Reactivity of 1-phenylsulfinyl-2-phenylsulfanylethylene (SOSE) with O-nucleophiles generated by potassium tert-butoxide

Article abstract of DOI:10.1016/j.tetlet.2007.03.125

E-1-Phenylsulfinyl-2-phenylsulfanylethylene (E-SOSE) reacts with O-nucleophiles generated by means of t-BuOK via an addition-elimination mechanism, thus affording the product of substitution of the phenylsulfanyl group in a stereo-conservative process. When used alone, the strongly basic and hindered tert-butoxide brings about elimination of either the phenylthiolate or phenylsulfinate groups. Z-SOSE is much more prone to elimination: either with t-BuOK alone or with other O-nucleophiles generated by t-BuOK, it always leads to products derived from elimination. Other alkaline tert-butoxides or other bases appear not as effective in generating species nucleophilic enough to react with E-SOSE.

Full text of DOI:10.1016/j.tetlet.2007.03.125

Tetrahedron Letters 48 (2007) 3699–3703
Reactivity of 1-phenylsulfinyl-2-phenylsulfanylethylene
(SOSE) with O-nucleophiles generated by potassium tert-butoxide
Leonardo Pellizzaro,a Elena Cabianca,a,b Arnaud Tatiboue¨t,b Pierluigi Padovan,a
Fabrizio Fabris,a Patrick Rollinb,* and Ottorino De Lucchia,*
a
`
Dipartimento di Chimica, Universita Ca’ Foscari di Venezia, Dorsoduro 2137, I-30123 Venezia, Italy
bInstitut de Chimie Organique et Analytique, associe´ au CNRS, Universite´ d’Orle´ans, B.P. 6759, F-45067 Orle´ans, France
Received 6 February 2007; revised 19 March 2007; accepted 21 March 2007
Available online 25 March 2007
Abstract—E-1-Phenylsulfinyl-2-phenylsulfanylethylene (E-SOSE) reacts with O-nucleophiles generated by means of t-BuOK via an
addition–elimination mechanism, thus affording the product of substitution of the phenylsulfanyl group in a stereo-conservative
process. When used alone, the strongly basic and hindered tert-butoxide brings about elimination of either the phenylthiolate
or phenylsulfinate groups. Z-SOSE is much more prone to elimination: either with t-BuOK alone or with other O-nucleophiles
generated by t-BuOK, it always leads to products derived from elimination. Other alkaline tert-butoxides or other bases appear
not as effective in generating species nucleophilic enough to react with E-SOSE.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Nucleophilic substitution reactions on vic-disubstituted
X
X
Z
Z
- HY
elimination
(fast)
Z
X
X
ethenes may occur either via an elimination–addition
(E–AdN) or an addition–elimination (AdN–E) mecha-
nism. The actual sequence of events depends on a num-
ber of features among which the E or Z stereochemistry
of the olefinic substrate, the electrophilicity of the
double bond (i.e., the electron withdrawing capacity as
well as the nucleofugal ability of the substituents), the
nucleophilicity of the incoming nucleophile and the
reaction conditions.1 Customarily, strongly electrophilic
alkenes undergo addition of the nucleophile before elim-
ination (i.e., the AdN–E mechanism) while less electro-
philic alkenes first eliminate the leaving nucleophile
before the addition of the incoming nucleophile (i.e.,
the E–AdN mechanism). A simple and direct, though
not exhaustive, perception of the implication of either
one of the two mechanisms is given by the stereospecific-
ity of the reaction and by the difference in reactivity of
the E- and Z-isomers. Indeed, the E–AdN mechanism
implies that both Z and E compounds afford the Z
product and that the E isomer is less reactive, while
the AdN–E is stereo-conservative with Z- and E-isomers
exhibiting comparable reactivity (Scheme 1).2
addition
X
X
Y
Z
H
Z
Z
- Y
elimination
Y
H
Y
addition
X
H
X
H
- HY
elimination
(slow)
X
X
Z
Z
Z
addition
Z
H
Z
Y
Z
- Y
elimination
Y
H
Y
addition
H
X
H
X
Scheme 1. Elimination–addition versus addition–elimination in nucle-
ophilic substitutions on vic-disubstituted ethenes.
