Asymmetric synthesis of epoxides from aromatic aldehydes and benzyl halides catalyzed by C2 symmetric optically active sulfides having a binaphthyl skeleton

Article abstract of DOI:10.1002/hc.10028

The catalytic formation of optically active trans-stilbene oxides with moderate enantioselectivities from sulfur ylides and aldehydes was described. The epoxides were formed by the reaction of aromatic aldehydes with benzyl bromide or iodide. A C₂ symmetric optically active sulfide having a binaphthyl skeleton was used a catalyst in the synthesis.

Full text of DOI:10.1002/hc.10028

Heteroatom Chemistry
Volume 13, Number 3, 2002
Asymmetric Synthesis of Epoxides from
Aromatic Aldehydes and Benzyl Halides
Catalyzed by C Symmetric Optically Active
2
Sulfides Having a Binaphthyl Skeleton
Yoshihiro Miyake, Arihiro Oyamada, Yoshiaki Nishibayashi,
and Sakae Uemura
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering,
Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
Received 28 August 2001; revised 25 September 2001
trans-epoxides as major products. If chiral sulfur
ABSTRACT: Reactions of aromatic aldehydes with
ylides were used, optically active epoxides might be
benzyl bromide or iodide in the presence of a cat-
obtained. The first attempt by Trost and co-workers
alytic amount (10 mol%) of a C2 symmetric sulfide
in 1973 [3] to prepare optically active epoxides via
having a binaphthyl skeleton afford the corresponding
chiral sulfur ylides resulted in failure, and since then
trans-stilbene oxides in moderate to good yields with
many asymmetric reactions have been investigated.
moderate enantioselectivities (up to 55% enantiomeric
Recently, reactions of a stoichiometric amount of
excess). The addition of tetra-n-butylammonium io-
chiral sulfonium salts [4] with aldehydes have been
dide to the catalytic reaction system much improves
investigated to afford the corresponding optically ac-
C
the yield of the epoxides. 2002 Wiley Periodicals, Inc.
tive trans-epoxides with high enantioselectivities.
Heteroatom Chem 13:270–275, 2002; Published online
In the stoichiometric reaction of sulfur ylides
in Wiley Interscience (www.interscience.wiley.com). DOI
with aldehydes, sulfides are recovered together with
10.1002/hc.10028
the formation of epoxides. If sulfur ylides can be
regenerated from the recovered sulfides in situ, the
epoxide formation should be achieved in the pres-
INTRODUCTION
ence of a catalytic amount of sulfides. In fact, suc-
cessful examples of such catalytic reaction have been
reported [5–8], but turnover frequencies (TOF) are
quite low except for the case reported by Aggarwal
[6]. These results prompted us to develop a more
effective catalytic system for the synthesis of opti-
cally active trans-epoxides. Herein, we describe the
catalytic formation of optically active trans-stilbene
oxides from sulfur ylides and aldehydes by using
a C2 symmetric optically active sulfide having a
binaphthyl skeleton 1 [9] (Fig. 1).
Optically active epoxides are versatile intermedi-
ates in the synthesis of pharmaceuticals and natu-
ral products. Direct asymmetric oxidation of alkenes
has been studied as a synthetic method for the prepa-
ration of the corresponding cis-epoxides with high
enantioselectivities [1]. In sharp contrast, the meth-
ods for the preparation of trans-epoxides with high
enantioselectivities reported so far have been lim-
ited to only a few cases [2]. Reactions of sulfur ylides
with aldehydes are known to give the corresponding
RESULTS AND DISCUSSION
Correspondence to: Sakae Uemura; e-mail: uemura@sci.kyoto-
u.ac.jp.
