Electrochemical activation of dimethyl disulfide for electrophilic aromatic substitution

Full text of DOI:10.1021/jo010156x

4
440
J . Org. Chem. 2001, 66, 4440-4443
Electr och em ica l Activa tion of Dim eth yl
Disu lfid e for Electr op h ilic Ar om a tic
Su bstitu tion
electrode using the technique of cyclic voltammetry up
to a scan rate of 500 mV/s. The oxidation peak of
anthracene is about 400 mV more positive than that for
Me
in the presence of anthracene. Controlled potential
electrolysis of Me in MeCN containing anthracene, in
2 2 2 2
S . Consequently, Me S may be selectively oxidized
Richard S. Glass,* Viatcheslav V. J ouikov, and
Nina V. Bojkova
2
S
2
Department of Chemistry, The University of Arizona,
Tucson,Arizona 85721
a divided cell, produced 9-methylthioanthracene 1a in
74% yield and 9,10-di(methylthio)anthracene 1b in 8%
yield. The structures of both of these compounds were
rglass@u.arizona.edu
unequivocally assigned by comparison with authentic
Received February 8, 2001
9,10
samples.
However, in addition to these products small
amounts of 9,10-anthraquinone, its bis(dimethylthio)-
ketal 2 and a dimer tentatively identified as 3 were
In tr od u ction
To effect electrophilic aromatic substitution, disulfides
need to be activated with Lewis or Bronsted acids.1-3
However, electrochemical oxidation of disulfides should
also activate disulfides for electrophilic aromatic substi-
tution by forming the corresponding radical cations,
dications, or species with electrophilic sulfur derived from
these intermediates.4,5 The potential advantages of elec-
trochemical activation are the avoidance of heavy metals
6
and acidic conditions. Do et al. reported the exhaustive
2 2
electrooxidation of disulfides in CH Cl to give formally
+
sulfenium cations RS . The sulfur electrophile produced
could effect substitution with highly activated phenols
in 26-77% yield but with the less activated anisoles the
found. Structure 2 was assigned on the basis of its spectra
and hydrolysis to 9,10-anthraquinone. Structure 3 was
assigned on the basis of its spectra and in analogy with
7
yields were only 11-35%. Glass and J ouikov reported
-
the reported dimerization of 9-methoxyanthracene on 2e
2 2 2
that electrooxidation of Me S in liquid SO gave a potent
oxidation.11 The formation of 9,10-anthraquinone, 2,
and 3 result from overoxidation of the methylthiation
products. Overoxidation occurred despite the fact that the
potential of the working electrode was maintained at the
12
methylthiating agent that reacted with a large range of
arenes, from strongly activated to weakly activated, in
good to excellent yields. In both of these methods, an
electrophilic thiating agent is prepared electrochemically,
and then, in a subsequent step, it is added to the arene
of interest. Alkylthioarenes have been used as pesticidal
2 2
foot of the oxidation peak of Me S to avoid oxidation of
the reaction products. To avoid this problem the strategy
outlined below was investigated.
2
,6
and pharmaceutical intermediates, as antioxidants and
Anodic oxidation of anthracene13 and 9,10-diphenylan-
8
as precursors to conducting materials. This procedure
thracene14 in the presence of pyridine produces adducts
requires that the electrophilic sulfur species persist until
added to the arene. Since disulfide radical cations and
dications are unstable intermediates, it was deemed
advantageous to have the reacting arene present as these
species are generated. This paper reports our studies of
4
a and 4b, respectively. These products form by nucleo-
philic addition of pyridine to dication 5a and 5b, respec-
tively. Furthermore, treatment of 4a with 1 mol of cold
2 2
the electrochemical oxidation of Me S in the presence
of arenes. Since methylthiation of arenes generates
products that are easier to oxidize than the starting
arene, overoxidation of the product has been observed.
Consequently, a strategy to avoid this problem was
investigated and the successful strategy is reported
here.