For example, either Z- or E-1,2-bis(phenylsulfonyl)eth-
ylenes (BPSE) react via addition–elimination (affording
stereospecifically substitution products with conserva-
tion of the stereochemistry),3 while Z- and E-dichloro-
ethylenes react via an elimination–addition mechanism:
in fact, only the Z-isomer reacts whereas the E is not
reactive because of the unfavourable antiperiplanar
alignment of the leaving group in the elimination step.4
Keywords: Vinyl sulfoxides; Michael addition; Alkaline tert-butoxides.
*
Because of the low electron withdrawing ability
of its substituents, the recently introduced
Corresponding authors. Tel.: +39 041 234 8546; fax: +39 041 234
8517 (O.D.L.); e-mail: delucchi@unive.it
0040-4039/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.03.125

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L. Pellizzaro et al. / Tetrahedron Letters 48 (2007) 3699–3703
similar results, affording nearly quantitative yields of
- PhS
Nu
b-phenylsulfinyldimethylacetal 2 (R = Me)7 under iden-
tical reaction conditions, t-BuOLi proved less reactive
(ca. 40% yield only). The reaction was unsuccessful with
amines (entries 4–8), or with stronger bases (entries
9–11). Interestingly, the reaction also proceeded with
benzotriazole and imidazole (entries 12 and 13), though
in moderate yields.
PhS
SOPh
Nu
SOPh
SOPh
addition
elimination
(fast)
Scheme 2. Reactivity of Z-SOSE with nucleophiles.
1-phenylsulfinyl-2-phenylsulfanylethylene (SOSE) was
expected to behave similarly to dichloroethylene: indeed
only the Z-isomer was reactive towards oxygen nucleo-
philes generated by means of LiHMDS (Scheme 2).
Both BPSE and SOSE revealed useful for the introduc-
tion of robust acetalic protecting groups for carbo-
hydrates.5,6 Although in the case of BPSE both Z- and
E-isomers can be used, the presence of a sole oxygen
atom in the structure of SOSE offers clear advantage
in terms of atom economy, and the presence of a stable
stereogenic centre in the sulfinyl group is a further syn-
thetic opportunity. In this work, we report the possibil-
ity to tune nucleophilicity versus basicity of the oxygen
centres of alcohols and diols to such an extent that
E-SOSE can also be rendered synthetically useful.
Application of the t-BuOK procedure to diverse
alcohols with variable steric hindrance (entries 14–17)
furnished the corresponding alkoxyvinyl sulfoxides 1,9
whereas the related acetals 2 were only detected as
traces. Most likely, the bulkiness of both partners can
be taken as responsible for preventing the second Mi-
chael addition. In contrast, diols (entries 18 and 19) were
converted as expected5 into the corresponding cyclic
acetals: in such cases, the intramolecularity of the reac-
tion helps in driving the reaction to the final
product.10,11
Contrary to the above results, the reaction of Z-SOSE
with O-nucleophiles generated by t-BuOK did not afford
the expected substitution products, but led to apparent
reduction of the sulfinyl group to produce fair yields
of Z-1,2-bis(phenylsulfanyl)ethylene 3.12 It is therefore
not possible to use t-BuOK as a base to promote substi-
tution on Z-SOSE, whereas LiHMDS has given good
results with a number of O-nucleophiles, including
terpenols reported in Table 1 (entries 14–17).13 The
formation of bis-sulfide 3 is observed when either Z-
In details, it was observed that alkoxides generated by
t-BuOK in THF react stereospecifically with E-SOSE
to afford products resulting from a substitution of the
phenylsulfanyl group (Table 1). The reaction of E-SOSE
with methanol was taken as the model reaction where to
test the effect of the counterion Li+ versus Na+ versus
K+ (entries 1–3). While t-BuONa and t-BuOK gave
Table 1. Reaction of E-SOSE with O-nucleophiles generated by different bases
ROH, base
PhOS
PhOS
OR
OR
+
E-SOSE
THF
0 °C
OR
2
1
Entry
ROH
Base
Enolether 1
Acetal 2
1
2
3
MeOH
MeOH
MeOH
MeOH
t-BuOK
t-BuONa
t-BuOLi
Et3N
—
—
—
—
98%
98%
40%
—
4
5
6
7
8
MeOH
MeOH
MeOH
MeOH
TMEDA
i-Pr2NH
HMDS
DBU
—
—
—
—
—
—
—
—
9
MeOH
MeOH
MeOH
MeOH
NaH
n-BuLi
LDA
—
—
—
—
Traces
Traces
—
50%
50%
Traces
Traces
Traces
6%
10
11
12
13
14
15
16
17
18
19
Imidazole
MeOH
Benzotriazole
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
—
(À)-Menthol
(À)-endo-Borneol
(+)-endo-Fenchol
(+)-Isopinocampheol
1,2:5,6-Di-O-isopropylidene-D-mannitol
1,3:4,6-Di-O-benzylidene-D-mannitol8
45%
40%
20%
26%
—
80%
50%
—
General procedure: To a solution of alcohol or diol (10.0 or 5.0 mmol) in dry THF (10 mL) maintained at 0 ꢁC under argon, the base (10.0 mmol)
was added. The resulting mixture was stirred at 0 ꢁC for 15 min and a solution of E-SOSE (5.0 mmol) in dry THF (2 mL) was added by syringe. The
resulting solution was maintained at 0 ꢁC for 5 h then poured into cold water (50 mL) and extracted with diethyl ether (3 · 30 mL). The combined
organic extracts were dried over MgSO4 and concentrated under reduced pressure. The residue was analyzed by GC–MS and 1H NMR and purified
by FC. All new compounds gave satisfactory analytical data. Selected spectroscopic data are reported in the references.

