Regioselective synthesis of β- and γ-thujaplicins

Article abstract of DOI:10.1016/S0040-4020(00)00690-6

β-Thujaplicin (hinokitiol) 1 and γ-thujaplicin 2, as the first naturally occurring monocyclic tropolone, were regioselectively synthesized from (R)-(+)-limonene, by using different dienyl silyl ether intermediates, 7 and 10, in 18% overall yield via 11 steps and 22% overall yield via 10 steps, respectively. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00690-6

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 7741±7745
Regioselective Synthesis of b- and g-Thujaplicins
*
Min-Gyu Soung, Masanao Matsui and Takeshi Kitahara
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi,
Bunkyo-ku, Tokyo 113-8657, Japan
Received 14 June 2000; accepted 21 July 2000
AbstractÐb-Thujaplicin (hinokitiol) 1 and g-thujaplicin 2, as the ®rst naturally occurring monocyclic tropolone, were regioselectively
synthesized from (R)-(1)-limonene, by using different dienyl silyl ether intermediates, 7 and 10, in 18% overall yield via 11 steps and 22%
overall yield via 10 steps, respectively. q 2000 Elsevier Science Ltd. All rights reserved.
Introduction
starting from commercially available (R)-(1)-limonene by
construction of the cycloheptanone ring based on the Lewis
acid-promoted intramolecular aldol condensation of acetal
with enol silyl ether,8 and regioselective a-hydroxylation of
the enone via dienyl silyl ethers prepared either kinetically
or thermodynamically.
b- and g-Thujaplicins (4- and 5-isopropyltropolones) were
isolated from Chamaecyparis taiwanesis Masamune et
Suzuki1 and Thuja plicata D. Don2 as naturally occurring
monocyclic tropolones, and these are the ®rst examples of
non-benzenoid aromatics. Particularly, their antibacterial
and antifungal activities, which evidently impart decay-
resistant property to the heart-wood, have aroused much
interest.3
The synthesis of 1 and 2 can be planned according to the
retrosynthetic analysis shown in Scheme 1. It is conceivable
that 1 and 2 will be constructed from the key intermediates,
the dienyl silyl ethers A and B, by the regioselective
a-hydroxylation and oxidation. Both A and B are derivable
from the common cycloheptanone C, which should be
obtained by using the Lewis acid-mediated intramolecular
aldol reaction via enol silyl ether D, derivable from (R)-(1)-
limonene.
Various synthetic approaches to these compounds have
traditionally been achieved by the cycloaddition of iso-
propylcyclopentadiene and dichloro ketene,4 1,3-dipolar
cycloaddition of 5-isopropyl-1-methyl-3-oxidopyridinium,5
the ring expansion of 2-isopropylcyclohexanone,6 and
regiocontrolled hydroxylation of oxyallyl [413] cyclo-
adducts.7f Despite the considerable theoretical, biological
and synthetic interest in tropolones, study on regioselective
synthetic routes from the same intermediate to these
compounds has not been carried out so far.7 (Fig. 1).
Results and Discussion
Scheme 2 shows our synthetic route leading to 1 and 2.
In this paper, we describe a novel and useful regioselective
synthesis of b-thujaplicin (hinokitiol) 1 and g-thujaplicin 2
The kinetic dienyl silyl ether 4 was obtained from the
known acetal ketone 39 in high yield by employing lithium
diisopropylamide (LDA, 1.0 equiv.) and chlorotrimethyl-
silane (TMSCl, 2.0 equiv., THF, 2788C).10 Cyclization to
the seven-membered ring was investigated with a variety of
Lewis acids (TMSOTf, ZnBr2´Et2O and TiCl4). In this reac-
tion with TMSOTf or ZnBr2´Et2O, the yield of the desired
cycloheptanone 5 was quite low (below 30%), and con-
siderable amounts of the aldehyde were detected in the
NMR spectra of the crude products. When the reaction
was carried out with a catalytic amount of TiCl4, the acetal
group of 4 was hydrolyzed into the aldehyde. On the
contrary, the reaction with TiCl4 (1.2 equiv., CH2Cl2,
2788C) was found to proceed quite nicely, giving an
inseparable diastereomeric mixture (1:1) of 5 in 82% yield
via two steps.
