Novel stereoselective synthesis of (Z)-α,β-unsaturated esters by hydrostannylation-Stille tandem reaction of alkynyl esters with aryl iodides

Article abstract of DOI:10.3184/174751911X13192956847054

(Z)-α,β-Unsaturated esters can be stereoselectively synthesised in one pot under mild conditions and in good yields, by the hydrostannylation of alkynyl esters followed by Stille cross-coupling with aryl iodides.

Full text of DOI:10.3184/174751911X13192956847054

JOURNAL OF CHEMICAL RESEARCH 2011
RESEARCH PAPER 637
NOVEMBER, 637–639
Novel stereoselective synthesis of (Z)-a,b-unsaturated esters by
hydrostannylation-Stille tandem reaction of alkynyl esters with aryl
iodides
Jianying Lia,b, Yan Yua, Mingzhu Chenga and Mingzhong Caia*
aDepartment of Chemistry, Jiangxi Normal University, Nanchang 330022, P. R. China
bDepartment of Chemistry, Jingdezhen Comprehensive College, Jingdezhen 333000, P. R. China
(Z)-a,b-Unsaturated esters can be stereoselectively synthesised in one pot under mild conditions and in good yields,
by the hydrostannylation of alkynyl esters followed by Stille cross-coupling with aryl iodides.
Keywords: hydrostannylation, (Z)-α,β-unsaturated ester, alkynyl ester, Stille coupling, tandem reaction, natural product
synthesis
The synthesis of α,β-unsaturated esters has received consider-
able attention because they are essential intermediates in
natural product synthesis.1–4 The great synthetic value of these
α,β-unsaturated esters derives from the fact that the positions
α, β and γ to the ester groups can be activated and function-
alised by various means. A variety of methods for the synthesis
of α,β-unsaturated esters have been developed. Of these meth-
ods, the Wittig reaction using aldehydes and phosphorus ylides
still occupies a prominent position.5–10 However, the reaction
is limited frequently by the oxidation, decomposition, or poly-
merisation of the aldehydes employed. In order to avoid use
of aldehydes as substrates, several methods for the one-pot
oxidation-Wittig reaction of alcohols with phosphorus ylides
have been devised.11–15 Most of them, however, suffer from
the use of hazardous oxidants and/or the requirement of an
activation process. Recently, a one-pot alcohol oxidation-
Wittig reaction catalysed by ruthenium using air or oxygen as
oxidant has been reported.16,17 Deng et al. reported that silyl
ethers could be deprotected and oxidised with Dess-Martin
periodinane, and the resulting aldehydes could be directly
converted into the corresponding α,β-unsaturated esters in one
pot with stabilised phosphoranes.18 Concellon and Bardales
described the synthesis of α,β-unsaturated esters by highly
stereoselective β-elimination of 2,3-epoxy-esters promoted by
SmI2.19 Despite considerable methodological differentiation
the majority of the reported procedures suffer from some
drawbacks such as significant by-product formation, the use
of hazardous oxidants and moderate yields. Most of them are
only suitable for the synthesis of disubstituted (E)-α,β-unsatu-
rated esters. The stereoselective synthesis of trisubstituted
α,β-unsaturated esters has received less attention. Therefore,
there is still a need for the development of selective and
better strategies for the one-pot synthesis of trisubstituted
α,β-unsaturated esters.
Stille coupling reaction are acknowledged as useful tools for
constructing complex organic molecules. However, to the best
of our knowledge, there have been no reports on palladium-
catalysed tandem hydrostannylation-Stille coupling reaction
of tributyltin hydride with alkynyl esters and aryl iodides to
date. Here we report that (Z)-α,β-unsaturated esters can be
stereoselectively synthesised in one pot under mild conditions,
and in good yields by the hydrostannylation of alkynyl esters
followed by Stille cross-coupling with aryl iodides.
