Stereoselective synthesis of substituted all-trans 1,3,5,7-octatetraenes by a modified Ramberg-B?cklund reaction

Article abstract of DOI:10.1016/S0040-4020(01)01224-8

The reaction of allylic dienylic sulfone with dibromodifiuoromethane in the presence of alumina-supported KOH in dichloromethane solution results in facile rearrangement affording the corresponding all-trans 1,3,5,7-octatetraenes in excellent yields. This result shows that the double bonds of stereochemically defined allylic dienylic sulfone retain their stereochemistry and the newly formed double bond has an (E)-configurafion in the modified Rambeig-B?cklund procedure.

Full text of DOI:10.1016/S0040-4020(01)01224-8

TETRAHEDRON
Pergamon
Tetrahedron 58 (2002) 1301±1307
Stereoselective synthesis of substituted all-trans
È
1,3,5,7-octatetraenes by a modi®ed Ramberg±Backlund reaction
Xiao-Ping Caop
Department of Chemistry and National Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000,
People's Republic of China
Received 21 August 2001; revised 8 November 2001; accepted 6 December 2001
AbstractÐThe reaction of allylic dienylic sulfone with dibromodi¯uoromethane in the presence of alumina-supported KOH in dichloro-
methane solution results in facile rearrangement affording the corresponding all-trans 1,3,5,7-octatetraenes in excellent yields. This result
shows that the double bonds of stereochemically de®ned allylic dienylic sulfone retain their stereochemistry and the newly formed double
È
bond has an (E)-con®guration in the modi®ed Ramberg±Backlund procedure. q 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
trienediolates generated from hexa-2,4-dienoic acid to
a,b-unsaturated ketone, which underwent a facile acid-
catalyzed dehydration to give retinoic acid. Paquette8 also
reported an interesting [212] cycloreversion of endo,
endo-7,8-diphenylbicyclo[4.1.1]octa-2,4-diene, which on
irradiation gave all-trans-1,8-diphenyl-1,3,5,7-octatetraene.
Prompted by these studies, we wish to report our stereo-
selective construction section of octatetraenes in this paper.
The conjugated 1,3,5,7-tetraene is an important structural
unit in various classes of natural products such as lipoxin
B4, retinoic acid, navenone C, and chrysophysarin A.1 It has
also been shown that conjugated polyenes are potentially
useful compounds for electronic and non-linear optical
materials.2 In the literature, there are only a few general
strategies for the stereocontrolled construction of the tetra-
ene unit. This is mainly due to the instability and the facile
(E)±(Z) isomerization of tetraene systems.3 Synthetic
methods for the construction of conjugated octatetraenes
that relied on the Wittig ole®nation invariably gave a
mixture of geometrical isomers of octatetraenes.4 Akhtar5
utilized a combination of nucleophilic displacement by
lithium phenylacetylide with 1,4-dibromobutene and
base-catalyzed isomerization, and then copper-catalyzed
coupling of styrylacetylene, followed by reduction to
prepare the geometrical isomers of 1,8-diphenyl-1,3,5,7-
octatetraene. Soullez6 described the bromine±lithium
exchange of v-bromo polyenol ethers, generated in situ
from 5-bromopenta-2,4-dienal, followed by condensation
with carbonyl compounds to give conjugated octatetraenes.
However, it is only very recently that the stereoselective
synthesis of octatetraenes began to emerge. Alami7 reported
that sequential palladium copper co-catalyzed coupling of
terminal acetylenes and trans-enyne to a stereochemically
de®ned 1,2-dichloroethylene, followed by selective syn-
reduction of the triple bond moieties with activated zinc
gave stereochemically-de®ned octatetraenes. This synthetic
method was applied to an ef®cient convergent synthesis of
lipoxin B4.1d Mestres1e reported the addition of lithium
2. Results and discussion
In our previous studies9 on the stereoselective synthesis of
polyenes, we reported that conjugated trienes and enediynes
È
could be prepared by our modi®ed Ramberg±Backlund
reaction, from the corresponding diallylic sulfones and
dipropargylic sulfones. This synthetic method was applied
to the synthesis of natural products containing a triene unit
such as Galbanolenes. Reported herein are our ®ndings
that allylic dienylic sulfones, when subjected to our
È
Ramberg±Backlund reaction conditions, provide all-trans
octatetraenes in good yield. The procedure reported here
started with an allylic dienylic sulfone 1 (Scheme 1), with
three of the four double bonds already in place and the
fourth one to be realized by our modi®ed Ramberg±
È
Baklund procedure. This disconnection approach relied on
the stereocontrolled synthesis of an allylic dienylic sulfone
1, which was in turn prepared by a stereocontrolled prepa-
ration of dienylic halides 2 and dienylic thiolacetate 3.
There are two general approaches for the assembly of allylic
dienylic sul®des 4 from which the corresponding sulfone 1
could be obtained after oxidation. One makes use of the
coupling reaction between a stereode®ned dienylic thio-
lacetate 3 to a geometrically pure allylic halide 5. T he
alternative is to couple an allylic thiolacetate 6 to a dienylic
halide 2. These two procedures invariably demanded a
È
Keywords: octatetraenes; allylic dienylic sulfones; Ramberg±Backlund
reaction.
Fax: 186-931-8912582; e-mail: wangql@lzu.edu.cn
p
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(01)01224-8

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X.-P. Cao / Tetrahedron 58 (2002) 1301±1307
1
2
4
5
3
1
2
3
4
5
È
Scheme 1. Synthesis of 1,3,5,7-octatraenes via Ramberg±Backlund reaction: (a) R ˆC6H5, R , R , R ˆH, R ˆMe; (b) R ˆC6H5, R , R ˆMe, R , R ˆH;
(c) R1ˆC6H5, R2, R4ˆMe, R3, R5ˆH; (d) R1ˆC6H5, R2, R4, R5ˆMe, R3ˆH; (e) R1, R4ˆC6H5, R2, R3, R5ˆH; (f) R1, R4ˆC6H5, R2ˆMe, R3, R5ˆH;
(g) R1ˆC6H5, R2, R3, R5ˆH, R4ˆSiMe3.
stereoselective preparation of dienyl alcohol 7, the common
intermediate for the requisite halide 2 and thiolacetate 3.
