Synthesis of Allylsilanes via Nickel-Catalyzed Cross-Coupling of Silicon Nucleophiles with Allyl Alcohols

Article abstract of DOI:10.1021/acs.orglett.9b02946

NiCl₂(PMe₃)₂-catalyzed reaction of allyl alcohols with silylzinc reagents, including PhMe₂SiZnCl, Ph₂MeSiZnCl, and Ph₃SiZnCl, was performed, achieving allylsilanes in high yields. Aryl- and heteroaryl-substituted allyl alcohols, (E)-3-arylprop-2-en-1-ols, 1-aryl-prop-2-en-1-ols, and (E)-1-phenylpent-1-en-3-ol can be employed in the transformation. A range of functional groups as well as heteroaryl groups were tolerated. Reaction exhibited high regioselectivity and E/Z-selectivity when 1- or 3-aryl-substituted allyl alcohols were used as the substrates. Reaction of chiral allyl alcohol, (S,E)-1-phenylpent-1-en-3-ol, yielded a configuration-inversion product (R,E)-dimethyl(phenyl)(1-phenylpent-1-en-3-yl)silane.

Full text of DOI:10.1021/acs.orglett.9b02946

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Synthesis of Allylsilanes via Nickel-Catalyzed Cross-Coupling of
Silicon Nucleophiles with Allyl Alcohols
Bo Yang† and Zhong-Xia Wang*,†,‡
†CAS Key Laboratory of Soft Matter Chemistry and Department of Chemistry, University of Science and Technology of China,
Hefei, Anhui 230026, People’s Republic of China
‡Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, People’s Republic of China
S
* Supporting Information
ABSTRACT: NiCl2(PMe3)2-catalyzed reaction of allyl alco-
hols with silylzinc reagents, including PhMe2SiZnCl,
Ph2MeSiZnCl, and Ph3SiZnCl, was performed, achieving
allylsilanes in high yields. Aryl- and heteroaryl-substituted
allyl alcohols, (E)-3-arylprop-2-en-1-ols, 1-aryl-prop-2-en-1-ols, and (E)-1-phenylpent-1-en-3-ol can be employed in the
transformation. A range of functional groups as well as heteroaryl groups were tolerated. Reaction exhibited high regioselectivity
and E/Z-selectivity when 1- or 3-aryl-substituted allyl alcohols were used as the substrates. Reaction of chiral allyl alcohol, (S,E)-
1-phenylpent-1-en-3-ol, yielded a configuration-inversion product (R,E)-dimethyl(phenyl)(1-phenylpent-1-en-3-yl)silane.
llylsilanes are important building blocks in view of the
Areactivity of both alkenes and metal-allyl reagents, which
have been widely applied in organic synthesis and materials
science.1 A range of methods for synthesis of allylsilanes have
been developed. Among them, silylation of allylic substrates
with silicon nucleophilic reagents such as silylzinc,2 silylmag-
nesium,3 silyltin,4 and silylboron5 reagents, as well as
disilanes,4,6 under palladium or copper catalysis, has attracted
great attention. The allylic substrates were mainly allyl halides
and allyl alcohol derivatives such as allylic ethers, allylic
carboxylates, allylic carbonates, and allylic phosphates. Allyl
alcohols themselves as electrophiles have seldom been
reported, because of poor leaving ability of the hydroxyl
group and the presence of an acidic proton.5e,6f,g However, allyl
halides and allyl alcohol derivatives are often prepared from
allyl alcohols. Hence, direct silylation of allyl alcohols is more
step- and atom-economical.
of allyl alcohol derivatives with silicon-based nucleophiles.2−5
However, the reaction of 1a with 2a did not occur in the
presence of CuI or [Pd(π-allyl)Cl]2 (see Table 1, entries 2 and
3). This probably results from a difficult oxidation addition
process of copper or palladium with a metal salt of allylic
alcohol, whereas nickel can catalyze the reactions of alkoxide
salts or phenoxide salts via the C−O bond cleavage.7,8 Hence,
nickel catalysts were tested next. When NiCl2(dppe) was used
as the catalyst, the reaction gave the expected product 3a in
29% yield (Table 1, entry 4). This positive result motivated us
to examine other nickel catalysts. NiCl2(dppp), NiCl2(dppf),
and NiCl2(PPh3)2 exhibited a similar catalytic activity to
NiCl2(dppe) (Table 1, entries 5−7). While NiCl2(PCy3)2 was
ineffective (Table 1, entry 8). Further tests showed that
NiCl2(PMe3)2 was a more effective catalyst than those
mentioned above. In the presence of 10 mol % NiCl2(PMe3)2,
the reaction of 1a with 2a gave the desired product in 88%
yield (Table 1, entry 9). We also found that phosphorus-
ligand-free nickel complexes such as NiCl2(DME) and
NiBr2(glyme) were inefficient (Table 1, entries 10 and 11).
