Synthesis of Annulated Carbazoles via FeCl 3/SnCl 4- Mediated Domino Reaction of Vinyl Ketone Tethered Bromomethylindoles with Arenes and Heteroarenes

SYNTHESIS

0

3

9

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7

8

1

4

3

7

-

2

1

0

X

Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart

2021, 53, A–O

paper

A

en

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

Synthesis of Annulated Carbazoles via FeCl₃/SnCl₄-Mediated

Domino Reaction of Vinyl Ketone Tethered Bromomethylindoles

with Arenes and Heteroarenes

Velu Saravanan

COCH₃

(Het)ArH

Lewis acid

Arasambattu K. Mohanakrishnan*

0

-0

0

2

-

3

7

5

8

-

4

5

7

8

(Het)Ar

rt or reflux

N

Department of Organic Chemistry, University of Madras,

Guindy Campus, Chennai 600 025, Tamil Nadu, India

mohan_67@hotmail.com

Br

N

35 examples

42–84%

SO₂Ph

mohanakrishnan@unom.ac.in

ADeMreapasaiaClrmotmmrbroaeehntsatptunooaKnfk.dOrMiirnsgohgahnnAaiuncta@hCkohurrneismohmnisa.tanrcy.,inUniversity of Madras, Guindy Campus, Chennai 600 025, Tamil Nadu, India

Received: 12.01.2021

Accepted after revision: 10.02.2021

Published online: 10.02.2021

arenes as well as heteroarenes followed by intramolecular

cyclization and aromatization. After these reports, synthe-

sis of various types of benzannulated carbazoles are real-

ized through umpolung strategy, that is, by reacting a nuc-

leophilic indole unit with electrophilic bidentate benzene

counter parts⁸(Scheme 1b).

DOI: 10.1055/a-1387-9479; Art ID: ss-2021-t0014-op

Abstract One-pot synthesis of aryl- as well as heteroaryl-annulated

carbazoles was achieved from 2/3-bromomethylindoles involving Lewis

acid mediated domino reaction with arenes as well as heteroarenes via

successive Friedel–Crafts intermolecular as well as intramolecular alkyla-

tions followed by elimination of acetone. Further, the bis-domino reac-

tion of 2,5-bis(bromomethyl)pyrrole was also carried out with selected

heteroarenes. Additionally, the synthesized thienocarbazoles and thieno-

dibenzofurans were successfully utilized for a second-generation domi-

no reaction.

CO₂Et

(Het)ArH

EtO₂C

OAc

(Het)ArH

(Het)Ar

1a

Lewis acid

Br

SO₂Ph

Br

N

SO₂Ph

CO₂Et

CHO

R³

Key words carbazole, indole, pyrrole, Friedel–Crafts alkylation,

Michael addition

Ph

CHO

1b

X

CH(OEt)₂

OH

X

R²

Carbazole and its derivatives constitute an important

class of bio-active natural products.¹Substituted and annu-

lated carbazole derivatives are an important class of anti-

cancer agents that have been increased significantly in the

past few decades.²Recent interest on aryl- and heteroaryl-

fused carbazoles are due to their potent biological activities

and also to their wide applications in materials science.^3,4In

addition, the annulated carbazole derivatives are also wide-

ly applied in optical devices owing to their photorefractive,

hole transporting, and light-emitting properties.⁵

Our first report on the syntheses of aryl- and hetero-

aryl-annulated carbazoles employed a ZnBr₂-mediated

domino reaction of N-protected 2/3-bromomethylindoles

containing malonylidene unit with arenes as well as hetero-

arenes.⁶Later on, the methodology could be successfully

extended with diacetoxymethine-tethered bromomethylin-

doles to afford the cyclo[b]annulated carbazoles⁷(Scheme

1a). In these methods, we have exploited the respective N-

Ph

X = NH, N-PG

Ph

Scheme 1 Summary of recent annulated carbazole syntheses from in-

doles

Recently, we also achieved a straightforward synthesis

of annulated cyclo[b]carbazoles involving the SnCl₄-mediat-

ed one-pot arylation, cyclization, and aromatization reac-

tion sequence from 3-acetyl/aroyl-2-pivaloyloxymethyl-

indoles.⁹The main drawbacks of our methodologies are

moderate reactivity of the malonylidene-tethered bromo-

methylindoles and the stability as well as arylation selectiv-

ity associated with the bromomethylindoles containing ac-

etoxymethine unit.

In a further continuation of our studies on the domino

reaction, we wish to extend the synthesis of highly -conju-

gated heteroacenes by modifying the leaving group for in-

creasing the yield of the products. Initially, when we tested

the reaction of 3-bromomethylindole 1¹⁰containing a vinyl

ester unit with benzene/veratrole in the presence of 20

phenylsulfonyl 2/3-bromomethylindoles containing

masked aldehyde unit as an electrophilic bidentate synthon

undergoing successive arylation with a wide variety of

a

Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

mol% FeCl₃in 1,2-dichloroethane (1,2-DCE) at reflux it fur-

nished the respective 2-benzylindoles 2a and 2b in moder-

ate yields. Under these reaction conditions, the benzylated

indoles failed to undergo any further cyclization to produce

the expected carbazole 3a/3b (Scheme 2).

Table 1 Catalytic Efficiency of Lewis Acids as a Catalyst in the Domino

Reaction of 3-Bromomethylindole 4 with Veratrole

Entry

LA (20 mol%)^a

Time (h)

Yield (%)^b

1

2

ZnBr₂

24

8

10

54

56

62

69

67

0^c

ZnCl₂

R¹

benzene/

Br

3

BF₃·OEt₂

SnCl₄

R¹

veratrole

R¹

CO₂Et

4

FeCl₃, 1,2-DCE

reflux, 12 h

N

CO₂Et

N

SO₂Ph

5

Zn(OTf)₂

FeCl₃

6

SO₂Ph

2a R¹= H (54%)

2b R¹= OCH₃(58%)

1

3a R¹= H (0%)

3b R¹= OCH₃(0%)

6

4

7

InCl₃

8

OCH₃

veratrole

FeCl₃(20 mol%)

Br

8

InBr₃

8

COCH₃

1,2-DCE, reflux

69%

9

Sc(OTf)₃

Yb(OTf)₃

24

N

SO₂Ph

10

0^c

SO₂Ph

4

3b

^aSynthesis of dimethoxybenzo[b]carbazole 3b was accomplished using 3-

bromomethylindole 4 (1 equiv), veratrole (1.1 equiv), and Lewis acid (LA;

0.2 equiv) in 1,2-DCE at reflux.

Scheme 2 Reaction of 3-bromomethylindole 1 with benzene/veratrole

^bIsolated yield of 3b after column chromatography.

^cUnreacted bromomethylindole 4.

It has been observed that an intermolecular Michael ad-

dition of cinnamic ester with veratrole could be successfully

performed using an excess of FeCl₃.¹¹However, the ob-

served intramolecular Michael addition failure in the case

of 2a/2b even with excess of FeCl₃might be due to the less

reactivity of vinyl ester. Hence, we planned to change the

aldehyde masking unit from vinyl ester into more reactive

methyl vinyl ketone. As expected, the reaction of bromo-

methylindole 4¹⁰with veratrole in the presence of FeCl₃led

to the isolation of annulated carbazole 3b in 69% yield

(Scheme 2).

curring with phenyl ring. The mechanism of formation of

carbazoles 3c–h from 4 is depicted in Scheme 3. The tenta-

tive mechanistic visualization for the formation of carba-

zole has been explained (Scheme 3). The initially formed

arylmethylindoles 6a underwent FeCl₃-catalyzed intramo-

lecular Friedel–Crafts alkylation at the -position of methyl

vinyl ketone (MVK) unit followed by aromatization to afford

ArH

Br

FeCl₃(20 mol%)

Ar

Next, we initiated our study to understand the effect of

Lewis acids on the observed domino reaction. The domino

reaction of 3-bromomethylindole 4 in the presence of ZnBr₂

and ZnCl₂in 1,2-DCE at reflux afforded annulated carbazole

in a very low yield. Further prolonging the reaction by re-

fluxing for 24 hours also did not increase the yield (Table 1,

entries 1, 2). Similarly, the cascade reaction of bromome-

thylindole 4 with veratrole using BF₃·OEt₂, SnCl₄, Zn(OTf)₂,

InBr₃, and InCl₃gave aza-tetracene 3b in 54%, 56%, 62%, 69%

and 67% yield, respectively (entries 3–5, 7, 8). The use

Sc(OTf)₃and Yb(OTf)₃did not give the annulated product, it

failed to induce even the initial veratrylation, only the start-

ing material 4 could be recovered unchanged (entries 9, 10).

Adopting the standard procedure, next, we extended the

scope of the reaction with different arenes. The domino re-

action of 3-bromomethylindole 4 with xylenes and benzo-

dioxole using 20 mol% FeCl₃afforded the corresponding an-

nulated carbazoles 3c–f in 64–70% yields (Scheme 3). Simi-

larly, the synthesis of naphtho[b]carbazoles 3g,h has also

been achieved in 74% and 76% yields. However, the reaction

of bromomethylindole 4 with benzene produced only the

3-benzylindole 5. Obviously, the subsequent FeCl₃-cata-

lyzed intramolecular Friedel–Crafts alkylation of 5 is not oc-

COCH₃

1,2-DCE, reflux

N

64–76%

SO₂Ph

3c–h

4

R⁴

O

R³

R²

O

R¹

N

R¹

SO₂Ph

3f (70%)

N

SO₂Ph

3c R¹, R⁴= H; R², R³= CH₃(67%)

3d R¹, R³= H; R², R⁴= CH₃(68%)

3e R¹, R⁴= CH₃; R², R³= H (64%)

3g R¹= H (74%)

3h R¹= CH₃(76%)

Ph

CH₃

N

O

SO₂Ph

5 (68%)

Ar

FeCl₃

4

N

H

– HBr

SO₂Ph

6a

6b

O

FeCl₃

H

Ar

3c–h

– CH₃COCH₃

– FeCl₃

N

SO₂Ph

6c

O

Cl₃Fe

Scheme 3 Synthesis of benzo[b]annulated carbazoles 3c–h and 3-ben-

zylindole 5

C

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

intermediate dihydrocrbazoles 6c. The dihydrocrbazoles 6c

upon aromatization via FeCl₃-induced elimination of ace-

tone unit¹²lead to the carbazoles 3c–h.

with benzo[b]thiophene led to an inseparable mixture of

carbazoles 7d and 7d′ (1:0.4 ratio based on ¹H NMR) in 78%

yield. The structures of the carbazoles 7d and 7d′ were as-

signed based on our earlier report.^6b

Next, the reaction of bromomethylindole 4 with het-

eroarene, bithiophene using 20 mol% FeCl₃at reflux pro-

duced the annulated carbazole 7a only in 30% yield (Table 2,

entry 1). However, the annulation of the bromomethylin-

dole 4 using 20 mol% of ZnBr₂, FeCl₃, BF₃·OEt₂, Zn(OTf)₂, In-

Br₃, and InCl₃in 1,2-DCE at room temperature led to the iso-

lation of the thieno[b]carbazole 7a in 48%, 46%, 64%, 68%,

70% and 68% yield, respectively (entries 2–5, 8, 9). The reac-

tion of 4 with bithiophene in the presence of Lewis acids

such as Sc(OTf)₃and Yb(OTf)₃failed to produce the annulat-

ed product 7a (entries 10, 11). Among the various Lewis ac-

ids employed, the use of 20 mol% of SnCl₄in 1,2-DCE at

room temperature afforded annulated product 7a in a com-

paratively better yield (entry 7). Thus, the above-men-

tioned results clearly indicate that the thiophene/bithio-

phene in the presence of Lewis acids at a refluxing condi-

tion of 1,2-DCE may induce an unwanted self-

polymerization (entry 1). Hence, the Lewis acids could be

used as a suitable catalyst for domino reaction of the bro-

momethylindole 4 with bithiophene only at room tempera-

ture.

Het-ArH

SnCl₄(20 mol%)

Br

Het-Ar

COCH₃

1,2-DCE, rt

N

SO₂Ph

62–84%

SO₂Ph

7b–k

4

R¹

S

N

S

N

SO₂Ph

7b R¹= H (65%)

R¹

SO₂Ph

7d/7d' (78%)

SO₂Ph

X

7c R¹= CH₃(76%)

X

O

R¹

N

R¹

N

X

SO₂Ph

7f X = S, R¹

7g X = S, R¹= CH₃(71%)

7e (84%)

SO₂Ph

S

= H (67%)

S

N

PhO₂S

7h (69%)

N

SO₂Ph

N

7i (70%)

N

SO₂Ph

C₆H₁₃

SO₂Ph

7j (63%)

7k (62%)

Table 2 Effect of Different Lewis Acids on the Domino Reaction of 3-

Bromomethylindole 4 with Bithiophene

Scheme 4 Synthesis of hetero-annulated carbazoles 7b–k

Entry

LA (20 mol%)^a

Time (h)

Yield (%)^b

Annulation of 2-bromomethylindole 4 with benzo[b]-

furan produced the expected benzofuranocarbazole 7e in

84% yield.¹³To our delight, the reaction of bromomethylin-

dole 4 with trithienylbenzenes using SnCl₄at room tem-

perature led to the isolation of the corresponding mono-an-

nulated thienocarbazole 7f as well as 7g in 67% and 71%

yield, respectively. Further domino reaction of bromome-

thylindole 4 with thiophene-, indole-, and pyrrole-based

heteroarenes led to the formation of corresponding annu-

lated carbazoles 7h–k in 62–70% yields (Scheme 4).¹⁴

To understand the role of leaving group, the annulation

of 3-bromomethylindole bearing phenyl vinyl ketone (PVK)

was planned. Accordingly, Wittig reaction of the 1-phenyl-

sulfonyl-2-methylindole-3-carboxaldehyde^6bwith (benzo-

ylmethylene)triphenylphosphorane followed by benzylic

bromination afforded the required bromo compound 8.

