From thiophene S-oxides to 7-thiabicyclo[2.2.1]hept-5-enes

Article abstract of DOI:10.3184/030823409X12562932030738

Oligocycles with a 7-thiabicyclo[2.2.1]hept-5-ene unit have been prepared stereoselectively by cycloaddition of thiophene S-oxides to alkenes and subsequent deoxygenation of the sulfoxy bridge of the cycloadducts with PBr ₃.

Full text of DOI:10.3184/030823409X12562932030738

702 RESEARCH PAPER
NOVEMBER, 702–704
JOURNAL OF CHEMICAL RESEARCH 2009
From thiophene s-oxides to 7-thiabicyclo[2.2.1]hept-5-enes
Yuan-Qiang Lia, Carolin Thiemannb, Daisuke Ohiraa, Shuntaro Matakab, Masashi Tashirob and
Thies Thiemanna,b,c*
aInterdisciplinary Graduate School of Engineering Sciences and bInstitute of Materials Chemistry and Engineering,
Kyushu University, 6-1, Kasuga-koh-en, Kasuga-shi 816-8580, Fukuoka-ken, Japan
cPresent address: Department of Chemistry, Faculty of Sciences, United Arab Emirates University, PO Box 17551, Al Ain,
United Arab Emirates
Oligocycles with a 7-thiabicyclo[2.2.1]hept-5-ene unit have been prepared stereoselectively by cycloaddition of
thiophene S-oxides to alkenes and subsequent deoxygenation of the sulfoxy bridge of the cycloadducts with PBr3.
Keywords: thiophene S-oxides, cycloaddition, phosphorus tribromide, deoxygenation
Thiophene S-oxides such as 4a–c, which can be prepared
by oxidation of thiophenes with m-CPBA in the presence
published previously.10 The stereochemical outcome of the
reactions can be predicted from extensive work on single
crystal X-ray analysis on cycloadducts of thiophene S-oxides
and alkenes carried out by us and others.3,11-13
Reaction with PBr3 deoxygenates 7-thiabicyclo[2.2.1]
heptene S-oxides 6, 7, and 9a/b efficiently to 7-thiabicyclo-
[2.2.1]heptenes 10, 11, and 12a/b, respectively. A temperature
of 0°C must be maintained carefully during the addition of
PBr3. Temperatures higher than 25°C should also be avoided
during the reaction itself. Elevated temperatures favour the
extrusion of the entire SO-bridge and lead to mixtures of
aromatic systems and cyclohexadienes.
of BF3 Et2O1 or with H2O2 in the presence of a protic acid,2
.
are good dienes in cycloaddition reactions.3 With alkenes
as dienophiles, they yield 7-thiabicyclo[2.2.1]hept-5-ene
S-oxides3 (see also Scheme 2). These cycloadducts are good
precursors to multifunctionalised arenes,4 to cyclohexadienes5
and in certain cases to diaryl disulfides.6 Previously, the authors
have used this combination of reaction to construct such
diverse molecules as crown ethers,7 cyclophanes8 and amino
acids.9 We have reported one example of a transformation of
a 7-thiabicyclo[2.2.1]heptene S-oxide to a 7-thiabicyclo[2.2.1]
heptene.5 We now report that this deoxygenation of bridged
sulfoxides to bridged sulfides is a general reaction.
In conclusion, we have shown that oligocycles with a
7-thiabicyclo[2.2.1]hept-5-ene unit can be prepared with total
stereochemical control in very few steps.
Thiophene S-oxides 4 undergo facile cycloaddition to
alkenes 3, 5, and 8 (Scheme 2). Thus, a solution in chloroform
of 3,4-dibromo-2,5-thiophene S-oxide (4a), accessible from
3,4-dibromo-2,5-dimethylthiophene in one step, was heated
with dibutyl maleate (5) to give cycloadduct 6 in good yield.
Cycloadduct 6 is formed stereoselectively as the endo-product.
