Lewis-acid-mediated domino reactions of Bis(diacetoxymethyl)-substituted arenes and heteroarenes

Article abstract of DOI:10.1002/ejoc.201001174

A one-pot synthesis of annulated heterocycles involving a Lewis-acid-mediated domino reaction of bis(diacetoxymethyl)-substituted arenes and heteroarenes is described. The reaction of the tetraacetates with arenes and heteroarenes leads to the formation o

Full text of DOI:10.1002/ejoc.201001174

FULL PAPER
DOI: 10.1002/ejoc.201001174
Lewis-Acid-Mediated Domino Reactions of Bis(diacetoxymethyl)-Substituted
Arenes and Heteroarenes
J. Arul Clement,[a] Ramakrishnan Sivasakthikumaran,[a]
Arasambattu K. Mohanakrishnan,*[a] S. Sundaramoorthy,[b] and Devadasan Velmurugan[b]
Keywords: Lewis acids / Arylation / Cyclization / Domino reactions / Annulation
A one-pot synthesis of annulated heterocycles involving a
Lewis-acid-mediated domino reaction of bis(diacetoxymeth-
yl)-substituted arenes and heteroarenes is described. The re-
action of the tetraacetates with arenes and heteroarenes
leads to the formation of 1,1-bis-arylated diacetates upon eli-
mination followed by electrocyclohetero-arylated intermedi-
ate may lead to the formation of bis-arylated 1,1-diacetates,
which on cyclization followed by aromatization furnish annu-
lated heterocycles.
ZnBr2/SiO2. Liu and co-workers[15] achieved the synthesis
of 9-arylanthracene as well as naphtho[b]thiophenes by tri-
fluoromethanesulfonic acid catalyzed annulation of diacet-
ates. The same group also reported the synthesis of indenyl
ketones,[16a] fluorenes, and heterocycle-fused indenes[16b] as
well as xanthenes[16c] that involved either Brønsted acid or
Lewis acid catalyzed cyclization reactions. An efficient syn-
thesis of the anthracene derivatives has also been realized
by Surya Prakash et al. by the reaction of phthalaldehyde
with alkylbenzenes under superelectrophilic conditions.[17]
The Lewis-acid-mediated domino reaction has been suc-
cessfully employed in the synthesis of a wide variety of
polycyclic heterocycles.[18] As a continuation of our interest
in the synthesis of π-conjugated heterocycles involving
Lewis acids,[19] we report herein our results on the annu-
lation of bis(diacetoxymethyl)-substituted arenes and
heteroarenes.
Introduction
Highly π-extended aromatic compounds are currently at-
tracting attention as organic semiconductors for various ap-
plications including organic light-emitting diodes (OLEDs),
photovoltaic cells, and organic field-effect transistors
(OFETs).[1] Among such aromatic compounds, higher oli-
goacenes such as naphthacene[2] and pentacene[3] are essen-
tial as an active layer in high-performance OFETs. It is well
known that polyacene analogues, especially pentacene,
show great electron mobility and can be used as charge car-
riers.[4] Anthracene and its derivatives are one of the most
important classes of polycyclic aromatic compounds.[5] An-
thracenes possess efficient photochromic properties and
have found applications in data storage and as molecular
switches.[6] Substituted anthracenes have been prepared, for
example, by Friedel–Crafts reactions,[7] aromatic cyclodehy-
dration,[8] Elbs reactions,[9] Lewis-acid-induced Bradsher-
type reactions of diarylmethanes,[10] and homologation me-
diated by metallacycles.[11]
Recently, Beller and co-workers reported[12] a facile
FeCl3-catalyzed arylation of benzylic alcohol, benzylic acet-
ate, and benzyl carboxylates with arenes affording the cor-
responding biaryls. An easy access to the triarylmethane
derivatives has been achieved by the reaction of aromatic
aldehydes with arenes in the presence of FeCl3 and acetic
anhydride.[13] Kodomari et al. reported[14] a convenient syn-
thesis of 9,10-diarylanthracenes by the reaction of aromatic
aldehydes and arenes in the presence of acetyl bromide and
Results and Discussion
The reaction of phthalaldehyde (1) with electron-rich ar-
enes such as anisole, 1,2-dimethoxybenzene, or 1,3-dimeth-
oxybenzene in the presence of CH3COCl(Br)/ZnBr2 at
room temperature was found to be successful, affording the
expected products 3a–c in 45–61% yields, respectively
(Scheme 1).
However, the similar reaction of phthalaldehyde (1) with
o- or p-xylene in the presence of CH3COCl(Br)/ZnBr2 failed
to produce the expected annulation product. Moreover, this
methodology could not be applied to heteroarenes because
they are susceptible to acetylation. Hence, an alternative an-
nulation protocol involving the reaction of pre-prepared tet-
raacetate with arenes catalyzed by a Lewis acid was pro-
posed. Accordingly, the required tetraacetate 4 was pre-
[a] Department of Organic Chemistry, University of Madras,
Guindy Campus,
Chennai 600025, India
Fax: +91-44-22352494
E-mail: mohan_67@hotmail.com
[b] Centre of Advanced study in Crystallography and Biophysics,
University of Madras, Guindy Campus,
Chennai 600025, India
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A. K. Mohanakrishnan et al.
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Scheme 4. Preparation of naphtho[2,3-b]thiophenes 7a and 7d.
The structures of heterocycles 7a and 7d were charac-
1
terized by H and 13C NMR spectral analysis. As a repre-
Scheme 1. Domino reactions of phthalaldehyde with arenes.
1
sentative case, the H NMR spectra (region: 7.7–8.6 ppm)
of a mixture (ca. 1:0.3) of 6a and 7a and that of pure isomer
7a are presented in parts a and b of Figure 1. A perfect
merging of the H NMR signal of the minor component in
the mixture of 6a and 7a was confirmed (Figure 1, c) by the
addition of pure 7a.
pared either from the phthalaldehyde (1) following the pub-
lished procedure[20] or from the tetrabromo compound 5[21]
(Scheme 2).
1
Scheme 2. Preparation of 1,2-bis(diacetoxymethyl)benzene (4).
Having prepared tetraacetate 4, its Lewis-acid-mediated
annulation with arenes was planned. However, all our
attempts to perform domino reactions of 4 with electron-
rich arenes, anisole, veratrole, or xylenes in the presence of
a catalytic amount of a Lewis acid such as FeCl3, ZnBr2,
or BF3·OEt2 were found to be unsuccessful. However, the
reaction of tetraacetate 4 with 2-substituted thiophenes in
the presence of 40 mol-% (3 drops) of BF3·OEt2 led to the
isolation of a mixture of 9- and 4-substituted naphtho[2,3-
b]thiophenes 6a,b and 7a,b (Scheme 3). Fortunately, the
reaction of 4 with 2-iodothiophene, 2-methylthiophene,
or 2-hexylthiophene led to the formation of 9-substituted
naphtho[2,3-b]thiophenes 6c–e as a single isomer.
Figure 1. a) 1H NMR spectrum (region: 7.7–8.6 ppm) of a mixture
of 6a + 7a (1:0.3) prepared using tetraacetate 4. b) 1H NMR spec-
trum (7.6–8.7 ppm) of 7a prepared according to ref.[15]. c) 1H NMR
spectrum (7.6–8.7 ppm) of a mixture of 6a + 7a after the addition
of pure compound 7a.
Finally, the structure of 9-(5-methylthiophen-2-yl)-
naphtho[2,3-b]thiophene (6d) was confirmed by single-
crystal X-ray diffraction analysis (Figure 2).
Scheme 3. Domino reactions of 4 with 2-substituted thiophenes.