Next, the annulation of the bromo compound 8 with 1,2-di-

methoxybenzene and naphthalene using 20 mol% FeCl₃in

1,2-DCE at reflux gave the corresponding annulated carba-

zoles 3b and 3g in 65% and 77% yield, respectively (Scheme

5). The domino reaction of the bromo compound 8 with he-

teroarenes, bithiophene and 2-methylthiophene, in 1,2-

DCE at room temperature furnished the corresponding

known annulated heterocycles 7a and 7c in 74% and 70%

yield, respectively. Similarly, the annulation of the bromo

compound 8 with benzo[b]furan using 20 mol% SnCl₄in

1,2-DCE afforded the benzofuranocarbazole 7e in a good

c

1

2

FeCl₃

0.5

6

30

36

48

64

68

64

72

70

68

0^d

ZnCl₂

3

ZnBr₂

4

FeCl₃

6

5

Zn(OTf)₂

BF₃·OEt₂

SnCl₄

3

6

7

3

8

InCl₃

6

9

InBr₃

6

10

11

Sc(OTf)₃

Yb(OTf)₃

24

0^d

^aAnnulation of 3-bromomethylindole 4 (1 equiv) with bithiophene (1.1

equiv) using Lewis acid (20 mol%) in 1,2-DCE at rt.

^bIsolated yield of 7a after column chromatography.

^cReaction was carried at reflux.

^dUnreacted bromomethylindole 4.

By adopting the established conditions, syntheses of

distinctively substituted hetero-annulated carbazoles were

achieved (Scheme 4). The cascade reaction of 3-bromo-

methylindole 4 with 2-methylthiophene as well as thiophene

using SnCl₄at room temperature furnished the correspond-

ing thienocarbazoles 7b,c in 65% and 76% yield, respective-

ly. Ambiguously, the annulation of bromomethylindole 4

D

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

yield. Comparatively, the domino reaction of the 3-bro-

momethylindoles 4 and 8 containing MVK as well as PVK

produced the annulated carbazoles in almost comparable

yields. Hence, it may be concluded that the leaving group

(acetone/acetophenone) is not having any significant role

on the yields of the domino reaction (Scheme 5).

structures of the representative annulated carbazoles 3g

and 10j were confirmed by single crystal X-ray analyses

(Figure 1 and Figure 2).¹⁵

(Het)ArH

FeCl₃/SnCl₄

COCH₃

(20 mol%)

(Het)Ar

Br

1,2-DCE, reflux or rt

N

59–76%

(Het)ArH

SO₂Ph

9

FeCl₃/SnCl₄

(20 mol%)

R¹

Br

(Het)Ar

O

R⁴

R³

R²

COPh

1,2-DCE

reflux or rt

65–77%

N

O

SO₂Ph

N

8

3b,h, 7a,c,h

SO₂Ph

N

R¹

10b R¹= H (62%)

10c R¹= CH₃(65%

3f (63%)

SO₂Ph

OCH₃

3b R¹, R⁴= H; R², R³= OCH₃(62%)

3c R¹, R⁴= H; R², R³= CH₃(61%)

3e R¹, R⁴= CH₃; R², R³= H (59%)

10a R¹, R³= CH₃; R², R⁴= H (64%)

S

OCH₃

+

N

S

SO₂Ph

R¹

7d'/7d (67%)

3g (77%)

3b (65%)

C₆H₁₃

N

S

O

S

R¹

N

SO₂Ph

10d R¹= H (61%)

10e R¹= CH₃(72%)

10f R¹= thienyl (65%)

N

O

N

SO₂Ph

7a R¹= thienyl (74%)

7c R¹= CH₃(70%)

10g (76%)

7e (76%)

10h (65%)

S

Scheme 5 Annulation of phenyl vinyl ketone-tethered 3-bromome-

thylindole 8. Reagents and conditions: The reaction of 8 with arenes

(ArH) was performed using 20 mol% of FeCl₃in 1,2-DCE at reflux. The

reaction of 8 with heteroarenes (Het-ArH) was performed using 20

mol% of SnCl₄in 1,2-DCE at rt.

C₆H₁₃

N

S

11

C₆H₁₃

N

S

10j (63%)

N

SO₂Ph

10i (63%)

With a working catalytic system, next, we investigated

the domino reaction of isomeric 2-bromomethylindole 9¹⁰

with arenes and heteroarenes. As expected, the domino re-

action of the 2-bromomethylindole 9 with 1,2-dimethoxy-

benzne and xylenes in 1,2-DCE at reflux furnished the cor-

responding annulated carbazoles 3b,c, 10a, and 3e in 59–

64% yields (Scheme 6). Similarly, the annulation of 2-bro-

momethylindole 9 with 1,3-benzoxazole and naphthalenes

also produced the respective carbazoles 3f and 10b,c in 62–

65% yields. As observed for isomeric 3-bromomethylindole

4, 2-bromomethylindole 9 also reacts with thiophenes in

the presence of 20 mol% SnCl₄at room temperature to af-

ford thieno[b]carbazoles 10d–f in 61–72% yields (Scheme

6). Similar to the case of 3-bromomethylindole 4, the cas-

cade reaction of 2-bromomethylindole 9 with benzothio-

phene gave only an inseparable mixture of carbazoles 7d′

and 7d (1:0.4 ratio based on ¹H NMR) in 67% yield. The tan-

dem annulation of 2-bromomethylindole 9 could be suc-

cessfully performed with benzofuran, N-hexylindole, and

1,3,5-trithienylbenzene to give the corresponding annulat-

ed carbazoles 10g–i in 65–76% yields. Surprisingly, the an-

nulation of 2-bromomethylindole 9 with thienocarbazole

11 using SnCl₄at room temperature furnished the bent

heptacene 10j as an exclusive product in 63% yield (Scheme

6). Obviously, the preferential indolylmethylation at the

carbazole 6-position of 11 is favored by the combined elec-

tronic influence of thiophene as well as carbazole units. The

Scheme 6 Domino reaction of 2-bromomethylindole 9 with arenes

and heteroarenes. Reagents and conditions: The reaction of 9 with

arenes (ArH) was performed using 20 mol% of FeCl₃in 1,2-DCE at

reflux. The reaction of 9 with heteroarenes (Het-ArH) was performed

using 20 mol% of SnCl₄in 1,2-DCE at rt.

Figure 1 Molecular structure of carbazole 3g in the crystal (triclininc, p1):

ORTEP plot showing thermal ellipsoids at the 50% probability level.¹⁵

E

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

O

Ph

Het-ArH

SnCl₄(40 mol%)

Ph

Het-Ar

Br

1,2-DCE, rt

N

SO₂Ph

15a–c

14

S

N

SO₂Ph

15a (67%)

C₆H₁₃

N

C₆H₁₃

N

O

Figure 2 Molecular structure of carbazole 10j in the crystal (triclininc,

p1): ORTEP plot showing thermal ellipsoids at the 50% probability lev-

el.¹⁵

N

SO₂Ph

15c (62%)

SO₂Ph

15b (71%)

Scheme 8 Synthesis of C₂-symmetric heterocycles 15a–c

Further, as a representative case, the domino reaction of

3-bromomethylthiophene 12 containing a phenyl vinyl ke-

tone unit with benzofuran using 20 mol% of SnCl₄at room

temperature for 6 hours gave thienodibenzofuran 13 in 42%

yield (Scheme 7).

S

N

S

Br

SO₂Ph

N

O

C₆H₁₃

16

COCH₃

Ph

SnCl₄(20 mol%)

1,2-DCE, rt

4 h

N

O

benzofuran

N

SO₂Ph

S

SnCl₄(20 mol%)

C₆H₁₃

17a (68%)

4

S

1,2-DCE, rt

3 h

Br

13 (42%)

12

O

Scheme 7 Synthesis of thienodibenzofuran 13

O

13

4

S

SnCl₄(20 mol%)

1,2-DCE, rt

4 h

N

S

SO₂Ph

+

To further extend the scope of the reaction, the synthe-

sis of C₂-symmetric carbazoles was investigated. Due to the

difficulty associated with the separation of MVK analogue

of 1-phenylsulfonyl-2,5-dimethylpyrrole 3,4-dicarboxalde-

hyde from triphenylphosphene oxide, a phenyl vinyl ketone

tethered 2,5-bis(bromomethyl)pyrrole 14 was prepared

from pyrrole 3,4-dialdehyde⁹via Wittig reaction with (ben-

zoylmethylene)triphenylphosphorane at reflux in toluene

followed by benzylic bromination. To our delight, the domi-

no reaction of bis(bromomethyl)pyrrole 14 with 2-meth-

ylthiophene, benzofuran, and N-hexylindole using 40 mol%

of SnCl₄at room temperature produced the symmetric

thienocarbazole, benzofuranocarbazole, and indolocarba-

zole 15a–c in 67%, 71% and 62% yield, respectively (Scheme

8).

O

N

SO₂Ph

17b/17b' (62%)

Scheme 9 Second-generation domino reaction

In summary, we have developed a simple annulation

protocol for 2/3-(bromomethyl)indoles containing methyl

vinyl ketone unit at the adjacent position. The observed an-

nulation was initiated by a Lewis acid mediated aryla-

tion/heteroarylation at the bromomethyl carbon followed

by an intramolecular Michael addition and subsequent aro-

matization via an elimination of acetone unit. The present

protocol employing bromomethylindole containing masked

aldehyde unit as an electrophilic bidentate synthon fur-

nished a wide variety of aryl- as well as heteroaryl-annulat-

ed benzo[b]carbazoles in good yields. Compared to the ex-

isting methods wherein indole is used as nucleophilic

counter parts,⁸our method is more advantageous since the

domino reaction could be successfully performed with dif-

ferent types of arenes as well as heteroarenes to furnish

structurally diverse type of annulated carbazoles.

Finally, a second-generation domino reaction was car-

ried out utilizing the synthesized annulated carbazole 13

and 16 (Scheme 9). Serendipitously, the cascade reaction of

3-bromomethylindole 4 with thienocarbazole 16 (prepared

from carbazole 7b via desulfonation and N-hexylation) us-

ing SnCl₄afforded the linear heptacene 17a as an exclusive

product in 68% yield. It is obvious that on the contrary to

thienocarbazole 11, in the case of isomeric thioenocarba-

zole 13, the nucleophilicity is enriched at the thiophene 2-

position favoring the formation of the linear heptacene 17a.

However, the domino reaction of bromomethyindole 4 with

thienodibenzofuran 13 furnished only an inseparable mix-

All melting points were uncorrected. Solvents were dried by standard

procedures. All the experiments carried out under N₂atmosphere,

unless otherwise stated. The progression of all the reaction was mon-

itored by TLC using hexanes/EtOAc mixture. Column chromatography

was carried out on silica gel (230–400 mesh, Merck) by increasing po-

larity. ¹H, ¹³C and DEPT spectra were recorded in CDCl₃using TMS as

1

ture of isomers 17b and 17b′ (1:1 ration based on H NMR

spectrum) in 62% yield.

F

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

an internal standard on Bruker 300 MHz and 400 MHz spectrometer

at rt. Chemical shift values were quoted in parts per million (ppm)

and coupling constants were quoted in hertz (Hz). HRMS were re-

corded on JEOL GC Mate II (EI) and Xevo G2S QTof instruments.

Annulated Carbazoles; General Procedure

To a mixture of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) and anhyd

FeCl₃(0.015 g, 0.01 mmol) in anhyd 1,2-DCE (10 mL) was added the

respective arene (0.53 mmol), and the mixture was refluxed under N₂

atmosphere until the reaction was completed (TLC). After completion

of the reaction (TLC), the mixture was poured into ice-water (30 mL)

containing concd HCl (3 mL). The organic layer was separated and the

aqueous layer was extracted with DCM (2 × 20 mL). The combined or-

ganic layers were washed with H₂O (2 × 20 mL) and dried (Na₂SO₄).

Removal of solvent followed by column chromatographic purification

(silica gel, hexane/EtOAc) furnished the required annulated benzo-

[b]carbazole.

Ethyl (E)-3-[3-Benzyl-1-(phenylsulfonyl)-1H-indol-2-yl]acrylate

(2a)

To a solution bromo compound 1 (0.2 g, 0.446 mmol) in anhyd ben-

zene (20 mL) was added anhyd FeCl₃(0.01 g, 0.089 mmol) and the re-

action mixture was refluxed for 12 h. After completion of the reaction

(monitored by TLC), the mixture was washed with H₂O (2 × 10 mL)

and dried (Na₂SO₄). Evaporation of the solvent followed by column

chromatographic purification (silica gel, EtOAc/hexane 1:9) afforded

2a as a colorless solid; yield: 0.107 g (54%); mp 146–148 °C.

8,9-Dimethoxy-5-(phenylsulfonyl)-5H-benzo[b]carbazole (3b)

¹H NMR (CDCl₃, 300 MHz):  = 8.25 (d, J = 8.4 Hz, 1 H), 8.19 (d, J = 15.9

Hz, 1 H), 7.67–7.64 (m, 2 H), 7.52 (t, J = 7.5 Hz, 1 H), 7.40–7.32 (m, 3

H), 7.24 (d, J = 6.9 Hz, 1 H), 7.21–7.14 (m, 4 H), 6.85–6.82 (m, 2 H),

6.00 (d, J = 16.2 Hz, 1 H), 4.27 (q, J = 7.2 Hz, 2 H), 4.10 (s, 2 H), 1.34 (t,

J = 7.05 Hz, 3 H).

¹³C NMR (CDCl₃, 75 MHz):  = 166.2, 138.5, 137.7, 137.4, 134.1, 133.8,

133.3, 131.3, 129.0, 128.7, 127.7, 126.7, 126.6, 126.4, 126.0, 124.5,

122.2, 120.4, 115.9, 60.9, 30.7, 14.3.

