Enantioselective formal synthesis of (+)-precapnelladiene by chiral copper-catalyzed asymmetric [2+2]-cycloaddition reaction

Article abstract of DOI:10.1016/j.tet.2006.10.072

Enantioselective short formal synthesis of (+)-precapnelladiene (1) was achieved from a bicyclo[3.2.0]heptane derivative, which was prepared enantioselectively by chiral copper-catalyzed [2+2]-cycloaddition reaction of 2-methoxycarbonyl-2-cyclopenten-1-on

Full text of DOI:10.1016/j.tet.2006.10.072

Tetrahedron 63 (2007) 510–513
Enantioselective formal synthesis of (D)-precapnelladiene by
chiral copper-catalyzed asymmetric [2D2]-cycloaddition reaction
*
Yosuke Takenaka, Hisanaka Ito and Kazuo Iguchi
*
School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
Received 4 September 2006; accepted 2 October 2006
Available online 15 November 2006
Abstract—Enantioselective short formal synthesis of (+)-precapnelladiene (1) was achieved from a bicyclo[3.2.0]heptane derivative, which
was prepared enantioselectively by chiral copper-catalyzed [2+2]-cycloaddition reaction of 2-methoxycarbonyl-2-cyclopenten-1-one with
phenylthioacetylene developed by us.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
the utility of our enantioselective [2+2]-cycloaddition
reaction, the preparation of the key intermediate 2 for the
synthesis of (+)-precapnelladiene (1) was examined.
Precapnelladiene (1), isolated by Djerassi et al. from the soft
coral, Capnella imbricata, is a sesquiterpene having a unique
bicyclo[6.3.0]dodecane skeleton (Fig. 1).1 Djerassi also pro-
posed that precapnelladiene (1) was a precursor for the bio-
synthesis of tricyclic D9(12)-capnellene. Its unique structural
character has attracted the attention of synthetic organic
chemists and some synthetic studies have been reported.2–6
Most of them were, however, synthesis of 1 as a racemic
form. One reason was that the [a]D value was not reported
in the original paper. Only one example of the total synthesis
of (8R,11R)-(ꢀ)-precapnelladiene was reported as an opti-
cally active form by Inouye et al.5
Oxy-Cope
Rearrangement
1
reported by
Moore et al.6
H
OPO(OPh)2
OLi
O
H
H
2
Moore et al. also reported the total synthesis of (ꢁ)-precap-
nelladiene through oxy-Cope rearrangement from the key
intermediate 2, which has a bicyclo[3.2.0]heptane skeleton,
and the following palladium-catalyzed coupling reaction
of the methyl group is shown in Scheme 1.6 We recently
reported a catalytic enantioselective [2+2]-cycloaddition
reaction using a chiral copper catalyst (Scheme 1).7,8 This
reaction is useful for the construction of the bicyclo[3.2.0]-
heptane skeleton as an optically active form. To demonstrate
Chiral Copper Catalyzed
Enantioselective
O
O
CO2Me
SPh
SPh
CO2Me
[2+2]-cycloaddition
+
H
3
4
5
O
O
O
N
N
Cu2+
O
chiral copper catalyst
H
H
11
Scheme 1. Our synthetic plan for compound 1.
8
H
H
9(12)-capnellene
precapnelladiene (1)
Δ
2. Results and discussion
2.1. Retrosynthetic analysis
Figure 1.
