Synthesis of Cyclo[b]fused Carbazoles via SnCl4-Mediated Domino Reaction of 2-Indolylmethylpivalates with Arenes and Heteroarenes

Article abstract of DOI:10.1021/acs.joc.6b01646

A straightforward synthesis of aryl and heteroaryl-annulated cyclo[b]carbazoles has been developed via SnCl₄-mediated one-pot arylation, cyclization and aromatization reaction sequence from 3-acetyl/aroyl-2-pivaloyloxymethylindoles. The startin

Full text of DOI:10.1021/acs.joc.6b01646

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Note
Synthesis of Cyclo[b]fused Carbazoles via SnCl4-mediated Domino
Reaction of 2-Indolylmethylpivalates with Arenes and Heteroarenes
Velu Saravanan, Thiyagarajan Mageshwaran, and Arasambattu Kannan Mohanakrishnan
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b01646 • Publication Date (Web): 26 Aug 2016
Downloaded from http://pubs.acs.org on August 30, 2016
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Synthesis of Cyclo[b]fused Carbazoles via SnCl -mediated
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Domino Reaction of 2-Indolylmethylpivalates with Arenes
and Heteroarenes
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Velu Saravanan, Thiyagarajan Mageshwaran and Arasambattu K. Mohanakrishnan*
Department of Organic Chemistry, School of Chemistry, University of Madras
Guindy Campus, Chennai 600 025, Tamil Nadu, India
Email: mohanakrishnan@unom.ac.in; mohan_67@hotmail.com
ABSTRACT:
A
straightforward synthesis of aryl and heteroarylꢀannulated
ꢀmediated one pot arylation, cyclization and
cyclo[b]carbazoles has been developed via SnCl
4
aromatization reaction sequence from 3ꢀacetyl/aroylꢀ2ꢀpivaloyloxymethyl indoles. The
starting material is easily accessible from commercially available 2ꢀmethylindole via Friedel–
Crafts acylation, bromination and pivaloylation. Remarkably, electron withdrawing/donating
aroyl units including heterocyclic systems are well tolerated in the present domino reaction
protocol. Furthermore, this methodology could be extended to the synthesis of
dibenzofurocarbazole via bisꢀannulation of 2,5ꢀbisꢀ(2ꢀpivaloyloxymethyl)pyrrole.
Over the years, the structural features and potential biological properties of the carbazole
1
alkaloids stimulated research in this area. Isolation and synthesis of biologically active
2
aꢀd
2e
carbazole alkaloids have been reviewed in detail by Knӧlker and Mal. Arylꢀ and heteroꢀ
aryl fused carbazoles are often explored because of their pharmacological activities and
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applications in material sciences. The benzo[b]carbazole derivatives showed remarkable
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cytostatic activity against leukemia type L 1210 cell culture. Recently, a variety of benzoꢀ
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and naphthoꢀcarbazole analogs were investigated as potential anticancer agents.
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Furthermore, because of promising optical and chemical properties of annulated
benzocarbazoles, they have been exploited as functional building blocks in the construction
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of optoelectronic devices.
In the past few decades, several methods were developed for the synthesis of the parent
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system of benzo[b]carbazole. Kano et al. reported the first synthesis of benzo[b]carbazole
involving pyrolysis of Nꢀfree indole. Later, the synthesis of benzo[b]carbazole was achieved
8
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via benzannulation of indoles, Fischer indolization of phenylhydrazones, Nenitzescu
1
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indolization of pꢀbenzoquinone aminomethylene indanone, and Diels–Alder reaction of
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pyranoindolones, furanoindoles and 2,4ꢀdihydropyrroloindole with aryne.
Several strategies have been reported for the syntheses of aryl and heteroarylꢀannulated
carbazoles (Figure 1) through intramolecular dehydroꢀDiels–Alder reactions of Nꢀ(oꢀ
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ethynyl)aryl ynamides, Pdꢀcatalyzed domino reaction of 2ꢀalkynylbenzaldehydes with
1
5
indoles,
reaction between 2ꢀethynylꢀNꢀtriphenylphosphoranylidene anilines and
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diazoketones via ketenimine intermediates, CuI ꢀcatalyzed Friedel–Crafts alkylation of 2ꢀ
2
(2ꢀ(alkynyl)benzylidene)malonates with indoles followed by electrophilic cyclization and
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aromatization, ironꢀcatalyzed domino isomerization/cyclodehydration sequences from
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substituted 2ꢀ[(indolineꢀ3ꢀylidene)(methyl)]benzaldehydes,
Brønsted acidꢀcatalyzed
1
9
reactions of indoles with oꢀ[αꢀ(hydroxy)benzyl]benzaldehyde acetals, and ironꢀcatalyzed 5ꢀ
2
0
exoꢀdig cyclization and a subsequent electrocyclization.
Figure 1. Syntheses of Cyclo[b]fused carbazoles.
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However, most of these protocols have disadvantages such as harsh reaction conditions
and restricted substitution in both aryl and heteroaryl system. Therefore, the development of a
facile approach for benzo[b]carbazoles from a readily available starting material and costꢀ
effective method is highly desirable. Our strategy is to utilize easily accessible 1ꢀ
phenylsulfonylꢀ2ꢀbromomethylindole and arenes as well as heteoarenes as synthetic
equivalents for the construction of the annulated carbazoles. In our earlier reports, the 2/3ꢀ
bromomethylindoles which have adjacent carbonyl groups masked either as diethyl
21
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malonylidene or diacetoxymethine were explored for annulation strategy. However,
moderate reactivity of the malonylidene tethered bromomethylindole and the less stable
nature of the acetoxymethine unit limited the substrate scope of these methodologies. To
overcome these short comings, we report herein, an annulation protocol by employing
2ꢀpivaloyloxymethylindole that contain an unmasked carbonyl group at 3ꢀposition as a
bidentate synthon for the construction of diversely substituted carbazole derivatives.
Till date, several methods have been developed for the arylation of bromomethyl
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compounds. However, no literature reports are available for the arylation of bromomethyl
compounds that contain electron withdrawing ketone functionality at the adjacent position.
21
Based on our earlier reports on ZnBr
2
ꢀmediated domino reactions, the initial phenylation of
2
4
2ꢀbromomethylmethylindole 1 using 20 mol% ZnBr was unsuccessful even at refluxing
2
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condition (Scheme 1). In addition, increasing the ZnBr equivalents was also of no use and
only led to the recovery of the starting material. Even though, the bromo compound 1
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underwent ZnBr
2
ꢀmediated Arbuzov reaction, it has failed to undergo the acetamidation
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6
reaction. Obviously, the reactivity of the bromo compound is sufficient only for
phosphorous nucleophile and not for carbon and nitrogen nucleophiles. To enhance the
possibility of arylation, bromo compound 1 was converted into acetate 3 and pivalate 4.
Scheme 1. Reactivity of 2-bromomethylindole 1, 2-acetoxymethylindole 3 and
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2-pivaloyloxymethylindole 4.
As expected, the phenylation of acetoxymethylindole 3 with benzene at reflux afforded the
benzylindole 2, but only in 38% yield. Under identical conditions, the reaction of
ꢀpivaloyloxymethylindole 4 with benzene led to the formation of 2 in 63% yield. The
formation of phenylation product 2 from acetate 3 and pivalate 4 confirmed the coordination
of ZnBr on to benzyloxy carbonyl units.
Next, arylation of pivaloyloxymethylindole 4 with various arenes was investigated. To our
surprise, the reaction of pivalate 4 with mꢀxylene using 1.2 equiv of ZnBr in 1,2ꢀDCE at
2
2
2
reflux for 9 h provided the arylation and annulation products 5a and 6a in 46% and 12%
yields, respectively (Scheme 2). The reaction of pivalate 4 with naphthalene also produced
both the naphthylated indole 5b and annulated carbazole 6b.
Scheme 2. Arylation vs annulation of 2-pivaloyloxymethylindole 4.
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To enhance the feasibility of annulation products, the reaction of 4 with naphthalene was
tested using different Lewis acids (Table 1).
Table 1. Effect of Lewis acids (LA) on annulation of 2ꢀpivaloyloxymethylindole 4
with naphthalene
a
b
Entry
1
2
3
4
LA
ZnBr
AlCl
CuBr
Zn(OTf)
FeCl
Time (h) Yield (%)
c
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>10
nr
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nr
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3
54
68
63
72
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73
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SnCl4
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BF .OEt
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8
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InCl3
InBr3
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Cu(OTf)
2
12
a
Annulation of 2ꢀpivaloyloxymethylindole 4 (1 equiv) with naphthalene (1.1 equiv) using Lewis acid (1.2 equiv)
b
c
in 1,2ꢀDCE at reflux. Isolated yield of 6b by column chromatography. A major portion of naphthylated
compound 5b was also formed.
The reaction of pivaloyloxymethylindole 4 with naphthalene using 1.2 equiv of ZnBr
AlCl afforded carbazole 6b in poor yields (entries 1 and 2) along with major portion of
naphthylated compound 5b. Obviously, the ZnBr /AlCl is not favoring the intramolecular
2
or
3
2
3
cyclization of 5b to form the carbazole 6b. Under identical conditions, the reaction of
pivaloyloxymethylindole 4 with naphthalene in the presence of 1.2 equiv CuBr /Zn(OTf)
failed to produce even the arylated compound 5b (entries 2 and 3). However, the reaction of
pivalate 4 with naphthalene using 1.2 equiv FeCl , SnCl and BF .OEt in 1,2ꢀDCE under
reflux furnished carbazole 6b in 54%, 68% and 63% yields, respectively (entries 5ꢀ7). In the
presence of expensive Lewis acids such as InCl , InBr and Cu(OTf)2, the domino reaction of
2
2
3
4
3
2
3
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pivaloyloxymethylindole 4 proceeded in better yields than the other Lewis acids (entries 8ꢀ
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0). The above mentioned results indicated that the stronger Lewis acids are favoring both
naphthylation as well as cyclization (entries 5ꢀ10). Since, the reaction requires a minimum of
.2 eq of Lewis acid, the further annulations of pivaloyloxymethylindole 4 with arenes were
performed with SnCl , which is less expensive.
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The requirement of 1.2 equiv of SnCl
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for annulation could be explained through the
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formation of intermediate 7 followed by its aromatization via elimination of Sn(OH)Cl
Scheme 3)
Scheme 3: Proposed mechanism for SnCl
3
(
.
4
-mediated annulation of 4.