Palladium-catalysed hydrostannylation of alkynes provides
a simple, general route for the synthesis of vinylstannanes.24
Rossi et al.25 reported palladium-catalysed hydrostannylation
of alkynyl esters in THF. In order to prepare highly selectively
(E)-α-stannyl-α,β-unsaturated esters, we investigated palla-
dium-catalysed hydrostannylation of alkynyl esters with
Bu3SnH in benzene at room temperature and found that
benzene was a better solvent than THF and that (E)-α-stannyl-
α,β-unsaturated esters 2 were obtained with high regio- and
stereoselectivity in high yields (Scheme 1).
Investigations of the crude products 2 by 1H NMR spectros-
copy (400 MHz) showed isomeric purities of more than 98%.
One olefinic proton signal of compounds 2a and 2b splits
characteristically into a triplet at δ = 6.04 with coupling
constant J = 6.8–7.2 Hz, which indicated that the hydrostan-
nylation of the alkynyl esters had taken place with strong
preference for the addition of the tin atom at the carbon adja-
cent to the ester group. The stereochemistry of the addition
was readily apparent from the 1H NMR spectra of compounds
2a–c which showed a (3JSn-H) coupling constant of 64 Hz, fully
in accord with an E geometry and overall cis addition of tin
hydride.26
(E)-α-Stannyl-α,β-unsaturated esters 2 are difunctional
group reagents in which two synthetically versatile groups are
linked to the same olefinic carbon atom and can be considered
both as vinylstannanes and as α,β-unsaturated esters. It is
well known that vinylstannanes can undergo the palladium-
catalysed cross-coupling reaction with organic halides.27,28
Considering the fact that both the hydrostannylation and Stille
The tandem reaction has recently been of interest in organic
synthesis because it offers a convenient and economical
method by which to prepare target organic molecules.20–23
The palladium-catalysed hydrostannylation of alkynes and the
Scheme 1
* Correspondent. E-mail: caimzhong@163.com

638 JOURNAL OF CHEMICAL RESEARCH 2011
reactions were catalysed by palladium complexes, we tried
to combine the two reactions in one pot to synthesise
stereoselectively (Z)-α,β-unsaturated esters (Scheme 2).
Table 1 Synthesis of (Z)-α,β-unsaturated esters 4
Entry
R
Ar
Product
Yield/%a
1
2
n-C4H9
n-C4H9
n-C4H9
n-C4H9
n-C4H9
n-C4H9
Ph
Ph
4a
4b
4c
4d
4e
4f
4g
4h
4i
76
74
65
80
79
75
84
73
71
79
74
83
We found that, after the hydrostannylation reaction
of alkynyl esters 1 with Bu3SnH using 2 mol% Pd(PPh3)4 in
benzene at 25 °C for 4 h, solvent removal under reduced pres-
sure and stirring of the residue with DMF, aryl iodides 3 and
75 mol% CuI at room temperature for 8 h, (Z)-α,β-unsaturated
esters 4 were obtained in good yields. The experimental results
are summarised in Table 1. It was found that DMF was the best
solvent among those tested, such as benzene and THF for the
Stille coupling of the intermediates 2 with aryl iodides. As
shown in Table 1, the hydrostannylation- Stille tandem reac-
tion of Bu3SnH with a variety of alkynyl esters and aryl iodides
proceeded smoothly under mild conditions to afford stereose-
lectively the corresponding (Z)-α,β-unsaturated esters 4.
However, the Stille coupling reaction of the intermediates 2
with aryl bromides didn’t occur under the same conditions.
It is well documented that the Stille cross-coupling reaction
of vinylstannanes with organic halides in the presence of a
palladium catalyst occurs with retention of configuration.27,28
In addition, the (Z)-configuration of the compound 4c was
3-MeC6H4
4-MeOC6H4
2-Thienyl
4-O2NC6H4
1-naphthyl
Ph
3
4
5
6
7
8
Ph
4-ClC6H4
4-MeOC6H4
1-naphthyl
2-Thienyl
3-MeC6H4
9
Ph
10
11
12
Ph
4j
4k
4l
Ph
H
a Isolated yield based on the alkynyl esters 1 used.