Several synthetic methods were tried. In the end, the
dienylic alcohol 7 was secured by the Wittig reaction
followed by reduction.
azodicarboxylate (DIAD), or it could be converted to the
corresponding dienylic chloride 2 by reaction with thionyl
chloride. In situ cleavage of the acetyl moiety of 3 with
potassium hydroxide in methanol followed by allylation of
the resulting dienylic thiol with stereode®ned allyl chloride
5 in benzene, provided the allylic dienylic sul®de 4 in good
yield. Alternatively, coupling of the dienylic chloride 2 with
the thiolacetate 6 prepared from the allylic alcohol 9 also
afforded the allylic dienylic su®de 4 in good yield (Table 1)
with no SN20 substitution products. As expected, the stereo-
chemistry of the double bonds was retained during these
transformations. The sul®de 4 could be transformed into
the corresponding sulfone 1 with retention of double bond
geometries by oxone oxidation in dichloromethane or
The starting material was the aromatic aldehyde 8 (R1ˆPh,
R2ˆH or Me). Reaction of 8 with ethyl (triphenylphosphor-
anylidene) acetate afforded the dienylic ester with good
(E)-selectivity, followed by reduction of the ester moiety
with DIBAL to furnish the dienylic alcohol 7 in quantitative
yield. This dienylic alcohol 7 was converted to the thio-
lacetate 3 via the Mitsunobu10 reaction with thiolacetic
acid in the presence of triphenylphosphine and diisopropyl
Table 1. Yields (%) of sul®des 4, sulfones 1, and tetraenes 10
Entry
Sul®de 4
Yields
Sulfone 1
Yields
Tetraene 10
Yields
(coupling constants
of newly formed
CvC bond)
a
81
93
90
85
87 (Jˆ15.5)
89 (Jˆ15.6)
b
c
81
90
66
84
83
70
92 (Jˆ15.6)
90 (Jˆ15.5)
90a
d
e
f
82
81
90
90
80a
g
87 (Jˆ15.0)
a
Coupling constants cannot be resolved (500 MHz NMR) due to overlapping signals.

X.-P. Cao / Tetrahedron 58 (2002) 1301±1307
1303
methanol in excellent yield. Subjecting the allylic dienylic
sulfone 1 to our previously described modi®ed Ramberg±
spectrometer. Aromatic aldehydes and allylic alcohols
were purchased from Aldrich Chemical Company and
used without further puri®cation.
È
Backlund reaction protocol (CBr2F2, KOH-on-Al2O3, CH2Cl2)
invariably gave the geometrically de®ned 1,3,5,7-octa-
tetraene 10 in good yield with the newly formed double
bond having the (E)-con®guration. Examination of the 13C
NMR spectra of the products indicated the presence of one
isomer in each case. Thus, the stereoselectivity of the
reaction was .95% for this reaction.
4.2. General procedure for the preparation of allyl
dienylic sul®des 4
Method A. The stereochemically pure dienylic thioacetate
3 (5 mmol) was added to a solution of KOH (5 mmol) and
Na2S2O3´5H2O (10 mg) in methanol (10 ml). The resulting
mixture was stirred at 08C under nitrogen for 30 min. The
methanol was removed in vacuo, and the solvent was
changed to benzene (10 ml). To this thiolate solution was
then added dropwise the stereochemically pure allylic
halide 5 (5 mmol) over a period of 5 min and stirring
was continued for 1 h at 208C. The reaction mixture
was poured into water (10 ml) and extracted with
Et2O (3£20 ml). The combined extracts were washed
(saturated NaCl solution), dried (MgSO4), ®ltered and
concentrated in vacuo. Flash chromatography of the
residue over silica gel (hexane/ethyl acetateˆ100:1)
afforded the sul®de 4.
The issue of stereochemistry of the newly formed carbon
carbon double bond was determined by H NMR spectro-
1
scopy. Apart from 10e and 10f, the (E)-con®guration of the
newly formed carbon carbon double bond in all cases was
3
readily diagnosed by large JHCvCH coupling constants
(15.6±15.0 Hz) between the pertinent ole®nic protons.
The other three double bonds, again retained their stereo-
chemical integrity as suggested by H NMR spectroscopy.
1
For the known diphenyl octatetraene 10e, the stereo-
chemistry was resolved by comparison of its physical
and spectroscopic properties to those reported in the
literatures.5,8 The diphenyl substituted tetraene derivatives
10e and 10f have better stability than the other tetraenes
towards light and heat. The terminal tetraenes 10a and
10b were less stable and tended to decompose in standing
at rt.
Method B. The stereochemically pure allylic thioacetate 6
(5 mmol) was added to a solution of KOH (5 mmol) and
Na2S2O3´5H2O (10 mg) in methanol (10 ml). The resulting
mixture was stirred at 08C under nitrogen for 30 min. The
methanol was removed in vacuo, and the solvent was
changed to benzene (10 ml). To this thiolate solution was
then added dropwise the stereochemically pure dienylic
halide 2 (5 mmol) over a period of 5 min and stirring was
continued for 1 h at 208C. The reaction mixture was then
worked up following the same procedure as that described
in Method A.
3. Conclusion
We have presented a rapid route to stereochemically de®ned
octatetraenes. The synthetic transformation utilizes readily
available aromatic aldehydes and allylic alcohols as starting
materials. The synthetic routes are facile and the reactions
can be performed in molar scales. We have also shown that
the double bonds of stereochemically de®ned allylic
dienylic sulfone retain their stereochemistry, and that the
newly formed double bond has an (E)-con®guration in our
The following allylic dienylic sul®des were prepared:
4.2.1. 2-Methyl-2-propenyl 50-phenyl-(20E,40E)-penta-
dienyl sul®de (4a). Oil (Method B, 81%). IR nmax 3022,
2910, 1646, 1371, 987, 895, 748 cm21; dH (250 MHz,
CDCl3) 7.40±7.21 (5H, m, ArH), 6.77 (1H, dd, Jˆ15.5,
10.1 Hz, 40-H), 6.50 (1H, d, Jˆ15.5 Hz, 50-H), 6.20 (1H,
dd, Jˆ15.4, 10.1 Hz, 30-H), 5.73 (1H, dt, Jˆ15.4, 7.7 Hz,
20-H), 4.89±4.88 (1H, m, 3-H), 4.84±4.83 (1H, m, 3-H),
3.15 (2H, d, Jˆ7.7 Hz, CH2S), 3.08 (2H, s, CH2S), 1.83
(3H, s, Me); dC (62.5 MHz, CDCl3) 141.2, 137.3, 132.9,
131.9, 130.0, 128.6, 128.3, 127.4, 126.3, 113.4, 38.3
(CH2S), 33.1 (CH2S), 20.8; m/z (EI) 230 (M1, 2), 174
(M12C4H8, 9), 143 (34), 131 (100), 103 (66), 91 (33%);
HRMS (EI): M1, found 230.1139. C15H18S requires
230.1129.