2002 Wiley Periodicals, Inc.
First, the treatment of benzaldehyde with benzyl bro-
mide in the presence of a stoichiometric amount of
270
c

Asymmetric Synthesis of Epoxides from Aromatic Aldehydes and Benzyl Halides 271
NaI prevented the formation of the epoxide (Table
1, entries 6 and 7). Reactions in chlorobenzene and
CCl4 gave the epoxide with 62% ee and 61% ee, re-
spectively, but the yields of the epoxide were quite
low (Table 1, entries 8 and 9). Reaction in DMSO pro-
duced the epoxide in good yield, but with no enan-
tioselectivity (Table 1, entry 10). As KOH is not sol-
uble in CH2Cl2, the reactions were carried out in the
presence of a small amount of water to dissolve KOH.
As a result, the product yields increased, but the
enantioselectivity was lowered, unfortunately (en-
try 12). In various other solvents, no fruitful results
were obtained in either product yield or enantios-
electivity. The reaction at 0 C proceeded slowly to
give the epoxide in low yield with 53% ee (Table 1,
entry 14).
The molecular structure of the sulfide 1 was un-
ambiguously clarified by an X-ray structural deter-
mination, and an Oak Ridge thermal ellipsoid plot
(ORTEP) drawing of one of the three independent
molecules of compound 1 in each unit cell is shown
in Fig. 2. This ORTEP drawing clearly shows that
the space around the sulfur atom may be sterically
only slightly hindered. As the introduction of phenyl
groups to the 2,6-positions of compound 1 makes
the space around the sulfur atom sterically more
hindered and higher asymmetric induction may be
FIGURE 1
C symmetric optically active sulfide.
2
sulfide 1 [10] (to the aldehyde) and KOH in CH2Cl2
at room temperature for 24 h afforded trans-stilbene
oxide in 66% yield with 54% enantiomeric excess
(ee). No cis-stilbene oxide was detected by GLC
and 1H NMR spectroscopy. Since the stoichiometric
reaction proceeded smoothly, we next attempted the
catalytic reaction by using 0.1 equiv (to the aldehyde)
of 1 under similar reaction conditions (Eq. 1).
(1)
Typical results are shown in Table 1. trans-Stilbene
oxide was produced in 15% yield with 47% ee (S,
S) in 48 h (Table 1, entry 1). Interestingly, the ad-
dition of tetra-n-butylammonium iodide (n-Bu4NI)
to the reaction system much improved the yield of
trans-stilbene oxide to 44% with 50% ee (S, S) in 24
h (Table 1, entry 2) [11]. Other bases such as KO-t-
Bu, K2CO3, and Et3N were revealed to be ineffective
(Table 1, entries 2–5) and the addition of AgOTf or
TABLE 1 Asymmetric Synthesis of trans-Stilbene Oxide us-
ing Several Bases and Additivesa
Entry Solvent
Base Additive (equiv) Yield (%)b ee (%)c
1d
2
CH2Cl2 KOH
CH2Cl2 KOH
CH2Cl2 KO-t-Bu n-Bu4NI (1.2) Trace
–
15
44
47
50
–
41
–
n-Bu4NI (1.2)
3d
4
CH2Cl2 K2CO3 n-Bu4NI (1.2)
4
0
5
6
7
8
9
10
CH2Cl2 Et3N
CH2Cl2 KOH
CH2Cl2 KOH
C6H5Cl KOH
n-Bu4NI (1.2)
AgOTf (1.2)
Nal (1.2)
Trace
7
–
18
62
61
0
–
32
4
n-Bu4NI (1.2) Trace
CCI4
KOH
n-Bu4NI (1.2)
n-Bu4NI (1.2)
n-Bu4NI (1.2)
n-Bu4NI (1.2)
n-Bu4NI (1.2)
n-Bu4NI (1.2)
11
69
0
96
57
8
DMSO KOH
CH3CN KOH
CH2Cl2 KOH
CH3CN KOH
CH2Cl2 KOH
11
12e
13e
14f
53
aReaction conditions: benzaldehyde (0.5 mmol), benzyl bromide
(0.6 mmol), 1 (0.05 mmol), base (0.6 mmol), solvent (0.4 ml), room
temperature, and 24 h under N2.
