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Chemistry Letters Vol.34, No.6 (2005)
Trimethylsilyl Triflate Mediated New Carbon–Carbon Bond Forming Reactions
between Benzyl Diphenylphosphinates and Organosilicon Compounds
Yohei Kobashi,y;yy Tomofumi Minowa,y;yy and Teruaki Mukaiyamaꢀy;yy
yCenter for Basic Research, The Kitasato Institute (TCI), 6-15-5 Toshima, Kita-ku, Tokyo 114-0003
yyKitasato Institute for Life Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641
(Received February 24, 2005; CL-050234)
The trimethylsilyl triflate mediated reaction of benzyl
Table 1. Reactions of 4-n-heptylbenzyl diphenylphosphinate
(1) and allyltrimethylsilane in the presence of various Lewis
acids
diphenylphosphinate with allyltrimethylsilane or trimethylsilyl
enolate afforded the corresponding cross-coupling products in
good yields.
TMS
O
(1.0 equiv.)
Lewis acid
(1.0 equiv.)
Ph2PO
C7H15
C7H15
A carbon–carbon bond forming reaction by using Lewis
acid promoters is one of the important tools for the syntheses
of complex organic compounds and many examples have been
reported;1 for example, an allylation of an electrophile by using
allyltrimethylsilane in the presence of a Lewis acid, the Sakurai–
Hosomi reaction, gives the corresponding product in high
yield.1c,1d On the other hand, allylations at sp3-carbon by promo-
tion of a Lewis acid is known to be quite difficult2 and few ex-
amples have been reported with some limitations.3
Recently, etherification reactions between alkyl diphenyl-
phosphinate and alkoxytrimethylsilanes in the presence of tri-
methylsilyl triflate (TMSOTf) was reported from our group.4
This reaction proceeded efficiently because of the strong affinity
of alkyl diphenylphosphinate toward TMSOTf and a highly
electrophilic property of the phosphonium salt intermediate.
Then, a carbon–carbon bond forming reaction between alkyl
diphenylphosphinate and carbon nucleophiles was planned in
order to extend this unique properties.
1
2
CHCl3, rt, 7 h
Entry Lewis acid Yield/% Entry Lewis acid Yield/%
1
2
3
4
5
6
7
8
9
TiCl4
SnCl4
AlCl3
N.D.a
N.D.a
N.D.a
N.D.b
N.R.
N.R.
N.R.
N.D.
N.D.
N.D.
N.D.
12
13
14
15
16
17
18c
Yb(OTf)3
Cu(OTf)2
Zn(OTf)2
Hf(OTf)4
La(OTf)3
Gd(OTf)3
TESOTf
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
35
31
29
36
59
MgBr2OEt2
BF3OEt2
LiClO4
LiBF4
Sn(OTf)2
AgOTf
19c TBDMSOTf
20c
21c
TIPSOTf
TMSOTf
10b
11
Mg(OTf)2
Sc(OTf)3
22c,d TMSOTf
a4-n-Heptylbenzyl chloride was obtained in moderate to high
b
yields (Entry 1: 87%, Entry 2: 57%, Entry 3: 44%). 4-n-Hep-
tylbenzyl bromide was obtained in 88% yield. cThe reaction
was performed at 0 ꢁC for 1 h. d3.0 equiv. of allyltrimethylsilane
was used.
In this communication, we would like to report an efficient
method for carbon–carbon bond forming reaction between ben-
zyl diphenylphosphinate and various electrophiles in the pres-
ence of TMSOTf.
afford the corresponding cross-coupling products in 72–83%
yields (Table 2, Entries 3–5).6 4-Phenylbenzyl diphenylphosphi-
nate (3) also reacted with 9 at 0 ꢁC in chloroform (Table 2,
Entry 6). However, 4-methoxycarbonylbenzyl diphenylphosphi-
nate (4) having an electron-withdrawing group at C-4 position
reacted with 9 at the refluxing temperature to afford the cross-
coupling products in good yields (Table 2, Entries 7–8). When
chiral phosphinate 5 was used, the corresponding racemic prod-
uct was obtained, and the result indicates that this reaction pro-
ceeded via SN1 mechanism (Table 2, Entry 9). In the case when
3,3-diphenylpropyl diphenylphosphinate (6), a non-benzylic
substrate, was used, the corresponding ꢀ-elimination product
14 was formed in 56% yield (Table 2, Entry 10). Trimethylsilyl
enolates 11–13 also worked as useful nucleophiles of this reac-
tion and the corresponding cross-coupling compounds were af-
forded in good yields (Table 2, Entries 11–13).
In the first place, allylations of 4-n-heptylbenzyl diphenyl-
phosphinate5 (1) with allyltrimethylsilane were tried in the pres-
ence of various Lewis acids in chloroform at room temperature
(Table 1). When TiCl4, SnCl4, AlCl3, or MgBr2OEt2 was used,
the corresponding 4-n-heptylbenzyl halide was afforded in mod-
erate to high yields (Table 1, Entry 1–4). No reaction took place
when other Lewis acids including BF3OEt2, LiClO4, LiBF4, and
various metal triflates were used (Table 1, Entries 5–17). On the
other hand, the use of trialkylsilyl triflate effectively promoted
the reaction and the desired 2 was afforded in moderate yields
(Table 1, Entries 18–21). It is noted that a higher yield of 2
was attained effectively by increasing the amount of allyltri-
methylsilane (Table 1, Entry 22)
Next, carbon–carbon bond forming reactions between ben-
zyl diphenylphosphinates and organosilicon compounds were
tried in the presence of TMSOTf. When allyltrimethylsilane
(7) was used as an allylation reagent, 1,2-dimethoxyethane
was found to be the most effective solvent and 2 was obtained
in 77% yield (Table 2, Entry 2). Similarly, (2-methylallyl)tri-
methylsilane (8), (3,3-dimethylallyl)trimethylsilane (9), and (3-
chloroallyl)trimethylsilane (10) reacted with 1 in chloroform to
The typical experimental procedure is described for the re-
action of 17 and 9 (Table 1, Entry 3): to a stirred mixture of 1
(81.3 mg, 0.20 mmol) and 9 (42.7 mg, 0.30 mmol) in chloroform
(1 mL) was added trimethylsilyl triflate (36.1 mL, 0.20 mmol) at
0 ꢁC. The mixture was stirred for 1 h at 0 ꢁC and then quenched
with sat. NaHCO3. After the resulting mixture was extracted
Copyright ꢀ 2005 The Chemical Society of Japan
Kobashi, Yohei
