[4 + 2] Cycloaddition of thiophene S-monoxides to activated methylenecyclopropanes

Article abstract of DOI:10.1039/b003850o

Thiophene S-oxides 4 have been shown to undergo [4 + 2] cycloadditions with methylenecyclopropanes 2 with one or two electron acceptor substituents, i.e. even the tetrasubstituted 2-chloro-2-cyclopropylideneacetate 2c reacted well. However, for the tetrasubstituted alkene bi(cyclopropylidene) 2f high pressure had to be applied to make it react with 4. Only one diastereoisomer was formed in all the reactions. X-Ray crystal structure analyses of two of the cycloadducts, 3a and 3f, have been performed, their relative configuration determined as being endo,syn. The Wittig olefination of cyclopropanone hemiacetal to generate the methylenecyclopropanes and the subsequent cycloaddition can be carried out in a one-pot operation. This procedure is one of many potential one-pot or multi-component reactions involving stabilized phosphoranes. A further example of this type of reaction is shown in the novel desilylation-Wittig olefination of 1-ethoxy-1-trimethylsilyloxycyclopropane 5 to yield in one step cyclopropylideneacetates, e.g. 2a. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b003850o

View Article Online / Journal Homepage / Table of Contents for this issue
[4 ϩ 2] Cycloaddition of thiophene S-monoxides to activated
methylenecyclopropanes
Thies Thiemann,*a Daisuke Ohira,b Yuanqiang Li,b Tsuyoshi Sawada,a Shuntaro Mataka,a
Karsten Rauch,c Mathias Noltemeyerd and Armin de Meijere*c
1
a Institute of Advanced Material Study, Kyushu University, Kasuga-koh-en, Kasuga-shi,
Fukuoka 816-8580, Japan
b Graduate School of Engineering Sciences, Kyushu University, Kasuga-koh-en, Kasuga-shi,
Fukuoka 816-8580, Japan
c Institut für Organische Chemie, Georg-August Universität, Tammannstr. 2,
D-37077 Göttingen, Germany
d Institut für Anorganische Chemie, Georg-August Universität, Tammannstr. 2,
D-37077 Göttingen, Germany
Received (in Cambridge, UK) 15th May 2000, Accepted 3rd July 2000
Published on the Web 8th August 2000
Thiophene S-oxides 4 have been shown to undergo [4 ϩ 2] cycloadditions with methylenecyclopropanes 2 with one or
two electron acceptor substituents, i.e. even the tetrasubstituted 2-chloro-2-cyclopropylideneacetate 2c reacted well.
However, for the tetrasubstituted alkene bi(cyclopropylidene) 2f high pressure had to be applied to make it react with
4. Only one diastereoisomer was formed in all the reactions. X-Ray crystal structure analyses of two of the
cycloadducts, 3a and 3f, have been performed, their relative configuration determined as being endo,syn. The Wittig
olefination of cyclopropanone hemiacetal to generate the methylenecyclopropanes and the subsequent cycloaddition
can be carried out in a one-pot operation. This procedure is one of many potential one-pot or multi-component
reactions involving stabilized phosphoranes. A further example of this type of reaction is shown in the novel
desilylation–Wittig olefination of 1-ethoxy-1-trimethylsilyloxycyclopropane 5 to yield in one step
cyclopropylideneacetates, e.g. 2a.
Introduction
Results and discussion
While many thiophenes1 1 do not undergo cycloaddition reac-
tions, and the cycloadditions of thiophene S,S-dioxides2 for the
most part necessitate higher reaction temperatures, cycloaddi-
tion of dienophiles to thiophene S-monoxides 4, prepared
in situ by oxidation of thiophenes,3 (Path A, Scheme 1) is pos-
sible at temperatures as low as Ϫ20 ЊC.4 Recently, thiophene
S-monoxides have been isolated prior to further reactions4,5
(Path B, Scheme 1). While a number of differently substituted
The unsubstituted and the 2-bromosubstituted cyclopropylide-
neacetates and certain cyclopropylidenealkanones6 have been
prepared by Wittig olefination either of the cyclopropanone
ethyl hemiacetal with the corresponding phosphorane 7
(Scheme 2, reaction 1)8a,b or of a suitably protected α,β-
Scheme 2 Known synthetic approaches to methylenecyclopropanes.
diketone or α-ketoaldehyde with cyclopropylidenetriphenyl-
phosphorane 7a9 (Scheme 2, reaction 2). The cyclopropanone
hemiacetal 6 can be prepared in two steps from ethyl 3-
chloropropionate.10a–c The second step, the methanolysis of the
1-ethoxy-1-trimethylsilyloxycyclopropane 5,10a requires some
care as the separation of the cyclopropanone hemiacetal 6 from
the methanol, used in the solvolysis10b,c is often time consum-
ing. This is greatly facilitated by applying a one pot procedure
to convert 1-ethoxy-1-trimethylsilyloxycyclopropane 511 dir-
ectly to the cyclopropylideneacetates, e.g., 2a. The trimethyl-
silyloxy group is cleaved off by fluoride, the anion formed is
protonated by benzoic acid, and the Wittig olefination ensues at
Scheme 1
thiophenes/thiophene S-monoxides and dienophiles have been
studied,5 clearly the use of a greater variety of dienophiles
would be required in order to assess the scope of the cyclo-
addition reaction. Especially, the effect of steric hindrance and
strain in the dienophile needs to be studied. Suitable candidates
for this study are the methylenecyclopropane derivatives 2.6
As methylenecyclopropanes are themselves susceptible to oxi-
dation by MCPBA,7 their cycloaddition reactions can only be
carried out with isolated thiophene S-monoxides (Path B).
2968
J. Chem. Soc., Perkin Trans. 1, 2000, 2968–2976
This journal is © The Royal Society of Chemistry 2000
DOI: 10.1039/b003850o

View Article Online
Table 1 Cycloaddition of thiophene S-oxides with methylenecyclopropanes
Entry
X1
X2
R1
R2
Conditions
Yield (%)
1 (4c)
2 (4a)
3 (4c)
4 (4d)
5 (4c)
6 (4a)
7 (4c)
8 (4a)
9 (4c)
Me
Me
Me
Me
Me
Me
Me
Me
Me
Bn
COOMe
COOEt
COOH
COOMe
Cl (2c)
H (2a)
H (2d)
H (2e)
Cl (2c)
(2f)
CHCl3, 60 ЊC, 24 h
CHCl3, 60 ЊC, 20 h
CHCl3, 60 ЊC, 56 h
CHCl3, 60 ЊC, 19 h
CH3CN, 60 ЊC, 24 h, 10 kbar
CH3CN, 60 ЊC, 5 d, 10 kbar
CH3CN, 60 ЊC, 5 d, 10 kbar
CH3CN, 60 ЊC, 24 h, 10 kbar
CH3CN, 60 ЊC, 24 h, 10 kbar
60 (3a)
85 (3b)
50 (3c)a
67 (3d)
92 (3a)
48 (3e)
43 (3f)
31 (3e)
39 (3f)
p-But–Bn
Bn
Br
Bn
COOMe
p-But–Bn
Bn
–(CH2CH2)–
–(CH2CH2)–
–(CH2CH2)–
–(CH2CH2)–
(2f)
p-But–Bn
Bn
(2f)
(2f)
a Isolated as its methyl ester, see below.
elevated temperature (80 ЊC) under benzoic acid catalysis as has
been described by Spitzner and Swoboda8b for the olefination
of 1-ethoxy-1-hydroxycyclopropane 6. 1.3 to 1.4 equivalents of
benzoic acid are used for every equivalent of 1-ethoxy-1-
silyloxycyclopropane 5 (Scheme 2). It is not possible, however,
to use the same procedure to prepare the corresponding cyclo-
propylidenealkanones, e.g., 2b, because, although they are
formed, they undergo subsequent side reactions (Scheme 3).
addition of benzoic acid, as basic conditions facilitate the ring
opening of the intermediate anion of the cyclopropanone
hemiacetal 6 to the ethyl propionate homoenolate, which is
protonated and cleaved to the propionate anion that sub-
sequently adds to the cyclopropylidenealkanone 2b to give 9b.
When benzoic acid is substituted by aq. 10% HCl (10% excess
with respect to 1-ethoxycyclopropanolate formed), the resulting
solution washed with water and the benzene solution after
drying used directly for the subsequent Wittig olefination, the
product 2b also is formed in mediocre yields (10%) only. Thus,
for the preparation of cyclopropylidenealkanones the two-step
procedure with isolated 1-ethoxycyclopropanol 6 is preferable.8
Methyl 2-chloro-2-cyclopropylideneacetate8c and bi(cyclo-
propylidene)8d,e were prepared according to well established
literature procedures.
The thiophene S-monoxides 4 can be prepared easily by
oxidation of the corresponding thiophenes 1 with MCPBA
in the presence of a Lewis acid, e.g. BF3ؒEt2O (Scheme 4). It
Scheme 4 Preparation of thiophene S-oxides.
is advantageous for the thiophenes used to possess an electron-
donating substituent in positions 2 and 5, e.g. alkyl groups.
Positions 3 and 4 can accommodate a variety of substituents,
such as slightly electron-withdrawing functionalities, as in 3,4-
dibromo-2,5-dimethylthiophene S-monoxide 4d.
In general, thiophene S-oxides 4 react readily with methyl-
enecyclopropanes 2, which have one electron-withdrawing
group (Table 1). Even the tetrasubstituted alkene, methyl 2-
chloro-2-cyclopropylideneacetate 2c, undergoes the cyclo-
addition reaction. In this case, the steric hindrance of the
substituents is counteracted by the two electron-withdrawing
functionalities.13,14 3-Cyclopropylidenebutan-2-one 2g, another
Scheme 3 One-pot desilyation–Wittig olefination.