FIGURE 2 The ORTEP drawing of optically active sul-
˚
fide 1. Selected bond lengths, angles, torsion angle (A, deg,
deg): S1 C1 = 1.85(1); C1 C2 = 1.52(2); C2 C3 = 1.38(2);
C3 C4 = 1.48(1); C4 C5 = 1.39(2); C5 C6 = 1.51(2);
C6 S1 = 1.85(1); C1 S1 C6 = 100.4(6); S1 C1 C2 =
bGLC yield after column chromatography.
cDetermined by HPLC.
d Reaction time was 48 h.
e H2O (40 l) was added.
109.6(10);
58(1).
S1 C6 C5 = 110.0(9);
C2 C3 C4 C5 =
fAt 0 C.

272 Miyake et al.
expected [12], we prepared the optically active sul-
fide 2 (Fig. 1). Unfortunately, however, the reaction of
benzaldehyde with benzyl bromide in the presence
of compound 2 (10 mol%) gave only a trace amount
of stilbene oxide.
Reactions using other aldehydes and benzyl
halides were next investigated in the presence of a
catalytic amount of the sulfide 1 (Eq. 2).
(2)
Typical results are shown in Table 2. A higher
yield of trans-stilbene oxide was obtained when ben-
zyl iodide was used in place of benzyl bromide
(Table 2, entries 1 vs. 2). It is noteworthy that the ad-
dition of n-Bu4NI improved the yield of trans-stilbene
oxide even when benzyl iodide was used (Table 2,
entries 2 and 3). The reaction of benzyl iodide with
other aromatic aldehydes was then examined in the
presence of n-Bu4NI (Eq. 2). The substituent at the
para-position of these aldehydes had a major effect
on the yield of the corresponding epoxides. The re-
action of p-methylbenzaldehyde proceeded slowly to
give the corresponding epoxide in low yield (Table 2,
entry 4), while p-chlorobenzaldehyde gave a simi-
lar result as with benzaldehyde (Table 2, entry 5).
On the contrary, p-nitrobenzaldehyde was almost
completely consumed, but the expected epoxide was
produced and isolated in only low yield because of
the formation of various unidentified products. The
best enantioselectivity (55% ee) was obtained when
2-naphtaldehyde was used as the aldehyde (Table 2,
entry 8).
SCHEME 1 Plausible reaction pathway.
A plausible reaction pathway is shown in
Scheme 1. The reaction of the sulfide 1 with benzyl
halide affords a sulfonium salt (I) which gives
the corresponding sulfur ylide (II) by deprotona-
tion with KOH. The nucleophilic addition of II to
the aldehyde results in the formation of the trans-
epoxide, together with the starting sulfide 1. In our
catalytic system, asymmetric induction can be ratio-
nalized by assuming the model shown in Scheme 2.
Thus, the sulfur ylide II may exist in the form de-
picted in the scheme that emphasizes the interaction
between the phenyl group and the binaphthyl skele-
ton. The nucleophilic attack of the carbon of com-
pound II to the re face of the aldehyde would be fa-
vored leading to the formation of trans-(S,S)-stilbene
oxide consistent with the experimental result. The re-
action of benzyl bromide with iodide anion derived
from n-Bu4NI affords the more reactive benzyl io-
dide in situ and the tetra-n-butylammonium cation
may also play some role as a phase transfer catalyst
to accelerate the reaction, although the details of the
reaction mechanism are not yet clear. In a separate
experiment, we confirmed that the BF4 analogue of
TABLE 2 Asymmetric Synthesis of trans-Stilbene Oxide
Derivatives using Other Aromatic Aldehydesa
Entry
R
X
Yield (%)b ee (%)c Con g.
