Ligand-Controlled Regiodivergent Silylation of Allylic Alcohols by Ni/Cu Catalysis for the Synthesis of Functionalized Allylsilanes

Article abstract of DOI:10.1021/acs.orglett.9b03822

The first Ni/Cu-catalyzed regiodivergent synthesis of allylsilanes directly from allylic alcohols through modulating the steric and electronic properties of the ligands on the nickel catalyst has been developed. Good yields and excellent selectivity were obtained regardless of whether linear or α-branched allylic alcohols were utilized. Mechanistic studies indicate that an allyloxyboronate species is formed during the reaction, which likely serves as an activated intermediate toward the oxidative addition of the C(allyl)-O bond.

Full text of DOI:10.1021/acs.orglett.9b03822

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Ligand-Controlled Regiodivergent Silylation of Allylic Alcohols by
Ni/Cu Catalysis for the Synthesis of Functionalized Allylsilanes
Yi Gan, Wei Xu, and Yuanhong Liu*
State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic
Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Lu, Shanghai 200032, People’s
Republic of China
S
* Supporting Information
ABSTRACT: The first Ni/Cu-catalyzed regiodivergent syn-
thesis of allylsilanes directly from allylic alcohols through
modulating the steric and electronic properties of the ligands
on the nickel catalyst has been developed. Good yields and
excellent selectivity were obtained regardless of whether linear
or α-branched allylic alcohols were utilized. Mechanistic
studies indicate that an allyloxyboronate species is formed
during the reaction, which likely serves as an activated
intermediate toward the oxidative addition of the C(allyl)−O bond.
llylsilanes are highly important reagents in organic
synthesis because of their chemical stability, diverse
Scheme 1. Metal-Catalyzed Silylation of Allylic
Electrophiles
A
reactivities, and low toxicity.1 They serve as one of the most
versatile of the silicon-containing carbon nucleophiles for
various transformations such as allylation of electrophiles (i.e.,
Hosomi−Sakurai reaction),2a coupling reactions such as
Hiyama coupling,2b,c fluorodesilylation,2d access to carbo- or
heterocycles,2e,f ring-closing and cross-metathesis processes,2g
etc.1b As a result, many efficient methods have been developed
for their synthesis. Traditionally, they were prepared through
silylation of allylic organometallics,3a hydrosilylation of 1,3-
dienes,3b Wittig reactions with β-silylethylidene-
phosphoranes,3c etc.3 However, the substrate scope and
regioselectivity were not always satisfactory. In recent years,
transition-metal-catalyzed silylation of allylic electrophiles with
silicon sources such as bimetallic reagents (e.g.,
(PhMe2Si)2Zn),4 disilanes,5 silylenes,6 silylboronates,7 etc.
have proved to be promising protocols for the construction
of allylsilanes (Scheme 1). Most of these studies use allylic
-halides, -ethers, -esters, and -phosphates as the allylic
components. Compared with these activated substrates, allylic
alcohols are much more attractive for cross-coupling reactions
because they are readily available and do not require
prefunctionalization. However, due to the acidity of the OH
moiety and the poor leaving ability of the hydroxyl group,
coupling with the unprotected allylic alcohols is highly
challenging.8 To the best of our knowledge, there are rare
examples of silylation by direct use of allylic alcohols.9 In 2011,
reported yet. In addition, regioselective synthesis of branched
allylic silanes still remains a formidable challenge10 since the
silylation tends to occur at the less-hindered terminus of the
allyl group, especially when palladium was used as the
catalyst.5a−e Herein, we wish to describe a first Ni-/Cu-
catalyzed regiodivergent silylation of allylic alcohols with an
interelement Si−B reagent. The regioselectivity can be
controlled by the appropriate choice of the ligands, allowing
C−Si bond formation at the either end of the allyl terminus.
