Pd-catalyzed coupling reaction of allyl and propargyl ethers with chlorosilanes

Article abstract of DOI:10.1246/cl.2007.236

Pd-catalyzed synthesis of allylsilanes from chlorosilanes and allyl ethers is described. The reaction proceeds efficiently at room temperature by the use of phenyl or vinyl Grignard reagent in the presence of palladium catalysts. The present method can also be applied to synthesis of propargylsilanes by the use of propargyl ethers. Copyright

Full text of DOI:10.1246/cl.2007.236

236
Chemistry Letters Vol.36, No.2 (2007)
Pd-catalyzed Coupling Reaction of Allyl and Propargyl Ethers with Chlorosilanes
Yoshitaka Naitoh,1 Fumiaki Bando,1 Jun Terao,Ã2 Kazutaka Otsuki,1 Hitoshi Kuniyasu,1 and Nobuaki KambeÃ1
1Department of Applied Chemistry, Graduate School of Engineering, Osaka University,
2-1 Yamadaoka, Suita, Osaka 565-0871
2Science and Technology Center for Atoms, Molecules and Ions Control, Graduate School of Engineering,
Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871
(Received October 31, 2006; CL-061279; E-mail: terao@chem.eng.osaka-u.ac.jp, kambe@chem.eng.osaka-u.ac.jp)
Table 1. Preparation of allylsilanes from allyl ethersa
Pd-catalyzed synthesis of allylsilanes from chlorosilanes
3 mol % Pd(acac)2
240 mol % Ph-MgBr
and allyl ethers is described. The reaction proceeds efficiently
at room temperature by the use of phenyl or vinyl Grignard re-
agent in the presence of palladium catalysts. The present method
can also be applied to synthesis of propargylsilanes by the use of
propargyl ethers.
R'
SiR3
R'
OR
+
R3Si-Cl
THF, 25 °C, 3 h
Yieldb/% [E/Z]d
88
R'
OR
Entry
1
Product
R3Si-Cl
Et3Si-Cl
OPh
OPh
SiEt3
3
Allyl alcohols and their derivatives are useful synthetic
intermediates as the versatile sources of allylic carbon units in
organic synthesis. There have been developed a number of ally-
lation reactions using allyl alcohol derivatives such as allyl
ethers, acetates, carbonates, sulfonates, etc. by the aid of transi-
tion-metal catalysts.1 We have recently developed a new method
for allylation of chlorosilanes or alkyl halides with allyl ethers
by the aid of NiCl2 as a catalyst in the presence of vinyl Grignard
reagents.2 Here, we disclose that Pd also catalyzes reaction of
chlorosilanes with allyl ethers to give allylsilanes under mild
conditions in the presence of phenyl or vinyl Grignard reagents
by choosing appropriate ligands (eq 1).
2
3
SiPh3
97
86
Ph3Si-Cl
4
SinPr3
1
nPr3Si-Cl
nPr3Si-Cl
OSiMe3
OSiMe3
4
Ph
Ph
SinPr3
96c
100/0
5
nPent
OSiMe3 nPent
nPent
SinPr3
nPr3Si-Cl
nPr3Si-Cl
5
6
76
75
76/24
76/24
6
6
nPent
SinPr3
OSiMe3
aChlorosilane (1.2 mmol), allyl ether (1 mmol), Pd(acac)2 (0.03
cat. Pd
mmol), PhMgBr (2.4 mmol), THF, 25 ꢀC, 3 h. bGC yield. cNMR
yield. Determined by NMR.
Aryl or Vinyl Grignard reagent
d
OR'
SiR3
+
R3Si-Cl
(1)
THF, 25 °C
ethers are shown in Table 1. Et3SiCl and Ph3SiCl can be em-
ployed to afford 3 and 4 in 88 and 97% yield, respectively
(Entries 1 and 2). Allyl trimethylsilyl ether, easily available from
the corresponding allyl alcohol, gave an allylsilane 1 in 86%
yield (Entry 3). When (E)-cinnamyloxytrimethylsilane was
used, (E)-cinnamylsilane 5 was obtained as a sole product
(Entry 4). An allyl ether having a pentyl substituent at the ꢀ-car-
bon [E/Z = 100/0] afforded the corresponding allylsilane 6 in
76% yield as a 76:24 mixture of E/Z isomers without the forma-
tion of its regioisomer (Entry 5). It should be noted that 6 was
also formed from ꢁ-pentyl-substitued allyl ether in the same
regio- and stereoselectivities as Entry 5 (Entry 6), suggesting
that these two reactions proceed via the same intermediate.
We next applied this procedure to propargylation of chloro-
silanes. Under similar conditions as those of eq 2, reaction of
Et3Si–Cl with propargyl trimethylsilyl ether afforded expected
propargyl silane 7 in 70% yield (eq 3).