Interestingly, benzoic acid acts as a Michael nucleophile under
these conditions to yield the benzoate 9a as a side product,
which has also been observed in the Wittig reaction with the
isolated cyclopropanone hemiacetal 6.12 Conia et al. also
reported a similar Michael adduct as a side product with m-
chlorobenzoic acid acting as a nucleophile in the treatment of a
cyclopropylidenealkanone with MCPBA.7 Furthermore, it is
important to adjust the pH of the reaction mixture carefully by
J. Chem. Soc., Perkin Trans. 1, 2000, 2968–2976
2969

View Article Online
Table 2 Thiabicyclo[2.2.1]heptene S-oxides by one-pot Wittig olefination and cycloaddition reaction
Phosphorane/equiv. alkene
Entry
X1
X2
R1
R2
Conditions
Yield (%)
1 (4a)
2 (4c)
3 (4c)
4 (4c)
5 (4b)
Me
Me
Me
Me
Me
Bn-p-But
Bn
Bn
Bn
Ph-p-OMe
COPh
H 7c/2b
H 7d/2j
H 7e/2k
H 7f/2m
H 7b/2a
C6H6, 80 ЊC, 24 h
C6H6, 80 ЊC, 22 h
C6H6, 80 ЊC, 56 h
C6H6, 80 ЊC, 10 h ϩ 22 h
C6H6, 80 ЊC, 2 h ϩ 22 h
90 (3h)
91 (3i)
52 (3j)
71 (3k)
67 (3m)
COPh-p-Cl
COMe
CN
COOEt
tetrasubstituted methylenecyclopropane, but with one electron-
withdrawing and one electron-donating substituent, failed to
react. The thiophene S-monoxides generally are better dienes in
the [4 ϩ 2] cycloaddition than the corresponding thiophene
S,S-dioxides as can be seen from the fact that most tetraalkyl-
substituted thiophene S,S-dioxides give no cycloadducts under
the conditions used for the monoxides. Thus, no reaction could
be observed between 2,3,4,5-tetramethylthiophene S,S-dioxide
(1.7 × 10Ϫ1 M in CDCl3) and methyl cyclopropylideneacetate
2c (5.1 × 10Ϫ1 M in CDCl3) at 60 ЊC even after 48 h. More-
over, it must be noted that the reactivity of the methylene-
cyclopropanes is due to their inherent strain. Thus, methyl
cyclopentylideneacetate 2h gave no cycloaddition product with
3,4-dibromo-2,5-dimethylthiophene S-oxide 4d after 24 h at
60 ЊC.
At room temperature and ambient pressure, the reaction of
the 2,5-dimethyl-3,4-bis(phenylmethyl)thiophene S-oxide 4c
with bi(cyclopropylidene) 2f proceeds, at best, very slowly. At
an early stage of the reaction, however, it is noticeable that a
considerable proportion of thiophene S-oxide is reduced to the
thiophene. Under high pressure (10 kbar) the cycloadduct of
2f with 4c can be obtained in good yield.15,16
One remarkable example is the cycloaddition of 4c to cyclo-
propylideneacetic acid 2d, as carboxylic acids themselves are
rarely used in cycloaddition reactions. Two products were
formed, one of which at first could not be identified; the
other product was the cycloadduct 3c (Scheme 5). As the two
products could not be separated, they were converted with
ethereal diazomethane solution to their respective methyl esters,
which could be separated easily by column chromatography.
Interestingly, the second product 3g-II was the Michael
adduct of the primary cycloadduct 3c and a second molecule of
cyclopropylideneacetic acid 2d. The Wittig olefination of
cyclopropanone hemiacetal 6 to yield the acceptor-substituted
methylenecyclopropane and its subsequent cycloaddition to
a thiophene S-monoxide 4 can be performed as a one-pot
reaction (Table 2). This has been carried out with both the
intermediate cyanomethylenecyclopropane (2m)17 and the
cyclopropylidenemethyl phenyl ketone (2b). The thiophene S-
monoxide 4 can be added to the reaction mixture after the
Wittig olefination has taken place, but it can also be present as
a component from the beginning, while the Wittig reaction is
going on. The stabilised phosphoranes of type 7 are compatible
with a variety of reaction conditions. Thus, in principle, a
number of multiple step, one-pot reactions can be devised,
which involve Wittig olefination with these conjugated
phosphoranes.18,19
Scheme 5
a mixture with 3,4-dibromo-2,5-dimethylthiophene S-oxide 4d
(Scheme 6). While 2e as a trisubsubstituted alkene is sterically
less congested than the tetrasubstituted 2i, the latter is more
electron-deficient than 2e. Nevertheless, the thiophene S-oxide
4d reacted exclusively with 2e. The reaction of 4d with methyl 2-
bromo-2-cyclopropylidenecarboxylate 2i at 61 ЊC (refluxing
CHCl3) proceeds very sluggishly. When the reaction temper-
ature is raised to 110 ЊC (refluxing toluene), dimerisation of 4d
and deoxygenation20 to 3,4-dibromo-2,5-dimethylthiophene
become the major competing reactions.
In the cycloadditions of compounds 4 five new stereocenters
are formed, yet only a single diastereoisomer could be isolated
in all of the cycloadditions. All products have the endo-
configuration. One of the five stereocenters is located at the
sulfur of the 7-thiabicyclo[2.2.1]heptene S-oxides 3. As proven
by X-ray crystal structure analyses for two of the cycloadducts
(Figs. 1 and 2), the sulfoxide oxygen sits on the side of the
attached former dienophile (i.e., formed by syn-addition). The
stereochemistry is the same as that reported for the oxidative
cycloaddition of thiophenes to alkenes.3b,d,5a,c The stereochem-
ical outcome can be rationalized by the same effect originally
proposed by Cieplak21 to account for the contribution of
remote substituents in cyclohexanones. This was later used to
Competition experiments between different methylenecyclo-
propanes as dienophiles have been carried out. Thus, one
equivalent each of methyl cyclopropylideneacetate 2e and
methyl bromocyclopropylideneacetate 2i have been reacted as
2970
J. Chem. Soc., Perkin Trans. 1, 2000, 2968–2976

View Article Online
with a JEOL EX-270 and a Bruker AM 250 spectrometer. The
chemical reported shifts are relative to TMS (solvent CDCl3,
unless otherwise noted). mc refers to a centred multiplet. Mass
spectra were measured with a JMS-01-SG-2 spectrometer,
a Varian MAT CH7 and a Varian MAT 731 spectrometer (EI,
70 eV).
3,4-Dibenzyl-2,5-dimethylthiophene S-monoxide 4c,5a methyl
2-chloro-2-cyclopropylideneacetate 2c,8b,c bi(cyclopropylidene)
2f,8d 2-cyclopropylidenebutanone 2g,9 cyclopropylideneprop-
anone 2k9 and 1-ethoxy-1-hydroxycyclopropane 610 were
prepared according to literature procedures. Methyl bromo-
cyclopropylideneacetate 2m was synthesized by a procedure
analogous to that reported by Osborne,8a from cycloprop-
anone hemiacetal 6 and methoxycarbonylbromomethylene-
phosphorane.22 The phosphoranes 7 were prepared according
Fig. 1 ORTEP drawing of 3a.
to
a
procedure by Ramirez and Dershowitz.18 Methyl
cyclopentylideneacetate 2h was prepared directly from cyclo-
pentanone by Wittig olefination.
2,5-Dimethyl-3,4-bis(p-methoxyphenyl)thiophene 1c
A mixture of 3,4-dibromothiophene 1a (1.00 g, 3.70 mmol),
p-methoxyphenylboronic acid (2.26 g, 14.8 mmol) and
tetrakis(triphenylphosphine)palladium(0) (25 mg, 2.1 × 10Ϫ2
mmol) in 2 M aq. Na2CO3 (14 mL) and DME (8 mL) was
stirred under an inert atmosphere at 75 ЊC for 8 h. Then the
cooled reaction mixture was poured into a mixture of water
(100 mL) and chloroform (100 mL). The separated aq. phase
was extracted with chloroform (3 × 30 mL), and the collected
organic phase was washed with water (2 × 30 mL), aq. Na2CO3
(3 × 30 mL), and dried over anhydrous MgSO4. The filtered
solution was concentrated in vacuo, and the residue subjected to
column chromatography on silica gel (eluting with ether–
hexane 1:10) to give a colorless oil (Rf 0.42 [ether–hexane
1:10]). The oil included residual p-methoxyphenylboronic acid
which crystallized out in hexane. The solution was then filtered
and concentrated. Two crystallizations gave pure 1c from the
filtrate as a colorless solid (933 mg, 3.06 mmol, 83%); mp 69–
71 ЊC (decomp.); IR (KBr) ν 3034, 2950, 2910, 1609, 1525, 1463,
Fig. 2 ORTEP drawing of 3f.
1
1440, 1295, 1283, 1246, 1175, 1162, 1034, 832, 592 cmϪ1; H
NMR (270 MHz, CDCl3) δ 2.33 (s, 6H, 2 CH3), 3.75 (s, 6H, 2
3
3
OCH3), 6.75 (d, 4H, J 8.9 Hz), 6.91 (d, 4H, J 8.9 Hz); 13C
NMR (67.8 MHz, CDCl3, DEPT 90, DEPT 135) δ 13.96 (ϩ,
CH3), 55.04 (ϩ, OCH3), 113.54 (CH), 129.25 (Cquat), 130.73
(Cquat), 131.29 (CH), 138.65 (Cquat), 157.88 (Cquat); MS (70 eV)
m/z (%) 324 (Mϩ, 100), 309 (Mϩ Ϫ CH3, 12). HRMS Found:
324.1184; calcd. for C20H20O2S: 324.1183. Anal. calcd. for
C20H20O2S (324.44) C, 74.04; H, 6.21. Found C, 74.03; H, 6.27%.
