Tandem Michael addition/ylide olefination reaction for the synthesis of highly functionalized cyclohexadiene derivatives

Article abstract of DOI:10.1016/j.tet.2008.06.048

A tandem Michael addition/ylide olefination for the rapid creation of highly functionalized cyclohexadiene is developed. The tandem annulation reactions afford versatile cyclohexadienes in good to excellent isolated yields. This method has been successfully applied to the synthesis of three biologically active molecules.

Full text of DOI:10.1016/j.tet.2008.06.048

Tetrahedron 64 (2008) 8149–8154
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Tandem Michael addition/ylide olefination reaction for the synthesis of highly
functionalized cyclohexadiene derivatives
,
Long-Wu Ye a, Xun Han b, Xiu-Li Sun a, Yong Tang a
*
a State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, China
b Department for Intensive Instruction, Nanjing University, Nanjing 210093, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A tandem Michael addition/ylide olefination for the rapid creation of highly functionalized cyclo-
hexadiene is developed. The tandem annulation reactions afford versatile cyclohexadienes in good to
excellent isolated yields. This method has been successfully applied to the synthesis of three biologically
active molecules.
Received 30 April 2008
Received in revised form 9 June 2008
Accepted 13 June 2008
Available online 19 June 2008
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
carbonyl compounds.8c The reactions of crotonate arsonium ylide
with conjugate aldehydes were also documented but afforded
Cyclohexadienes are very important subunits in a number of
biologically active compounds1 such as antibacterially active agent
A,1a antimicrobially active agent B,1c and calcium channel modu-
lator C,1e as well as versatile intermediates2 in organic synthesis
(Fig. 1). Although several synthetic methods have been devel-
oped,3,2a a few are involved in the direct synthesis with high se-
lectivity. Ylide reactions have been developed as one of the
powerful approaches for the preparation of alkenes,4 cyclopro-
panes,5 epoxides,5a,d,6 and aziridines5b,c,7 due to its unambiguous
positioning and good stereoselectivity. Allylic phosphorus ylides
have been employed for the construction of cyclohexadiene de-
rivatives via ylide-initiated Michael addition/olefination reaction,8
however, low yields (<50%) were obtained in the reaction of the
a mixture of Wittig products and cyclohexadienes (Scheme 1).8a
H
_
O
+
+
Ph3As
CO2Me
CO2Me
CO2Me
THF, rt
36% yield
63% yield
30% yield
DMPU, 0 °C 40% yield
Scheme 1. Condensation reaction of crotonate arsonium ylide with crotonal.
In a previous study on ylide chemistry,9 we developed a tandem
corresponding crotonate-derived ylide with
a
,b
-unsaturated
reaction of allylic sulfur ylides with a,b-unsaturated ketones for the
preparation of functionalized multisubstituted cyclohexadiene
epoxides with multiple stereogenic centers (Scheme 2).10 Very re-
cently, we found that the extension of the sulfur ylide to the cor-
responding phosphorus ylide in the aforementioned reaction
resulted in the formation of versatile cyclohexadienes in good to
excellent yields with excellent chemoselectivities and regiose-
lectivities, and the direct Wittig olefination products did not ob-
served at all even when conjugate aldehydes were employed
(Scheme 3). Compared with the reaction of the corresponding
arsonium ylide,8a both the selectivities and the yields of cyclo-
hexadienes have been improved greatly. This reaction proves to be
useful in the synthesis of some biologically active molecules such as
fungicide. In this paper, we wish to report these results in details.
Br
F
MeO2C
CO2Me
NH
CHO
MeO2C
CO2Me
Br
antibacterial agent A
antimicrobial activity B calcium channel modulator C
Figure 1. Examples of biologically active compounds containing cyclohexadiene.
* Corresponding author. Tel.: þ86 21 54925156; fax: þ86 21 54925078.
E-mail address: tangy@mail.sioc.ac.cn (Y. Tang).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.06.048

8150
L.-W. Ye et al. / Tetrahedron 64 (2008) 8149–8154
Table 2
H
MeO2C
Tandem Michael addition/ylide olefination reaction for the synthesis of highly
COR2
K2CO3
CH3CN
0 °C or -20 °C
functionalized cyclohexadiene derivativesa
Me2S
Br
CO2Me
+ R1
O
R2
R1
R2
_
1
2
R1
R2
3
Br
+
R
1 = Aryl, Alkyl, H
R2 = Aryl, CF3
60-93% yield
Ph3P
CO2R
2
O
R1
4a: R = Me
4b: R = Et
4c: R = Bu
Cs2CO3, THF, 60 °C
Scheme 2. Tandem Michael addition/ylide epoxidation reaction for the synthesis of
CO2R
5
t
highly functionalized cyclohexadiene epoxide derivatives.
Entry
2
R1
R2
5
Yieldb (%)
1
2a
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2o
2p
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
4-F–C6H4
Ph
Ph
Styryl
Me
CO2Me
CO2Et
P(O)(OMe)2
H
5a
5a0
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
96
91
98
89
93
91
96
99
86
71
65
72
99
72
51
81
76
R2
2c
3
R1
R2
Cs2CO3
THF, 60 °C
+
4-Br–C6H4
4-OMe–C6H4
2-Br–C6H4
2-OMe–C6H4
4-CH3–C6H4
3,4-(OMe)2–C6H3
Me
Styryl
Ph
Ph
Ph
+
Ph3P
CO2R
_
4
5
6
Br
R1
CO2R
O
2
51-99% yield
4
5
R1 = Aryl, Alkyl
R
7
2 = Aryl, Alkyl, H, CO2R, P(O)(OMe)2
8d
9
Scheme 3. Synthesis of highly functionalized cyclohexadiene derivatives.
10
11
12
13
14
15
16e,f
17e
2. Result and discussion
Me
Me
Ph
Initially, it was found that allylic phosphonium salt 4a, after
treatment with tBuOK for 45 min, reacted with chalcone 2a afford-
ing cyclohexadiene 5a as a single product in 78% yield (entry 1, Table
1). To optimize this tandem Michael addition/ylide olefination re-
action, several reaction conditions were investigated using chalcone
2a as a model substrate. As shown in Table 1, both the base and the
reaction temperature influenced the yields. Compared with NaH,
Me
H
a
Reagents and conditions: Cs2CO3 (130 mg, 0.40 mmol), 4a (144 mg, 0.33 mmol)
in THF (2.5 mL), room temperature, 45 min, then 2 (0.25 mmol) in THF (2.5 mL) was
added and stirred for another 44–72 h at 60 ꢀC.
b
Isolated yield.
