Cycloaddition of thiophene S-oxides to allenes, alkynes and to benzyne

Article abstract of DOI:10.1039/b303091c

Thiophenes have been treated with alkynes in the presence of m-chloroperoxybenzoic acid to give substituted arenes as cycloadducts. Alternatively, thiophene S-oxides have been prepared by oxidation from thiophenes and have been subjected to cycloaddition with alkynes in a subsequent step. The outcome of the reaction is dependent on the steric demand of the thiophene S-oxide. Some thiophene S-oxides can be reacted at temperatures as high as 140°C without decomposition. Thiophenes as deoxygenated products are the main by-products. Reactions of thiophene S-oxides with allenes give in part thiabicyclo[2.2.1]heptene S-oxides of type 12a and 13 along with aromatized products. Thiophene S-oxides also cycloadd to benzyne.

Full text of DOI:10.1039/b303091c

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Cycloaddition of thiophene S-oxides to allenes, alkynes and to
benzyne
Thies Thiemann,*a Hideki Fujii,b Daisuke Ohira,b Kazuya Arima,b Yuanqiang Lib and
Shuntaro Matakaa
a
Institute of Advanced Material Study, Kyushu University, 6-1, Kasuga-koh-en, Kasuga-shi,
Fukuoka 816-8560, Japan. E-mail: thies@cm.Kyushu-u.ac.jp
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1,
Kasuga-koh-en, Kasuga-shi, Fukuoka 816-8560, Japan
b
Received (in Montpellier, France) 14th March 2003, Accepted 2nd May 2003
First published as an Advance Article on the web 9th July 2003
Thiophenes have been treated with alkynes in the presence of m-chloroperoxybenzoic acid to give
substituted arenes as cycloadducts. Alternatively, thiophene S-oxides have been prepared by oxidation
from thiophenes and have been subjected to cycloaddition with alkynes in a subsequent step. The
outcome of the reaction is dependent on the steric demand of the thiophene S-oxide. Some thiophene
S-oxides can be reacted at temperatures as high as 140 ꢀC without decomposition. Thiophenes as
deoxygenated products are the main by-products. Reactions of thiophene S-oxides with allenes give in part
thiabicyclo[2.2.1]heptene S-oxides of type 12a and 13 along with aromatized products. Thiophene
S-oxides also cycloadd to benzyne.
Introduction
Until about 10 years ago, thiophene S-oxides1 2 were quite
elusive molecules. They had been postulated as reactive inter-
mediates in the peracid-mediated oxidation of thiophenes 1
to thiophene S,S-dioxides, where dimerisation products, so-
called sesquioxides,2 could be isolated that clearly stemmed
from the reaction of intermediately formed thiophene S-oxi-
des 2, reacting in these cases as both dienes and dienophiles.
Later these reactive species were prepared and reacted in situ
with a number of alkenes, where again the intermediate thio-
phene S-oxides 2 reacted as dienes in a formal [4 + 2]-cyclo-
addition,3 but where the thiophene S-oxides were not isolated
as such. Nevertheless in the last 8 years, two main routes
towards the synthesis of these compounds have been estab-
lished: a) by oxidation of the corresponding thiophenes;4
and b) by the reaction of alkynes with zirconocene dichloride
via the corresponding substituted zirconacyclopentadienes,
Scheme 1 Synthesis of thiophene S-oxides 2a–c.
which with sulfur dioxide or thionyl chloride are transformed
to the thiophene S-oxides.5 (Scheme 1) Also these isolated
thiophene S-oxides are effective dienes in [4 + 2]-cycloaddition
reactions with alkenes,6 where alkenes, that are normally sus-
ceptible to reaction with peracids, such as methylenecyclopro-
panes,6c also can be used. Often, the sulfur originating from
the thiophene can be extruded in a subsequent step from
the primary cycloadducts. This method not only presents a
two-step route to functionalised arenes from thiophenes under
mild conditions, but may also may point to a way of desulfur-
izing thiophene containing fuels, although in the latter case
the nature of the oxidant needs to be changed; dibenzothio-
phenes, however, will not be converted. It is not yet clear what
versatility thiophene S-oxides 2 possess as dienes in [4 + 2]-
cycloaddition reactions. In the following the reactivity of
thiophene S-oxides 2, both as reactive intermediates and as
isolated species, towards alkynes, allenes and benzyne will
be discussed.
Results and discussion
Cycloaddition of thiophene S-oxides with alkynes
Substituted thiophene S-oxides 2 may be viewed as reactive
dienes and can be utilized as the 4p-component in Diels–Alder
type reactions.3,6 When thiophenes 1 are reacted with m-chloro-
peroxybenzoic acid in the presence of alkynes 3 substituted
arenes 6 can be isolated, albeit in varying and usually in quite
low yields (Table 1). These reactions are run in dichloro-
methane at 0 ꢀC. In order for the reactions to proceed, the
alkynes have to be substituted with electron-withdrawing sub-
stituents and the thiophenes have to be substituted at least at
positions C2/C5 with electron donating groups. In the reac-
tions, thiophene S-oxides are produced in situ, which cycloadd
to the alkynes (Scheme 2). Thiabicyclo[2.2.1]heptadienes 5 as
DOI: 10.1039/b303091c
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Table 1 Cycloaddition of thiophene S-oxides prepared in situ with
alkynes
the primary cycloadducts cannot be isolated, but sponta-
neously extrude the SO-bridge under the conditions used to
form the substituted aromatic compounds 6. In these reactions
it could be seen that both electronic factors as well as steric fac-
tors play an important role in the outcome of the reaction,
especially to determine whether the cycloaddition proceeds at
all. Generally, the limiting factors peculiar to thiophene S-oxi-
des are the ease of self dimerisation, shared with some other
cyclic dienes, and the oxidation of the thiophene S-oxides to
thiophene S,S-dioxides, when the reactions are performed
under these oxidizing conditions. The thiophene S,S-dioxides
are not reactive as dienes under the conditions described, but
necessitate higher reaction temperatures.
It is much more difficult to oxidize thiophenes with electron-
withdrawing substituents (Scheme 3). Nevertheless, it is possi-
ble to subject methyl thienylcarboxylates such as 1e and 1f
to an oxidative cycloaddition when heating a mixture of 1e
or 1f with an excess of acetylene in presence of m-CPBA.
The product, however, can only be isolated in a low yield.
Additionally, the reaction times are long.
