A one-pot synthesis of (E,E)-1-Arylseleno-substituted 1,5-dien-3-ynes by palladium-catalysed three component cross-coupling reaction

Article abstract of DOI:10.3184/030823410X12878393498458

(E,E)-1-Arylseleno-substituted 1,5-dien-3-ynes can be stereoselectively synthesised in one pot, in good yields with high stereoselectivity, by the Pd(PPh₃)₄-catalysed Stille coupling of (E)-1-iodo-2-arylselenoethenes with trimethylst

Full text of DOI:10.3184/030823410X12878393498458

JOURNAL OF CHEMICAL RESEARCH 2010
RESEARCH PAPER 627
NOVEMBER, 627–629
A one-pot synthesis of (E,E)-1-arylseleno-substituted 1,5-dien-3-ynes by
palladium-catalysed three component cross-coupling reaction
Fang Yaoa,b, Wenyan Haoa and Mingzhong Caia*
aDepartment of Chemistry, Jiangxi Normal University, Nanchang 330022, P. R. China
bDepartment of Chemistry and Pharmaceutical Engineering, West Branch of Zhejiang University ofTechnology, Quzhou 324000, P. R. China
(E,E)-1-Arylseleno-substituted 1,5-dien-3-ynes can be stereoselectively synthesised in one pot, in good yields with
high stereoselectivity, by the Pd(PPh3)4-catalysed Stille coupling of (E)-1-iodo-2-arylselenoethenes with trimethyl-
stannyl(trimethylsilyl)ethyne,followedbythecross-couplingwith(E)-vinyliodidesinthepresenceoftris(diethylamino)
sulfonium trimethyldifluorosilicate (TASF).
Keywords: (E)-1-iodo-2-arylselenoethene, Stille coupling, vinyl iodide, 1,5-dien-3-yne, tandem reaction, stereoselective
synthesis
Enyne systems have attracted much attention from synthetic
organic chemists as they show interesting chemical and bio-
logical reactivities.1–3 Stereodefined conjugated polyenynes
containing an internal carbon-carbon triple bond unit are
widely distributed in nature and show interesting biological
activities.4,5 Recently, dienyne compounds have attracted
much interest since they are important building blocks for the
formation of natural products in organic synthesis.6–10 Uenishi
and Matsui reported the stereocontrolled synthesis of dienynes
by stepwise Suzuki/Sonogashira coupling reactions of 1,1-
dibromoalk-1-enes.11 Sato and coworkers reported that conju-
gated diynes underwent selective mono-titanation with a Ti(II)
reagent to give 1:1 diyne-titanium alkoxide complexes, which
reactedwithanotheracetylenetogivestereo-defineddienynes.12
van Otterlo et al. described the synthesis of dienynes from
alkenes and diynes using ruthenium-mediated ring-closing
metathesis.13 Shi and coworkers14 reported that 2-iodo-4-
(phenylchalcogenyl)but-1-enes can be enynylated with alkynes
catalysed by Pd(OAc)2 to give conjugated dienynes. The for-
mation of dienynes containing metal or heteroatom functional
groups has also attracted considerable interest in organic syn-
thesis because many useful functional group transformations
can be achieved by introduction and removal of metal or het-
eroatom functions. Alami and Ferri reported the regioselective
synthesis of stannylated dienynes by the palladium-catalysed
hydrostannylation of enediynes.15 However, the synthesis
of heteroatom-substituted 1,5-dien-3-ynes has received less
attention. The tandem reaction has recently been of interest for
organic synthesis because it offers a convenient and economi-
cal method with which to prepare target organic molecules.16–19
We now report that (E,E)-1-arylseleno-substituted 1,5-dien-3-
ynes can be conveniently synthesised in one pot, in good yields
with high stereoselectivity, by the Stille coupling of (E)-1-
iodo-2-arylselenoethenes 1 with trimethylstannyl(trimethylsil
yl)ethyne, followed by the cross-coupling with (E)-vinyl
iodides 3 in the presence of tris(diethylamino)sulfonium
trimethyldifluorosilicate (TASF).
(E)-1-Iodo-2-arylselenoethenes 1 were easily prepared by
the hydrozirconation of arylselenoacetylenes, followed by the
reaction with iodine according to a literature procedure.20 The
Stille coupling reaction of (E)-1-iodo-2-arylselenoethenes 1
with trimethylstannyl(trimethylsilyl)ethyne in the presence of
Pd(PPh3)4 in THF gave stereoselectively (E)-1-arylseleno-4-
(trimethylsilyl)but-1-en-3-ynes 2 in high yields (Scheme 1).
