[4+2]-Cycloaddition of sterically hindered thiophene S-oxides to alkenes and SO extrusion reactions of the cycloadducts

Full text of DOI:10.1080/10426507.2015.1100191

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
[4+2]-Cycloaddition Of Sterically Hindered
Thiophene S-Oxides To Alkenes And So Extrusion
Reactions Of The Cycloadducts
Thies Thiemann, Jesus Iniesta & David J. Walton
To cite this article: Thies Thiemann, Jesus Iniesta & David J. Walton (2016): [4+2]-Cycloaddition
Of Sterically Hindered Thiophene S-Oxides To Alkenes And So Extrusion Reactions
Of The Cycloadducts, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:
10.1080/10426507.2015.1100191
To link to this article: http://dx.doi.org/10.1080/10426507.2015.1100191
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Date: 30 March 2016, At: 16:27

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[4+2]-CYCLOADDITION OF STERICALLY HINDERED THIOPHENE S-OXIDES TO
ALKENES AND SO EXTRUSION REACTIONS OF THE CYCLOADDUCTS
Thies Thiemanna,*,#, Jesus Iniestab,c, David J. Waltond
aInstitute of Materials Chemistry, Kyushu University, Kasuga-koh-en, Kasuga-shi 816-8580,
Japan
bInstitute of Electrochemistry, University of Alicante, 03690, San Vicente del Raspeig, Alicante,
Spain
cPhysical Chemistry Department, University of Alicante, 03690, San Vicente del Raspeig,
Alicante, Spain
dSchool of Health and Life Sciences, Coventry University, Priory Street, Coventry, CV1 5FB,
UK
#current address: Department of Chemistry, United Arab Emirates University, PO Box 15551, Al
Ain, Abu Dhabi, United Arab Emirates; thies@uaeu.ac.ae; thiesthiemann@yahoo.de
*Corresponding Author Email: thiesthiemann@yahoo.de
Abstract
Cycloaddition reactions of 2,5-di-tert-butylthiophene S-oxide and 2,3,4,5-tetrakis(p-
tolyl)thiophene S-oxide with alkenes are described. The reactivity of 2,5-di-tert-butylthiophene
S-oxide as diene in Diels Alder reactions is compared with 2,5-di-tert-butylthiophene S,S-dioxide.
The thermal and photochemical SO extrusion reactions of the cycloadducts under formation of
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highly substituted aromatic compounds are exemplified.
Ph-p-Me
Ph-p-Me
Ph-p-Me
O
O
O
p-Me-Ph
p-Me-Ph
p-Me-Ph
p-Me-Ph
p-Me-Ph
p-Me-Ph
h
SO
S
O
CD2Cl2
Ph-p-Me
Ph-p-Me
Ph-p-Me
Keywords
thiophene S,S-dioxide, thiophene S-oxide, cycloaddition, SO extrusion
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INTRODUCTION
Easy synthetic access to arenes with neighboring sterically exacting substituents is still of
great interest.1 One preparative route to arenes is via [4+2]-cycloaddition and subsequent
oxidative aromatization.2 For a more facile approach to substituted arenes via [4+2]-
cycloaddition, it is advisable to introduce at least two double bonds into the constructed ring
system during the cycloaddition. This can be achieved by the right selection of the dienophile in
form of an acetylene,2,3 an allene4 or an aryne5 in case of an areno-annelation reaction.
Alternatively, the additional unsaturation can be introduced by choosing a cyclic dienophile,
which would lead to a bicyclic system with a bridged 6-membered carbocycle, where the bridge
would be extruded or opened in a subsequent reaction step, which simultaneously introduces the
additional unsaturation into the carbocycle. Use of a cyclic diene has the advantage of a locked-
in cisoid diene system, ideal for the cycloaddition. Typical examples of such cyclic dienes that
lead to bicyclic cycloadducts with an extrusable bridge are pyrones,6 cyclopentadienones,7
furans8 and thiophenes9 and their derivatives. While furans, especially those with electron-
donating substituents, are passable dienes for Diels-Alder type cycloadditions, thiophenes are not,
where in fact only a handful of specifically substituted thiophenes9 have been used successfully.
Thiophenes, however, can be oxidized to thiophene oxides, and these are classical cyclic dienes.
Thiophene S,S-dioxides10 have been used as diene components in cycloaddition reactions for
some time, while the preparation of thiophene S-oxides and their use as substrates in
cycloaddition reactions have been studied more recently.11,12 For the most part, thiophene S,S-
dioxides are thermally and photochemically13 much more stable than thiophene S-oxides. On the
other hand, as dienes in Diels Alder type reactions, thiophene S-oxides have been found
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generally more reactive than the corresponding thiophene S,S-dioxides. In the following, the
authors show the reactivity of a tetraarylthiophene S-oxide and of 2,5-tert-butylthiophene S-
oxide as diene components in Diels Alder reactions with alkenes. As contrast, comparative
cycloadditions with tetraphenylcyclopentadienone (tetracyclone) and with 2,5-di-tert-
butylthiophene S,S-dioxide are shown. Also, photochemically and thermally driven
transformations of the 7-thia-bicyclo[2.2.1]hept-5-ene S-oxides as the primary cycloadducts to
the corresponding substituted arenes and cyclohexadienes are exemplified. Overall, the
cycloaddition of alkenes to thiophene S-oxides with bulky substituents at positions C2 and C5
with a subsequent SO-extrusion reaction is to be seen as an additional route to oligo-substituted
arenes with bulky neighboring groups.