Alternatively, thiophene S-oxides with electron-donating or
slightly electron-withdrawing substituents can be prepared and
isolated. Then, they can be reacted with alkynes in a second
step. For these studies, three differently substituted thiophene
S-oxides, tetraphenylthiophene S-oxide (2c), tetramethylthio-
phene S-oxide (2b), and di-tert-butylthiophene S-oxide (2a)
have been used. 2c is a sterically congested compound with
substituents of slightly withdrawing nature. 2b is sterically a
less exacting molecule with electron donating substituents,
while 2a is sterically hindered, where the tert-butyl groups
are electron-donating. 2c was prepared by the reaction of
diphenylethyne (tolane) (1) with zirconocene dichloride,5 while
2a and 2b were obtained from the oxidation of tetra-
methylthiophene (1b) and 2,5-di-tert-butylthiophene (1a),
respectively, with m-CPBA in the presence of BF3ꢁEt2O as a
Lewis acid catalyst (Scheme 1).4b,6a,7 When the thiophene
S-oxides were reacted with alkynes with one or both substitu-
Scheme 3 Oxidative cycloaddition of electron-poor thiophenes with
alkynes.
ents of electron-withdrawing character, the reactions pro-
ceeded smoothly to give the aromatic products in good
yields (Table 2). Side products were the thiophenes, which
are produced at higher temperature by simple deoxygena-
tion. Mixing of thiophene S-oxide 2b and dimethyl acetylene-
dicarboxylate (3b) without addition of solvent resulted
in an exothermic reaction. Tolane (3h) on the other hand
did not react with either 2b or 2c. When 2b was reacted
with phenylacetylene as a solvent at 100 ꢀC, 6u could be
isolated.
For alkynes with two electron withdrawing groups the thio-
phene S-oxide is the preferable reaction partner when com-
pared to an analogously substituted thiophene S,S-dioxide.
When higher reaction temperatures are necessary, such as with
sterically more demanding alkynes, the thiophene S,S-diox-
ides8 are more advantageous to use. While their reactivity
may be lower, their stability is inherently greater, as side reac-
tions due to deoxygenation of the starting material can be
avoided. Also, the dimerisation of similarly substituted thio-
phene S,S-dioxides can be suppressed more readily than with
the thiophene S-oxides. In general, the tetraphenylcyclopenta-
dienone (tetracyclone) (7), which has been frequently used as
the diene component in [4 + 2]-cycloaddition reactions,9 most
recently also in the preparation of novel materials,10 gives
slightly higher yields than tetraphenylthiophene S-oxide (2c),
when reacted with the same alkynes (Scheme 4).
It must be remarked, however, that tetraphenylthiophene
S-oxide (2c) is compatible with reaction temperatures as high
as 140 ꢀC (Scheme 5). This can be seen in the reaction of 2c
with ethyl o-tolylpropiolate (3i). Reaction of 2,5-di-tert-
butylthiophene S-oxide (2a) with dimethyl acetylenedicarbox-
ylate (3b) at 135 ꢀC also gave the cycloadduct as product,
albeit with a larger amount of thiophene 1a as the deoxy-
genation product.11 On the other hand, the tetramethyl-
substituted analog can decompose even at temperatures as
low as 100 ꢀC, if it cannot react with its partner at that
temperature.
Thiophene S-oxides are non-planar compounds.12 Thus, the
X-ray of 2,5-diphenylthiophene S-oxide has shown that the
pyramidalised sulfur is positioned outside of the plane defined
by the four carbon atoms of the heterocyclic structure. The
oxygen of the sulfoxy-moiety is located on the opposing
side of the ring. In contrast, the cyclopentadienone system in
tetraphenylcyclopentadienone is planar.13 Consequently, the
thiophene S-oxide is sterically more exacting than the cor-
responding cyclopentadienones.
Scheme 2
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Table 2 Cycloaddition of thiophene S-oxides with alkynes
While dibenzothiophene S-oxides14 in their reactivity may
be viewed as sulfoxy bridged biphenylenes rather than dibenzo-
annelated thiophene S-oxides, benzothiophene S-oxides still
possess chemical reactivity partly reminiscent of the non-anne-
lated thiophene S-oxides. The study of 2-methylbenzo[b]thio-
phene S-oxide (8)8 and of a number of aryl-substituted
benzothiophene S-oxides showed that these molecules can also
be subjected to cycloaddition reactions with alkynes and also
alkenes, albeit at higher temperatures and under long reaction
times. Reaction products are naphthalenes in the case of the
reactions with alkynes and phthalimidodihydronaphthalenes
in the case of the reaction with N-phenylmaleimide. Again,
deoxygenation of the benzothiophene S-oxide to the ben-
zothiophenes 10 is the main side-reaction (Scheme 6). Other
cycloaddition reactions of this sort with the aromatic ring
system providing part of the diene system have only been
infrequently reported. Examples have come from cyclo-
addition reactions of methylindenes16 and of phenaleno[1,9-
bc]furan17 with dimethyl acetylenedicarboxylate.
and cycloadducts had been obtained as a single diastereo-
isomer in relatively good yield.6c Due to the oxidizability of
the strained olefin, some thiophene S-oxide was lost at the
time due to deoxygenation. Taking the reaction one step fur-
ther, from ethyl acrylate via ethyl cyclopropylideneacetate,
the authors decided to look at the reactivity of the thiophene
S-oxides towards allenes 11 (Scheme 7), such as towards ethyl
propadienoate (11b). When comparing 11b and ethyl cyclopro-
pylideneacetate,6c it is evident that the olefinic moiety in 11b
possesses less strain energy than that of the methylenecyclo-
propane, nevertheless, mono-substituted 11b is sterically less
exacting than cyclopropylideneacetate.
On the other hand, cycloaddition of 11b to thiophene S-oxi-
des 2 would give bridged thiabicyclo[2.2.1]heptene S-oxides
such as 13, which additionally possess an exo-methylene func-
tion. It is known that the cycloaddition of methylenecyclo-
propanes results in the formation of a spirocyclopropane unit,
which is quite stable under the conditions of its formation and
suppresses the extrusion of the SO-bridge and the concurrent
aromatisation of the molecules. On the other hand,
Cycloaddition of thiophene S-oxides with allenes
Reactions of thiophene S-oxides such as 2b with alkylidene-
cyclopropanes have already been carried out by the authors6c
Scheme 4
Scheme 5 Reactions of thiophene S-oxides at elevated temperatures.
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at the sulfur is explained by a p-selectivity in the cycloaddition
due to the ‘‘Cieplak-effect’’, an effect first proposed by Cie-
plak18 to account for the directing effects of remote substitu-
ents in addition reactions to substituted cyclohexanones.
