Unexpected pyrolytic behaviour of substituted benzo[c]thiopyran and thieno[2,3-c]thiopyran s,s-dioxides

Article abstract of DOI:10.1071/CH14155

Flash vacuum pyrolysis (FVP) of benzo[c]thiopyran S,S-dioxide (1) results in formation of indene and 2-vinylbenzaldehyde as previously described. A range of eight analogues with various substitution patterns are found to behave differently. In general, there is no extrusion of SO2 to give products analogous to indene, but unsaturated carbonyl products analogous to 2-vinylbenzaldehyde are formed in most cases by way of ring expansion to a 7-membered ring sultine, extrusion of SO, and intramolecular hydrogen atom transfer. Other processes observed include formation of anthracene via an isomeric 7-membered sultine with loss of SO, CO and methane or butane, and formation of 4-ethylidene-4,5- dihydrocyclobuta[b]thiophenes by way of SO loss, a radical rearrangement, and extrusion of acetone. The analogues with a halogen substituent at position 8 on the benzene ring require a higher temperature to react and give naphthalene resulting from net elimination of HX and SO₂. The X-ray crystal structure of 1 is also reported.

Full text of DOI:10.1071/CH14155

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2014, 67, 1288–1295
Full Paper
http://dx.doi.org/10.1071/CH14155
Unexpected Pyrolytic Behaviour of Substituted Benzo[c]
thiopyran and Thieno[2,3-c]thiopyran S,S-dioxides
A C
,
A
B
R. Alan Aitken,
Cle´mence Hauduc, M. Selim Hossain,
A
B
A
Emily McHale, Adrian L. Schwan, Alexandra M. Z. Slawin,
A
and Colin A. Stewart
A
School of Chemistry, University of St Andrews, North Haugh,
St Andrews, Fife, KY16 9ST, UK.
B
Department of Chemistry, University of Guelph, Guelph,
Ontario, N1G 2W1, Canada.
C
Corresponding author. Email: raa@st-and.ac.uk
Flash vacuum pyrolysis (FVP) of benzo[c]thiopyran S,S-dioxide (1) results in formation of indene and 2-vinylbenzalde-
hyde as previously described. A range of eight analogues with various substitution patterns are found to behave differently.
In general, there is no extrusion of SO2 to give products analogous to indene, but unsaturated carbonyl products analogous
to 2-vinylbenzaldehyde are formed in most cases by way of ring expansion to a 7-membered ring sultine, extrusion of SO,
and intramolecular hydrogen atom transfer. Other processes observed include formation of anthracene via an isomeric
7-membered sultine with loss of SO, CO and methane or butane, and formation of 4-ethylidene-4,5-dihydrocyclobuta[b]
thiophenes by way of SO loss, a radical rearrangement, and extrusion of acetone. The analogues with a halogen substituent
at position 8 on the benzene ring require a higher temperature to react and give naphthalene resulting from net elimination
of HX and SO2. The X-ray crystal structure of 1 is also reported.
Manuscript received: 16 March 2014.
Manuscript accepted: 23 April 2014.
Published online: 30 May 2014.
Introduction
Oxidation of 11 to the corresponding sulfone 12 proved to be the
lowest yielding step of the synthesis. Still and co-workers
obtained a 42-% yield using peracetic acid,[8] but we found
that our method using potassium permanganate under phase-
transfer conditions in the presence of benzoic acid[9] was slightly
better. The borohydride reduction of 12 proceeded smoothly
under the reported conditions[10] to give alcohol 13 for which
1H and 13C NMR data are reported for the first time. Stirring
alcohol 13 in concentrated sulfuric acid resulted in dehydration
to give the target compound 1 as colourless crystals. Remark-
ably, no 13C NMR data of such a fundamental compound appear
to have been reported to date.
Thermal decomposition of cyclic sulfones, resulting in extru-
sion of either SO2 or other fragments, has been extensively
investigated and forms the basis of several useful synthetic
methods.[1,2] In this context, the benzo[c]thiopyran S,S-dioxide
ring system has been relatively little studied, although
brief reports of both pyrolysis[3] and photolysis[4] of the parent
compound 1 have appeared some years ago. Recently, some
of us have developed a new synthetic approach to substituted
compounds of this type.[5] In this paper, we describe the
pyrolytic behaviour of a wide range of differently substituted
aromatic-fused thiopyran S,S-dioxides 2–9 (Chart 1).
Slow evaporation of a solution of 1 in diethyl ether gave good
quality crystals suitable for X-ray diffraction analysis and the
resulting structure is illustrated in Fig. 1. This shows rather long
C–S bonds, the presence of sp3 C(1) in the ring with SO2, and
C¼C all fused to the benzene ring resulting in significant non-
planarity with the SO2 being slightly above and C(1) signifi-
cantly below the plane defined by C(8A), C(4A), C(4), and C(3).
As far as we can determine, no X-ray structure of a com-
pound with the benzo[c]thiopyran ring system has been
reported previously and certainly no S,S-dioxide. However,
there are a few examples of sulfones of the isomeric benzo[b]
thiopyran structure such as 14,[11] 15,[12] 16,[13] and the trans-
cyclopentane-fused compounds 17 and 18.[14] Among these, 16
shows a very similar non-planarity to 1 at adjacent CH2 and SO2
groups (Chart 2).
