Copper-Catalyzed Cross-Coupling of Vinyliodonium Salts and Zinc-Based Silicon Nucleophiles

Article abstract of DOI:10.1021/acs.orglett.8b03714

A silylation of vinyliodonium salts using zinc-based silicon reagents as nucleophiles is reported. This cross-coupling is catalyzed by copper, and vinylsilanes are obtained in high yield likely following a Cu(I)/Cu(III) reaction mechanism. The procedure i

Full text of DOI:10.1021/acs.orglett.8b03714

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Copper-Catalyzed Cross-Coupling of Vinyliodonium Salts and Zinc-
Based Silicon Nucleophiles
Liangliang Zhang and Martin Oestreich*
Institut fur Chemie, Technische Universitat Berlin, Strasse des 17. Juni 115, 10623 Berlin, Germany
̈
̈
S
* Supporting Information
ABSTRACT: A silylation of vinyliodonium salts using zinc-based
silicon reagents as nucleophiles is reported. This cross-coupling is
catalyzed by copper, and vinylsilanes are obtained in high yield likely
following a Cu(I)/Cu(III) reaction mechanism. The procedure is
operationally simple, neither air- nor moisture-sensitive, and tolerant of
a range of functional groups. The new method is an addition to the still limited number of transition-metal-catalyzed vinyl
C(sp2)−Si cross-coupling reactions.
he vinylsilane motif is a valuable linchpin in synthetic
chemistry,1 and there are several methods available to
Scheme 1. Cross-Coupling of Vinyl C(sp2)−X Bonds and
Silicon (Pro)Nucleophiles
T
reliably prepare this compound class.2 However, the cross-
coupling of vinyl C(sp2)−X bonds and silicon (pro)-
nucleophiles is relatively unexplored. Early work by Oshima3
and Trost4 demonstrated that palladium−phosphine com-
plexes catalyze the coupling of vinyl phosphates as well as
iodides and aluminum-based silicon nucleophiles (Scheme 1,
top). Oshima’s work also included magnesium reagents.
Shortly thereafter, it was Hiyama to introduce an unreactive
disilane as a silicon pronucleophile to these palladium-
catalyzed cross-couplings.5 Aside from an additional recent
example by Martin,6 where vinyl ethers were shown to couple
with a silyl boronate pronucleophile under nickel catalysis,
these have been the sole reports of such transformations.7 It
must be noted though that there is a broadly applicable,
stoichiometric variant by Oshima that makes use of tris-
(triorganosilyl)-substituted low-valent manganese ate com-
plexes.8 Also, single examples of vinyl iodides either directly
using the silyl lithium9 or an in situ prepared silyl copper10
reagent were described. To close this gap, we disclose here a
robust C(sp2)−Si cross-coupling of vinyliodonium salts11 and
zinc-based silicon nucleophiles12 catalyzed by copper (Scheme
1, bottom).
The reaction of vinyliodonium triflate 1a and triorganosi-
lylzinc reagent 2a to afford vinylsilane 3aa was chosen as the
model reaction (Table 1). After optimization (see the
Supporting Information for details), Cu(OTf)2 and Cu(OAc)2
in THF as solvent emerged as good precatalysts for this
coupling (entries 1 and 2). Vinyliodonium salts with other
common counteranions such as tosylate and tetrafluoroborate
furnished lower yields (entries 3 and 4). For comparison,
yields were significantly diminished with (CuOTf)2·PhMe and
CuCl (entries 5 and 6). With no changes to the standard setup,
both the silyl lithium and the silyl magnesium reagent resulted
in low yields (entries 7 and 8). Importantly, hardly any
vinylsilane was obtained when replacing the vinyliodonium salt
by the corresponding vinyl iodide (entry 9). The reactions
were routinely run at 0 °C, and no effect was seen at slightly
higher or lower reaction temperatures (entries 10 and 11). The
reaction also proceeded equally well open to air or in wet THF
Received: November 20, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b03714
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
(3aa−fa). A thien-3-yl group was also tolerated (3ga).