Cycloadditions of thiophene S-monoxides have been predicted
to occur anti to the lone electron-pair on the sulfur, which is
the better hyperconjugative donor when compared to the oxy-
gen of the sulfoxy-moiety. The lone-pair electron orbital at the
sulfur will stabilize the vacant s*-orbitals of the developing
incipient s-bonds better than would any orbital associated
with the oxygen. The activation barriers of both syn- and
anti-addition have been calculated previously by semi-empiri-
cal methods19 for dimethylthiophene S-oxide and maleic
anhydride as well as at the RHG/6-31G* level for thiophene
S-oxide and ethylene, where the barrier for the syn-addition
was found to be lower by 9 kcal molꢂ1 than that for the
anti-addition.6d
Interestingly, in the reaction of the tetraphenylthiophene
S-oxide (2c) and allene 11b only the aromatized products
14a and 14b could be isolated. This seems to indicate that
the steric factor is important for the non-selectivity of the
attack, i.e. both olefinic moieties of the allene react equally;
while one is favored electronically, as can be seen in the reac-
tion of 2b with 11b, the other is favored sterically. Also the
aromatisation of the primary cycloadduct decreases some
steric congestion.
Scheme 6 Cycloaddition of 2-methylbenzothiophene S-oxide (8).
aromatisation is seen partly in the reaction of thiophene S-oxi-
des with 1,2-disubstituted alkenes. Thus, some aromatisation
was expected to occur in the case of the reaction of 2b with
ethyl propandienoate (11b) via isomerisation of the exo-olefin
to an endo-olefin, which, as a thiabicyclo[2.2.1]heptadiene S-
oxide, would spontaneously extrude the SO-bridge and would
form a functionalized arene. Surprisingly, when 2b was heated
with 11b in chloroform at 60 ꢀC for 12 h only the cycloadduct
13 could be observed. The yield is very close to that found for
the same reaction of a thiophene S-oxide with ethyl cyclopro-
pylidene acetate.6c Pertinent 13C NMR data of the compound
13 (Fig. 1) are the chemical shifts, dC ¼ 69/75 ppm, of the two
quaternary carbons, which are indicative for the bridge head
carbons of the sulfoxy bridge; also informative are the absorp-
tions of the carbons of the exo-methylene functionality with
the methylene carbon at dC ¼ 111 ppm and the quaternary
carbon at dC ¼ 147 ppm. 13 is formed as one isomer only.
Because of the evidence collected from cycloadducts of thio-
phene S-oxides with alkenes both by the authors as well as
by others, it can be inferred that the stereochemistry of 13 is
endo with the lone pair of the electron pair on sulfur pointing
towards the newly formed double bond within the carbocyclic
framework. The stereoselective formation of the chiral centre
As the appended phenyl substituents are not in full conjuga-
tion to the aromatic core, due to out of plane rotation, stabi-
lisation through conjugation with the phenyl substituents
may not necessarily play an important role in the release of
the sulfoxy bridge, when one compares the situation with that
of the reaction of 2c with 11c, where cycloadduct 16a can be
isolated, although also here a larger amount of aromatized
16b is formed.
Scheme 7 Cycloaddition reactions of thiophene S-oxides with allenes.
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S,S-dioxides,23 the yield of the former is better, most likely
due to the lower reaction temperature used.
Conclusions
In conclusion, thiophene S-oxides react as diene component
with alkynes, where the best yields are obtained when the
thiophene S-oxides are donor, the alkynes are acceptor substi-
tuted. While strongly electron-acceptor substituted thiophene
S-oxides have not yet been isolated in pure form, the corres-
pondingly substituted thiophenes can be made to undergo oxi-
dative cycloaddition reactions with alkynes under forcing
conditions. The reaction of thiophene S-oxides with allenes
furnishes in part thiabicyclo[2.2.1]heptene S-oxides with an
exo-methylene unit. Thiophene S-oxides also react with
benzyne, formed in situ.
Fig. 1 Typical 13C-NMR data of methylenethiabicyclo[2,2,1]heptene
S-oxides.
Reaction of tetramethylthiophene S-oxide (2b) and phenyl-
allene (11a) again leads to two products, 12a and 12b, stem-
ming from comparative reactivity of the two olefinic moities
of the allene. Here, the phenyl substituted olefinic moiety is
not as favored electronically as in 11b and thus a greater reac-
tivity balance is found between the sterically less exacting, non-
substituted olefinic moiety and the phenyl substituted moiety.
No aromatized products have been isolated from this reaction.
With the donor substituent allene 11c, tetramethylthiophene
S-oxide (2b) and tetraphenylthiophene S-oxide (2c) show
comparative reactivity. Both react at the non-substituted side.
In both cases similar yields are found and similar amounts of
aromatized product are observed. The initially formed enol
ethers, which can be observed by 1H NMR spectroscopy before
the work up, albeit not in a pure state, are hydrolysed during
work up to the corresponding aldehydes 15a/b and 16a/b.
Experimental
General methods and materials
Melting points were measured on a Yanaco microscopic hot-
stage and are uncorrected. Infrared spectra were measured
with JASCO IR-700 and Nippon Denshi JIR-AQ2OM machi-
nes.1H- and 13C-NMR spectra were recorded with a JEOL
EX-270 spectrometer. The chemical shifts are relative to
TMS (solvent CDCl3 , unless otherwise noted). Partly the
interpretation of the 13C-NMR data was aided by DEPT (Dis-
tortionless Enhancement by Polarisation Transfer) experi-
ments: (+) denotes primary and tertiary, (ꢂ) secondary and
Cquat quaternary carbons. Mass spectra were measured with
a JMS-01-SG-2 spectrometer (EI, 70 eV). Column chromato-
graphy was carried out on Wakogel 300. All experiments were
purged with argon at the start.
Cycloaddition of thiophene S-oxide to benzyne
In their study of the reactivity of substituted thiophene S-oxi-
des as diene components in Diels–Alder type reactions, the
authors have also recently employed benzyne (19) as the ene-
component. While there are a number of methods20 towards
the preparation of benzyne, in this case it was important to
use a procedure under mild, non-reductive and not too basic
conditions. This is offered by the method of T. Kitamura
et al.21 from o-(trimethylsilyl)phenyl(phenyl)iodonium triflate
(17), which can be prepared from o-dichlorobenzene in two
steps. When tetrabutylammonium fluoride is added to 1722 in
THF, benzyne is formed in situ. It can be reacted with thio-
phene S-oxides. When a 1:1 mixture of thiophene S-oxide
2d6c and 19 (i.e., in situ derived from 17) were reacted accord-
ingly, the cycloadduct 18 was obtained in 55% yield (Scheme 8).