1
2
3
4
5
6
7
8
Ph
Br
I
I
I
I
I
I
I
44
79
26
13
51
50
43
29
52
50
51
28
55
(S, S )
(S, S )
(S, S )
(S, S )
(S, S )
(–)
Ph
Phd
p-MeC6H4
p-CIC6H4
p-NO2C6H4
1-Naphthyl
2-Naphthyl
e
6f
15
(–)
(–)
30f
aReaction conditions: benzaldehyde (0.5 mmol), benzyl halide
(0.6 mmol), 1 (0.05 mmol), KOH (0.6 mmol), n-Bu4NI (0.6 mmol),
CH2Cl2 (0.4 ml), room temperature, and 24 h under N2.
b GLC yield after column chromatography.
c Determined by HPLC.
d In the absence of n-Bu4NI.
e Reaction time was 6 h.
f Isolated yield.
SCHEME 2 Asymmetric induction model.

Asymmetric Synthesis of Epoxides from Aromatic Aldehydes and Benzyl Halides 273
(R)-4,5-Dihydro-3H-dinaphtho[2,1-c:10,20-e]thiepin
(1) was prepared from (R)-BINOL according to the
literature method [10].
Preparation of (R)-2,6-Diphenyl-4,5-dihydro-3H-
dinaphtho[2,1-c:10,20-e]thiepin (2)
SCHEME 3 Reaction of sulfonium salt with benzaldehyde.
This compound was prepared from (R)-3,30-dipheny-
lbinaphthol [12] according to the literature method
[10]: A pale yellow solid; 1H NMR (CDCl3, 300 MHz):
3.34 (d, J = 12.8 Hz, 2H), 3.58 (d, J = 12.8 Hz, 2H),
7.23–7.93 (m, 20H); 13C NMR (CDCl3, 75.45 MHz):
29.3, 125.9, 126.0, 127.0, 127.3, 128.2, 129.7, 130.2,
131.1, 131.7, 132.4, 134.7, 139.2, 141.1; HRMS Calcd
for C34H24S m/z 464.1599 (M+), Found 464.1614.
compound I (3), prepared separately, reacted with
benzaldehyde in the presence of KOH (1.2 equiv)
in CH2Cl2 at room temperature for 1 h to afford a
37% yield of trans-stilbene oxide with 33% ee (S,
S) (Scheme 3). The enantioselectivity obtained here
was slightly lower than that of the catalytic reaction
(Table 2, entries 1 and 2). This result may suggest
that the counter anion of the sulfonium salt plays
some role in the asymmetric induction.
In conclusion, we found that a C2 symmetric sul-
fide having a binaphthyl skeleton 1 worked as a chiral
catalyst in the presence of n-Bu4NI for the asymmet-
ric reaction between aromatic aldehydes and benzyl
halides to give the corresponding trans-stilbene ox-
ides in moderate to good yields (up to 79%) with
moderate enantioselectivities (up to 55% ee).
General Procedure for Asymmetric Synthesis
of Epoxides using Benzyl Iodide
After benzene was removed from a benzene solution
of benzyl iodide (0.24 M; 1.0 ml, 0.24 mmol) under
reduced pressure, CH2Cl2 (0.4 ml) was added and the
mixture was stirred at room temperature under ni-
trogen. The sulfide (0.02 mmol), n-Bu4NI (88.7 mg,
0.24 mmol), pulverized KOH (13.5 mg, 0.24 mmol),
and the aldehyde (0.20 mmol) were added to the
mixture and then the reaction mixture was stirred
for 24 h. The resulting mixture was treated with
water (10 ml), extracted with CH2Cl2, dried over
MgSO4, filtered, and the filtrate was evaporated. The
residue was purified by column chromatography
using hexane/CH2Cl2 as an eluent.
EXPERIMENTAL
General
1H and 13C NMR spectra were measured on JEOL
EX-400, JEOL JNM-AL300, and JEOL JNM-GSX270
spectrometers for solutions in CDCl3 with Me4Si as
an internal standard. GLC analyses were carried out
with a Shimadzu GC-14A instrument equipped with
a CPB 10-S25-050 (Shimadzu, fused silica capillary
column, 0.33 mm 25 m, 5.0 mm film thickness) col-
umn using helium as the carrier gas. GLC yields were
determined using biphenyl as an internal standard.
