-
ethynylanisole (1b) (132 mg, 1.00 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane) afforded analytically pure 2b (262 mg, 69%, Z/E
>98:2) as a colorless oil.
1H NMR (C6D6, 400 MHz) δ 7.38 (d, J=14.5 Hz, 1H), 7.32–
7.27 (m, 2H), 7.19–7.16 (m, 2H), 5.99 (d, J=14.5 Hz, 1H),
1.99 (s, 3H), 0.23 (s, 27H). 13C NMR (C6D6, 100 MHz) δ
146.7, 138.7, 137.7, 129.0, 126.9, 123.7, 15.5, 1.5. IR (neat) ν
2948, 2892, 1595, 1491, 1398, 1241, 822, 684, 622 cmÀ 1.
HRMS (ESI) calcd for [C18H36SSi4 +H]+ 397.1688 found
397.1697.
1H NMR (C6D6, 400 MHz) δ 7.81 (d, J=14.4 Hz, 1H), 7.53–
7.51 (m, 1H), 7.08 (ddd, J=7.9, 7.8, 1.7 Hz, 1H), 6.90 (t, J=
7.4 Hz, 1H), 6.52–6.50 (m, 1H), 6.03 (d, J=14.4 Hz, 1H), 3.31
(s, 3H), 0.21 (s, 27H). 13C NMR (C6D6, 100 MHz) δ 157.7,
143.9, 130.9, 129.5, 129.2, 123.5, 120.8, 110.5, 54.9, 1.5. IR
(neat) ν 2948, 2893, 1590, 1483, 1241, 824, 747, 684,
622 cmÀ 1. HRMS (ESI) for [C18H36OSi4 +Na]+ 403.1735
found 403.1753.
(Z)-2-(3-chlorostyryl)-1,1,1,3,3,3-hexamethyl-
2-(trimethylsilyl)trisilane (2f)
Prepared according to the general procedure A from 1-chloro-3-
ethynylbenzene (1f) (137 mg, 1.00 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane) afforded analytically pure 2f (300 mg, 78%, Z/E
>98:2) as a colorless oil.
(Z)-2-(3-methoxystyryl)-1,1,1,3,3,3-hexamethyl-
2-(trimethylsilyl)trisilane (2c)
Prepared according to the general procedure A from 3-
ethynylanisole (1c) (132 mg, 1.00 mmol) using a larger amount
of Et2Zn (1.0 M in hexane, 1.10 mL, 1.10 mmol). Purification
of the crude product (Z/E >98:2) by flash chromatography on
silica gel (pentane/Et2O 100:0 then 98:2) afforded analytically
pure 2c (342 mg, 90%, Z/E >98:2) as a colorless oil.
1H NMR (C6D6, 400 MHz) δ 7.38 (t, J=1.8 Hz, 1H), 7.22 (d,
J=14.6 Hz, 1H), 7.09–7.06 (m, 1H), 7.01 (ddd, J=8.0, 2.0,
1.0 Hz, 1H), 6.85 (t, J=7.8 Hz, 1H), 6.01 (d, J=14.6 Hz, 1H),
0.21 (s, 27H). 13C NMR (C6D6, 100 MHz) δ 145.8, 143.0,
134.8, 129.9, 128.2, 127.8, 126.6, 126.5, 1.5. IR (neat) ν 2947,
2893, 1560, 1243, 862, 829, 789, 681, 623 cmÀ 1. HRMS
(APCI) calcd for [C17H33ClSi4 +H]+ 385.1421 found 385.1422.
1H NMR (C6D6, 400 MHz) δ 7.44 (d, J=14.5 Hz, 1H), 7.12–
7.04 (m, 2H), 6.97 (brs, 1H), 6.64–6.61 (m, 1H), 6.01 (d, J=
14.5 Hz, 1H), 3.32 (s, 3H), 0.24 (s, 27H). 13C NMR (C6D6,
100 MHz) δ 160.3, 147.3, 142.6, 129.7, 124.8, 120.8, 115.1,
112.5, 54.8, 1.5. IR (neat) ν 2949, 2894, 1751, 1242, 1050, 825,
788, 685, 623 cmÀ 1. HRMS (ESI) calcd for [C18H36OSi4 +Na]+
403.1735 found 403.1746.
(Z)-2-(4-chlorostyryl)-1,1,1,3,3,3-hexamethyl-
2-(trimethylsilyl)trisilane (2g)
Prepared according to the general procedure A from 1-chloro-4-
ethynylbenzene (1g) (137 mg, 1.00 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane) afforded analytically pure 2g (295 mg, 77%, Z/E
>98:2) as a colorless oil. The spectral data was in good
agreement with that previously reported.[10l]
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1H NMR (C6D6, 400 MHz) δ 7.24 (d, J=14.5 Hz, 1H), 7.18–
7.13 (m, 4H), 5.99 (d, J=14.5 Hz, 1H), 0.19 (s, 27H). 13C
NMR (C6D6, 100 MHz) δ 145.8, 139.3, 133.6, 129.8, 128.9,
125.4, 1.5.
2k (184 mg, 45%, Z/E >98:2) as a colorless oil. The spectral
data was in good agreement with that previously reported.[10l]
1H NMR (C6D6, 400 MHz) δ 8.21–8.19 (m, 2H), 7.38–7.36 (m,
2H), 7.32 (d, J=14.6 Hz, 1H), 6.10 (d, J=14.6 Hz, 1H), 3.48
(s, 3H), 0.19 (s, 27H). 13C NMR (C6D6, 100 MHz) δ 166.4,
146.1, 145.1, 130.2, 129.8, 128.4, 127.5, 51.6, 1.5.
(Z)-2-(2-bromostyryl)-1,1,1,3,3,3-hexamethyl-
2-(trimethylsilyl)trisilane (2h)
(Z)-1,1,1,3,3,3-hexamethyl-2-[2-(naphtalen-2-yl)
vinyl]-2-(trimethylsilyl)trisilane (2m)
Prepared according to the general procedure A from 1-bromo-2-
ethynylbenzene (1h) (181 mg, 1.00 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane) afforded analytically pure 2h (236 mg, 55%, Z/E
>98:2) as a colorless oil.