Figure 1.
Keywords: b-thujaplicin (hinokitiol); g-thujaplicin; thermodynamic dienyl
silyl ether; limonene.
* Corresponding author. Tel.: 181-3-5841-5119; fax: 181-3-5841-8019;
e-mail: atkita@mail.ecc.u-tokyo.ac.jp
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00690-6

7742
M.-G. Soung et al. / Tetrahedron 56 (2000) 7741±7745
Scheme 1.
Scheme 2.
1
steps. Comparison of the H NMR data of the synthetic
Elimination of the methoxyl group of 5 was achieved
by re¯uxing with a catalytic amount (10% (W/W)) of
Ê
p-toluenesulfonic acid and molecular sieves (4 A) in dry
b-thujaplicin 1 with those of the literature1 completely
con®rmed the identity of 1.
benzene to give cycloheptenone 6 in 63% yield. A dienyl
silyl ether 7, quite unstable, was obtained by the reaction
with LDA (1.0 equiv.) and TMSCl (2.0 equiv., THF,
2158C) in 90% yield after non-aqueous workup. Without
further puri®cation, oxidation of 7 was carried with MCPBA
(1.2 equiv., n-hexane, 08C); then, treatment with triethyl-
amine trihydro¯uoride (Et3N´3HF, 1.0 equiv., CH2Cl2)11
gave an inseparable diastereomeric mixture (1:1) of 8 in
80% yield via two steps.
For the synthesis of g-thujaplicin 2, the thermodynamically
more stable dienyl silyl ether 10 was required, but the
desired product could not be obtained by using several
bases (NaH, KH, and Et3N) from 6. However, one-pot
reaction of 5 with iodotrimethylsilane (TMSI, 1.3 equiv.)
and hexamethyldisilazane (HMDS, 1.5 equiv., CH2Cl2,
2158C) was found to proceed very nicely, and the desired
product 10 was obtained in 92% yield. The regiochemical
outcome of the reaction was established by observation of
the coupling patterns among the C2±C5 protons in the H±H
COSY spectrum (300 MHz, CDCl3). This allowed a
characteristic assignment of the C4±H and C5±H coupling
and the chemical shift (dˆ5.49, dd, Jˆ4, 12 Hz) of the
C4-H, which showed that 10 had been prepared from 5.
This process may be applicable to the preparation of
thermodynamically stable dienyl silyl ethers from linear
and/or cyclic b-alkoxy ketones.
This a-hydroxy cycloheptenone 8 was a very unstable
compound, which was easily oxidized. Oxidation of alcohol
8 with Dess±Martin periodinane12 in CH2Cl2 cleanly
afforded cycloheptenedione 9 in 88% yield, which was
also unstable and easily enolizable.
The ®nal step was the aromatization of 9 to b-thujaplicin 1.
When 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ)13
was employed as the dehydrogenating reagent, the desired
1 could not be obtained. So, we examined bromination of 9
with pyrrolidone hydrotribromide (PHT)14 and successive
dehydrobromination with LiBr±Li2CO3 in DMF, and
succeeded in obtaining 1 in 71% yield via the two
Similarly to the synthesis of 1, we carried out MCPBA
oxidation and treatment of Et3N´3HF and obtained an
inseparable diastereomeric mixture (1:1) of a-hydroxy
cycloheptenone 11 in 55% yield via two steps. Dess±Martin

M.-G. Soung et al. / Tetrahedron 56 (2000) 7741±7745
7743
oxidation (94%) of alcohol 11, bromination with PHT and
dehydrobromination with LiBr±Li2CO3 afforded 2 from 12
in 75% yield via two steps. The 1H NMR data of synthetic 2
were completely indistinguishable from those reported.1
3H), 1.98 (t, Jˆ8 Hz, 2H), 1.75±1.33 (m, 6H), 0.82 (d,
Jˆ7 Hz, 3H), 0.81 (d, Jˆ7 Hz, 3H), 0.18 (s, 9H).