Szabo et al.5d reported a palladium-catalyzed silylation of allylic
́
alcohols with excellent linear regioselectivity.5d,e In 2013, Li et
al.7e developed a copper-catalyzed synthesis of allylic silanes
from Morita−Baylis−Hillman (MBH) alcohols. Although
advances have been achieved, only linear regioisomers were
afforded by these methods. The controllable regiodivergent
silylation from the common allylic alcohols have not been
Received: October 26, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b03822
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Considering that boron-containing reagent might act as a
Lewis acid to assist the C−OH bond cleavage,11 we envisioned
that the use of silylboranes should be feasible for direct
silylation reaction from allylic alcohols. Our investigation
commenced with the cross-coupling of 5-phenylpent-1-en-3-ol
1a with Et3SiBpin 2a using nickel catalysts. After tremendous
effort in evaluation of nickel sources, ligands, bases or other
additives, etc. we found that CuF2 played a key role in the
effective transformation.12,13 Thus, the allylsilanes (3a and 4a)
could be obtained in 94% combined yield with excellent
regioselectivity (3a:4a = 97:3) with 5 mol % Ni(COD)2, 10
mol % PEt3 in the presence of 15 mol % CuF2 in toluene at 60
°C (Table 1, entry 1). Without CuF2, only 9% of the desired
To our delight, the use of dcype enhanced the
regioselectivity significantly, but with a low yield of 4a (entry
10). Interestingly, a slight increase in temperature (70 °C) led
to a remarkable improvement in the yield (70%, entry 11).
Changing the solvent to DMF further improved the yield of 4a
to 93%, but the E/Z selectivity was unsatisfactory (entry 12).
We were pleased to find that the use of 8-(diphenyl-
phosphanyl)quinoline L1 provided 4a in 93% yield with an
excellent linear to branch ratio and high stereoselectivity (entry
13). Lowering the temperature to 60 °C afforded similar
results (entry 14). Control experiments revealed that a nickel
catalyst, ligand, and CuF2 were all crucial for the reaction
(entries 2 and 15).
Encouraged by these results, we concentrated on the
examination of the substrate scope by using either PEt3 or
L1 as the ligand (Table 2). In all cases, the reaction took place
efficiently to furnish the branched products 3 or linear
products 4 in good to excellent yields and high regioselectivity,
depending on the ligand employed. In addition, the linear
allylic silanes 4 were produced with high stereoselectivity
favoring E-configurated isomers (in all cases, the E/Z isomer
ratio is ≥10:1 except for 4o). The tethered phenyl ring on the
allylic alcohols bearing methoxy (3b, 4b), ester (3c, 4c), and
fluoro (3d, 4d) substituents worked well, and the nickel-
catalyzed activation of C−O (1b) and C−F (1d) bonds was
not observed. Linear allylic alcohol (1e), a regioisomer of 1a,
coupled well with Et3SiBpin to give the same product 3a using
PEt3 and 4a using L1, indicating that the reaction may occur
via a π-allylnickel intermediate. Linear alcohols that have a
primary alkyl group such as n-propyl or n-hexyl at the γ-
position of the allylic moiety also underwent silylation reaction
smoothly to afford the corresponding products in good yields
and high regioselectivity (3f−3g, 4f−4g). For branched
alcohols, a variety of functional groups, including 1-naphthyl
(3h, 4h), heteroarene (3i, 4i), alkene (3j, 4j), free hydroxyl
(3k, 4k), and silyl ether (3l, 4l), on the alkyl chain were well
tolerated in the reaction system. When a substrate bearing a
secondary alkyl group at the α-position of the allylic alcohol
such as 1m was subjected to the conditions with Ni/L1, most
of the starting materials remained unchanged, possibly due to
the steric effect at the allylic carbon. After some trials, it was
found that the yield of the desired 4m could be improved
significantly to 80% with high stereoselectivity (E/Z = 10:1) by
using dcype as the ligand at higher temperature (70 °C). It
seems that a balance of electronic and steric factors of the
ligand governs the catalytic activity of the nickel catalyst.
Under similar conditions, a good yield and high E/Z selectivity
were also achieved for 4n. Introduction of a methyl group at
the alkene moiety resulted in the formation of the branched
product 3o in 84% yield. The corresponding linear product 4o
was formed in 59% yield using dcype in toluene with lower E/
Z selectivity (5:1). The results suggest that the steric hindrance
around the allylic motif has an important impact on the
reaction efficiency and selectivity.
