The effects of the electron-donating methoxy group on the photoisomerization of 4-methyl-2,4,6-triaryl-4H-thiopyran-1,1-dioxides

Article abstract of DOI:10.1080/104265090930218

Syntheses and photoisomerization of the new sulfone derivatives, 4-anisyl-4-methyl-2,6-diphenyl-4H-thiopyran-1,1-dioxide and 2,6-dianisyl-4- methyl-4-phenyl-4H-thiopyran-1,1-dioxide, are described. The relative molar ratios of the regioselective photoprod

Full text of DOI:10.1080/104265090930218

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The Effects of the Electron-
Donating Methoxy Group on
the Photoisomerization of
4-Methyl-2,4,6-triaryl-4H-
thiopyran-1,1-dioxides
Hooshang Pirelahi a , Farnaz Jafarpour a , Ghasem
Rezanejadebardajee a , Javad Amanishamsabaad a &
Arash Mouradzadegun b
a Department of Chemistry, University of Tehran,
Tehran, Iran
b Department of Chemistry, College of Science,
University of Shahid Chamran, Ahvaz, Iran
Published online: 16 Aug 2006.
To cite this article: Hooshang Pirelahi , Farnaz Jafarpour , Ghasem
Rezanejadebardajee , Javad Amanishamsabaad & Arash Mouradzadegun (2005): The
Effects of the Electron-Donating Methoxy Group on the Photoisomerization of 4-
Methyl-2,4,6-triaryl-4H-thiopyran-1,1-dioxides, Phosphorus, Sulfur, and Silicon and the
Related Elements, 180:11, 2555-2561
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Phosphorus, Sulfur, and Silicon, 180:2555–2561, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/104265090930218
The Effects of the Electron-Donating Methoxy Group
on the Photoisomerization of
4-Methyl-2,4,6-triaryl-4H-thiopyran-1,1-dioxides
Hooshang Pirelahi
Farnaz Jafarpour
Ghasem Rezanejadebardajee
Javad Amanishamsabaad
Department of Chemistry, University of Tehran, Tehran, Iran
Arash Mouradzadegun
Department of Chemistry, College of Science, University of Shahid
Chamran, Ahvaz, Iran
Syntheses and photoisomerization of the new sulfone derivatives, 4-anisyl-4-methyl-
2,6-diphenyl-4H-thiopyran-1,1-dioxide and 2,6-dianisyl-4-methyl-4-phenyl-4H-
thiopyran-1,1-dioxide, are described. The relative molar ratios of the regioselective
photoproducts were compared with those of the unsubstituted model compound
1
under identical experimental conditions using H NMR spectroscopy. The results
that were observed are discussed on the basis of a vinyl-vinyl thia-di-π-methane
rearrangement.
Keywords 4H-Thiopyran-1,1-dioxides; Di-π-methane rearrangement; photoisomeriza-
tion; regioselectivity
INTRODUCTION
In the course of our studies on photoisomerization of 2,4,4,6-tetra-
substituted 4H-thiopyrans,1,2 recently we reported on the synthe-
sis and photochemical transformation of 4-methyl-2,4,6-triphenyl-4H-
thiopyran-1,1-dioxide 1a which, unlike those of the previously reported
tetraaryl analogues,3 upon irradiation with a low-pressure mercury
lamp, underwent rearrangement in high regioselectivity to form two
bicyclic stereoisomers, anti-2a and syn-2a, without SO2 extruded
byproducts.4
Received October 26, 2004; accepted November 30, 2004.
The support of this investigation by the Research Council at the University of Tehran
through Grant No. 559/1/514 is gratefully acknowledged.
Address correspondence to Hooshang Pirelahi, University of Tehran, Department of
Chemistry, PO Box 13145-143, Tehran, Iran. E-mail: pirelahi@khayam.ut.ac.ir
2555

