Synthesis of carbazoles and 1,2-dihydrocarbazoles by domino 'twofold Heck-6π-electrocyclization' reactions of di- and tribromo-N-methylindoles

Article abstract of DOI:10.1055/s-0029-1217357

The palladium(0)-catalyzed Heck cross-coupling reaction of 2,3-dibromo- and 2,3,6-tribromo-N-methylindole, using Pd(OAc)₂ as the catalyst and a novel biaryl monophosphine ligand developed by Buchwald and co-workers, afforded the corresponding d

Full text of DOI:10.1055/s-0029-1217357

1
822
LETTER
Synthesis of Carbazoles and 1,2-Dihydrocarbazoles by Domino ‘Twofold
Heck–6p-Electrocyclization’ Reactions of Di- and Tribromo-N-methylindoles
a
a
a,b
S
M
ynthesis of Carbazole
u
s
and 1, 2-Dih
n
ydrocarbazo
a
les war Hussain, Đăng Thanh Tùng, Peter Langer*
a
Institut für Chemie, Universität Rostock, Albert Einstein Str. 3a, 18059 Rostock, Germany
Leibniz-Institut für Katalyse an der Universität Rostock e.V., Albert Einstein Str. 29a, 18059 Rostock, Germany
Fax +49(381)4986412; E-mail: peter.langer@uni-rostock.de
b
Received 19 February 2009
pyrroles,10 and selenophenes,11 by site-selective Suzuki
reactions of tetrabromothiophene, tetrabromo-N-meth-
ylpyrrole, and tetrabromoselenophene, respectively. Grib-
Abstract: The palladium(0)-catalyzed Heck cross-coupling reac-
tion of 2,3-dibromo- and 2,3,6-tribromo-N-methylindole, using
Pd(OAc) as the catalyst and a novel biaryl monophosphine ligand
2
developed by Buchwald and co-workers, afforded the correspond- ble and Liu reported the synthesis of 2,3-diarylindoles by
ing di- and trialkenylindoles in high yields. The formation of 1,2- twofold Suzuki reactions of 2,3-dihalo-N-(phenylsulfo-
nyl)indoles.12 Other palladium(0)-catalyzed cross-cou-
pling reactions of 2,3-dihaloindoles have, to the best of
our knowledge, not been reported to date. De Meijere and
co-workers reported twofold Heck reactions of 1,2-dibro-
dihydrocarbazoles by a domino ‘twofold Heck–6p-electrocycliza-
tion’ was observed when the reaction was carried out at 120 °C rath-
er than 90 °C.
Key Words: cross-coupling, electrocyclic reactions, nitrogen het-
erocycles, Heck reaction, palladium
mocycloalk-1-enes and related substrates and subsequent
1
3
6
‘
p-electrocyclization. It occurred to us that domino
twofold Heck–6p-electrocyclization’ might provide a
Carbazoles are of considerable pharmacological rele- useful method for the direct and convenient synthesis of
vance (antifungal, antibiotic, and antitumor activity) and dihydrocarbazoles and carbazoles. Herein, we report pre-
1
,2
occur in a variety of natural products. Knölker and co- liminary results of these studies.
workers reported elegant syntheses of carbazoles based on
2
,3-Dibromo-N-methylindole (2a) has been recently pre-
(
stoichiometric) iron-mediated cyclizations1d and on
pared in 64% yield by reaction of N-methylindole (1) with
Buchwald–Hartwig reaction of aryl halides with anilines
1
4
copper(II) bromide. We have found that the reaction of
3
and subsequent oxidative cyclization. Ackermann and
N-methylindole (1) with NBS (2.1 equiv) in THF (–78 °C,
co-workers have recently reported an efficient synthesis
of indoles and carbazoles by a new palladium-catalyzed
domino ‘NH–CH activation’ reaction of anilines with 1,2-
4
h) resulted in selective formation of 2,3-dibromo-N-
15
methylindole (2a) in 90% yield (Scheme 1). In addition,
we have prepared 2,3,6-tribromo-N-methylindole (2b) in
4
dihaloalkenes. Carbazoles have been prepared also by
9
4% yield by reaction of 1 with NBS (3.1 equiv) in THF
5
Diels–Alder reactions of 2- or 3-vinylindoles. Kano and
(
–78 °C, 4 h).
co-workers were the first to report the synthesis of carba-
6
zoles by 6p-electrocyclization of 2,3-di(alkenyl)indoles.
