Synthesis of dibenzothiophenes and carbazoles by sequential 'tetra-fold heck/6 π-electrocyclization/dehydrogenation' reactions of tetrabromothiophene and tetrabromo-N-methylpyrrole

Article abstract of DOI:10.1002/adsc.201200057

Dibenzothiophenes and carbazoles were prepared by tetrafold Heck reactions of tetrabromothiophene and N-methyltetrabromopyrrole and subsequent 6π-electrocyclization and dehydrogenation. A number of reactions could be successfully carried out as domino reactions in only one synthetic step. Copyright

Full text of DOI:10.1002/adsc.201200057

UPDATES
DOI: 10.1002/adsc.201200057
Synthesis of Dibenzothiophenes and Carbazoles by Sequential
ꢀTetra-Fold Heck/6p-Electrocyclization/Dehydrogenationꢁ
Reactions of Tetrabromothiophene and
Tetrabromo-N-methylpyrrole
Serge-Mithꢀrand Tengho Toguem,a Ingo Knepper,a Peter Ehlers,a,b Tung T. Dang,a
Tamꢁs Patonay,c and Peter Langera,b,*
a
Institut fꢂr Chemie, Universitꢃt Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany
Fax : (+49)-(0)381-498-6412; e-mail: peter.langer@uni-rostock.de
Leibniz-Institut fꢂr Katalyse an der Universitꢃt Rostock e.V., Albert Einstein Str. 29a, 18059 Rostock, Germany
Department of Organic Chemistry, University of Debrecen, H-4032 Debrecen, Egyetem tꢀr 1, Hungary
b
c
Received: January 20, 2012; Revised: March 21, 2012; Published online: May 29, 2012
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201200057.
Abstract: Dibenzothiophenes and carbazoles were
prepared by tetrafold Heck reactions of tetrabro-
mothiophene and N-methyltetrabromopyrrole and
subsequent 6p-electrocyclization and dehydrogena-
tion. A number of reactions could be successfully
carried out as domino reactions in only one synthet-
ic step.
ral, anti-inflammatory and antimalarial activity.[14]
Thiophene-containing molecules are also important in
material sciences, due to their electronic properties,
such as luminescence, fluorescence, redox activity,
non-linear optical chromism and electron transport.[15]
This includes, for example, dibenzothiophenes,[15j]
[2,2’;5’,2“]terthiophenes,[15k–n] and thienyl-diynes.[15o–q]
Dibenzothiophene was first synthesized in 1870 by
heating of diphenyl sulfide in the presence of iron
nails.[16] Later, a large number of methods for the syn-
thesis of dibenzothiophenes by various methods have
been reported.[17] For example, Nielsen and co-work-
ers recently reported an efficient three-step protocol
for the synthesis of functionalized dibenzothiophenes
based on palladium-catalyzed carbon-carbon and
carbon-sulfur bond formations.[18] The carbazole
Keywords: cyclizations; domino reactions; Heck re-
action; heterocycles; palladium
Introduction
The parent dibenzothiophene occurs in the phenan- system was first synthesized by the method of Graebe
threne fraction of coal tar and was first isolated by and Ullmann based on the reaction of o-aminodiphe-
Kruber.[1] Dibenzothiophene and its alkylated deriva- nylamine with nitrous acid to give 1-phenyl-1H-
tives represent one of the most abundant types of benzo[d]ACHTUNTRGNEUNG[1,2,3]triazole and subsequent loss of nitro-
sulfur-containing compounds in crude oil.[2] It has gen upon heating.[19] Carbazoles have been also pre-
been shown that dibenzothiophene derivatives, such pared from cyclohexanone phenylhydrazone using the
as 4,6-dimethyldibenzothiophene, exhibit estrogenic Fischer indole synthesis.[20] Several other methods for
activity.[3] Many dibenzothiophenes have been report- the synthesis of carbazoles have been reported.[21] Re-
ed to show antitumor,[4] genotoxic,[5] antiprotozoal,[6] cently, Ackermann et al. reported an efficient synthe-
antidiabetic,[7] and antimicrobial[8] activity. The carba- sis of carbazoles by a new palladium-catalyzed
ꢀ
ꢀ
zole (dibenzopyrrole) system is found in many phar- domino ꢄN H/C H activationꢅ reaction of anilines
macologically relevant natural products. Examples in- with 1,2-dihaloalkenes.[22]
clude clausenapine,[9] 3-methylcarbazole,[10] mukoni-
Some years ago, de Meijere and co-workers report-
dine[11] and koenoline.[12] The carbazole moiety occurs ed the synthesis of benzene derivatives by two-fold
in several clinically used drugs. For example, caprofen Heck reactions of 1,2-dibromoalkenes and subsequent
has been used for the treatment of arthritis in man 6p-electrocyclization.[23] This work has been applied
and in animals and carvedilol has been used for the to the synthesis of heterocycles.[23c–e] Following a retro-
treatment of hypertension.[13] Carbazoles have attract- synthetic analysis (Scheme 1), we considered that car-
ed much attention because of their antibiotic, antivi- bazoles, dibenzothiophenes and dibenzofurans might
Adv. Synth. Catal. 2012, 354, 1819 – 1826
ꢆ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1819

Serge-Mithꢀrand Tengho Toguem et al.
UPDATES
Scheme 1. Retrosynthetic analysis.
be prepared by a similar strategy starting with pyr-
role, thiophene and furan, respectively. Herein, we
report the synthesis of functionalized dibenzothio-
phenes and carbazoles by tetra-fold Heck reactions of
tetrabromothiophene and tetrabromo-N-methylpyr-
role and subsequent 6p-electrocyclization and dehy-
drogenation. Suzuki–Miyaura and Sonogashira reac-
tions of tetrabromothiophene,[24] tetrabromo-N-meth-
ylpyrrole,[25] and tetrabromofuran[26] have been previ-
ously reported. In contrast, Heck reactions of these
interesting, highly brominated substrates are, to the
best of our knowledge, unknown to date. We also
studied the photophysical properties of the products
(absorption and fluorescence).
Scheme 3. Synthesis of 3a–j and 4a–j. Reagents and condi-
tions: i, 2a (1 equiv.), alkenes (5.0 equiv.), PdACHTUNGTRENNUNG(OAc)2
(3 mol%), PCy3 (5 mol%), Na2CO3, DMF, 908C, 12 h; ii, di-
phenyl ether, 2008C, 24 h; iii, Pd/C (10 mol%), diphenyl
ether, 2008C, 48 h.