For example, chlorotripropylsilane reacted with allyl phenyl
ether in the presence of PhMgBr and a catalytic amount of
Pd(acac)2 in THF at 25 ꢀC for 1 h to give allyltripropylsilane 1
in quantitative yield (eq 2). In this reaction, only a trace amount
of allylbenzene (<1%) was formed. Pd(dba)2 and PdCl2(PPh3)2
also afforded 1 in high yields. When PdCl2(dppf) was used, how-
ever, 1 was obtained in only a 3% yield and conventional cross-
coupling between allyl ether and PhMgBr took place preferen-
tially to form allylbenzene 2 in 70% yield.3 It should be noted
that Ni complexes, either Ni(acac)2 or NiCl2(PPh3)2, afforded
2 exclusively. In the Pd(acac)2 system, vinyl Grignard reagent
also promoted silylation to give 1 quantitatively (>98%). On
the other hand, n-butyl Grignard reagent gave 42% yield of 1.
3 mol % cat.
240 mol % Ph-MgBr
SinPr3
Ph
(2)
nPr3Si-Cl
1.2 mmol
OPh
+
+
THF, 25 °C, 1 h
1
1
2
2
1.0 mmol
GC yield (%)
3 mol % Pd(acac)2
cat.
240 mol % Ph-MgBr
Et
Et
(3)
+
Et3Si-Cl
SiEt3
OSiMe3
1.0 mmol
THF, 25 °C, 6 h
Pd(acac)2
Pd(dba)2
>98%
92%
94%
3%
<1%
3%
7, 70%
1.2 mmol
PdCl2(PPh3)2
PdCl2(dppf)
Ni(acac)2
6%
A plausible reaction pathway is outlined in Scheme 1.
Pd(acac)2 is reduced by RMgX to afford Pd0 via 8 (R = Ph)
with the concomitant formation of biphenyl. Thus, formed
Pd0 undergoes oxidative addition toward allyl ether to afford
(ꢂ-allyl)palladium complex 9. Subsequent reaction of 9 with 2
70%
91%
96%
<1%
<1%
NiCl2(PPh3)2
Results obtained using some other chlorosilanes and allyl
Copyright Ó 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.2 (2007)
237
nPent
MgBr
nPr3Si-Cl
+
OPh
(5)
THF, 25 °C, 0.5 h
R-R
M0
15
nPent
nPent
SinPr3
+
SinPr3
R-MgX
MX2
R
M
8
R
M = Pd(dppf)
or Ni
R = Ph
16; 88% (E/Z = 72/28)
17; 10%
M
Conditions
SiR'3
Et3Si-Cl
nPent
OPh
9
2
+
(6)
PhO
THF, 25 °C, 3 h
1
18
nPent
R-MgX
nPent
SiEt3
+
reductive coupling
R'3Si-Cl
SiEt3
20
Conditions
3 mol % NiCl2, 240 mol %
3 mol % Pd(acac)2, 240 mol % Ph-MgBr
19
−
69% (E/Z = 63/37)
61% (E/Z = 83/17)
4%
0%
MgCl
R = Et
MgX
M
M
+
MgX
β
-H elimination
−8
R
R
R
In conclusion, carbon–silicon bond-forming reaction be-
tween allyl ethers and chlorosilanes can be achieved successfully
by the combined use of Pd catalysts, such as Pd(acac)2,
Pd(dba)2, or PdCl2(PPh3)2, and phenyl or vinyl Grignard
reagents. This reaction competes with reduction of allyl ethers
when EtMgBr was employed and suppressed when Ni com-
plexes on PdCl2(dppf) were used.
12
11
10
R-MgX
H
M = Pd
R = Ph, Vinyl
Scheme 1. A plausible reaction pathways.
equivalents of RMgX via (ꢂ-allyl)palladium complex 10 gives
anionic (ꢂ-allyl)palladium complex 11,4 which react with
chlorosilanes to afford 1 and R2Pd 8. As an alternative pathway,
free allyl Grignard reagent 12 formed from 11 may also react
with chlorosilanes to give allylsilanes.
This study was supported by Industrial Technology Re-
search Grant Program in 2006 from New Energy and Industrial
Technolgy Development Organization (NEDO).
Interesting results of eq 1 that different products were
obtained by changing the catalyst can be explained as follows.
When PdCl2(dppf)5 and Ni complexes6 are used instead of
Pd(acac)2, the reductive coupling of 10 leading to allylbenzene
2 predominates over the formation of 11 via 10.
