Generation of Sulfur Ylides from Sulfonium Salts and Their Reactions. Comparative Study of Electrochemical Reduction with the Base Method and Mechanism Elucidation by the MO Method

Article abstract of DOI:10.1246/bcsj.76.2155

The cathodic reduction of sulfonium salts in acetonitrile in the presence and absence of benzaldehyde was carried out. Results were compared with results of the base method. In the presence of benzaldehyde, the electrochemical reduction gave epoxides as a result of the Corey-Chaykovsky reaction, thus confirming ylide formation. The electrochemical reduction of sulfonium salts without benzaldehyde yielded rearrangement products in high yield. On the contrary, upon base treatment of sulfonium salts without benzaldehyde, symmetrical epoxides derived from the benzyl group of the sulfonium salt are obtained as main products as a result of the auto oxidation of the sulfur ylide. The reaction mechanisms were elucidated based on the results obtained by a semi-empirical molecular orbital method.

Full text of DOI:10.1246/bcsj.76.2155

Ó 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 2155–2165 (2003) 2155
Generation of Sulfur Ylides from Sulfonium Salts and Their Reactions.
Comparative Study of Electrochemical Reduction with the Base Method
and Mechanism Elucidation by the MO Method
ꢀ
Yuichi Okazaki, Fumio Ando, and Jugo Koketsu
Department of Applied Chemistry, College of Engineering, Chubu University, Kasugai 487-8501
Received May 19, 2003; E-mail: jkoketsu@isc.chubu.ac.jp
The cathodic reduction of sulfonium salts in acetonitrile in the presence and absence of benzaldehyde was carried
out. Results were compared with results of the base method. In the presence of benzaldehyde, the electrochemical re-
duction gave epoxides as a result of the Corey–Chaykovsky reaction, thus confirming ylide formation. The electrochem-
ical reduction of sulfonium salts without benzaldehyde yielded rearrangement products in high yield. On the contrary,
upon base treatment of sulfonium salts without benzaldehyde, symmetrical epoxides derived from the benzyl group of
the sulfonium salt are obtained as main products as a result of the auto oxidation of the sulfur ylide. The reaction mech-
anisms were elucidated based on the results obtained by a semi-empirical molecular orbital method.
Phosphorus and sulfur ylide (abbreviated as P–Y and S–Y
hereafter), are important intermediates as carbanions in syn-
thetic chemistry. S–Ys are extensively utilized in organic
chemistry to achieve the stepwise insertion of a methylene or
substituted methylene across the double bond of a carbonyl,
an imine, or an electrophilic olefin to give an epoxide, aziridine
or a cyclopropane, respectively. The reactivities of the carban-
ions depend on either the substituents on the carbanions or the
sort of central heteroatom of the 15-group elements1–3 (N, P, As
etc.) or of the 16-group elements4,5 (S, Se etc.) which carry the
positive charge. In this study, we investigated the generation of
S–Y by electrochemical reduction and their reactions. As inter-
mediates in organic syntheses, especially the S–Y has been uti-
lized for getting a wide variety of epoxides derivatives.6,7 Be-
cause the sulfur atom of the S–Y has poor affinity with the oxy-
gen atom, the popular Corey–Chaykovsky reaction with car-
bonyl compounds occurs, producing epoxides instead of the
olefin. Among many reactions of ylides, the rearrangement re-
actions8–10 of the S–Ys have stirred up interest in many re-
searchers owing to their weaker affinity with carbon compared
with those of P–Ys. The S–Y is stabilized by the (p–d) ꢀ con-
jugated system11 i.e. the anionic charge is delocalized by d or-
bital on the sulfur atom. But theoretical calculations revealed
the fact that the S–Y carbanion will interact with a S–C non-
bonding orbital.12 The substituent effect on carbanion is a great
factor in S–Y stability, and the electron-withdrawing groups
(EWG) stabilize S–Y by the delocalization of the negative
charge on the carbanion.
stable ylides.19,20 The method (2) is known to be simple and to
give stable ylide in high yields. As a minor method, only a few
papers has reported the utilization of an electrochemical reduc-
tion of S-salts21–23 for generation of S–Ys.
We have reported the generation of P–Y by the electrochem-
ical reduction of phosphonium salts24 and we found that the P–
Ys were obtained by a one-electron reductive process. In this
experiment, we used the electrochemical reduction method
for S-salts to produce S–Ys and we compared the reaction prod-
ucts with those obtained from the base method. We found that
the S–Y generation occurred under mild conditions at 22 ꢂC un-
der a nitrogen atmosphere. The electrochemical reduction
method is found to be simple and clean for giving S–Ys,
and easy work-up is also promised. We tried the Corey–
Chaykovsky reactions of the S–Y generated by the electro-
chemical reduction method with benzaldehyde and obtained
the corresponding epoxides as the main products. Without
benzaldehyde, the S–Ys undergo the Sommelet–Hauser rear-
rangement easily, in a way similar to that reported on the nitro-
gen ylide along with the dimer formation of benzyl groups.
Vedejs et al. reported a [2,3] Wittig rearrangement of S–Y that
contains allylic substituent to give a macro-cyclic molecule.25
Some theoretical studies from the view point of stereo chemis-
try are reported and the energy differences in the transition state
are discussed.26 In regard to the Sommelet–Hauser rearrange-
ment, Okada et al.27 reported the synthesis of thiepin deriva-
tives through skeletal reconstruction of S–Y with two benzyl
groups on the sulfur atom. An ab initio MO calculation at
ꢀ
Various synthetic methods of S–Y have been proposed by
many researchers.13–16 Generally it is found that (1) ꢁ-dehy-
droganation from sulfonium salt (abbreviated as S-salt) as the
precursor of S–Y by base17 and (2) addition reactions of alkyl-
idene to a sulfide18 are well-known methods to get the S–Ys.
Although reaction (1) is the major method for obtaining the
S–Y from S-salts, strong bases such as butyllithium and
DMSOꢁ are required to abstract an ꢁ-proton in the case of un-
HF/6-31G basis set was used to elucidate the reaction
mechanism.28 However, the sulfonium salts in their study have
two benzyl groups and there is no competition between stable
ylide and unstable ylide. In this report, we describe the electro-
chemical generations of S–Y with a benzyl group in S-salts and
the route determination of the following Sommelet–Hauser re-
arrangement from benzyl tetrahydrothiophenium salt (BTHT)
and from benzyl diethyl sulfonium salt (BDES) to detect the
Published on the web November 15, 2003; DOI 10.1246/bcsj.76.2155

2156 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)
Rearrangement of S-Ylide Generated by EC-Method
1-(4-Bromobenzyl)-tetrahydrothiophenium Bromide (c):
ꢂ
presence of any differences between ring structure and open
chain structure. In order to clarify the mechanism of their reac-
tions, all minimum or saddle points of the reaction profile were
optimized. And also, the bond energies and spin density distri-
butions were used to explain the reaction path found in the elec-
trochemical reduction of the S-salts.