To extend the scope of this reaction protocol, the domino reaction of
pivaloyloxymethylindole 4 was performed with arenes and heteroarenes using SnCl as the
4
mediator. First, the reaction of pivalate 4 with mꢀxylene was performed under standard
reaction condition, which led to the isolation of benzocarbazole 6a in 61% yield. The reaction
of pivalate
naphtho[b]carbazoles 6b and 6c in 68% and 65% yields, respectively. The domino reaction of
with pꢀxylene, 2,3ꢀdimethylanisole, 1,2ꢀdimethoxybenzene, oꢀxylene and 1,3
benzenedioxole using 1.2 equiv of SnCl afforded annulated carbazoles 6d-h in 56%–68%
4
with naphthalene and 1ꢀmethylnaphthalene also produced the
4
4
yields (Scheme 4). Obviously, the domino reaction of the pivalate 4 with benzene stops at the
arylation stage, whereas in the case of substituted benzenes, the further reaction of the
arylated compounds facilitated by the electron releasing substitutents led to the formation of
carbazoles 6a-h.
Scheme 4. Structures of annulated carbazoles 6a-h synthesized using SnCl4.
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4
Next, the domino reaction of pivalate 4 with thiophene using 1.2 equiv of SnCl in 1,2ꢀ
DCE afforded thieno[b]carbazole 8a in 62% yield (Scheme 5). To our delight, the annulation
of pivalate 4 with 2ꢀmethylthiophene and bithiophene also afforded the heteroannulated
carbazoles 8b and 8c in 76% and 70% yields, respectively.
Ambiguously, the domino reaction of the pivalate 4 with thianaphthene using SnCl at
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room temperature for 3 h gave an inseparable mixture of the isomeric carbazoles 8d and 8d'
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1:0.4 ratio based on H NMR spectrum) in 74% yield. The structures of benzo[b]thieno
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carbazoles 8d and 8d' could be assigned based on our earlier reports. Under identical
conditions, the domino reaction of the pivalate 4 with Nꢀsulfonyl pyrrole/benzo[b]furan led to
the formation of respective heterocycles 8e and 8f. Furthermore, the domino reaction of
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pivalate 4 with naphtho[b]thiophene afforded heterocycle 8g. To our delight, the reaction of
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pivalate 4 with 1,3,5ꢀtrithienyl benzene/1,3,5ꢀtris(3ꢀmethylthienyl)benzene also produced
the corresponding complex heterocycles 8h and 8i in 64% and 67% yields (Scheme 5).
Scheme 5. Synthesis of hetero-annulated carbazoles 8a-i.
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Next, to generalize the scope of the reaction, synthesis of cyclo[b]carbazoles containing an
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aryl unit at the Cꢀ4 position was investigated. An aroylation of 2ꢀmethylindole produced the
corresponding aroylindole 9a-d, which upon bromination followed by the pivalic acid
displacement gave the corresponding pivaloyloxyindoles 11a-d. The annulation reaction of
these pivalates 11a-d with arenes as well as heteroarenes furnished the carbazoles 12a-d,
1
3a-d, 14a-d, 15a-d and 16a-d (Scheme 6).
As expected, the reaction of pivalates 11a-d with 1ꢀmethylnaphthalene in the presence of
4
SnCl in 1,2ꢀDCE at reflux led to the isolation of respective naphtho[b]carbazoles 12a-d in
61%–73% yields. Electron releasingꢀaroyl units containing pivalates 11a/11b required longer
reaction time for annulation than electron deficientꢀaroyl units based counter parts 11c/11d.
Likewise, the domino reaction of pivalates 11a-d with veratrole produced the corresponding
benzo[b]carbazoles 13a-d in 58%, 64%, 72% and 70% yields. Similarly, the reaction of
pivalates 11a-d with the heteroarenes such as 2ꢀmethylthiophene, 1,3,5ꢀtrithienyl benzene
and benzo[b]furan afforded heteroꢀannulated carbazoles 14a-d, 15a-d and 16a-d in good
yields (Scheme 6). Invariably, the electron withdrawing aroyl units containing pivalates
1
1c/11d produced better yields of annulated carbazoles than the electron releasing aroyl units
tethered pivalates 11a/11b.
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Scheme 6. Preparation of 4-aryl annulated/heteroannulated carbazoles 12a-d to 16a-d.
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Next, the domino reaction of 3ꢀthienoyl 2ꢀpivaloyloxymethylindole 17 with representative
arenes and heteroarenes afforded the respective 4ꢀthienyl cyclo[b]fused carbazoles 18a-e in
57%–69% yields (Scheme 7).
Scheme 7. Synthesis of 4-(thienyl) annulated/heteroannulated carbazoles 18a-e.
The domino reaction of pivaloyloxymethylindoles 11a-d/17 confirmed that the formation
of the annulated carbazoles is more facile and also produced better yields with electron
withdrawing 4ꢀnitrobenzoyl/4ꢀchlorobenzoyl unit rather than the donating systems such as
veratroyl and 2ꢀthienoyl.
The structure of the representative heteroannulated carbazoles 14c and 16c were
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unambiguously confirmed by single crystal Xꢀray diffraction analyses (see SI).
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Finally, bisꢀannulation of the 2,5ꢀbis(pivaloyloxmethyl)dibenzoyl pyrrole 19 with
benzo[b]furan afforded the dibenzofuro carbazole 20 as a colorless solid in 71% yield
(
Scheme 8). The structure of the carbazole 20 was confirmed through a single crystal Xꢀray
3
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diffraction analysis (see SI).
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Scheme 8. Synthesis of symmetric hetero-annulated carbazole.
O
O
Ph Ph
Ph
PivO
Ph
OPiv
Benzofuran
SnCl (2.4 eq)
4
O
O
N
1,2-DCE, rt
30 min, 71%
N
SO
2
Ph
1
9
20
SO Ph
2
In summary, we have developed an efficient and straightforward protocol for the synthesis
of arylꢀ and heteroarylꢀannulated cyclo[b]carbazoles via one pot arylation of 1ꢀ
phenylsulfonylꢀ2ꢀpivaloyloxymethylindole followed by cyclization and aromatization. A
wide range of the annulated carbazoles containing an easily removable phenylsulfonyl group
was prepared to generalize the scope of the reaction. The influence of the electronic effect on
annulations was investigated by incorporating the electron donating/withdrawing aroyl units.
Finally, the symmetrical dibenzofuro[b]carbazole was synthesized through bisꢀannulation of
1
ꢀphenylsulfonylꢀ2,5ꢀbis(pivaloyloxymethyl)pyrrole. The structures of the representative
heteroannulated carbazoles were confirmed through single crystal Xꢀray analyses. Since, our
methodology relies on benzylic bromination for accessing the required pivalates, the presence
of electron withdrawing 1ꢀphenylsulfonyl group on indole nitrogen is indispensable.
Experimental Section
General remarks. Melting points were uncorrected. Solvents were dried by standard
procedures. All the experiments carried out under the nitrogen atmosphere unless otherwise
stated. The Lewis acids were used in the form of anhydrous condition under nitrogen
atmosphere. The progression of all the reaction was monitored by TLC using hexane/ethyl
acetate mixtures as eluent. Column chromatography was carried out on Silica gel (230ꢀ400
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mesh, Merck) by using increasing polarity. Infrared spectra were recorded neat and reported
−1
1
13
3 6
in cm . H, C and DEPTꢀ135 spectra were recorded in CDCl and DMSOꢀd using TMS as
an internal standard on a 300 MHz spectrometer at room temperature. Chemical shift values
were quoted in parts per million (ppm) and coupling constants (J) were quoted in hertz (Hz).
Highꢀresolution mass spectra (HRMS) were recorded on EI and ESI mass spectrometers.
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(
3-Acetyl-1-(phenylsulfonyl)-1H-indol-2-yl)methyl acetate (3).
ꢀbromomethylindole 1 (1.0 g, 2.55 mmol) and potassium acetate (0.5 g, 5.10 mmol) in DMF
10 mL) was stirred at room temperature for 8 h. After completion of the reaction (TLC), it
A
suspension of
2
(
was poured over crushed ice (100 g) containing Conc. HCl (5 mL). The precipitate obtained
was filtered, washed with water (200 mL) and dried (CaCl ). The crystallization of crude
2
product from MeOH (5 mL) afforded indolylmethyl acetate 3 as a colorless solid (0.766 g,
o
ꢀ1 1
8
1%); mp 114ꢀ116 C. IR (neat): 1743 (ester), 1673 (CO), 1380 & 1180 (SO
2
) cm . HꢀNMR
(
300 MHz, CDCl ): δ 8.24 (d, J = 8.1 Hz, 1H), 7.94ꢀ7.90 (m, 3 H), 7.61 (t, J = 7.5 Hz, 1H),
3
13
7.51ꢀ7.36 (m, 4H), 5.75 (s, 2H), 2.70 (s, 3H), 2.02 (s, 3H) ppm. CꢀNMR (75 MHz, CDCl ):
3
δ 195.9, 170.0, 138.8, 136.9, 136.2, 134.4, 129.4, 126.7, 126.3, 126.2, 124.8, 124.7, 121.5,
1
1
4
3
14.8, 56.4, 31.8, 20.7 ppm. Deptꢀ135 (75 MHz, CDCl ): δ 134.4, 129.4, 126.8, 126.3, 124.7,
21.5, 114.8, 56.4, 31.9, 20.7 ppm. Elemental Analysis Calcd for C19
.61; N, 3.77; S, 8.63. Found: C, 61.26; H, 4.46; N, 3.53; S, 8.39.
5
H17NO S: C, 61.44; H,
(3-Acetyl-1-(phenylsulfonyl)-1H-indol-2-yl)methyl pivalate (4). To a solution of
ꢀbromomethylindole 1 (5.0 g, 12.75 mmol) in dry THF (120 mL), potassium carbonate (5.28
2
g, 38.26 mmol) and pivalic acid (2.60 g, 25.51 mmol) were added. The reaction mixture was
allowed to stir at room temperature for 12 h. After completion of the reaction (TLC), the
solvent was removed under reduced pressure. Then, the residue was diluted with DCM (100
mL), washed with water (3 x 50 mL) and dried (Na SO ). Removal of solvent followed by
2
4
trituration of the crude product with MeOH (15 mL) furnished pivalate 4 as a colorless solid
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6
o
ꢀ1
2
(4.68 g, 89%); mp 122ꢀ124 C. IR (neat): 1730, (ester) 1676 (CO), 1382 & 1180 (SO ) cm .
1
3
HꢀNMR (300 MHz, CDCl ): δ 8.19 (d, J = 7.8 Hz, 1H), 7.96ꢀ7.94 (m, 1H), 7.88 (d, J = 7.8
Hz, 2H), 7.58 (t, J = 7.5 Hz, 1H), 7.49ꢀ7.34 (m, 4H), 5.68 (s, 2H), 2.67 (s, 3H), 1.22 (s, 9H)
13
ppm. CꢀNMR (75 MHz, CDCl ): δ 195.5, 177.6, 138.4, 137.6, 136.1, 134.5, 129.5, 126.6,
3
0
1
2
3
4
5
6
7
8
9
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8
9
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8
9
0
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8
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0
126.4, 126.2, 124.8, 124.7, 121.7, 114.8, 56.5, 38.9, 31.7, 27.2 ppm. Deptꢀ135 (75 MHz,
CDCl
3
): δ 134.5, 129.5, 126.6, 126.2, 124.8, 121.7, 114.8, 56.5, 31.7, 27.2 ppm. Elemental
S: C, 63.90; H, 5.61; N, 3.39; S, 7.75; Found C, 63.74; H,
Analysis Calcd for C22
H
23NO
5
5.44; N, 3.27; S, 7.59.
