Novel chemical behaviour of a [2,3] sigmatropic rearrangement product of 2-phenyltetrahydrothiopyranium 1-methylide

Article abstract of DOI:10.1039/a802309c

1,3,4,5,6,11a-Hexahydro-7E-2-benzothionine 5, which is a [2,3] sigmatropic rearrangement product of 2-phenyltetrahydrothiopyranium 1-methylide 8, has been synthesized by reaction of 1-methyl-2-phenyltetrahydrothiopyranium triflate 3 with sodium amide in liquid ammonia or by the fluoride ion-induced desilylation of trans-2-phenyl-1-[(trimethylsilyl)methyl]tetrahydrothiopyranium perchlorate trans-7. Compound 5 is stable at room temperature and reverts to ylide 8 by ring-opening.

Full text of DOI:10.1039/a802309c

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Novel chemical behaviour of a [2,3] sigmatropic rearrangement
product of 2-phenyltetrahydrothiopyranium 1-methylide
Satoshi Doi, Naohiro Shirai and Yoshiro Sato*
Faculty of Pharmaceutical Sciences, Nagoya City University, Tanabe-dori, Mizuho-ku,
Nagoya 467, Japan
1,3,4,5,6,11a-Hexahydro-7E-2-benzothionine 5, which is a [2,3] sigmatropic rearrangement product
of 2-phenyltetrahydrothiopyranium 1-methylide 8, has been synthesized by reaction of 1-methyl-2-
phenyltetrahydrothiopyranium triflate 3 with sodium amide in liquid ammonia or by the fluoride ion-
induced desilylation of trans-2-phenyl-1-[(trimethylsilyl)methyl]tetrahydrothiopyranium perchlorate
trans-7. Compound 5 is stable at room temperature and reverts to ylide 8 by ring-opening.
perchlorate 7 as a single product, which was temporarily con-
sidered to have a trans configuration (Scheme 2).
Introduction
Sommelet–Hauser rearrangement of α-aryl-substituted cyclic
ammonium and sulfonium alkylides is useful for synthesizing
medium-sized heterocyclic compounds by three-carbon ring
enlargement.1 The reaction of 1,1-dimethyl-2-phenylpiper-
idinium iodide 1 with sodium amide in liquid ammonia gave
2-methyl-2,3,4,5,6,7-hexahydro-1H-2-benzazonine 2 (83%) by
ylide rearrangement (Scheme 1).2 However, similar treatment of
The reaction of trans-7 with caesium fluoride at 0 ЊC in DME
under nitrogen gave a 75:21:4 mixture of products 5 ([2,3]
sigmatropic rearrangement product of ylide 8), 6 (demethylene
product of 8) and (E)-methylsulfanyl-1-phenylpent-1-ene 11
(Hoffmann degradation product of ylide 8) in a total yield 54%
after 3 h of stirring. However, the total yield decreased to 37%
and the proportions changed to 55:29:14 when the same reac-
tion was quenched after 24 h of stirring (Scheme 2, Table 1,
entries 1 and 2). The yield of compound 11 increased when the
reaction was carried out at 25 ЊC, and compound 11 became the
main product at 70 ЊC (entries 3 and 4). Prolongation of the
reaction time produced similar changes in the total yield and
the product proportions in the reaction in DMSO, although
appreciable amounts of compound 4 and 1,3,4,5,6,7-hexa-
hydro-2-benzothionine 12 (Sommelet–Hauser rearrangement
product) were formed (compare entries 9 and 10).
We previously reported that bicyclic isotoluene compounds,
which are formed by [2,3] sigmatropic rearrangement of ylides
in non-basic media, are mostly stable at rt and are aromatized
to Sommelet–Hauser rearrangement products by the aid of a
strong base, e.g. in the presence of DBU or in a solution of
potassium hydroxide in ethanol.4,5 When the reactions in entries
2, 3 and 10 were repeated in the presence of DBU, the yield of
compound 12 increased at 25 ЊC with a decrease in that of
compound 5, whereas there was little change at 0 ЊC (compare
entry 3 with 6, 10 with 11, and 2 with 5). These results show that
compound 5 was fairly stable in basic media at lower temper-
ature, and are consistent with the fact that compound 5 was not
aromatized in a solution of sodium amide in liquid ammonia at
Ϫ40 ЊC.