Extending the reaction time did not improve the yield (Table
1, entry 12). Increasing the loading of 2a to 1.5 equiv led to the
increase of 3a yield (Table 1, entry 13). When the reaction was
performed in other solvents such as THF/toluene (3:1),
nBu2O/toluene (1:3), and toluene, a loading of 1.2 equiv of 2a
was sufficient. Among the alternative solvents, both toluene
and toluene/nBu2O (3/1) were more suitable for this
transformation (Table 1, entries 14−16). When 5 mol %
NiCl2(PMe3)2 was used, the reaction gave a slightly lower yield
(Table 1, entry 17). Finally, we demonstrated that the reaction
can go to completion at room temperature within 5 h. The
We recently developed a method for construction of C(allyl)
−
C(aryl/alkenyl) bonds by nickel-catalyzed cross-coupling of allyl
alcohols with arylzinc or alkenylzinc reagents.7 The reaction
showed high regioselectivity and E/Z-selectivity, giving linear
and E configuration products in most cases. This methodology
was expected to extend to the synthesis of allylsilanes from allyl
alcohols. For this purpose, we explored reaction of allyl
alcohols with silylzinc reagents. Herein, we report the results.
The reaction of cinnamyl alcohol (1a) with PhMe2SiZnCl
(2a) was employed to optimize the reaction conditions.
Because of the presence of the acidic proton, excess organozinc
reagent or a strong base was required to convert the cinnamyl
alcohol to its salts prior to performing the reaction. We used
1.2 equiv of MeZnCl to grab the proton, in view of our
previous report.7 In the absence of a transition-metal catalyst,
the cross-coupling cannot occur in tetrahydrofuran (THF) at
80 °C (Table 1, entry 1). According to the reports in the
literature, copper or palladium can catalyze the cross-coupling
Received: August 19, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.9b02946
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
(1s), (E)-3-(benzo[d][1,3]dioxol-5-yl)prop-2-en-1-ol (1t),
(E)-3-(naphthalen-2-yl)prop-2-en-1-ol (1u), and (E)-3-(naph-
thalen-1-yl)prop-2-en-1-ol (1v), displayed reactivity similar to
that of (E)-3-phenylprop-2-en-1-ol (Table 2, entries 18−21).
We also examined the reactivity of (E)-4-phenylbut-3-en-2-ol
(1w) and (E)-1,3-diphenylprop-2-en-1-ol (1x). Their reaction
required longer time and gave excellent product yields (Table
2, entries 22 and 23). (E)-2-Methyl-3-phenylprop-2-en-1-ol
(1y) showed relatively low reactivity. Its reaction with 2a was
performed at 80 °C and led to the desired product in 56%
yield, as a mixture of Z and E isomers (Table 2, entry 24). The
catalytic system was also used to perform the transformation of
alkyl-substituted allyl alcohols. Reaction of these substrates
required longer time and higher temperature. For example,
reaction of (E)-6-(4-methoxyphenyl)hex-2-en-1-ol (1z) and
(E)-3-(tetrahydro-2H-pyran-4-yl)prop-2-en-1-ol (1za) with 2a
at 80 °C for 24 h resulted in the mixtures of linear and
branched coupling products in 86% and 80% total yields,
respectively (Table 2, entries 25 and 26) (see the mechanism
discussion section below).
Several heteroaryl-substituted allyl alcohols were also
examined under the optimized conditions. As shown in
Scheme 1, furan-2-yl-, thiophen-2-yl-, pyridin-2-yl-, benzo[b]-
thiophen-3-yl-, and 1-methyl-1H-indol-5-yl-substituted allyl
alcohols were demonstrated to be suitable substrates for the
coupling, leading to the desired products in excellent yields.
Reaction of (E)-3-(thiophen-2-yl)prop-2-en-1-ol with 2a
required a longer reaction time and gave the desired product
in 85% yield, as a mixture of Z and E isomers.
Reactivity of 1-arylprop-2-en-1-ols was also examined using
PhMe2SiZnCl as the nucleophilic reagent (see Scheme 2). A
mixture of toluene and nBu2O (3:1) were demonstrated to be
superior to toluene as a solvent, and the reaction time was
prolonged to 24 h to ensure the complete consumption of the
1-arylprop-2-en-1-ols. Linear allylsilanes were formed in each
case. Reaction of 1-phenylprop-2-en-1-ol and 1-(4-substituted
phenyl)prop-2-en-1-ols with electron-donor groups on the
phenyl rings gave the products in yields of 83%−86%. Reaction
of 1-(4-substituted phenyl)prop-2-en-1-ols with electron-with-
drawing groups on the phenyl rings resulted in slightly lower
product yields.