The (E)-configuration of compounds 2a-c was confirmed by
1
their H NMR spectra, which showed two doublets in the
δ = 7.21–5.64 with a coupling constant of 15.6–16.0 Hz.
Hatanaka and Hiyama reported that in the presence of a
palladium catalyst and tris(diethylamino)sulfonium trimethyl-
difluorosilicate (TASF), alkynylsilanes can react with
alkenyl halides to give the corresponding coupled products in
a stereospecific and chemoselective manner.21 Considering
the fact that both the Stille coupling and the cross-coupling
reactions of alkynylsilanes with alkenyl halides were catalysed
by palladium complexes, we tried to combine the two reac-
tions, in one pot, to synthesise stereoselectively (E,E)-1-
arylseleno-substituted 1,5-dien-3-ynes. The basic concept of
our reaction is illustrated in Scheme 2.
We found that, if after the Stille coupling of (E)-1-iodo-
2-arylselenoethenes 1 with trimethylstannyl(trimethylsilyl)
ethyne (1.2 equiv) using 5 mol% Pd(PPh3)4 in THF at 50 °C for
3 h, (E)-vinyl iodides and TASF (2.4 equiv) were added at
–78 °C and the mixture was slowly warmed to ambient tem-
perature and then allowed to react at 50 °C for 2 h, (E,E)-
1-arylseleno-substituted 1,5-dien-3-ynes 4 were obtained in
good yields. The experimental results are summarised in Table
1. It was found that the kind of the palladium catalyst is critical
for the success of the tandem reaction and Pd(PPh3)4 was the
most efficient. PdCl2(PPh3)2- and PdCl2(MeCN)2-catalysed
Scheme 1
* Correspondent. E-mail: caimzhong@163.com

628 JOURNAL OF CHEMICAL RESEARCH 2010
Scheme 2
were determined on an FTS-185 instrument as neat films. Mass
spectra were obtained on a Finigan 8239 mass spectrometer. Micro-
analyses were measured using a Yanaco MT-3 CHN microelemental
analyser.All reactions were carried out in pre-dried glassware (150 °C,
4 h and cooled under a stream of dry Ar).
tandem reactions gave a relatively large amount of protodesi-
lylation products of the intermediates 2. The use of (η3-
C3H5PdCl)2 as the catalyst, which was effective for the TASF-
mediated reaction of alkynyltrimethylsilanes with alkenyl
halides, resulted in extensive homo-coupling of trimethylstan-
nyl(trimethylsilyl)ethynetoproduce1,4-bis(trimethylsilyl)buta-
1,3-diyne.21 As shown in Table 1, the tandem Stille/cross-
coupling reaction of trimethylstannyl(trimethylsilyl)ethyne
with a variety of (E)-1-iodo-2-arylselenoethenes and (E)-
vinyl iodides proceeded smoothly under mild conditions to
afford stereoselectively the corresponding (E,E)-1-arylseleno-
substituted 1,5-dien-3-ynes 4.
The stereochemistry of compounds 4 was easily established
since their 1H NMR spectra give rise to three or four doublets
at δ = 7.15–5.55 with a coupling constant of 15.6–16.0 Hz.
The results summarised in Table 1 show the following salient
features of the novel process. The palladium(0) catalyst
[Pd(PPh3)4] can be applied in a single flask to double-coupling
reactions based on the reactivity difference between Me3Sn
and Me3Si groups. The tandem reaction proceeds with reten-
tion of the double bond geometry of the alkenyl iodides as is
often the case with the coupling reaction of organotin and
organosilicon compounds.
Synthesis of (E)-1-arylseleno-4-(trimethylsilyl)but-1-en-3-ynes 2a–c;
general procedure
Trimethylstannyl(trimethylsilyl)ethyne (1.2 mmol) was added to a
solution of (E)-1-iodo-2-arylselenoethene 1 (1.0 mmol) and Pd(PPh3)4
(0.05 mmol) in THF (10 mL) under an argon atmosphere at room
temperature. The resulting mixture was then stirred at 50 °C and the
reaction was monitored by TLC (SiO2) until the compound 1 was con-
sumed (3 h). The reaction mixture was cooled to room temperature,
diluted with diethyl ether (50 mL), filtered and then treated with 20%
aqueous KF (10 mL) for 30 min before being dried and concentrated.