Results and Discussion
Before embarking on the pyrolysis of the new compounds, we
decided to re-examine the parent compound 1. The preparation
of 1 was first described by Pagani and co-workers in 1967,[6] but
with few details. The synthetic sequence used is shown in
Scheme 1, and since details of many of the steps and inter-
mediates have not been readily accessible to date, the detailed
procedures are given in the Experimental section. The starting
material benzylthioacetic acid (10) was readily prepared by
reaction between chloroacetic acid and benzyl mercaptan,[7] and
when this was treated with P2O5 in hot toluene, rather than
the benzene used in the literature procedure,[7] the cyclic ketone
11 was formed in moderate yield. Using a base extraction for the
work-up, any unreacted 10 could be recovered for re-use.
Journal compilation Ó CSIRO 2014
www.publish.csiro.au/journals/ajc

Pyrolysis of Ring-fused Thiopyran S,S-dioxides
1289
Me
Ph
Bu
Ph
Ph
Ph
Bu
Ph
SO2
SO2
SO2
SO2
SO2
S
S
1
2
3
4
5
t-Bu
Me
Me
Me
SO2
S
SO2
SO2
SO2
I
Br
6
8
9
7
Chart 1.
O
KMnO4, PTC
PhCO2H
O
P2O5/celite
toluene
CH2Cl2, H2O
OH
S
50 %
S
63 %
SO2
O
10
11
12
NaBH4
aq MeOH
84 %
OH
conc.
H2SO4
SO2
SO2
87 %
1
13
Scheme 1. Synthesis of compound 1.
be explained by an initial ring-expansion of the sulfone to a
sultine isomer 21 that was isolated in the photolysis of 1.[4] As
reported previously,[3] homolysis of the S–O bond in 21 fol-
lowed by loss of SO and intramolecular hydrogen atom abstrac-
tion readily give 2-vinylbenzaldehyde (20).
C(4)
C(5)
C(4A)
C(8A)
C(3)
S(2)
C(6)
We now focused our attention on the substituted compounds,
and 2 was also found to undergo almost complete reaction upon
FVP at 7008C. The major product 2-isopropenylbenzophenone
(22) (42 %) was readily identified based on its spectra. Although
this compound was first reported long ago,[15] and its photo-
chemistry has been of recent interest,[16] no spectroscopic data
are available for comparison. However, the good quality of the
resulting 1H and 13C NMR spectra allowed confirmation of the
identity of the compound, particularly because this exact prod-
uct is expected based from the process analogous to formation of
2-vinylbenzaldehyde (20) from 1. Interestingly, the substituted
indene expected from SO2 extrusion was completely absent,
although its spectra were available for comparison.[17] The other
major product turned out quite unexpectedly to be anthracene
(24) (20 %). It appears that two isomeric sultines are involved,
with 25 giving the major product 22, whereas the isomeric
sultine 26 seems more likely to yield anthracene by sequential
loss of SO, CO, and methane (Scheme 3).
O(2)
O(1)
C(7)
C(1)
C(8)
Fig. 1. X-ray structure of compound 1. Selected bond lengths, angles, and
torsion angles: C(4A)–C(4) 1.462(4), C(4)–C(3) 1.342(5), C(3)–S(2) 1.726
˚
(3), S(2)–C(1) 1.767(3), C(1)–C(8A) 1.509(4), C(8A)–C(4A) 1.402(4) A;
C(4A)–C(4)–C(3) 125.7 (3), C(4)–C(3)–S(2) 120.3(2), C(3)–S(2)–C(1)
102.90(15), S(2)–C(1)–C(8A) 115.0(2), C(1)–S(2)–C(3)–C(4) 30.9(4), S
(2)–C(3)–C(4)–C(4A) ꢁ9.1(5), C(8A)–C(1)–S(2)–C(3) ꢁ40.2(3), S(2)–C
(1)–C(8A)–C(4A) 30.6(4)8.
The pyrolytic behaviour of compound 1 was investigated.
Conducting flash vacuum pyrolysis (FVP) in a 30 ꢀ 2.5 cm
furnace tube, operating at pressures in the range of 10ꢁ3–10ꢁ2
Torr, afforded an almost complete reaction at 7008C (,5–10 %
starting material). In agreement with the previous report,[3] the
major products were found to be indene (19) and 2-vinyl-
benzaldehyde (20) (Scheme 2). Direct extrusion of SO2 to give
indene (19) is the major process, in agreement with the typical
behaviour of many cyclic sulfones.[1,2] The formation of 20 may
Further support for these routes was provided by the pyroly-
sis of the 4-butyl compound 3 that behaved in an exactly
analogous way upon FVP at 7008C, giving the unsaturated
ketone 23 as the main product (39 %) after purification and
anthracene (15 %) as minor product.

1290
R. A. Aitken et al.
O
Me
N
Ph
Ph
N
SC6H4CH3-p
SC6H4CH3-p
S
O2
S
O2
S
O2
14
15
16
S
O2
S
O2
Me
17
18
Chart 2.
ꢀSO2
SO2
1
19
SO
SO
ꢀSO
H
CHO
O
O
O
21
20
Scheme 2. Mechanisms observed in the FVP of 1 at 7008C.
R
O
R
R
R
SO
SO
H
ꢀSO
SO2
O
O
Ph
Ph
Ph
Ph
2
3
R ꢁ Me
R ꢁ Bu
25
R
R
R
O
R
Ph
O
O
ꢀSO
O
SO
22 R ꢁ Me
23 R ꢁ Bu
S
O
Ph
Ph
H
Ph
26
R
R
H
R
H
O
ꢀCO
ꢀRH
24
Ph
Scheme 3. Mechanisms proposed in the FVP of 2 and 3 at 7008C.