HPLC analyses were carried out on a HITACHI L-
7100 instrument with an L-7300 column oven and
an L-7400 UV detector using a Daicel Chiralcel OD
column. Column chromatographies were performed
with Merck silica gel 60.
trans-2,3-Diphenyloxirane. A White solid; mp
62–64 C (lit. 61–63 C) [13]; 1H NMR (CDCl3,
300 MHz): 3.87 (s, 2H), 7.30–7.45 (m, 10H). The ee
value was determined by HPLC analysis with a Dai-
cel Chiralcel OD column (eluent: hexane/2-propanol
= 95:5, flow rate: 1.0 ml/min, column temperature:
25 C, retention time: 7.3 min (S, S), 14.5 min (R, R)).
trans-2-(p-Chlorophenyl)-3-phenyloxirane [13]. A
white solid; mp 86–88 C; 1H NMR (CDCl3, 300 MHz):
3.82 (d, J = 1.8 Hz, 1H), 3.84 (d, J = 1.8 Hz, 1H),
7.24–7.42 (m, 9H). The ee value was determined
by HPLC analysis with a Daicel Chiralcel OD
column (eluent: hexane/2-propanol = 95:5, flow rate:
1.0 ml/min, column temperature: 25 C, retention
time: 8.4 min (S, S), 10.4 min (R, R)).
Materials
Tetrahydrofuran (THF) was freshly distilled over
sodium benzophenone ketyl just before use. Dich-
loromethane (CH2Cl2) and acetonitrile were distilled
over calcium hydride under argon. Benzalde-
hyde was distilled under reduced pressure. Other
commercially available organic and inorganic
compounds were used without further purification.
Benzyl iodide in benzene solution was prepared by
ion exchange of benzyl chloride with sodium iodide.
trans-2-(p-Tolyl)-3-phenyloxirane. A white solid;
mp 70–72 C (lit. 72–73 C) [13]; 1H NMR (CDCl3,
400 MHz):
2.37 (s, 3H), 3.83 (d, J = 1.8 Hz,
1H), 3.86 (d, J = 1.8 Hz, 1H), 7.18–7.41 (m, 9H).
The ee value was determined by HPLC analysis

274 Miyake et al.
TABLE 3 Summary of Crystallographic Data of Compound 1
with a Daicel Chiralcel OD column (eluent: hexane/
2-propanol = 95:5, flow rate: 0.5 ml/min, column
temperature: 25 C, retention time: 12.0 min (S, S),
18.2 min (R, R)).
Empirical formula
Formula weight
Crystal system
Space group
C22H16S
312.43
Orthorhombic
P212121(#19)
Colorless
Crystal color
trans-2-(p-Nitrophenyl)-3-phenyloxirane. A pale
yellow solid; mp 75–77 C (lit. 73–75 C) [13]; 1H NMR
(CDCl3, 300 MHz): 3.85 (d, J = 1.5 Hz, 1H), 3.97
(d, J = 1.5 Hz, 1H), 7.25–7.45 (m, 5H), 7.52 (d, J =
8.7 Hz, 2H), 8.25 (d, J = 8.7 Hz, 2H). The ee value
was determined by HPLC analysis with a Daicel
Chiralcel OD column (eluent: hexane/2-propanol =
90:10, flow rate: 1.0 ml/min, column temperature:
25 C, retention time: 16.2 min, 20.7 min).
Lattice parameters
˚
a (A)
22.229 (10)
25.594 (8)
8.59 (2)
4888 (9)
12
1.273
1.95
1968.00
˚
b (A)
˚
c (A)
3
˚
V (A )
Z
3
Dcalc (g cm
(Mo Kα) (cm
F(000)
)
1
)
Diffractometer
Radiation
Rigaku AFC7R
˚
Mo Kα ( = 0.71069 A)
trans-2-(1-Naphthyl)-3-phenyloxirane [14]. A co-
graphite monochromated
lorless oil; 1H NMR (CDCl3, 300 MHz):
3.86
Temp. ( C)
Scan type
Max. 2θ ( )
No. of reflections measured
No. of observations
(I > 3.00 (I ))
Structure soln
Refinement
No. of variables
Reflection/parameter ratio
Residuals: R; Rw
23.0
ω
55.0
5126
2200
(br s, 1H), 4.49 (s, 1H), 7.38–7.99 (m, 12H); 13C
NMR (CDCl3, 75.45 MHz): 61.1, 62.0, 122.0, 122.9,
125.6, 125.9, 126.4, 128.2, 128.4, 128.7, 131.2, 133.2,
133.3, 137.2. The ee value was determined by HPLC
analysis with a Daicel Chiralcel OD column (eluent:
hexane/2-propanol = 95:5, flow rate: 1.0 ml/min, col-
umn temperature: 25 C, retention time: 14.4 min,
19.4 min).
Direct methods (SIR92)
Full-matrix least squares
532
4.14
0.067; 0.066
1.15
Goodness of fit (GOF)
Max shift/error in final cycle
trans-2-(2-Naphthyl)-3-phenyloxirane [15]. A
white solid; mp 114–116 C; 1H NMR (CDCl3,
300 MHz): 3.97 (d, J = 1.5 Hz, 1H), 4.04 (d, J =
1.5 Hz, 1H), 7.34–7.88 (m, 12H); 13C NMR (CDCl3,
75.45 MHz): 63.0, 63.1, 122.8, 125.0, 125.5, 126.2,
126.4, 127.79, 127.83, 128.36, 128.43, 128.6, 133.2,
133.4, 134.6, 137.1. The ee value was determined
by HPLC analysis with a Daicel Chiralcel OD col-
umn (eluent: hexane/2-propanol = 98:2, flow rate:
1.0 ml/min, column temperature: 25 C, retention
time: 30.9 min, 34.9 min).
6.61
0.26
Maximum peak in final diff
3
˚
map (e A
)
Minimum peak in final diff
0.20
3
˚
map (e A
)
structure was solved by direct methods (SIR92).
Three independent molecules of compound 1 occupy
a unit cell. The structure of these three independent
molecules are almost the same. The carbon atoms
at C5-8 positions of the binaphthyl ring were re-
fined isotropically. All other non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were
included, but not refined. The weighting scheme
ω = 1/ 2(F0) with (F0) from counting statics gave
satisfactory agreement analyses.
X-ray Structural Analysis of 1
A single crystal of 1 (C22H16S) suitable for X-ray
analysis was prepared by recrystallization from
CH2Cl2–n-hexane. Diffraction data were collected
on a Rigaku AFC-7R four-circle automated diffrac-
Preparation of Sulfonium Salt 3
˚
tometer with Mo-K␣ (␭ = 0.719 A) radiation and a
graphite monochromator at 23 C using the ␻
2
A mixture of optically active sulfide 1 (234 mg,
0.750 mmol) and benzyl bromide (0.09 ml,
0.75 mmol) was stirred in CH2Cl2 (5 ml) at
room temperature under nitrogen. AgBF4 (146 mg,
0.750 mmol) was added to the mixture and then the
reaction mixture was stirred for 5 h. Removal of the
precipitates from the mixture by use of Celite and
evaporation of the solvent gave a crude solid product.
The crude product was washed with Et2O to give a
scan technique. Details of the X-ray diffraction study
are summarized in Table 3. For a structure analysis
and refinement, computations were performed us-
ing the TEXAN [16] crystallographic software pack-
age of Molecular Structure. Neutral atom scattering
factors were taken from Ref. [17]. Anomalous dis-
persion effects were included in Fcalc [18]; the val-
ues of 1f 0 and 1f 00 were those of Ref. [19]. The

Asymmetric Synthesis of Epoxides from Aromatic Aldehydes and Benzyl Halides 275
[3] Trost, B. M.; Hammen, R. F. J Am Chem Soc 1973,
95, 962–964.
[4] Li, A.-H.; Dai, L.-X.; Aggarwal, V. K. Chem Rev 1997,
97, 2340–2372.