When the reaction in DME was carried out in air, the amount
of acyclic ketone 4 did not increase in the presence of DBU,
while the product became a complex mixture in the absence of
DBU (entries 7 and 8). Thus in the reaction of compound trans-
7 with caesium fluoride, there was little formation of ketone 4
and air did not appear to have any effect; that is, compound 4
was not formed from ylide 8.
Prolongation of the reaction time decreased the total yields
and changed the product proportions; the yields of compounds
6 and 11 increased and that of the isotoluene 5 decreased (com-
pare entry 1 with 2, and 9 with 10). When compound 5 was
dissolved again in DME and the solution stirred at rt for 20 h,
however, no appreciable changes were observed, while arom-
atization to compound 12 was completed after 72 h in the pres-
ence of DBU (Table 2, entries 1–3). In a DMSO solution, half
of bicycle 5 was aromatized to compound 12 after 20 h in the
absence of DBU (entry 4). Compounds 6 and 11 did not
appear. On the other hand, when compound 5 was dissolved in
i
N
I –
Ph
N
Me2
Me
2
4
1
O
Me
Ph
S
i
ii
Ph
S
– OTf
Me
S
3
5
Scheme 1 Reagents and conditions: i, NaNH2, liquid NH3, 3 h, in air;
ii, NaNH2, liquid NH3, 3 h, under N2
1-methyl-2-phenyltetrahydrothiopyranium trifluoromethane-
sulfonate (triflate) 3 did not give the corresponding ring-
enlargement product 1,3,4,5,6,7-hexahydro-2-benzothionine
12, but rather gave 5-methylsulfanyl-1-phenylpentan-1-one 4
(57%).
The carbonyl oxygen of compound 4 should originate from
air because the reagents and the solvent used do not have
available oxygens. When the reaction was carried out under
nitrogen, the product changed to 1,3,4,5,6,11a-hexahydro-7E-
2-benzothionine 5 (isotoluene compound, 62%). These results
led us to question whether products 4 and 5 were formed from
the same intermediate. Fluoride ion-induced desilylation of
[(trimethylsilyl)methyl]-ammonium and -sulfonium salts is an
excellent method for regioselective ylide formation.3,4 We report
here the reaction of trans-2-phenyl-1-[(trimethylsilyl)methyl]-
tetrahydrothiopyranium perchlorate 7 with caesium fluoride.
Results and discussion
Treatment of 2-phenyltetrahydrothiopyran 6 with (trimethyl-
silyl)methyl triflate followed by sodium perchlorate gave
2-phenyl-1-[(trimethylsilyl)methyl]tetrahydrothiopyranium
J. Chem. Soc., Perkin Trans. 1, 1998
2181

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Table 1 Reaction of trans-2-phenyl-1-[(trimethylsilyl)methyl]tetrahydrothiopyranium perchlorate trans-7 with CsF
Reaction conditions
Product proportionsa
Entry
Solvent
Atmosphere
Additive
Temp. (T/ЊC)
Time (t/h)
Total yield (%)
4
5
6
11
12
1
2
3
4
5
6
7
8
9
DME
DME
DME
DME
DME
DME
DME
DME
DMSO
DMSO
DMSO
N2
N2
N2
N2
N2
N2
Air
Air
N2
N2
N2
0
0
25
70
0
25
25
25
25
25
25
3
24
24
24
24
24
3
3
3
24
24
54
37
45
85
41
93
0
2
2
0
6
0
75
55
38
0
59
9
21
29
15
4
14
43
0
0
2
<1
9
16
<1 >98
13
38
DBU
DBU
13
37
Complex mixture
DBU
54
67
47
77
4
0
11
1
20
67
17
0
34
0
15
24
36
28
38
25
6
5
19
50
10
11
DBU
a Proportions of the products were determined by integration of the 1H signals at 400 MHz.