RESULTS AND DISCUSSION
First was tested the reactivity of alkenes towards tetrakis(p-tolyl)thiophene S-oxide (1a),
which was synthesized via reaction of thionyl chloride with tetrakis(p-
tolyl)zirconacyclopentadiene, produced from bis(cyclopentadienyl)zirconium(IV) dichloride and
bis(p-tolyl)acetylene, following an analogous procedure.4,9,14 It must be noted that the
cycloaddition of tetraarylthiophene S-oxides with alkynes has been studied previously,4,15 but not
with alkenes. Here, tetrakis(p-tolyl)thiophene S-oxide (1a) was reacted with a number of
dienophiles in CHCl3 (Scheme 1). To many of the dienophiles with two or one electron
o
withdrawing group, tetrakis(p-tolyl)thiophene S-oxide (1a) already cycloadds at 50 C in
acceptable yields, although tetrakis(p-tolyl)thiophene S-oxide (1a) does not react well with (E)-
1,2-dibenzoylethene (2f) at 50°C, so that the reaction temperature in this case had to be raised to
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70 oC. Even then, the yield of the cycloadduct 3g remained poor. 1a itself is thermally relatively
stable, although thiophene S-oxides are generally known to be thermally relatively labile. When
heated to 70°C in chloroform for 11 h, 1a was recovered unchanged. With maleic anhydride (2b)
o
and N-phenylmaleimide (2a) at 50 C, 1a gave the corresponding cycloadducts 3a and 3b in
excellent yield. 3b was hydrolyzed to the diacid 3c (BzlNMe3OH, H2O),16 which was
subsequently converted with an ethereal solution of diazomethane to diester 3d, which was also
produced directly in a cycloaddition of 1a with dimethyl maleate (2c) (Scheme 1).
In all cycloaddition reactions above, the products were formed as one stereoisomer, only.
This stereoselectivity has been remarked upon previously in analogous reactions, where the
stereochemistry of the cycloadducts could be determined by single crystal X-ray structure
analysis.17 The reactions show endo-selectivity, indicating kinetic control of the product, with the
lone electron pair on sulfur of the sulfoxy-bridge lying on the side of the newly formed double
bond of the product. The stereoselectivity at sulfur is governed by the Cieplak effect.18
Experimental observations in Diels-Alder reactions of dienophiles with 5-substituted
cyclopentadienes have shown that the dienophiles will approach anti to the antiperiplanar -bond
that is the better donor at the 5-position of the cyclopentadiene. The lone-pair electron orbital on
sulfur stabilizes the vacant *-orbital of the developing incipient -bonds better than the lone-
pair electron orbitals of the oxygen of the sulfoxy moiety.
When comparing tetraarylthiophene S-oxides with tetraarylcyclopentadienones (tetracyclones) as
dienes in cycloaddition reactions, it must be noted that tetracyclones for the most part necessitate
higher reaction temperatures than their tetraarylthiophene S-oxide counterparts. When stirring a
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mixture of tetraphenylthiophene S-oxide (1b), tetraphenylcyclopentadienone (4a) (or tetrakis-p-
tolylthiophene-S-oxide (1a) and 3,4-bis(p-tolyl)-2,5-diphenylcyclopentadienone (4b) and N-
phenylmaleimide (2a) in deuterated chloroform, only the cycloadduct 3i (and 3a, respectively) of
the tetraarylthiophene S-oxide with N-phenylmaleimide was obtained (Scheme 2).
Tetracyclones are usually thermally much more stable than tetraarylthiophene-S-oxides. Never-
theless, tetracyclones are not stable at elevated temperatures under all conditions. Thus, the au-
thors have shown that tetracyclones convert to -pyrones when heated in aerated diphenyl
ether,19 a solvent that is frequently used as a solvent for Diels-Alder type cycloaddition reactions
at higher temperatures. Also, tetracyclones have been shown to be reductants at elevated
temperatures, such as in the case of the cycloaddition of tetraphenylcyclopentadienone to
benzothiophene-S,S-dioxide, where excess tetraphenylcyclopentadienone reduces the sulfone
moiety in the cycloadduct, in juxtaposition to the same reaction with tetraphenylthiophene S-ox-
ide, where the sulfone moiety in the cycloadduct remains intact.20 Nevertheless, cycloaddition re-
actions of tetracyclones under microwave irradiation21 and under solvent free conditions7c have
recently provided additional possibilities of preparing oligoarylbenzenes under milder conditions.
Therefore, tetraarylthiophene S-oxides and tetracyclones can be seen as complimentary diene
substrates for the preparation of oligoarylbenzenes and of generally oligosubstituted benzenes,
complimentary also, as the strategy of preparation differs and, depending on the substitution, one
or the other preparation may be preferred due to ease of access. Tetraarylcyclopentadienones can
be prepared by Weiss reaction, which for instance would not allow an easy preparation of
tetracyclones with four different aryl groups. Also, alkyl-substituted cyclopentadienones are not
easily accessible22 and often react as dienophile rather than as diene.23 The preparation of
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thiophene S-oxides by oxidation of the corresponding thiophenes limits the substitution pattern
of the thiophene S-oxides to the substitution pattern of the corresponding thiophenes, where it
must be ascertained that the substituents still allow for a smooth oxidation of the thiophene to the
thiophene S-oxide to occur.
Next, 2,5-bis(tert-butyl)thiophene S-oxide (1c),24 prepared by oxidation of 2,5-bis(tert-
butyl)thiophene with m-CPBA in the presence of BF3·Et2O,4 was found to cycloadd to
o
dienophiles with one electron-withdrawing substituent at 60 C. Cycloadducts 5 were obtained
with 60 – 65% yield, again as single isomers (Scheme 3). The tert-butyl ester 5c could be
hydrolyzed to carboxylic acid 5d without affecting the SO bridge. The reaction of 2,5-di-tert-
butylthiophene S-oxide (1c) with p-naphthoquinone (2i) gave cycloadduct 5b in 72% yield
(Scheme 3).
The reactivity of 2,5-di-tert-butylthiophene S-oxide (1c) in the cycloaddition reactions
above was compared to that of 2,5-di-tert-butylthiophene S,S-dioxide (6), prepared by oxidation
of 2,5-di-tert-butylthiophene with m-CPBA in the absence of BF3·Et2O. No reaction took place
o
between 2,5-di-tert-butylthiophene S,S-dioxide (6) and dienophiles 2 at 60 C. With mono- and
disubstituted acetylene dienophiles such as with benzyl propiolate, ethyl propiolate and diethyl
acetylenedicarboxylate, 6 did not undergo a cycloaddition at even 100 oC. p-Naphthoquinone (2i)
o
and N-(p-chlorophenyl)maleimide (2h) cycloadded to 6, but at reaction temperatures of 195 C
o
and at 140 C, respectively. For these reactions diphenyl ether was used as solvent. At the
reaction temperatures, the SO2 bridge of the primary cycloadducts extruded cleanly and in the
case of the reaction with p-naphthoquinone (2i), 1,4-di-tert-butylanthraquinone (7b), and in the
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case of the reaction with N-(p-chlorophenyl)maleimide (2h), a mixture of the corresponding di-
tert-butylphthalimide (7a) and di-tert-butyldihydrophthalimide (8a) was obtained (Scheme 4).