Table 1. Synthesis of 3a–j and 4a–j.
3, 4
R
Yield [%] (3)[a] Yield [%] (4)[a]
a
b
c
d
e
f
g
h
i
CO2Me
CO2Et
CO2-n-Bu
CO2-i-Bu
CO2(2-ethylhexyl) 52
CO2-n-hexyl
Ph
4-t-Bu-C6H4
4-MeO-C6H4
4-Me-C6H4
71
54
51
68
60
51
59
62
70
73
74
63
67
59
63
80
72
62
78
Results and Discussion
Tetrabromothiophene (2a), tetrabromo-N-methylpyr-
role (2b) and tetrabromofuran (2c) were prepared in
good yields according to procedures reported in the
literature (Scheme 2).[27]
j
[a]
Yields of isolated products.
The Heck cross-coupling reaction of tetrabromo-
thiophene (2a) with 5.0 equiv. of alkenes 2a–j (908C, (3 mol%) in the presence of PCy3 (5 mol%) as the
12 h) afforded the tetra(alkenyl)thiophenes 3a–j catalyst and Na2CO3 as the base. The use of triethyla-
(Scheme 3, Table 1). The best yields were obtained mine resulted in partial reduction of 2a (replacement
AHCTUNGTRENNUNG
when the reactions were carried out using PdACHTNUGTRNEUNG(OAc)2 of bromine by hydrogen atoms). Heating of a diphenyl
ether solution of 3a–j for 24 h at 2008C and subse-
quent addition of Pd/C and heating for further 48 h at
2008C afforded dibenzothiophenes 4a–j in good
yields (Scheme 2, Table 1). The reactions proceeded
by 6p-electrocyclization and subsequent Pd/C-cata-
lyzed dehydrogenation. Low yields were obtained
when the reactions were carried out at 140 instead of
2008C. The use of acrylonitrile or nitroethene instead
of acrylates or styrenes proved to be unsuccessful
(formation of a complex mixture).
During the optimization, the temperature also
proved to be an important parameter. Interestingly,
products 4a–g could be prepared from 2a in only one
synthetic step when the reactions were carried out at
1408C (Scheme 4). This is interesting because the
thermal
transformation
of
isolated
tetra-
Scheme 2. Synthesis of 2a–c (see ref.[27]).
ACHTUNGTREN(NGNU alkenyl)thiophenes 3 into dibenzothiophenes 4 (vide
1820
asc.wiley-vch.de
ꢆ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 1819 – 1826

Synthesis of Dibenzothiophenes and Carbazoles
Table 3. Optimization of the reaction conditions.
R
Base
Solvent T [8C
t
Yield [%]
]
[h] (4)[a]
CO2-i-Bu
CO2-i-Bu
CO2-i-Bu
CO2-n-Bu
CO2-n-Bu
CO2-n-Bu
CO2-i-Bu
CO2-i-Bu
CO2-n-Bu
CO2-n-Bu
CO2(2-ethyl-
hexyl)
Na2CO3 DMF
Na2CO3 DMF
Na2CO3 DMF
K2CO3 DMF
K2CO3 DMF
K2CO3 DMF
140
120
90
120
140
90
120
140
90
24 52
24 31
Scheme 4. Synthesis of 4a–g. Reagents and conditions: i, 2a
(1 equiv.), alkenes (5.0 equiv.), PdACTHNUTRGEN(UNG OAc)2 (3 mol%), P(Cy)3
(5 mol%), Na2CO3, DMF, 1408C, 24 h.
[b]
24
–
24 40
24 26
[b]
24
12
24
24
–
0
0
0
Et3N
Et3N
Et3N
DMF
DMF
DMF
supra) required 2008C and the yields decreased when
the reactions were carried out at 1408C. Therefore,
we believe that, in the case of the domino reaction,
the cyclization proceeds by a Pd-catalyzed mecha-
nism. The products were formed by a domino ꢄtetra-
fold Heck/6p-electrocyclization/dehydrogenationꢅ re-
action. The yields of the domino reactions (in the
range 36–52%) were comparable to the combined
yields of the sequential syntheses (Scheme 3, Table 2).
Although Suzuki–Miyaura reactions of 2a have been
reported to proceed with very good regioselectivity in
favour of positions 2 and 5,[24] all attempts to induce
regioselective Heck reactions of 2a, using 2.0 equiva-
lents of the alkene, failed.
Na2CO3 toluene 110
Na2CO3 xylene 150
24 traces
12 traces
CO2-i-Bu
K3PO4 DMF
140
24 traces
[a]
Isolated yields; tetra
lated.
TetraACTHNUTRGENUG(N alkenyl)thiophenes 3 were isolated.
ACHTUNGTRNE(NUNG alkenyl)thiophenes 3 were not iso-
[b]
The base plays also a very important role in the re-
action (Table 3). The use of triethylamine resulted in
the formation of a mixture of mono-, di- and tri-
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
yields than K2CO3. The use of DMF as the solvent
proved to be important. Not even trace amounts of
product were observed when the reactions carried out
in toluene and xylene.
The Heck reaction of tetrabromo-N-methylpyrrole
(2b) with acrylates 2 (5.0 equiv.) afforded the tetra-
ACHTUNGTRENNUNG
Scheme 5. Synthesis of 5a–g and 6a, b, d–g. Reagents and
conditions: i, 2b (1 equiv.), acrylates (5.0 equiv.), Pd(OAc)2
(5 mol%), P(Cy)3 (10 mol%), Et3N, DMF, 908C, 12 h; ii, di-
phenyl ether, 2008C, 24 h; iii, Pd/C (10 mol%), diphenyl
ether, 2008C, 48 h.
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
the catalyst in the presence of tricyclohexylphosphine
(PCy3, 10 mol%) or SPhos (10 mol%) (Table 5). In
the reactions PCy3 was employed, due to its lower
price as compared to SPhos. During the optimization,
the temperature also proved to be an important pa-
rameter. A clean transformation was observed when
the reaction was carried out at 908C. We have men-
tioned above that the use of triethylamine resulted in
failure of the Heck reaction in the case of tetrabro-
mothiophene because of reduction. In contrast, in the
case of tetrabromo-N-methylpyrrole the employment
of triethylamine gave better yields of Heck products
than the use of sodium carbonate. This might be ex-
plained by the fact that pyrroles are more electron-
rich than thiophenes and thus less prone to reduction.