Table 2 Change in 1,3,4,5,6,11a-hexahydro-7E-2-benzothionine 5 at room temperature
Product proportions
Entry
Solvent
Base
Time (t/h)
Yield (%)
5
6
11
12
1
2
3
4
5
DME
DME
DME
DMSO
EtOH
20
20
72
20
20
85
93
96
83
77
100
35
0
44
0
0
0
0
0
0
0
0
0
51
0
DBU
DBU
65
100
56
10% KOH
30
19
Ph
S
i
Ph
S
Ph
S
–
–
SiMe3
trans-7(e)
ii
ClO4
ClO4
3
6
Me3Si
trans-7(a)
iii
ii
Ph
O •
O2
O
S
S
H
– CH2
Ph
S
•
S
Ph
– CH2
Me
Me
8(e)
10
8(a)
9
5
6
4
Me
S
Ph
DBU
S
11
12
Scheme 2 Reagents and conditions: i, Me3SiCH2OTf, CH2Cl2, NaClO4; ii, CsF, DME or DMSO, Ϫ40 ЊC, rt or 70 ЊC, 3–24 h; iii, NaNH2, liquid
NH3, 3 h
a solution of 10% potassium hydroxide in ethanol and the solu-
tion kept for 20 h, compounds 6 and 11 were competitively
formed with aromatization to compound 12 (entry 4).
above mentioned decrease in the total yields and the change in
product proportions with prolongation of the reaction time.
The equilibrium between compounds 5 and 8 lies to the right
in an ethanol solution due to the contribution of sulfonium
ethoxide 3Ј, and thus gave mainly compounds 6 and 11 rather
than compound 12 (Schemes 2 and 3). Although the equi-
librium almost lies to the left in DME, since no change occurred
when compound 5 was dissolved in DME, the reaction of ylide
8 with benzaldehyde resulted in high yields of products 6 and 14.
Since the ratio of diaxial conformers 7(a) and 8(a) to di-
equatorial conformers 7(e) and 8(e) may increase with an
increase in temperature, the yield of acyclic compound 11
which is generated from ylide 8(a) increases at higher temper-
ature (Scheme 2). Benzylide 9 is initially formed in the reaction
It is unlikely that compounds 6 and 11 were formed directly
from compound 5 because the former is a demethylene product
of ylide 8 and the latter is a Hofmann degradation product.
This result suggests that ylide 8 was present in the solution. A
solution of compound 5 and benzaldehyde in DME in a ratio
of 1:1, when stored at rt for 20 h, gave a mixture of substrate 5
(45% recovery), compound 6 (49%) and 2-phenyloxirane 14
(47%) (Scheme 3). Compounds 6 and 14 are the products of the
reaction of ylide 8 with benzaldehyde.6
A reverse reaction of bicycle 5 to ylide 8 occurs in competi-
tion with aromatization to compound 12, and may cause the
2182
J. Chem. Soc., Perkin Trans. 1, 1998

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added to the residue, and the mixture was extracted with Et2O.
EtOH
The ethereal extract was dried (MgSO4), and concentrated
under reduced pressure to give 5-methylsulfanyl-1-phenylpentan-
1-one 4 (236 mg, 57%) as an oil, bp 100 ЊC (2 mmHg) (Found:
C, 69.1; H, 7.8. C12H16OS requires C, 69.2; H, 7.7%); νmax(KBr)/
cmϪ1 2949, 2915 and 1680; δH(500 MHz; CDCl3; Me4Si) 1.70
(2 H, m), 1.86 (2 H, m), 2.10 (3 H, s), 2.55 (2 H, t, J 7.3), 3.00
(2 H, t, J 7.3), 7.46 (2 H, m), 7.56 (1 H, m) and 7.95 (2 H, m);
δC(125 MHz; CDCl3; Me4Si) 15.5, 23.4, 28.7, 34.0, 38.0, 128.0
(2 C), 128.6 (2 C), 133.0, 137.0 and 199.9; m/z 210 (Mϩ ϩ 2,
2%), 209 (Mϩ ϩ 1, 8), 208 (Mϩ, 23), 161 (64), 105 (100), 77 (76)
and 61 (20).