To a solution of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) and vera-

trole (0.073 g, 0.53 mmol) in anhyd 1,2-DCE (10 mL) was added anhyd

FeCl₃(0.015 g, 0.096 mmol) and the mixture was refluxed under N₂

atmosphere for 4 h. The usual workup following the above-men-

tioned general procedure gave annulated carbazole 3b as a colorless

solid; yield: 0.137 g (69%); mp 136–138 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.49 (s, 1 H), 8.21 (d, J = 8.4 Hz, 1 H),

8.03 (s, 1 H), 7.81 (d, J = 7.5 Hz, 1 H), 7.72 (d, J = 7.5 Hz, 2 H), 7.40–7.35

(m, 1 H), 7.32–7.25 (m, 2 H), 7.21–7.14 (m, 3 H), 7.10 (s, 1 H), 3.97 (s,

3 H), 3.92 (s, 3 H).

¹³C NMR (75 MHz, CDCl₃):  = 149.9, 149.2, 139.5, 137.7, 136.3, 133.7,

129.1, 129.0, 127.7, 126.7, 126.5, 125.2, 124.2, 120.2, 116.8, 115.3,

110.9, 106.6, 106.0, 55.9 (2 C).

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₄H₁₉NO₄S [M + H]⁺: 418.1113;

found: 418.1104.

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₆H₂₄NO₄S [M + H]⁺: 446.1426;

found: 446.1417.

Ethyl (E)-3-[3-(3,4-Dimethoxybenzyl)-1-(phenylsulfonyl)-1H-in-

dol-2-yl]acrylate (2b)

A mixture of bromo compound 1 (0.2 g, 0.446 mmol), veratrole (0.07

g, 0.491 mmol), and anhyd FeCl₃(0.01 g, 0.089 mmol) in anhyd 1,2-

DCE (10 mL) was refluxed for 12 h. Then, the usual workup as de-

scribed above, followed by column chromatographic purification (sili-

ca gel, EtOAc/hexane 1:9) afforded arylated product 2b as a colorless

solid; yield: 0.14 g (58%); mp 136–138 °C.

¹H NMR (CDCl₃, 300 MHz):  = 8.27–8.19 (m, 2 H), 7.69 (d, J = 7.2 Hz, 2

H), 7.51 (t, J = 7.35 Hz, 1 H), 7.42–7.35 (m, 3 H), 7.33–7.26 (m, 2 H),

7.23–7.17 (m, 1 H), 6.63 (d, J = 8.1 Hz, 1 H), 6.54 (s, 1 H), 6.30 (d, J = 8.4

Hz, 1 H), 6.03 (d, J = 16.2 Hz, 1 H), 4.28 (q, J = 7.11 Hz, 2 H), 4.05 (s, 2

H), 3.81 (s, 3 H), 3.67 (s, 3 H), 1.35 (t, J = 7.2 Hz, 3 H).

For further spectroscopic data, see ref. 7.

8,9-Dimethyl-5-(phenylsulfonyl)-5H-benzo[b]carbazole (3c)

Domino reaction of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) with

o-xylene (0.076 g, 0.718 mmol) using anhyd FeCl₃(0.015 g, 0.096

mmol) in anhyd 1,2-DCE (10 mL) at reflux for 4 h, followed by workup

and column chromatographic purification (silica gel, EtOAc/hexane

1:9) adopting the above mentioned general procedure afforded carba-

zole 3c as a colorless solid; yield: 0.123 g (67%); mp 202–204 °C.

¹³C NMR (CDCl₃, 75 MHz):  = 166.2, 149.1, 147.6, 137.6, 137.5, 134.0,

133.8, 133.1, 131.2, 129.0, 126.7, 126.6, 125.9, 124.5, 124.5, 122.4,

120.4, 119.6, 115.7, 111.4, 111.3, 60.9, 55.9, 55.8, 30.3, 14.3.

¹H NMR (300 MHz, CDCl₃):  = 8.51 (s, 1 H), 8.22 (d, J = 8.4 Hz, 1 H),

8.03 (s, 1 H), 7.82 (d, J = 7.5 Hz, 1 H), 7.72–7.69 (m, 3 H), 7.55 (s, 1 H),

7.39 (t, J = 7.5 Hz, 1 H), 7.28–7.22 (m, 2 H), 7.15–7.10 (m, 2 H), 2.37 (s,

3 H), 2.33 (s, 3 H).

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₈H₂₈NO₆S [M + H]⁺: 506.1637;

¹³C NMR (75 MHz, CDCl₃):  = 139.8, 137.6, 136.7, 136.0, 135.0, 133.6,

132.0, 129.6, 128.9, 128.0, 127.8, 127.3, 126.7, 126.5, 126.1, 124.2,

120.4, 117.3, 115.3, 111.3, 20.3, 20.1.

found: 506.1631.

(E)-4-[3-(Bromomethyl)-1-(phenylsulfonyl)-1H-indol-2-yl]but-3-

en-2-one (4)

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₄H₁₉NO₂S [M⁺]: 385.1136;

To a solution of 1-phenylsulfonyl-2-methylindole¹⁰(2.0 g, 8.85 mmol)

in anhyd CCl₄(50 mL) were added AIBN (0.05 g) and finely powdered

NBS (1.89 g, 10.62 mmol). The reaction mixture was refluxed for 2 h

and cooled to rt. The floated succinimide was filtered off and washed

with CCl₄(15 mL). The combined filtrates were concentrated in vacuo

to afford 4 as a light brown solid; yield: 3.40 g (92%); mp 134–136 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.21 (d, J = 8.4 Hz, 1 H), 8.10 (d, J = 16.5

Hz, 1 H), 7.69 (d, J = 7.8 Hz, 2 H), 7.61 (d, J = 7.8 Hz, 1 H), 7.53 (d, J =

7.35 Hz, 1 H), 7.46–7.33 (m, 4 H), 6.61 (d, J = 16.5 Hz, 1 H), 4.60 (s, 2

H), 2.51 (s, 3 H).

found: 385.1125.

For further spectroscopic data, see ref. 7.

8,10-Dimethyl-5-(phenylsulfonyl)-5H-benzo[b]carbazole (3d)

The reaction of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) with

m-xylene (0.076 g, 0.718 mmol) using anhyd FeCl₃(0.015 g, 0.096

mmol) in anhyd 1,2-DCE (10 mL) at reflux for 4 h, followed by workup

and column chromatographic purification (silica gel, EtOAc/hexane

1:9) adopting the above-mentioned general procedure afforded annu-

lated carbazole 3d as a colorless solid; yield: 0.125 g (68%); mp 206–

208 °C.

¹³C NMR (75 MHz, CDCl₃):  = 197.9, 137.7, 137.0, 134.3, 133.5, 132.9,

132.5, 129.3, 128.8, 127.0, 126.6, 124.6, 122.0, 119.8, 115.2, 27.2, 22.9.

For further spectroscopic data, see ref. 10.

G

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

¹H NMR (300 MHz, CDCl₃):  = 8.54 (s, 1 H), 8.29 (s, 1 H), 8.24 (d, J =

8.4 Hz, 1 H), 7.91 (d, J = 7.5 Hz, 1 H), 7.72 (d, J = 7.8 Hz, 2 H), 7.59 (s, 1

H), 7.41 (t, J = 7.65 Hz, 1 H), 7.31–7.23 (m, 2 H), 7.18–7.13 (m, 2 H),

7.08 (s, 1 H), 2.64 (s, 3 H), 2.43 (s, 3 H).

¹³C NMR (75 MHz, CDCl₃):  = 139.9, 137.7, 137.2, 135.5, 134.1, 133.7,

133.6, 129.0, 128.4, 12832, 128.0, 126.9, 126.5, 125.9, 125.8, 124.2,

120.4, 115.4, 114.7, 112.1, 21.8, 19.6.

¹³C NMR (75 MHz, CDCl₃):  = 139.6, 137.6, 137.4, 133.8, 131.9, 131.6,

130.2, 129.0, 128.6, 128.1, 127.4, 127.3, 126.7, 126.5 (2 C), 126.4,

126.3, 124.2, 122.4, 120.4, 115.3, 113.6, 113.3.

HRMS (EI, Q-TOF): m/z calcd for C₂₆H₁₈NO₂S [M⁺]: 407.0980; found:

407.0968.

For further spectroscopic data, see ref. 7.

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₄H₂₀NO₂S [M + H]⁺: 386.1215;

found: 386.1199.

X-ray Crystallographic Data for Compound 3g¹⁵

Single-crystal of compound 3g was obtained by crystallization from

CHCl₃and all calculations were performed with the SHELXL-97 pro-

gram.¹⁶C₂₆H₁₇NO₂S, MW = 407.46 gmol^–1, triclinic crystal system,

space group P-1, Z = 2. a = 7.7051 (2) Å, b = 10.4586 (2) Å, c = 12.1532

(3) Å,  = 100.599 (1)°,  = 91.487 (1)°,  = 93.818 (1)°, V = 959.79 (4)

Å³and D_calc= 1.410 Mg m^–3. In total, 3762 independent reflections

were collected, of which 3045 were considered as observed [I >2(I)].

The structure was solved by direct methods and refined by full-ma-

trix least-squares procedures to final R-value of 3.70%.

For further spectroscopic data, see ref. 7.

7,10-Dimethyl-5-(phenylsulfonyl)-5H-benzo[b]carbazole (3e)

To a solution of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) and p-xy-

lene (0.076 g, 0.718 mmol) in anhyd 1,2-DCE (10 mL) was added an-

hyd FeCl₃(0.015 g, 0.096 mmol) and the mixture was refluxed under

N₂atmosphere for 4 h. The usual workup following the above-men-

tioned general procedure gave annulated carbazole 3e as a colorless

solid; yield: 0.118 g (64%); mp 184–186 °C.

5-Methyl-8-(phenylsulfonyl)-8H-naphtho[2,1-b]carbazole (3h)

¹H NMR (300 MHz, CDCl₃):  = 8.79 (s, 1 H), 8.37 (s, 1 H), 8.27 (d, J =

8.4 Hz, 1 H), 7.95 (d, J = 7.8 Hz, 1 H), 7.73 (d, J = 7.5 Hz, 2 H), 7.44 (t, J =

7.65 Hz, 1 H), 7.30 (t, J = 7.5 Hz, 2 H), 7.20–7.12 (m, 4 H), 2.74 (s, 3 H),

2.66 (s, 3 H).

¹³C NMR (75 MHz, CDCl₃):  = 140.1, 137.6, 137.0, 133.7, 132.7, 132.5,

132.4, 130.0, 129.0, 128.2, 126.6, 126.5, 126.0, 125.5, 124.2, 120.5,

115.4, 115.3, 109.3, 20.0, 19.7.

The domino reaction of 3-bromomethylindole 4 (0.2 g, 0.48 mmol)

with 1-methylnaphthalene (0.075 g, 0.53 mmol) using anhyd FeCl₃

(0.015 g, 0.096 mmol) in anhyd 1,2-DCE (10 mL) at reflux for 4 h, fol-

lowed by usual workup and column chromatographic purification

(silica gel, EtOAc/hexane 1:9) gave naphtho[b]carbazole 3h as a color-

less solid; yield: 0.153 g (76%); mp 210–212 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.93 (s, 1 H), 8.64 (d, J = 7.5 Hz, 1 H),

8.55 (s, 1 H), 8.25 (d, J = 8.4 Hz, 1 H), 7.96–7.92 (m, 2 H), 7.75 (d, J = 7.5

Hz, 2 H), 7.61 (s, 1 H), 7.58–7.53 (m, 2 H), 7.42 (t, J = 7.8 Hz, 1 H),

7.33–7.26 (m, 2 H), 7.18–7.13 (m, 2 H), 2.63 (s, 3 H).

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₄H₁₉NO₂S [M⁺]: 385.1136;

found: 385.1128.

For further spectroscopic data, see ref. 7.

¹³C NMR (75 MHz, CDCl₃):  = 139.5, 137.7, 137.5, 133.7, 132.9, 131.9,

131.7, 130.3, 129.0, 127.8, 127.3, 126.7 (2 C), 126.4 (2 C), 125.7, 124.7,

124.2, 122.8, 120.2, 115.3, 113.5, 112.6, 20.1.

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₇H₁₉NO₂SNa [M + Na]⁺:

444.1034; found: 444.1032.

8,9-Dihydro[1,3]dioxo-5-(phenylsulfonyl)-5H-benzo[b]carbazole

(3f)

To a solution of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) and 1,3-

benzodioxole (0.064 g, 0.53 mmol) in anhyd 1,2-DCE (10 mL) was

added anhyd FeCl₃(0.015 g, 0.096 mmol) and the mixture was re-

fluxed for 4 h. Then, the usual workup and column chromatographic

purification (silica gel, EtOAc/hexane 2:8) adopting the above men-

tioned general procedure furnished annulated carbazole 3f as a color-

less solid; yield: 0.134 g (70%); mp 250–252 °C.

For further spectroscopic data, see ref. 7.

(E)-4-[3-Benzyl-1-(phenylsulfonyl)-1H-indol-2-yl]but-3-en-2-one

(5)

¹H NMR (300 MHz, CDCl₃):  = 8.58 (s, 1 H), 8.44 (s, 1 H), 8.24 (d, J =

8.1 Hz, 1 H), 8.13 (d, J = 7.5 Hz, 1 H), 7.86 (d, J = 7.5 Hz, 2 H), 7.61–7.56

(m, 3 H), 7.48–7.40 (m, 4 H), 6.16 (s, 2 H).

¹³C NMR (75 MHz, CDCl₃):  = 148.0, 147.3, 138.6, 136.4, 135.5, 134.6,

130.1, 129.6, 128.2, 127.5, 126.2, 125.9, 124.6, 124.4, 120.7, 118.0,

114.7, 111.1, 104.0, 103.2, 101.4.