2,5-Dimethyl-3,4-bis(p-tert-butylphenylmethyl)thiophene 1b
At 0 ЊC 2,5-dimethyl-3,4-bis(chloromethyl)thiophene (2.0 g, 9.6
mmol) in anhydrous p-tert-butylbenzene (40 mL) was added
slowly to a solution of titanium tetrachloride (0.75 g, 0.42 mL,
3.9 mmol) in anhydrous p-tert-butylbenzene (30 mL). The
reaction mixture was allowed to warm to rt, stirred for 2 h and
then heated under reflux for 1 h. Thereafter it was cooled to rt,
and ice water (50 g) was added. The layers were separated, and
the aqueous layer was extracted with ether (3 × 30 mL). The
combined organic phase was washed with water (3 × 30 mL),
brine (2 × 30 mL), and dried over anhydrous MgSO4. The
solvent was evaporated in vacuo, and the residue subjected to
column chromatography on silica gel (eluting with hexane) to
give 1b (1.82 g, 4.5 mmol, 47%) as colorless crystals, mp 95–
96 ЊC (ether); IR (KBr) ν 2960, 2910, 2866, 1513, 1413, 1391,
1360, 1285, 815, 546 cmϪ1; 1H NMR (270 MHz, CDCl3) δ 1.28
(s, 18H, 6 CH3), 2.30 (s, 6H, 2 CH3), 3.70 (s, 4H, 2 PhCH2), 6.92
Scheme 6 Competition of trisubstituted 2e and tetrasubstituted 2i in
the reaction with 4d.
account for the π-selectivity of 5-substituted cyclopentadienes
in Diels–Alder reactions. According to this rule the stronger
σ-electron donor directs the incoming dienophile anti to it. In
case of the cycloaddition of thiophene S-monoxides, the lone
electron pair on sulfur should be a stronger σ-donor than the
oxygen atom with its lone electron pairs. Thus, because of the
better orbital geometry the sulfur can stabilize better the incipi-
ent σ*-bonds of the cycloadduct from an anti position.
Experimental
General
3
3
Melting points were measured on a Reichert microscopic hot
stage and are uncorrected. Infrared spectra were measured with
JASCO IR-700, Bruker IFS 66 and Nippon Denshi JIR-
(d, 4H, J 8.2 Hz), 7.22 (d, 4H, J 8.2 Hz); 13C NMR (67.9
MHz) δ 13.37, 31.39, 32.18, 34.29, 125.16, 127.31, 130.35,
135.70, 137.25, 148.48; MS (70 eV) m/z (%) 404 (Mϩ, 100), 389
(Mϩ Ϫ CH3, 13), 213 (73). HRMS Found: 404.2540; calcd. for
1
AQ2OM machines. H- and 13C-NMR spectra were recorded
J. Chem. Soc., Perkin Trans. 1, 2000, 2968–2976
2971

View Article Online
C28H36S: 404.2538. Anal. calcd. for C28H36S (404.65) C, 83.11;
H, 8.97. Found C, 82.86; H, 8.96%.
(MCPBA) (716 mg, 4.14 mmol) in anhydrous CH2Cl2 (20 mL)
was added dropwise. The reaction mixture was stirred at
Ϫ20 ЊC for 2 h. Then the suspension was poured into a mixture
of conc. aq. NaHCO3 (30 mL) and CH2Cl2 (80 mL). The result-
ing mixture was stirred for 20 min at rt. The organic phase was
separated, and the aqueous phase was extracted with CH2Cl2
(3 × 20 mL). The combined organic phases were washed with
water (2 × 20 mL), brine (20 mL), and dried over MgSO4. After
removal of the solvent in vacuo, the residue was subjected to
flash chromatography on silica gel (eluting with ether) to give 4a
(1.02 mg, 77%) as colorless crystals; mp 153–155 ЊC; IR (KBr)
Ethyl cyclopropylideneacetate 2a
To a stirred solution of 1-ethoxy-1-trimethylsilyloxycyclo-
propane 5 (870 mg, 5.0 mmol) in benzene (15 mL) was added in
portions a well homogenized melt of tetrabutylammonium
fluoride (1.305 g, 5.0 mmol), benzoic acid (730 mg, 6.0 mmol)
and (ethoxycarbonylmethylene)triphenylphosphorane 7b (2.09
g, 6.0 mmol) within 15 min. The mixture was kept at room
temperature for 1 h. Afterwards it was stirred at 80 ЊC for 2.5 h.
The cooled mixture was poured into water (50 mL). The phases
were separated, the aqueous phase extracted with diethyl ether
(2 × 10 mL), and the combined organic phases were dried over
anhydrous MgSO4. Careful evaporation of the solvent gave a
residue which was chromatographed on silica gel (hexane–ether
2.5:1). Careful evaporation of the solvent gave pure 2a (330
mg, 54%). The analytical data were identical to those
reported.8b
1
ν 2960, 1512, 1363, 1269, 1028, 816, 547 cmϪ1; H NMR (270
MHz, CDCl3) δ 1.30 (s, 18H, 2 But), 2.24 (s, 6H, 2 CH3), 3.45
(4H, 2 CH2), 6.96 (d, 4H, J 8.3 Hz), 7.29 (d, 4H, J 8.3 Hz); 13
C
NMR (99.5 MHz, CDCl3) δ 10.59, 31.34, 31.76, 34.41, 125.69,
127.62, 134.17, 138.89, 142.64, 149.66; MS (70 eV) m/z (%) 420
(Mϩ, 21), 404 (Mϩ Ϫ O, 65), 331 (69), 199 (64), 147 (100). Anal.
calcd. for C28H36OSؒ0.5H2O (429.67) C, 78.27; H, 8.67. Found
C, 78.77; H, 8.49%.
2,5-Dimethyl-3,4-bis(p-methoxyphenyl)thiophene S-oxide 4b
Reaction of 1-ethoxy-1-trimethylsilyloxycyclopropane (5) with
(benzoylmethylene)triphenylphosphorane (7c) under benzoic acid
catalysis (1.2 equiv. PhCOOH)
At Ϫ20 ЊC and under an inert atmosphere, BF3ؒEt2O (1.5 mL,
11.9 mmol) was slowly added to a solution of 1c (500 mg, 1.54
mmol) in anhydrous CH2Cl2 (10 mL). After 10 min, a solution
of MCPBA (300 mg, 1.73 mmol) in anhydrous CH2Cl2 (10 mL)
was slowly added to the reaction mixture. The resulting mixture
was stirred for 3 h at Ϫ20 ЊC. Then it was poured into a solu-
tion of aq. NaHCO3 (100 mL) and CH2Cl2 (50 mL) and the
mixture stirred for 20 min at rt. The two phases were separated,
the aqueous phase extracted with CH2Cl2 (3 × 50 mL), and the
collected organic phase was washed with water (2 × 50 mL).
The solution was dried over anhydrous MgSO4 and concen-
trated in vacuo. The residue was subjected to column chromato-
graphy on silica gel (eluting with ether) to give 4b (255 mg, 0.75
mmol, 49%) as colorless crystals, Rf 0.34 (ether), mp (ether)
149–151 ЊC (decomp.); IR (KBr) ν 3048, 3004, 2960, 2932, 2908,
To a stirred solution of 1-ethoxy-1-trimethylsilyloxycyclo-
propane 5 (870 mg, 5.0 mmol) in benzene (15 mL) was added in
portions a well homogenized melt of tetrabutylammonium
fluoride (1.31 g, 5.0 mmol), benzoic acid (730 mg, 6.0 mmol)
and (benzoylmethylene)triphenylphosphorane 7c (2.09 g, 6.0
mmol) within 15 min. The mixture was kept at room temper-
ature for 1 h. Afterwards it was stirred at 80 ЊC for 3 h. The
cooled mixture was poured into water (50 mL). The phases were
separated, the aqueous phase extracted with diethyl ether
(2 × 10 mL), and the combined phases were dried over
anhydrous MgSO4. Evaporation of the solvent gave a residue
which was separated on silica gel (hexane–ether 3:1) to give
fraction 1 (75 mg, 4%) cyclopropylideneacetophenone 2b, IR
(neat) ν 1723, 1687, 1599, 1450, 1360, 1265, 759, 690 cmϪ1; all
other spectroscopic data match those given in ref. 9a; fraction 2
(216 mg, 15%) 1-(1Ј-benzoyloxycyclopropyl)acetophenone 9a
as a colorless oil, Rf 0.32; IR (neat) ν 3062, 2914, 1722, 1681,
1606, 1510, 1460, 1289, 1244, 1180, 1031, 842, 802, 750 cmϪ1
;
1H NMR (270 MHz, CDCl3) δ 2.26 (s, 6H, 2 CH3), 3.78 (s, 6H,
2 OCH3), 6.77 (d, 4H, 3J 2.3 Hz, Ar-H), 6.84 (d, 4H, 3J 2.3 Hz,
Ar-H); 13C NMR (150 MHz, CDCl3) δ 11.55, 55.19, 113.53,
125.65, 130.69, 140.90, 141.58, 159.25; MS (FAB, 3-nitrobenzyl
alcohol) m/z (%) 341 (MHϩ, 100), 324 (Mϩ Ϫ O, 73). HRMS
(FAB) Found: 341.1211; calcd. for C20H20O3S: 341.1215
(MHϩ). Anal. calcd. for C20H20O3S (340.12) C, 70.56; H, 5.92.
Found C, 70.52; H, 5.96%.