L. Pellizzaro et al. / Tetrahedron Letters 48 (2007) 3699–3703
3701
Table 2. Reaction of Z-SOSE with bases
With a view to backing this hypothesis up, the experi-
ment was carried out at a lower temperature, allowing
to detect (GC–MS) a high concentration of 6,17 which
was finally isolated by flash chromatography, together
with alkynyl sulfoxide 7.18 In addition, the formation
of phenylsulfenate ion generated by the elimination pro-
cess, was corroborated by electrophilic trapping with
benzyl chloride (Scheme 4). Under such conditions, the
resulting sulfoxide 919 could be isolated in 40% yield.
base
PhOS
R
PhS
SPh
SOSE
THF, rt
4: R =
5: R =
t-BuO-
-Bu
3
n
Entry
SOSE isomer
Base
Bis-sulfide 3
Sulfoxide
1
2
3
4
5
6
7
8
Z
E
Z
Z
Z
Z
Z
Z
t-BuOK
t-BuOK
t-BuONa
t-BuOLi
KH
NaH
LiHMDS
n-BuLi
50%
50%
50%
—
—
—
4 (12%)
4 (12%)
4 (15%)
—
In addition, the parent sulfide 10 was also isolated in
moderate yield, confirming that t-BuOK eliminates indif-
ferently both the phenylsulfenate and the phenylthiolate
ions, because of the close acidity of the two vinylic
hydrogens in SOSE.
—
—
—
20%
50%
5 (Traces)
General procedure: To a solution of base (10.0 mmol) in dry THF
(10 mL) maintained at 0 ꢁC under argon a solution of E-SOSE
(5.0 mmol) in dry THF (2 mL) was added by syringe. The mixture was
stirred at 0 ꢁC for 15 min then left to rise to rt over 5 h. The mixture
was poured into cold water (50 mL) then extracted with diethyl ether
(3 · 30 mL). The combined organic extracts were dried over MgSO4
and concentrated under reduced pressure. The residue was analyzed by
Further confirmation of the process by reacting t-BuOK
with bicycloolefin 11,20 in which elimination is pre-
cluded: in such case, no bis-sulfide was formed (Scheme
5).
1
GC–MS and H NMR and purified by FC. All new compounds gave
With those data in hands, it can be assumed that in the
presence of t-BuOK, E- or Z-SOSE first eliminates
PhSOÀ or PhSÀ with formation of either alkyne 6 or
alkyne 7, which can undergo counter-addition of the
expelled anions, to finally afford bis-sulfide 3 and bis-
sulfoxide 8 (Scheme 3). Control experiments have shown
that 8 is not stable under the reaction conditions and
produces intractable mixtures of polar compounds. It
is therefore not detected and 3 appears as the only
apparent reaction product.
satisfactory analytical data. Selected spectroscopic data are reported in
the references.
or E-SOSE is reacted with t-BuOK alone (Table 2,
entries 1 and 2).
Together with 3 a little amount of the alkoxyvinyl
sulfoxide 414 is also produced despite the bulkiness of
the t-butoxide anion. It should be pointed out that both
t-BuOK and t-BuONa seem to be able to induce this
reaction (entries 1–3), whereas t-BuOLi (entry 4) is inop-
erative, as well as other strong bases (entries 5 and 6).