2556
H. Pirelahi et al.
To gain further information on this topic, the present investiga-
tion was undertaken to determine the effects of electron-donating
p-methoxy group on the phenyl substituents attached to 4- and 2,6-
positions of the sulfur ring. Accordingly, new tetrasubstituted 4-anisyl-
4-methyl-2,6-diphenyl-4H-thiopyran-1,1-dioxide 1b and 2,6-dianisyl-4-
methyl-4-phenyl-4H-thiopyran-1,1-dioxide 1c (Scheme 1) were selected
for synthesis and study.
SCHEME 1
RESULTS AND DISCUSSION
In order to compare the effects of the electron-donating p-methoxy
group on the efficiencies of anti- and syn-bicyclic stereoisomers 2b–2c,
photolyses of degassed 3 × 10−2 M solutions of 1a–1c in chloroform-d1
were performed under identical experimental conditions and the results
were compared with those of the model compound 1a. Irradiations were
carried out in sealed NMR tubes by an unfiltered low-pressure mercury
lamp with a transmission maximum of 254 nm under an argon atmo-
1
sphere at room temperature. The reactions were followed by H NMR
and the spectra were recorded at different time intervals.
1
In the H NMR spectra, the corresponding signals of 1a–1c grad-
ually decreased, while six new characteristic sets of signals appeared
for anti- and syn-2a–2c isomers (Table I). Under prolonged irradiation,
the signals of 1a–1c disappeared and those of the bicyclic photoproducts
2a–2c began to decrease.
Owing to the stability of photoproducts at room temperature and
the selectivity of photoisomerization, we were able to isolate and iden-
tify the photoproducts in pure forms. As shown in Table I, cyclopropyl

Effects of the Electron-Donating Methoxy Group
2557
TABLE I The Characteristic Chemical Shifts (δ/ppm) and Coupling
Constants (J/Hz) for 4H-Thiopyran-1,1-dioxides 1a–1c and
Photoproducts 2a–2c in Chloroform-d1 as the Solvent (25◦C)
4H-Thiopyran-1,1-dioxide
δ (ppm)
Photoproducts
δ (ppm)
Compound Me-4 MeO H-3, H-5 Compound Me-6 MeO H-4 H-5
J
4,5
(Hz)
1a10
1b
1.81
—
6.32
6.30
6.25
anti-2a
syn-2a
anti-2b
syn-2b
anti-2c
syn-2c
1.27
1.84
—
—
6.86 3.04
7.02 3.71
3.8
3.8
3.5
3.9
3.4
3.9
1.84 3.82
1.85 3.81
1.26 3.76 6.82 3.02
1.83 3.68 7.07 3.58
1.31 3.73 6.71 2.95
1.61 3.68 6.88 3.53
3.82
1c
protons H-5 for the bicyclic sulfones syn-2a–2c are shifted more down-
field relative to anti-2a–2c because of the stronger anisotropic deshield-
ing effects of two syn-phenyl groups, whereas in the bicyclic sulfones
anti-2a–2c, the protons of the methyl groups are more shifted upfield
relative to syn-2a–2c because of the anisotropic shielding effects of the
phenyl groups at 1-positions.
The variations in molar ratios of 4H-thiopyrans 1a–1c and photo-
1
products 2a–2c in H NMR spectra that were recorded on repeated
irradiations are presented in Table II. Unlike those of some tetraaryl-
substituted sulfone derivatives reported earlier,3 no signs of SO2
TABLE II The Variations (%) of 4H-Thiopyran-1,1-dioxides 1a–1c and
Bicyclic Photoproducts 2a–2c During 480 min of Irradiation Under
Identical Experimental Conditions
Time (min), chloroform
Compound
15
30
45
60
120
180
240
360
5.1
4.0
0.0
18.5
28.5
24.6
18.0
23.4
39.4
480
0.0
2.1
0.0
17.7
29.9
22.4
16.2
18.4
30.3
1a
1b
1c
anti-2a
syn-2a
anti-2b
syn-2b
anti-2c
syn-2c
86.5
85.6
77.4
1.8
4.9
2.0
1.4
5.9
10.4
71.2
74.8
56.3
3.7
9.5
4.6
3.5
10.2
16.3
58.7
67.4
44.7
4.1
11.7
5.8
4.9
13.6
22.5
48.2
59.9
29.3
5.6
15.2
7.1
5.9
19.4
31.0
26.9
32.5
0.0
21.4
21.6
0.0
11.2
26.1
22.7
17.9
28.4
47.0
11.2
12.1
0.0
19.3
27.0
26.5
21.2
27.5
45.6
9.9
22.6
17.5
14.7
25.2
42.6

2558
H. Pirelahi et al.
1
extruded byproducts could be observed in the H NMR spectra. As is
clear from Table II, in each case, two stereoisomers are formed in the
reaction mixtures. The formation of two stereoisomers could be inter-
preted through vinyl-vinyl thia-di-π-methane rearrangement by con-
sidering the rotation around the C C bond as shown in Scheme 2. The
1H NMR data reveals that the transformation of 1c is more efficient
and the yields of photoproducts in 2c are considerably higher than in
2a and 2b. In the case of 2b, on the contrary to 2a and 2c, the anti-2b
is formed in a higher yield than syn-2b. This behavior could be due to
the increase in the half-life time required for the intersystem crossing
of the first singlet excited state.
SCHEME 2
In conclusion, the electron-donating p-methoxy group attached to the
4-phenyl ring of the sulfone increases the efficiency of anti-stereoisomer,
while on the 2,6-diphenyls, the efficiencies increase for both syn- and
anti-stereoisomers 2c relative to the stereoisomers 2a of the model com-
pound with no change of preference in the stereoisomers. This behavior
is consistent with the operation of two different favorable electronic ef-
fects of the p-methoxy group on two different transition states leading
to the corresponding photoproducts.
EXPERIMENTAL
Melting points were determined on a Gallenkamp melting point ap-
paratus and are uncorrected. UV absorption spectra were taken on
a Shimadzu 265-FW spectrophotometer. IR spectra were obtained on
a Shimadzu FT-IR 4300 spectrophotometer in KBr disks. 1H NMR