Using phosphonium salt 4c.
Using phosphonium salt 4b.
c
d
t
both BuOK and Cs2CO3 were better bases to promote the tandem
e
At room temperature.
Using 1.6 equiv tBuOK as a base.
f
reaction in THF (entries 2–4, Table 1). Elevating the reaction tem-
perature from 25 to 60 ꢀC increased the yield of 5a from 84% to 96%
(entries 3, 6–7, Table 1). One-pot addition of phosphonium salt 4a,
chalcone, and base resulted in an obvious decrease of the yield
(entry 5, Table 1). Although this reaction could be performed in both
toluene and acetonitrile, THF was optimal (entries 7–9, Table 1).
Encouraged by these results, the generality of this tandem re-
chemoselectivities and regioselectivities in good to excellent yields
(65–99%, entries 1–12, Table 2). Chalcones gave excellent results,
and both electron-donating and electron-withdrawing groups on
the aryl ring proved to be well-tolerated (entries 1–8, Table 2). (E)-
Methyl-2-oxo-4-phenylbut-3-enoate 2l, (E)-ethyl-2-oxopent-3-
enoate 2m, and but-2-enoyl-phosphonic acid dimethyl ester 2n
also gave the desired cyclohexadienes in good yields (entries 13–15,
action was examined by evaluating various
bonyl compounds under the optimal conditions. As shown in Table
2, both aryl and alkyl substituted -unsaturated ketones are good
a,b-unsaturated car-
Table 2). It is worth noting that a,b-unsaturated aldehydes 2o and
a,b
2p furnished the desired cyclohexadienes in good yields (entries
16–17, Table 2) and the direct Wittig olefination products were not
observed. Thus, the current reaction provides a highly efficient
method to construct the cyclohexadiene backbone with multi-
functional groups in one step.
2-Benzylidene-1,3-diphenyl-propane-1,3-dione 2q reacted with
allylic phosphonium salt 4a to furnish multisubstituted cyclo-
hexadiene 5q in 66% yield (Eq. 1). Noticeably, the diaster-
eoselectivity of this reaction is excellent and only one diastereomer
was observed.
substrates to give the cyclohexadiene derivatives with excellent
Table 1
Influence of reaction conditions on the tandem Michael addition/ylide olefination
reactiona
Ph
Ph
Ph
2a
O
+
Ph3P
CO2Me
_
Ph
CO2Me
base, solvent
25-60 °C
Br
4a
5a
O
Ph
Ph
Entry
Solvent
T (ꢀC)
Base
Yieldb (%)
Ph
Ph
COPh
Ph
1c
2
THF
THF
THF
THF
THF
THF
THF
CH3CN
CH3C6H5
25
25
25
25
25
50
60
60
60
tBuOK
tBuOK
Cs2CO3
NaH
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
78
83
84
26
43
89
96
73
48
+
O
2q
ð1Þ
Ph3P
Br
CO2Me
Cs2CO3, THF, rt
66% yield
3
CO2Me
4
4a
5q
single isomer
5d
6
7
8
9
The products were characterized by 1H NMR, 13C NMR, ele-
mental analysis, and mass spectra. Products 5d and 5q were further
confirmed by X-ray analysis (Fig. 2). The relative configuration of 5q
was determined by 1H NMR as well as X-ray analysis, in which the
substituted groups are located in trans-position.
a
Reagents and conditions: base (0.40 mmol), 4a (144 mg, 0.33 mmol) in solvent
(2.5 mL), room temperature, 45 min, then 2a (52 mg, 0.25 mmol) in solvent (2.5 mL)
was added and stirred for further 24–48 h at 25–60 ꢀC.
b
Isolated yield.
Base (1.2 equiv).
One-pot addition of 4a, Cs2CO3, and 2a.
This method proves to be very useful in organic synthesis.11,2a,b,d
As shown in Scheme 4, for example, reduction of 5a with DIBAL-H,
c
d

L.-W. Ye et al. / Tetrahedron 64 (2008) 8149–8154
8151
Ph
Ph
1) DIBAL-H, DCM, -78 °C
2) DMP, DCM, rt
Ph
CO2Me
5a
Ph
CHO
6
92% yield (two steps)
C6H4-4-F
C6H4-4-F
DDQ
toluene, reflux
94% yield
C6H3-3,4-(OMe)2
CO2Et
5g
C6H3-3,4-(OMe)2
CO2Et
fungicide 7
_
O
Br
+
OMe
Ph3P
4d
Cs2CO3, THF, rt
59% yield
MeO
OMe
2r
C6H4-4-OMe
C6H4-4-OMe
DDQ
toluene, reflux
96% yield
C6H3-3,5-(OMe)2
C6H3-3,5-(OMe)2
5r
8
5d
C6H4-4-OH
ref. 13
C6H3-3,5-(OH)2
proapoptotic agent 9
Scheme 4. The applications of the tandem reaction in the synthesis of biologically
active compounds.
R
R
O
O
H
Ph3P
CO2Me
Ph3P
CO2Me
II
I
R
R
Ph3P=O
O
CO2Me
Ph3P
CO2Me
III
5
Scheme 5. A possible mechanism.
3. Conclusion
5q
In summary, we have developed a tandem Michael addition/
ylide olefination reaction, providing an easy access to highly
functionalized cyclohexadiene derivatives in good to excellent
yields. The reaction displayed a good substrate scope and pro-
ceeded with excellent chemoselectivity and regioselectivity. The
applications of this reaction in the synthesis of biologically active
compounds 6, 7, and 9 have been achieved from readily available
starting materials under mild conditions. Further investigations on
its asymmetric version are in progress in our laboratory.
Figure 2. Molecular structure of compounds 5d and 5q.
followed by Dess–Martin oxidation, provided biologically active
compound 61a in 92% yield. Oxidation of 5g with dichloro-
dicyanoquinone (DDQ) afforded the fungicide 712 in 94% yield. In
addition, the reaction of allylic phosphonium salt 4d with chalcone
2r (THF, 1.6 equiv of Cs2CO3, rt; 59%), followed by DDQ oxidation
(DDQ, toluene, 120 ꢀC; 96%), afforded compound 8, which could be
easily transformed to proapoptotically active compound 9 by
demethylation with BBr3.13
4. Experimental
4.1. General
The present reaction could be accounted by a proposed mech-
anism as shown in Scheme 5. Ylide I, generated in situ from the
corresponding phosphonium salt 4a, underwent an intermolecular
Michael addition with
a
,
b
-unsaturated ketones to form in-
All reactions were carried out under N2 unless otherwise noted.