The reaction of 5 eq. of tetraphenylthiophene S-oxide (2c) with
17 at rt gave the respective cycloadduct in quantitative yield, as
calculated on 2c. A very good indication that from their chemi-
cal behavior, dibenzothiophene S-oxides should not be viewed
as annelated thiophene S-oxides but rather as sulfoxy-bridged
diaryls can be obtained from the fact that dibenzothiophene
S-oxide is totally unreactive towards benzyne (29) under the
conditions described above. When one compares the outcome
of the cycloaddition of thiophene S-oxide to benzyne with
published cycloaddition reactions of benzyne with thiophene
Dibenzoylacetylene (3e) was prepared from 1,2-dibenzoyl-
ethene by
a bromination/dehydrobromination [(a) Br2 ,
CCl4 ; (b) Et3N, benzene, 80 ꢀC] procedure. 3d was synthesized
from glyoxylic acid monohydrate via Wittig reaction with
carbomethoxymethylidenetriphenylphosphorane, addition of
bromine to the ensuing olefin (Br2 , CCl4), methylation of the
carboxylic acid (diazomethane) and dehydrobromination
(Et3N, benzene, 80 ꢀC). Allenes 11a, 11b, and 11c were pre-
pared by known methods.24 Phenylallene [phenylpropadiene]
(11a) was synthesized in a two step procedure via Skattebøl
rearrangement of 1,1-dibromo-2-phenylcyclopropane (MeLi,
ether).24a 1,1-Dibromo-2-phenylcyclopropane itself was pre-
pared by dibromocarbene addition to styrene, where the reac-
tion was run as a two-phase reaction under PTC-conditions
(bromoform, triethylbenzylammonium bromide, 50% aq.
NaOH, styrene)24b Allene 11b was prepared by Wittig olefina-
tion of acetyl chloride with ethoxycarbonylmethylidenetriphe-
nylphosphorane (Et3N, CH2Cl2).24c Octyloxyallene (11c) was
obtained in a two step procedure from propargyl bromide
by etherification with n-octanol to octylpropargyl ether and
subsequent base induced alkyne–allene isomerisation.24d
Thiophene S-oxides 2a,7 2b,6a 2c5 and 2d6c and dibenzothio-
phene S-oxide were prepared by oxidation of the correspond-
ing thiophenes and of dibenzothiophene, respectively. Also,
2-methylbenzothiophene S-oxide (8)15 was synthesized by oxi-
dation of 2-methylbenzothiophene (10) (m-CPBA, BF3ꢁEt2O,
CH2Cl2 , ꢂ18 ꢀC, 72%).
Transformations - representative examples25,26
In situ reaction of an electron-acceptor substituted thio-
phene with an alkyne. Oxidative cycloaddition of methyl
4,5-dimethylthiophenecarboxylate (1f) with dimethyl acetylene-
dicarboxylate (3b). A solution of methyl 4,5-dimethyl-
thiophenecarboxylate (1f) (222 mg, 1.30 mmol), dimethyl
Scheme 8 Reaction of a thiophene S-oxide with benzyne.
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acetylenedicarboxylate (3b) (927 mg, 6.53 mmol) and m-CPBA
(675 mg, 70 wt%, 2.74 mmol) was stirred under reflux for 85 h.
The cooled reaction mixture was poured into 10 wt% aq.
Na2CO3 . The mixture was stirred for 15 min. and then
the layers were separated. The organic layer was dried over
anhydrous MgSO4 and concentrated in vacuo. Column chro-
matography of the residue on silica gave trimethyl 4,5-
dimethylbenzene-1,2,3-tricarboxylate (6g) as a colorless solid
(55 mg, 0.20 mmol, 15%) Rf 0.2 (hexane/ether 1:1) mp 92–
93 ꢀC; IR (KBr) n 2996, 2952, 2848, 1726, 1436, 1283, 1247,
3-nitrobenzylalcohol) m/z (%) 498 (M+, 32), 467 (M+
ꢂ CH3O, 53). Calcd. for: C44H30O2 : C, 89.46; H, 5.12. Found:
C. 89.16; H, 5.17%.
Cycloaddition of 2-methylbenzo[b]thiophene S-oxide (8) with
dimethyl acetylenedicarboxylate (3b). A solution of 2-methyl-
benzo[b]thiophene S-oxide (8) (82 mg, 0.5 mmol) and dimethyl
acetylenedicarboxylate (3b) (172 mg, 1.0 mmol) in benzene (2
mL) was held at 80 ꢀC for 34 h. Thereafter, the cooled reaction
mixture was concentrated in vacuo. Column chromatography
of the residue on silica gel (hexane/ether 3:1) gave 2-methyl-
benzo[b]thiophene (10) (50 mg, 61%) and dimethyl 3-methyl-
naphthalene-1,2-dicarboxylate (9a) (45 mg, 35%): IR (KBr) n
2950, 2924, 2850, 1732, 1438, 1276, 1236, 1203, 1179, 1136,
1
1195, 1030, 1001, 961 cmꢂ1; H NMR (270 MHz, CDCl3) d
2.31 (s, 3H, CH3), 2.35 (s, 3H, CH3), 3.88 (s, 3H, COOCH3),
3.89 (s, 3H, COOCH3), 3.90 (s, 3H, COOCH3), 7.73 (s, 1H)
13C NMR (67.9 MHz, CDCl3) d 16.95, 20.31, 52.58, 52.74,
127.19, 130.89, 132.06, 133.01, 139.14, 139.89, 166.36, 168.17,
168.26; MS (70 eV) m/z (%) 280 (M+, 4.0), 249 (M+ ꢂ CH3O,
100), 248 (M+ ꢂ CH4O, 70). Anal. Calcd. for C14H16O6
(280.31): C, 59.99; H, 5.76. Found: C, 60.12; H, 5.87%.