1
Comparison of the H NMR spectra of the positional
isomers 6a,b and 7a,b revealed only a slight difference in
Figure 2. ORTEP diagram of compound 6d.
their spectral patterns. To verify the structures of positional
As expected, the annulation of tetraacetate 4 was success-
isomers 6 and 7, the 4-substituted heterocycles 7a and 7d fully achieved with complex heteroarenes in the presence of
were independently synthesized following the procedure[15] a catalytic amount of BF3·OEt2 affording the correspond-
reported by Liu and co-workers (Scheme 4).
ing fused heterocycles 6f–j in 49–58% yields (Table 1).
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Lewis-Acid-Mediated Domino Reactions
Table 1. Annulation of tetraacetate 4 with heteroarenes.
Scheme 5. Formation for isomeric diacetates 9 and 10.
annulation of tetraacetate 11 with heteroarenes such as 2-
methylthiophene, 2-hexylthiophene, and bithiophene in the
presence of BF3·OEt2 in 1,2-DCE at room temperature fur-
nished the corresponding heterocycles 12a–c in 45–60%
yields (Scheme 6).
Scheme 6. Domino reactions of tetraacetate 11.
Having achieved the smooth annulation of tetraacetates
4 and 11, the tetraacetate 13 was prepared from naphth-
alene-2,3-dicarbaldehyde.[24] As a representative case, the
domino reaction of tetraacetate 13 was successfully carried
out with heteroarenes such as 2-methylthiophene and benz-
ofuran to afford heterocycles 14 and 15 in moderate yields
(Scheme 7).
[a] Isolated yield after column chromatographic purification.
The domino reaction of 4 with bicyclic heteroarene 1-
hexylindole and benzo[b]furan led to the isolation of
heterocycles 6f and 6g in 55 and 51% yields, respectively
(entries 1 and 2). Similarly, the annulation of 4 with N-alk-
ylcarbazoles also afforded the expected products 6h and 6i
in 58 and 52% yields (entry 3). The annulation of 4 was also
successfully performed with 9,9-dihexyl-2,7-di(thiophen-2-
yl)fluorene[22] to furnish mixed heterocycle 6j in 49% yield
(entry 4).
It is clear that the domino reaction of 4 proceeds pre-
dominantly through the intermediacy of 1,1-diacetate 9
rather than 1,4-diacetate 10 to form the corresponding an-
nulation products 6 and 7 in major and minor amounts,
respectively. Clearly, in the case of 2-methythiophene and
other electron-rich heteroarenes only the corresponding 1,1-
diacetate was formed, which led to the isolation of hetero-
cycles 6d–j. The nucleophilic character of the heteroaryl
Scheme 7. Domino reactions of tetraacetate 13.
Towards a further generalization of the observed domino
unit facilitates the preferential formation of the 1,1-di- reaction protocol, tetraacetate derivatives of 1-(phenylsulf-
acetate 9 (Scheme 5). onyl)indole and benzo[b]thiophene were prepared by reac-
Next, the methoxy-tethered tetraacetate 11 was prepared tion of the corresponding dialdehydes 16a and 16b with
from 4,5-dimethoxyphthalaldehyde[23] following the pro- acetic anhydride in the presence of a catalytic amount of
cedure established for phthaldehyde (1). As expected, the RuCl3·7H2O in DCM (Scheme 8).
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Scheme 10. Mechanistic visualization of the domino reactions of
the tetraacetates 17a and 17b.
Scheme 8. Preparation of tetraacetates 17a and 17b.
As expected, the reactions of the indole-derived tetra-
acetate 17a and benzo[b]thienyl-derived tetraacetate 17b
with 2-hexylthiophene and bithiophene in the presence of a
catalytic amount of BF3·OEt2 at room temperature fol-
lowed by work-up and column chromatographic purifica-
tion furnished the corresponding annulated carbazoles 18a
and 18b and benzo[b]thiophenes 19a and 19b in 47–58%
yields. Similarly, the annulation of tetraacetates 17a and 17b
with benzofuran furnished the expected products 20 and 21
in 53 and 51% yields, respectively. Under identical condi-
tions, the reaction of tetraacetate 17b with N-ethylcarbazole
produced the annulated heterocycle 22 in 40% yield
(Scheme 9).
Conclusions
We have developed a simple and versatile domino reac-
tion protocol for bis(diacetoxymethyl)-substituted arenes
and heteroarenes by reaction with heteroarenes in the pres-
ence of a Lewis acid. A possible mechanism for the forma-
tion of the annulated heterocycles is proposed. Further
studies to extend the scope and synthetic utility of the dom-
ino reaction for the synthesis of complex heteroacenes are
in progress.
Experimental Section
General Methods: All reactions were carried out in oven-dried ap-
paratus using dry solvent under anhydrous conditions unless other-
wise noted. Analytical thin layer chromatography (TLC) was per-
formed on silica and the components were visualized by observa-
tion with iodine or under UV light. Flash chromatography was
performed on silica gel (230–400 mesh). NMR spectra (Bruker
300 MHz) were recorded in CDCl3 solution containing TMS as an
internal standard unless otherwise stated. Organic extracts were
dried with anhydrous Na2SO4. The multiplicities are abbreviated as
follows: s = singlet, d = doublet, t = triplet, q = quartet, m =
multiplet. Coupling constants (J) are reported in Hz. Carbon types
were determined from 13C NMR experiments. Elemental analyses
were performed with a Perkin–Elmer series II 2400 (IIT Madras)
elemental analyzer. Mass spectra were recorded with a JEOL DX
303 HF mass spectrometer.
3a: CH3COCl (1.74 g, 22.38 mmol), ZnBr2 (1.67 g, 7.46 mmol), an-
isole (2.41 g, 22.39 mmol), and silica gel (1 g) were added to a solu-
tion of phthalaldehyde (1; 0.5 g, 3.73 mmol) in dry benzene
(30 mL). The reaction mixture was stirred at room temperature for
10 h under N2. Filtration of the inorganic residue followed by re-
moval of the solvent and subsequent column chromatographic pu-
rification (n-hexane/ethyl acetate, 96:4) afforded 3a (0.71 g, 61%)
as a colorless solid, m.p. 169 °C (ref.[15] 175–176 °C). 1H NMR
(300 MHz, CDCl3): δ = 8.40 (s, 1 H, ArH), 8.01 (d, J = 8.1 Hz, 1
H, ArH), 7.94 (d, J = 9.0 Hz, 1 H, ArH), 7.67 (d, J = 8.7 Hz, 1 H,
ArH), 7.42–7.35 (m, 4 H, ArH), 7.19–7.12 (m, 3 H, ArH), 6.91 (s,
1 H, ArH), 3.96 (s, 3 H, OCH3), 3.74 (s, 3 H, OCH3) ppm. 13C
NMR (75.4 MHz, CDCl3): δ = 158.9, 157.0, 134.7, 132.3, 131.6,
131.2, 131.1, 130.1, 128.4, 128.1, 126.4 (2 C), 125.4, 124.2, 120.1,
114.1, 102.8, 55.4, 55.1 ppm. MS (EI): m/z (%) = 314 (50) [M]+.
C22H18O2 (314.13): calcd. C 84.05, H 5.77; found C 84.32, H 5.61.
Scheme 9. Domino reactions of tetraacetates 17a and 17b.
The formation of a single isomer in the reactions of tetra-
acetates 17a and 17b can be visualized through the prefer-
ential diarylation at the 3-position leading to the formation
of intermediate 1,1-diacetate 23 rather than 24 (Scheme 10).
Thus, the preferential formation of bis-heteroarylated 1,1-
diacetate in the case of symmetrical as well as unsymmetri-
cal tetraacetates is controlled by the electronic influence of
the heteroaryl units.
3b: The reaction of phthalaldehyde (1; 0.5 g, 3.73 mmol) with 1,2-
dimethoxybenzene (3.08 g, 22.38 mmol) in the presence of ZnBr2
(1.67 g, 7.46 mmol), CH3COCl (1.74 g, 22.38 mmol), and silica gel
(1 g) using the same procedure as that for the synthesis of 3a af-
forded compound 3b (0.62 g, 45%) as a colorless solid, m.p. 194 °C.