* Corresponding authors. Tel.: +81 42 676 5473; fax: +81 42 676 7282
(H.I.); tel.: +81 42 676 7273; fax: +81 42 676 7282 (K.I.); e-mail
addresses: itohisa@ls.toyaku.ac.jp; onocerin@ls.toyaku.ac.jp
Our retrosynthetic analysis of (+)-precapnelladiene (1) is
shown in Scheme 1. Compound 1 can be synthesized from
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.10.072

Y. Takenaka et al. / Tetrahedron 63 (2007) 510–513
511
2 by Moore’s reported procedure.6 Compound 2 would be
prepared from 3 through stereoselective introduction of
a methyl group on the cyclopentane ring, conversion of the
angular ester group to an isopropenyl group, and hydrolysis
of vinyl sulfide to a carbonyl group. Compound 3 was
already synthesized by our group as a key intermediate for
an enantioselective total synthesis of tricycloclavulone.7,8
convex face. The Crabtree catalyst (Ir(cod)py(PCy3)PF6)
was employed for the reduction of the exo-methylene group;
however, a complex mixture was obtained due to the reduc-
tion of the carbon–carbon double bond in the cyclobutene
ring. Reduction of the exo-methylene group of 8 proceeded
by the use of Wilkinson catalyst (Rh(PPh3)3Cl) in a highly
diastereoselective manner and compound 9 was obtained
in 66% yield (diastereomeric ratio was 11:1). The stereo-
chemistry of compound 9 was determined by comparison
with the reported data6 after converting 9 to the known com-
pound 2. To increase the optical purity of 9, recrystallization
was examined; however, the crystals of 9 were obtained as
a racemic form and enantiomeric excess of compound 9 in
solution was increased up to 84% ee. With the increase of
optical purity, compound 9 did not crystallize. Therefore,
semi-preparative chiral HPLC (Chiralcel OD-H) was em-
ployed to increase the optical purity of 9 and the separation
of both enantiomers was easily achieved to afford compound
9 in 99% ee (hexane/IPA¼99:1; flow rate, 4.0 mL/min;
(ꢀ)-9 (major enantiomer), tR¼17.0 min; (+)-9 (minor
enantiomer), tR¼21.5 min). Oxidation of the hydroxyl group
of 9 with Dess–Martin periodinane followed by the Wittig
reaction of the resulting aldehyde 10 gave compound 11.
Hydrolysis of the vinyl sulfide moiety of 11 was examined
by treating with HgCl2. Although, the HgCl2-mediated hy-
drolysis of the vinyl sulfide moiety of compound 9 smoothly
proceeded to give the ketone compound in excellent yield
(99% yield), similar hydrolysis of 11 gave compound 2 in
20% yield. We also examined other Hg salts; however,
compound 2 was not obtained. Conversion of 2 to precapnel-
ladiene (1) was achieved in two steps through vinylation
of the carbonyl moiety of 2 and subsequent oxy-Cope
rearrangement followed by palladium-catalyzed coupling
reaction of the methyl group according to the reported
procedure.6 The spectral data of compound 2,6 precapnella-
diene (1),1 and the absolute value of optical rotation5 were
identical with those of the literature.
2.2. Synthesis of (D)-precapnelladiene (1)
Compound 3 was prepared by chiral copper complex-
catalyzed enantioselective [2+2]-cycloaddition reaction
(Scheme 2).7,8 In the presence of 10 mol % of a chiral copper
catalyst, which can be prepared from copper(II) chloride,
silver hexafluoroantimonate, and chiral ligand 6, the [2+2]-
cycloaddition reaction of 4 with 5 proceeded at ꢀ78 ꢂC and
compound (1R,5S)-3 was obtained in 73% yield (68% ee).
O
CO2Me
SPh
ligand 6
O
SPh
CuCl2, AgSbF6
1
CO2Me
+
CH2Cl2, -78 °C
5
H
73% yield
68% ee
(1R,5S)-(-)-3
4
5
O
O
O
N
N
O
6
Scheme 2. Enantioselective [2+2]-cycloaddition reaction.
Stereoselective introduction of the methyl group on the
cyclopentane ring was achieved by the following procedure
(Scheme 3). The ketone moiety of compound 3 was con-
verted to an exo-methylene group by Wittig reaction and 7
was obtained in 76% yield. For the diastereoselective reduc-
tion of the exo-methylene group, the angular ester group of 7
was reduced to a hydroxyl group to afford 8. Coordination of
the hydroxyl group at the angular position with the catalyst
for the hydrogenation would result in the more favored
approach of the catalyst to the exo-methylene from the
3. Conclusion
Enantioselective formal synthesis of (+)-precapnelladiene
(1) was achieved through an enantioselective [2+2]-cyclo-
addition reaction developed by us. The key intermediate 2
was synthesized from 2-methoxycarbonyl-2-cyclopenten-1-
one (4) in seven steps.
OH
O
CO2Me
SPh
CO2Me
SPh
SPh
b
a
H
H
H
3
7
8
OH
O
4. Experimental
4.1. General
SPh
SPh
c
d
e
H
H
9
10
All reactions were carried out under an argon atmosphere.
Unless otherwise noted, materials were obtained from com-
mercial suppliers and used without further purification. H
O
2 steps6
SPh
11
f
(+)-1
1
and 13C NMR spectra were measured on a Bruker AV-300
and the chemical shifts are given in parts per million using
CHCl3 (7.26 ppm) in CDCl3 for 1H NMR and CDCl3
(77.0 ppm) for 13C NMR as an internal standard. IR spectra
were taken with a Perkin–Elmer PARAGON 1000 FT-IR and
only noteworthy absorptions were listed. Mass spectra were
measured on a Micromass LCT.