(B). The same reaction was carried out under N2 and worked
up to give 1,3,4,5,6,11a-hexahydro-7E-2-benzothionine 5 (499
mg, 62%), a non-distillable oil; δH(270 MHz; CDCl3; Me4Si)
1.60–1.78 (4 H, m), 1.91 (1 H, dd, J 10.7 and 14.2), 1.98–2.09
(1 H, m), 2.36–2.69 (4 H, m), 2.88 (1 H, dd, J 4.3 and 14.2), 5.72
(1 H, m), 5.95 (1 H, m), 6.11 (2 H, m) and 6.49 (1 H, d, J 9.6);
δC(125 MHz; CDCl3; Me4Si) 25.8, 26.1, 27.2, 35.2, 40.8, 47.1,
121.8, 123.05, 123.8, 130.2 and 132.9 (2 C); λmax(MeCN)/nm
315 (log ε dm3 molϪ1 cmϪ1 3.9).
S
– EtOH
Ph
S
Ph
S
– OEt
–
CH2
Me
5
8
3'
i
Ph
S
O –
Ph
13
O
+
6
Ph
14
Scheme 3 Reagents and conditions: i, PhCHO, DME, rt, 20 h
trans-2-Phenyl-1-[(trimethylsilyl)methyl]tetrahydrothiopyranium
perchlorate (trans-7)
of compound 3 with sodium amide in liquid ammonia, and
then comes into equilibrium with ylides 8(a) and 8(e).7 In air,
rapid oxidation of compound 9 with oxygen leads to ketone 4,
whereas isomerization to ylide 8 becomes the main path under
(Trimethylsilyl)methyl triflate (7.10 g, 30.0 mmol) was added to
a solution of compound 6 (3.62 g, 20.3 mmol) in CH2Cl2 (20
cm3) at rt. The mixture was stirred for 3 h and concentrated
under reduced pressure. The residue was dissolved in CH2Cl2
(10 cm3) and the solution was stirred with aq. NaClO4 (7.93 g,
64.7 mmol in 40 cm3) overnight. The CH2Cl2 layer was separated
and the aqueous layer was extracted with CH2Cl2. The com-
bined CH2Cl2 layers were dried (MgSO4), and concentrated
under reduced pressure, and the residue was recrystallized from
ethyl acetate to give the title salt trans-7 (6.34 g, 86%), mp 121–
122 ЊC (Found: C, 49.1; H, 6.9. C15H25ClO4SSi requires C, 49.4;
H, 6.9%); νmax(KBr)/cmϪ1 2946, 1445, 1256, 1088 and 851;
δH(270 MHz; CDCl3; Me4Si) 0.13 (9 H, s), 1.93 (1 H, AB-q,
J 13.9), 2.05–2.25 (4 H, m), 2.43 (2 H, d, J 14.8), 3.01 (1 H,
AB-q, J 13.9), 3.50 (1 H, m), 3.82 (1 H, m), 4.95 (1 H, dd, J 3.0
and 11.9) and 7.43–7.49 (5 H, m).
nitrogen. The relative energy of isomer 8(e) is 3.2 kcal molϪ1
†
lower than that of isomer 8(a), and that for ylide 9 is 2.2 kcal
molϪ1 lower than that for ylide 8(e) based on calculations at the
Becke3LYP/6-31G* level.8 These small differences in energy
may allow the equilibrium among isomers 8(a), 8(e) and 9 to
occur.
Experimental
DME, DMSO and DBU were dried by distillation from CaH2.
CsF was dried over P2O5 at 180 ЊC under reduced pressure.
Distillation was performed on a Büchi Kugelrohr distillation
apparatus. All mps (Yananco micro melting point apparatus)
and bps (oven temperature) are uncorrected. 1H and 13C NMR
spectra were recorded on a JEOL JNM-A500, LA-400 or
EX-270 spectrometer. J-Values are given in Hz. IR spectra were
obtained on a Jasco FT-IR 5300 spectrometer, and UV-visible
spectra were measured on a Shimadzu UV-240 spectro-
photometer.
Reaction of the salt trans-7 with CsF
(Entries 1 and 2 in Table 1). CsF (0.62 g, 4.1 mmol) was added
to a solution of the salt trans-7 (0.73 g, 2.0 mmol) in DME
(10 cm3) under N2 and the mixture was stirred at 0 ЊC for 3 or
24 h. The mixture was poured into water and extracted with
Et2O. The ethereal extract was dried (MgSO4), and concentrated
under reduced pressure to give a mixture of products 4, 5, 6 and
(E)-5-methylsulfanyl-1-phenylpent-1-ene 11 (after 3 h, total 204
mg, 54%, proportions 0:75:21:4; after 24 h, total yield 139 mg,
37%, proportions 2:55:29:14). Isolation of each compound
was difficult due to insufficient separation on silica gel columns.