White crystal; mp 120–123 C; IR (KBr Tablet) 2941 (m), 2831
(m), 1850–1550 (w), 1583 (s), 1483 (s), 1402 (m), 1220 (m),
1
1067 (m), 833 (m), 713 (m), 594 [C–Br] (s) cmꢁ1. H NMR (400
MHz, D2O) ꢂ 7.47 (2H, d, H-5, J ¼ 8:3 Hz), 7.23 (2H, d, H-6, J ¼
8:3 Hz), 4.33 (2H, s, H-3), 3.28 (4H, m, H-1), 2.12 (4H, m, H-2);
13C NMR (100 MHz, D2O) ꢂ 42.44 (C-1), 28.15 (C-2), 44.90 (C-3),
127.38 (C-4), 132.57 (C-5), 131.96 (C-6), 123.75 (C-7). Anal.
Calcd for C11H14Br2S: C 39.08, H 4.17%. Found: C 39.01, H
3.87%.
Experimental
Materials. Tetrahydrothiophene, diethyl sulfide, benzyl bro-
mide, 4-methylbenzyl bromide, 4-bromobenzyl bromide, 4-cyano-
benzyl bromide, 4-nitrobenzyl bromide, benzaldehyde, sodium
amide, acetonitrile, and tetraethylammonium perchlorate are com-
mercial products. All the liquid reagent materials were used after
purification by distillation. 1H NMR and 13C NMR were recorded
on JEOL JNM-A series spectrometers in CDCl3 solvent. Mass
spectra were obtained on a SHIMADZU GCMS-QP2010. The
melting point was measured on a SEIKO INSTRUMENTS TG-
DTA SSC/5200H. IR spectra were recorded on SHIMADZU
FTIR-8700. Electric current was recorded on NIKKO KEISOKU
DIGITAL COULOMB METER NDCM-1. Column chromatogra-
phy for purification was performed using Mallinckrodt silica gel
(100 mesh) with CHCl3 as eluent.
Synthesis of the Sulfonium Salts. In ethyl ether solvent, the
sulfonium salts were synthesized by the reaction of tetrahydrothio-
phene or diethyl sulfide with equimolar corresponding benzyl bro-
mide and this p-substituent. Reaction conditions are at room tem-
perature into an argon gas. The melting point, IR spectra,
1H NMR, 13C NMR spectra data and elemental analysis of the
BTHT and BDES are shown below. The numbering systems of
the compounds are specified as described in Chart 1.
1-(4-Cyanobenzyl)-tetrahydrothiophenium Bromide (d):
ꢂ
White crystal; mp 104–107 C; IR (KBr Tablet) 2995 (w), 2810
(w), 2224 [CN] (m), 1850–1650 (w), 1590 (m), 1504 (m), 1409
(m), 1239 (m), 829 (m), 734 (m) cmꢁ1
.
1H NMR (400 MHz,
CDCl3) ꢂ 7.56 (2H, d, H-5, J ¼ 8:5 Hz), 7.44 (2H, d, H-6, J ¼
8:7 Hz), 4.41 (2H, s, H-3), 2.75 (4H, m, H-1), 1.86 (4H, m, H-
2); 13C NMR (100 MHz, CDCl3) ꢂ 44.04 (C-1), 31.43 (C-2),
45.93 (C-3), 142.73 (C-4), 132.48 (C-5), 129.63 (C-6), 118.29
(C-7), 112.01 (R). Anal. Calcd for C12H14NBrS: C 50.71, H
4.96, N 4.93%. Found: C 50.74, H 4.83, N 4.94%.
1-(4-Nitrobenzyl)-tetrahydrothiophenium Bromide (e):
Yellow solid; mp 95–97 ꢂC; IR (KBr Tablet) 2927 (w), 2814
(w), 1850–1650 (w), 1597 (m), 1540 [NO2] (s), 1517 (s), 1226
(m), 800 (m), 752 (m) cmꢁ1 1H NMR (400 MHz, D2O) ꢂ 8.13
.
(2H, d, H-5, J ¼ 8:5 Hz), 7.59 (2H, d, H-6, J ¼ 8:8 Hz), 4.52
(2H, s, H-3), 3.45 (4H, m, H-1), 2.23 (4H, m, H-2); 13C NMR
(100 MHz, D2O) ꢂ 43.04 (C-1), 28.24 (C-2), 44.56 (C-3), 124.48
(C-4), 135.93 (C-5), 131.44 (C-6), 148.20 (C-7). Anal. Calcd for
C11H14NO2BrS: C 43.43, H 4.64, N 4.60%. Found: C 43.87, H
4.58, N 4.45%.
BDES. Benzyldiethylsulfonium Bromide (f): White crystal;
ꢂ
BTHT.
White crystal; mp 119–121 C; IR (KBr Tablet) 2945 (m), 2821
(m), 1850–1550 (w), 1497 (m), 1456 (m), 1418 (m), 1257 (m),
1-Benzyltetrahydrothiophenium Bromide (a):
ꢂ
mp 88–91 C; IR (KBr Tablet) 2992 (m), 2881 (m), 1850–1550
(w), 1497 (m), 1456 (m), 1418 (m), 1267 (m), 775 (m), 707 (m)
cmꢁ1
.
1H NMR (400 MHz, CDCl3) ꢂ 7.66 (2H, d, H-5, J ¼ 7:3
772 (m), 705 (m) cmꢁ1
.
1H NMR (400 MHz, CDCl3) ꢂ 7.52
Hz), 7.31 (2H, t, H-6, J ¼ 7:2 Hz), 7.30 (1H, t, H-7, J ¼ 7:8
Hz), 5.26 (2H, s, H-3), 3.72–3.64 (4H, m, H-1), 1.35 (6H, m, H-
2); 13C NMR (100 MHz, CDCl3) ꢂ 33.59 (C-1), 9.58 (C-2),
43.41 (C-3), 127.45 (C-4), 130.30 (C-5), 129.00 (C-6), 129.42
(C-7). Anal. Calcd for C11H17BrS: C 50.58, H 6.56%. Found:
C 50.23, H 6.66%.
(2H, d, H-5, J ¼ 5:9 Hz), 7.22 (1H, t, H-7, J ¼ 7:1 Hz), 7.20
(2H, t, H-6, J ¼ 7:8 Hz), 4.40 (2H, s, H-3), 2.72 (4H, m, H-1),
1.85 (4H, m, H-2); 13C NMR (100 MHz, CDCl3) ꢂ 42.87 (C-1),
28.34 (C-2), 45.59 (C-3), 128.66 (C-4), 130.48 (C-5), 128.89 (C-
6), 129.83 (C-7). Anal. Calcd for C11H15BrS: C 50.97, H
5.83%. Found: C 50.95, H 5.84%.
Diethyl-(4-methybenzyl)-sulfonium Bromide (g):
White
1-(4-Methylbenzyl)-tetrahydrothiophenium Bromide (b):
White crystal; mp 127–130 ꢂC; IR (KBr Tablet) 2939 (s), 2879
(m), 2826 (m), 1850–1550 (w), 1516 (m), 1410 (m), 1192 (m),
crystal; mp 90–93 ꢂC; IR (KBr Tablet) 2956 (m), 2864 (m),
1850–1550 (w), 1510 (m), 1411 (m), 1192 (m), 826 (m), 725
(m) cmꢁ1
.
1H NMR (400 MHz, CDCl3) ꢂ 7.24 (2H, d, H-6, J ¼
826 (m), 725 (m) cmꢁ1
.