È
modi®ed Ramberg±Backlund procedure. This is similar
to the case of dibenzyl sulfones, diallylic sulfones, and
dipropargylic sulfones which we reported earlier.9 Other
applications of our procedure are under investigation in
our laboratories.
4. Experimental
4.1. General methods and materials
Melting points were measured on a Reichert Microscope
apparatus and are uncorrected. IR spectra were recorded
on a Nicolet 205 FT-IR spectrophotometer and reported in
wavenumbers (cm21). 1H and 13C NMR spectra were
recorded on a Bruker Cryospec WM 250 spectrometer
4.2.2. 2-Methyl-2-propenyl 40-methyl-50-phenyl-(20E,40E)-
pentadienyl sul®de (4b). Oil (Method A, 93%). (Found: C,
78.59; H, 8.30. C16H20S requires C, 78.65, H, 8.26%); IR
nmax 3022, 1597, 1213, 916, 746 cm21; dH (250 MHz,
CDCl3) 7.37±7.22 (5H, m, ArH), 6.47 (1H, s, 50-H), 6.27
(1H, d, Jˆ15.4 Hz, 30-H), 5.73 (1H, dt, Jˆ15.4, 7.9 Hz,
20-H), 4.89 (1H, s, 3-H), 4.86±4.85 (1H, m, 3-H), 3.19
(2H, d, Jˆ7.9 Hz, CH2S), 3.10 (2H, s, CH2S), 2.01 (3H, s,
Me), 1.84 (3H, d, Jˆ0.6 Hz, Me); dC (62.5 MHz, CDCl3)
141.3, 137.8, 137.7, 135.0, 130.8, 129.1, 128.0, 126.5,
125.0, 113.4, 38.2 (CH2S), 33.3 (CH2S), 20.8, 13.9; m/z
1
(250 MHz for H and 62.5 MHz for 13C) or Bruker ARX
500 spectrometer (500 MHz for 1H). Samples were
measured in CDCl3, with Me4Si as an internal standard for
1H NMR, and CDCl3 for 13C NMR. Mass spectra (MS) data
were obtained on a Finnegan MAT95 or VG 7070F mass
spectrometer. Elemental analyses were carried out by
Medac Ltd, Uxbridge, UK or the Shanghai Institute of
Organic Chemistry, People's Republic of China. UV±
Visible light spectra were recorded on a Hitachi U-2000

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X.-P. Cao / Tetrahedron 58 (2002) 1301±1307
(EI) 244 (M1, 8), 188 (M12C4H8, 31), 157 (M12C4H7S,
92), 142 (M12C5H10S, 44), 129 (M12C6H11S, 100), 115
(45), 77 (17%).
4.2.7. 5-Phenyl-(2E,4E)-pentadienyl 30-trimethylsilyl-
(20E)-propenyl sul®de (4g). Oil (Method A, 81%). IR
nmax 3022, 1597, 1213, 745 cm21; dH (250 MHz, CDCl3)
7.44±7.29 (5H, m, ArH), 6.81 (1H, dd, Jˆ15.7, 10.4 Hz,
4-H), 6.53 (1H, d, Jˆ15.7 Hz, 5-H), 6.24 (1H, dd, Jˆ15.1,
10.4 Hz, vCH), 5.98 (1H, dt, Jˆ18.4, 6.5 Hz, 20-H), 5.80
(1H, dt, Jˆ15.0, 10.4 Hz, vCH), 5.75 (1H, d, Jˆ18.4 Hz,
30-H), 3.19 (4H, d, Jˆ6.5 Hz, CH2S), 0.10 (9H, s, Si(CH3)3);
dC (62.5 MHz, CDCl3) 141.6, 137.3, 133.5, 133.0, 132.0,
130.1, 128.6, 128.3, 127.5, 126.3, 36.3 (CH2S), 32.9
(CH2S), 21.2 (Si(CH3)3); m/z (EI) 288 (M1, ,1), 43
(100%); HRMS (EI): M12H, found 287.1302. C17H23SSi
requires 287.1290.
4.2.3. (2E)-Butenyl 40-methyl-50-phenyl-(20E,40E)-penta-
dienyl sul®de (4c). Oil (Method A, 81%). IR nmax 3022,
1646, 1371, 987, 895, 748 cm21; dH (250 MHz, CDCl3)
7.37±7.21 (5H, m, ArH), 6.48 (1H, s, 50-H), 6.27 (1H, dq,
Jˆ15.4, 0.8 Hz, 30-H), 5.73 (1H, dt, Jˆ15.4, 7.4 Hz, vCH,
20-H), 5.53 (1H, dt, Jˆ15.4, 7.4 Hz, vCH), 5.42 (1H, dtq,
Jˆ15.4, 7.4, 1.1 Hz, vCH), 3.21 (2H, d, Jˆ7.4 Hz, CH2S),
3.10 (2H, d, Jˆ7.4 Hz, CH2S), 2.01 (3H, d, Jˆ1.1 Hz, Me),
1.67 (3H, d, Jˆ7.4 Hz, Me); dC (62.5 MHz, CDCl3) 137.8,
137.6, 135.1, 130.8, 129.1, 128.2, 128.1, 127.2, 126.5,
125.3, 33.3 (CH2S), 33.0 (CH2S), 17.6, 13.9; m/z (EI) 244
(M1, 9), 189 (M12C4H7, 31), 157 (M12C4H7S, 100), 142
(M12C5H10S, 22), 129 (M12C6H11S, 53), 115 (23), 91
(18%); HRMS (EI): M1, found 244.1277. C16H20S requires
244.1286.
4.2.8. Dienylic alcohol 7. To a stirred solution of ethyl-
(triphenylphosphoranylidene)acetate (100 mmol) in dry
benzene (100 ml) was added cinnamaldehyde or 4-methyl
cinnamaldehyde 8 (90 mmol) dropwise at 08C under
nitrogen. The resulting solution was stirred at rt for 5 h.
The reaction mixture was then poured into ice water and
the aqueous phase extracted with ethyl acetate (3£50 ml).