1H NMR (300 MHz, CDCl3): δ = 8.18 (s, 2 H, ArH), 7.92–7.87
(m, 2 H, ArH), 7.40–7.33 (m, 2 H, ArH), 7.16 (s, 1 H, ArH), 6.92–
6.83 (m, 3 H, ArH), 4.01 (s, 6 H, OCH3), 3.85 (s, 6 H, OCH3) ppm.
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Lewis-Acid-Mediated Domino Reactions
13C NMR (75.4 MHz, CDCl3): δ = 150.1, 149.1, 148.0, 146.1, 6.95–6.93 (m, ArH) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 142.3,
130.8, 128.6, 127.6, 124.6, 124.5, 124.3, 123.9, 121.5, 120.9, 120.2,
114.6, 111.4, 110.8, 107.8, 104.9, 104.3, 55.9, 55.8 ppm. MS (EI):
m/z (%) = 374 (54) [M]+. C24H22O4 (374.15): calcd. C 76.99, H
5.92; found C 76.72, H 6.14.
140.2, 140.1, 139.3, 138.6, 137.9, 131.5, 130.8, 130.5, 130.4, 130.2,
129.9, 129.2, 129.1, 128.5, 127.5, 126.4, 126.3, 126.2, 126.0, 125.8,
125.7, 125.5, 124.6, 124.3, 123.8, 121.9, 121.1, 118.4, 113.7,
113.1 ppm.
3c: The reaction of phthalaldehyde (1; 0.5 g, 3.73 mmol) with 1,3-
dimethoxybenzene (3.08 g, 22.38 mmol) using the same procedure
as that for the synthesis of 3a afforded compound 3c (0.71 g, 51%)
as a colorless solid, m.p. 156 °C. 1H NMR (300 MHz, CDCl3): δ =
6c: The reaction of 4 (0.5 g, 1.47 mmol) with 2-iodothiophene
(0.93 g, 4.43 mmol) in the presence of BF3·OEt2 (40 mg) using the
above-mentioned procedure followed by column chromatographic
purification (n-hexane/ethyl acetate, 98:2) led to the isolation of
8.78 (s, 1 H, ArH), 8.0 (d, J = 8.1 Hz, 1 H, ArH), 7.51 (d, J = compound 6c (0.07 g, 10%) as a pale-brown solid, m.p. 171 °C. 1H
8.4 Hz, 1 H, ArH), 7.37–7.27 (m, 2 H, ArH), 7.15 (d, J = 7.8 Hz,
1 H, ArH), 6.70–6.67 (m, 2 H, ArH), 6.41 (d, J = 4.8 Hz, 2 H,
NMR (300 MHz, CDCl3): δ = 8.29 (s, 1 H, ArH), 7.97 (d, J =
8.4 Hz, 1 H, ArH), 7.90 (d, J = 8.1 Hz, 1 H, ArH), 7.54–7.40 (m,
ArH), 4.04 (s, 3 H, OCH3), 3.93 (s, 3 H, OCH3), 3.69 (s, 3 H, 4 H, ArH), 6.88 (d, J = 3.6 Hz, 1 H, ArH) ppm. 13C NMR
OCH3), 3.59 (s, 3 H, OCH3) ppm. 13C NMR (75.4 MHz, CDCl3):
δ = 160.7, 158.9, 157.4, 156.8, 133.1, 132.1, 131.7, 130.9, 129.7,
129.1, 126.2, 125.6, 123.8, 122.1, 121.2, 120.4, 104.8, 99.2, 97.0,
(75.4 MHz, CDCl3): δ = 144.9, 141.7, 140.3, 138.8, 137.3, 133.3,
130.7, 130.6, 130.3, 127.6, 126.1, 126, 125.9, 123.8, 120.5 ppm. MS
(EI): m/z (%) = 518 (37) [M]+. C16H8I2S2 (517.82): calcd. C 37.09,
95.4, 55.8, 55.7, 55.4, 55.1 ppm. MS (EI): m/z (%) = 374 (45) H 1.56, S 12.38; found C 37.34, H 1.85, S 12.62.
[M]+. C24H22O4 (374.15): calcd. C 76.99, H 5.92; found C 77.18, H
5.83.
6d: The reaction of 4 (0.5 g, 1.47 mmol) with 2-methylthiophene
(0.43 g, 4.43 mmol) in the presence of BF3·OEt2 (40 mg) using the
above-mentioned procedure followed by column chromatographic
purification (n-hexane/ethyl acetate, 98:2) afforded compound 6d
(0.21 g, 48%) as a colorless solid, m.p. 88 °C. 1H NMR (300 MHz,
CDCl3): δ = 8.11 (s, 1 H, ArH), 8.04 (d, J = 7.8 Hz, 1 H, ArH),
7.94 (d, J = 7.5 Hz, 1 H, ArH), 7.44–7.41 (m, 2 H, ArH), 7.08–
7.05 (m, 2 H, ArH), 6.90 (s, 1 H, ArH), 2.60 (s, 3 H, CH3), 2.55
(s, 3 H, CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 143.3, 141.5,
141.1, 139.2, 136.8, 131.6, 129.6, 128.5, 128.3, 125.5, 125.1, 124.7,
121.2, 120.8, 16.6, 15.4 ppm. MS (EI): m/z (%) = 294 (51) [M]+.
C18H14S2 (294.05): calcd. C 73.43, H 4.79, S 21.78; found C 73.69,
H 4.66, S 21.92.
Preparation of Benzene-Derived Tetraacetate 4
From Phthaldehyde (1): RuCl3·7H2O (0.23 g, 1.11 mmol) was added
to a solution of phthaldehyde (1; 3 g, 22.38 mmol) and acetic anhy-
dride (13.69 g, 134.32 mmol) in DCM (100 mL) and the mixture
was stirred at room temperature for 8 h. It was then diluted with
DCM (50 mL) and washed with saturated NaHCO3 solution
(3ϫ15 mL) followed by brine solution. The organic layer was then
dried (Na2SO4) and concentrated in vacuo to afford 4 (6.12 g, 81%)
as a colorless solid, m.p. 132 °C. 1H NMR (300 MHz, CDCl3): δ =
8.0 (s, 2 H, ArH), 7.64–7.61 (m, 2 H, ArH), 7.49–7.45 (m, 2 H,
ArH), 2.11 (s, 12 H, OAc) ppm. 13C NMR (75.4 MHz, CDCl3): δ
= 168.4, 133.7, 130.0, 128.4, 88.3, 20.8 ppm. MS (EI): m/z (%) =
338 (60) [M]+.
For single-crystal X-ray analysis of 6d, all calculations were per-
formed by using the SHELXL-97 program.[25] Crystal data of 6d:
C18H14S2, M = 294.41 gmol–1, triclinic crystal system, space group
From Tetrabromo Compound 5: KOAc (2.80 g, 28.50 mmol) was
added to a solution of tetrabromo compound 5[21] (2 g, 4.75 mmol)
in DMF (20 mL) and the reaction mixture was stirred at room
temperature for 24 h. It was then poured into ice–water, extracted
with DCM (2ϫ15 mL), and dried (Na2SO4). Removal of the sol-
vent led to the isolation of 4 (1.06 g, 66%) as a colorless solid, m.p.
132 °C.
¯
P1, Z = 2, a = 7.2672(9), b = 9.7350(12), c = 11.3376(14) Å, α =
89.647(7), β = 82.381(7), γ = 68.381(6)°, V = 737.04(12) Å3, DX
=
1.327 Mgm–3. In total, 13430 independent reflections were col-
lected of which 3634 were considered as observed [IϾ2σ(I)]. The
structure was solved by direct methods and refined by full-matrix
least-squares procedures to give a final R value of 3.72%.