Other silicon nucleophiles were also tested. Both
Ph2MeSiZnCl and Ph3SiZnCl exhibited excellent reactivity.
Their reaction with cinnamyl alcohol afforded the correspond-
ing products in yields of 99% and 91%, respectively (see
Scheme 3). Reaction of Ph3SiZnCl required a longer reaction
time to make the alcohol convert completely.
Table 1. Optimization of Reaction Conditions
b
entry
catalyst
solvent
yield (%)
1
2
3
4
5
6
7
8
9
−
CuI
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
none
none
none
29
34
24
31
trace
88
10
5
88
92
92
97
97
93
97 (90 )
c
[Pd(π-allyl)Cl]2
NiCl2(dppe)
NiCl2(dppp)
NiCl2(dppf)
NiCl2(PPh3)2
NiCl2(PCy3)2
NiCl2(PMe3)2
NiCl2(DME)
NiBr2(glyme)
NiCl2(PMe3)2
NiCl2(PMe3)2
NiCl2(PMe3)2
NiCl2(PMe3)2
NiCl2(PMe3)2
NiCl2(PMe3)2
NiCl2(PMe3)2
10
11
d
12
e
13
14
15
16
THF/toluene (3/1)
toluene/nBu2O (3/1)
toluene
toluene
toluene
c
17
f
g
18
a
Unless otherwise specified, the reactions were performed on a 0.2
mmol scale, according to the conditions indicated by the above
equation. Isolated yield. 5 mol % catalyst was employed. The
b
c
d
e
f
reaction was run for 18 h. 1.5 equiv of 2a was employed. The
g
reaction was performed at room temperature for 5 h. 2 mmol scale.
reaction on a 2 mmol scale also proceeded well under the
conditions (Table 1, entry 18).
With the optimized conditions in hand, we explored the
scope of allyl alcohols using PhMe2SiZnCl (2a) as the
nucleophilic reagent (see Table 2). Thus, allyl alcohols was
first treated with MeZnCl. The reaction with PhMe2SiZnCl
then was run in toluene at room temperature for 5 h, using
Ni(PMe3)Cl2 (10 mol %) as a catalyst. A range of 3-
(substituted phenyl)prop-2-en-1-ols were tested and demon-
strated to be suitable for the transformation. The allyl alcohols
with either electron-rich or electron-poor substituted phenyl
gave excellent product yields (Table 2, entries 1−9 and 11−
17). It seems that the electron effect of the substituents on the
phenyl rings makes no difference to the reaction. The coupling
of (E)-3-(4-methoxyphenyl)prop-2-en-1-ol was also performed
on a 4 mmol scale and gave 3c in 87% isolated yield (Table 2,
entry 2). Functional groups on the phenyl rings, including p-
tBu, p-OMe, p-NMe2, p-SMe, p-CF3, p-OCF3, p-OCHF2, p-F,
p-Cl, p-CO2Me, p-CONEt2, m-OMe, m-OPh, m-CF3, o-Ph, and
o-F, were tolerated.
We also examined the potential use of the allylsilanes
produced in this work. It was demonstrated that the resultant
allylsilane, cinnamyldimethyl(phenyl)silane, can be utilized as
an allylating agent with high regioselectivity when reacted with
Ph2CHOH in the presence of InCl3 (see Scheme 4).9
Prelimilary experiments to evaluate the plausible reaction
mechanism were performed (see Scheme S9 in the Supporting
Information). The reaction of cinnamyl alcohol (1a) with
PhMe2SiZnCl (2a) was not affected by (1-cyclopropylvinyl)-
benzene additive. When 1.0 equiv of (1-cyclopropylvinyl)-
benzene was added to the reaction system, the catalytic process
gave the desired coupling product in 97% yield, along with
recovery of (1-cyclopropyl-vinyl)benzene in 94% yield (see
Scheme S9a in the Supporting Information). This is
inconsistent with a free radical process. The combination of
Ni(COD)2 and PMe3 exhibited almost the same catalytic
However, the bromo substituent in (E)-3-(4-bromophenyl)
prop-2-en-1-ol (1k) cannot be tolerated. Reaction of 1k with
PhMe2SiZnCl under the standard conditions afforded (E)-3-
(4-(dimethyl(phenyl)silyl)phenyl)prop-2-en-1-ol (3k) in 72%
yield, along with (E)-(3-(4-(dimethyl(phenyl)silyl)phenyl)-
allyl)dimethyl(phenyl)silane (3ka) in 27% yield (Table 2,
entry 10). It seems that the bromo substituent is more reactive
than the hydroxy group in 1k under the standard conditions.
