Chlorotrimethylsilane: A powerful Lewis acidic catalyst in Michael-type Friedel-Crafts reactions of indoles and enones

Article abstract of DOI:10.1080/00397910701544737

Catalytic amount of chlorotrimethylsilane (TMSCl) was found to be an effective silicon Lewis acid catalyst in catalyzing the Michael-type Friedel-Crafts reactions of indoles and chalcones to afford corresponding 3-substituted indole derivatives in good to

Full text of DOI:10.1080/00397910701544737

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Chlorotrimethylsilane: A Powerful Lewis
Acidic Catalyst in Michael‐Type Friedel–Crafts
Reactions of Indoles and Enones
Li‐Wen Xu a b , Wei Zhou a , Lei Yang a & Chun‐Gu Xia a
a State Key Laboratory for Oxo Synthesis and Selective Oxidation , Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences and Graduate
School of the Chinese Academy of Sciences , Lanzhou, China
b Key Laboratory of Organosilicon Chemistry and Material Technology of
Ministry of Education , Hangzhou Normal University , Hangzhou, China
Published online: 10 Sep 2007.
To cite this article: Li‐Wen Xu , Wei Zhou , Lei Yang & Chun‐Gu Xia (2007) Chlorotrimethylsilane: A
Powerful Lewis Acidic Catalyst in Michael‐Type Friedel–Crafts Reactions of Indoles and Enones, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:18,
3095-3104, DOI: 10.1080/00397910701544737
To link to this article: http://dx.doi.org/10.1080/00397910701544737
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Synthetic Communicationsw, 37: 3095–3104, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701544737
Chlorotrimethylsilane: A Powerful Lewis
Acidic Catalyst in Michael-Type
Friedel–Crafts Reactions of Indoles
and Enones
Li-Wen Xu
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences and Graduate
School of the Chinese Academy of Sciences, Lanzhou, China and Key
Laboratory of Organosilicon Chemistry and Material Technology of
Ministry of Education, Hangzhou Normal University, Hangzhou, China
Wei Zhou, Lei Yang, and Chun-Gu Xia
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences and Graduate
School of the Chinese Academy of Sciences, Lanzhou, China
Abstract: Catalytic amount of chlorotrimethylsilane (TMSCl) was found to be an
effective silicon Lewis acid catalyst in catalyzing the Michael-type Friedel–Crafts
reactions of indoles and chalcones to afford corresponding 3-substituted indole deriva-
tives in good to excellent yields. The method is metal-free, has mild reaction con-
ditions, and generates good yields of products with greater selectivity, which make it
a useful and attractive process for the synthesis of different indole derivatives.
Keywords: dual activation, enone, Friedel–Crafts reaction, indole, silane
Among various synthetic applications of silane (organosilicon compounds),[1]
the transformations utilizing derivatives containing leaving groups at the
Received November 21, 2006
Address correspondence to Li-Wen Xu, State Key Laboratory for Oxo Synthesis
and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of
Sciences and Graduate School of the Chinese Academy of Sciences, Lanzhou 730000,
China. E-mail: licpxulw@yahoo.com
3095

3096
L.-W. Xu et al.
silicon atom have become especially widespread. The behavior of these
compounds is determined primarily by the tendency of the silicon atom to
expand its valence shell, giving rise to five- and six-coordinate intermedi-
ates.[2] This property allows one to consider silanes as Lewis acids, thereby
justifying their use as mediators in carbon–carbon bond-forming reactions.
The past four decades witnessed a tremendous development in the use of orga-
nosilicon compounds (silanes) for organic synthesis.[1b–e] The observation of
the trialkylsilyl cation R3Siþ, which is apparently the strongest silicon Lewis
acid (SLA), has attracted considerable attention. Silicon Lewis acids (silanes)
offer some advantages over traditional metal-centered activators. For example,
silanes are compatible with many synthetically valuable C-nucleophiles and
heteroatom, such as silyl enol ethers, allyl organometallic reagents,
cuprates, phosphine, and carbamate.[3] Among the silane compounds, chloro-
trimethylsilane (TMSCl) is one of the most useful reagents, is a highly reactive
silylating agent, and has numerous applications in organic synthesis and
catalysis.[4] TMSCl can facilitate the conjugate addition of organocopper
and other organometallic reagents to different acceptors efficiently[5] and
has been widely used as promoter or additive in several transition metal–or
Lewis acid–catalyzed reaction transformations.[6] However, its direct use as
a catalyst in organic reactions is rarely reported.[7] Herein, we report our
findings, focusing on the TMSCl-catalyzed Michael-type Friedel–Crafts
reactions of indoles and enones.