The product proportions were determined by integration of the
1H signals at 400 MHz in the NMR spectra of the mixture.
Compound 11: δH(400 MHz; CDCl3; Me4Si) 1.74–1.80 (2 H,
m), 2.10 (3 H, s), 2.29–2.34 (2 H, m), 2.53 (2 H, t, J 7.3), 6.19
(1 H, dt, J 15.8 and 7.3), 6.40 (1 H, d, J 15.8) and 7.17–7.35
(5 H, m); δC(125 MHz; CDCl3; Me4Si) 15.5, 28.7, 32.0,
33.7, 126.0 (2 C), 127.0, 128.5 (2 C), 129.7, 130.6 and 137.6; m/z
(GC-EI) 192.0961 (Mϩ. C12H16S requires M, 192.0973), 194
(Mϩ ϩ 2, 3%), 193 (Mϩ ϩ 1, 9), 192 (Mϩ, 62), 144 (52), 129
(100), 115 (35) and 91 (28).
1-Methyl-2-phenyltetrahydrothiopyranium trifluoromethane-
sulfonate (triflate) 3
Methyl triflate (7.80 g, 47.5 mmol) was added to a solution of
2-phenyltetrahydrothiopyran9 6 (5.84 g, 32.7 mmol) in CH2Cl2
(50 cm3) at rt and the mixture was stirred for 3 h. The solvent
was evaporated off under reduced pressure and the residue was
washed with Et2O to give the title salt 3 (10.98 g, 95%), mp 81–
82 ЊC (Found: C, 45.3; H, 5.0. C13H17F3O3S2 requires C, 45.6; H,
5.0%); νmax(KBr)/cmϪ1 3023, 2934, 1424, 1262, 1163, 1030 and
639; δH(500 MHz; CDCl3; Me4Si) 1.89–2.19 (4 H, m), 2.39–2.46
(2 H, m), 2.82 (3 H, s), 3.78–3.90 (2 H, m), 4.95 (1 H, dd, J 2.44
and 12.82) and 7.44–7.47 (5 H, m); δC(100 MHz; CDCl3; Me4Si)
22.6, 23.3, 23.9, 32.4, 40.8, 58.8, 128.3 (2 C), 129.9 (2 C), 130.4
and 133.0.
Reaction of salt 3 with NaNH2 in liquid NH3
(Entry 3). The same reaction was carried out at rt for 24 h to
give a mixture of products 4, 5, 6, 11 and 12 (total yield 246 mg,
45%, proportions 2:38:15:43:2).
(Entry 4). The same reaction was carried out at 70 ЊC for 24 h
and the product worked up to give compound 11 (328 mg,
85%).
(A). Salt 3 (690 mg, 2.0 mmol) was added portionwise to a
solution of NaNH2 [from Na metal (70 mg, 3.0 mmol)] in liquid
NH3 (20 cm3, NH3 vapour condensed in dry air), and the mix-
ture was stirred for 3 h. NH4Cl (109 mg, 2.0 mmol) was added
to the mixture and NH3 was evaporated off. Water (20 cm3) was
(Entries 5 and 6). CsF (0.62 g, 4.1 mmol) was added to a
solution of the salt trans-7 (0.73 g, 2.0 mmol) and DBU (0.61 g,
† 1 cal = 4.184 J.
J. Chem. Soc., Perkin Trans. 1, 1998
2183

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4.0 mmol) in DME (10 cm3) at 0 or 25 ЊC and the mixture was
stirred for 24 h and worked up to give a mixture of products 4,
5, 6, 11 and 12 (at 0 ЊC, total yield 157 mg, 41%, proportions
6:59:13:13:9; at 25 ЊC, total yield 348 mg, 93%, proportions
0:9:38:37:16).