Cycloadducts 9a/b are also endo-products and are formed as
one stereoisomer only, with the lone electron pair on sulfur
being on the same side as the newly formed double bond of
the cycloadducts. Compounds 9a/b can also be formed in a
one-pot oxidation-cycloaddition reaction of the corresponding
thiophenes and N-phenylmaleimides 8a/b by the action of
meta chloroperoxybenzoic acid (m-CPBA) in the presence
Experimental
General
Melting points were determined on
a Mitamurariken MELT
THERMO and are uncorrected. IR spectra were recorded on a
JASCO-102 spectrometer. NMR spectra were recorded at 270 MHz
(proton) and at 67.8 MHz (carbon-13) with a JEOL EX-270
spectrometer. The chemical shifts are relative to TMS (solvent
CDCl3, unless noted otherwise). DEPT (Distortionless Enhancement
by Polarisation Transfer) was used to help assign the carbon signals,
where (+) denotes primary and tertiary, (–) secondary and Cquat
quaternary carbons. Mass spectra were measured with a JMS-01-
SG-2 spectrometer (EI, 70 eV). Column chromatography was carried
out Wako gel C300. Thiophene S-oxides 4 were prepared by oxidation
of the corresponding thiophenes with meta-chloroperoxybenzoic acid
of BF3 Et2O.1,3 The yield of the cycloaddition of the isolated
.
thiophene S-oxides 4b/c and the thiophene S-oxides formed
in situ in the one-pot procedure are comparable. Compound 7
is formed as the exo-endo product, with all nine stereocentres
controlled over the course of two consecutive cycloaddition
reactions. The first of these cycloadditions involves the
(m-CPBA) in the presence of BF3 Et2O, as reported previously.14
.
9a1 was prepared analogous to 9b (see below). DMF was dried over
CaH2 and distilled. PBr3 was distilled before use.
3,4-Dibenzoyltricyclo[4.2.102,5]nona-3,7-diene (3): A solution of
tetracyclo[3.2.0.02,704,6]heptane (1, 100 mg, 1.09 mmol) and
dibenzoylacetylene (2, 234 mg, 1.00 mmol) in CCl4 (2 mL) was
held at reflux for 48 h. Thereafter, CCl4 was removed in vacuo
and the residue was subjected to column chromatography on silica
gel (hexane/ether 1:2) to give 3 (270 mg, 85%) as a pale yellow
solid, m.p. 104°C. (Found: M+, 326.1309. C23H18O2 requires M+,
synthesis of a dienophile 3,4-dibenzoyl-tricyclo[4.2.102,5
]
nona-3,7-diene (3) itself, which is achieved by reaction of
quadricyclane (1) with dibenzoylacetylene (2) (Scheme 1),
reminiscent of the reaction of quadricyclane with alkynes,
O
COPh
Ph
CCl4
+
D
Ph
COPh
O
1
3
(85%)
2
Scheme 1 Synthesis of dienophile 3,4-dibenzoyl-tricyclo[4.2.102,5]nona-3,7-diene (3).
* Correspondent. E-mail: thies@uaeu.ac.ae
PAPER: JC090803

JOURNAL OF CHEMICAL RESEARCH 2009 703
Br
Br
CO2Bu
CO2Bu
Br
Br
CO2Bu
CHCl3
+
SO
S
O
D
CO2Bu
4a
5
6
(89%)
O
O
Br
Br
Br
Br
Ph
Ph
Ph
CHCl3
+
SO
S
O
D
Ph
O
O
3
7
(82%)
4a
O
O
R
R
R
R
CHCl3
SO
N-Ph-p-X
N-Ph-p-X
S
O
+
D
O
O
4b: R = CH3, 4c: R = CH2Ph
8a: X = Cl; 8b: X = H
9a: R = CH3, X = Cl (78%)
9b: R = CH2Ph, X = H (75%)
Scheme 2 Cycloaddition of thiophene S-oxides to alkenes.
