Facile synthesis of substituted furo-and pyrano-carbazoles

Article abstract of DOI:10.1080/00397911.2011.573173

Simple and efficient method for the synthesis of substituted furo-and pyrano-carbazole derivatives from 1-hydroxycarbazoles was described.

Full text of DOI:10.1080/00397911.2011.573173

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Facile Synthesis of Substituted Furo- and
Pyrano-Carbazoles
Kumaresan Prabakaran a & Karnam Jayarampillai Rajendra Prasad a
a Department of Chemistry, Bharathiar University, Coimbatore,
Tamilnadu, India
Accepted author version posted online: 10 Jan 2012.Published
online: 21 Jun 2012.
To cite this article: Kumaresan Prabakaran & Karnam Jayarampillai Rajendra Prasad (2012)
Facile Synthesis of Substituted Furo- and Pyrano-Carbazoles, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 42:20, 2966-2980,
DOI: 10.1080/00397911.2011.573173
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Synthetic Communications1, 42: 2966–2980, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.573173
FACILE SYNTHESIS OF SUBSTITUTED FURO- AND
PYRANO-CARBAZOLES
Kumaresan Prabakaran and Karnam Jayarampillai
Rajendra Prasad
Department of Chemistry, Bharathiar University, Coimbatore, Tamilnadu,
India
GRAPHICAL ABSTRACT
Abstract Simple and efficient method for the synthesis of substituted furo- and
pyrano-carbazole derivatives from 1-hydroxycarbazoles was described.
Keywords Furo[2,3-a]carbazole; 1-hydroxycarbazole; 1-hydroxycarbazole-2-carbalde-
hyde; 3-substituted pyrano[3,4-a]carbazoles; 3,4,5,6-tetrahydro-isochromeno[3,4-a]carba-
zoles
INTRODUCTION
Carbazoles constitute an important class of heterocycles that are known for
their potent antitumor, antibacterial, anti-inflammatory, psychotropic, and antihis-
tamine properties.[1–5] Naturally occurring 1-oxygenated carbazoles have attracted
great interest because of their diverse and significant biological activity.[6] These
alkaloids are mainly extracted from species of the genera Murraya and Clausena,
and in the case of 2- and 3-substituted families, their biogenesis has been established.
The isolation of girinimbine (I) was the first report of a naturally occurring pyrano-
carbazole alkaloid.[7] Ito and Furukawa reported the isolation of furostifoline (II)
from M. euchrestifolia, the first furocarbazole alkaloid from the natural source.[8]
Later, clauszoline-H (III), isolated from the roots of C. excavata, was the first
example of naturally occurring 1-oxygenated pyrano[2,3-a]carbazole alkaloid[9]
(Fig. 1). Moreover, from the synthetic viewpoint, the carbazole framework has
been an attractive target in the development of novel and efficient strategies for
the synthesis of natural and hetero-fused carbazoles. Besides, oxygen-containing
Received February 14, 2011.
Address correspondence to Karnam Jayarampillai Rajendra Prasad, Department of Chemistry,
Bharathiar University, Coimbatore 641 046, Tamilnadu, India. E-mail: prasad_125@yahoo.com
2966

FURO- AND PYRANO-CARBAZOLES
2967
Figure 1. Oxygenated carbazole alkaloids.
hetero-annulated carbazoles have proved to be a popular synthetic target, and a wide
variety of synthetic strategies have been reported.[10]
On the background of these findings, we are interested in the development of
methods for the efficient and rapid synthesis of the derivatives of furo- and
pyrano-carbazoles, especially because, many methods involving multistep reactions,
lower yields, longer reaction time, and the high cost of palladium are unsatisfactory.
Recently, we have reported some simple methods for the synthesis of furo- and
pyrano-fused carbazoles.[11,12] In continuation of our interest in oxygen containing
hetero-annulated carbazole analog, herein we describe a simple, economical, and
effective one- or two-step procedure for the synthesis of furo- and pyrano-carbazoles
from 1-hydroxycarbazole as a starting material. These starting materials were easily
prepared from 2,3,4,9-tetrahydrocarbazole-1-one.[13,14]
RESULTS AND DISCUSSION
In connection with our recent work on the synthesis of oxygen-containing hetero-
annulated carbazoles, we were interested in the synthesis of furo- and pyrano-
carbazoles utilizing 1-hydroxycarbazoles as synthon. For the synthesis of furo[2,3-
a]carbazoles (3), 1-(2-oxo-2-phenylethoxy)-9H-carbazole (2) is a possible intermediate
and may be prepared by O-alkylation, as shown in Scheme 1. Initially, 1-hydroxycar-
bazole (1) was treated with 2-bromoacetophenone in the presence of K2CO3 in acetone
at refluxing temperature to yield the expected compound 2. To get the furo[2,3-a]car-
bazoles (3), various reaction conditions were adopted for the cyclization of 6-methyl-1-
(2-oxo-2-phenylethoxy)-9H-carbazole (2a) to improve the yield of the product. The
cyclodehydration of compound 2a with H2SO4 at 80ꢀC gave 3a in poor yield. In the
case of H3PO4 under toluene, refluxing condition gave moderate yield. The use of Lewis
acids for the condensation of compound 2a did not lead to an increase in the yield of
the product, but the cyclocondendation of 2a with polyphosphoric acid (PPA) at 85 ꢀC
and P2O5 in toluene at 100 ꢀC proceeds more smoothly and gave good yield of product.
Details of all reaction conditions that were checked are given in Table 1. Furthermore,
the general scope of this reaction was tested under identical reaction condition on
2(b–d) to the corresponding products 3 (b–d) good yields.
Next, we attempted to synthesize furo[2,3-a]carbazole-2,3(10H)-dione (4) in a
one-step method, as shown in Scheme 2. In this method, the synthon 1-hydroxy-
carbazole (1) was treated with oxalylchloride in trifluoroacetic acid at steam bath
temperature and yielded a single product. The infrared (IR) and 1H NMR spectrum
of the obtained compound reveals the absence of –OH and –NH proton. All the

2968
K. PRABAKARAN AND K. J. R. PRASAD
Scheme 1. Synthesis of 3-phenyl-10H-furo[2,3-a]carbazoles (3a–d).