A mixture of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) and anhyd

FeCl₃(0.015 g, 0.096 mmol) in anhyd benzene (10 mL) was refluxed

for 24 h. Then, the usual workup and column chromatographic purifi-

cation (silica gel, EtOAc/hexane 1:9) adopting the above mentioned

general procedure produced 3-benzylindole 5 as a colorless solid;

yield: 0.135 g (68%); mp 128–130 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.25 (d, J = 8.4 Hz, 1 H), 8.08 (d, J = 16.5

Hz, 1 H), 7.62 (d, J = 7.5 Hz, 2 H), 7.52 (t, J = 7.2 Hz, 1 H), 7.41–7.32 (m,

3 H), 7.27–7.20 (m, 2 H), 7.15–7.13 (m, 3 H), 6.82–6.79 (m, 2 H), 6.21

(d, J = 16.8 Hz, 1 H), 4.10 (s, 2 H), 2.43 (s, 3 H).

¹³C NMR (75 MHz, CDCl₃):  = 198.5, 138.4, 137.9, 137.2, 134.0, 133.7,

133.2, 131.5, 131.0, 129.1, 128.7, 127.7, 126.8, 126.6, 124.8, 120.5,

116.0, 30.7, 26.8.

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₄H₂₂NO₃S [M + H]⁺: 416.1302;

found: 416.1309.

Anal. Calcd for C₂₃H₁₅NOS: C, 68.81; H, 3.77; N, 3.49; S, 7.99. Found: C,

68.66; H, 3.79; N, 3.23; S, 7.76.

8-(Phenylsulfonyl)-8H-naphtho[2,1-b]carbazole (3g)

Annulation of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) with naph-

thalene (0.068 g, 0.53 mmol) using anhyd FeCl₃(0.015 g, 0.096 mmol)

in anhyd 1,2-DCE (10 mL) at reflux for 4 h, followed by usual work up

and column chromatographic purification (silica gel, EtOAc/hexane

1:9) afforded annulated carbazole 3g as a colorless solid; yield: 0.144

g (74%); mp 184–186 °C.

Hetero-Annulated Carbazoles; General Procedure

¹H NMR (300 MHz, CDCl₃):  = 8.99 (s, 1 H), 8.65–8.61 (m, 2 H), 8.26

(d, J = 8.1 Hz, 1 H), 7.97 (d, J = 7.5 Hz, 1 H), 7.79–7.73 (m, 4 H), 7.65–

7.62 (m, 1 H), 7.58–7.41 (m, 3 H), 7.34–7.25 (m, 2 H), 7.18–7.13 (m, 2

H).

A solution of 3-bromomethylindole 4 (0.48 mmol), the respective he-

teroarene (0.53 mmol), and anhyd SnCl₄(0.096 mmol) in anhyd 1,2-

DCE (10 mL) was stirred at rt under N₂atmosphere. After the comple-

tion of the reaction (TLC), the mixture was poured into ice-water

H

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

(30 mL) containing concd HCl (3 mL). The organic layer was separated

and the aqueous layer was extracted with DCM (2 × 20 mL). The com-

bined organic layers were washed with H₂O (2 × 20 mL) and dried

(Na₂SO₄). Removal of solvent followed by column chromatographic

purification (silica gel, hexane/EtOAc) afforded the required hetero-

annulated carbazole.

7-(Phenylsulfonyl)benzo[b]thieno[3,2-b]carbazole (7d)/11-(Phe-

nylsulfonyl)benzo[b]thieno[2,3-b]carbazole (7d′)

To a solution of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) in anhyd

1,2-DCE (10 mL) were added anhyd SnCl₄(0.025 g, 0.096 mmol) and

benzo[b]thiophene (0.071 g, 0.53 mmol) and the mixture was stirred

at rt under N₂atmosphere for 3 h. The usual workup adopting the

above mentioned general procedure, followed by column chromato-

graphic purification (silica gel, EtOAc/hexane 1:9) gave an inseparable

mixture of carbazoles 7d and 7d′ as a colorless solid; yield: 0.154 g

(78%); mp 174–176 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.96 (s), 8.67 (s), 8.40 (s), 8.22 (d, J = 8.1

Hz), 8.09–8.03 (m), 7.86 (d, J = 7.5 Hz), 7.77–7.71 (m), 7.42–7.25 (m),

7.71 (t, J = 7.8 Hz).

¹³C NMR (75 MHz, CDCl₃):  = 140.1, 139.5, 139.4, 139.3, 138.9, 137.8,

137.7, 137.6, 134.9, 133.9 (2 C), 132.4, 129.1 (2 C), 127.9, 127.6, 127.2,

126.7 (2 C), 126.5 (2 C), 126.4, 124.7, 124.6, 124.3, 124.2, 122.9, 122.8,

121.9, 121.3, 120.1, 120.0, 115.4, 115.3, 113.6, 112.3, 108.8, 107.9.

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₄H₁₅NO₂S₂Na [M + Na]⁺:

436.0442; found: 436.0442.

5-(Phenylsulfonyl)-2-(thiophen-2-yl)-5H-thieno[3,2-b]carbazole

(7a)

The domino reaction of 3-bromomethylindole 4 (0.2 g, 0.48 mmol)

with bithiophene (0.087 g, 0.53 mmol) using anhyd SnCl₄(0.025 g,

0.096 mmol) in anhyd 1,2-DCE (10 mL) adopting the above-men-

tioned general procedure followed by column chromatographic puri-

fication (silica gel, EtOAc/hexane 1:9) furnished annulated carbazole

7a as a colorless solid; yield: 0.153 g (72%); mp 230–232 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.57 (s, 1 H), 8.24 (d, J = 8.1 Hz, 1 H),

8.10 (s, 1 H), 7.79 (d, J = 7.5 Hz, 1 H), 7.73 (d, J = 7.5 Hz, 2 H), 7.46 (s, 1

H), 7.43–7.33 (m, 3 H), 7.31–7.17 (m, 4 H), 7.01–6.98 (m, 1 H).

¹³C NMR (75 MHz, CDCl₃):  = 140.1, 139.3, 138.5, 137.6, 137.3, 137.0,

135.5, 133.8, 129.0, 128.0, 127.6, 126.5, 126.1, 125.8, 125.3, 125.1,

124.2, 120.2 (2 C), 115.3, 113.0, 109.3.

For further spectroscopic data, see ref. 6b.

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₄H₁₅NO₂S₃Na [M + Na]⁺:

468.0163; found: 468.0143.

11-(Phenylsulfonyl)-11H-benzofuro[3,2-b]carbazole (7e)

The domino reaction of 3-bromomethylindole 4 (0.2 g, 0.48 mmol)

with benzo[b]furan (0.062 g, 0.53 mmol) using anhyd SnCl₄(0.025 g,

0.096 mmol) in anhyd 1,2-DCE (10 mL) adopting the above men-

tioned general procedure, followed by column chromatographic puri-

fication (silica gel, EtOAc/hexane 1:9) furnished benzofurano[b]car-

bazole 7e as a colorless solid; yield: 0.160 g (84%); mp 208–210 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.89 (s, 1 H), 8.35 (d, J = 8.1 Hz, 1 H),

8.12 (d, J = 7.2 Hz, 1 H), 7.95 (s, 1 H), 7.92 (d, J = 7.8 Hz, 1 H), 7.80 (d,

J = 7.5 Hz, 2 H), 7.58–7.51 (m, 3 H), 7.42–7.35 (m, 3 H), 7.29–7.26 (m,

2 H).

For further spectroscopic data, see ref. 7.

5-(Phenylsulfonyl)-5H-thieno[3,2-b]carbazole (7b)

The domino reaction of 3-bromomethylindole 4 (0.2 g, 0.48 mmol)

with thiophene (0.08 g, 0.957 mmol) using anhyd SnCl₄(0.025 g,

0.096 mmol) at rt for 3 h, followed by workup and column chromato-

graphic purification (silica gel, EtOAc/hexane 5:95) afforded thie-

no[b]carbazole 7b as a colorless solid; yield: 0.113 g (65%); mp 176–

178 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.66 (s, 1 H), 8.24 (d, J = 8.4 Hz, 1 H),

8.21 (s, 1 H), 7.80 (d, J = 7.5 Hz, 1 H), 7.71 (d, J = 7.5 Hz, 2 H), 7.43–7.38

(m, 3 H), 7.32–7.23 (m, 2 H), 7.16 (t, J = 7.5 Hz, 2 H).

¹³C NMR (75 MHz, CDCl₃):  = 157.2, 153.6, 139.4, 137.6, 134.9, 133.8,

129.0, 127.8, 127.7, 126.7 (2 C), 126.5, 124.6, 124.5, 124.2, 122.9,

121.0, 120.1, 115.6, 111.7, 107.1, 102.2.

¹³C NMR (75 MHz, CDCl₃):  = 139.5, 139.4, 137.7, 136.8, 136.2, 133.8,

129.0, 127.7, 126.5, 126.2, 125.1, 124.3, 124.2, 120.1, 115.4, 113.4,

109.6.

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₄H₁₆NO₃S [M + H]⁺: 398.0851;

found: 398.0849.

For further spectroscopic data, see ref. 7.

Anal. Calcd for C₂₀H₁₃NO₂S₂: C, 66.09; H, 3.61; N, 3.85; S, 17.64.

Found: C, 65.82; H, 3.43; N, 3.69; S, 17.52.

2-[3,5-Di(thiophen-2-yl)phenyl]-5-(phenylsulfonyl)-5H-thieno-

[3,2-b]carbazole (7f)

2-Methyl-5-(phenylsulfonyl)-5H-thieno[3,2-b]carbazole (7c)

The domino reaction of 3-bromomethylindole 4 (0.2 g, 0.48 mmol)

with 2,2′-(5-(thiophen-3-yl)-1,3-phenylene)dithiophene (0.17 g, 0.53

mmol) using anhyd SnCl₄(0.025 g, 0.096 mmol) in anhyd 1,2-DCE (10

mL) at rt for 6 h, followed by workup and column chromatographic

purification (silica gel, EtOAc/hexane 1:9) adopting the general proce-

dure as mentioned above afforded 7f as a light brown solid; yield:

0.193 g (67%); mp 176–178 °C.

The annulation of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) with 2-

methylthiophene (0.025 g, 0.53 mmol) in the presence of anhyd SnCl₄

(0.151 g, 0.096 mmol) in anhyd 1,2-DCE (10 mL) at rt for 3 h, followed

by workup and column chromatographic purification (silica gel,

EtOAc/hexane 1:9) led to the isolation of thieno[b]carbazole 7c as a

colorless solid; yield: 0.137 g (76%); mp 196–198 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.56 (s, 1 H), 8.30 (d, J = 8.4 Hz, 1 H),

8.20 (s, 1 H), 7.82 (d, J = 7.5 Hz, 1 H), 7.77 (d, J = 7.8 Hz, 2 H), 7.44 (t, J =

7.8 Hz, 1 H), 7.38–7.28 (m, 2 H), 7.25–7.20 (m, 2 H), 7.09 (s, 1 H), 2.59

(s, 3 H).

¹³C NMR (75 MHz, CDCl₃):  = 142.5, 140.3, 139.1, 137.7, 136.7, 136.2,

133.7, 129.0, 127.3, 124.5, 126.4, 124.2, 122.1, 119.8, 115.3, 113.0,

108.6, 16.5.

¹H NMR (300 MHz, CDCl₃):  = 8.65 (s, 1 H), 8.25 (d, J = 8.1 Hz, 1 H),

8.17 (s, 1 H), 7.82 (d, J = 7.5 Hz, 1 H), 7.75–7.69 (m, 6 H), 7.43–7.36 (m,

4 H), 7.32–7.25 (m, 3 H), 7.22–7.18 (m, 2 H), 7.08–7.07 (m, 2 H).

¹³C NMR (75 MHz, CDCl₃):  = 144.5, 143.3, 140.3, 139.4, 137.7, 137.0,

136.0, 135.9, 135.5, 133.8, 129.1, 128.2, 127.8, 126.5, 126.1, 125.6,

125.3, 124.2, 124.0, 123.6, 123.1, 120.7, 120.1, 115.4, 113.2, 109.6.

HRMS (ESI-TOF, MeOH): m/z calcd for C₃₄H₂₁NO₂S₄[M⁺]: 603.0455;

found: 603.0458.

HRMS (ESI-Ion trap, MeOH): m/z calcd for C₂₁H₁₅NO₂S₂Na [M + Na]⁺:

400.0442; found: 400.0437.

For further spectroscopic data, see ref. 7.

I

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

2-[3,5-Bis(3-methylthiophen-2-yl)phenyl]-3-methyl-5-(phenyl-

1,9-Bis(phenylsulfonyl)-1,9-dihydropyrrolo[2,3-b]carbazole (7j)

sulfonyl)-5H-thieno[3,2-b]carbazole (7g)

The annulation of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) with 1-

phenylsulfonylpyrrole (0.109 g, 0.53 mmol) using anhyd SnCl₄(0.025

g, 0.096 mmol) in anhyd 1,2-DCE (10 mL) at rt for 3 h followed work-

up and column chromatographic purification (silica gel, EtOAc/hex-

ane 2:8) adopting the general procedure yielded pyrrolocarbazole 7j

as a colorless solid; yield: 0.130 g (63%); mp 254–256 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.47 (d, J = 7.8 Hz, 2 H), 8.30 (d, J = 8.4

Hz, 1 H), 8.00 (d, J = 7.5 Hz, 1 H), 7.88 (d, J = 7.5 Hz, 2 H), 7.77 (d, J = 7.5

Hz, 2 H), 7.64 (d, J = 4.2 Hz, 1 H), 7.51–7.46 (m, 2 H), 7.43–7.36 (m, 4

H), 7.29–7.24 (m, 2 H), 6.82 (d, J = 4.2 Hz, 1 H).