The employment of styrene instead of acrylates
proved to be unsuccessful, due to decomposition
under the reaction conditions employed. Tetra-
Table 2. Synthesis of 4a–g.
4 R
Base
Solvent T
t
Yield [%]
[8C ] [h] (4)[a]
a CO2Me
b CO2Et
Na2CO3 DMF
Na2CO3 DMF
K2CO3 DMF
Na2CO3 DMF
140
140
120
140
120
24 43
24 38
24 40
24 52
24 36
c
CO2-n-Bu
d CO2-i-Bu
e CO2(2-ethyl- Na2CO3 DMF
hexyl)
f
CO2-n-hexyl Na2CO3 DMF
140
140
24 40
36 48
g Ph
Na2CO3 DMF
[a]
Yields of isolated products.
ACHTUNGTREN(NGNU alkenyl)-N-methylpyrroles 5a–g were transformed
Adv. Synth. Catal. 2012, 354, 1819 – 1826
ꢆ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1821

Serge-Mithꢀrand Tengho Toguem et al.
UPDATES
Table 4. Synthesis of 5a–g and 6a, b, d–g.
Table 6. Influence of the temperature on the 6p-electrocycli-
zation.
5, 6
R
Yield [%] (5)[a] Yield [%] (6)[a]
T [8C ]
t [h]
Yield [%] (6a)[a]
Yield [%] (6f)[a]
a
b
c
d
e
f
CO2-n-Bu
CO2-i-Bu
CO2-t-Bu
CO2-n-hexyl
CO2Me
65
55
71
73
52
69
75
89
–
140
200
96
72
21
75
12
63
[b]
80
69
63
82
[a]
Yields of isolated products.
CO2Et
g
h
CO2(2-ethylhexyl) 75
[b]
[c]
Ph
–
–
[a]
Yields of isolated products.
Complex mixture.
Experiment was not carried out
[b]
[c]
Scheme 6. Synthesis of 7a, b. Reagents and conditions: i, 2c
(1.0 equiv.), acrylate (5.0 equiv.), Pd(OAc)2 (3 mol%),
AHCTUNGTRENNUNG
into carbazoles 6a, b, d–g by heating in diphenyl ether P(Cy)3 (5 mol%), Na2CO3, DMF, 908C, 8 h.
for 24 h at 2008C and subsequent addition of Pd/C
and heating for further 48 h at 2008C (63–89% yield).
The reactions proceeded by 6p-electrocyclization and
subsequent Pd/C-catalyzed dehydrogenation. Low
Table 7. Synthesis of 7a, b.
yields were observed when the reactions were carried
out at 1408C for 96 h instead of 2008C for 72 h
(Table 6). The Heck reaction of 2b with acrylates, car-
ried out at 140 instead of 908C, resulted in the forma-
tion of complex mixtures. The formation of carbazoles
by a domino reaction proved to be not possible. Simi-
lar to substrate 2a, all attempts to induce regioselec-
tive Suzuki–Miyaura reactions of 2b failed.
7
R
Base
Solvent T [8C ] t [h] % (7)[a]
a
b
c
CO2-i-Bu Na2CO3 DMF
90
8
27
CO2Me Na2CO3 DMF
CO2-i-Bu Na2CO3 DMF
CO2-i-Bu Et3N DMF
100
140
90
8
8
12
19
traces
traces
d
[a]
Yields of isolated products.
The Heck reaction of tetrabromofuran (2c) with
5.0 equiv. of alkenes 2 (90–1008C, 8 h) afforded the
tetraACHTUNGTRENNUNG(alkenyl)furans 7a, b (Scheme 6, Table 7) in low
Table 8. General overview of the UV-Vis data of selected
compounds 3 and 4 (in CH2Cl2).
yield. The reactions were carried out under the same
conditions as in the case of tetrabromothiophene (2a).
Despite much efforts, the yields could not be opti-
mized by variation of the conditions. The yields were
low because of the unstable nature of the products
and losses (due to decomposition) during the condi-
tions of their formation and during chromatography.
Heating of (slightly impure) 7a, b in the presence of
Compound
lmax [nm]
Sh1 [nm]
4a
4d
4f
4g
4i
258
264
265
270
278
274
290
287
289
340
342
338
342
346
313
323
316
354
343
343
401
416
4j
Pd/C at 120–2008C for 12–36 h in diphenyl ether re- 3c
sulted in the formation of complex mixtures, due to
decomposition.
3d
3e
3g
3j
The UV-Vis spectra of tetra
ACHTUNGERTN(NUNG alkenyl)thiophenes 3d,
g and of dibenzothiophenes 4d, g, containing an ester
Table 5. Optimization of the reaction conditions for the synthesis 5a and 5e.
Catalyst
T [8C]
Yield [%] (5a)[a]
Yield [%] (5e)[a]
5 mol% Pd
5 mol% Pd
5 mol% Pd
5 mol% Pd
5 mol% Pd
N
90
90
120
120
140
65
71
48
21
13
52
55
[b]
–
–
[b]
[b]
–
[a]
Yields of isolated products; carbazoles 6 were not isolated.
Experiment was not carried out
[b]
1822
asc.wiley-vch.de
ꢆ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 1819 – 1826

Synthesis of Dibenzothiophenes and Carbazoles
Table 9. Structure and lmax values of compounds 3g, 3h and
3i.
type of ester group seems to have an influence on the
emission (products 4a and 4d). This is unusual be-
cause the alkyl substituents of the ester group possess
no p- or n-electrons. Thus, the red shift of compound
4d presumably has steric reasons (maybe due to or-
thogonal twisting of the ester group with regard to
the p-system.
Compound
R
lmax, emission [nm]
3g
3h
3i
Ph
465
480
490
4-t-Bu-C6H4
4-MeO-C6H4
A strong bathochromic shift (about 120 nm) is ob-
served for the emission of tetraACTHUNTGRNEUNG(alkenyl)thiophene 3i
as compared to dibenzothiophene 4i (Table 11). This
is a general trend which might be explained by the
presence of a 1,3,5-hexatriene system in case of the
Table 10. lmax values of compounds 4a, 4d and 4i.
Compound
R
lmax, emission [nm]
tetraACTHNUTRGNEUG(N alkenyl)thiophene (Table 11).
4a
4d
4i
CO2Me
CO2-i-Bu
4-MeO-C6H4
365
395
370
Conclusions
We have reported the synthesis of tetra-
Table 11. Emission wavelengths of 4a, 4d, 4i, 3g, 3h, 3i and
3j.