Under the same conditions, the thiophene-fused compounds
4 and 5 gave the unsaturated ketone products 27 and 28,
respectively, in agreement with the behaviour of 2 and 3. In
the case of 4, an additional isomeric product was isolated after
purification of the product 27 by preparative TLC on silica gel,
and seemed likely to have the benzothienocycloheptadienone
structure 29. This was most obvious from the absence of signals
corresponding to ¼CH2 (dH 4.96, dC 116.1) and aromatic CH, to
be replaced by adjacent aliphatic CH2 (dH 3.55 or 3.04, dC 39.0)
and CH (dH 3.20, dC 39.3) groups. This tricyclic product was
absent in the initial pyrolysate and we speculate that it is formed
on silica via a Friedel–Crafts-type intramolecular alkylation of
the benzene ring by the highly electrophilic alkene function in
27 (Scheme 4). In this case, all the products identified were
derived from the sultine 30 and there was no sign of products
derived from ring-expansion in the other sense.

Pyrolysis of Ring-fused Thiopyran S,S-dioxides
1291
R
O
R
R
R
SO
O
SO
ꢀSO
H
SO2
S
S
S
S
O
Ph
Ph
Ph
Bu
Ph
30
4
5
R ꢁ Bu
Ph
R
ꢁ
R
Bu
Bu
prep. TLC
(27)
ꢃ
ꢂ
Hꢃ
H
O
S
S
S
ꢃ
S
Ph
27 R ꢁ Bu
28 R Ph
Oꢀ
Oꢀ
O
29
ꢁ
Scheme 4. Mechanisms proposed in the FVP of 4 and 5 at 7008C.
t-Bu
t-Bu
t-Bu
t-Bu
SO
SO
ꢀSO
H
S
SO2
S
S
O
O
S
O
6
35
Me
Me
CHMe
Me
Me
CHMe
CHMe
H
·
t-Bu
S
ꢀMe2CO
O
S
S
CH2
O
O
S
38
37
36
H
Me
31
CH2
Me
ꢀMe
ꢃ
S
S
S
S
S
CH2
32
33
34
39
40
Scheme 5. Mechanisms proposed in the FVP of 6 at 7008C.
The other thiophene-fused compound investigated was 6,
with a tert-butyl group at the 4-position and an unsubstituted
position 7. As before, the main product formed upon FVP at
7008C was the unsaturated aldehyde 31, formed as usual by loss
of SO from the sultine and intramolecular hydrogen atom
abstraction (Scheme 5). This was obtained pure in 21 % yield
by preparative TLC, but a second fraction proved to contain
products with an unexpected structure. Detailed analysis of the
1H NMR spectrum including COSY studies suggested these to
be (E)- and (Z)-4-ethylidene-4,5-dihydrocyclobuta[b]thiophene
(32) (6 %) and (33) (3 %), respectively, and 4-methylene-
4,5-dihydrocyclobuta[b]thiophene (34) (1 %). The spectroscopic
data were in almost perfect agreement with those of the
corresponding ethylidene- and methylene-benzocyclobutenes,
and the consistent pattern of chemical shifts also allowed
assignment of the (E) and (Z) isomers.[18]
The formation of these products can be explained, as shown
in Scheme 5, by an alternative process open to the diradical 35,
namely a 1,3-methyl group shift from the tert-butyl group to the
alkenyl radical giving 36. Although no analogous radical
process has apparently been observed before in solution, the
conversion of the non-stabilised vinyl radical 35 into the tertiary
allylic radical 36 is expected to be highly favourable. The
resulting stable tertiary radical site can pair up with the alkoxy
radical to give the thienopyran 37 which is then ideally set up to
extrude acetone. Acetone was present in the crude pyrolysate, as
indicated by its NMR signals at dH 2.10 and dC 30.5 and 205.4.
The electrocyclic ring closure of the resulting species 38 to give
32 and 33 is of some interest[19] since the corresponding 2,3-bis
(methylene)-2,3-dihydrothiophene 39 was generated under sim-
ilar conditions and found not to undergo ring-closure to the
dihydrocyclobutathiophene 40.[20] This finding was confirmed
later by gas phase equilibrium studies, which did however
report such a cyclisation being achieved photochemically in
an argon matrix.[21] It appears that by adding an extra carbon,
the equilibrium position can be reversed such that 38 is an
unstable intermediate involved in the subsequent formation of
the stable electrocyclisation products 32 and 33. In the corre-
sponding benzo-fused system, this is also the case with the two
stable ethylidenebenzocyclobutene isomers undergoing inter-
conversion via an unstable ring-opened allenic form.[18]
The next compounds examined were the 8-halo-4-methyl
compounds 7 and 8. Rather surprisingly, these were recovered
unchanged from FVP at 7008C. It was only at 8008C that
compounds 7 and 8 reacted completely to give single major
product naphthalene (41) (50 % from 7, 65 % from 8). Elemental

1292
R. A. Aitken et al.
Me
Me
Me
H
Me
ꢀX•
SO2
SO2
SO2
SO2
X
ꢀSO2
7 X ꢁ Br
8 X ꢁ I
Me
ꢀH•
rearrangement
41
42
Scheme 6. Mechanism proposed in the pyrolysis of 7 and 8 at 8008C.
