Reactivity of 2-methylene-1,3-dicarbonyl compounds: Catalytic enantioselective Diels-Alder reaction

Article abstract of DOI:10.1016/S0957-4166(01)00559-6

The catalytic enantioselective Diels-Alder reaction of 1,1-dicarbonylethenes 3 with cyclopentadiene in the presence of Ti-TADDOLs, Mg-Ph-box and Mg-Ph-mox complexes was investigated. Although both exo- and enantioselectivity with Ti-TADDOL catalysts were

Full text of DOI:10.1016/S0957-4166(01)00559-6

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 3113–3118
Reactivity of 2-methylene-1,3-dicarbonyl compounds: catalytic
enantioselective Diels–Alder reaction
Masashige Yamauchi,* Takashi Aoki, Ming-Zhu Li† and Yuko Honda
Faculty of Pharmaceutical Sciences, Josai University, Keyakidai, Sakado, Saitama 350-0295, Japan
Received 10 October 2001; accepted 6 December 2001
Abstract—The catalytic enantioselective Diels–Alder reaction of 1,1-dicarbonylethenes 3 with cyclopentadiene in the presence of
Ti-TADDOLs, Mg–Ph-box and Mg–Ph-mox complexes was investigated. Although both exo- and enantioselectivity with
Ti-TADDOL catalysts were poor, they were much improved using Mg–Ph-box or Mg–Ph-mox complexes as chiral catalysts.
Thus, 3 was an efficient two-point binding dienophile and the non-C2-symmetric Ph-mox 8 could be used as a chiral ligand.
© 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
bonyl groups are different, with cyclopentadiene in the
presence of a chiral Lewis acid to produce the chiral
Diels–Alder adduct 4. Ethyl 2-benzoylacrylate 3a5 and
1-phenyl-2-methylenebutane-1,3-dione 3b5 were chosen
as dienophiles and TADDOLs 5 and Ph-box 6 as chiral
ligands (Chart 1).
Recently, a great deal of effort has been devoted to the
development of catalytic enantioselective Diels–Alder
reactions.1 C2-Symmetric ligands, such as tetra-
aryldioxolanedimethanols (TADDOLs)2 and bis(oxazo-
lines) (boxes),3 and metal complexes have been proven
to be excellent catalysts in the reaction. In most cases
3-alkenoyl derivatives of 1,3-oxazolidine-2-ones have
been used as two-point binding dienophiles. The previ-
ous report4 from this laboratory described the Lewis
acid-catalyzed diastereoselective Diels–Alder reaction
using (1R,2S,5R)-5-methyl-2-(1-methyl-1-phenylethyl)-
cyclohexyl-2-benzoylacrylate 1 as a dienophile. This
report has demonstrated that the reaction proceeds via
a two-point binding transition state 2 in which the
p-stacking of the chelated conjugated system and ben-
zene ring of the phenylmenthyl group restricts the
attack of the diene from the back side, and steric
hindrance from the benzoyl moiety blocks the approach
of the diene to the benzoyl group because the benzene
ring is situated perpendicular to the conjugated ene-
dione system. From these results it was anticipated that
the enantioselective reaction would be achieved from
the reaction of 1,1-dicarbonylethene 3, whose two car-
M
Ph
O
O
O
O
Ph
O
O
2
1
O
O
a ; R = OEt
b ; R = Me
Ph
R
3
Ar
Ar
Ar
Et Et
OH
O
O
O
O
Ph
N
N
OH
Me
Ar
Ph
Ph
5
a ; Ar = C6H5
b ; Ar = 4-CH3OC6H4
6
* Corresponding author. Tel.: +81 49 271 7681; fax: +81 49 271 7984;
e-mail: yamauchi@josai.ac.jp
† Present address: Department of Pharmacy, Yanbian Medical Col-
lege, Yanji City, Jilin Prov., China 133000.
Chart 1.
0957-4166/01/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(01)00559-6

3114
M. Yamauchi et al. / Tetrahedron: Asymmetry 12 (2001) 3113–3118
2. Results and discussion
improved with the complex prepared in refluxing
CH3CN (entry 5). The diastereoisomers produced were
chromatographically homogeneous in TLC and could
not be resolved by column or medium pressure chro-
matography, however, the diastereomeric ratio could be
Our initial efforts were focused on the possibility that
ethyl 2-benzoylacrylate 3a should be a good two-point
binding dienophile in an enantiomeric Diels–Alder
reaction.