1
-Phenylsulfonyl 2-benzyl-3-acetylindole (2) from 2-acetoxymethylindole. A mixture of
2ꢀacetoxymethylindole 3 (0.2 g, 0.54 mmol) and ZnBr (0.145 g, 0.65 mmol) in dry benzene
2
(
10 mL) was refluxed under nitrogen atmosphere for 24 h. Then, it was poured over ice water
100 mL) containing Conc. HCl (3 mL), the organic layer was separated and the aqueous
(
layer was extracted with DCM (2 x 20 mL). The combined extract was washed with water (2
x 15 mL) and dried (Na SO ). Removal of solvent followed by column chromatographic
2
4
purification (Silica gel, EtOAcꢀhexane 1:9) led to the isolation of 2ꢀbenzylindole 2 as a
o
ꢀ
colorless solid (0.079 g, 38%); mp 164ꢀ166 C. IR (neat): 1670 (CO) 1380 & 1182 (SO
2
) cm
1
1
.
HꢀNMR (300 MHz, CDCl
.38ꢀ7.35 (m, 2H), 7.24ꢀ7.16 (m, 5H), 7.12ꢀ7.10 (m, 2H), 4.92 (s, 2H), 2.63 (s, 3H) ppm. Cꢀ
NMR (75 MHz, CDCl ): δ 195.9, 144.1, 138.4, 137.6, 136.1, 134.0, 129.2, 128.5 (2C), 127.0,
3
): δ 8.26ꢀ8.23 (m, 1H), 7.97ꢀ7.94 (m, 1H), 7.43ꢀ7.40 (m, 3H),
13
7
3
1
26.6, 126.4, 125.1, 124.5, 122.2, 121.1, 115.0, 32.0, 31.9 ppm. Deptꢀ135 (75 MHz, CDCl3):
δ 134.0, 129.2 128.5 (2C), 126.7, 126.4, 125.2, 124.5, 121.1, 115.0, 32.1, 31.9 ppm. HRMS
+
+
(
ESIꢀTOF, DCM): m/z Calcd for C23
Preparation of 2-benzylindole (2) from 2-pivaloyloxymethylindole. To a solution of indolꢀ
ꢀylmethyl pivalate 4 (0.2 g, 0.48 mmol) in dry benzene (10 mL), ZnBr (0.131 g, 0.58
3
H19NO S + H [M+H] : 390.1164; Found 390.1153.
2
2
mmol) was added and it was refluxed for 8 h under nitrogen atmosphere. Then, the usual
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work up adopting the above mentioned procedure followed by column chromatographic
purification (Silica gel, EtOAcꢀhexane 1:9) furnished the 2ꢀbenzylindole 2 as a colorless solid
(0.118 g, 63%).
Annulation of pivalate 4 with m-xylene. A mixture of pivalate 4 (0.2 g, 0.48 mmol), ZnBr2
(0.131 g, 0.58 mmol) and mꢀxylene (0.15 g, 1.45 mmol) in dry DCE (10 mL) was refluxed
under nitrogen atmosphere for 9 h. Then, the usual workup followed by column
chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) afforded carbazole 6a. Further
elution of the column afforded arylated product 5a.
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1-(2-(2,4-Dimethylbenzyl)-1-(phenylsulfonyl)-1H-indol-3-yl)ethanone (5a). Colorless
o
ꢀ1 1
solid (0.093 g, 46%); mp 160ꢀ162 C. IR (neat): 1666 (CO), 1380 & 1176 (SO ) cm . Hꢀ
2
3
NMR (300 MHz, CDCl ): δ 8.26ꢀ8.23 (m, 1H), 7.98ꢀ7.95 (m, 1H), 7.43ꢀ7.40 (m, 2H), 7.37ꢀ
7
1
.31 (m, 3H), 7.18ꢀ7.13 (m, 2H), 6.95 (s, 1H), 6.49 (d, J = 7.8 Hz, 1H), 6.20 (d, J = 7.8 Hz,
13
3
H), 4.68 (s, 2H), 2.49 (s, 3H), 2.36 (s, 3H), 2.17 (s, 3H) ppm. CꢀNMR (75 MHz, CDCl ): δ
195.7, 144.1, 138.4, 136.2, 135.7, 135.6, 133.8, 132.8, 130.9, 129.0, 127.0, 126.7, 126.6,
1
25.1, 124.5, 122.5, 121.2, 114.8, 31.6, 29.2, 20.8, 19.7 ppm. Deptꢀ135 (75 MHz, CDCl ): δ
3
133.8, 131.0, 129.1, 126.7, 126.6, 125.1, 124.5, 121.3, 114.8, 31.7, 29.2, 20.9, 19.8 ppm.
+
HRMS (EI, 70 eV): m/z Calcd for C25
H23NO
3
S [M ]: 417.1399; Found 417.1397.
7,9,11-Trimethyl-5-(phenylsulfonyl)-5H-benzo[b]carbazole (6a). Colorless solid (0.023 g,
o
1
12%); mp > 300 C. HꢀNMR (300 MHz, CDCl ): δ 8.72 (s, 1H), 8.37 (d, J = 8.1 Hz, 1H),
3
8.16 (d, J = 7.8 Hz, 1H), 7.81 (s, 1H), 7.71 (d, J = 7.5 Hz, 2H), 7.45 (t, J = 7.35 Hz, 1H),
13
7
.36ꢀ7.29 (m, 2H), 7.20ꢀ7.17 (m, 3H), 3.00 (s, 3H), 2.77 (s, 3H), 2.48 (s, 3H) ppm. CꢀNMR
3
(75 MHz, CDCl ): δ 140.3, 137.6, 136.4, 134.7, 134.0, 133.6, 130.4, 130.3, 129.0, 128.9,
127.7, 127.4, 126.5, 124.4, 124.1, 123.7, 121.1, 115.3, 106.8, 22.0, 20.2, 15.7 ppm. Deptꢀ135
(
75 MHz, CDCl ): δ 133.7, 129.0, 128.9, 127.4, 126.5, 124.1, 123.7, 121.1, 115.3, 106.8,
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+
2
22.1, 20.2, 15.7 ppm ppm. HRMS (ESIꢀTOF, MeOH): m/z Calcd for C25H21NO S + H
+
[
M+H] 400.1371; Found 400.1362.
Annulation of pivalate 4 with naphthalene. A mixture of 2ꢀindolylmethyl pivalate 4 (0.2 g,
.48 mmol), ZnBr (0.131 g, 0.58 mmol) and naphthalene (0.068 g, 0.53 mmol) in dry DCE
0
2
0
1
2
3
4
5
6
7
8
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0
1
2
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8
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2
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4
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8
9
0
(10 mL) was refluxed under nitrogen atmosphere for 9 h. Then, the usual work up adopting
the above mentioned procedure followed by column chromatographic purification (Silica gel,
EtOAcꢀhexane 1:9) gave carbazole 6b. Further elution of the column afforded arylated
product 5b.
1
-(2-(Naphthalen-1-ylmethyl)-1-(phenylsulfonyl)-1H-indol-3-yl)ethanone (5b). Colorless
o
ꢀ1 1
solid (0.123 g, 58%); mp 176ꢀ178 C. IR (neat): 1670 (CO), 1380 & 1182 (SO ) cm . Hꢀ
2
NMR (300 MHz, CDCl
.88 (d, J = 8.1 Hz, 1H), 7.66ꢀ7.62 (m, 2H), 7.58ꢀ7.53 (m, 1H), 7.48ꢀ7.36 (m, 5H), 7.14 (t,
J = 8 Hz, 2H), 7.00 (t, J = 7.7 Hz, 1H), 6.49 (d, J = 7.2 Hz, 1H), 5.33 (s, 2H), 2.53 (s, 3H)
3
): δ 8.41ꢀ8.38 (m, 1H), 8.19 (d, J = 8.4 Hz, 1H), 8.12ꢀ8.09 (m, 1H),
7
13
ppm. CꢀNMR (75 MHz, CDCl ): δ 195.6, 143.4, 138.4, 136.5, 134.0, 133.7, 133.6, 131.6,
3
1
1
1
29.0, 128.8, 127.1, 127.0, 126.6, 126.4, 125.9, 125.3, 124.6, 124.3, 123.1, 122.8, 121.4,
14.9, 31.6, 29.2 ppm. Deptꢀ135 (75 MHz, CDCl ): δ 134.0, 129.0, 128.8, 127.0, 126.6,
3
26.4, 125.9, 125.4, 124.7, 124.3, 123.1, 121.4, 114.9, 31.7, 29.2 ppm. HRMS (EI, 70 eV):
+
m/z Calcd for C27
H
21NO
3
S [M ] 439.1242; Found 439.1240.
7-Methyl-12-(phenylsulfonyl)-12H-naphtho[1,2-b]carbazole (6b). Colorless solid (0.033
o
1
g, 16%); mp 238ꢀ240 C. HꢀNMR (300 MHz, CDCl ): δ 9.62 (s, 1H), 8.92 (d, J = 8.1 Hz,
3
1
H), 8.46 (d, J = 8.4 Hz, 1H), 8.22 (d, J = 7.8 Hz, 1H), 8.11 (d, J = 9.3 Hz, 1H), 7.90 (d, J =
.5 Hz, 1H), 7.82 (d, J = 7.8 Hz, 2H), 7.76ꢀ7.73 (m, 2H), 7.67ꢀ7.62 (m, 1H), 7.53 (t, J = 7.8
7
1
3
Hz, 1H), 7.44ꢀ7.34 (m, 2H), 7.25ꢀ7.20 (m, 2H), 3.10 (s, 3H) ppm. CꢀNMR (75 MHz,
CDCl ): δ 139.9, 137.7, 137.5, 133.8, 131.7, 130.8, 130.0, 129.9, 129.0, 128.4, 127.9, 127.5,
3
1
27.4, 126.9, 126.8, 126.5, 126.0, 124.7, 124.2, 123.5, 123.4, 122.4, 115.3, 106.1, 15.9 ppm.
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Deptꢀ135 (75 MHz, CDCl
3
): δ 133.8, 129.0, 128.4, 127.4, 126.9, 126.8, 126.5, 126.0, 124.2,
123.5 (2C), 122.4, 115.3, 106.1, 15.9 ppm. HRMS (ESIꢀTOF, MeOH): m/z Calcd for
+
+
C
27 2
H19NO S + Na [M+Na] 444.1034; Found 444.1032.