The combined organic solvents were dried (MgSO4),
®ltered, evaporated in vacuo and puri®ed by ¯ash chroma-
tography on silica gel with hexane/ethyl acetate (3:1
gradient to 1:1) as eluent to give ethyl 5-phenyl-(2E,4E)-
pentadioate (91% yield) and ethyl 4-methyl-5-phenyl-
(2E,4E)-pentadienoate (88% yield), respectively. To a
stirred solution of DIBAL (100 ml, 1.0 M in hexane) was
added the ester (50 mmol) at 08C under nitrogen. The
resulting solution was stirred at rt for 1 h. The reaction
mixture was then poured into ice water and the aqueous
phase extracted with ethyl acetate (3£50 ml). The combined
organic solvents were dried (MgSO4), ®ltered, concentrated
in vacuo to give either 5-phenyl-(2E,4E)-pentadienol (95%
yield) or 4-methyl-5-phenyl-(2E,4E)-pentadienol (91%
yield). These dienylic alcohols have already been
described.11,12 For 5-phenyl-(2E,4E)-pentadienol: IR nmax
3412, 2969, 1635, 1213, 930, 721 cm21; dH (250 MHz,
CDCl3) 7.34±7.19 (5H, m, ArH), 6.52±5.90 (4H, m,
vCH), 4.26 (2H, d, Jˆ6.0 Hz, CH2), 1.86 (1H, s, OH);
dC (62.5 MHz, CDCl3) 137.2, 132.6, 132.1, 131.6, 129.0,
128.7, 127.5, 126.4, 63.2; HRMS (EI): M1, found 160.0883.
C11H12O requires 160.0889. For 4-methyl-5-phenyl-
(2E,4E)-pentadienol: IR nmax 3401, 2987, 1610, 1213,
948, 725 cm21; dH (250 MHz, CDCl3) 7.34±7.19 (5H, m,
ArH), 6.52 (1H, s, 5-H), 6.44 (1H, d, Jˆ15.7 Hz, 3-H), 5.92
(1H, dt, Jˆ15.7, 6.0 Hz, 2-H), 4.26 (2H, d, Jˆ6.0 Hz, CH2),
2.35 (3H, s, 4-Me), 1.86 (1H, s, OH); dC (62.5 MHz, CDCl3)
137.0, 132.7, 132.5, 131.6, 129.3, 128.1, 127.6, 126.4, 63.3,
13.8; m/z (EI) 174 (M1, 23), 156 (M12H2O, 33), 143 (100),
128 (56), 115 (43), 91 (74%); HRMS (EI): M1, found
174.1039. C12H14O requires 174.1045.
4.2.4. 3-Methyl-2-butenyl 40-methyl-50-phenyl-(20E,40E)-
pentadienyl sul®de (4d). Oil (Method A, 90%). IR nmax
3012, 1488, 1291, 751 cm21; dH (250 MHz, CDCl3) 7.40±
7.22 (5H, m, ArH), 6.51 (1H, s, 50-H), 6.32 (1H, d, Jˆ
15.5 Hz, 30-H), 5.84 (1H, dt, Jˆ15.5, 7.6 Hz, 20-H), 5.30±
5.26 (1H, m, 2-H), 3.23 (2H, d, Jˆ7.6 Hz, CH2S), 3.17 (2H,
d, Jˆ7.6 Hz, CH2S), 2.05 (3H, s, Me), 1.79 (3H, s, Me), 1.71
(3H, s, Me); dC (62.5 MHz, CDCl3) 137.8, 137.4, 135.1,
130.8, 129.3, 129.1, 128.1, 126.5, 125.5, 120.7, 33.8
(CH2S), 28.8 (CH2S), 25.6, 17.8, 13.9; m/z (EI) 258 (M1,
9), 189 (M12C5H9, 46), 157 (M12C5H9S, 100), 105
(35%); HRMS (EI): M1, found 258.1434. C17H22S requires
258.1442.
4.2.5. (E)-Cinnamyl 50-phenyl-(20E,40E)-pentadienyl
sul®de (4e). Oil (Method B, 66%). IR nmax 3021, 1597,
1213, 960, 696 cm21; dH (250 MHz, CDCl3) 7.34±7.14
(10H, m, ArH), 6.72 (1H, dd, Jˆ15.4, 10.4 Hz, vCH),
6.44 (1H, d, Jˆ15.4 Hz, vCH), 6.38 (1H, Jˆ15.4 Hz,
vCH), 6.18 (1H, dd, Jˆ15.4, 10.4 Hz, vCH), 6.11 (1H,
dt, Jˆ15.4, 7.5 Hz, vCH), 5.70 (1H, dt, Jˆ15.4, 7.5 Hz,
vCH), 3.21 (2H, d, Jˆ7.5 Hz, CH2S), 3.20 (2H, d, Jˆ
7.5 Hz, CH2S); dC (62.5 MHz, CDCl3) 137.9, 137.4,
133.8, 133.1, 132.7, 130.7, 129.3 (overlapping signals),
128.9, 128.2 (overlapping signals), 127.0 (overlapping
signals), 126.6, 33.9 (CH2S), 33.6 (CH2S); m/z (EI) 292
(M1, 2), 143 (M12PhC3H4S, 40), 117 (M12PhC5H6S,
100), 91 (67), 77 (34%); HRMS (EI): M1, found
292.1277. C20H20S requires 292.1286.
4.2.6. (E)-Cinnamyl 40-methyl-50-phenyl-(20E,40E)-
pentadienyl sul®de (4f). Oil (Method A, 82%). (Found:
C, 82.35; H, 7.47. C21H22S requires C, 82.31, H, 7.24%);
IR nmax 3054, 1492, 1394, 808 cm21; dH (250 MHz, CDCl3)
7.41±7.20 (10H, m, ArH), 6.48 (1H, s, 50-H), 6.46 (1H, d,
Jˆ15.4 Hz, vCH), 6.30 (1H, d, Jˆ15.3 Hz, vCH), 6.19
(1H, dt, Jˆ15.4, 7.3 Hz, vCH), 5.74 (1H, dt, Jˆ15.3,
7.3 Hz, vCH), 3.32 (2H, d, Jˆ7.3 Hz, SCH2), 3.28 (2H,
d, Jˆ7.3 Hz, SCH2), 2.01 (3H, s, Me); dC (62.5 MHz,
CDCl3) 137.9, 137.7, 136.8, 135.1, 132.4, 130.9, 129.2,
128.5, 128.1, 127.5, 126.6, 126.3, 126.1, 125.2, 33.4 (over-
lapping signals, CH2S), 14.0 (Me); m/z (EI) 306 (M1, 5), 67
(100%).