A
ACHTUNGTNER(NUNG alkenyl)-N-methylpyrroles
AHCTUNGTRENNUNG
tetra-fold Heck cross-coupling reactions of tetrabro-
minated thiophene, N-methypyrrole and furan, re-
Compound
lmax, emission [nm]
4a
4d
4i
3g
3h
3i
365
395
370
465
480
490
480
spectively. The tetra
AHCTUNGTREG(NNUN alkenyl)-N-methylpyrroles were transformed, by Pd/
C-catalyzed electrocyclization and dehydrogenation,
into the corresponding dibenzothiophenes and carba-
zoles, respectively. The absorption and fluorescence
properties of the products were studied.
ACHTUNGTRNE(NUNG alkenyl)thiophenes and tetra-
3j
Experimental Section
group (3d, 4d) or a phenyl group (3g, 4g), are shown
in Table 8. Compounds 3d, 4g and 4d show lmax values
in the range of 260–290 nm, while the lmax value of 3g
is shifted about 80 nm to higher wavelengths. The
transition with the lowest energies S1 S0 belongs to
the tetra
General Procedure A for the Synthesis of 2,3,4,5-
Tetra
ACHUTGTNRNEUG(N alkenyl)thiophenes and 2,3,4,5-tetraACHTUTGNREN(NUNG alkenyl)-
!
furans
ACHTUNGTRENNUNG(styryl)thiophenes (as shown for 3g). The In a pressure tube (glass bomb) a suspension of PdACHTUNGTRENNUNG(OAc)2
(3.4 mg, 0.015 mmol, 3 mol%) and P(Cy)3 (7 mg,
0,025 mmol, 5 mol%) in DMF (5 mL) was purged with
argon and stirred at 208C to give a yellowish clear solution.
To the stirred solution were added 2a or 2c (0.5 mmol),
Na2CO3 (216 mg, 4.0 mmol) and the alkene (1.25 equiv. per
bromine atom of the substrate). The reaction mixture was
stirred at 90–1008C for 12 h. The solution was poured into
H2O, brine, and EtOAc (25 mL each) and the organic and
the aqueous layers were separated. The latter was extracted
with EtOAc (3ꢇ25 mL), dried (Na2SO4), filtered, and con-
tetra(alkenyl)thiophenes generally show absorptions
ACHTUNGTRENNUNG
at lower energies than the corresponding dibenzothio-
phene derivatives. This can be explained by the pres-
ence of a 1,3,5-hexatriene system in the case of the
tetraACHTUNGTRENNUNG(alkenyl)thiophenes. Substituents located at the
tetraaryldibenzothiophenes (4g, 4i and 4j) have a low
impact on the absorption spectra. The presence of
donor substituents located at the phenyl group results
in a small bathochromic shift of lmax (Table 8).
Products 3 and 4 exhibit fluorescence properties. centrated under vacuum. The residue was purified by flash
column chromatography (flash silica gel, eluent: n-heptane-
EtOAc).
The fluorescence spectra were recorded in dichloro-
methane (cꢁ10ꢀ3–10ꢀ4 mol/L; excitation wavelength:
250 nm). Table 9 shows the fluorescence spectra of
(2E,2’E,2’’E,2’’’E)-Tetramethyl
2,3,4,5-tetrayl)tetraacrylate (3a): Starting with 2a (200 mg,
0.5 mmol), methyl acrylate (0.23 mL, 2.5 mmol), Pd(OAc)2
3,3’,3’’,3’’’-(thiophene-
three tetraACHTUNGTRENNUNG(styryl)thiophenes (3g, 3h and 3i). The com-
ACHTUNGTRENNUNG
pounds show emissions in the range of 465–490 nm.
The presence of donor substituents located at the 4-
position of the phenyl group leads to a bathochromic
shift of the emission.
(3.4 mg, 3 mol%), P(Cy)3 (7 mg, 5 mol%), Na2CO3 (216 mg,
4.0 mmol), and DMF (5 mL) (908C, 12 h) according to gen-
eral procedure A, product 3a was prepared as a yellowish
solid; yield: 149 mg (71%), mp 80–828C. 1H NMR
(300 MHz, CDCl3): d=3.75 (s, 6H, 2OCH3), 3.77 (s, 6H,
Dibenzothiophenes 4a, 4d and 4i show emissions in
the range of 365–395 nm (Table 10). Surprisingly, the 2OCH3), 6.04 (d, 2H, J=16.0 Hz, 2CH), 6.28 (d, 2H, J=
Adv. Synth. Catal. 2012, 354, 1819 – 1826
ꢆ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1823

Serge-Mithꢀrand Tengho Toguem et al.
UPDATES
15.7 Hz, 2CH), 7.61 (d, 2H, J=16.0 Hz, 2CH), 7.76 (d, 2H,
J=15.7 Hz, 2CH); 13C NMR (62 MHz, CDCl3): d=52.0
(2OCH3), 52.1 (2OCH3), 121.1 (2CH), 125.8 (2CH), 133.8
(2CH), 135.4 (2CH), 138.3 (2C), 139.0 (2C), 166.0 (2CO),
166.2 (2CO); IR (KBr): v=3000, 2952, 2921, 2848 (w), 1710
(s), 1615, 1432, 1306 (m), 1267, 1192, 1164 (s), 1081, 1018
(m), 964 (s), 919, 852, 801, 735, 701, 657, 575 cmꢀ1 (m); MS
(EI, 70 eV): m/z (%)=420 (28) [M]+, 389 (12), 361 (25), 360
(33), 331 (10), 330 (18), 329 (100), 327 (16), 302 (10), 301
(20), 297 (15), 285 (30), 270 (10), 269 (29), 242 (16), 211
(23), 198 (11), 184 (29), 183 (12), 139 (11), 59 (18); HR-MS
(EI, 70 eV): m/z=420.08705,calcd. for C20H20O8S [M]+:
420.08734.
procedure B as a brownish oil; yield: 117 mg (40%).