1068 cmꢂ1 1H NMR (270 MHz, CDCl3) d 2.56 (s, 3H,
;
CH3), 3.94 (s, 3H, COOCH3), 3.99 (s, 3H, COOCH3), 7.51–
7.56 (m, 2H), 7.77 (m, 2H), 8.07–8.12 (m, 1H) 13C NMR
(67.8 MHz, CDCl3 , DEPT 90, DEPT 135) d 20.47 (+, CH3),
52.51 (+, COOCH3), 52.69 (+, COOCH3), 125.71 (+, CH),
127.13 (+, CH), 127.53 (+, CH), 127.74 (+, CH), 128.17
(Cquat), 130.49 (Cquat), 131.28 (Cquat), 131.71 (+, CH), 132.36
Cycloaddition of an isolated thiophene S-oxide with an
alkyne. Preparation of methyl 2-benzoyl-3,6-bis(tert-butyl)-
benzoate (6s). A solution of 2,5-di-tert-butylthiophene S-oxide
(2a) (106 mg, 0.5 mmol) and methyl 3-benzoylpropiolate (3d)
(94 mg, 0.5 mmol) in benzene (2 mL) was kept at 80 ꢀC for
36 h. Thereafter, the mixture was separated by column chro-
matography on silica gel (benzene) to give methyl 2-benzoyl-
3,6-bis-(tert-butyl)benzoate (6s) (40 mg, 23%) IR (neat) n
3064, 2960, 2870, 1733, 1675, 1450, 1362, 1283, 1260, 1241,
1204, 1170, 1107, 713, 653 cmꢂ1; 1H NMR (270 MHz, CDCl3)
d 1.26 (s, 9H, But), 1.35 (s, 9H, But), 3.28 (s, 3H, COOCH3),
7.32–8.25 (m, partially broad, 7H) 13C NMR (67.8 MHz,
CDCl3) d 35.81, 36.23, 51.61, 127.83, 128.12, 128.33, 128.68,
128.96, 129.34, 131.12, 133.33, 136.98, 138.18, 136.98, 144.62,
145.37, 170.40, 199.62; MS (70 eV) m/z (%) 352 (M+, 1.4),
=
(Cquat), 134.07 (Cquat), 168.37 (Cquat , C O), 168.68 (Cquat
,
+
=
C O) MS (70 eV) m/z (%) 258 (M , 60), 227 (96), 226 (96),
168 (100). HRMS Found: 258.0894. Calcd. for C15H14O4 :
258.0892.
Cycloaddition reaction of a thiophene S-oxide with an allene.
A mixture of phenylpropadiene (11a) (100 mg, 0.86 mmol) and
tetramethylthiophene S-oxide (2b) (134 mg, 0.86 mmol) in
chloroform (1 mL) was placed into a pressure tube and deaer-
ated. Then, the mixture was stirred at 60 ꢀC for 12 h. The pro-
ducts were separated by column chromatography on silica gel
and by TLC plate to give 12a (60 mg, 26%) and 12b (41 mg,
18%). (12a): IR (KBr) n 3056, 3030, 2970, 2924, 1642, 1598,
105 (C6H5CO+, 100), 77 (C6H+
,
352.2032. Calcd. for C23H28O3 : 352.2038.
59). HRMS Found:
1492, 1449, 1376, 1090, 1063, 913, 768, 705 cmꢂ1; H NMR
1
5
(270 MHz, CDCl3) d 1.30 (s, 3H, CH3), 1.37 (s, 3H, CH3),
1.59 (s, 3H, CH3), 1.81 (s, 3H, CH3), 4.12 (m, 1H)**, 5.05
(d, 1H, 2J 2.3 Hz), 5.18 (d, 1H, 2J, 2.3 Hz), 6.98–7.02 (m,
2H, phenyl-H), 7.23–7.27 (m, 3H, phenyl-H) 13C NMR (67.8
MHz, DEPT 90, DEPT 135) d 10.57 (+, CH3), 10.98 (+,
CH3), 12.29 (+, CH3), 12.64 (+, CH3), 53.53 (+, CH), 70.91
(Cquat), 75.54 (Cquat), 111.57 (ꢂ), 127.06 (+, CH), 128.12 (+,
CH), 129.42 (+, CH), 130.69 (Cquat), 131.68 (Cquat), 139.23
Cycloaddition of a thiophene S-oxide with an alkyne at an
elevated temperature. Synthesis of ethyl 2-(o-tolyl)-3,4,5,6-
tetraphenylbenzoate (6w). A mixture of ethyl o-tolylpropiolate
(3i) (47 mg, 0.25 mmol) and tetraphenylthiophene S-oxide
(2c) (50 mg, 0.125 mmol) in diphenyl ether (800 mg) was
heated under argon at 130 ꢀC for 10 h. Column chromato-
graphy on silica gel (hexane/ether 10:1) gave ethyl 2-(o-
tolyl)-3,4,5,6-tetraphenylbenzoate (6w) (30 mg, 44%) as a
colorless solid: IR (KBr) n 3054, 3024, 2978, 2924, 1730,
1
(Cquat), 152.24 (Cquat) (12b): H NMR (270 MHz, CDCl3) d
1.52 (s, 3H, CH3), 1.63 (s, 3H, CH3), 1.70 (s, 3H, CH3), 1.74
2
4
(s, 3H, CH3), 2.61 (dd, 1H, J 16.2 Hz, J 2.0 Hz), 3.09 (dd,
1H, 2J 16.2 Hz, 4J 1.8 Hz), 6.31 (dd, 4J 2.0 Hz, 4J 1.8 Hz),
7.20–7.42 (m, 5H) 13C NMR (67.8 MHz, CDCl3 , DEPT 90,
DEPT 135) d 11.00 (+, CH3), 11.50 (+, CH3), 13.64 (+,
CH3), 15.24 (+, CH3), 37.38 (ꢂ), 67.64 (Cquat), 77.70 (Cquat),
124.60 (+, CH), 126.92 (+, CH), 128.24 (+, CH), 129.45 (+,
CH), 131.50 (Cquat), 132.60 (Cquat), 137.34 (Cquat), 141.04
(Cquat). *The assignment of the C-signals has been aided by
DEPT experiments (DEPT ¼ Distortionless Enhancement of
Polarisation Transfer), where (+) denotes primary and tertiary
carbons, (ꢂ) secondary carbons and (Cquat) quaternary car-
bons. **1H–1H COSY experiment shows that in 12a there
is a long-range coupling between the methine proton on the
carbocycle adjacent to the phenyl substituent and both
exo-methylene protons; from the 270 MHz 1H NMR spectrum
it has not been possible to obtain the coupling constants for
either of the couplings.