The annulation of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) with

1,3,5-tris(3-methylthiophen-2-yl)benzene (0.193 g, 0.53 mmol) using

anhyd SnCl₄(0.025 g, 0.096 mmol) in anhyd 1,2-DCE at rt for 6 h, fol-

lowed by workup and column chromatographic purification (silica

gel, EtOAc/hexane 1:9) adopting the above mentioned general proce-

dure afforded carbazole 7g as a colorless solid; yield: 0.219 g (71%);

mp 174–176 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.60 (s, 1 H), 8.27 (d, J = 8.4 Hz, 1 H),

8.23 (s, 1 H), 7.86 (d, J = 7.5 Hz, 1 H), 7.74 (d, J = 7.5 Hz, 2 H), 7.56–7.53

(m, 3 H), 7.45–7.40 (m, 1 H), 7.36–7.31 (m, 2 H), 7.24 (d, J = 7.8 Hz, 2

H), 7.20–7.18 (m, 2 H), 6.90 (d, J = 8.1 Hz, 2 H), 2.62 (s, 3 H), 2.37 (s, 6

H).

¹³C NMR (75 MHz, CDCl₃):  = 139.2, 138.2, 137.7, 135.6, 133.9, 133.8,

132.5, 131.1, 129.4, 129.0, 127.8, 127.6, 126.7, 126.5, 125.0, 124.1,

120.1, 115.3, 110.2, 107.3, 104.6.

¹³C NMR (75 MHz, CDCl₃):  = 141.2, 139.4, 138.8, 137.7, 137.0, 136.9,

135.6, 135.4, 135.2, 133.9, 133.8, 131.4, 129.1, 129.0, 128.8, 128.4,

127.7, 126.5, 126.3, 125.2, 124.3, 1240.0, 120.1, 115.4, 113.,2, 108.4,

15.2, 13.3.

HRMS (ESI-Ion trap, MeOH): m/z calcd for C₃₇H₂₇NO₂S₄Na [M + Na]⁺:

668.0822; found: 668.0827.

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₆H₁₈N₂O₄S₂[M]⁺: 486.0708;

found: 486.0703.

5-Hexyl-7-(phenylsulfonyl)-5,7-dihydroindolo[2,3-b]carbazole

(7k)

The domino reaction 3-bromomethylindole 4 (0.2 g, 0.48 mmol) with

1-hexylindole (0.132 g, 0.53 mmol) using anhyd SnCl₄(0.025 g, 0.096

mmol) in anhyd 1,2-DCE (10 mL) at rt for 3 h followed workup and

column chromatographic purification (silica gel, EtOAc/hexane 1:9)

adopting the general procedure gave indolo[b]carbazole 7k as a color-

less solid; yield: 0.142 g (62%); mp 260–262 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.96 (s, 1 H), 8.29 (d, J = 8.4 Hz, 1 H),

8.21 (d, J = 7.5 Hz, 1 H), 7.90 (d, J = 7.5 Hz, 1 H), 7.72 (d, J = 7.5 Hz, 2 H),

7.68 (s, 1 H), 7.47–7.27 (m, 6 H), 7.23 (t, J = 7.5 Hz, 1 H), 7.18–7.13 (m,

2 H), 4.27 (t, J = 7.35 Hz, 2 H), 1.83 (q, J = 7.35 Hz, 2 H), 1.36–1.29 (m, 2

H), 1.25–1.23 (m, 4 H) 0.79 (d, J = 6.9 Hz, 3 H).

4,4-Di-(p-tolyl)-4H-indeno[1,2-b]thiophenocarbazole (7h)

The domino reaction of 3-bromomethylindole 4 (0.2 g, 0.48 mmol)

with 4,4-di-p-tolyl-4H-indeno[1,2-b]thiophene (0.185 g, 0.53 mmol)

in the presence of anhyd SnCl₄(0.025 g, 0.096 mmol) in anhyd 1,2-

DCE at r.t. for 6 h followed by workup and column chromatographic

purification (silica gel, EtOAc/hexane 1:9) furnished hetero-annulated

carbazole 7h as a colorless solid; yield: 0.208 g (69%); mp 182–184 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.42 (s, 1 H), 8.26 (d, J = 8.4 Hz, 1 H),

8.21 (s, 1 H), 7.80 (d, J = 7.5 Hz, 1 H), 7.48–7.38 (m, 5 H), 7.28 (t, J = 7.8

Hz, 3 H), 7.21–7.19 (m, 6 H), 7.06–6.98 (m, 5 H), 2.25 (m, 6 H).

¹³C NMR (75 MHz, CDCl₃):  = 156.8, 148.3, 143.3, 140.6, 139.8, 139.3,

137.4, 137.1, 136.7, 136.6, 133.8, 133.6, 129.2, 128.7, 128.5, 127.6,

127.5, 127.1, 126.6, 126.3, 125.3, 124.5, 124.3, 120.0, 119.8, 115.5

114.8, 108.5, 63.9, 21.1.

¹³C NMR (75 MHz, CDCl₃):  = 141.7, 139.4, 138.4, 137.6, 133.5, 132.7,

128.8, 127.4, 127.2, 126.5, 126.3, 125.9, 129.0, 123.6, 112.9, 120.7,

119.8, 118.9, 115.7, 108.7, 106.9, 98.5, 43.3, 31.6, 28.8, 27.0, 22.5,

14.0.

HRMS (ESI-TOF, MeOH): m/z calcd for

C₃₀H₂₉N₂O₂S [M +

H]⁺:

HRMS (ESI, Q-TOF): m/z calcd for C₄₁H₂₉NO₂S₂[M⁺]: 631.1640; found:

481.1950; found: 481.1943.

631.1642.

For further spectroscopic data, see ref. 7.

(E)-3-[3-Methyl-1-(phenylsulfonyl)-1H-indol-2-yl]-1-phenylprop-

9-(Phenylsulfonyl)-7-(p-tolyl)naphtho[b]thieno[3,2-b]carbazole

2-en-1-one

(7i)

A solution of 1-phenylsulfonyl-3-methylindole-2-carboxaldehyde (3

g, 10.03 mmol) and benzoylmethylenetriphenylphosphorane (5.71 g,

15.05 mmol) in anhyd toluene (70 mL) was refluxed for 12 h. After

completion of the reaction (monitored by TLC), removal of solvent in

vacuo followed by crystallization of the crude product from MeOH af-

forded the title vinyl indole as a colorless solid; yield: 3.54 g (84%);

mp 150–151 °C.

The reaction of 3-bromomethylindole 4 (0.2 g, 0.48 mmol) with

naphtho[b]thiophene (0.144 g, 0.53 mmol) using anhyd SnCl₄(0.025

g, 0.096 mmol) in anhyd 1,2-DCE at rt for 4 h followed by workup and

column chromatographic purification (silica gel, EtOAc/hexane 1:9)

gave carbazole 7i as a colorless solid; yield: 0.185 g (70%); mp 202–

204 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.62 (s, 1 H), 8.57 (s, 2 H), 8.25 (d, J =

8.4 Hz, 1 H), 8.01–7.94 (m, 2 H), 7.73 (d, J = 7.5 Hz, 3 H), 7.45–7.40 (m,

3 H), 7.37–7.32 (m, 6 H), 7.23–7.18 (m, 2 H), 2.45 (m, 3 H).

¹H NMR (300 MHz, CDCl₃):  = 8.25–8.22 (m, 1 H), 7.97–7.91 (m, 3 H),

7.83–7.80 (m, 1 H), 7.75 (d, J = 7.8 Hz, 1 H), 7.51 (d, J = 15.6 Hz, 1 H),

7.52–7.37 (m, 6 H), 7.34–7.31 (m, 3 H), 2.71 (s, 3 H).

¹³C NMR (75 MHz, CDCl₃):  = 140.5, 138.9, 138.7, 138.4, 138.1, 137.7,

135.7, 133.9, 133.4, 132.5, 131.6, 131.0, 129.8, 129.7, 129.1, 128.5,

127.5, 126.5, 126.4, 126.0, 125.2, 125.1, 124.6, 124.3, 119.9, 119.2,

115.3, 112.8, 108.7, 21.5.

¹³C NMR (75 MHz, CDCl₃):  = 190.3, 1414.0, 138.9, 138.3, 136.8,

135.7, 134.2, 132.8, 129.5, 128.7, 128.4, 127.4, 126.5, 125.0, 124.4,

122.3, 120.0, 116.8, 114.8, 13.4.

Anal. Calcd for C₂₄H₁₉NO₃S: C, 71.80; H, 4.77; N, 3.49; S, 7.99. Found:

C, 71.61; H, 4.64; N, 3.26; S, 7.73.

HRMS (ESI-TOF, MeOH): m/z calcd for C₃₅H₂₄NO₂S₂[M

+

H]⁺:

554.1248; found: 554.1248.

J

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

(E)-3-[3-(Bromomethyl)-1-(phenylsulfonyl)-1H-indol-2-yl]-1-

(E)-4-[2-(Bromomethyl)-1-(phenylsulfonyl)-1H-indol-3-yl]but-3-

phenylprop-2-en-1-one (8)

en-2-one (9)

To a solution of the above prepared (E)-3-[3-methyl-1-(phenylsulfo-

nyl)-1H-indol-2-yl]-1-phenylprop-2-en-1-one (3.0 g, 7.48 mmol) and

AIBN (0.05 g) in anhyd CCl₄(30 mL), finely powdered NBS (1.7 g, 9.72

mmol) was added. The reaction mixture was refluxed for 2 h and then

cooled to rt. The floated succinimide was filtered off and washed with

CCl₄(10 mL). The combined filtrates were concentrated in vacuo and

the crude product was washed with MeOH (10 mL) to afford bromo

compound 8 as a pale yellow solid; yield: 3.30 g (87%); mp 128–130

°C.

¹H NMR (300 MHz, CDCl₃):  = 8.31–8.26 (m, 2 H), 8.09 (d, J = 7.5 Hz, 2

H),), 7.76 (d, J = 7.5 Hz, 2 H), 7.62 (t, J = 7.5 Hz, 2 H), 7.56–7.47 (m, 4

H), 7.44–7.35 (m, 4 H), 4.69 (s, 2 H).

¹³C NMR (75 MHz, CDCl₃):  = 189.2, 138.4, 137.6, 137.3, 134.8, 134.2,

133.3, 132.6, 129.3, 128.9, 128.8, 128.7, 128.6, 127.0, 126.8, 124.6,

121.5, 119.6, 115.4, 23.8.

To a solution of 1-phenylsulfonyl-2-methylindole¹⁰(3.0 g, 8.85 mmol)

in anhyd CCl₄(50 mL) were added AIBN (0.05 g) and finely powdered

NBS (1.89 g, 10.62 mmol). The reaction mixture was refluxed for 2 h

and cooled to rt. The floated succinimide was filtered off and washed

with CCl₄(15 mL). The combined filtrates were concentrated in vacuo

to afford bromo compound 9 as a light brown solid; yield: 2.84 g

(76%); mp 122–124 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.16 (d, J = 8.4 Hz, 1 H), 7.96 (d, J = 7.5

Hz, 2 H), 7.80–7.70 (m, 2 H), 7.60–7.55 (m, 1 H), 7.48–7.32 (m, 4 H),

6.93 (d, J = 16.2 Hz, 1 H), 5.20 (s, 2 H), 2.42 (s, 3 H).

¹³C NMR (75 MHz, CDCl₃):  = 197.8, 138.8, 137.1, 136.8, 134.4, 132.1,

129.9, 129.4, 127.1, 127.0,126.6, 124.7, 120.6, 119.4, 115.21, 28.1,

21.5.

For further spectroscopic data, see ref. 10.

Anal. Calcd for C₂₄H₁₈BrNO₃S: C, 60.01; H, 3.78; N, 2.92; S, 6.68.

Found: C, 59.84; H, 3.53; N, 2.69; S, 6.46.

7,9-Dimethyl-5-(phenylsulfonyl)-5H-benzo[b]carbazole (10a)

To a solution of 2-bromomethylindole 9 (0.2 g, 0.48 mmol) and m-xy-

lene (0.076 g, 0.718 mmol) in anhyd 1,2-DCE (10 mL) was added an-

hyd FeCl₃(0.01 g, 0.096) and the mixture was refluxed under N₂at-

mosphere for 6 h. Then, the usual workup, followed by column chro-

matographic purification (silica gel, EtOAc/hexane 1:9) gave

benzo[b]carbazole 10a as a colorless solid; yield: 0.118 g (64%); mp

206–208 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.72 (s, 1 H), 8.25 (d, J = 8.1 Hz, 1 H),

8.09 (s, 1 H), 7.86 (d, J = 7.8 Hz, 1 H), 7.70 (d, J = 7.5 Hz, 2 H), 7.47–7.40

(m, 2 H), 7.30–7.25 (m, 2 H), 7.17–7.12 (m, 3 H), 2.73 (s, 3 H), 2.40 (s,

3 H).

8,9-Dimethoxy-5-(phenylsulfonyl)-5H-benzo[b]carbazole (3b)

The domino reaction of 3-bromomethylindole 8 (0.2 g, 0.417 mmol)

with veratrole (0.058 g, 0.459 mmol) using anhyd FeCl₃(0.014 g,

0.084 mmol) in anhyd 1,2-DCE (10 mL) at rt for 4 h, followed by work-

up and column chromatographic purification (silica gel, EtOAc/hex-

ane 1:9) gave benzo[b]carbazole 3b as a colorless solid; yield: 0.113 g

(65%).

8-(Phenylsulfonyl)-8H-naphtho[2,1-b]carbazole (3g)

¹³C NMR (75 MHz, CDCl₃):  = 140.1, 137.6, 136.8, 134.5, 134.3, 133.7,

131.1, 130.6, 129.3, 129.0 (2 C), 128.2, 126.6, 126.5, 125.2, 124.3,

120.6, 118.2, 115.5, 108.8, 21.6, 19.9.