1
determined from the H NMR spectrum, as mentioned
in our previous report (Scheme 3).4
First the reactions were carried out with TADDOL–
titanium combination. The catalysts were prepared
according to Narasaka’s procedure.2b As can be seen
from Table 1, reducing the temperature of the reaction
has almost no effect on the exo–endo (4a–x:4a–n)6 ratio
or on the enantioselectivity with both 5a and 5b lig-
ands, and both the exo-selectivities and enantioselectiv-
ities were moderate and poor (Scheme 1). Since all of
the exo-products separated by preparative HPLC are
levorotatory, the quaternary carbon of the predominant
exo-adduct has S-configuration (vide infra).
As 3a proved to be a suitable dienophile, we next
examined the reaction using N-[(1R)-2-chloro-1-
phenylethyl]-2-ethyl-2-[(4R)-4-phenyl-4,5-dihydrooxaz-
ol-2-yl]butyramide (Ph-mox) 8 as a chiral ligand.
Ligand 8 was synthesized by treatment of the dichloride
7 (which was prepared from 2,2-diethyl-N,N%-bis-[(1R)-
2-hydroxy-1-phenylethyl)-malonamide)7
with
an
equimolar amount of NaOH in MeOH–H2O at 60°C.
Ligand 8 exists as colorless prisms (mp 127–128°C from
ethyl acetate). The reaction using the complex prepared
from 8:MgI2:I2 (1:1:1) in CH2Cl2 at room temperature
also gave poor enantioselectivity (entry 6). However,
when the reaction was performed with the same com-
plex prepared in refluxing CH3CN, the e.e. of product
increased to 87% (entry 8). Interestingly, the enantiose-
lectivities of reactions with the complex prepared from
MgI2:8:I2 (1:2:2) (half amounts of Lewis acid compared
with entry 7) were almost equal or slightly higher (entry
9). All exo-products obtained with 6 and 8 were dextro-
rotatory, and enantioselectivities were determined by
analytical HPLC. In order to confirm the absolute
configuration, enantiomerically pure 4a–x, obtained by
recrystallization of the exo-product (entry 9), was
treated with bromine in CCl4. The product showed
carbonyl absorptions at 1786 and 1674 cm−1 in the IR
Next oxazoline–magnesium combinations were exam-
ined. The reactions were carried out as follows. The
catalyst was prepared under the conditions shown in
Table 2. The solvent was removed and the resulting
complex was dissolved in CH2Cl2 and cooled to the
requisite temperature. To this solution enedione 3a or
3b was added and then cyclopentadiene was added
slowly to the mixture (Scheme 2).
In order to test for temperature dependency, the reac-
tions were carried out with the catalyst prepared from
3,3-bis(4-phenyl-4,5-dihydrooxazol-2-yl)pentane
(Ph-
box) 6, MgI2 and I2 in CH3CN. Lowering the tempera-
ture from −15 to −90°C provided product with
significantly improved enantioselectivity (entries 2–4).
In the reaction with the complex prepared from 6, MgI2
and I2 in CH2Cl2 at room temperature using Corey’s
procedure,3c the enantioselectivity was somewhat infe-
rior to that in CH3CN (entries 1 and 4). However, both
exo-selectivity and enantioselectivity were much
1
spectrum and its H NMR spectral pattern was very
similar to that8 of 9-bromo-5-oxatricyclo[4.2.1.03.7]-
nonane-4-one. X-Ray crystallographic analysis9 shows
that the product has the structure 9 and therefore the
quaternary carbon of the Diels–Alder adduct 4a–x is
R-configured. Since the Ph-mox 8 was recovered almost
Table 1. Enantioselective Diels–Alder reaction of 3a with cyclopentadiene using TADDOLs 5a and 5b as Lewis acid
catalysts
Entry
Ligand
T (°C)
Yield (%)
4a–x:4a–n
% e.e. of 4a–x
1
2
3
4
5
6
5a
5a
5a
5b
5b
5b
0
−40
−80
0
−15
−40
65
69
61
72
65
62
82:18
85:15
86:14
86:14
87:13
85:15
24
22
18
16
24
24
TADDOLs
TiCl2(OiPr)2
O
O
O
O
Ph
EtO
4a-x
EtO
Ph
OEt
+
Ph
4a-n
O
O
3a
toluene
Scheme 1.

