Syntheses of β,β-Diarylvinyl Phenyl Ketones by Benzotriazole-Mediated Tandem Coupling-Elimination

Full text of DOI:10.1021/jo9800199

3450
J . Org. Chem. 1998, 63, 3450-3453
Notes
Ta ble 1. Exp er im en ta l Con d ition s for th e Syn th esis of
â,â-Dia r ylvin yl P h en yl Keton es 4a -f
Syn th eses of â,â-Dia r ylvin yl P h en yl
Keton es by Ben zotr ia zole-Med ia ted
Ta n d em Cou p lin g-Elim in a tion
reaction conditions intermediate 3
temp, time, isolated conversiona yield
entry
RLi
solv
°C
h
yield, %
of 2, %
of 4, %
Alan R. Katritzky,* Sergey N. Denisenko,
Daniela C. Oniciu, and Ion Ghiviriga
a
BuLi
BuLi
BuLi
s-BuLi THF rt
s-BuLi THF rt
s-BuLi THF rt
s-BuLi THF rt
THF rt
THF reflux
THF rt
3
52b
100
100
85
100
75
95
95
95
91c
90
70
60
43
84
90
81
a d
b
3
12
12
72
10
10
10
Center for Heterocyclic Compounds,
Department of Chemistry, University of Florida,
Gainesville, Florida 32611-7200
c
d
ef
fe
gf
BuLi
THF rt
Received J anuary 6, 1998
a
The conversion of compound 2 to intermediate 3 were mea-
sured by performing of GC and NMR analysis of the reaction
mixture. The crude product was pure by NMR and further
In tr od u ction
b
purification by column chromatography was performed only for
â,â-Diarylvinyl phenyl ketones are frequently observed
in natural products and are widely used versatile organic
synthons; for example, (i) they can be epoxidized1,2 and
then converted into cumarones and flavones,2 (ii) they
can be added to aromatics to give polyaryl substituted
ketones,3 or (iii) they can be simply hydrogenated to give
ketones.4
The most important synthesis of â,â-diarylvinyl phenyl
ketones, direct aldol condensation, suffers limitations due
to cross-coupling and Michael-type reactions, which can-
not be always overcome by recent alternatives.5,6 The
well-known acylation of olefins to such R,â-enones is
frequently limited by the formation of numerous byprod-
ucts.7 Photodecarbonylation of aryl-substituted furan-
ones affords â,â-diarylvinyl phenyl ketones in good
yields.8,9 A recent comprehensive review10 confirms that
additional general and versatile pathways to â,â-di-
arylvinyl phenyl ketones would be valuable.
analytical purposes. c From intermediate 3 by refluxing in 1,2-
d
dichloroethane for 3 h. Reference 18. e Reference 19. fReference
18.
1a -g and benzotriazole under acid conditions.11,12 They
were usually obtained as mixtures of their 1- and
2-benzotriazolyl isomers (Bt-1 and Bt-2) and used without
further purification. Lithiated N-(diarylmethyl)benzo-
triazoles 2a -g reacted with R-bromoacetophenone to give
benzotriazole derivatives 3a -g with high conversions
(Scheme 1, Table 1) according to the GC and NMR
analysis of the crude reaction mixtures. Only intermedi-
ate 3a was separated, as an example for analytical
purposes, whereas intermediates 3b-g were transformed
without isolation. The removal of benzotriazole from
isolated 3a to give the â-substituted R,â-enones 4a was
achieved with zinc bromide (0.05 equiv, in refluxing 1,2-
dichloroethane); enones 4b-g were prepared using BuLi
(0.05-0.08 equiv, at room temperature), in one-pot
syntheses directly from 2a -g. For compounds 4c-f, the
conversion is improved by using s-BuLi instead of BuLi
(yields and experimental conditions are presented in
Table 1). With one exception (compound 4d ), yields are
particularly good for the synthesis of symmetrically
substituted enones.