Among the Friedel–Crafts reactions, the Michael-type Friedel-Crafts
addition of indoles to electron-deficient olefins and a,b-unsaturated enones
is a very important process because it is involved in the total synthesis
of a class of bioactive indole alkaloids such as the hapalindoles and other
3-substituted indoles derivatives, which are important substructures and
building blocks for the synthesis of natural products and therapeutic
agents.[8] During past years, a variety of transition metal salts, such as
[11]
Zr(OTf)4,[9] Bi(OTf)3,[10] CeCl3 7H2O-NaI,
InBr3,[12] and other transition
.
metal–based Lewis acid catalysts[13] or organic molecular catalysts (organo-
catalysis),[14] have been applied in this reaction for the preparation of
3-substituted indoles. However, some drawbacks still exist in previous
synthetic methods (e.g., the use of expensive stoichiometric amounts of
Lewis acidic catalysts and toxic heavy metals). Hence, searching for cheaper,
simpler, and more efficient procedures (simple chemistry), including metal-
free catalysts, is very attractive.
RESULTS AND DISCUSSION
To establish suitable Friedel–Crafts reaction conditions, we employed the
reaction of indole with chalcone as a model in the presence of catalytic
TMSCl (Scheme 1). The results of the TMSCl-catalyzed Friedel–Crafts
reactions in various conditions are summarized in Table 1. Among these

Chlorotrimethylsilane
3097
Scheme 1.
solvents, lower or nonpolar ones were proven to be effective for the reaction.
CH2Cl2 provided the best result, but no reaction occurred in DMF probably
because of the strong interaction between TMSCl and DMF. When the
amount of TMSCl was reduced to 10 mol%, a slightly lower yield was
obtained. Under the optimized mild condition (20 mol% of TMSCl, 1 equiv.
chalcone, and 1.1 equiv. indole in CH2Cl2 at room temperature), the target
compound 3a was obtained in good yield (75%).
Under the optimized mild condition (20 mol% of TMSCl, 1 equiv.
chalcone, and 1.1 equiv. indole in CH2Cl2 at room temperature), the target
Table 1. TMSCl-catalyzed Michael-type Friedel–Crafts reactions of indole with
chalcone under different conditions
Entry
Solvent
Yield (%)a
1
2
CH2Cl2
Toluene
CH3CN
Acetone
DMF
75
56
3
62
4
Trace
0
73
5
6
Et2O
THF
7
15
8
CH2Cl2
CH2Cl2
CH2Cl2
54b
61c
70d
9
10
aUnless noted, all of the reactions were carried out with 20 mol% of TMSCl, and
indole/chalcone ¼ 1.1/1 at room temperature for 24 h.
bUsing 10 mol% of TMSCl as catalyst.
cAt reflux.
dUsing 15 mol% of TMSCl as catalyst.

3098
L.-W. Xu et al.
compound 3a was obtained in good yield. Then we investigated various
indoles and enones for Michael-type Friedel–Crafts reactions (Table 2). As
shown in Table 2, the yields were very sensitive to the substrates employed.