Me
Me
Me
ꢀSO2
SO2
9
43
44
ꢀCO
Me
Me
Me
O
Me
SO
SO
H
ꢀSO
CHO
O
O
45
46
Scheme 7. Mechanisms proposed in the pyrolysis of 9 at 7008C.
iodine was also observed in the cold trap in the latter case and
it seemed likely that there was an initial loss of a halogen
atom, generating the aryl radical (Scheme 6). This then under-
goes intramolecular hydrogen atom abstraction to give the
stabilised benzylic radical which is set up to cyclise upon
interaction with the double bond to give a new episulfone-
containing benzylic radical. Loss of SO2 is expected to occur
readily[1] and further loss of a hydrogen atom would give
benzofulvene (42). From the seminal work of Brown, this is
well known to isomerise readily to naphthalene under such FVP
conditions.[22] The markedly higher reaction temperature
requirements for these two compounds when compared with
those employed for other compounds are believed to be due to
steric buttressing from the large halogen atom, discouraging ring
expansion or diradical formation and preventing reaction until
sufficient energy is present for C–X bond fission. A similar
effect has been reported recently in Grainger’s work on 2,7-di-
tert-butylnaphtho[1,8-c,d][1,2]dithiole 1,2-dioxides.[23]
Finally, the naphtho-fused compound 9 was examined and
was found to react completely upon FVP at 7008C, producing a
mixture of two hydrocarbons: methylcyclopenta[a]naphthalene
(43) formed by simple extrusion of SO2 and 2-isopropenyl-
naphthalene (44). The latter was readily identified by compari-
son with literature NMR data,[24,25] and its formation involved
initial ring expansion to the sultine 45, followed by the usual loss
of SO and hydrogen atom transfer giving the aldehyde 46,
followed by decarbonylation (Scheme 7).
extrusion of SO2 is uncommon with most products formed via
ring expansion to 7-membered ring sulfines that subsequently
lose SO, and the resulting diradicals undergo further transfor-
mations. Thus, compounds 2–6 all give an unsaturated carbonyl
compound as the main product (22, 23, 27, 28, and 31), whereas
an isomeric sultine leads to anthracene as a minor product in the
case of 2 and 3 and product 27 is observed to undergo an
interesting cyclisation on silica. Unexpectedly, reaction
involving 6 produces (E) and (Z) isomers of 4-ethylidene-4,5-
dihydrocyclobuta[b]thiophene (32) and (33) as a result of a
novel rearrangement of the diradical 35 to give 36, followed by
extrusion of acetone from the thieno[2,3-c]pyran intermediate
37. The two 8-halo-4-methyl compounds 7 and 8 react only at a
higher temperature than the other compounds and give naph-
thalene as the only major product in a mechanism involving a
series of rearrangements and formation and isomerisation of
benzofulvene. The naphtho compound 9 undergoes direct loss
of SO2 to give 43 as the main product and in this case, aldehyde
46 expected from the usual sultine route undergoes loss of CO to
afford a minor hydrocarbon product 44. Overall, the pattern of
reactivity appears to be highly sensitive to the nature and posi-
tion of substituents, suggesting that examination of a wider
range of such substrates may lead to the discovery of further
unexpected and novel thermal processes.
Experimental
Melting points were determined on a Reichert hot-stage appa-
ratus and are uncorrected. 1H and 13C NMR spectra were
recorded on a Bruker Avance 300 spectrometer (at 300 and
75 MHz, respectively); chemical shifts are reported in ppm (d)
using TMS as internal reference and coupling constants (J) are
Conclusions
Examining a variety of substituted analogues of benzo[c]
thiopyran S,S-dioxide 1 under FVP conditions reveals that direct

Pyrolysis of Ring-fused Thiopyran S,S-dioxides
1293
given in Hz. High-resolution mass spectrometry (HRMS) data
were obtained on a Micromass GCT mass spectrometer using
electrospray ionisation. Compounds 2–9 were prepared as pre-
viously reported.[5]
literature.[10,27] dC 137.9 (CH), 130.4 (CH), 130.0 (CH), 129.9
(CH), 129.2 (CH), 128.7 (C), 128.4 (C), 127.2 (CH), 54.5 (CH2).
Crystallographic Data for 1
Compound 1, C9H8O2S, M 180.21, colourless platelet.
Monoclinic, space group Cc, a 9.543(9), b 11.071(8), c 8.888
3,4-Dihydrobenzo[c]thiopyran-4-one (11)
3
(8) A, b 118.785(18)8, V 823.0(12) A , Z 4, Dc 1.454 Mg m
ꢁ3
˚
˚
A solution of benzylthioacetic acid (10)[7] (20.1 g, 110 mmol) in
toluene (75 mL) was stirred vigorously while a thin paste of
P2O5 (30 g, 211 mmol) and celite (15 g) in toluene (100 mL)
were added slowly. After the addition, the mixture was heated
under reflux for 3 h. The solution was filtered and the filtrate was
washed with 2 M NaOH to remove any uncyclised starting
material (the NaOH extract could be neutralised with 2 M HCl
and extraction with toluene, drying, and evaporation led to
recovery of unreacted 10). Drying and evaporation under
reduced pressure then gave the product 11 (11.42 g, 63 %) as a
yellow oil. dH 8.07 (1H, dd, J 7.5, 1.5), 7.44 (1H, td, J 7.5, 1.5),
7.35 (1H, t, J 7.5), 7.18 (1H, d, J 7.5), 3.90 (2H, s), 3.53 (2H, s).
The data are in agreement with the literature.[26]
,
T 125(2) K, 3072 reflections, 1307 unique (Rint 0.049).
R1 0.0354, wR2 0.0856, R indices based on 1295 data with
I . 2s(I), 109 parameters. Data were recorded using a Rigaku
˚
MM007, MoKa radiation (confocal optic, l 0.71073 A) and
Saturn detector. The structure was solved by direct methods
and refined using full-matrix least-squares methods.