To a solution of crude 4 (6.0 g) in dry CH2Cl2 (80 ml) was
rapidly added TiCl4 (24.0 ml, 24.1 mmol, 1.0 M in CH2Cl2)
at 2788C and the whole was stirred for 10 min under an
atmosphere of N2. The reaction mixture was diluted with
saturated aqueous NaHCO3 solution and extracted with
CH2Cl2±H2O. The organic layer was washed with brine,
dried over anhydrous MgSO4 and concentrated under
reduced pressure. The residue was puri®ed with SiO2
column chromatography (EtOAc±n-hexaneˆ1:8) to give
3.1 g (71% in two steps) of b-methoxycycloheptanone 5
(ˆC) as a pale yellow oil.
In summary, both b-thujaplicin 1 and g-thujaplicin 2 were
synthesized from (R)-(1)-limonene in overall 18% yield via
11 steps and 22% yield via 10 steps, respectively. The key
step was the regioselective formation of the different
types of dienyl silyl ethers 7 and 10 from the same inter-
mediate 5 and their conversion to isomeric ketols 8 and 11,
respectively.
Experimental
5. IR nmax (®lm) 2955, 1702, 1714, 1463, 1369, 1250, 1194,
1091, 1006 cm21; 1H NMR (300 MHz, CDCl3) dˆ3.68 (bt,
Jˆ6 Hz, 1H), 3.32 (bs, 3H), 3.29 (bs, 3H), 2.91±2.05 (m,
4H), 1.70±1.25 (m, 6H), 0.91±0.81 (m, 6H); Anal. Calcd for
C11H20O2: C, 71.70; H, 10.94%. Found: C, 71.85; H,
10.82%.
Infrared spectra (IR) were measured on a Jasco FT/IR-230
spectrometer. Proton magnetic resonance spectra (1H NMR)
were recorded at 300 MHz on JEOL JNM-AL 300 spectro-
meter. Chemical shifts are reported in parts per million (d)
relative to internal chloroform (d 7.24). Optical rotations
were measured on a Jasco DIP-1000 polarimeter. Analytical
thin-layer chromatography (TLC) was carried out using
0.25 mm Merck silica gel 60 F254 precoated glass-backed
plates. Compounds were visualized by ultraviolet light
(254 nm), iodine vapor, iron(III) chloride in chloroform
solution, or phosphomolybdic acid spray reagents. Column
chromatography was performed on Merck silica gel 60 and
Cica silica gel 60 N (neutral). All solvents used were of
reagent grade. Tetrahydrofuran was distilled over benzo-
phenone and sodium prior to use. Dichloromethane and
benzene were distilled from calcium hydride and stored
(5R)-5-Isopropyl-2-cyclohepten-1-one, 6. To a solution
of 5 (2.5 g, 10.1 mmol) in dry C6H6 (50 ml) was added
p-toluenesulfonic acid (0.5 g, 2.7 mmol) and molecular
Ê
sieves (4 A) (10.0 g), and then the mixture was re¯uxed
for 1 h under an atmosphere of N2. The reaction mixture
was diluted with EtOAc and ®ltered. The ®ltrate was
washed with saturated aqueous NaHCO3 solution, water,
and brine. The organic layer was dried over anhydrous
MgSO4 and concentrated. The residual oil was puri®ed by
SiO2 column chromatography (EtOAc±n-hexaneˆ1:6) to
give 1.1 g (63%) of 6 as a pale yellow oil.
Ê
over 4 A molecular sieves.
6. [a]2D3ˆ141.9 (cˆ1.0, CHCl3); IR nmax (®lm) 2960, 2880,
1
1665, 1460, 1395, 1260, 1090, 922, 805 cm21; H NMR
(3R)-3-Isopropyl-1,1-dimethoxyheptan-6-one, 3. This
compound was prepared from (R)-(1)-limonene according
to the known procedure9 in 87% yield via two steps.