Prepared according to general procedure A from 2-ethynyl-
naphtalene (1m) (152 mg, 1.00 mmol). Purification of the crude
product (Z/E >98:2) by flash chromatography on silica gel
(pentane) afforded analytically pure 2m (220 mg, 55%, Z/E >
98:2) as a colorless oil.
1H NMR (C6D6, 400 MHz) δ 7.48 (dd, J=14.4, 0.4 Hz, 1H),
7.39–7.35 (m, 2H), 7.00–6.96 (m, 1H), 6.72–6.68 (m, 1H), 6.02
(d, J=14.4 Hz, 1H), 0.17 (s, 27H). 13C NMR (C6D6, 100 MHz)
δ 146.7, 141.7, 132.9, 130.2, 129.2, 127.7, 126.6, 124.5, 1.4. IR
(neat) ν 2946, 2893, 2360, 2341, 1461, 1433, 1243, 1026,
831 cmÀ 1. HRMS (ESI) calcd for [C17H33BrSi4 +Na]+
453.0715 found 453.0717.
1H NMR (C6D6, 400 MHz) δ 7.78–7.74 (m, 2H), 7.67–7.65 (m,
1H), 7.61–7.55 (m, 3H), 7.29–7.20 (m, 2H), 6.11 (d, J=
14.5 Hz, 1H), 0.23 (s, 27H). 13C NMR (C6D6, 100 MHz) δ
147.5, 138.7, 134.0, 133.4, 128.3, 128.2, 127.3, 126.7, 126.6,
126.2, 124.6, 1.6 (1 C signal is not visible). IR (neat) ν 2947,
2892, 1242, 892, 826, 776, 746, 684 cmÀ 1. HRMS (APCI) calcd
for [C21H36Si4 +H]+ 401.1967 found 401.1965.
(Z)-2-(4-bromostyryl)-1,1,1,3,3,3-hexamethyl-
2-(trimethylsilyl)trisilane (2i)
(Z)-2-(2,6-dichlorostyryl)-1,1,1,3,3,3-hexamethyl-
2-(trimethylsilyl)trisilane (2n)
Prepared according to the general procedure A from 1-bromo-4-
ethynylbenzene (1i) (181 mg, 1.00 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane) afforded analytically pure 2i (219 mg, 51%, Z/E
>98:2) as a colorless oil.
Prepared according to the general procedure A from 1,3-
dichloro-2-ethynylbenzene (1n) (171 mg, 1.00 mmol). Purifica-
tion of the crude product (Z/E >98:2) by flash chromatography
on silica gel (pentane) afforded analytically pure 2n (266 mg,
63%, Z/E >98:2) as a white solid.
1H NMR (C6D6, 400 MHz) δ 7.34–7.31 (m, 2H), 7.21 (d, J=
14.5 Hz, 1H), 7.08–7.05 (m, 2H), 6.00 (d, J=14.5 Hz, 1H),
0.18 (s, 27H). 13C NMR (C6D6, 100 MHz) δ 145.8, 139.7,
131.8, 130.1, 125.6, 121.7, 1.5. IR (neat) ν 2948, 2892, 1483,
1243, 826, 685, 622 cmÀ 1. HRMS (APCI) calcd for
[C17H33BrSi4 +H]+ 429.0915 found 429.0915.
1H NMR (C6D6, 400 MHz) δ 6.96 (d, J=8.1 Hz, 2H), 6.91 (d,
J=14.8 Hz, 1H), 6.56–6.51 (m, 1H), 6.22 (d, J=14.8 Hz, 1H),
0.17 (s, 27H). 13C NMR (C6D6, 100 MHz) δ 139.7, 139.4,
135.2, 132.6, 128.9, 128.2, 1.5. IR (neat) ν 2948, 2893, 1557,
1427, 1244, 824, 793, 773, 686, 622 cmÀ 1. HRMS (APCI) calcd
for [C17H32Cl2Si4 +H]+ 419.1031 found 419.1031. Mp: 63 C.
°
(Z)-1,1,1,3,3,3-hexamethyl-2-[4-(trifluoromethyl)
styryl]-2-(trimethylsilyl)trisilane (2j)
(Z)-2-[2-(1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)
trisilan-2-yl)vinyl]pyridine (2o)
Prepared according to the general procedure A from 1-ethynyl-
4-(trifluoromethyl)benzene (1j) (170 mg, 1.00 mmol). Purifica-
tion of the crude product (Z/E >98:2) by flash chromatography
on silica gel (pentane) afforded analytically pure 2j (336 mg,
80%, Z/E >98:2) as a colorless oil. The spectral data was in
good agreement with that previously reported.[10d]
Prepared according to the general procedure A from 2-
ethynylpyridine (1o) (25 μL, 0.25 mmol) using a larger amount
of Et2Zn (1.0 M in hexane, 0.27 mL, 0.27 mmol). Purification
of the crude product (Z/E >98:2) by flash chromatography on
silica gel (pentane/Et2O 100:0 then 99:1) afforded analytically
pure 2o (56 mg, 64%, Z/E >98:2) as a colorless oil.
1H NMR (CDCl3, 400 MHz) δ 7.58–7.56 (m, 2H), 7.46–7.41
(m, 3H), 6.07 (d, J=14.7 Hz, 1H), 0.14 (s, 27H). 13C NMR
(CDCl3, 100 MHz) δ 145.0, 144.2, 129.3 (q, J=32.6 Hz),
128.4, 128.2, 125.4 (q, J=3.8 Hz), 124.4 (q, J=271.4 Hz), 1.4.
19F NMR (CDCl3, 376 MHz) δ À 62.48.