M. Yamauchi et al. / Tetrahedron: Asymmetry 12 (2001) 3113–3118
3115
Table 2. Enantioselective Diels–Alder reaction of 3a and 3b with cyclopentadiene using Ph-box 6 and Ph-mox 8 as chiral
ligands
Entry
R
Catalyst
I2
Reaction conditions
Product
% e.e. of 4xb
Ligand
(equiv.)
MgI2
(equiv.)
Conditions
T (°C)
t (h)
Yield
4–x: 4–na
(equiv.)
(%)
1
2
3
4
5
6
7
8
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
Me
6 (0.2)
6 (0.2)
6 (0.2)
6 (0.2)
6 (0.2)
8 (0.2)
8 (0.2)
8 (0.2)
8 (0.4)
6 (0.2)
8 (0.2)
8 (0.2)
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.1
0.2
0.2
0.2
0.1
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.4
0.2
0.2
0.2
CH2Cl2, rt, 3 h
CH3CN, rt, 1 h
CH3CN, rt, 1 h
CH3CN, rt, 1 h
CH3CN, reflux, 1 h
CH2Cl2, rt, 3 h
CH3CN, reflux, 1 h
CH3CN, reflux, 1 h
CH3CN, reflux, 1 h
CH3CN, reflux, 1 h
CH3CN, reflux, 1 h
CH3CN, reflux, 1 h
−90
−15
−50
−90
−90
−90
−90
−90
−90
−90
−90
−90
6
2
4
7
6
6
6
8
8
74
70
76
75
81
76
88
88
75
77
84
78
97:3
96:4
98:4
70
18
42
78
85
18
87
87
89
78
69
81
98:2
\99:1
\99:1
\99:1
\99:1
\99:1
98:2
9
10
11
12
12
15
21
Me
Me
97:3
97:3
a Ratios were determined by 1H NMR (olefinic protons).
b % e.e. was determined by HPLC using a Chiralcel OD column.
O
R
Ph-box or Ph-mox
MgI2, I2
O
O
O
R
Ph
Ph
R
+
O
Ph
O
3
4-x
4-n
a ; R = OEt
b ; R = Me
CH2Cl2
Scheme 2.
Et Et
Et Et
pendicular to the ene in the fixed metal-chelated ene-
dione.4 The sense of the asymmetric induction in the
reaction with Ph-box 6 can be rationalized by assuming
that the reaction proceeds via the intermediacy of a
square-planar 103d or an octahedral 113g rather than a
tetrahedral 123c complex. Both the square-planar and
the octahedral models predict that cyclopentadiene
should approach to the re face in the case of 3a and to
the si face in the case of 3b of a chelated dienophile.
Whereas the tetrahedral model predicts that cyclopen-
tadiene approaches from the opposite face (if the reac-
tion take place). Another possibility that the reaction
might not occur in the tetrahedral model is not
neglected because both phenyl groups hinder cyclopen-
tadiene from approaching to the both sides. In the case
of Ph-mox 8 as a ligand somewhat C2-symmetric-like
transition state must also be taken into account. In
O
O
O
O
1 equiv NaOH
MeOH/H2O
Cl
Cl
Cl
NHHN
Ph
NH
Ph
N
Ph
Ph
7
8
Scheme 3.
quantitatively from column chromatography after the
reaction, the possibility of conversion of Ph-mox 8 into
Ph-box 6 during the preparation of the chiral catalyst
or the reaction was eliminated (Scheme 4).
The reaction of 1-phenyl-2-methylenebutane-1,3-dione
3b was also examined. All reactions were carried out at
−90°C, with the catalyst prepared previously in reflux-
ing CH3CN. The reactions gave products with enan-
tioselectivities of up to 81%. Both the exo-selectivity
and enantioselectivity were lower than those in the case
of 3a, which might be due to steric hindrance from the
methyl group which is larger than the oxygen of the
ethoxy group in the fixed transition state.
1
order to resolve this problem we obtained the H NMR
spectra of complexes prepared from equimolar amounts
of Lewis acid and chiral ligand. In the 1H NMR
spectrum of the Ph-mox 8–Mg complex prepared in
refluxing CH3CN, only one set of signals corresponding
O
O
Ph
Br2
Ph
Br
CCl4
O
OEt
O
4a-x
As mentioned earlier, the observed high diastereoselec-
tivity can be rationalised as being due to the steric
hindrance from the benzene ring situated nearly per-
O
9
Scheme 4.