1H NMR (400 MHz, CDCl3) ꢂ 7.22
7:2 Hz), 7.12 (2H, d, H-5, J ¼ 7:7 Hz), 5.21 (2H, s, H-3), 3.70
(4H, m, H-1), 2.53 (3H, s, R), 1.38 (6H, m, H-2); 13C NMR (100
MHz, CDCl3) ꢂ 33.82 (C-1), 9.98 (C-2), 43.77 (C-3), 134.74 (C-
4), 130.25 (C-5), 130.66 (C-6), 124.13 (C-7), 21.23 (R). Anal.
Calcd for C12H21BrS: C 52.36, H 6.96%. Found: C 52.41, H
6.78%.
(2H, d, H-6, J ¼ 6:2 Hz), 7.13 (2H, d, H-5, J ¼ 7:7 Hz), 4.41
(2H, s, H-3), 2.75 (4H, m, H-1), 2.29 (3H, s, R), 1.86 (4H, m, H-
2); 13C NMR (100 MHz, CDCl3) ꢂ 42.81 (C-1), 28.46 (C-2),
45.80 (C-3), 139.58 (C-4), 128.53 (C-5), 129.03 (C-6), 125.28
(C-7), 20.78 (R). Anal. Calcd for C12H19BrS: C 52.75, H
6.27%. Found: C 52.80, H 6.19%.
Diethyl-(4-bromobenzyl)-sulfonium Bromide (h):
White
Chart 1.

Y. Okazaki et al.
Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2157
crystal; mp 115–118 ꢂC; IR (KBr Tablet) 2931 (m), 2835 (m),
1850–1550 (w), 1587 (m), 1483 (m), 1400 (m), 1220 (m), 1064
erties, spectral data, and elemental analyses as listed in the
following. Different products are obtained according to the differ-
ence in the reduction method and p-substituent on the benzyl
groups. When the substituent group is an electron-donating group
(EDG), the electrochemical reduction of BTHT gave the rear-
ranged product in high yield. Conversely, when the substituent
group on the benzyl group is an electron-withdrawing group
(EWG), the electrochemical reduction generated radical coupling
products of the benzyl group in the yields of 50–90% and the rest
was mostly the reactant.
In the base method, all of the BTHT generated S–Ys and the au-
toxidation of the S–Ys led to the formation of symmetric epoxides,
along with minor amounts of the rearrangement products. Howev-
er, in the case of the BDES salts with a p-methyl or bromo-sub-
stituent, the rearrangement reaction dominated with minor
amounts of the epoxide. All isolated epoxides had the Z-conforma-
tions and there were no peaks corresponding to E-isomers in 1H or
13C NMR spectra.
(m), 833 (s), 711 (m), 594 [C–Br] (s) cmꢁ1
.
1H NMR (400
MHz, CDCl3) ꢂ 7.55 (2H, d, H-5, J ¼ 8:3 Hz), 7.24 (2H, d, H-6,
J ¼ 8:3 Hz), 5.30 (2H, s, H-3), 3.72–3.60 (4H, m, H-1), 1.33
(6H, m, H-2); 13C NMR (100 MHz, CDCl3) ꢂ 33.81 (C-1), 9.86
(C-2), 43.01 (C-3), 126.87 (C-4), 132.40 (C-5), 132.23 (C-6),
124.14 (C-7). Anal. Calcd for C11H16Br2S: C 38.85, H 4.74%.
Found: C 38.62, H 4.80%.
Diethyl-(4-cyanꢂ obenzyl)-sulfonium Bromide (i): White crys-
tal; mp 114–116 C; IR (KBr Tablet) 2994 (w), 2813 (w), 2226
[CN] (m), 1850–1650 (w), 1606 (m), 1506 (m), 1413 (m), 1228
(m), 846 (m), 829 (m), 738 (m) cmꢁ1 1H NMR (400 MHz, CDCl3)
.
ꢂ 7.55 (2H, d, H-5, J ¼ 8:4 Hz), 7.33 (2H, d, H-6, J ¼ 8:6 Hz),
4.40 (2H, s, H-3), 3.65–3.54 (4H, m, H-1), 1.47 (6H, m, H-2);
13C NMR (100 MHz, CDCl3) ꢂ 35.39 (C-1), 9.50 (C-2), 35.22
(C-3), 143.10 (C-4), 132.11 (C-5), 129.31 (C-6), 118.39 (C-7),
111.79 (R). Anal. Calcd for C12H16NBrS: C 50.35, H 5.63, N
4.89%. Found: C 50.34, H 5.23, N 4.90%.
In the electrochemical reduction of BDES, the same rearrange-
ment occurred, along with coupling reactions as for BTHT, but the
yields are high compared to those from BTHT, especially in the
case of rearrangement of S–Y with Me and Br substituents.
Products from BTHT. 2-Tetrahydrothionyl-2-methylben-
zene [1]: Yellow liquid; bp 165–168 ꢂC; IR (KBr Coat) 3024
(m), 2947 (m), 2860 (m), 1850–1650 (w), 1602 (m), 1493 (m),
Diethyl-(4-nitrobenzyl)-sulfonium Bromide (j): Yellow sol-
id; mp 97–99 ꢂC; IR (KBr Tablet) 2926 (w), 2800 (w), 1850–1650
(w), 1604 (m), 1540 [NO2] (s), 1510 (s), 1226 (m), 854 (m), 798
(m), 752 (m), 694 (m) cmꢁ1
.
1H NMR (400 MHz, CDCl3) ꢂ
8.10 (2H, d, H-5, J ¼ 8:8 Hz), 7.39 (2H, d, H-6, J ¼ 8:8 Hz),
4.45 (2H, s, H-3), 3.70 (4H, m, H-1), 1.42 (6H, m, H-2); 13C NMR
(100 MHz, CDCl3) ꢂ 33.59 (C-1), 9.54 (C-2), 35.25 (C-3), 144.70
(C-4), 129.49 (C-5), 123.60 (C-6), 147.49 (C-7). Anal. Calcd for
C11H16NO2BrS: C 43.15, H 5.27, N 4.57%. Found: C 43.21, H
5.37, N 4.17%.
1440 (m), 1317 (m), 1195 (m), 760 (m) cmꢁ1
.
1H NMR (400
MHz, CDCl3) ꢂ 7.48–6.82 (4H, m, H-6,7,8,9), 4.61 (1H, t, H-4,
J ¼ 8:1 Hz), 3.01–2.76 (2H, m, H-1), 2.25–2.09 (2H, m, H-2),
2.21 (3H, s, H-11), 1.92–1.73 (2H, m, H-3); 13C NMR (100
MHz, CDCl3) ꢂ 38.67 (C-1), 31.22 (C-2), 33.88 (C-3), 49.01 (C-
4), 141.95 (C-5), 126.31 (C-6), 127.84 (C-7), 130.04 (C-8),
125.61 (C-9), 135.09 (C-10), 19.92 (C-11); MS m=z 178 [Mþ],
163 [Mþ ꢁ CH3] (15), 135 (43), 91 (87). Anal. Calcd for C11H14S:
C 74.10, H 7.91%. Found: C 74.04, H 7.66%.
2-Tetrahydrothionyl-2,5-dimethylbenzene [2]: Yellow liq-
uid; bp 181–183 ꢂC; IR (KBr Coat) 3016 (m), 2925 (m), 2860
(m), 1850–1650 (w), 1612 (m), 1500 (m), 1440 (m), 1379 (m),
1037 (m), 810 (m) cmꢁ1 1H NMR (400 MHz, CDCl3) ꢂ 7.31–
.