For the reactions of N-unsubstituted indoles (indole and 5-bromo-indole)
with enones bearing an H- or Cl-group, good yields could be obtained
(entries 2 to 3, 12); modest yields were obtained with enones bearing a
methoxyl group (entry 5). This may be due to the strong interaction
between TMSCl and N–H of indole, which disfavored the 1,4-counjugate
addition to methoxyl-substituted enones. It should be emphasized that in the
cases using N-substituted and C-2 substituted indoles, the corresponding
yields with different enones were good to excellent (entries 6 to 11, up to
almost quantitative conversion). Nearly all reactions are clean, and the
target compounds are obtained in good yields with no formation of
side products such as dimers or trimers, which are normally observed by the
influence of strong acids. Judging from these findings, the mechanism of
TMSCl-catalyzed Friedel–Crafts reaction of indole with chalcone
proceeds possibly through the generation of silyl enol ether by the conjugate
addition of indole to chalcone; then the Cl- would attack the TMS group of
the silyl enol ether to regenerate TMSCl together with the formation of
product 3a.[15]
Encouraged by these results, we next evaluated this protocol for the
reaction of 2-cyclohexen-1-one with indole. Unfortunately, the conversion
is poor and only trace product was obtained (less than 10% of isolated
Table 2. TMSCl-catalyzed Michael-type Friedel–Crafts reactions of indoles with
chalconesa
Entry
R1
R2
R3
Product
Yield (%)b
1
2
H
H
p-Cl
o-Cl
p-OCH3
H
N-CH3
H
3b
3c
97
71
90
65
55
97
94
88
99
99
95
68
55
H
3
H
H
3d
3e
4
H
p-OCH3
H
5
H
3f
6
H
p-Cl
p-OCH3
H
N-CH3
N-CH3
N-CH3
2-CH3
2-CH3
2-CH3
5-Br
5-Br
3 g
3 h
3i
7
H
p-OCH3
8
9
H
H
H
H
H
H
3j
10
11
12
13
p-Cl
p-OCH3
H
3 k
3l
3 m
3n
p-Cl
aUnless noted, all of the reactions were carried out with 20 mol% of TMSCl and
indole/chalcone ¼ 1.1/1 at room temperature for 24 h.
bIsolated yield.

Chlorotrimethylsilane
3099
Scheme 2.
yield). We also tried to explore the catalytic activities of TMSCl in the aza-
Michael reaction of a,b-ethylenic compounds with indoles; as shown in
Scheme 2, no any products was detected after 24 h. This clearly showed
chlorotrimethylsilane (TMSCl) is suitable only to activate chalcones and
failed in the case of cyclic enones, a,b-unsaturated esters, and acrylonitrile
for this Friedel–Crafts reaction. This selectivity could be useful for complex
molecules with the existence of these blocks in synthetic applications.
In summary, we have demonstrated that simple TMSCl is an effective
and promising catalyst for the Michael-type Friedel–Crafts reactions of
indoles with chalcones. This novel entry has the advantages of being
metal-free, using mild reaction conditions, and generating good yields of
products with greater selectivity, which make it a useful and attractive
process for the synthesis of indole derivates. This work offers good
examples for the application of Lewis acidic silane catalyst for novel
Friedel–Crafts reactions of indoles with chalcones. Application to enantio-
selective variants with chiral silane in asymmetric Michael-type Friedel–
Crafts reactions on the basis of these new findings is in progress in our
laboratories.
EXPERIMENTAL
All reaction flasks and solvents were dried according to standard methods
prior to use. Flash-column chromatography was performed over silica
(100–200 mesh). NMR spectra were recorded on a 400-MHz spectrometer.
13C NMR spectra were obtained with broadband proton decoupling. For
spectra recorded in CDCl3, unless noted, chemical shifts were recorded
relative to the internal TMS (tetramethylsilane) reference signal. IR spectra
were recorded using a FTIR apparatus. Thin-layer chromatography was
performed using silica. TMSCl was distilled with Mg prior to use.

3100
L.-W. Xu et al.
Typical Michael-Type Friedel–Crafts Reaction Procedure (3a–3n)
TMSCl (0.1 mmol) was added into a solution of enone (0.5 mmol) and indol
(0.55 mmol) in freshly distilled CH2Cl2 (3 mL). After stirring at room temp-
erature for 24 h, the mixture was diluted with H2O (10 mL) and extracted with
EtOAc (3 ꢀ 15 mL). The combined organic layers were dried (Na2SO4), con-
centrated in vacuo, and purified by column chromatography on silica gel
(EtOAc–pet. ether, 1:5) to gain the pure product.