We now present a new benzotriazole-mediated route
to â-substituted R,â-enones utilizing the corresponding
diarylmethanols or diarylmethyl halides and R-bromoac-
etophenone.
Resu lts a n d Discu ssion
N-(Diarylmethyl)benzotriazoles 2a -g were prepared
by the reaction of their corresponding secondary alcohols
Benzotriazol-1-ylphenyl(4-tolyl)methane (2c) reacted
with R-bromoacetophenone by following the same pat-
tern, and afforded the enone 4c, as a mixture of isomers
in a ratio of 1:2.
(1) Baumstark, A. L.; Harden, J r., D. B. J . Org. Chem. 1993, 58,
7615.
(2) Patonay, T.; Levai, A.; Nemes, C.; Timar, T.; Toth, G.; Adam,
W. J . Org. Chem. 1996, 61, 5375.
(3) Cho, C. S.; Motofusa, S.-i.; Ohe, K.; Uemura, S. Bull. Chem. Soc.
J pn. 1996, 69, 2341.
(4) Ravasio, N.; Antenori, M.; Gargano, M.; Mastrorilli, P. Tetrahe-
dron Lett. 1996, 37, 3259.
(5) Amorese, A.; Arcadi, A.; Bernocchi, E.; Cacchi, S.; Cerrini, S.;
Fedeli, W.; Ortar, G. Tetrahedron 1989, 45, 813.
(6) Bartoli, G.; Marcantoni, E.; Petrini, M.; Sambri, L. Chem. Eur.
J . 1996, 2, 913.
(7) Nenitzescu, C. D.; Balaban, A. T. In Friedel-Crafts and Related
Reactions; Olah, G. A., Ed.; Interscience: London, 1964; Vol. 3, p 1033.
(8) Gopidas, K. R.; Lohray, B. B.; Rajadurai, S.; Das, P. K.; George,
M. V. J . Org. Chem. 1987, 52, 2831.
1
The structure of products 4a -g was confirmed by H,
13C, and two-dimensional NMR: signals at ca. 6.90-7.15
ppm provided clear evidence for the presence of a
hydrogen atom connected to a conjugated double bond.
In the 13C NMR spectrum, signals at ca. 138-156 ppm
for CHdC and at ca. 192-195 ppm for C)O are charac-
teristic for an enone system and were unequivocally
assigned in each case.
This approach is not applicable to the synthesis of
â-alkyl-â-arylvinylphenyl ketones, as the analogous com-
pounds of type 3 were not obtained. We also failed to
(9) Pratapan, S.; Ashok, K.; Cyr, D. R.; Das, P. K.; George, M. V. J .
Org. Chem. 1988, 53, 5826.
(10) Ebenezer, W. J .; Wight, P. In Comprehensive Organic Func-
tional Group Transformations; Katritzky, A. R.; Meth-Cohn, O.; Rees,
C. W., Eds.; Pergamon: Cambridge, 1995; Vol. 3, p 205.
(11) Katritzky, A. R.; Perumal, S.; Fan, W.-Q. J . Chem. Soc., Perkin
Trans. 2 1990, 2059.
(12) Katritzky, A. R.; Yang, B. J . Heterocycl. Chem. 1996, 33, 607.