CCDC-783657 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
6a and 7a: Thiophene (0.37 g, 4.43 mmol) and BF3·OEt2 (40 mg)
were added to a solution of 4 (0.5 g, 1.47 mmol) in dry DCE
(20 mL). The reaction mixture was then stirred at room tempera-
ture for 4 h under N2. Removal of the solvent followed by column
chromatographic purification (n-hexane/ethyl acetate, 98:2) fur-
nished a mixture of the annulated heterocycles 6a and 7a in a 8:2
ratio as a yellow solid (0.20 g, 55%), m.p. 77–80 °C. 1H NMR
6e: The reaction of 4 (0.5 g, 1.47 mmol) with 2-hexylthiophene
(0.75 g, 4.4 mmol) in the presence of BF3·OEt2 (40 mg) using the
above-mentioned procedure followed by column chromatographic
(300 MHz, CDCl3): δ = 8.41 (s, ArH), 8.34 (s, ArH), 8.03–7.92 (m, purification (n-hexane/ethyl acetate, 98:2) afforded compound 6e
ArH), 7.94–7.92 (m, ArH), 7.58–7.56 (m, ArH), 7.48–7.43 (m, (0.37 g, 58%) as a thick yellow liquid. 1H NMR (300 MHz,
ArH), 7.33–7.26 (m, ArH) ppm. 13C NMR (75.4 MHz, CDCl3): δ
= 141.3, 139.6, 131.1, 138.2, 137.6, 131.4, 131.0, 130.4, 130.1, 128.9,
128.8, 128.6, 128.5, 128.3, 127.5, 127.4, 127.1, 126.7, 126.4, 126.3,
CDCl3): δ = 8.07–8.04 (m, 2 H, ArH), 7.89–7.85 (m, 1 H, ArH),
7.39–7.37 (m, 2 H, ArH), 7.08 (d, J = 3.3 Hz, 1 H, ArH), 6.98 (s,
1 H, ArH), 6.87 (d, J = 3.6 Hz, 1 H, ArH), 2.88 (t, J = 7.6 Hz, 2
126.2, 125.7, 125.4, 125.3, 125.1, 124.9, 123.8, 123.7, 122.5, H, ArH), 2.80 (t, J = 7.6 Hz, 2 H, CH2), 1.77–1.67 (m, 4 H, CH2),
121.6 ppm.
1.43–1.26 (m, 12 H, CH2), 0.91–0.84 (m, 6 H, CH3) ppm. 13C NMR
(75.4 MHz, CDCl3): δ = 149.3, 147.3, 141.2, 139.2, 136.3, 131.7,
129.7, 128.4, 128.3, 125.8, 125.3, 125.2, 124.7, 124.3, 120.9, 120.1,
31.7 (2 C), 31.4, 30.8, 30.4, 29.1, 29.0, 22.7, 22.6, 14.2 ppm. MS
(EI): m/z (%) = 434 (54) [M]+. C28H34S2 (434.21): calcd. C 77.36,
H 7.88, S 14.75; found C 77.52, H 7.93, S 14.62.
6b and 7b: The reaction of 4 (0.5 g, 1.47 mmol) with 2-bromothio-
phene (0.72 g, 4.43 mmol) in the presence of BF3·OEt2 (40 mg)
using the above-mentioned procedure followed by column chroma-
tographic purification (n-hexane/ethyl acetate, 98:2) afforded a mix-
ture of the heterocycles 6b and 7b as a yellow solid (0.26 g, 42%),
1
m.p. 124–125 °C. H NMR (300 MHz, CDCl3): δ = 8.25 (s, ArH),
8.20 (s, ArH), 7.98 (d, J = 8.4 Hz, ArH), 7.93 (d, J = 7.8 Hz, ArH),
6f: The reaction of 4 (0.5 g, 1.47 mmol) with 1-hexylindole (0.89 g,
4.43 mmol) in the presence of BF3·OEt2 (40 mg) using the above-
7.53–7.43 (m, ArH), 7.31–7.20 (m, ArH), 7.06–7.04 (m, ArH), mentioned procedure led to the isolation of the heterocycle 6f
Eur. J. Org. Chem. 2011, 569–577
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573

A. K. Mohanakrishnan et al.
FULL PAPER
(0.40 g, 55%) as a colorless solid, m.p. 154 °C. 1H NMR (300 MHz,
CDCl3): δ = 8.64 (s, 1 H, ArH), 8.26 (d, J = 8.1 Hz, 1 H, ArH),
8.07 (d, J = 8.7 Hz, 1 H, ArH), 7.66 (d, J = 8.7 Hz, 1 H, ArH),
7.51–7.46 (m, 2 H, ArH), 7.39–7.33 (m, 1 H, ArH), 7.30–7.22 (m,
BF3·OEt2 (40 mg) using the above-mentioned procedure led to the
isolation of the heterocycle 6j (0.79 g, 49%) as a yellow solid, m.p.
140 °C. 1H NMR (300 MHz, CDCl3): δ = 8.26 (s, 1 H, ArH), 8.16–
8.15 (m, 1 H, ArH), 7.98–7.96 (m, 1 H, ArH), 7.78–7.62 (m, 10 H,
5 H, ArH), 7.18 (d, J = 7.8 Hz, 1 H, ArH), 7.01 (t, J = 7.5 Hz, 1 ArH), 7.64–7.59 (m, 5 H, ArH), 7.49–7.46 (m, 3 H, ArH), 7.39–
H, ArH), 4.28 (t, J = 7.2 Hz, 2 H, NCH2), 3.74 (t, J = 6.8 Hz, 2 7.32 (m, 3 H, ArH), 7.28–7.27 (m, 1 H, ArH), 7.10–7.07 (m, 1 H,
H, NCH2), 1.98–1.95 (m, 2 H, CH2), 1.47–1.33 (m, 10 H, CH2),
1.04–0.99 (m, 3 H, CH3), 0.93–0.83 (m, 4 H, CH2), 0.81–0.71 (m,
3 H, CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 143.9, 139.2,
136.1, 134.2, 130.1, 128.3, 128.2, 128.1, 127.2, 126.0, 125.6, 124.8,
123.0, 122.5, 122.1, 120.7, 119.7, 118.9, 118.4, 110.9, 110.7, 109.6,
ArH), 2.05–2.04 (m, 8 H, CH2), 1.07–0.91 (m, 24 H, CH2), 0.78–
0.70 (m, 20 H, CH2CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ =
151.9 (2 C), 151.8, (2 C) 146.8, 146.5, 145.2, 145.1, 141.5, 140.9,
140.6, 140.3 (2 C) 140.0, 139.6, 138.2, 135.9, 133.7, 133.4, 133.3,
133.2, 133.1, 132.8, 131.9, 130.3, 129.9, 128.5, 128.1, 125.8, 125.7,
108.8, 100.9, 46.6, 44.3, 31.6, 31.3, 30.6, 28.9, 26.9, 26.5, 22.7, 14.2, 125.3, 125.1, 124.9, 124.7, 124.6, 123.3, 123.0, 122.9, 122.3, 120.9,
14.1 ppm. MS (EI): m/z (%) = 500 (44) [M]+. C36H40N2 (500.32):
calcd. C 86.35, H 8.05, N 5.59; found C 86.13, H 8.14, N 5.72.
120.4, 120.2, 119.9, 118.8, 55.5, 55.4, 40.5, 40.5, 31.5, 31.5, 29.7,
29.7, 23.8, 22.6, 22.6, 14.1, 14.0 ppm. MS (EI): m/z (%) = 1094 (22)
[M]+. C74H78S4 (1094.49): calcd. C 81.12, H 7.18, S 11.71; found
C 81.38, H 7.27, S 11.57.