Data
3a: 1H NMR (400 MHz, CDCl3): d ¼ 7.97 (bs, 1H), 7.93 (d, J ¼ 7.2 Hz, 2H),
7.53 (t, J ¼ 7.4 Hz, 1H), 7.40–7.44 (m, 3H), 7.35 (d, J ¼ 7.2 Hz, 2H), 7.23–
7.31 (m, 3H), 7.14 (q, J ¼ 7.2, 7.2 Hz, 2H), 7.01 (t, J ¼ 7.4 Hz, 1H), 6.96
(s, 1H), 5.07 (t, J ¼ 7.2 Hz, 1H), 3.81 (dd, J ¼ 6.8, 6.8 Hz, 1H), 3.72 (dd,
J ¼ 7.6, 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3): d ¼ 198.6, 144.2,
137.0, 136.6, 133.0, 128.6, 128.4, 128.1, 127.8, 126.6, 126.3, 122.1, 121.4,
119.5, 119.4, 119.2, 111.1, 45.2, 38.1; IR (KBr): 3462, 3078, 3056, 3024,
1669, 1597, 1580, 1490, 758, 746, 703, 692 cm21; MS (EI): m/z ¼ 325.
3b: 1H NMR (400 MHz, CDCl3): d ¼ 7.93 (d, J ¼ 7.2 Hz, 2H), 7.53
(t, J ¼ 7.4 Hz, 1H), 7.40–7.45 (m, 3H), 7.36 (d, J ¼ 7.6 Hz, 2H), 7.24–
7.28 (m, 3H), 7.16 (q, J ¼ 7.2, 7.2 Hz, 2H), 7.00 (t, J ¼ 7.4 Hz, 1H), 6.83
(s, 1H), 5.06 (t, J ¼ 7.2 Hz, 1H), 3.80 (dd, J ¼ 6.8, 6.8 Hz, 1H), 3.74 (dd,
J ¼ 7.6, 6.0 Hz, 1H), 3.71 (s, 3H); 13C NMR (100 MHz, CDCl3):
d ¼ 198.5, 144.4, 137.3, 137.2, 132.9, 128.5, 128.4, 128.1, 127.8, 127.0,
126.2, 121.7, 119.6, 118.8, 117.8, 109.2, 45.3, 38.1, 33.8, 32.6; IR (KBr):
3431, 1674, 1596, 1488, 1448, 1247, 740, 749 cm21; MS (EI): m/z ¼ 339.
3c: 1H NMR (400 MHz, CDCl3): d ¼ 8.00 (bs, 1H), 7.92 (d, J ¼ 7.6 Hz, 2H),
7.54 (t, J ¼ 7.0 Hz, 1H), 7.42 (t, J ¼ 6.8 Hz, 2H), 7.38 (d, J ¼ 8.4 Hz, 1H),
7.32 (d, J ¼ 8.0 Hz, 1H), 7.24–7.28 (m, 2H), 7.18–7.22 (m, 2H), 7.15
(t, J ¼ 7.6 Hz, 1H), 7.01 (t, J ¼ 7.4 Hz, 1H), 6.97 (s, 1H), 5.03
(t, J ¼ 7.2 Hz, 1H), 3.79 (dd, J ¼ 6.8, 6.4 Hz, 1H), 3.68 (dd, J ¼ 8.0,
8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3): d ¼ 198.2, 142.7, 136.9, 136.6,
133.2, 131.9, 129.2, 128.6, 128.5, 128.0, 126.4, 122.3, 121.3, 119.5, 119.4,
118.9, 111.2, 44.9, 37.5; IR (KBr): 3398, 3084, 3056, 3026, 1681, 1596,
1579, 1489, 820, 768, 746, 689 cm21; MS (EI): m/z ¼ 359.
3d: 1H NMR (400 MHz, CDCl3): d ¼ 7.99 (s, 1H), 7.97 (s, 2H), 7.55
(t, J ¼ 7.2 Hz, 1H), 7.38–7.46 (m, 3H), 7.32 (d, J ¼ 8.0 Hz, 1H), 7.26
(s, 1H), 7.20–7.24 (m, 1H), 7.08–7.17 (m, 3H), 7.02 (t, J ¼ 7.6 Hz, 2H),
5.54 (t, J ¼ 7.4 Hz, 1H), 3.80 (dd, J ¼ 8.8, 8.8 Hz, 1H), 3.68 (dd, J ¼ 6.4,
6.4 Hz, 1H); 13C NMR (100 MHz, CDCl3): d ¼ 198.0, 141.6, 136.9, 136.6,
133.6, 133.0, 129.8, 129.0, 128.6, 128.2, 127.6, 126.9, 126.7, 122.2, 122.0,

Chlorotrimethylsilane
3101
119.5, 119.5, 117.8, 111.1, 44.2, 34.9; IR (KBr): 3375, 3056, 1677, 1619,
1595, 1577, 768, 754, 742, 685 cm21; MS (EI): m/z ¼ 359.