Table 1. Cyclocondendation of 1-(2-oxo-2-phenylethoxy)-9H-carbazole (2) under various conditions
Entry
Substrate
Condition
Temp. (ꢀC) = time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
2a
2a
2a
2a
2a
2a
2b
2c
2d
H2SO4
80=6
100=12
110=6
100=8
85=4
18
15
30
45
60
72
70
74
74
BF3.(OEt)3
H3PO4=toluene
POCl3
PPA
P2O5=toluene
P2O5=toluene
P2O5=toluene
P2O5=toluene
100=2
100=2
100=2
100=2
Scheme 2. Synthesis of [1,4]oxazino[2,3,4-j,k]carbazole-1,2-diones (5a–d).

FURO- AND PYRANO-CARBAZOLES
2969
Table 2. Reaction of 1-hydroxycarbazole with ethyl 2-oxocyclohexanane-carboxylate
under various conditions
Entry
Substrate
Condition
H2SO4
CF3COOH
Temp. (ꢀC)=time (h)
Yield (%) (6:7)
1
2
3
4
5
6
7
1a
1a
1a
1a
1b
1c
1d
80=6
100=12
rt=24
80=6
5:24
45:20
nr
ZnCl2=POCl3
ZnCl2=POCl3
ZnCl2=POCl3
ZnCl2=POCl3
ZnCl2=POCl3
15:68
12:72
0:74
80=6
80=6
80=6
18:70
Notes. rt, room temperature; nr, no reaction.
spectral details attest that the obtained compounds are [1,4]oxazino[2,3,4-
jk]carbazole-1,2-dione (5), not the expected target product 4.
Further, our interest turned synthesis of pyranocarbazole from 1-hydroxycar-
bazole. Thus, 1-hydroxycarbazole was treated with ethyl 2-oxocyclohexanane-
carboxylate under ZnCl2=POCl3 (Table 2). No reaction was observed at room
temperature even after 24 h; heating of the mixture to 80 ꢀC for 8 h did, however,
afford two products with the target compounds 3,4,5,6-tetrahydroisochro-
meno[3,4-a]carbazol-2(13H)-one (7) along with the unexpected product 10-hydroxy-
6,7-dihydro-4H-indolo[3,2,1-de]phenanthridin-8(5H)-one (6) (Scheme 3). Compound
1c afforded 7c without the unexpected product 6c. For the unintended compounds 6,
the cyclization that occurred at C-8 of the carbazole skeleton was attested by its
1HNMR spectrum, which showed the presence of an OH proton as well as the number
and type of signals in the aromatic region expected for compounds 6a, 6b, and 6d. The
failure of compound 6c to cyclize can be readily explained by the methyl substituent
at carbon atom C8, which prevents reaction at this position. In the case of H2SO4 or
trifluoroacetic acid, the yield of the product was low. The best results were obtained in
ZnCl2=POCl3 condition by the reduced yield of 6.
Amino derivatives of carbazoles have potential to be significantly active in the
treatment of both Alzheimer’s disease and cancer.[15] Incorporation of amino groups
into the carbazole systems would enhance the hydrophilicity of the molecule and
therefore increase their water solubility.[16] Further, the sulfur atom will enhance
Scheme 3. Synthesis of indolo[3,2,1-de]phenanthridine (6a, b, d) and isochromeno[3, 4-a]carbazole (7a–d).

2970
K. PRABAKARAN AND K. J. R. PRASAD
Scheme 4. Synthesis of 3-substituted pyrano[2,3-a]carbazoles (9 and 10a–d).
activities of this molecule like the establishment of additional long-distance hydrogen
bonds with the DNA chain or in photochemical properties or phototherapy applica-
tions.[17] These observations encouraged us to synthesize some of these new products
with expected biological activity.
For the synthesis of substituted 3-amino- and 3-mercapto-pyrano[2,3-a]carba-
zoles, suitably substituted 1-hydroxycarbazol-2-carbaldehydes (7) were required. It
was envisaged that these compounds could be prepared from the Vilsmeier–Haack
reaction of 1-hydroxycarbazoles (1).[13] 3-Amino-pyrano[2,3-a]carbazoles (8) was
obtained by the reaction of 1-hydroxycarbazol-2-carbaldehyde with glycine under
pyridine refluxing condition, in the presence of a catalytic amount of piperidine.
The IR spectra of the compound 8a displayed the absorption bands at 3422, 3341,
3208, and 1708 cmꢁ1 corresponds to NH, NH2, and O-CO groups. Further, its
NMR spectral details reveals the obtained, as expected, 3-amino-pyrano[2,3-
a]carbazol-2-one (8). 3-Mercapto-pyrano[2,3-a]carbazoles was prepared under the
same reaction condition from 1-hydroxycarbazol-2-carbaldehydes (7) thioglycolic
acid (Scheme 4).
In summary, we have developed a simple and efficient high-yielding method-
ology for the synthesis of 3-phenyl-furo[2,3-a]carbazoles, tetrahydro-isochromeno
[3,4-a]carbazoles, 3-amino[2,3-a]carbazoles, and 3-mercapto-pyrano[2,3-a]carbazoles
from 1-hydroxycarbazoles.
EXPERIMENTAL
Melting points (mp) were determined on a Mettler FP 51 apparatus (Mettler
Instruments, Switzerland) and are uncorrected. IR spectra were recorded on a
Schimadzu FTIR-8201PC spectrophotometer (Schimadzu, Japan) using KBr discs.