4.2.9. Dienylic thioacetate 3 or allylic thioacetate 6. A
solution of DIAD (10 mmol) in dry benzene (10 ml) was
added to
a stirred solution of triphenylphosphine
(10 mmol) in benzene (100 ml) at 08C. The resulting red
solution was kept at 08C for 15 min and then a precooled
(08C) mixture of the stereochemically pure dienylic alcohol
7 or allyl alcohol 9 (10 mmol) and thioacetic acid (10 mmol)
in dry benzene (20 ml) was added in one portion. The
mixture was stirred at 208C for 1 h and solvent was removed
in vacuo. Flash chromatography of the residue over silica

X.-P. Cao / Tetrahedron 58 (2002) 1301±1307
1305
gel (hexane/ethyl acetateˆ10:1) afforded either the dienylic
thioacetate 3 or allylic thioacetate 6. For 4-methyl-5-
phenyl-(2E,4E)-pentadienyl thioacetate 3: (Found: C,
72.08; H, 6.74. C14H16OS requires C, 72.37, H, 6.94); IR
nmax 3067, 2965, 1635, 965, 687 cm21; dH (250 MHz,
CDCl3) 7.36±7.18 (5H, m, ArH), 6.49 (1H, s, 5-H), 6.41
(1H, d, Jˆ15.4 Hz, 3-H), 5.72 (1H, dt, Jˆ15.4, 7.0 Hz, 2-H),
3.64 (2H, d, Jˆ7.0 Hz, CH2), 2.34 (3H, s, CH3CvO), 1.96
(3H, s, CH3); dC (62.5 MHz, CDCl3) 195.0 (CvO), 138.5,
137.7, 134.9, 131.5, 129.1, 128.1, 126.6, 123.6, 31.8, 30.4,
13.8; m/z (EI) 232 (M1, 18), 189 (M12CH3CO, 13), 157
(M12CH3COS, 100), 142 (45), 129 (87), 115 (45), 105
(41), 91 (44), 77 (23%). Cinnamyl thioacetate has already
been described.13 For 2-methyl-2-propenyl thioacetate 6: IR
nmax 3022, 2910, 1646, 1371, 691 cm21; dH (250 MHz,
CDCl3) 4.89±4.88 (1H, m, 3-H), 4.84±4.83 (1H, m, 3-H),
3.08 (2H, s, CH2S), 2.34 (3H, s, CH3CvO), 1.83 (3H, s,
Me); dC (62.5 MHz, CDCl3) 190.1 (CvO), 141.2, 113.4,
38.3 (CH2S), 30.4, 20.8; m/z (EI) 130 (M1, 2), 75 (M12
C4H7, 9), 55 (100%); HRMS (EI): M1, found 130.0450.
C6H10OS requires 130.0453.
(M1, ,1), 157 (M12C4H7SO2, 100), 129 (61%); HRMS
(EI): M1, found 276.1183. C16H20O2S requires 276.1185.
4.3.3. (2E)-Butenyl 40-methyl-50-phenyl-(20E,40E)-penta-
dienyl sulfone (1c). White solid (84%). Mp 1248C; IR nmax
3051, 1414, 1292 (OvSvO), 1119 (OvSvO), 978, 758,
728 cm21; dH (250 MHz, CDCl3) 7.39±7.22 (5H, m, ArH),
6.58 (1H, s, 50-H), 6.40 (1H, d, Jˆ15.6 Hz, 30-H), 5.88 (1H,
dt, Jˆ15.6, 6.5 Hz, vCH), 5.78 (1H, dt, Jˆ15.6, 7.6 Hz,
vCH), 5.58 (1H, dtq, Jˆ15.6, 7.6, 1.6 Hz, vCH), 3.80 (2H,
d, Jˆ7.6 Hz, CH2SO2), 3.67 (2H, d, Jˆ7.6 Hz, CH2SO2),
2.03 (3H, s, Me), 1.80 (3H, d, Jˆ7.6 Hz, Me); dC
(62.5 MHz, CDCl3) 143.9, 136.9, 136.1, 134.3, 133.5,
129.0, 128.0, 126.9, 117.2, 114.1, 55.6 (CH2SO2), 55.4
(CH2SO2), 18.0 (Me), 13.6 (Me); m/z (EI, 20 eV)
276 (M1, ,1), 157 (M12C4H7SO2, 100), 91 (22%);
HRMS (EI): M1, found 276.1180. C16H20O2S requires
276.1185.
4.3.4. 3-Methyl-2-butenyl 40-methyl-50-phenyl-(20E,40E)-
pentadienyl sulfone (1d). White solid (83%). Mp 1328C; IR
nmax 2978, 1668, 1291 (OvSvO), 1119 (OvSvO), 977,
734, 695 cm21; dH (250 MHz, CDCl3) 7.38±7.22 (5H, m,
ArH), 6.57 (1H, s, 50-H), 6.50 (1H, d, Jˆ15.6 Hz, 30-H),
5.77 (1H, dt, Jˆ15.6, 7.8 Hz, 20-H), 5.32 (1H, t, Jˆ
7.8 Hz, 2-H), 3.74 (2H, d, Jˆ7.8 Hz, CH2SO2), 3.70 (2H,
d, Jˆ7.8 Hz, CH2SO2), 2.03 (3H, s, Me), 1.85 (3H, s, Me),
1.61 (3H, s, Me); dC (62.5 MHz, CDCl3) 143.0, 142.5,
137.1, 134.4, 133.7, 129.2, 128.2, 127.0, 114.3, 110.4,
56.2 (CH2SO2), 52.0 (CH2SO2), 25.9 (Me), 18.5 (Me),
13.8 (Me); m/z (EI, 20 eV) 290 (M1, ,1), 157 (M12
C5H9SO2, 100), 69 (45%); HRMS (EI): M1, found
290.1350. C17H22O2S requires 290.1341.
4.3. General procedure for the preparation of allylic
dienylic sulfones 1
A mixture of the sul®de 4 (5 mmol) and oxone (25 mmol) in
CH2Cl2/MeOH (2:1, 30 ml) was stirred at rt for 3±5 days.