1H NMR (C6D6, 400 MHz) δ 8.48–8.46 (m, 1H), 7.20 (d, J=
14.1 Hz, 1H), 6.99 (td, J=7.6, 1.8 Hz, 1H), 6.69–6.67 (m, 1H),
6.54 (ddd, J=7.5, 4.9, 1.2 Hz, 1H), 6.35–6.31 (m, 1H), 0.32 (s,
27H). 13C NMR (C6D6, 100 MHz) δ 157.3, 149.1, 144.4, 136.1,
131.2, 124.7, 121.7, 1.8. IR (neat) ν 2950, 2894, 1585, 1427,
1242, 826, 804, 743, 685, 625, 524 cmÀ 1. HRMS (ESI) calcd
for [C16H33NSi4 +H]+ 352.1763 found 352.1749.
(Z)-methyl 4-[2-(1,1,1,3,3,3-hexamethyl-2-(trimeth-
ylsilyl)trisilan-2-yl)vinyl]benzoate (2k)
Prepared according to the general procedure A from methyl 4-
ethynylbenzoate (1k) (160 mg, 1.00 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane/Et2O 100:0 then 99:1) afforded analytically pure
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(Z)-3-[2-(1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)
trisilan-2-yl)vinyl]pyridine (2p)
2-[1,1,1,3,3,3-Hexamethyl-2-(trimethylsilyl)trisilan-
2-yl]-1-(naphtalen-2-yl)ethenone (3m)
Prepared according to the general procedure A from 3-
ethynylpyridine (1p) (103 mg, 1.00 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane/Et2O 90:10) afforded analytically pure 2p
(244 mg, 69%, Z/E >98:2) as a colorless oil. The spectral data
was in good agreement with that previously reported.[10l]
A fraction containing analytically pure 3m was isolated during
purification of the crude mixture of the reaction of 1m
according to general procedure A.
1H NMR (C6D6, 400 MHz) δ 8.41–8.40 (m, 1H), 8.21 (dd, J=
8.6, 1.8 Hz, 1H), 7.67–7.65 (m, 1H), 7.58 (d, J=8.7 Hz, 1H),
7.53–7.50 (m, 1H), 7.24–7.18 (m, 2H), 2.80 (s, 2H), 0.21 (s,
27H). 13C NMR (C6D6, 100 MHz) δ 199.4, 135.8, 135.7, 133.0,
130.2, 129.7, 128.8, 128.1, 126.9, 125.2, 21.3, 1.1. HRMS
(ESI) calcd for [C21H36OSi4 +H]+ 439.1735 found 439.1719.
1H NMR (C6D6, 400 MHz) δ 8.84 (d, J=2.2 Hz, 1H), 8.42 (dd,
J=7.8, 1.6 Hz, 1H), 7.28–7.25 (m, 1H), 7,18 (d, J=14.6 Hz,
1H), 6.73 (ddd, J=7.8, 4.8, 0.7 Hz, 1H), 6.06 (d, J=14.6 Hz,
1H), 0.20 (s, 27H). 13C NMR (C6D6, 100 MHz) δ 149.4, 148.9,
143.4, 136.2, 134.9, 127.7, 123.2, 1.4.
2-[1,1,1,3,3,3-Hexamethyl-2-(trimethylsilyl)trisilan-
2-yl]-1-(5-methylthiophen-2-yl)ethenone (3q)
(Z)-1,1,1,3,3,3-hexamethyl-2-[2-(5-methylthiophen-
2-yl)vinyl]-2-(trimethylsilyl)trisilane (2q)
A fraction containing analytically pure 3q was isolated during
purification of the crude mixture of the reaction of 1q according
to general procedure A.
Prepared according to the general procedure A from 5-methyl-
2-ethynylthiophene (1q) (122 mg, 1.00 mmol). Purification of
the crude product (Z/E >98:2) by flash chromatography on
silica gel (pentane) afforded analytically pure 2q (125 mg,
34%, Z/E >98:2) as a colorless oil.
1H NMR (C6D6, 400 MHz) δ 7.26 (d, J=3.7 Hz, 1H), 6.35–
6.34 (m, 1H), 2.52 (s, 2H), 1.94 (d, J=0.7 Hz, 3H), 0.25 (s,
27H). 13C NMR (C6D6, 100 MHz) δ 192.2, 149.1, 144.3, 131.8,
126.6, 21.8, 15.6, 1.1. HRMS (ESI) calcd for [C16H34OSSi4 +
Na]+ 409.1300 found 409.1293.
1H NMR (C6D6, 400 MHz) δ 7.33 (d, J=14.4 Hz, 1H), 6.90 (d,
J=3.4 Hz, 1H), 6.45–6.44 (m, 1H), 5.87 (d, J=14.4 Hz, 1H),
2.12 (brs, 3H), 0.28 (s, 27H). 13C NMR (C6D6, 100 MHz) δ
142.2, 140.1, 139.3, 126.2, 125.8, 123.8, 15.2, 1.8. IR (neat) ν
2947, 2892, 1242, 826, 800, 684, 622 cmÀ 1. HRMS (ESI) calcd
for [C16H34SSi4 +Na]+ 393.1350 found 393.1364.
(Z)-1,1,1,3,3,3-hexamethyl-2-(1-phenylprop-1-en-
2-yl)-2-(trimethylsilyl)trisilane (5)
A Schlenk flask was charged with AIBN (9 mg, 0.05 mmol)
and tris(trimethylsilyl)silane (0.31 mL, 1.0 mmol) and placed
under Ar. Et2Zn (0.53 mL, 1.0 M in hexanes, 0.53 mmol) was
2-[1,1,1,3,3,3-Hexamethyl-2-(trimethylsilyl)trisilan-
2-yl]-1-phenylethenone (3a)
°
added and the mixture was heated at 80 C for 20 min. The
°
resulting pale-yellow turbid mixture was then cooled to 0 C
A fraction containing analytically pure 3a was isolated during
purification of the crude mixture of the reaction of phenyl-
acetylene (1a) according to general procedure A.
and diluted in n-hexane (0.36 mL). 1-Phenyl-1-propyne (32 μL,
0.25 mmol) and Et2Zn (0.50 mL, 1.0 M in hexanes, 0.50 mmol)
°
were added successively. The mixture was heated at 40 C for
16 h. It was then cooled, diluted with CH2Cl2 (15 mL), and
quenched with aq. NH4Cl/NH3 (2:1) (8 mL). The layers were
separated and the aqueous one was extracted with CH2Cl2 (2×
10 mL). The combined organics were washed with brine
(10 mL), dried (Na2SO4), filtered and concentrated under
reduced pressure. The crude product was purified by flash
column chromatography on silica gel (cyclohexane) to afford
analytically pure 5 (46 mg, 49%, Z/E=91:9) as a colorless oil.