3116
M. Yamauchi et al. / Tetrahedron: Asymmetry 12 (2001) 3113–3118
to oxazoline ring protons and amide side-chain protons
was observed. The signals for the oxazoline ring pro-
tons were broadened and observed ca. 0.2 ppm
downfield of the corresponding peak for Ph-mox 8,
while the methylene protons of the amide side-chain,
which appeared as double AB quartets in the spectrum
of 8, were seen as a broad doublet in 8–Mg (ca. 0.15
downfield shift) and the methyne proton was slightly
broadened (ca. 0.5 ppm downfield shift). On the other
hand, in the spectrum of the 8–Mg complex prepared at
room temperature, the signals in the region of 4–6 ppm
were complicated. Some of the signals were not identi-
cal with those of 8-Mg complex prepared in refluxing
CH3CN, and of the parent ligand 8. From these results
we concluded that chelation was not complete at room
temperature and conformational rigidity was achieved
only in the 8–Mg complex prepared in refluxing
CH3CN. Thus, a plausible transition state is shown as
13 in Fig. 2, in which hydrogen bonding between the
chloride and the amide hydrogen plays an important
role. PM3 calculations on the 8–Mg complex reveal
that the optimal conformation of the complex has a
structure like 13 from which the enedione is omitted.
It was thought that usage of bis(amide) 7 as a chiral
ligand may also be possible provided the amide side-
chains are fixed in the transition state. In fact the
Diels–Alder reaction of 3a and cyclopentadiene with
7–Mg complex, prepared in refluxing CH3CN, gave the
exo-products 4a–x in ca. 80% e.e., less satisfactory than
in the case of 8.
3. Experimental
3.1. General
Melting points are uncorrected. MgSO4 was used to dry
organic layers after extraction. Column chromatogra-
phy was performed with Silica Gel 60 (Spherical, Kanto
Chemical Co.). HPLC was carried out with a Daisel
Chiralcel OD column (0.46×25 cm; eluent 0.1% propan-
2-ol in hexane). NMR spectra were recorded in chloro-
form-d at 270 MHz for 1H and 67.89 MHz for 13C
NMR using tetramethylsilane as an internal standard.
IR spectra were determined either neat or in KBr
pellets. High-resolution mass spectra were recorded at
70 eV.
3.2. General procedure for reaction of 3a with
titanium–TADDOL complex
Under an argon atmosphere, to
a solution of
TiCl2(OiPr)2 (21.2 mg, 0.098 mmol) in toluene (2 mL)
was added a solution of the chiral TADDOL (0.098
,
mmol) in toluene (2 mL) and 4 A MS (120 mg) at room
temperature, and the mixture was stirred for 1 h, then
cooled to the temperature shown in Table 1, and a
solution of 3a (200 mg, 0.98 mmol) in toluene (4 mL)
was added. Stirring was continued for 0.5 h and a
solution of cyclopentadiene (65 mg, 0.98 mmol) in
toluene (5 mL) was added over a period of 2 h. The
reaction mixture was stirred overnight at the same
temperature, and then pH 7 phosphate buffer (10 mL)
was added to the mixture. The organic layer was
extracted with ethyl acetate (3×10 mL). The combined
extracts were dried and evaporated. The residue was
purified by column chromatography to give the Diels–
Alder adducts (Table 1).
3.3. N,N%-Bis[(1R)-2-chloro-1-phenylethyl]2,2-
diethyl-1,3-propanediamide 7
A solution of N,N%-bis[(1R)-2-hydroxy-1-phenylethyl]-
2,2-diethylmalonamide (7.7 g, 22 mmol) in SOCl2 (33
mL, 0.45 mol) was heated under reflux for 4 h. Excess
SOCl2 was evaporated and the residue was dissolved in
CH2Cl2 (100 mL) and washed with H2O (50 mL×2) and
saturated aqueous NaHCO3 (50 mL). The organic layer
was dried and evaporated. The resulting residue was
purified by column chromatography (CHCl3) to yield 7
(3.98 g, 91%); mp 157–159°C (from CHCl3), IR 3300,
1
1640 cm−1; H NMR l 0.87 (t, J=7.5 Hz, 6H), 1.97 (q,
J=7.5 Hz, 4H), 3.79 (dd, J=11.5, 6.1 Hz, 2H), 3.88
(dd, J=11.5, 5.0 Hz, 2H), 5.38 (br t, J=6.3 Hz, 2H),
7.26–7.35 (m, 10H), 7.91 (br d, J=7.5 Hz, 2H); 13C
Figure 2.