1H NMR and 13C NMR spectra were recorded on Bruker AMX 500 [500 MHz
(1H) and 125 MHz (13C) NMR] spectrometers using tetramethylsilane (TMS) as
the internal reference. The chemical shifts are expressed in parts per million
(ppm). Mass spectra (MS) were recorded on an AutoSpec EIþ Shimadzu QP 2010
Plus Gas chromatography (GC)–MS mass spectrometer. Microanalyses were
performed on a Vario EL III model CHNS analyser (Vario, Germany) at the
Department of Chemistry, Bharathiar University. The purity of the products was
tested by thin-layer chromatography (TLC) with plates coated with silica gel-G, with
petroleum ether and ethyl acetate as developing solvents.

FURO- AND PYRANO-CARBAZOLES
2971
2-(9H-Carbazol-1’-yloxy)-1’-phenylethanones (2)
General procedure. A mixture of the respective 1-hydroxycarbazoles (1,
2.5 mmol), x-bromoacetophenone (2.5 mmol), and ignited K2CO3 (0.345 g, 5 mmol)
in 10 mL acetone was refluxed in a steam bath for 6 h. The reaction mixture was
monitored by TLC. After completion of the reaction, the excess solvent was
removed, dissolved in ice water, and neutralized with ice-cold 1:1 HCl. The solid
separated was filtered, washed with water, and dried. Then, it was purified by column
chromatography over silica gel using petroleum ether and ethylacetate (97:3) as
eluant to get the respective 2-(9H-carbazol-1-yloxy)-1-phenylethanones (2).
2-(6-Methyl-9H-carbazol-1’-yloxy)-1’-phenylethanone (2a). Orange solid;
mp 192 ꢀC; yield: 512 mg (65%); IR (KBr, cmꢁ1) nmax: 3349, 1701, 1545, 1252, 1155;
1H NMR (500 MHz, CDCl3) (ppm) d: 8.54 (b s, 1H, N9-H), 8.08 (s, 1H, C5-H), 8.04
0
0
(d d, 2H, C2 - & C6 -H, Jm ¼ 1.00 Hz, Jo ¼ 8.20 Hz), 7.80 (d d, 1H, C4-H,
0
0
Jm ¼ 1.50 Hz, Jo ¼ 7.50 Hz), 7.65 (t, 1H, C4 -H, J ¼ 8.00 Hz), 7.55 (t, 2H, C3 - &
0
C5 -H, J ¼ 8.00 Hz), 7.48 (d, 1H, C8-H, J ¼ 8.00 Hz), 7.29 (d, 1H, C7-H, J ¼ 8.00 Hz),
7.15 (t, 1H, C3-H, J ¼ 7.50 Hz), 6.95 (d, 1H, C2-H, J ¼ 8.00 Hz), 5.48 (s, 2H, O-CH2),
2.54 (s, 3H, C6-CH3);13C NMR (125 MHz, CDCl3) (ppm) d: 189.68 (C¼O), 137.31
0
0
(C1), 134.88 (C8a), 133.45 (C1 ), 131.60 (C9a), 131.14 (C4 ), 129.46 (C6), 127.92
0
0
0
0
(C2 , C6 ), 127.08 (C3 , C5 ), 126.25 (C4b), 126.18 (C5), 122.14 (C4a), 120.15 (C2),
119.02 (C7), 117.76 (C3), 117.35 (C4), 110.96 (C8), 72.51 (O-CH2), 21.18 (C6-CH3);
MS: m=z (%) 315 (Mþ, 100), 301 (60), 210 (75), 196 (24), 105 (15). Anal. calcd.
for C21H17NO2: C, 80.00; H, 5.43; N, 4.44%. Found: C, 79.92; H, 5.54; N, 4.38%.
2-(7-Methyl-9H-carbazol-1’-yloxy)-1’-phenylethanone (2b). Orange solid;
mp 158 ꢀC; yield: 535 mg (68%); IR (KBr, cmꢁ1) nmax: 3309, 1699, 1562, 1255, 1153;
1H NMR (500 MHz, CDCl3) (ppm) d:0 8.52 (b s, 1H, N9-H), 8.07 (d, 1H, C5-H,
0
J ¼ 7.75 Hz), 8.01 (d d, 2H, C2 - & C6 -H, Jm ¼ 2.00 Hz, Jo ¼ 8.20 Hz), 7.81 (d d,
0
1H, C4-H, Jm ¼ 1.50 Hz, Jo ¼ 8.00 Hz), 7.63 (t, 1H, C4 -H, J ¼ 8.00 Hz), 7.57 (t,
0
0
2H, C3 - & C5 -H, J ¼ 8.00 Hz), 7.28 (d, 1H, C6-H, J ¼ 7.75 Hz), 7.21 (s, 1H, C8-
H), 7.15 (t, 1H, C3-H, J ¼ 8.00 Hz), 6.95 (d, 1H, C2-H, J ¼ 8.00 Hz), 5.44 (s, 2H,
O-CH2), 2.54 (s, 3H, C7-CH3); 13C NMR (125 MHz,0 CDCl3) (ppm) d: 190.12
0
0
(CO), 137.97 (C8a), 137.60 (C1), 133.00 (C1 ), 131.11 (C4 ), 130.72 (C7), 128.04 (C2
0
0
0
& C6 ), 127.16 (C3 & C5 ), 124.42 (C5), 122.83 (C4b), 122.08 (C9a), 121.98 (C4a),
121.45 (C6), 119.88 (C2), 118.12 (C3), 117.18 (C4), 112.12 (C8), 72.14 (OCH2), 2093
(C7-CH3); MS: m=z (%) 315 (Mþ, 100), 314 (18), 301 (65), 210 (30), 196 (32), 111
(50), 105 (20). Anal. calcd. for C21H17NO2: C, 80.00; H, 5.43; N, 4.44%. Found:
C, 80.08; H, 5.48; N, 4.34%.