1H NMR (CDCl3, 400 MHz) δ 7.93–7.91 (m, 2H), 7.56–7.52
(m, 1H), 7.44 (t, J=7.5 Hz, 2H), 2.76 (s, 2H), 0.13 (s, 27 H).
13C NMR (CDCl3, 100 MHz) δ 201.1, 138.0, 132.8, 128.7,
128.6, 21.6, 1.0. HRMS (ESI) calcd for [C17H34OSi4 +H]+
367.1759 found 367.1760.
2-[1,1,1,3,3,3-Hexamethyl-2-(trimethylsilyl)trisilan-
2-yl]-1-(2-methoxyphenyl)ethenone (3b)
1
(Z-5): H NMR (CDCl3, 400 MHz) δ 7.36–7.32 (m, 3H), 7.30–
7.25 (m, 3H), 2.18 (brs, 3H), 0.18 (s, 27H). 13C NMR (CDCl3,
100 MHz) δ 142.5, 141.2, 134.7, 129.0, 128.5, 126.8, 32.4, 2.6.
The spectral data was in good agreement with that previously
reported.[10l]
A fraction containing analytically pure 3b was isolated during
purification of the crude mixture of the reaction of 1b according
to general procedure A.
1H NMR (C6D6, 400 MHz) δ 7.98 (dt, J=7.6, 2.0 Hz, 1H), 7.04
(ddd, J=8.3, 7.3, 2.0 Hz, 1H), 6.75 (td, J=7.6, 1.0 Hz, 1H),
6.42 (d, J=8.3 Hz, 1H), 3.25 (s, 3H), 3.10 (s, 2H), 0.25 (s,
27H). 13C NMR (C6D6, 100 MHz) δ 200.8, 158.7, 133.0, 132.1,
129.8, 121.0, 111.8, 55.0, 26.4, 1.1. HRMS (ESI) calcd for
[C18H36O2Si4 +H]+ 397.1865 found 397.1867.
(Z)-2-[2-(2-methoxyphenyl)penta-1,4-dienyl]-
1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilane
(6b)
Prepared according to the general procedure B from 2-
ethynylanisole (1b) (132 mg, 1.00 mmol) and allyl bromide
(0.44 mL, 5.0 mmol). Purification of the crude product (Z/E >
98:2) by flash chromatography on silica gel (pentane) afforded
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analytically pure 6b (270 mg, 64%, Z/E >98:2) as a colorless
oil.
1.2 Hz, 1H), 5.71 (ddt, J=17.0, 10.2, 6.8 Hz, 1H), 4.98–4.88
(m, 2H), 2.98–2.95 (m, 2H), 0.17 (s, 27H). 13C NMR (C6D6,
75 MHz) δ 155.6, 147.1, 136.2, 134.7, 130.1, 128.7, 127.6,
126.7, 121.5, 116.8, 47.9, 1.4. IR (neat) ν 2948, 2893, 2361,
2341, 1243, 831, 686, 623 cmÀ 1. HRMS (APCI) calcd for
[C20H37ClSi4 +H]+ 425.1734 found 425.1733.
1H NMR (C6D6, 400 MHz) δ 7.16–7.14 (m, 1H), 7.06 (ddd, J=
8.2, 7.5, 1.8 Hz, 1H), 6.88–6.84 (m, 1H), 6.53–6.51 (m, 1H),
5.94–5.85 (m, 2H), 5.00–4.95 (m, 2H), 3.31 (s, 3H), 3.29 (ddt,
J=6.9, 1.3, 1.2 Hz, 2H), 0.20 (s, 27H). 13C NMR (C6D6,
100 MHz) δ 157.0, 155.8, 137.1, 134.2, 131.2, 128.8, 120.9,
120.3, 116.0, 110.9, 54.7, 46.7, 1.4. IR (neat) ν 2948, 2893,
1487, 1434, 1240, 826, 750, 686, 623 cmÀ 1. HRMS (ESI) calcd
for [C21H40OSi4 +Na]+ 443.2048 found 443.2049.
(Z)-2-[2-(4-chlorophenyl)penta-1,4-dienyl]-
1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilane
(6g)
Prepared according to the general procedure B from 1-chloro-4-
ethynylbenzene (1g) (34 mg, 0.25 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane) afforded analytically pure 6g (87 mg, 82%, Z/E >
98:2) as a colorless oil.
(Z)-2-[2-(3-methoxyphenyl)penta-1,4-dienyl]-
1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilane
(6c)
Prepared according to the general procedure B from 3-
ethynylanisole (1c) (33 mg, 0.25 mmol). A more important
amount of Et2Zn (1.0 M in hexane, 0.27 mL, 0.27 mmol,
1.1 equiv.) was introduced in this case. Purification of the crude
product (Z/E >98:2) by flash chromatography on silica gel
(pentane) afforded analytically pure 6c (76 mg, 72%, Z/E >
98:2) as a colorless oil.
1H NMR (C6D6, 400 MHz) δ 7.15–7.13 (m, 2H), 7.00–6.97 (m,
2H), 5.79 (t, J=1.2 Hz, 1H), 5.73 (ddt, J=16.9, 10.1, 6.8 Hz,
1H), 4.99–4.91 (m, 2H), 3.00 (dqapp, J=6.8, 1.2 Hz, 2H), 0.15
(s, 27H). 13C NMR (C6D6, 100 MHz) δ 155.7, 143.3, 136.3,
133.5, 129.9, 128.9, 121.2, 116.7, 47.8, 1.4. IR (neat) ν 2947,
2893, 2360, 2341, 1487, 1393, 1091, 830, 784, 685, 623 cmÀ 1.
HRMS (APCI) calcd for [C20H37ClSi4 +H]+ 425.1734 found
425.1733.