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₄H₁₉NO₂S [M⁺]: 385.1136;

found: 385.1130.

A mixture of 3-bromomethylindole 8 (0.2 g, 0.48 mmol), naphthalene

(0.059 g, 0.459 mmol), and anhyd FeCl₃(0.014 g, 0.084 mmol) in an-

hyd 1,2-DCE (10 mL) was refluxed for 4 h. Then, the usual work up,

followed by column chromatographic purification (silica gel, EtOAc/

hexane 1:9) afforded carbazole 3g as a colorless solid; yield: 0.130 g

(77%).

For further spectroscopic data, see ref. 7.

2-Methyl-5-(phenylsulfonyl)-5H-thieno[3,2-b]carbazole (7a)

12-(Phenylsulfonyl)-12H-naphtho[1,2-b]carbazole (10b)

The annulation of 3-bromomethylindole 8 (0.2 g, 0.417 mmol) with

2-methylthiophene (0.045 g, 0.459 mmol) using anhyd SnCl₄(0.151 g,

0.58 mmol) in anhyd 1,2-DCE (10 mL) at rt for 3 h, followed by usual

workup and column chromatographic purification (silica gel, EtOAc/

hexane 1:9) afforded thieno[b]carbazole 7a as a colorless solid; yield:

0.116 g (74%).

A mixture of 2-bromomethylindole 9 (0.2 g, 0.48 mmol), anhyd FeCl₃

(0.015 g, 0.096 mmol), and naphthalene (0.076 g, 0.53 mmol) in an-

hyd 1,2-DCE (10 mL) was refluxed for 4 h. Then, the usual workup,

followed by the column chromatographic purification (silica gel,

EtOAc/hexane 1:9) gave naphthocarbazole 10b as a colorless solid;

yield: 0.121 g (62%); mp 210–212 °C.

¹H NMR (300 MHz, CDCl₃):  = 9.58 (s, 1 H), 8.84 (d, J = 8.1 Hz, 1 H),

8.31 (d, J = 8.1 Hz, 1 H), 8.26 (s, 1 H), 7.94 (d, J = 7.2 Hz, 1 H), 7.84 (d,

J = 7.5 Hz, 1 H), 7.78–7.73 (m, 3 H), 7.70–7.64 (m, 2 H), 7.58 (t, J = 7.2

Hz, 1 H), 7.47 (t, J = 7.65 Hz, 1 H), 7.36–7.29 (m, 2 H), 7.20–7.15 (m, 2

H).

¹³C NMR (75 MHz, CDCl₃):  = 139.8, 137.9, 137.6, 133.8, 132.1, 130.6,

130.3, 130.1, 129.1, 129.0, 128.6, 128.2, 127.0, 126.9, 126.8, 126.5,

126.4, 126.3, 124.3, 123.2, 120.5, 119.2, 115.5, 108.2.

5-(Phenylsulfonyl)-2-(thiophen-2-yl)-5H-thieno[3,2-b]carbazole

(7c)

A solution of 3-bromomethylindole 8 (0.2 g, 0.417 mmol), bithio-

phene (0.054 g, 0.459 mmol), and anhyd SnCl₄(0.025 g, 0.096 mmol)

in anhyd 1,2-DCE (10 mL) was stirred at rt for 3 h. Then, the usual

workup, followed by column chromatographic purification (silica gel,

EtOAc/hexane 1:9), furnished annulated carbazole 7c as a colorless

solid; yield: 0.130 g (70%).

HRMS (EI, Q-TOF): m/z calcd for C₂₆H₁₇NO₂S [M⁺]: 407.0980; found:

407.0971.

11-(Phenylsulfonyl)-11H-benzofuro[3,2-b]carbazole (7e)

The reaction of 3-bromomethylindole 8 (0.2 g, 0.417 mmol) with ben-

zofuran (0.054 g, 0.459 mmol) in the presence of anhyd SnCl₄(0.025

g, 0.096 mmol) at rt for 3 h, followed by workup and column chro-

matographic purification (silica gel, EtOAc/hexane 1:9) furnished

benzofurano[b]carbazole 7e as a colorless solid; yield: 0.126 g (76%).

For further spectroscopic data, see ref. 7.

K

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

5-Methyl-12-(phenylsulfonyl)-12H-naphtho[1,2-b]carbazole (10c)

9-(Phenylsulfonyl)-2-(thiophen-2-yl)-9H-thieno[2,3-b]carbazole

(10f)

The domino reaction of 2-bromomethylindole 9 (0.2 g, 0.48 mmol)

with 1-methylnaphthalene (0.082 g, 0.53 mmol) using anhyd FeCl₃

(0.015 g, 0.096 mmol) in anhyd 1,2-DCE (10 mL) at reflux for 4 h, fol-

lowed by the usual workup and column chromatographic purification

(silica gel, EtOAc/hexane 1:9) furnished naphtho[b]carbazole 10c as a

colorless solid; yield: 0.131 g (65%); mp 204–206 °C.

¹H NMR (300 MHz, CDCl₃):  = 9.42 (s, 1 H), 8.76 (d, J = 7.8 Hz, 1 H),

8.22 (d, J = 8.4 Hz, 1 H), 7.90 (s, 1 H), 7.86 (d, J = 8.1 Hz, 1 H), 7.73 (d,

J = 7.8 Hz, 1 H), 7.68 (d, J = 7.5 Hz, 2 H), 7.61–7.49 (m, 2 H), 7.38–7.35

(m, 2 H), 7.22–7.13 (m, 2 H), 7.06–7.01 (m, 2 H), 2.51 (s, 3 H).

Annulation of 2-bromomethylindole 9 (0.2 g, 0.48 mmol) with bithio-

phene (0.087 g, 0.53 mmol) using anhyd SnCl₄(0.025 g, 0.096 mmol)

in anhyd 1,2-DCE (10 mL) adopting the above mentioned general pro-

cedure, followed by workup and column chromatographic purifica-

tion (silica gel, EtOAc/hexane 1:9) furnished thienocarbazole 10f as a

colorless solid; yield: 0.138 g (65%); mp 186–188 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.61 (s, 1 H), 8.20 (d, J = 8.4 Hz, 1 H),

7.95 (s, 1 H), 7.75–7.69 (m, 3 H), 7.37 (t, J = 7.65 Hz, 1 H), 7.30–7.20

(m, 3 H), 7.18–7.13 (m, 4 H), 6.93 (t, J = 7.2 Hz, 1 H).

¹³C NMR (75 MHz, CDCl₃):  = 139.7, 137.7, 137.3, 133.8, 132.2, 131.9,

130.6, 129.5, 129.1, 129.0, 128.0, 126.9, 126.6, 126.5, 126.4, 124.8,

124.3, 123.4, 120.5, 118.3, 115.5, 108.0, 20.0.

¹³C NMR (75 MHz, CDCl₃):  = 139.0, 138.9, 137.5, 137.3, 137.2, 137.1,

136.4, 133.8, 129.0, 128.0, 127.6, 126.4, 125.6, 125.4, 125.1, 124.1,

120.0, 119.0, 115.3, 113.8, 108.2.

Anal. Calcd for C₂₇H₁₉NO₂S: C, 76.93; H, 4.54; N, 3.32; S, 7.61. Found:

C, 76.71; H, 4.37; N, 3.09; S, 7.46.

Anal. Calcd for C₂₄H₁₅NO₂S₃: C, 64.69; H, 3.39; N, 3.14; S, 21.59.

Found: C, 64.47; H, 3.12; N, 3.02; S, 21.37.

For further spectroscopic data, see ref. 7.

9-(Phenylsulfonyl)-9H-thieno[2,3-b]carbazole (10d)

7-(Phenylsulfonyl)benzo[b]thieno[3,2-b]carbazole (7d)/11-(Phe-

nylsulfonyl)benzo[b]thieno[2,3-b]carbazole (7d′)

To a solution of 2-bromomethylindole 9 (0.2 g, 0.48 mmol) and thio-

phene (0.08 g, 0.957 mmol) in anhyd 1,2-DCE (10 mL) was added an-

hyd SnCl₄(0.025 g, 0.096 mmol) and the reaction mixture was stirred

at rt for 3 h. Then, the mixture was poured into ice-water (30 mL)

containing concd HCl (3 mL). The organic layer was separated and the

aqueous layer was extracted with DCM (2 × 20 mL). The combined ex-

tracts were washed with H₂O (3 × 30 mL) and dried (Na₂SO₄). Removal

of solvent followed by column chromatographic purification (silica

gel, EtOAc/hexane 1:9) afforded thieno[b]carbazole 10d as a colorless

solid; yield: 0.106 g (61%); mp 170–172 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.76 (s, 1 H), 8.25 (d, J = 7.8 Hz, 1 H),

8.19 (s, 1 H), 7.85 (d, J = 7.5 Hz, 1 H), 7.73 (d, J = 7.5 Hz, 3 H), 7.44–7.39

(m, 2 H), 7.33–7.26 (m, 2 H), 7.20 (t, J = 7.8 Hz, 2 H).

¹³C NMR (75 MHz, CDCl₃):  = 139.7, 139.1, 137.6, 136.5, 133.8, 129.0,

127.6, 126.6, 126.5 (2 C), 125.2, 124.1, 123.4, 120.1 115.3, 114.1,

108.5.

To a solution of 2-bromomethylindole 9 (0.2 g, 0.48 mmol) in anhyd

1,2-DCE (10 mL) were added anhyd SnCl₄(0.025 g, 0.096 mmol) and

benzo[b]thiophene (0.071 g, 0.53 mmol) and the mixture was stirred

at rt for 3 h. Then, the usual workup and column chromatographic pu-

rification (silica gel, EtOAc/hexane 1:9) led to the isolation of an in-

separable mixture of isomeric carbazoles 7d and 7d′ as a colorless sol-

id; yield: 0.132 g (67%); mp 230–232 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.99 (s), 8.69 (s), 8.45 (s), 8.24 (d, J = 7.8

Hz), 8.14 (s), 8.09–8.08 (m), 7.91–7.88 (m), 7.80 (d, J = 7.8 Hz), 7.75–

7.71 (m), 7.41–7.34 (m), 7.32–7.25 (m), 7.22–7.14 (m).

¹³C NMR (75 MHz, CDCl₃):  = 139.5, 139.4 (2 C), 137.7, 137.6, 136.7,

135.7, 135.5, 135.4, 133.9, 133.8, 129.1 (2 C), 127.9, 127.6, 127.1,

126.8, 126.7, 126.5 (2 C), 126.0, 124.7, 124.6, 124.3, 124.2, 122.9,

122.8, 121.9, 121.3, 120.1, 115.5, 115.3, 113.6, 112.3, 108.8, 108.0.

Anal. Calcd for C₂₄H₁₅NO₂S₂: C, 69.71; H, 3.66; N, 3.39; S, 15.51.

Found: C, 69.47; H, 3.39; N, 3.24; S, 15.24.

Anal. Calcd for C₂₀H₁₃NO₂S₂: C, 66.09; H, 3.61; N, 3.85; S, 17.64.

Found: C, 65.87; H, 3.49; N, 3.92; S, 17.38.

For further spectroscopic data, see ref. 7.

2-Methyl-9-(phenylsulfonyl)-9H-thieno[2,3-b]carbazole (10e)

7-(Phenylsulfonyl)-7H-benzofuro[2,3-b]carbazole (10g)

The domino reaction of 2-bromomethylindole 9 (0.2 g, 0.48 mmol)

with 2-methylthiophene (0.052 g, 0.53 mmol) using anhyd SnCl₄

(0.025 g, 0.096 mmol) in anhyd 1,2-DCE (10 mL) at rt for 3 h, followed

by workup and column chromatographic purification (silica gel,

EtOAc/hexane 1:9) gave thieno[b]carbazole 10e as a colorless solid;

yield: 0.130 g (72%); mp 206–208 °C.

The domino reaction of 2-bromomethylindole 9 (0.2 g, 0.48 mmol)

with benzofuran (0.062 g, 0.53 mmol) using anhyd SnCl₄(0.025 g,

0.096 mmol) in anhyd 1,2-DCE (10 mL) adopting the general proce-

dure, followed by workup and column chromatographic purification

(silica gel, EtOAc/hexane 1:9) gave benzofuranocarbazole 10g as a col-

orless solid; yield: 0.144 g (76%); mp 190–192 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.62 (s, 1 H), 8.22 (d, J = 8.1 Hz, 1 H),

7.96 (s, 1 H), 7.79 (d, J = 7.5 Hz, 1 H), 7.70 (d, J = 7.5 Hz, 2 H), 7.38 (t, J =

7.65 Hz, 1 H), 7.32–7.23 (m, 2 H), 7.19–7.14 (m, 2 H), 6.91 (s, 1 H),

2.51 (s, 3 H).

¹³C NMR (75 MHz, CDCl₃):  = 141.1, 139.7, 138.9, 137.7, 137.4, 135.8,

133.7, 129.0, 127.3, 126.8, 126.4, 124.9, 124.0, 121.0, 119.9, 115.3,

112.9, 108.2, 16.3.

¹H NMR (300 MHz, CDCl₃):  = 8.44 (s, 1 H), 8.27–8.25 (m, 2 H), 7.87

(t, J = 6.9 Hz, 2 H), 7.75 (d, J = 7.8 Hz, 2 H), 7.49 (d, J = 8.1 Hz, 1 H),

7.42–7.26 (m, 5 H), 7.24–7.16 (m, 2 H).

¹³C NMR (75 MHz, CDCl₃):  = 157.0, 156.1, 138.9, 138.0, 137.6, 133.9,

129.0, 127.1, 126.9, 126.5, 126.4, 124.2, 123.9, 122.9, 122.8, 121.6,

120.4, 119.7, 115.2, 111.6, 111.1, 98.9.