Resu lts
base affords the rearomatized anthracene derivative 1c.13
By analogy, electrophilic methylthiation of anthracene
generates 5c, which on nucleophilic attack by pyridine
gives adduct 4c. Adduct 4c should be difficult to oxidize
in comparison with 1a and 1b because the anthracene
In acetonitrile Me
2
S
2
shows an irreversible first oxida-
in MeCN reference
tion peak at 1.05 V vs Ag/0.1M AgNO
3
(
(
(
(
(
1) Farah, B. S.; Gilbert, E. E. J . Org. Chem. 1963, 28, 2807.
2) Ranken, P. F.; McKinnie, B. G. Synthesis 1984, 117.
3) Ranken, P. F.; McKinnie, B. G. J . Org. Chem. 1989, 54, 2985.
4) Glass, R. S. Top. Curr. Chem. 1999, 205, 1.
(9) Saeva, F. D.; Breslin, D. T. J . Org. Chem. 1989, 54, 712.
(10) Engman, L.; Hellberg, J . S. E. J . Organomet. Chem. 1985, 296,
357.
5) Electrophilic aromatic iodination using electrochemically pro-
duced species has been reported: Miller, L. L.; Hoffmann, A. K. J . Am.
Chem. Soc. 1967, 89, 593; Miller, L. L.; Watkins, B. F. Ibid. 1976, 98,
(11) Parker, V. D. Acc. Chem. Res. 1984, 17, 243.
(12) Alternatively 2 may result from attack by a MeS donor on 1b
+
1
515.
(
6) Do, Q. T.; Elothmani, D.; Le Guillanton, G. Tetrahedron Lett.
2 2
and trapping of the resulting cation by Me S .
1
998, 39, 4657.
(
(
(13) Lund, H. Acta Chem. Scand. 1957, 11, 1323.
(14) Shang, D. T.; Blount, H. J . Electroanal. Chem. Interfac Elec-
trochem. 1974, 54, 305.
7) Glass, R. S.; J ouikov, V. V. Tetrahedron Lett. 1999, 40, 6357.
8) Heywang, G.; Born, L.; Roth, S. Synth. Met. 1991, 41-43, 1073.
1
0.1021/jo010156x CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/11/2001

Notes
J . Org. Chem., Vol. 66, No. 12, 2001 4441
ring is replaced by two benzene rings and the methylthio
group is not attached to the aromatic moieties. Elimina-
+
tion of PyrH from 4c produces 1a .
2 2
Controlled potential electrolysis of Me S in the pres-
ence of anthracene and pyridine did not give any pyri-
dinium adduct but only products derived from electro-
philic substitution. However, phenanthrene, acenaph-
thylene,15 and cyclohexene all produce the corresponding
adducts 6-8, respectively, when a solution of these
2 2
compounds, Me S , and pyridine is electrooxidized. These
+
MeS donor species which is not feasible for anthracene
(
+
and formation of 13 from anthracene and MeS is
apparently also unfavorable). The formation of thiira-
nium salts 11 and 12 also accounts for the formation of
trans-products 6 and 7, respectively, since backside
displacement by pyridine on the thiiranium salts would
preferentially produce these products. It has been re-
ported 2
4,25
2 2
that anodic oxidation of Me S in acetonitrile
in the presence of alkenes gives products resulting from
anti addition owing to the intermediacy of thiiranium
salts which undergo backside nucleophilic displacement
by acetonitrile. Similarly we have also found that oxida-
tion of Me S in acetonitrile in the presence of cyclohex-
ene and pyridine affords trans adduct 8 apparently by
nucleophilic attack of pyridine on the corresponding
thiiranium salt.
adducts can also be prepared in good yields by the
1
6
reaction of [(MeS)
threne, acenaphthylene, and cyclohexene in CH
structures of these adducts including stereochemistry,
were determined spectroscopically. In addition, the struc-
ture of (7)SbCl was unequivocally established by X-ray
2
SMe]SbCl
6
and pyridine with phenan-
2
Cl . The
2
1
7-21
2
2
6
crystallographic analysis. Treatment of 6 with sodium
methoxide in anhydrous methanol produced 9-methylth-
iophenanthrene, 9,22 in 61% isolated yield. Reaction of 7
with DBU formed 10 in 76% isolated yield.