Electrochemical Reduction. In a 0.1 dL electrolytic cell which
has a porous cup made of ceramics as a divider membrane, 0.2 mol
of the S-salt was dissolved in 0.05 dL of acetonitrile at the cathodic
side of the cell. In an anodic side, 0.01 dL of acetonitrile which
contains 0.01 mol of tetraethylammonium perchlorate was used
as the electrolyte. As the electrodes, two platinum plates (2 ꢃ 2
cm) were equipped in the cell. The cathodic reduction was carried
ꢂ
out under condition of ꢁ2:5 V vs SCE at 22 C under a nitrogen
gas flow. After 1 F/mol of electricity based on the S-salts was
passed, the reaction products were dissolved in diethyl ether and
extracted with the same amount of water to remove inorganic
salts. And the organic solution was dried over Na2SO4. After
the solvent was removed by evaporation, the products were puri-
fied by column chromatography on silica-gel adsorbent using
CHCl3 as eluent. In the case of the Corey–Chaykovsky reactions,
an equimolar amount of benzaldehyde was dissolved in the cathod-
ic solution and the same work up was carried out.
6.80 (3H, m, H-6,8,9), 4.59 (1H, t, H-4, J ¼ 8:1 Hz), 3.03–2.74
(2H, m, H-1), 2.32–2.11 (2H, m, H-2), 2.22–2.20 (6H, s, H-
11,12), 1.95–1.82 (2H, m, H-3); 13C NMR (100 MHz, CDCl3) ꢂ
38.35 (C-1), 30.66 (C-2), 32.94 (C-3), 48.38 (C-4), 140.20 (C-5),
127.03 (C-6), 132.41 (C-7), 129.96 (C-8), 127.22 (C-9), 135.34
(C-10), 20.97 (C-11), 19.02 (C-12); MS m=z 192 [Mþ], 177 [Mþ
ꢁ CH3] (15), 163 (29), 149 (43), 133 (59) 117 (75). Anal. Calcd
for C12H16S: C 74.55, H 8.86%. Found: C 74.57, H 8.30%.
2-Tetrahydrothionyl-2-methyl-5-bromobenzene [3]: Yel-
Base Method. In acetonitrile solvent, 0.2 mol of the S-salts
were dissolved; after an equimolar amount of sodium amide was
added, the solution was refluxed for 2 h. The work-up method
was the same as in the case of the electrochemical reduction meth-
od.
Computational Method. Semi-empirical calculations were
carried out using PM3 method implemented in Prime Power 200
at Chubu university computer center. Each transition state pos-
sesses only one imaginary frequency for the vibrational analysis,
corresponding to the appropriate coordinate of the reaction. An
IRC calculation was performed for the transition state to confirm
that it is a true transition state.
ꢂ
low liquid; bp 186–188 C; IR (KBr Coat) 2947 (m), 2860 (m),
1850–1650 (w), 1589 (m), 1487 (m), 1440 (m), 1404 (m), 1070
(m), 1010 (m), 810 (m), 808 (m) cmꢁ1
.
1H NMR (400 MHz,
CDCl3) ꢂ 7.64–6.85 (4H, m, H-6,8,9), 4.56 (1H, t, H-4, J ¼ 8:1
Hz), 3.03–2.88 (2H, m, H-1), 2.27–2.04 (2H, m, H-2), 2.21 (3H,
s, H-11), 1.92–1.76 (2H, m, H-3); 13C NMR (100 MHz, CDCl3)
ꢂ 38.38 (C-1), 30.60 (C-2), 33.08 (C-3), 48.07 (C-4), 143.20 (C-
5), 129.43 (C-6), 119.72 (C-7), 131.74 (C-8), 129.62 (C-9),
134.49 (C-10), 19.10 (C-11); MS m=z 257 [Mþ], 242 [Mþ
ꢁ
CH3] (15), 163 [Mþ ꢁ CH3Br] (94), 150 (107), 134 (123), 118
(139). Anal. Calcd for C11H13BrS: C 51.37, H 5.09%. Found:
C 51.79, H 4.61%.
Reaction Products. The reaction products from BTHT and
BDES are summarized in the Tables 1 and 2, respectively; they
are numbered [1]–[15] and their yields are recorded in the same
column. Their structures were determined based on physical prop-
4,40-Dicyanobibenzyl [4]: White crystal; mp 190–193 ꢂC; IR
(KBr Tablet) 3057 (m), 2933 (m), 2223 [CN] (s), 1850–1650 (w),
1602 (m), 1504 (m), 1413 (m), 1176 (m), 835 (m), 557 (m) cmꢁ1
.

2158 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)
Rearrangement of S-Ylide Generated by EC-Method
Table 1. Reduction Products and Their Yields from BTHT Salts (%)
Synthetic methods
Electro reduction
with PhCHO
Base method
main products
Base method
side products
Salt
Electro reduction
(a)
(b)
(c)
(d)
(e)
—
—
Table 2. Reduction Products and Their Yields from BDES Salts (%)
Synthetic methods
Electro reduction
with PhCHO
Base method
main products
Base method
side products
Salt
Electro reduction
(f)
(g)
(h)
(i)
(j)
—
—

Y. Okazaki et al.
Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2159
(m), 835 (m), 522 [C–Br] (m) cmꢁ1 1H NMR (400 MHz, CDCl3)
ꢂ 7.34 (2H, d, H-2, J ¼ 8:5 Hz), 7.07 (2H, d, H-3, J ¼ 8:5 Hz),
3.64 (2H, s, H-5); 13C NMR (100 MHz, CDCl3) ꢂ 122.33 (C-1),
131.72 (C-2), 127.09 (C-3), 135.72 (C-4), 62.17 (C-5); MS m=z
275 [Mþ ꢁ Br] (81), 194 [Mþ ꢁ Br2] (162), 176 (178), 166
(190), 150 (206), 104 (250). Anal. Calcd for C14H10Br2O: C
85.68, H, 6.71%. Found: C 85.29, H 7.69%.
1H NMR (400 MHz, CDCl3) ꢂ 7.50 (4H, d, H-4, J ¼ 8:1 Hz), 7.20
(4H, d, H-3, J ¼ 14:8 Hz), 2.92 (4H, s, H-1); 13C NMR (100 MHz,
CDCl3) ꢂ 37.13 (C-1), 118.82 (C-2), 130.21 (C-3), 132.23 (C-4),
146.03 (C-5), 110.14 (C-6); MS m=z 232 [Mþ], 205 [Mþ ꢁ CN]
(27), 175 (57), 130 (102), 117 (115). Anal. Calcd for C16H12N2:
C 82.97, H 5.20, N 12.01%. Found: C 82.73, H 5.21, N 12.06%.
4,40-Dinitrobibenzyl [5]: Yellow crystal; mp 165–168 ꢂC; IR
(KBr Tablet) 3111 (m), 2937 (m), 1850–1650 (w), 1606 (m), 1593
(m), 1512 [NO2] (s), 1340 (m), 1107 (m), 852 (m), 752 (m), 698
.
trans-4,40-Dicyanostilbene Oxide [11]: White crystal; mp
103–106 ꢂC; IR (KBr Tablet) 3033 (m), 2933 (m), 2223 [CN]
(s), 1850–1650 (w), 1604 (m), 1541 (m), 1498 (m), 1402 (m),
(m) cmꢁ1
.