All solvents were purified according to standard methods prior to
use. 1H NMR and 13C NMR spectra were recorded in chloroform-d3
on a VARIAN Mercury 300.
termediate II. Proton transfer of intermediate III, followed by an
intramolecular ylide olefination afforded the desired cyclo-
hexadiene derivative 5. A clear mechanism waits for further study.

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L.-W. Ye et al. / Tetrahedron 64 (2008) 8149–8154
4.2. Representative procedure for the synthesis of highly
functionalized cyclohexadiene derivatives
7.17–7.08 (m, 2H), 7.04–6.98 (m,1H), 6.54 (dd, J¼6.3 and 3.0 Hz,1H),
4.67 (dd, J¼10.8 and 1.8 Hz, 1H), 3.68 (s, 3H), 3.25–3.15 (m, 1H), 2.99
(dd, J¼17.7 and 2.1 Hz, 1H); 13C NMR (75 MHz, CDCl3):
d 167.1, 141.7,
4.2.1. Preparation of 4,6-diphenyl-cyclohexa-1,3-dienecarboxylic
acid methyl ester 5a
140.0, 139.6, 136.0, 133.3, 128.5, 128.4, 128.3, 128.2, 127.6, 127.3,
125.5, 123.7, 119.5, 51.8, 35.9, 32.9. IR n
/cmꢁ1: 2950 (m), 1707 (s),
Cs2CO3 (130 mg, 0.40 mmol) was added to a solution of phos-
phonium salt 4a (144 mg, 0.33 mmol) in THF (2.5 mL), and the
resulting mixture was stirred at room temperature for 45 min.
Chalcone 2a (52 mg, 0.25 mmol) in THF (2.5 mL) was added and the
reaction mixture was stirred at 60 ꢀC for 48 h. After the reaction was
complete (monitored by TLC), the reaction mixture was passed
through a glass funnel with a thin layer of silica gel, and eluted with
ethyl acetate. The filtrate was concentrated and the residue was pu-
rified by flash column chromatography to afford cyclohexadiene 5a
as white solid (mp 96–97 ꢀC). Yield 70 mg (96%); 1H NMR (300 MHz,
1560 (m), 1435 (m), 1269 (m), 751 (m), 692 (m), 671 (m); MS (ESI,
positive mode, m/z): 425 (MþMeOHþNaþ), 423 (MþMeOHþNaþ),
393 (MþNaþ), 391 (MþNaþ), 371 (MþHþ), 369 (MþHþ). Anal. calcd
for C20H17O2Br: C, 65.05; H, 4.64. Found: C, 64.72; H, 4.69.
4.2.6. 6-(2-Methoxy-phenyl)-4-phenyl-cyclohexa-1,3-
dienecarboxylic acid methyl ester 5e
Yield 91% (a white solid, mp 161–162 ꢀC, 68 h); 1H NMR
(300 MHz, CDCl3, TMS):
d
7.51 (d, J¼5.7 Hz, 1H), 7.36–7.21 (m, 5H),
7.13 (t, J¼7.8 Hz,1H), 7.05 (d, J¼7.8 Hz,1H), 6.85 (d, J¼8.1 Hz,1H), 6.76
(t, J¼7.5 Hz,1H), 6.50(dd, J¼5.7and2.4 Hz,1H), 4.66 (d, J¼8.7 Hz,1H),
3.89(s, 3H), 3.67(s, 3H), 3.19–3.09(m,1H), 2.95(dd, J¼17.7and1.2 Hz,
CDCl3, TMS):
d
7.44–7.13 (m,11H), 6.53 (dd, J¼6.0 and 3.0 Hz,1H), 4.18
(dd, J¼1.8 and 9.9 Hz, 1H), 3.70 (s, 3H), 3.29–3.19 (m, 1H), 3.02 (dd,
J¼18 and 2.7 Hz,1H); 13C NMR (75 MHz, CDCl3):
d
167.4, 158.7, 142.6,
1H); 13C NMR (75 MHz, CDCl3):
d 167.4, 156.5, 142.2, 140.0, 135.7,
141.7, 139.7, 134.6, 128.5, 128.4, 128.3, 127.1, 126.6, 125.5, 119.7, 51.7,
129.1, 128.3, 128.1, 127.9, 127.5 (0), 127.4 (6), 125.5, 120.1, 119.5, 110.7,
36.8, 34.5. IR
n
/cmꢁ1: 2948 (m),1705(s),1561 (m),1493(m),1082(m),
55.5, 51.6, 33.1, 29.7. IR
n
/cmꢁ1: 2950 (m),1709 (s),1565 (m),1488 (m),
747 (m), 697; MS (EI, m/z, rel intensity): 290 (Mþ, 77.4), 231 (100).
1433 (m), 1028 (m), 856 (m), 760 (m), 699 (m); MS (ESI, positive
mode, m/z): 375 (MþMeOHþNaþ), 343 (MþNaþ), 321 (MþHþ). Anal.
calcd for C21H20O3: C, 78.73; H, 6.29. Found: C, 78.88; H, 6.29.
Anal. calcd for C20H18O2: C, 82.73; H, 6.25. Found: C, 82.83; H, 6.18.