1
1599, 1283, 1253, 1107, 1025, 713, 690 cmϪ1; H NMR (270
MHz, CDCl3) δ 0.99 (mc, 2H, cyclopr.-H), 1.13 (mc, 2H,
cyclopr.-H), 3.62 (s, 2H), 7.35–7.42 (m, 4H), 7.48–7.55 (m, 2H),
7.92–7.97 (m, 2H); 13C NMR (99.5 MHz, CDCl3) δ 11.97,
42.83, 56.91, 128.27, 128.29, 128.59, 129.59, 130.15, 133.06,
133.17, 137.07, 166.90, 197.20; MS (EI, 70 eV) m/z (%) 280
(Mϩ, 0.6), 175 (Mϩ Ϫ PhCO, 15), 161 (Mϩ Ϫ PhCOCH2, 25),
159 (Mϩ Ϫ PhCOO, 21), 105 (100); MS (FAB, 3-nitrobenzyl
alcohol) 281 (MHϩ, 39), 159 (57), 105 (23). HRMS Found:
281.1180; calcd. for C18H17O3: 281.1178 (MHϩ); and fraction 3
(150 mg, 14%) 1-(1Ј-propionyloxycyclopropyl)acetophenone 9b
as a colorless solid, Rf 0.25, mp (ether–hexane) 83–84 ЊC; IR
(KBr) ν 2982, 2942, 1735, 1687, 1450, 1420, 1216, 1192, 744,
Methyl 7-oxo-3Ј-chloro-5Ј,6Ј-dibenzyl-1Ј,4Ј-dimethylspiro[cyclo-
propane-1,2Ј-[7]thiabicyclo[2.2.1]hept[5]ene]-3Ј-carboxylate 3a
2,5-Dimethyl-3,4-bis(phenylmethyl)thiophene
S-oxide
4c
(188 mg, 0.61 mmol) and methyl 2-chloro-2-cyclopropyl-
ideneacetate 2c (87 mg, 0.81 mmol) in chloroform (1 mL) were
stirred at rt for 11 h. After this time no products could be
detected in the 1H NMR spectrum of the reaction mixture.
2,5-Dimethyl-3,4-bis(phenylmethyl)thiophene S-oxide 4c
(188 mg, mmol) and methyl 2-chloro-2-cyclopropylideneacetate
2c (87 mg, mmol) in chloroform (1 mL) were stirred at 60 ЊC for
24 h. The solution was cooled, concentrated in vacuo, and the
residue was subjected to column chromatography on silica gel
(ether–hexane 1:2) to give dimethyl (E)-7,8-dichlorodispiro-
[2.0.2.2.]octane-7,8-dicarboxylic acid (10 mg, 11%) as a color-
less solid; IR (KBr) ν 3066, 3026, 3002, 2960, 1741, 1510, 1493,
1450, 1263, 1032, 935, 732 cmϪ1; 1H NMR (250 MHz, CDCl3)
δ 0.62 (m, 4H, cycloprop.-H), 0.97 (m, 4H, cycloprop.-H), 3.88
(s, 3H, 2 OCH3); 13C NMR (62.9 MHz, CDCl3, INEPT) δ 9.14
(Ϫ, CH2, 2C), 10.70 (Ϫ, CH2, 2C), 33.07 (Cquat, 2C),
53.29 (ϩ, OCH3), 75.75 (C, 2Cquat), 166.83 (Cquat, 2C, COOMe)
and methyl 7Ј-oxo-3-chloro-5Ј,6Ј-dibenzyl-1Ј,4Ј-dimethylspiro-
[cyclopropane-1,2Ј[7]thiabicyclo[2.2.1]hept[5]ene]-3Ј-carb-
oxylate 3a (166 mg, 60%), IR (KBr) ν 3060, 3024, 2946, 1736,
688 cmϪ1
;
1H NMR (270 MHz, CDCl3) δ 0.87 (mc, 2H,
3
cyclopr.-H), 0.97 (mc, 2H, cyclopr.-H), 1.03 (t, 3H, J 7.6 Hz),
2.18 (q, 2H, 3J 7.6 Hz), 3.48 (s, 2H), 7.46 (m, 2H), 7.55 (m, 1H),
7.95 (m, 2H); 13C NMR (99.5 MHz, CDCl3) δ 8.88, 11.93,
27.76, 42.70, 56.38, 128.36, 128.68, 133.29, 137.22, 174.91,
197.43; MS (FAB, 3-nitrobenzyl alcohol) m/z (%) 233 (MHϩ,
100), 159 (52), 105 (23).
3,4-Bis(tert-butylphenylmethyl)-2,5-dimethylthiophene S-
monoxide 4a
At Ϫ20 ЊC and under an inert atmosphere, BF3ؒEt2O (3.6 mL,
28.5 mmol) was added to a solution of 3,4-bis(tert-butyl-
phenylmethyl)-2,5-dimethylthiophene 1b (1.28 g, 3.17 mmol)
in anhydrous CH2Cl2 (20 mL). The solution was stirred for
10 min at Ϫ20 ЊC, then a solution of m-chloroperbenzoic acid
2972
J. Chem. Soc., Perkin Trans. 1, 2000, 2968–2976

View Article Online
1
2
2
1494, 1453, 1248, 1109, 1076, 1028, 729, 697 cmϪ1; H NMR
1H, benzyl-CH, J 12.5 Hz), 3.88 (d, 1H, benzyl-CH, J 12.5
2
(270 MHz, CDCl3) δ Ϫ0.62 (m, 1H, cycloprop.-H), 0.47 (m,
1H, cycloprop.-H), 1.11 (m, 1H, cycloprop.-H), 1.19 (s, 3H,
CH3), 1.34 (m, 1H, cycloprop.-H), 1.74 (s, 3H, CH3), 3.23 (d,
1H, benzyl-CH, J 15.2 Hz), 3.77 (d, 1H, benzyl-CH, J 12.5
Hz), 3.78 (s, 3H, COOCH3), 3.83 (d, 1H, benzyl-CH, J 12.5
Hz), 4.12 (d, 1H, benzyl-CH, J 16.1 Hz), 7.12–7.33 (m, 10H);
not all the proton signals are listed. To the mixture 3c/3c-II in
ether (5 mL) was added a solution of diazomethane23 (prepared
from nitrosomethylurea23a) in ether at 0 ЊC. The reaction
mixture was kept at rt for 12 h. Afterwards the solvent was
evaporated in vacuo. The residue was subjected to column
chromatography on silica gel (ether–hexane 3:1) to give 3g and
3g-II.
2
2
2
2
Hz), 4.05 (d, 1H, benzyl-CH, J 15.2 Hz), 7.05 (m, 2H), 7.18–
7.34 (m, 8H); 13C NMR (67.9 MHz, CDCl3, DEPT) δ 7.64 (Ϫ,
CH2, cycloprop.-C), 9.51 (ϩ, CH3), 12.47 (Ϫ, CH2, cycloprop.-
C), 12.85 (ϩ, CH), 32.96 (Ϫ, CH2, 2C), 37.09 (Cquat), 52.80
(ϩ, OCH3), 72.33 (Cquat), 76.10 (Cquat), 81.83 (Cquat), 126.45
(ϩ, CH), 126.83 (ϩ, CH), 128.05 (ϩ, CH, 2C), 128.48 (ϩ, CH,
2C), 128.68 (ϩ, CH), 129.02 (ϩ, CH), 136.03 (Cquat), 137.14
(Cquat), 138.53 (Cquat), 140.77 (Cquat), 168.75 (Cquat, COOMe);
MS (FAB, 3-nitrobenzyl alcohol) m/z (%) 457 ([37ClMHϩ], 4.6),
455 ([35ClMHϩ], 10.7). Anal. calcd. for C26H27ClO3S (455.01)
C, 68.63; H, 5.98. Found: C, 68.34; H, 5.88%.
Methyl
7Ј-oxo-1Ј,4Ј-dimethyl-5Ј,6Ј-bis(phenylmethyl)spiro-
[cyclopropane-1,2Ј-[7Ј]thiabicyclo[2.2.1]hept[5]ene]-3Ј-carb-
oxylate 3g. 40 mg, 45%; Rf 0.4; mp 180–181 ЊC; IR (KBr)
ν 3080, 3022, 2924, 1725, 1602, 1494, 1453, 1427, 1347, 1194,
1092, 1068, 792, 724, 698 cmϪ1; H NMR (270 MHz, CDCl3)
1
δ Ϫ0.79 (m, 1H, cyclopr.-H), Ϫ0.06 (m, 1H, cyclopr.-H), 0.73
(m, 1H, cyclopr.-H), 0.84 (m, 1H, cyclopr.-H), 1.10 (s, 3H,
CH3), 1.34 (s, 3H, CH3), 3.28 (d, 1H, benzyl-CH, 2J 15. 2 Hz),
2
Ethyl 7Ј-oxo-5Ј,6Ј-bis(p-tert-butylphenylmethyl)-1Ј,4Ј-dimethyl-
spiro[cyclopropane-1,2Ј-[7]thiabicyclo[2.2.1]hept[5]ene]-3Ј-carb-
oxylate 3b
3.51 (s, 1H), 3.68 (d, 1H, benzyl-CH, J 16.5 Hz), 3.70 (s, 3H,
2
COOCH3), 3.87 (d, 1H, benzyl-CH, J 15.2 Hz), 4.12 (d, 1H,
benzyl-CH, J 16.5 Hz), 7.15–7.32 (m, 10H); 13C NMR (67.9
2
MHz, CDCl3) δ 3.79, 9.09, 9.81, 13.32, 29.59, 32.65, 32.99,
51.71, 56.73, 71.19, 73.24, 126.38, 126.57, 128.16 (2C), 128.37
(2C), 128.62 (2C), 129.20 (2C), 136.03, 137.32, 137.93, 138.81,
172.23; MS (FAB, 3-nitrobenzyl alcohol) m/z (%) 421 (MHϩ,
100), 372 (Mϩ Ϫ SO, 87), HRMS Found: 421.1838; calcd. for
C26H29O3S: 421.1837.