3e: 1H NMR (400 MHz, CDCl3): d ¼ 7.97 (bs, 1H), 7.92 (d, J ¼ 8.0 Hz, 2H),
7.52 (t, J ¼ 7.2 Hz, 1H), 7.39–7.44 (m, 3H), 7.30 (d, J ¼ 8.0 Hz, 1H), 7.25
(s, 1H), 7.22–7.24 (m, 1H), 7.13 (t, J ¼ 7.6 Hz, 1H), 7.00 (t, J ¼ 7.6 Hz,
1H), 6.96 (s, 1H), 6.78 (d, J ¼ 7.2 Hz, 2H), 5.00 (t, J ¼ 7.4 Hz, 1H), 3.78
(dd, J ¼ 6.8, 6.4 Hz, 1H), 3.73 (s, 3H), 3.68 (dd, J ¼ 8.0, 7.6 Hz, 1H); 13C
NMR (100 MHz, CDCl3): d ¼ 198.7, 158.0, 137.2, 136.7, 136.3, 132.9,
128.7, 128.5, 128.1, 126.6, 122.1, 121.3, 119.7, 119.6, 119.4, 113.8, 111.1,
55.2, 45.4, 37.5; IR (KBr): 3422, 1670, 1250, 1032 cm21; MS (EI):
m/z ¼ 355.
3f: 1H NMR (400 MHz, CDCl3): d ¼ 7.98 (bs, 1H), 7.92 (d, J ¼ 8.8 Hz, 2H),
7.43 (d, J ¼ 8.4 Hz, 1H), 7.29–7.35 (m, 3H), 7.24 (t, J ¼ 7.4 Hz, 2H), 7.14
(q, J ¼ 6.8, 8.0 Hz 2H), 6.97–7.03 (m, 2H), 6.89 (d, J ¼ 8.8 Hz, 2H), 5.06
(t, J ¼ 7.4 Hz, 1H), 3.84 (s, 3H), 3.76 (dd, J ¼ 7.2, 6.8 Hz, 1H), 3.66 (dd,
J ¼ 8.0, 7.2 Hz, 1H); 13C NMR (100 MHz, CDCl3): d ¼ 197.0, 163.4,
144.4, 136.6, 130.4, 128.4, 127.8, 126.7, 126.2, 122.1, 121.4, 119.6, 119.3,
113.7, 111.1, 55.4, 44.8, 38.4; IR (KBr): 3432, 1665, 1265, 1023 cm21; MS
(EI): m/z ¼ 355.
3g: 1H NMR (400 MHz, CDCl3): d ¼ 7.93 (d, J ¼ 8.0 Hz, 2H), 7.55
(t, J ¼ 7.4 Hz, 1H), 7.39–7.46 (m, 3H), 7.28 (t, J ¼ 8.2 Hz, 3H), 7.17–7.23
(m, 3H), 7.02 (t, J ¼ 7.4 Hz, 1H), 6.82 (s, 1H), 5.03 (t, J ¼ 7.2 Hz, 1H),
3.79 (dd, J ¼ 6.0, 6.4 Hz, 1H), 3.70 (dd, J ¼ 8.4, 8.4 Hz, 1H), 3.73 (s, 3H);
13C NMR (100 MHz, CDCl3): d ¼ 198.2, 142.9, 137.4, 137.0, 133.1, 131.9,
129.2, 128.6, 128.1, 126.8, 126.2, 121.8, 119.4, 119.0, 117.4, 109.3, 45.1,
37.5, 33.8, 32.7; IR (KBr): 3432, 1673, 1594, 1486, 1469, 1247, 745,
690 cm21; MS (EI): m/z ¼ 373.