4.2.2. 4,6-Diphenyl-cyclohexa-1,3-dienecarboxylic acid tert-butyl
ester 5a0
4.2.7. 4-Phenyl-6-p-tolyl-cyclohexa-1,3-dienecarboxylic acid
methyl ester 5f
Yield 91% (colorless oil, 51 h); 1H NMR (300 MHz, CDCl3, TMS):
d
7.42–7.39 (m, 2H), 7.33–7.15 (m, 9H), 6.51 (dd, J¼6.0 and 2.7 Hz,
Yield 96% (colorless oil, 66 h); 1H NMR (300 MHz, CDCl3, TMS):
1H), 4.12 (dd, J¼2.1 and 9.9 Hz, 1H), 3.27–3.17 (m, 1H), 2.99 (dd,
d
7.41–7.38 (m, 3H), 7.38–7.16 (m, 5H), 7.02 (d, J¼8.1 Hz, 2H), 6.53–
J¼17.7 and 2.7 Hz, 1H), 1.40 (s, 9H); 13C NMR (75 MHz, CDCl3):
6.50 (m, 1H), 4.15 (d, J¼9.9 Hz, 1H), 3.70 (s, 3H), 3.27–3.17 (m, 1H),
d
166.3, 143.3, 140.9, 139.9, 133.6, 130.6, 128.5, 128.3, 128.1, 127.1,
3.00 (dd, J¼17.7 and 1.5 Hz, 1H), 2.25 (s, 3H); 13C NMR (75 MHz,
126.4, 125.5, 119.8, 80.3, 37.4, 34.6, 28.0. IR
n
/cmꢁ1: 2926 (m), 1700
CDCl3): d 167.4, 141.7, 139.7 (3), 139.6 (7), 136.1, 134.4, 129.1, 128.7,
(s), 1561 (m), 1494 (m), 1367 (m), 751 (m), 697 (m); MS (EI, m/z, rel
intensity): 332 (Mþ, 6.8), 230 (100). HRMS (EI) calcd for C23H24O2
(Mþ): 332.1776. Found: 332.1765.
128.4, 128.2, 127.0, 125.5, 119.6, 51.6, 36.5, 34.6, 20.9. IR n :
/cmꢁ1
2948 (m), 1718 (s), 1688 (m), 1560 (m), 1434 (m), 1081 (m), 818 (m),
759 (m), 693 (m); MS (ESI, positive mode, m/z): 359
(MþMeOHþNaþ), 327 (MþNaþ), 305 (MþHþ). HRMS (EI) calcd for
4.2.3. 6-(4-Bromo-phenyl)-4-phenyl-cyclohexa-1,3-
dienecarboxylic acid methyl ester 5b
C
21H20O2 (Mþ): 304.1463. Found: 304.1465.
Yield 98% (a white solid, mp 141–142 ꢀC, 57 h); 1H NMR
4.2.8. 6-(3,4-Dimethoxy-phenyl)-4-(4-fluoro-phenyl)-cyclohexa-
1,3-dienecarboxylic acid methyl ester 5g
(300 MHz, CDCl3, TMS):
d
7.43–7.23 (m, 8H), 7.16 (d, J¼8.4 Hz, 2H),
6.52 (dd, J¼6.0 and 3.0 Hz, 1H), 4.12 (d, J¼9.9 Hz, 1H), 3.70 (s, 3H),
Yield 99% (pale yellow oil, 63 h); 1H NMR (300 MHz, CDCl3,
3.27–3.17 (m, 1H), 2.96 (dd, J¼17.7 and 1.8 Hz, 1H); 13C NMR
TMS):
d
7.40–7.35 (m, 3H), 7.02–6.78 (m, 4H), 6.70 (d, J¼8.4 Hz, 1H),
(75 MHz, CDCl3):
d
167.2, 141.6 (0), 141.5 (8), 139.4, 134.8, 131.5,
6.45 (dd, J¼2.7 and 6.0 Hz, 1H), 4.22–4.09 (m, 3H), 3.79 (s, 3H), 3.78
(s, 3H), 3.25–3.15 (m, 1H), 2.96 (dd, J¼17 and 1.8 Hz, 1H), 1.25 (t,
128.9, 128.5 (3), 128.4 (7), 128.0, 125.5, 120.5, 119.6, 51.7, 36.4, 34.4.
IR
n
/cmꢁ1: 2948 (m), 1705 (s), 1561 (m), 1485 (m), 1368 (m), 778
J¼7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3):
d 166.7, 148.5, 147.5, 140.5
(m), 693 (m), 492 (m); MS (ESI, positive mode, m/z): 425
(MþMeOHþNaþ), 423 (MþMeOHþNaþ), 393 (MþNaþ), 391
(MþNaþ), 371 (MþHþ), 369 (MþHþ). HRMS (EI) calcd for
(d, J¼0.9 Hz), 135.8 (d, J¼3.5 Hz), 135.3, 133.6, 129.0, 127.1 (d,
J¼7.5 Hz), 119.1 (d, J¼2.1 Hz), 118.8, 115.4, 115.1, 110.8, 110.3, 60.3,
55.5 (0), 55.4 (8), 36.3, 34.6,14.0. IR n
/cmꢁ1: 2934 (m),1700 (s),1599
C
20H17O2Br (Mþ): 368.0412. Found: 368.0418.
(m), 1561 (m), 1509 (m), 1464 (m), 1230 (m), 1028 (m), 830 (m), 771
(m); MS (EI, m/z, rel intensity): 382 (Mþ, 100), 309 (92.9). HRMS (EI)
calcd for C23H23FO4 (Mþ): 382.1580. Found: 382.1578.
4.2.4. 6-(4-Methoxy-phenyl)-4-phenyl-cyclohexa-1,3-diene-
carboxylic acid methyl ester 5c
Yield 89% (a yellow solid, mp 157–158 ꢀC, 56 h); 1H NMR
4.2.9. 6-Methyl-4-phenyl-cyclohexa-1,3-dienecarboxylic acid
methyl ester 5h
(300 MHz, CDCl3, TMS):
d
7.43–7.19 (m, 8H), 6.75 (d, J¼8.7 Hz, 2H),
6.52 (dd, J¼6.0 and 3.0 Hz, 1H), 4.13 (d, J¼9.6 Hz, 1H), 3.73 (s, 3H),
Yield 86% (colorless oil, 44 h); 1H NMR (300 MHz, CDCl3, TMS):
3.71 (s, 3H), 3.27–3.17 (m, 1H), 2.99 (dd, J¼17.4 and 1.5 Hz, 1H); 13
C
d
7.42 (d, J¼7.2 Hz, 2H), 7.31–7.17 (m, 3H), 7.05 (d, J¼6.3 Hz, 1H),
NMR (75 MHz, CDCl3):
d
167.5,158.3,141.7,139.8,134.8,134.3,128.9,
6.36 (dd, J¼5.7 and 2.7 Hz, 1H), 3.70 (s, 3H), 2.94–2.76 (m, 2H), 2.54
128.5, 128.3,128.1, 125.6,119.6,113.8, 55.1, 51.7, 36.1, 34.7. IR n :
/cmꢁ1
(d, J¼17 Hz, 1H), 0.95 (d, J¼6.6 Hz, 3H); 13C NMR (75 MHz, CDCl3):
2949 (m),1709 (s),1608 (m),1560 (m),1510 (m),1435 (m),1082 (m),
831 (m), 760 (m), 696 (m); MS (ESI, positive mode, m/z): 375
(MþMeOHþNaþ), 343 (MþNaþ). Anal. calcd for C21H20O3: C, 78.73;
H, 6.29. Found: C, 78.80; H, 6.29.
d 167.6, 141.3, 140.3, 132.8, 131.5, 128.5, 128.1, 125.4, 119.0, 51.5, 33.3,
26.5, 17.7. IR n
/cmꢁ1: 2954 (m), 1705 (s), 1560 (m), 1435 (m), 1089
(m), 753 (m), 693 (m); MS (ESI, positive mode, m/z): 229 (MþHþ).