[5] Furukawa, N.; Sugihara, Y.; Fujihara, H. J Org Chem
1989, 54, 4222–4224.
[6] (a) Aggarwal, V. K. Synlett 1998, 329–336; (b)
Aggarwal, V. K.; Alonso, E.; Hynd, G.; Lydon, K. M.;
Palmer, M. J.; Porcelloni, M.; Studley, J. R. Angew
Chem Int Ed 2001, 40, 1430–1433.
white solid in 82% yield (304 mg, 0.620 mmol); mp
149–151 C; H NMR (400 MHz, CD2Cl2) 3.63 (d,
1
J = 11.7 Hz, 1H), 3.99 (d, J = 14.7 Hz, 1H), 4.39
(d, J = 12.5 Hz, 1H), 4.47 (d, J = 14.7 Hz, 1H), 4.62
(d, J = 12.5 Hz, 1H), 4.64 (d, J = 11.7 Hz, 1H), 7.23–
8.27 (m, 20H); 13C NMR (CD2Cl2, 100 MHz): 39.3,
42.4, 44.4, 122.2, 126.1, 126.5, 126.7, 127.1, 127.31,
127.34, 127.5, 128.4, 129.7, 130.0, 130.1, 130.4, 130.5,
131.5, 135.9; HRMS Calcd for C29H23S m/z 403.1520
(M+ BF4), Found 403.1510.
[7] Li, A.-H.; Dai, L.-X.; Hou, X.-L.; Huang, Y.-Z.; Li, F.-W.
J Org Chem 1996, 61, 489–493.
[8] (a) Julienne, K.; Metzner, P. J Org Chem 1998, 63,
4532–4534; (b) Julienne, K.; Metzner, P.; Henryon, V. J
Chem Soc, Perkin Trans 1 1999, 731–736; (c) Zanardi,
J.; Leriverend, C.; Aubert, D.; Julienne, K.; Metzner,
P. J Org Chem 2001, 66, 5620–5623.
[9] Miyake, Y.; Oyamada, A.; Nishibayashi, Y.; Uemura, S.
Presented at the 79th Annual Meeting of the Chemical
Society of Japan, Kobe, Japan, March, 2001; p. 1160,
Abstract 2H216.
[10] Stara´, I. G.; Stary, P.; Tichy, M.; Za´vada, J.; Fiedler, P.
J Org Chem 1994, 59, 1326–1332.
[11] Quite recently, Metzner and co-workers indepen-
dently reported that the addition of n-Bu4NI im-
proved the yields of the epoxides [8c].
[12] Chong, J. M.; Shen, L.; Taylor, N. J. J Am Chem
Soc 2000, 122, 1822–1823; In this paper, higher
enantioselectivities in asymmetric 1,4-addition of
alkynylboronates to enones were obtained when (R)-
3,30-diphenylbinaphthol was used in place of (R)-
binaphthol.
[13] Solladie´-Cavallo, A.; Diep-Vohuule, A.; Sunjic, V.;
Vinkovic, V. Tetrahedron: Asymmetry 1996, 7, 1783–
1788.
Reaction of Sulfonium Salt 3 with Benzaldehyde
A mixture of the sulfonium salt 3 (98 mg, 0.20 mmol)
and pulverized KOH (13.5 mg, 0.240 mmol) was
stirred in CH2Cl2 (4 ml) at room temperature un-
der nitrogen for 15 min. Benzaldehyde (20.3 ␮l,
0.2 mmol) was added to the mixture and then the
reaction mixture was stirred for 1 h. The resulting
mixture was treated with water (10 ml), extracted
with CH2Cl2, dried over MgSO4, and filtered. The
filtrate contained 2,3-diphenyloxirane in 37% GLC
yield (14.5 mg, 0.074 mmol, biphenyl as internal
standard). The filtrate was then evaporated to leave
a residue which was purified by column chromatog-
raphy using hexane/CH2Cl2 as an eluent, the enan-
tioselectivity of the product oxirane being 33% ee.
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