S0022-3263(98)00019-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/28/1998

Notes
J . Org. Chem., Vol. 63, No. 10, 1998 3451
Sch em e 1
7.36 ppm, and at position 7 on the benzotriazol-1-yl (7.81
ppm). This later NOE, together with the chemical shift
of its attached carbon (59.3 ppm) proves that the proton
at 8.20 ppm is R to a benzotriazol-1-yl. The protons at
7.36 ppm are directly connected to a carbon of double
intensity which should be in the ortho position of one of
the phenyl groups; there are four double intensity
carbons in the spectrum. The other phenyl group is
attached to the carbonyl at 195.8 ppm because this
carbon experiences polarization transfer from the protons
at 7.98 ppm. In addition, this carbonyl is correlated to
the AB protons (4.90 and 4.95 ppm). Irradiation of these
protons in the NOE difference experiment produced an
increase of the signals at 7.98 ppm (which confirms the
phenacyl fragment), at 8.20 ppm (which confirms the
proximity of the aliphatic methine and methylene), and
for the doublet at 7.67 ppm. This latter NOE indicated
that the phenacyl moiety is in the position 3 of the
remaining fragment, a benzothiazole, and that the pro-
tons at 7.67 ppm are in position 4. If the phenacyl group
was in position 2, an NOE to the phenylene protons
would be less likely to be seen. Besides, no NOE to the
phenylene protons was observed when the proton at 8.20
ppm was irradiated.
In compound 9, the only aliphatic carbon is linked to
the oxygen as revealed by its chemical shift (78.3 ppm).
The proton bound to this carbon (6.59 ppm) displays long-
range correlations in the HMBC with the carbons at
127.4 and 151.0 ppm. The carbon at 127.4 ppm is of
double intensity and the proton directly bound to it is a
doublet at 7.51 ppm; thus it is in the ortho position of a
phenyl which is connected to the aliphatic methine. This
is also confirmed by the positive NOE observed at 7.51
ppm when the proton at 6.59 ppm was irradiated. As
indicated by its long-range correlation with the proton
at 6.59 ppm and its chemical shift, the quaternary carbon
at 151.0 ppm is also bound to the oxygen. In addition,
this carbon has a phenyl group attached to it because it
displays polarization transfer from the proton at 7.73
ppm (doublet) which is bound to a carbon of double
intensity (125.0 ppm). The methine group at 94.6 and
6.72 ppm is connected to the carbon at 151.0 ppm, as
indicated by the polarization transfer from its proton to
this carbon and by its low 13C chemical shift typical for
an enol ether. In addition, the protons at 7.73 ppm
experienced a positive NOE when this methine proton
(6.72 ppm) was irradiated.
synthesize â-heteroaryl-â-arylvinylphenyl ketones. For
furan the precursor to 3 underwent deprotonation at the
R-carbon in the furan ring. For benzothiophene, the
reaction took another course: compound 6 (obtained by
reacting benzotriazole with alcohol 5) on treatment with
BuLi (1 equiv) and R- bromoacetophenone gave a mixture
of 7 and 9 in ratio 2:1. Compound 7 is formed as result
of electrophilic attack of R-bromoacetophenone at the 3
position of the benzothiophene ring b. Such γ-regiose-
lectivity is known13 for a benzotriazolyl-stabilized allyl
anions. The mechanism of formation of 9 is unclear: it
appears not to involve intermediate 8; treatment of
compound 7 with 1 equiv of BuLi in THF did not lead to
the formation of 9 (Scheme 2). Heteroatom-bridged
pyranes of type 9 appear to have previously been un-
known.
Str u ctu r a l Assign m en t of Com p ou n d s 7 a n d 9.
The structures of compounds 7 and 9 were elucidated by
NMR, on basis of the direct and long-range 1H-13C
correlations [HETCOR and LRHETC15 experiments for
7 and indirect detection experiments (HMQC and HMBC)
The elemental analysis of 9 indicated that the rest of
the molecule is a benzothiophene moiety. The attach-
ment of the unsaturated methine group to position 3 of
the benzothiophene was demonstrated by the positive
NOE at 7.81 ppm when the proton at 6.72 ppm was
irradiated and by the long-range correlations of this
proton with the carbons at 135.7 and 134.3 ppm.
1
for 9, which was available in smaller amounts], H-1H
correlations (COSY), and NOE difference experiments.
The HETCOR experiment was run with preservation of
the 1H-1H couplings in f1. The 1H and 13C chemical
shifts, together with the observed long-range hetero-
nuclear correlations, are presented in Figure 1.