2-(8-Methyl-9H-carbazol-1’-yloxy)-1’-phenylethanone (2c). Orange solid;
mp 189 ꢀC; yield: 519 mg (66%); IR (KBr, cmꢁ1) nmax: 3256, 1700, 1565, 1249, 1145;
1
0
H NMR (500 MHz, CDCl3) (ppm) d: 8.54 (b s, 1H, N9-H), 8.06 (d d, 2H, C2 - &
0
C6 -H, Jm ¼ 1.50 Hz, Jo ¼ 8.25 Hz), 8.03 (d, 1H, C5-H, J ¼ 8.00 Hz), 7.61 (t, 1H,
0
0
0
C4 -H, J ¼ 8.25 Hz), 7.56 (t, 2H, C3 - & C5 -H, J ¼ 8.25 Hz), 7.35 (d, 1H, C7-H,
J ¼ 8.00 Hz), 7.17–7.15 (m, 2H, C3- & C6-H), 6.96 (d, 1H, C2-H, J ¼ 8.00 Hz), 5.41
(s, 2H, O-CH2), 2.61 (s, 3H, C8-CH3); 13C NMR (125 MHz, CDCl3) (ppm) d:
0
0
0
189.46 (CO), 137.52 (C8a), 136.82 (C1), 133.16 (C1 ), 131.07 (C4 ), 127.98 (C2 &
0
0
0
C6 ), 127.31 (C3 & C5 ), 125.73 (C6), 125.08 (C4b), 123.52 (C9a), 122.43 (C5),

2972
K. PRABAKARAN AND K. J. R. PRASAD
121.30 (C8), 120.98 (C4a), 120.69 (C7), 119.94 (C2), 117.82 (C4), 117.31 (C3), 72.93
(OCH2), 17.41 (C8-CH3); MS: m=z (%) 315 (Mþ, 100), 301 (58), 287 (35), 210
(38), 196 (22), 84 (28). Anal. calcd. for C21H17NO2: C, 80.00; H, 5.43; N, 4.44%.
Found: C, 79.96; H, 5.39; N, 4.40%.
2-(9H-Carbazol-1’-yloxy)-1’-phenylethanone (2d). Orange solid; mp
212 ꢀC; yield: 526 mg (70%); IR (KBr, cmꢁ1) nmax: 3301, 1701, 1543, 1248, 1150;
1H NMR (500 MHz, CDCl3) (ppm) d:0 8.50 (b s, 1H, N9-H), 8.09 (d, 1H, C5-H,
0
J ¼ 7.50 Hz), 8.06 (d d, 2H, C2 - & C6 -H, Jm ¼ 1.00 Hz, Jo ¼ 8.00 Hz), 7.78 (d d,
0
1H, C4-H, Jm ¼ 1.00 Hz, Jo ¼ 7.50 Hz), 7.66 (t, 1H, C4 -H, J ¼ 8.00 Hz), 7.55 (t,
0
0
2H, C3 - & C5 -H, J ¼ 8.00 Hz), 7.51 (d d, 1H, C7-H, Jm ¼ 1.00 Hz, Jo ¼ 7.50 Hz),
7.44 (t, 1H, C8-H, J ¼ 8.00 Hz), 7.25 (t, 1H, C2-H, Jm ¼ 1.00 Hz, Jo ¼ 7.50 Hz), 7.13
(t, 1H, C3-H, J ¼ 8.00 Hz), 6.93 (d, 1H, C2-H, J ¼ 8.00 Hz), 5.45 (s, 2H, O-CH2);
13C NMR0 (125 MHz, CDCl3) (ppm) 0d: 189.55 (CO), 138.01 (C1), 136.56 (C8a),
0
0
0
0
133.50 (C1 ), 131.42 (C4 ), 127.66 (C2 & C6 ), 127.20 (C3 & C5 ), 124.84 (C4b),
123.08 (C9a), 122.88 (C7), 121.87 (C5), 121.31 (C4a), 120.54 (C6), 120.32 (C2),
118.02 (C3), 117.75 (C4), 113.45 (C8), 73.10 (OCH2); MS: m=z (%) 301 (Mþ, 100),
224 (32), 182 (80), 166 (18), 115 (12), 102 (25). Anal. calcd. for C20H15NO2: C,
79.73; H, 4.98; N, 4.65%. Found: C, 79.70; H, 5.05; N, 4.52%.
3-Phenyl-10H-furo[2,3-a]carbazoles (3)
General procedure. A mixture of 2-(9H-carbazol-1-yloxy)-1-phenyletha-
nones (2, 1 mmol) and P2O5 (0.709 g, 5 mmol) in 10 mL toluene was heated at
100 ꢀC for 2 h. After completion of the reaction, the mixture was washed with excess
toluene and evaporated by vaccum. The crude product obtained was purified by col-
umn chromotography using petroleum ether and ethylacetate (90:10) to afford
3-phenyl-10H-furo[2,3-a]carbazoles (3).
7-Methyl-3-phenyl-10H-furo[2,3-a]carbazole (3a). Yellow solid; mp
257 ꢀC; yield: 214 mg (72%); IR (KBr, cmꢁ1) nmax: 3353, 2916, 1567, 1285; 1H
NMR (500 MHz, CDCl3) (ppm) d: 8.60 (b s, 1H, N10-H), 8.08 (s, 1H, C2-H), 7.99
0
(s, 1H, C6-H), 7.90 (d, 1H, C4-H, J ¼ 8.00 Hz), 7.54–7.50 (m, 4H, C5-, C9-, C2
&
0
0
0
0
C6 -H), 7.45–7.43 (m, 3H, C3 -, C4 - & C5 -H), 7.32 (d, 1H, C8-H, J ¼ 8.00 Hz), 2.55
(s, 3H, C7-CH3); 13C NMR (125 MHz, CDCl3) (ppm)0d: 150.08 (C10b), 138.00 (C2),
0
0
0
135.32 (C9a), 130.90 (C1 ), 129.88 (C7), 128.16 (C3 , C5 ), 127.22 (C10a), 127.05 (C4 ),
0
0
126.92 (C2 , C6 ), 126.12 (C5b), 125.64 (C3a), 126.02 (C6), 121.92 (C5), 121.20 (C3),
119.84 (C4), 118.74 (C8), 118.41 (C5a), 111.00 (C9), 21.89 (C7-CH3); MS: m=z (%)
297 (Mþ, 100), 282 (60), 220 (35), 195 (22), 179 (25), 129 (22). Anal. calcd. for
C21H15NO: C, 84.85; H, 5.05; N, 4.71%. Found: C, 84.80; H, 5.07; N, 4.63%.