The reaction mixture was ®ltered through a pad of silica gel
and the ®ltered cake was washed with CH2Cl2/EtOAc (2:1,
50 ml). The ®ltrate was concentrated in vacuo. Flash
chromatography of the residue over silica gel (hexane/
ethyl acetateˆ10:1 gradient to 1:1) afforded the following
sulfone:
4.3.5. (E)-Cinnamyl 50-phenyl-(20E,40E)-pentadienyl sul-
fone (1e). White solid (70%). Mp 2018C; (Found: C, 73.82;
H, 6.09. C20H20O2S requires C, 74.04, H, 6.21%); IR nmax
2959, 1325 (OvSvO), 1135 (OvSvO), 892, 760,
691 cm21; dH (250 MHz, CDCl3) 7.45±7.25 (10H, m,
ArH), 6.82 (1H, dd, Jˆ15.5, 10.0 Hz, vCH), 6.69 (1H, d,
Jˆ15.5 Hz, vCH), 6.61 (1H, d, Jˆ15.5 Hz, vCH), 6.49
(1H, dd, Jˆ15.5, 10.0 Hz, vCH), 6.26 (1H, dt, Jˆ15.5,
7.6 Hz, vCH), 5.84 (1H, dt, Jˆ15.5, 7.6 Hz, vCH), 3.88
(2H, d, Jˆ7.6 Hz, CH2SO2), 3.82 (2H, d, Jˆ7.6 Hz,
CH2SO2); dC (62.5 MHz, CDCl3) 140.2, 139.8, 137.0,
136.1, 135.8 (overlapping signals), 129.4, 129.3, 128.9,
127.7, 127.4, 127.3, 119.0, 115.9, 56.8 (CH2SO2), 56.6
(CH2SO2); m/z (EI, 20 eV) 324 (M1, 1), 143 (M12
C9H9SO2 100), 91 (13%).
4.3.1. 2-Methyl-2-propenyl 50-phenyl-(20E,40E)-penta-
dienyl sulfone (1a). White solid (90%). Mp 1108C;
(Found: C, 68.80; H, 7.11. C15H18O2S requires C, 68.67,
H, 6.91%); IR nmax 3030, 1492, 1290 (OvSvO), 1120
(OvSvO), 924, 795, 691 cm21; dH (250 MHz, CDCl3)
7.43±7.26 (5H, m, ArH), 6.81 (1H, dd, Jˆ15.5, 10.4 Hz,
40-H), 6.62 (1H, d, Jˆ15.5 Hz, 50-H), 6.49 (1H, dd, Jˆ15.5,
10.4 Hz, 30-H), 5.82 (1H, dt, Jˆ15.5, 7.7 Hz, 20-H), 5.25
(1H, t, Jˆ1.4 Hz, 3-H), 5.10 (1H, s, 3-H), 3.83 (2H, d, Jˆ
7.7 Hz, CH2SO2), 3.68 (2H, s, CH2SO2), 1.99 (3H, s, Me);
dC (62.5 MHz, CDCl3) 139.4, 136.6, 135.0, 134.0, 128.7,
128.2, 127.2, 126.6, 120.5, 118.6, 60.0 (CH2SO2), 56.1
(CH2SO2), 22.7 (Me); m/z (EI, 20 eV) 262 (M1, 2), 144
(40), 143 (M12C4H7SO2, 100), 128 (98), 91 (17%);
HRMS (EI): M1, found 262.1032. C15H18O2S requires
262.1028.
4.3.6. (E)-Cinnamyl 40-methyl-50-phenyl-(20E,40E)-
pentadienyl sulfone (1f). White solid (90%). Mp 2288C;
(Found: C, 74.61; H, 6.32. C21H22O2S requires C, 74.52,
H, 6.55%); IR nmax 3058, 1451, 1292 (OvSvO), 1116
(OvSvO), 957, 751, 692 cm21; dH (250 MHz, CDCl3)
7.41±7.25 (10H, m, ArH), 6.70 (1H, d, Jˆ15.9 Hz,
vCH), 6.55 (1H, s, 50-H), 6.51 (1H, d, Jˆ15.5 Hz,
vCH), 6.27 (1H, dt, Jˆ15.9, 7.5 Hz, vCH), 5.81 (1H, dt,
Jˆ15.5, 7.7 Hz, vCH), 3.90 (2H, d, Jˆ7.5 Hz, CH2SO2),
3.85 (2H, Jˆ7.7 Hz, CH2SO2), 2.03 (3H, s, Me); dC
(62.5 MHz, CDCl3) 144.4, 139.1, 137.1, 135.6, 134.5,
133.9, 129.2, 128.8, 128.7, 128.2, 127.1, 126.7, 115.4,
114.2, 56.3 (CH2SO2), 56.2 (CH2SO2), 13.8 (Me); m/z (EI,
4.3.2. 2-Methyl-2-propenyl 40-methyl-50-phenyl-(20E,40E)-
pentadienyl sulfone (1b). White solid (85%). Mp 1218C; IR
nmax 3086, 1413, 1282 (OvSvO), 1119 (OvSvO), 978,
712, 696 cm21; dH (250 MHz, CDCl3) 7.35±7.17 (5H, m,
ArH), 6.54 (1H, s, 50-H), 6.48 (1H, d, Jˆ15.5 Hz, 30-H),
5.74 (1H, dt, Jˆ15.5, 7.5 Hz, 20-H), 5.23±5.21 (1H, m,
2-H), 5.07 (1H, s, 2-H), 3.82 (2H, d, Jˆ7.5 Hz, CH2SO2),
3.65 (2H, s, CH2SO2), 1.99 (3H, s, Me), 1.96 (3H, s, Me); dC
(62.5 MHz, CDCl3) 144.4, 137.1, 134.5, 134.5, 133.8,
129.2, 128.2, 127.1, 120.5, 114.3, 59.9 (CH2SO2), 56.2
(CH2SO2), 22.7 (Me), 13.8 (Me); m/z (EI, 20 eV) 276

1306
X.-P. Cao / Tetrahedron 58 (2002) 1301±1307
20 eV) 338 (M1, ,1), 189 (1), 157 (M12PhC3H4O2S, 100),
129 (42), 91 (19%).
10.0 Hz, vCH, 4-H), 6.39 (1H, d, Jˆ15.6 Hz, 6-H), 6.36
(1H, dd, Jˆ15.6, 10.0 Hz, vCH, 5-H), 5.01 (1H, s, 8-H),
5.00 (1H, s, 8-H), 2.05 (3H, s, Me), 1.91 (3H, s, Me); dC
(62.5 MHz, CDCl3) 142.3, 138.4, 137.9, 136.0, 135.4,
131.7, 129.7, 129.2, 128.8, 128.1, 126.5, 116.6, 18.5 (Me),
13.9 (Me); m/z (EI) 210 (M1, 100), 195 (27), 165 (18), 155
(16), 131 (22), 115 (28), 91 (47), 77 (23%); HRMS (EI):
M1, found 210.1418. C16H18 requires 210.1409.