1H NMR (300 MHz, CDCl3): d=0.91 (t, 6H, J=7.3 Hz,
2CH3), 0.92 (t, 6H, J=7.4 Hz, 2CH3), 1.35–1.45 (m, 8H,
4CH2), 1.64–1.75 (m, 8H, 4CH2), 4.30 (t, 4H, J=6.7 Hz,
2CH2O), 4.31 (t, 4H, J=6.7 Hz, 2CH2O), 8.15 (s, 2H,
ArH), 8.52 (s, 2H, ArH); 13C NMR (75 MHz, CDCl3): d=
12.7 (4CH3), 18.2 (4CH2), 29.5 (2CH2), 29.6 (2CH2), 64.9
(2CH2O), 65.0 (2CH2O), 122.3 (2CH), 122.7 (2CH), 128.1
(2C), 130.9 (2C), 134.9 (2C), 142.0 (2C), 166.2 (2CO),
166.3 (2CO); IR (KBr): v=2953, 2925, 2856 (m), 1716 (s),
1608, 1547, 1466, 1379 (m), 1268, 1240, 1119, 1097 (s), 991,
897, 781 (m), 746, 600, 542 cmꢀ1 (w); MS (EI, 70 eV): m/z
(%)=584 (39) [M]+, 528 (10), 457 (10), 456 (31), 457 (100),
399 (50), 360 (17), 343 (27), 342 (12), 325 (27), 254 (12), 57
(14), 44 (16), 41 (21); HR-MS (ESI): m/z=585.2517, calcd.
for C32H41O8S [M+H]+: 585.2516.
General Procedure B for the One-Pot Synthesis of
Dibenzothiophenes (4)
General Procedure D for the Synthesis of 2,3,4,5-
In a pressure tube (glass bomb) a suspension of PdACTHNUTRGNEUNG(OAc)2
Tetraalkenyl-N-methylpyrroles (5)
(3.4 mg, 3 mol%) and P(Cy)3 (7 mg, 0,025 mmol, 5 mol%) in
DMF (5 mL) was purged with argon and stirred at 208C to
give a yellowish clear solution. To the stirred solution were
added 2a (200 mg, 0.5 mmol), Na2CO3 (216 mg, 4.0 mmol)
and the alkene or styrene (5.0 equiv. per bromine atom of
the substrate). The reaction mixture was stirred at 1408C for
24–36 h. The solution was poured into H2O, brine and
EtOAc (25 mL each) and the organic and the aqueous
layers were separated. The latter was extracted with EtOAc
(3ꢇ25 mL), dried (Na2SO4), filtered, and concentrated
under vacuum. The residue was purified by flash column
chromatography (flash silica gel, eluent: n-heptane-
EtOAc).
In a pressure tube (glass bomb) a suspension of PdACHTUNGTRENNUNG(OAc)2
(12 mg, 0.05 mmol, 5 mol%) and P(Cy)3 (28 mg, 0,1 mmol,
10 mol%) in DMF (5 mL) was purged with argon and
stirred at 208C to give a yellowish or brownish transparent
solution. To the stirred solution were added the brominated
pyrrole 2b (1.0 mmol), NEt3 (1.1 mL, 8.0 mmol) and the
alkene (1.25 equiv. per Br). The reaction mixture was stirred
at 908C for 12 h. The solution was cooled to 208C, poured
into H2O and CH2Cl2 (25 mL each), and the organic and the
aqueous layer were separated. The latter was extracted with
CH2Cl2 (3ꢇ25 mL). The combined organic layers were
washed with H2O (3ꢇ20 mL), dried (Na2SO4), and concen-
trated under vacuum. The residue was purified by chroma-
tography (flash silica gel, heptanes/EtOAc).
General Procedure C for the Synthesis of Dibenzo-
thiophenes (4)
(2E,2’E,2’’E,2’’’E)-Tetrabutyl-3,3’,3’’,3’’’-(1-methyl-1H-pyr-
role-2,3,4,5-tetrayl)tetraacrylate (5a): Product 5a was pre-
pared starting with 2b (392 mg, 1.0 mmol), n-butyl acrylate
(0.72 mL, 5.0 mmol), PdACHTNUGTRENUNG(OAc)2 (11 mg, 5 mol%) , P(Cy)3
(28 mg, 10 mol%), NEt3 (1.10 mL, 8.0 mmol), DMF (5 mL)
A diphenyl ether solution (3 mL) of 3a–j was stirred at
2008C for 24 h in a pressure tube. The solution was allowed
to cool to 208C and Pd/C (30 mg, 10 mol%) was added. The
solution was stirred at 2008C for 48 h under an argon atmos-
phere. The reaction mixture was filtered and the filtrate was
concentrated under vacuum. The residue was purified by
chromatography (flash silica gel, eluent: heptanes-EtOAc).
(908C, 12 h) following general procedure D as a brownish
1
oil; yield: 380 mg (65%). H NMR (300 MHz, CDCl3): d=
0.89 (t, 12H, J=7.4 Hz, 4CH3), 1.30–1.40 (m, 8H, 4CH2),
1.58–1.65 (m, 8H, 4CH2), 3.71 (s, 3H, NCH3), 4.14 (t, 4H,
J=6.7 Hz, 2CH2O), 4.16 (t, 4H, J=6.7 Hz, 2CH2O), 6.02
(d, 2H, J=16.0 Hz, 2CH), 6.12 (d, 2H, J=16.1 Hz, 2CH),
7.58 (d, 2H, J=16.1 Hz, 2CH), 7.65 (d, 2H, J=16.0 Hz,
2CH); 13C NMR (62 MHz, CDCl3): d=13.7 (2CH3), 13.8
(2CH3), 19.1 (2CH2), 19.2 (2CH2), 30.6 (2CH2), 30.7
(2CH2), 34.2 (NCH3), 64.5 (2CH2O), 64.8 (2CH2O), 121.9
(2CH), 122.2 (2C), 122.5 (2CH), 130.5 (2CH), 132.8 (2C),
135.7 (2CH), 166.4 (2CO), 166.6 (2CO); IR (KBr): v=
2957, 2933 (m), 2872 (w), 1705 (s), 1618 (m), 1453, 1383 (w),
1278, 1247 (m), 1161 (s), 1062, 1023, 964, 858, 735 (m), 653,
611 cmꢀ1 (w); MS (EI, 70 eV): m/z (%)=585 (44) [M]+, 512
(12), 484 (21), 428 (12), 410 (100), 354 (14), 310 (30), 254
(22), 252 (15), 226 (17), 182 (17), 173 (11), 57 (23), 41 (17);
HR-MS (EI, 70 eV): m/z=585.32935, calcd. for C33H47NO8
[M+]: 585.32962.