Exp er im en ta l Section
1H and 13C NMR spectra were recorded in the solvent
indicated with 0.5% TMS as internal standard at 250.13 and
6
2.9 MHz, respectively. Thick-layer chromatography was done
using silica gel plates. Column chromatography was accom-
plished with silica gel (75-125 µm). Electrochemical experiments
were done using three electrodes in a two-compartment cell with
a potentiostat. A Pt gauze (3 × 5 cm) was used as the anode
and Al foil (5 × 10 cm) as the cathode.
Electr olysis of Me
solution of Me
2 2
S in th e P r esen ce of An th r a cen e. A
(310 mg, 3.3 mmol) and anthracene (534 mg,
2
S
2
3
.0 mmol) dissolved in anhydrous acetonitrile (25 mL) containing
Discu ssion
NaClO
4
(850 mg, 7 mmol) was electrooxidized at +0.85V vs Ag/
in acetonitrile. After an amount of electricity
corresponding to 2 F/mol of Me was passed, the current
0
.1 M AgNO
3
While the electrophile which effects electrophilic aro-
matic substitution on anthracene in acetonitrile on
S is not clear, 9-methylthioanthracene
2 2
a is formed in good yield along with some of the bis-
2
S
2
dropped to approximately 10% of its initial value and the
electrolysis was stopped. The solvent was removed by evapora-
tion in vacuo, and the residue was extracted with cold distilled
water to remove NaClO
matographed on silica gel plates using hexanes:CH
eluent. The fractions collected were the following: 1a , 494 mg
oxidation of Me
1
substituted product 1b. However, products resulting from
further oxidation of 1a and 1b are formed as well. The
strategy of forming adducts by electrophilic addition of
MeS followed by nucleophilic addition of pyridine to
prevent overoxidation and subsequent rearomatization
proved successful for phenanthrene and acenaphthylene.
Surprisingly anthracene does not form an adduct under
these conditions. However, this may be explained by the
formation of thiiranium salts 11 and 12, respectively, on
reaction of phenanthrene and acenaphthylene with the
4
. The organic residue was then chro-
2
2
Cl (1:1) as
(
74% yield), mp 63-64 °C (identical with authentic compound
+
23
1
by H NMR and mass spectroscopy and mmp); 1b, 85.9 mg (11%
yield), mp 161-162 °C (identical with authentic compound by
1
H NMR and mass spectroscopy and mmp); 3, 60 mg (5% yield):
H NMR (CDCl
1
3
) δ 2.39 (s, 6H), 7.45 (m, 4H), 7.62 (m, 4H), 8.0
(
2
3
m, 4H), 8.9 (d, 4H, J ) 8.9 Hz); MS (EI) 446, 431, 384, 352,
86, 271, 209, 175, 166, 111; 2, ca. 13 mg of crude product (1-
% yield): 1H NMR (CDCl
) δ 2.18 (s, 12H), 7.68 (m, 4H); 8.58
3
(m, 4H); MS (EI) 364, 349, 334, 317, 270, 240, 176, 111, 104;
anthraquinone, 59 mg (10% yield), mp 284-285 °C (identical
(
15) Anodic oxidation of Me
2
S
2
and acenaphthylene in the absence
with authentic compound).
of pyridine resulted in the apparent acid-catalyzed polymerization of
acenaphthylene after the passage of a small amount of electricity.
2 2
Electr olysis of Me S in th e P r esen ce of P h en a n th r en e,
Acen a p h th ylen e, or Cycloh exen e a n d P yr id in e. All elec-
trolyses were carried out in a two compartment cell of 30 mL
volume separated by a sintered glass diaphragm. The working
electrode was a Pt gauze cylinder (1.2 cm diameter, 4 cm length),
the counter electrode Al foil (30 cm2 area) and the reference
(
(
(
(
(
(
16) Weiss, R.; Schlierf, C. Synthesis 1976, 323.