Con clu sion
Compound 7 contained a benzotriazole moiety as
revealed by the 13C signals at 145.1, 119.3, and 110.9
ppm, which are typical for positions 3a, 4, and 7 in
1-benzotriazole. Irradiation of the proton at 8.20 ppm
produced positive NOE’s at the AB (4.90, 4.95 ppm), at
The reaction of N-(diarylmethyl)benzotriazoles with
R-bromoacetophenone, followed by elimination of benzo-
triazole, as a tandem reaction, furnished â,â-diarylvinyl
phenyl ketones in good to excellent yields. Nonsym-
metrically substituted enones are obtained as mixtures
of cis and trans isomers. A different reaction course was
evidenced for 1-(R-benzothiophenyl)-1-phenylmethylben-
zotriazole: the heterocycle was capable of forming a
carbanion in the presence of s-BuLi and hence made
(13) Katritzky, A. R., J iang, J . J . Org. Chem. 1995, 60, 7597.
(14) Krishnamurthy, V. V.; Nunlist, R. J . Magn. Reson. 1988, 80,
280.
(15) Katritzky, A. R.; Ghiviriga, I.; Cundy, D. J . Heterocycles 1994,
38, 1041.

3452 J . Org. Chem., Vol. 63, No. 10, 1998
Notes
F igu r e 1. Complete 1H and 13C NMR Assignments for 2-{2-[1H-1,2,3-Benzotriazol-1-yl(phenyl)methyl]benzo[b]thiophen-3-yl}-
1-phenyl-1-ethanone (7) and 1,3-Diphenyl-1-H-benzo[4,5]thieno[2,3-c]pyran (9).
20 mmol) in THF (10 mL) was added. The mixture was allowed
to warm to room temperature and after 1.5 h was treated with
saturated NH4Cl and extracted with CH2Cl2. The organic layer
was washed with 5% NaOH and brine and then dried (MgSO4).
The solvent was removed in vacuo to give 4.5 g (18.7 mmol, 97%)
of crystals with a purity of 98.5% (by GC). Recrystallization from
diethyl ether/hexanes yielded 3.58 g (80%) of light yellow prisms
with mp 85.0-86.0 °C: 1H NMR 7.78-7.72 (m, 1H), 7.68-7.62
(m, 1H), 7.49-7.20 (m, 7H), 7.08 (s, 1H), 6.10 (s, 1H), 2.63 (br s,
1H); 13C NMR δ 148.8, 142.4, 139.6, 139.2, 128.2 (2C), 127.7,
126.2 (2C), 123.9, 123.8, 123.3, 122.1, 120.8, 72.4. Anal. Calcd
for C15H12OS: C, 74.96; H, 5.04. Found: C, 74.76; H, 4.67.
Sch em e 2
Gen er a l P r oced u r e for th e P r ep a r a tion of 1-Dia r yl-
m eth ylben zotr ia zoles 2e,g a n d 6. A mixture of benzotriazole
(7.26 g, 61 mmol) and the appropriate carbinol 1 (55.6 mmol)
was stirred for 8 h in benzene (200 mL) under reflux, in the
presence of a catalytic amount of p-toluenesulfonic acid mono-
hydrate. The water formed during the reaction was azeotropi-
cally removed by using a Dean-Stark apparatus. The reaction
mixture was washed with Na2CO3 (10%), dried (MgSO4), and
concentrated, to give a mixture of the benzotriazol-1-yl and -2-
yl isomers. The benzotriazol-1-yl isomer was separated by flash
column chromatography or recrystallization, for analytical
purposes.