8-Methyl-3-phenyl-10H-furo[2,3-a]carbazole (3b). Yellow solid; mp
259 ꢀC; yield: 208 mg (70%); IR (KBr, cmꢁ1) nmax: 3308, 2925, 1591, 1455, 1242;
1H NMR (500 MHz, CDCl3) (ppm) d: 8.58 (b s, 1H, N10-H), 8.07 (s, 1H, C2-H),
7.98 (d, 1H, C6-H, J ¼ 7.75 Hz), 7.88 (d, 1H, C4-H, J ¼ 8.00 Hz), 7.56–7.52 (m,
0
0
0
0
3H, C5-, C2 & C6 -H), 7.46–7.43 (m, 3H, C3-, C4 - & C5 -H), 7.22 (s, 1H, C9-H),
7.12 (d, 1H, C7-H, J ¼ 7.75 Hz), 2.54 (s, 3H, C8-CH3); 13C NMR (125 MHz, CDCl3)
0
(ppm) d: 150.41 (C10b), 137.78 (C2), 136.97 (C9a), 130.53 (C1 ), 130.15 (C8), 128.31

FURO- AND PYRANO-CARBAZOLES
2973
0
0
0
0
0
(C3 & C5 ), 127.12 (C2 & C6 ), 126.88 (C4 ), 124.89 (C3a), 123.01 (C5b), 122.59 (C10a),
121.76 (C3), 121.41 (C5), 120.96 (C7), 120.43 (C5a), 118.99 (C4), 117.78 (C6), 113.11
(C9), 21.14 (C8-CH3); MS: m=z (%) 297 (Mþ, 85), 296 (100), 282 (20), 220 (11), 195
(15), 165 (38), 104 (40). Anal. calcd. for C21H15NO: C, 84.85; H, 5.05; N, 4.71%.
Found: C, 84.88; H, 5.01; N, 4.63%.
9-Methyl-3-phenyl-10H-furo[2,3-a]carbazole (3c). Yellow solid; mp
274 ꢀC; yield: 219 mg (74%); IR (KBr, cmꢁ1) nmax: 3254, 2924, 1588, 1456, 1243;
1H NMR (500 MHz, CDCl3) (ppm) d: 8.61 (b s, 1H, N10-H), 8.11 (s, 1H, C2-H),
7.95 (d, 1H, C6-H, J ¼ 8.00 Hz), 7.89 (d, 1H, C4-H, J ¼ 8.00 Hz), 7.56 (d, 3H, C5-H,
0
0
0
0
&
J ¼ 8.00 Hz), 7.54–7.51 (m, 2H, C2 - & C6 -H), 7.45–7.42 (m, 3H, C3 -, C4
0
C5 -H), 7.34 (d, 1H, C8-H, J ¼ 8.00 Hz), 7.16 (t, 1H, C7-H, J ¼ 8.00 Hz), 2.61 (s,
3H, C9-CH3); 13C NMR0 (125 MHz, CDCl3) (ppm) d: 149.094 (C10b), 138.11 (C2),
0
0
0
0
136.83 (C9a), 130.83 (C1 ), 128.11 (C3 & C5 ), 126.79 (C4 ), 126.74 (C2 & C4 ),
125.53 (C7), 125.19 (C3a), 124.79 (C5b), 122.93 (C10a), 121.43 (C9), 120.89 (C5),
120.73 (C8), 120.31 (C5a), 119.71 (C4), 117.41 (C6), 17.42 (C9-CH3); MS: m=z
(%) 297 (Mþ, 100), 296 (75), 282 (15), 220 (45), 195 (18), 102 (25). Anal. calcd.
for C21H15NO: C, 84.85; H, 5.05; N, 4.71%. Found: C, 84.79; H, 5.11; N, 4.58%.
3-Phenyl-10H-furo[2,3-a]carbazole (3d). Yellow solid; mp 282 ꢀC; yield:
209 mg (74%); IR (KBr, cmꢁ1) nmax: 3301, 2918, 1590; 1H NMR (500 MHz, CDCl3)
(ppm) d: 8.57 (b s, 1H, N10-H), 8.13 (s, 1H, C2-H), 8.03 (d, 1H, C6-H, J ¼ 7.75 Hz),
0
7.90 (d, 1H, C4-H, J ¼ 7.50 Hz), 7.55 (d, 1H, C5-H, J ¼ 7.50 Hz), 7.52 (d, 2H, C2 - &
0
0
0
&
C6 -H, J ¼ 7.75 Hz), 7.49 (d, 1H, C9-H, J ¼ 7.75 Hz), 7.46–7.41 (m, 3H, C3 -, C4
C5 -H), 7.38 (t, 1H, C8-H, J ¼ 7.75 Hz), 7.18 (t, 1H, C7-H, J ¼ 7.75 Hz); 13C NMR
0
0
(125 MHz, 0CDCl3) (ppm) d: 151.21 (C10b), 138.18 (C2), 135.98 (C9a), 129.99 (C1 ),
0
0
0
0
127.87 (C3 & C5 ), 126.83 (C2 & C6 ), 126.66 (C4 ), 125.32 (C3a), 124.89 (C5b),
122.79 (C10a), 122.46 (C8), 121.65 (C5a), 121.45 (C5), 120.93 (C3), 120.15 (C7),
119.10 (C4), 118.11 (C6), 112.81 (C9); MS: m=z (%) 283 (Mþ, 100), 282 (52), 206
(30), 181 (25), 141 (18). Anal. calcd. for C20H13NO: C, 84.80; H, 4.59; N, 4.94%.