4 h. After removal of the solvent under reduced pressure, the
residue was diluted with light petroleum ether (20 mL) and filtered
to remove the palladium catalyst. The resulting solution was concen-
trated under reduced pressure and the residue was purified by flash
chromatography on silica gel (eluent: light petroleum ether/EtOAc,
19:1).
2a: Oil. IR (film): ν (cm−1) 2958, 2929, 1709, 1603, 1464, 1182,
1038; 1H NMR (400 MHz, CDCl3): δ 6.04 (t, J = 6.8 Hz, 3JSn-H = 64 Hz,
1H), 4.14 (q, J = 7.2 Hz, 2H), 2.44–2.40 (m, 2H), 1.58–1.26 (m, 19H),
0.95–0.84 (m, 18H); 13C NMR (100 MHz, CDCl3): δ 171.3, 153.6,
135.6, 59.9, 31.8, 31.4, 29.9, 27.3, 22.3, 14.4, 13.9, 13.7, 10.3; MS
(EI): m/z (%) 446 (M+, 2.3), 389 (69), 387 (48), 205 (50), 105 (100),
73 (75); Anal. Calcd for C21H42O2Sn: C, 56.64; H, 9.50. Found: C,
56.34; H, 9.25%.
1
confirmed by the NOESY in the H NMR spectrum. An
enhancement of the allylic protons was observed as the vinylic
proton (δ = 6.08) of 4c was irradiated. There was a correlation
between the vinylic proton (δ = 6.08) and aromatic protons
(δ = 7.24–7.26). A correlation between the allylic protons and
aromatic protons (δ = 7.24–7.26) was not observed. The NOE
results indicate that the compound 4c has the expected (Z)-
configuration and the palladium-catalysed cross-coupling
reaction of (E)-α-stannyl-α,β-unsaturated esters 2 with aryl
iodides occurs with the configuration retention of the starting
intermediates 2.
In summary, we have developed an efficient and stereose-
lective one-pot method for the synthesis of trisubstituted
(Z)-α,β-unsaturated esters by the hydrostannylation-Stille
coupling tandem reaction of alkynyl esters with aryl iodides.
The present method has the advantages of readily available
starting materials, straightforward and simple procedures,
mild reaction conditions and good yields. The procedure
should find wide application to the synthesis of a large array
of naturally occurring substances having the trisubstituted
(Z)-α,β-unsaturated ester system.
2b: Oil. IR (film): ν (cm−1) 2957, 2927, 1709, 1603, 1464, 1377,
1180; 1H NMR (400 MHz, CDCl3): δ 6.04 (t, J = 7.2 Hz, 3JSn-H = 64 Hz,
1H), 4.14 (q, J = 7.2 Hz, 2H), 2.45–2.39 (m, 2H), 1.53–1.26 (m, 23H),
0.96–0.84 (m, 18H); 13C NMR (100 MHz, CDCl3): δ 171.3, 153.7,
135.5, 59.9, 32.1, 31.7, 29.2, 29.0, 28.9, 27.3, 22.6, 14.4, 14.1, 13.7,
10.3; MS (EI): m/z (%) 417 (M+-Bu, 100), 371 (21), 291 (19), 235
(28), 179 (38); Anal. Calcd for C23H46O2Sn: C, 58.36; H, 9.79. Found:
C, 58.08; H, 9.62%.
2c: Oil. IR (film): ν (cm−1) 3059, 2958, 2923, 1700, 1596, 1463,
1183, 1034, 788, 695; 1H NMR (400 MHz, CDCl3): δ 7.32–7.29 (m,
5H), 6.70 (s, 3JSn–H = 64 Hz, 1H), 4.17 (q, J = 7.2 Hz, 2H), 1.58–1.52
(m, 6H), 1.37–1.32 (m, 6H), 1.22 (t, J = 7.2 Hz, 3H), 1.07 (t,
J = 8.0 Hz, 6H), 0.91 (t, J = 7.2 Hz, 9H); 13C NMR (100 MHz, CDCl3):
δ 173.2, 142.1, 139.8, 137.0, 128.3, 128.1, 128.0, 60.3, 28.9, 27.3,
14.2, 13.7, 10.6; MS (EI): m/z (%) 466 (M+, 1.5), 409 (100), 407 (87),
179 (54), 177 (46); Anal. Calcd for C23H38O2Sn: C, 59.37; H, 8.23.