HRMS (EI) calcd for C15H16O2 (Mþ): 228.1150. Found: 228.1147.
4.2.5. 6-(2-Bromo-phenyl)-4-phenyl-cyclohexa-1,3-
dienecarboxylic acid methyl ester 5d
4.2.10. 4-Phenyl-6-styryl-cyclohexa-1,3-dienecarboxylic acid
methyl ester 5i
Yield 93% (a white solid, mp 143–144 ꢀC, 66 h); 1H NMR
Yield 71% (colorless oil, 60 h); 1H NMR (300 MHz, CDCl3, TMS):
(300 MHz, CDCl3, TMS):
d
7.58–7.55 (m, 2H), 7.37–7.22 (m, 5H),
d
7.52 (d, J¼6.9 Hz, 2H), 7.39–7.13 (m, 9H), 6.52–6.44 (m, 2H), 6.23

L.-W. Ye et al. / Tetrahedron 64 (2008) 8149–8154
8153
(dd, J¼15.9 and 7.5 Hz, 1H), 3.78 (s, 3H), 3.71 (t, J¼7.5 Hz, 1H), 3.07–
2.89 (m, 2H); 13C NMR (75 MHz, CDCl3):
167.3, 141.8, 139.7, 137.3,
133.9, 129.9, 128.7, 128.6, 128.4, 128.3, 127.8, 127.1, 126.2, 125.6,
119.5, 51.7, 34.8, 32.0. IR
/cmꢁ1: 2948 (m), 1705 (s), 1557 (m), 1434
4.2.16. 6-Phenyl-cyclohexa-1,3-dienecarboxylic acid
d
methyl ester 5o
Yield 81% (colorless oil, 56 h); 1H NMR (300 MHz, CDCl3, TMS):
d 7.29–7.17 (m, 6H), 6.18–6.12 (m, 1H), 6.02–5.96 (m, 1H), 4.01 (dd,
n
(m), 1267 (m), 1085 (s), 757 (m), 693 (m); MS (ESI, positive mode,
m/z): 371 (MþMeOHþNaþ), 339 (MþNaþ), 317 (MþHþ). HRMS (EI)
calcd for C22H20O2 (Mþ): 316.1463. Found: 316.1458.
J¼10.5 and 1.2 Hz, 1H), 3.68 (s, 3H), 2.95–2.83 (m, 1H), 2.61–2.52
(m, 1H); 13C NMR (75 MHz, CDCl3):
167.5, 142.6, 133.8, 131.7, 129.1,
128.3, 127.2, 126.6, 123.7, 51.7, 35.6, 32.1. IR
/cmꢁ1: 2950 (m), 1709
d
n
(s), 1575 (m), 1435 (m), 1092 (m), 699 (m); MS (EI, m/z, rel in-
tensity): 214 (Mþ, 13.8), 57 (100). HRMS (EI) calcd for C14H14O2
(Mþ): 214.0994. Found: 214.0992.
4.2.11. 6-Phenyl-4-styryl-cyclohexa-1,3-dienecarboxylic acid
methyl ester 5j
Yield 65% (a white solid, mp 113–114 ꢀC, 58 h); 1H NMR
(300 MHz, CDCl3, TMS):
d
7.43–7.12 (m,11H), 6.89 (d, J¼16.5 Hz,1H),
4.2.17. 6-Methyl-cyclohexa-1,3-dienecarboxylic acid
methyl ester 5p8f
6.67 (d, J¼16.2 Hz, 1H), 6.24 (d, J¼6.0 Hz, 1H), 4.17 (t, J¼5.7 Hz, 1H),
3.70 (s, 3H), 2.97 (d, J¼5.7 Hz, 2H); 13C NMR (75 MHz, CDCl3):
d
167.3,
Yield 76% (colorless oil, 65 h); 1H NMR (300 MHz, CDCl3, TMS):
143.2,140.4,136.8,134.5,130.7,129.6,129.4,128.9,128.7,128.4,128.1,
d
6.98–6.96 (m, 1H), 6.03 (t, J¼3.0 Hz, 2H), 3.76 (s, 3H), 2.85–2.75
127.1,126.7,124.1, 51.7, 36.7, 31.2. IR
n
/cmꢁ1: 2948 (m),1704 (s),1542
(m,1H), 2.57–2.48 (m, 1H), 2.22–2.14 (m, 1H), 0.99 (d, J¼7.2 Hz, 3H);
(m),1434 (m),1263 (m),1074 (s), 750 (m), 697 (m); MS (ESI, positive
mode, m/z): 371 (MþMeOHþNaþ), 339 (MþNaþ), 317 (MþHþ).
HRMS (EI) calcd for C22H20O2 (Mþ): 316.1463. Found: 316.1465.
13C NMR (75 MHz, CDCl3):
30.6, 25.2, 17.6.