Crystallographic data (excluding structure factors) for the
structure included in this paper have been deposited at the
Cambridge Crystallographic Data Centre as supplementary
publication No. CCDC-782442. Copies of the data can be
obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK; fax: þ 44 1223 336 033;
email: deposit@ccdc.cam.ac.uk.
3,4-Dihydrobenzo[c]thiopyran-4-one
2,2-Dioxide (12)
Flash Vacuum Pyrolysis (FVP)
The apparatus used for this study was as described pre-
viously.[29] All pyrolyses were conducted at pressures in the
range of 10ꢁ3–10ꢁ2 Torr. Under these conditions, the contact
time in the hot zone was estimated to be 1–10 ms. Products were
identified by NMR comparison with authentic materials and
A solution of 11 (11.42 g, 69.6 mmol) and benzoic acid (8.49 g,
69.6 mmol) in CH2Cl2 (500 mL) were stirred vigorously
with a solution of KMnO4 (22 g, 139 mmol) and benzyl-
triethylammonium chloride (1.58 g, 7 mmol) in water (1 L) for
18 h. Solid sodium metabisulfite was added to dissolve the
MnO2 present and the mixture was filtered. The organic layer
was separated, washed with aqueous hydrazine hydrochloride
solution, dried, and evaporated under reduced pressure to give
the product 12 (6.94 g, 50 %) as a yellow oil. dH 8.23 (1H, dd,
J 7.8, 1.5), 7.68 (1H, td, J 7.8, 1.5), 7.55 (1H, t, J 7.8), 7.37 (1H,
d, J 7.8), 4.55 (2H, s), 4.25 (2H, s); the data are in agreement with
the literature.[27] dC 186.2 (CO), 135.3 (CH), 132.3 (C), 130.6
(C), 130.3 (CH), 129.6 (CH), 129.5 (CH), 62.0 (CH2), 55.2
(CH2); the data are in agreement with the literature.[28]
1
yields were determined by calibration of the H NMR spectra
by adding an accurately weighed quantity of a solvent, such as
CH2Cl2, and comparing integrals, a procedure estimated to be
accurate to ꢂ10 %.
FVP of Benzo[c]thiopyran S,S-dioxide (1)
Compound 1 (500 mg) was subjected to FVP at 7008C and the
major products were identified as follows. Indene (19) (23 %
yield). dH 7.60–7.20 (4H, m), 6.88 (1H, dtd, J 5, 2, 1), 6.55 (1H,
dt, J 5, 2), 3.39 (2H, m); the data are in agreement with the
literature.[30] dC 144.8 (C), 143.6 (C), 133.8 (CH), 132.0 (CH),
126.2 (CH), 124.5 (CH), 123.7 (CH), 120.9 (CH), 39.0 (CH2);
the data are in agreement with the literature.[31]
3,4-Dihydro-4-hydroxybenzo[c]thiopyran
2,2-Dioxide (13)
A suspension of 12 (2.34 g, 11.9 mmol) in methanol/water (3: 1,
60 mL) was stirred while a solution of NaBH4 (0.51 g,
13.3 mmol) in water (20 mL) was added dropwise. After stirring
for 12 h, 2 M HCl was added until pH 3 was reached and then
the mixture was partly evaporated to remove the methanol. The
residuewas extracted with CH2Cl2, and was driedand evaporated
to give the product 13 (1.98 g, 84 %) as a yellow oil. nmax (neat)/
cmꢁ1 3470, 1601, 1456, 1305, 1124, 704, 696. dH 7.52 (1H, dd, J
7.5, 1.5), 7.44–7.34 (2H, m), 7.16 (1H, d, J 7.5), 5.27 (1H, t,
J 4.8), 4.41 and 4.26 (2H, AB pattern, J 15.6), 3.52 (2H, d, J 4.8),
3.25 (1H, br s). dC 135.3 (C), 129.9 (CH), 129.3 (CH), 129.2
(CH), 129.1 (CH), 127.4 (C), 69.1 (CH), 55.8 (CH2), 54.6 (CH2).
2-Vinylbenzaldehyde (20) (18 % yield). dH 10.28 (1H, s),
7.84 (1H, dd, J 7, 1), 7.70–7.50 (4H, m), 5.69 (1H, dd, J 17, 1),
5.51 (1H, dd, J 11, 1); the data are in agreement with the
literature.[32] dC 192.4 (CO), 140.5 (C), 134.1 (CH), 133.3
(CH), 132.8 (C), 131.2 (CH), 127.9 (CH), 127.4 (CH), 119.4
(CH2); the data are in agreement with the literature.[33]
FVP of 4-Methyl-1-phenylbenzo[c]thiopyran
S,S-dioxide (2)
Compound 2 (200 mg) was subjected to FVP at 7008C and the
products were isolated by preparative TLC (SiO2, hexane/
diethyl ether, 4 : 1) and identified spectroscopically as follows.
2-Isopropenylbenzophenone (22) (69 mg, 42 %). RF 0.60. nmax
(neat)/cmꢁ1 1717, 1674, 1598, 1493, 1447, 1263, 1073, 700. dH
7.75–7.72 (2H, m), 7.60–7.35 (7H, m), 4.954 (1H, quin, J 1.5,
¼CH), 4.851 (1H, dq, J 1.5, 0.9, ¼CH), 1.94 (3H, dd, J 1.5, 0.9,
CH3). dC 198.8 (CO), 143.8 (C), 142.8 (C),138.2 (C), 137.8 (C),
132.9 (CH), 130.0 (CH), 129.8 (2CH), 128.4 (CH), 128.2 (2CH),
127.8 (CH), 126.8 (CH), 117.3 (¼CH2), 23.7 (CH3). m/z
(HRMS) 223.1116; MþþH requires 223.1123.