326.1307). nmax (neat/cm-1) 2994, 2974, 2948, 1648, 1598, 1449,
1317, 1290, 1279, 947, 865, 703, 660; dH (270 MHz, CDCl3) 1.55
(1H, d, 2J = 9.6 Hz), 1.74 (1H, d, 2J = 9.6 Hz), 2.89 (2H, d, J = 1.7 Hz),
2.91 (2H, brs), 6.52 (2H, s), 7.22–7.72 (10H, m); dC (67.8 MHz,
CDCl3) 39.4, 40.1, 45.4, 128.5, 128.8, 133.2, 136.0, 136.7, 149.9,
190.8; MS (EI, 70 eV) m/z (%) = 326 (M+) (30).
Dibutyl 2,3-dibromo-1,4-dimethyl-7-thiabicyclo[2.2.1]hept-2-ene-5,
6-dicarboxylate 7-oxide (6): A mixture of 3,4-dibromo-2,5-dimethyl-
thiophene S-oxide (4a) (150 mg, 0.52 mmol) and dibutyl maleate (5)
237 mg, 1.04 mmol) in chloroform (2 mL) was heated under reflux
for 24 h. Thereafter, the solution was cooled and concentrated in
vacuo. The residue was subjected to column chromatography on silca
gel (hexane/ether 2:1) to give 6 (240 mg, 89%) as a colourless solid;
m.p. 69–70°C. (Found: M+, 513.9848. C18H26O579Br81BrS requires
M+, 513.9847). nmax (neat/cm-1) 2960, 2870, 1737, 1566, 1450, 1383,
1328, 1282, 1246, 1171, 1146, 1110, 1084, 1063, 1025, 950. dH (270
MHz, CDCl3) 0.93 (6H, t, 3J = 7.2 Hz, 2 CH3), 1.36 (4H, m), 1.59 (4H,
m), 1.68 (6H, s, 2 CH3), 3.89 (2H, s), 4.04 (4H, m); dC (67.8 MHz,
CDCl3, DEPT 90, DEPT 135) 13.7 (+, 2C, CH3), 15.5 (+, 2C, CH3),
N-Phenyl-5,6-benzyl-1,4-dimethyl-7-thiabicyclo[2.2.1]hept-5-
ene-2,3-carboxamide 7-oxide (9b): A solution of 3,4-dibenzyl-
2,5-dimethylthiophene S-oxide (4c, 406 mg, 1.32 mmol) and
N-phenylmaleimide (8b, 250 mg, 1.45 mmol) in CHCl3 (4 mL) was
stirred at 60°C for 18 h under an inert atmosphere. Thereafter, the
solvent was evaporated in vacuo and the residue was subjected to
a short column chromatography on silica gel (ether/CHCl3/hexane
2:1:1) to give 9b (475 mg, 75%) as a colourless solid, m.p. 73°C.