While producing minor amounts of 3 (entry 7),
LiHMDS was observed to isomerize Z-SOSE into
E-SOSE in relevant amounts. Butyl lithium (entry 8)
furnished 3 in good yield together with only traces of
the 2-C-butyl derivative 5.15
The observation that the E-isomer appears as reactive
towards t-BuOK as the Z-isomer implies that despite
of the poor electron withdrawing character of its substit-
uents, SOSE reacts via an addition–elimination mecha-
nism, similarly to BPSE and unlike a number of
related alkenes (e.g., dichloroalkenes). In order to ascer-
tain that unexpected behaviour, we attempted to evalu-
ate the electrophilic character of the olefin by taking the
13C NMR chemical shifts of the sp2 carbons as elec-
tronic density probes. Even though being aware of the
perturbation of the chemical shifts value induced by
anisotropy, our aim was to establish some kind of pre-
dictive rule for the reactivity of electrophilic alkenes to-
wards nucleophilic substitution (i.e., AdN–E vs E–AdN).
The hypothesis was partially confirmed by observing
that the d value for Z-BPSE (140.5 ppm) is comparable
to those of Z-SOSE (138.6 ppm for the @CH–SOPh),
while systems that react through an elimination–addi-
This unexpected conversion of SOSE into 3 prompted us
to further investigate16 the mechanism of formation of
the bis-sulfide, a direct ‘reduction’ of the sulfinyl group
appearing highly improbable. When carried out in the
presence of cyclohexene or triphenylphosphine, the reac-
tion expectedly revealed no oxidation products. More
realistic stands the hypothesis of a scrambling of substit-
uents through formation of the transient alkynyl sulfide
6 via an E–AdN process (Scheme 3).
PhS
SPh
H
SPh
PhSO
PhS
base
6
7
3
PhOS
SPh
-SOSE
+
PhOS
SOPh
SOPh
Z
H
8
not stable in the
reaction conditions
scrambling
Scheme 3. Mechanism proposed to explain the formation of 3.

3702
L. Pellizzaro et al. / Tetrahedron Letters 48 (2007) 3699–3703
131.3 (CH–para-PhSO), 144.0 (CIV–PhSO). MS: m/z 237
t-BuOK
THF, rt
[M+Na]+.
SPh
BnSOPh
Z-SOSE BnCl
BnSPh
8. Diol prepared according to: Baggett, N.; Stribblehill, P. J.
Chem. Soc., Perkin Trans. 1 1977, 1123–1126.
9. Selected spectroscopy data for the (E)-alkoxyvinyl sulfox-
3
9
10
Scheme 4. Trapping experiment of the transient sulfide and sulfenate.
1
ide derived from (À)-menthol (2 epimeric sulfoxides): H
NMR (CDCl3) d 0.75, 0.79 (2d, 3H, J8À9 = J8À10 = 7.0,
Me), 0.89–0.95 (m, 8H, 2Me, H-4b, H-6b), 0.98–1.13 (m,
1H, H-3b), 1.19–1.45 (m, 2H, H-2, H-5), 1.68 (br d, 2H, H-
3a, H-4a), 1.99–2.11 (m, 2H, H-6a, H-8), 3.68–3.80 (m,
1H, H-1), 5.77 (d, 1H, Jvic = 12.7, H-2vinyl), 7.22, 7.25 (2d,
1H, Jvic = 12.5, 12.7, H-1vinyl), 7.44–7.50 (m, 3H, H–
PhSO), 7.59–7.63 (m, 2H, ortho-H–PhSO). 13C NMR
(CDCl3) d 16.4, 20.7 (C-9, C-10), 22.0 (C-7), 23.4 (C-3),
26.0 (C-8), 31.5 (C-5), 34.1 (C-4), 40.5, 40.8 (C-6), 47.5 (C-
2), 83.2, 83.6 (C-1), 112,2, 112.3 (C-2vinyl), 124.4 (CH–
ortho-PhSO), 129.1 (CH–meta-PhSO), 130.3 (CH–para-
PhSO), 145.5 (CIV–PhSO), 158.0 (C-1vinyl). MS: m/z 329
[M+Na]+.
t
-BuOK
SPh
SOPh
SPh
SPh
THF, rt
11
Scheme 5. Experiment confirming the elimination–addition path for
the formation of bis-sulfide 3.
tion mechanism, typically Z-1,2-dichloroethylene, dis-
play a much different chemical shift (120.0 ppm).