Anal. Calcd for C₂₄H₁₅NO₃S: C, 72.53; H, 3.80; N, 3.52; S, 8.07. Found:

C, 72.29; H, 3.58; N, 3.27; S, 7.81.

Anal. Calcd for C₂₁H₁₅NO₂S₂: C, 66.82; H, 4.01; N, 3.71; S, 16.99.

Found: C, 66.58; H, 3.86; N, 3.69; S, 16.73.

For further spectroscopic data, see ref. 7.

L

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

5-Hexyl-11-(phenylsulfonyl)-5,11-dihydroindolo[3,2-b]carbazole

X-ray Crystallographic Data for Compound 10j¹⁵

(10h)

Single-crystal of compound 10j was obtained by crystallization from

CHCl₃and all calculations were performed with the SHELXL-97 pro-

gram.¹⁶C₃₆H₃₀N₂O₂S₂, MW = 586.74 gmol^–1, triclinic crystal system,

space group P-1, Z = 2. a = 8.6065 (3) Å, b = 12.5672 (4) Å, c = 13.8313

(4) Å,  = 98.402 (2)°,  = 97.736 (2),  = 99.150 (2)°, V = 1441.89 (8) Å³

and D_calc= 1.351 Mg m⁻³. In total, 8914 independent reflections were

collected, of which 4614 were considered as observed [I >2(I)]. The

structure was solved by direct methods and refined by full-matrix

least-squares procedures to final R-value of 5.95%.

The domino reaction of 2-bromomethylindole 9 (0.2 g, 0.48 mmol)

with 1-hexylindole (0.106 g, 0.53 mmol) using anhyd SnCl₄(0.025 g,

0.096 mmol) in anhyd 1,2-DCE (10 mL) following the general proce-

dure gave indolocarbazole 10h as a colorless solid; yield: 0.149 g

(65%); mp 164–166 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.93 (s, 1 H), 8.26 (d, J = 8.1 Hz, 1 H),

8.18 (d, J = 7.8 Hz, 1 H), 7.85 (d, J = 7.5 Hz, 1 H), 7.69 (d, J = 7.5 Hz, 2 H),

7.62 (s, 1 H), 7.43–7.34 (m, 2 H), 7.31–7.16 (m, 4 H), 7.10 (t, J = 7.65

Hz, 2 H), 4.20 (t, J = 7.2 Hz, 2 H), 1.80–1.73 (m, 4 H), 1.31–1.27 (m, 2

H), 1.20–1.19 (m, 4 H), 0.76 (d, J = 6.3 Hz, 1 H).

10-Hexyl-10H-thieno[2,3-a]carbazole (11)

¹³C NMR (75 MHz, CDCl₃):  = 141.7, 139.4, 138.4, 137.6, 133.6, 132.7,

128.9, 127.4, 127.2, 126.5, 126.3, 125.9, 124.0, 123.6, 122.9, 120.7,

119.8, 118.9, 115.7, 108.7, 106.9, 98.6, 43.3, 31.6, 28.9, 27.0, 22.6,

14.1.

To a solution of thieno[a]carbazole (0.8 g, 2.20 mmol) in DMSO (15

mL) was added 30% aq NaOH (10 mL) and the heterogeneous solution

was stirred at rt for 6 h. After completion of the reaction (TLC), the

mixture was poured over crushed ice (50 g) containing concd HCl (5

mL). The solid obtained was filtered, washed with H₂O (30 mL), and

dried. The crude product was washed with 5% EtOAc/hexane (10 mL)

to afford N-free carbazole. To a solution of N-free carbazole (0.35 g,

1.56 mmol) in toluene (10 mL) were added 1-bromohexane (0.3 mL,

2.03 mmol), Bu₄NBr (0.05 g) and 50% aq NaOH (10 mL). Then, the re-

action mixture was heated at 80 °C for 8 h. After completion of hexyl-

ation, the organic layer was separated and the aqueous layer was ex-

tracted with EtOAc (3 × 20 mL). The combined organic layers were

washed with H₂O (2 × 20 mL) and dried (Na₂SO₄). Removal of solvent

followed by column chromatographic purification led to the isolation

of 11 as a colorless liquid; yield: 0.40 g (85%).

HRMS (ESI-TOF, MeOH): m/z calcd for C₃₀H₂₉N₂O₂S [M

+

H]⁺:

481.1950; found: 481.1948.

For further spectroscopic data, see ref. 7.

2-[3,5-Di(thiophen-2-yl)phenyl]-9-(phenylsulfonyl)-9H-thieno-

[2,3-b]carbazole (10i)

The annulation of 2-bromomethylindole 9 (0.2 g, 0.48 mmol) with

1,3,5-tri(thiophen-2-yl)benzene (0.170 g, 0.53 mmol) using anhyd

SnCl₄(0.025 g, 0.096 mmol) adopting the general procedure, followed

by workup and column chromatographic purification (silica gel,

EtOAc/hexane 1:9) gave carbazole 10i as a colorless solid; yield: 0.182

g (63%); mp 128–130 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.69 (s, 1 H), 8.22 (d, J = 8.1 Hz, 1 H),

8.07 (s, 1 H), 7.79 (d, J = 7.8 Hz, 1 H), 7.75–7.63 (m, 5 H), 7.52 (s, 1 H),

7.41–7.33 (m, 4 H), 7.26–7.16 (m, 5 H), 7.05–7.02 (m, 2 H).

¹H NMR (CDCl₃, 400 MHz):  = 8.03 (d, J = 7.6 Hz, 1 H, ArH), 7.97 (d, J =

8.0 Hz, 1 H, ArH), 7.57 (d, J = 8.4 Hz, 1 H, ArH), 7.43 (d, J = 5.6 Hz, 2 H,

ArH ), 7.37–7.34 (m, 3 H, ArH), 4.48 (t, J = 7.8 Hz, 2 H, NCH₂), 1.83 (t,

J = 7.6 Hz, 2 H, CH₂), 1.42–1.20 (m, 6 H, CH₃), 0.78 (t, J = 6.8 Hz, 3 H,

CH₃).

¹³C NMR (CDCl₃, 100 MHz):  = 139.7, 139.4, 135.4, 125.1, 124.8,

123.8, 123.4, 120.0, 119.3, 118.5, 117.3, 115.2, 109.0, 44.8, 31.5, 30.7,

26.7, 22.5, 14.0.

¹³C NMR (75 MHz, CDCl₃):  = 143.4, 143.3, 139.5, 139.0, 137.7, 137.4,

136.6, 135.8, 135.4, 133.9, 129.1, 128.2, 128.1, 127.7, 126.5, 125.5 (2

C), 124.2, 124.0, 123.4, 123.0, 120.0, 119.7, 115.3, 114.2, 108.4.

HRMS (ESI-TOF, MeOH): m/z calcd for C₁₅H₁₀S₂[M⁺]: 603.0455; found:

603.0453.

Anal. Calcd for C₂₀H₂₁NS; C, 78.13; H, 6.88; N, 4.56; S, 10.43. Found: C,

78.26; H, 6.61; N, 4.52; S, 10.20.

For further spectroscopic data, see ref. 7.

(E)-3-(3-Methylthiophen-2-yl)-1-phenylprop-2-en-1-one

To a stirred solution of 3-methylthiophene-2-carboxaldehyde (90%;

2.2 g, 15.9 mmol) and acetophenone (2 g, 16.6 mmol) in EtOH (30 mL)

at 0–10 °C was slowly added a solution of NaOH (2 g) in H₂O (2 mL).

The reaction mixture was then stirred at the same temperature for 2

h and then poured over crushed ice (200 g) and acidified with concd

HCl (10 mL). The yellow solid obtained was then filtered and dried to

afford the title compound; yield: 3.1 g (86%); mp 52–53 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.08–8.01 (m, 3 H), 7.61–7.48 (m, 3 H),

7.33–7.27 (m, 2 H), 6.91 (d, J = 5.1 Hz, 1 H), 2.41 (s, 3 H).

¹³C NMR (75 MHz, CDCl₃):  = 189.7, 142.5, 138.5, 135.5, 134.6, 132.5,

5-Hexyl-10-(phenylsulfonyl)-5,10-dihydrocarbazolo[2,3-c]thieno-

[2,3-a]carbazole (10j)

The domino reaction of 2-bromomethylindole 9 (0.20 g, 0.48 mmol)

with thienocarbazole 11¹⁷(0.16 g, 0.52 mmol) using anhyd SnCl₄

(0.025 g, 0.096 mmol) in anhyd 1,2-DCE (10 mL) at rt for 2 h, followed

by usual workup and column chromatographic purification (silica gel;

EtOAc/hexane 3:97) furnished benzo[b]carbazole 10j as a colorless

solid; yield: 0.177 g (63%); mp 144–148 °C.

¹H NMR (CDCl₃, 300 MHz ):  = 9.30 (s, 1 H, ArH), 9.16 (s, 1 H, ArH),

8.58 (d, J = 7.5 Hz, 1 H, ArH), 8.37 (d, J = 8.4 Hz, 1 H, ArH), 8.32 (d, J =

5.4 Hz, 1 H, ArH), 8.13 (d, J = 7.2 Hz, 1 H, ArH), 7.81 (d, J = 7.5 Hz, 2 H,

ArH), 7.67 (d, J = 5.4 Hz, 1 H, ArH), 7.57–7.30 (m, 6 H, ArH), 7.25–7.20

(m, 2 H, ArH), 4.63 (t, J = 7.6 Hz, CH₂), 1.96–1.94 (m, 2 H, CH₂), 1.93–

1.36 (m, 6 H, CH₂), 0.92–0.90 (m, 3 H, CH₃).

131.4, 128.5, 128.3, 127.2, 120.1, 14.2.

(E)-3-(3-Bromomethylthiophen-2-yl)-1-phenylprop-2-en-1-one

(12)

¹³C NMR (CDCl₃, 75 MHz):  = 139.5, 139.0, 137.7, 137.4, 136.7, 133.7,

129.0, 128.4, 127.4, 127.0, 126.5, 124.2, 123.9, 123.7, 123.2, 123.0,

122.7, 121.6, 120.9, 120.0, 115.4, 115.2, 112.5, 109.5, 108.3, 44.9, 31.6,

30.7, 26.7, 22.6, 14.0.

HRMS (ESI-TOF): m/z calcd for C₃₆H₃₁N₂O₂S₂[M + H]⁺: 587.1827;

found: 587.1819.

To a solution of thze above prepared(E)-3-(3-methylthiophen-2-yl)-

1-phenylprop-2-en-1-one (2.5 g, 10.95 mmol) in anhyd CCl₄(40 mL)

were added a catalytic amount of AIBN (0.1 g) and finely powdered

NBS (2.34 g, 13.14 mmol). The reaction mixture was then refluxed for

2 h and cooled to rt. The floated succinimide was filtered off and

washed with CCl₄(10 mL). The solvent was then removed in vacuo to

afford bromo compound 12 as a thick liquid; yield: 2.9 g (86%).

M

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

¹H NMR (300 MHz, CDCl₃):  = 8.06–8.01 (m, 3 H), 7.62–7.58 (m, 1 H),

7.53–7.48 (m, 2 H), 7.47–7.35 (m, 2 H), 7.12–7.11 (d, J = 5.1 Hz, 1 H),

4.62 (s, 2 H).

¹³C NMR (75 MHz, CDCl₃):  = 189.5, 140.8, 137.9, 133.6, 133.0, 130.6,

128.7, 128.5, 127.9, 121.9, 24.1.

2,7-Dimethyl-10-(phenylsulfonyl)-10H-dithieno[2,3-b:3′,2′-h]car-

bazole (15a)

To a solution of 2,5-bis(bromomethyl)pyrrole 14 (0.2 g, 0.31 mmol)

and 2-methylthiophene (0.066 g, 0.67 mmol) in anhyd 1,2-DCE (10

mL), was added anhyd SnCl₄(0.032 g, 0.12 mmol) and the mixture

stirred at rt for 3 h. Then, the mixture was poured into ice-water (50

mL). The organic layer was separated and the aqueous layer was ex-

tracted with DCM (2 × 20 mL). The combined extracts were washed

with H₂O (3 × 50 mL) and dried (Na₂SO₄). Removal of solvent, followed

by column chromatographic purification (silica gel, EtOAc/hexane

1:9) afforded hetero-annulated carbazole 15a as a colorless solid;

yield: 0.092 g (67%); mp 290–292 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.70 (s, 2 H), 8.13 (s, 2 H), 7.79 (d, J =

7.8 Hz, 2 H), 7.41 (t, J = 7.35 Hz, 1 H), 7.30–7.25 (m, 2 H), 7.06 (s, 2 H),

2.64 (s, 6 H).

¹³C NMR (75 MHz, CDCl₃):  = 141.2, 139.6, 137.4, 136.4, 133.7, 129.0,

126.5, 125.2, 121.0, 112.8, 108.5, 96.1, 16.4.

Anal. Calcd for C₁₄H₁₁BrOS: C, 54.74; H, 3.61; S, 10.44. Found: C,

54.56; H, 3.52; S, 10.61.

Benzo[b]thieno[2,3-f]benzofuran (13)

To a solution of bromo compound 12 (0.2 g, 0.65 mmol) in anhyd

1,2-DCE (5 mL) were added anhyd SnCl₄(0.033 g, 0.13 mmol) and

benzofuran (0.085 g, 0.71 mmol). Then, the reaction mixture was

stirred at rt under N₂atmosphere for 3 h. The subsequent workup,

followed by column chromatographic purification (silica gel, EtOAc/

hexane 2:98) afforded dibenzothiophene 13 as a red solid; yield:

0.06 g (42%); mp 178–180 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.41 (s, 1 H), 8.03–7.99 (m, 1 H), 7.95

(s, 1 H), 7.58–7.54 (m, 2 H), 7.50–7.46 (m, 1 H), 7.44–7.43 (m, 1 H),

7.38–7.34 (m, 1 H).