(300 MHz, CDCl3) dˆ6.60 (dd, Jˆ2, 12 Hz, 1H), 5.97
(dd, Jˆ1, 12 Hz, 1H), 2.69±2.49 (m, 2H), 2.48±2.21 (m,
2H), 1.82±1.49 (m, 3H), 0.88 (d, Jˆ7 Hz, 3H), 0.87 (d,
Jˆ7 Hz, 3H); Anal. Calcd for C10H16O: C, 78.90; H,
10.59%. Found: C, 78.70; H, 10.54%.
1
Analytical data (bp, [a]D, IR, and H NMR) of 3 were
completely indistinguishable from those reported.9
(5R)-5-Isopropyl-3-methoxycycloheptanone, 5. To a solu-
tion of diisopropylamine (4.2 ml, 30.1 mmol) in dry THF
(50 ml) was added n-butyllithium (18.5 ml, 27.8 mmol,
1.5 M in n-hexane) at 2158C and the mixture was allowed
to warm up to 08C for 30 min and then cooled to 2788C. A
solution of 3 (5.0 g, 23.2 mmol) in dry THF (20 ml) was
added over 10 min and the mixture was stirred at 2788C
for 1 h under an atmosphere of N2. Chlorotrimethylsilane
(TMSCl, 8.8 ml, 69.5 mmol) was added, and the mixture
was stirred for 2 h while the temperature was warmed
slowly up to room temperature.
(5S)-7-Hydroxy-5-isopropyl-2-cyclohepten-1-one, 8. To a
solution of diisopropylamine (1.2 ml, 8.2 mmol) in dry THF
(20 ml) was added n-butyllithium (10.5 ml, 15.8 mmol,
1.5 M in n-hexane) at 2158C, and the mixture was allowed
to warm up to 08C for 30 min and then recooled to 2158C. A
solution of 6 (1.0 g, 6.6 mmol) in THF (10 ml) was added
over 10 min and the mixture was stirred at 2158C for
30 min under an atmosphere of N2. TMSCl (1.7 g,
13.1 mmol) was added and the reaction mixture was stirred
for 30 min while the temperature was warmed slowly to
room temperature.
The solvent was removed under reduced pressure and dry
n-pentane was added to the residue. The pentane extract was
®ltered through a celite pad and the ®ltrate was evaporated
to afford 6.0 g of crude enol silyl ether 4 (ˆD) as a pale
yellow oil, which was directly used for the next step without
further puri®cation.
The solvent was removed under reduced pressure and dry
n-pentane was added to the residue. The pentane extract was
®ltered through a celite pad and then evaporated to afford
1.4 g (90%) of crude dienyl silyl ether 7 (ˆA) as a pale
yellow oil, which was directly used for the next step without
further puri®cation.
4. IR nmax (®lm) 2960, 1640, 1254, 1122, 1060, 1019,
;
Jˆ6 Hz, 1H), 4.01 (d, Jˆ6 Hz, 2H), 3.29 (s, 3H), 3.28 (s,
853 cm21
1H NMR (300 MHz, CDCl3) dˆ4.41 (t,
To a solution of 7 (1.3 g, 6.0 mmol) in dry n-hexane (30 ml)
was added m-chloroperbenzoic acid (MCPBA, 1.3 g,

7744
M.-G. Soung et al. / Tetrahedron 56 (2000) 7741±7745
7.2 mmol) at 2158C and the mixture was stirred at room
temperature for 4 h. The reaction mixture was ®ltered
through a Celite pad and the solvent was removed under
reduced pressure. The residue was mixed with dry CH2Cl2
(50 ml) and triethylamine trihydro¯uoride (Et3N´3HF, 1.0 g,
6.0 mmol) and the solution was stirred for 2 h at room
temperature. The reaction mixture was washed with satu-
rated aqueous NaHCO3 solution and brine, and dried over
anhydrous MgSO4. The solution was removed and the
residue was puri®ed by neutral SiO2 column chromato-
graphy (EtOAc±n-hexaneˆ1:8) to give 0.8 g (80% in two
steps) of a diastereomeric mixture (1:1) of 8 as a clear oil.