6g: The reaction of 4 (0.5 g, 1.47 mmol) with benzo[b]furan (0.52 g,
4.43 mmol) in the presence of BF3·OEt2 (40 mg) using the above-
mentioned procedure led to the isolation of the heterocycle 6g
(0.25 g, 51%) as a colorless solid, m.p. 152 °C. 1H NMR (300 MHz,
CDCl3): δ = 8.61 (d, J = 8.7 Hz, 1 H, ArH), 8.46 (s, 1 H, ArH),
8.07 (d, J = 7.8 Hz, 2 H, ArH), 7.78–7.75 (m, 1 H, ArH), 7.67 (d,
J = 7.8 Hz, 1 H, ArH), 7.62–7.58 (m, 2 H, ArH), 7.55–7.51 (m, 2
H, ArH), 7.45 (s, 1 H, ArH), 7.41–7.34 (m, 3 H, ArH) ppm. 13C
NMR (75.4 MHz, CDCl3): δ = 157.5, 155.1, 153.1, 150.5, 130.9,
130.6, 128.9, 128.6, 126.7, 125.9, 125.1, 124.6, 124.5, 123.7, 123.1,
123.0, 121.3, 121.2, 120.7, 111.8, 111.5, 109.5, 109.0 ppm. MS (EI):
m/z (%) = 334 (52) [M]+. C24H14O2 (334.10): calcd. C 86.21, H
4.22; found C 86.05, H 4.13.
7a: The reaction of phthalaldehyde (1; 1.0 g, 7.46 mmol) with
freshly prepared 2-thienylmagnesium bromide (3 equiv.) followed
by protection of the resulting diol using pivaloyl chloride and sub-
sequent triflic acid catalyzed cyclization following the published
procedure[15] gave known compound 7a (0.95 g, 55%) as a yellow
1
liquid. H NMR (300 MHz, CDCl3): δ = 8.42 (s, 1 H, ArH), 8.01
(d, J = 8.4 Hz, 1 H, ArH), 7.95 (d, J = 8.1 Hz, 1 H, ArH), 7.56–
7.40 (m, 4 H, ArH), 7.31–7.22 (m, 3 H, ArH) ppm. 13C NMR
(75.4 MHz, CDCl3): δ = 139.6, 139.1, 137.6, 131.0, 130.5, 128.8,
128.4, 127.6, 127.2, 126.5, 126.4, 126.3, 125.5, 125.3, 123.8,
121.6 ppm.
6h: The reaction of 4 (0.5 g, 1.47 mmol) with N-ethylcarbazole
(0.87 g, 4.43 mmol) in the presence of BF3·OEt2 (40 mg) using the
above-mentioned procedure led to the isolation of the heterocycle
6h (0.42 g, 58%) as a pale-yellow solid, m.p. 178 °C. 1H NMR
(300 MHz, CDCl3): δ = 8.60 (s, 1 H, ArH), 8.46 (s, 1 H, ArH),
7d: The reaction of phthalaldehyde (1; 1.0 g, 7.46 mmol) with
freshly prepared 5-methyl-2-thienylmagnesium bromide followed
by protection of the resulting diol using pivaloyl chloride and sub-
sequent triflic acid catalyzed cyclization following the published[15]
8.25 (s, 1 H, ArH), 8.06–8.02 (m, 2 H, ArH), 7.90 (d, J = 7.5 Hz, procedure furnished compound 7d (1.1 g, 60%) as a colorless fluffy
1
1 H, ArH), 7.79 (s, 1 H, ArH), 7.74 (d, J = 9.0 Hz, 1 H, ArH),
7.62–7.57 (m, 2 H, ArH), 7.49–7.37 (m, 4 H, ArH), 7.24–7.19 (m,
solid, m.p. 99 °C. H NMR (300 MHz, CDCl3): δ = 8.22 (s, 1 H,
ArH), 8.02 (d, J = 9.0 Hz, 1 H, ArH), 7.85 (d, J = 9.6 Hz, 1 H,
3 H, ArH), 7.04 (d, J = 7.2 Hz, 1 H, ArH), 4.50–4.47 (m, 2 H, ArH), 7.45–7.35 (m, 2 H, ArH), 6.98 (s, 1 H, ArH), 6.94 (d, J =
CH2), 4.35–4.33 (m, 2 H, CH2), 1.59–1.54 (m, 3 H, CH3), 1.48– 3.3 Hz, 1 H, ArH), 6.87–6.86 (m, 1 H, ArH), 2.59 (s, 3 H, CH3),
1.46 (m, 3 H, CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 143.6,
140.5, 140.1, 139.5, 138.4, 131.2, 129.8, 129.3, 128.9, 127.8, 127.7,
127.4, 126.9, 125.9, 124.7, 124.3, 123.7, 123.4, 123.2, 123.1, 121.5,
120.7, 119.0, 118.6, 118.2, 108.7, 108.4, 107.6, 101.2, 37.8, 37.6,
14.1, 13.1 ppm. MS (EI): m/z (%) = 488 (50) [M]+. C36H28N2
(488.22): calcd. C 88.49, H 5.78, N 5.73; found C 88.71, H 5.65, N
5.68.
2.54 (s, 3 H, CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 142.8,
140.7, 140.5, 138.2, 137.0, 130.6, 130.5, 128.5, 127.4, 126.2, 125.3,
125.1, 124.8, 121.4, 120.8, 18.7, 15.4 ppm. MS (EI): m/z (%) = 294
(58) [M]+. C18H14S2 (294.05): calcd. C 73.43, H 4.79, S 21.78; found
C 73.65, H 4.69, S 21.95.
Tetraacetate 11: The reaction of 4,5-dimethoxybenzene-1,2-dicarb-
aldehyde[23] (1 g, 5.15 mmol) with acetic anhydride (3.15 g,
30.30 mmol) in the presence of RuCl3·7H2O (0.05 g, 0.25 mmol)
following the procedure similar to that for the synthesis of 4 af-
forded 10 (1.41 g, 69%) as a pale-yellow solid, m.p. 114 °C. 1H
NMR (300 MHz, CDCl3): δ = 7.92 (s, 2 H, ArH), 7.07 (s, 2 H,
ArH), 3.90–3.86 (m, 6 H, OCH3), 2.09–2.04 (m, 12 H, OAc) ppm.
13C NMR (75.4 MHz, CDCl3): δ = 168.4, 149.9, 126.5, 110.9, 88.3,
56.1, 20.81 ppm. MS (EI): m/z (%) = 398 (57) [M]+.
6i: The reaction of 4 (0.5 g, 1.47 mmol) with N-(2-ethylhexyl)carb-
azole (1.23 g, 4.43 mmol) in the presence of BF3·OEt2 (40 mg) using
the above-mentioned procedure led to the isolation of the heterocy-
cle 6i (0.50 g, 52%) as a brown solid, m.p. 126 °C. 1H NMR
(300 MHz, CDCl3): δ = 8.64 (s, 1 H, ArH), 8.45 (d, J = 6.9 Hz, 1
H, ArH), 8.26 (d, J = 5.7 Hz, 1 H, ArH), 8.10–8.03 (m, 2 H, ArH),
7.91–7.88 (m, 1 H, ArH), 7.80–7.76 (m, 2 H, ArH), 7.61–7.59 (m,
2 H, ArH), 7.50–7.48 (m, 2 H, ArH), 7.43–7.41 (m, 2 H, ArH),
7.29–7.23 (m, 3 H, ArH), 7.09–7.06 (m, 1 H, ArH), 4.34–4.31 (m,
2 H, NCH2), 4.18–4.16 (m, 2 H, NCH2), 2.14–2.12 (m, 2 H, CH),
1.52–1.35 (m, 16 H, CH2), 1.04–0.94 (m, 12 H, CH3) ppm. 13C
NMR (75.4 MHz, CDCl3): δ = 144.6, 141.5, 141.2, 140.5, 138.4,
131.2, 129.8, 129.2, 128.9, 127.7, 127.6, 127.4, 127.3, 126.7, 125.8,
124.7, 124.4, 124.1, 120.5, 118.9, 118.6, 118.1, 109.2, 108.9, 108.2,
101.7, 47.7, 39.7, 38.9, 31.2, 28.9, 26.9, 24.7, 24.6, 23.2, 14.1,
11.1 ppm. MS (EI): m/z (%) = 656 (45) [M]+. C48H52N2 (656.41):
calcd. C 87.76, H 7.98, N 4.26; found C 87.53, H 7.84, N 4.41.