(Found: M+, 481.1718. C30H27NO3S requires M+, 481.1712). nmax
(KBr/cm-1) 1700, 1060; dH (270 MHz, CDCl3) 1.67 (6H, s, 2 CH3),
2
3.56 (2H, d, J = 16.0 Hz), 3.76 (2H, s), 3.82 (2H, d, 2J = 16.0 Hz),
7.04–7.52 (15H, m); dC (67.8 MHz, CDCl3) 13.5, 32.7, 51.2, 73.9,
126.1, 126.8, 128.4, 128.7, 128.8, 129.0, 129.1, 131.6, 137.0, 137.1,
174.1; MS (EI, 70 eV) m/z (%) = 433 (M+-SO, 47), 342 (6.9), 193
(100). Anal Calcd for C30H27NO3S (481.60): C, 74.82; H, 5.65; N,
2.91. Found: C, 74.82; H, 5.84; N, 2.83%.
Dibutyl 2,3-dibromo-1,4-dimethyl-7-thiabicyclo[2.2.1]hept-2-ene-
5,6-dicarboxylate (10): A solution of 7 (114 mg, 0.22 mmol) and PBr3
(110 µL, 313 mg, 1.16 mmol) in dry DMF (2.0 mL) was set at 0°C
and stirred at r.t. for 25 min. Thereafter, the mixture was cooled again
to 0°C and ether (10 mL) was added. Then, water (300 µL) was added
dropwise. The mixture was extracted with water (15 mL) and ether
(2 × 15 mL). The combined organic phase was dried over anhydrous
MgSO4 and concentrated in vacuo. Column chromatography on silica
gel (hexane/ether 2.5:1) gave 10 (71 mg, 65%) as a colourless oil.
(Found: M+, 497.9896. C18H26O479Br81BrS requires M+, 497.9899).
nmax (neat/cm-1) 2956, 2854, 1748, 1587, 1459, 1382, 1195; dH
19.1 (–, 2C), 30.4 (–, 2C), 52.7 (+, 2C, CH), 65.6 (–, 2C), 75.2 (Cquat
,
2C), 125.4 (Cquat, 2C), 169.1 (Cquat, 2C). MS (70 eV) m/z (%) = 516
([81Br2]M+, 4), 514 ([81Br79Br]M+, 8), 512 ([79Br2]M+, 4), 468 ([81Br2]
M+-SO, 38), 264 (100).
5,6-Dibenzoyl-11,12-dibromo-1,10-dimethyl-14-thiapentacyclo-
[8.2.1.1.3,80.2,90.4,7]penta-deca-5,11-diene 14-oxide (7): A solution of
3 (100 mg, 0.31 mmol) and 4a (44 mg, 0.15 mmol) in chloroform
(1.5 mL) was held at reflux for 21 h. Then, the cooled solution was
concentrated in vacuo and subjected to column chromatography on
silica gel (ether/hexane 1:1) to give 7 (75 mg, 82%) as a colourless
solid; m.p. 184°C. (Found: MH+, 612.9870. C29H25O379Br81BrS
requires MH+, 612.9873 [FAB]). nmax (KBr/cm-1) 3054, 3026, 2960,
2920, 1653, 1597, 1444, 1315, 1286, 1110, 712, 687, 656; dH (270
MHz, CDCl3) 1.48 (2H, m), 1.65 (6H, s, 2 CH3), 2.51 (2H, bs), 2.52
(2H, bs), 3.07 (2H, bs), 7.18–7.24 (4H, m), 7.33–7.39 (2H, m), 7.60–
7.63 (4H, m); 13dC (67.8 MHz, CDCl3, DEPT, DEPT 135) 16.2 (+,
2C, CH3), 27.8 (–, 2C), 35.0 (+, 2C, CH), 42.3 (+, 2C, CH), 53.3 (+,
2C, CH), 77.2 (Cquat, 2C), 125.8 (Cquat, 2C), 128.5 (+, 4C, CH), 128.8
(+, 4C, CH), 133.4 (+, 2C, CH), 136.4 (Cquat, 2C), 145.9 (Cquat, 2C),
190.5 (Cquat, 2C, C=O); MS (FAB, 3-nitrobenzyl alcohol) m/z (%) =
613 (MH+, 35), 564 (15).
3
(270 MHz, CDCl3) 0.92 (6H, t, J = 7.5 Hz, 2 CH3), 1.20–1.34 (4H,
m), 1.56 (4H, m), 1.78 (6H, s, 2 CH3), 3.94 (2H, s), 3.92–4.10 (4H,
m); dC (67.8 MHz, CDCl3) 13.7 (+, 2C, CH3), 19.2 (+, 2C, CH3 and
2C, CH2), 30.5 (–, 2C), 60.7 (+, 2C, CH), 65.1 (–, 2C), 65.9 (Cquat
,
2C), 132.3 (Cquat, 2C), 169.3 (Cquat, 2C, C=O); MS (70 eV) m/z (%) =
500 ([81Br2]M+, 10), 498 ([79Br81Br]M+, 19), 496 ([79Br2]M+, 10), 419
(M+-Br, 31), 417 (M+-Br, 30), 308 (94), 271 (52), 269 (100), 267 (50).