Br
Later, this approach has been also studied by Pindur and
Adam. However, the synthesis of the starting materials
7
i
Br
was not straightforward and required many steps which is
a severe drawback of this method. 2,3-Di(alkenyl)indoles
were prepared by Pd(II)-catalyzed reaction of carbon
atom C-3 of 2-formylindoles with alkenes to give 2-
formyl-3-vinylindoles which were transformed into the
desired products by Wittig reaction. However, this ap-
proach is not general. The alternative strategy, based on
the double Wittig reaction of (unstable) 2,3-diformyl-N-
methylindole, has been reported to proceed in low yield.
N
N
Me
Me
2a 90%
1
ii
Br
Br
N
Br
Me
b 94%
2
In recent years, it has been shown that polyhalogenated Scheme 1 Bromination of N-methylindole (1). Reagents and condi-
tions: i, NBS (2.1 equiv), THF, –78 °C, 4 h; ii, NBS (3.1 equiv), THF,
heterocycles can undergo site-selective palladium(0)-
catalyzed cross-coupling reactions by selective activation
–
78 °C, 4 h, then 20 °C, 14 h.
of a single halogen atom. The site selectivity is controlled
8
by electronic and steric parameters. Recently, we have The Heck reaction of 2a with acrylates 3c–g afforded the
reported the synthesis of aryl-substituted thiophenes,9 2,3-di(alkenyl)indoles 4c–g in good yields (Scheme 2,
Table 1). The best yields were obtained when the reac-
tions were carried out using Pd(OAc) (5 mol%) and the
biaryl monophosphine ligand L (10 mol%, Figure 1)
which has been recently developed by Buchwald and co-
SYNLETT 2009, No. 11, pp 1822–1826
Advanced online publication: 12.06.2009
DOI: 10.1055/s-0029-1217357; Art ID: G07209ST
x
x
.x
x
.2
0
0
9
2
©
Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of Carbazoles and 1,2-Dihydrocarbazoles
1823
1
6
workers. The reactions were carried out in DMF at 90 °C Table 1 Synthesis of 4c–h and 5a–c,e,f,i
for 36 hours. The employment of Pd(PPh ) was less suc-
3
4
Compd 4, 5
R
Yield of 4 (%)a Yield of 5 (%)a
cessful in terms of yield. Recently, Li and Wang
1
7
reported that triethanolamine represents an efficient and
reusable combined base, ligand, and solvent for palladi-
um(0)-catalyzed Heck reactions. The application of these
conditions to the reaction of 2a with acrylate 3h proved to
be successful and resulted in the formation of 4h in 74%
yield.
–b
4a, 5a
4b, 5b
4c, 5c
4d, 5d
Me
77
93
77
–b
Et
–b
n-Bu
i-Bu
n-Hex
t-Bu
i-Oct
72
69
77
78
76
The Pd(OAc) /L-catalyzed reaction of 2a with acrylates 4e, 5e
81
85
–b
2
3
a–c,e,f,i, carried out at 120 °C rather than 90 °C, afford-
1
8
4f, 5f
ed the 1,2-dihydrocarbazoles 5a–c,e,f,i in good yields.