Table 1. Optimization of the Reaction Conditions
derivation from standard
conditions
yield 3a + 4a
ab
4a
,
entry
(%)
3a/4a (E/Z)
c
1
2
none
no CuF2
94 (91)
9
97:3
−
3
4
5
6
7
8
9
10
11
Cu(OAc)2 instead of CuF2
AgF instead of CuF2
17
44
91
92
88
22
43
39
82:18
91:9
93:7
92:8
88:12
23:77
81:19
1:>99
1:99
10 mol % PEt2Ph instead of PEt3
10 mol % PEtPh2 instead of PEt3
10 mol % PPh3 instead of PEt3
10 mol % PCy3 instead of PEt3
5 mol % dppb instead of PEt3
5 mol % dcype instead of PEt3
5:1
5:1
5:1
5 mol % dcype instead of PEt3 at
70 °C
70
12
13
14
15
5 mol % dcype instead of PEt3 in
93
1:99
1:99
1:99
4:1
DMF at 70 °C
10 mol % L1 instead of PEt3 in
DMF at 70 °C
10 mol % L1 instead of PEt3 in
93
11:1
12:1
c
92 (84)
0
DMF
d
no Ni(COD)2 or no PEt3
a
Reaction conditions: Ni(COD)2 (5 mol %), Ligand, CuF2 or
additive (15 mol %), 1a (0.3 mmol), 2a (0.36 mmol) in solvent (1.0
b
mL). NMR yields using 1,3,5-trimethoxybenzene as the internal
c
d
standard. Isolated yield. Without PEt3, 1-phenylpentan-3-one was
formed in 89% NMR yield.
products were obtained (entry 2). Other additives such as
Cu(OAc)2 and AgF were far less effective (entries 3−4). These
results also indicated that, in the presence of less-hindered
ligands such as PEt3, the branched product 3a was formed
predominantly. It should be noted that no additional base such
as NaOH, NaOMe, KF, or CsF was required for this
transformation, which was often used in copper-catalyzed
silyation of allylic substrates7a−d or nickel-catalyzed silylation
of aryl electrophiles such as esters.12 The effects of other
ligands were also examined. Subtle changes in the electronic
and steric environment of the monodentate ligands such as
PEt2Ph, PEtPh2, or PPh3 resulted in slightly lower b/l
selectivity (entries 5−7). Surprisingly, the use of bulky PCy3
resulted in a selectivity switch to give the linear product 4a as
the major product, albeit with a low yield (entry 8). Inspired
by this result, further screening of the ligands was carried out
to improve the yield and regioselectivity of the linear products.
Prompted by our initial results, we next investigated the
silylation of allylic alcohols bearing an aryl group at the C-3 or
C-1 position (Table 3). Under the standard conditions with
PEt3, a 79% yield of the silylated products 6a and 7a were
obtained through the reaction of cinnamyl alcohol 5a with
Et3SiBpin (Table 3, entry 1). However, the site selectivity was
not satisfactory (6a: 7a = 1:3). All attempts to improve the
regioselectivity toward the branched isomers were not
successful. To our delight, the use of dcype as the ligand was
B
DOI: 10.1021/acs.orglett.9b03822
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Organic Letters
Letter
Table 2. Scope of the Ni-Catalyzed Regiodivergent
Silylation of Allylic Alcohols
Table 3. Scope of the Ni-Catalyzed Silylation of Aryl-
Substituted Allylic Alcohols
a
b
Isolated yields. 5 mol % Ni(COD)2 and 15 mol % CuF2 were used.
c
Containing small amounts of impurity.
phenyl ring did not interfere, indicating that the reaction was
not sensitive to the steric effects (6h, 6i). 1,3-Disubstituted
alcohols were silylated in 27−55% yields using PEt3 as the
ligand (6l, 6m). Substrate 5n bearing a methyl group at the C-
2 position could be successfully converted to silane 6n using
L1 as the ligand.
a
d
h
b
c
4a−4o were all obtained in ≥30:1 l/b ratio. NMR yield. dr = 1.1:1.
e
f
g
dr = 1.1:1. 5 mol % dcype was used, 70 °C. dr = 1.5:1. dr = 1.5:1.
5 mol % dcype was used in toluene, 80 °C.
The reactivity of other silylboranes were also evaluated.
Gratifyingly, Et2MeSiBpin and PhMe2SiBpin also showed
excellent reactivity, furnishing the corresponding silanes 3
and 4 in good to excellent yields (Table 4). Excellent branched
or linear regioselectivity was also observed in these cases.