When ethylmagnesium chloride (R = Et) is employed, ꢃ-
hydrogen elimination from 10 may compete with the silylation
processes. In fact, a reaction of Pr3SiCl with cinnamyl trimethyl-
silyl ether in the presence of EtMgBr afforded 1-propenylben-
zene 13 as a by-product in 19% yield along with 57% of allyl-
silane 5 and a trace amount of 14 (eq 4), however, 13 was not
formed when PhMgBr was used (Table 1, Entry 4).
References and Notes
1
a) J. Tsuji, Palladium Reagents and Catalysts, John Wiley &
Sons, Inc., Chichester, 1995, pp. 345–356. b) Handbook of
Organopalladium Chemistry for Organic Synthesis, ed. by
E. Negishi, Wiley, New York, 2002, Vol. 2.1.1-4, pp. 1669–
1793. c) Y. Tamaru, in Handbook of Organopalladium
Chemistry for Organic Synthesis, ed. by E. Negishi, Wiley,
New York, 2002, Vol. 2.3.4, pp. 1917–1943. d) J. Tsuji,
Palladium Reagents and Catalysts: New Perspectives for
the 21st Century, John Wiley & Sons, Inc., Chichester,
2004, pp. 431–517.
2
3
J. Terao, H. Watabe, H. Watanabe, N. Kambe, Adv. Synth.
Catal. 2004, 346, 1674.
3 mol % Pd(acac)2
240 mol % Et-MgBr
a) C. Chuit, H. Felkin, C. Frajerman, G. Roussi, G.
Swierczewski, Chem. Commun. 1968, 1604. b) T. Hayashi,
M. Konishi, K. Yokota, M. Kumada, J. Chem. Soc., Chem.
Commun. 1981, 313. c) H. Sugimura, H. Takei, Chem. Lett.
1984, 1505.
nPr3Si-Cl
1.2 mmol
Ph
OSiMe3
1.0 mmol
(4)
+
THF, 25 °C, 1 h
Ph
Et
14; <1%
Ph
+
Ph
SinPr3
+
4
a) S. Holle, P. W. Jolly, R. Mynott, R. Z. Salz, Z. Natur-
forsch., B: Anorg. Chem., Org. Chem. 1982, 37, 675. b)
P. W. Jolly, Angew. Chem., Int. Ed. Engl. 1985, 24, 283. c) B.
5; 57%
13; 19%
In order to shed light on an active intermediate that reacts
with chlorosilanes, we compared regioselectivities of the present
reaction with these of direct reaction of chlorosilane with an
allyl Grignard reagent. When (E)-oct-2-enylmagnesium bromide
15, generated from Rieke magnesium and the corresponding
allyl ether,7 was allowed to react with nPr3SiCl, regioisomers
16 and 17 were obtained in 88 and 10% yields within 30 min,
respectively (eq 5).8 This is in large contrast to the fact that a
single regioisomer 16 was obtained exclusively as shown in
Table 1, Entry 5.
When we carried out the reaction of Et3SiCl with ꢀ-pentyl-
substitued allyl ether 18 in the presence of 3 mol % of NiCl2 and
240 mol % of CH2=CHMgCl, regioisomers 19 and 20 were
obtained in 69 and 4% yields, respectively. On the other hand,
no evidence for the formation of 20 was detected in the palladi-
um-catalyzed system (eq 6). These results suggest that free
allyl Grignard reagents may not be formed in the present reac-
tion system.
´
Bogdanovic, S. C. Huckett, U. Wilczok, A. Rufinska, Angew.
Chem., Int. Ed. Engl. 1988, 27, 1513. d) D. Alberti, R.
`
Goddard, A. Rufinska, K.-R. Porschke, Organometallics
`
¨
2003, 22, 4025.
5
6
a) T. Hayashi, M. Konishi, M. Kumada, Tetrahedron Lett.
1979, 20, 1871. b) T. Hayashi, M. Konishi, M. Kumada, J.
Organomet. Chem. 1980, 186, C1. c) T. Hayashi, M. Konishi,
Y. Kobori, M. Kumada, T. Higuchi, K. Hirotu, J. Am. Chem.
Soc. 1984, 106, 158.
a) H. Kurosawa, H. Ohnishi, M. Emoto, N. Chatani, Y.
Kawasaki, S. Murai, I. Ikeda, Organometallics 1990, 9,
3038. b) H. Kurosawa, S. Ogoshi, Bull. Chem. Soc. Jpn.
1998, 71, 973.
7
8
E. Bartmann, J. Organomet. Chem. 1987, 332, 19.
It is also known that crotyl Grignard reagent reacts with
Me3SiCl giving rise to a mixture of (but-2-enyl)trimethyl-
silane and (1-methyl-2-propenyl)trimethylsilane, see: A.
Hosomi, H. Iguchi, H. Sakurai, Chem. Lett. 1982, 223.
Published on the web (Advance View) January 6, 2007; doi:10.1246/cl.2007.236