Oxidative extrusion of the sulfoxy bridge in cycloadducts similar to 3 and 5 have been reported
to have been accomplished thermally25 or at room temperature when the reactions were run
electrochemically,26 photochemically27 or using KMnO4 as oxidant under phase transfer
conditions25. Nevertheless, the electrochemical oxidative SO extrusion often leads to blockage of
the electrodes after some time due to fouling. The oxidative extrusion with KMnO4 under phase
transfer conditions can lead to variable results. Thus far, the photochemical SO extrusion has
been studied for two cycloadducts, only.27
Thermal SO-extrusion reactions with 7-thiabicyclo[2.2.1]hept-5-ene S-oxides occur only at
relatively high temperatures. Thus, 3a does not extrude SO even when kept at 130 °C (12 h) in
diphenylether. However, when 3a is heated in diphenylether at 160 °C for 14h, the SO-extruded
and aromatized product 9a can be isolated with 75% yield (Scheme 5). At that temperature, the
extrusion reaction is still slow, so that after 4h an appreciable amount of starting material can be
o
detected. Higher reaction temperatures (180 C) and shortened reaction times (9h) give 9a with
slightly lower yield.
1,4-Di-tert-butylthiabicyclo[2.2.1]hept-5-ene S-oxides 5 were found to extrude SO more readily
(Scheme 6). When N-(p-chlorophenyl)-1,4-di-tert-butyl-7-thiabicyclo[2.2.1]hept-5-ene-2,3-
o
dicarboxamide S-oxide (5a) was heated in diphenyl ether at 140 C for 1 h, N-(p-chlorophenyl)-
3,6-di-tert-butylphthalimide (7a) was found with 74% yield, the remainder being starting
o
material. Raising the temperature to 170 C did not improve the yield of 7a, however, and
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produced a small amount (5%) of N-(p-chlorophenyl)-3,6-di-tert-butyl-1,2-dihydrophthalimide
(8a). Heating acetyl-1,4-di-tert-butyl-7-thiabicyclo[2.2.1]hept-5-ene S-oxide (5e) in diphenyl
ether at 140 oC for 30 min gives 30% 2,5-di-tert-butylacetophenone (7c) with 60% of the starting
o
material remaining (Scheme 6). After 1 h at 140 C, 2,5-di-tert-butylacetophenone (7c), which
had been prepared previously by more tedious routes, was produced in 65% yield.28 Again, the
tetrakis-(p-tolyl) substituted analog 3e required higher reaction temperatures and longer reaction
times to give 9b with 70% yield (Scheme 5).
Some years ago, the authors studied the SO-photo-extrusion at room temperature of two 7-
thiabicyclo[2.2.1]hept-5-ene S-oxides, namely the products stemming formally from the
cycloaddition of 2,5-dimethylthiophene S-oxide and of 2,3,4,5-tetramethylthiophene S-oxide
with N-phenylmaleimide.27 In both cases the SO bridge could be extruded photochemically to
give methyl substituted N-phenylphthalimides as the aromatized products.27 In the following, it
was investigated whether this SO-photo-extrusion, which finds its counter-part in the photo-
extusion of the CO bridge in cycloadducts of tetraarylcyclopentadienones and alkenes,29 can be
carried out with the cycloadducts prepared above. The cycloadducts were photo-irradiated in
CD2Cl2 at  > 222 nm without use of sensitizer. The reactions were screened for the aromatized
compounds as the desired products. However no identification of potential minor side-products
was carried out. The photoreactions were monitored by 1H NMR spectroscopy. Photo-irradiation
of tetraphenyl-7-thiabicyclo[2.2.1]hept-5-ene S-oxide 3i gave a mixture of dihydrophthalimide
8b and phthalimide 9c (Scheme 7). It is believed that the dihydrophthalimide is an intermediate
in the photo-extrusion/oxidation reaction and that the extruded sulfur monoxide (SO) oxidizes 8b
to 9c. SO is a triplet in its ground state (Χ3Σ) and has two excited states (a1Δ) and (b1Σ), 17.6
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kcal/mol and 30.0 kcal/mol above the ground state, respectively.30 The mercury lamp used in our
experiment would have sufficient energy to elevate SO from (Χ3Σ) to (a1Δ). Nevertheless, SO
(a1Δ) deactivates quickly to SO (Χ3Σ).31 Also SO (Χ3Σ) has a short lifetime in solution but has
been trapped in cycloaddition reactions, previously.32 In the present case, it is not clear whether
SO (a1Δ) or SO (Χ3Σ) is responsible for the aromatization step or whether another pathway
operates. In the photoreaction of 3a, 3a was applied to a preparative TLC plate (20 × 20 cm,
silica gel 60 F254 2 mm, with concentration zone, from Merck KGaA). The plate was developed
with ether/hexane 1:1, until a zone of starting material separated clearly from the line of
application (from the concentration zone). Then, the zone was photo-irradiated directly with a
UVP-Mineralight Lamp, model UVGL-15, at  = 254 nm. The plate was irradiated for 3 × 20
min. Once the two were well separated, the zone containing the starting material was photo-
irradiated again (3 × 20 min.), where the product zone was protected from the irradiation by a
cover of aluminum foil. The process was repeated one more time to give a total irradiation time
of 3 h. Overall, the photo-irradiation gave phthalimide 9a with 55% yield. Scheme 7 shows
further examples of SO-photo-extrusion with 7-thiabicyclo[2.2.1]hept-5-ene S-oxide substrates 3
leading to the aromatized products 9.