The formation of these products can be explained by a 4g, 5g
domino ‘twofold Heck–6p-electrocyclization’ cyclization
and subsequent double-bond migration. The initially
formed 2,3-dihydrocarbazoles undergo a rearrangement
into the more stable 1,2-dihydrocarbazoles. For the elec-
trocyclization, a thermally induced process appears to be
more likely as the product distribution (formation of 4 or
4
4
h, 5h
i, 5i
CH CH(Et)Bu 74
–b
2
–b
(CH ) NMe
2
79
2
2
a
Yields of isolated products based on 2a.
Experiment was not carried out.
b
5
) depends on the temperature. In addition, heating of 4f
(
120 °C) results in formation of 5f in good yield.
achieved when the reaction is carried out using Pd/C (10
mol%) in refluxing xylene (Scheme 3).19
CO2R
CO2R
CO2n-Bu
CO2n-Bu
i or ii
CO2n-Bu
N
CO2n-Bu
i
Br
Me
c–h
N
Me
4
N
Me
c
CO2R
a–i
Br
CO2R
CO2R
3
N
5
6 100%
Me
2a
iii
Scheme 3 Synthesis of carbazole 6. Reagents and conditions: i, Pd/
C (10 mol%), xylene, reflux, 48 h.
N
Me
a–c,e,f,i
5
The Pd(OAc) /L-catalyzed reaction of 2a with acryl
2
nitrile (120 °C, 48 h) afforded the unexpected carbazole 7
in 49% yield (Scheme 4). The formation of 7 can be ex-
0 °C, 36 h; ii, for 4h: Pd(OAc) (5 mol%), N(CH CH OH) (3 mL), plained by twofold Heck reaction of 2a to give intermedi-
0 °C, 36 h; iii, Pd(OAc) (5 mol%), L (10 mol%), Et N (8.0 equiv), ate A, electrocyclization (intermediate B), base-mediated
Scheme 2 Synthesis of 4c–h and 5a–c,e,f,i. Reagents and condi-
tions: i, for 4c–g: Pd(OAc) (5 mol%), L (10 mol%), Et N, DMF,
2
3
9
2 2 2 3
9
2
3
DMF, 120 °C, 48 h.
conjugate addition to give intermediate C, and subsequent
aromatization by elimination of HCN. This process was
not observed for the reaction of 2a with acrylates. This
might be explained by the assumption that the Michael
reaction is reversible. In case of the reaction of 2a with
acryl nitrile the Michael reaction may become irreversible
by the subsequent elimination of cyanide and aromatiza-
tion.
PCy2
OMe
L =
Cy = cyclohexyl
MeO
Figure 1 Biaryl monophosphine ligand developed by Buchwald
and co-workers (ref. 16)
The Pd(OAc) /L-catalyzed reaction of 2,3,6-tribromo-N-
2
methylindole (2b) with acrylate 3f (90 °C, 36 h) afforded
the di(alkenyl)indole 8 in 75% yield (Scheme 5). The site-
selective formation of 8 is worth to be noted because Ohta
Heating of a dioxane solution of 1,2-dihydrocarbazole 5c
in the presence of DDQ resulted in the formation of car-
bazole 6, albeit in only 20% yield. Pindur reported the
DDQ-mediated formation of 2,3-di(methoxycarbonyl)-N-
phenylsulfonylcarbazole from the corresponding 1,2-di-
hydrocarbazole in equally low yield (18%). We have
found that a dramatic increase of the yield (100%) can be
20
and co-workers reported that the site selectivity of the
Suzuki reaction of 3,6-dibromo-N-TBDS-indole was in
favor of carbon atom C-6. Our result can be explained by
the assumption that the first Heck reaction of 2b occurs at
carbon C-2, which is most electron deficient, to give inter-
mediate D (Figure 2). Due to the electron-withdrawing
character of the 2-(tert-butoxycarbonyl)alkenyl substitu-
Synlett 2009, No. 11, 1822–1826 © Thieme Stuttgart · New York