The residue was purified by column chromatography on silica gel,
eluting with light petroleum (b.p. 30–60 °C).
(E)-1-Phenylseleno-4-trimethylsilylbut-1-en-3-yne (2a): Colourless
oil. IR (film): ν (cm−1) 3059, 2958, 2142, 1712, 1578, 1250, 844, 760,
690; 1H NMR (CDCl3): δ 7.54–7.51 (m, 2H), 7.34–7.32 (m, 3H), 7.21
(d, J = 16.0 Hz, 1H), 5.71 (d, J = 16.0 Hz, 1H), 0.16 (s, 9H); 13C NMR
(CDCl3): δ 136.4, 134.1, 129.6, 128.3, 127.8, 111.7, 103.3, 95.2, -0.1;
MS: m/z 279 (M+, 12), 250 (55), 78 (44), 73 (100). Anal. Calcd for
C13H16SiSe: C, 55.89; H, 5.77. Found: C, 55.68; H, 5.56%.
In summary, we have developed an efficient and stereose-
lective one-pot method for the synthesis of (E,E)-1-arylseleno-
substituted 1,5-dien-3-ynes 4 by the Pd(PPh3)4-catalysed Stille
coupling of (E)-1-iodo-2-arylselenoethenes with trimethyl-
stannyl(trimethylsilyl)ethyne, followed by the cross-coupling
with (E)-vinyl iodides in the presence of tris(diethylamino)-
sulfonium trimethyldifluorosilicate (TASF). The present
method has the advantages of readily available starting materi-
als, straightforward and simple procedures, mild reaction con-
ditions, high stereoselectivity and good yields. The procedure
should find wide application to the synthesis of a large array of
naturally occurring substances having the conjugated dienyne
system.
(E)-1-(4-Methylphenyl)seleno-4-trimethylsilylbut-1-en-3-yne (2b):
Colourless oil. IR (film): ν (cm−1) 3033, 2961, 2163, 1704, 1563,
1251, 844, 803, 760; 1H NMR (CDCl3): δ 7.43–7.41 (m, 2H), 7.19 (d,
J = 15.6 Hz, 1H), 7.14 (d, J = 8.0 Hz, 2H), 5.64 (d, J = 15.6 Hz, 1H),
2.35 (s, 3H), 0.16 (s, 9H); 13C NMR (CDCl3): δ 138.8, 137.1, 134.7,
130.5, 123.9, 111.1, 103.6, 95.1, 21.3, 0.1; MS: m/z 294 (M+, 14), 263
(33), 91 (35), 73 (100). Anal. Calcd for C14H18SiSe: C, 57.31; H,
6.18%. Found: C, 57.58; H, 6.29%. (E)-1-(4-Chlorophenyl)seleno-4-
trimethylsilylbut-1-en-3-yne
(E)-1-(4-Methylphenyl)seleno-4-trimethylsilylbut-1-en-3-yne (2c):
Colourless oil. IR (film): ν (cm−1) 3031, 2957, 2166, 1706, 1556,
1
1473, 1254, 842, 824, 760; H NMR (CDCl3): δ 7.46–7.43 (m, 2H),
7.31–7.28 (m, 2H), 7.15 (d, J = 15.6 Hz, 1H), 5.73 (d, J = 15.6 Hz,
1H), 0.17 (s, 9H); 13C NMR (CDCl3): δ 135.5, 135.4, 134.9, 129.9,
126.2, 112.6, 103.1, 95.8, 0.0; MS: m/z 314 (M+, 35Cl, 32), 191 (100),
189 (56), 156 (50), 73 (33). Anal. Calcd for C13H15SiSeCl: C, 49.75;
H, 4.82. Found: C, 49.48; H, 4.56%.