9H -9-(Ben zot r ia zol-1-yl)t h ioxa n t h en e (2e). Hexanes/
ethyl acetate (4:1) was used as the eluent to give white crystals
(52%, yield of both isomers 95%): mp 159.0-160.5 °C; 1H NMR
δ 8.03-8.08 (m, 1H), 7.50-7.45 (m, 3H), 7.35-7.22 (m, 4H),
7.21-7.07 (m, 5H); 13C NMR δ 146.3, 146.3, 131.8 (2C), 131.6,
129.1 (3C), 128.5 (2C), 127.3, 126.6 (2C), 126.2 (2C), 123.8, 119.8,
110.8, 62.1. Anal. Calcd for C19H13N3S: C, 72.35; H, 4.16; N,
13.33. Found: C, 72.40; H, 4.22; N, 13.39.
9H-9-(Ben zotr ia zol-1-yl)xa n th en e (2g) was recrystallized
from toluene/diethyl ether to give colorless crystals (79%, yield
of both isomers 95%): mp 190.0-192.0 °C; 1H NMR δ 8.02 (d, J
) 8.3 Hz, 1H), 7.63 (s, 1H), 7.45-7.10 (m, 8H), 7.04 (t, J ) 7.4
Hz, 2H), 6.86 (d, J ) 8.0 Hz, 1H); 13C NMR δ 151.0 (2C); 147.0;
131.0; 130.4 (2C), 129.3 (2C), 127.3, 124.0 (2C), 123.8, 120.0,
117.0 (2C), 116.9 (2C), 110.1, 55.4. Anal. Calcd for C19H13N3O:
C, 76.23; H, 4.39; N, 14.04. Found: C, 76.27; H, 4.17; N, 14.22.
(Be n zot r ia zol-1-yl)(b e n zot h iop h e n -2-yl)p h e n ylm e t h -
a n e (6). Recrystallized from diethyl ether to give white crystals
(60%, yield of both isomers 88%); mp 113.0-127.0 °C; 1H NMR
δ 8.14-8.10 (m, 1H), 7.78-7.71 (m, 1H), 7.71-7.65 (m, 1H), 7.64
(s, 1H), 7.42-7.20 (m, 10H), 7.13 (s, 1H); 13C NMR δ 146.4, 141.3,
140.2, 138.8, 137.1, 132.6, 128.9 (3C), 127.8 (2C), 127.5, 124.9,
124.9, 124.6, 124.0, 123.9, 122.3, 120.2, 110.5, 63.5. Anal. Calcd
for C21H15N3S: C, 73.87; H, 4.44; N, 12.31. Found: C, 73.52;
H, 4.38; N, 12.24.
9,10-Dih ydr o-10-m eth yl-9-(ben zotr iazol-1-yl)acr idin e (2f).
A mixture of benzotriazole (1.19 g, 10 mmol), NaH (0.40 g of
60% solution in mineral oil, 10 mmol), and the 10-methylacri-
dinium iodide 1f (10 mmol) was stirred for 1 h in dry THF (50
mL) at room temperature. The reaction mixture was washed
with Na2CO3 (10%), dried (MgSO4), and concentrated, to give a
possible the annulation to a fused 7H-thieno[3,4-c]pyran.
This synthon is envisaged as a valuable precursor in the
synthesis of thienopyrylium salts.16
Exp er im en ta l Section
Gen er a l. Melting points were determined with a hot-stage
apparatus and are uncorrected. NMR spectra were recorded in
CDCl3 with TMS as the internal standard for 1H (300 MHz) and
solvent as the internal standard for 13C (75 MHz), unless
otherwise stated. The abbreviations for the multiplicity of the
proton signals are as follows: qv for quintet, sx for sextet, and
h for heptet. THF was distilled under nitrogen immediately
prior to use from sodium/benzophenone. All reactions with air-
sensitive compounds were carried out under an argon atmo-
sphere. Column chromatography was conducted with silica gel
230-400 mesh.
Thioxantene-9-ol (1e) was prepared according to the literature
method.17 Benzotriazol-1-yl-diarylmethanes 2a -d were pre-
pared as previously reported.11,12
(Ben zoth iop h en -2-yl)p h en ylm eth a n ol (5). To a solution
of benzothiophene (2.6 g, 19.37 mmol) in THF (50 mL) at -78
°C was added BuLi (13.3 mL, 1.6 M in cyclohexane, 21 mmol).