When 2 equiv of PhMe2SiZnCl were used, the reaction
resulted in 3ka in 99% yield. Other 3-arylprop-2-en-1-ols, such
as (E)-3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)prop-2-en-1-ol
B
DOI: 10.1021/acs.orglett.9b02946
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
Table 2. Scope of Allyl Alcohols
a
Unless otherwise specified, the reactions were carried out on a 0.2 mmol scale according to the conditions indicated by the above equation.
bIsolated yield. c4 mmol scale. dThe yields of 3k and 3ka were 72% and 27%, respectively. e2.0 equiv of 2a were used. fThe reaction was performed
g
h
in THF at 80 °C. Reaction time was 24 h. Reaction temperature was 80 °C.
activity as NiCl2(PMe3)2 (see Scheme S9b in the Supporting
Information). Furthermore, a small amount of PhMe2Si-
SiMe2Ph was detected when NiCl2(PMe3)2 was employed as
the catalyst (5.1% based on cinnamyl alcohol). The fact that
the isolated PhMe2Si-SiMe2Ph was less than the theoretical
amount might be because a portion of NiCl2(PMe3)2 was
reduced by the unconsumed MeZnCl. These experimental
facts imply the reaction might proceed through a Ni(0)/Ni(II)
cycle. Next, we found that the reaction of racemic (E)-1-
phenylpent-1-en-3-ol (rac-1zo) with PhMe2SiZnCl under
standard conditions gave racemic (E)-dimethyl(phenyl)(1-
phenylpent-1-en-3-yl)silane (rac-3zo) in 91% yield. Whereas
reaction of (S)-1zo with 2a produced (R)-3zo (see Schemes
S9c and S9d in the Supporting Information). Hence, we
inferred that the reaction might involve a SN2 process. On the
basis of the above experimental facts and the related reports in
the literature,2b,10 a plausible catalytic cycle is outlined in
Scheme 5. Thus, allylic alcohol was first converted to the
corresponding salt A. Meanwhile, NiCl2(PMe3)2 was reduced
to active Ni(0) species B by R3SiZnCl along with the
formation of R3Si-SiR3. Oxidative addition with inversion of
the Ni(0) species with A results in a [σ, π]-type Ni(II)
intermediate C. Subsequently, transmetalation of C with
R3SiZnCl forms complex D. When R is a aryl group, D
prefers to directly undergo reductive elimilation to give α-
silylated product E with the inversion of configuration. When
R′ is a aryl group, D prefers to isomerize to form a more stable
[σ, π]-type Ni(II) intermediate G via a π-allyl Ni(II)
intermediate F. Reductive elimilation of G leads to γ-silylated
product H. If both R and R′ are alkyl groups or protons, the
C
DOI: 10.1021/acs.orglett.9b02946
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 1. Reaction of Heteroaryl Allyl Alcohols with
PhMe2SiZnCl
Scheme 5. Proposed Catalytic Cycle
Scheme 2. Reaction of 1-Arylprop-2-en-1-ols with
PhMe2SiZnCl
reaction might proceed via a Ni(0)/Ni(II) catalytic cycle and
[σ, π]-type allyl nickel intermediates.
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.9b02946.
Scheme 3. Reaction of (E)-3-Phenylprop-2-en-1-ol with
Ph2MeSiZnCl and Ph3SiZnCl
Experimental procedures, full analysis data for new
compounds, and copies of NMR spectra (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: zxwang@ustc.edu.cn.
ORCID
Scheme 4. Reaction of Cinnamyldimethyl(phenyl)silane
with Diphenylmethanol
Bo Yang: 0000-0003-0612-5712
Zhong-Xia Wang: 0000-0001-8126-8778
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
reaction leads to the products with poor regioselectivity,
because none of the intermediates D and G is dominant (see
Table 2, entries 25 and 26).
This work was supported by the National Natural Science
Foundation of China (Grant No. 21772186) and the National
Basic Research Program of China (Grant No.
2015CB856600). We thank Y.-Y. Kong for her help in
performing additional experiments.
In summary, we developed a synthetic method of allylic
silanes via NiCl2(PMe3)2-catalyzed reaction of allyl alcohols
with silylzinc reagents under mild conditions. The method
suits for a broad scope of substrates. PhMe2SiZnCl,
Ph2MeSiZnCl and Ph3SiZnCl are suitable nucleophilic species.
Aryl and heteroaryl-substituted allyl alcohols, (E)-3-arylprop-2-
en-1-ols, 1-aryl-prop-2-en-1-ols, and (E)-1-phenylpent-1-en-3-
ol are suitable electrophilic substrates. A range of functional
groups were tolerated. Reaction also showed high regiose-
lectivity and E/Z-selectivity when 1- or 3-aryl-substituted allyl
alcohols were used as the substrates. Reaction of chiral allyl
alcohol, (S,E)-1-phenylpent-1-en-3-ol, yielded a configuration-
inversion product (R,E)-dimethyl(phenyl)(1-phenylpent-1-en-
3-yl)silane. Preliminary mechanism studies showed that the
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