To understand the reaction mechanism, we performed
various control experiments monitored by NMR spectra14
(Figure 1; for entries a−d, toluene-d8 was used as the solvent).
When a mixture of allylic alcohol 1a with Et3SiBpin was stirred
at 60 °C for 12 h, no reaction occurred, indicating that the
activation of allylic alcohol through coordination with Si−B
reagent is not operative in this reaction. However, when CuF2
or CuF2 with PEt3 was added to the mixture, a set of new peaks
appeared, which was assigned to be an allyloxyboronate (allyl-
OBpin) 8 (Figure 1c−d and Scheme 2, eq 1). Boronic ester 8
was confirmed by independent synthesis through the reaction
of allylic alcohol 1a with HBpin (neat)15 (Figure 1e).
According to above results, we considered that allylic alcohol
found to be highly active and selective for linear product 6a in
DMF, furnishing 6a with an E-configuration exclusively in high
yield (entry 2). The conditions with dcype proved successful
for the synthesis of various linear allylic silanes (6a−6k). It
should be noted that, in the cases of the branched alcohols,
better product yields were obtained by using THF as the
solvent at 70 °C (entries 6−12). Sterically bulky 9-anthracyl-
substituted allylic alcohol was tolerated well (6c). Substrates
with furan or 3-pyridyl groups were also compatible (6d, 6k).
In the former case, a mixture of E/Z isomers was produced.
Branched alcohols reacted cleanly with excellent E-selectivity,
regardless of the electronic nature of the substituent at the aryl
ring (entries 6−11). A range of functional groups such as −Me,
−NMe2, and −OMe were well tolerated. The presence of an
ortho-substituent such as a 2-Me or 2-OMe group on the
C
DOI: 10.1021/acs.orglett.9b03822
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
involving direct oxidative addition of allylic alcohol by Ni(0)
followed by transmetalation with Cu−Si species could not be
excluded.14
Table 4. Substrate Scope for the Silylborane Compounds
In summary, we have developed the first Ni/Cu20-catalyzed
regiodivergent synthesis of allylsilanes directly from alcohols
through modulating the steric and electronic properties of the
ligands on the nickel catalyst. Mechanistic studies indicate that
an allyl-OBpin species is formed during the reaction, which
likely serves as an activated intermediate toward the oxidative
addition of the C(allyl)−O bond. Further investigations into
the reaction mechanism and the explorations of related
transformations using allylic alcohols are in progress.
a
4p and 4q were obtained in ≥30:1 l/b ratio.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.9b03822.
Experimental details and spectroscopic characterization
of all new compounds (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: yhliu@sioc.ac.cn.
ORCID
Yuanhong Liu: 0000-0003-1153-5695
Notes
1
Figure 1. H NMR spectra: (a) 1a; (b) 1a + Et3SiBpin (1 equiv) at
The authors declare no competing financial interest.
60 °C for 12 h; (c) 1a + Et3SiBpin (1 equiv) + CuF2 (1 equiv) at 60
°C for 12 h; (d) 1a + Et3SiBpin (1 equiv) + CuF2 (1 equiv) + PEt3 (1
equiv) at 60 °C for 12 h; (e) 1a + HBpin (1.1 equiv), rt, 6 h.
ACKNOWLEDGMENTS
■
We thank the National Key R&D Program of China
(2016YFA0202900), the Strategic Priority Research Program
of the Chinese Academy of Sciences (XDB20000000), and
Science and Technology Commission of Shanghai Municipal-
ity (18XD1405000) for financial support.
Scheme 2. Mechanistic Studies
REFERENCES
■
(1) For reviews, see: (a) Langkopf, E.; Schinzer, D. Uses of Silicon-
Containing Compounds in the Synthesis of Natural Products. Chem.
Rev. 1995, 95, 1375−1408. (b) Chabaud, L.; James, P.; Landais, Y.
Allylsilanes in Organic Synthesis − Recent Developments. Eur. J. Org.
Chem. 2004, 2004, 3173−3199.
(2) (a) Hosomi, A.; Miura, K. Development of New Reagents
Containing Silicon and Related Metals and Application to Practical
Organic Syntheses. Bull. Chem. Soc. Jpn. 2004, 77, 835−851.