After 10 min at -78 °C and 20 min at room temperature, the
temperature was lowered to -78 °C and benzaldehyde (2.13 g,
(16) Friedrichsen, W. In Comprehensive Heterocyclic Chemistry;
Katritzky, A. R., Rees, C. W., Eds.; Pergamon: Cambridge, 1984; Vol.
4, p 973.
(17) Price, C. C.; Hori, M.; Parasaran, T.; Polk, M. J . Am. Chem.
Soc. 1963, 85, 2278.

Notes
J . Org. Chem., Vol. 63, No. 10, 1998 3453
mixture of the benzotriazol-1-yl and -2-yl isomers. The benzo-
triazol-1-yl isomer was separated by recrystallization from
2-propanol to give white crystals (75%, yield of both isomers
89%): mp 168.0-169.5 °C; 1H NMR δ 8.00-7.93 (d, J ) 7.6 Hz,
1H), 7.63 (s, 1H), 7.34 (t, J ) 8.3 Hz, 2H), 7.30-7.06 (m, 7H),
6.9 (t, J ) 7.0 Hz, 2H), 3.60 (s, 3H); 13C NMR δ 146.5, 141.4
(2C), 131.1, 118.0 (2C), 129.5 (4C), 126.8, 123.4, 120.7 (2C), 119.6,
112.9 (2C), 110.3, 59.8, 33.0. Anal. Calcd for C20H16N4: C, 76.89;
H, 5.17; N, 17.94. Found: C, 76.76; H, 5.13; N, 17.93.
1-(Ben zotr iazol-1-yl)-1,1,3-tr is(ph en yl)pr opan -3-on e (3a).
To a stirred solution of benzotriazol-1-yl-diphenylmethane 2a
(0.77 g, 2.7 mmol) in THF (25 mL) at -78 °C was added a
solution of BuLi (1.88 mL, 1.6 M in cyclohexane, 3 mmol). The
mixture was stirred at this temperature for 30 min, then
2-bromoacetophenone (0.537 g, 2.7 mmol) in THF (5 mL) was
slowly added while the solution stirred. The reaction mixture
was kept at -78 °C for 2 h and for an additional 12 h at room
temperature and then was quenched with cold saturated NH4-
Cl. The reaction mixture was extracted with diethyl ether (50
mL), and the organic layer was dried (MgSO4). The solvent was
evaporated under vacuum to give the crude product, which was
purified by recrystallization from diethyl ether, to afford the pure
compound as white crystals (0.57 g, 52%): mp 149.0-151.0 °C;
1H NMR δ 8.05 (d, J ) 8.2 Hz, 1H), 7.97 (d, J ) 7.1 Hz, 2H),
7.55 (t, J ) 7.4 Hz, 1H), 7.46-7.38 (m, J ) 8.0 Hz, 2H), 7.36-
7.21 (m, 11H), 7.12 (t, J ) 7.7 Hz, 1H), 6.44 (d, J ) 8.5 Hz, 1H),
5.0 (s, 2H); 13C NMR δ 194.3, 146.4, 140.3 (2C), 137.2, 133.3,
132.9, 128.4 (2C), 128.3 (4C), 128.0 (2C), 127.9 (6C), 126.7, 123.5,
119.9, 112.8, 72.4, 50.7. Anal. Calcd for C27H21N3O: C, 80.36;
H, 5.26; N, 10.42. Found: C, 80.51; H, 5.51; N, 10.50.