A solution of 3,4-bis(p-tert-butylphenylmethyl)-2,5-dimethyl-
thiophene S-monoxide 4a (112 mg, 0.265 mmol) and ethyl
cyclopropylideneacetate 2a (67 mg, 0.53 mmol) in CDCl3 (2
mL) were kept at 60 ЊC. According to an 1H NMR spectrum of
the reaction mixture, complete reaction of the thiophene S-
oxide had occurred after 19.5 h to give the cycloadduct 3b as a
single stereoisomer. Column chromatography of the mixture on
silica gel (ether–hexane 2:1) gave 3b as a colorless solid; Rf 0.5;
IR (neat) ν 3086, 2962, 1733, 1513, 1181, 1094, 1065, 1030, 910,
1-(Methoxycarbonylmethyl)cyclopropyl 7Ј-oxo-1Ј,4Ј-dimethyl
-5Ј,6Ј-bis(phenylmethyl)spiro[cyclopropane-1,2Ј-[7]thiabi-
732 cmϪ1 1H NMR (270 MHz, CDCl3) δ Ϫ0.83 (m, 1H,
;
cyclo[2.2.1]hept[5Ј]ene]-3Ј-carboxylate 3g-II. 41 mg, 38%,
Colorless needles; Rf 0.2; mp 145–146 ЊC; IR (KBr) ν 3064,
3026, 3004, 2924, 1742, 1452, 1439, 1201, 1170, 1143, 1064,
1023, 731, 719, 698 cmϪ1; 1H NMR (270 MHz, CDCl3) δ Ϫ0.84
(m, 1H, cyclopr.-H), Ϫ0.04 (m, 1H, cyclopr.-H), 0.66 (m, 1H,
cyclopr.-H), 0.86 (m, 1H, cyclopr.-H), 0.97 (m, 4H, cyclopr.-H),
1.09 (s, 3H, CH3), 1.33 (s, 3H, CH3), 2.76 (d, 1H, H-C2Љ, 2J 15.5
Hz), 2.86 (d, 1H, H-C2Љ, 2J 15.5 Hz), 3.27 (d, 1H, benzyl-CH, 2J
15.5 Hz), 3.41 (s, 1H), 3.71 (s, 3H, COOCH3), 3.72 (d, 1H,
cyclopr.-H), 0.01 (m, 1H, cyclopr.-H), 0.72 (m, 1H, cyclopr.-H),
0.89 (m, 1H, cyclopr.-H), 1.09 (s, 3H, CH3), 1.29 (s, 9H, But),
1.31 (t, 3H, CH3), 1.31 (s, 9H, But), 1.35 (s, 3H, CH3), 3.25 (d,
2
1H, benzyl-CH, J 15.1 Hz), 3.47 (s, 1H), 3.64 (d, 1H, benzyl-
2
CH, J 15.1 Hz), 3.83 (d, 1H, benzyl-CH, 2J 15.1 Hz), 4.07 (d,
2
1H, benzyl-CH, J 15.1 Hz), 4.17 (dq, 2H), 7.10 (m, 4H), 7.27
(m, 4H); 13C NMR (67.9 MHz, CDCl3, DEPT) δ 3.42 (Ϫ,
cyclopr.), 9.09 (ϩ, CH3), 9.69 (Ϫ, cyclopr.), 13.30 (ϩ, CH3),
14.36 (ϩ, CH3), 29.45 (Cquat), 31.36 (ϩ, CH3, 6C), 32.08 (Ϫ,
CH2), 32.47 (Ϫ, CH2), 34.36 (Cquat), 56.62 (ϩ, CH), 60.55 (Ϫ,
OCH2), 71.14 (Cquat), 73.16 (Cquat), 125.10 (ϩ, CHarom.), 125.60
(ϩ, CHarom.), 127.80 (ϩ, CHarom.), 128.84 (ϩ, CHarom.), 134.32
(Cquat), 135.76 (Cquat), 135.94 (Cquat), 137.84 (Cquat), 149.18
2
2
benzyl-CH, J 16.5 Hz), 3.88 (d, 1H, benzyl-CH, J 15.5 Hz),
4.12 (d, 1H, benzyl-CH, J 16.5 Hz), 7.14–7.33 (m, 10H); 13C
2
NMR (67.9 MHz, CDCl3) δ 3.22, 9.04, 9.63, 12.09, 12.47, 13.06,
29.51, 32.61, 32.97, 39.94, 51.91, 56.35, 57.11, 71.19, 73.24,
126.38, 126.61, 128.16 (2C), 128.37 (2C), 128.62 (2C), 129.16
(2C), 136.03, 137.32, 138.00, 138.85, 170.67, 171.96; MS (FAB,
3-nitrobenzyl alcohol) m/z (%) 519 (MHϩ, 61), 470 (Mϩ Ϫ SO,
38). HRMS Found: 519.2212; calcd. for C31H35O5S: 519.2205.
(Cquat), 149.45 (Cquat), 171.66 (Cquat, C᎐O); MS (FAB, 3-
᎐
nitrobenzyl alcohol) m/z (%) 547 (MHϩ, 33), 498 (M+-SO, 21).
Anal. calcd. for C35H46O3S (546.81) C, 76.88; H, 8.48. Found:
C, 76.59; H, 8.45.
7Ј-Oxo-3Ј-acetyl-5Ј,6Ј-dibenzyl-1Ј,4Ј-dimethylspiro[cyclo-
propane-1,2Ј-[7]thiabicyclo[2.2.1]hept[5]ene] 3j
7Ј-Oxo-1Ј,4Ј-dimethyl-5Ј,6Ј-bis(phenylmethyl)spiro[cycloprop-
ane-1,2Ј-[7]thiabicyclo[2.2.1]hept[5]ene]-3Ј-carboxylic acid 3c
Variant 1. A solution of 3,4-dibenzyl-2,5-dimethylthiophene
S-monoxide 4c (112 mg, 0.265 mmol) and cyclopropylidene-
propanone 2k (51 mg, 0.53 mmol) in CDCl3 (2 mL) was kept at
60 ЊC. 1H NMR spectra of the mixture were recorded after 8.5,
17, and 25.5 h. Then the reaction mixture was concentrated in
vacuo. The residue was subjected to column chromatography on
silica gel (ether–hexane 4:1) to give 3j (37 mg, 35%) as a color-
less oil; Rf (ether–hexane 4:1) 0.2; 1H NMR (270 MHz, CDCl3)
δ 0.81 (m, 1H, cyclopr.-H), Ϫ0.07 (m, 1H, cyclopr.-H), 0.60 (m,
1H, cyclopr.-H), 1.10 (m, 1H, cyclopr.-H), 1.16 (s, 3H, CH3),
1.97 (s, 3H, CH3), 1.99 (s, 3H, CH3), 3.12 (d, 1H, benzyl-CH, 2J
15.2 Hz), 3.32 (s, 1H), 3.48 (d, 1H, benzyl-CH, 2J 16.7 Hz), 3.80
(d, 1H, benzyl-CH, 2J 15.2 Hz), 4.06 (d, 1H, benzyl-CH, 2J 16.7
Hz), 7.01–7.17 (m, 10H); MS (FAB, 3-nitrobenzyl alcohol) m/z
(%) 405 (MHϩ, 10). Anal. calcd. for C26H28O2S (404.57) C,
77.19; H, 6.98. Found: C, 77.15; H, 6.92%.
A solution of 2,5-dimethyl-3,4-bis(phenylmethyl)thiophene S-
oxide 4c (67 mg, 0.21 mmol) and cyclopropylideneacetic acid
2d (73 mg, 0.74 mmol) in CDCl3 (2 mL) was heated under
reflux for 56 h, after which time complete reaction of 4c had
occurred according to the 1H NMR spectrum. The mixture was
concentrated in vacuo. Unreacted 2d was recovered by column
chromatography on silica gel (ether). The products 3c/3c-II
(ratio 1:1), however, could not be separated and were analysed
as a mixture. The NMR signals were assigned to the products
by 1H-COSY in the following way: 1H NMR (270 MHz,
CDCl3) δ 3c: Ϫ0.75 (m, 1H, cyclopr.-H), 0.15 (m, 1H, cyclopr.-
H), 0.78 (m, 1H, cyclopr.-H), 1.11 (s, 3H, CH3), 2.39 (s, 3H,
2
CH3), 3.29 (1H, benzyl-CH, J 16.2 Hz), 3.55 (s, 1H), 3.66 (d,
2
2
1H, benzyl-CH, J 12.5 Hz), 3.87 (d, 1H, benzyl-CH, J 12.5
2
Hz), 4.09 (d, 1H, benzyl-CH, J 16.2 Hz), 7.12–7.33 (m, 10H);
3c-II: δ Ϫ0.87 (m, 1H, cyclopr.-H), Ϫ0.07 (m, 1H, cyclopr.-H),
1.08 (s, 3H, CH3), 2.78 (d, 1H, 2J 16.5 Hz), 2.90 (d, 1H, 2J 16.5
Hz), 3.26 (d, 1H, benzyl-CH, 2J 16.1 Hz), 3.43 (s, 1H), 3.73 (d,
Variant 2. A mixture of 1-ethoxycyclopropanol 6 (175 mg,
1.7 mmol), (acetylmethylene)triphenylphosphorane 7e (2.15
J. Chem. Soc., Perkin Trans. 1, 2000, 2968–2976
2973

View Article Online
mmol), benzoic acid (12.0 mg, 0.10 mmol) and 4c (52 mg, 0.17
mmol) in benzene (3 mL) was stirred under reflux for 56 h. The
reaction mixture was cooled and concentrated in vacuo. The
residue was subjected to column chromatography on silica gel
(ether–hexane 4:1) to give 3j (35 mg, 52%).