(Entry 7). The same mixture of salt trans-7 and CsF in DME
described for entries 1 and 2 was stirred in dry air at rt for 3 h
and worked up to give a complex mixture which was difficult to
separate.
Reaction of bicycle 5 with benzaldehyde
A solution of compound 5 (328 mg, 1.71 mmol) and benzalde-
hyde (181 mg, 1.71 mmol) in DME (5 cm3) was stirred at rt for
20 h under N2. The mixture was mixed with water and extracted
with Et2O. The extract was dried (MgSO4) and concentrated to
give a mixture of starting material 5, isomer 6 and phenyl-
oxirane 14 (total 368 mg, 5 0.78 mmol, 6 0.84 mmol, 14 0.81
mmol). The structure of compound 14 was confirmed by com-
1
parison with an authentic sample by GLC-MS and H NMR
(Entry 8). The same mixture of salt trans-7, CsF and DBU
described for entry 6 was stirred in air for 3 h and worked up to
give a mixture of compounds 4, 5, 6, 11 and 12 (total yield 203
mg, 54%, proportions 4:20:34:36:6).
spectra. Mole ratios of the products were determined by inte-
gration of the 1H signals at 500 MHz.
Computational methods
(Entries 9 and 10). CsF (0.62 g, 4.1 mmol) was added to a
solution of salt trans-7 (0.73 g, 2.0 mmol) in DMSO (10 cm3)
and the mixture was stirred at rt for 3 or 24 h under N2 and
was then worked up to give a mixture of compounds 4, 5, 6, 11
and 12 (after 3 h, total yield 256 mg, 67%, proportions
0:67:0:28:5; after 24 h, total yield 199 mg, 47%, proportions
11:17:15:38:19).
(Entry 11). CsF (0.62 g, 4.1 mmol) was added to a solution of
salt trans-7 (0.73 g, 2.0 mmol) and DBU (0.61 g, 4.0 mmol) in
DMSO (10 cm3) at rt under N2 and the mixture was stirred for
24 h and then worked up to give a mixture of compounds 4, 6,
11 and 12 (total yield 290 mg, 77%, proportions 1:24:25:50).
Starting geometries for the calculations were obtained with
MOL-MOLIS (Daikin Industries, Ltd., Shinjiku-ku, Tokyo,
Japan). Calculations for salt 7 were performed at the restricted
Hartree–Fock (RHF) level with the AM1 method10 in the
MOPAC 93 program.11 Geometries were optimized with the
Eigenvector Following routine. Calculations for ylides 8 and
9 were carried out using the GAUSSIAN 94 package.12
Geometries for ylides 8 and 9 were initially optimized at the
HF/3-21G* level.13 Finally, further geometry optimizations
were performed using the Becke3LYP/6-31G* level.8
References
1 M. Hesse, Ring Enlargement in Organic Chemistry, VCH, New York,
1991, p. 83; R. Brückner, Comprehensive Orgainc Synthesis, ed.
B. M. Trost and I. Fleming, Pergamon Press, Oxford, 1991, vol. 6,
p. 873.
2 D. Lednicer and C. R. Hauser, J. Am. Chem. Soc., 1957, 79, 4449.
3 E. Vedejs and F. G. West, Chem. Rev., 1986, 86, 941; Y. Sato and
N. Shirai, Yakugaku Zasshi, 1994, 114, 880.
Change of bicycle 5 in DME
(Entry 1 in Table 2). A solution of compound 5 (132 mg,
0.686 mmol) in DME (5 cm3) was stirred at rt under N2 for 20 h.
The mixture was poured into water (40 cm3) and extracted with
Et2O. The extract was dried (MgSO4) and concentrated to
recover starting material 5 (112 mg, 85%).
4 T. Tanzawa, M. Ichioka, N. Shirai and Y. Sato, J. Chem. Soc., Perkin
Trans. 1, 1995, 431; T. Tanzawa, N. Shirai, Y. Sato, K. Hatano and
Y. Kurono, J. Chem. Soc., Perkin Trans. 1, 1995, 2845; T. Kitano,
N. Shirai and Y. Sato, J. Chem. Soc., Perkin Trans. 1, 1997, 715.
5 Y. Sato, N. Shirai, Y. Machida, E. Ito, T. Yasui, Y. Kurono and
K. Hatano, J. Org. Chem., 1992, 57, 6711.
6 B. M. Trost and L. S. Melvin, Jr, Sulfur Ylides, Academic Press,
New York, 1975, p. 51.