1,3,3-Tr is(p h en yl)p r op en -1-on e (4a ). To a stirred solution
of 3-benzotriazol-1-yl-1,3,3-tris(phenyl)propan-1-one 3a (0.45 g,
1.12 mmol) in 1,2-dichloroethane (10 mL) at 20 °C a were added
few crystals of ZnBr2, and the mixture was stirred at reflux for
3 h. The precipitate was filtered, and the organic layer was
washed with water (2 mL) and dried (MgSO4). In vacuo removal
of the solvent gave the pure product as a yellow oil, which
crystallized on standing, to give yellow crystals (290 mg, 91%):
mp 88.0-90.0 °C (diethyl ether);18 1H NMR δ 7.94 (dd, J ) 7.1,
1.4 Hz, 2H), 7.50 (tt, J ) 7.4, 7.1, 1.4 Hz, 1H), 7.46-7.34 (m,
7H), 7.33-7.25 (m, 3H), 7.25-7.17 (m, 2H), 7.15 (s, 1H); 13C
NMR δ 192.7, 154.7, 141.3, 138.9, 138.1, 132.6, 129.7 (2C), 129.3,
128.7 (2C), 128.5 (2C), 128.4 (2C), 128.3 (3C), 128.0 (2C), 124.0.
Gen er a l P r oced u r e for th e P r ep a r a tion of Su bstitu ted
1-P r op en on es 4b-g. To a stirred solution of the mixture of
1- and 2-isomers of compound 2 (3.1 mmol) in THF (25 mL) at
-78 °C was added BuLi (2.2 mL, 1.6 M in cyclohexane, 3.4
mmol). The mixture was stirred at this temperature for 30 min,
then 2-bromoacetophenone (0.611 g, 3.1 mmol) in THF (5 mL)
was slowly added while the solution stirred. The reaction
mixture was kept at -78 °C for 2 h and for an additional 12 h
at room temperature and then was quenched with cold saturated
NH4Cl. The reaction mixture was extracted with diethyl ether
(50 mL), and the organic layer was dried (MgSO4). The solvent
was removed under vacuum to give the crude product, which
was isolated by column chromatography or recrystallization.
When compound 2b was used as a starting material, compound
3b was obtained after the reaction was quenched (by NMR), but
the benzotriazole was eliminated during the separations.
2-{2-[1H-1,2,3-(Ben zotr ia zol-1-yl)(p h en yl)m eth yl]ben zo-
[b]th iop h en -3-yl}-1-p h en yl-1-eth a n on e (7). To a stirred
solution of benzotriazol-1-yl-(2-benzothiophenyl)phenylmethane
(0.973 g, 2.85 mmol) in THF (25 mL) at -78 °C was added a
solution of BuLi (2 mL, 1.6 M in cyclohexane, 3.2 mmol). The
mixture was stirred at -78 °C for 30 min, then 2-bromoac-
etophenone (0.570 g, 2.85 mmol) in THF (5 mL) was added
slowly. After the mixture stirred for 30 min at -78 °C and 12
h at room temperature, diethyl ether (50 mL) was added and
the reaction mixture was washed with saturated NH4Cl solution
and dried (MgSO4). The solvent was evaporated in vacuo, and
the oily residue was separated by column chromatography on
silica gel with hexane/ethyl acetate (20:1) as eluent to give the
product as a first fraction (655 mg, 50%): white crystals, mp
172.0-174.0 °C; for 1H and 13C NMR assignments, see Figure
1. Anal. Calcd for C29H21N3OS: N, 9.15. Found: N, 8.87.
1,3-Dip h en yl-1-H-ben zo[4,5]th ien o[2,3-c]p yr a n (9) was
separated by column chromatography on silica gel with hexane/
ethyl acetate (20:1) as eluent, as the second fraction of the above-
mentioned procedure to yield an oil (235 mg, 25%); for 1H and
13C NMR assignments, see Figure 1; HRMS (CI) calcd for C23H16
OS 340.0921, found 340.0938.
-
Su p p or tin g In for m a tion Ava ila ble: Characterization
data for compounds 4b-g and discussion of structure assign-
ment by NMR for compounds 7 and 9; spectral data for 4b,c
and 9 (8 pages). This material is contained in libraries on
microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
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