General procedure for the synthesis of annulated carbazoles (6a-h). A solution of 2ꢀ
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indolylmethyl pivalate 4 (0.2 g, 0.48 mmol), SnCl (0.151 g, 0.58 mmol) and arene (0.53
4
mmol) in dry DCE (10 mL) was refluxed under nitrogen atmosphere until the reaction was
completed (TLC). Then, the reaction mixture was poured into ice water (30 mL) containing
Conc. HCl (3 mL), the organic layer was separated and the aqueous layer was extracted with
DCM (2 x 20 mL). The combined organic layer was washed with water (2 x 20 mL) and
dried (Na SO ). Removal of solvent followed by column chromatographic purification (Silica
2
4
gel, EtOAcꢀhexane 1:9) furnished annulated benzo[b]carbazoles 6a-h.
,9,11-Trimethyl-5-(phenylsulfonyl)-5H-benzo[b]carbazole 6a. The reaction of pivalate 4
0.2 g, 0.48 mmol) with mꢀxylene (0.151 g, 1.45 mmol) using SnCl (0.151 g, 0.58 mmol) in
7
(
4
dry DCE (10 mL) at reflux for 6 h under nitrogen atmosphere followed by workup and
column chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) afforded carbazole 6a
as a colorless solid (0.118 g, 61%).
7-Methyl-12-(phenylsulfonyl)-12H-naphtho[1,2-b]carbazole (6b). The annulation of
pivalate 4 (0.2 g, 0.48 mmol) with naphthalene (0.068 g, 0.53 mmol) in the presence of SnCl
4
(0.151 g, 0.58 mmol) in dry DCE (10 mL) at reflux for 6 h followed by usual work up and
column chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) furnished carbazole 6b
as a colorless solid (0.134 g, 68%).
5
,7-Dimethyl-12-(phenylsulfonyl)-12H-naphtho[1,2-b]carbazole (6c). The reaction of
pivalate 4 (0.2 g, 0.48 mmol) with 1ꢀmethylnaphthalene (0.076 g, 0.53 mmol) using SnCl
0.151 g, 0.58 mmol) in dry DCE (10 mL) at reflux for 6 h followed by workup and column
4
(
chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) gave naphthocarbazole 6c as a
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5
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6
o
1
colorless solid (0.137 g, 65%); mp 254ꢀ256 C. HꢀNMR (300 MHz, CDCl
.95 (d, J = 8.1 Hz, 1H), 8.45 (d, J = 7.8 Hz, 1H), 8.20 (d, J = 7.5 Hz, 1H), 8.06 (d, J = 7.5
Hz, 1H), 7.92 (s, 1H), 7.80 (d, J = 7.8 Hz, 2H), 7.75ꢀ7.66 (m, 2H), 7.52 (t, J = 7.2 Hz, 1H),
3
): δ 9.59 (s, 1H),
8
1
3
7
.42ꢀ7.33 (m, 2H), 7.25ꢀ7.19 (m, 2H), 3.06 (s, 3H), 2.76 (s, 3H) ppm. CꢀNMR (75 MHz,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
CDCl ): δ 139.9, 137.7, 137.0, 133.7, 131.8, 131.5, 130.9, 129.4, 129.0, 127.8, 127.6, 127.2,
3
1
1
1
26.9, 126.5, 124.7, 124.6, 124.1, 123.8, 123.4, 122.2, 115.4, 106.0, 20.6, 15.8 ppm. Deptꢀ
35 (75 MHz, CDCl
3
): δ 133.7, 129.0, 127.2, 126.9, 126.5, 124.6, 124.2, 123.8, 123.5, 122.2,
+
15.4, 106.0, 20.6, 15.8 ppm. HRMS (EI, 70 eV): m/z Calcd for C28
H
21NO
2
S [M ] 435.1293;
Found 435.1290.
7,10,11-Trimethyl-5-(phenylsulfonyl)-5H-benzo[b]carbazole (6d). To solution of pivalate
4
(0.2 g, 0.48 mmol) in dry DCE (10 mL), SnCl
4
(0.151 g, 0.58 mmol) and pꢀxylene (0.154 g,
1
.45 mmol) were added and refluxed for 6 h. The usual workup followed by the column
chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) afforded benzocarbazole 6d as a
o
1
colorless solid (0.108 g, 56%); mp 174ꢀ176 C. HꢀNMR (300 MHz, DMSOꢀd ): δ 8.68 (s,
6
1
H), 8.37 (d, J = 8.7 Hz, 1H), 8.28 (d, J = 7.8 Hz, 1H), 7.82 (d, J = 7.5 Hz, 1H), 7.67ꢀ7.60
(
m, 1H), 7.58ꢀ7.42 (m, 4H), 7.36ꢀ7.31 (m, 1H), 7.25ꢀ7.23 (m, 1H), 3.18 (s, 3H), 2.89 (s, 3H),
1
3
2
.76 (s, 3H) ppm. CꢀNMR (75 MHz, DMSOꢀd
6
): δ 139.3, 136.2, 135.5, 134.6, 133.2, 132.8,
1
32.0, 131.9, 131.0, 129.6, 128.6, 127.9, 126.6, 126.5, 126.1, 125.1, 124.5, 124.3, 114.5,
106.3, 25.8, 21.2, 20.1 ppm. Deptꢀ135 (75 MHz, DMSOꢀd ): δ 134.7, 129.7, 128.7, 128.0,
6
1
26.5, 126.2, 124.6, 124.3 114.6, 106.4, 25.9, 21.3, 20.1 ppm. Elemental Analysis Calcd for
S: C, 75.16; H, 5.30; N, 3.51; S, 8.03: Found C, 75.02; H, 5.18; N, 3.39; S, 8.14.
-Methoxy-7,8,11-trimethyl-5-(phenylsulfonyl)-5H-benzo[b]carbazole (6e). The
25 2
C H21NO
9
annulation of pivalate 4 (0.2 g, 0.48 mmol) with 2,3ꢀdimethylanisole (0.072 g, 0.53 mmol)
using SnCl (0.151 g, 0.58 mmol) adopting the aboveꢀmentioned procedure followed by
4
column chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) afforded carbazole 6e as
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o
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a colorless solid (0.139 g, 67%); mp 272ꢀ274 C. HꢀNMR (300 MHz, CDCl
3
): δ 8.87 (s,
H), 8.46 (d, J = 8.1 Hz, 1H), 8.19 (d, J = 7.8 Hz, 1H), 7.83ꢀ7.78 (m, 3H), 7.52 (t, J = 7.7 Hz,
H), 7.42ꢀ7.35 (m, 2H), 7.26ꢀ7.12 (m, 2H), 4.02 (s, 3H), 3.02 (s, 3H), 2.50 (s, 3H), 2.44 (s,
1
1
3
13
H) ppm. CꢀNMR (75 MHz, CDCl ): δ 153.8, 140.3, 137.7, 136.6, 135.3, 133.6, 129.6,
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
128.9, 128.7, 127.7, 127.3, 126.6, 126.3, 126.0, 124.2, 124.0, 123.6, 119.5, 115.2, 104.6,
3
61.4, 21.2, 15.5, 12.6 ppm. Deptꢀ135 (75 MHz, CDCl ): δ 133.6, 128.9, 127.4, 126.6, 124.1,
123.6, 119.5, 115.3, 104.6, 61.4, 21.2, 15.5, 12.6 ppm. HRMS (EI, 70 eV): m/z Calcd for
+
C
26
H
23NO
3
S [M ] 429.1399; Found 429.1390.
8
,9-Dimethoxy-11-methyl-5-(phenylsulfonyl)-5H-benzo[b]carbazole (6f). The domino
reaction of pivalate 4 (0.2 g, 0.48 mmol) with veratrole (0.073 g, 0.53 mmol) in the presence
of SnCl (0.151 g, 0.58 mmol) adopting the aboveꢀmentioned procedure followed by the
column chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) gave carbazole 6f as a
4
o
1
3
colorless solid (0.134 g, 64%); mp 256ꢀ258 C. HꢀNMR (300 MHz, CDCl ): δ 8.54 (s, 1H),
8.38 (d, J = 8.4 Hz, 1H), 8.16 (d, J = 7.5 Hz, 1H), 7.79 (d, J = 7.8 Hz, 2H), 7.48 (t, J = 7.7
Hz, 1H), 7.39ꢀ7.35 (m, 3H), 7.32 (s, 1H), 7.28ꢀ7.23 (m, 2H), 4.08 (s, 3H), 4.06 (s, 3H) 2.99
13
(
s, 3H) ppm. CꢀNMR (75 MHz, DMSOꢀd
6
): δ 149.7, 149.0, 138.7, 136.5, 135.1, 134.6,
1
29.6, 128.8, 127.8, 127.3, 127.0, 126.2, 125.3, 124.5, 123.5, 122.0, 114.5, 108.5, 107.5,
02.9, 55.5 (2C), 15.5 ppm. Deptꢀ135 (75 MHz, DMSOꢀd ): δ 134.5, 129.5, 127.2, 126.1,
1
6
124.4, 123.4, 114.4, 108.4, 107.4, 102.8, 55.5, 55.4, 15.4 ppm. HRMS (ESIꢀion trap, MeOH):
+
+
m/z Calcd for C H NO S + Na [M+Na] 454.1089; Found 454.1084.
25
21
4
8,9,11-Trimethyl-5-(phenylsulfonyl)-5H-benzo[b]carbazole (6g). The annulation of
pivalate 4 (0.2 g, 0.48 mmol) with oꢀxylene (0.056 g, 0.53 mmol) using SnCl (0.151 g, 0.58
4
mmol) adopting the aboveꢀmentioned procedure followed by column chromatographic
purification (Silica gel, EtOAcꢀhexane 1:9) gave carbazole 6g as a colorless solid (0.114 g,
o
1
5
9%); mp > 300 C. HꢀNMR (300 MHz, CDCl ꢀDMSOꢀd (4:1)): δ 8.44 (s, 1H), 8.26 (d, J =
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8.4 Hz, 1H), 8.10 (d, J = 7.5 Hz, 1H), 7.86 (s, 1H), 7.70ꢀ7.67 (m, 3H), 7.41 (t, J = 7.05 Hz,
1H), 7.32ꢀ7.28 (m, 2H), 7.16 (t, J = 7.5 Hz, 2H), 2.94 (s, 3H), 2.40 (s, 3H), 2.39 (s, 3H) ppm.
13
CꢀNMR (75 MHz, CDCl
31.7, 128.9, 128.8, 128.4, 128.3, 127.8, 127.2, 126.4, 124.1, 123.9, 123.5, 123.3, 115.1,
109.4, 20.6, 20.0, 15.3 ppm. Deptꢀ135 (75 MHz, CDCl ꢀDMSOꢀd (4:1)): δ 133.7, 128.9,
3 6
ꢀDMSOꢀd (4:1)): δ 139.9, 137.4, 136.4, 135.6, 134.7, 133.7,
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
6
128.4, 127.2, 126.4, 124.1, 123.5, 123.3, 115.0, 109.3, 20.6, 20.0, 15.3 ppm. Elemental
Analysis Calcd for C25 S: C, 75.16; H, 5.30; N, 3.51; S, 8.03: Found C, 75.24; H,
H21NO
2
5.12; N, 3.37; S, 7.88.