Found: C, 84.74; H, 4.63; N, 4.83%.
[1,4]Oxazino[2,3,4-j,k]carbazole-1,2-diones (5)
General procedure. A solution of the appropriate 1-hydroxycarbazoles (1,
1 mmol) and oxalyl chloride (1.2 mmol) in trifluoroacetic acid (7 mL) was refluxed
in a water bath for 12 h. After completion of the reaction, the excess solvent was eva-
porated under reduced pressure. The crude product thus obtained was extracted with
ethyl acetate, washed with water, dried over anhydrous Na2SO4, and purified by col-
umn chromatography over silica gel using petroleum ether–ethyl acetate (95:5) as a
eluant to yield [1,4]oxazino[2,3,4-j,k]carbazole-1,2-diones (5).
8-Methyl-[1,4]oxazino[2,3,4-j,k]carbazole-1,2-dione (5a). Yellow solid;
1
mp 250 ꢀC; yield: 196 mg (78%); IR (KBr, cmꢁ1) nmax: 2919, 1771, 1720, 1455; H
NMR (500 MHz, CDCl3) (ppm) d: 8.30 (d, 1H, C6-H, J ¼ 8.28 Hz), 7.82 (s, 1H,
C7-H), 7.76 (d, 1H, C4-H, J ¼ 8.28 Hz), 7.45 (t, 1H, C5-H, J ¼ 8.28 Hz), 7.41 (d,
1H, C10-H, J ¼ 8.16 Hz), 7.30 (d, 1H, C9-H, J ¼ 8.16 Hz), 2.56 (s, 3H, C8-CH3);
13C NMR (125 MHz, CDCl3) (ppm) d: 153.78 (C2 ¼ O), 146.22 (C1 ¼ O), 137.75

2974
K. PRABAKARAN AND K. J. R. PRASAD
(C3a), 137.13 (C11a), 134.47 (C8), 129.72 (C7), 127.20 (C10a), 125.70 (C4), 125.57 (C6b),
123.54 (C6a), 121.74 (C9), 117.19 (C5), 116.75 (C6), 112.86 (C10), 21.59 (C8-CH3); MS:
m=z (%) 251 (Mþ, 100), 250 (35), 195 (15), 179 (20), 128 (11), 89 (22). Anal. calcd. for
C15H9NO3: C, 71.71; H, 3.58; N, 5.58%. Found: C, 71.78; H, 3.55; N, 5.75%.
9-Methyl-[1,4]oxazino[2,3,4-j,k]carbazole-1,2-dione (5b). Yellow solid;
mp 199 ꢀC; yield: 186 mg (74%); IR (KBr, cmꢁ1) nmax: 2921, 1774, 1722, 1545,
1
1140; H NMR (500 MHz, CDCl3) (ppm) d: 10.62 (s, 1H, C10-H), 8.02 (d d, 1H,
C6-H, Jm ¼ 2.00, Jo ¼ 8.25 Hz), 7.80 (d, 1H, C7-H, J ¼ 8.00 Hz), 7.22 (t, 1H, C5-H,
J ¼ 8.00 Hz), 7.13 (d, 1H, C4-H, J ¼ 8.00 Hz), 6.97 (d, 1H, C8-H, J ¼ 8.00 Hz), 2.98
(s, 3H, C9-CH3); 13C NMR (125 MHz, CDCl3) (ppm) d: 153.66 (C2 ¼ O), 146.35
(C1 ¼ O), 138.12 (C4a), 137.75 (C10a), 136.86 (C11a), 130.42 (C9), 125.36 (C4),
124.10 (C6a), 123.01 (C6b), 122.41 (C7), 121.38 (C8), 117.12 (C5), 116.18 (C6),
113.26 (C10), 21.42 (C9-CH3); MS: m=z (%) 251 (Mþ, 100), 250 (24), 236 (48), 195
(12), 179 (50), 153 (15), 128 (18), 89 (10). Anal. calcd. for C15H9NO3: C, 71.71; H,
3.58; N, 5.58%. Found: C, 71.79; H, 3.56; N, 5.82%.
10-Methyl-[1,4]oxazino[2,3,4-j,k]carbazole-1,2-dione (5c). Yellow solid;
mp 201 ꢀC; yield: 200 mg (80%); IR (KBr, cmꢁ1) nmax: 2925, 1773, 1725, 1591,
1448, 1245, 1155; 1H NMR (500 MHz, CDCl3) (ppm) d: 7.89 (d d, 1H, C7-H,
Jm ¼ 1.00, Jo ¼ 7.50 Hz), 7.82 (d d, 1H, C6-H, Jm ¼ 1.00, Jo ¼ 8.00 Hz), 7.48 (t, 2H,
C5-, C8-H, J ¼ 8.00 Hz), 7.42 (d, 1H, C9-H, J ¼ 7.50 Hz), 7.34 (d d, 1H, C4-H,
Jm ¼ 1.00, Jo ¼ 8.00 Hz), 2.98 (s, 3H, C10-CH3); 13C NMR (125 MHz, CDCl3)
(ppm) d: 154.03 (C2 ¼ O), 146.40 (C1 ¼ O), 139.00 (C3a), 137.72 (C11a), 137.15
(C10a), 125.41 (C4), 125.08 (C8), 124.93 (C6b), 123.61 (C6a), 123.00 (C10), 122.34
(C9), 121.15 (C7), 118.04 (C5), 117.22 (C6), 18.40 (C10-CH3); MS: m=z (%) 251
(Mþ, 100), 236 (20), 223 (38), 195 (15), 179 (25), 128 (32), 102 (10), 89 (50). Anal.
calcd. for C15H9NO3: C, 71.71; H, 3.58; N, 5.58%. Found: C, 71.66; H, 3.62; N,
5.61%.