(b) Denmark, S. E.; Werner, N. S. Cross-Coupling of Aromatic
Bromides with Allylic Silanolate Salts. J. Am. Chem. Soc. 2008, 130,
16382−16393. (c) Hatanaka, Y.; Ebina, Y.; Hiyama, T. γ-Selective
Cross-Coupling Reaction of Allyltrifluorosilanes: A New Approach to
Regiochemical Control in Allylic Systems. J. Am. Chem. Soc. 1991,
113, 7075−7076. (d) Thibaudeau, S.; Gouverneur, V. Sequential
Cross-Metathesis/Electrophilic Fluorodesilylation: A Novel Entry to
Functionalized Allylic Fluorides. Org. Lett. 2003, 5, 4891−4893.
(e) Brengel, G. P.; Rithner, C.; Meyers, A. I. [2 + 2] and [3 + 2]
Cycloadditions of Triisopropylallylsilane to α,β-Unsaturated Bicyclic
Lactams. J. Org. Chem. 1994, 59, 5144−5146. (f) Angle, S. R.; El-Said,
N. A. Stereoselective Synthesis of Tetrahydrofurans via Formal [3 +
2]-Cycloaddition of Aldehydes and Allylsilanes. Formal Total
Synthesis of the Muscarine Alkaloids (−)-Allomuscarine and
(+)-Epimuscarine. J. Am. Chem. Soc. 2002, 124, 3608−3613.
(g) Chang, S.; Grubbs, R. H. A Simple Method To Polyhydroxylated
Olefinic Molecules Using Ring-Closing Olefin Metathesis. Tetrahe-
dron Lett. 1997, 38, 4757−4760.
might be activated through the formation of a boronic ester,
and CuF2 may play a role in assisting the formation of
boronate 8, while generating a Cu−Si species16−18 simulta-
neously. To determine whether boronic ester serves as the
efficient reaction intermediate or not, the reaction of in situ
generated 8 with 2a was carried out under the standard
reaction conditions. As expected, the desired silylated product
3a was obtained in good yield with excellent regioselectivity
(Scheme 2, eq 2).19 The detailed mechanistic discussions
should await further studies. Based on the above results, one
possible reaction pathway might involve the following steps:
(a) formation of allyl-OBpin and Cu−Si species through the
reaction of allylic alcohol, Si−B reagent 2, and CuF2; (b)
oxidative addition of allyl-OBpin with Ni(0) to give a π-
allylnickel(II) complex; (c) transmetalation of Cu−Si species
to π-allylnickel(II) complex followed by reductive elimination
to afford the silylated products.14 However, Si−B reagent
might be activated by CuF2 directly; thus, the reaction pathway
D
DOI: 10.1021/acs.orglett.9b03822
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(3) (a) Gilman, H.; Zuech, E. A. Selective Reactions of the Silicon-
Hydrogen Group with Grignard Reagents. The Preparation of Some
Unsymmetrical Silane Derivatives. J. Am. Chem. Soc. 1959, 81, 5925−
5928. (b) Tsuji, J.; Hara, M.; Ohno, K. Palladium Catalyzed
Hydrosilylation Of Monoenes And Conjugated Dienes. Tetrahedron
1974, 30, 2143−2146. (c) Seyferth, D.; Wursthorn, K. R.;
Mammarella, R. E. A General Route to Terminally Substituted Allylic
Derivatives of Silicon and Tin. Preparation of Allylic Lithium
Reagents. J. Org. Chem. 1977, 42, 3104−3106. (d) Fleming, I.;
Marchi, D., Jr. A New Synthesis of Allylsilanes. Synthesis 1981, 1981,
560−561. (e) Fleming, I.; Higgins, D.; Lawrence, N. J.; Thomas, A. P.
A Regioselective and Stereospecific Synthesis of Allylsilanes from
Secondary Allylic Alcohol Derivatives. J. Chem. Soc., Perkin Trans. 1
1992, 3331−3349. For reviews, see: (f) Sarkar, T. K. Methods for the
Synthesis of Allylsilanes. Part 1. Synthesis 1990, 1990, 969−983.
(g) Sarkar, T. K. Methods for the Synthesis of Allylsilanes. Part 2.
Synthesis 1990, 1990, 1101−1111.
(4) (a) Lipshutz, B. H.; Sclafani, J. A.; Takanami, T. Silyl Cuprate
Couplings: Less Silicon, Accelerated, Yet Catalytic in Copper. J. Am.