1H NMR (C6D6, 300 MHz) δ 7.13–7.07 (m, 1H), 6.94 (brs, 1H),
6.89–6.87 (m, 1H), 6.67–6.63 (m, 1H), 5.90–5.76 (m, 2H),
5.00–4.96 (m, 2H), 3.37 (s, 3H), 3.15–3.12 (m, 2H), 0.22 (s,
27H). 13C NMR (C6D6, 75 MHz) δ 160.2, 157.0, 146.6, 136.7,
129.8, 121.0, 120.0, 116.4, 115.1, 112.3, 54.8, 48.1, 1.5. IR
(neat) ν 2894, 2835, 2361, 2341, 1574, 1243, 833, 687 cmÀ 1.
HRMS (ESI) calcd for [C21H40OSi4 +Na]+ 443.2048 found
443.2041.
(Z)-2-[2-(2-bromophenyl)penta-1,4-dienyl]-
1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilane
(6h)
Prepared according to the general procedure B from 1-bromo-2-
ethynylbenzene (1h) (45 mg, 0.25 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane) afforded analytically pure 6h (83 mg, 71%, Z/E >
98:2) as a colorless oil.
(Z)-1,1,1,3,3,3-hexamethyl-2-[2-(4-(methylthio)
phenyl)penta-1,4-dienyl]-2-(trimethylsilyl)trisilane
(6e)
1H NMR (C6D6, 400 MHz) δ 7.36 (dd, J=8.0, 1.1 Hz, 1H),
7.03 (dd, J=7.5, 1.8 Hz, 1H), 6.93 (ddd, J=7.5, 7.4, 1.2 Hz,
1H), 6.70 (ddd, J=7.9, 7.5, 1.8 Hz, 1H), 5.89 (t, J=1.3 Hz,
1H), 5.81 (ddt, J=17.1, 10.1, 7.0 Hz, 1H), 4.98 (ddt, J=10.1,
2.0, 1.0 Hz, 1H), 4.91–4.90 (m, 1H), 3.19–3.07 (m, 2H), 0.18
(s, 27H). 13C NMR (C6D6, 100 MHz) δ 155.7, 145.7, 136.2,
133.3, 131.4, 128.9, 127.6, 123.3, 122.8, 116.9, 46.5, 1.5. IR
(neat) ν 2946, 2892, 2360, 2341, 1463, 1431, 1242, 830 cmÀ 1.
HRMS (ESI) calcd for [C20H37BrSi4 +Na]+ 493.1028 found
493.0979.
Prepared according to the general procedure B from 1-ethynyl-
4-(methylthio)benzene (1e) (37 mg, 0.25 mmol). Purification of
the crude product (Z/E >98:2) by flash chromatography on
silica gel (pentane) afforded analytically pure 6e (82 mg, 76%,
Z/E >98:2) as a colorless oil.
1H NMR (C6D6, 400 MHz) δ 7.16–7.11 (m, 4H), 5.81–5.77 (m,
2H), 5.01–4.96 (m, 2H), 3.11 (dq, J=6.8, 1.3 Hz, 2H), 2.03 (s,
3H), 0.18 (s, 27H). 13C NMR (C6D6, 100 MHz) δ 156.5, 141.8,
138.2, 136.7, 129.0, 127.4, 120.3, 116.5, 47.9, 15.8, 1.5. IR
(neat) ν 2946, 2892, 1584, 1242, 1093, 830, 684 cmÀ 1. HRMS
(ESI) calcd for [C21H40SSi4 +Na]+ 459.1820 found 459.1833.
(Z)-2-[2-(4-bromophenyl)penta-1,4-dienyl]-
1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilane
(6i)
(Z)-2-[2-(3-chlorophenyl)penta-1,4-dienyl]-
1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilane
(6f)
Prepared according to the general procedure B from 1-bromo-4-
ethynylbenzene (1i) (45 mg, 0.25 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane) afforded analytically pure 6i (103 mg, 88%, Z/E
>98:2) as a colorless oil.
Prepared according to the general procedure B from 1-chloro-3-
ethynylbenzene (1f) (34 mg, 0.25 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane) afforded analytically pure 6f (76 mg, 72%, Z/E >
98:2) as a colorless oil.
1H NMR (C6D6, 400 MHz) δ 7.30–7.28 (m, 2H), 6.92–6.90 (m,
2H), 5.78–5.77 (m, 1H), 5.72 (ddt, J=16.9, 10.1, 6.8 Hz, 1H),
4.98–4.90 (m, 2H), 3.01–2.97 (m, 2H), 0.13 (s, 27H). 13C NMR
(C6D6, 100 MHz) δ 155.7, 143.8, 136.3, 131.9, 130.3, 121.5,
1H NMR (C6D6, 300 MHz) δ 7.31 (t, J=1.8 Hz, 1H), 7.06–7.02
(m, 1H), 6.97–6.94 (m, 1H), 6.88–6.83 (m, 1H), 5.81 (t, J=
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121.2, 116.7, 47.8, 1.4. IR (neat) ν 2947, 2892, 2360, 1483,
1242, 1071, 992, 830, 684, 622 cmÀ 1. HRMS (APCI) calcd for
[C20H37BrSi4 +H]+ 469.1228 found 469.1227.
(Z)-2-[1-(1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)
trisilan-2-yl)penta-1,4-dien-2-yl]pyridine (6o)
Prepared according to the general procedure B from 2-
ethynylpyridine (1o) (25 μL, 0.25 mmol). A more important
amount of Et2Zn (1.0 M in hexane, 0.27 mL, 0.27 mmol,
1.1 equiv.) was introduced in this case. Purification of the crude
product (Z/E >98:2) by flash chromatography on silica gel
(pentane/Et2O 100:0 then 99:1) afforded analytically pure 6o
(62 mg, 64%, Z/E >98:2) as a colorless oil.