5,6-Dibenzoyl-11,12-dibromo-1,10-dimethyl-14-thiapentacyclo-
[8.2.1.1.3,80.2,90.4,7]penta-deca-5,11-diene (11): A solution of
7
(67 mg, 0.11 mmol) and PBr3 (110 µL, 313 mg, 1.16 mmol) in dry
DMF (1.5 mL) was set at 0°C and stirred at r.t. for 25 min. Thereafter,
the mixture was cooled again to 0°C and ether (10 mL) was added.
Then, water (300 µL) was added dropwise. The mixture was
extracted with water (15 mL) and ether (2 × 15 mL). The combined
PAPER: JC090803

704 JOURNAL OF CHEMICAL RESEARCH 2009
Br
Br
CO2Bu
Br
Br
CO2Bu
PBr3
SO
S
DMF
CO2Bu
CO2Bu
6
(65%)
10
O
O
Br
Br
Ph
Ph
Br
Br
Ph
Ph
PBr3
S
SO
DMF
O
O
11
(30%)
7
R1
R1
O
O
O
R2
R2
R2
PBr3
SO
N-Ph-p-X
S
N-Ph-p-X
DMF
R2
O
R1
R1
1
2
1
2
12a
: R =CH3, R =H, X=Cl (67%)
9a
R =CH3, R =H, X=Cl
12b: R1=CH3, R2=CH2Ph, X=H (68%)
9b: R1=CH3, R2=CH2Ph, X=H
Scheme 3 Deoxygenation of compounds with a 7-thiabicyclo[2.2.1]heptene S-oxide subunit.
organic phase was dried over anhydrous MgSO4 and concentrated
3060, 3024, 2980, 2930, 2870, 1775, 1706, 1600, 1494, 1453, 1382,
1184, 1029, 750, 728, 714, 692; dH (270 MHz, CDCl3) 1.77 (6H, s,
2 CH3), 3.30 (2H, d, 2J = 15.9 Hz), 3.76 (2H, d, 2J = 15.9 Hz), 3.85
(2H, s), 7.15–7.32 (12H, m), 7.42–7.53 (3H, m); dC (67.8 MHz,
CDCl3, DEPT 90, DEPT 135) 18.0 (+, 2C, CH3), 33.2 (–, 2C, CH2Ph),
59.0 (+, 2C, CH), 66.5 (Cquat, 2C), 126.2 (4C, +, CH), 126.4 (2C, +,
CH), 128.4 (4C, +, CH), 128.6 (2C, +, CH), 128.8 (2C, +, CH), 129.3
(+, CH), 131.5 (2C, Cquat), 138.6 (2C, Cquat), 144.8 (Cquat), 173.6 (2C,
Cquat, C=O); MS (70 eV) m/z (%) = 465 (M+, 3), 433 (M+-S, 38), 292
(100), 173 (44). Anal. Calcd for C30H27NO2S (465.61): C, 77.39; H,
5.85; N, 3.01. Found: C, 77.21; H, 5.86; N, 2.99%.