7-Methyl-12-(phenylsulfonyl)-12H-naphtho[1,2-b]carbazole (6h). The annulation of
pivalate 4 (0.2 g, 0.48 mmol) with 1,3ꢀbenzodioxole (0.065 g, 0.53 mmol) using SnCl (0.151
4
g, 0.58 mmol) adopting the above mentioned procedure followed by column chromatographic
purification (Silica gel, EtOAcꢀhexane 1:9) afforded carbazole 6h as a colorless solid (0.124
o
1
g, 62%); mp 232ꢀ234 C. HꢀNMR (300 MHz, CDCl
3
): δ 8.50 (s, 1H), 8.39 (d, J = 7.8 Hz,
1H), 8.16 (d, J = 7.5 Hz, 1H), 7.78 (d, J = 7.2 Hz, 2H), 7.51ꢀ7.46 (m, 3H), 7.40ꢀ7.35 (m, 2H),
1
3
7
1
1
.30ꢀ7.26 (m, 2H), 6.07 (s, 2H, CH ), 2.96 (s, 3H) ppm. CꢀNMR (75 MHz, CDCl ): δ
2
3
47.6, 139.7, 137.7, 136.3, 133.7, 130.3, 128.9, 128.1, 127.7, 127.1, 127.0, 126.6, 124.1,
23.4, 123.3, 115.2, 109.9, 104.6, 101.3 (CH ), 100.1, 15.9 ppm. Deptꢀ135 (75 MHz,
): δ 133.7, 128.9, 127.1, 126.5, 124.1, 123.3, 115.2, 109.9, 104.6, 101.3 (CH ), 100.1,
15.9 ppm. HRMS (EI, 70 eV): m/z Calcd for C H NO S [M ] 415.0878; Found 415.0875.
2
CDCl
3
2
+
24
17
4
General procedure for the preparation of heteroannulated carbazoles (8a-i). A solution
of 2ꢀindolylmethyl pivalate 4 (0.48 mmol), heteroarene (0.53 mmol) and SnCl (0.58 mmol)
4
in dry DCE (10 mL) was stirred at room temperature under nitrogen atmosphere. After the
completion of the reaction (TLC), it was then poured into ice water (30 mL) containing Conc.
HCl (3 mL). The organic layer was separated and the aqueous layer was extracted with DCM
(2 x 20 mL). The combined organic layer was washed with water (2 x 20 mL) and dried
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(Na
2
SO
4
). Removal of solvent followed by column chromatographic purification (Silica gel,
EtOAcꢀhexane) afforded heteroannulated carbazoles 8a-i.
-Methyl-9-(phenylsulfonyl)-9H-thieno[2,3-b]carbazole (8a). The reaction of pivalate 4
0.2 g, 0.48 mmol) with thiophene (0.081 g, 0.96 mmol) using SnCl (0.151 g, 0.58 mmol)
4
(
4
10
11
12
13
14
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53
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59
60
adopting the above mentioned procedure followed by column chromatographic purification
Silica gel, EtOAcꢀhexane 1:9) gave thienocarbazole 8a as a colorless solid (0.113 g, 62%);
(
o
1
mp 224ꢀ226 C. HꢀNMR (300 MHz, CDCl
3
): δ 8.68 (s, 1H), 8.32 (d, J = 8.1 Hz, 1H), 8.02
(d, J = 7.5 Hz, 1H), 7.71 (d, J = 7.5 Hz, 2H), 7,45ꢀ7.41 (m, 2H), 7.38ꢀ7.36 (m, 1H), 7.31 (d, J
13
=
7.2 Hz, 2H), 7.21ꢀ7.17 (m, 2H), 2.91 (s, 3H) ppm. CꢀNMR (75 MHz, CDCl ): δ 139.4,
3
139.2, 137.8, 136.7 (2C), 133.7, 129.0, 127.5, 127.3, 126.8, 126.5, 125.5, 124.0, 122.9, 122,7,
121.7, 115.2, 106.1, 17.4 ppm. Deptꢀ135 (75 MHz, CDCl
3
): δ 133.7, 129.0, 126.8, 126.5,
125.5, 124.0, 122.7, 121.7, 115.2, 106.1, 17.4 ppm. HRMS (ESIꢀion trap, MeOH): m/z Calcd
+
+
2 2
for C21H15NO S + Na [M+Na] 400.0442; Found 400.0437.
2,4-Dimethyl-9-(phenylsulfonyl)-9H-thieno[2,3-b]carbazole (8b). The annulation of
pivalate 4 (0.2 g, 0.48 mmol) with 2ꢀmethylthiophene (0.052 g, 0.53 mmol) in the presence of
4
SnCl (0.151 g, 0.58 mmol) adopting the above mentioned procedure followed by column
chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) furnished thieno[b]carbazole 8b
o
1
as a colorless solid (0.144 g, 76%); mp 248ꢀ250 C. HꢀNMR (300 MHz, CDCl
3
): δ 8.54 (s,
1H), 8.30 (d, J = 8.1 Hz, 1H), 7.98 (d, J = 7.8 Hz, 1H), 7.69 (d, J = 7.8 Hz, 2H), 7.38 (t, J =
7
3
1
.8 Hz, 1H), 7.29 (q, J = 8.2 Hz, 2H), 7.20ꢀ7.15 (m, 2H), 7.05 (s, 1H), 2.81 (s, 3H), 2.53 (s,
13
H) ppm. CꢀNMR (75 MHz, CDCl
3
): δ 139.9, 139.3, 139.0, 137.7, 137.3, 136.0, 133.6,
28.9, 127.7, 126.5 (2C), 126.2, 123.9, 122.6, 119.3, 115.1, 105.8, 17.3, 16.4 ppm. Deptꢀ135
): δ 132.7, 127.9, 125.5 (2C), 122.9, 121.6, 118.3, 114.1, 104.7, 16.3, 15.4
(75 MHz, CDCl
ppm. HRMS (ESIꢀion trap, MeOH): m/z Calcd for C H NO S + Na [M+Na] 414.0598;
3
+
+
22
17
2 2
Found 414.0587.
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4-Methyl-9-(phenylsulfonyl)-2-(thiophen-2-yl)-9H-thieno[2,3-b]carbazole
(8c).
The
domino reaction of pivalate 4 (0.2 g, 0.48 mmol) with bithiophene (0.088 g, 0.53 mmol)
using SnCl (0.151 g, 0.58 mmol) adopting the above mentioned procedure followed by
column chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) afforded carbazole 8c as
4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
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0
1
2
3
4
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
o
1
a colorless solid (0.156 g, 70%); mp 252ꢀ254 C. HꢀNMR (300 MHz, CDCl ): δ 8.59 (s,
3
1H), 8.31 (d, J = 8.1 Hz, 1H), 8.02 (d, J = 7.5 Hz, 1H), 7.72 (d, J = 7.8 Hz, 2H), 7.49 (s, 1H),
13
7.44ꢀ7.28 (m, 3H), 7.24ꢀ7.23 (m, 4H), 7.02ꢀ6.99 (m, 1H), 2.90 (s, 3H) ppm. CꢀNMR (75
3
MHz, CDCl ): δ 139.1, 138.8, 137.7, 137.5, 137.3, 136.7, 136.3, 133.8, 129.0, 128.0, 127.4,
127.2, 126.8, 126.5, 125.4, 125.1, 124.1, 123.2, 122.7, 117.5, 115.2, 105.8, 17.4 ppm. Deptꢀ
135 (75 MHz, CDCl ): δ 132.8, 128.0, 127.0, 125.8, 125.5, 124.4, 124.1, 123.1, 121.7, 116.5,
3
+
2 3
114.2, 104.8, 16.4 ppm. HRMS (ESIꢀion trap, MeOH): m/z Calcd for C25H17NO S + Na
+
[
M+Na] 482.0319; Found 482.0310.
6
-Methyl-11-(phenylsulfonyl)-benzo[b]thieno[2,3-b]carbazole
(phenylsulfonyl)-benzo[b]thieno[3,2-b]carbazole (8d/8d’). The domino reaction of pivalate
(0.2 g, 0.48 mmol) with thianaphthene (0.071 g, 0.53 mmol) using SnCl (0.151 g, 0.58
and
11-methyl-7-
4
4
mmol) in DCE (10 mL) at room temperature for 3 h followed by column chromatographic
purification (Silica gel, EtOAcꢀhexane 1:9) led to an inseparable mixture of carbazoles 8d
o
1
and 8d’as a colorless solid (0.153 g, 74%); mp 244ꢀ246 C. HꢀNMR (300 MHz, CDCl
3
): δ
9.02 (s), 8.74 (s), 8.44ꢀ8.40 (m), 8.35ꢀ8.32 (m), 8.21 (d, J = 7.8 Hz), 8.09 (d, J = 7.5 Hz),
7.89ꢀ7.85 (m), 7.81ꢀ7.78 (m), 7.54ꢀ7.44 (m), 7.40 (t, J = 7.5 Hz), 7.31ꢀ7.23 (m), 3.29 (s), 2.94
13
(
s) ppm. CꢀNMR (75 MHz, CDCl
3
): δ 139.8, 139.7, 139.4, 139.0, 137.7, 137.5, 137.2,
136.7, 136.3, 136.1, 134.6, 133.8 (2C), 131.2, 130.3, 129.1, 129.0, 127.4, 127.1, 127.0, 126.9,
126.7, 126.5 (2C), 125.8, 125.0, 124.6, 124.4, 124.3, 124.2, 124.1, 122.9, 122.7, 122.1, 115.3,
1
15.2, 106.2, 105.6, 19.2, 18.4 ppm. Deptꢀ135 (75 MHz, CDCl ): δ 133.9, 133.8, 129.1,
3
129.0, 127.1, 127.0, 126.7, 126.5 (2C), 125.8, 125.0, 124.6, 124.3, 124.2, 124.1, 122.9, 122.7,
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122.1, 115.3, 115.2, 106.2, 105.6, 19.2, 18.4 ppm. HRMS (ESIꢀion trap, MeOH): m/z Calcd
+
+
for C25
H
17NO
2
S
2
+ H [M+H] 428.0779; Found 428.0785.