10. Selected spectroscopy data for the b-phenylsulfinylacetal
derived from 1,2:5,6-di-O-isopropylidene-D-mannitol (2
epimeric sulfoxides): 1H NMR (CDCl3) d 2.99–3.23 (m,
CH2SOPh), 5.43–5.46 (m, CH–CH2SOPh). 13C NMR
(CDCl3) d 62.2, 62.3 (CH2SOPh), 66.1, 66.6 (C-1, C-6),
99.9 (CH–CH2SOPh), 124.0 (CH–ortho-PhSO), 129.3
In summary, the above results highlight a strong depen-
dence on the nature of the base used to generate the
nucleophilic species. Z-SOSE reacts smoothly with O-
nucleophiles generated with LiHMDS as base, while
O-nucleophiles generated by potassium tert-butoxide re-
act with E-SOSE. Thus the use of SOSE as a simple and
advantageous protective reagent in carbohydrate chem-
istry is general for both isomers when the appropriate
reaction conditions are applied.
(CH–meta-PhSO), 131.2 (CH–para-PhSO), 144.0 (CIV
–
PhSO). MS: m/z 435 [M+Na]+.
11. Selected spectroscopy data for the b-phenylsulfinylacetal
derived from 1,3:4,6-di-O-benzylidene-D-mannitol (2 epi-
meric sulfoxides): 1H NMR (CDCl3) d 2.9–3.2 (m,
CH2SOPh), 5.26, 5.36 (2 dd, CH–CH2SOPh), 5.48, 5.52
(2s, CH–Ph). 13C NMR (CDCl3) d 59.9, 61.1 (CH2SOPh),
67.0, 67.1, 68.7, 68.8 (C-1, C-2, C-5, C-6), 81.8 (C-3, C-4),
95.9, 96.0 (CH–CH2SOPh), 100.8, 100.9 (CH–Ph), 123.9,
124.0 (CH–ortho-PhSO), 129.0, 129.4 (CH–meta-PhSO),
131.4 (CH–para-PhSO), 143.1, 143.6 (CIV–PhSO). MS:
m/z 531.5 [M+Na]+.
Acknowledgements
This work was co-funded by MIUR (Rome) within the
national PRIN framework. We also thank EGIDE for
support.
12. (a) Cusa, N. W.; McCombie, H. J. Chem. Soc. 1937, 767–
770; (b) Truce, W. E.; Boudakian, M. M.; Heine, R. F.;
McManimie, R. J. J. Am. Chem. Soc. 1956, 78, 2743–2748.
´
13. Cabianca, E. Ph.D. Thesis, Orleans (2004).
14. Selected spectroscopy data for 4: 1H NMR (CDCl3) d 1.36
(s, 9H, CMe3), 5.36 (d, 1H, Jvic = 7.8, H-2), 6.83 (d, 1H,
H-1), 7.6–7.7 (m, 2H, ortho-H–PhSO), 7.40–7.55 (m, 3H,
H–PhSO). 13C NMR (CDCl3) d 27.7 (Me), 79.8 (CIV–t-
Bu), 112.4 (C-1), 123.6 (CH–ortho-PhSO), 128.6 (CH–
meta-PhSO), 129.8 (CH–para-PhSO), 145.7 (CIV–PhSO),
148.6 (C-2). MS: m/z 247.5 [M+Na]+.
15. Cardellicchio, C.; Fiandanese, V.; Naso, F. J. Org. Chem.
1992, 57, 1718–1722.
16. The reaction furnished the same results using diethyl ether
or NMP instead of THF, whereas no reaction took place
in dichloromethane.
References and notes
1. Patai, S.; Rappoport, Z. The Chemistry of Alkenes; Wiley
Interscience: New York, NY, 1964; pp 525–546.
2. Such a rather simplified statement finds exceptions due to
the non-stereospecific syn addition of nucleophiles to
electrophilic alkynes and to Z to E isomerism under the
reaction conditions.