tion of 8 (0.5 g, 3.0 mmol) in dry CH2Cl2 (20 ml) was added
Dess±Martin periodinane (1.5 g, 3.6 mmol) and the mixture
was stirred at room temperature for 1 h. The reaction
mixture was diluted with Et2O, washed with saturated
aqueous NaHCO3 solution and brine and dried over
anhydrous MgSO4. The solvent was removed and the resi-
due was puri®ed by neutral SiO2 column chromatography
(EtOAc±n-hexaneˆ1:10) to give 0.4 g (88%) of cyclo-
heptenedione 9 as a pale yellow oil.
9. IR nmax (®lm) 2962, 2875, 1714, 1668, 1469, 1392, 1285,
934 cm21; 1H NMR (300 MHz, CDCl3) dˆ6.85 (ddd, Jˆ4,
6, 12 Hz, 1H), 6.20 (ddd, Jˆ1, 2, 12 Hz, 1H), 2.80±2.61 (m,
1H), 2.59±2.50 (m, 1H), 2.45±2.30 (m, 2H), 2.10±1.91 (m,
1H), 1.85±1.67 (m, 1H), 0.93 (d, Jˆ7 Hz, 3H), 0.93 (d,
Jˆ7 Hz, 3H); Anal. Calcd for C10H14O2: C, 72.26; H,
8.49%. Found: C, 71.91; H, 8.53%.
8. IR nmax (®lm) 3457, 2958, 2873, 1667, 1463, 1391, 1261,
1089 cm21; 1H NMR (300 MHz, CDCl3) dˆ6.94 (dd, Jˆ6,
12 Hz, 0.5H), 6.68 (dd, Jˆ6, 12 Hz, 0.5H), 6.14 (dt, Jˆ,1,
12 Hz, 1H), 4.32 (ddd, Jˆ2, 3, 12 Hz, 0.5H), 4.14 (ddd,
Jˆ2, 3, 12 Hz, 0.5H), 4.02 (d, Jˆ2 Hz, 0.5H), 3.81 (d,
Jˆ2 Hz, 0.5H), 2.48±2.27 (m, 1H), 2.25±2.10 (m, 1H),
2.05±1.85 (m, 1H), 1.72±1.40 (m, 2H), 0.90 (d, Jˆ7 Hz,
3H), 0.87 (d, Jˆ7 Hz, 3H); HRMS (FAB, glycerol, 1 N HCl
added) (M1112H2O) Calcd for C10H15O: 151.1044;
Found: 151.1116.
(5S)-5-Isopropyl-3-cycloheptene-1,2-dione, 12. In the
same manner as described above, 11 (200 mg,
1.203 mmol) gave 186 mg (94%) of 12 as a pale yellow oil.
12. IR nmax (®lm) 2960, 1714, 1668, 1463, 1390, 1283,
1104, 935, 825 cm21
;
1H NMR (300 MHz, CDCl3)
(5S)-5-Isopropyl-1-trimethylsilyloxymethyl-1,3-cyclohep-
tene, 10. To a solution of 5 (1.5 g, 8.2 mmol) in dry CH2Cl2
(30 ml) was added iodotrimethylsilane (TMSI, 1.4 ml,
9.8 mmol) and hexa-methyldisilazane (HMDS, 2.2 ml,
1.1 mmol) at 2788C under an atmosphere of N2. The reac-
tion mixture was stirred for 4 h while the temperature was
warmed slowly to room temperature.
dˆ6.73 (ddd, Jˆ1, 4, 13 Hz, 1H), 6.23 (dd, Jˆ3, 13 Hz,
1H), 2.85 (ddd, Jˆ3, 7, 17 Hz, 1H), 2.60 (ddd, Jˆ3, 11,
17 Hz, 1H), 2.40±2.30 (m, 1H), 2.02 (dtdd, Jˆ1, 3, 7,
14 Hz, 1H), 1.92 (dh, Jˆ2, 7 Hz, 1H), 1.75 (dddd, Jˆ4, 7,
11, 14 Hz, 1H), 0.96 (d, Jˆ7 Hz, 3H), 0.95 (d, Jˆ7 Hz, 3H);
Anal. Calcd for C10H14O2: C, 72.26; H, 8.49%. Found: C,
72.12; H, 8.63%.