Benzo[c]thiopyran 2,2-Dioxide (1)
A mixture of 13 (2.3 g) and concentrated H2SO4 (10 mL) was
stirred at room temperature (RT) for 3 h. The resulting clear
brown solution was poured onto ice and the mixture was
extracted with petroleum (2 ꢀ 25 mL), and dried and evaporated
to give the product 1 (1.84 g, 87 %) as colourless crystals, mp
108–1108C (lit. 1118C[10]). dH 7.43–7.34 (3H, m), 7.30–7.25
(1H, m), 7.16 (1H, d, J 10.5, 4-H), 6.63 (1H, dt, J 10.5, 0.6, 3-H),
4.41 (2H, d, J 0.6); the data are in agreement with the
Anthracene (24) (26 mg, 20 %). RF 0.85. dH 8.43 (2H, s,
9/10-H), 8.01 (4H, m, 1/4/5/8-H), 7.46 (4H, m, 2/3/6/7-H);

1294
R. A. Aitken et al.
second-order pattern is in agreement with simulation using
J1,2 ¼ J3,4 ¼ 8.5, J2,3 ¼ 6, J1,3 ¼ J2,4 ¼ 0.5. dC 128.1 (4CH),
126.2 (2CH), 125.3 (4CH); the data are in agreement with the
literature.[30]
FVP of 4-(Tert-butyl)thieno[2,3-c]thiopyran
6,6-dioxide (6)
Compound 6 (65.6 mg) was subjected to FVP at 7008C and the
products were separated by preparative TLC (SiO2, hexane/
diethyl ether, 1 : 1) to give two fractions: (1) 3-(2,2-dimethyl-
1-methylenepropyl)thiophene-2-carbaldehyde (31) (11 mg,
21 %) as a colourless oil. RF 0.70. nmax (neat)/cmꢁ1 1706, 1603,
1439, 1367, 1265, 1163, 737. dH 9.81 (1H, d, J 1.3, CHO),
7.62 (1H, dd, J 5.0, 1.3, ArH), 7.02 (1H, d, J 5.0, ArH), 5.45 (1H,
d, J 1.3, ¼CH), 4.97 (1H, d, J 1.3, ¼CH), 1.15 (3H, s, CH3).
dC 184.6 (CHO), 154.4 (C), 151.4 (C), 132.7 (CH), 130.5 (CH),
116.2 (¼CH2), 43.0 (C), 29.6 (CH3). m/z (HRMS) 217.0659;
MþþNa requires 217.0663; and (2) and a yellow oil, RF 0.50,
and proved to be a mixture of the following compounds.
(E)-4-ethylidene-4,5-dihydrocyclobuta[b]thiophene (32) (6 %
yield). dH 7.84 (1H, d, J 4.8, ArH), 7.18 (1H, d, J 4.8, ArH), 6.05
(1H, qt, J 7.0, 1.7, ¼CH), 3.44 (2H, dq, J 1.7, 0.8, CH2), 1.85
(3H, dt, J 7.0, 0.8, CH3).
FVP of 4-Butyl-1-phenylbenzo[c]thiopyran
S,S-dioxide (3)
Compound 3 (201 mg) was subjected to FVP at 7008C and the
products were isolated by preparative TLC (SiO2, petroleum/
diethyl ether, 20 : 1) and identified as follows. 2-(Hex-1-en-2-yl)
benzophenone (23) (65 mg, 39 %) as a red oil. RF 0.40. nmax
(neat)/cmꢁ1 2960, 1707, 1666, 1597, 1449, 1265, 738, 700. dH
7.76–7.72 (2H, m, ArH), 7.57–7.31 (7H, m, ArH), 4.96 (1H, q,
J 1.5, ¼CH2), 4.91 (1H, dt, J 1.5, 0.6, ¼CH2), 2.23 (2H, t, J 7.8,
CH2), 1.26–1.17 (4H, m, 2 ꢀ CH2), 0.80 (3H, t, J 7.2, CH3).
dC 198.8 (CO), 148.5 (C), 142.7 (C), 138.3 (C), 137.8 (C), 132.9
(CH), 129.94 (2CH), 129.90 (CH), 128.5 (CH), 128.3 (CH),
128.2 (2CH), 126.6 (CH), 115.7 (¼CH2), 36.7 (CH2), 29.9
(CH2), 22.3 (CH2), 13.9 (CH3). m/z (HRMS) 265.1593; MþþH
requires 265.1592.
(Z)-4-Ethylidene-4,5-dihydrocyclobuta[b]thiophene
(33)
(3 % yield). dH 7.92 (1H, d, J 5.0, ArH), 7.39 (1H, d, J 5.0,
ArH), 5.68 (1H, qt, J 7.2, 1.2, ¼CH), 3.50 (2H, quin, J 1.2, CH2),
2.05 (3H, dt, J 7.2, 1.2, CH3).
m/z (HRMS) 137.0384; MþþH requires 137.0425.
4-Methylene-4,5-dihydrocyclobuta[b]thiophene (34) (1 %
yield). dH 7.88 (1H, d, J 4.8, ArH), 7.25 (1H, d, J 4.8, ArH),
5.54 (1H, t, J 1.8, ¼CH), 5.23 (1H, t, J 1.3, ¼CH), 3.53 (2H, dd,
J 1.8, 1.3, CH2).
Anthracene (24) (16 mg, 15 %). RF 0.75. Spectrum is as
above.