1
824
M. Hussain et al.
LETTER
CN
Br
1
st attack
CN
Br
CN
N
Br
Br
N
TBDS
N
Me
7
49%
Me
Ohta et al. (ref. 20)
2a
1
st attack
Br
Br
CN
CN
CN
CO2t-Bu
Br
CN
N
N
Br
Br
CN
Me
Me
N
2b
1st attack
D
N
Me
A
Me
Figure 2 Possible explanation for the site-selective formation of 8
and 9
C
The Pd(OAc) /L-catalyzed reaction of 2b with an excess
CN
2
Et3N
of acrylates 3a,e,f (90 °C, 36 h) afforded the 2,3,6-
tris(alkenyl)indoles 10a,e,f in good yields (Scheme 6,
Table 2). The cross-coupling reactions of 2b with 3a–g,
carried out at 120 °C rather than 90 °C, gave the 7-alke-
nyl-1,2-dihydrocarbazoles 11a–g.
CN
CN
N
Me
B
Scheme 4 Possible mechanism of the formation of 7. Reagents and
conditions: i, Pd(OAc) (5 mol%), L (10 mol%), Et N, DMF, 120 °C,
CO2R
2
3
48 h.
CO2R
CO2R
N
Me
3
a–g
ent, carbon C-3 becomes more electron deficient and,
thus, more reactive than C-6. Alternatively, the site selec-
tivity might be due to a proximity effect, wherein a labile
coordination between the newly installed alkene and
Pd(0) favors the second oxidative addition on the neigh-
boring bromine atom. This might also explain the obser-
vation that the reaction of 2,3-dibromoindole (2a) with
only one equivalent of acrylate mainly results in the for-
mation of 2,3-di[2-(alkoxycarbonyl)ethenyl]indole 4 and
Br
i
RO2C
10a,e,f
CO2R
CO2R
Br
N
Br
ii
Me
2
b
N
CO2R
Me
3a–g
RO2C
1
1a–g
starting material. The Pd(OAc) /L-catalyzed reaction of Scheme 6 Synthesis of 10a,e,f and 11a–g. Reagents and conditions:
2
2
9
b with acrylate 3d, carried out at 120 °C rather than i, Pd(OAc)
0 °C, afforded the 1,2-dihydrocarbazole 9 in 73% yield
2
(5 mol%), L (10 mol%), Et
N, DMF, 90 °C, 36 h; ii,
3
Pd(OAc) (5 mol%), L (10 mol%), Et N, DMF, 120 °C, 48 h.
2
3
(
Scheme 5).
Table 2 Synthesis of 10a,e,f and 11a–g
CO2R
CO2R
Compd 10, 11
0a, 11a
10b, 11b
R
Yield of 10 (%)a
Yield of 11 (%)a
1
Me
69
–b
–b
–b
74
76
–b
79
67
95
72
74
79
74
N
Br
Et
Me
i
1
1
0c, 11c
0d, 11d
n-Bu
i-Bu
n-Hex
t-Bu
i-Oct
Br
8 (R = t-Bu) 75%
CO2R
CO2R
Br
N
3d,f
Br
CO2R
10e, 11e
10f, 11f
Me
2b
ii
N
Br
Me
1
0g, 11g
9
(R = i-Bu) 73%
a
Yields of isolated products based on 2b.
Experiment was not carried out.
Scheme 5 Synthesis of 8 and 9. Reagents and conditions: i,
Pd(OAc) (5 mol%), L (10 mol%), Et N, DMF, 90 °C, 24 h; ii,
b
2
3
Pd(OAc) (5 mol%), L (10 mol%), Et N, DMF, 120 °C, 48 h.
2
3
In conclusion, we have reported the synthesis of di- and
trialkenylindoles by palladium(0)-catalyzed Heck cross-
Synlett 2009, No. 11, 1822–1826 © Thieme Stuttgart · New York

LETTER
Synthesis of Carbazoles and 1,2-Dihydrocarbazoles
1825
coupling reactions of di- and tribromo-N-methylindoles.