1H NMR (400 MHz, CDCl3) ꢂ 8.08 (4H, d, H-4, J ¼
8:5 Hz), 7.22 (4H, d, H-3, J ¼ 12:7 Hz), 3.01 (4H, s, H-1);
13C NMR (100 MHz, CDCl3) ꢂ 36.88 (C-1), 148.07 (C-2),
123.74 (C-3), 129.30 (C-4), 146.59 (C-5); MS m=z 272 [Mþ],
226 [Mþ ꢁ NO2] (46), 178 (94), 136 (136). Anal. Calcd for
C14H12N2O4: C 61.76, H 4.44, N 10.29%. Found: C 61.69, H
4.26, N 10.06%.
1110 (m), 835 (m), 827 (m) cmꢁ1 1H NMR (400 MHz, CDCl3)
.
ꢂ 7.62 (4H, d, H-2, J ¼ 9:0 Hz), 7.40 (4H, d, H-3, J ¼ 8:7 Hz),
3.83 (2H, s, H-5); 13C NMR (100 MHz, CDCl3) ꢂ 112.37 (C-1),
118.37 (C-2), 132.72 (C-3), 126.14 (C-4), 141.39 (C-5), 62.07
(C-5); MS m=z 246 [Mþ], 220 [Mþ ꢁ CN] (26), 210 (36), 193
(53), 147 (99), 135 (111), 104 (142). Anal. Calcd for C16H10N2O:
C 78.04, H 4.09, N 11.38%. Found: C 77.68, H 4.58, N 11.09%.
trans-4,40-Dinitrostilbene Oxide [12]: Yellow crystal; mp
128–130 ꢂC; IR (KBr Tablet) 3118 (m), 3030 (m), 1850–1650
(w), 1600 (m), 1506 [NO2] (s), 1352 (m), 1012 (m), 1107 (m),
trans-Stilbene Oxide [6]: White crystal; mp 65–67 ꢂC; IR
(KBr Tablet) 3030 (m), 2933 (m), 1850–1650 (w), 1609 (m),
1492 (m), 1452 (m), 1271 (m), 1026 (m), 891 (m), 750 (m), 696
(m) cmꢁ1
.
1H NMR (400 MHz, CDCl3) ꢂ 7.98 (2H, s, H-1),
7.19 (4H, d, H-3, J ¼ 2:2 Hz), 6.94 (4H, t, H-2, J ¼ 10:5 Hz),
3.70 (2H, s, H-5); 13C NMR (100 MHz, CDCl3) ꢂ 128.12 (C-1),
128.22 (C-2), 125.08 (C-3), 136.69 (C-4), 62.39 (C-5); MS m=z
196 [Mþ], 177 (19), 166 (30), 151 (45), 104 (92), 90 (106). Anal.
Calcd for C14H12O: C 85.68, H 6.16%. Found: C 85.46, H 5.92%.
trans-4-Methylstilbene Oxide [7]: White crystal; mp 43–45
ꢂC; IR (KBr Tablet) 3038 (m), 2960 (m), 1850–1650 (w), 1517
(m), 1450 (m), 1271 (m), 1109 (m), 1070 (m), 817 (m), 769 (m),
850 (m), 813 (m) cmꢁ1 1H NMR (400 MHz, CDCl3) ꢂ 8.10
.
(4H, d, H-2, J ¼ 8:6 Hz), 7.45 (4H, d, H-3, J ¼ 8:8 Hz), 3.92
(2H, s, H-5); 13C NMR (100 MHz, CDCl3) ꢂ 148.29 (C-1),
123.60 (C-2), 126.91 (C-3), 147.06 (C-4), 63.08 (C-5); MS m=z
287 [Mþ], 239 [Mþ ꢁ NO2] (46), 223 (64), 211 (76), 194 (93),
176 (111), 150 (137), 104 (183). Anal. Calcd for C14H10N2O3:
C 58.75, H 3.52, N 9.79%. Found: C 58.35, H 3.47, N 9.45%.
Products from BDES. 1-(2-Methylphenyl)-diethyl Sulfide
738 (m), 698 (m) cmꢁ1
.
1H NMR (400 MHz, CDCl3) ꢂ 7.23–
[13]: Yellow liquid; bp 160–162 C; IR (KBr Coat) 3024 (m),
2947 (m), 2860 (m), 1850–1650 (w), 1602 (m), 1493 (m), 1440
ꢂ
7.01 (5H, m, H-9,10,11), 6.96 (4H, d, H-2,3, J ¼ 11:5 Hz), 3.61
(1H, s, H-7), 3.58 (1H, s, H-6), 2.10 (3H, s, H-1); 13C NMR (100
MHz, CDCl3) ꢂ 20.84 (C-1), 137.11 (C-2), 128.91 (C-3), 125.19
(C-4), 132.58 (C-5), 62.47 (C-6), 62.33 (C-7), 129.31 (C-8),
126.47 (C-9), 128.18 (C-10), 128.02 (C-11); MS m=z 210 [Mþ],
195 [Mþ ꢁ CH3] (15), 181 (29), 166 (44), 152 (58), 103 (107).
Anal. Calcd for C15H14O: C 85.68, H 6.71%. Found: C 85.73, H
6.70%.
(m), 1317 (m), 1195 (m), 760 (m) cmꢁ1
.
1H NMR (400 MHz,
CDCl3) ꢂ 7.39–6.99 (4H, m, H-6,7,8,9), 4.15 (1H, d, H-3, J ¼
7:1 Hz), 2.29 (2H, d, H-2, J ¼ 8:1 Hz), 2.30 (3H, s, H-11), 1.45
(3H, m, H-4), 1.12–1.08 (3H, m, H-1); 13C NMR (100 MHz,
CDCl3) ꢂ 24.82 (C-1), 14.46 (C-2), 21.77 (C-3), 38.98 (C-4),
141.52 (C-5), 126.34 (C-6), 128.25 (C-7), 130.12 (C-8), 126.19
(C-9), 135.01 (C-10), 19.17 (C-11); MS m=z 180 [Mþ], 165 [Mþ
ꢁ CH3] (15), 149 (31), 134 (46), 119 (61), 103 (77). Anal. Calcd
for C11H16S: C 73.27, H 8.94%. Found: C 73.25, H 8.61%.
1-(2,4-Dimethylphenyl)-diethyl Sulfide [14]: Yellow liquid;
bp 163–165 ꢂC; IR (KBr Coat) 3016 (m), 2925 (m), 2860 (m),
1850–1650 (w), 1612 (m), 1500 (m), 1440 (m), 1379 (m), 1037
trans-4-Bromostilbene Oxide [8]: White crystal; mp 83–85
ꢂC; IR (KBr Tablet) 3041 (m), 2979 (m), 1850–1650 (w), 1593
(m), 1488 (m), 1460 (m), 1423 (m), 1070 (m), 1008 (m), 839
(m), 788 (m), 748 (m), 513 [C–Br] (m) cmꢁ1
.