7 C. L. Bumgardner, H. Hsu, F. Afghahi, W. L. Robert and S. T.
Purrington, J. Org. Chem., 1979, 44, 2348.
8 (a) A. D. Becke, Phys. Rev. A, 1988, 38, 3098; (b) C. Lee, W. Yang
and R. G. Parr, Phys. Rev. A, 1988, 37, 785.
9 D. L. Tuleen and R. H. Bennet, J. Heterocycl. Chem., 1969, 6, 115.
10 AM1: M. J. S. Dewar, E. G. Zoebish, E. F. Healy and J. J. P. Stewart,
J. Am. Chem. Soc., 1985, 107, 3902.
11 MOPAC 93 ver. 2: J. J. P. Stewart, JCPE P081, JCPE Newsletter,
1995, 6, 76.
12 Revision D.4, M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W.
Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A.
Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham,
V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B. B.
Stefanov, A. Nanyakkara, M. Challacombe, C. Y. Peng, P. Y. Ayala,
W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts,
R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P.
Stewart, M. Head-Gordon, C. Gonzalez and J. A. Pople, Gaussian,
Inc., Pittsburgh, PA, 1995.
13 B. G. Johnson, P. M. W. Gill and J. A. Pople, J. Chem. Phys.,
(a) 1992, 97, 7846; (b) 1993, 98, 5612; (c) P. M. W. Gill, B. G.
Johnson, J. A. Pople and M. J. Frisch, Chem. Phys. Lett., 1992, 197,
499.
(Entries 2 and 3). To a solution of compound 5 (269 mg, 1.40
mmol) in DME (5 cm3) was added DBU (426 mg, 2.80 mmol)
under N2 and the mixture was stirred at rt for 20 or 72 h and
then worked up in a manner similar to that described above to
give a mixture of starting material 5 and isomer 12 (total 250
mg, 93%, ratio 35:65) after 20 h, and to give almost pure isomer
12 (257 mg, 96%) after 72 h.
Compound 12: bp 115–120 ЊC (1.3 mmHg), mp 50–51 ЊC
(Found: C, 74.8; H, 8.5. C12H16S requires C, 74.9; H, 8.4%);
νmax(KBr)/cmϪ1 2922, 1443 and 754; δH(500 MHz; CDCl3;
Me4Si) 1.35–1.42 (2 H, m), 1.62–1.68 (2 H, m), 1.76–1.82 (2 H,
m), 2.70–2.75 (4 H, m), 3.80 (2 H, s) and 7.12–7.22 (4 H, m);
δC(125 MHz; CDCl3; Me4Si) 21.5, 30.9, 31.7, 32.6, 33.6, 36.8,
126.5, 127.2, 129.5, 129.7, 139.5 and 140.9; m/z 194 (Mϩ ϩ 2,
6%), 193 (Mϩ ϩ 1, 14), 192 (Mϩ, 100), 143 (43), 131 (31), 115
(32), 104 (45) and 87 (91).
(Entry 4). A solution of compound 5 (266 mg, 1.383 mmol)
in DMSO (5 cm3) was stirred at rt under N2 for 20 h. The
mixture was treated in a manner similar to that described above
to give a mixture of starting material 5 and isomer 12 (total 222
mg, 83%, ratio 44:56).
Change of bicycle 5 in a KOH–EtOH solution
(Entry 5 in Table 2). To a solution of 10% KOH in EtOH (10
cm3) was added bicycle 5 (0.499 g, 2.59 mmol), and the mixture
was stirred at rt for 24 h. The mixture was mixed with water (50
cm3), extracted with Et2O, and the extract was dried (MgSO4)
and concentrated to give a mixture of compounds 6, 11 and 12
(total yield 375 mg, 77%, proportions 30:51:19). The product
proportion were determined by integration of the 1H signals at
500 MHz in the NMR spectra.
Paper 8/02309C
Received 24th March 1998
Accepted 12th May 1998
2184
J. Chem. Soc., Perkin Trans. 1, 1998