Experimental
1H NMR spectra were recorded on a Bruker AC-P400 (400 MHz)
spectrometer with TMS as an internal standard using CDCl3 as the
solvent. 13C NMR (100 MHz) spectra were recorded on a Bruker AC-
P400 (400 MHz) spectrometer using CDCl3 as the solvent. IR spectra
Synthesis of (E,E)-1-arylseleno-substituted 1,5-dien-3-ynes 4a-g;
general procedure
Trimethylstannyl(trimethylsilyl)ethyne (1.2 mmol) was added to a
solution of (E)-1-iodo-2-arylselenoethene 1 (1.0 mmol) and Pd(PPh3)4
(0.05 mmol) in THF (10 mL) under an argon atmosphere at room
temperature. The resulting mixture was then stirred at 50 °C and the
reaction was monitored by TLC (SiO2) until the compound 1 was
consumed (3 h). (E)-vinyl iodide 3 (1.0 mmol) and a solution of TASF
(0.69 M, 2.4 mmol) in THF (3.5 mL) were added at –78 °C. The
mixture was slowly warmed to room temperature, allowed to react at
50 °C for 2 h, then cooled to room temperature, and finally was
quenched with aq. sodium bicarbonate. The mixture was extracted
with diethyl ether (2 × 30 mL), the ether solution was treated with
20% aqueous KF (10 mL) for 30 min before being dried and concen-
trated. The residue was purified by column chromatography on silica
gel, eluting with light petroleum (b.p. 30–60 °C).
Table 1 Synthesis of (E,E)-1-arylseleno-substituted 1,5-dien-
3-ynes 4a
Entry
Ar
R
Product
Yield /%b
1
2
3
4
5
6
7
Ph
n-C4H9
4a
4b
4c
4d
4e
4f
79
82
85
80
84
80
78
Ph
CH3OCH2
Ph
Ph
4-ClC6H4
4-ClC6H4
4-CH3C6H4
4-CH3C6H4
n-C4H9
CH3OCH2
n-C6H13
CH3OCH2
4g
a The reactions were performed with 1.2 mmol of trimethylstan
nyl(trimethylsilyl)ethyne, 1.0 mmol of 1, 0.05 mmol of Pd(PPh3)4,
1.0 mmol of 3 and 2.4 mmol of TASF in THF (13.5 mL) under
Ar.
(1E,5E)-1-Phenylselenodeca-1,5-dien-3-yne (4a): Colourless oil.
IR (film): ν (cm−1) 3018, 2957, 2927, 2174, 1578, 1477, 1438, 926,
1
b Isolated yield based on the 1 used.
735, 690; H NMR (CDCl3): δ 7.533–7.51 (m, 2H), 7.34–7.26 (m,

JOURNAL OF CHEMICAL RESEARCH 2010 629
3H), 7.08 (d, J = 16.0 Hz, 1H), 6.13 (dt, J = 16.0, 7.2 Hz, 1H), 5.89 (d,
J = 16.0 Hz, 1H), 5.56 (d, J = 16.0 Hz, 1H), 2.12–2.08 (m, 2H), 1.39–
1.30 (m, 4H), 0.89 (t, J = 7.2 Hz, 3H); 13C NMR (CDCl3): δ 145.1,
133.5, 133.2, 129.5, 129.3, 128.0, 113.0, 109.4, 89.4, 86.4, 32.9, 30.8,
22.1, 13.9; MS: m/z 290 (M+, 43), 233 (32), 165 (100), 128 (53),
78 (84), 77 (66). Anal. Calcd for C16H18Se: C, 66.42; H, 6.27. Found:
C, 66.19; H, 6.08%.
109.5, 89.2, 86.5, 33.2, 31.7, 28.8, 28.7, 22.6, 21.2, 14.1; MS: m/z 332
(M+, 81), 247 (59), 181 (64), 165 (100), 91 (91). Anal. Calcd for
C19H24Se: C, 68.86; H, 7.30. Found: C, 68.62; H, 7.09%.
(1E,5E)-1-(4-Methylphenyl)seleno-7-methoxyhepta-1,5-dien-3-yne
(4g): Colourless oil. IR (film): ν (cm−1) 2958, 2180, 1557, 1497, 1119,
927, 867, 805; 1H NMR (CDCl3): δ 7.44–7.42 (m, 2H), 7.16–7.14 (m,
2H), 7.11 (d, J = 15.6 Hz, 1H), 6.10 (dt, J = 15.6, 5.6 Hz, 1H), 5.84 (d,
J = 15.6 Hz, 1H), 5.80 (d, J = 15.6 Hz, 1H), 3.95 (d, J = 5.6 Hz, 2H),
3.34 (s, 3H), 2.36 (s, 3H); 13C NMR (CDCl3): δ 139.3, 134.5, 133.9,
129.5, 129.2, 128.5, 112.3, 111.5, 88.6, 88.2, 72.5, 58.3, 21.5; MS:
m/z 292 (M+, 35), 165 (100), 91 (78). Anal. Calcd for C15H16OSe: C,
61.85; H, 5.54. Found: C, 61.57; H, 5.38%.