4.3.7. 5-Phenyl-(2E,4E)-pentadienyl 30-trimethylsilyl-
(20E)-propenyl sulfone (1g). White solid (90%). Mp
1758C; IR nmax 3028, 1377, 1290 (OvSvO), 1119
(OvSvO), 978, 921, 720 cm21; dH (250 MHz, CDCl3)
7.38±7.18 (5H, m, ArH), 6.75 (1H, dd, Jˆ15.6, 10.4 Hz,
4-H), 6.56 (1H, d, Jˆ15.6 Hz, 5-H), 6.39 (1H, dd, Jˆ15.6,
10.4 Hz, 3-H), 6.10 (1H, d, Jˆ18.5 Hz, 30-H), 6.05±5.94
(1H, m, 20-H), 5.75 (1H, dt, Jˆ15.2, 7.5 Hz, 2-H), 3.73
(2H, d, Jˆ7.5 Hz, CH2SO2), 3.70 (2H, d, Jˆ7.5 Hz,
CH2SO2), 20.60 (9H, s, Si(CH3)3); dC (62.5 MHz, CDCl3)
143.0, 139.4, 136.6, 135.1, 131.4, 128.7, 128.2, 127.1,
126.6, 118.5, 59.0 (CH2SO2), 56.0 (CH2SO2), 21.6
(Si(CH3)3); m/z (EI, 20 eV) 320 (M1, 4), 128 (100), 115
(55), 77 (49%); HRMS (EI): M1, found 320.1265.
C17H24O2SSi requires 320.1267.
4.4.3. (1E,3E,5E,7E)-2-Methyl-1-phenyl-1,3,5,7-nona-
tetraene (10c). Yellow oil (92%). IR nmax 2984, 1674,
1367, 992, 734, 701 cm21; UV lmax (log 1): 244 (4.6),
278 (4.6), 381 (3.8) nm; dH (500 MHz, CDCl3) 7.35±7.29
(4H, m, ArH), 7.21 (1H, t, Jˆ7.5 Hz, ArH), 6.51 (1H, s,
1-H), 6.38 (1H, d, Jˆ15.5 Hz, 3-H), 6.34 (1H, dd, Jˆ15.6,
10.1 Hz, vCH), 6.27 (1H, dd, Jˆ15.6, 10.1 Hz, vCH),
6.23 (1H, dd, Jˆ15.6, 10.1 Hz, vCH), 6.14 (1H, ddq,
Jˆ15.1, 10.1, 2.0 Hz, 7-H), 5.74 (1H, dq, Jˆ15.1, 6.5 Hz,
8-H), 2.04 (3H, s, Me), 1.80 (3H, d, Jˆ6.5 Hz, Me); dC
(62.5 MHz, CDCl3) 138.6, 137.3, 136.1, 133.1, 132.0,
131.3, 130.8, 129.8, 129.2, 128.9, 128.1, 126.5, 18.3, 13.9;
m/z (EI) 210 (M1, 30), 169 (18), 115 (26), 91 (53), 77
(40%); HRMS (EI): M1, found 210.1404. C16H18 requires
210.1409.
4.4. General procedure for the preparation of 1,3,5,7-
octatraenes 10
The sulfone 1 (1 mmol) was added to a stirred suspension of
alumina-supported KOH (10 mmol of KOH)9 in CF2Br2/
CH2Cl2 (1:10 10 ml) at 08C. The mixture was then stirred
for 10 min to 2 h. The reaction mixture was ®ltered through
a pad of celite and the ®ltered cake was washed thoroughly
with CH2Cl2. The ®ltrate was concentrated in vacuo to give
the crude octatetraene 10. Flash chromatography over silica
gel (hexane) afforded the 1,3,5,7-octatetraenes. Phenyl
substituted octatetraenes are more stable. However, terminal
octatetraenes are less stable and tend to polymerize upon
concentration to give white precipitates even stored at
2208C in the dark in hexane solution. As a result, we
were unable to obtain satisfactory high-resolution mass
data or elemental analysis data for compounds 10a and 10b.
4.4.4. (1E,3E,5E)-2,8-Dimethyl-1-phenyl-1,3,5,7-nona-
tetraene (10d). Yellow oil (90%). (Found: C, 90.85; H,
8.70. C17H20 requires C, 91.01, H, 8.99); IR nmax 2984,
1674, 1376, 992, 734, 701 cm21; UV lmax (log 1): 215
(4.5), 241 (4.7), 284 (4.7), 381 (2.5) nm; dH (500 MHz,
CDCl3) 7.35±7.20 (5H, m, ArH), 6.51 (1H, s, 1-H), 6.49
(1H, dd, Jˆ15.5, 11.0 Hz, vCH), 6.44 (1H, dd, Jˆ15.5,
9.5 Hz, vCH), 6.40 (1H, d, Jˆ15.1 Hz, 3-H), 6.24 (1H,
dd, Jˆ15.1, 9.5 Hz, vCH), 5.92 (1H, d, Jˆ11.0 Hz, 7-H),
2.05 (3H, s, Me), 1.83 (3H, s, Me), 1.81 (3H, s, Me); dC
(62.5 MHz, CDCl3) 137.9, 136.6, 135.4, 135.0, 131.7,
130.9, 130.1, 129.7, 129.4, 128.1, 126.4, 125.7, 26.2 (Me),
21.0 (Me), 18.5 (Me); m/z (EI) 224 (M1, 43), 210 (28), 165
(47), 129 (37), 115 (59), 105 (31), 91 (84%).
The following 1,3,5,7-octatetraenes were prepared:
4.4.1. (1E,3E,5E)-7-Methyl-1-phenyl-1,3,5,7-octatetraene
(10a). Yellow oil (87%). IR nmax 3029, 1878, 1360, 993,
734, 700 cm21; UV lmax (log 1): 242 (4.6), 278 (4.6), 311
(4.4), 324 (4.5), 337 (4.5), 381 (4.4) nm; dH (500 MHz,
CDCl3) 7.40 (2H, t, Jˆ7.6 Hz, ArH), 7.31 (2H, t, Jˆ
7.6 Hz, ArH), 7.21 (1H, t, Jˆ7.6 Hz, ArH), 6.85 (1H, dd,
Jˆ15.5, 10.3 Hz, vCH), 6.56 (1H, d, Jˆ15.5 Hz, 1-H),
6.45 (1H, dd, Jˆ15.5, 10.3 Hz, vCH), 6.40 (1H, dd, Jˆ
15.5, 8.4 Hz, vCH), 6.38 (1H, d, Jˆ15.5 Hz, 6-H), 6.31
(1H, dd, Jˆ15.5, 8.4 Hz, vCH), 5.03 (1H, s, 8-H), 5.01
(1H, s, 8-H), 1.90 (3H, s, Me); dC (62.5 MHz, CDCl3)
142.2, 137.5, 135.9, 133.6, 133.3, 132.4, 129.3, 129.2,
128.6, 127.5, 126.4, 117.0, 18.5 (Me); m/z (EI) 196 (M1,
2),165 (5), 131 (19), 117 (16), 105 (57), 91 (42), 77 (46%);
HRMS (EI): M1, found 196.1243. C15H16 requires
196.1253.
