Intramolecular acylation of α-sulfinyl carbanions with masked α,β-unsaturated esters: a general strategy to 5-alkylidene-2-cyclopentenones

Article abstract of DOI:10.1016/j.tet.2006.12.036

A general method for the preparation of 5-alkylidene-2-cyclopentenones and their 2-phenylsulfanyl substituted derivatives, involving the intramolecular acylation of α-sulfinyl carbanions with cyclopentadiene-α,β-unsaturated esters as the key reaction followed by flash vacuum pyrolysis, is described. The reactions start from readily available Diels-Alder adducts, synthons of α-carbanions of α,β-unsaturated esters.

Full text of DOI:10.1016/j.tet.2006.12.036

Tetrahedron 63 (2007) 1806–1820
Intramolecular acylation of a-sulfinyl carbanions with masked
a,b-unsaturated esters: a general strategy to 5-alkylidene-
2-cyclopentenones
*
Manat Pohmakotr, Sirinporn Thamapipol, Patoomratana Tuchinda and Vichai Reutrakul
*
Department of Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand
Received 17 August 2006; revised 1 December 2006; accepted 14 December 2006
Available online 17 December 2006
Abstract—A general method for the preparation of 5-alkylidene-2-cyclopentenones and their 2-phenylsulfanyl substituted derivatives,
involving the intramolecular acylation of a-sulfinyl carbanions with cyclopentadiene-a,b-unsaturated esters as the key reaction followed
by flash vacuum pyrolysis, is described. The reactions start from readily available Diels–Alder adducts, synthons of a-carbanions of a,b-
unsaturated esters.
Ó 2006 Elsevier Ltd. All rights reserved.
O
PhS
1. Introduction
O
O
OEt
δ+
R
X
Functionalized cyclopentenones are a commonly encoun-
tered structural unit in a number of prostaglandins and vari-
ous bioactive natural products.1 Furthermore, they are found
to be versatile building block for the synthesis of some
bioactive compounds possessing cyclopentane units. The
development of strategies for the construction of these units
and related structures has been of considerable interest in
synthetic organic chemistry. These methods include the in-
tramolecular aldol reaction,2 the Pauson–Khand reaction,3
the Nazarov cyclization,4,5 and metal–carbene strategies.6
As part of our study on the intramolecular acylation of
a-sulfinyl carbanions for the preparation of cyclopentenone
derivatives,7 we have reported a general synthesis of 5-alkyl-
idene-4-hydroxy-2-cyclopentenones.8 In the present work, a
general route to 5-alkylidene-2-cyclopentenones9 and 5-al-
kylidene-2-phenylsulfanyl-2-cyclopentenones 1 is reported.
R
δ+
CO2Et
R
Br
1 X = H, SPh
Scheme 1.
2
2. Results and discussion
The synthetic route for the preparation of 5-alkylidene-2-
cyclopentenonesstartedfromreadilyavailablebicyclicesters
3. The key reaction involves intramolecular acylation of the
a-sulfinyl carbanions derived from sulfoxides 6 leading to
spirocyclopentanones 7 (Scheme 2), which are precursors
forthepreparationofcyclopentenones8,9, and11(Scheme 3).
R
R
LDA/THF,
-78 °C, 2 h
PhS(CH2)3Br
HMPA
-78 °C to rt
Our annulation strategy is based on the reaction of an
a-carbanion synthon 2 of a,b-unsaturated esters with 3-bro-
mo-1-phenylsulfinylpropane followed by a tandem intra-
molecular acylation and sulfoxide elimination as outlined
in Scheme 1. Cyclopentadiene-a,b-unsaturated ester Diels–
Alder adducts were used as masked a-carbanions of a,
b-unsaturated esters 2.10
OEt
Li
C
O
CO2Et
3
4
R
R
2.2 eq LDA/THF
-78 °C to rt
SPh
(O)n
CO2Et
O
SPh
5, n = 0
6, n = 1
O
7
NaIO4
Scheme 2.
Keywords: a-Sulfinyl carbanion; Intramolecular acylation; 5-Alkylidene-
2-cyclopentenones.
The results of preparations are summarized in Table 1. The
requisite starting sulfoxides 5 were obtained in two steps,
* Corresponding authors. Tel.: +66 2 2015158; fax: +66 2 6445126; e-mail
addresses: scmpk@mahidol.ac.th; scvrt@mahidol.ac.th
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.12.036

M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
1807
chromatography. The major 2-endo,3-exo-isomers of 5b
and 5c could be explained from the fact that alkylation of
the enolate anions 4b and 4c occurred from the less hindered
exo-face. Alkylation of compound 3d gave the alkylated
product 5d in 47% yield as the sole product. A comparable
yield (45%) of 5d was achieved when the alkylation was per-
formed in the presence of 1 equiv of NaI instead of HMPA.
The relative stereochemistry at 2- and 3-positions of 2-
endo,3-exo-5b and the minor 2-endo,3-endo-isomer of 5c
was confirmed by NOE experiments as indicated in Figures
1 and 2.
O
R
R
toluene/reflux
CaCO3
FVP
R
O
O
SPh
O
8
7
9
TFAA/CH3CN
0 °C to rt
O
R
FVP
PhS
R
O
SPh
Oxidation of the diastereomeric mixtures of 5a–c and 5d
was accomplished by using NaIO4 in aqueous methanol at
0 ꢁC to room temperature to furnish the corresponding
sulfoxides 6a–d in good yields as diastereomeric mixtures.
The 2-endo,3-exo-isomer of 6c was isolated in pure form
by preparative thin-layer chromatography, and its relative
stereochemistry was established by the NOE experiment as
illustrated in Figure 3.
10
11
Scheme 3.
Table 1. Preparation of compounds 5, 6, and 7
Entry 3 (endo:exo)
Yields of
Yields of
Yields of
5 (%)a,b
6 (%)a,b
7 (%)a,b
1
2
3
3a, R¼H (>99:1)
5a (90)
3b, R¼CH3 (50:50) 5b (67)
6a (98)
6b (84)
6c (85)
7a (90)
7b (80)
7c (70)
Cyclization of the diastereomeric mixtures of the sulfoxides
6 to the required spiro-ketosulfoxides 7 was successfully
effected by using LDA (2.2 equiv) in THF at ꢀ78 ꢁC for
2 h, and at 0 ꢁC for 2 h, followed by slowly warming up to
room temperature overnight. The reaction proceeded via
the intramolecular acylation of the initially formed a-sulfi-
nyl carbanions of the sulfoxides 6. As expected, spiro-keto-
sulfoxides 7a–c were obtained in good yields as mixtures of
diastereomers. Attempts to separate these diastereomers
were not made, since it was expected that all of them
could be converted into the required 5-alkylidene-2-cyclo-
pentenones 9 and 11. On the other hand, under the standard
3c, R¼Ph (65:35)
5c (60)
H
OH
O
SPh
SPh
(O)n
O
7dA (52)
O
4
O
O
O
5d, n = 0 (47)
6d, n = 1 (80)
3d, (>99:1)
O
HO
SPh
O
4%
3.5%
7dB (30)
7
Hb
Ha
H
1.7%
3.3%
a
Yields of isolated products.
Obtained as a mixture of diastereomers (see Section 4).
CH
3
b
6.6%
3'
H
4
Hb
5
6
3
Ha
1
2
SPh
1'
H
2'
beginning with bicyclic esters 3. Thus, treatment of a mixture
(endo:exo >99:1 with respect to the ester group) of bicyclic
ester 3a with lithium diisopropylamide (LDA, 1.1 equiv) in
THF at ꢀ78 ꢁC (2 h), followed by trapping of the resulting
enolate anion 4a with 3-bromo-1-phenylsulfanylpropane
in the presence of hexamethylphosphoramide (HMPA) at
ꢀ78 ꢁC to room temperature overnight afforded the corre-
sponding alkylated product 5a in 90% yield after chromato-
graphy, as a 86:14 mixture of endo:exo esters. The endo
stereoselectivity for the formation of 5a was presumably
due to the fact that alkylation of the preformed enolate anion
4a occurred preferentially from the less hindered exo-face
leading to an endo-ester 5a as the major isomer. Attempted
separation of both isomers by preparative thin-layer chroma-
tography was unsuccessful. Only a small amount of the
endo-ester 5a was obtained. Similarly, 5b and 5c were pre-
pared as mixtures of diastereomers, employing the standard
conditions as for 5a starting from the mixtures of endo- and
exo-isomers of bicyclic esters 3b and 3c. The 2-endo,3-exo-
and 2-endo,3-endo-isomers of 5c could be separated by
preparative thin-layer chromatography in 44 and 16% yields,
respectively. On the other hand, a 7:29:11:53 mixture of four
diastereomers of 5b was achieved under the standard condi-
tions and the major 2-endo,3-exo-isomer of 5b was obtained
in a small amount after careful preparative thin-layer
H
H
CO2Et
Figure 1. Observed NOE for 2-endo,3-exo-5b.
3.8%
7
Hb
Ha
3.8%
H
5.4%
2.9%
H
Ha
H
4
Hb
5
3
1
6
2
3'
SPh
Ph 1'
2'
H
H
CO2Et
Figure 2. Observed NOE for the minor 2-endo,3-endo-isomer of 5c.
23.3%
11.3%
7
Hb
Ha
3.8%
H
2.6%X
3
Ph
H
Hb
4
5
Ha
1
6
2
3'
SPh
O
1'
H
2'
H
H
CO Et
2
Figure 3. Observed NOE for the 2-endo,3-exo-isomer of 6c.

1808
M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
Table 3. Preparation of spirocyclopentenones 10 by the Pummerer
rearrangement of 7 and their pyrolyses to 2-phenylsulfanyl-5-alkylidene-
2-cyclopentenones 11
conditions for the cyclization, the sulfoxide 6d provided
a mixture of compounds 7dA and 7dB in 52 and 30% yields,
respectively. The formation of 7dB resulted from lactol
formation of the initially cyclized product 7dA. The results
are summarized in Table 1.
Entry
7
10a (% Yield)
11a (% Yield)
O
PhS
1
7a, R¼H (87:13)
10a (80)
Having the spiro-ketosulfoxides 7 in hand, the sulfoxide
elimination of 7a and 7b was investigated. Under reflux in
toluene in the presence of CaCO3 for 15 h, 7a and 7b pro-
vided the corresponding spirocyclopentenones 8a and 8b
in 70 and 75% yields, respectively, as mixtures of diastereo-
mers. No traces of a-alkylidene cyclopentenones 9a,b arisen
from the retro-Diels–Alder reactions of compounds 7a and
7b could be detected. However, flash vacuum pyrolysis of
the diastereomeric mixtures of spiro-ketosulfoxides 7a–c
and 7dB at 375–450 ꢁC (0.03–0.05 mmHg) gave quantita-
tive yields of the corresponding a-alkylidene cyclopent-
enones 9a–c. Compounds 9b and 9c were obtained in good
yields after preparative thin-layer chromatography, while
compound 9a is unstable due to rapid polymerization: puri-
fication was unsuccessful by preparative thin-layer chroma-
tography. A low yield of compound 9d (30% yield) was
obtained presumably due to its decomposition under the
pyrolytic conditions. The formation of 9 resulted from the
tandem reaction involving the sulfoxide elimination fol-
lowed by the retro-Diels–Alder reaction. The results are
shown in Table 2.
11a (93)
O
PhS
2
3
7b, R¼CH3
10b (74)
CH3
11b (96)
O
PhS
PhS
7c, R¼Ph (78:22)
10c (78)
Ph
11c (76)
OH
O
OH
4
7dA and 7dB
O
SPh
11d (20)
10d (78)
a
Yields of isolated products.
This result may be due to its rapid decomposition under
the FVP conditions.
3. Conclusion
It was anticipated that the spiro-ketosulfoxides 7 could be
used as precursors to functionalized cyclopentenones of
types 10 and 11, which might be useful for further synthetic
applications. Thus, the spiro-ketosulfoxides 7a–c were trans-
formed into the corresponding phenylsulfanyl-substituted
spirocyclopentenones 10a–c in good yields by performing
the second generation Pummerer rearrangement using
trifluoroacetic anhydride in acetonitrile at 0 ꢁC to room
temperature overnight (Scheme 3). Flash vacuum pyrolyses
of 10a–c afforded good yields of the expected cyclopent-
enones 11a–c. However, under the same conditions, 10d
provided 11d in only 20% yield (Scheme 3 and Table 3).
In summary, the synthetic utility of the intramolecular
acylation of a-sulfinyl carbanion as a general method for
the syntheses of 5-alkylidene-2-cyclopentenones and their
2-phenylsulfanyl substituted derivatives, starting from
Diels–Alder adducts of cyclopentadiene-a,b-unsaturated
esters, is demonstrated. The method could be applied to
the preparation of a wide range of cyclopentanoid natural
products.
4. Experimental
4.1. General
1
The H and 13C NMR spectra were recorded on Bruker
Table 2. Preparation of 5-alkylidene-2-cyclopentenones 9
% Yielda (E:Z ratio)
DPX-300 (300 MHz), Bruker DPX-400 (400 MHz), and
Bruker DPX-500 (500 MHz) spectrometer in CDCl3 using
tetramethylsilane as an internal standard. The chemical
shifts (d) reported are given in parts per million (ppm) and
the coupling constants (J) are in hertz (Hz). Melting points
were recorded on a Buchi 501 Melting Point Apparatus
and are uncorrected. The IR spectra were recorded on
a GX FTIR system Perkin–Elmer infrared spectrometer.
The mass spectra were recorded by using a Thermo Finnigan
Polaris Q mass spectrometer. The high-resolution mass
spectra were recorded on HR-TOF-MS Micromass model,
Chiangmai University. The elemental analyses were
performed by a Perkin–Elmer Elemental Analyzer 2400
CHN. All glasswares and syringes were oven-dried and
kept in a desiccator before use. The molarity of n-BuLi
(in hexane) was determined by titration with diphenylacetic
acid in THF at 0 ꢁC. Tetrahydrofuran (THF) was
distilled from sodium-benzophenone ketyl. Acetonitrile,
dichloromethane, diisopropylamine, hexamethylphosphor-
amide (HMPA), triethylamine, and toluene were dried by
Entry
Spiro-sulfoxide 7
Product 9
O
1
7a
Quantitative
9a
O
2
3
7b
7c
82 (83:17)b
CH3
9b
O
85 (E-isomer)
Ph
9c
OH
O
4
7d
30 (Z-isomer)
9d
a
Isolated yields.
The ratio was determined by integration of the ethylenic proton of the
crude product.
b