[1,4]Oxazino[2,3,4-j,k]carbazole-1,2-dione (5d). Yellow solid; mp 212 ꢀC;
yield: 194 mg (82%); IR (KBr, cmꢁ1) nmax: 2925, 1773, 1725, 1591, 1448, 1245,
1
1155; H NMR (500 MHz, CDCl3) (ppm) d: 8.08 (d, 1H, C7-H, J ¼ 8.00 Hz), 7.71
(d, 1H, C6-H, J ¼ 8.00 Hz), 7.49 (d, 1H, C10-H, J ¼ 8.00 Hz), 7.45 (d t, 1H, C9-H,
Jm ¼ 1.00, Jo ¼ 8.00 Hz), 7.26 (d t, 1H, C8-H, Jm ¼ 1.00, Jo ¼ 8.00 Hz), 7.10 (t, 1H,
C5-H, J ¼ 8.00 Hz), 6.86 (d, 1H, C4-H, J ¼ 8.00 Hz); 13C NMR (125 MHz, CDCl3)
(ppm) d: 153.75 (C2 ¼ O), 146.30 (C1 ¼ O), 138.88 (C3a), 137.38 (C11a), 136.10
(C10a), 126.01 (C4), 125.60 (C6b), 124.21 (C9), 123.40 (C6a), 122.94 (C8), 122.12
(C7), 118.62 (C5), 116.93 (C6), 113.48 (C10); MS: m=z (%) 237 (Mþ, 100), 236 (40),
209 (18), 181 (75), 165 (30), 140 (18), 114 (20). Anal. calcd. for C14H7NO3: C,
70.88; H, 2.95; N, 5.90%. Found: C, 70.94; H, 2.98; N, 5.68%.
10-Hydroxy-4,5,6,7-tetrahydro-indolo[3,2,1-de]phenanthridin-
8-ones (6) and 3,4,5,6-Tetrahydroisochromeno[3,4-a]carbazol-
2(13H)-ones (7)
General procedure. An appropriate mixture of the respective 1-hydroxycar-
bazoles (1, 1 mmol) and ethyl 2-oxocyclohexan-2-carboxylate (1 mmol) is treated

FURO- AND PYRANO-CARBAZOLES
2975
with fused ZnCl2=POCl3 (1.5 g=6 mL) at 80 ꢀC for 6 h. The reaction was monitored
by TLC. After completion of the reaction, the mixture was poured onto crushed ice
and extracted with ethyl acetate. The organic phase was dried (anhydrous Na2SO4),
evaporated, and purified by column chromatography over silica gel using petroleum
ether=ethyl acetate (99:1) and (95:5) as eluant to get the products 10-hydroxy-4,5,
6,7-tetrahydro-indolo[3,2,1-d,e]phenanthridin-8-ones (6) and 3,4,5,6-tetrahydro iso-
chromeno [3,4-a]carbazol-2(13H)-ones (7) respectively.
10-Hydroxy-2-methyl-4,5,6,7-tetrahydro-indolo[3,2,1-d,e]phenanthridꢁin1-
8-one (6a). Yellowish white solid; mp 202 ꢀC; yield: 45 mg (15%); IR (KBr, cm
)
1
n
max: 3430, 2928, 1629, 1593, 1966; H NMR (400 MHz, CDCl3) (ppm) d: 12.53
(s, 1H, C10-H), 7.84 (s, 1H, C1-H), 7.54 (s, 1H, C3-H), 7.42 (d d, 1H, C13-H,
Jm ¼ 1.04 Hz, Jo ¼ 7.56 Hz), 7.32 (t, 1H, C12-H, J ¼ 7.98 Hz), 7.05 (d d, 1H, C11-H,
Jm ¼ 1.04 Hz, Jo ¼ 8.04 Hz), 3.04–3.02 (m, 2H, C7-H2), 2.77–2.75 (m, 2H, C4-H2),
2.61 (s, 3H, C2-CH3), 1.95–1.90 (m, 4H, C5- & C6-H2); 13C NMR (100 MHz, CDCl3)
(ppm) d: 160.12 (C¼O), 146.72 (C10), 142.23 (C3b), 134.21 (C2), 130.37 (C3b’), 128.80
(C7a), 128.06 (C3), 126.53 (C9a), 124.78 (C13b), 123.01 (C12), 122.34 (C1), 118.80
(C13a), 118.21 (C3a), 116.00 (C11), 110.95 (C13), 25.67 (C4-H2), 23.96 (C7-H2), 21.68
(C2-CH3), 21.53 (C5-H2), 21.00 (C6-H2); MS: m=z (%) 303 (Mþ, 100), 302 (80),
285 (29), 229 (15), 175 (22), 127 (11), 95 (18). Anal. calcd. for C20H17NO2: C,
79.21; H, 5.61; N, 4.62%. Found: C, 79.26; H, 5.59; N, 4.57%.
10-Methyl-3,4,5,6-tetrahydroisochromeno[3,4-a]carbazol-2(13H)-one (7a).
White solid; mp 199 ꢀC; yield: 206 mg (68%); IR (KBr, cmꢁ1) nmax: 3284, 2925, 1710,
1
1606; H NMR (400 MHz, CDCl3) (ppm) d: 8.82 (b s, 1H, N13-H), 8.64 (d, 1H,
C9-H, Jm ¼ 1.48 Hz), 8.08 (d, 1H, C7-H, J ¼ 7.88 Hz), 7.79 (d, 1H, C12-H,
J ¼ 7.48 Hz), 7.38–7.30 (m, 2H, C8- & C11-H), 2.94–2.89 (m, 2H, C3-H2), 2.64–2.60
(m, 2H, C6-H2), 2.56 (s, 3H, C10-CH3), 1.96–1.88 (m, 4H, C5 & C6-H2); 13C NMR
(100 MHz, CDCl3) (ppm) d: 161.70 (C¼O), 141.50 (C6a), 137.40 (C13b), 134.58
(C12a), 134.15 (C10), 127.66 (C2a), 127.10 (C13a), 126.98 (C8b), 123.27 (C9), 122.38
(C11), 118.32 (C6b), 118.11 (C8a), 115.54 (C8), 111.23 (C12), 110.48 (C7), 26.36 (C6-
H2), 23.80 (C3-H2), 21.78 (C5-H2), 21.43 (C10-CH3), 21.16 (C4-H2); MS: m=z (%)
303 (Mþ, 100), 302 (16), 247 (29), 236 (15), 197 (22), 179 (26), 129 (10). Anal. calcd.
for C20H17NO2: C, 79.21; H, 5.61; N, 4.62%. Found: C, 79.24; H, 5.63; N, 4.65%.