12a: The reaction of 11 (0.5 g, 1.25 mmol) with 2-methylthiophene
(0.36 g, 3.76 mmol) in the presence of BF3·OEt2 (40 mg) following
the same procedure as that used for the synthesis of 6d afforded
compound 12a (0.22 g, 52%) as a light-brown solid, m.p. 146 °C.
1H NMR (300 MHz, CDCl3): δ = 7.84 (s, 1 H, ArH), 7.27 (s, 1 H,
ArH), 7.07–7.08 (m, 1 H, ArH), 7.01–7.0 (m, 1 H, ArH), 6.89 (s, 1
H, ArH), 6.80 (s, 1 H, ArH), 3.91 (s, 3 H, OCH3), 3.79 (s, 3 H,
OCH3), 2.52 (s, 3 H, CH3), 2.44 (s, 3 H, CH3) ppm. 13C NMR
(75.4 MHz, CDCl3): δ = 149.3, 148.9, 141.7, 140.9, 139.8, 137.9,
137.4, 128.2, 127.8, 125.8, 125.6, 123.9, 121.2, 119.2, 106.0, 103.6,
55.8 (2 C), 16.4, 15.5 ppm. MS (EI): m/z (%) = 354 (56) [M]+.
6j: The reaction of 4 (0.5 g, 1.47 mmol) with 9,9-dihexyl-2,7-di-
(thiophen-2-yl)fluorene[22] (2.21 g, 4.43 mmol) in the presence of
574
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 569–577

Lewis-Acid-Mediated Domino Reactions
C20H18O2S2 (354.07): calcd. C 67.76, H 5.12, S 18.09; found C
67.92, H 5.25, S 17.91.
111.1 ppm. MS (EI): m/z (%) = 384 (43) [M]+. C28H16O2 (384.12):
calcd. C 87.48, H 4.20; found C 87.25, H 4.03.
Benzo[b]thiophene-2,3-dicarbaldehyde (16b): Paraformaldehyde
(5.5 g, 183.3 mmol) and 33% HBr in acetic acid (45 mL) were
added to a solution of benzo[b]thiophene (10 g, 74.63 mmol) in ace-
tic acid (50 mL). The reaction mixture was stirred for 12 h at room
temperature. The precipitated solid was filtered, washed with water
several times, and dried to yield 2,3-bis(bromomethyl)benzo[b]thio-
phene (19.5 g, 81%) as a colorless solid. Sodium hydrogen carbon-
ate (15.75 g, 187 mmol) was added to a solution of the bis(bromo-
methyl)benzo[b]thiophene (10 g, 31.25 mmol) in acetonitrile
(125 mL) and water (10 mL) and the mixture was heated at reflux
for 8 h. Then the solvent was completely removed and the sticky
residue was extracted with DCM (3ϫ30 mL), dried (Na2SO4), and
concentrated in vacuo to give 2,3-bis(hydroxymethyl)benzo[b]thio-
phene (4.6 g, 76%) as a colorless solid. Active manganese dioxide
(13 g) was added to a solution of the diol (3.5 g, 18.04 mmol) in
DCE (100 mL) and the mixture was heated at reflux for 8 h. The
progress of the reaction was monitored by TLC until the disappear-
ance of the starting material. Then the inorganic solid was filtered
off and washed with CHCl3 (3ϫ20 mL). Removal of the solvent
afforded the dialdehyde 16b (2.38 g, 69%) as colorless solid, m.p.
108 °C (ref.[27] 112–113 °C). 1H NMR (300 MHz, CDCl3): δ =
10.84 (s, 1 H, ArH), 10.68 (s, 1 H, ArH), 8.60 (d, J = 8.1 Hz, 1 H,
ArH), 7.92–7.90 (m, 1 H, ArH), 7.57–7.54 (m, 2 H, ArH) ppm.
13C NMR (75.4 MHz, CDCl3): δ = 183.32, 182.74, 149.05, 140.47,
135.98, 135.77, 127.75, 126.07, 125.28, 121.94 ppm.
12b: The reaction of 11 (0.5 g, 1.25 mmol) with 2-hexylthiophene
(0.63 g, 3.76 mmol) in the presence of BF3·OEt2 (40 mg) following
the same procedure as that used for the synthesis of 6d afforded
compound 12b (0.37 g, 60%) as
a
thick liquid. 1H NMR
(300 MHz, CDCl3): δ = 7.89 (s, 1 H), 7.29 (s, 1 H, ArH), 7.11 (s,
1 H, ArH), 7.05 (d, J = 3.3 Hz, 1 H, ArH), 6.95 (s, 1 H, ArH),
6.83 (d, J = 3.3 Hz, 1 H, ArH), 3.95 (s, 3 H, OCH3), 3.81 (s, 3 H,
OCH3), 2.84 (t, J = 7.7 Hz, 2 H, CH2), 2.78 (t, J = 7.7 Hz, 2 H,
CH2), 1.75–1.61 (m, 4 H, CH2), 1.37–1.25 (m, 12 H, CH2), 0.86–
0.79 (m, 6 H, CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 149.2,
148.9, 147.7, 147.1, 139.3, 137.8, 137.0, 127.9, 127.8, 125.8, 124.2
(2 C), 119.9 (2 C), 105.9, 103.6, 55.8, 55.7, 31.6 (2 C), 31.2, 30.8,
30.3, 28.9, 28.8, 22.6 (2 C), 14.1 ppm. MS (EI): m/z (%) = 494 (44)
[M]+. C30H38O2S2 (494.23): calcd. C 72.83, H 7.74, S 12.96; found
C 73.02, H 7.81, S 12.79.
12c: The reaction of 11 (0.5 g, 1.25 mmol) with bithiophene (0.62 g,
3.76 mmol) in the presence of BF3·OEt2 (40 mg) following the same
procedure as that used for the synthesis of 6d afforded compound
12c (0.28 g, 45%) as a colorless solid, m.p. 206 °C. 1H NMR
(300 MHz, CDCl3): δ = 7.96 (s, 1 H, ArH), 7.36 (s, 1 H, ArH),
7.29–7.27 (m, 2 H, ArH), 7.22–7.17 (m, 5 H, ArH), 7.12 (s, 1 H,
ArH), 6.99–6.96 (m, 2 H, ArH), 3.96 (s, 3 H, OCH3), 3.83 (s, 3 H,
OCH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 149.9, 149.3,
138.9, 138.7, 138.3, 137.8, 137.7, 137.5, 137.2, 129.2, 128.1, 127.9
(2 C), 126.5, 125.7, 125.4, 124.6, 124.1, 123.9, 123.1, 120.6, 119.1,
106.1, 103.3, 55.9 ppm. MS (EI): m/z (%) = 490 (38) [M]+.
C26H18O2S4 (490.02): calcd. C 63.64, H 3.70, S 26.14; found C
63.88, H 3.59, S 26.02.
Tetraacetate 17a: The reaction of 1-phenylsulfonylindole-2,3-di-
carbaldehyde (16a;[26] (1 g, 3.19 mmol) with acetic anhydride
(1.96 g, 19.16 mmol) in the presence of RuCl3·7H2O (0.05 g,
0.25 mmol) following the procedure similar to that used for the
synthesis of 4 furnished 17a (1.25 g, 76%) as a colorless solid, m.p.