17) Dewar, M. J . S.; Fahey, R. C. J . Am. Chem. Soc. 1963, 85, 2245.
18) Dewar, M. J . S.; Fahey, R. C. J . Am. Chem. Soc. 1963, 85, 2704.
19) Mueller, W. H.; Butler, P. E. J . Am. Chem. Soc. 1966, 88, 2866.
20) Sternhell, S.; Westerman, P. W. J . Org. Chem. 1974, 39, 3794.
21) Olsen, S. C.; Christophersen, C. Acta Chem. Scand. 1975, B29,
3
electrode Ag/0.1M AgNO in acetonitrile. A typical solution
contained phenanthrene, acenaphthylene or cyclohexene (6.5
7
17.
(
(
22) Sipil a¨ , K.; Hase, T. Synth. Commun. 1997, 27, 1391.
23) A possible intermediate in these reactions is an N-methylthi-
opyridinium salt. However, attempts to isolate such a salt were
unsuccessful: Caserio, M. C.; Kim, J . K. J . Am. Chem. Soc. 1982, 104,
(24) Bewick, A.; Coe, D. E.; Mellor, J . M.; Owton, W. M. J . Chem.
Soc., Perkin Trans. 1 1985, 1033.
3
231; Kim, J . K.; Souma, Y.; Beutow, N.; Ibbeson, C.; Caserio, M. C.
(25) Bewick, A.; Coe, D. E.; Libert, M.; Mellor, J . M. J . Electroanal.
Chem., Interfac. Electrochem. 1983, 144, 235.
J . Org. Chem. 1989, 54, 1714.

4
442 J . Org. Chem., Vol. 66, No. 12, 2001
Notes
mmol), Me
2
S
2
(0.30 g, 3.2 mmol), pyridine (1.2 g, 15 mmol), and
129.5, 144.5, 147.6; HR MS (FAB) Calcd for C12
Found: 208.1163.
H
18NS: 208.1160.
NaClO (1.5 g, 10 mmol) dissolved in acetonitrile (30 mL). The
4
electrolyses were carried out at an applied potential of 1.0-1.2
V until the amount of electricity corresponding to 2 F/mol was
passed. The analyte was rotary evaporated and the residue
extracted with hexane to leave a solid which was extracted with
X-r a y Cr ysta llogr a p h ic An a lysis of 7‚SbCl . Crystals of
6
7‚SbCl suitable for X-ray crystallographic analysis were grown
6
by vapor diffusing pentane into a CH Cl solution of 7‚SbCl .
2
2
6
A red, irregular block of C18H16NSSbCl having approximate
6
CH
2
Cl
2
. The organic extracts were combined, washed with 0.1
dimensions of 0.119 × 0.340 × 0.374 mm was mounted on a glass
fiber in a random orientation with epoxy. Examination of the
crystal on a Bruker SMART 1000 CCD detector X-ray diffrac-
tometer at 298(2) K and a power setting of 50 kV, 40 mA showed
measurable diffraction to at least θ ) 27.50°. Data were collected
on the SMART1000 system26 using graphite monochromated Mo
KR radiation (λ ) 0.71073 Å).
M aqueous HCl solution, dried, and rotary evaporated, and the
residue was purified by column chromatography when necessary.
6
, 46% yield: 1H NMR,13 C NMR, and FAB MS are the same
as those for 6 obtained by reaction of phenanthrene with [(MeS)
SMe] SbCl and pyridine.
, 72% yield: 1H NMR,13 C NMR, and FAB MS are the same
as those for 7 prepared by reaction of acenaphthylene with
(MeS) SMe]SbCl and pyridine.
, 92% yield: 1H NMR,13 C NMR, and FAB MS are the same
as those for 8 obtained by reaction of cyclohexene with
(MeS) SMe]SbCl and pyridine.