Found: C, 59.57; H, 8.35%.
2d: Oil. IR (film): ν (cm−1) 2958, 2929, 1709, 1603, 1464, 1182,
Experimental
1
3
1H and 13C NMR spectra were recorded on a Bruker AC-P400
(400 MHz) spectrometer with TMS as an internal standard using
CDCl3 as the solvent. IR spectra were determined on an FTS-185
instrument as neat films. Mass spectra were obtained on a Finnigan
8239 mass spectrometer. Microanalyses 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. Benzene was distilled from sodium prior to use.
DMF was dried by distillation over calcium hydride.
1038; H NMR (400 MHz, CDCl3): δ 6.91 (d, J = 2.4 Hz, JSn-H
=
3
116 Hz, 1H), 5.91 (d, J = 2.4 Hz, JSn-H = 58 Hz, 1H), 4.19 (q,
J = 7.2 Hz, 2H), 1.54–1.45 (m, 6H), 1.35–1.26 (m, 9H), 1.02–0.95 (m,
6H), 0.89 (t, J = 7.2 Hz, 9H); 13C NMR (100 MHz, CDCl3): δ 170.6,
146.2, 139.8, 60.6, 28.9, 27.3, 14.3, 13.7, 10.1; MS (EI): m/z (%) 389
(M+, 3.5), 332 (M+-Bu, 100), 205 (50), 105 (97), 73 (75); Anal. Calcd
for C17H34O2Sn: C, 52.47; H, 8.81. Found: C, 52.18; H, 8.64%.
Synthesis of (Z)-α,β-unsaturated esters (4a–l); general procedure
A 25 mL, two-necked, round-bottom flask equipped with a magnetic
stir bar and argon was charged sequentially with alkynyl ester
(1.0 mmol), benzene (4 mL), Pd(PPh3)4 (0.02 mmol) and Bu3SnH
(1.05 mmol) in an argon atmosphere. The mixture was stirred at room
temperature for 4 h. Then the solvent was removed under reduced
pressure and the residue was dissolved in DMF (8 mL). Aryl iodide
(1.1 mmol) and CuI (0.75 mmol) were added and the mixture
Synthesis of (E)-α-stannyl-α,β-unsaturated esters 2a–d; general
procedure
A 25 mL, two-necked, round-bottom flask equipped with a magnetic
stir bar, and argon was charged sequentially with alkynyl ester (1 mmol),
benzene (4 mL), Pd(PPh3)4 (0.02 mmol) and Bu3SnH (1.05 mmol) in
an argon atmosphere. The mixture was stirred at room temperature for
Scheme 2

JOURNAL OF CHEMICAL RESEARCH 2011 639
was stirred for 8 h at 25 °C and monitored by TLC (SiO2) for the
disappearance of the intermediate 2. The reaction mixture was diluted
with diethyl ether (30 mL), filtered and then washed with 20% aque-
ous KF (10 mL) for 30 min before the organic layer was separated,
dried and concentrated. The concentrate was purified by column
chromatography on silica gel, eluting with a mixture of diethyl ether
and light petroleum ether.
J = 8.4 Hz, 2H), 7.38–7.27 (m, 5H), 6.95 (s, 1H), 6.90 (d, J = 8.4 Hz,
2H), 4.26 (q, J = 7.2 Hz, 2H), 3.82 (s, 3H), 1.19 (t, J = 7.2 Hz, 3H);
13C NMR (CDCl3): δ 169.9, 159.8, 136.0, 134.8, 129.5, 129.4, 128.4,
128.2, 128.0, 127.7, 114.1, 61.3, 55.4, 13.9; MS (EI): m/z 282 (M+,
54), 209 (100), 165 (49); Anal. Calcd for C18H18O3: C, 76.57; H, 6.43.
Found: C, 76.33; H, 6.15%.