Tetramethyl dibenzoACTHNUTRGNEUNG[b,d]thiophene-2,3,7,8-tetracarboxy-
late (4a): Product 4a was prepared starting with 3a (100 mg,
0.24 mmol), following general procedure C, as a white solid;
1
yield: 59 mg (60%), mp.=146–1488C. H NMR (300 MHz,
CDCl3): d=3.90 (s, 6H, 2CH3O), 3.92 (s, 6H, 2CH3O), 8.15
(s, 2H, ArH), 8.54 (s, 2H, ArH); 13C NMR (62 MHz,
CDCl3): d=51.9 (2CH3O), 52.0 (2CH3O), 122.4 (2CH),
122.8 (2CH), 127.5 (2C), 130.6 (2C), 134.9 (2C), 142.3
(2C), 166.4 (2CO), 166.7 (2CO); IR (KBr): v=2999, 2951,
2923, 2850 (w), 1716 (s), 1600, 1548, 1465 (w), 1431 (m),
1351, 1316 (w), 1270, 1243 (m), 1191 (m), 1123, 1094 (s),
1012, 962, 896, 881, 820, 781, 746 (m), 609, 575 cmꢀ1 (w);
GC-MS (EI, 70 eV): m/z (%)=416 (57) [M]+, 386 (21), 385
(100), 339 (11), 268 (13); HR-MS (EI, 70 eV): m/z=
416.05600, calcd. for C20H16O8S [M]+: 416.05604.
Tetrabutyl dibenzo
(4c): Product 4c was prepared starting with 2a (200 mg,
0.5 mmol), n-butyl acrylate (0.36 mL, 2.5 mmol), Pd(OAc)2
ACHTUNGTRENUN[NG b,d]thiophene-2,3,7,8-tetracarboxylate
AHCTUNGTRENNUNG
(3.4 mg, 3 mol%), P(Cy)3 (7 mg, 5 mol%), Na2CO3 (216 mg,
4.0 mmol), DMF (5 mL) (1408C, 24 h) according to general
1824
asc.wiley-vch.de
ꢆ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 1819 – 1826

Synthesis of Dibenzothiophenes and Carbazoles
References
General Procedure E for the Synthesis of Carbazoles
(6)
[1] O. Kruber, Ber. Dtsch. Chem. Ges. 1874, 174, 185.
[2] a) W. A. Carruthers, G. Douglas, J. Chem. Soc. 1964,
4077; b) W. A. Carruthers, G. Douglas, J. Chem. Soc.
1959, 2813.
[3] Y. Mori, S. Taneda, H. Hayashi, A. Sakushima, K.
Kamata, A. K. Suzuki, S. Yoshino, M. Sakata, M. Sagai,
K. Seki, Biol. Pharm. Bull. 2002, 25, 145.
[4] M.-J. R. P. Queiroz, A. S. Abreu, M. S. D. Carvalho,
P. M. T. Ferreira, N. Nazareth, M. S.-J. Nascimento,
Bioorg. Med. Chem. 2008, 16, 5584.
A diphenyl ether solution (3 mL) of 5a–g (0.25 mmol) was
stirred at 2008C for 24 h in a pressure tube. The solution
was allowed to cool to 208C and Pd/C (30 mg, 10 mol%)
was added. The solution was stirred at 2008C for 48 h under
an argon atmosphere. The reaction mixture was filtered and
the filtrate was concentrated under vacuum. The residue
was purified by chromatography (flash silica gel, eluent:
heptanes/EtOAc).
Tetrabutyl-9-methyl-9H-carbazole-2,3,6,7-tetracarboxylate
(6a): Compound 6a was synthesized starting with 5a
(100 mg, 0.17 mmol), following general procedure E, as
a brownish oil; yield: 74 mg (75%). 1H NMR (300 MHz,
CDCl3): d=0.90 (t, 6H, J=7.4 Hz, 2CH3), 0.92 (t, 6H, J=
7.3 Hz, 2CH3), 1.33–1.48 (m, 8H, 4CH2), 1.64–1.75 (m, 8H,
4CH2), 3.86 (s, 3H, NCH3), 4.28 (t, 4H, J=6.7 Hz, 2CH2O),
4.30 (t, 4H, J=6.7 Hz, 2CH2O), 7.62 (s, 2H, ArH), 8.50 (s,
2H, ArH); 13C NMR (75 MHz, CDCl3): d=13.7 (2CH3),
13.8 (2CH3), 19.2 (2CH2), 19.3 (2CH2), 29.8 (NCH3), 30.6
(2CH2), 30.8 (2CH2), 65.5 (2CH2O), 65.9 (2CH2O), 109.7
(2CH), 123.0 (2CH), 123.1 (4C), 132.6 (2C), 142.8 (2C),
167.3 (2CO), 168.8 (2CO); IR (KBr): v=2957, 2932 (m),
2872 (w), 1712 (s), 1634, 1601, 1563 (w), 1457 (m), 1384,
1340 (w), 1254, 1230, 1107, 1084, 1074 (s), 1018, 961, 784
(m), 681, 603 cmꢀ1 (w); MS (EI, 70 eV): m/z (%)=581 (100)
[M]+, 525 (12), 453 (23), 422 (85), 396 (21), 340 (11), 322
(25), 173 (11); HR-MS (ESI): m/z=582.3064, calcd. for
C33H44NO8 [M+H]+: 582.3061.
[5] Y. Xu, X. Qian, W. Yao, P. Mao, J. Cui, Bioorg. Med.
Chem. 2003, 11, 5427.
[6] D. A. Patrick, J. E. Hall, B. C. Bender, D. R. McCurdy,
W. D. Wilson, F. A. Tanious, S. Saha, R. R. Tidwell,
Eur. J. Med. Chem. 1999, 575.
[7] J. Wrobel, J. Sredy, C. Moxham, A. Dietrich Z. Li,
D. R. Sawicki, L. Seestaller, L. Wu, A. Katz, D. Sulli-
van, C. Tio, Z.-Y. Zhang, J. Med. Chem. 1999, 42, 3199.
[8] A. M. El-Naggar, F. S. M. Ahmed, S. G. Donia, J.
Indian Chem. Soc. 1983, 60, 479.
[9] J. Bergman, B. Pelcman, Pure Appl. Chem. 1990, 62,
10, 1967.
[10] A. Chakraborty, B. K. Chowdhury, S. S. Jash, G. K.
Biswas, S. K. Bhattacharyya, P. Bhattacharyya, Phyto-
chemistry 1992, 31, 2503.