d 167.7, 132.2, 131.9, 131.6, 122.9, 51.5,
4.2.18. 5-Benzoyl-4,6-diphenyl-cyclohexa-1,3-dienecarboxylic acid
methyl ester 5q
4.2.12. 4-Methyl-6-phenyl-cyclohexa-1,3-dienecarboxylic acid
methyl ester 5k
Yield 66% (a white solid, mp 125–126 ꢀC, 70 h); 1H NMR
Yield 72% (a white solid, mp 70–71 ꢀC, 72 h); 1H NMR (300 MHz,
(300 MHz, CDCl3, TMS):
7.39–7.24 (m, 8H), 6.92 (d, J¼6.0 Hz, 1H), 4.95 (s, 1H), 4.38 (s, 1H),
3.63 (s, 3H); 13C NMR (75 MHz, CDCl3):
195.7, 166.6, 141.7, 139.2,
138.9, 134.5, 134.0, 133.5, 129.0, 128.9 (3), 128.9 (2), 128.6, 128.5,
127.5, 127.2, 127.1, 125.6, 123.0, 52.1, 51.7, 41.3. IR
/cmꢁ1: 2948 (m),
d
8.07 (d, J¼7.2 Hz, 2H), 7.67–7.42 (m, 6H),
CDCl3, TMS):
d 7.26–7.17 (m, 6H), 5.92–5.90 (m, 1H), 4.00 (d,
J¼10.2 Hz, 1H), 3.67 (s, 3H), 2.88 (dd, J¼18.0 and 10.8 Hz, 1H), 2.36
d
(d, J¼18.0 Hz, 1H), 1.79 (s, 3H); 13C NMR (75 MHz, CDCl3):
d 167.6,
143.5, 142.7, 134.9, 128.3, 127.0, 126.5 (1), 126.4 (6), 118.9, 51.5, 37.4,
n
36.7, 23.8. IR
n
/cmꢁ1: 2949 (m), 1709 (s), 1589 (s), 1435 (m), 1076
1707 (s), 1596 (m), 1436 (m), 1260 (m), 1082 (s), 751 (m), 697 (m);
MS (ESI, positive mode, m/z): 395 (MþHþ). Anal. calcd for C27H22O3:
C, 82.21; H, 5.62. Found: C, 82.58; H, 5.59.
(m), 760 (m), 699 (m); MS (ESI, positive mode, m/z): 283
(MþMeOHþNaþ), 251 (MþNaþ), 229 (MþHþ). HRMS (EI) calcd for
C
15H16O2 (Mþ): 228.1150. Found: 228.1152.
4.2.19. 1,3-Dimethoxy-5-[5-(4-methoxy-phenyl)-cyclohexa-2,4-
dienyl]-benzene 5r
4.2.13. 5-Phenyl-cyclohexa-1,3-diene-1,4-dicarboxylic acid
dimethyl ester 5l
Yield 59% (a white solid, mp 74–75 ꢀC, 31 h); 1H NMR (300 MHz,
Yield 99% (a white solid, mp 77–78 ꢀC, 46 h); 1H NMR (300 MHz,
CDCl3, TMS):
d
7.37 (d, J¼9.0 Hz, 2H), 6.85 (d, J¼8.7 Hz, 2H), 6.50 (d,
CDCl3, TMS):
J¼9.9 and 2.4 Hz, 1H), 3.72 (s, 3H), 3.71 (s, 3H), 3.08–2.87 (m, 2H);
13C NMR (75 MHz, CDCl3):
166.7, 166.6, 141.4, 134.5, 132.3, 131.2,
128.5, 127.1, 126.9, 52.0 (4), 51.9 (6), 36.5, 30.7. IR
/cmꢁ1: 2951 (m),
d
7.36 (d, J¼6.3 Hz, 1H), 7.27–7.16 (m, 6H), 4.17 (dd,
J¼2.4 Hz, 2H), 6.35–6.28 (m, 2H), 6.22–6.16 (m, 1H), 5.85 (dd, J¼9.6
and 3.3 Hz, 1H), 3.79 (s, 3H), 3.77–3.65 (m, 7H), 2.92–2.69 (m, 2H);
d
13C NMR (75 MHz, CDCl3):
d
160.7, 158.9, 148.0, 135.3, 133.2, 128.5,
n
126.1,125.5,118.5,113.7,105.6, 98.2, 55.2, 41.4, 34.6. IR
n
/cmꢁ1: 2930
1712 (s), 1641 (m), 1435 (m), 1092 (m), 734 (m), 700 (m); MS (EI,
(m), 1606 (s), 1512 (m), 1460 (m), 1154 (m), 1065 (m), 831 (m), 750
(m); MS (EI, m/z, rel intensity): 322 (Mþ, 100), 171 (53.8). Anal. calcd
for C21H22O3: C, 78.23; H, 6.88. Found: C, 78.20; H, 6.94.
m/z, rel intensity): 272 (Mþ, 44.8), 213 (100). HRMS (EI) calcd for
C
16H16O4 (Mþ): 272.1049. Found: 272.1052.
4.2.14. 5-Methyl-cyclohexa-1,3-diene-1,4-dicarboxylic acid 1-ethyl
ester 4-methyl ester 5m
4.3. Representative procedure for the synthesis of 4,
6-diphenyl-cyclohexa-1,3-dienecarbaldehyde 6
Yield 72% (colorless oil, 54 h); 1H NMR (300 MHz, CDCl3, TMS):
d
7.09–7.03 (m, 2H), 4.25 (q, J¼7.2 Hz, 2H), 3.78 (s, 3H), 3.01–2.90
(m, 1H), 2.71–2.50 (m, 2H), 1.33 (t, J¼7.2 Hz, 3H), 0.99 (d, J¼7.2 Hz,
3H); 13C NMR (75 MHz, CDCl3):
166.8 (7), 166.8 (5), 137.9, 131.4,
130.4, 60.8, 51.9, 29.2, 26.3, 17.8, 14.2. IR
/cmꢁ1: 2959 (m), 1709 (s),
4.3.1. Preparation of 4,6-diphenyl-cyclohexa-1,3-diene-
carbaldehyde 6
d
DIBAL-H (1.0 M in toluene, 1.5 mL, 1.5 mmol) was added drop-
wise to a solution of 5a (145 mg, 0.50 mmol) in dry dichloro-
methane (2 mL) at ꢁ78 ꢀC. After 1 h, the reaction mixture was
warmed to 0 ꢀC and quenched with 5 mL of Rochelle’s salt solution.