CONCLUSIONS
Both 2,5-di-tert-butylthiophene S-oxide (1c) and 2,3,4,5-tetrakis(p-tolyl)thiophene S-oxide (1a)
undergo cycloaddition reactions with mono- and bis-acceptor substituted alkenes furnishing
highly substituted 7-thiabicyclo[2.2.1]hept-5-ene S-oxides 3 and 5 with acceptable yields. The
reactivity difference between 2,5-di-tert-butylthiophene S-oxide (1c) and 2,5-di-tert-
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butylthiophene S,S-dioxide (6) is pronounced, where 2,5-di-tert-butylthiophene S-oxide (1c)
o
cycloadds to many of the electron-poor alkenes at 60 C, while 2,5-di-tert-butylthiophene S,S-
o
dioxide (6) needs 140 C or more. Tetraarylthiophene S-oxides such as 1a and 1b are building
blocks for oligoarylbenzenes and can be used alternatively to tetraarylcyclopentadienones
(tetracyclones). Nevertheless, the SO-extrusion of the 7-thiabicyclo[2.2.1]hept-5-ene S-oxides 3
o
and 5 remains problematic, with needed temperatures of 140 C or above. Nevertheless, the
thermal extrusion yields some interesting, highly substituted aromatic compounds such as 7c or
9e,33 which were not easily accessible previously. Photochemical SO-extrusion has been carried
out successfully with six cycloadducts (3a, 3d-f, and 3i), although reaction times remain long.
EXPERIMENTAL
General remarks
Melting points (mp., uncorrected) were determined on a Yanaco microscope hotstage. IR spectra
1
(υmax, KBr/cm1) were measured with a JASCO IR-700 instrument. H NMR spectra (at 270
MHz and 395.7 MHz) and 13C NMR spectra (at 67.8 MHz and 99.45 MHz) were recorded with a
JEOL EX-270 and a JEOL Lambda 400 FT-NMR spectrometer, respectively. The chemical
shifts are relative to TMS (solvent CDCl3). MS were measured with a JMS-01-SG-2-
spectrometer (EI, 70 eV). Column chromatography was carried out on Wakogel C-300. For the
photo-irradiation in solution, a 1 kW Tokyo Rigaku high-pressure mercury lamp was used. The
photochemistry on silica gel was carried out with a UVP-Mineralight Lamp, model UVGL-15, at
 = 254 nm. PLC plates (20 × 20 cm; silica gel 60 F254 2 mm from Merck KGaA) were used.
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2,5-Di-tert-butylthiophene S,S-dioxide (6)34 and 2,5-di-tert-butylthiophene S-oxide (1c)4
were prepared analogous to known procedures.
Tetrakis(p-tolyl)thiophene S-oxide (1a).
In an inert atmosphere, n-BuLi (1.59 M, 21.5 mL, 3.32 mmol) was added to a slurry of
zirconocene dichloride (5.0 g, 17.1 mmol) and bis(p-tolyl)acetylene (7.5 g, 34.2 mmol) in dry
THF (150 mL) at 78 oC. Subsequently, the mixture was warmed to rt. and stirred for 3 h. Next,
o
the solution was cooled to 0 C and thionyl chloride (2.2 g, 18.8 mmol) in hexane (10 mL) was
added within 30 min. The resulting mixture was stirred at rt for 3 h. After the reaction was
complete, the mixture was poured into conc. aq. NaHCO3 (200 mL). The product was extracted
with CH2Cl2 (200 mL) and the organic phase was washed with water (200 mL), dried over
anhydrous MgSO4 and concentrated in vacuo. The residue was purified by flash column
chromatography on silica gel (hexane/ether 1:1) to give 1a (4.72 g, 10.2 mmol, 60%) as a pale
o
yellow solid; mp. 110 C. IR: 3025, 2918, 1502, 1324, 1182, 1116, 1087, 1062, 1018, 851, 832,
819, 731, 539, 519. 1H NMR (270 MHz): δ 2.26 (s, 6H, 2 CH3), 2.30 (s, 6H, 2 CH3), 6.80 (d, 4H,
3
3
3
3J = 8.3 Hz), 6.94 (d, 4H, J = 7.9 Hz), 7.07 (d, 4H, J = 7.9 Hz), 7.25 (d, 4H, J = 8.1 Hz). 13C
NMR (67.8 MHz): δ 21.2, 127.9, 128.9, 129.3, 129.6, 129.7, 130.6, 137.8, 138.4, 140.8, 145.3.
MS (FAB, 3-nitrobenzyl alcohol): m/z [MH+] 461 (70), [M+O] 444 (100), [M+S] 428 (20),
[M+SO] 412 (30). Calcd. for C32H29OS: 461.1939. Found: 461.1940. HRMS Calcd. for C32H28:
412.2191. Found: 412.2194. HRMS Calcd. for C32H28O: 428.2140. Found: 428.1247. Anal.
Calcd. for C32H28OS·0.25 H2O (465.13); C, 82.63; H, 6.12%. Found C, 82.92; H, 6.31%.
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N-Phenyl-3,4,5,6-tetrakis(p-tolyl)-7-thia-bicyclo[2.2.1]hept-5-ene-2,3-carboxamide
7-oxide (3a).
A solution of tetrakis(p-tolyl)thiophene S-oxide (1a, 87 mg, 0.19 mmol) and N-phenylmaleimide
o
(2a, 40 mg, 0.23 mmol) in CHCl3 (1.5 mL) was heated for 14 h at 50 C. The solution was
concentrated in vacuo, and the residue was subjected to column chromatography on silica gel
o
(hexane/ether 1:1) to give 3a (107 mg, 89%) as a colorless solid, mp. 296 C. IR: 3026, 2918,
1716 (C=O), 1503, 1377, 1188, 1102, 799, 753, 729. 1H NMR (270 MHz): δ 2.14 (s, 6H, 2 CH3),
3
2.30 (s, 6H, 2 CH3), 4.95 (s, 2H), 6.62 (d, 4H, 3J = 7.9 Hz), 6.71 (d, 4H, J = 7.9 Hz), 7.00 (vs,
13
8H), 7.24 – 7.36 (m, 5H). C NMR (67.8 MHz): δ 21.1 50.1, 80.5, 126.1, 126.4, 128.5, 128.9,
129.1, 129.2, 130.1, 130.5, 131.8, 134.2, 137.4, 138.0, 138.3, 174.3. MS (FAB, 3-nitrobenzyl
alcohol): m/z [MH+] 634 (35), [M+SO] 585 (100), 438 (36). MS (EI, 70 eV): m/z [M+SO] 585
(100), 444 (44), 438 (41). HRMS Found: 634.2418. Calcd. for C42H (MH+, FAB). Anal. Calcd.
for C42H35O3NS (657.82); C, 79.59; H, 5.57; N, 2.21. Found C, 79.31; H, 5.66; N, 2.17%.