The solvent was removed under reduced pressure and dry
n-pentane was added to the residue. The pentane extract was
®ltered through a ¯orisil column and then evaporated to
afford 1.8 g (90%) of dienyl silyl ether 10 (ˆB) as a pale
yellow oil, which was used for the next step without further
puri®cation.
b-Thujaplicin (hinokitiol), 1
To a solution of 9 (150 mg, 0.902 mmol) in dry THF (10 ml)
was added pyrrolidone hydrotribromide (PHT, 490 mg,
0.988 mmol) and the mixture was stirred at room tempera-
ture for 1 h under an atmosphere of N2. The reaction mixture
was diluted with Et2O and ®ltered through a celite pad. The
®ltrate was washed with saturated aqueous NaHCO3 solu-
tion and brine, and dried over anhydrous MgSO4. After
removal of the solvent, the residue was dissolved in dry
DMF (15 ml) and the mixture was re¯uxed with LiBr
(100 mg, 1.152 mmol) and Li2CO3 (85 mg, 1.152 mmol)
for 2 h under an atmosphere of N2. The cooled reaction
mixture was treated with 1N HCl solution and extracted
with Et2O. The extract was washed with brine and dried
over anhydrous MgSO4. The solvent was removed under
reduced pressure and the residue was puri®ed by SiO2
column chromatography (EtOAc±n-hexaneˆ1:1) to give
100 mg (71% in two steps) of 1 as a white solid.
10. IR nmax (®lm) 2994, 1507, 1347, 1109, 999, 794 cm21
;
1H NMR (300 MHz, CDCl3) dˆ5.56 (ddd, Jˆ2, 7, 12 Hz,
1H), 5.49 (dd, Jˆ4, 12 Hz, 1H), 5.13 (d, Jˆ7 Hz, 1H),
2.45±2.30 (m, 2H), 2.15±2.05 (m, 1H), 1.75±1.61 (m,
3H), 0.90 (d, Jˆ7 Hz, 3H), 0.89 (d, Jˆ7 Hz, 3H), 0.18 (s,
9H).
(5S)-2-Hydroxy-5-isopropyl-3-cyclohepten-1-one, 11. In
the same manner as described above, silyl enol ether 10
(1.0 g, 4.5 mmol) gave 0.4 g (55% in two steps) of a dia-
stereomeric mixture of 11 as a clear oil.
11. IR nmax (®lm) 3457, 2958, 1667, 1463, 1391, 1261,
;
1089 cm21
1H NMR (300 MHz, CDCl3) dˆ5.76 (ddd,
1. Mp 49±508C (lit. 52±52.58C);1 IR nmax (®lm) 3196, 2965,
1
2872, 1612, 1543, 1471, 1365, 947, 824 cm21; H NMR
Jˆ3, 5, 12 Hz, 0.5H), 5.52 (ddd, Jˆ3, 5, 12 Hz, 0.5H),
5.44 (ddd, Jˆ2, 5, 12 Hz, 0.5H), 5.36 (ddd, Jˆ2, 5,
12 Hz, 0.5H), 5.30 (dd, Jˆ3, 5 Hz, 0.5H), 5.14 (dd, Jˆ3,
5 Hz, 0.5H), 2.86±2.71 (m, 1H), 2.64±2.46 (m, 1H), 2.26±
2.10 (m, 1H), 2.06±1.74 (m, 3H), 0.93 (d, Jˆ7 Hz, 3H),
0.92 (d, Jˆ7 Hz, 3H); HRMS (FAB, glycerol, 1 N HCl
added) (M1112H2O) Calcd for C10H15O: 151.1044;
Found: 151.1078.