Tetraacetate 13: The reaction of naphthalene-1,2-dicarbaldehyde[24]
(1 g, 5.43 mmol) with acetic anhydride (3.32 g, 32.60 mmol) in the
presence of RuCl3·7H2O (0.05 g, 0.25 mmol) following the pro-
cedure similar to that used for the synthesis of 4 furnished 13
(1.19 g, 65%) as a colorless solid, m.p. 158 °C. 1H NMR (300 MHz,
CDCl3): δ = 8.47 (s, 2 H, ArH), 7.99 (s, 2 H, ArH), 7.60–7.56 (m,
4 H, ArH), 2.22–2.18 (m, 12 H, OAc) ppm. 13C NMR (75.4 MHz,
CDCl3): δ = 170.6, 131.7, 127.4, 126.8, 126.2, 124.5, 93.8, 20.7 ppm.
MS (EI): m/z (%) = 338 (50) [M]+.
1
138 °C. H NMR (300 MHz, CDCl3): δ = 8.55 (s, 1 H, ArH), 8.53
(s, 1 H, ArH), 8.14 (d, J = 8.4 Hz, 1 H, ArH), 8.05 (d, J = 7.8 Hz,
2 H, ArH), 7.93 (d, J = 7.8 Hz, 1 H, ArH), 7.60 (d, J = 7.35 Hz,
1 H, ArH), 7.56–7.46 (m, 2 H, ArH), 7.43–7.38 (m, 1 H, ArH),
7.34–7.29 (m, 1 H, ArH), 2.15 (s, 6 H, OAc), 2.08 (s, 6 H,
OAc) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 168.4, 168.2, 138.1,
136.1, 134.3, 132.1, 129.4, 127.2, 126.6, 126.4, 124.1, 122.1, 119.2,
114.8, 84.9, 84.1, 20.8, 20.6 ppm. MS (EI): m/z (%) = 517 (60)
[M]+.
14: The reaction of 13 (0.3 g, 0.77 mmol) with 2-methylthiophene
(0.23 g, 2.31 mmol) in the presence of BF3·OEt2 (40 mg) following
the same procedure as that used for the synthesis of 6d afforded
compound 14 (0.11 g, 43%) as a colorless solid, m.p. 178 °C. 1H
NMR (300 MHz, CDCl3): δ = 8.63 (s, 1 H, ArH), 8.55 (s, 1 H,
ArH), 8.28 (s, 1 H, ArH), 8.0–7.97 (m, 1 H, ArH), 7.94–7.92 (m, 1
H, ArH), 7.42–7.38 (m, 2 H, ArH), 7.05–7.04 (m, 1 H, ArH), 6.98–
6.96 (m, 2 H, ArH), 2.65 (s, 3 H, CH3), 2.56 (s, 3 H, CH3) ppm.
13C NMR (75.4 MHz, CDCl3): δ = 141.1, 139.8, 137.5, 131.5,
131.2, 129.8, 129.5, 128.8, 128.5, 127.7, 127.6, 126.4, 125.8, 125.6,
125.1, 124.8, 123.9, 121.1 ppm. MS (EI): m/z (%) = 344 (59) [M]+.
C22H16S2 (344.07): calcd. C 76.70, H 4.68, S 18.62; found C 76.45,
H 4.73, S 18.79.
Tetraacetate 17b: The reaction of benzo[b]thiophene-2,3-dicarb-
aldehyde (16b; 1 g, 5.26 mmol) with acetic anhydride (3.25 g,
31.86 mmol) in the presence of RuCl3·7H2O (0.05 g, 0.25 mmol)
following the procedure similar to that used for the synthesis of 4
furnished 17b (1.35 g, 65%) as a light-brown solid, m.p. 158 °C. 1H
NMR (300 MHz, CDCl3): δ = 8.37 (s, 1 H, ArH), δ = 8.21 (s, 1 H,
ArH), 8.12 (d, J = 7.5 Hz, 1 H, ArH), 7.84 (d, J = 7.2 Hz, 1 H,
ArH), 7.44–7.40 (m, 2 H, ArH), 2.22–2.08 (m, 12 H, OAc) ppm.
13C NMR (75.4 MHz, CDCl3): δ = 168.6, 168.2, 139.0, 138.9,
136.7, 128.8, 125.8, 124.9, 124.1, 122.5, 85.0, 20.7 ppm. MS (EI):
m/z (%) = 394 (52) [M]+.
18a: The reaction of 17a (0.5 g, 0.96 mmol) with 2-hexylthiophene
(0.48 g, 2.90 mmol) in the presence of BF3·OEt2 (40 mg) following
the same procedure as that used for the synthesis of 6d afforded
15: The reaction of 13 (0.3 g, 0.77 mmol) with benzo[b]furan (0.7 g,
2.31 mmol) in the presence of BF3·OEt2 (40 mg) following the same
procedure as that used for the synthesis of 6d afforded compound
15 (0.11 g, 38%) as a colorless solid, m.p. 205 °C. 1H NMR
(300 MHz, CDCl3): δ = 8.72 (s, 1 H, ArH), 8.61 (s, 1 H, ArH),
8.16 (s, 1 H, ArH), 8.05–7.92 (m, 2 H, ArH), 7.85–7.80 (m, 2 H,
1
compound 18a (0.34 g, 58%) as a colorless solid, m.p. 104 °C. H
NMR (300 MHz, CDCl3): δ = 8.58 (s, 1 H, ArH), 8.24 (d, J =
8.4 Hz, 1 H, ArH), 7.74 (d, J = 8.7 Hz, 2 H, ArH), 7.35–7.31 (m,
2 H, ArH), 7.24–7.19 (m, 2 H, ArH), 7.09–7.03 (m, 3 H, ArH),
6.89 (d, J = 3.3 Hz, 1 H, ArH), 6.82 (d, J = 3.3 Hz, 1 H, ArH),
ArH), 7.54–7.42 (m, 6 H, ArH), 7.40–7.14 (m, 3 H, ArH) ppm. 13
C
NMR (75.4 MHz, CDCl3): δ = 155.2, 149.8, 145.8, 141.5, 139.2, 2.86–2.77 (m, 4 H, CH2), 1.70–1.62 (m, 4 H, CH2), 1.32–1.22 (m,
134.8, 128.5, 127.8, 126.5, 124.7, 123.3 (2 C), 121.4, 120.8, 113.6,
12 H, CH2), 0.84–0.80 (m, 6 H, CH3) ppm. 13C NMR (75.4 MHz,
Eur. J. Org. Chem. 2011, 569–577
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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A. K. Mohanakrishnan et al.
FULL PAPER
CDCl3): δ = 149.3, 147.8, 139.3 (2 C), 137.8, 137.1, 135.3, 133.8,
129.1, 127.3, 127.1, 126.6, 126.1, 124.6, 123.8, 123.4, 122.7, 122.3,
121.0, 114.9, 108.4, 31.6, 31.2, 31.1, 30.3, 28.9, 28.8, 22.6, 22.5,
14.1 ppm. MS (EI): m/z (%) = 613 (45) [M]+. C36H39NO2S3
(613.21): calcd. C 70.43, H 6.40, N 2.28, S 15.67; found C 70.69,
H 6.53, N 2.13, S 15.52.