1601, 1495, 1441, 1406, 1327, 1229, 1158, 1063, 697 cmꢂ1
;
1H NMR (270 MHz, CDCl3) d 0.67 (t, 3H, J 7.2 Hz), 2.11
(s, 3H, CH3), 3.61 (q, 2H, 3J 7.2 Hz), 6.71–7.31 (m, 24H)
13C NMR (67.8 MHz, CDCl3) d 13.31, 20.49, 60.45, 124.33,
125.44, 125.53, 125.66, 126.36, 126.57, 126.61, 126.66, 127.22,
127.27, 129.16, 129.97, 130.17, 130.33, 130.72, 131.12, 131.25,
131.34, 131.44, 136.55, 137.77, 138.29, 139.17, 139.21, 139.42,
139.89, 140.29, 140.36, 142.05, 168.66; MS (FAB, 3-nitro-
benzyl alcohol) m/z (%) 545 (MH+, 18), 544 (M+, 16), 499
(M+ ꢂ C2H5O, 14)
3
Comparative cycloaddition of tetraphenylcyclopentadienone
[tetracyclone] (7) and of tetraphenylthiophene S-oxide (2c).
Synthesis of dimethyl 3,4,5,6-tetraphenylbenzene-1,2-dicarboxy-
late (6i). Method A: A mixture of tetracyclone (7) (100 mg,
0.26 mmol) and dimethyl acetylenedicarboxylate (3b) (140
mg) in chloroform (2 mL) was kept at 70 ꢀC for 9 h. There-
after, the mixture was subjected to column chromatography
on silica gel to give the starting material, tetracyclone (7),
(11 mg, 11%) and 6i (140 mg, 80%). Method B: A mixture of
tetraphenylthiophene S-oxide (2c) (100 mg, 0.247 mmol) and
dimethyl acetylenedicarboxylate (3b) (140 mg, 1.0 mmol) in
chloroform (2 mL) was kept at 70 ꢀC for 10 h. Column chro-
matography on silica gel gave 6i (87 mg, 71%). MS (FAB,
1,4-Dimethyl-2,3-bis(p-methoxyphenyl)naphthalene (18). reac-
tion of a thiophene S-oxide with benzyne, formed in situ.
At 0 ꢀC and within 10 min, a solution of tetra-n-butylammo-
nium fluoride (TBAF) (78 mg, 0.3 mmol) in THF (0.5 mL)
was slowly added to a mixture of 2d (68 mg, 0.2 mmol) and
17 (100 mg, 0.2 mmol) in CH2Cl2 (1 mL). The resulting solu-
tion was stirred for 1 h at rt. Then, water (5 mL) was added
1382
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Brand, A. J. Berresheim, L. Przybilla, H. J. Rader and K. Mullen,
¨
Chem. Eur. J, 2002, 8, 1424
and the reaction mixture was extracted with CH2Cl2 (3 ꢃ 5
mL). The organic phase was dried over anhydrous MgSO4
and concentrated in vacuo. The residue was subjected to col-
umn chromatography on silica gel to give 18 (40 mg, 55%)
as colorless needles: IR (KBr) n 3064, 2992, 2920, 1610,
11 (a) For commentary on the deoxygenation of thiophene S-oxides,
see: ref. 1a and K. Kumazoe, K. Arima, S. Mataka, D. Walton
and T. Thiemann, J. Chem. Res., 2003, (S) 60; (M) 248; (b) For
photochemical deoxygenation at lower temperatures, see: K.
Arima, D. Ohira, S. Mataka and T. Thiemann, submitted to
Photochem. Photobiol. Sci.
12 (a) P. Pouzet, I. Erdelmeier, D. Ginderow, J.-P. Mornon, P. M.
Dansette and D. Mansuy, J. Heterocycl. Chem., 1997, 34, 1567;
(b) Also, calculations have predicted the non-planarity of thio-
phene S-oxides: J. A. Hashmall, V. Horak, L. E. Khoo, C. O.
Quicksall and M. K. Sun, J. Am. Chem. Soc., 1981, 103, 289;
(c) J. S. Amato, S. Karady, R. A. Reamer, H. B. Schlegel, J. P.
Springer and L. M. Weinstock, J. Am. Chem. Soc., 1982, 104,
1375; (d ) I. Rojas, J. Phys. Org. Chem., 1992, 5, 74.
1
1513, 1286, 1035, 759 cmꢂ1; H NMR (270 MHz, CDCl3) d
2.43 (s, 6H, 2 CH3), 3.75 (s, 6H, 2 OCH3), 6.70 (d, 2H, 3J
3
8.7 Hz), 6.87 (d, 2H, J 8.7 Hz), 7.56 (m, 2H), 8.12 (m, 2H)
13C NMR (67.8 MHz, CDCl3 , DEPT 90, DEPT 135)* d
16.87 (2C, 2 CH3), 55.07 (2C, 2 OCH3), 125.01 (2C, CH),
125.62 (2C, CH), 129.77 (2C, Cquat), 131.37 (4C, CH), 132.02
(2C, Cquat), 134.30 (2C, Cquat), 139.44 (2C, Cquat), 157.52
(2C, Cquat) MS (70 eV) m/z (%) 368 (M+, 100). HRMS Found:
368.1779. Calcd. for C26H24O2 : 368.1776 (M+).
13 J. C. Barnes, W. M. Horspool and F. I. Mackie, Acta Crystallogr.,
Sect. C, 1991, 164.
14 (a) For a review on dibenzothiophene S-oxides, see: T. Thiemann,
K. Arima and S. Mataka, Rep. Inst. Adv. Mat. Study Kyushu
Univ., 2000, 14(1), 37–45; Chem. Abstr., 2001, 134, 173 925u; (b)
for a review on benzothiophene S-oxides, see: T. Thiemann, K.
Arima, K. Kumazoe and S. Mataka, Rep. Inst. Adv. Mat. Study
Kyushu Univ., 2000, 14(2), 139–148; Chem. Abstr., 2001, 326,
134 318a.
References
1
(a) For a recent review on thiophene S-oxides, see: T. Thiemann and
K. Gopal Dongol, J. Chem. Res. (S), 2002, 303.; (b) See also :
J. Nakayama, Bull Chem. Soc. Jpn., 2000, 73, 1; (c) J.
Nakayama and Y. Sugihara, Sulfur Rep., 1997, 19, 349.
2
(a) M. Prochazka, Collect. Czech Chem. Commun., 1965, 30, 1158;
(b) W. Davies, N. Gamble, F. C. James and W. Savige, Chem. Ind.
(London), 1952, 804; (c) J. Melles and H. J. Backer, Recl. Trav.