1.13 (s, 3H, CH3), 1.44 (s, 3H, CH3), 3.35 (d, 1H, benzyl-CH, 2J
15.2 Hz), 3.40 (s, 1H), 3.64 (d, 1H, benzyl-CH, 2J 16.2 Hz), 3.92
(d, 1H, benzyl-CH, 2J 15.2 Hz), 4.15 (d, 1H, benzyl-CH, 2J 16.2
Hz), 7.15–7.36 (m, 10H); 13C NMR (67.9 MHz, CDCl3) δ 4.55,
8.89, 10.82, 12.99, 28.84, 32.39, 32.65, 45.26, 71.07, 73.60,
118.52, 126.81, 127.01, 128.05 (2C), 128.59 (2C), 128.84 (2C),
129.02 (2C), 134.28, 136.35, 137.64, 140.81; MS (FAB,
3-nitrobenzyl alcohol) m/z (%) 388 (MϩHϩ, 100), 339
(Mϩ Ϫ SO, 74). HRMS Found: 388.1731; calcd. for C25H26-
ONS: 388.1735. Anal. calcd. for C25H26ONS (388.55) C, 77.28;
H, 6.74; N, 3.60%.
7Ј-Oxo-3Ј-benzoyl-5Ј,6Ј-bis(p-tert-butylbenzyl)-1Ј,4Ј-dimethyl-
spiro[cyclopropane-1,2Ј-[7]thiabicyclo[2.2.1]hept[5]ene] 3h—
one-pot Wittig olefination–cycloaddition reaction
A mixture of 1-ethoxycyclopropanol 6 (175 mg, 1.7 mmol),
(benzoylmethylene)triphenylphosphorane (810 mg, 2.13
mmol), benzoic acid (12.7 mg, 0.11 mmol) and 4a (71.4 mg,
0.17 mmol) in benzene (3 mL) was stirred under reflux for 22 h.
The reaction mixture was cooled to rt and concentrated in
vacuo. The residue was subjected to column chromatography on
silica gel (ether–hexane 3:1) to give 3h (89 mg, 90% based on
4a); Rf 0.4; 1H NMR (270 MHz, CDCl3) δ Ϫ0.86 (m, 1H,
cyclopr.-H), Ϫ0.32 (m, 1H, cyclopr.-H), 0.67 (m, 1H, cyclopr.-
H), 0.84 (m, 1H, cyclopr.-H), 1.11 (s, 3H, CH3), 1.27 (s, 9H,
But), 1.29 (s, 3H, CH3), 1.30 (s, 9H, But), 3.28 (d, 1H, benzyl-
Ethyl 7Ј-oxo-1Ј,4Ј-dimethyl-5Ј,6Ј-bis(p-methoxyphenyl)spiro-
[cyclopropane-1,2Ј-[7]thiabicyclo[2.2.1]hept[5]ene]-3Ј-
carboxylate 3m
A mixture of 1-hydroxy-1-ethoxycyclopropane 6 (175 mg, 1.70
mmol), (ethoxycarbonylmethylene)triphenylphosphorane 7b
(740 mg, 2.13 mmol), 2,5-dimethyl-3,4-bis(p-methoxyphenyl)-
thiophene S-oxide 4b (77 mg, 0.23 mmol), and benzoic acid
(50 mg, 0.41 mmol) in benzene (4 mL) was heated under reflux
for 21 h. The reaction mixture was concentrated in vacuo and
directly submitted to column chromatography on silica gel
(eluting with ether–hexane 2:1) to give 3m (91 mg, 85%); Rf
0.25; IR (neat) ν 2930, 2836, 1735, 1607, 1510, 1246, 1175, 1032
cmϪ1; 1H NMR (270 MHz, CDCl3) δ 0.54 (m, 1H, cyclopr.-H),
0.62 (m, 1H, cyclopr.-H), 0.95 (m, 1H, cyclopr.-H), 1.03 (s, 3H,
3
CH, J 15.1 Hz), 3.66 (d, 1H, benzyl-CH, 3J 16.5 Hz), 3.89 (d,
3
3
1H, benzyl-CH, J 15.1 Hz), 4.18 (d, 1H, benzyl-CH, J 16.5
3
3
Hz), 4.66 (s, 1H), 7.13 (d, 2H, J 8.2 Hz), 7.29 (2d, 4H, J 8.2
Hz), 7.59 (m, 1H), 7.90 (d, 2H, 3J 8.5 Hz); MS (70 eV) m/z (%)
574 (Mϩ, 7). Anal. calcd. for C39H42O2S (574.82) C, 81.49; H,
7.36. Found: C, 81.24; H, 7.25%.
3
CH3), 1.08 (m, 1H, cyclopr.-H), 1.22 (t, 3H, J 7.2 Hz), 1.49
(s, 3H, CH3), 3.69 (s, 1H), 3.73 (s, 3H, p-OCH3), 3.74 (s, 3H,
7Ј-Oxo-3Ј-(p-chlorobenzoyl)-5Ј,6Ј-dibenzyl-1Ј,4Ј-dimethylspiro-
[cyclopropane-1,2Ј-[7]thiabicyclo[2.2.1]hept[5]ene] 3i
p-OCH3), 4.15 (q, 2H, 3J 7.2 Hz), 6.70 (d, 2H, 3J 8.9 Hz), 6.72
3
3
3
(d, 2H, J 8.6 Hz), 6.94 (d, 2H, J 8.9 Hz), 7.05 (d, 2H, J 8.6
Hz); 13C NMR (67.8 MHz, CDCl3, DEPT 90, DEPT 135)
δ 3.88 (Ϫ, cyclopr.), 9.18 (Ϫ, cyclopr.), 10.20 (CH3), 14.17
(CH3), 14.54 (CH3), 29.70 (Cquat, cyclopr.), 50.04 (2 OCH3),
56.26 (CH), 60.71 (Ϫ, OCH2), 72.24 (Cquat), 73.64 (Cquat),
113.09 (CH), 113.49 (CH), 113.62 (Cquat), 126.79 (Cquat),
130.65 (CH), 131.48 (CH), 138.34 (Cquat), 140.63 (Cquat), 158.56
A mixture of 1-ethoxycyclopropanol 6 (204 mg, 2.0 mmol),
(p-chlorobenzoylmethylene)triphenylphosphorane 7d (830 mg,
2.0 mmol), benzoic acid (10 mg, 0.095 mmol) and 4c (50 mg,
0.16 mmol) in benzene (10 mL) were stirred under reflux for
22 h and worked up as described above to give 3i (75 mg, 91%) as
a colorless oil; IR (CHCl3) ν 3062, 3026, 2970, 1733, 1679, 1588,
1453, 1092 cmϪ1; 1H NMR (270 MHz, CDCl3) δ Ϫ0.87 (m, 1H,
cyclopr.-H), Ϫ0.34 (m, 1H, cyclopr.-H), 0.65 (m, 1H, cyclopr.-
H), 0.83 (m, 1H, cyclopr.-H), 1.11 (3H, s, CH3), 1.29 (3H, s,
CH3), 3.30 (d, 1H, benzyl-CH, 2J 15.2 Hz), 3.69 (d, 1H, benzyl-
(Cquat, 2C), 171.71 (Cquat, C᎐O); MS (FAB, 3-nitrobenzyl
᎐
alcohol) m/z (%) 467 (MHϩ, 23), 418 (Mϩ Ϫ SO, 88), 390
([418] Ϫ C2H4, 25), 345 ([418] Ϫ COOC2H5, 100); MS (FAB,
glycerine) m/z (%) 467 (MHϩ, 34), 418 (Mϩ Ϫ SO, 33), 345
([418 Ϫ COOC2H5, 40). HRMS Found: 467.1892; calcd. for
C27H31O5S: 467.1892.
2
CH, J 16.5 Hz), 3.93 (d, 1H, benzyl-CH, 2J 15.2 Hz), 4.22 (d,
2
1H, benzyl-CH, J 16.5 Hz), 4.60 (s, 1H), 7.20–7.27 (m, 10H),
7.45 (d, 2H, 3J 8.5 Hz), 7.87 (d, 2H, 3J 8.5 Hz); 13C NMR (67.9
MHz, CDCl3, DEPT 90, DEPT 135) δ 4.01 (Ϫ, cyclopr.-C),
9.51 (Ϫ, cyclopr.-C), 9.58 (CH3), 14.11 (CH3), 31.29 (Cquat),
33.15 (Ϫ, benzyl-C), 33.61 (Ϫ, benzyl-C), 56.37 (ϩ, CH), 73.06
(Cquat), 74.31 (Cquat), 126.79 (ϩ, CH), 126.97 (ϩ, CH), 128.61
(ϩ, CH), 128.81 (ϩ, CH), 129.40 (ϩ, CH), 129.72 (ϩ, CH),
129.76 (ϩ, CH), 136.91 (Cquat), 137.30 (Cquat), 137.37 (Cquat),
Attempted cycloaddition of tetramethylthiophene S,S-dioxide to
ethyl cyclopropylideneacetate
A solution of tetramethylthiophene S,S-dioxide (58 mg, 0.33
mmol) and ethyl cyclopropylideneacetate (130 mg, 1.03 mmol)
1
in CDCl3 (2 mL) was kept at 60 ЊC. H NMR spectra were
recorded after 10.5, 24, and 48 h. No reaction products could be
detected.
137.77 (Cquat), 139.34 (Cquat), 140.81 (Cquat), 199.53 (Cquat, C᎐O);
᎐
MS (FAB, 3-nitrobenzyl alcohol) m/z (%) 503 ([37Cl]MHϩ, 5.2),
501 ([35Cl]MHϩ, 12), 452 (Mϩ Ϫ SO, 6.4). HRMS (FAB)
Found: 501.1655; calcd. for C31H30 [35Cl]O2S: 501.1655.