4j: Oil. IR (film): ν (cm−1) 3058, 2981, 2935, 1716, 1623, 1591,
4a: Oil. IR (film): ν (cm−1) 2958, 2928, 2857, 1717, 1464, 1371,
1
1495, 1447, 1371, 1212, 1170, 1095, 1023, 797, 776, 696; H NMR
1
1195, 1036, 758, 697; H NMR (CDCl3): δ 7.33–7.27 (m, 5H), 6.16
(CDCl3): δ 8.12–8.10 (m, 1H), 7.87–7.83 (m, 2H), 7.55–7.44 (m, 6H),
7.39–7.32 (m, 3H), 6.97 (s, 1H), 4.17 (q, J = 7.2 Hz, 2H), 1.10 (t,
J = 7.2 Hz, 3H); 13C NMR (CDCl3): δ 169.1, 137.6, 136.6, 135.7,
134.1, 133.8, 131.9, 128.7, 128.6, 128.5, 128.4, 127.3, 126.4, 126.0,
125.4, 125.3, 61.2, 13.9; MS (EI): m/z 302 (M+, 19), 229 (100); Anal.
Calcd for C21H18O2: C, 83.42; H, 6.00. Found: C, 83.15; H, 5.75%.
4k: Oil. IR (film): ν (cm−1) 3073, 2981, 1724, 1611, 1447, 1377,
1219, 1182, 1022, 753, 696; 1H NMR (CDCl3): δ 7.37–7.28 (m, 5H),
7.24 (d, J = 5.6 Hz, 1H), 7.09 (d, J = 3.6 Hz, 1H), 7.07 (s, 1H), 7.02–
7.00 (m, 1H), 4.28 (q, J = 7.2 Hz, 2H), 1.20 (t, J = 7.2 Hz, 3H); 13C
NMR (CDCl3): δ 168.4, 140.7, 135.4, 129.5, 129.2, 128.5, 128.3,
128.2, 127.8, 125.8, 125.4, 61.6, 13.9; MS (EI): m/z 258 (M+, 100),
184 (75), 135 (62); Anal. Calcd for C15H14O2S: C, 69.74; H, 5.46.
Found: C, 69.48; H, 5.71%.
(t, J = 7.8 Hz, 1H), 4.29 (q, J = 7.2 Hz, 2H), 2.45–2.39 (m, 2H), 1.50–
1.46 (m, 2H), 1.41–1.36 (m, 2H), 1.32 (t, J = 7.2 Hz, 3H), 0.92
(t, J = 7.2 Hz, 3H); 13C NMR (CDCl3): δ 168.4, 139.6, 137.9, 134.7,
128.3, 127.4, 127.1, 60.7, 31.5, 29.8, 22.4, 14.3, 13.9; MS (EI): m/z
232 (M+, 55), 203 (54), 157 (55), 129 (57), 115 (100); Anal. Calcd for
C15H20O2: C, 77.55; H, 8.68. Found: C, 77.28; H, 8.47%.
4b: Oil. IR (film): ν (cm−1) 2958, 2928, 2859, 1723, 1605, 1465,
1
1370, 1205, 1175, 1036, 786, 701; H NMR (CDCl3): δ 7.26–7.07
(m, 5H), 6.14 (t, J = 7.8 Hz, 1H), 4.29 (q, J = 7.2 Hz, 2H), 2.42–2.36
(m, 2H), 2.34 (s, 3H), 1.50–1.45 (m, 2H), 1.42–1.36 (m, 2H), 1.32
(t, J = 7.2 Hz, 3H), 0.93 (t, J = 7.4 Hz, 3H); 13C NMR (CDCl3): δ
168.5, 139.0, 137.9, 137.8, 134.8, 128.3, 128.2, 127.7, 124.1, 60.7,
31.5, 29.8, 22.4, 21.4, 14.3, 13.9; MS (EI): m/z 246 (M+, 97), 171
(100), 143 (45), 129 (68), 115 (47); Anal. Calcd for C16H22O2: C,
78.01; H, 9.00. Found: C, 78.18; H, 8.86%.