[11] T.-S. Wu, S.-C. Huang, J.-S. Lai, C.-M. Teng, F.-N. Ko,
C.-S. Kuoh, Phytochemistry 1993, 32, 2449.
[12] M. Fiebig, J. M. Pezzuto, D. D. Soejarto, A. D. King-
horn, Phytochemistry 1985, 24, 3041.
[13] H.-J. Knçlker Top. Curr. Chem. 2005, 244, 115.
[14] a) D. P. Chakraborty, B. K. Barman, P. K. Bose, Tetrahe-
dron 1965, 21, 68; b) T.-S. Wu, S.-C. Huang, P.-L. Wu,
Tetrahedron Lett. 1996, 37, 781; c) H.-J. Knçlker, K. R.
Reddy, The Alkaloids: Chemistry and Biology, Elsevier,
Amsterdam, 2008, Vol. 65, p 181.
Synthesis of TetraACTHNUTRGENUGN(alkenyl)furans (7)
(2E,2’E,2’’E,2’’’E)-Tetrabutyl-3,3’,3’’,3’’’-(furan-2,3,4,5-tetra-
yl)tetraacrylate (7a): Product 7a was prepared starting with
2c (200 mg, 0.5 mmol), n-butyl acrylate (0.36 mL, 2.5 mmol),
PdACHTUNGTRENNUNG(OAc)2 (3.4 mg, 3 mol%), P(Cy)3 (7 mg, 5 mol%),
Na2CO3 (216 mg, 4.0 mmol), and DMF (5 mL) (908C, 8 h)
[15] For oligothiophenes with low-lying triplet states, see:
a) F. Garnier, Angew. Chem. 1989, 101, 529; Angew.
Chem. Int. Ed. Engl. 1989, 28, 513; b) F. Garnier, A.
Yassar, R. Hajlaoui, G. Horowitz, F. Deloffre, B.
Servet, S. Ries, P. Alnot, J. Am. Chem. Soc. 1993, 115,
8716; c) F. Garnier, R. Hajlaoui, A. Yassar, P. Srivasta-
va, Science 1994, 265, 1684; d) A. Dodabalapur, L.
Torsi, H. E. Katz, Science 1995, 268, 270; e) A. Doda-
balapur, L. J. Rothberg, A. W. P. Fung, H. E. Katz, Sci-
ence 1996, 272, 1462; f) T. Noda, H. Ogawa, N. Noma,
Y. Shirota, Appl. Phys. Lett. 1997, 70, 699; g) T. Noda,
I. Imae, N. Noma, Y. Shirota, Adv. Mater. 1997, 9, 239;
h) Y. Cui, X. Zhang, S. A. Jenekhe, Marcomolecules,
1999, 32, 3824; i) S. Thayumanavan, J. Mendez, S. R.
Marder, J. Org. Chem. 1999, 64, 4289; j) Y. Mori, S.
Taneda, H. Hayashi, A. Sakushima, K. Kamata, A. K.
Suzuki, S. Yoshino, M. Sakata, M. Sagai, K.-i. Seki,
Biol. Pharm. Bull. 2002, 25, 145; k) P. Liu, Y. Zhang, G.
Feng, J. Hu, X. Zhou, Q. Zhao, Y. Xu, Z. Tong, W.
Deng, Tetrahedron 2004, 60, 5259; l) U. Huss, T. Ring-
bom, P. Perera, L. Bohlin, M. Vasaenge, J. Nat. Prod.
2002, 65, 1517; m) V. G. Albano, M. Bandini, M. Meluc-
ci, M. Monari, F. Piccinelli, S. Tommasi, A. Umani-
Ronchi, Adv. Synth. Catal. 2005, 347, 1507; n) M. Me-
lucci, G. Barbarella, M. Zambianchi, P. D. Pietro, A.
according to general procedure A as a brownish oil; yield:
77 mg (27%). H NMR (300 MHz, CDCl3): d=0.90 (t, 12H,
1
J=7.3 Hz, 4CH3), 1.33–1.40 (m, 8H, 4CH2), 1.58–1.67 (m,
8H, 4CH2), 4.16 (t, 4H, J=6.6 Hz, 2CH2O), 6.15 (d, 2H,
J=16.0 Hz, 2CH), 6.52 (d, 2H, J=15.6 Hz, 2CH), 7.47 (d,
2H, J=16.0 Hz, 2CH), 7.55 (d, 2H, J=16.1 Hz, 2CH);
13C NMR (62 MHz, CDCl3): d=13.7 (4CH3), 19.1 (4CH2),
30.5 (2CH2), 30.6 (2CH2), 64.8 (2CH2O), 64.9 (2CH2O),
121.1 (2CH), 124.3 (2C), 124.7 (2CH), 126.9 (2CH), 132.1
(2CH), 150.5 (2C), 165.8 (2CO), 166.2 (2CO); IR (KBr):
v=2956, 2939, 2870 (w), 1707 (s), 1618 (m), 1393 (w), 1308
(m), 1161 (s), 1061, 1023, 855 (m), 730, 576 cmꢀ1 (w); MS
(EI, 70 eV): m/z (%)=572 (90) [M]+, 499 (20), 470 (27), 415
(15), 413 (11), 397 (64), 341 (24), 313 (17), 297 (67), 285
(15), 269 (11), 241 (73), 239 (21), 213 (20), 195 (60), 169
(19), 57 (100), 55 (15), 44 (30), 41 (63); HR-MS (ESI): m/
z=595.28691, calcd. for C32H44NaO9 [M+Na]+: 595.28775.
Acknowledgements
Financial support by the DAAD (scholarship for S. M. T. T.)
and by the Interdisciplinary Faculty of the University of Ro-
stock (scholarship for S. R.) is gratefully acknowledged.
Adv. Synth. Catal. 2012, 354, 1819 – 1826
ꢆ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1825

Serge-Mithꢀrand Tengho Toguem et al.
UPDATES
Bongini, J. Org. Chem. 2004, 69, 4821; o) M. Ciofalo, S.
Petruso, D. Schillaci, Planta Med. 1996, 62, 374; p) G.
Guillet, B. J. R. Philogene, J. OꢅMeara, T. Durst, J. T.
Arnason, Phytochemistry 1997, 46, 495; q) K. Kawai,
A. Sugimoto, H. Yoshida, S. Tojo, M. Fujitsuka, T.
Majima, Bioorg. Med. Chem. Lett. 2005, 15, 4547; r) F.