N-(p-Chlorophenyl)-1,4-di-tert-butyl-7-thiabicyclo[2.2.1]hept-5-ene-2,3-
dicarboxamide S-oxide (5a).
A mixture of 2,5-di-tert-butylthiophene S-oxide (1c, 80 mg, 0.38 mmol) and N-(p-
chlorophenyl)maleimide (2h, 79 mg, 0.38 mmol) in CHCl3 (1.5 mL) was heated for 12 h at 60
oC. The solution was concentrated in vacuo, and the residue was subjected to column
chromatography on silica gel (chloroform/hexane/ether 1:1:1) to give 5a (142 mg, 89%) as a
1
colorless solid, mp. 213oC. IR: 1710 (C=O). H NMR (270 MHz): δ 1.32 (s, 18H, 6 CH3), 7.11
3
(d, 2H, 3J = 8.0 Hz), 7.34 (d, 2H, J = 8.0 Hz). 13C NMR (67.8 MHz): δ 28.7 (6C, 6 CH3), 33.5
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(2C, Cquat, C(CH3)3), 48.3 (2C, CH), 80.7 (2C, Cquat), 127.9 (2C, CH), 129.3 (2C, CH), 129.5
(Cquat), 130.3 (2C, CH), 134.7 (Cquat), 173.9 (2C, Cquat, CO). MS (FAB, 3-nitrobenzyl alcohol):
m/z [[37Cl]MH+] 422 (7), [[35Cl]MH+] 420 (17), [[35Cl]M+SO] 371 (13), 154 (100), 136 (82).
HRMS Found: 420.1396. Calcd. for C22H27O3N35ClS: 420.1400 ([35Cl]MH+, FAB).
N-(p-Chlorophenyl)-3,6-di-tert-butylphthalimide (7a).
Method A: A solution of 6 (196 mg, 0.86 mmol) and N-chlorophenylmaleimide (2h, 284 mg,
o
1.37 mmol) in deaerated diphenyl ether (1 g, 930 μL) was heated at 140 C for 17 h. Thereafter,
the cooled solution was subjected to column chromatography on silica gel (hexane to elute the
solvent, then hexane/CHCl3/ether 2:1:1) to give 7a (110 mg, 35%) as a colorless solid, mp. 214
1
3
oC. H NMR (270 MHz): 1.54 (s, 18H, 2 But), 7.40 (d, 2H, J = 8.9 Hz), 7.48 (d, 2H, 3J = 8.9
13
Hz), 7.71 (s, 2H); C NMR (67.8 MHz): δ 30.5 (6C, 6 CH3), 36.0 (2C, Cquat, C(CH3)3), 129.0
(2C, CH), 129.7 (2C, CH), 132.1 (Cquat), 133.5 (2C, CH), 142.5 (Cquat), 150.1 (2C, Cquat), 157.6
(2C, Cquat), 188.8 (2C, Cquat, CO). MS (EI, 70 eV): m/z [[37Cl]M+] 371 (37), [[35Cl]M+] 369
(100), [[35Cl]M+CH3] 354 (84). HMRS Found: 369.1496. Calcd. for C22H24O2N35Cl: 369.1496
and N-(p-chlorophenyl)-3,6-di-tert-butyl-1,2-dihydrophthalimide (8a) (16 mg, 5%) as a colorless
o
1
solid, mp. 200 C. H NMR(270 MHz): δ 1.19 (s, 18H, 2 But), 3.91 (s, 2H), 6.06 (s, 2H), 7.28
3
3
13
(d, 2H, J = 8.6 Hz), 7.41 (d, 2H, J = 8.6 Hz); C NMR (67.8 MHz): δ 29.9 (6C, 6CH3), 36.0
(2C, Cquat, C(CH3)3), 47.4 (2C, CH), 120.8 (2C, CH), 126.7 (2C, CH), 129.6 (2C, CH), 131.1
(Cquat), 134.4 (Cquat), 139.9 (Cquat), 178.0 (2C, Cquat, CO); MS (EI, 70 eV): m/z [[37Cl]M+] 373
(11), [[35Cl]M+] 371 (31), [[35Cl]M+CH3] 356 (19), 175 (100). HRMS Found: 371.1654. Calcd.
for C22H26O2N35Cl: 371.1652.
14
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o
Method B: A solution of 5a (50 mg, 0.12 mmol) in diphenyl ether (2 mL) was heated at 170 C
for 1 h. Thereafter, the cooled solution was subjected to column chromatography on silica gel
(hexane to elute the solvent, then hexane/CHCl3/ether 2:1:1) to give 7a (30.6 mg, 69%) and N-
(p-chlorophenyl)-3,6-bis(tert-butyl)-1,2-dihydrophthalimide (8a) (2.4 mg, 5%).
N-Phenyl-3,4,5,6-tetrakis(p-tolyl)phthalimide (9a).
Method A: N-Phenyl-1,4,5,6-tetrakis(p-tolyl)-7-thiabicyclo[2.2.1]hept-5-ene-2,3-dicarboxamide
o
S-oxide (3a, 33 mg, 0.05 mmol) in diphenyl ether (450 mg, 420 μL) was heated to 180 C for 9
h. Thereafter, the cooled solution was subjected to column chromatography on silica gel (initially
hexane, to elute the solvent diphenyl ether, then hexane/ether 1:1) to give 9a (20 mg, 65%) as a
colorless solid; IR: 2920, 1721 (C=O), 1601, 1368, 1114, 805, 763, 722. 1H NMR (270 MHz): δ
3
3
2.12 (s, 6H, 2 CH3), 2.27 (s, 6H, 2 CH3), 6.62 (d, 4H, J = 7.9 Hz), 6.71 (d, 4H, J = 7.9 Hz),
7.00 (vs, 8H), 7.24 – 7.36 (m, 5H). MS (FAB, 3-nitrobenzyl alcohol): m/z 584 (MH+, 49). HRMS
Found: 584.2591. Calcd. for C42H34O2N: 584.2590 (MH+).