21: The reaction of 17b (0.5 g, 1.26 mmol) with benzo[b]furan
(0.45 g, 3.80 mmol) in the presence of BF3·OEt2 (40 mg) following
the same procedure as that used for the synthesis of 6d afforded
compound 21 (0.25 g, 51%) as a colorless solid, m.p. 150 °C. 1H
NMR (300 MHz, CDCl3): δ = 8.45 (s, 1 H, ArH), 8.02 (d, J =
7.5 Hz, 1 H, ArH), 7.86–7.80 (m, 2 H, ArH), 7.63–7.61 (m, 1 H,
ArH), 7.56–7.50 (m, 1 H, ArH), 7.49 (d, J = 6.9 Hz, 1 H, ArH),
7.42–7.34 (m, 4 H, ArH), 7.31–7.25 (m, 2 H, ArH), 7.21–7.16 (m,
1 H, ArH) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 157.2, 155.1,
153.6, 148.8, 140.8, 134.9, 134.8, 133.4, 128.9, 128.0, 126.8, 124.8,
124.6, 124.2, 124.1, 123.4, 123.2, 123.1, 122.7, 121.5, 120.9, 115.4,
111.9, 111.8, 110.6, 108.6 ppm. MS (EI): m/z (%) = 390 (59) [M]+.
C26H14O2S (390.07): calcd. C 79.98, H 3.61, S 8.21; found C 79.79,
H 3.74, S 8.34.
18b: The reaction of 17a (0.5 g, 0.96 mmol) with bithiophene
(0.48 g, 2.90 mmol) in the presence of BF3·OEt2 (40 mg) following
the same procedure as that used for the synthesis of 6d afforded
1
compound 18b (0.29 g, 49%) as a colorless solid, m.p. 142 °C. H
NMR (300 MHz, CDCl3): δ = 8.73 (s, 1 H, ArH), 8.35 (d, J =
8.4 Hz, 1 H, ArH), 7.85 (d, J = 7.2 Hz, 2 H, ArH), 7.56 (s, 1 H,
ArH), 7.44–7.40 (m, 2 H, ArH), 7.34–7.23 (m, 4 H, ArH), 7.16–
7.10 (m, 5 H, ArH), 7.03–6.98 (m, 3 H, ArH) ppm. 13C NMR
(75.4 MHz, CDCl3): δ = 139.5, 139.4, 139.3, 137.7, 137.4, 137.2,
136.9, 136.4, 133.9, 129.2, 128.7, 128.1, 127.9, 127.8, 127.6, 126.6,
125.9, 125.6, 125.4, 124.9, 124.4, 124.2 (2 C), 124.1, 123.8, 122.4,
120.1, 114.9, 109.3 ppm. MS (EI): m/z (%) = 609 (52) [M]+.
C33H19NO2S5 (609.01): calcd. C 63.03, H 3.14, N 2.30, S 26.29;
found C 63.32, H 3.21, N 2.18, S 26.19.
22: The reaction of 17b (0.5 g, 1.26 mmol) with N-ethylcarbazole
(0.74 g, 3.80 mmol) in the presence of BF3·OEt2 (40 mg) following
the same procedure as that used for the synthesis of 6d afforded
compound 22 (0.28 g, 40%) as a light-yellow solid, m.p. 244 °C. 1H
NMR (300 MHz, CDCl3): δ = 9.24 (s, 1 H, ArH), 8.69 (d, J =
7.8 Hz, 1 H, ArH), 8.15 (s, 1 H, ArH), 7.98 (d, J = 7.5 Hz, 1 H,
ArH), 7.73 (d, J = 7.8 Hz, 1 H, ArH), 7.68–7.60 (m, 3 H, ArH),
7.56–7.52 (m, 1 H, ArH), 7.51–7.46 (m, 4 H, ArH), 7.42–7.39 (m,
3 H, ArH), 6.83 (t, J = 7.7 Hz, 1 H, ArH), 6.56 (d, J = 8.1 Hz, 1
H, ArH), 4.49–4.40 (m, 4 H, CH2), 1.56–1.51 (m, 6 H, CH3) ppm.
13C NMR (75.4 MHz, CDCl3): δ = 140.5, 139.7, 138.9, 138.8,
138.2, 137.5, 136.4, 130.3, 130.1, 128.9, 127.6, 127.2, 126.5, 126.1,
126.0, 125.2, 124.0, 123.9, 123.8, 123.6, 122.9, 122.4, 122.0, 121.9,
120.7, 119.9, 119.1, 115.4, 113.5, 109.8, 109.3, 109.2, 108.7, 37.9,
37.7, 14.4, 14.0 ppm. MS (EI): m/z (%) = 544 (31) [M]+. C38H28N2S
(544.19): calcd. C 83.79, H 5.18, N 5.14, S 5.89; found C 83.95, H
5.09, N 5.06, S 6.01.
19a: The reaction of 17b (0.5 g, 1.26 mmol) with 2-hexylthiophene
(0.63 g, 3.80 mmol) in the presence of BF3·OEt2 (40 mg) following
the same procedure as that used for the synthesis of 6d afforded
compound 19a (0.34 g, 54%) as
a
thick liquid. 1H NMR
(300 MHz, CDCl3): δ = 8.24 (s, 1 H, ArH), 8.07–8.04 (m, 1 H,
ArH), 7.71–7.69 (m, 1 H, ArH), 7.40–7.35 (m, 3 H, ArH), 7.03 (s,
1 H, ArH), 6.82 (d, J = 3.3 Hz, 1 H, ArH), 2.81 (t, J = 6.6 Hz, 4
H, CH2), 1.67 (t, J = 7.2 Hz, 4 H, CH2), 1.25–1.24 (m, 12 H, CH2),
0.83–0.80 (m, 6 H, CH3) ppm. 13C NMR (75.4 MHz, CDCl3): δ =
147.1, 139.5, 138.9, 138.8, 137.1, 135.9, 135.5, 134.1, 127.6, 126.7,
124.3, 123.7, 122.6, 121.4, 120.7, 114.1, 31.6, 30.9, 30.3, 29.8, 28.9
(2 C), 22.6, 14.1 ppm. MS (EI): m/z (%) = 490 (47) [M]+. C30H34S3
(490.18): calcd. C 73.42, H 6.98, S 19.60; found C 73.18, H 7.11, S
19.71.
Acknowledgments
We thank the Department of Science and Technology (DST), New
Delhi for financial support. J. A. thanks the Council of Scientific
and Industrial Research (CSIR), New Delhi for an SRF fellowship.
R. S. thanks the University Grants Commission (UGC), New
Delhi for a JRF fellowship. The authors thank the Department of
Science and Technology (DST-FIST) for a 300-MHz NMR spec-
trometer. The authors also thank the University of Madras for fin-
ancial support through the DST-PURSE program.
19b: The reaction of 17b (0.5 g, 1.26 mmol) with bithiophene
(0.63 g, 3.80 mmol) in the presence of BF3·OEt2 (40 mg) following
the same procedure as that used for the synthesis of 6d afforded
1
compound 19b (0.29 g, 47%) as a colorless solid, m.p. 172 °C. H
NMR (300 MHz, CDCl3): δ = 8.17 (s, 1 H, ArH), 8.80 (d, J =
7.8 Hz, 1 H, ArH), 7.46 (s, 1 H, ArH), 7.40–7.32 (m, 2 H, ArH),
7.28–7.23 (m, 4 H, ArH), 7.21–7.15 (m, 2 H, ArH), 7.08–7.01 (m,
3 H, ArH) ppm. 13C NMR (75.4 MHz, CDCl3): δ = 140.8, 140.2,
139.5, 138.8, 137.7, 137.6, 137.3, 137.1, 134.6, 131.6, 128.5, 128.1,
127.9, 127.8, 126.7, 125.9, 125.5, 124.9, 124.8, 124.4, 124.3, 124.2,
123.8, 122.6, 118.6, 117.1 ppm. MS (EI): m/z (%) = 486 (40) [M]+.
C26H14S5 (485.97): calcd. C 64.16, H 2.90, S 32.94; found C 64.01,
H 3.03, S 33.09.
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Received: August 19, 2010
Published Online: November 26, 2010
Eur. J. Org. Chem. 2011, 569–577
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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