4-Methyl-1,9-bis(phenylsulfonyl)-1,9-dihydropyrrolo[2,3-b]carbazole (8e). The domino
reaction of pivalate 4 (0.2 g, 0.48 mmol) with Nꢀsulfonyl pyrrole (0.11 g, 0.53 mmol) using
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
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29
30
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
SnCl (0.151 g, 0.58 mmol) adopting the procedure similar to that of 8a followed by workup
4
and column chromatographic purification (Silica gel, EtOAcꢀhexane 2:8) furnished
o
1
pyrolocarbazole 8e as a colorless solid (0.158 g, 65%); mp 258ꢀ260 C. HꢀNMR (300 MHz,
CDCl ): δ 8.78 (s, 1H), 8.34 (d, J = 8.1 Hz, 1H), 7.95 (d, J = 7.5 Hz, 3H), 7.69 (d, J = 7.8 Hz,
H), 7.60 (d, J = 8.4 Hz, 1H), 7.49 (t, J = 7.2 Hz, 1H), 7.43ꢀ7.38 (m, 3H), 7.35ꢀ7.26 (m, 2H),
3
2
1
3
7.21ꢀ7.16 (m, 2H), 6.75 (d, J = 8.4 Hz, 1H), 2.75 (s, 3H) ppm. CꢀNMR (75 MHz, CDCl ): δ
3
1
1
1
39.2, 138.0, 137.7, 136.7, 133.9, 133.7, 129.4, 129.0, 128.2, 127.2, 126.6, 126.5, 126.4,
25.1, 124.0, 122.4, 121.5, 115.1, 107.1, 97.9, 16.6 ppm. Deptꢀ135 (75 MHz, CDCl ): δ
3
33.9, 133.8, 129.4, 129.0, 127.2, 126.6, 126.5, 126.3, 124.0, 122.4, 115.1, 107.2, 97.9, 16.6
+
ppm. HRMS (EI, 70 eV): m/z Calcd for C H N O S [M ] 500.0864; Found 500.0861.
27
20
2
4 2
1
2-Methyl-7-(phenylsulfonyl)-7H-benzofuro[2,3-b]carbazole (8f). The domino reaction of
pivalate 4 (0.2 g, 0.48 mmol) with benzofuran (0.063 g, 0.53 mmol) using SnCl (0.151 g,
.58 mmol) in dry DCE (10 mL) at room temperature followed by workup and column
chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) gave benzofuro[2,3ꢀb]carbazole
4
0
o
1
8f as a colorless solid (0.155 g, 78%); mp 256ꢀ258 C. HꢀNMR (300 MHz, CDCl ): δ 8.50
3
(s, 1H), 8.43 (d, J = 8.4 Hz, 1H), 8.17ꢀ8.14 (m, 2H), 7.83 (d, J = 7.5 Hz, 2H), 7.61 (d, J = 8.1
13
Hz, 1H), 7.49ꢀ7.37 (m, 5H), 7.32ꢀ7.26 (m, 2H), 3.19 (s, 3H) ppm. CꢀNMR (75 MHz,
3
CDCl ): δ 156.9, 155.7, 139.0, 138.2, 137.7, 133.8, 129.0, 128.2, 127.3, 126.5 (2C), 126.2,
124.1, 122.8, 122.3, 122.2, 121.2, 120.6, 115.1, 111.6, 96.3, 17.1 ppm. Deptꢀ135 (75 MHz,
CDCl ): δ 133.9, 129.1, 126.5 (2C), 126.2, 124.1, 122.8, 122.3, 122.2, 115.1, 111.6, 96.3,
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4
4
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5
5
5
5
5
5
5
5
6
+
+
3
17.1 ppm. HRMS (ESIꢀion trap, MeOH): m/z Calcd for C25H17NO S + Na [M+Na]
434.0827; Found 434.0822.
8
-Methyl-13-(phenylsulfonyl)-naphtho[b]thieno[2,3-b]carbazole (8g). The domino
28
reaction of pivalate 4 (0.2 g, 0.48 mmol) with naphtho[b]thiophene (0.089 g, 0.53 mmol)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
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8
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0
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1
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3
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
using SnCl (0.151 g, 0.58 mmol) in 1,2ꢀDCE at room temperature for 7 h followed by
4
column chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) gave carbazole 8g as a
o
1
colorless solid (0.134 g, 58%); mp >300 C. HꢀNMR (300 MHz, DMSOꢀd
.58 (s, 1H), 8.39 (d, J = 8.4 Hz, 1H), 8.31ꢀ8.25 (m, 2H), 8.06ꢀ8.03 (m, 1H), 7.97 (d, J = 7.8
Hz, 2H), 7.68ꢀ7.58 (m, 4H), 7.54ꢀ7.46 (m, 3H), 2.96 (s, 3H) ppm. Due to the solubility
6
): δ 9.16 (s, 2H),
8
13
problem of the carbazole 8g, C NMR could not be recorded. HRMS (EI, 70 eV): m/z Calcd
+
for C29
H
19NO
2
S
2
[M ] 477.0857; Found 477.0850.
2
-(3,5-Di(thiophen-2-yl)phenyl)-4-methyl-9-(phenylsulfonyl)-9H-thieno[2,3-b]carbazole
(
8h). The domino reaction of pivalate 4 (0.2 g, 0.48 mmol) with 1,3,5ꢀtri(thiophenꢀ2ꢀ
yl)benzene (0.172 g, 0.53 mmol) in the presence of SnCl (0.151 g, 0.58 mmol) in 1,2ꢀDCE
4
at room temperature for 5 h followed by work up and column chromatographic purification
(
Silica gel, EtOAcꢀhexane 1:9) afforded carbazole 8h as a colorless solid (0.191 g, 64%); mp
o
1
1
72ꢀ174 C. HꢀNMR (300 MHz, CDCl
7.5 Hz, 1H), 7.86 (s, 2H), 7.82 (d, J = 6.9 Hz, 4H), 7.52 (d, J = 7.8 Hz, 1H), 7.47ꢀ7.44 (m,
3H), 7.42ꢀ7.41 (m, 1H), 7.38 (d, J = 7.8 Hz, 2H), 7.33ꢀ7.28 (m, 2H), 7.17ꢀ7.14 (m, 2H), 3.06
3
): δ 8.75 (s, 1H), 8.41 (d, J = 8.1 Hz, 1H), 8.14 (d, J
=
1
3
(
s, 3H) ppm. CꢀNMR (75 MHz, CDCl ): δ 143.4, 142.3, 139.3, 139.2, 137.7, 137.5, 136.8,
3
1
35.9, 135.7, 133.8, 129.1, 128.2, 127.5 (2C), 126.9, 126.5, 125.6, 124.1 (2C), 123.5, 123.2,
23.1, 122.8, 118.1, 115.2, 106.0, 17.5 ppm. Deptꢀ135 (75 MHz, CDCl ): δ 133.8, 129.1,
1
3
128.2, 126.9, 126.6, 125.6, 124.1 (2C), 123.5, 123.1, 122.8, 118.1, 115.2, 106.0, 17.5 ppm.
+
HRMS (EI, 70 eV): m/z Calcd for C H NO S [M ] 617.0612; Found 617.0610.
35
23
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2-(3,5-Bis(3-methylthiophen-2-yl)phenyl)-3,4-dimethyl-9-(phenylsulfonyl)-9H-
thieno[2,3-b]carbazole (8i). The domino reaction of pivalate 4 (0.2 g, 0.48 mmol) with
4
1,3,5ꢀtris(3ꢀmethylthiophenꢀ2ꢀyl)benzene (0.195 g, 0.53 mmol) using SnCl (0.151 g, 0.58
mmol) in 1,2ꢀDCE at room temperature for 6 h followed by workup and column
10
11
12
13
14
15
16
17
18
19
20
21
22
23
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26
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41
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44
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46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
chromatographic purification (Silica gel, EtOAcꢀhexane 1:9) afforded carbazole 8i as a
o
1
colorless solid (0.214 g, 67%); mp 184ꢀ186 C. HꢀNMR (300 MHz, CDCl
3
): δ 8.60 (s, 1H),
.31 (d, J = 8.1 Hz, 1H), 8.02 (d, J = 7.8 Hz, 1H), 7.70 (d, J = 7.5 Hz, 2H), 7.51ꢀ7.49 (m,
H), 7.38 (t, J = 7.7 Hz, 1H), 7.33ꢀ7.24 (m, 2H), 7.20ꢀ7.15 (m, 4H), 6.88ꢀ7.87 (m, 2H), 3.06
8
3
13
(
s, 3H), 2.67 (s, 3H), 2.34 (s, 6H) ppm. CꢀNMR (75 MHz, CDCl ): δ 139.6, 139.2, 137.7,
3
137.6, 137.0, 136.6, 136.3, 135.5, 135.4, 133.9, 133.7, 131.3, 129.6, 129.3, 129.0, 128.9 (2C),
27.7, 126.7, 126.5, 124.1, 124.0, (2C), 123.2, 115.1, 106.0, 18.2, 17.6, 15.2 ppm. Deptꢀ135
1
(75 MHz, CDCl
3
): δ 133.8, 131.3, 129.3, 129.0, 128.9, 126.7, 126.5, 124.0 (2C), 123.2,
+
115.2, 106.0, 18.2, 17.7, 15.2 ppm. HRMS (EI, 70 eV): m/z Calcd for C38
H29NO
2
S
4
[M ]
659.1081; Found 659.1080.
General procedure for the preparation of benzoylindoles (9a-d). To a solution of aroyl
o
chloride (11.07 mmol) in dry DCM (15 mL) at 0 C, SnCl
4
(2.88 g, 11.07 mmol) was added
2
9
dropwise for 5 min. To this, Nꢀphenylsulfonylꢀ2ꢀmethylindole (2 g, 7.38 mmol) in dry
DCM (10 mL) was added (5 min) and allowed to stir at room temperature. After completion
of the reaction (monitored by TLC), it was poured into iceꢀwater (50 mL) containing Conc.
HCl (10 mL). The organic layer was separated and the aqueous layer was extracted with
DCM (2 x 20 mL). The combined organic layer was washed with water (3 x 25 mL) and
dried (Na
column chromatographic purification (Silica gel, EtOAcꢀhexane) furnished benzoyl indoles
a-d.
2 4
SO ). The subsequent purification of crude product either by MeOH washing or
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(3,4-Dimethoxyphenyl)(2-(2,4-dimethylbenzyl)-1-(phenylsulfonyl)-1H-indol-3-
29
yl)methanone (9a). The FriedelꢀCrafts benzoylation of Nꢀphenylsulfonylꢀ2ꢀmethylindole (2
g, 7.38 mmol) with veratroyl chloride (2.23 g, 11.07 mmol) in the presence of SnCl (2.88 g,
1.07 mmol) in dry DCM (20 mL) adopting the above mentioned procedure followed by
trituration of the crude with MeOH (5 mL) gave veratroylindole 9a as a colorless solid (2.79
4
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
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1
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3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
o
ꢀ1 1
g, 87%); mp 164ꢀ166 C. IR (neat): 1641 (CO), 1378 & 1182 (SO
MHz, CDCl ): δ 8.27 (d, J = 8.4 Hz, 1H), 7.87 (d, J = 7.5 Hz, 2H), 7.61 (t, J = 7.35 Hz, 1H),
.51ꢀ7.45 (m, 3H), 7.36ꢀ7.31 (m, 3H), 7.23ꢀ7.18 (m, 1H), 6.84 (d, J = 8.4 Hz, 1H), 3.95 (s,
2
) cm . HꢀNMR (300
3
7
3
13
H), 3.89 (s, 3H), 2.62 (s, 3H) ppm. CꢀNMR (75 MHz, CDCl ): δ 191.4, 153.6, 149.0,
3
139.7, 138.8, 135.8, 134.1, 131.4, 129.5, 128.3, 126.5, 125.1, 124.7, 123.9, 120.6, 120.6,
3
114.2, 111.2, 110.0, 56.0, 55.9, 14.5 ppm. Deptꢀ135 (75 MHz, CDCl ): δ 133.2, 128.6, 125.5,
124.2, 123.8, 123.0, 119.7, 113.3, 110.3, 109.1, 55.1, 55.0, 13.6 ppm. HRMS (EI, 70 eV):
+
m/z Calcd for C24
H
21NO
5
S [M ] 435.1140; Found 435.1137.