Method B: 3a (19.7 mg, 0.031 mmol) was dissolved in CHCl3 (2 mL) and applied to a prepara-
tive TLC plate (20 × 20 cm, silica gel 60 F254 2 mm, with concentration zone, from Merck
KGaA). The plate was run with ether/hexane 1:1, until a zone of starting material separated
clearly from the line of application (from the concentration zone). Then, the zone was photo-
irradiated directly with a UVP-Mineralight Lamp, model UVGL-15, at  = 254 nm. The plate
was irradiated for 3 × 20 min. Then, the plate was developed once more with hexane/ether 1:1, to
separate the product from the starting material. Once the two were well separated, the zone con-
taining the starting material was photo-irradiated again (3 × 20 min.), where the product zone
15
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was protected from the irradiation by a cover of aluminum foil. The process was repeated once
more to give a total irradiation time of 3 h. Thereafter, the remaining starting material was
separated from the zones of product formed in the three photo-irradiation processes. The product
containing silica gel was taken off the plate and transferred to a short column fitted with a cotton
pad. The substance was eluted off the column with ether. The column was washed once with
CHCl3. The eluted fractions were concentrated in vacuo to give 9a (10 mg, 55%).
2,3,4,5-Tetrakis(p-tolyl)acetophenone (9b)
Method A: A solution of 3e (50 mg, 9.4·10-5 mol) in diphenyl ether (500 mg, 460 μL) was heated
to 170 oC for 9 h. The cooled solution was subjected directly to column chromatography on silica
gel (initially hexane to elute the solvent, thereafter hexane/ether 1:1) to give 9b (31.5 mg, 70 %)
1
as a colorless solid. IR: 3022, 2920, 2856, 1688, 1517, 111, 1029, 813. H NMR (270 MHz):
1.90 (s, 3H, COCH3), 2.12 (s, 3H, CH3), 2.14 (s, 3H, CH3), 2.27 (s, 6H, 2 CH3), 6.59 – 6.74 (m,
8H), 6.89 (d, 2H, 3J = 8.1 Hz), 6.93 (d, 2H, 3J = 8.1 Hz), 6.97 (vs, 4H); MS (EI, 70 eV): m/z [M+]
480 (100), [M+CH3] 465 (54), [M+C2H2O] 438 (41), 149 (29). HRMS Found: 480.2456.
Calcd. for C36H22O: 480.2453.
Method B: A solution of 3e (16.6 mg, 3.1 × 105 mol) in CD2Cl2 (0.5 mL) was photo-irradiated
with a 1 kW Tokyo Rigaku high-pressure mercury lamp, with the reaction system cooled at rt.
The mixture was analyzed by 1H NMR spectroscopy after 30 min., 2.5 h and 4 h, after which the
photo-irradiation was stopped. The mixture was subjected to column chromatography on silica
gel (hexane/ether 1:1) to give 9b (9.8 mg, 65%).
16
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Acknowledgements
This project was supported in part by ESPRC (in UK) and J. Iniesta thanks the ESPRC for
funding of a stay at Kyushu University, Fukuoka, Japan. The authors thank Ms. Y. Tanaka for
carrying out the mass and high resolution mass spectroscopic measurements of the compounds.
The elemental analyses were carried out at the Central Analysis Center, Hakozaki Campus,
Kyushu University.
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REFERENCES
[1]
[2]
[3]
[4]
[5]
(a) Yoshida, K.; Horiuchi, S.; Iwadate, N.; Kawagoe, F.; Imamoto, T. Synlett 2007,
15611562. (b) Yoshida, K.; Hayashi, A; Yanagisawa, Org. Lett. 2011, 9, 46274630.
(a) Hilt, G.; Danz, M. Synthesis 2008, 22572263. (b) Hilt, G.; Smolko, K. I. Angew.
Chem. Int. Ed. 2003, 42, 27952797.
(a) Horie, H.; Kurahashi, T.; Matsubara, S. J. Chem. Soc., Chem. Commun. 2012,
38663868.
Thiemann, T.; Fujii, H.; Ohira, D.; Arima, K.; Li, Y. Q.; Mataka, S. New J. Chem. 2003,
27, 13771384.
(a) Pérez, D.; Peňa, D.; Guitián, E. Eur. J. Org. Chem. 2013, 59816013; (b) Hayes, M.
E.; Shinokubo, H.; Danheiser, R. L. Org. Lett. 2005, 7, 39173920.
[6]
[7]
(a) Woodard, B. T.; Posner, G. H. Advances in Cycloaddition 1999, 5, 4783. (b)
Delaney, P. M.; Moore, J. E.; Harrity, J. P. A. J. Chem. Soc., Chem. Commun. 2006,
33233325.
(a) Buszek, K. R. Tetraphenylcyclopentadienone, e-EROS Encyclopedia of Reagents for
Organic Synthesis, 2001; (b) Hapke, M.; Gutnov, A.; Weding, N.; Spannenberg, A.;
Fischer, C.; Benkhäuser-Schunk C.; Heller, B. Eur. J. Org. Chem. 2010, 509–514. (c)
Khazaei, A.; Zolfigol, M. A.; Manesh, A. A. J. Chin. Chem. Soc. 2013, 52, 515518.
[8]
Padwa, A.; Dimitroff, M.; Waterson, A. G.; Wu, T. J. Org. Chem. 1997, 62, 40884096.
18
ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
[9]
(a) Kumamoto, K.; Fukuda, I.; Kotsuki, H. Angew. Chem. Int. Ed. Engl. 2004, 43,
20152017. (b) Helder, R.; Wynberg, H. Tetrahedron Lett. 1972, 605608. (c). Kuhn,
H.-J.; Gollnick, K. Chem. Ber. 1973, 106, 674696. (d) Corral, C.; Lissavetzky, J.;
Manzanares, I. Synthesis 1997, 2931.
[10] (a) Melles, J. L. Recl. Trav. Chim. Pays-Bas 1952, 71, 869878. (b) Nakayama, J.;
Hirashima, A. J. Am. Chem. Soc. 1990, 112, 76487653. (c) Moiseev, A. M.; Tyurin, D.