H
[α]D = +69.0°
H
2
lit.5 [α]D = -70.7°
Scheme 3. (a) Methyltriphenylphosphonium bromide, n-BuLi, ether, 0 ꢂC,
76%; (b) LiAlH4, ether, 0 ꢂC, 98%; (c) Rh(PPh3)3Cl, H2, CH2Cl2, rt, 66%
(11:1); (d) Dess–Martin periodinane, NaHCO3, CH2Cl2, rt, 88%; (e) isopro-
pyltriphenylphosphonium iodide, n-BuLi, THF, ꢀ78 ꢂC, 86%; (f) HgCl2,
CH3CN, H2O, 70 ꢂC, 20%.

512
Y. Takenaka et al. / Tetrahedron 63 (2007) 510–513
4.2. (1R,5S)-1-Methoxycarbonyl-2-oxo-7-(phenylthio)-
bicyclo[3.2.0]hept-6-ene (3)
4.4. (1R,5S)-1-Hydroxymethyl-2-methylene-7-phenyl-
sulfanylbicyclo[3.2.0]hept-6-ene (8)
A suspension of copper(II) chloride (960 mg, 7.14 mmol)
and ligand 6 (4.25 g, 8.57 mmol) in CH2Cl2 (100 mL) was
stirred at ambient temperature for 1.5 h and silver hexa-
fluoroantimonate (5.15 g, 15.0 mmol) was added to the re-
sulting mixture in the dark. After the mixture was stirred
for 3 h at ambient temperature, a solution of 2-methoxy-
carbonyl-2-cyclohexen-1-one (4) (5.0 g, 35.9 mmol) and
phenylthioacetylene (5) (5.7 g, 42.8 mmol) in CH2Cl2
(100 mL) was added to the mixture at ꢀ78 ꢂC. After stir-
ring the mixture for 1.5 h at the same temperature, phos-
phate buffer (pH 6.86, 150 mL) was added to the mixture
and the mixture was extracted with AcOEt. The organic
layer was washed with brine and dried over MgSO4. Filtra-
tion and concentration of the mixture under reduced pres-
sure gave a crude material, which was purified by silica
gel column chromatography (hexane/AcOEt, 7:1) to afford
compound 3 (7.18 g, 26.2 mmol) in 73% yield, 68% ee
(Chiralcel OD-H, hexane/IPA¼99:1). Pale yellow oil.
[a]2D2 ꢀ451 (c 0.775, CHCl3). IR (neat) n, cmꢀ1: 1746,
1731, 1294, 747. 1H NMR (300 MHz, CDCl3) d: 1.89
(1H, br dd, J¼9.1, 13.5 Hz), 2.13 (1H, dddd, J¼6.9, 8.7,
11.9, 13.5 Hz), 2.39 (1H, ddd, J¼1.0, 8.7, 18.3 Hz), 3.02
(1H, ddd, J¼9.1, 11.9, 18.3 Hz), 3.67 (1H, d, J¼6.9 Hz),
3.75 (3H, s), 5.88 (1H, s), 7.26–7.38 (3H, m), 7.49–7.53
(2H, m). 13C NMR (75 MHz, CDCl3) d: 22.4 (CH2), 34.9
(CH2), 48.3 (CH), 52.3 (CH3), 66.2 (C), 128.8 (CH),
129.4 (CH), 129.7 (C), 133.0 (CH), 133.8 (CH), 140.5
(C), 167.6 (C), 208.4 (C). EIMS m/z: 274 (M+). Anal.
Calcd for C15H14O3S: C, 65.67; H, 5.14. Found: C,
65.55; H, 5.11.
To a solution of 7 (378 mg, 1.39 mmol) in ether (10 mL)
was added LiAlH4 (53 mg, 1.39 mmol) at 0 ꢂC and the mix-
ture was stirred at the same temperature for 1 h. Saturated
aqueous Rochelle salt was added to the mixture and the
mixture was stirred at ambient temperature for 30 min.