M. Yamauchi et al. / Tetrahedron: Asymmetry 12 (2001) 3113–3118
3117
NMR l 9.5, 30.9, 47.6, 54.0, 58.4, 126.5, 128.1, 128.8,
138.5, 172.8. [h]1D8 −78.0 (c 1.00, CHCl3). Anal. calcd for
C23H28N2O2Cl2: C, 63.45; H, 6.48; N, 6.43. Found: C,
63.29; H, 6.49; N, 6.33%.
3.5.2. (1R,2S,4R)-1-[2-Benzoylbicyclo[2.2.1]hept-5-ene-2-
yl]ethanone 4b–x. Colorless prisms (from petroleum
1
ether); mp 88–89°C; IR 1715, 1672 cm−1; H NMR l
1.45 (br d, J=8.8 Hz, 1H), 1.57 (br d, J=8.8 Hz, 1H),
1.89 (dd, J=12.0, 3.5 Hz, 1H), 2.03 (s, 3H), 2.59 (dd,
J=12.0, 2.5 Hz, 1H), 2.93 (br s, 1H) 3.82 (br s, 1H),
5.89 (dd, J=5.8, 3.0 Hz, 1H), 6.34 (dd, J=5.8, 3.0 Hz,
1H), 7.41 (t, J=7.3 Hz, 2H), 7.52 (t, J=7.3 Hz, 1H),
7.87 (d, J=7.3 Hz, 2H); 13C NMR l 27.7, 34.3, 43.2,
49.7, 49.9, 73.8, 128.5, 129.6, 131.3, 133.2, 136.0, 140.8,
198.8, 204.3. [h]2D1 +546.4 (c 3.86, CHCl3). Anal. calcd
for C16H16O2: C, 79.97; H, 6.71 Found: C, 79.95; H,
6.84%. HRMS calcd for C16H16O2: 240.1150. Found:
240.1148.
3.4. N-[(1R)-2-Chloro-1-phenylethyl] 2-ethyl-2-[(4R)-4-
phenyl-4,5-dihydrooxazol-2-yl]butyramide 8
To a solution of 7 (3.104 g, 7.1 mmol) in MeOH (150
mL) was added NaOH (284 mg, 7.1 mmol) in H2O (40
mL) at 50°C and the reaction mixture was stirred for 1
h at the same temperature. The mixture was concen-
trated to 1/5 of its original volume and extracted with
CH2Cl2 (2×20 mL). The organic layer was washed with
water (2×10 mL), dried and evaporated. The product
was then purified by column chromatography (0.5%
acetone in CH2Cl2) to give crystalline 8 (2.354 g, 83%)
as colorless prisms (from AcOEt); mp 127–128°C; IR
3.6. (1R,3R,6R,7S)-3-Benzoyl-9-bromo-5-oxatricyclo-
[4.2.1.03,7]nonane-4-one 9
1
3210, 1660 cm−1; H NMR l 0.74 (t, J=7.5 Hz, 3H),
Bromine (160 mg, 1 mmol) was added dropwise into a
solution of enantiomerically pure 4a–x (73 mg, 0.27
mmol) in CCl4 (4 mL) at −8°C (ice-salt bath). Stirring
was continued for 1 h at the same temperature and then
for a further 2 h at rt. The reaction mixture was diluted
with CH2Cl2 (10 mL) and washed with a 5% Na2S2O3
solution (2×10 mL) and brine (10 mL). The organic
layer was dried and evaporated. Recrystallization of the
residual solid with AcOEt–hexane gave colorless prisms
0.91 (t, J=7.5 Hz, 3H), 1.85 (q, J=7.5 Hz, 2H), 2.11
(q, J=7.5 Hz, 2H), 3.75 (dd, J=11.2, 6.1 Hz, 1H), 3.84
(dd, J=11.2, 5.1 Hz, 1H), 4.11 (t, J=8.5 Hz, 1H), 4.70
(dd, J=10.0, 8.5 Hz, 1H), 5.38–5.48 (m, 2H), 7.24–7.40
(m, 10H), 10.88 (d, J=7.5 Hz, 1H); 13C NMR l 9.8,
10.0, 30.9, 31.4, 48.1, 54.3, 54.7, 69.2, 73.7, 126.2, 126.7,
127.6, 128.4, 128.7, 139.0, 141.5, 170.0, 170.9. [h]D18
−15.1 (c 1.26, CHCl3). Anal. calcd for C23H27N2O2Cl:
C, 69.25; H, 6.82; N, 7.02. Found: C, 69.20; H, 6.81; N,
6.98%.