The reactions were carried out at 90 °C using a novel bi-
aryl monophosphine ligand developed by Buchwald and
co-workers. 1,2-Dihydrocarbazoles were formed by a
domino ‘twofold Heck–6p-electrocyclization’ when the
reaction was carried out at 120 °C rather than 90 °C. The
site selectivity of the Heck reaction of 2,3,6-tribromo-N-
methylindoles was in favor of carbon atoms C-2 and C-3.
Some of the 1,2-dihydrocarbazoles prepared were trans-
formed, by Pd/C-catalyzed dehydrogenation, into the cor-
responding carbazoles in high yield.
(12) Liu, Y.; Gribble, G. W. Tetrahedron Lett. 2000, 41, 8717.
(
13) Voigt, K.; von Zezschwitz, P.; Rosauer, K.; Lansky, A.;
Adams, A.; Reiser, O.; de Meijere, A. Eur. J. Org. Chem.
1
998, 1521; and references cited therein.
14) Tang, S.; Li, J.-H.; Xie, Y.-X.; Wang, N.-X. Synthesis 2007,
535.
(
(
1
15) Synthesis of 2,3-Dibromo-N-methylindole (2a)
To a THF solution (20 mL) of N-methylindole (1, 1.0 mL,
8.0 mmol) was added portionwise NBS (3.30 g, 18.4 mmol)
at –78 °C, and the soln was stirred at this temperature for 4
h. To the soln was added water (25 mL). The organic and the
aqueous layer were separated and the latter was extracted
with CH Cl (3 × 25 mL). The combined organic layers were
2
2
washed with a saturated aqueous soln of NaHCO , dried
3
(
Na SO ), filtered and concentrated in vacuo. The residue
2 4
Acknowledgment
was purified by flash silica column chromatography (pure
Financial support by the State of Pakistan (HEC scholarship for M.
H.) and from the State of Vietnam (MOET scholarship for T. T. D.)
is gratefully acknowledged.
heptanes) to yield 2a as a colorless solid (1.83 g, 90%).
(16) Billingsley, K.; Buchwald, S. L. J. Am. Chem. Soc. 2007,
129, 3358; and references cited therein..
(
(
17) Li, H. J.; Wang, L. Eur. J. Org. Chem. 2006, 5099.
18) General procedure for Heck cross-coupling reactions. In
References and Notes
a pressure tube (glass bomb) a suspension of Pd(OAc) (12
2
mg, 0.05 mmol, 1.25 mol% per Br) and dicyclohexyl (2',6'-
dimethoxybiphenyl-2-yl) phosphine (L) (41 mg, 0.10 mmol)
in DMF (5 mL) was purged with argon and stirred at 20 °C
to get a yellowish or brownish transparent soln. To the
stirred soln were added the brominated indole 2a,b (1.0
(
1) Reviews: (a) Brossi, A. In The Alkaloids, Vol. 26; Cordell,
G. A., Ed.; Academic Press: New York, 1985, 1.
(
b) Bhattacharrya, P.; Chakraborthy, D. P. Prog. Chem. Org.
Nat. Prod. 1987, 52, 160. (c) Maryanoff, B. E.; Reitz, A. B.
Chem. Rev. 1989, 89, 863. (d) Knölker, H.-J.; Reddy, K. R.
Chem. Rev. 2002, 102, 4303. (e) Chakraborty, D. P.; Roy, S.
Prog. Chem. Org. Nat. Prod. 1991, 57, 71. (f) Chakraborty,
D. P. In The Alkaloids, Vol. 44; Cordell, G. A., Ed.;
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Top. Curr. Chem. 2005, 244, 115. (h) Knölker, H.-J.;
Reddy, K. R. In The Alkaloids, Vol. 65; Cordell, G. A., Ed.;
Academic Press: Amsterdam, 2008, 1. (i)Pindur, U. Chimia
mmol), Et N (1.1 mL, 8.0 mmol) and the acrylate (1.25
3
equiv. per Br). The reaction mixture was stirred at 120 °C for
4
8 h. The soln was cooled to 20 °C, poured into H O, and
2
CH Cl (25 mL each), and the organic and the aqueous layer
2
2
were separated. The latter was extracted with CH Cl (3 × 25
2
2
mL). The combined organic layers were washed with H O
2
(
3 × 20 mL), dried (Na SO ), and concentrated in vacuo. The
2
4
residue was purified by chromatography (flash silica gel,
heptanes–EtOAc).