Bohlmann, R. Zdero, Chem. Ber. 1970, 103, 834.
[16] J. Stenhouse, Justus Liebigs Ann. Chem. 1870, 156, 332.
[17] a) K. Rabindran, B. D. Tilak, Proc. Indian Acad. Sci.
Sect. A. 1952, 36, 411; b) E. B. McCall, British Patent
701,267, 1953; Chem. Abstr. 1955, 49, 4027; c) M.
Kienle, A. Unsinn, P. Knochel, Angew. Chem. 2010,
122, 4860; Angew. Chem. Int. Ed. 2010, 49, 4751; d) S.
Rodriguez-Aristegui, K. M. Clapham, L. Barrett, C.
Cano, M. Desage-El Murr, R. J. Griffin, I. R. Hardcas-
tle, S. L. Payne, T. Rennison, C. Richardson, B. T.
Golding, Org. Biomol. Chem. 2011, 9, 6066; e) V. B.
Pandya, M. R. Jain, B. V. Chaugule, J. S. Patel, B. M.
Parmar, J. K. Joshi, P. R. Patel, Synth. Commun. 2012,
42, 497; f) R. Samanta, A. P. Antonchick, Angew.
Chem. 2011, 123, 5323; Angew. Chem. Int. Ed. 2011, 50,
5217; g) T. H. Jepsen, M. Larsen, M. Jørgensen, K. A.
Solanko, A. D. Bond, A. Kadziola, M. B. Nielsen, Eur.
J. Org. Chem. 2011, 53.
3493; g) J. Bergman, B. Pelcman, Pure Appl. Chem.
1990, 62,1967; h) R. B. Bedford, M. Betham, J. Org.
Chem. 2006, 71, 9403; i) S. W. Youn, J. H. Bihn, B. S.
Kim, Org. Lett. 2011, 13, 3738; j) R. Sanz, Y. Feman-
dez, M. P. Castroviejo, A. Perez, F. J. Fafianas, J. Org.
Chem. 2006, 71, 6291; k) G. S. Wang, J. Li, T. Guo, Z.
Lin, G. Jia, Organometallics 2009, 28, 6847; l) R. Sanz,
J. Escribano, M. R. Pedrosa, R. Aguado, F. J. Arnꢁiz,
Adv. Synth. Catal. 2007, 349, 713.
[22] L. Ackermann, A. Althamme, Angew. Chem. 2007,
119, 1652; Angew. Chem. Int. Ed. 2007, 46, 1627.
[23] a) O. Reiser, S. Reichow, A. de Meijere, Angew. Chem.
1987, 99, 1285; Angew. Chem. Int. Ed. Engl. 1987, 26,
1277; b) K. Voigt, P. von Zezschwitz, K. Rosauer, A.
Lansky, A. Adams, O. Reiser, A. de Meijere, Eur. J.
Org. Chem. 1998, 1521. For applications in heterocyclic
synthesis, see: c) R. Deshpande, L. Jiang, G. Schmidt, J.
Rakovan, X. Wang, K. Wheeler, H. Wang, Org. Lett.
2009, 11, 4251; d) M. Hussain, T. T. Dang, P. Langer,
Synlett 2009, 1822; e) G. A. Salman, A. Ali, M. Hus-
sain, R. A. Khera, P. Langer, Synthesis 2011, 2208, and
references cited therein.
[24] For Suzuki reactions: a) T. T. Dang, T. T. Dang, N.
Rasool, A. Villinger, P. Langer, Adv. Synth. Catal. 2009,
351, 1595. For Sonogashira reactions: b) T. X. Neenan,
G. M. Whitesides, J. Org. Chem. 1988, 53, 2489; c) S. H.
Eichhorn, A. J. Paraskos, K. Kishikawa, T. M. Swager,
J. Am. Chem. Soc. 2002, 124, 12742. For Suzuki reac-
tions of tetrabromoselenophene, see: d) T. T. Dang, A.
Villinger, P. Langer, Adv. Synth. Catal. 2008, 350, 2109.
[25] For Suzuki reactions: a) T. T. Dang, T. T. Dang, R.
Ahmad, H. Reinke, P. Langer, Tetrahedron Lett. 2008,
49, 1698. For Sonogashira reactions: b) F. Ullah, T. T.
Dang, J. Heinicke, A. Villinger, P. Langer, Synlett 2009,
838.
[18] T. H. Jepsen, M. Larsen; M. Jørgensen, K. A. Solanko;
A. D. Bond, A. Kadziola, M. B Nielsen, Eur. J. Org.
Chem. 2011, 53.
[19] C. Graebe, F. Ullmann, Justus Liebigs Ann. Chem.
1896, 291, 16.
[20] For reviews of classic synthetic approaches to indoles,
see: a) D. R. Dalton, The Alkaloids: The Fundament
Chemistry, Maercel Dekker, New York, 1979; b) G. A.
Cordell, Introduction to Alkaloids, Wiley-Interscience,
New York, 1981.
[21] a) B. Liꢀgault, D. Lee, M. P. Huestis, D. R. Stuart, K.
Fagnou, J. Org. Chem. 2008, 73, 5022; b) B. J. Stokes, B.
[26] M. Hussain, R. A. Khera, N. T. Hung, P. Langer, Org.
Biomol. Chem. 2011, 9, 370.
´
Jovanovic, H. Dong, K. J. Richert, R. D. Riell, T. G.
Driver, J. Org. Chem. 2009, 74, 3225; c) W. Kong, C.
Fu, S. Ma, Org. Biomol. Chem. 2012, 10, 2164; d) J. A.
Jordan-Hore, C. C. C. Johansson, M. Gulias, E. M.
Beck, M. J. Gaunt, J. Am. Chem. Soc. 2008, 130, 16184;
e) C. Praveen, P. T. Perumal, Synlett 2011, 268; f) L.
Ackermann, A. Althammer, P. Mayer, Synthesis 2009,
[27] a) K. Araki, H. Endo, G. Masuda, T. Ogawa, Chem.
Eur. J. 2004, 10, 3331; b) M. Janda, J. Srogl, I. Stibor,
M. Nemec, P. Vopatrna, Synthesis 1972, 545; c) H. M.
Gilow, D. E. Burton, J. Org. Chem. 1981, 46, 2221;
d) C. W. Shoppee, J. Chem. Soc. Perkin Trans. 1 1985,
45.
1826
asc.wiley-vch.de
ꢆ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 1819 – 1826