Likewise, β-alkyl-substituted vinyliodonium salts reacted in
good yields (3ha−la). A C(sp3)−Cl bond was also compatible
with the reaction conditions (3ma). Further substitution of the
vinyl group was not detrimental, and both α,β- and β,β-
disubstituted vinyliodonium triflates reacted cleanly to give
3na−pa. Conversely, the coupling of the parent unsubstituted
vinyliodonium triflate did not stop at the stage of the
corresponding vinylsilane (not shown); it was too reactive,
and a complex reaction mixture was formed. It is important to
note that we could not verify the stereospecificity of this cross-
coupling as Z-configured vinyliodonium salts undergo rapid β-
elimination.13
Table 1. Selected Examples of the Reaction Optimization
b
entry
copper salt
Cu(OTf)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
(CuOTf)2·PhMe
CuCl
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
variation
yield (%)
c
d
1
2
3
4
5
6
7
none
none
82 (80 )
73
51
70
20
30
9
TsO− instead of TfO−
BF4 instead of TfO−
−
none
none
When subjecting α-CF3-substituted vinyliodonium salt14 1q
to the cross-coupling procedure, we identified compound 4qa
containing two silyl groups in the reaction mixture (Scheme 3).
Me2PhSiLi instead of 2a
Me2PhSiMgX instead of 2a
β-iodostyrene instead of 1a
rt instead of 0 °C
−20 °C instead of 0 °C
open to air
8
9
15
12
75
78
81
79
10
10
11
12
13
14
Scheme 3. Copper-Catalyzed C(sp2)−Si Cross-Coupling
Coupled with Allylic Displacement
added H2O (2.0 equiv)
none
a
All reactions were performed on a 0.20 mmol scale for 12 h.
Determined by GLC analysis with tetracosane as an internal
b
c
d
standard. Reaction time is 30 min. Yield of isolated product after
purification by flash chromatography on silica gel.
Increasing the amount of zinc reagent 2a from 1.2 to 2.2 equiv
led to the formation of 4qa in 51% isolated yield. The
incorporation of the second silyl group is likely to be the result
of a copper-catalyzed allylic substitution of the intermediate
allyl fluoride.15
The cross-coupling was then extended to other zinc reagents
2b−e, and isolated yields for 3ab−ae were high throughout,
even for the tert-butyl-substituted derivatives (Scheme 4).
(entries 12 and 13). With no catalyst, 10% of the vinylsilane
did form (entry 14).
With the standard protocol established, we next investigated
the reaction scope for various vinyliodonium triflates (Scheme
2). Yields were consistently high for the β-aryl-substituted
model substrate and its electronically modified derivatives
Scheme 2. Scope I: Variation of the Vinyliodonium
a b
,
Triflate
Scheme 4. Scope II: Variation of the Zinc-Based Silicon
Nucleophile
a b
,
a
b
All reactions performed on a 0.20 mmol scale. Isolated yield after
flash chromatography on silica gel.
Based on literature precedence,16 we propose the oxidative
addition−reductive elimination Cu(I)/Cu(III) cycle outlined
in Scheme 5. We point out, however, that yields were
significantly lower with Cu(I) than with Cu(II) salts as
precatalysts (e.g., Table 1, entry 1 versus entry 5). A radical
pathway appears unlikely as the addition of 2.5 equiv of
TEMPO had no effect on the reaction outcome (see the
Supporting Information for details). Moreover, the aryl iodide
byproduct, that is o-iodotoluene, was recovered in 89% isolated
yield for the model reaction (cf. Table 1, entry 1).
a
b
All reactions performed on a 0.20 mmol scale. Isolated yield after
c
flash chromatography on silica gel. A reaction on a 1.00 mmol scale
furnished 80% isolated yield (see Supporting Information for details).
B
DOI: 10.1021/acs.orglett.8b03714
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(5) Hatanaka, Y.; Hiyama, T. Tetrahedron Lett. 1987, 28, 4715−
4718.
Scheme 5. Proposed Catalytic Cycle for Copper-Catalyzed
C(sp2)−Si Cross-Coupling of Vinyliodonium Salts
(6) Zarate, C.; Nakajima, M.; Martin, R. J. Am. Chem. Soc. 2017, 139,
1191−1197.
(7) Recently, the cross-coupling of vinyl C(sp2)−F bonds and silyl
boronates was accomplished under copper catalysis: (a) Tan, D.-H.;
Lin, E.; Ji, W.-W.; Zeng, Y.-F.; Fan, W.-X.; Li, Q.; Gao, H.; Wang, H.
Adv. Synth. Catal. 2018, 360, 1032−1037. (b) Sakaguchi, H.; Ohashi,
M.; Ogoshi, S. Angew. Chem., Int. Ed. 2018, 57, 328−332.
(8) (a) Fugami, K.; Oshima, K.; Utimoto, K.; Nozaki, H.
Tetrahedron Lett. 1986, 27, 2161−2164. (b) Fugami, K.; Hibino, J.-
i.; Nakatsukasa, S.; Matsubara, S.; Oshima, K.; Utimoto, K.; Nozaki,
H. Tetrahedron 1988, 44, 4277−4292.
(9) Yamamoto, E.; Ukigai, S.; Ito, H. Synlett 2017, 28, 2460−2464.