33
(2-Methyl-1-(phenylsulfonyl)-1H-indol-3-yl)(phenyl)methanone (9b). The FriedelꢀCrafts
2
9
reaction of Nꢀphenylsulfonylꢀ2ꢀmethylindole (2 g, 7.38 mmol) with benzoyl chloride (1.56
g, 11.07 mmol) using SnCl (2.88 g, 11.07 mmol) adopting the above mentioned procedure
followed by workup afforded benzoylindole 9b as a colorless solid (2.54 g, 92%); mp 138ꢀ
4
o
33
o
ꢀ1 1
1
40 C (Lit. 130.5ꢀ132 C). IR (neat): 1648 (CO), 1380 & 1184 (SO
2
) cm . HꢀNMR (300
MHz, CDCl ): δ 8.27 (d, J = 8.7 Hz, 1H), 7.87 (d, J = 7.8 Hz, 2H), 7.76 (d, J = 7.2 Hz, 2H),
3
7.62ꢀ7.56 (m, 2H), 7.50ꢀ7.41 (m, 4H), 7.35ꢀ7.25 (m, 2H), 7.21ꢀ7.16 (m, 1H), 2.62 (s, 3H)
13
ppm. CꢀNMR (75 MHz, CDCl
3
): δ 193.0, 141.0, 139.0, 138.9, 136.0, 134.3, 133.2, 129.6
(2C), 128.6, 128.2, 126.6, 124.9, 124.1, 120.7, 120.5, 114.4, 14.6 ppm. Deptꢀ135 (75 MHz,
3
CDCl ): δ 134.3, 133.2, 129.6 (2C), 128.6, 126.6, 124.9, 124.1, 120.7, 114.3, 14.7 ppm.
(2-Methyl-1-(phenylsulfonyl)-1H-indol-3-yl)(4-nitrophenyl)methanone (9c). The Friedelꢀ
29
Crafts benzoylation of Nꢀphenylsulfonylꢀ2ꢀmethylindole (2 g, 7.38 mmol) with 4ꢀ
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nitrobenzoyl chloride (2.06 g, 11.07) using SnCl
4
(2.88 g, 11.07 mmol) in dry DCM (30 mL)
at room temperature for 48 h followed by workup and column chromatographic purification
(Silica gel, EtOAcꢀhexane 2:8) furnished benzoylindole 9c as a colorless solid (1.92 g, 62%);
o
ꢀ1 1
mp 162ꢀ164 C. IR (neat): 1652 (CO), 1526 & 1346 (NO ), 1381 & 1186 (SO ) cm . Hꢀ
2
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
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27
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44
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47
48
49
50
51
52
53
54
55
56
57
58
59
60
NMR (300 MHz, CDCl ): δ 8.30 (d, J = 8.4 Hz, 3H), 7.91 (d, J = 8.1 Hz, 4H), 7.65 (t, J =
3
7.35 Hz, 1H), 7.56ꢀ7.51 (m, 2H), 7.39ꢀ7.35 (m, 1H), 7.24ꢀ7.19 (m, 1H) 2.69 (s, 3H) ppm.
13
CꢀNMR (75 MHz, CDCl
3
): δ 191.0, 150.2, 144.0, 142.7, 138.7, 135.9, 134.5, 130.4, 129.7,
127.4, 126.6, 125.2, 124.4, 123.9, 120.5, 119.3, 114.5, 14.6 ppm. Deptꢀ135 (75 MHz,
CDCl ): δ 134.6, 130.4, 129.7, 126.6, 125.2, 124.4, 123.9, 120.5, 114.5, 14.7 ppm. HRMS
3
+
(EI, 70 eV): m/z Calcd for C H N O S [M ] 420.0780; Found 420.0770.
2
2
16
2
5
(4-Chlorophenyl)(2-methyl-1-(phenylsulfonyl)-1H-indol-3-yl)methanone
(9d).
The
29
FriedelꢀCrafts benzoylation of Nꢀphenylsulfonylꢀ2ꢀmethylindole (2 g, 7.38 mmol) with 4ꢀ
4
chlorobenzoyl chloride (1.94 g, 11.07 mmol) using SnCl (2.88 g, 11.07 mmol) in dry DCM
(30 mL) at room temperature for 24 h followed by workup and column chromatographic
purification (Silica gel, EtOAcꢀhexane 2:8) gave 4ꢀchlorobenzoylindole 9d as a colorless
o
ꢀ1 1
solid (2.30 g, 76%); mp 92ꢀ94 C. IR (neat): 1650 (CO), 1380 & 1186 (SO
2
) cm . HꢀNMR
(
300 MHz, CDCl ): δ 8.30 (d, J = 8.4 Hz, 1H), 7.90 (d, J = 7.5 Hz, 2H), 7.73 (t, J = 8.4 Hz,
3
2H), 7.62 (d, J = 8.4 Hz, 2H), 7.36 (t, J = 7.7 Hz, 1H), 7.29ꢀ7.19 (m, 2H), 2.66 (s, 3H) ppm.
1
3
CꢀNMR (75 MHz, CDCl ): δ 191.6, 141.3, 139.6, 138.8, 137.2, 135.9, 134.4, 131.0, 129.6,
3
129.0, 127.9, 126.6, 125.0, 124.2, 120.6, 120.0, 114.4, 14.6 ppm. Deptꢀ135 (75 MHz,
CDCl
3
): δ 134.4, 131.0, 129.6, 129.0, 126.6, 125.0, 124.2, 120.6, 114.4, 14.6 ppm. HRMS
+
(EI, 70 eV): m/z Calcd for C22
H16ClNO
3
S [M ] 409.0539; Found 409.0535.
General procedure for the preparation of 2-bromomethylindoles (10a-d). To a solution
of Nꢀphenylsulfonylꢀ2ꢀmethylindole 9a-d (1 equiv) and AIBN (0.05 g) in dry CCl (30 mL)
4
freshly recrystallized NBS (1.2 equiv) was added. The reaction mixture was refluxed and
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cooled to room temperature. The floated succinimide was filtered off and washed with carbon
tetrachloride (10 mL). The combined filtrate was concentrated in vacuo to afford bromo
compounds 10a-d.
(2-(Bromomethyl)-1-(phenylsulfonyl)-1H-indol-3-yl)(3,4-dimethoxyphenyl)methanone
0
1
2
3
4
5
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8
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7
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8
9
0
(10a). The benzylic bromination of 2ꢀmethylindole 9a (1.5 g, 3.45) using NBS (0.74 g, 4.14
mmol) and AIBN (0.05 g) adopting the above mentioned procedure followed by workup and
removal of solvent furnished bromo compound 10a as a brown solid (1.61 g, 91%); mp 158ꢀ
o
ꢀ1 1
1
60 C. IR (neat): 1646 (CO), 1378 & 1176 (SO
d, J = 8.7 Hz, 1H), 8.02 (d, J = 7.8 Hz, 2H), 7.64ꢀ7.59 (m, 1H), 7.53ꢀ7.48 (m, 3H), 7.40ꢀ7.30
(m, 2H), 7.24ꢀ7.19 (m, 2H), 6.83 (d, J = 8.4 Hz, 1H), 5.16 (s, 2H), 3.95 (s, 3H), 3.91 (s, 3H)
2 3
) cm . HꢀNMR (300 MHz, CDCl ): δ 8.13
(
13
ppm. CꢀNMR (75 MHz, CDCl
3
): δ 190.6, 154.1, 149.2, 138.4, 138.2, 136.0, 134.4, 130.9,
129.4, 127.8, 127.1, 126.3, 125.7, 124.3, 123.7, 121.6, 114.8, 111.1, 110.1, 56.2, 56.1, 21.7
ppm. Deptꢀ135 (75 MHz, CDCl
3
): δ 134.5, 129.4, 127.1, 126.3, 125.7, 124.3, 121.6, 114.8,
+
111.1, 110.0, 56.2, 56.1, 21.8 ppm. HRMS (EI, 70 eV): m/z Calcd for C H BrNO S [M ]
2
4
20
5
513.0246; Found 513.0244.
33
(2-(Bromomethyl)-1-(phenylsulfonyl)-1H-indol-3-yl)(phenyl)methanone (10b).
The
benzylic bromination of 2ꢀmethylindole 9b (1.5 g, 4.00 mmol) using NBS (0.85 g, 4.8 mmol)
and AIBN (0.05 g) adopting the above mentioned procedure gave bromo compound 10b as a
o
33
o
brown solid (1.71 g, 94%); mp 146ꢀ148 C (Lit. 156ꢀ158 C). IR (neat): 1652 (CO), 1378 &
ꢀ
1 1
1
186 (SO ) cm . HꢀNMR (300 MHz, CDCl ): δ 8.13 (d, J = 8.7 Hz, 1H), 8.03 (d, J = 7.5
2
3
Hz, 2H), 7.78ꢀ7.76 (m, 2H), 7.61 (t, J = 7.7 Hz, 2H), 7.52ꢀ7.42 (m, 4H), 7.39ꢀ7.33 (m, 1H),
1
3
7
.18ꢀ7.08 (m, 2H), 5.21 (s, 2H) ppm. CꢀNMR (75 MHz, CDCl
3
): δ 192.2, 139.3, 138.3,
138.2, 135.9, 134.5, 133.6, 129.6, 129.4, 128.6, 127.4, 127.1, 126.2, 124.3, 123.0, 121.5,
1
14.7, 21.4 ppm. Deptꢀ135 (75 MHz, CDCl ): δ 134.6, 133.7, 129.7, 129.5, 128.7, 127.2,
3
126.3, 124.4, 121.6, 114.8, 21.5 ppm.
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(2-(Bromomethyl)-1-(phenylsulfonyl)-1H-indol-3-yl)(4-nitrophenyl)methanone
(10c).