(1E,5E)-1-Phenylselenodeca-1,5-dien-3-yne (4b): Colourless oil.
IR (film): ν (cm−1) 3054, 2924, 2175, 1578, 1554, 1477, 1438, 1120,
1
928, 738, 690; H NMR (CDCl3): δ 7.54–7.52 (m, 2H), 7.35–7.32
(m, 3H), 7.14 (d, J = 15.6 Hz, 1H), 6.13 (dt, J = 15.6, 5.6 Hz, 1H),
5.86 (d, J = 15.6 Hz, 1H), 5.82 (d, J = 15.6 Hz, 1H), 3.96 (d, J = 5.6
Hz, 2H), 3.34 (s, 3H); 13C NMR (CDCl3): δ 139.1, 134.6, 133.7, 129.6,
129.5, 128.2, 112.1, 111.6, 88.5, 88.2, 72.3, 58.2; MS: m/z 278 (M+,
57), 165 (100), 152 (51), 121 (45), 78 (87), 77 (99), 63 (65). Anal.
Calcd for C14H14OSe: C, 60.65; H, 5.09. Found: C, 60.40; H, 4.88%.
(1E,5E)-1-Phenylseleno-6-phenylhexa-1,5-dien-3-yne(4c):Colour-
less oil. IR (film): ν (cm−1) 3058, 2957, 2175, 1597, 1548, 1492, 928,
867, 734, 691; 1H NMR (CDCl3): δ 7.55-7.52 (m, 2H), 7.42–7.37 (m,
2H), 7.29–7.25 (m, 6H), 7.12 (d, J = 16.0 Hz, 1H), 7.05 (d, J = 16.0
Hz, 1H), 6.09 (d, J = 16.0 Hz, 1H), 5.86 (d, J = 16.0 Hz, 1H); 13C
NMR (CDCl3): δ 145.4, 136.5, 133.7, 132.5, 130.3, 129.6, 129.4,
128.2, 126.7, 123.1, 113.3, 109.7, 90.2, 87.1; MS: m/z 310 (M+, 100),
165 (84), 153 (45), 123 (38), 77 (71). Anal. Calcd for C18H14Se: C,
69.90; H, 4.56. Found: C, 69.62; H, 4.70%.
We thank the National Natural Science Foundation of China
(Project No. 20862008) and the Natural Science Foundation
of Jiangxi Province of China (2008GQH0034) for financial
support.
Received 11 September 2010; accepted 18 December 2010
Paper 1000348 doi: 10.3184/030823410X12878393498458
Published online: 24 November 2010
References
(1E,5E)-1-(4-Chlorophenyl)selenodeca-1,5-dien-3-yne (4d): Col-
1
R. Kouno, T. Okauchi, M. Nakamura, J. Ichikawa and T. Minami, J. Org.
ourless oil. IR (film): ν (cm−1) 3020, 2957, 2928, 2183, 1558, 1474,
Chem., 1998, 63, 6239.
1
1387, 1090, 926, 814, 730; H NMR (CDCl3): δ 7.47–7.43 (m, 2H),
2
3
S. Ikeda and Y. Sato, J. Am. Chem. Soc., 1994, 116, 5975.
H.A. Stefani, R. Cella, F.A. Dorr, C.M.P. Pereira, G. Zeni and M. Gomes,
Tetrahedron Lett., 2005, 46, 563.
7.31–7.26 (m, 2H), 7.02 (d, J = 16.0 Hz, 1H), 6.14 (dt, J = 15.6, 7.2
Hz, 1H), 5.89 (d, J = 15.6 Hz, 1H), 5.56 (d, J = 16.0 Hz, 1H), 2.14–
2.09 (m, 2H), 1.41–1.25 (m, 4H), 0.89 (t, J = 7.2 Hz, 3H); 13C NMR
(CDCl3): δ 145.5, 144.5, 134.7, 132.3, 129.7, 126.8, 113.8, 109.3,
89.8, 86.1, 32.9, 30.8, 22.1, 13.9; MS: m/z 324 (M+, 35Cl, 84), 232
(39), 165 (100), 152 (35). Anal. Calcd for C16H17SeCl: C, 59.35; H,
5.29. Found: C, 59.52; H, 5.48%.
4
5
E.R.H. Jones and V. Thaller, The chemistry of carbon-carbon triple bond,
Part II; S. Patai, Ed.; Interscience; New York, 1978, p 621.