(10) Lipshutz, B. H.; Reuter, D. C.; Ellsworth, E. L. J. Org. Chem.
1989, 54, 4975−4977.
(11) Selected reviews on reactions of vinyliodonium salts:
(a) Zhdankin, V. V.; Stang, P. J. Chem. Rev. 2008, 108, 5299−5358.
(b) Stang, P. J. J. Org. Chem. 2003, 68, 2997−3008.
(12) Selected original work of zinc-based silicon reagents:
(a) Okuda, Y.; Wakamatsu, K.; Tu
Nozaki, H. Tetrahedron Lett. 1985, 26, 4629−4632. (b) Wakamatsu,
K.; Nonaka, T.; Okuda, Y.; Tuckmantel, W.; Oshima, K.; Utimoto, K.;
̈
ckmantel, W.; Oshima, K.;
̈
Nozaki, H. Tetrahedron 1986, 42, 4427−4436. (c) Nakamura, S.;
Uchiyama, M.; Ohwada, T. J. Am. Chem. Soc. 2004, 126, 11146−
11147. (d) Auer, G.; Oestreich, M. Chem. Commun. 2006, 311−313.
(e) Azuma, H.; Okano, K.; Tokuyama, H. Chem. Lett. 2011, 40, 959−
961. (f) Fopp, C.; Romain, E.; Isaac, K.; Chemla, F.; Ferreira, F.;
Jackowski, O.; Oestreich, M.; Perez-Luna, A. Org. Lett. 2016, 18,
2054−2057. (g) Chu, C. K.; Liang, Y.; Fu, G. C. J. Am. Chem. Soc.
2016, 138, 6404−6407. Reviews of zinc-based silicon nucleophiles:
(h) Nakamura, S.; Yonehara, M.; Uchiyama, M. Chem. - Eur. J. 2008,
14, 1068−1078. (i) Weickgenannt, A.; Oestreich, M. Chem. - Eur. J.
2010, 16, 402−412.
In summary, we have introduced here a copper-catalyzed
cross-coupling of vinyliodonium salts and silicon zinc reagents
that enables the preparation of vinylsilanes with a broad
substitution pattern.
ASSOCIATED CONTENT
* Supporting Information
■
S
(13) Ochiai, M.; Oshima, K.; Masaki, Y. J. Chem. Soc., Chem.
Commun. 1991, 0, 869−870.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b03714.
́
́
́
́
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(14) Meszaros, A.; Szekely, A.; Stirling, A.; Novak, Z. Angew. Chem.,
Int. Ed. 2018, 57, 6643−6647.
Experimental details, characterization, and spectroscopic
data (PDF)
(15) Selected references on copper-catalyzed allylic substitution of
α-(trifluoromethyl)alkenes: (a) Kitazume, T.; Ohnogi, T.; Miyauchi,
H.; Yamazaki, T. J. Org. Chem. 1989, 54, 5630−5632. (b) Xu, Y.; Jin,
F.; Huang, W. J. Org. Chem. 1994, 59, 2638−2641. (c) Dai, W.; Lin,
Y.; Wan, Y.; Cao, S. Org. Chem. Front. 2018, 5, 55−58. (d) Wang, M.;
Pu, X.; Zhao, Y.; Wang, P.; Li, Z.; Zhu, C.; Shi, Z. J. Am. Chem. Soc.
2018, 140, 9061−9065. (e) Kojima, R.; Akiyama, S.; Ito, H. Angew.
Chem., Int. Ed. 2018, 57, 7196−7199. (f) Gao, P.; Yuan, C.; Zhao, Y.;
Shi, Z. Chem. 2018, 4, 2201−2211.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: martin.oestreich@tu-berlin.de.
ORCID
Liangliang Zhang: 0000-0001-7637-8702
Martin Oestreich: 0000-0002-1487-9218
Notes
(16) (a) Skucas, E.; MacMillan, D. W. C. J. Am. Chem. Soc. 2012,
134, 9090−9093. (b) Suero, M. G.; Bayle, E. D.; Collins, B. S. L.;
Gaunt, M. J. J. Am. Chem. Soc. 2013, 135, 5332−5335. (c) Liu, C.;
Wang, Q. Angew. Chem., Int. Ed. 2018, 57, 4727−4731.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
L.Z. thanks the China Scholarship Council for a predoctoral
fellowship (2017−2021), and M.O. is indebted to the Einstein
Foundation (Berlin) for an endowed professorship.
REFERENCES
■
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DOI: 10.1021/acs.orglett.8b03714
Org. Lett. XXXX, XXX, XXX−XXX