Chem. Soc. 1998, 120, 4021−4022. (b) Oestreich, M.; Auer, G.
Practical Synthesis of Allylic Silanes from Allylic Esters and
Carbamates by Stereoselective Copper-Catalyzed Allylic Substitution
Reactions. Adv. Synth. Catal. 2005, 347, 637−640. (c) Schmidtmann,
E. S.; Oestreich, M. Mechanistic insight into copper-catalysed allylic
substitutions with bis(triorganosilyl) zincs. Enantiospecific prepara-
tion of α-chiral silanes. Chem. Commun. 2006, 3643−3645. (d) Vyas,
D. J.; Oestreich, M. Expedient access to branched allylic silanes by
copper-catalysed allylic substitution of linear allylic halides. Chem.
Commun. 2010, 46, 568−570. (e) Hensel, A.; Oestreich, M.
Asymmetric Catalysis with Silicon-Based Cuprates: Enantio- and
Regioselective Allylic Substitution of Linear Precursors. Chem. - Eur. J.
2015, 21, 9062−9065.
Hartmann, E.; Mewald, M. Activation of the Si−B Interelement Bond:
Mechanism, Catalysis, and Synthesis. Chem. Rev. 2013, 113, 402−441.
(8) For reviews, see: (a) Sundararaju, B.; Achard, M.; Bruneau, C.
Transition metal catalyzed nucleophilic allylic substitution: activation
of allylic alcohols via π-allylic species. Chem. Soc. Rev. 2012, 41,
4467−4483. (b) Butt, N. A.; Zhang, W. Transition metal-catalyzed
allylic substitution reactions with unactivated allylic substrates. Chem.
Soc. Rev. 2015, 44, 7929−7967.
(9) Just before our submission, a Ni-catalyzed silylation of allylic
alcohols with R3SiZnCl to linear allylic silanes was reported; see:
Yang, B.; Wang, Z.-X. Synthesis of Allylsilanes via Nickel-Catalyzed
Cross-Coupling of Silicon Nucleophiles with Allyl Alcohols. Org. Lett.
2019, 21, 7965−7969.
(10) For the synthesis of branched allylic silanes by copper catalysis,
see ref 4d,e and ref 7a−d.
(11) For example: (a) Tsukamoto, H.; Sato, M.; Kondo, Y.
Palladium(0)-catalyzed direct cross-coupling reaction of allyl alcohols
with aryl- and vinyl-boronic acids. Chem. Commun. 2004, 1200−1201.
(b) Tsukamoto, H.; Uchiyama, T.; Suzuki, T.; Kondo, Y. Palladium-
(0)-catalyzed direct cross-coupling reaction of allylic alcohols with
aryl- and alkenylboronic acids. Org. Biomol. Chem. 2008, 6, 3005−
3013.
(12) For Ni-catalyzed silylation reactions involving CuF2: (a) Zarate,
C.; Martin, R. A Mild Ni/Cu-Catalyzed Silylation via C−O Cleavage.
J. Am. Chem. Soc. 2014, 136, 2236−2239. (b) Guo, L.;
Chatupheeraphat, A.; Rueping, M. Decarbonylative Silylation of
Esters by Combined Nickel and Copper Catalysis for the Synthesis of
Arylsilanes and Heteroarylsilanes. Angew. Chem., Int. Ed. 2016, 55,
11810−11813. (c) Pu, X.; Hu, J.; Zhao, Y.; Shi, Z. Nickel-Catalyzed
Decarbonylative Borylation and Silylation of Esters. ACS Catal. 2016,
́
6, 6692−6698. (d) Somerville, R. J.; Hale, L. V. A.; Gomez-Bengoa,
2
́
E.; Bures, J.; Martin, R. Intermediacy of Ni−Ni Species in sp C−O
(5) (a) Tsuji, Y.; Kajita, S.; Isobe, S.; Funato, M. Palladium-
Catalyzed Silylation of Allylic Acetates with Hexamethyldisilane or
(Trimethylsilyl)tributylstannane. J. Org. Chem. 1993, 58, 3607−3608.
(b) Tsuji, Y.; Funato, M.; Ozawa, M.; Ogiyama, H.; Kajita, S.;
Kawamura, T. Silylation of Allylic Trifluoroacetates and Acetates
Using Organodisilanes Catalyzed by Palladium Complex. J. Org.