(Z)-1,1,1,3,3,3-hexamethyl-2-[2-(4-(trifluoromethyl)
phenyl)penta-1,4-dienyl]-2-(trimethylsilyl)trisilane
(6j)
Prepared according to the general procedure B from 1-ethynyl-
4-(trifluoromethyl)benzene (1j) (43 mg, 0.25 mmol). Purifica-
tion of the crude product (Z/E >98:2) by flash chromatography
on silica gel (pentane) afforded analytically pure 6j (104 mg,
91%, Z/E >98:2) as a colorless oil.
1H NMR (C6D6, 400 MHz) δ 8.50 (ddd, J=4.8, 1.8, 1.0 Hz,
1H), 7.13–7.05 (m, 2H), 6.61 (ddd, J=7.2, 4.8, 1.5 Hz, 1H),
6.14 (t, J=1.1 Hz, 1H), 5.87 (ddt, J=16.6, 10.1, 6.4 Hz, 1H),
5.06–4.98 (m, 2H), 3.29 (dqapp, J=6.4, 1.3 Hz, 2H), 0.26 (s,
27H). 13C NMR (C6D6, 100 MHz) δ 160.2, 153.6, 149.4, 137.1,
136.1, 125.8, 122.1, 121.8, 116.3, 44.6, 1.7. IR (neat) ν 2948,
2893, 2362, 1584, 1426, 1241, 823, 743, 684, 623 cmÀ 1.
HRMS (ESI) calcd for [C19H37NSi4 +H]+ 392.2076 found
392.2092.
1H NMR (CDCl3, 400 MHz) δ 7.58–7.56 (m, 2H), 7.33–7.31
(m, 2H), 5.76 (ddt, J=16.9, 10.1, 6.8 Hz, 1H), 5.73 (t, J=
1.2 Hz, 1H), 5.05–4.97 (m, 2H), 3.15 (dqapp, J=6.8, 1.3 Hz,
2H), 0.04 (s, 27H). 13C NMR (CDCl3, 100 MHz) δ 154.8,
148.6, 136.1, 129.4 (q, J=32.4 Hz), 128.7, 124.4 (q, J=
272.0 Hz), 125.5 (q, J=3.7 Hz), 122.5, 116.8, 47.7, 1.2. 19F
NMR (CDCl3, 376 MHz) δ À 62.6. IR (neat) ν 2949, 2895,
2360, 2341, 1324, 1244, 1167, 1129, 1067, 832 cmÀ 1. HRMS
(APCI) calcd for [C21H37F3Si4 +H]+ 459.1997 found 459.1995.
(Z)-3-[1-(1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)
trisilan-2-yl)penta-1,4-dien-2-yl]pyridine (6p)
Prepared according to the general procedure B from 3-
ethynylpyridine (1p) (26 mg, 0.25 mmol). Purification of the
crude product (Z/E >98:2) by flash chromatography on silica
gel (pentane/Et2O, 90:10) afforded analytically pure 6p (68 mg,
69%, Z/E >98:2) as a colorless oil.
(Z)-1,1,1,3,3,3-hexamethyl-2-[2-(naphtalen-2-yl)
penta-1,4-dienyl]-2-(trimethylsilyl)trisilane (6m)
Prepared according to the general procedure B from 2-ethynyl-
naphtalene (1m) (38 mg, 0.25 mmol). Purification of the crude
product (Z/E >98:2) by flash chromatography on silica gel
(pentane) afforded analytically pure 6m (50 mg, 45%, Z/E >
98:2) as a colorless oil.
1H NMR (C6D6, 400 MHz) δ 8.75 (d, J=1.4 Hz, 1H), 8.46 (dd,
J=4.7, 1.4 Hz, 1H), 7.23–7.20 (m, 1H), 6.75 (dd, J=7.8,
4.7 Hz, 1H), 5.88 (t, J=1.2 Hz, 1H), 5.70 (ddt, J=16.9, 10.1,
6.8 Hz, 1H), 4.96–4.88 (m, 2H), 2.98–2.96 (m, 2H), 0.17 (s,
27H). 13C NMR (C6D6, 100 MHz) δ 153.2, 149.7, 149.1, 140.1,
136.1, 134.9, 123.2, 122.9, 116.9, 47.6, 1.3. IR (neat) ν 2947,
2893, 2360, 1408, 1243, 830, 716, 685, 623 cmÀ 1. HRMS (ESI)
calcd for [C19H37NSi4 +H]+ 392.2076 found 392.2078.
1H NMR (C6D6, 400 MHz) δ 7.75–7.73 (m, 2H), 7.64–7.61 (m,
2H), 7.35–7.33 (m, 1H), 7.30–7.22 (m, 2H), 5.93 (t, J=1.2 Hz,
1H), 5.86 (ddt, J=16.1, 10.8, 6.8 Hz, 1H), 5.03–4.98 (m, 2H),
3.22–3.19 (m, 2H), 0.15 (s, 27H). 13C NMR (C6D6, 100 MHz) δ
157.2, 142.7, 136.6, 134.0, 133.2, 128.5, 127.1, 126.9, 126.6,
126.1, 120.4, 116.5, 48.1, 1.5 (2 C signals are not visible). IR
(neat) ν 2948, 2893, 2360, 2342, 1243, 832 cmÀ 1. HRMS (ESI)
calcd for [C24H40Si4 +Na]+ 463.2099 found 463.2120.
(E)-2-[2-(3-methoxyphenyl)-2-(tributylstannyl)
vinyl]-1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)
trisilane (7)
(Z)-2-[2-(2,6-dichlorophenyl)penta-1,4-dienyl]-
1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilane
(6n)
A Schlenk tube was charged with 3-ethynylanisole (1c) (33 mg,
0.25 mmol) and a suspension of [(Me3Si)3Si]2Zn (155 mg,
°
0.27 mmol) in n-hexane (2 mL) was added at À 30 C, followed
by Et2Zn (1.0 M in hexane, 0.27 mL, 0.27 mmol). The turbid
mixture was stirred at this temperature for 3 h, and then
CuCN·2LiCl (1.0 M in THF, 0.30 mL, 0.30 mmol) was added,
followed by tributyl(chloro)stannane (0.34 mL, 1.25 mmol).