Chim. Pays-Bas, 1953, 72, 491; (d ) W. Davies and F. C. James,
J. Chem. Soc., 1954, 15; (e) K. Okita and S. Kambara, Kogyo
Kagaku Zasshi, 1956, 59, 547; ( f ) W. J. M. van Tilborg, Synth.
Commun., 1976, 6, 583; (g) R. E. Merrill and G. Sherwood,
J. Heterocycl. Chem., 1977, 14, 1251.
15 2-Methylbenzothiophene S-oxide (8) is a known material which
had been synthesized previously from the corresponding
benzothiophene by oxidation with p-nitroperoxybenzoic acid:
´
P. Geneste, J. Grimaud, J. L. Olive and S. N. Ung, Bull. Soc.
Chim. Fr., 1977, 271.
16 D. W. Jones, J. Chem. Soc., Perkin Trans. 1, 1979, 673.
17 S. Weeralungo, M. Austrup and R. Rodrigo, J. Chem. Soc.,
Perkin Trans. 1, 1988, 3169.
3
(a) K. Torssell, Acta Chem. Scand. (Ser. B), 1976, 353; (b) A. M.
Naperstkow, J. B. Macaulay, M. J. Newlands and A. G. Fallis,
Tetrahedron Lett., 1989, 30, 5077; (c) Y.-Q. Li, T. Thiemann, T.
Sawada and M. Tashiro, J. Chem. Soc., Perkin Trans., 1994, 1,
2323; (d ) C. Thiemann, T. Thiemann, Y.-Q. Li, T. Sawada, Y.
Nagano and M. Tashiro, Bull. Chem. Soc. Jpn., 1994, 67, 1886;
(e) T. Thiemann, Y.-Q. Li, S. Mataka and M. Tashiro, J. Chem.
Res. (S), 1995, 384; (M) 1995, 2364; ( f ) T. Thiemann, M. L.
18 (a) A. S. Cieplak, J. Am. Chem. Soc., 1981, 103, 4540; (b) A. S.
Cieplak, B. D. Tait and C. R. Johnson, J. Am. Chem. Soc.,
1989, 111, 8447; (c) for a review, see: A. S. Cieplak, Chem. Rev.,
1999, 99, 1265.
19 (a) N. F. Werstiuk and J. Ma, Can. J. Chem., 1994, 72, 2493; (b)
B. S. Jursic, J. Heterocycl. Chem., 1995, 32, 1445; (c) B. S. Jursic,
J. Mol. Struct. (THEOCHEM), 1998, 454, 105; (d ) B. S. Jursic,
J. Mol. Struct. (THEOCHEM), 1999, 459, 215.
´
20 (a) For preparation and use of benzyne as dienophile, see:
R. W. Hoffmann, Dehydrobenzenes and Cycloalkynes, Academic
Press, New York, 1967, pp. 200; (b) For further use of benzyne
prepared in situ, see: M. R. Bryce and J. M. Vernon, Adv. Hetero-
cycl. Chem, 1981, 28, 183.
21 T. Kitamura, M. Yamane, K. Inoue, M. Todaka, N. Fukatsu,
Z. Meng and Y. Fujiwara, J. Am. Chem. Soc., 1999, 121, 11 674.
22 The authors thank Prof. Dr. T. Kitamura of Saga University for
a generous donation of 17.
Sa e Melo, A. S. Campos Neves, Y. Li, S. Mataka, M. Tashiro,
U. Geissler and D. Walton, J. Chem. Res. (S), 1998, 346.
(a) P. Pouzet, I. Erdelmeier, D. Ginderow, J.-P. Mornon, P.
Dansette and D. Mansuy, J. Chem. Soc., Chem. Commun., 1995,
473; (b) Y. Q. Li, M. Matsuda, T. Thiemann, T. Sawada, S.
Mataka and M. Tashiro, Synlett, 1996, 461; (c) J. Nakayama,
T. Yu, Y. Sugihara and A. Ishii, Chem. Lett., 1997, 499; (d )
N. Furukawa, S. Zhang, S. Sato and M. Higaki, Heterocycles,
1997, 44, 61.
4
5
6
(a) P. J. Fagan and W. A. Nugent, J. Am. Chem. Soc., 1988, 110,
2310; (b) F. Meier-Brocks and E. Weiss, J. Organomet. Chem.,
1993, 453, 33; (c) P. J. Fagan, W. A. Nugent and J. C. Calabrese,
J. Am. Chem. Soc., 1994, 116, 1880; (d ) B. T. Jiang and T. D.
Tilley, J. Am. Chem. Soc., 1999, 121, 9744; (e) M. C. Suh and
B. T. Jiang, Angew. Chem., 2000, 112, 2992; M. C. Suh and
B. T. Jiang, Angew. Chem., 2000, 39, 2870.
(a) Y. Q. Li, T. Thiemann, T. Sawada, S. Mataka and M. Tashiro,
J. Org. Chem., 1997, 62, 7926; (b) Y. Q. Li, T. Thiemann, K.
Mimura, T. Sawada, S. Mataka and M. Tashiro, Eur. J. Org.
Chem., 1998, 1841; (c) T. Thiemann, D. Ohira, Y. Q. Li, T.
Sawada, S. Mataka, K. Rauch, M. Noltemeyer and A. de Meijere,
J. Chem. Soc., Perkin Trans. 1, 2000, 2968; (d ) N. Furukawa,
S.-Z. Zhang, E. Horn, O. Takahashi, S. Sato, M. Yokoyama
and K. Yamaguchi, Heterocycles, 1998, 47, 793.
2,5-Bis(tert-butyl)thiophene S-oxide was one of the very first
thiophene S-oxides to be synthesized. In the original synthesis
m-CPBA was used in absence of a Lewis acid the described yield
was very low: W. L. Mock, J. Am. Chem. Soc., 1970, 92, 7610.
For the cycloaddition of sterically hindered thiophene S,S-diox-
ides to dimethyl acetylenedicarboxylate, see: J. Nakayama, R.
Hasemi, K. Yoshimura, Y. Sugihara, S. Yamaoka and N.
Nakamura, J. Org. Chem., 1998, 63, 4912.
(a) I. Benghait and E. I. Becker, J. Org. Chem., 1958, 23, 885; (b)
T. K. Bandyopadhyay and A. J. Bhattacharya, Ind. J. Chem. Sect.
B, 1980, 19B, 439; (c) D. N. Matthews and E. I. Becker, J. Org.
Chem., 1966, 31, 1135.
23 J. Nakayama and K. Yoshimura, Tetrahedron Lett., 1994, 35,
2709.