1H NMR (400
MHz, CDCl3) ꢂ 7.38 (2H, d, H-3, J ¼ 8:3 Hz), 7.24–7.22 (5H,
m, H-2,9,10), 7.09 (2H, d, H-8, J ¼ 8:8 Hz), 3.70–3.66 (2H, m,
H-5,6); 13C NMR (100 MHz, CDCl3) ꢂ 121.93 (C-1), 131.65 (C-
2), 126.98 (C-3), 136.52 (C-4), 61.89 (C-5), 62.57 (C-6), 135.99
(C-7), 125.31 (C-8), 128.38 (C-9), 128.32 (C-10); MS m=z 275
[Mþ], 194 [Mþ ꢁ Br] (81), 176 (99), 166 (109), 150 (125), 104
(171). Anal. Calcd for C14H11BrO: C 61.11, H 4.03%. Found:
C 61.43, H 4.01%.
(m), 810 (m) cmꢁ1
.
1H NMR (400 MHz, CDCl3) ꢂ 7.16–6.75
(3H, m, H-6,8,9), 4.08 (1H, d, H-3, J ¼ 7:3 Hz), 2.26 (2H, d, H-
2, J ¼ 9:5 Hz), 2.21 (3H, s, H-11), 2.18 (3H, s, H-12) 1.41 (3H,
m, H-4), 1.01 (3H, m, H-1); 13C NMR (100 MHz, CDCl3) ꢂ
24.71 (C-1), 14.31 (C-2), 21.65 (C-3), 38.83 (C-4), 141.11 (C-5),
127.05 (C-6), 131.62 (C-7), 129.88 (C-8), 126.78 (C-9), 135.22
(C-10), 19.17 (C-11), 20.78 (C-12); MS m=z 194 [Mþ], 179 [Mþ
ꢁ CH3] (15), 163 (31), 149 (45), 133 (61), 117 (77), 105 (89).
Anal. Calcd for C12H18S: C 74.16, H 9.34%. Found: C 74.57, H
9.15%.
trans-4,40-Dimethylstilbene Oxide [9]: White crystal; mp 80–
82 ꢂC; IR (KBr Tablet) 3039 (m), 2864 (m), 1850–1650 (w), 1608
(m), 1514 (m), 1278 (m), 1018 (m), 879 (m), 839 (m), 806 (m)
1
cmꢁ1. H NMR (400 MHz, CDCl3) ꢂ 7.08 (4H, d, H-3,4, J ¼ 8:3
1-(2-Methyl-4-bromophenyl)-diethyl Sulfide [15]: Yellow
liquid; bp 177–180 ꢂC; IR (KBr Coat) 2947 (m), 2860 (m),
1850–1650 (w), 1589 (m), 1487 (m), 1440 (m), 1404 (m), 1070
Hz), 7.00 (4H, d, H-4, J ¼ 8:5 Hz), 3.66 (2H, s, H-6), 2.19 (3H,
s, H-1); 13C NMR (100 MHz, CDCl3) ꢂ 21.06 (C-1), 137.81 (C-
2), 129.06 (C-3), 125.29 (C-4), 134.11 (C-5), 62.60 (C-6), 27.56
(C-7); MS m=z 224 [Mþ], 209 [Mþ ꢁ CH3] (15), 195 (29), 180
(44), 165 (59), 104 (124). Anal. Calcd for C16H16O: C 85.68, H
6.71%. Found: C 85.29, H 7.69%.
(m), 1010 (m), 810 (m), 808 (m) cmꢁ1
.
1H NMR (400 MHz,
CDCl3) ꢂ 7.51–6.84 (4H, m, H-6,8,9), 4.20 (1H, d, H-3, J ¼ 7:1
Hz), 2.35 (2H, d, H-2, J ¼ 11:9 Hz), 2.19 (3H, s, H-11), 1.40
(3H, m, H-4), 1.03 (3H, m, H-1); 13C NMR (100 MHz, CDCl3) ꢂ
24.83 (C-1), 14.38 (C-2), 21.62 (C-3), 38.80 (C-4), 143.95 (C-5),
129.38 (C-6), 119.84 (C-7), 131.73 (C-8), 129.33 (C-9), 133.95
(C-10), 18.67 (C-11); MS m=z 259 [Mþ], 244 [Mþ ꢁ CH3] (15),
trans-4,40-Dibromostilbene Oxide [10]: White crystal; mp
101–104 ꢂC; IR (KBr Tablet) 3003 (m), 2933 (m), 1850–1650
(w), 1591 (m), 1487 (m), 1438 (m), 1402 (m), 1074 (m), 1010

2160 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)
Rearrangement of S-Ylide Generated by EC-Method
165 [Mþ ꢁ CH3Br] (94), 150 (109), 134 (125), 118 (141). Anal.
Calcd for C11H15BrS: C 50.97; H, 5.83%. Found: C, 51.19; H,
5.44%.
Electrochemical generation of S–Y progresses as a one-elec-
tron reduction process, since S-salt disappeared nearly 100%
when 1 F/mol of electric current has been passed. In the pres-
ence of benzaldehyde, the electrochemical reduction of S-salts
which have EDG substituents such as methyl and bromo
groups gives epoxides in high yields as a result of the Corey–
Chaykovsky reaction. On the contrary, the main products of
this reaction without benzaldehyde proved to be interesting re-
arrangement products that are numbered as [1]–[3] and [13]–
[15] in Tables 1 and 2.
In the electrochemical reduction method without the pres-
ence of benzaldehyde, the rearrangement compound is the main
product, and no oxidation of the ylide to produce aldehydes
occurred. This fact may be ascribed to retardation of oxidiza-
tion because of the reductive surroundings of the cathode. On
the other hand, S-salts which have an EWG, such as a nitro and
a cyano group, gave benzyl dimers, and no generation of S–Ys
could be confirmed.
The electrochemical reduction might proceed through a 3-
way mechanism as described in Scheme 2. The two routes des-
ignated R1 and R2 route are based on the positional difference
of hydrogen abstraction. Furthermore, R3 corresponds to a
dimerization route of benzyl radicals generated from the radical
intermediate from the S-salt.
The reaction with benzaldehyde progresses following the R1
route. In the case of S–Ys, nucleophilic reaction to a carbonyl
group creates an epoxide and is different from the reaction of
P–Y because of the weaker affinity of S to oxygen atom than
Discussion
Organosulfides have been applied as synthetic raw materials
for S-salts, sulfoxides, sulfones, and the other sulfur
compounds. Among them, S-salts are important compounds
for the synthesis of S–Ys. Under gentle conditions and without
catalyst, we prepared S-salts by the reaction of alkyl halides
with aliphatic sulfides. The electrophilic reaction of alkyl hal-
ides to the sulfur atom of sulfides is the rate-determining step.
And the reaction is fast when the alkyl halide gives a stable car-
bocation.
The generation of S–Ys by a base such as sodium amide has
been confirmed by reactions with many carbonyl compounds.29
However, without the presence of carbonyl compounds, the
ylides gave symmetrical epoxides derived from the benzyl
groups on the salt as a result of an oxidation reaction caused
by coexisting oxygen as shown in Scheme 1. Along with the
epoxides, the rearrangement compounds [1]–[3] and [13]–
[15] were found as minor products; their yields obtained from
1H NMR are shown in Tables 1 and 2. In the case of the S–
Ys having an EWG on a benzyl group, stable ylides formed
by standing for a long period and a small amount of epoxide
was produced via autoxidization. The generated benzaldehyde
reacted with residual S–Y immediately after its formation, so
no benzaldehyde was detected during the autoxidization.