Rea ction of P h en a n th r en e w ith [(MeS)
P yr id in e. A solution of phenanthrene (546 mg, 3.07 mmol)
dissolved in anhydrous CH Cl (1.0 mL) was added to a solution
of [(MeS) SMe]SbCl (1.38 g, 2.90 mmol) dissolved in anhydrous
CH Cl (18 mL) with stirring. The color of the solution changed
to deep purple. A solution of pyridine (246 mg, 3.11 mmol) in
CH Cl (1.0 mL) was added after 1 min whereupon the purple
2
6
7
Initial cell constants were determined from reflections ob-
tained in three orthogonal 5 deg wedges of reciprocal space. Final
cell constants and an orientation matrix for integration were
determined from reflections obtained throughout the full data
set. A total of 1868 frames at 1 detector setting covering 0° <
[
2
6
8
[
2
6
2
θ < 56° were collected, having an omega scan width of 0.3 and
2
6
SMe]SbCl a n d
an exposure time of 10 s. The frames were integrated using the
27
Bruker SAINT software package’s narrow frame algorithm. A
2
2
total of 39885 reflections were integrated and retained of which
2
6
5
σ
388 were unique (〈redundancy〉 ) 7.4, Rint ) 3.9%, R ) 3.0%).
2
2
Of the unique reflections, 3433 (63.7%) were observed >2σ(I).
The final orthorhombic cell parameters of a ) 18.3477(16), b )
2
2
1
(
3.3296(12), c ) 19.1538(15), R ) â ) γ ) 90, volume ) 4684.4-
3
color disappeared and a yellow precipitate formed. The mixture
was stirred at room temperature for 23 h. The mixture was then
7) Å are based on the refinement of the XYZ-centroids of 8192
reflections with I > 10 σ(I) covering the range of 2.17 < θ <
7.50. Empirical absorption and decay corrections were applied
filtered and the orange precipitate washed with CH
2 2
Cl . After
2
being dried in vacuo, 6 was obtained as orange crystals (1.1 g,
using the program SADABS. The absorption coefficient is 1.957
5
1
1
9% yield): mp 124-125 °C (dec); IR (KBr) 3121, 3073, 2917,
mm-1, Tmin ) 0.775610, and Tmax ) 0.980669. For Z ) 8 and
702, 1623, 1477, 1434, 1358, 1249, 1219, 1165, 1123, 1053,
FW ) 612.83 the calculated density is 1.738 g/cm . Systematic
3
024, 961, 749, 706, 673, 626, cm-1; 1H NMR [(CD
3 2
) CO] δ 2.20
absences and intensity statistics indicate the space group to be
Pbcn (#60) which was consistent with refinement.
(
s, 3H), 4.94 (d, 1H, J ) 1.3 Hz), 6.69 (d, 1H, J ) 1.3 Hz), 7.36
(m, 2H), 7.54 (m, 2H), 7.77 (m,2H), 8.15 (m,3H), 8.25 (d, 1H, J
The structure was solved using SHELXS in the Bruker
1
3
)
7.6 Hz), 8.65 (t, 1H, J ) 7.7 Hz), 8.89 (d, 2H, J ) 5.8 Hz);
CO] δ 15.0, 50.8, 72.3, 125.7, 125.9, 127.2, 129.6,
30.2, 130.4, 130.5, 131.1, 131.5, 132.6, 132.8, 133.0, 135.6, 144.3,
C
28
SHELXTL (Version 5.0) software package. Refinements were
NMR [(CD
3
)
2
performed using the freely available SHELXL and illustrations
were made using XP. Solution was achieved utilizing direct
methods followed by Fourier synthesis. Hydrogen atoms were
added at idealized positions, constrained to ride on the atom to
which they are bonded and given thermal parameters equal to
1.2 or 1.5 times Uiso of that bonded atom. The final anisotropic
1
1
3
47.6; HRMS (FAB) Calcd for C20
04.1150.