D.; Balenkova, E. S.; Nenajdenko, V. G. Tetrahedron 2006, 62, 41394145. (d) Van
Tilborg, W. J. M.; Smael, P.; Viser, T. P.; Louwenhoven, C. G.; Reinhoudt, D. N. Rec.
Trav. Chim. Pays-Bas, 1975, 94, 85–88.
[11] (a) Li, Y. Q.; Matsuda, M.; Thiemann, T.; Sawada, T.; Mataka, S.; Tashiro, M. Synlett
1996, 461464. (b) Furukawa, N.; Zhang, S.-Z.; Sato, S.; Higaki, M. Heterocycles 1997,
44, 6166. (c) Li, Y. Q.; Thiemann, T.; Sawada, T.; Mataka, S.; Tashiro, M. J. Org.
Chem. 1997, 62, 79267936. (d) Nakayama, J.; Yu, T.; Sugihara, Y.; Ishii, A. Chem.
Lett. 1997, 26, 499500. (e) Furukawa, N.; Zhang, S.-Z.; Horn, E.; Takahashi, O.; Sato,
S.; Heterocycles 1998, 47, 793809. (f) Takayama, J.; Sugihara, Y.; Takayanagi, T.;
Nakayama, J. Tetrahedron Lett. 2005, 46, 41654169. (g) Pouzet, P.; Erdelmeier, I.;
Ginderow, D.; Mornon, J.-P.; Dansette, P. M.; Mansuy D. J. Chem. Soc., Chem.
Commun. 1995, 473474.
[12] (a) For reviews, see: Lu, Y.; Dong, Z.; Wang, P.; Zhou, H.-B. Top. Heterocycl. Chem.
2015, 39, 227–294. (b) Thiemann, T.; Iniesta, J. Research Trends in Heterocyclic
19
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ACCEPTED MANUSCRIPT
Chemistry 2011, 15, 71–88. (c) Thiemann, T.; Gopal Dongol, K. J. Chem. Res. (S) 2002,
26, 303 – 308; (M) 2002, 701–708. (d) Thiemann, T.; Walton, D. J.; Brett, A. O.; Iniesta,
J.; Marken, F.; Li, Y. Q. ARKIVOC 2009, Vol. ix, 96–113. (e) Nakayama, J. Bull. Chem.
Soc. Jpn. 2000, 73, 117.
[13] (a) Arima, K.; Ohira, D.; Watanabe, M.; Miura, A.; Mataka, S.; Thiemann, T.; Iniesta, J.;
Walton, D. Photochem. Photobiol. Sci. 2005, 4, 808-816; (b) Nakayama, J.; Hiraiwa, S.
Fujihara, T. Sulfur Chem. 2008, 29, 243250; (c) Heying, M. J.; Nag, M.; Jenks, W. S. J.
Phys. Chem. Org. 2008, 21, 915924.
[14] Jiang, B.; Tilley, T. D. J. Am. Chem. Soc. 1999, 121, 97449745.
[15] Suzuki, S.; Segawa, Y.; Itami, K.; Yamaguchi, J. Nature Chemistry 2015, 7, 227–233.
[16] Landini, D.; Rolla, F. J. Org. Chem. 1982, 47, 154–157.
[17] (a) Li, Y. Q.; Thiemann, T.; Mimura, K.; Sawada, T.; Mataka, S.; Tashiro, M. Eur. J.
Org. Chem. 1998, 1841–1850. (b) Thiemann, T.; Li, Y. Q.; Thiemann, C.; Sawada, T.;
Ohira, D.; Tashiro, M.; Mataka, S. Heterocycles 2000, 52, 12151230.
[18] (a) Cieplak, A. S. J. Am. Chem. Soc. 1981, 103, 4540–4552. (b) Cieplak, A. S.; Tait, B.
D.; Johnson, C. R. J. Am. Chem. Soc. 1989, 111, 8447–8462. (c) Cieplak, A. S. Chem.
Rev. 1999, 99, 12651336.
[19] Thiemann, T.; Iniesta, J.; Walton, D. J. Chem. Res. 2008, 32, 173–180.
[20] Iniesta, J.; Matsumoto, T.; Thiemann, T. J. Chem. Res. 2008, 32, 119–114.
20
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ACCEPTED MANUSCRIPT
[21] (a) Fogel, Y.; Zhi, L.; Rouhanipour, A.; Andrienko, D.; Räder, H. J.; Műllen, K.
Macromolecules, 2009, 42, 68786884. (b) Englert, J. M.; Malig, J.; Zamolo, V. A.;
Hirsch, A.; Jux, N. J. Chem. Soc., Chem. Commun. 2013, 49, 48274829.
[22] (a) Luo, Q.; Wang, C.; Zhang, W.-X.; Xi, Z. J. Chem. Soc., Chem. Commun. 2008, 1593–
1595; (b) Xi, Z.; Song, Q. J. Org. Chem. 2000, 65, 91579159.
[23] Harmata, M.; Gomes, M. G. Eur. J. Org. Chem. 2006, 2273–2277.
[24] Mock, W. L., J. Am. Chem. Soc. 1970, 92, 7610–7612.
[25] Li, Y. Q.; Thiemann, T; Sawada, T.; Tashiro, M. J. Chem. Soc., Perkin Trans. 1, 1994,
23232329.
[26] Thiemann, T.; Sa e Melo, M. L.; Campos Neves, A. S.; Li, Y. Q.; Mataka, S.; Tashiro,
M.; Geiβler, U.; Walton, D. J. Chem. Res. 1998, 22, 346347.
[27] Thiemann, C.; Thiemann, T.; Li, Y. Q.; Sawada, T.; Nagano, Y.; Tashiro, M. Bull. Chem.
Soc. Jpn. 1994, 67, 18861893.
[28] (a) Nightingale, D. V.; Hucker, H. B. J. Org. Chem. 1953, 48, 1529–1537. (b) Kagechika,
H.; Kawachi, E.; Hashimoto, Y.; Shudo, K. J. Med. Chem. 1988, 31, 2182–2192. (c)
Sudha, S.; Palanichamy, M.; Balasubramanian, V. V.; Arabindoo, B.; Murugesan, V. J.
Mol. Catal. A 2006, 255, 220–229. (d) Dhami, K. S.; Stothers, J. B.; Tetrahedron Lett.