Scheme 1.
Scheme 2.

Y. Okazaki et al.
Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2161
Scheme 3.
Scheme 4.
that of P atom. For cleaving the intermediate four-membered
ring and forming C–C double bond, high activation energy is
required because of steric strain, and sulfide is eliminated
through a SN2 type reaction of oxygen to carbon atom. Gener-
ally, sulfides are known as good leaving groups, and this is a
reason why epoxides are formed by the R1 route. In all electro-
chemical reductions, the hydrogen molecule generation was
observed at the cathodic electrode, indicating the coupling re-
action of generated hydrogen atoms.
of S-Ylide which has two benzyl groups on sulfur atom have
been reported.27 However, there is no report on Sommelet–
Hauser rearrangements of S–Y which has only one benzyl
group which enforce the rearrangement through unstable S–
Y. In this experiment, Sommelet–Hauser rearrangement prod-
ucts are formed through an unstable ylide R2 which may exist
in equilibrium with stable ylide R1. Although the starting ylide
is unstable in R2 route, the transition state of the rearrangement
is stabilized because both the cation on the S atom and the anion
can delocalize into benzene rings in the R2 route. A possible
rearrangement through stable S–Y in R1 route shown in the
equation may give eight-membered products through transition
state A1. Both routes R1 and R2 will give transition states
obeying the Woodward–Hoffmann rule, i.e., 5 orbitals and 6
electrons as shown in Scheme 4.
In order to elucidate the reason why this S–H rearrangement
proceeds through the unstable Ylide B instead of stable Ylide
A, we calculated the energy surfaces and the geometries of
all the reactants, intermediates and transition states on the sur-
face of the R1 and R2 routes by using the PM3 Hamiltonian; an
energy diagram of the reaction of BTHT that has no substituent
on the benzyl group is presented in Fig. 1. In this figure, the
heat of formation of proton was subtracted from that of sulfo-
nium ion; also, from the heats of formation of each epoxide,
that of benzaldehyde was taken away.
Besides the reactions of S–Y with electrophiles such as car-
bonyl compounds, imines and olefins, characteristic rearrange-
ment reactions have fascinated many investigators. The [1,2]-
Stevens rearrangement found in N–Ys are also reported with S–
Y
30 having an aryl group at the ꢃ-position. This rearrangement
could be a radical process, because sigmatropic rearrangements
which include four electrons in three orbitals pictured in
Scheme 3 are forbidden by the Woodward–Hoffmann rule.
The products [1]–[3] and [13]–[15] found in this study come
from the [2,3] sigmatropic Sommelet–Hauser rearrangement
of S–Ys by the R2 route. Regarding N–Y, many Sommelet–
Hauser rearrangements have been reported so far.31 The migra-
tion of one of the substituents on the heteroatom, in this case the
nitrogen atom, to the ortho position of the aromatic ring of the
benzyl group occurred. In the case of S–Y, a similar [2,3]
Wittig rearrangement and the Sommelet–Hauser rearrangement

2162 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)
Rearrangement of S-Ylide Generated by EC-Method
Fig. 1. Energy surfaces of the Sommelet–Hauser rearrangement.
The difference in the heat of formations between stable Ylide
A and unstable Ylide B is 9.3 kcal/mol. The possible reaction
products of each, Ylide A and Ylide B, with benzaldehyde are
indicated as Epoxide A and Epoxide B; the heats of formation
were nearly equal. However the experimental results showed
that the reaction product of S–Y with benzaldehyde is Epoxide
A; therefore, the stable Ylide A must have reacted immediately
after its formation with benzaldehyde. For without benzalde-
hyde Ylide A cannot rearrange to form Product A, because
the activation energy of TS A1 is obviously 30.1 kcal/mol
higher than that of TS B1. And the activation energy of the fol-
lowing hydrogen migration is lower by 7.4 kcal/mol in TS B2
than in TS A2, indicating the preferential formation of Product
B. And it is clear that the dramatic stability difference between
TS A1 and TS B1 is the main factor of route determination.
The R2 route from Ylide B to EFB is the real path of this re-
arrangement and involves a sigmatropic rearrangement reac-
tion with cleavage of the S–C11 ꢄ bond. And the ꢀ electrons
on the benzene ring can interact with the partial positive charge
generated on C11. This resonance stabilization decreases the
activation energy to TS B1 from unstable Ylide B. On the con-
trary, the interaction of the partial positive charge generated on
C4 atoms of TS A1 with benzene ring is not large enough to sta-
bilize the transition state TS A1. The differences of electron
density changes between Ylide A and TS A1, and also between
Ylide B and TS B1, are shown in Fig 2. The electron densities
Fig. 2. The differences of electron densities between Ylide
A and TS A1, Ylide B and TS B1.
on the benzene ring appear to be larger in the TS B1 than in the
TS A1. In the case of TS B1, the electrons at anion and cation
on S atom delocalize more to the benzene ring than in the case
of TS A1. This is the reason why TS B1 is more stable than TS
A1 and why no rearrangement via R1 route occurs.
The weaker bond strength of ` bond in radical intermediate
compared to ꢀ bonds may be an another factor to control the

Y. Okazaki et al.
Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2163
reaction path. The bond strengths of ˆ and ˜ do not differ so
much; therefore the C–H bond fission does not contribute to the
route determination. The hydrogen migration from this inter-
mediate EFB to TS B2 is a [1,3] sigmatropic rearrangement
and is suprafacial, as the dihedral angle of C3–C4–C5–H1
changes from ꢁ68:2ꢂ to ꢁ121:1ꢂ. C10–C11 becomes a single
bond upon the migration, thus leading to the regeneration of the
benzene ring. The geometrical figures of the R1 and R2 route
are shown in the Figs. 3 and 4 and the relevant dihedral angles
are listed in Table 3. We also calculated the two-centered bond
Fig. 3. Optimized structures of the R1 route.
Fig. 4. Optimized structures of the R2 route.

2164 Bull. Chem. Soc. Jpn., 76, No. 11 (2003)
Rearrangement of S-Ylide Generated by EC-Method
Table 3. Dihedral Angles of Optimized Structures in R1 and R2 Route
R1
R2
Ylide A
TS A1
EF A
TS A2
Product A
Ylide B
TS B1
EF B
TS B2
Product B
S–C11–C10–C5
C4–S–C11–C10
C4–S–C10–C5
S–C4–C5–C10
C4–C5–C10–C11
C11–C10–C5–H1
C3–C4–C5–H1
ꢁ17:5
ꢁ50:5
ꢁ61:9
35.5
ꢁ12:5
ꢁ23:8
ꢁ36:6
45.0
ꢁ43:3
ꢁ45:4
ꢁ22:1
2.3
ꢁ27:3
ꢁ33:9
73.3
ꢁ52:7
ꢁ46:5
ꢁ1:7
ꢁ40:7
14.7
ꢁ17:0
52.4
ꢁ30:6
ꢁ41:3
ꢁ47:5
88.5
ꢁ60:7
ꢁ18:6
ꢁ1:0
ꢁ84:2
76.9
3.2
39.8
2.5
ꢁ56:7
27.8
ꢁ19:1
51.6
ꢁ24:1
ꢁ40:4
ꢁ21:8
ꢁ41:9
5.2
ꢁ35:1
83.3
ꢁ67:4
ꢁ35:9
ꢁ68:2
ꢁ28:6
ꢁ2:1
23.7
ꢁ40:9
ꢁ28:6
2.9
ꢁ61:4
26.0
47.5
ꢁ35:8
74.7
ꢁ50:0
ꢁ1:7
ꢁ26:8
22.8
ꢁ72:3
4.6
ꢁ121:1
1.4
29.9
ꢁ23:1
ꢁ106:6
energies and spin densities of the radical intermediates from
BTHT and BDES to elucidate the bond fission on the radical
intermediate. The results are summarized in Tables 4–7 and
Figs. 5, 6 where the atom numbers and bond numbers are
defined.