The mixture was extracted with AcOEt and the organic
layer was washed with brine, dried over MgSO4, and con-
centrated under reduced pressure. The residue was purified
by silica gel column chromatography (hexane/AcOEt, 5:1)
to afford 8 (332 mg, 1.36 mmol) as a pale yellow oil in
98% yield, 68% ee. [a]2D7 ꢀ266.5 (c 0.89, CHCl3). IR
(neat) n, cmꢀ1: 3402, 1652, 1558. 1H NMR (300 MHz,
CDCl3) d: 1.42–1.62 (2H, m), 2.36 (1H, dd, J¼6.8,
15.2 Hz), 2.69–2.84 (1H, m), 3.22 (1H, d, J¼6.7 Hz),
3.76 (1H, d, J¼11.5 Hz), 3.82 (1H, d, J¼11.5 Hz), 4.82
(1H, d, J¼2.4 Hz), 5.04 (1H, d, J¼2.4 Hz), 5.81 (1H, d,
J¼0.7 Hz), 7.28–7.37 (3H, m), 7.47–7.53 (2H, m). 13C
NMR (75 MHz, CDCl3) d: 25.2, 32.5, 49.7, 62.4, 64.0,
107.1, 128.2, 129.1, 130.8, 131.4, 133.2, 140.7, 149.0.
HRESIMS calcd for C15H17OS: 245.1000 (M+H)+; found:
245.1006.
4.5. (1S,2S,5S)-1-Hydroxymethyl-2-methyl-7-phenyl-
sulfanylbicyclo[3.2.0]hept-6-ene (9)
A mixture of 8 (125 mg, 0.512 mmol) and tris(triphenyl-
phosphine)rhodium chloride (47 mg, 0.051 mmol) in
CH2Cl2 (4 mL) was stirred under a hydrogen atmosphere
at ambient temperature for 4 h. The mixture was concen-
trated under reduced pressure and the residue was purified
by silica gel column chromatography (hexane/AcOEt, 8:1)
to afford a mixture of 9 and diastereomer 90 (diastereomeric
ratio¼11:1, 83.8 mg, 0.34 mmol) as a pale yellow oil in
98% yield. After separation of diastereomers 9 and 90, enan-
tiomers of compound 9 were separated by the semi-prepar-
ative chiralcel OD-H column (hexane/IPA¼99:1, flow rate,
4.0 mL/min; (ꢀ)-9 (major), tR¼17.0 min; (+)-9 (minor),
tR¼21.5 min) to afford almost optically pure 9 (99% ee).
Compound 9: pale yellow oil (99% ee). [a]2D5 ꢀ67.8 (c
1.75, CHCl3). IR (neat) n, cmꢀ1: 3370, 2931, 2858, 1582,
1558. 1H NMR (300 MHz, CDCl3) d: 1.14 (3H, d,
J¼6.2 Hz), 1.26–1.40 (1H, m), 1.43 (1H, dd, J¼5.2,
13.0 Hz), 1.56–1.82 (3H, m), 2.89 (1H, d, J¼6.6 Hz),
3.68 (1H, d, J¼11.4 Hz), 3.89 (1H, d, J¼11.4 Hz), 5.62
(1H, d, J¼0.8 Hz), 7.27–7.38 (3H, m), 7.49–7.55 (2H, m).
13C NMR (75 MHz, CDCl3) d: 15.1, 26.0, 32.8, 35.8,
48.1, 64.6, 65.4, 128.0, 129.05, 129.1, 131.5, 132.9,
138.1. HRESIMS calcd for C15H19OS: 247.1157 (M+H)+;
found: 247.1149. Compound 90: pale yellow oil (68% ee).
[a]2D2 ꢀ46.6 (c 0.58, CHCl3). IR (neat) n, cmꢀ1: 3402,
4.3. (1R,5S)-1-Methoxycarbonyl-2-methylene-7-phenyl-
sulfanylbicyclo[3.2.0]hept-6-ene (7)
A solution of n-BuLi (1.22 M in hexane, 3.6 mL,
4.37 mmol) was added to a suspension of methyltriphenyl-
phosphonium bromide (1.69 g, 4.73 mmol) in ether
(10 mL) at 0 ꢂC and the resulting mixture was stirred at
ambient temperature for 3 h. A solution of 3 (500 mg,
1.82 mmol) in ether (5 mL) was added to the mixture at
0 ꢂC and the mixture was stirred at ambient temperature
for 3 h. The mixture was diluted with ether and then water
was added. The mixture was extracted with ether and the
organic layer was washed with brine and dried over
MgSO4. Filtration and concentration of the mixture under
reduced pressure gave a crude material, which was
purified by silica gel column chromatography (hexane/
AcOEt, 20:1) to afford compound 7 (376 mg, 1.38 mmol)
as a pale yellow oil in 76% yield, 68% ee. [a]2D7 ꢀ320.0
1
(c 0.80, CHCl3). IR (neat) n, cmꢀ1: 1728, 1652, 1558. H
1
NMR (300 MHz, CDCl3) d: 1.56 (1H, dd, J¼7.6, 12.7 Hz),
1.61–1.76 (1H, m), 2.23 (1H, dd, J¼7.2, 15.3 Hz), 2.64–
2.79 (1H, m), 3.57 (1H, d, J¼6.7 Hz), 3.72 (3H, s), 5.06
(1H, br d, J¼2.6 Hz), 5.10 (1H, br d, J¼2.3 Hz), 5.64 (1H,
s), 7.27–7.37 (3H, m), 7.46–7.53 (2H, m). 13C NMR
(75 MHz, CDCl3) d: 25.7, 31.5, 51.8, 52.2, 65.4, 109.7,
128.0, 129.0, 130.3, 130.7, 133.3, 140.3, 146.7, 171.1. HRE-
SIMS calcd for C16H17O2S: 273.0949 (M+H)+; found:
273.0935.