4.4.5. (1E,3E,5E,7E)-1,8-Diphenyl-1,3,5,7-octatetraene
(10e). Yellow solid (90%). Mp 233±2358C (lit.8 2358C);
IR nmax 3012, 1488, 1072, 996, 748, 692 cm21; UV lmax
(log 1): 211 (5.4), 250 (2.1), 256 (2.9), 350 (4.9) nm; dH
(500 MHz, CDCl3) 7.41 (4H, d, Jˆ7.5 Hz, ArH), 7.33
(4H, t, Jˆ7.5 Hz, ArH), 7.22 (2H, t, Jˆ7.5 Hz, ArH), 6.86
(2H, dd, Jˆ15.0, 7.7 Hz, vCH), 6.58 (2H, d, Jˆ7.7 Hz,
vCH), 6.45 (4H, m, vCH); dC (62.5 MHz, CDCl3)
137.6, 133.5 (overlapping signals), 132.8, 129.3, 128.7,
127.6, 126.4; m/z (EI) 258 (M1, 100), 215 (10), 167 (72),
154 (51), 128 (38), 91 (32%); HRMS (EI): M1, found
258.1420. C20H18 requires 258.1409.
4.4.6. (1E,3E,5E,7E)-1,8-Diphenyl-2-methyl-1,3,5,7-octa-
traene (10f). Yellow solid (80%). Mp 2108C; IR nmax 3021,
1446, 1120, 997, 810, 752, 703 cm21; UV lmax (log 1): 231
(4.9), 287 (3.9), 361 (4.8), 381 (4.9), 402 (4.9) nm; dH
(500 MHz, CDCl3) 7.33 (2H, d, Jˆ7.5 Hz, ArH), 7.29±
7.23 (6H, m, ArH), 7.16±7.13 (2H, m, ArH), 6.81 (1H,
ddd, Jˆ15.5, 7.5, 3.5 Hz, vCH), 6.49 (1H, s, 1-H), 6.48
(1H, d, Jˆ15.5 Hz), 6.44±6.35 (4H, m), 2.00 (3H, s, Me);
dC (62.5 MHz, CDCl3) 138.6, 137.9, 137.6, 136.1, 133.9,
133.0, 132.3, 132.1, 129.4, 129.2, 128.8, 128.6, 128.2,
4.4.2.
(1E,3E,5E)-2,7-Dimethyl-1-phenyl-1,3,5,7-octa-
tetraene (10b). Yellow oil (89%). IR nmax 2983, 1679,
1453, 1377, 1002, 912, 734, 701 cm21; UV lmax (log 1):
210 (5.1), 250 (4.5), 300 (4.7), 315 (4.7), 329 (4.8), 345
(4.9), 381 (3.7) nm; dH (500 MHz, CDCl3) 7.36±7.30 (4H,
m, ArH), 7.23 (1H, t, Jˆ7.5 Hz, ArH), 6.54 (1H, s, 1-H),
6.49 (1H, d, Jˆ15.5 Hz, 3-H), 6.45 (1H, dd, Jˆ15.5,

X.-P. Cao / Tetrahedron 58 (2002) 1301±1307
1307
127.4, 126.6, 126.3, 13.9 (Me); m/z (EI) 272 (M1, 100), 180
(23), 164 (19), 117 (55), 91 (17%); HRMS (EI): M1, found
272.1571. C21H20 requires 272.1566.
Chim. Acta 1978, 61, 2697±2708. (c) Ramamurthy, V.;
Denny, M.; Liu, R. S. H. Tetrahedron Lett. 1981, 22, 2463±
2466. (d) Alami, M.; Crousse, B.; Linstrumelle, G.; Manbu,
L.; Larcheveque, M. Synlett 1993, 217±218. (e) Aurell, M. J.;
Ceita, L.; Mestres, R.; Parra, M.; Tortajada, A. Tetrahedron
1995, 51, 3915±3928. (f) Irene, I.; Salvatore, D. C.;
Francesco, D. R.; Aldo, S. Tetrahedron Lett. 2000, 41,
3975±3978. (g) Eisenbarth, S.; Steffan, B. Tetrahedron
2000, 56, 363±365.
4.4.7. (1E,3E,5E,7E)-1-Phenyl-8-trimethylsilyl-1,3,5,7-
octatetraene (10g). Yellow oil (87%). (Found: C, 80.02;
H, 8.53. C17H22Si requires C, 80.25, H, 8.71); IR nmax
2956, 1682, 1455, 1251, 1014, 843, 750, 692 cm21; UV
lmax (log 1): 250 (4.4), 329 (4.7) nm; dH (500 MHz,
CDCl3) 7.40 (2H, d, Jˆ7.5 Hz, ArH), 7.32 (2H, t, Jˆ
7.5 Hz, ArH), 7.23 (1H, t, Jˆ7.5 Hz, ArH), 6.85 (1H, dd,
Jˆ15.5, 10.5 Hz, vCH), 6.59 (1H, d, Jˆ18.0, 10.5 Hz,
7-H), 6.57 (1H, d, Jˆ15.5 Hz, 1-H), 6.44 (1H, dd, Jˆ15.5,
10.5 Hz, vCH), 6.41 (1H, dd, Jˆ15.0, 10.5 Hz, vCH),
6.34 (1H, dd, Jˆ15.0, 10.5 Hz, vCH), 6.29 (1H, dd,
Jˆ15.5, 10.5 Hz, vCH), 5.93 (1H, d, Jˆ18.0 Hz, 8-H),
20.10 (9H, s, Si(CH3)3); dC (62.5 MHz, CDCl3) 144.1,
137.5, 135.8, 135.1, 134.0, 133.4, 133.3, 132.8, 129.2,
128.7, 127.5, 126.4, 21.28 (Si(CH3)3); m/z (EI) 254 (M1,
19), 180 (6), 115 (5), 73 (100), 59 (23%).
2. Martin, R. E.; Diederich, F. Angew. Chem., Int. Ed. Engl.
1999, 38, 1350±1377.
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The author gratefully acknowledges the ®nancial support of
the National Natural Science Foundation of China (NSFC,
QTprogram) and Foundation for University Key Teacher
by the Ministry of Education, and would also like to thank
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The Chinese University of Hong Kong, for their helpful
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