1964, 631–639. (e) Dhami, K. S.; Stothers, J. B. Can. J. Chem. 1965, 479–497.
[29] Fuchs, B. Isr. J. Chem. 1968, 6, 517–520.
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[30] Swope, W. C.; Lee, Y.-P.; Schaefer III, H. F. J. Chem. Phys. 1979, 71, 37613769.
[31]
Beckenridge, W. H.; Miller, T. A, J. Chem. Phys. 1972, 56, 465474.
[32] Chao, P.; Lemal, D. M. J. Am. Chem. Soc. 1973, 95, 920–922.
[33] Tong, L.; Lau, H.; Ho, D. M.; Pascal, Jr., R. A. J. Am. Chem. Soc. 1998, 120, 6000–6006.
[34] Van Tilborg, W. J. M. Synth. Commun. 1976, 6, 583–589.
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Ph-p-Me
O
O
Ph-p-Me
p-Me-Ph
p-Me-Ph
p-Me--Ph
SO
+
N
Ph
N
Ph
Ph-p-Me
CHCl3
S
p-Me-Ph
3a
89%
O
O
O
1a
2a
Ph-p-Me
Ph-p-Me
O
O
p-Me-Ph
p-Me-Ph
SO
O
O
1a
+
CHCl3
O
3b
O
Ph-p-Me
2b
94%
BzlNMe3OH, H2O
84%
Ph-p-Me
CO2Me
CO2Me
p-Me-Ph
p-Me-Ph
CO2R
R = H (3c)
SO
CH2N2
1a
+
R = CH3 (3d)
CHCl3
97%
CO2R
2c
Ph-p-Me
Ph-p-Me
68%
O
O
p-Me-Ph
SO
CHCl3
+
+
1a
1a
p-Me-Ph
83%
2d
3e
Ph-p-Me
Ph-p-Me
O
O
p-Me-Ph
SO
CHCl3
p-Me-Ph
42%
3f
2e
Ph-p-Me
Ph-p-Me
O
O
p-Me-Ph
Ph
Ph
Ph
Ph
SO
+
1a
CHCl3
p-Me-Ph
3g
2f
28%
Ph-p-Me
Ph-p-Me
O
O
CN
p-Me-Ph
CN
+
1a
SO
CHCl3
NC
p-Me-Ph
CN
2g
3h
Ph-p-Me
quant.
Scheme 1
23
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O
O
O
S
O
R-Ph
Ph-R
H
Ph
S
H
45 ºC
R-Ph
O
Ph-R
+
+
Ph
N
Ph
CDCl3
R-Ph
R-Ph
R-Ph
R-Ph
N
Ph-R
Ph-R
O
Ph
O
2 eq.
2a
1 eq.
1 eq.
1b: R = H
4a: R = H
3a (R = CH3), 3i (R = H) form exclusively
1a: R = CH3
4b: R = CH3
(the reaction completes at 45 ºC in 90 min.)
Scheme 2
24
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But
O
O
But
N
Ph-p-Cl
SO
N
Ph-p-Cl
+
S
But
CHCl3
89%
5a
O
1c
2h
O
O
But
But
O
O
1c
+
SO
CHCl3
5b
2i
But
But
O
O
72%
O
O
R = But
(5c)
OR
HCl
OBut
SO
Hexadec(Bu)3P+Br-
R = H
(5d)
1c
+
CHCl3
89%
61%
2j
But
But
O
O
SO
CHCl3
68%
1c
+
5e
2d
But
But
O
O
SO
1c
+
CHCl3
63%
2e
5f
But
Scheme 3
25
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But
But
O
O
O
But
140 oC
+
N
Ph-p-Cl
N
Ph-p-Cl
N
Ph-p-
Cl
+
S
But
diphenyl ether
O
O
O
O
O
But
But
But
2h
6
7a
8a
35%
5%
O
O
But
195 oC
+
S
But
diphenyl ether
O
O
55%
But
O
O
6
2i
7b
Scheme 4
26
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Ph-p-Me
Ph-p-Me
O
O
p-Me-Ph
p-Me-Ph
p-Me-Ph
180 oC, 9h
SO
N
Ph
N
Ph
diphenyl ether
p-Me-Ph
O
O
Ph-p-Me
Ph-p-Me
Ph-p-Me
9a
65% (160 oC, 14h: 75%)
3a
Ph-p-Me
O
O
p-Me-Ph
p-Me-Ph
p-Me-Ph
p-Me-Ph
170 oC, 9h
SO
diphenyl ether
70%
3e
Ph-p-Me
9b
Ph-p-Me
Scheme 5
27
ACCEPTED MANUSCRIPT

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But
But
But
O
O
O
170 oC, 1h
SO
N
Ph-p-Cl
+
Ph-p-Cl
N
Ph-p-Cl
N
diphenyl ether
O
O
O
O
But
But
But
But
But
69%
5%
5a
8a
7a
O
140 oC, 1h
SO
diphenyl ether
But
65%
5e
But
7c
Scheme 6
28
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Ph-p-R
Ph-p-R
Ph
O
O
O
H
p-R-Ph
p-R-Ph
Ph
Ph
h
SO
N
Ph
N
Ph
N
Ph
(CD2Cl2
or on silica gel)
+
p-R-Ph
p-R-Ph
H
O
O
O
R = H: 3i
R = Me: 3a
Ph-p-R
Ph-p-Me
Ph-p-R
Ph-p-Me
9c: R = H (54%)
9a: R = Me (55%)
8b
Ph
O
34%
O
p-Me-Ph
p-Me-Ph
p-Me-Ph
h
OMe
OMe
OMe
OMe
SO
CD2Cl2
p-Me-Ph
9d
O
O
3d
Ph-p-Me
Ph-p-Me
O
Ph-p-Me
Ph-p-Me
91%
O
p-Me-Ph
p-Me-Ph
p-Me-Ph
p-Me-Ph
h
SO
CD2Cl2
9e
84%
Ph-p-Me
Ph-p-Me
3f
Ph-p-Me
Ph-p-Me
O
O
p-Me-Ph
p-Me-Ph
p-Me-Ph
p-Me-Ph
h
SO
CD2Cl2
65%
9b
3e
Ph-p-Me
Ph-p-Me
Scheme 7
29
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