1
990, 44, 406. (j) Bergman, J.; Pelcman, B. Pure Appl.
Chem. 1990, 62, 1967. (k) Moody, C. J. Synlett 1994, 681.
Diethyl 9-Methyl-2,9-dihydro-1H-carbazole-2,3-
dicarboxylate (5b)
(l) Kirsch, G. H. Curr. Org. Chem. 2001, 5, 507.
(
m) Lemster, T.; Pindur, U. Recent Res. Dev. Org. Bioorg.
Product 5b was prepared starting with 2a (367 mg, 1.0
mmol) as a yellow solid (297 mg, 93%), mp 100–103 °C. H
Chem. 2002, 5, 99. (n) Knölker, H.-J. Curr. Org. Synth.
004, 1, 309.
1
2
NMR (250 MHz, CDCl ): d = 1.10 (s, 3 H, CH ), 1.30 (s, 3
3
3
(
2) For some recent contributions, see: (a) Bedford, R. B.;
Betham, M. J. Org. Chem. 2006, 71, 9403. (b) Lebold,
T. P.; Kerr, M. A. Org. Lett. 2007, 9, 1883. (c) Watanabe,
T.; Ueda, S.; Inuki, S.; Oishi, S.; Fujii, N.; Ohno, H. Chem.
Commun. 2007, 4516. (d) Jean, D. J. Jr.; Poon, S. F.;
Schwarzbach, J. L. Org. Lett. 2007, 9, 4893. (e) Liu, C.-Y.;
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M. R.; Ashburn, B. O.; Perkins, J. R.; Carter, R. G. J. Org.
Chem. 2007, 72, 9857.
H,CH ), 2.90 (dd, 1 H , J = 8.8, 17.1 Hz, H-1), 3.50 (dd, 1
3
a
H , J = 2.6, 17.2 Hz, H-1), 3.60 (s, 3 H, NCH ), 3.90–4.10
b
3
(
m, 3 H, H and CH O), 4.20 (q, J = 7.1, 13.5 Hz, 2 H,
a 2
CH O), 7.10–7.20 (m, 3 H, ArH), 7.50–7.60 (m, 1 H, ArH),
2
1
3
7
(
.90 (s, 1 H, H-4). C NMR (75 MHz, CDCl ): d = 13.0
CH ), 13.5 (CH ), 22.8 (CH ), 28.7 (CH, C-4), 37.7
3
3 3 2
(
NCH ), 59.3 (CH O), 60.1 (CH O), 108.3 (C), 108.6 (CH),
3 2 2
1
1
2
1
6
15.4 (C), 116.9, 120.0, 120.8 (CH), 124.1(C), 131.2 (CH),
37.0, 138.6 (C), 166.3, 172.3 (CO). IR (KBr): n = 2981,
928, 2854(w), 1725(s), 1629, 1599(w), 1470 1454(m),
372, 1261, 1238(s), 1109, 1079, 147(m), 787, 747, 723,
(
3) (a) Forke, R.; Krahl, M. P.; Däbritz, F.; Jäger, A.; Knölker,
H.-J. Synlett 2008, 1870. (b) Forke, R.; Krahl, M. P.;
Krause, T.; Schlechtingen, G.; Knölker, H.-J. Synlett 2007,
–
1
08, 561(w)cm . GC-MS (EI, 70 eV): m/z (%) = 325(89)
2
68.