M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
1809
distilling over calcium hydride. Merck silica gel 60H and 60
PF245 were used for column chromatography and prepara-
tive thin-layer chromatography, respectively.
4.2.2. Ethyl 2-(30-phenylsulfanylpropyl)-3-methylbicy-
clo[2.2.1]hept-5-ene-2-carboxylate (5b). According to the
general procedure described for compound 5a, a solution
of a 50:50 mixture of endo- and exo-3b (0.45 g, 2.5 mmol)
in THF (1 mL) was added dropwise to a THF (8 mL)
solution of LDA (3 mmol) at ꢀ78 ꢁC under an argon atmo-
sphere. After stirring at ꢀ78 ꢁC for 2 h, HMPA (1.2 mL) was
added followed by the addition of a THF (3 mL) solution of
3-bromo-1-phenylsulfanylpropane (0.578 g, 2.5 mmol).
After usual work-up, the crude product was purified by
column chromatography (silica gel, 0.5–2% ethyl acetate
in hexanes) to give a pure colorless viscous liquid of 5b
(0.554 g, 67% yield) as a 7:29:11:53 mixture of exo,endo:
endo,endo:exo,exo:endo,exo-isomers. The mixture was used
for further oxidation.
4.2. Preparation of sulfides 5
4.2.1. Ethyl 2-(30-phenylsulfanylpropyl)bicyclo[2.2.1]-
hept-5-ene-2-carboxylate (5a). General procedure: A
THF solution (4 mL) of endo-3a (1.66 g, 10 mmol) was
added slowly to a solution of LDA (12 mmol) at ꢀ78 ꢁC
under an argon atmosphere [prepared by reacting diisopro-
pylamine (1.7 mL, 12 mmol) in THF (30 mL) with n-BuLi
(1.41 M in hexane, 8.5 mL, 12 mmol) at ꢀ78 ꢁC]. After stir-
ring at ꢀ78 ꢁC for 2 h, HMPA (2.0 mL) was added, followed
by the addition of a THF (10 mL) solution of 3-bromo-1-
phenylsulfanylpropane (2.52 g, 12 mmol). The resulting
solution was stirred at ꢀ78 ꢁC to room temperature over-
night, quenched with a saturated aqueous NH4Cl solution
(40 mL), and extracted with hexanes (5ꢂ100 mL). The
combined organic layers were washed with water and brine,
and dried (anhyd Na2SO4). The organic phase was concen-
trated to give a 86:14 mixture of endo- and exo-isomers of
the crude product as a viscous liquid. The ratio of the isomers
Compound 5b (a mixture of four isomers): 1H NMR
(300 MHz, CDCl3): d 7.40–7.14 (m, ArH), 6.37 (dd,
J¼5.4, 3.0 Hz, CH]CH), 6.20 (dd, J¼5.6, 3.0 Hz,
CH]CH), 6.14–6.04 (m, CH]CH), 4.16–3.90 (m,
CO2CH2CH3), 3.03 (br s, CHCH]CHCH), 3.00–2.77 (m,
CH2SPh and CHCH]CHCH), 2.66 and 2.61 (each br s,
CHCH]CHCH), 2.38 (br s, CHCH]CHCH), 2.19–1.98
(m, CHCH3 and CHHCH2CH2SPh), 1.93–1.45 (m,
CH2CH2CH2SPh and CH2), 1.43 (d, J¼8.7 Hz, CHH),
1.35 (dd, J¼9.0, 1.6 Hz, CHH), 1.28–1.14 (m, CO2CH2CH3
and CHCH3), 1.10 (d, J¼7.2 Hz, CHCH3), 0.92 (d,
J¼7.2 Hz, CHCH3), 0.86 (d, J¼7.2 Hz, CHCH3).
1
was determined by H NMR of the olefinic protons. The
crude product was purified by column chromatography
(silica gel, 0.5–2% ethyl acetate in hexanes) to give a pure
colorless viscous liquid of a 86:14 ratio of endo:exo-5a
1
(2.86 g, 90% yield). H NMR (300 MHz, CDCl3): d 7.40–
7.12 (m, 10H, ArH of endo- and exo-isomers), 6.23 (m,
1H, CH]CH of exo-isomer), 6.15 (dd, J¼5.6, 3.0 Hz,
1H, CH]CH of endo-isomer), 6.04 (m, 1H, CH]CH of
exo-isomer), 5.96 (dd, J¼5.6, 2.8 Hz, 1H, CH]CH of
endo-isomer), 4.10–3.95 (m, 4H, CO2CH2CH3 of endo-
and exo-isomers), 2.98–2.77 [m, 8H, (CH2SPh and
CHCH]CHCH) of endo- and exo-isomers], 2.20–1.37 (m,
16H, CH2(CH2)2SPh, CH2CCO2Et, CH2CH2SPh, and CH2
of endo- and exo-isomers), 1.27–1.15 (m, 6H, CO2CH2CH3
of endo- and exo-isomers).
CH3
H
CO2Et
SPh
endo,exo-5b
A pure colorless viscous liquid of endo,exo-isomer of 5b was
obtained in a small quantity by careful preparative thin-layer
chromatography. endo,exo-5b: 1H NMR (300 MHz,
CDCl3): d 7.29–7.03 (m, 5H, ArH), 6.10 (dd, J¼5.4,
3.0 Hz, 1H, CH]CH), 5.99 (dd, J¼5.4, 2.7 Hz, 1H,
CH]CH), 3.91 (m, 2H, CO2CH2CH3), 2.83 (t, J¼6.6 Hz,
2H, CH2SPh), 2.72 (br s, 1H, CHCH]CHCH), 2.27 (br s,
1H, CHCH]CHCH), 1.95 (dq, J¼7.0, 1.4 Hz, 1H,
CHCH3), 1.82–1.40 (m, 5H, CH2CH2CH2SPh and CHH),
1.26 (dd, J¼9.0, 1.5 Hz, 1H, CHH), 1.08 (t, J¼7.1 Hz, 3H,
CO2CH2CH3), 1.00 (d, J¼7.0 Hz, 3H, CHCH3). 13C NMR
(75 MHz, CDCl3): d 176.7 (C]O), 138.2 (CH), 136.2 (C),
136.2 (CH), 129.2 (2ꢂCH), 128.8 (2ꢂCH), 125.9 (CH),
59.9 (CH2), 55.4 (C), 49.7 (CH), 49.4 (CH), 43.7 (CH2),
40.6 (CH), 34.2 (CH2), 34.1 (SCH2), 25.8 (CH2), 16.8
(CH3), 14.2 (CH3). IR (neat): nmax 3059w, 2963s, 1725s,
1585w, 1481m, 1439m, 1240s, 1175m, 1148m, 1026m,
738s, 718m, 691m cmꢀ1. MS: m/z (%) relative intensity
331 (M++1, 13), 330 (M+, 26), 286 (19), 285 (100), 265
(14), 264 (54), 219 (18), 191 (12), 190 (27), 156 (17), 155
(98), 149 (38), 127 (33), 109 (20), 82 (48), 79 (20), 77 (9),
65 (7). Anal. Calcd for C20H26O2S: C, 72.69; H, 7.93.
Found: C, 72.83; H, 8.18.
A pure endo-5a was obtained in 68% yield after prepara-
tive thin-layer chromatography (PLC) (2% ethyl acetate
in hexanes). 1H NMR (300 MHz, CDCl3): d 7.34–7.16
(m, 5H, ArH), 6.16 (dd, J¼5.6, 2.9 Hz, 1H, CH]CH),
5.99 (dd, J¼5.6, 2.8 Hz, 1H, CH]CH), 4.04 (m, 2H,
CO2CH2CH3), 2.90 (t, J¼6.9 Hz, 2H, CH2SPh), 2.84
(br s, 2H, CHCH]CHCH), 2.05 (dt, J¼12.5, 4.8 Hz,
1H, CHH(CH2)2SPh), 1.88 (dd, J¼12.0, 2.5 Hz, 1H,
CHHCCO2Et), 1.80–1.40 (m, 6H, CHHCH2CH2SPh,
CHHCCO2Et, and CH2), 1.19 (t, J¼7.1 Hz, 3H,
CO2CH2CH3). 13C NMR (75 MHz, CDCl3): d 176.0
(C]O), 138.2 (CH), 136.3 (C), 134.6 (CH), 129.1
(2ꢂCH), 128.8 (2ꢂCH), 125.8 (CH), 60.1 (CH2), 54.3
(C), 50.7 (CH), 47.1 (CH2), 42.6 (CH), 39.0 (CH2), 35.7
(CH2), 33.9 (SCH2), 25.5 (CH2), 14.2 (CH3). IR (neat):
nmax 3060w, 2976s, 1728s, 1584w, 1481m, 1439m,
1334m, 1243s, 1184s, 1159s, 1114m, 1096m, 1060m,
1026m, 739s, 712s, 691m cmꢀ1. MS: m/z (%) relative in-
tensity 318 (M++2, 6), 317 (M++1, 25), 316 (M+, 50),
273 (7), 272 (19), 271 (100), 250 (13), 242 (15), 205
(8), 176 (12), 165 (15), 160 (21), 149 (77), 141 (49),
134 (13), 114 (19), 95 (12), 67 (24), 66 (8). Anal. Calcd
for C19H24O2S: C, 72.11; H, 7.64. Found: C, 72.19; H,
7.80.
4.2.3. Ethyl 2-(30-phenylsulfanylpropyl)-3-phenylbicy-
clo[2.2.1]hept-5-ene-2-carboxylate (5c). According to the
general procedure described for compound 5a, a solution
of a 65:35 mixture of endo- and exo-3c (0.60 g, 2.5 mmol)

1810
M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
in THF (1 mL) was added dropwise to a solution of
LDA (3 mmol) in THF (8 mL) at ꢀ78 ꢁC under an argon
atmosphere. After stirring at ꢀ78 ꢁC for 2 h, HMPA (1.2 mL)
was added, followed by the addition of a THF (4 mL)
solution of 3-bromo-1-phenylsulfanylpropane (0.695 g,
3 mmol). After usual work-up, the crude product was puri-
fied by column chromatography (silica gel, 0.2–2% ethyl
acetate in hexanes) to give 5c (0.631 g, 64% yield) as
a 70:30 mixture of endo,exo- and endo,endo-isomers.
1H, CHPh), 2.91 (br s, 1H, CHCH]CHCH), 2.87–2.76
(m, 3H, CHCH]CHCH and CH2SPh), 2.27 (dt, J¼
12.7, 4.1 Hz, 1H, CHH(CH2)2SPh), 1.87–1.61 (m, 3H,
CHHCHHCH2SPh and CHH), 1.49–1.27 (m, 2H, CHH
and CHHCH2SPh), 0.55 (t, J¼7.1 Hz, 3H, CO2CH2CH3).
13C NMR (75 MHz, CDCl3): d 174.5 (C]O), 142.5 (C),
139.9 (CH), 136.2 (C), 133.9 (CH), 129.2 (2ꢂCH), 128.8
(2ꢂCH), 128.6 (2ꢂCH), 127.5 (2ꢂCH), 126.1 (CH),
125.9 (CH), 63.1 (C), 60.0 (CH), 59.8 (CH2), 49.4 (CH),
48.2 (CH), 47.8 (CH2), 40.6 (CH2), 33.9 (SCH2), 25.4
(CH2), 13.3 (CH3). IR (neat): nmax 3060w, 2975s, 1721s,
1602w, 1584m, 1495m, 1480m, 1454m, 1439m, 1319w,
1237s, 1169m, 1148m, 1093m, 1026m, 740s, 703m,
691m cmꢀ1. MS: m/z (%) relative intensity 392 (M+, 1),
348 (5), 327 (4), 326 (21), 320 (22), 319 (84), 281 (7), 252
(13), 241 (22), 236 (12), 235 (13), 218 (15), 217 (56), 209
(59), 189 (31), 182 (22), 177 (30), 171 (47), 167 (17), 165
(14), 149 (45), 143 (100), 142 (38), 141 (24), 128 (39),
123 (16), 115 (38), 91 (29), 77 (16), 65 (12). HRMS (ESI-
TOF) calcd for C25H28O2SNa: 415.1708; found: 415.1708.
Ph
H
H
CO2Et
SPh
Ph
CO2Et
SPh
endo,exo-5c
endo,endo-5c
A mixture of endo,exo- and endo,endo-5c: 1H NMR
(300 MHz, CDCl3): d 7.40–7.01 (m, 20H, ArH of endo,exo-
and endo,endo-isomers), 6.67 (m, 1H, CH]CH of
endo,endo-isomer), 6.36 (dd, J¼5.4, 3.2 Hz, 1H, CH]CH
of endo,exo-isomer), 6.22 (m, 2H, CH]CH of endo,exo-
and endo,endo-isomers), 4.09 (m, 2H, CO2CH2CH3
of endo,exo-isomer), 3.65 (m, 1H, CO2CHHCH3 of
endo,endo-isomer), 3.37 (m, 1H, CO2CHHCH3 of
endo,endo-isomer), 3.25 (s, 1H, CHPh of endo,exo-isomer),
3.11 (d, J¼3.0 Hz, 1H, CHPh of endo,endo-isomer), 3.02–
2.83 [m, 6H, CHCH]CHCH of endo,exo-isomers and
(CHCH]CHCH and CH2SPh) of endo,endo-isomer], 2.54
(m, 2H, CH2SPh of endo,exo-isomer), 2.35 (dt, J¼12.8,
4.1 Hz, 1H, CHH(CH2)2SPh of endo,endo-isomer), 2.02
(d, J¼9.0 Hz, 1H, CHH of endo,exo-isomer), 1.94–1.67
(m, 3H, CHHCHHCH2SPh and CHH of endo,endo-isomer),
1.65–1.47 [m, 4H, (CHH and CHHCH2SPh) of endo,endo-
isomer and (CHH and CHH(CH2)2SPh) of endo,exo-iso-
mer], 1.45–1.17 (m, 6H, CHHCH2SPh, CO2CH2CH3 and
CHH(CH2)2SPh of endo,exo-isomer), 0.12 (t, J¼7.2 Hz,
3H, CO2CH2CH3 of endo,endo-isomer).
4.2.4. 2-(30-Phenylsulfanylpropyl)-3-(hydroxymethyl)bi-
cyclo[2.2.1]hept-5-ene-2-carboxylic acid lactone (5d).
According to the general procedure described for compound
5a, a solution of endo-3d (0.376 g, 2.5 mmol) in THF (1 mL)
was added dropwise to a solution of LDA (3.75 mmol) in
THF (8 mL) at ꢀ78 ꢁC under an argon atmosphere. After
stirring at ꢀ78 ꢁC for 2 h, HMPA (1.2 mL) was added
followed by the addition of a THF (5 mL) solution of
3-bromo-1-phenylsulfanylpropane (2.31 g, 10 mmol). After
usual work-up, the crude product was purified by column
chromatography (silica gel, 10–20% ethyl acetate in hex-
anes) to give a colorless solid of endo-5d (0.354 g, 47%
yield, mp 70–72 ꢁC) and the starting material 3d (0.131 g,
35% yield). The reaction proceeded to give a comparable
yield of 5d (45% yield), when NaI (0.09 g, 0.6 mmol) was
used instead of HMPA.
The endo,exo- and endo,endo-isomers were separated by
PLC to give endo,exo-5c (0.433 g, 44% yield) and
endo,endo-5c (0.158 g, 16% yield) as pale yellow viscous
liquids. endo,exo-5c (less polar): 1H NMR (300 MHz,
CDCl3): d 7.35–7.00 (m, 10H, ArH), 6.29 (dd, J¼5.5,
3.2 Hz, 1H, CH]CH), 6.12 (dd, J¼5.5, 2.8 Hz, 1H,
CH]CH), 4.00 (m, 2H, CO2CH2CH3), 3.17 (br s,
1H, CHPh), 2.90 (br s, 1H, CHCH]CHCH), 2.85 (br s,
1H, CHCH]CHCH), 2.45 (m, 2H, CH2SPh), 1.92 (d,
J¼8.7 Hz, 1H, CHH), 1.54 (dd, J¼8.7, 1.3 Hz, 1H, CHH),
1.39 (m, 1H, CHH(CH2)2SPh), 1.30–1.10 (m, 6H,
CHHCH2CH2SPh and CO2CH2CH3). IR (neat): nmax
3060m, 2974s, 1721s, 1601m, 1584m, 1495m, 1481s,
1454s, 1320m, 1237s, 1169s, 1148s, 1092s, 1025s, 740s,
703s, 692s cmꢀ1. MS: m/z (%) relative intensity 393
(M++1, 5), 392 (M+, 3), 348 (11), 347 (46), 327 (21), 326
(85), 319 (8), 281 (9), 252 (16), 235 (11), 224 (7), 218 (15),
217 (78), 189 (25), 177 (34), 171 (47), 150 (30), 149 (43),
143 (100), 142 (37), 128 (19), 115 (18), 91 (14), 66 (7), 65 (8).
SPh
O
O
endo-5d
1H NMR (300 MHz, CDCl3): d 7.28–7.05 (m, 5H, ArH),
6.23 (dd, J¼5.2, 2.8 Hz, 1H, CH]CH), 6.17 (dd, J¼5.2,
2.8 Hz, 1H, CH]CH), 4.00 (app. t, J¼9.6 Hz, 1H,
CO2CHH), 3.65 (dd, J¼9.6, 2.8 Hz, 1H, CO2CHH), 3.00–
2.85 (m, 2H, CHHSPh and CHCH]CHCH), 2.85–2.71
(m, 2H, CHHSPh and CHCH]CHCH), 2.55 (td, J¼8.7,
3.6 Hz, 1H, CHCH2OCO), 2.05 (m, 1H, CHHCH2CH2SPh),
1.77–1.53 (m, 5H, CH2 and CHHCH2CH2SPh). 13C NMR
(75 MHz, CDCl3): d 180.0 (C]O), 137.9 (CH), 136.0 (C),
134.5 (CH), 129.3 (2ꢂCH), 128.9 (2ꢂCH), 126.1 (CH),
69.3 (CH2), 58.7 (C), 51.4 (CH), 49.8 (CH2), 46.6 (CH),
45.2 (CH), 35.9 (CH2), 33.8 (CH2), 26.00 (CH2). IR
(neat): nmax 3060w, 2972s, 2909m, 1757s, 1583m, 1481m,
1439m, 1381m, 1229m, 1181s, 1148m, 1057m, 1000m,
742s, 692m cmꢀ1. MS: m/z (%) relative intensity 301
(M++1, 23), 300 (M+, 30), 234 (12), 191 (16), 135 (3), 125
(100), 110 (9), 97 (5), 81 (10), 79 (22), 77 (13), 66 (8), 65
(7). Anal. Calcd for C18H20O2S: C, 71.96; H, 6.71. Found:
C, 71.69; H, 6.71.
1
endo,endo-5c (more polar): H NMR (300 MHz, CDCl3):
d 7.30–6.90 (m, 10H, ArH), 6.58 (dd, J¼5.2, 3.2 Hz, 1H,
CH]CH), 6.13 (dd, J¼5.2, 3.0 Hz, 1H, CH]CH), 3.56
(dq, J¼10.7, 7.1, 7.1 Hz, 1H, CO2CHHCH3), 3.29 (dq,
J¼10.7, 7.2, 7.1 Hz, 1H, CO2CHHCH3), 3.05 (d, J¼2.9 Hz,