Reactions under high pressure
Ethyl
7Ј-oxo-5Ј,6Јbis(p-tert-butylphenylmethyl)-2Ј-chloro-
7Ј-Oxo-5Ј,6Ј-bis(phenylmethyl)-3Ј-cyano-1Ј,4Ј-dimethylspiro-
[cyclopropane-1,2Ј-[7]thiabicyclo[2.2.1]hept[5]ene] 3k
1Ј,4Ј-dimethylspiro[cyclopropane-1,2Ј-[7]thiabicyclo[2.2.1]hept-
[5]ene]-3Ј-carboxylate 3b—cycloaddition reaction under high
pressure. A mixture of 4a (42 mg, 0.1 mmol) and 2c (29 mg,
0.2 mmol) in acetonitrile (3 mL) was heated at 60 ЊC under a
pressure of 10 kbar for 24 h. After concentration in vacuo the
residue was chromatographed on silica gel to give 3b (52 mg,
92%) as colorless crystals; Rf 0.70 (ether). The spectroscopic
data were identical with those of 3b, as listed above.
A mixture of 1-ethoxycyclopropanol 6 (350 mg, 3.4 mmol),
(cyanomethylene)triphenylphosphorane 7f18 (1.28 g, 4.26
mmol) and benzoic acid (10 mg, 9 × 10Ϫ2 mmol) in benzene
(3 mL) was stirred under reflux for 10 h. Thereafter 4c (75 mg,
0.24 mmol) was added to the cooled solution, and the mixture
was stirred under reflux for an additional 22 h. The reaction
mixture was concentrated in vacuo and subjected to column
chromatography on silica gel (ether–hexane 3:1) to afford 3k
(66 mg, 71%) as a colorless solid; Rf 0.37; mp 134–135 ЊC
(CHCl3–hexane 1:4); IR (KBr) ν 3080, 3026, 2924, 2232, 1603,
1494, 1450, 1105, 1076, 1031, 748, 726, 697 cmϪ1; 1H NMR (270
MHz, CDCl3) δ Ϫ0.59 (m, 1H, cyclopr.-H), 0.39 (m, 1H,
cyclopr.-H), 0.77 (m, 1H, cyclopr.-H), 0.95 (m, 1H, cyclopr.-H),
5Ј,6Ј-Dibenzyl-1Ј,4Ј-dimethyl-7Ј-oxodispiro[cyclopropane-
1,2Ј-[7]thiabicyclo[2.2.1]hept[5]ene-3Ј,1Љ-cyclopropane] 3f.
mixture of 4c (62 mg, 0.2 mmol) and 2f (80 mg, 1.0 mmol) in
acetonitrile (3 mL) was heated at 60 ЊC under a pressure of 10
kbar for 5 d. After concentration of the solution in vacuo the
residue was subjected to column chromatography on silica gel
A
2974
J. Chem. Soc., Perkin Trans. 1, 2000, 2968–2976

View Article Online
Table 3 Experimental crystallographic details for 3a and 3f
to give 3f (37 mg, 48%) as a colorless solid; mp 120 ЊC; Rf 0.37
(ether); IR (KBr) ν 3061, 3025, 1601, 1494, 1451, 1123, 1090,
1
1063, 728, 698 cmϪ1; H NMR (250 MHz, CDCl3) δ Ϫ0.31–
Compound
3a
3f
Ϫ0.20 (m, 4H), 0.33 (m, 2H), 0.68 (m, 2H), 1.11 (6H, s, 2 CH3),
3.64 (s, 4H, 2 CH2), 7.14–7.32 (m, 10H, arom. H); 13C NMR
(62.9 MHz, CDCl3, DEPT) δ 1.77 (Ϫ), 6.20 (Ϫ), 9.73 (ϩ, CH3),
29.40 (Cquat), 32.40 (Ϫ), 72.07 (Cquat), 128.50 (ϩ, CH), 128.46
(ϩ,CH), 128.52 (ϩ, CH), 137.52 (Cquat), 137.90 (Cquat); MS (70
eV) m/z (%) 388 (Mϩ, 9), 372 (Mϩ Ϫ CH3, 9), 340 (Mϩ Ϫ SO,
58), 312 (100). Anal. calcd. for C26H28SO (388.57) C, 80.37; H,
7.26. Found C, 80.20; H, 7.43%.
Formula
M
Crystal system
Space group
a/Å
b/Å
c/Å
C26H27ClO3S
454.99
Orthohombic
Pna21
11.807(2)
20.089(2)
9.866(2)
C26H28OS
388.54
Monoclinic
P21/c
13.131(2)
14.125(2)
11.6791(14)
97.061(12)
2149.8(5)
1.200
β/Њ
V/Å3
2340.1(7)
1.291
4
µ(Co-Kα) 0.71073
296(2)
11348
5791
2106
280
0.0524
0.1318
The same reaction was carried out in acetonitrile (2 mL) for
24 h under otherwise identical conditions to give 3f (24 mg,
31%).
Dcalc/g cmϪ3
Z
4
µ(Cu-Kα)/Å
T/K
Measured data
Unique data
Observed data
No. of parameters
R
µ(Co-Kα) 0.71073
150(2)
2837
2817
2807
255
0.0419
0.0930
5Ј,6Ј-Bis(p-tert-butylphenylmethyl)-1Ј,4Ј-dimethyl-7Ј-oxodi-
spiro[cyclopropane-1,2Ј-[7]thiabicyclo[2.2.1]hept[5]ene-3Ј,1Љ-
cyclopropane] 3e. A mixture of 4a (84 mg, 0.2 mmol) and 2f
(80 mg, 1.0 mmol) in acetonitrile (3 mL) was heated at 60 ЊC
under a pressure of 10 kbar for 5 d. After concentration of the
solution in vacuo the residue was subjected to column chrom-
atography on silica gel to give 3e (43 mg, 43%) as a colorless
Rw
X-Ray crystallographic structure analysis of 3a†
1
solid; mp 93 ЊC; Rf 0.37 (ether); H NMR (250 MHz, CDCl3)
δ Ϫ0.32–Ϫ0.21 (m, 4H), 0.31 (m, 2H), 0.68 (m, 2H), 1.11 (s, 6H,
Intensity data were collected with an Enraf-Nonius CAD4
diffractometer. The structure was solved by direct methods
(SIR-97).24 All non-hydrogen atoms were located in successive
difference Fourier syntheses. Hydrogen atoms were located
3
2 CH3), 1.31 (s, 18, 2 But), 3.60 (s, 4H, 2 CH2), 7.08 (d, 4H, J
8.3 Hz), 7.30 (d, 4H, 3J 8.3 Hz); 13C NMR (62.9 MHz, CDCl3,
DEPT) δ 1.71 (Ϫ), 6.17 (Ϫ), 9.73 (ϩ), 29.43 (Cquat), 31.32 (ϩ),
31.84 (Ϫ), 34.35 (Cquat), 72.05 (Cquat), 125.27 (ϩ), 128.20 (ϩ),
134.86 (Cquat), 137.42 (Cquat), 149.41 (Cquat); MS (70 eV) m/z (%)
500 (Mϩ, 16), 485 (Mϩ Ϫ CH3, 22), 452 (Mϩ Ϫ SO, 56), 424
(100). HRMS Found: 500.3112; calcd. for C34H44OS: 500.3113.
The same reaction was carried out in acetonitrile (2 mL) for
24 h under otherwise identical conditions to give 3e (39 mg,
39%).
by calculation with
ω
a
riding model, weighting scheme
2
Ϫ1 = σ2(Fo ) ϩ (0.0376 P)2 ϩ 0.00P, where 3 P = (Fo2 ϩ 2Fc2).
All non-hydrogen atoms treated anisotropically were refined
by full-matrix least-squares calculation. Hydrogen atoms
treated isotropically were refined by full-matrix least-squares
calculation. All calculations were performed with an IBM
RISC System/6000 380 computer using SHELXL-97.25 The
final cell parameters and specific data collection parameters are
summarised in Table 3.
Attempted cycloaddition of 3,4-bis(p-methoxyphenyl)-2,5-
dimethylthiophene S-oxide to methyl cyclopentylideneacetate
X-Ray crystallographic structure analysis of 3f†
A mixture of 4b (50 mg, 0.15 mmol) and 2h (56 mg, 0.36 mmol)
in CDCl3 (2 mL) was heated at 60 ЊC for 24 h. No product could
Intensity data were collected at 150(2) K on an Enraf-Nonius
CAD-4 diffractometer using graphite-monochromated Mo-Kα
radiation and ω/2θ scan mode. The structure was solved by
direct methods (SHELXS-86) and refined anisotropically
(non-hydrogen atoms) by the full-matrix least-squares method
on F2 (SHELXL-93). Parameters of crystal data collection and
structure refinement are presented in Table 3.
1
be detected in the H NMR spectrum of the crude reaction
mixture.