4l: Oil. IR (film): ν (cm−1) 2981, 2925, 1722, 1605, 1584, 1488,
1
1446, 1368, 1225, 1162, 1103, 792, 714; H NMR (CDCl3): δ 7.27–
4c: Oil. IR (film): ν (cm−1) 2927, 2857, 1722, 1609, 1512, 1465,
1371, 1249, 1196, 1037, 830; 1H NMR (CDCl3): δ 7.26–7.24 (m, 2H),
6.86–6.84 (m, 2H), 6.08 (t, J = 7.8 Hz, 1H), 4.29 (q, J = 7.2 Hz, 2H),
3.81 (s, 3H), 2.42–2.36 (m, 2H), 1.50–1.46 (m, 2H), 1.41–1.35 (m,
2H), 1.32 (t, J = 7.2 Hz, 3H), 0.92 (t, J = 7.4 Hz, 3H); 13C NMR
(CDCl3): δ 168.6, 159.1, 137.9, 134.1, 130.5, 128.2, 113.7, 60.7, 55.3,
31.6, 29.8, 22.4, 14.3, 13.9; MS (EI): m/z 262 (M+, 100), 187 (69), 145
(52); Anal. Calcd for C16H22O3: C, 73.25; H, 8.45. Found: C, 73.47; H,
8.21%.
7.13 (m, 4H), 6.31 (s, 1H), 5.86 (s, 1H), 4.28 (q, J = 7.2 Hz, 2H), 2.36
(s, 3H), 1.31 (t, J = 7.2 Hz, 3H); 13C NMR (CDCl3): δ 167.0, 141.7,
137.7, 136.7, 129.0, 128.9, 128.0, 126.2, 125.4, 61.1, 21.5, 14.2. Anal.
Calcd for C12H14O2: C, 75.76; H, 7.42. Found: C, 75.48; H, 7.23%.
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.
4d: Oil. IR (film): ν (cm−1) 2958, 2930, 2860, 1723, 1465, 1375,
1262, 1183, 1025, 696; 1H NMR (CDCl3): δ 7.26–7.17 (m, 1H), 7.03–
6.94 (m, 2H), 6.29 (t, J = 7.8 Hz, 1H), 4.33 (q, J = 7.2 Hz, 2H), 2.43–
2.37 (m, 2H), 1.50–1.44 (m, 2H), 1.40–1.34 (m, 5H), 0.92 (t,
J = 7.2 Hz, 3H); 13C NMR (CDCl3): δ 167.1, 140.6, 138.7, 128.4,
127.2, 124.9, 124.6, 61.1, 31.4, 29.8, 22.5, 14.3, 14.0; MS (EI): m/z
238 (M+, 56), 192 (51), 182 (87), 163 (100);Anal. Calcd for C13H18O2S:
C, 65.51; H, 7.61. Found: C, 65.22; H, 7.51%.
Received 28 September 2011; accepted 13 October 2011
Paper 1100910 doi: 10.3184/174751911X13192956847054
Published online: 22 November 2011
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4e: Oil. IR (film): ν (cm−1) 2960, 2932, 2861, 1722, 1629, 1597,
1
A.S. Kireev, O.N. Nadein, V.J. Agustin, N.E. Bush, A. Evidente,
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1520, 1345, 1199, 1110, 1037, 855; H NMR (CDCl3): δ 8.19–8.16
(m, 2H), 7.50–7.47 (m, 2H), 6.34 (t, J = 7.8 Hz, 1H), 4.31 (q,
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277 (M+, 100), 194 (36), 115 (45); Anal. Calcd for C15H19NO4: C,
64.97; H, 6.91. Found: C, 64.68; H, 6.67%.