M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
1811
4.3. Preparation of sulfoxides 6
isomers), 2.79–2.57 (m, 6H, CH2SOPh and CHCH]CHCH
of endo,exo- and endo,endo-isomers), 2.49 (br s, 1H,
CHCH]CHCH of endo,endo-isomer), 2.25 (br s, 1H,
CHCH]CHCH of endo,exo-isomer), 2.00–1.80 [m, 3H,
(CHCH3 and CHHCH2CH2SOPh) of endo,endo-isomer
and CHCH3 of endo,exo-isomer], 1.80–1.34 [m, 10H,
(CH2 and CHHCH2CH2SOPh) of endo,endo-isomer and
(CHH and CH2CH2CH2SOPh) of endo,exo-isomer], 1.26
(dd, J¼9.1, 1.4 Hz, 1H, CHH of endo,exo-isomer), 1.15
(dt, J¼7.6, 1.7 Hz, 3H, CO2CH2CH3 of endo,endo-isomer),
1.10 (m, 3H, CO2CH2CH3 of endo,exo-isomer), 0.95 (d,
J¼7.3 Hz, 3H, CHCH3 of endo,exo-isomer), 0.78 (m,
3H, CHCH3 of endo,endo-isomer). 13C NMR (75 MHz,
CDCl3): d 176.4 (2ꢂC]O), 143.9 and 143.7 (C), 138.2
(2ꢂCH), 136.2 and 136.1 (CH), 131.0 and 130.9 (CH),
129.2 and 129.1 (2ꢂCH), 124.0 (4ꢂCH), 60.0 and 60.0
(CH2), 57.7 and 57.3 (CH2), 55.4 (2ꢂC), 49.5 and 49.1
(CH), 48.9 and 48.3 (CH), 45.9 and 43.7 (CH2), 40.7 and
40.6 (CH), 34.1 and 34.0 (CH2), 19.5 and 18.9 (CH2),
16.8 (2ꢂCH3), 14.2 (2ꢂCH3). IR (neat): nmax 3059w,
2963s, 1722s, 1583w, 1463m, 1444m, 1369m, 1384m,
1340w, 1237s, 1176m, 1145m, 1088s, 1050s, 1023m,
749m, 693m cmꢀ1. MS: m/z (%) relative intensity 348
(M++1, 12), 347 (M+, 52), 329 (28), 301 (23), 283 (18),
281 (18), 236 (13), 235 (81), 175 (14), 156 (17),
155 (100), 147 (14), 128 (16), 127 (45), 110 (44), 105
(12), 91 (17), 82 (94), 79 (62), 77 (21), 66 (8). HRMS
(ESI-TOF) calcd for C20H27O3S: 347.1681; found:
347.1681.
4.3.1. Ethyl 2-(30-phenylsulfinylpropyl)bicyclo[2.2.1]-
hept-5-ene-2-carboxylate (6a). General procedure: A solu-
tion of endo-5a (3.91 g, 12.37 mmol) in methanol (50 mL)
was added dropwise to a suspension of powdered NaIO4
(2.65 g, 12.37 mmol) in water (17 mL) at 0 ꢁC. The mixture
was stirred at 0 ꢁC to room temperature overnight. The pre-
cipitates of NaIO3 were filtered and washed several times
with ethyl acetate. The organic layer was separated and the
aqueous layer was extracted with ethyl acetate. The com-
bined organic layers were washed with water, brine and
dried over anhyd Na2SO4. Filtration followed by evaporation
gave a yellow liquid, which was purified by column chroma-
tography (silica gel, 30% ethyl acetate in hexanes) to furnish
a pure colorless viscous liquid of endo-6a (4.03 g, 98%
1
yield). H NMR (300 MHz, CDCl3): d 7.60–7.37 (m, 5H,
ArH), 6.07 (dd, J¼5.5, 2.9 Hz, 1H, CH]CH), 5.89 (dd,
J¼5.5, 2.7 Hz, 1H, CH]CH), 3.95 (m, 2H, CO2CH2CH3),
2.70, (m, 4H, CH2SOPh and CHCH]CHCH), 2.02–1.28
(m, 8H, CH2CH2CH2SOPh, CH2, and CH2CCO2Et), 1.10
(dt, J¼7.1, 2.3 Hz, 3H, CO2CH2CH3). 13C NMR (75 MHz,
CDCl3): d 175.7 (2ꢂC]O), 143.8 and 143.7 (C), 138.3
and 138.2 (CH), 134.5 and 134.5 (CH), 130.9 (2ꢂCH),
129.1 (4ꢂCH), 123.9 (4ꢂCH), 60.2 (2ꢂCH2), 57.4 and
57.3 (CH2), 54.4 (2ꢂC), 50.7 and 50.6 (CH), 47.1
(2ꢂCH2), 42.6 (2ꢂCH), 39.1 and 39.0 (CH2), 35.8 and
35.6 (CH2), 19.3 and 19.2 (CH2), 14.2 (2ꢂCH3). IR (neat):
nmax 3060m, 2976s, 1728s, 1583w, 1478m, 1445s, 1336m,
1240s, 1185s, 1160s, 1087s, 1044s, 751s, 713s,
693m cmꢀ1. MS: m/z (%) relative intensity 334 (M++1, 8),
333 (M+, 36), 315 (26), 287 (13), 267 (16), 221 (39), 161
(16), 143 (52), 141 (100), 114 (54), 96 (29), 91 (16), 67
(26), 66 (10). Anal. Calcd for C19H24O3S: C, 68.64; H,
7.28. Found: C, 69.09; H, 7.52.
4.3.3. Ethyl 2-(30-phenylsulfinylpropyl)-3-phenylbicy-
clo[2.2.1]hept-5-ene-2-carboxylate (6c). According to the
general procedure described for compound 6a, a mixture of
powdered NaIO4 (0.565 g, 2.64 mmol) in water (4 mL) and
a solution of a 70:30 diastereomeric mixture of endo,exo-
and endo,endo-5c (0.864 g, 2.20 mmol) in methanol
(8 mL) was stirred at 0 ꢁC to room temperature overnight.
The crude product was purified by column chromatography
(silica gel, 25% ethyl acetate in hexanes) to give a pure
pale yellow viscous liquid of 6c (0.77 g, 85% yield) as a
67:33 diastereomeric mixture of endo,exo- and endo,endo-
isomers.
4.3.2. Ethyl 2-(30-phenylsulfinylpropyl)-3-methylbicy-
clo[2.2.1]hept-5-ene-2-carboxylate (6b). According to the
general procedure described for compound 6a, a mixture
of powdered NaIO4 (1.35 g, 6.32 mmol) in water (8 mL)
and a solution of a 7:29:11:53 mixture of diastereomers of
5b (2.00 g, 6.32 mmol) in methanol (23 mL) was stirred at
0 ꢁC to room temperature overnight. The organic layer was
separated and the aqueous layer was extracted with ethyl
acetate and concentrated to give a 4:20:6:70 diastereomeric
mixture of isomers of a crude product 6b as a viscous liquid.
The crude product was purified by column chromatography
(silica gel, 30% ethyl acetate in hexanes) to give a pure
colorless viscous liquid of 6b (1.84 g, 84% yield) as a 93:7
mixture of endo,exo- and endo,endo-isomers.
Ph
H
H
SPh
O
Ph
SPh
O
CO2Et
CO2Et
endo,exo-6c
endo,endo-6c
A mixture of endo,exo- and endo,endo-6c: 1H NMR
(300 MHz, CDCl3): d 7.65–7.45 (m, 10H, SOArH of
endo,exo- and endo,endo-isomers), 7.38–6.95 (m, 10H,
ArH of endo,exo- and endo,endo-isomers), 6.65 (br s, 1H,
CH]CH of endo,endo-isomer), 6.35 (m, 1H, CH]CH of
endo,exo-isomer), 6.23 (br s, 2H, CH]CH of endo,exo-
and endo,endo-isomers), 4.20–3.98 (m, 2H, CO2CH2 of
endo,exo-isomer), 3.64 (m, 1H, CO2CHH of endo,endo-
isomer), 3.37 (m, 1H, CO2CHH of endo,endo-isomer),
3.24 (s, 1H, CHPh of endo,exo-isomer), 3.09 (d, J¼3.0 Hz,
1H, CHPh of endo,endo-isomer), 3.00 (br s, 2H, CHCH]
CHCH of endo,exo- and endo,endo-isomers), 2.94 (br s,
1H, CHCH]CHCH of endo,exo-isomer), 2.89 (br s, 1H,
CHCH]CHCH of endo,endo-isomer), 2.78 (m, 2H,
CH3
H
H
CO2Et
SPh
O
CH3
CO2Et
SPh
O
endo,exo-6b
endo,endo-6b
1H NMR (300 MHz, CDCl3): d 7.57–7.34 (m, 10H, ArH of
endo,exo- and endo,endo-isomers), 6.22 (m, 1H, CH]CH
of endo,endo-isomer), 6.07 (dd, J¼5.5, 3.0 Hz, 1H,
CH]CH of endo,exo-isomer), 5.95 (dd, J¼5.5, 2.7 Hz,
2H, CH]CH of endo,exo- and endo,endo-isomers), 4.07–
3.77 (m, 4H, CO2CH2CH3 of endo,exo- and endo,endo-