Chem. 1996, 61, 5779−5787. (c) Moser, R.; Nishikata, T.; Lipshutz,
B. H. Pd-Catalyzed Synthesis of Allylic Silanes from Allylic Ethers.
Bond Cleavage of Aryl Esters: Relevance in Catalytic C−Si Bond
Formation. J. Am. Chem. Soc. 2018, 140, 8771−8780. (e) Wang, X.;
Wang, Z.; Nishihara, Y. Nickel/copper-cocatalyzed decarbonylative
silylation of acyl fluorides. Chem. Commun. 2019, 55, 10507−10510.
(13) For CuF2-promoted coupling reactions of aryl silanes, see:
(a) Shi, W.-J.; Zhao, H.-W.; Wang, Y.; Cao, Z.-C.; Zhang, L.-S.; Yu,
D.-G.; Shi, Z.-J. Nickel- or Iron-Catalyzed Cross-Coupling of Aryl
Carbamates with Arylsilanes. Adv. Synth. Catal. 2016, 358, 2410−
2416. For LCuF or in situ generated CuF promoted coupling
reactions of aryl silanes, see: (b) Herron, J. R.; Ball, Z. T. Synthesis
and Reactivity of Functionalized Arylcopper Compounds by Trans-
metalation of Organosilanes. J. Am. Chem. Soc. 2008, 130, 16486−
16487. (c) Gurung, S. K.; Thapa, S.; Vangala, A. S.; Giri, R. Copper-
Catalyzed Hiyama Coupling of (Hetero)aryltriethoxysilanes with
(Hetero)aryl Iodides. Org. Lett. 2013, 15, 5378−5381. For LCuF
promoted addition of a silylboronate reagent to aldehydes, see:
́
Org. Lett. 2010, 12, 28−31. (d) Selander, N.; Paasch, J. R.; Szabo, K. J.
Palladium-Catalyzed Allylic C−OH Functionalization for Efficient
Synthesis of Functionalized Allylsilanes. J. Am. Chem. Soc. 2011, 133,
́
409−411. (e) Larsson, J. M.; Szabo, K. J. Mechanistic Investigation of
the Palladium-Catalyzed Synthesis of Allylic Silanes and Boronates
from Allylic Alcohols. J. Am. Chem. Soc. 2013, 135, 443−455. (f) Ito,
H.; Horita, Y.; Sawamura, M. Copper(I)-Catalyzed Allylic Sub-
stitution of Silyl Nucleophiles through Si-Si Bond Activation. Adv.
Synth. Catal. 2012, 354, 813−817.
́
(d) Cirriez, V.; Rasson, C.; Hermant, T.; Petrignet, J.; Alvarez, J. D.;
(6) Bourque, L. E.; Cleary, P. A.; Woerpel, K. A. Metal-Catalyzed
Silylene Insertions of Allylic Ethers: Stereoselective Formation of
Chiral Allylic Silanes. J. Am. Chem. Soc. 2007, 129, 12602−12603.
(7) (a) Vyas, D. J.; Oestreich, M. Copper-Catalyzed Si-B Bond
Activation in Branched-Selective Allylic Substitution of Linear Allylic
Chlorides. Angew. Chem., Int. Ed. 2010, 49, 8513−8515. (b) Hazra, C.
K.; Irran, E.; Oestreich, M. Regio- and Diastereoselective Copper(I)-
Catalyzed Allylic Substitution of δ-Hydroxy Allylic Chlorides by a
Silicon Nucleophile. Eur. J. Org. Chem. 2013, 2013, 4903−4908.
(c) Delvos, L. B.; Vyas, D. J.; Oestreich, M. Asymmetric Synthesis of
α-Chiral Allylic Silanes by Enantioconvergent γ-Selective Copper(I)-
Catalyzed Allylic Silylation. Angew. Chem., Int. Ed. 2013, 52, 4650−
4653. (d) Takeda, M.; Shintani, R.; Hayashi, T. Enantioselective
Synthesis of α-Tri- and α-Tetrasubstituted Allylsilanes by Copper-
Catalyzed Asymmetric Allylic Substitution of Allyl Phosphates with
Silylboronates. J. Org. Chem. 2013, 78, 5007−5017. (e) Xuan, Q.-Q.;
Zhong, N.-J.; Ren, C.-L.; Liu, L.; Wang, D.; Chen, Y.-J.; Li, C.-J.