The benzylic bromination of 2ꢀmethylindole 9c (1.5 g, 3.57 mmol) using NBS (0.76 g, 4.29
mmol) in and AIBN (0.05 g) adopting the above mentioned procedure gave bromo compound
o
1
0c as a colorless solid (1.53 g, 86%); mp 66ꢀ68 C. IR (neat): 1660 (CO), 1526 & 1348
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
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29
30
31
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34
35
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38
39
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47
48
49
50
51
52
53
54
55
56
57
58
59
60
ꢀ
1 1
(NO ) 1379 & 1186 (SO ) cm . HꢀNMR (300 MHz, CDCl ): δ 8.22 (d, J = 8.1 Hz, 2H),
2
2
3
8
.08 (d, J = 8.4 Hz, 1H), 7.98 (d, J = 8.1 Hz, 2H), 7.84 (d, J = 8.4 Hz, 2H), 7.60ꢀ7.55 (m,
H), 7.45 (t, J = 7.35 Hz, 2H), 7.30 (t, J = 7.8 Hz, 1H), 7.11ꢀ7.06 (m, 1H), 6.88 (d, J = 8.1
1
1
3
Hz, 1H), 5.17 (s, 2H) ppm. CꢀNMR (75 MHz, CDCl
3
): δ 190.6, 150.5, 143.2, 140.9, 138.1,
1
35.9, 134.8, 130.5, 129.6, 127.3, 126.7, 126.6, 124.7, 124.0, 123.9, 121.2, 115.0, 21.0 ppm.
Deptꢀ135 (75 MHz, CDCl ): δ 134.8, 130.5, 129.6, 127.3, 126.6, 124.7, 123.9, 121.2, 115.0,
3
+
2
1.0 ppm. HRMS (EI, 70 eV): m/z Calcd for C22
97.9881.
H
15BrN
2
O
5
S [M ] 497.9885; Found
4
(
2-(Bromomethyl)-1-(phenylsulfonyl)-1H-indol-3-yl)(4-chlorophenyl)methanone (10d).
The benzylic bromination of 2ꢀmethylindole 9d (1.5 g, 7.32 mmol) using NBS (0.78 g, 4.39
mmol) and AIBN (0.05 g) following the above mentioned procedure furnished bromo
o
compound 10d as a colorless solid (1.65 g, 92%); mp 132ꢀ134 C. IR (neat): 1652 (CO) 1378
ꢀ1 1
&
1186 (SO
2 3
) cm . HꢀNMR (300 MHz, CDCl ): δ 8.16 (d, J = 8.4 Hz, 1H), 8.09ꢀ8.05 (m,
2
H), 7.74 (d, J = 8.4 Hz, 2H), 7.66ꢀ7.60 (m, 1H), 7.54ꢀ7.49 (m, 2H), 7.45ꢀ7.36 (m, 3H), 7.18
13
(t, J = 8 Hz, 1H), 7.11ꢀ7.09 (m, 1H), 5.24 (s, 2H) ppm. CꢀNMR (75 MHz, CDCl ): δ 190.9,
3
1
1
1
40.2, 139.6, 138.3, 136.5, 135.9, 134.6, 131.1, 129.5, 129.1, 127.2, 126.4, 124.5, 122.4,
21.4, 114.9, 21.3 ppm. Deptꢀ135 (75 MHz, CDCl ): δ 134.6, 131.1, 129.5, 129.1, 127.2,
26.4, 124.5, 121.4, 114.8, 21.3 ppm. Elemental Analysis Calcd for C22 15BrClNO S: C,
3
H
3
54.06; H, 3.09; Br, 16.35; Cl, 7.25; N, 2.87; O, 9.82; S, 6.56: Found C, 53.94; H, 3.16; N,
+
2
.69; O, 9.68; S, 6.37. HRMS (EI, 70 eV): m/z Calcd for C H BrClNO S [M ] 486.9645;
22
15
3
Found 486.9640.
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General procedure for the preparation of pivaloyloxyindoles (11a-d). To a stirred
solution of 2ꢀbromomethylindoles 10a-d (1 equiv) in dry THF (30 mL), potassium carbonate
(3 equiv) and pivalic acid (2 equiv) were added. The reaction mixture was allowed to stir at
room temperature until the reaction was completed (TLC). Then, the usual work up adopting
0
1
2
3
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8
9
0
1
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8
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8
9
0
the above mentioned procedure 4 furnished pivalates 11a-d.
(3-(3,4-Dimethoxybenzoyl)-1-(phenylsulfonyl)-1H-indol-2-yl)methyl pivalate (11a). The
pivaloylation of 2ꢀbromomethylindole 10a (1.5 g, 2.92 mmol) using pivalic acid (0.60 g, 5.84
mmol) and potassium carbonate (1.21 g, 8.75 mmol) adopting the above mentioned
procedure followed by workup and trituration of crude product with MeOH (5 mL) gave
o
pivalate 11a as a colorless solid (1.40 g, 90%); mp 148ꢀ150 C. IR (neat): 1728 (ester), 1646
ꢀ
1 1
(
CO), 1380 & 1178 (SO
d, J = 7.8 Hz, 2H), 7.53ꢀ7.46 (m, 2H), 7.42ꢀ7.36 (m, 2H), 7.33ꢀ7.28 (m, 2H), 7.26ꢀ7.23 (m,
H), 7.19ꢀ7.13 (m, 1H), 6.73 (d, J = 8.4 Hz, 1H), 5.33 (s, 2H), 3.86 (s, 3H), 3.84 (s, 3H), 1.08
2 3
) cm . HꢀNMR (300 MHz, CDCl ): δ 8.09 (d, J = 8.4 Hz, 1H), 7.81
(
1
1
3
(s, 9H) ppm. CꢀNMR (75 MHz, CDCl ): δ 190.5, 177.5, 154.1, 149.3, 138.6, 136.1, 135.2,
3
1
5
1
34.3, 131.1, 129.5, 127.9, 126.6, 126.2, 125.8, 124.7, 124.3, 121.4, 114.7, 110.1, 109.9,
7.0, 56.1 (2C), 38.8, 27.1 ppm. Deptꢀ135 (75 MHz, CDCl ): δ 134.3, 129.5, 126.6, 126.2,
25.8, 124.3, 121.4, 114.7, 110.9, 109.9, 57.0, 56.1 (2C), 27.1 ppm. Elemental Analysis
3
Calcd for C29
S, 5.76.
7
H29NO S; C, 65.03; H, 5.46; N, 2.62; S, 5.99; Found C, 64.86; H, 5.28; N, 2.48;
(3-Benzoyl-1-(phenylsulfonyl)-1H-indol-2-yl)methyl pivalate (11b). The pivaloylation of
2ꢀbromomethylindole 10b (1.5 g, 3.30 mmol) using pivalic acid (0.67 g, 6.61 mmol) and
potassium carbonate (1.36 g, 9.91 mmol) adopting the above mentioned procedure followed
by workup and trituration of crude product with MeOH (5 mL) afforded pivalate 11b as a
o
colorless solid (1.44 g, 92%); mp 134ꢀ136 C. IR (neat): 1730 (ester), 1654 (CO), 1380 &
ꢀ1
1
1
184 (SO ) cm . HꢀNMR (300 MHz, CDCl ): δ 8.18 (d, J = 8.4 Hz, 1H), 7.89 (d, J = 7.8
2
3
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Page 29 of 52
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
Hz, 2H), 7.82 (d, J = 7.8 Hz, 2H), 7.63ꢀ7.56 (m, 2H), 7.49ꢀ7.42 (m, 4H), 7.38 (d, J = 8.1 Hz,
1
3
2
1
1
3
H), 7.24 (d, J = 8.4 Hz, 1H), 5.40 (s, 2H), 1.15 (s, 9H) ppm. CꢀNMR (75 MHz, CDCl ): δ
92.1, 177.4, 138.6, 138.3, 136.2, 136.1, 134.3, 133.7, 129.7, 129.5, 128.6, 127.7, 126.6,
26.3, 124.4, 124.3, 121.4, 114.7, 56.8, 38.8, 27.1 ppm. Deptꢀ135 (75 MHz, CDCl ): δ 134.4,
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
133.7, 129.7, 129.6, 128.7, 126.7, 126.3, 124.4, 121.5, 114.7, 56.8, 27.1 ppm. Elemental
Analysis Calcd for C27 S; C, 68.19; H, 5.30; N, 2.95; S, 6.74; Found C, 68.02; H,
.39; N, 2.72; S, 6.57.
3-(4-Nitrobenzoyl)-1-(phenylsulfonyl)-1H-indol-2-yl)methyl The
H25NO
5
5
(
pivalate
(11c).
pivaloylation of 2ꢀbromomethylindole 10c (1.5 g, 3.01 mmol) using pivalic acid (0.61 g, 6.01
mmol) and potassium carbonate (1.24 g, 9.02 mmol) adopting the above mentioned
procedure followed by column chromatographic purification (Silica gel, EtOAcꢀhexane 2:8)
o
afforded pivaloyloxyindole 11c as a brown solid ( 1.22 g, 78%); mp 118ꢀ120 C. IR (neat):
ꢀ1 1
1
2 2
730 (ester), 1662 (CO), 1528 &1348 (NO ), 1382 & 1185 (SO ) cm . HꢀNMR (300 MHz,
CDCl ): δ 8.22 (d, J = 8.7 Hz, 2H), 8.12 (d, J = 8.4 Hz, 1H), 7.89 (d, J = 8.7 Hz, 2H), 7.85 (d,
3
J = 7.8 Hz, 2H), 7.55 (t, J = 7.4 Hz, 1H), 7.45ꢀ7.40 (m, 2H), 7.37ꢀ7.32 (m, 1H), 7.19ꢀ7.16 (m,
13
2
1
1
H), 5.37 (s, 2H), 1.07 (s, 9H) ppm. CꢀNMR (75 MHz, CDCl
3
): δ 190.3, 177.5, 150.5,
43.1, 138.4, 137.5, 136.1, 134.6, 130.6, 129.7, 127.0, 126.7, 126.6, 124.7, 123.8, 123.0,
21.2, 114.9, 56.4, 38.8, 27.1 ppm. Deptꢀ135 (75 MHz, CDCl ): δ 134.6, 130.6, 129.7, 126.8,
3
126.6, 124.7, 123.8, 121.2, 114.9, 56.4, 27.1 ppm. Elemental Analysis Calcd for
C H N O S: C, 62.30; H, 4.65; N, 5.38; S, 6.16: Found C, 62.14; H, 4.42; N, 5.24; S, 6.04.
27
24
2
7
(3-(4-Chlorobenzoyl)-1-(phenylsulfonyl)-1H-indol-2-yl)methyl pivalate (11d). The
pivaloylation of 2ꢀbromomethylindole 10d (1.5 g, 3.07 mmol) using pivalic acid (0.63 g, 6.13
mmol) and potassium carbonate (1.27 g, 9.20 mmol) adopting the aboveꢀmentioned
procedure by work up and trituration of crude product with MeOH (5 mL) afforded pivalate
o
1
1d as a colorless solid (1.29 g, 83%); mp 138ꢀ140 C. IR (neat): 1730 (ester), 1654 (CO),
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