3h: 1H NMR (400 MHz, CDCl3): d ¼ 7.93 (d, J ¼ 8.0 Hz, 2H), 7.53
(t, J ¼ 7.2 Hz, 1H), 7.43 (t, J ¼ 7.6 Hz, 3H), 7.24–7.28 (m, 3H), 7.18
(t, J ¼ 7.6 Hz, 1H), 7.01 (t, J ¼ 7.2 Hz, 1H), 6.78–6.82 (m, 3H), 5.00
(t, J ¼ 7.2 Hz, 1H), 3.78 (dd, J ¼ 6.4, 6.4 Hz, 1H), 3.75 (s, 3H), 3.72
(s, 3H), 3.70 (dd, J ¼ 6.8, 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3):
d ¼ 198.6, 158.0, 137.4, 137.2, 136.5, 132.9, 128.7, 128.5, 128.1, 127.0,
126.1, 121.6, 119.6, 118.8, 118.2, 113.8, 109.2, 55.2, 45.5, 37.4, 32.7; IR
(KBr): 3426, 1676, 1611, 1510, 1466, 1252, 740, 691 cm21; MS (EI): m/
z ¼ 369.
3i: 1H NMR (400 MHz, CDCl3): d ¼ 7.92 (d, J ¼ 9.2 Hz, 2H), 7.44
(d, J ¼ 8.4 Hz, 1H), 7.35 (d, J ¼ 7.6 Hz, 2H), 7.23–7.27 (m, 3H), 7.16
(q, J ¼ 7.6, 7.6 Hz, 2H), 7.00 (t, J ¼ 7.4 Hz, 1H), 6.89 (d, J ¼ 8.8 Hz, 2H),
6.82 (s, 1H), 5.05 (t, J ¼ 7.0 Hz, 1H), 3.83 (s, 3H), 3.70 (s, 3H), 3.70 (dd,
J ¼ 10.0, 8.8 Hz, 1H), 3.69 (dd, J ¼ 8.8, 8.8 Hz, 1H); 13C NMR (100 MHz,
CDCl3): d ¼ 197.0, 163.4, 144.5, 137.3, 130.3, 130.3, 128.4, 127.8, 127.0,

3102
L.-W. Xu et al.
126.2, 126.1, 121.6, 119.6, 118.8, 117.9, 113.6, 109.1, 55.4, 44.9, 38.2, 32.6;
IR (KBr): 3433, 1667, 1601, 1575, 1484, 1418, 1247, 1185, 1024, 747,
701 cm21; MS (EI): m/z ¼ 369.
3j: 1H NMR (400 MHz, CDCl3): d ¼ 7.90 (d, J ¼ 7.6 Hz, 2H), 7.78 (bs, 1H),
7.50 (d, J ¼ 7.2 Hz, 2H), 7.37–7.41 (m, 4H), 7.14–7.29 (m, 4H), 6.99–7.10
(m, 2H), 5.12 (t, J ¼ 6.8 Hz, 1H), 3.99 (dd, J ¼ 7.6, 8.4 Hz, 1H), 3.92 (dd,
J ¼ 7.6, 6.8 Hz, 1H), 2.39 (s, 3H); 13C NMR (100 MHz, CDCl3):
d ¼ 199.1, 144.2, 137.1, 135.4, 132.8, 131.7, 128.4, 128.2, 128.0, 127.5,
125.9, 120.7, 119.1, 119.1, 113.6, 110.4, 43.5, 36.8, 12.1; IR (KBr): 3410,
3350, 1671, 1459, 1448, 1261, 1206, 753, 740, 691 cm21; MS (EI):
m/z ¼ 339.