F. Bohlmann, T. Burkhardt and C. Zdero, Naturally occurring acetylenes,
Academic, New York, 1973.
6
7
8
9
F.D. Boyer, I. Hanna and L. Ricard, Org. Lett., 2001, 3, 3095.
E.M. Codesido, L. Castedo and J.R. Granja, Org. Lett., 2001, 3, 1483.
B.P. Peppers and S.T. Diver, J. Am. Chem. Soc., 2004, 126, 9524.
R. Garcia-Fandino, E.M. Codesido, E. Sobarzo-Sanchez, L. Castedo and
J.R. Granja, Org. Lett., 2004, 6, 193.
(1E,5E)-1-(4-Chlorophenyl)seleno-7-methoxyhepta-1,5-dien-3-yne
(4e): Colourless oil. IR (film): ν (cm−1) 3036, 2958, 2174, 1582, 1548,
1
1479, 1121, 927, 867, 815, 732; H NMR (CDCl3): δ 7.42–7.39 (m,
2H), 7.31–7.29 (m, 2H), 7.15 (d, J = 15.6 Hz, 1H), 6.14 (dt, J = 15.6,
5.6 Hz, 1H), 5.88 (d, J = 15.6 Hz, 1H), 5.83 (d, J = 15.6 Hz, 1H), 3.97
(d, J = 5.6 Hz, 2H), 3.35 (s, 3H); 13C NMR (CDCl3): δ 146.2, 134.8,
133.9, 129.8, 129.4, 128.5, 112.3, 111.8, 88.7, 88.4, 72.5, 58.3; MS:
m/z312(M+, 35Cl, 42), 165(100), 45(74).Anal. CalcdforC14H13OSeCl:
C, 53.94; H, 4.20. Found: C, 53.67; H, 4.39%.
(1E,5E)-1-(4-Methylphenyl)seleno-1,5-dodecadien-3-yne (4f): Col-
ourless oil. IR (film): ν (cm−1) 3020, 2956, 2926, 2182, 1645, 1559,
1490, 926, 803; 1H NMR (CDCl3): δ 7.41 (d, J = 8.0 Hz, 2H), 7.13 (d,
J = 8.0 Hz, 2H), 7.06 (d, J = 16.0 Hz, 1H), 6.11 (dt, J = 16.0, 7.2 Hz,
1H), 5.80 (d, J = 16.0 Hz, 1H), 5.55 (d, J = 16.0 Hz, 1H), 2.34 (s, 3H),
2.14–2.05 (m, 2H), 1.39–1.25 (m, 8H), 0.87 (t, J = 6.8 Hz, 3H); 13C
NMR (CDCl3): δ 145.0, 138.3, 134.0, 133.9, 130.3, 124.5, 112.1,
10 F.D. Boyer and I. Hanna, Org. Lett., 2007, 9, 2293.
11 J. Uenishi and K. Matsui, Tetrahedron Lett., 2001, 42, 4353.
12 C. Delas, H, Urabe and F. Sato, Chem. Commun., 2002, 272.
13 W.A.L. van Otterlo, E.L. Ngidi, C.B. de Koning and M.A. Fernandes,
Tetrahedron Lett., 2004, 45, 659.
14 M. Shi, L.-P. Liu and J. Tang, Org. Lett., 2005, 7, 3085.
15 F. Frri and M. Alami, Tetrahedron Lett., 1996, 37, 7971.
16 G.H. Posner, Chem. Rev., 1986, 86, 831.
17 L.F. Tietze and U. Beifuss, Angew. Chem. Int. Ed., 1993, 32, 131.
18 L.F. Tietze, Chem. Rev., 1996, 96, 115.
19 X. Huang and M. Xia, Org. Lett., 2002, 4, 1331.
20 L.-S. Zhu, Z.-Z. Huang and X. Huang, J. Chem. Res., 1996, 112.
21 Y. Hatanaka and T. Hiyama, J. Org. Chem., 1988, 53, 918.

Copyright of Journal of Chemical Research is the property of Science Reviews 2000 Ltd. and its content may
not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written
permission. However, users may print, download, or email articles for individual use.