generate S–Y, judging from the complete recovery of benzalde-
hyde, and radical coupling products of benzyl groups were ob-
tained in high yield. The S–benzyl bond of trivalent sulfur rad-
icals obtained by one electron reduction of the S-salt is weak-
ened because of the dispersion of electron spin density to neigh-
boring carbon atoms by the strong EWG. This fact can be
substantiated by the theoretical calculations as follows.
When S–Y has a benzyl group with a strong EWG such as a
CN, or a NO2 group, the electrochemical reduction does not
Fig. 5. Geometries and definitions of BTHT.
Fig. 6. Geometries and definitions of BDES.
Table 4. The Bond Energies (eV) of Radical Intermediates
from BTHT
Table 6. The Bond Energies (eV) of Radical Intermediates
from BDES
Substituent R
Substituent R
H
Me
Br
CN
NO2
H
Me
Br
CN
NO2
ꢀ
`
´
ˆ
˜
ꢁ11:35
ꢁ7:92
ꢁ11:36
ꢁ7:90
ꢁ11:35
ꢁ7:78
ꢁ11:35
ꢁ7:65
ꢁ11:35
ꢁ7:51
ꢀ
`
´
ˆ
˜
ꢁ10:77
ꢁ8:50
ꢁ10:57
ꢁ8:71
ꢁ10:64
ꢁ8:53
ꢁ10:71
ꢁ8:34
ꢁ10:81
ꢁ8:14
ꢁ14:83
ꢁ12:74
ꢁ12:67
ꢁ14:84
ꢁ12:74
ꢁ12:67
ꢁ14:88
ꢁ12:75
ꢁ12:67
ꢁ14:99
ꢁ12:75
ꢁ12:68
ꢁ15:16
ꢁ12:76
ꢁ12:70
ꢁ14:75
ꢁ12:68
ꢁ12:66
ꢁ14:71
ꢁ12:68
ꢁ12:66
ꢁ14:76
ꢁ12:68
ꢁ12:67
ꢁ14:86
ꢁ12:68
ꢁ12:68
ꢁ15:01
ꢁ12:68
ꢁ12:69
Table 5. The Spin Densities of Radical Intermediates from
BTHT
Table 7. The Spin Densities of Radical Intermediates from
BDES
Substituent R
Substituent R
H
Me
Br
CN
NO2
H
Me
Br
CN
NO2
S
C4
C11
0.33
0.28
0.50
0.29
0.28
0.50
0.33
0.26
0.51
0.30
0.24
0.52
0.31
0.21
0.52
S
C4
C11
0.23
0.28
0.44
0.23
0.29
0.41
0.24
0.27
0.43
0.24
0.25
0.44
0.26
0.22
0.45

Y. Okazaki et al.
Bull. Chem. Soc. Jpn., 76, No. 11 (2003) 2165
7
2724 (1968).
E. J. Corey, K. Lin, and M. Jautelat, J. Am. Chem. Soc., 90,
In the two-centered bond energies, the ` bond of radical in-
termediates of BTHT and BDES were significantly decreased
by the effect of a CN or NO2 group in the p-position of the
benzyl group. In addition, it is clear that the ´ bond is
strengthened. A very characteristic dispersion of radical spin
density for each substituent is shown in Tables 4 and 6. Con-
cerning each radical intermediate with EDG group, the highest
spin density is found on C11. In fact, the reduction of S-salts in
the presence of benzaldehyde, the S–Y generation, occurred via
the R1 route, i.e., the hydrogen radical was abstracted from this
carbon. While the radical intermediates with EWG have the
same amounts of spin density on C11, the bond strength on
` bond decreases considerably, about 6–7 kcal/mol; this fact
allows the cleavage of benzyl radical which is stabilized by
the EWG group.
8
9
T. Tompson and T. S. Stevens, J. Chem. Soc., 1932, 69.
J. E. Baldwin and R. E. Hackler, J. Am. Chem. Soc., 91,
3646 (1969).
10 G. B. Payne, J. Org. Chem., 32, 3351 (1967).
11 J. March, ‘‘Advanced Organic Chemistry,’’ Wiley, New
York (1992), p. 38.
12 T. Naito, S. Nagase, and H. Yamataka, J. Am. Chem. Soc.,
116, 10080 (1994).
13 B. M. Trost, Acc. Chem. Res., 7, 85 (1974).
14 C. R. Johnson, Acc. Chem. Res., 6, 341 (1973).
15 A. W. Johnson, ‘‘Ylide Chemistry,’’ Academic Press, N.Y.
(1966).
16 E. Block, ‘‘Reaction of Organosulfure Compounds,’’ Aca-
demic Press, N.Y. (1978).
17 G. Schmidt, J. Gosselck, and M. Jautelat, Tetrahedron Lett.,
10, 3445 (1969).
Summary
The electrochemical reduction of sulfonium salts having a
benzyl group with p-EDG gave a stable S-Ylide A. This fact
was confirmed by a Corey–Chaykovsky reaction of the ylide
with benzaldehyde. In the absence of benzaldehyde, the
Sommelet–Hauser rearrangement of the ylide occurred. On
the contrary, the same reduction of sulfonium salt having a ben-
zyl group with p-EWG formed the coupling products of the
benzyl group instead of forming S-Ylide. The results were
compared with those obtained by the normal base method.
By using semi-empirical MO calculations, we compared the re-
action path of the ylide generations and the two routes of the
possible Sommelet–Hauser rearrangement.
18 J. Diekmann, J. Org. Chem., 30, 2272 (1965).
19 B. M. Trost and R. W. LaRochelle, J. Am. Chem. Soc., 92,
5804 (1970).
20 J. Adams, L. Hoffman, and B. M. Trost, J. Org. Chem., 35,
1600 (1970).
21 J. Gordeler, ‘‘Sulfonium Compounds in Methoden der
Organischen Chemie,’’ Georg Thieme Verlag, Stuttgart (1955),
Vol. i.
22 A. Ghanimi and J. Simonet, New J. Chem., 21, 257 (1997).
23 E. A. H. Hall and J. Simonet, J. Electroanal. Chem., 100,
197 (1979).
24 K. Makita, F. Ando, Y. Ninomiya, and J. Koketsu, Nippon
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25 E. Vedejs, Acc. Chem. Res., 17, 358 (1984).
26 Y. D. Wu and K. N. Houk, J. Org. Chem., 56, 5657 (1991).
27 K. Okada and M. Tanaka, J. Chem. Soc., Perkin Trans. 1,
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