1812
M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
CH2SOPh of endo,endo-isomer), 2.53–2.20 (m, 3H,
CH2SOPh of endo,exo-isomer and CHH(CH2)2SOPh
of endo,endo-isomer), 2.00–1.05 [m, 14H, (CH2 and
CHHCH2CH2SOPh) of endo,endo-isomer and (CH2,
CH2CH2CH2SOPh and CO2CH2CH3) of endo,exo-isomer],
0.64 (td, J¼13.1, 6.8 Hz, 3H, CO2CH2CH3 of endo,endo-
isomer).
4.4. Preparation of spiro-sulfoxides 7 by cyclization of
sulfoxides 6
4.4.1. 20-Oxo-30-phenylsulfinylcyclopentane-10-spiro-2-
bicyclo[2.2.1]hept-5-ene (7a). General procedure: A solu-
tion of a 86:14 mixture of endo- and exo-6a (0.50 g,
1.5 mmol) in THF (4.50 mL) was added dropwise at
ꢀ78 ꢁC to a solution of lithium diisopropylamide (LDA) un-
der an argon atmosphere [prepared by reacting diisopropyl-
amine (0.47 mL, 3.30 mmol) in THF (5 mL) with n-BuLi
(1.41 M in hexane, 2.55 mL, 3.30 mmol) at ꢀ78 ꢁC for
1 h]. The mixture was stirred at ꢀ78 ꢁC for 2 h, 0 ꢁC for
2 h and then quenched with a saturated NH4Cl solution
(6 mL). The mixture was extracted with EtOAc
(3ꢂ25 mL). The combined organic layers were washed
with water, brine and dried over anhyd Na2SO4. After re-
moval of solvent under reduced pressure, a crude product
7a was purified by preparative thin-layer chromatography
(silica gel, 20% ethyl acetate in hexanes) to give three bands
(PLC1, PLC2, and PLC3) of 7a (0.387 g, 90% combined
yield) as a diastereomeric mixture.
A pure endo,exo-6c was partially obtained by PLC as a pale
yellow viscous liquid. 1H NMR (300 MHz, CDCl3): d 7.59–
7.34 (m, 5H, SOArH), 7.30–7.05 (m, 5H, ArH), 6.29 (m,
1H, CH]CH), 6.14 (m, 1H, CH]CH), 4.01 (m, 2H,
CO2CH2CH3), 3.17 (d, J¼2.2 Hz, 1H, CHPh), 2.95 (d,
J¼6.7 Hz, 1H, CHCH]CHCH), 2.85 (br s, 1H,
CHCH]CHCH), 2.46–2.14 (m, 2H, CH2SOPh), 1.95–
1.00 (m, 9H, CH2CH2CH2SOPh, CO2CH2CH3, and CH2).
13C NMR (75 MHz, CDCl3): d 176.2 (2ꢂC]O), 143.8
and 143.4 (C), 141.5 and 141.5 (C), 139.7 (2ꢂCH), 137.4
(2ꢂCH), 130.9 and 130.7 (CH), 129.1 and 129.0 (2ꢂCH),
127.9 (8ꢂCH), 126.1 (2ꢂCH), 123.9 and 123.8 (2ꢂCH),
60.44 and 60.36 (CH2), 57.65 and 56.63 (OSCH), 57.1
(2ꢂC), 51.68 and 51.65 (CH), 48.1 and 48.0 (CH), 47.2
(2ꢂCH), 45.31 and 45.27 (CH2), 36.0 and 35.8 (CH2),
19.2 and 17.9 (CH2), 14.3 and 14.2 (CH3). IR (neat): nmax
3060m, 3028m, 2977s, 1728s, 1716s, 1602m, 1583w,
1495m, 1478m, 1454s, 1445s, 1368m, 1323m, 1234s,
1165s, 1145s, 1089s, 1046s, 911m, 750s, 701s cmꢀ1. MS:
m/z (%) relative intensity 409 (M+, 10), 391 (3), 344 (11),
343 (41), 297 (31), 283 (7), 279 (6), 247 (13), 217 (39),
209 (9), 189 (27), 172 (18), 171 (100), 144 (21), 143 (67),
129 (19), 128 (20), 117 (15), 115 (19), 91 (15), 77 (6), 66
(5), 65 (6). HRMS (ESI-TOF) calcd for C25H28O3SNa:
431.1657; found: 431.1656.
PLC1 (less polar): a pure isomer as a white solid (43 mg,
1
10% yield, mp 116–118 ꢁC). H NMR (300 MHz, CDCl3):
d 7.60–7.36 (m, 5H, ArH), 6.23 (dd, J¼5.5, 3.0 Hz, 1H,
CH]CH), 6.05 (dd, J¼5.5, 3.1 Hz, 1H, CH]CH), 3.26
(dd, J¼9.8, 8.6 Hz, 1H, CHSOPh), 3.15 (br s, 1H,
CHCH]CHCH), 2.86 (br s, 1H, CHCH]CHCH), 2.37
(m, 1H, CHHCH2CHSOPh), 2.10 (dd, J¼11.5, 3.6 Hz,
1H, CHHCCO), 1.85–1.31 (m, 4H, CHH and
CHHCH2CHSOPh), 1.21 (d, J¼8.9 Hz, 1H, CHH), 0.74
(dd, J¼11.5, 2.9 Hz, 1H, CHHCCO). 13C NMR (75 MHz,
CDCl3): d 214.0 (C]O), 142.3 (C), 140.6 (CH), 133.4
(CH), 130.9 (CH), 129.2 (2ꢂCH), 123.9 (2ꢂCH), 71.4
(CH), 57.5 (C), 45.58 (CH), 45.56 (CH2), 43.1 (CH), 37.6
(CH2), 33.0 (CH2), 14.8 (CH2). IR (Nujol): nmax 2955s,
1724m, 1334w, 1235w, 1163w, 1086w, 1046m, 1029w,
754w, 740w, 725m, 691w cmꢀ1. MS: m/z (%) relative inten-
sity 287 (M++1, 14), 269 (6), 162 (12), 161 (100), 143 (20),
133 (10), 128 (12), 126 (8), 117 (6), 105 (13), 97 (12), 95
(35), 91 (21), 79 (11), 78 (14), 77 (11), 67 (17), 66 (11),
65 (12).
4.3.4. 2-(30-Phenylsulfinylpropyl)-3-(hydroxymethyl)bi-
cyclo[2.2.1]hept-5-ene-2-carboxylic acid lactone (6d).
According to the general procedure described for compound
6a, a mixture of powdered NaIO4 (0.757 g, 3.54 mmol)
in water (5 mL) and a solution of endo-5d (0.887 g,
2.95 mmol) in methanol (10 mL) was stirred at 0 ꢁC to
room temperature overnight. The crude product was purified
by column chromatography (silica gel, 40–50% ethyl acetate
in hexanes) to give a pure colorless solid of endo-6d (0.75 g,
1
80% yield, mp 86–88 ꢁC). H NMR (300 MHz, CDCl3):
PLC2 (more polar): a pure isomer as a white solid (0.168 g,
1
d 7.60–7.40 (m, 5H, ArH), 6.24 (br s, 2H, CH]CH),
4.10 (td, J¼23.4, 9.3 Hz, 1H, CO2CHHCH3), 3.70 (m,
1H, CO2CHHCH3), 3.00 (br s, 1H, CHCH]CHCH),
2.85–2.61 (m, 4H, CH2SOPh, CHCH2OCO, and
CHCH]CHCH), 2.61–1.41 (m, 6H, CH2CH2CH2SOPh
39% yield, mp 119–121 ꢁC). H NMR (300 MHz, CDCl3):
d 7.61–7.36 (m, 5H, ArH), 6.22 (dd, J¼5.6, 3.0 Hz, 1H,
CH]CH), 5.80 (dd, J¼5.6, 2.9 Hz, 1H, CH]CH), 3.24
(app. t, J¼9.6 Hz, 1H, CHSOPh), 3.07 (br s, 1H,
CHCH]CHCH), 2.83 (br s, 1H, CHCH]CHCH), 2.50
(m, 1H, CHHCH2CHSOPh), 2.07 (dd, J¼12.4, 7.2 Hz,
1H, CHHCHSOPh), 1.95 (dd, J¼12.4, 6.8 Hz, 1H,
CHHCHSOPh), 1.60–1.33 (m, 5H, CH2, CH2CCO and
CHHCH2CHSOPh). 13C NMR (75 MHz, CDCl3): d 213.1
(C]O), 142.4 (C), 137.8 (CH), 132.6 (CH), 130.9 (CH),
129.2 (2ꢂCH), 123.9 (2ꢂCH), 71.1 (CH), 56.9 (C), 49.0
(CH), 48.6 (CH2), 42.9 (CH), 38.4 (CH2), 35.0 (CH2), 15.0
(CH2). IR (Nujol): nmax 2955s, 1727m, 1334w, 1238w,
and CH2). 13C NMR (75 MHz, CDCl3):
d 179.7
(2ꢂC]O), 143.6 and 143.1 (C), 137.5 (2ꢂCH), 134.5
(2ꢂCH), 130.9 (2ꢂCH), 129.1 (4ꢂCH), 123.7 and 123.6
(2ꢂCH), 69.2 (2ꢂCH2O), 58.6 (2ꢂC), 57.0 and 56.4
(CH2), 51.3 and 51.2 (CH), 49.7 and 49.6 (CH2), 46.50
and 46.48 (CH), 44.72 and 44.67 (CH), 35.9 and 35.3
(CH2), 20.0 and 18.7 (CH2). IR (neat): nmax 3061w, 2973s,
1755s, 1643w, 1479m, 1444m, 1382m, 1342w, 1219m,
1183s, 1147m, 1088m, 1038s, 999s, 751s, 694m cmꢀ1
.
1085w, 1048m, 1020w, 760w, 743w, 728m, 692w cmꢀ1
.
MS: m/z (%) relative intensity 317 (M+, 10), 299 (2), 251
(3), 199 (11), 191 (6), 126 (9), 125 (100), 115 (4), 107 (3),
97 (16), 91 (9), 81 (17), 79 (50), 78 (10), 77 (28), 66 (7),
65 (8). HRMS (ESI-TOF) calcd for C18H20O3SNa:
339.1031; found: 339.1031.
MS: m/z (%) relative intensity 286 (M+, 3), 267 (11), 243
(23), 231 (23), 205 (14), 203 (12), 201 (20), 193 (19), 181
(69), 178 (24), 149 (31), 143 (23), 131 (100), 125 (34), 121
(22), 109 (21), 99 (24), 97 (21), 95 (26), 93 (25), 83 (24),
81 (41), 79 (27), 77 (22), 69 (80), 67 (38), 65 (12), 51 (8).

M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
1813
PLC3 (most polar): a 69:31 mixture of two isomers (A-
and B-isomers) (0.176 g, 41% yield, mp 122–125 ꢁC).
1H NMR (300 MHz, CDCl3): d 7.70–7.45 (m, 10H, ArH of
A- and B-isomers), 6.31 (dd, J¼5.5, 3.0 Hz, 1H, CH]CH
of B-isomer), 6.20 (dd, J¼5.5, 3.1 Hz, 1H, CH]CH of
A-isomer), 5.94 (dd, J¼5.5, 2.8 Hz, 1H, CH]CH of B-iso-
mer), 5.68 (dd, J¼5.5, 2.9 Hz, 1H, CH]CH of A-isomer),
3.82 (app. t, J¼9.3 Hz, 1H, CHSOPh of A-isomer), 3.41
(dd, J¼9.4, 5.2 Hz, 1H, CHSOPh of B-isomer), 2.94
(br s, 1H, CHCH]CHCH of B-isomer), 2.84 (br s, 1H,
CHCH]CHCH of A-isomer), 2.75 (br s, 1H, CHCH]
CHCH of B-isomer), 2.51 (m, 1H, CHHCH2CHSOPh
of B-isomer), 2.43–2.30 (m, 2H, CHHCH2CHSOPh and
CHCH]CHCH of A-isomer), 2.28–2.12 (m, 2H,
CHHCH2CHSOPh of A- and B-isomers), 2.10–1.84 (m,
4H, CH2CHSOPh of A- and B-isomers), 1.66 (d,
J¼11.8 Hz, 1H, CHHCCO of B-isomer), 1.60–1.22 [m,
7H, (CH2, CHHCCO, and CH2CCO) of A-isomer and
(CH2 and CHHCCO) of B-isomer]. 13C NMR (75 MHz,
CDCl3) of A-isomer: d 212.1 (C]O), 140.6 (C), 137.6
(CH), 132.7 (CH), 131.5 (CH), 128.9 (2ꢂCH), 125.3
(2ꢂCH), 69.0 (CH), 56.7 (C), 49.5 (CH), 48.8 (CH2), 42.7
(CH), 39.8 (CH2), 35.7 (CH2), 19.7 (CH2); B-isomer:
d 213.0 (C]O), 142.7 (C), 138.3 (CH), 132.3 (CH), 131.0
(CH), 129.2 (2ꢂCH), 124.2 (2ꢂCH), 71.0 (CH), 56.9 (C),
51.2 (CH), 49.3 (CH2), 43.0 (CH), 39.1 (CH2), 36.5 (CH2),
17.0 (CH2). IR (Nujol): nmax 2956s, 1735m, 1476m,
1444m, 1334m, 1238w, 1083m, 1042m, 1024m, 755m,
746m, 721m, 689m cmꢀ1. MS: m/z (%) relative intensity
286 (M+, 8), 281 (18), 243 (16), 231 (22), 203 (27), 201
(46), 193 (26), 181 (60), 159 (25), 149 (57), 143 (27), 131
(94), 125 (100), 121 (32), 117 (34), 109 (31), 99 (82), 97
(35), 95 (54), 93 (46), 91 (40), 81 (80), 79 (41), 77 (35), 69
(86), 67 (53). Anal. Calcd for C17H18O2S: C, 71.30; H,
6.64. Found: C, 71.15; H, 6.50.
149 (10), 147 (10), 133 (9), 129 (13), 125 (12), 110 (13),
109 (100), 105 (18), 97 (16), 93 (25), 91 (46), 81 (27), 79
(54), 77 (59), 66 (13), 65 (23).
PLC2 (more polar): a pale yellow solid of a mixture of dia-
stereomers (0.158 g, 23% yield): 1H NMR (300 MHz,
CDCl3): d 7.60–7.35 (m, ArH), 6.30–6.20 (m, olefinic pro-
tons), 6.29–6.00 (m, olefinic protons), 5.77 (dd, J¼5.2,
2.8 Hz, olefinic proton of the major isomer), 5.60 (dd,
J¼5.6, 2.8 Hz, olefinic proton of the minor isomer), 4.01
(d, J¼9.3 Hz, CHSOPh of the minor isomer), 3.90–3.69
(m, CHSOPh of the minor isomer), 3.20 (m, CHSOPh of
the major isomer), 3.02 (br s, CHCH]CHCH of the major
isomer), 2.90 (br s, CHCH]CHCH of the minor isomer),
2.85 (br s, CHCH]CHCH of minor isomer), 2.73–1.13
(m, CHCH]CHCH, CH2CH2CHSOPh, CHCH3 and CH2
of the major and minor isomers), 1.10–0.63 (m, CHCH3 of
the major and minor isomers), 0.55 (d, J¼7.2 Hz, CHCH3
of the minor isomer), 0.35 (d, J¼7.3 Hz, CHCH3 of the mi-
nor isomer). IR (CHCl3): nmax 3067w, 3010s, 2968s, 1728s,
1584w, 1478m, 1458m, 1445m, 1341w, 1315m, 1150m,
1086s, 1042m, 1023m, 690m cmꢀ1. MS: m/z (%) relative in-
tensity 300 (M+, 2), 251 (2), 235 (11), 176 (17), 175 (100),
157 (53), 147 (28), 142 (17), 133 (17), 129 (27), 125 (22),
119 (20), 115 (17), 110 (19), 109 (99), 105 (34), 97 (38),
93 (19), 91 (60), 81 (30), 79 (66), 77 (55), 66 (22), 65 (31).
PLC3 (most polar): a pale yellow viscous liquid of a 66:34
mixture of two diastereomers (A- and B-isomers) (0.253 g,
37% yield). 1H NMR (400 MHz, CDCl3): d 7.67–7.45
(m, 10H, ArH of A- and B-isomers), 6.39 (dd, J¼5.7,
3.1 Hz, 1H, CH]CH of A-isomer), 6.26 (dd, J¼5.6,
3.1 Hz, 1H, CH]CH of B-isomer), 5.76 (dd, J¼5.7,
2.9 Hz, 1H, CH]CH of A-isomer), 5.56 (dd, J¼5.6, 2.9 Hz,
1H, CH]CH of B-isomer), 3.76 (dd, J¼10.4, 8.9 Hz, 1H,
CHSOPh of B-isomer), 3.39 (dd, J¼9.8, 3.3 Hz, 1H,
CHSOPh of A-isomer), 2.71 (br s, 1H, CHCH]CHCH of
A-isomer), 2.55–2.47 (m, 3H, CHCH]CHCH of A-isomer
and CH2CH2CHSOPh of B-isomer), 2.43–2.23 (m, 4H,
CH2CH2CHSOPh of A-isomer and CHCH]CHCH of
B-isomer), 2.08–1.68 [m, 6H, (CH2CHSOPh and CHCH3)
of A-isomer and (CH2CHSOPh and CHCH3) of B-isomer],
1.66 (d, J¼8.9 Hz, 1H, CHH of A-isomer), 1.52 (d,
J¼8.8 Hz, 1H, CHH of B-isomer), 1.45 (ddd, J¼8.9, 3.5,
1.7 Hz, 1H, CHH of A-isomer), 1.33 (ddd, J¼8.8, 3.3,
1.7 Hz, 1H, CHH of B-isomer), 1.01 (d, J¼7.2 Hz, 3H,
CHCH3 of A-isomer), 0.93 (d, J¼7.2 Hz, 3H, CHCH3 of
B-isomer). 13C NMR (100 MHz, CDCl3) of A-isomer:
d 213.6 (CO), 143.7 (C), 139.9 (CH), 131.8 (CH), 131.6
(CH), 129.8 (2ꢂCH), 125.0 (2ꢂCH), 71.3 (CH), 60.0 (C),
52.9 (CH), 51.3 (CH), 47.1 (CH2), 41.2 (CH), 32.4 (CH2),
18.8 (CH2), 18.3 (CH3); B-isomer: d 212.4 (CO), 153.2
(C), 138.8 (CH), 132.8 (CH), 132.1 (CH), 129.5 (2ꢂCH),
126.0 (2ꢂCH), 69.7 (CH), 60.0 (C), 51.2 (CH), 51.2 (CH),
46.7 (CH2), 41.8 (CH), 31.1 (CH2), 20.9 (CH2), 18.3
(CH3). IR (CHCl3): nmax 3066w, 3010s, 2969s, 1726s,
1584w, 1478m, 1464m, 1445m, 1332w, 1154w, 1086m,
1048m, 1024m, 691m cmꢀ1. MS: m/z (%) relative intensity
300 (M+, 10), 254 (6), 217 (10), 175 (74), 157 (43), 147 (21),
142 (18), 129 (25), 110 (31), 109 (100), 105 (28), 97 (17),
91 (56), 81 (33), 79 (62), 77 (44), 66 (18), 65 (22). Anal.
Calcd for C18H20O2S: C, 71.97; H, 6.71. Found: C, 71.83;
H, 6.87.
4.4.2. 20-Oxo-30-phenylsulfinylcyclopentane-10-spiro-2-
(3-methylbicyclo[2.2.1]hept-5-ene) (7b). According to the
general procedure described for compound 7a, a diastereo-
meric mixture of 6b (0.79 g, 2.28 mmol) was reacted with
LDA (5.02 mmol) in THF (7 mL) to give a crude product,
which was purified by preparative thin-layer chromato-
graphy (silica gel, 20% ethyl acetate in hexanes) to give
three bands (PLC1, PLC2, and PLC3) of 7b (0.548 g, 80%
combined yield) as a diastereomeric mixture.
PLC1 (less polar): a pale yellow solid of a mixture of diaste-
reomers (0.137 g, 20% yield): 1H NMR (300 MHz, CDCl3):
d 7.60–7.38 (m, ArH), 6.30–6.20 (m, olefinic protons), 6.18–
5.98 (m, olefinic protons), 4.10 (m, CHSOPh of the minor
isomer), 3.30–3.17 [m, (CHSOPh and CHCH]CHCH) of
the major isomer and CHSOPh of the minor isomer], 2.86
(br s, CHCH]CHCH of the minor isomer), 2.75–2.55 (m,
CHCH]CHCH of the major and minor isomers), 2.54–
1.75 [m, CH2CH2CHSOPh of the major isomer and
(CH2CH2CHSOPh, CHH, and CHCH]CHCH) of the mi-
nor isomer], 1.70 (d, J¼8.7 Hz, CHH of the major isomer),
1.67–0.50 [m, CH2, (CH2CHSOPh and CHCH3) of the major
and minor isomers], 0.13 (d, J¼7.3 Hz, CHCH3 of the minor
isomer). IR (CHCl3): nmax 3064w, 3010s, 2969s, 1726s,
1584w, 1478m, 1445m, 1345w, 1317m, 1158m, 1085s,
1048m, 691m, 665m cmꢀ1. MS: m/z (%) relative intensity
300 (M+, 2), 251 (5), 235 (9), 217 (8), 175 (33), 157 (15),