H
18NS: 304.1160. Found:
Rea ction of Acen a p h th ylen e w ith [(MeS)
2
SMe]SbCl
6
a n d P yr id in e. The reaction was carried out as above except
using acenaphthylene (146 mg, 0.96 mmol) and anhydrous
2
full-matrix least squares refinement based on F of all reflections
pyridine (164 mg, 2.08 mmol) dissolved in CH
to [(MeS) SMe]SbCl (446 g, 0.935 mmol) dissolved in CH
8 mL). After 20 h at room temperature, the mixture was
2
Cl
2
(2 mL) added
converged (maximum shift/esd ) 0.002) at R
0.1065 and goodness-of-fit ) 1.015. “Conventional” refinement
indices using the 3433 reflections with F > 4 σ(F) are R )
1
) 0.0669, wR )
2
2
6
2
Cl
2
(
1
1
0.0370, wR2 ) 0.0953. The model consisted of 245 variable
parameters, 64 constraints, and 0 restraints. There were six
correlation coefficients greater than 0.50. Three connected the
concentrated on a rotary evaporator and analyzed by H NMR
spectroscopy showing acenaphthylene (0.5 mmol, 48% conver-
sion) and 7 (0.4 mmol, 86% yield). This residue was purified by
column chromatography on silica gel eluting with CH
2
Cl
2
to give
Uii of Sb with the overall scale factor. The highest peak on the
3
7
1
1
as its SbCl
6
salt as a red solid: 162 mg (58% yield): mp 164-
final difference map was 0.662 e/Å located 0.19 Å from SB1.
3
The lowest peak on the final difference map was -0.542 e/Å
66 °C (dec); IR (KBr) 3125, 3078, 2917, 2359, 2336, 1699, 1623,
484, 1424, 1358, 1259, 1202, 1146, 974, 825, 789, 752, 706, 679;
located 0.93 Å from S1. Scattering factors and anomalous
dispersion were taken from International Tables.29
1
H NMR [(CD
.07 (d, 1H, J ) 3.3 Hz), 7.6 (d, 1H, J ) 6.8 Hz), 7.7 (m, 2H), 7.8
d, 1H, J ) 7.0 Hz), 8.00 (d, 1H, J ) 8.2 Hz), 8.09 (d, 1H, J )
.0 Hz), 8.36 (t, 2H, J ) 7.0 Hz), 8.85 (t, 1H, J ) 7.7 Hz), 9.18
3 2
) CO] δ 2.07 (s, 3H), 5.33 (d, 1H, J ) 3.3, Hz),
7
(
8
The larger than normal thermal parameters for atoms C3
through C8 of the naphthalene ring are due to a temperature-
dependent packing disorder.
Deh yd r op yr id in a tion of Ad d u ct 6. A solution of NaOMe
was prepared by adding sodium metal (18 mg, 0.78 mmol) to
anhydrous MeOH (1.0 mL). This solution was added to a solution
of adduct 6 (66 mg, 0.10 mmol) dissolved in anhydrous THF (1.0
mL) at room temperature. After 1 h a precipitate formed, the
solvents were rotary evaporated, and water (5 mL) was added.
1
3
(m, 2H); C NMR[(CD
3
)
2
CO)] δ 12.1, 58.0, 82.3, 122.6, 123.5,
25.9, 128.1, 129.8, 130.2, 130.4, 132.2, 137.7, 138.6, 139.7, 144.7,
48.1; FAB-MS m/z 278. Anal. Calcd for C18 NSSb: C,
5.28; H 2.61; Cl, 34.72. Found: C, 35.32; H, 2.62; Cl, 35.54.
Rea ction of Cycloh exen e w ith [(MeS) SMe]SbCl a n d
P yr id in e. The reaction was carried as above using [(MeS) SMe]-
SbCl (687 mg, 1.45 mmol) dissolved in CH Cl (11 mL) and
adding cyclohexene (141 mg, 1.72 mmol) and pyridine (422 mg,
.34 mmol) in CH Cl (1 mL). After standing 18 h at room
temperature, the mixture was filtered, washed with CH Cl , and
1
1
3
H
16Cl
6
2
6
2
The mixture was extracted with CH
combined extracts washed with 5% aqueous HCl solution and
then brine. The organic phase was separated, dried (anhyd
2
Cl
2
(3 × 10 mL), and the
6
2
2
5
2
2
4
MgSO ), filtered, concentrated by rotary evaporation, and chro-
2
2
dried to give 8 as yellow crystals (480 mg, 61% yield) which was
recrystallized by vapor diffusion of pentane into a THF solu-
tion: mp 176-179 °C (dec); IR (KBr) 3126, 3080, 2939, 2859,
(26) Bruker 1997 SMART Reference Manual Version 5.0, Bruker
AXS Inc., Madison, WI.