4) Ackermann, L.; Althammer, A. Angew. Chem. Int. Ed. 2007,
6, 1627.
+
[
M – 2] (carbazole), 280(13), 252(100), 208(07), 179(13).
(
+
+
HRMS (ESI ): m/z calcd for C H NO [M – 2] (carbazole):
1
9
19
4
4
325.13141; found: 325.13161.
(
(
5) Pindur, U. Heterocycles 2008, 27, 1253.
6) Kano, S.; Sugino, E.; Shibuya, S.; Hibino, S. J. Org. Chem.
(
19) Dibutyl 9-Methyl-9H-carbazole-2,3-dicarboxylate (6)
To xylene (5 mL) were added 5c (100 mg, 0.26 mmol) and
Pd/C (10 mg, 10 mol%). The soln was stirred under reflux
for 48 h under argon atmosphere. The reaction mixture was
filtered, and the filtrate was concentrated in vacuo to give 6
1981, 46, 3856.
(
7) Pindur, U.; Adam, R. Helv. Chim. Acta 1990, 73, 827.
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1
as a light yellow solid (99 mg, 100%). H NMR (250 MHz,
(
9) Dang, T. T.; Rasool, N.; Dang, T. T.; Reinke, H.; Langer, P.
CDCl ): d = 0.90 (t, 3 H, J = 7.4 Hz, CH ), 0.90 (t, 3 H,
3
3
Tetrahedron Lett. 2007, 48, 845.
J = 7.3 Hz, CH ), 1.30–1.50 (m, 4 H, 2 CH ), 1.60–1.80 (m,
3
2
(
(
10) Dang, T. T.; Dang, T. T.; Ahmad, R.; Reinke, H.; Langer, P.
4
H, 2 CH ), 3.80 (s, 3 H, NCH ), 4.30 (t, 2 H, J = 6.8 Hz,
2
3
Tetrahedron Lett. 2008, 49, 1698.
CH O), 4.30 (t, 2 H, J = 6.7 Hz, CH O), 7.20–7.30 (m, 1 H,
2
2
11) Dang, T. T.; Villinger, A.; Langer, P. Adv. Synth. Catal.
ArH), 7.30–7.40 (m, 1 H, ArH), 7.40–7.50 (m, 1 H, ArH),
2008, 350, 2109.
Synlett 2009, No. 11, 1822–1826 © Thieme Stuttgart · New York

1
826
M. Hussain et al.
LETTER
–
1
7
.60 (s, 1 H, H-1), 8.00–8.10 (m, 1 H, ArH), 8.40 (s, 1 H,
743, 721(m), 632, 608, 561(w)cm . GC-MS (EI, 70 eV):
13
+
H-4). C NMR (62 MHz, CDCl ): d = 13.7, 13.8 (CH ),
m/z (%) = 381(56) [M ], 308(15), 280(100), 224(87),
212(27), 206(77), 180(10), 152(11). HRMS (EI, 70 eV):
m/z calcd for C H NO [M ]: 381.19401; found:
3
3
19.2, 19.3 (CH ), 29.4 (NCH ), 30.6, 30.8 (CH ), 65.3, 65.7
2
3
2
+
(
CH O), 109.0, 109.1, 120.2, 121.0 (CH), 121.7, 122.2 (C),
2
23 27
4
122.4 (CH), 123.6 (C), 127.1 (CH), 131.1, 141.5, 142,1 (C),
167.9, 169.4 (CO). IR (KBr): n = 2956, 2931, 2871(w),
1709(s), 1464, 1387, 1362, 1340, 1325(m)1255, 1221(s),
1131, 1106, 1077, 1045(m), 950, 902, 843, 829(w), 784,
381.19422.
(20) Kawasaki, I.; Yamashita, M.; Ohta, S. Chem. Pharm. Bull.
1996, 44, 1831.
Synlett 2009, No. 11, 1822–1826 © Thieme Stuttgart · New York