1814
M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
4.4.3. 20-Oxo-30-phenylsulfinylcyclopentane-10-spiro-2-
(3-phenyl-bicyclo[2.2.1]hept-5-ene) (7c). According to
the general procedure described for compound 7a,
a 70:30 mixture of endo,exo- and endo,endo-6c (1.27 g,
3.22 mmol) was reacted with LDA (7.09 mmol) in THF
(10 mL) to give a crude product, which was purified by pre-
parative thin-layer chromatography (silica gel, 20% ethyl
acetate in hexanes) to give two bands (PLC1 and PLC2) of
7c (0.817 g, 70% combined yield) as a diastereomeric mix-
ture. 1H NMR (300 MHz, CDCl3) of a mixture of four dia-
stereomers of 7c (A-, B-, C-, and D-isomers): d 7.59–7.36
(m, 20H, SOArH), 7.29–6.88 (m, 20H, ArH), 6.46 (m, 3H,
CH]CH of A-, B-, and D-isomers), 6.35 (m, 2H,
CH]CH of A-isomer and CH]CH of C-isomer), 5.94
(dd, J¼5.5, 2.9 Hz, CH]CH of D-isomer), 5.88 (dd,
J¼5.6, 2.9 Hz, 1H, CH]CH of B-isomer), 5.73 (dd, J¼
5.5, 2.9 Hz, 1H, CH]CH of C-isomer), 3.58 (app. t,
J¼9.4 Hz, 1H, CHSOPh of C-isomer), 3.39 (dd, J¼9.3,
4.6 Hz, 1H, CHSOPh of B-isomer), 3.33 (d, J¼2.9 Hz, 1H,
CHPh of A-isomer), 3.24–2.82 [m, 10H, CHCH]CHCH
of A-isomer, (CHCH]CHCH and CHPh) of B- and C-iso-
mers and (CHSOPh, CHCH]CHCH, and CHPh) of D-iso-
mer], 2.77 (br s, 1H, CHCH]CHCH of B-isomer), 2.60 (dd,
J¼9.5, 6.6 Hz, 1H, CHSOPh of A-isomer), 2.50 (br s, 1H,
CHCH]CHCH of C-isomer), 2.43–2.02 (m, 7H, CH2CCO
of A-, B-, and C-isomers and CHHCCO of D-isomer), 1.95
(d, J¼8.9 Hz, 2H, CHH of A- and D-isomers), 1.90–1.12 [m,
16H, (CHH and CH2CHSOPh) of A-isomer, (CH2 and
CH2CHSOPh) of B- and C-isomers and (CH2 and
CHHCH2CHSOPh) of D-isomer].
CHHCH2CHSOPh), 1.95 (d, J¼8.8 Hz, 1H, CHH), 1.67
(d, J¼8.8 Hz, 1H, CHH), 1.45 (m, 1H, CHHCH2CHSOPh),
1.40–1.10 (m, 2H, CH2CHSOPh). 13C NMR (75 MHz,
CDCl3): d 212.6 (C]O), 142.1 (C), 141.9 (C), 139.3
(CH), 133.7 (CH), 130.8 (CH), 129.1 (2ꢂCH), 128.4
(2ꢂCH), 128.1 (2ꢂCH), 126.2 (CH), 123.8 (2ꢂCH), 70.8
(CH), 61.2 (C), 52.3 (CH), 49.1 (CH), 48.4 (CH), 47.9
(CH2), 31.5 (CH2), 14.9 (CH2). IR (CHCl3): nmax 3066w,
3010m, 1729s, 1602w, 1584w, 1498m, 1478w, 1446m,
1332w, 1242m, 1153m, 1086m, 1051m, 705m cmꢀ1. MS:
m/z (%) relative intensity 363 (M+, 2), 297 (13), 237 (42),
236 (12), 219 (10), 172 (31), 171 (100), 170 (14), 169
(38), 154 (9), 153 (21), 129 (16), 128 (20), 115 (18), 92
(15), 78 (7), 66 (5), 65 (6). Anal. Calcd for C23H22O2S: C,
76.21; H, 6.12. Found: C, 76.06; H, 6.32.
4.4.4. 20-Oxo-30-phenylsulfinylcyclopentane-10-spiro-2-
(3-hydroxymethylbicyclo[2.2.1]hept-5-ene) (7dA) and
compound 7dB. According to the general procedure de-
scribed for compound 7a, a 90:10 diastereomeric mixture
of 6d (0.442 g, 1.40 mmol) was reacted with LDA
(3.08 mmol) in THF (4.5 mL) to give a crude product, which
was purified by preparative thin-layer chromatography (sil-
ica gel, 70% ethyl acetate in hexanes) to afford two bands
(PLC1 and PLC2) of products (0.365 g, 82% combined
yield).
PLC1 (less polar) was obtained as a colorless solid of a single
diastereomer of 7dB (0.135 g, 30% yield, mp 134–136 ꢁC).
1H NMR (300 MHz, CDCl3): d 7.75–7.47 (m, 5H, ArH),
6.57 (dd, J¼5.6, 3.0 Hz, 1H, CH]CH), 6.15 (dd, J¼5.6,
2.9 Hz, 1H, CH]CH), 4.10 (app. t, J¼8.5 Hz, 1H,
CHHO), 3.49 (app. t, J¼8.5 Hz, 1H, CHHO), 3.05 (dd,
J¼12.0, 6.1 Hz, 1H, CHSOPh), 2.87–2.74 (m, 2H,
CHCH]CHCH and CHCH2O), 2.65 (br s, 1H, OH), 2.58
(br s, 1H, CHCH]CHCH), 2.00–1.70 (m, 5H,
CH2CHHCHSOPh and CH2), 1.27 (m, 1H, CHHCHSOPh).
13C NMR (75 MHz, CDCl3): d 143.4 (C), 138.8 (CH), 132.5
(CH), 131.5 (CH), 129.2 (2ꢂCH), 124.5 (2ꢂCH), 112.2 (C–
O), 74.6 (CH), 70.7 (CH2), 68.2 (C), 60.3 (CH), 53.7 (CH2),
51.6 (CH), 44.3 (CH), 39.4 (CH2), 23.2 (CH2). IR (Nujol):
nmax 3385m, 3053w, 2956s, 1441m, 1253w, 1242w,
1173w, 1027m, 1013m, 995m, 748m, 700w cmꢀ1. MS:
m/z (%) relative intensity 316 (M+, 1), 299 (12), 233 (48),
191 (75), 173 (50), 160 (36), 153 (38), 145 (64), 135 (28),
129 (30), 125 (100), 117 (49), 97 (32), 91 (68), 79 (61), 77
(60), 66 (39), 65 (37), 51 (26). HRMS (ESI-TOF) calcd for
C18H20O3SNa: 339.1031; found: 339.1031.
PLC1 (less polar): 0.630 g, 54% yield as a yellow solid
of three isomers (A-, B-, and C-isomers). 1H NMR
(300 MHz, CDCl3): d 7.59–7.32 (m, 15H, SOArH), 7.30–
6.88 (m, 15H, ArH), 6.45 (m, 2H, CH]CH of A- and B-iso-
mers), 6.35 (m, 2H, CH]CH of A-isomer and CH]CH of
C-isomer), 5.87 (dd, J¼5.6, 2.8 Hz, CH]CH of B-isomer),
5.72 (dd, J¼5.6, 2.9 Hz, 1H, CH]CH of C-isomer), 3.59
(app. t, J¼9.4 Hz, 1H, CHSOPh of C-isomer), 3.38 (dd,
J¼9.3, 4.6 Hz, 1H, CHSOPh of B-isomer), 3.33 (d,
J¼2.9 Hz, 1H, CHPh of A-isomer), 3.13–2.86 [m, 6H,
CHCH]CHCH of A-isomer and (CHCH]CHCH and
CHPh) of B- and C-isomers], 2.76 (br s, 1H, CHCH]CHCH
of B-isomer), 2.60 (dd, J¼9.6, 6.6 Hz, 1H, CHSOPh of A-
isomer), 2.50 (br s, 1H, CHCH]CHCH of C-isomer),
2.44–2.02 (m, 6H, CH2CCO of A-, B-, and C-isomers),
1.95 (d, J¼8.2 Hz, 1H, CHH of A-isomer), 1.90–1.10 [m,
11H, (CHH and CH2CHSOPh) of A-isomer and (CH2 and
CH2CHSOPh) of B- and C-isomers]. IR (CHCl3): nmax
3436w, 3066w, 3012s, 1729s, 1602w, 1498w, 1478w,
1445m, 1332w, 1241m, 1175w, 1153w, 1086m, 1050m,
706m cmꢀ1. MS: m/z (%) relative intensity 363 (M+, 1),
298 (3), 297 (14), 237 (16), 236 (4), 219 (3), 173 (5), 172
(31), 171 (100), 170 (10), 169 (30), 153 (20), 141 (11),
129 (11), 128 (14), 115 (13), 91 (7), 78 (7), 66 (4), 65 (6).
PLC2 (more polar) was obtained as a pale yellow solid of
7dA (0.231 g, 52% yield) as a mixture of diastereomers:
1H NMR (300 MHz, CDCl3): d 7.70–7.35 (m, ArH), 6.52
(m, an olefinic proton of the minor isomer), 6.40 (dd,
J¼5.6, 3.0 Hz, olefinic proton of the major isomer), 6.27
(m, an olefinic proton of the major isomer), 6.20 (m, an ole-
finic proton of the minor isomer), 6.15–5.95 (m, olefinic pro-
tons of the minor isomer), 4.04 (app. t, J¼8.6 Hz, CHHOH
of the major isomer), 3.70 (app. t, J¼8.8 Hz, CHHOH of
the minor isomer), 3.50–3.28 (m, CHHOH of the major
and minor isomers), 3.22 (app. t, J¼10.7 Hz, CHSOPh of
the minor isomer), 3.14–2.95 (m, CHSOPh of the major
and minor isomers), 2.88–2.50 [m, (CHCH]CHCH and
CHCH2OH) of the major isomer and CHCH]CHCH of
PLC2 (more polar): a pale yellow solid of a pure D-isomer
(0.187 g, 16% yield, mp 142–144 ꢁC). 1H NMR
(300 MHz, CDCl3): d 7.58–7.32 (m, 5H, SOArH), 7.30–
6.84 (m, 5H, ArH), 6.44 (dd, J¼5.4, 3.2 Hz, 1H,
CH]CH), 5.94 (dd, J¼5.4, 2.9 Hz, 1H, CH]CH), 3.26–
3.12 (m, 2H, CHCH]CHCH and CHSOPh), 3.08 (br s,
1H, CHCH]CHCH), 3.00 (br s, 1H, CHPh), 2.39 (m, 1H,