2945, 2873, 1584, 1558. H NMR (300 MHz, CDCl3) d:
0.86 (3H, d, J¼7.7 Hz), 1.33–1.61 (4H, m), 2.03–2.21
(2H, m), 2.86 (1H, d, J¼6.6 Hz), 3.74 (1H, dd, J¼6.4,
11.3 Hz), 3.86 (1H, dd, J¼5.3, 11.3 Hz), 5.69 (1H, d,
J¼0.6 Hz), 7.29–7.38 (3H, m), 7.49–7.55 (2H, m). 13C
NMR (75 MHz, CDCl3) d: 14.5, 23.9, 31.5, 32.1, 47.5,
63.5, 65.7, 128.1, 128.7, 129.2, 131.1, 133.1, 141.5. HRE-
SIMS calcd for C15H19OS: 247.1157 (M+H)+; found:
247.1142.

Y. Takenaka et al. / Tetrahedron 63 (2007) 510–513
513
4.6. (1S,2S,5S)-1-Formyl-2-methyl-7-phenylsulfanyl-
bicyclo[3.2.0]hept-6-ene (10)
0.282 mmol) at ambient temperature and the mixture was
stirred at 70 ꢂC for 3 h. Water was added to the mixture
and the resulting mixture was extracted with ether. The
organic layer was washed with brine, dried over MgSO4,
and concentrated under reduced pressure. The residue was
purified by silica gel column chromatography (hexane/
CHCl3, 1:2) to afford 2 (5.0 mg, 0.028 mmol) as a colorless
oil in 20% yield. [a]2D8 +26.7 (c 0.43, CHCl3). IR (neat) n,
cmꢀ1: 2925, 1771. 1H NMR (300 MHz, CDCl3) d: 1.04 (3H,
d, J¼6.6 Hz), 1.39–1.47 (1H, m), 1.64 (3H, d, J¼1.0 Hz),
1.71 (3H, d, J¼1.3 Hz), 1.82 (1H, dd, J¼6.2, 12.8 Hz),
1.90–2.08 (3H, m), 2.43 (1H, dd, J¼4.5, 18.5 Hz), 2.82–
2.91 (1H, m), 3.15 (1H, dd, J¼9.2, 18.5 Hz), 5.27 (1H, s).
13C NMR (75 MHz, CDCl3) d: 14.5, 19.4, 26.4, 32.3, 33.1,
37.5, 47.5, 49.5, 78.9, 123.5, 135.0, 214.4. HRESIMS calcd
for C12H19O: 179.1436 (M+H)+; found: 179.1422.
To a solution of 9 (46 mg, 0.187 mmol) in CH2Cl2 (1 mL)
were added NaHCO3 (31 mg, 0.187 mmol) and Dess–Martin
periodinane (95 mg, 0.224 mmol) at ambient temperature
and the mixture was stirred at the same temperature for 1 h.