(27) Bruker 1997 SAINT Reference Manual Version 5.0, Bruker AXS
Inc., Madison, WI.
-
1
1
1
626, 1484, 1441, 1322, 1282, 1211, 1157, 772, 678 cm
NMR [(CD CO] δ 1.61 (m, 2H), 1.73 (m, 1H), 1.89 (m, 1H), 1.91
s, 3H), 2.00 (m, 1H), 2.32 (m, 2H), 2.51 (m, 1H), 3.33 (dd, 1H,
J ) 4.0, 11.4 Hz), 4.83 (dd, 1H, J ) 4.0 and 11.7 Hz), 8.34 (t,
H, J ) 7.2 Hz), 8.81 (t, 1H, J ) 7.7 Hz), 9.26 (d, 2H, J ) 6.6
; H
3 2
)
(
28) Bruker 1997 SHELXTL Reference Manual Version 5.0, Bruker
AXS, Inc., Madison, WI, USA
29) International Tables for X-ray Crystallography; A. J . C. Wilson,
(
(
2
Ed.; Kluwer Academic Publishers: Boston, 1992; Vol. C, Tables 4.2.6.8
and 6.1.1.4.
1
3
3 2
Hz); C NMR [(CD ) CO] δ 12.3, 25.5, 26.1, 33.6, 34.4, 49.4, 76.1,

Notes
J . Org. Chem., Vol. 66, No. 12, 2001 4443
matographed on silica gel (eluting with CH
2
Cl
2
/pentane) to give
Ack n ow led gm en t. The authors gratefully acknowl-
edge support of this work by the Albemarle Corporation.
The mass spectra were measured at the Mass Spec-
trometry Facility at the University of Arizona. The
X-ray structure was determined at the Molecular Struc-
ture Laboratory at the University of Arizona, using the
diffractometer purchased with NSF Grant CHE-9610374.
2
2
pure 9 (14 mg, 61% yield).
Deh yd r op yr id in a tion of Ad d u ct 7. Treatment of adduct
(160 mg, 0.42 mmol) with DBU (109 mg, 0.70 mmol) in
7
‚ClO
4
anhydrous THF (20.0 mL) resulted in the formation of a deep
red color. After 18 h at room temperature, the mixture was
rotary evaporated and the residue dissolved in CHCl
chromalographed through a short silica gel column with CH
Cl :pentane (1:10) to give 10 as an orange oil (64 mg, 76%
yield): IR (neat) 3035, 2915, 2843, 1596, 1477, 1461, 1427, 1311,
3
and then
2
-
2
Su p p or tin g In for m a tion Ava ila ble: ORTEP drawing of
1
6
1
1
1
106, 1034, 928, 825, 769 cm-1; 1H NMR (CDCl
.58 (s, 1H), 7.44 (m, 2H), 7.52 (m, 1H), 7.63 (m, 1H), 7.70 (d,
H, J ) 6.8 Hz), 7.80 (d, 1H, J ) 8.1 Hz); 13C NMR (CDCl
) δ
5.4, 119.6, 121.0, 121.7, 125.2, 127.3, 127.9, 128.0, 129.1, 138.7,
39.7, 141.1; HR MS (FAB) Calcd for C13 10S: 198.0503.
3
) δ 2.62 (s, 3H),
7
6
‚SbCl , tables of crystallographic data, selected bond lengths
1
13
6
and bond angles for 7‚SbCl , H and C NMR spectroscopic
data for 6, 7, and 8. This material is available free of charge
3
via the Internet at http://pubs.acs.org.
H
Found: 198.0506.
J O010156X