M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
1815
the minor isomer], 2.50–2.08 (m, CH2CH2CHSOPh,
OH, and CHCH2OH) of the minor isomer and
(CHHCH2CHSOPh and OH) of the major isomer), 2.08–
1.45 [m, (CHHCH2CHSOPh and CH2) of the major and mi-
nor isomers], 1.35 (d, J¼9.4 Hz, CHH of the minor isomer).
IR (neat): nmax 3419s, 3060m, 2964s, 2874s, 1728s, 1651w,
1583w, 1479s, 1445s, 1341m, 1256s, 1085s, 1046s, 997s,
752s, 695s cmꢀ1. MS: m/z (%) relative intensity 317 (M+,
4), 299 (13), 233 (38), 191 (86), 173 (53), 160 (32), 153
(33), 145 (59), 135 (23), 131 (23), 126 (29), 125 (100),
117 (44), 107 (28), 97 (26), 92 (68), 79 (62), 77 (39), 66
(28), 65 (28), 51 (19). HRMS (ESI-TOF) calcd for
C18H20O3SNa: 339.1031; found: 339.1029.
6.16 (td, J¼5.9, 2.2 Hz, 1H, CH]CHCO), 5.99 (dd,
J¼5.5, 2.9 Hz, 1H, CH]CH), 2.98 (d, J¼0.7 Hz,
1H, CHCH]CHCH), 2.90 (dd, J¼19.0, 2.2 Hz, 1H,
CHHCH]CHCO), 2.73 (dd, J¼19.0, 2.4 Hz, 1H,
CHHCH]CHCO), 2.51 (br s, 1H, CHCH]CHCH), 1.69
(dd, J¼11.9, 3.6 Hz, 1H, CHHCCO), 1.50 (m, 3H, CH2
and CHHCCO). 13C NMR (75 MHz, CDCl3): d 211.8
(C]O), 161.0 (CH), 133.6 (CH), 132.6 (CH), 54.6 (CH),
52.4 (C), 50.1 (CH2), 47.2 (CH2), 43.5 (CH), 39.3 (CH2).
IR (neat): nmax 3063m, 2964s, 1699s, 1593m, 1475m,
1443m, 1328s, 1309m, 1146s, 1078m, 797m, 753s, 717m,
687s, 595s cmꢀ1. MS: m/z (%) relative intensity 160 (M+,
4), 159 (15), 141 (28), 131 (11), 125 (100), 115 (8), 109
(21), 97 (23), 95 (28), 91 (10), 77 (56), 65 (21), 51 (18).
HRMS (ESI-TOF) calcd for C11H12ONa: 183.0786; found:
183.0786.
4.5. Preparation of spirocyclopentenones 8
4.5.1. 20-Oxocyclopent-30-ene-10-spiro-2-bicyclo[2.2.1]-
hept-5-ene (8a). A diastereomeric mixture of 7a (1 g,
3.5 mmol) was dissolved in dry toluene (10 mL) and dry
CaCO3 (0.35 g, 3.5 mmol) was added. The mixture was re-
fluxed under an argon atmosphere overnight. The precipitate
of CaCO3 was filtered and washed with ethyl acetate. The
organic layer was concentrated to give an 88:12 mixture of
endo- and exo-8a, which was purified by column chromato-
graphy (silica gel, 10% ethyl acetate in hexanes) to give two
fractions of 8a (0.395 g, 70% combined yield).
4.5.2. 20-Oxocyclopent-30-ene-10-spiro-2-(3-methyl-
bicyclo[2.2.1]hept-5-ene) (8b). A diastereomeric mixture
of 7b (0.40 g, 1.33 mmol) was dissolved in dry toluene
(5 mL) and dry CaCO3 (0.13 g, 1.33 mmol) was added.
The mixture was refluxed under an argon atmosphere over-
night. The crude product was purified by column chromato-
graphy (silica gel, 10% ethyl acetate in hexanes) to give two
fractions of 8b (0.174 g, 75% combined yield).
CH3
O
CH3
O
O
endo,endo-8b
endo,exo-8b
O
endo-8a
exo-8a
The first fraction (less polar) was obtained as a pale yellow
liquid of pure endo,endo-8b (21 mg, 19% yield). H NMR
1
The first fraction (less polar) of a 91:9 mixture of endo- and
exo-8a was obtained as a pale yellow liquid (45 mg, 8%
yield). H NMR (300 MHz, CDCl3): d 7.62 (td, J¼5.8,
(400 MHz, CDCl3): d 7.62 (td, J¼5.9, 2.8 Hz, 1H,
CH]CHCO), 6.31 (2dd, J¼5.7, 2.9 Hz, 2H, CH]CH),
6.06 (td, J¼5.9, 2.1 Hz, 1H, CH]CHCO), 2.90 (td, ABX
system, J¼19.2, 2.4 Hz, 1H, CHHCH]CHCO), 2.79 (td,
ABX system, J¼19.2, 2.5 Hz, 1H, CHHCH]CHCO),
2.74 (m, 1H, CHCH]CHCH), 2.57 (br s, 1H,
CHCH]CHCH), 2.37 (dq, J¼7.2, 3.3 Hz, 1H, CHCH3),
1.57 (d, J¼8.4 Hz, 1H, CHH), 1.51 (td, J¼8.4, 1.7 Hz, 1H,
CHH), 0.84 (d, J¼7.2 Hz, 3H, CHCH3). 13C NMR
(100 MHz, CDCl3): d 211.5 (C]O), 161.7 (CH), 136.7
(CH), 135.6 (CH), 135.1 (CH), 55.6 (CH), 50.4 (CH), 50.0
(CH2), 49.7 (CH2), 49.6 (CH), 30.3 (C), 17.0 (CH3). IR
(CHCl3): nmax 3064w, 3020m, 2965m, 2876w, 1694s,
1596w, 1448m, 1346m, 1325m, 1261w, 1147s, 1085m,
1014m, 688m, 597s cmꢀ1. MS: m/z (%) relative intensity
175 (M++1, 7), 167 (11), 149 (34), 141 (12), 125 (100),
109 (28), 99 (36), 97 (31), 95 (11), 91 (13), 81 (27), 79
(13), 77 (59), 69 (18), 67 (12), 65 (18). HRMS (ESI-TOF)
calcd for C12H14ONa: 197.0942; found: 197.0943.
1
2.8 Hz, 2H, CH]CHCO of endo- and exo-isomers), 6.38
(dd, J¼5.6, 3.1 Hz, 1H, CH]CH of exo-isomer), 6.34 (m,
1H, CH]CH of endo-isomer), 6.17 [dd, J¼5.4, 2.9 Hz,
2H, (CH]CH and CH]CHCO) of exo-isomer and
CH]CHCO of endo-isomer], 5.97 (dd, J¼5.7, 3.1 Hz,
1H, CH]CH of endo-isomer), 2.94 (br s, 1H,
CHCH]CHCH of endo- and exo-isomers), 2.82 (dd,
J¼18.7, 2.8 Hz, 1H, CHHCCO of endo-isomer), 2.71–2.57
[m, 4H, (CHHCH]CHCO and CHCH]CHCH) of
exo- and endo-isomers], 2.38 (dd, J¼19.5, 2.3 Hz,
1H, CHHCH]CHCO of exo-isomer), 2.28 (d, J¼8.5 Hz,
1H, CHH of exo-isomer), 2.12 (dd, J¼11.4, 3.6 Hz, 1H,
CHHCCO of exo-isomer), 1.69 (dd, J¼11.5, 3.7 Hz, 1H,
CHHCCO of endo-isomer), 1.59–1.44 (m, 3H, CH2 and
CHHCCO of endo-isomer), 1.32 (d, J¼8.5 Hz, 1H, CHH
of exo-isomer), 1.08 (dd, J¼11.4, 2.9 Hz, 1H, CHHCCO
of exo-isomer). IR (neat): nmax 3063m, 2964s, 1695s,
1592m, 1475m, 1442m, 1344s, 1307m, 1147s, 1086m,
1016m, 798m, 755m, 723m, 690w, 596w cmꢀ1. MS: m/z
(%) relative intensity 160 (M+, 78), 149 (89), 131 (76),
130 (35), 129 (36), 125 (54), 115 (36), 105 (56), 99 (40),
91 (80), 81 (59), 78 (45), 77 (100), 67 (67), 55 (79).
The second fraction (more polar) was obtained as a 73:37
mixture of endo,exo- and endo,endo-isomers (0.13 g, 56%
yield) as a pale yellow liquid. 1H NMR (300 MHz,
CDCl3): d 7.59–7.50 (m, 2H, CH]CHCO of endo,exo-
and endo,endo-isomers), 6.34 (dd, J¼5.6, 3.2 Hz, 1H,
CH]CH of endo,exo-isomer), 6.20 (m, 2H, CH]CH
of endo,endo-isomer), 6.02 (td, J¼3.6, 2.2 Hz, 1H, CH]
CHCO of endo,exo-isomer), 5.96 (td, J¼3.6, 2.2 Hz,
1H, CH]CHCO of endo,endo-isomer), 5.83 (dd, J¼5.6,
The second fraction (more polar) of endo-8a was obtained as
a pale yellow liquid (0.35 g, 62% yield). 1H NMR
(300 MHz, CDCl3): d 7.65 (td, J¼5.9, 2.7 Hz, 1H,
CH]CHCO), 6.35 (dd, J¼5.5, 3.0 Hz, 1H, CH]CH),

1816
M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
2.9 Hz, 1H, CH]CH of endo,exo-isomer), 2.90 (dd,
J¼19.0, 2.1 Hz, 1H, CHHCH]CHCO of endo,exo-isomer),
2.80 (dd, J¼19.2, 2.3 Hz, 1H, CHHCH]CHCO of
endo,endo-isomer), 2.74–2.60 (m, 2H, CHHCH]CHCO
and CHCH]CHCH of endo,endo-isomer), 2.47 (br s,
1H, CHCH]CHCH of endo,endo-isomer), 2.42 (br s,
1H, CHCH]CHCH of endo,exo-isomer), 2.37 (br s, 1H,
CHCH]CHCH of endo,exo-isomer), 2.32–2.22 (m, 2H,
CHHCH]CHCO of endo,exo-isomer and CHCH3 of
endo,endo-isomer), 1.74 (q, J¼7.0 Hz, 1H, CHCH3 of
endo,exo-isomer), 1.55–1.33 (m, 4H, CH2 of endo,exo-
and endo,endo-isomers), 0.94 (d, J¼7.0 Hz, 3H, CHCH3
of endo,exo-isomer), 0.74 (d, J¼7.2 Hz, 3H, CHCH3 of
endo,endo-isomer). IR (neat): nmax 3063m, 2960s, 2873m,
1698s, 1594m, 1449m, 1376w, 1343m, 1200m, 1147s,
1078m, 1016w, 753m, 730m, 688m, 596s cmꢀ1. MS: m/z
(%) relative intensity 175 (M++1, 28), 174 (M+, 41), 173
(26), 161 (17), 149 (20), 147 (30), 145 (30), 133 (35), 131
(34), 125 (23), 115 (20), 110 (25), 109 (100), 107 (26), 95
(22), 91 (62), 81 (30), 79 (48), 77 (46), 67 (14), 66 (20),
65 (23), 51 (13).
1440m, 1415m, 1351m, 1272m, 1222s, 1092w, 977w,
940m, 782s, 765s, 737s cmꢀ1. MS: m/z (%) relative intensity
219 (2M++2, 9), 218 (2M++1, 46), 168 (M++60, 11), 149
(M++41, 15), 110 (M++2, 100), 109 (M++1, 90), 108 (M+,
23), 95 (15), 91 (17), 81 (40), 79 (67), 77 (42), 66 (21), 65
(23), 51 (13).
4.6.3. 5-Phenylidene-2-cyclopentenone (9c).9c Flash vac-
uum pyrolysis of PLC2 of 7c (100 mg, 0.28 mmol) gave
a crude pyrolysate of the (E)-isomer of 9c, which was purified
by preparative thin-layer chromatography (silica gel, 15%
ethyl acetate in hexanes) to give a pale yellow solid of
(E)-9c (40.5 mg, 85% yield, mp 66–69 ꢁC). 1H NMR
(300 MHz, CDCl3): d 7.68 (m, 1H, CHPh), 7.63–7.32 (m,
6H, ArH and CH]CHCO), 6.48 (td, J¼6.0, 2.1 Hz, 1H,
CH]CHCO), 3.59 (d, J¼1.7 Hz, 2H, CH2). 13C NMR
(75 MHz, CDCl3): d 197.5 (C]O), 157.1 (CH), 135.5
(CH), 135.1 (C), 132.3 (C), 132.1 (CH), 130.4 (2ꢂCH),
129.5 (CH), 128.9 (2ꢂCH), 34.3 (CH2). IR (Nujol): nmax
1688s, 1633s, 1590m, 1572m, 1493m, 1374w, 1292w,
1273m, 1228m, 1186s, 1099m, 950m, 789s, 690m cmꢀ1
.
MS: m/z (%) relative intensity 171 (M++1, 8), 170 (34),
169 (100), 143 (16), 141 (36), 116 (8), 115 (29), 89 (6), 63 (6).
4.6. Flash vacuum pyrolysis of compounds 6 leading to
5-alkylidene-2-cyclopentenones
4.6.4. 5-(Hydroxymethyl)methylidene-2-cyclopentenone
(9d). Flash vacuum pyrolysis of a mixture of diastereomeric
mixture of 7dA (70 mg, 0.22 mmol) (conditions: oven tem-
perature 250 ꢁC, column temperature 450 ꢁC, pressure
0.05 mmHg) gave a crude pyrolysate of 9d, which was puri-
fied by preparative thin-layer chromatography (silica gel,
40% ethyl acetate in hexanes) to give a pale yellow liquid of
4.6.1. 5-Methylene-2-cyclopentenone (9a).9b Flash vac-
uum pyrolysis of a diastereomeric mixture of 7a (100 mg,
0.35 mmol) (conditions: oven temperature 240 ꢁC; column
temperature 375 ꢁC; pressure 0.03 mmHg) gave a crude col-
orless pyrolysate of 9a in quantitative yield. Purification of
1
9a was unsuccessful due to its rapid decomposition. H
1
NMR (300 MHz, CDCl3): d 7.55 (app. t, J¼3.1 Hz, 1H,
CH]CHCO), 6.30 (td, J¼5.7, 3.0 Hz, 1H, CH]CHCO),
6.03 (s, 1H, CHH]CCO), 5.37 (s, 1H, CHH]CCO), 3.17
(s, 2H, CH2). IR (CHCl3): nmax 3015s, 2970m, 1701s,
1650s, 1582m, 1430m, 1416m, 1344m, 1253m, 1138m,
933m, 909s, 836m, 747m, 697m cmꢀ1. MS: m/z (%) relative
intensity 95 (M++1, 100).
a labile (Z)-9d (8.3 mg, 30% yield). H NMR (300 MHz,
CDCl3): d 7.56 (m, 1H, CH]CHCO), 6.60 (app. t,
J¼5.4 Hz, 1H, CHCH2OH), 6.34 (td, J¼6.0, 2.2 Hz, 1H,
CH]CHCO), 4.43 (d, J¼5.4 Hz, 2H, CH2OH), 3.23
(s, 2H, CH2), 1.60 (br s, 1H, OH). 13C NMR (75 MHz,
CDCl3): d 195.6 (C]O), 157.6 (CH), 135.8 (CH), 132.6
(C), 129.3 and 129.1 (CH), 60.9 (CH2OH), 32.2 (CH2). IR
(neat): nmax 3420s, 2964s, 2926s, 1699s, 1447w, 1413w,
1261s, 1091s, 1022s, 800s, 736w cmꢀ1. MS: m/z (%) rela-
tive intensity 125 (M++1, 21), 124 (M+, 8), 123 (18), 121
(23), 120 (16), 115 (13), 111 (24), 105 (23), 97 (28), 95
(100), 92 (38), 91 (28), 83 (29), 81 (39), 78 (58), 77 (66),
71 (22), 69 (28), 67 (73), 65 (42), 63 (23), 57 (32), 55
(42), 51 (20). HRMS (ESI-TOF) calcd for C7H8O2SNa:
147.0422; found: 147.0424.
4.6.2. 5-Ethylidene-2-cyclopentenone (9b).9c Flash vac-
uum pyrolysis of a diastereomeric mixture of 7b (100 mg,
0.33 mmol) gave a 85:15 mixture of E:Z-isomers of a crude
pyrolysate of 9b, which was purified by preparative thin-
layer chromatography (silica gel, 15% ethyl acetate in hex-
anes) to give a yellow liquid of the E-isomer of 9b (28 mg,
82% yield). The Z-isomer of 9b was not obtained in pure
1
form. H NMR (300 MHz, CDCl3) of the crude product of
9b containing a mixture of E- and Z-isomers: d 7.60–7.00
(m, 7H, CH]CHCO of E- and Z-isomers), 6.63 (q,
J¼6.9 Hz, 1H, C]CHCH3 of E-isomer), 6.30 (app. d,
J¼6.0 Hz, 2H, CH]CHCO of E- and Z-isomers), 6.13 (m,
1H, C]CHCH3 of Z-isomer), 3.13 (br s, 2H, CH2 of E-iso-
mer), 2.54 (s, 2H, CH2 of Z-isomer), 2.18 (d, J¼7.3 Hz,
3H, C]CHCH3 of Z-isomer), 1.82 (d, J¼6.9 Hz, 3H,
C]CHCH3 of E-isomer).
4.7. The Pummerer rearrangement of spiro-sulfoxides
6: preparation of spirocyclopentenones 10
4.7.1. 20-Oxo-30-phenylsulfanylcyclopent-30-ene-10-spiro-
2-bicyclo[2.2.1]hept-5-ene (10a). General procedure: Tri-
fluoroacetic anhydride (0.08 mL, 0.60 mmol) was added
slowly to an acetonitrile solution (3 mL) of an 88:12 dia-
stereomeric mixture of 7a (0.172 g, 0.6 mmol) under an
argon atmosphere at 0 ꢁC. The resulting solution was stirred
at 0 ꢁC to room temperature overnight. The mixture was
quenched with water (3 mL) and extracted with EtOAc
(3ꢂ25 mL). The combined organic layers were washed
with water, brine and dried over anhyd Na2SO4. The organic
phase was concentrated and purified by column chromato-
graphy to give an 88:12 mixture of endo- and exo-isomers
of 10a. The mixture of endo- and exo-10a were separated
(E)-9b: 1H NMR (300 MHz, CDCl3): d 7.52 (m, 1H,
CH]CHCO), 6.59 (q, J¼7.0 Hz, 1H, C]CHCH3), 6.28
(td, J¼5.9, 2.1 Hz, 1H, CH]CHCO), 3.13 (br s, 2H,
CH2), 1.81 (d, J¼7.0 Hz, 3H, C]CHCH3). 13C NMR
(75 MHz, CDCl3): d 196.2 (C]O), 156.8 (CH), 135.9
(CH), 135.1 (C), 130.7 (CH), 31.8 (CH2), 15.0 (CH3). IR
(neat): nmax 3058m, 2961m, 2915m, 1699s, 1656s, 1582m,