A solution of sodium thiosulfate was added to the mixture
and the mixture was extracted with AcOEt. The organic layer
was washed with brine, dried over MgSO4, and concentrated
under reduced pressure. The residuewas purified by silica gel
column chromatography (hexane/AcOEt, 8:1) to afford 10
(40 mg, 1.64 mmol) as a pale yellow oil in 88% yield. [a]D22
+0.84 (c 0.95, CHCl3). IR (neat) n, cmꢀ1: 2928, 1710,
1558. 1H NMR (300 MHz, CDCl3) d: 1.17 (3H, d, J¼
6.8 Hz), 1.31–1.46 (1H, m), 1.50 (1H, dd, J¼6.1, 12.9 Hz),
1.60–1.75 (1H, m), 1.82–1.90 (1H, m), 2.17–2.30 (1H, m),
3.17 (1H, d, J¼6.8 Hz), 5.83 (1H, s), 7.30–7.41 (3H, m),
7.50–7.56 (2H, m), 9.71 (1H, s). 13C NMR (75 MHz,
CDCl3) d: 15.0, 26.6, 32.5, 33.5, 49.4, 73.3, 128.5, 129.3,
131.1, 131.5, 133.4, 137.5, 201.6. HRESIMS calcd for
C15H17OS: 245.1000 (M+H)+; found: 245.0999.
4.9. Data of synthetic (D)-precapnelladiene (1)1,5,6
Colorless oil. [a]2D2 +69.0 (c 0.113, CHCl3). IR (neat) n,
1
cmꢀ1: 2952, 2866, 1458, 1374, 1358. H NMR (300 MHz,
CDCl3) d: 0.97 (3H, s), 0.99 (3H, s), 1.04 (3H, d, J¼
6.8 Hz), 1.17–1.28 (1H, m), 1.36–1.47 (1H, m), 1.63 (3H,
s), 1.50–1.81 (4H, m), 2.29–2.44 (2H, m), 2.90 (1H, dd, J¼
9.5, 13.5 Hz), 3.44–3.57 (1H, m), 5.02 (1H, d, J¼1.6 Hz),
5.33 (1H, t, J¼8.2 Hz). 13C NMR (75 MHz, CDCl3) d:
22.0, 26.7, 29.8, 31.3, 31.4, 33.6, 38.7, 38.8, 39.6, 40.4,
42.3, 121.8, 130.3, 136.3, 145.5.
4.7. (1S,2S,5S)-2-Methyl-1-(2-methyl-1-propenyl)-7-
phenylsulfanylbicyclo[3.2.0]hept-6-ene (11)
A solution of n-BuLi (1.2 M in hexane, 0.16 mL, 0.197 mmol)
was added to a suspension of isopropyltriphenylphosphonium
iodide (93 mg, 0.213 mmol) in THF (0.5 mL) at ꢀ78 ꢂC and
the mixture was stirred at ambient temperature for 30 min. A
solution of 10 (40 mg, 0.164 mmol) in THF (1 mL) was added
to the mixture at ꢀ78 ꢂC and the mixture was stirred at the
same temperature for 2 h. The mixture was diluted with ether
and then water was added. The mixture was extracted with
AcOEt and the organic layer was washed with brine and dried
overMgSO4. Filtrationand concentration ofthe mixture under
reduced pressure gave a crude material, which was purified by
silica gel column chromatography (hexane) to afford com-
pound 11 (38 mg, 0.141 mmol) as a pale yellow oil in 86%
yield. [a]2D8 ꢀ75.0 (c 1.01, CHCl3). IR (neat) n, cmꢀ1: 2931,
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J. Am. Chem. Soc. 2004, 126, 4520–4521.
1
2856, 1560. H NMR (300 MHz, CDCl3) d: 1.10 (3H, d,
J¼6.3 Hz), 1.41–1.60 (3H, m), 1.66–1.78 (2H, m), 1.73 (3H,
d, J¼1.0 Hz), 1.77 (3H, d, J¼1.3 Hz), 3.05 (1H, d, J¼
5.4 Hz), 5.48 (1H, s), 5.50 (1H, d, J¼1.0 Hz), 7.27–7.37
(3H, m), 7.50–7.57 (2H, m). 13C NMR (75 MHz, CDCl3) d:
14.9, 19.0, 26.6, 26.7, 32.1, 41.6, 52.7, 63.4, 125.2, 127.1,
127.7, 129.0, 132.1, 133.0, 133.9, 140.9. HRESIMS calcd
for C18H23S: 271.1520 (M+H)+; found: 271.1538.
4.8. (1S,2S,5S)-2-Methyl-1-(2-methyl-1-propenyl)-
bicyclo[3.2.0]heptan-7-one (2)
To a solution of 11 (38 mg, 0.141 mmol) in CH3CN
(0.75 mL) and water (0.25 mL) was added HgCl2 (77 mg,
8. Takenaka, Y.; Ito, H.; Hasegawa, M.; Iguchi, K. Tetrahedron
2006, 62, 3380–3388.