Effects of the Electron-Donating Methoxy Group
2559
spectra were recorded on Bruker Ac-80 or 500 MHz FT-NMR spectrome-
ters relative to internal standard tetramethylsilane. Mass spectra were
determined with a Finningan MAT-TSQ 70 mass spectrometer. Photol-
yses were performed using a low-pressure mercury lamp with a trans-
mission maximum at λ = 254 nm (85% transmission) and transmitted
light from 254–579 nm (15% transmission).
Syntheses
The new 4H-thiopyran-1,1-dioxides 1b–1c were synthesized from the
reaction of the corresponding 4H-thiopyrans (0.5 mmol) with hydrogen
peroxide of 30% (0.8 mL) in acetic acid (10 mL) at 60◦C. The reactions
were followed by TLC until the transitionally formed 4H-thiopyran-1-
oxides disappeared and the transformations were completed. Then they
were cooled and poured on to ice (20 g). White precipitates were col-
lected and recrystallized from ethanol to give 1b (96.5%) and 1c (91%).
The model compound 1a was synthesized by the method previously
described.4,5
4-Anisyl-4-methyl-2,6-diphenyl-4H-thiopyran-1,1-dioxide (1b)
Colorless crystals. m.p. 165–166◦C. Anal. Calcd. for C25H22O3S
(402.51): C, 74.60; H, 5.51; S, 7.97. Found: C, 74.46; H, 5.57; S, 7.83.
1H NMR (500 MHz, CDCl3): δ 1.84 (s, Me), 3.82 (s, MeO), 6.30 (s, H-3,
H-5), 6.80–7.74 (m, 14H, Ph). EI-MS: m/z 402 (M·+, 5.1), 387 (M Me,
29), 338 (M SO2, 100). UV (MeOH) λmax (logε) nm: 241 (4.36). IR (KBr)
(νmax, cm−1): 1128, 1288 (SO2).
2,6-Dianisyl-4-methyl-4-phenyl-4H-thiopyran-1,1-dioxide (1c)
Colorless crystals. m.p. 136–137◦C. Anal. Calcd. for C26H24O4S
(432.54): C, 72.20; H, 5.59; S, 7.41. Found: C, 72.04; H, 5.54; S, 7.30.
1H NMR (500 MHz, CDCl3): δ 1.85 (s, Me), 3.81(s, 2 MeO), 6.25 (s, H-3,
H-5), 6.85–7.66 (m, 13H, Ph). EI-MS: m/z 432 (M·+, 44.8), 417 (M Me,
2.1), 368 (M SO2, 100). UV (EtOH) λmax (logε) nm: 260 (4.4). IR (KBr)
(νmax, cm−1): 1128, 1290 (SO2).
General Procedure for Photolysis
3 × 10−2 M solutions of 4H-thiopyran-1,1-dioxides 1a–1c were prepared
in chloroform-d1 in NMR tubes, then were degassed and sealed under
Ar. Irradiations were carried out by a low-pressure mercury lamp with
a transmission maximum of 254 nm at room temperature. The progress
1
of the photochemical reactions were followed by H NMR at different
time intervals.