Prepared according to the general procedure B from 1,3-
dichloro-2-ethynylbenzene (1n) (43 mg, 0.25 mmol). Purifica-
tion of the crude product (Z/E >98:2) by flash chromatography
on silica gel (pentane) afforded a mixture of 6n (72 mg, 63%,
Z/E >98:2) and 2n (10 mg, 10%, Z/E >98:2) that could not be
separated.
°
The mixture was stirred overnight at À 30 C and then diluted
with CH2Cl2 (15 mL) and quenched with aqueous NH4Cl/NH3
(2:1) (2 mL). The layers were separated and the aqueous one
was extracted with CH2Cl2 (2×15 mL). The combined organics
were washed with brine (2×5 mL), dried (Na2SO4), filtered and
concentrated under reduced pressure to afford the crude product
(E/Z >98:2). Purification by flash chromatography on silica gel
(pentane) afforded analytically pure 7 (101 mg, 0.15 mmol,
60%, E/Z >98:2) as a colorless oil and product 2c (19 mg,
20%).
1H NMR (C6D6, 400 MHz) δ 6.96 (d, J=8.1 Hz, 2H), 6.50 (t,
J=8.1 Hz, 1H), 6.10 (t, J=1.5 Hz, 1H), 5.96 (ddt, J=17.1,
10.1, 7.1 Hz, 1H), 5.05–5.02 (m, 1H), 5.00–4.95 (m, 1H), 3.06–
3.03 (m, 2H), 0.22 (s, 27H). 13C NMR (C6D6, 100 MHz) δ
149.7, 142.6, 135.6, 134.7, 128.9, 128.5, 125.8, 117.6, 44.9, 1.6.
HRMS (APCI) calcd for [C20H36Cl2Si4 +H]+ 459.1344 found
459.1333.
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1H NMR (C6D6, 400 MHz) δ 7.12–7.09 (m, 1H), 6.77–6.75 (m,
1H), 6.73–6.71 (m, 1H), 6.58 (ddd, J=8.2, 2.6, 0.9 Hz, 1H),
6.41 (s, 1H), 3.44 (s, 3H), 1.59–1.54 (m, 6H), 1.40–1.30 (m,
6H), 1.00–0.96 (m, 6H), 0.95–0.91 (m, 9H), 0.24 (s, 27H). 13C
NMR (C6D6, 100 MHz) δ 168.5, 160.4, 150.8, 136.6, 129.9,
119.1, 112.9, 110.8, 54.8, 29.6, 27.9, 14.0, 11.0, 1.5. IR (neat) ν
2954, 2926, 1594, 1574, 1242, 828, 685, 622 cmÀ 1. HRMS
(ESI) calcd for [C30H62OSi4Sn+Na]+ 693.2792 found
693.2770.
2016, 18, 2054; b) C. Fopp, K. Isaac, E. Romain, F.
Chemla, F. Ferreira, O. Jackowski, M. Oestreich, A.
Perez-Luna, Synthesis 2017, 49, 724–735.
[10] For the most representative examples, see: a) B. Kop-
ping, C. Chatgilialoglu, M. Zehnder, B. Giese, J. Org.
Chem. 1992, 57, 3994–4000; b) K. Miura, K. Oshima, K.
Utimoto, Bull. Chem. Soc. Jpn. 1993, 66, 2356–2364;
c) Y. Liu, S. Yamazaki, S. Yamabe, J. Org. Chem. 2005,
70, 556–561; d) Y. Liu, S. Yamazaki, S. Yamabe, Y.
Nakato, J. Mater. Chem. 2005, 15, 4906–4913; e) H.
Yasuda, Y. Uenoyama, O. Nobuta, S. Kobayashi, I. Ryu,
Tetrahedron Lett. 2008, 49, 367–370; f) Z. Wang, J. P.
Pitteloud, L. Montes, M. Rapp, D. Derane, S. F. Wnuk,
Tetrahedron 2008, 64, 5322–5327; g) J. Wang, Z. Zhu,
W. Huang, M. Deng, X. Zhou, J. Organomet. Chem.
2008, 693, 2188–2192; h) A. Odedra, K. Geyer, T.
Gustafsson, R. Gilmour, P. H. Seeberger, Chem. Com-
mun. 2008, 26, 3025–3027; i) A. Postigo, S. Kopsov,
S. S. Zlotsky, C. Ferreri, C. Chatgilialoglu, Organo-
metallics 2009, 28, 3282–3287; j) S. Kobayashi, H.
Kuroda, Y. Ohtsuka, T. Kashihara, A. Masuyama, K.
Watanabe, Tetrahedron 2013, 69, 2251–2259; k) X.
Yang, C. Wang, Angew. Chem. Int. Ed. 2018, 57, 923–
928; l) J. Zhu, W.-C. Cui, S. Wang, Z.-J. Yao, Org. Lett.
2018, 20, 3174–3178.
Computational Details. The calculations were carried out with
the Gaussian09 package.[32] All geometries were calculated
using Density Functional Theory (DFT) with the hybrid
B3PW91 level of theory.[33] The 6-31-G(d,p) basis set[34] is used
for all atoms. The geometry optimizations were performed
without any constraint and the nature of the extrema (minima
and transition states) were verified by analytical calculations of
frequencies. In particular the connection between the transition
state and minima was verified by carrying out a small displace-
ment along the reaction coordinate in each direction and
optimizing geometry starting from these structures.
Acknowledgements
This research was supported by the Deutsche Forschungsge-
meinschaft (Oe 249/7-1) and by the Agence Nationale de la
°
Recherche (SATRAZ Project, grant n 2011-INTB-1015-01).
[11] The Z-configuration of the vinylsilanes was unambigu-
1
3
LabEx MiChem (Investissement d’Avenir program under refer-
ence ANR-11-IDEX-0004-02) is also gratefully acknowledged
for financial support.
ously determined by H NMR on the basis of the JH-H
coupling constant of the vinylic protons (which were in
the range [14.1 Hz, 14.8 Hz]).
[12] Z. Chen, Y.-X. Zhang, Y. An, X.-L. Song, Y.-H. Wang,
L.-L. Zhu, L. Guo, Eur. J. Org. Chem. 2009, 5146–5152.