The mixture was stirred vigorously for 2 h, the layers were sepa-
rated, and the aqueous layer was extracted with dichloromethane
(2ꢂ10 mL). The organic layers were dried with sodium sulfate and
concentrated to give the crude alcohol, which was used directly in
the next step.
n
1437 (m), 1259 (m), 1095 (m), 740 (m); MS (EI, m/z, rel intensity):
224 (Mþ, 14.0), 91 (100). HRMS (EI) calcd for C12H16O4 (Mþ):
224.1049. Found: 224.1042.
4.2.15. 4-(Dimethoxy-phosphoryl)-6-methyl-cyclohexa-1,3-
dienecarboxylic acid methyl ester 5n
Yield 51% (colorless oil, 52 h); 1H NMR (300 MHz, CDCl3, TMS):
d
7.06–6.90 (m, 2H), 3.82 (s, 3H), 3.79 (d, J¼6.0 Hz, 3H), 3.75 (d,
In a flame-dried round bottom flask, a solution of the obtained
crude alcohol was dissolved in dichloromethane (5 mL), Dess–
Martin periodinane (DMP) (254 mg, 0.60 mmol) was added to the
solution directly and the solution was then allowed to stir at am-
bient temperature for 10 min. The solution was filtered through
Celite 545 and then concentrated in vacuo. The residue was sub-
jected to column chromatography to provide 61a as pale yellow
J¼5.7 Hz, 3H), 3.00–2.93 (m, 1H), 2.61–2.50 (m, 1H), 2.45–2.36 (m,
1H), 1.02 (d, J¼6.9 Hz, 3H); 13C NMR (75 MHz, CDCl3):
d 137.6 (d,
J¼4.0 Hz), 135.1 (d, J¼10.4 Hz), 132.0 (d, J¼11.3 Hz), 129.5 (d, J¼
19.3 Hz), 126.8, 52.5 (t, J¼5.1 Hz), 52.0 (d, J¼0.9 Hz), 29.8 (d,
J¼7.9 Hz), 25.6 (d, J¼8.3 Hz), 17.3 (d, J¼1.1 Hz). IR
n
/cmꢁ1: 2956 (m),
1709 (s), 1438 (m), 1258 (m), 1054 (m), 827 (m); MS (ESI, positive
mode, m/z): 315 (MþMeOHþNaþ), 283 (MþNaþ), 261 (MþHþ).
HRMS (EI) calcd for C11H17O5P (Mþ): 260.0814. Found: 260.0818.
liquid. Yield 119 mg (92%); 1H NMR (300 MHz, CDCl3, TMS):
(s, 1H), 7.45 (dd, J¼8.1 and 1.8 Hz, 2H), 7.36–7.05 (m, 9H), 6.63 (dd,
d 9.58

8154
L.-W. Ye et al. / Tetrahedron 64 (2008) 8149–8154
Sommermeyer, H.; Glaser, T.; Wittka, R.; De Vry, J.-M.-V. EP 698597, 1996; Chem.
Abstr. 1996, 124, 342867.
J¼6.0 and 2.4 Hz, 1H), 4.22 (dd, J¼9.0 and 2.1 Hz, 1H), 3.24–3.05 (m,
2H); 13C NMR (75 MHz, CDCl3):
192.0, 145.3, 143.4, 142.3, 139.2,
138.3, 128.9, 128.6, 128.4, 127.0, 126.7, 125.7, 119.7, 34.2, 33.9. IR
d
2. (a) Hong, B.-C.; Wu, M.-F.; Tseng, H.-C.; Huang, G.-F.; Su, C.-F.; Liao, J.-H. J. Org.
Chem. 2007, 72, 8459; (b) Vosburg, D. A.; Weiler, S.; Sorensen, E. J. Angew. Chem.,
Int. Ed. 1999, 38, 971; (c) Maurinsh, Y.; Schraml, J.; Winter, H. D.; Blaton, N.;
Peeters, O.; Lescrinier, E.; Rozenski, J.; Aerschot, A. V.; Clercq, E. D.; Busson, R.;
Herdewijn, P. J. Org. Chem. 1997, 62, 2861; (d) Davies, S. G.; Bhalay, G. Tetra-
hedron: Asymmetry 1996, 7, 1595; (e) Urones, J. G.; Marcos, I. S.; Basabe, P.; Diez,
D.; Garrido, N. M. Phytochemistry 1994, 35, 713.
3. (a) Hong, B.-C.; Wu, M.-F.; Tseng, H.-C.; Liao, J.-H. Org. Lett. 2006, 8, 2217; (b)
Newman, L. M.; Garcia, H.; Hudlicky, T.; Selifonov, S. A. Tetrahedron 2004, 60,
729; (c) Stratakis, M.; Stavroulakis, M.; Sofikiti, N. J. Phys. Org. Chem. 2003, 16,
16; (d) Xi, Z.; Li, Z.; Umeda, C.; Guan, H.; Li, P.; Kotora, M.; Takahashi, T.
Tetrahedron 2002, 58, 1107; (e) Saito, S.; Sone, T.; Murase, M.; Yamamoto, H.
J. Am. Chem. Soc. 2000, 122, 10216; (f) Climent, M.-J.; Miranda, M. A.; Roth, H. D.
Eur. J. Org. Chem. 2000, 8, 1563.
4. For reviews, please see: (a) Kolodiazhnyi, O. I. Phosphorus Ylides: Chemistry and
Application in Organic Synthesis; Wiley-VCH: New York, NY, 1999; (b) Maryanoff,
B. E.; Reitz, A. B. Chem. Rev. 1989, 89, 863; Selected recent examples, see: (c)
Robiette, R.; Richardson, J.; Aggarwal, V. K.; Harvey, J. N. J. Am. Chem. Soc. 2006,
128, 2394; (d) Robiette, R.; Richardson, J.; Aggarwal, V. K.; Harvey, J. N. J. Am.
Chem. Soc. 2005, 127, 13468; (e) Aggarwal, V. K.; Fulton, J. R.; Sheldon, C. G.; de
Vincente, J. J. Am. Chem. Soc. 2003, 125, 6034.
5. For reviews, please see: (a) Ye, S.; Tang, Y.; Sun, X.-L. Synlett 2005, 2720; (b)
Lebel, H.; Marcoux, J.-F.; Charette, A. B. Chem. Rev. 2003, 103, 977; (c) Dai, L.-X.;
Hou, X.-L.; Zhou, Y.-G. Pure Appl. Chem. 1999, 71, 369; (d) Li, A.-H.; Dai, L.-X.;
Aggarwal, V. K. Chem. Rev. 1997, 97, 2641; Selected recent examples, see: (e)
Johansson, C. C. C.; Bremeyer, N.; Ley, S. V.; Owen, D. R.; Smith, S. C.; Gaunt, M. J.
Angew. Chem., Int. Ed. 2006, 45, 6024; (f) Aggarwal, V. K.; Grange, E. Chem. Eur. J.
2006, 12, 568; (g) Kunz, R. K.; Macmillan, D. W. C. J. Am. Chem. Soc. 2005, 127,
3240; (h) Papageorgious, C. D.; Cubillo de Dios, M. A.; Ley, S. V.; Gaunt, M. J.