2560
H. Pirelahi et al.
Photoproducts
Irradiations in chloroform gave a mixture of two photoproducts, anti-2b
and syn-2b for 1b and anti-2c and syn-2c for 1c, accompanied by the
1
corresponding starting materials as evidenced by H NMR. The pho-
toproducts were isolated by PLC on neutral alumina with n-hexane:
dichloromethane (80:20) or petroleum ether 40–60◦C:diethylether
(35:65) as an eluent and was purified by recrystallization from ethanol.
Anti-6-Anisyl-6-methyl-1,3-diphenyl-2-thiabicyclo[3.1.0]hex-
3-ene-2,2-dioxide (Anti-2b)
Colorless crystals. m.p. 261–262◦C. Anal. Calcd. for C25H22O3S
(402.51): C, 74.60; H, 5.51; S, 7.97. Found: C, 74.73; H, 5.58; S, 8.06.
1H NMR (500 MHz, CDCl3): δ 1.26 (3H, s, Me), 3.02 (1H, d, 3 J = 3.5 Hz,
H-5), 3.76 (3H, s, MeO), 6.82 (1H, d, 3 J = 3.5 Hz, H-4), 6.84–7.80 (14H,
m, Ph). EI-MS: m/z 402 (M·+, 6.6), 338 (M SO2, 100), 323 (M SO2 Me,
98). UV (MeOH) λmax (logε) nm: 267 (2.9), 221 (3.1). IR (KBr) (νmax
,
cm−1): 1139, 1292 (SO2).
Syn-6-Anisyl-6-methyl-1,3-diphenyl-2-thiabicyclo[3.1.0]hex-3-
ene-2,2-dioxide (Syn-2b)
Colorless crystals. m.p. 172–173◦C. Anal. Calcd. for C25H22O3S
(402.51): C, 74.60; H, 5.51; S, 7.97. Found: C, 74.81; H, 5.53; S, 8.11.
1H NMR (500 MHz, CDCl3): δ 1.83 (3H, s, Me), 3.58 (1H, d, 3 J = 3.9 Hz,
H-5), 3.68 (3H, s, MeO), 7.07 (1H, d, 3 J = 3.9 Hz, H-4), 6.68–7.47 (14H,
m, Ph). EI-MS: m/z 402 (M·+, 5.7), 338 (M SO2, 100), 323 (M SO2 Me,
98). UV (MeOH) λmax (logε) nm: 265 (3.2), 220 (3.3). IR (KBr) (νmax
,
cm−1): 1139, 1294 (SO2).
Anti-1,3-Dianisyl-6-methyl-6-phenyl-2-thiabicyclo[3.1.0]hex-3-
ene-2,2-dioxide (Anti-2c)
Colorless crystals. m.p. 237–238◦C. Anal. Calcd. for C26H24O4S
(432.54): C, 72.20; H, 5.59; S, 7.41. Found: C, 72.32; H, 5.63; S, 7.53.
1H NMR (500 MHz, CDCl3): δ 1.31 (3H, s, Me), 2.95 (1H d, 3 J = 3.4 Hz,
H-5), 3.73 (3H, s, MeO), 3.85 (3H, s, MeO), 6.71 (1H, d, 3 J = 3.4 Hz,
H-4), 6.77–7.41 (13H, m, Ph). EI-MS: m/z 432 (M·+, 1.5), 368 (M SO2,
100), 353 (M SO2 Me, 15). UV (EtOH) λmax (logε) nm: 282 (4.2), 233
(4.4). IR (KBr) (νmax, cm−1): 1138, 1296 (SO2).
Syn-1,3-Dianisyl-6-methyl-6-phenyl-2-thiabicyclo[3.1.0]hex-3-
ene-2,2-dioxide (Syn-2c)
Colorless crystals. m.p. 220–221◦C. Anal. Calcd. for C26H24O4S
(432.54): C, 72.20; H, 5.59; S, 7.41. Found: C, 72.11; H, 5.57; S, 7.28.

Effects of the Electron-Donating Methoxy Group
2561
3
1H NMR (500 MHz, CDCl3): δ 1.61 (3H, s, Me), 3.53 (1H, d, J = 3.9
Hz, H-5), 3.68 (3H, s, MeO), 3.82 (3H, s, MeO), 6.88 (1H, d, 3 J= 3.9 Hz,
H-4), 6.62–7.72 (13H, m, Ph). EI-MS: m/z 432 (M·+, 21), 368 (M SO2,
100), 353 (M SO2 Me, 40). UV (EtOH) λmax (logε) nm: 282 (4.3), 228
(4.4). IR (KBr) (νmax, cm−1): 1137, 1300 (SO2).
REFERENCES
[1] M. Taghizadeh and H. Pirelahi, Phosphorus, Sulfur and Silicon, 176, 9 (2001) and
references cited therein.
[2] H. Pirelahi, A. Atarodiekashani, S. M. Seyyedmoossavi, and H. Daryanavardedarga-
hani, Monatsh. Chem., 135, 973 (2004).
[3] P. Sebek, P. Sedmera, and J. Kuthan, Collect. Czech. Chem. Commun., 58, 869 (1993).
[4] A. Mouradzadegun and H. Pirelahi, J. Photochem. Photobiol. A: Chem., 138, 203
(2001).
[5] G. Suld and C. C. Price, J. Am. Chem. Soc., 84, 2090 (1962).