[13] In the case of 2-ethynlanisole (1b), 8% of the product
formed results from zinc/proton exchange between the
vinylzinc intermediate and the starting alkyne (see
Supporting Information for details).
[14] Y. Liang, J.-P. Pitteloud, S. F. Wnuk, J. Org. Chem.
2013, 78, 5761–5767.
[15] R. Dobrovetsky, Y. Kratish, B. Tumanskii, M. Botoshan-
sky, D. Bravo-Zhivotovskii, Y. Apeloig, Angew. Chem.
Int. Ed. 2012, 51, 4671–4675.
[16] [(Me3Si)3Si]2Zn, prepared according to the procedure
reported in ref 15, was either isolated (stored in glove-
box) and used pure as a solid or alternatively, generated
in-situ and used in solution immediately after its
preparation (see Supporting Information for details).
[17] Initiation of radical chains by oxydation of Et2Zn with
residual oxygen is a well-established process. For the
original work, see: a) I. Ryu, F. Araki, S. Minakata, M.
Komatsu, Tetrahedron Lett. 1998, 39, 6335–6336; For
most recent mechanistic considerations, see: b) J. Maury,
L. Feray, S. Bazin, J.-L. Clement, S. R. A. Marque, D.
Siri, M. P. Bertrand, Chem. Eur. J. 2011, 17, 1586–1595;
c) M. Kubisiak, K. Zelga, W. Bury, I. Justyniak, K.
Budny-Godlewski, Z. Ochal, J. Lewinski, Chem. Sci.
2015, 6, 3102–3108.
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[7] R. Shintani, H. Kurata, K. Nozaki, J. Org. Chem. 2016,
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[8] E. Romain, C. Fopp, F. Chemla, F. Ferreira, O.
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[18] It is documented that α-aryl-substituted vinylic radicals
abstract hydrogen atoms α to the oxygen atom of ethers
(ref 12). We speculate that for these substrates (1c and
[9] a) C. Fopp, E. Romain, K. Isaac, F. Chemla, F. Ferreira,
O. Jackowski, M. Oestreich, A. Perez-Luna, Org. Lett.
Adv. Synth. Catal. 2021, 363, 1–15
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asc.wiley-vch.de
1d), termination reactions may occur through atom
transfer from α-phenoxy H-atoms making radical chains
for details on the corresponding energetics and geo-
metrical data.
shorter. Increasing the amount of radical initiator should [27] See Table S1 and Figure S1 of the Supporting Informa-
compensate this effect and thus allow to drive the
reaction to completion.
tion.
[28] U. Wille, Chem. Rev. 2013, 113, 813–853.
[19] In preliminary studies, the silylzincation of phenyl- [29] W.-J. van Zeist, F. M. Bickelhaupt, Org. Biomol. Chem.
acetylene with [(Me3Si)3Si]2Zn in the presence of Et2Zn 2010, 8, 3118–3127.
(1.7 equiv.) was found to yield 2a in a low 33% yield [30] See Table S2 of the Supporting Information for the
and with no control of the double bond geometry (ref definition of the two terms.
9a). A possible explanation, is that in the presence of [31] M. F. Wisthoff, S. B. Pawley, A. P. Cinderella, D. A.
larger amounts of Et2Zn, competitive alkyne deprotona-
tion interferes with the silylzincation reaction.
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[20] A similar behavior at high temperature was observed for
the related germylzincation reaction, see: K. de la Vega-
Hernández, E. Romain, A. Coffinet, K. Bijouard, G.
Gontard, F. Chemla, F. Ferreira, O. Jackowski, A. Perez-
Luna, J. Am. Chem. Soc. 2018, 140, 17632–17642.
[21] The Z-configuration was determined for 6b on the basis
of NOESY experiments (see Supporting Information for
details) and inferred for the other products by comparison
of the NMR spectra.
[22] Z-to-E isomerization of β-stannyl vinylsilanes was
achieved through selective energy transfer photocatalysis
under irradiation at 364 nm. This approach, that can also
be regarded as an entry to formal silylstannylation of
alkynes, is not fully stereoselective (E/Z<82:18), see:
S. I. Faßbender, J. J. Molloy, C. Mück-Lichtenfeld, R.
Gilmour, Angew. Chem. Int. Ed. 2019, 58, 18619–18626.
[23] Compound 9-d1 was also the major product formed in the
reaction between 8 and (Me3Si)3SiH/Et2Zn, see ref 8.
[24] For a related example of the fragmentation of a β-alkoxy
zinc enolate, see: S. Giboulot, A. Perez-Luna, C. Botuha, [33] a) J. P. Perdew, Y. Wang, Phys. Rev. B 1992, 45, 13244–
F. Ferreira, F. Chemla, Tetrahedron Lett. 2008, 49, 3963–
13249; b) A. D. Becke, J. Chem. Phys. 1993, 98, 5648–
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5652.
1
[25] Determined by H NMR from the 9-d1/10=80:20 ratio [34] a) W. J. Hehre, R. Ditchfield, J. A. Pople, J. Chem. Phys.
measured in the crude product. The companying product
of β-fragmentation was not detected, likely because it
reacts subsequently as 1,4-acceptor, see ref 8.
1972, 56, 2257–2261; b) M. M. Francl, W. J. Pietro,
W. J. Hehre, J. S. Binkley, M. S. Gordon, D. J. DeFrees,
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[26] The addition at the α-carbon was found to be less
favorable. See Table S1 of the Supporting Information
Adv. Synth. Catal. 2021, 363, 1–15
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© 2021 Wiley-VCH GmbH
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These are not the final page numbers!

UPDATES
Development of a Radical Silylzincation of (Het)Aryl-Substi-
tuted Alkynes and Computational Insights into the Origin of
the trans-Stereoselectivity
Adv. Synth. Catal. 2021, 363, 1–15
E. Romain, K. de la Vega-Hernández, F. Guégan, J.
Sanz García, C. Fopp, F. Chemla, F. Ferreira, H. Gerard, O.
Jackowski, S. Halbert*, M. Oestreich*, A. Perez-Luna*