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4f: Oil. IR (film): ν (cm−1) 2958, 2929, 2859, 1714, 1508, 1465,
1370, 1203, 1174, 1034, 800; 1H NMR (CDCl3): δ 7.84–7.78 (m, 3H),
7.46–7.42 (m, 3H), 7.34 (d, J = 6.8 Hz, 1H), 6.23 (t, J = 7.4 Hz, 1H),
4.13 (q, J = 7.0 Hz, 2H), 2.74–2.69 (m, 2H), 1.58–1.38 (m, 4H), 1.13
(t, J = 7.0 Hz, 3H), 0.94 (t, J = 7.2 Hz, 3H); 13C NMR (CDCl3): δ
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125.7, 125.4, 125.3, 60.5, 31.6, 29.7, 22.6, 14.1, 14.0; MS (EI): m/z
282 (M+, 88), 209 (33), 165 (100); Anal. Calcd for C19H22O2: C, 80.81;
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14 A.G.M. Barrett, D. Hamprecht and M. Ohkubo, J. Org. Chem., 1997, 62,
9376.
4g: Oil. IR (film): ν (cm−1) 3058, 3027, 2981, 1716, 1599, 1496,
1448, 1373, 1182, 1023, 768, 695; 1H NMR (CDCl3): δ 7.49–7.46 (m,
2H), 7.39–7.28 (m, 8H), 7.03 (s, 1H), 4.26 (q, J = 7.2 Hz, 2H), 1.19 (t,
J = 7.2 Hz, 3H); 13C NMR (CDCl3): δ 169.6, 137.0, 135.8, 135.4,
131.2, 128.7, 128.5, 128.4, 128.3, 128.2, 126.4, 61.3, 13.9; MS (EI):
m/z 252 (M+, 98), 179 (100), 135 (65); Anal. Calcd for C17H16O2: C,
80.93; H, 6.39. Found: C, 80.68; H, 6.44%.
15 R.J.K. Taylor, M. Reid, J. Foot and S.A. Raw, Acc. Chem. Res., 2005, 38,
851.
16 G. Kim, D.G. Lee and S. Chang, Bull. Korean Chem. Soc., 2001, 22, 943.
17 E.Y. Lee, Y. Kim, J.S. Lee and J. Park, Eur. J. Org. Chem., 2009, 2943.
18 G. Deng, B. Xu and C. Liu, Tetrahedron, 2005, 61, 5818.
19 J.M. Concellon and E. Bardales, Org. Lett., 2002, 4, 189.
20 G.H. Posner, Chem. Rev., 1986, 86, 831.
4h: Oil. IR (film): ν (cm−1) 3058, 3027, 2981, 2958, 1719, 1621,
1591, 1494, 1447, 1372, 1184, 1093, 820, 753, 695; 1H NMR (CDCl3):
δ 7.40–7.26 (m, 9H), 7.00 (s, 1H), 4.24 (q, J = 7.2 Hz, 2H), 1.16 (t,
J = 7.2 Hz, 3H); 13C NMR (CDCl3): δ 169.2, 135.6, 135.5, 134.3,
134.2, 131.9, 128.9, 128.5, 128.3, 127.8, 61.5, 13.9; MS (EI): m/z 286
(M+, 35Cl, 9.8), 269 (100); Anal. Calcd for C17H15ClO2: C, 71.19; H,
5.27. Found: C, 70.92; H, 5.43%.
21 L.F. Tietze and U. Beifuss, Angew. Chem. Int. Ed., 1993, 32, 131.
22 L.F. Tietze, Chem. Rev., 1996, 96, 115.
23 X. Huang and M. Xia, Org. Lett., 2002, 4, 1331.
24 B.M. Trost and C.J. Li, Synthesis, 1994, 1267.
25 R. Rossi, A. Carpita and P. Cossi, Tetrahedron Lett., 1992, 33, 4495.
26 A.J. Leusink, H.A. Budding and J.W. Marsman, J. Organomet. Chem.,
1967, 9, 285.
4i: Oil. IR (film): ν (cm−1) 2958, 2933, 1723, 1607, 1514, 1464,
1446, 1373, 1250, 1178, 1032, 826, 697; 1H NMR (CDCl3): δ 7.40 (d,
27 J.K. Stille, Angew. Chem. Int. Ed., 1986, 25, 508.
28 T.N. Mitchell, J. Organomet. Chem., 1986, 304, 1.

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