FVP of 4-Butyl-7-phenylthieno[2,3-c]thiopyran
6,6-dioxide (4)
Compound 4 (130 mg) was subjected to FVP at 7008C and the
products were isolated by preparative TLC (SiO2, petroleum/
diethyl ether, 20 : 1) and identified as follows. 3-(Hex-1-en-
2-yl)-2-thienyl phenyl ketone 27 (17.1 mg, 16 %) as a brown oil.
RF 0.60. dH 8.04 (1H, dd, J 7.8, 1.5, ArH), 7.79 (1H, dd, J 8.4,
1.5, ArH), 7.57–7.36 (5H, m, ArH), 4.96 (2H, m, ¼CH2), 2.21
(2H, t, J 7.2, CH2), 1.30–1.20 (4H, m, 2 ꢀ CH2), 0.83 (3H, t, J 7,
CH3). dC 132.5 (CH), 129.8 (CH), 129.7 (CH), 129.5 (2CH),
128.1 (2CH), 116.1 (¼CH2), 36.4 (CH2), 30.1 (CH2), 22.3
(CH2), 13.89 (CH3), five C not apparent.
4-Butyl-4H-benzo[5,6]cyclohepta[1,2-b]thiophen-10(5H)-one
(29) (9.4 mg, 10 %) as a brown oil. RF 0.50. dH 8.03 (1H, dd, J
7.5, 1.8, ArH), 7.56 (1H, d, J 5.1, ArH), 7.55–7.38 (3H, m, ArH),
6.95 (1H, d, J 5.1, ArH), 3.55 (1H, dd, J 14.1, 2.4, CH2), 3.15–
3.25 (1H, m), 3.04 (1H, dd, J 14.1, 6.0, CH2), 1.55–1.60 (2H, m,
CH2), 1.45–1.30 (2H, m, CH2), 1.30–1.20 (2H, m, CH2), 0.80
(3H, t, J 7, CH3). dC 133.6, 132.5, 131.1, 130.8, 130.5, 127.0,
39.3 (CH), 39.0 (CH2), 33.2 (CH2), 29.8 (CH2), 22.6 (CH2),
13.95 (CH3), five C not apparent.
FVP of 8-Bromo-4-methylbenzo[c]thiopyran
S,S-dioxide (7)
Compound 7 (36.7 mg) was subjected to FVP at 8008C and gave
a single product identified as naphthalene 41 (50 %). dH 7.84
(4H, m, 1/4/5/8-H), 7.48 (4H, m, 2/3/6/7-H). dC 133.5 (2C),
127.8 (4CH), 125.8 (4CH).
FVP of 8-Iodo-4-methylbenzo[c]thiopyran
S,S-dioxide (8)
Compound 8 (100 mg) was subjected to FVP at 8008C and the
product was identified spectroscopically as naphthalene (41)
(65 % yield); spectrum is as above.
FVP of 4-Methylnaphtho[1,2-c]thiopyran
2,2-dioxide (9)
Compound 9 (52.3 mg) was subjected to FVP at 7008C and the
products were identified as follows. 3-Methyl-1H-cyclopent[a]
naphthalene (43) (30 % yield). dH 7.90–7.25 (6H, m, ArH), 6.29
(1H, m, CH), 3.63 (2H, m, CH2), 2.26 (3H, m, CH3). dC 128.8
(CH), 127.9 (CH), 126.9 (CH), 126.0 (CH), 124.4 (CH), 123.5
(CH), 118.5 (CH), 36.5 (CH2), 13.3 (CH3).
Data for mixture of 27 and 29: nmax (neat)/cmꢁ1 1771, 1721,
1619, 1594, 1449, 1416, 1312, 1268. m/z (HRMS) 293.0983;
MþþNa requires 293.0976.
2-Isopropenylnaphthalene (44) (15 % yield). dH 7.90–7.25
(7H, m, ArH), 5.53 (1H, s), 5.19 (1H, s), 2.26 (3H, s, CH3); the
data are in agreement with the literature.[24] dC 128.2 (CH),
127.7 (CH), 127.5 (CH), 126.1 (CH), 125.8 (CH), 124.2 (CH),
123.9 (CH), 113.0 (CH2), 21.9 (CH3); the data are in agreement
with the literature.[25]
FVP of 4,7-Diphenylthieno[2,3-c]thiopyran
6,6-dioxide (5)
Compound 5 (41.7 mg) was subjected to FVP at 7008C and a
single product was identified as follows: 3-(1-phenyl-1-
ethenyl)-2-thienyl phenyl ketone 28 (29.4 mg, 82 %) as a dark
oil. nmax (neat)/cmꢁ1 1640, 1597, 1447, 1394, 1264, 694. dH
7.58 (1H, d, J 5.1, CH), 7.54–7.10 (8H, m, ArH), 7.14 (1H, d,
J 5.1, CH), 6.92–6.89 (2H, m, ArH), 5.42 (1H, d, J 0.9, ¼CH2),
5.29 (1H, d, J 0.9, ¼CH2). dC 190.0 (CO), 146.2 (¼C), 144.1 (C),
140.7 (C), 138.1 (C), 132.2 (CH), 131.2 (CH), 129.9 (CH), 129.0
(2CH), 128.1 (2CH), 127.8 (2CH), 127.6 (CH), 126.7 (2CH),
116.8 (¼CH2), one quaternary C not apparent. m/z (HRMS)
313.0658; MþþNa requires 313.0663.
Supplementary Material
1H and 13C NMR spectra of all new compounds are available on
the Journal’s website.
Acknowledgement
MSH and ALS thank NSERC of Canada for support of this research.