M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
1817
1
by preparative thin-layer chromatography (silica gel, 5–10%
ethyl acetate in hexanes) to give two fractions (PLC1: endo-
isomer and PLC2: exo-isomer) of 10a (80% combined yield).
D-isomers) of 10b: H NMR (300 MHz, CDCl3): d 7.60–
7.20 (m, 20H, ArH), 6.95 (t, J¼3.0 Hz, 1H, CH]CSAr of
B-isomer), 6.92–6.85 (m, 3H, CH]CSAr of A-, C-, and
D-isomers), 6.42 (dd, J¼5.6, 3.0 Hz, 2H, CH]CH of
B- and D-isomers), 6.37–6.19 (m, 4H, CH]CH of A- and
C-isomers), 6.12 (m, 1H, CH]CH of D-isomer), 5.90 (dd,
J¼5.6, 2.8 Hz, 1H, CH]CH of B-isomer), 2.81 (dd,
J¼18.8, 2.8 Hz, 1H, CHHCH]CSAr of B-isomer), 2.86–
1.92 [m, 19H, (CH2CH]CSAr, CHCH]CHCH, and
CHCH3) of A-isomer, (CHHCH]CSAr and CHCH]
CHCH) of B-isomer, (CH2CH]CSAr, CHCH]CHCH,
CHCH3, and CHH) of C-isomer and (CH2CH]CSAr,
CHCH]CHCH, and CHCH3) of D-isomer], 1.87 (q,
J¼7.5 Hz, 1H, CHCH3 of B-isomer), 1.70–1.20 (m, 7H,
CH2 of A-, B-, and D-isomers and CHH of C-isomer), 1.04
(d, J¼7.5 Hz, 3H, CHCH3 of B-isomer), 0.94 (d, J¼7.8 Hz,
3H, CHCH3 of D-isomer), 0.85 (d, J¼7.2 Hz, 3H, CHCH3
of A-isomer), 0.76 (d, J¼7.2 Hz, 3H, CHCH3 of C-isomer).
O
SPh
O
SPh
exo-10a
endo-10a
PLC1 (less polar) was obtained as a pale yellow solid of exo-
10a (16.7 mg, 10% yield, mp 118–119 ꢁC): 1H NMR
(300 MHz, CDCl3): d 7.47–7.21 (m, 5H, ArH), 6.83
(t, J¼2.9 Hz, 1H, CH]CSAr), 6.30 (dd, J¼5.5, 3.0 Hz,
1H, CH]CH), 6.06 (dd, J¼5.5, 2.9 Hz, 1H, CH]CH),
2.89 (br s, 1H, CHCH]CHCH), 2.68 (br s, 1H, CHCH]
CHCH), 2.47 (dd, J¼19.4, 3.1 Hz, 1H, CHHCH]CSAr),
2.30–2.15 (m, 2H, CHHCH]CSAr and CHH), 2.10 (dd,
J¼11.4, 3.6 Hz, 1H, CHHCCO), 1.26 (d, J¼8.5 Hz, 1H,
CHH), 1.03 (dd, J¼11.4, 2.9 Hz, 1H, CHHCCO). 13C
NMR (75 MHz, CDCl3): d 208.5 (C]O), 153.1 (CH),
141.2 (C), 140.8 (CH), 135.2 (CH), 133.3 (2ꢂCH), 131.3
(C), 129.4 (2ꢂCH), 128.4 (CH), 53.7 (C), 51.3 (CH), 46.8
(CH2), 43.2 (CH), 42.9 (CH2), 41.6 (CH2). IR (CHCl3):
nmax 3064w, 3012m, 2967m, 1698s, 1630m, 1582m,
1477m, 1441m, 1373m, 1301m, 1276m, 1025m, 991w,
692m cmꢀ1. MS: m/z (%) relative intensity 268 (M+, 42),
235 (5), 219 (13), 218 (15), 204 (20), 203 (100), 202 (16),
174 (11), 173 (13), 167 (14), 149 (20), 141 (11), 129 (13),
97 (24), 91 (9), 77 (9), 65 (18).
O
O
CH3
SPh
H
H
CH3
SPh
exo,exo-10b(C)
exo,endo-10b(D)
PLC1 (less polar) was obtained as a yellow liquid of a 1.5:1
mixture of exo,exo- and exo,endo-diastereomers (C- and D-
isomers) (37 mg, 20% yield). 1H NMR (300 MHz, CDCl3):
d 7.45–7.20 (m, 10H, ArH of C- and D-isomers), 6.84
(t, J¼3.0 Hz, 1H, CH]CSAr of C-isomer), 6.80 (t,
J¼3.0 Hz, 1H, CH]CSAr of D-isomer), 6.34 (dd, J¼5.6,
3.1 Hz, 1H, CH]CH of D-isomer), 6.26 (dd, J¼
5.4, 3.0 Hz, 1H, CH]CH of C-isomer), 6.14 (dd, J¼5.4,
3.1 Hz, 1H, CH]CH of C-isomer), 6.04 (dd, J¼5.6,
2.9 Hz, 1H, CH]CH of D-isomer), 2.72–2.61 (m, 4H,
CHCH]CHCH of C- and D-isomers), 2.49–2.28 (m, 4H,
CHHCH]CSAr and CHCH3 of C- and D-isomers), 2.28–
2.17 (m, 2H, CHH of C-isomer and CHHCH]CSAr of
D-isomer), 2.08 (dd, J¼19.5, 3.1 Hz, 1H, CHHCH]CSAr
of C-isomer), 1.56 (d, J¼7.3 Hz, 1H, CHH of D-isomer),
1.31 (d, J¼7.3 Hz, 1H, CHH of D-isomer), 1.24 (d,
J¼8.6 Hz, 1H, CHH of C-isomer), 0.96 (d, J¼7.2 Hz, 3H,
CHCH3 of D-isomer), 0.66 (d, J¼7.2 Hz, 3H, CHCH3 of
C-isomer). IR (CHCl3): nmax 3064w, 2966m, 1695s,
1630w, 1583w, 1477m, 1441m, 1374m, 1302w, 1261m,
1087w, 1024w, 691m cmꢀ1. MS: m/z (%) relative intensity
282 (M+, 44), 218 (16), 217 (100), 216 (22), 188 (12), 173
(15), 111 (10), 110 (18), 91 (6), 79 (8), 77 (7), 66 (6), 65 (6).
PLC2 (more polar) was obtained as a pale yellow solid of
1
endo-10a (0.112 g, 70% yield, mp 128–130 ꢁC): H NMR
(300 MHz, CDCl3): d 7.55–7.27 (m, 5H, ArH), 6.92 (t,
J¼2.9 Hz, 1H, CH]CSAr), 6.34 (dd, J¼5.4, 3.1 Hz, 1H,
CH]CH), 5.97 (dd, J¼5.4, 2.9 Hz, 1H, CH]CH), 2.98
(br s, 1H, CHCH]CHCH), 2.82 (dd, J¼18.7, 2.7 Hz,
1H, CHHCH]CSAr), 2.64 (dd, J¼18.7, 3.2 Hz, 1H,
CHHCH]CSAr), 2.58 (br s, 1H, CHCH]CHCH), 1.71
(dd, J¼11.5, 3.7 Hz, 1H, CHHCCO), 1.60–1.40 (m, 3H,
CH2 and CHHCCO). 13C NMR (75 MHz, CDCl3): d
206.2 (C]O), 151.8 (CH), 141.8 (C), 138.2 (CH), 133.3
(CH), 132.5 (2ꢂCH), 131.3 (C), 129.4 (2ꢂCH), 128.3 (CH),
54.9 (CH), 53.6 (C), 49.9 (CH2), 45.7 (CH2), 43.6 (CH), 39.8
(CH2). IR (Nujol): nmax 3059w, 1699s, 1577m, 1468m,
1283m, 1273m, 1021m, 992m, 758m, 693m, 634w cmꢀ1
.
MS: m/z (%) relative intensity 270 (M++2, 19), 269
(M++1, 79), 268 (M+, 100), 235 (7), 203 (53), 202 (15),
174 (21), 173 (24), 159 (14), 158 (17), 141 (10), 129 (11),
115 (5), 97 (15), 91 (9), 65 (7). Anal. Calcd for C17H16OS:
C, 76.08; H, 6.01. Found: C, 75.75; H, 6.02.
PLC2 (more polar) was obtained as a yellow solid of
endo,endo-10b (A-isomer) (53 mg, 28% yield, mp 65–
1
4.7.2. 20-Oxo-30-phenylsulfanylcyclopent-30-ene-10-spiro-
2-(3-methylbicyclo[2.2.1]hept-5-ene) (10b). According to
the general procedure described for compound 10a, the reac-
tion of a diastereomeric mixture of 7b (0.20 g, 0.66 mmol)
with an acetonitrile solution (3 mL) of trifluoroacetic an-
hydride (0.08 mL, 0.60 mmol) gave a crude product of
a 34:44:13:9 mixture of isomers of 10b. It was purified by
preparative thin-layer chromatography (silica gel, 5–10%
ethyl acetate in hexanes) to give three fractions (PLC1,
PLC2, and PLC3) of 10b (0.138 g, 74% combined yield).
A mixture of endo,endo- and endo,exo-isomers (A- and
B-isomers) and exo,exo- and exo,endo-isomers (C- and
66 ꢁC). H NMR (300 MHz, CDCl3): d 7.46–7.20 (m, 5H,
ArH), 6.82 (t, J¼2.9 Hz, 1H, CH]CSAr), 6.27–6.15
(m, 2H, CH]CH), 2.75 (dd, J¼19.0, 2.9 Hz, 1H,
CHHCH]CSAr), 2.68–2.56 (m, 2H, CHCH]CHCH and
CHHCH]CSAr), 2.54 (br s, 1H, CHCH]CHCH), 2.30
(dq, J¼7.1, 3.2 Hz, 1H, CHCH3), 1.45 (m, 2H, CH2), 0.77
(d, J¼7.1 Hz, 3H, CHCH3). 13C NMR (75 MHz, CDCl3):
d 204.8 (C]O), 152.0 (CH), 142.3 (C), 135.7 (CH), 135.2
(CH), 133.5 (2ꢂCH), 131.3 (C), 129.3 (2ꢂCH), 128.3
(CH), 57.2 (C), 55.2 (CH), 50.0 (CH), 49.1 (CH2), 49.0
(CH), 47.3 (CH2), 16.3 (CH3). IR (neat): nmax 3061m,
2961s, 1699s, 1622s, 1583m, 1477m, 1440m, 1373m,