Angew. Chem., Int. Ed. 2004, 43, 4641; (i) Bremeyer, N.; Smith, S. C.; Gaunt, M. J.
Angew. Chem., Int. Ed. 2004, 43, 2681; (j) Papageorgious, C. D.; Ley, S. V.; Gaunt,
M. J. Angew. Chem., Int. Ed. 2003, 42, 828.
6. For reviews, see: (a) Aggarwal, V. K.; Winn, C. L. Acc. Chem. Res. 2004, 37, 611;
Selected recent examples, see: (b) Forbes, D. C.; Amin, S. R.; Bean, C. J.; Standen,
M. C. J. Org. Chem. 2006, 71, 8287; (c) Davoust, M.; Brie`re, J.-F.; Jaffre`s, P.-A.;
Metzner, P. J. Org. Chem. 2005, 70, 4166; (d) Aggarwal, V. K.; Bae, I.; Lee, H.-Y.;
Richardson, J.; Williams, D. T. Angew. Chem., Int. Ed. 2003, 42, 3274; (e)
Aggarwal, V. K.; Alonso, E.; Bae, I.; Hynd, G.; Lydon, K. M.; Palmer, M. J.; Patel,
M.; Porcelloni, M.; Richardson, J.; Stenson, R. A.; Studley, J. R.; Vasse, J.-L.; Winn,
C. L. J. Am. Chem. Soc. 2003, 125, 10926; (f) Li, K.; Deng, X.-M.; Tang, Y. Chem.
Commun. 2003, 2074; (g) Li, K.; Huang, Z. Z.; Tang, Y. Tetrahedron Lett. 2003, 44,
4137.
7. For recent examples, see: (a) Morton, D.; Pearson, D.; David, F.; Field, R. A.;
Stockman, R. A. Chem. Commun. 2006, 1833; (b) Zheng, J.-C.; Liao, W.-W.; Sun,
X.-X.; Sun, X.-L.; Tang, Y.; Dai, L.-X.; Deng, J.-G. Org. Lett. 2005, 7, 5789; (c)
Morton, D.; Pearson, D.; Field, R. A.; Stockman, R. A. Org. Lett. 2004, 6, 2377; (d)
Liao, W.-W.; Deng, X.-M.; Tang, Y. Chem. Commun. 2004, 1516; (e) Aggarwal,
V. K.; Vasse, J.-L. Org. Lett. 2003, 5, 3987.
n
/cmꢁ1: 2811 (m), 1667 (s), 1553 (m), 1493 (m), 1172 (m), 758 (m),
698 (m); MS (EI, m/z, rel intensity): 260 (Mþ, 100), 231 (72.1).
4.4. Representative procedure for the DDQ oxidation
4.4.1. Preparation of fungicide 7
DDQ (70 mg, 0.31 mmol) was added to a mixed solution of 5g
(96 mg, 0.25 mmol) in toluene (11 mL) and the resulting mixture
was stirred at 120 ꢀC for 35 h. After the reaction was complete
(monitored by TLC), the reaction mixture was passed through
a glass funnel with a thin layer of silica gel, and eluted with ethyl
acetate. The filtrate was concentrated and the residue was purified
by flash column chromatography to afford 712 as pale yellow oil.
Yield 94%; 1H NMR (300 MHz, CDCl3, TMS):
d
7.87 (d, J¼7.5 Hz, 1H),
7.62–7.55 (m, 4H), 7.15 (t, J¼8.4 Hz, 2H), 6.92–6.89 (m, 3H), 4.14 (q,
J¼7.2 Hz, 2H), 3.93 (s, 3H), 3.89 (s, 3H), 1.08 (t, J¼7.2 Hz, 3H); 13C
NMR (75 MHz, CDCl3):
d
168.6, 148.4 (d, J¼2.1 Hz), 142.7 (d,
J¼7.7 Hz), 135.9 (d, J¼3.2 Hz), 134.0, 130.3, 130.0, 129.1, 128.9, 128.8,
128.7, 125.3, 120.6, 115.9, 115.6, 111.7, 110.7, 60.9, 55.8 (2), 55.7 (9),
13.8. IR n
/cmꢁ1: 2936 (m), 1709 (s), 1604 (m), 1508 (m), 1028 (m),
830 (m); MS (EI, m/z, rel intensity): 380 (Mþ, 100), 220 (12.5).
4.4.2. Preparation of compound 813
Yield 96% (pale yellow oil, 17 h); 1H NMR (300 MHz, CDCl3,
TMS):
6.90 (d, J¼9.0 Hz, 2H), 6.69 (d, J¼2.1 Hz, 2H), 6.39 (t, J¼2.4 Hz, 1H),
3.75 (s, 9H); 13C NMR (75 MHz, CDCl3):
161.0, 143.5, 141.7, 141.3,
133.5, 129.1, 129.0, 128.2, 126.0, 125.7, 125.5, 114.2, 105.5, 99.3, 55.4,
55.3. IR
/cmꢁ1: 2960 (m), 1594 (s), 1517 (m), 1461 (m), 1247 (m),
d
7.66 (d, J¼1.2 Hz, 1H), 7.65–7.39 (m, 4H), 7.16–7.06 (m, 1H),
d
n
1155 (m), 1038 (m), 794 (m), 695 (m), 574 (m); MS (EI, m/z, rel in-
tensity): 320 (Mþ, 100), 305 (10.5).
Acknowledgements
We are grateful for the financial support from the Natural Sci-
ences Foundation of China, the Major State Basic Research De-
velopment Program (Grant No. 2006CB806105), the Chinese
Academy of Sciences, and the Science and Technology Commission
of Shanghai Municipality.
8. (a) Moorhoff, C. M. Synlett 1997, 126; (b) Yadav, J. S.; Srinivas, D. Tetrahedron Lett.
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(h) Howe, R. K. J. Am. Chem. Soc. 1971, 93, 3457.
9. (a) Ye, L.-W.; Sun, X.-L.; Wang, Q.-G.; Tang, Y. Angew. Chem., Int. Ed. 2007, 46,
5951; (b) Li, C.-Y.; Wang, X.-B.; Sun, X.-L.; Tang, Y.; Zheng, J.-C.; Xu, Z.-H.; Zhou,
Y.-G.; Dai, L.-X. J. Am. Chem. Soc. 2007, 129, 1494; (c) Ye, L.-W.; Sun, X.-L.; Li,
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Supplementary data
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2008.06.048.
References and notes
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