1
(80 mg, 92%); mp 170–172°C; IR 1786, 1674 cm−1; H
NMR l 1.69 (br d, J=11.9 Hz, 1H), 2.10 (dd, J=13.5,
2.2 Hz, 1H), 2.33 (br d, J=11.9 Hz, 1H), 2.79 (m, 1H),
2.84 (dd, J=13.5, 4.2 Hz, 1H), 3.85 (br d, J=5.2 Hz,
1H), 3.98 (d, J=2.2 Hz, 1H), 5.13 (br d, J=5.2 Hz,
1H), 7.47 (t, J=7.3 Hz, 2H), 7.59 (t, J=7.3 Hz, 1H),
7.90 (d, J=7.3 Hz, 2H); 13C NMR l 35.0, 38.6, 45.9,
51.3, 53.0, 56.9, 86.6, 128.6, 127.7, 133.7, 134.1, 176.5,
192.8. [h]2D5 −107 (c 0.35, CHCl3). Anal. calcd for
C15H13O3Br: C, 56.10; H, 4.08. Found: C, 56.12; H,
4.15. HRMS calcd for C15H13O3Br: 320.0048. Found:
320.0066.
3.5. General procedure for the reaction of enedione (3a
and 3b) with Ph-box- or Ph-mox–magnesium complex
A mixture of the ligand, MgI2 and I2 in the solvent was
treated under the conditions shown in Table 2. The
solvent was removed and the resulting complex was
dissolved in CH2Cl2 (4.0 mL) and cooled at −90°C, a
solution of 3 (1 mmol) in CH2Cl2 (6.0 mL) was added
and the resulting mixture was stirred for 30 min, then a
solution of cyclopentadiene (1.5 mmol) in CH2Cl2 (5.0
mL) was added slowly over a period of 3 h. When the
reaction was complete the reaction was quenched with
water and washed with 5% aqueous Na2S2O3. The
organic layer was dried and evaporated. The resulting
residue was subjected to column chromatography to
yield the adducts. Physical data and spectroscopic data
of the enantiomerically pure Diels–Alder adducts 4a–x
and 4b–x are shown below.
References
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Yamamoto, I.; Narasaka, K. Chem. Lett. 1995, 1129; (f)
Haase, C.; Sarko, C. R.; DiMare, M. J. Org. Chem. 1995,
60, 1777; (g) Seebach, D.; Dahinden, R.; Marti, R. E.;
3.5.1. (1R,2R,4R)-2-Benzoylbicyclo[2.2.1]hept-5-ene-2-
carboxylic acid ethyl ester 4a–x. Colorless needles (from
1
hexane); mp 107–109°C; IR 3444, 1735, 1678 cm−1; H
NMR l 0.98 (t, J=7.0 Hz, 3H), 1.53 (m, 2H), 2.01 (dd,
J=12.0, 3.5 Hz, 1H), 2.43 (dd, J=12.0, 2.5 Hz, 1H),
2.97 (br s, 1H) 3.67 (br s, 1H), 3.99 (dq, J=7.0, 2.5 Hz,
2H), 5.97 (dd, J=5.5, 3.0 Hz, 1H), 6.40 (dd, J=5.5, 3.0
Hz, 1H), 7.41 (t, J=7.3 Hz, 2H), 7.52 (t, J=7.3 Hz,
1H), 7.93 (d, J=7.3 Hz, 2H); 13C NMR l 13.8, 36.1,
43.0, 49.7, 50.1, 61.3, 64.0, 128.4, 129.1, 132.5, 132.9,
135.7, 140.5, 172.3, 197.1. [h]2D1 +303.0 (c 4.38, CHCl3).
Anal. calcd for C17H18O3: C, 75.53; H, 6.71. Found: C,
75.57; H, 6.71%. HRMS calcd for C17H18O3: 270.1255.
Found: 270.1248.

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M. Yamauchi et al. / Tetrahedron: Asymmetry 12 (2001) 3113–3118
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