1818
M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
1299m, 1146m, 1024m, 990m, 743m, 692m cmꢀ1. MS:
m/z (%) relative intensity 282 (M+, 100), 249 (13), 232
(15), 218 (15), 217 (75), 216 (59), 188 (32), 183 (23), 173
(40), 111 (26), 110 (63), 91 (22), 79 (16), 77 (25), 66 (18),
65 (14).
PLC1 (less polar) was obtained as a yellow solid of endo,exo-
10c (0.154 g, 57% yield, mp 95–98 ꢁC). 1H NMR
(300 MHz, CDCl3): d 7.42–6.90 (m, 10H, ArH and SArH),
6.73 (t, J¼3.0 Hz, 1H, CH]CSAr), 6.49 (dd, J¼5.5,
3.3 Hz, 1H, CH]CH), 6.05 (dd, J¼5.5, 2.8 Hz, 1H,
CH]CH), 3.08 (br s, 1H, CHCH]CHCH), 3.02 (s, 1H,
CHAr), 2.64 (br s, 1H, CHCH]CHCH), 2.15–1.98 (2dd,
J¼20.7, 2.7 Hz, 2H, CH2CH]CSAr), 1.85 (d, J¼8.6 Hz,
1H, CHH), 1.66 (dd, J¼8.6, 1.6 Hz, 1H, CHH). 13C NMR
(75 MHz, CDCl3): d 206.2 (C]O), 153.7 (CH), 142.3 (C),
141.0 (C), 139.7 (CH), 133.6 (CH), 133.1 (2ꢂCH), 131.4
(C), 129.3 (2ꢂCH), 128.6 (2ꢂCH), 128.3 (CH), 127.7
(2ꢂCH), 126.3 (CH), 58.2 (C), 55.4 (CH), 54.1 (CH), 49.4
(CH2), 48.4 (CHAr), 40.9 (CH2). IR (Nujol): nmax 3055w,
1695s, 1580m, 1456s, 1274m, 1023m, 1005w, 839m,
751m, 734m, 702m cmꢀ1. MS: m/z (%) relative intensity
344 (M+, 31), 279 (15), 278 (52), 277 (27), 173 (15), 170
(19), 169 (100), 142 (14), 141 (47), 129 (9), 116 (14), 115
(25), 91 (10), 65 (4).
PLC3 (most polar) was obtained as a yellow solid of
endo,exo-10b (B-isomer) (49 mg, 26% yield, mp 86–87 ꢁC).
1H NMR (300 MHz, CDCl3): d 7.50–7.28 (m, 5H, ArH),
6.96 (t, J¼3.0 Hz, 1H, CH]CSAr), 6.41 (dd, J¼5.5,
3.0 Hz, 1H, CH]CH), 5.89 (dd, J¼5.5, 2.8 Hz, 1H,
CH]CH), 2.90 (dd, J¼18.9, 2.7 Hz, 1H, CHHCH]CSAr),
2.52 (br s, 2H, CHCH]CHCH), 2.28 (dd, J¼18.9, 3.2 Hz,
1H, CHHCH]CSAr), 1.87 (dq, J¼7.3, 1.6 Hz, 1H,
CHCH3), 1.58 (d, J¼8.7 Hz, 1H, CHH), 1.46 (dd, J¼8.7,
1.6 Hz, 1H, CHH), 1.03 (d, J¼7.3 Hz, 3H, CHCH3). 13C
NMR (75 MHz, CDCl3): d 206.5 (C]O), 152.5 (CH),
141.2 (C), 139.1 (CH), 133.1 (2ꢂCH), 131.8 (CH), 131.4
(C), 129.3 (2ꢂCH), 128.3 (CH), 56.8 (C), 56.6 (CH), 51.0
(CH), 47.3 (CH2), 41.6 (CH), 39.5 (CH2), 18.7 (CH3). IR
(Nujol): nmax 3056w, 1695s, 1577m, 1456s, 1279m,
1020w, 1000w, 833m, 758m, 733m, 697m cmꢀ1. MS: m/z
(%) relative intensity 282 (M+, 100), 249 (9), 218 (17),
217 (94), 216 (48), 188 (21), 173 (30), 112 (21), 110 (28),
91 (11), 80 (11), 77 (11), 66 (9), 65 (7). HRMS (ESI-TOF)
calcd for C18H18OSNa: 305.0976; found: 305.0976.
PLC2 (more polar) was obtained as a pale yellow solid of
endo,endo-10c (54 mg, 20% yield, mp 118–120 ꢁC).
1H NMR (300 MHz, CDCl3): d 7.32–6.95 (m, 11H, ArH,
SArH and CH]CSAr), 6.57 (dd, J¼5.3, 2.9 Hz, 1H,
CH]CH), 6.28 (dd, J¼5.3, 3.2 Hz, 1H, CH]CH), 3.74
(d, J¼2.5 Hz, 1H, CHAr), 3.26 (br s, 1H, CHCH]CHCH),
3.16 (dd, J¼19.1, 2.8 Hz, 1H, CHHCH]CSAr), 2.91 (dd,
J¼19.1, 3.1 Hz, 1H, CHHCH]CSAr), 2.64 (br s, 1H,
CHCH]CHCH), 1.74 (d, J¼8.5 Hz, 1H, CHH), 1.65 (d,
J¼8.5 Hz, 1H, CHH). 13C NMR (75 MHz, CDCl3):
d 203.0 (C]O), 151.8 (CH), 142.5 (C), 140.4 (C), 135.8
(CH), 135.3 (CH), 132.7 (2ꢂCH), 131.5 (C), 129.2
(2ꢂCH), 128.6 (2ꢂCH), 127.9 (CH), 127.8 (2ꢂCH),
126.1 (CH), 61.3 (CH), 59.6 (C), 55.5 (CH), 49.9 (CH2),
48.1 (CHAr), 47.7 (CH2). IR (neat): nmax 3060s, 3025s,
2959s, 2247w, 2053w, 1952w, 1885w, 1714s, 1695s,
1682s, 1582s, 1496s, 1479s, 1441s, 1339s, 1277s, 1190m,
1147m, 1024m, 911m, 741s, 701s cmꢀ1. MS: m/z (%) rela-
tive intensity 344 (M+, 2), 280 (6), 279 (21), 278 (75), 173
(14), 170 (19), 169 (100), 142 (14), 141 (40), 129 (9), 116
(11), 115 (25), 91 (10), 65 (5). Anal. Calcd for C23H20OS:
C, 80.20; H, 5.85. Found: C, 79.97; H, 5.71.
4.7.3. 20-Oxo-30-phenylsulfanylcyclopent-30-ene-10-spiro-
2-(3-phenylbicyclo[2.2.1]hept-5-ene) (10c). According to
the general procedure described for compound 10a, the reac-
tion of a diastereomeric mixture of 7c (0.281 g, 0.78 mmol)
with an acetonitrile solution (4 mL) of trifluoroacetic an-
hydride (0.10 mL, 0.78 mmol) gave a 78:22 mixture of
endo,exo- and endo,endo-isomers of 10c. The mixture of
isomers was separated by preparative thin-layer chromato-
graphy (silica gel, 5–10% ethyl acetate in hexanes) to give
two fractions (PLC1 and PLC2) of 10c (0.208 g, 78% com-
bined yield). A mixture of endo,exo- and endo,endo-10c:
1H NMR (300 MHz, CDCl3): d 7.44–6.90 [m, 21H, (ArH
and SArH) of endo,exo-isomer and (ArH, CH]CSAr, and
SArH) of endo,endo-isomer], 6.72 (t, J¼3.0 Hz, 1H,
CH]CSAr of endo,exo-isomer), 6.54–6.45 (m, 2H,
CH]CH of endo,exo- and endo,endo-isomers), 6.21 (dd,
J¼5.6, 3.1 Hz, 1H, CH]CH of endo,endo-isomer), 6.04
(dd, J¼5.5, 2.8 Hz, 1H, CH]CH of endo,exo-isomer),
3.68 (d, J¼3.0 Hz, 1H, CHAr of endo,endo-isomer), 3.18
(br s, 1H, CHCH]CHCH of endo,endo-isomer), 3.15–
2.99 [m, 3H, (CHAr and CHCH]CHCH) of endo,exo-iso-
mer and CHHCH]CSAr of endo,endo-isomer), 2.85 (dd,
J¼19.1, 3.2 Hz, 1H, CHHCH]CSAr of endo,endo-isomer),
2.63 (br s, 2H, CHCH]CHCH of endo,exo- and endo,endo-
isomers), 2.15–1.94 (2dd, J¼20.3, 2.8 Hz, 2H,
CH2CH]CSAr of endo,exo-isomer), 1.85 (d, AB system,
J¼8.6 Hz, 1H, CHH of endo,exo-isomer), 1.68 (d,
J¼8.7 Hz, 2H, CHH of endo,exo- and endo,endo-isomers),
1.59 (d, J¼8.6 Hz, 1H, CHH of endo,endo-isomer).
4.7.4. 20-Oxo-30-phenylsulfanylcyclopent-30-ene-10-spiro-
2-(3-hydroxymethyl)bicyclo[2.2.1]hept-5-ene (10d). Ac-
cording to the general procedure described for compound
10a, the reaction of a mixture of 7dA and 7dB (0.316 g,
1 mmol) with an acetonitrile solution (5 mL) of trifluoroace-
ticanhydride (0.13 mL, 1 mmol) gavea crude product, which
was purified by preparative thin-layer chromatography (sil-
ica gel, 5–10% ethyl acetate in hexanes) to give a pure white
solid of 10d (0.232 g, 78% yield, mp 150–152 ꢁC).
OH
O
SPh
Ph
H
1H NMR (400 MHz, CDCl3): d 7.58–7.33 (m, 5H, ArH),
7.00 (t, J¼3.0 Hz, 1H, CH]CSAr), 6.33 (dd, J¼5.6,
3.2 Hz, 1H, CH]CH), 6.18 (dd, J¼5.6, 2.8 Hz, 1H,
CH]CH), 3.60 (m, 2H, CHCH2OH), 2.96–2.92 (m, 2H,
Ph
O
O
SPh
SPh
endo,endo-10c
endo,exo-10c

M. Pohmakotr et al. / Tetrahedron 63 (2007) 1806–1820
1819
CHCH]CHCH, and CHHCH]CSAr), 2.75 (dd, J¼18.8,
3.2 Hz, 1H, CHHCH]CSAr), 2.64 (br s, 1H,
CHCH]CHCH), 2.56 (ddd, J¼9.2, 5.5, 3.1 Hz, 1H,
CHCH2OH), 2.05 (br s, 1H, OH), 1.63–1.56 (m, 2H, CH2).
13C NMR (100 MHz, CDCl3): d 206.6 (C]O), 153.5
(CH), 142.3 (C), 136.5 (CH), 135.2 (CH), 133.8 (2ꢂCH),
132.0 (C), 130.0 (2ꢂCH), 129.0 (CH), 63.4 (CH2), 58.7
(CH), 56.9 (C), 56.0 (CH), 50.1 (CH2), 47.9 (CH2), 46.4
(CH). IR (CHCl3): nmax 3456m, 3026s, 3013s, 2971s,
1695s, 1583m, 1476m, 1441m, 1339m, 1305m, 1281m,
1025s, 833s, 692m cmꢀ1. MS: m/z (%) relative intensity
298 (M+, 8), 268 (32), 267 (25), 203 (17), 190 (30), 186
(18), 171 (23), 158 (100), 157 (58), 147 (10), 144 (14),
130 (18), 129 (54), 128 (33), 115 (19), 110 (16), 105 (9),
91 (16), 77 (15), 66 (17), 65 (18). HRMS (ESI-TOF) calcd
for C18H18O2SNa: 321.0925; found: 321.0927.
endo,exo- and endo,endo-10c (100 mg, 0.29 mmol) gave
a 86:14 mixture of (E)- and (Z)-11c. The crude product
was purified by preparative thin-layer chromatography (sil-
ica gel, 5–7% ethyl acetate in hexanes) to give a pale yellow
solid of (E)-11c (60 mg, 76% yield, mp 104–105 ꢁC). A
mixture of (E)- and (Z)-11c of the crude product: 1H NMR
(300 MHz, CDCl3): d 7.55–7.00 (m, 22H, ArH, SArH and
C]CHAr of E- and Z-isomers), 6.78 (app. t, J¼2.6 Hz,
1H, ArSC]CH of E-isomer), 6.69 (app. s, 1H, ArSC]CH
of Z-isomer), 3.44 (m, 2H, CH2 of E- and Z-isomers).
(E)-11c: 1H NMR (300 MHz, CDCl3): d 7.50–7.17 (m, 11H,
ArH, SArH and C]CHAr), 6.75 (m, 1H, CH]CSAr), 3.39
(app. t, J¼2.2 Hz, 2H, CH2). 13C NMR (75 MHz, CDCl3):
d 192.5 (C]O), 146.9 (CH), 144.6 (C), 134.9 (C), 133.8
(2ꢂCH), 133.1 (CH), 131.9 (CH), 130.6 (C), 130.5
(2ꢂCH), 129.7 (CH), 129.5 (2ꢂCH), 128.9 (2ꢂCH),
128.6 (CH), 33.4 (CH2). IR (Nujol): nmax 1687m, 1637m,
1568w, 1449m, 1285m, 1181m, 916m, 771m, 758m,
747m, 690m cmꢀ1. MS: m/z (%) relative intensity 280
(M++2, 35), 279 (M++1, 23), 278 (M+, 100), 277 (17), 250
(9), 234 (13), 218 (15), 178 (27), 173 (33), 171 (38), 169
(78), 167 (17), 149 (15), 110 (15). HRMS (ESI-TOF) calcd
for C18H14OSNa: 301.0663; found: 301.0663.
4.8. Flash vacuum pyrolysis of compounds 10 leading to
cyclopentenones 11
4.8.1. 5-Methylidene-2-phenylsulfanyl-2-cyclopentenone
(11a). Flash vacuum pyrolysis of a 87:13 mixture of endo-
and exo-10a (51 mg, 0.19 mmol) gave a crude pyrolysate,
which was purified by preparative thin-layer chromato-
graphy (silica gel, 5–7% ethyl acetate in hexanes) to give
a pale yellow solid of 11a (39 mg, 93% yield, mp 76–
4.8.4. 5-(Hydroxymethyl)methylidene-2-phenylsulfanyl-
2-cyclopentenone (11d). Flash vacuum pyrolysis of 10d
(100 mg, 0.29 mmol) (conditions: oven temperature 240 ꢁC,
column temperature 425 ꢁC, pressure 0.05 mmHg) gave
a crude pyrolysate, which was purified by preparative thin-
layer chromatography (silica gel, 15% ethyl acetate in hex-
anes) to give a pale yellow liquid of (Z)-11d (13.5 mg, 20%
1
78 ꢁC). H NMR (300 MHz, CDCl3): d 7.60–7.30 (m, 5H,
ArH), 6.85 (dt, J¼2.9, 0.9 Hz, 1H, CH]CSAr), 6.18 (m,
J¼0.9 Hz, 1H, CHH]CCO), 5.49 (app. d, J¼0.9 Hz, 1H,
CHH]CCO), 3.20 (td, J¼2.8, 1.5 Hz, 2H, CH2). 13C
NMR (75 MHz, CDCl3): d 191.5 (C]O), 148.2 (CH),
145.0 (C), 140.6 (C), 133.9 (2ꢂCH), 130.5 (C), 129.5
(2ꢂCH), 128.7 (CH), 118.6 (CH2), 32.9 (CH2). IR (Nujol):
nmax 2727w, 1699s, 1646m, 1581m, 1307m, 1282m,
1024m, 838w, 742s, 691s cmꢀ1. MS: m/z (%) relative inten-
sity 204 (M++2, 8), 203 (M++1, 28), 202 (M+, 100), 201 (18),
174 (25), 173 (48), 141 (11), 129 (11), 97 (42), 65 (12).
HRMS (ESI-TOF) calcd for C12H11OS: 203.0531; found:
203.0531.
1
yield). H NMR (300 MHz, CDCl3): d 7.52–7.25 (m, 5H,
ArH), 6.72 (s, 1H, CH]CSAr), 6.58 (t, J¼6.1 Hz, 1H,
C]CHCH2OH), 4.71 (d, J¼6.1 Hz, 2H, C]CHCH2OH),
3.15 (s, 2H, CH2), 1.60 (br s, 1H, OH). HRMS (ESI-TOF)
calcd for C13H12O2SNa: 255.0456; found: 255.0461.
Acknowledgements
4.8.2. 5-Ethylidene-2-phenylsulfanyl-2-cyclopentenone
(11b). Flash vacuum pyrolysis of a pure diastereomer of
10b obtained from PLC3 (47.4 mg, 0.168 mmol)gave acrude
pyrolysate, which was purified by preparative thin-layer
chromatography (silica gel, 5–7% ethyl acetate in hexanes)
to give a pale yellow solid of (E)-isomer of 11b (45.4 mg,
We thank the Postgraduate Education and Research Program
in Chemistry (PERCH) and the Thailand Research Fund
(BRG 49800005 to MP and the award of a Senior Research
Scholar to VR) for financial support.
1
96% yield, mp 66–68 ꢁC). H NMR (300 MHz, CDCl3):
References and notes
d 7.60–7.30 (m, 5H, ArH), 6.80–6.65 (m, 2H, CH]CSAr
and C]CHCH3), 3.13 (br s, 2H, CH2), 1.90 (d, J¼7.1 Hz,
3H, C]CHCH3). 13C NMR (75 MHz, CDCl3): d 191.3
(C]O), 146.8 (CH), 144.9 (C), 134.9 (C), 133.7 and 133.7
(2ꢂCH), 132.4 and 132.3 (CH), 131.0 and 130.9 (C), 129.5
and 129.4 (2ꢂCH), 128.53 and 128.49 (CH), 30.9 (CH2),
15.1 and 15.0 (CH3). IR (neat): nmax 2925m, 1696s, 1658s,
1651s, 1475w, 1440m, 1378m, 1263m, 1087w, 1024m,
865m, 740m, 690m cmꢀ1. MS: m/z (%) relative intensity
218 (M++2, 18), 217 (M++1, 36), 216 (M+, 100), 188 (34),
183 (23), 173 (47), 155 (16), 149 (15), 111 (31), 110 (74),
79 (18), 78 (17), 77 (43), 66 (14), 65 (15). HRMS (ESI-
TOF) calcd for C13H13OS: 217.0687; found: 217.0687.
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