Cu(II)-Catalyzed Allylic Silylation of Morita−Baylis−Hillman Alco-
hols via Dual Activation of Si−B Bond and Hydroxyl Group. J. Org.
Chem. 2013, 78, 11076−11081. For reviews, see: (f) Oestreich, M.;
Robeyns, K.; Riant, O. Copper-Catalyzed Addition of Nucleophilic
Silicon to Aldehydes. Angew. Chem., Int. Ed. 2013, 52, 1785−1788.
(14) For details, see Supporting Information.
(15) Romero, E. A.; Peltier, J. L.; Jazzar, R.; Bertrand, G. Catalyst-
free dehydrocoupling of amines, alcohols, and thiols with pinacol
borane and 9-borabicyclononane (9-BBN). Chem. Commun. 2016, 52,
10563−10565.
(16) For postulated formation of Cu−Si species by in situ formed
CuOR species with silylboronate reagent, see: (a) Vyas, D. J.; Hazra,
C. K.; Oestreich, M. Copper(I)-Catalyzed Regioselective Propargylic
Substitution Involving Si−B Bond Activation. Org. Lett. 2011, 13,
4462−4465. (b) See ref 7a. For the formation of IPrCu-SiMe2Ph
through the reaction of IPrCuOtBu with PhMe2SiBpin, see:
(c) Kleeberg, C.; Feldmann, E.; Hartmann, E.; Vyas, D. J.;
Oestreich, M. Copper-Catalyzed 1,2-Addition of Nucleophilic Silicon
to Aldehydes: Mechanistic Insight and Catalytic Systems. Chem. - Eur.
J. 2011, 17, 13538−13543. (d) Plotzitzka, J.; Kleeberg, C.
[(NHC)CuI−ER3] Complexes (ER3 = SiMe2Ph, SiPh3, SnMe3):
From Linear, Mononuclear Complexes to Polynuclear Complexes
E
DOI: 10.1021/acs.orglett.9b03822
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
with Ultrashort CuI···CuI Distances. Inorg. Chem. 2016, 55, 4813−
4823.
(17) For proposed formation of Cu-Si species in Cu(II)-catalyzed
silylation of alkenes with silylboronates, see: (a) Calderone, J. A.;
Santos, W. L. Copper(II)-Catalyzed Silyl Conjugate Addition to α,β-
Unsaturated Conjugated Compounds: Brønsted Base-Assisted
Activation of Si−B Bond in Water. Org. Lett. 2012, 14, 2090−2093.
(b) See ref 7e. (c) Da, B.-C.; Liang, Q.-J.; Luo, Y.-C.; Ahmad, T.; Xu,
Y.-H.; Loh, T.-P. Copper-Catalyzed Stereo- and Enantioselective 1,4-
Protosilylation of α,β-Unsaturated Ketimines To Synthesize Function-
alized Allylsilanes. ACS Catal. 2018, 8, 6239−6245.
(18) For CuF(PPh3)3·2MeOH promoted transmetalation of
silylborane to Cu-Si species, see: Cirriez, V.; Rasson, C.; Riant, O.
Synthesis of Acylsilanes by Copper(I)-Catalyzed Addition of Silicon
Nucleophiles onto Acid Derivatives. Adv. Synth. Catal. 2013, 355,
3137−3140.
(19) In the absence of CuF2, the silylated product was not observed
from 8.
(20) For the bimetallic strategy in cross-coupling reactions, for
example, see: (a) Fu, J.; Huo, X.; Li, B.; Zhang, W. Cooperative
bimetallic catalysis in asymmetric allylic substitution. Org. Biomol.
Chem. 2017, 15, 9747−9759. (b) Vercruysse, S.; Cornelissen, L.;
Nahra, F.; Collard, L.; Riant, O. CuI/Pd0 Cooperative Dual Catalysis:
Tunable Stereoselective Construction of Tetra-Substituted Alkenes.
Chem. - Eur. J. 2014, 20, 1834−1838.
F
DOI: 10.1021/acs.orglett.9b03822
Org. Lett. XXXX, XXX, XXX−XXX