in vacuo. The residue was subjected to column chromatography on
silica gel (hexane/ether 3:1) to give 11 (19 mg, 30%) as a colourless
solid, m.p. 176–179°C. (Found: MH+, 596.9922. C29H25O279Br81BrS
requires MH+, 596.9923 [FAB]). nmax (KBr/cm-1) 3058, 2960, 2922,
2856, 1651, 1598, 1446, 1314, 1284, 1262, 866, 741, 713, 689; dH (270
MHz, CDCl3) 1.56 (2H, bs), 1.72 (6H, s, 2 CH3), 2.38 (2H, s), 2.62
(2H, s), 2.99 (2H, s), 7.17–7.23 (4H, m), 7.32 – 7.38 (2H, m), 7.60–
7.63 (4H, m); dC (67.8 MHz, CDCl3, DEPT 90, DEPT 135) 20.5 (+,
2C, CH3), 35.4 (+, 2C, CH), 50.0 (+, 2C, CH), 62.3 (+, 2C, CH), 68.2
(+, 2C, CH), 128.9 (+, 4C, CH), 129.3 (+, 4C, CH), 132.5 (Cquat, 2C),
133.8 (+, 2C, CH), 137.0 (Cquat, 2C), 146.4 (Cquat, 2C), 191.1 (Cquat
,
2C, CO); MS (FAB, 3-nitrobenzyl alcohol) m/z (%) = 599 ([81Br2]
MH+, 0.9), 597 ([79Br81Br]MH+, 1.5), 595 ([79Br2]MH+, 0.85).
Received 29 September 2009; accepted 19 October 2009
Paper 09/0803 doi: 10.3184/030823409X12562932030738
Published online: 16 November 2009
N-(p-Chlorophenyl)-1,4-dimethyl-7-thiabicyclo[2.2.1]hept-5-ene-
2,3-dicarboxamide (12a): PBr3 (300 µL, 855 mg, 3.16 mmol) at 0°C
and within 25 min was added to a solution of 9a (100 mg, 0.30 mmol)
in dry DMF (2.5 mL). The resulting slurry was stirred at r.t. for
25 min, then cooled to 0°C and ether (15 mL) was added. Then,
water (300 µL) was added dropwise. Thereafter, the mixture was
extracted with water (15 mL) and ether (2 × 15 mL). The combined
organic phase was dried over anhydrous MgSO4 and concentrated in
vacuo. The residue was subjected to column chromatography on silica
gel (hexane/ether 2:1) to give 12a (64 mg, 67%) as colourless needles,
m.p. 153–154°C. (Found: M+, 320.0518. C16H15O2N35ClS requires
M+, 320.0512). nmax (KBr/cm-1) 3098, 2966, 2928, 2870, 1703,
1492, 1453, 1378, 1181, 1167, 1087, 836, 804, 741; dH (270 MHz,
CDCl3) 1.95 (6H, s, 2 CH3), 3.83 (2H, s), 6.31 (2H, s), 7.09 (2H, d,
3J = 8.6 Hz), 7.40 (2H, d, 3J = 8.6 Hz); dC (67.8 MHz, CDCl3, DEPT
90, DEPT 135) 18.3 (+, 2C, CH3), 57.8 (+, 2C, CH), 64.6 (Cquat, 2C),
127.6 (+, 2C, CH), 129.3 (+, 2C, CH), 129.9 (Cquat), 134.5 (Cquat),
141.2 (+, 2C, CH), 173.4 (Cquat, 2C, C=O); MS (70 eV) m/z (%) = 321
([37Cl]M+, 3), 319 ([35Cl]M+, 8), 207 (13), 112 (100). Anal Calcd
for C16H14NO2ClS (319.81): C, 60.09; H, 4.41; N, 4.38. Found: C,
60.17; H, 4.45; N, 4.43%.
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2
3
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7
8
9
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13, 648.
N-Phenyl-5,6-benzyl-1,4-dimethyl-7-thiabicyclo[2.2.1]hept-5-
ene-2,3-carboxamide (12b): A solution of 9b (50 mg, 0.10 mmol)
and PBr3 (150 µL, 427 mg, 1.58 mmol) in dry DMF (2.0 mL) was
reacted (addition time 20 min. at 0°C, reaction time 20 min. at
r.t.) and worked-up analogous to the preparation of 12a. Column
chromatography on silica gel (hexane/ether 3:1) gave 12b (33 mg,
68%) as colourless needles, m.p. 152–153°C (hexane). (Found: M+,
465.1766; C30H27O2NS requires M+, 465.1763). nmax (KBr/cm-1)
PAPER: JC090803