3. (a) Meek, J. S.; Fowler, J. S. J. Org. Chem. 1968, 33, 985–
991; (b) De Lucchi, O.; Pasquato, L.; Rollin, P.; Tati-
boue¨t, A. In e-EROS Enyclopedia of Reagents for Organic
Synthesis; John Wiley & Sons, Ltd, 2005. doi:10.1002/
´
17. Hunter, G. A.; McNab, H. Synthesis 1993, 1067–1068.
18. Laba, V. I.; Sviridova, A. V.; Prilezhaeva, E. N. Izv. Akad.
Nauk SSSR, Ser. Khim 1972, 1, 212–213, Selected spec-
troscopy data for 7: 1H NMR (CDCl3) d 3.73 (s, 1H,
acetylenic H) 7.55-7.59 (m, 3H, H–PhSO), 7.80–7.84 (m,
2H, ortho-H–PhSO). 13C NMR (CDCl3) d 81.8 (acetylenic
047084289X.rb183; (c) Cabianca, E.; Chery, F.; Rollin, P.;
De Lucchi, O.; Cossu, S. Synlett 2001, 1962–1964; (d)
Chery, F.; Desroses, M.; Tatiboue¨t, A.; Rollin, P.; De
Lucchi, O. Tetrahedron 2003, 59, 4563–4572.
´
4. Truce, W. E.; Boundakian, M. M.; Heine, R. F.;
McManimie, R. J. J. Am. Chem. Soc. 1956, 78, 2743–2748.
5. Cabianca, E.; Tatiboue¨t, A.; Fabris, F.; De Lucchi, O.;
Rollin, P. Tetrahedron Lett. 2005, 46, 1035–1037.
C
IV), 90.5 (acetylenic CH), 125.1 (2*CH–ortho-PhSO),
129.8 (2*CH–meta-PhSO), 132.2 (CH–para-PhSO), 143.2
´
(CIV–PhSO). MS: m/z 173 [M+Na]+.
6. Chery, F.; Rollin, P.; De Lucchi, O.; Cossu, S. Synthesis
19. Kakarla, R.; Dulina, R. G.; Hatzenbuhler, N. T.; Hui, Y.
W.; Sofia, M. J. J. Org. Chem. 1996, 61, 8347–8349.
20. Cyclopentadiene was added to a crude dichloromethane
solution of 1-phenylsulfinyl-2-phenylsulfanylacetylene
obtained by controlled m-CPBA oxidation of 1,2-
bis(phenylsulfanyl)acetylene (see: Pasquato, L.; De Luc-
chi, O.; Krotz, L. Tetrahedron Lett. 1991, 32, 2177–2178)
2001, 286–292.
7. Selected spectroscopic data for 2 (R@Me): 1H NMR
(CDCl3) d 2.96 (dd, 1H, Jgem = 13.1, H-1b), 3.12 (dd, 1H,
H-1a), 4.76 (dd, 1H, J1aÀ2 = 4.0, J1bÀ2 = 7.3, H-2), 7.49–
7.57 (m, 3H, H–PhSO), 7.6–7.7 (m, 2H, ortho-H–PhSO).
13C NMR (CDCl3) d 53.3, 54.7 (2 Me), 60.9 (C-1), 99.5 (C-
2), 123.9 (2*CH–ortho-PhSO), 129.4 (2*CH–meta-PhSO),

L. Pellizzaro et al. / Tetrahedron Letters 48 (2007) 3699–3703
3703
and 12 h refluxing of the mixture; flash-chromatography
purification afforded 11 as a 6:4 mixture of stereoisomers.
Selected spectroscopic data: 1H NMR (CDCl3) d 1.92,
2.13 (2 br d, J = 6.8, apical H-7), 3.38, 3.61 (2 br s,
bridgehead-H-1 and H-4 minor), 3.43, 3.88 (2 br s,
bridgehead-H-1 and H-4 major), 5.90 (dd, J = 4.6,
J = 3.0, vinyl-H major), 6.29 (dd, J = 4.6, J = 3.3, vinyl-
H major), 6.56 (dd, J = 4.9, J = 3.0, vinyl-H minor), 6.82
(dd, J = 4.9, J = 3.7, vinyl-H minor), 7.28–7.65 (series of
m, H-Ar). 13C NMR (CDCl3) d 48.2, 49.8, 55.7, 56.9, 68.2,
70.4, 124.0, 128.2, 128.3, 128.8, 128.9, 129.2, 129.3, 130.1,
132.0, 132.7, 137.6, 139.8, 140.0, 142.0, 142.2, 143.2, 148.9,
150.0, 156.9, 159.8. MS (EI): m/z 276 [M+ÀSO].