Pyrolysis of Ring-fused Thiopyran S,S-dioxides
1295
References
[17] L. M. Tolbert, J. Org. Chem. 1979, 44, 4584. doi:10.1021/
JO00393A027
[18] W. R. Roth, V. Rekowski, S. Bo¨rner, M. Quast, Liebigs Ann. Chem.
1996, 409.
[1] R. A. Aitken, I. Gosney, J. I. G. Cadogan, in Progress in Heterocyclic
Chemistry (Eds H. Suschitzky, E. F. V. Scriven) 1992, Vol. 4, pp. 1–32
(Pergamon Press: Oxford).
[19] S. J. Collier, R. C. Storr, in Progress in Heterocyclic Chemistry
(Eds G. W. Gribble, T. L. Gilchrist) 1998, Vol. 10, pp. 25–48
(Pergamon Press: Oxford).
[2] R. A. Aitken, I. Gosney, J. I. G. Cadogan, in Progress in Heterocyclic
Chemistry (Eds H. Suschitzky, E. F. V. Scriven) 1993, Vol. 5, pp. 1–33
(Pergamon Press: Oxford).
[20] P. M. S. Chauhan, G. Jenkins, S. M. Walker, R. C. Storr, Tetrahedron
Lett. 1988, 29, 117. doi:10.1016/0040-4039(88)80032-7
[21] N. Mu¨nzel, A. Schweig, Chem. Ber. 1988, 121, 791. doi:10.1002/
CBER.19881210426
[3] J. D. Finlay, C. R. Hall, D. J. H. Smith, Tetrahedron Lett. 1977, 18,
1149. doi:10.1016/S0040-4039(01)92855-2
[4] C. R. Hall, D. J. H. Smith, Tetrahedron Lett. 1974, 15, 3633.
doi:10.1016/S0040-4039(01)91986-0
[5] M. S. Hossain, A. L. Schwan, Org. Lett. 2011, 13, 5330. doi:10.1021/
OL202196Y
[6] G. Pagani, S. Maiorana, Chim. Ind. 1967, 49, 1347.
[7] A. K. Kiang, F. G. Mann, J. Chem. Soc. 1951, 1909. doi:10.1039/
JR9510001909
[8] I. W. J. Still, M. T. Thomas, J. Org. Chem. 1968, 33, 2730.
doi:10.1021/JO01271A025
[9] R. A. Aitken, S. T. E. Mesher, F. C. Ross, B. M. Ryan, Synthesis 1997,
787. doi:10.1055/S-1997-1414
[10] S. Bradamante, S. Maiorana, A. Mangia, G. Pagani, J. Chem. Soc. B
1971, 74. doi:10.1039/J29710000074
[11] C. Glidewell, J. N. Low, J. M. S. Skakle, J. L. Wardell, Acta Crys-
tallogr. C 2004, 60, o350. doi:10.1107/S0108270104006286
[12] G. D. Andreetti, G. Bocelli, P. Sgarabotto, Cryst. Struct. Commun.
1974, 3, 309.
[22] R. F. C. Brown, G. E. Gream, D. E. Peters, R. K. Solly, Aust. J. Chem.
1968, 21, 2223. doi:10.1071/CH9682223
[23] R. S. Grainger, B. Patel, B. M. Kariuki, Angew. Chem. Int. Ed. 2009,
48, 4832. doi:10.1002/ANIE.200901788
[24] L. H. Klemm, W. C. Solomon, A. P. Tamiz, J. Org. Chem. 1998, 63,
6503. doi:10.1021/JO9804902
[25] M.-Y. Lin, A. Das, R.-S. Liu, J. Am. Chem. Soc. 2006, 128, 9340.
doi:10.1021/JA062515H
[26] K. Toshima, K. Ohta, T. Ohtake, K. Tatsuta, J. Chem. Soc. Chem.
Commun. 1991, 694. doi:10.1039/C39910000694
[27] K. Toshima, K. Ohta, A. Ohtsuka, S. Matsumura, M. Nakata, J. Chem.
Soc. Chem. Commun. 1993, 1406. doi:10.1039/C39930001406
[28] M. S. Chauhan, I. W. J. Still, Can. J. Chem. 1975, 53, 2880.
doi:10.1139/V75-408
[29] R. A. Aitken, J. I. Atherton, J. Chem. Soc., Perkin Trans. 1 1994, 1281.
doi:10.1039/P19940001281
[13] G. D. Andreetti, G. Bocelli, P. Sgarabotto, Cryst. Struct. Commun.
[30] E. Pretsch, P. Bu¨hlmann, C. Affolter, Structure Determination of
Organic Compounds, 3rd Edn 2000 (Springer: Berlin).
[31] U. Edlund, Org. Magn. Resonance 1978, 11, 516. doi:10.1002/
MRC.1270111009
1974, 3, 313.
[14] L. T. Byrne, M. Phomakotr, C. Poolsanong, V. Reutrakul,
B. W. Skelton, A. H. White, Aust. J. Chem. 2003, 56, 715.
doi:10.1071/CH02134
[15] E. de B. Barnett, J. W. Cook, I. G. Nixon, J. Chem. Soc. 1927, 504.
doi:10.1039/JR9270000504
[32] E. Peyroux, F. Berthiol, H. Doucet, M. Santelli, Eur. J. Org. Chem.
2004, 1075. doi:10.1002/EJOC.200300627
[33] T. M. Gøgsig, L. S. Søbjerg, A. T. Lindhardt, (nee´ Hansen),
K. L. Jensen, T. Skrydstrup, J. Org. Chem. 2008, 73, 3404.
[16] A. K. C. Chu, M. F. Tchir, J. Chem. Soc. Chem. Commun. 1973, 619.
doi:10.1039/C39730000619