(300 MHz, CDCl3) dˆ7.33±7.18 (m, 3H), 6.94 (d,
Jˆ10 Hz, 1H), 2.87 (h, Jˆ7 Hz, 1H), 1.25 (d, Jˆ7 Hz,
6H); Anal. Calcd for C10H12O2: C, 73.15; H, 7.37%.
Found: C, 73.28; H, 7.37%.
g-Thujaplicin, 2
In the same manner as described above, 12 (70 mg,
0.421 mmol) gave 50 mg (75% in two steps) of 2 as an oil.
(6S)-6-Isopropyl-3-cycloheptene-1,2-dione, 9. To a solu-

M.-G. Soung et al. / Tetrahedron 56 (2000) 7741±7745
7745
2. Mp 78±798C (lit. 80±818C);2 IR nmax (®lm) 3206, 2965,
Chem. Soc. Jpn. 1960, 33, 1452. (b) Takaya, H.; Hayakawa, Y.;
Makino, S.; Noyori, R. J. Am. Chem. Soc. 1978, 100, 1778.
(c) Franck-Neumann, M.; Brion, F.; Martina, D. Tetrahedron
Lett. 1978, 19, 5033. (d) Banwell, M. G. Aust. J. Chem. 1991,
44, 1. (e) Banwell, M. G.; Cameron, J. M.; Collis, M. P.; Crisp,
G. T.; Gable, R. W.; Hamel, E.; Lambert, J. N.; Mackay, M. F.;
Reum, M. E.; Scoble, J. A. Aust. J. Chem. 1991, 44, 705. (f) Lee,
J. C.; Cho, S. Y.; Cha, J. K. Tetrahedron Lett. 1999, 40, 7675, and
references cited therein.
1
1617, 1556, 1468, 1265, 857 cm21; H NMR (300 MHz,
CDCl3) dˆ7.27 (d, Jˆ2 Hz, 4H), 2.84 (h, Jˆ7 Hz, 1H),
1.21 (d, Jˆ7 Hz, 6H); Anal. Calcd for C10H12O2: C,
73.15; H, 7.37%. Found: C, 73.18; H, 7.64%.
References
1. Nozoe, T. Nature (London) 1951, 167, 1055.
2. Erdtman, H.; Gripenberg, J. Nature (London) 1948, 161, 716.
3. Baillie; Freeman; Cook; Somerville Nature (London) 1950,
166, 65.
8. Mukaiyama, T. Tetrahedron 1999, 55, 8609.
9. Kitahara, T.; Mori, M.; Mori, K. Tetrahedron 1987, 43, 2689.
10. Krafft, M. E.; Holton, R. A. Tetrahedron Lett. 1983, 24, 1345.
11. Rubottom, G. M.; Gruber, J. M.; Juve, H. D.; Charleson, D. A.
Org. Synth. 1986, 64, 118.
4. Tanaka, K.; Yoshikoshi, A. Tetrahedron 1971, 27, 4889.
5. Tamura, Y.; Saito, T.; Kiyokawa, H.; Chen, L. C.; Ishibashi, H.
Tetrahedron Lett. 1977, 18, 4075.
12. Dess, D. B.; Martin, J. C. J. Am. Chem. Soc. 1991, 113, 7277.
13. Raddo, P. D.; Harvey, R. G. Tetrahedron Lett. 1988, 29, 3885.
14. Hankovszky, H. O.; Hideg, K.; Sar, P. C.; Lovas, M. J.;
Jerkovich, G. S. Synthesis 1990, 59.
6. Miyashita, M.; Hara, S.; Yoshikoshi, A. J. Org. Chem. 1987, 52,
2602.
7. For previous syntheses of 1, see: (a) Nozoe, T.; Asao, T. Bull.