24 (a) T. R. Chen, M. R. Anderson, S. Grossman and D. G. Peters,
J. Org. Chem., 1987, 52, 1231; (b) V. D. Novokreshchennykh,
S. S. Mochalov and Yu. S. Shabarov, Zh. Org. Khim., 1979, 15,
485 (Russ.)J. Org. Chem. USSR, 1979, 430 (Engl.) and ref. cited.;
(c) R. W. Lang and H.-J. Hansen, Helv. Chim. Acta, 1980, 63,
438; (d ) A. Hausherr, B. Orschel, S. Scherer and H.-U. Reissig,
Synthesis, 2001, 1377 and ref. cited.
25 All compounds were analysed by 1H and 13C NMR IR and MS.
All new compounds gave correct analytical and/or HRMS data.
A number of compounds had been synthesized before by alterna-
tive routes. For 6h and 6j see: W. Ried and K. Boenninghausen,
Ann., 1961, 639, 61. For 6m see:D. CriegeeP. Ludwig, Chem.
Ber., 1961, 94, 2038. For 6n see: J. Mueller andA. Huth, Tetrahe-
dron Lett., 1972, 1035. For 6u, see: J. Novrocik, M. Novrocikova
and J. Foniok, Collect. Czech Chem Commun., 1984, 49, 218.
26 Selected spectroscopic data: 6e: IR (KBr) n 2924, 1724, 1679, 1253
7
8
9
cmꢂ1 1H NMR (270 MHz, CDCl3) d 3.57 (s, 3H, COOCH3),
;
7.35–7.58 (m, 8H), 7.65 (dd, 1H, 3J 7.0 Hz, 4J 1.4 Hz), 7.73
(1H, dd, 3J 7.3 Hz, 4J 1.7 Hz), 7.83 (d, 1H, 3J 8.5 Hz), 8.02 (d,
1H, 3J 8.5 Hz) 13C NMR (67.9 MHz, CDCl3 , DEPT 90, DEPT
135) d 52.47 (COOCH3), 124.86 (Cquat), 128.47 (CH), 128.64
(CH), 129.00 (CH), 130.02 (CH), 131.73 (CH), 133.37 (CH),
133.85 (CH), 134.03 (CH), 136.10 (2C, Cquat), 137.21 (Cquat),
140.61 (Cquat), 141.69 (Cquat), 165.15 (Cquat , COOCH3), 194.55
(Cquat , CO), 194.75 (Cquat , CO) MS (FAB, 3-nitrobenzyl alcohol)
m/z (%) 425 (81BrMH+, 7.2), 423 (79BrMH+, 7.2). 6f:IR (neat) n
10 (a) R. E. Bauer, V. Enkelmann, V. M. Wiesler, A. J. Berresheim
and K. Mullen, Chem. Eur. J., 2002, 8, 3858; (b) S. M. Waybright,
3004, 2954, 2848, 1734, 1575, 1439, 1257 cmꢂ1 1H NMR (270
;
¨
K. McAlpine, H. Laskoski, M. D. Smith and U. H. F. Bunz,
J. Am. Chem. Soc., 2002, 124, 8661; (c) C. D. Simpson, J. D.
MHz, CDCl3) d 3.90 (s, 6H, 2 COOCH3), 3.94 (s, 3H, COOCH3),
7.75 (d 1H, 3J 8.2 Hz), 7.81 (d, 1H, 3J 8.2 Hz) 13C NMR (69.7
New J. Chem., 2003, 27, 1377–1384
1383

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MHz, CDCl3 , DEPT 90, DEPT 135) d 52.94, 53.10, 53.15, 124.46
(Cquat), 128.77 (Cquat), 128.91 (Cquat), 133.46 (CH), 134.65 (2C,
CH and Cquat), 165.35, 165.95, 165.56; MS (FAB, 3-nitrobenzyl
alcohol) m/z (%) 333 (81BrMH+, 4.9), 331 (79BrMH+, 3.3), 301
(KBr) n 3060, 2962, 1673, 1597, 1450, 1261, 1240 cmꢂ1
NMR (270 MHz, CDCl3)
1.21 (s, 18H, 2But), 7.62 (s,
2H) 7.34–8.15 (m, 10H) 13C NMR (67.8 MHz, CDCl3)
;
1H
d
d
32.43, 36.30, 127.94, 128.15, 129.81, 132.24, 136.58,
(
81BrMH+ ꢂ CH3O, 100), 299 (79BrMH+ ꢂ CH3O, 99.8). 6r:
139.28, 144.88, 199.91; MS (70 eV) m/z (%) 398 (M+, 37), 383
(M+ ꢂ CH3 , 73). HRMS Calcd. for C28H30O2 : 398.2246.
Found: 398.2246. 6x: 3006, 2950, 2866, 1728, 1436, 1293,
IR (neat) n 2962, 1726, 1466, 1364, 1303, 1284, 1272, 1240,
1113, 1061 cmꢂ1 1H NMR (270 MHz, CDCl3) d 1.30 (s, 9H,
;
But), 1.39 (s, 9H, But), 1.40 (t, 3H, 3J 7.3 Hz), 4.37 (q, 2H, 3J
7.3 Hz), 7.27 (d, 1H, 4J 2.0 Hz), 7.37 (dd, 1H, 3J 8.2 Hz, 4J 2.0
Hz) 7.40 (d, 1H, 3J 8.2 Hz) 13C NMR (67.8 MHz) d 14.07,
31.14, 31.37, 34.21, 35.47, 61.35, 125.30, 126.75, 126.83, 132.59,
144.27, 148.12, 172.59; MS (70 eV) m/z (%) 352 (M+, 1.5),
337 (M+ ꢂ CH3 , 4.5), 305 (14), 105 (100), 77 (59). HRMS
Calcd. for C23H28O3 : 352.2038. Found: 352.2023. 6t: IR
1244, 1204, 1164, 1121, 1090, 983, 826, 787, 703, 669 cmꢂ1 1H
;
NMR (270 MHz, CDCl3) d 1.36 (s, 18H, 2 But), 3.84 (s, 6H,
2 COOCH3), 7.47 (s, 2H) 13C NMR (67.8 MHz, CDCl3) d
31.27, 35.70, 52.36, 128.32, 131.37, 144.76, 170.99; MS (70 eV)
m/z (%) 306 (M+, 32), 291 (M+ ꢂ CH3 , 69), 275 (32), 259
(100), 243 (18), 227 (26). HRMS Calcd. for C18H26O4 :
306.1831. Found: 306.1827.
1384
New J. Chem., 2003, 27, 1377–1384