Competitive cycloaddition of methyl cyclopropylideneacetate 2e
and methyl 2-bromo-2-cyclopropylideneacetate 2i with 3,4-
dibromo-2,5-dimethylthiophene S-oxide 4d
A solution of 4d (50 mg, 0.175 mmol), 2i (67 mg, 0.35 mmol)
and 2e (39 mg, 0.35 mmol) in CHCl3 (2 mL) was heated under
reflux for 19 h. After the reaction mixture had cooled down to
rt, the volatile material was removed in vacuo. The residue was
subjected to column chromatography to give methyl 5Ј,6Ј-
dibromo-1Ј,4Ј-dimethyl-7-oxospiro[cyclopropane-1,2Ј-[7]thia-
bicyclo[2.2.1]hept[5]ene]-3Ј-carboxylate 3n (60 mg, 67%) as
colorless needles; mp 139.5–140.5 ЊC (hexane–ether 1:1); IR
(KBr) ν 3084, 2954, 1740, 1565, 1454, 1203, 1096, 1072, 1020,
791 cmϪ1; 1H NMR (250 MHz, CDCl3) δ 0.37 (m, 1H), 0.55 (m,
1H), 0.88–1.05 (m, 2H), 1.21 (s, 3H, CH3), 1.65 (s, 3H, CH3),
3.66 (s, 1H), 3.69 (s, 3H, COOCH3); 13C NMR (62.9 MHz,
CDCl3, DEPT 90, DEPT 135) δ 2.84 (Ϫ), 8.39 (Ϫ), 11.66 (ϩ,
CH3), 15.58 (ϩ, CH3), 29.50 (Cquat), 52.16 (ϩ, COOCH3), 55.22
(ϩ, CH), 73.87 (Cquat), 76.12 (Cquat), 125.55 (Cquat), 126.47
† CCDC reference number 207/455. See http://www.rsc.org/suppdata/
p1/b0/b003850o for crystallographic files in .cif format.
References
1 Notable exceptions are: (a) H. J. Kuhn and K. Gollnick, Tetrahedron
Lett., 1972, 1909 (thiophenes reacted at high temperatures);
(b) H. Kotsuki, S. Kitagawa, H. Nishizawa and T. Tokoroyama,
J. Org. Chem., 1978, 43, 1471 (thiophenes reacted under high
pressure); (c) R. Helder and H. Wynberg, Tetrahedron Lett., 1972,
605 (very reactive dienophiles); (d) J. Nakayama and K. Kuroda,
J. Am. Chem. Soc., 1993, 115, 4612 (strained thiophenes).
2 (a) P. H. Benders, D. N. Reinhoudt and W. P. Trompenaars,
Cycloaddition Reactions of Thiophenes, Thiophene 1-oxides, and
Thiophene 1,1-dioxides, in The Chemistry of Heterocyclic
Compounds, ed. S. Gronowitz, 1985, 44, 713; (b) A notable
exception is tetrachlorothiophene S,S-dioxide, which reacts with a
few dienophiles at ambient temperature: M. S. Raasch, J. Org.
Chem., 1980, 45, 856.
3 (a) K. Torssell, Acta Chem. Scand., Ser. B, 1976, 30, 353; (b) A. M.
Naperstkow, J. B. Macaulay, M. J. Newlands and A. G. Fallis,
Tetrahedron Lett., 1989, 30, 5077; (c) C. Thiemann, T. Thiemann,
Y. Q. Li, T. Sawada, Y. Nagano and M. Tashiro, Bull. Chem. Soc.
Jpn., 1994, 67, 1886; (d) Y. Q. Li, T. Thiemann, T. Sawada and
M. Tashiro, J. Chem. Soc., Perkin Trans. 1, 1994, 2323; (e)
(Cquat), 170.51 (Cquat, C᎐O); MS (FAB, 3-nitrobenzyl alcohol)
᎐
m/z (%) 401 (81Br2MHϩ, 7.9), 399 (79Br81BrMHϩ, 14.8),
397 (79Br2MHϩ, 7.2). HRMS Found: 398.9081; calcd. for
C12H15O379Br81BrS: 398.9088 (MHϩ, FAB). Anal. calcd. for
C12H14O3Br2S (398.10) C, 36.20; H, 3.54. Found C, 36.30; H,
3.56%.
Methyl 2-bromo-2-cyclopropylideneacetate 2i (50 mg, 75%)
was recovered.
J. Chem. Soc., Perkin Trans. 1, 2000, 2968–2976
2975

View Article Online
T. Thiemann, Y. Q. Li, S. Mataka and M. Tashiro, J. Chem. Res. (S),
1995, 384; T. Thiemann, Y. Q. Li, S. Mataka and M. Tashiro,
J. Chem. Res. (M), 1995, 2364; ( f ) T. Thiemann, M. L. Sá e Melo,
A. S. Campos Neves, Y. Q. Li, S. Mataka, M. Tashiro, U. Geißler and
D. Walton, J. Chem. Res. (S), 1998, 346.
4 (a) P. Pouzet, I. Erdelmeier, P. Ginderow, J. P. Mornon, D. M.
Dansette and D. Mansuy, J. Chem. Soc., Chem. Commun., 1995,
473; (b) Y. Li, M. Matsuda, T. Thiemann, T. Sawada, S. Mataka and
M. Tashiro, Synlett, 1996, 461; (c) N. Furukawa, S. Zhang, S. Sato
and N. Higaki, Heterocycles, 1997, 44, 61; (d) J. Nakayama,
H. Nagasawa, Y. Sugihara and A. Ishii, J. Am. Chem. Soc., 1997,
115, 9077.
12 T. Thiemann, PhD Dissertation, University of Hamburg, 1992.
13 A. de Meijere, S. Teichmann, F. Sayed-Mahdavi and S. Kohlstruk,
Liebigs Ann. Chem., 1996, 1989.
14 (a) T. Liese, S. Teichmann and A. de Meijere, Synthesis, 1988, 25;
(b) T. Liese, G. Splettstößer and A. de Meijere, Angew. Chem. 1982,
94, 799; T. Liese, G. Splettstößer and A. de Meijere, Angew. Chem.,
Int. Ed. Engl., 1982, 21, 790; Angew. Chem. Suppl., 1982, 1715.
15 T. Heiner, PhD Dissertation, University of Göttingen, 1996.
16 For further cycloaddition reactions of acceptor substituted
methylenecyclopropanes under high pressure, see: T. Heiner, S. I.
Kozhushkov, M. Noltemeyer, T. Haumann, R. Boese and A. de
Meijere, Tetrahedron, 1996, 52, 12185.
5 (a) Y. Li, T. Thiemann, T. Sawada, S. Mataka and M. Tashiro,
J. Org. Chem., 1997, 62, 7926; (b) Y. Li, T. Thiemann, K. Mimura,
T. Sawada, S. Mataka and M. Tashiro, Eur. J. Org. Chem., 1998,
1841; (c) T. Thiemann, Y. Li, C. Thiemann, T. Sawada, D. Ohira,
M. Tashiro and S. Mataka, Heterocycles, 2000, 52, 1215.
6 For a recent review on the synthesis of alkylidenecyclopropanes,
see: A. Brandi and A. Goti, Chem. Rev., 1998, 98, 589.
7 A. Lechevallier, F. Huet and J. M. Conia, Tetrahedron, 1983, 39,
3329.
8 (a) N. F. Osborne, J. Chem. Soc., Perkin Trans. 1, 1982, 1435;
(b) D. Spitzner and H. Swoboda, Tetrahedron Lett., 1986, 27, 1281;
(c) T. Liese, F. Jaekel and A. de Meijere, Org. Synth., 1990, 69, 148;
(d) A. de Meijere, S. I. Kozhushkov, T. Späth and N. S. Zefirov,
J. Org. Chem., 1993, 58, 502; (e) A. de Meijere, S. I. Kozhushkov and
T. Späth, Org. Synth., in the press.
9 (a) A. Lechevallier, F. Huet and J. M. Conia, Tetrahedron, 1983, 39,
3307; (b) F. Huet, A. Lechevallier and J. M. Conia, Tetrahedron
Lett., 1977, 2521.
10 (a) K. Rühlmann, Synthesis, 1971, 236; (b) J. Salaün, J. Org. Chem.,
1976, 41, 1237; (c) J. Salaün and J. Maguerite, Org. Synth., 1985, 63,
147.
17 (a) M. Mauduit, C. Kouklovsky and Y. Langlois, Tetrahedron Lett.,
1998, 39, 6857; (b) S. Trippett and D. M. Walker, J. Chem. Soc.,
1959, 3874.
18 F. Ramirez and S. Dershowitz, J. Org. Chem., 1957, 22, 41.
19 For the preparation and use of further stabilised phosphoranes, see:
T. Thiemann, K. Umeno, D. Ohira, E. Inohae, T. Sawada and
S. Mataka, New J. Chem., 1999, 23, 1067.
20 It has been found that thiophene S-oxides are also deoxygenated
photochemically at room temperature: T. Thiemann, D. Ohira,
K. Arima, T. Sawada, S. Mataka, F. Marken, R. G. Compton, S. D.
Bull and S. G. Davies, J. Phys. Org. Chem., in the press.
21 (a) A. S. Cieplak, J. Am. Chem. Soc., 1981, 103, 4540; (b) A. S.
Cieplak, J. Am. Chem. Soc., 1989, 111, 8447; (c) A. S. Cieplak,
Chem. Rev., 1999, 99, 1265.
22 N. F. Osborne, J. Chem. Soc., Perkin Trans. 1, 1982, 1429.
23 (a) F. Arndt, Org. Synth., 1943, Coll. Vol. 2, 461; (b) F. Arndt, Org.
Synth., 1943, Coll. Vol. 2, 165 (in the reaction of 3c, 3c-II the
ethereal solution of diazomethane was not distilled before use);
(c) see also: Autorenkollektiv, Organikum, VEB Deutscher Verlag
der Wissenschaften 1988, pp. 540, 552–555.
24 A. Altomare, M. Burla, G. Camalli, G. Cascarano, A. Giacovazzo,
G. Guagliardi and J. Polidori, J. Appl. Crystallogr., 1994, 27, 435.
25 G. M. Sheldrick, SHELXL-97, University of Göttingen, 1997.
11 1-Ethoxy-1-trimethylsilyloxycyclopropane is now also commercially
available (from Aldrich Co.).
2976
J. Chem. Soc., Perkin Trans. 1, 2000, 2968–2976