3k: 1H NMR (400 MHz, CDCl3): d ¼ 7.86 (d, J ¼ 7.6 Hz, 2H), 7.79 (bs, 1H),
7.48 (t, J ¼ 7.2 Hz, 1H), 7.34–7.43 (m, 3H), 7.16–7.27 (m, 5H), 6.97–7.08
(m, 2H), 5.04 (t, J ¼ 7.0 Hz, 1H), 3.89 (m, 1H), 3.87 (m, 1H), 2.34 (s, 3H);
13C NMR (100 MHz, CDCl3): d ¼ 198.8, 142.7, 137.0, 135.4, 133.0, 131.7,
131.5, 128.9, 128.5, 128.3, 128.0, 127.2, 120.8, 119.3, 118.9, 113.2, 110.5,
43.4, 36.2, 12.0; IR (KBr): 3410, 3350, 1671, 1597, 1456, 1261, 1206, 740,
692 cm21; MS (EI): m/z ¼ 373.
3l: 1H NMR (400 MHz, CDCl3): d ¼ 7.87 (d, J ¼ 7.6 Hz, 2H), 7.76 (bs, 1H),
7.45–7.50 (m, 2H), 7.36 (t, J ¼ 7.8 Hz, 2H), 7.22–7.27 (m, 2H), 7.19
(d, J ¼ 7.6 Hz, 1H), 6.96–7.07 (m, 2H), 6.77 (d, J ¼ 8.8 Hz, 2H), 5.02
(t, J ¼ 7.0 Hz, 1H), 3.89 (m, 1H), 3.87 (m, 1H), 3.72 (s, 3H), 2.35 (s, 3H);
13C NMR (100 MHz, CDCl3): d ¼ 199.2, 157.7, 137.2, 136.3, 135.5, 132.8,
131.5, 128.4, 128.0, 127.4, 120.7, 119.1, 113.8, 113.6, 110.4, 55.2, 43.8,
36.0, 12.1; IR (KBr): 3378, 1673, 1509, 1461, 1448, 1299, 1257, 1244,
1176, 1034, 744, 706 cm21; MS (EI): m/z ¼ 369.
1
3m: H NMR (400 MHz, CDCl3): d ¼ 8.01 (bs, 1H), 7.93 (d, J ¼ 7.2 Hz,
2H), 7.53–7.57 (m, 2H), 7.44 (t, J ¼ 7.6 Hz, 2H), 7.25–7.34 (m, 4H),
7.16–7.25 (m, 3H), 7.01 (s, 1H), 5.00 (t, J ¼ 7.2 Hz, 1H), 3.78 (dd,
J ¼ 6.8, 6.8 Hz, 1H), 3.70 (dd, J ¼ 6.8, 7.2 Hz, 1H); 13C NMR (100 MHz,
CDCl3): d ¼ 198.3, 143.8, 137.1, 135.2, 133.1, 128.6, 128.6, 128.4,
128.1, 127.7, 126.5, 125.1, 122.6, 122.1, 119.0, 112.8, 112.5, 45.2, 38.0; IR
(KBr): 3427, 1666, 1598, 1454, 1286, 1102, 798, 750 cm21; MS (EI):
m/z ¼ 404.
3n: 1H NMR (400 MHz, CDCl3): d ¼ 8.15 (bs, 1H), 7.92 (d, J ¼ 8.0 Hz, 2H),
7.56 (t, J ¼ 7.2 Hz, 1H), 7.50 (s, 1H), 7.44 (t, J ¼ 7.6 Hz, 2H), 7.14–7.26
(m, 6H), 6.96 (s, 1H), 4.97 (t, J ¼ 7.4 Hz, 1H), 3.75 (dd, J ¼ 7.2,
6.8 Hz, 1H), 3.66 (dd, J ¼ 7.2, 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3):
d ¼ 198.0, 142.3, 136.8, 135.2, 133.2, 132.1, 129.1, 128.7, 128.2, 128.0,
125.2, 122.5, 121.8, 118.5, 112.8, 112.6, 44.9, 37.3, 33.8; IR (KBr):
3455, 3350, 1678, 1595, 1487, 1458, 1446, 808, 689 cm21; MS (EI):
m/z ¼ 438.

Chlorotrimethylsilane
3103
ACKNOWLEDGMENTS
This work was supported by the National Nature Science Foundation of China
(Project No. 20572114). Xu L. W. is greatly indebted to Jacques Mortier and
´ ´
Anne-Sophie Castanet, CNRS and Universite du Maine, Unite de chimie
´ ´ ´
organique moleculaire et macromoleculaire (UMR 6011), Faculte des
sciences, for their help.
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