HRMS (ESI-Ion trap, MeOH): m/z calcd for C₂₄H₁₇NO₂S₃Na [M + Na]⁺:

470.0319; found: 470.0311.

¹³C NMR (75 MHz, CDCl₃):  = 157.1, 154.7, 139.1, 134.9, 127.8, 127.5,

123.8, 123.2, 122.7, 120.7 113.8, 111.6, 105.1.

7-(Phenylsulfonyl)-7H-dibenzofuro[2,3-b:3′,2′-h]carbazole (15b)

The domino reaction of 2,5-bis(bromomethyl)pyrrole 14 (0.2 g, 0.31

mmol) with benzofuran (0.08 g, 0.67 mmol) in anhyd 1,2-DCE (10

mL) using anhyd SnCl₄(0.032 g, 0.12 mmol) adopting the procedure

similar to that of 15a, followed by workup and column chromato-

graphic purification (silica gel, EtOAc/hexane 1:9) furnished benzo-

furanocarbazole 15b as colorless solid; yield: 0.106 g (71%); mp 298–

300 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.44 (d, J = 6.3 Hz, 2 H), 8.30 (d, J = 6.3

Hz, 2 H), 7.91 (t, J = 6.6 Hz, 2 H), 7.77 (t, J = 6.9 Hz, 2 H), 7.52–7.48 (m,

2 H), 7.42–7.37 (m, 2 H), 7.33–7.28 (m, 3 H), 7.23–7.16 (m, 2 H).

¹³C NMR (75 MHz, CDCl₃):  = 157.0, 155.8, 138.5, 137.4, 134.0, 129.1,

127.1, 126.6, 123.9, 123.0, 122.8, 121.7, 120.4, 111.7, 110.7, 99.2.

HRMS (ESI-Ion trap, MeOH): m/z calcd for C₃₀H₁₇NO₄SNa [M + Na]⁺:

510.0776; found: 510.0768.

Anal. Calcd for C₁₄H₈OS: C, 74.98; H, 3.60; S, 14.29. Found: C, 74.83; H,

3.48; S, 14.06.

For further spectroscopic data, see ref. 6d.

(2E,2′E)-3,3′-[2,5-Dimethyl-1-(phenylsulfonyl)-1H-pyrrole-3,4-di-

yl]bis(1-phenylprop-2-en-1-one)

A solution of pyrrole-3,4-dicarbaldehyde⁹(1 g, 3.43 mmol) and (ben-

zoylmethylene)triphenylphosphorane (3.91 g, 10.31 mmol) in anhyd

toluene (60 mL) was refluxed for 8 h. After completion of the reaction

(monitored by TLC), the solvent was evaporated under vacuo. The re-

sulting crude product upon crystallization from MeOH afforded 3,4-

divinylpyrrole as colorless solid; yield: 1.53 g (90%); mp 128–130 °C.

¹H NMR (300 MHz, CDCl₃):  = 7.96 (d, J = 7.5 Hz, 4 H), 7.86 (d, J = 15.6

Hz, 2 H), 7.78 (d, J = 7.5 Hz, 2 H), 7.68 (t, J = 7.2 Hz, 1 H), 7.60–7.52 (m,

4 H), 7.47–7.42 (m, 4 H), 7.22 (d, J = 15.6 Hz, 2 H), 2.60 (s, 6 H).

5,8-Dihexyl-14-(phenylsulfonyl)-8,14-dihydro-5H-pyrrolo-

[3,2-b:4,5-b′]dicarbazole (15c)

¹³C NMR (75 MHz, CDCl₃):  = 189.8, 139.5, 138.0, 136.4, 134.3, 134.0,

132.9, 129.8, 128.7, 128.4, 126.5, 125.1, 120.5, 13.4.

The domino reaction of 2,5-bis(bromomethyl)pyrrole 14 (0.2 g, 0.31

mmol) with N-hexylcarbazole (0.169 g, 0.67 mmol) in anhyd 1,2-DCE

(10 mL) using anhyd SnCl₄(0.032 g, 0.12 mmol) adopting the proce-

dure similar to that of 15a, followed by workup and column chro-

matographic purification (Silica gel, EtOAc/hexane 1:9) furnished

benzofuranocarbazole 15c as colorless solid; yield: 0.124 g (62%); mp

298–300 °C.

¹H NMR (300 MHz, CDCl₃):  = 9.01 (s, 2 H), 8.27 (d, J = 7.8 Hz, 2 H),

7.74–7.72 (m, 4 H), 7.50 (t, J = 7.5 Hz, 2 H), 7.41–7.38 (m, 2 H), 7.31–

7.25 (m, 2 H), 7.31–7.25 (m, 3 H), 7.11 (t, J = 7.8 Hz, 2 H), 4.34 (t, J =

7.05 Hz, 4 H), 1.93 (t, J = 6.3 Hz, 4 H), 1.46–1.29 (m, 12 H), 0.88 (t, J =

6.75 Hz, 6 H).

¹³C NMR (75 MHz, CDCl₃):  = 141.6, 138.5, 137.1, 133.6, 133.2, 128.7,

126.9, 126.6, 126.1, 123.3, 123.0, 120.7, 118.9, 108.7, 107.6, 98.3, 43.3,

31.6, 28.9, 27.1, 22.6, 14.1.

HRMS (ESI-TOF, MeOH): m/z calcd for C₄₂H₄₄N₃O₂S [M⁺]: 654.3154;

found: 654.3157.

HRMS (ESI-TOF, MeOH): m/z calcd for C₃₀H₂₆NO₄S [M + H]⁺: 496.1583;

found: 496.1580.

(2E,2′E)-3,3′-[2,5-Bis(bromomethyl)-1-(phenylsulfonyl)-1H-pyr-

role-3,4-diyl]bis(1-phenylprop-2-en-1-one) (14)

To a solution of the above prepared 2,5-dimethylpyrrole (1.0 g, 2.02

mmol) in anhyd CCl₄(50 mL) were added AIBN (0.05 g) and finely

powdered NBS (0.86 g, 4.84 mmol). The reaction mixture was re-

fluxed for 2 h and cooled to rt. The floated succinimide was filtered

off and washed with CCl₄(15 mL). The combined filtrates were con-

centrated in vacuo to afford 2,5-bis(bromomethyl)pyrrole 14 as a

brown solid; yield: 1.23 g (93%); mp 134–136 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.07 (d, J = 7.5 Hz, 6 H), 7.86 (d, J = 15.9

Hz, 2 H), 7.72 (t, J = 7.5 Hz, 1 H), 7.66–7.58 (m, 6 H), 7.51 (t, J = 7.5 Hz,

4 H), 5.01 (s, 4 H).

¹³C NMR (75 MHz, CDCl₃):  = 189.1, 138.6, 137.4, 135.0, 133.4, 133.1,

129.9, 128.9, 128.7, 127.6, 127.4, 124.7, 22.4.

Anal. Calcd for C₃₀H₂₃Br₂NO₄S: C, 55.15; H, 3.55; N, 2.14; S, 4.91.

Found: C, 54.97; H, 3.38; N, 2.26; S, 4.72.

N

V. Saravanan, A. K. Mohanakrishnan

Paper

Synthesis

5-Hexyl-5H-thieno[3,2-b]carbazole (16)

graphic purification (silica gel; EtOAc/hexane 3:97) to afford an in-

separable mixture of benzothieno[3,2-b]dibenzothiophene 17b and

17b′ as a colorless solid; yield: 0.149 g (62%); mp 296–298 °C.

¹H NMR (300 MHz, CDCl₃):  = 9.28 (s, 1 H), 9.19 (s, 1 H), 8.92 (s, 1 H),

8.86 (s, 4 H), 8.77–8.75 (m, 4 H), 8.34–8.28 (m, 4 H), 8.24–8.23 (m, 3

H), 8.02 (d, J = 7.2 Hz, 2 H), 7.96 (t, J = 8.1 Hz, 2 H), 7.78–7.73 (m, 2 H),

7.62–7.58 (m, 2 H), 7.54–7.47 (m, 7 H).

To a solution of 5-(phenylsulfonyl)-5H-thieno[3,2-b]carbazole (7b;

0.5 g, 1.37 mmol) in DMSO (15 mL) was added aq 30% NaOH (5 mL)

and the heterogeneous solution was stirred for 3 h. After the comple-

tion of the reaction (TLC), the mixture was poured over crushed ice

(50 mL) containing concd HCl (5 mL). The solid obtained was filtered,

washed with H₂O (30 mL) and dried (Na₂SO₄). The crude product was

washed with 5% EtOAc/hexane (10 mL) to afford 5H-thieno[3,2-b]car-

bazole (0.27 g). The thieno[3,2-b]carbazole was used as such in the

next step without any further purification. To a suspension of NaH

(0.107 g, 2.24 mmol) in anhyd THF (mL) at 0 °C, 5H-thieno[3,2-b]car-

bazole (0.25 g, 1.12 mmol) was added. After the addition was com-

pleted, the reaction mixture was stirred at rt for 2 h and then cooled

to 0 °C. To this, a solution of hexyl bromide (0.22 g, 1.13 mmol) in THF

(2 mL) was added and stirred for 10 min. Then, the mixture was

stirred at rt for 12 h and poured over crushed ice (50 g) containing

NH₄Cl (5 g). The mixture was extracted with DCM (30 mL) and the

DCM layer was washed with H₂O (3 × 20 mL) and dried (Na₂SO₄). The

solvent was removed under vacuo and the crude product was purified

by column chromatography (silica gel, EtOAc/hexane 1:9) to afford 5-

hexylthieno[3,2-b]carbazole 16 as a white solid; yield: 0.23 g (56%);

mp 86–88 °C.

HRMS (ESI-TOF, MeOH): m/z calcd for C₃₀H₁₈NO₃S₂[M⁺]: 504.0728;

found: 504.0727.

Conflict of Interest

The authors declare no conflict of interest.

Funding Information

This work was funded by the Council of Scientific and Industrial Re-

search (CSIR) Project [02(0376)/19/EMR-II] and University Grants

Commission (UGC)-Mid Career Award [F-19-230/2018(BSR)], New

Delhi.

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¹H NMR (300 MHz, CDCl₃):  = 8.51 (s, 1 H), 8.11–8.09 (d, J = 7.5 Hz, 1

H), 7.71 (s, 1 H), 7.48–7.33 (m, 4 H), 7.22–7.17 (m, 1 H), 4.29 (t, J = 7.2

Hz, 2 H), 1.92–1.84 (m, 2 H), 1.43–1.29 (m, 6 H), 0.88–0.83 (t, J = 6.9

Hz, 3 H).

¹³C NMR (75 MHz, CDCl₃):  = 142.1, 139.8, 138.5, 131.6, 126.6, 126.2,

123.6, 123.0, 122.4, 120.5, 118.7, 113.6, 108.4, 101.8, 43.4, 31.7, 28.7,

27.1, 22.6, 14.0.

Acknowledgment

V. S. thanks Council of Scientific and Industrial Research (CSIR) New

Delhi for a fellowship. The authors thank the Department of Science

and Technology Funds for the Improvement of Science and Technolo-

gy (DST-FIST) New Delhi for NMR and HRMS facilities.

HRMS (ESI-TOF, MeOH): m/z calcd for C₂₀H₂₁NS [M⁺]: 307.1395;

found: 307.1402.

Supporting Information

Supporting information for this article is available online at

Annulated Carbazole (17a)

https://doi.org/10.1055/a-1387-9479. Su

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The domino reaction 3-bromomethylindole 4 (0.2 g, 0.48 mmol) with

5-hexyl-5H-thieno[3,2-b]carbazole (16; 0.22 g, 0.72 mmol) using an-

hyd SnCl₄(0.025 g, 0.096 mmol) in anhyd 1,2-DCE (10 mL) at rt for 4

h, followed by usual workup and column chromatographic purifica-

tion (silica gel, EtOAc/hexane 1:9) adopting the above mentioned

general procedure afforded carbazole 17a as a colorless solid; yield:

0.191 g (68%); mp 148–150 °C.

¹H NMR (300 MHz, CDCl₃):  = 8.85 (s, 1 H), 8.64–8.63 (m, 2 H), 8.46

(s, 1 H), 8.33 (d, J = 8.1 Hz, 1 H), 8.00 (d, J = 7.5 Hz, 1 H), 7.89 (d, J = 7.8

Hz, 2 H), 7.80 (s, 1 H), 7.69 (s, 1 H), 7.57–7.46 (m, 3 H), 7.43–7.37 (m, 2

H), 7.32–7.27 (m, 2 H), 4.35 (t, J = 7.05 Hz, 2 H), 2.03–1.98 (m, 2 H),

1.46–1.36 (m, 4 H), 0.94 (t, J = 6.9 Hz, 3 H).

¹³C NMR (75 MHz, CDCl₃):  = 142.0, 139.8, 139.5, 137.8, 137.3, 133.7,

132.8, 131.4, 129.0, 127.7, 127.3, 127.0, 126.6, 125.4, 124.8, 124.3 (2

C), 123.7, 122.4, 120.2,118.9, 118.8, 115.3, 114.4, 110.8, 102.8, 101.4,

43.5, 31.7, 28.2, 27.2, 22.7, 14.1.

HRMS (ESI-TOF, MeOH): m/z calcd for C₃₆H₃₁N₂O₂S₂[M + H]⁺:

587.1827; found: 587.1824.

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Article Doi

Synthesis of Annulated Carbazoles via FeCl 3/SnCl 4- Mediated Domino Reaction of Vinyl Ketone Tethered Bromomethylindoles with Arenes and Heteroarenes

DOI: 10.1055/a-1387-9479

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Full text of DOI:10.1055/a-1387-9479

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