10-Hydroxy-3-methyl-4,5,6,7-tetrahydro-indolo[3,2,1-d,e]phenanthridꢁin1-
8-one (6b). Yellowish white solid; mp 213 ꢀC; yield: 36 mg (12%); IR (KBr, cm
)
1
n
max: 3430, 2942, 1631; H NMR (400 MHz, CDCl3) (ppm) d: 12.75 (s, 1H, C10-
H), 7.82 (d, 1H, C1-H, J ¼ 7.48 Hz), 7.45 (d, 1H, C13-H, J ¼ 7.98 Hz), 7.30 (t, 1H,
C12-H, J ¼ 7.98 Hz), 7.10–7.05 (m, 2H, C2- & C11-H), 3.06–3.03 (m, 2H, C7-H2),
2.85 (s, 3H, C3-CH3), 2.76–2.74 (m, 2H, C4-H2), 1.97–1.92 (m, 4H, C5- & C6-H2);
13C NMR (125 MHz, CDCl3) (ppm) d: 160.21 (CO), 146.56 (C10), 141.79 (C3b),
130.72 (C3), 130.41 (C3b0), 128.47 (C7a), 126.43 (C9a), 125.11 (C13b), 122.97 (C12),
121.25 (C2), 119.19 (C1), 118.76 (C13a), 118.32 (C3a), 115.89 (C11), 110.83 (C13),
25.27 (C4), 23.83 (C7), 21.54 (C3-CH3), 21.41 (C5), 21.12 (C6); MS: m=z (%) 303
(Mþ, 100), 302 (65), 285 (16), 277 (29), 229 (15), 175 (22), 127 (14), 89 (10). Anal.
calcd. for C20H17NO2: C, 79.21; H, 5.61; N, 4.62%. Found: C, 79.17; H, 5.62; N,
4.70%.

2976
K. PRABAKARAN AND K. J. R. PRASAD
11-Methyl-3,4,5,6-tetrahydroisochromeno[3,4-a]carbazol-2(13H)-one (7b).
Yellow solid; mp 194 ꢀC; yield: 218 mg (72%); IR (KBr, cmꢁ1) nmax: 3272, 2942,
1
1688, 1592; H NMR (400 MHz, CDCl3) (ppm) d: 8.72 (b s, 1H, N13-H), 8.58 (d,
1H, C9-H, J ¼ 8.20 Hz), 8.06 (d, 1H, C7-H, J ¼ 8.16 Hz), 7.50 (d, 1H, C10-H,
J ¼ 8.20 Hz), 7.41 (s, 1H, C2-H), 7.22 (d, 1H, C8-H, J ¼ 8.16 Hz), 2.98–2.94 (m,
2H, C3-H2), 2.65–2.63 (m, 2H, C6-H2), 2.51 (s, 3H, C11-CH3), 1.95–1.89 (m, 4H,
C4- & C5-H); 13C NMR (125 MHz, CDCl3) (ppm) d: 161.44 (CO), 141.16 (C6a),
139.02 (C13b), 137.27 (C12a), 130.40 (C11), 127.40 (C2a), 122.72 (C13a), 122.31 (C8b),
121.62 (C10), 119.93 (C8a), 118.31 (C9), 117.99 (C6b), 115.14 (C8), 113.10 (C12),
110.18 (C7), 26.14 (C6), 23.63 (C3), 21.60 (C5), 21.36 (C11-CH3), 21.21 (C4); MS:
m=z (%) 303 (Mþ, 100), 302 (12), 275 (29), 247 (15), 236 (22), 197 (10), 121 (15),
102 (22). Anal. calcd. for C20H17NO2: C, 79.21; H, 5.61; N, 4.62%. Found: C,
79.16; H, 5.57; N, 4.58%.
12-Methyl-3,4,5,6-tetrahydroisochromeno[3,4-a]carbazol-2(13H)-one (7c).
Yellow solid; mp 253 ꢀC; yield: 224 mg (74%); IR (KBr, cmꢁ1) nmax: 3377, 2960,
1
1687, 1595; H NMR (400 MHz, CDCl3) (ppm) d: 8.78 (b s, 1H, N13-H), 8.56 (d,
1H, C9-H, J ¼ 8.00 Hz), 8.07 (d, 1H, C7-H, J ¼ 8.20 Hz), 7.52 (d, 1H, C11-H,
J ¼ 8.00), 7.40 (d, 1H, C8-H, J ¼ 8.20 Hz), 7.22 (t, 1H, C10-H, J ¼ 8.00 Hz),
2.98–2.93 (m, 2H, C3-H2), 2.66–2.63 (m, 2H, C6-H2), 2.61 (s, 3H, C12-CH3),
1.97–1.90 (m, 4H, C4- & C5-H); 13C NMR (125 MHz, CDCl3) (ppm) d: 161.38
(CO), 141.11 (C6a), 139.13 (C13b), 137.12 (C12a), 127.68 (C2a), 125.33 (C10), 125.03
(C8b), 122.63 (C13a), 121.88 (C12), 121.10 (C11), 120.81 (C8a), 118.31 (C9), 117.83
(C6b), 115.19 (C8), 110.63 (C7), 26.12 (C6), 23.67 (C3), 22.01 (C5), 21.32 (C4), 17.78
(C12-CH3); MS: m=z (%) 303 (Mþ, 100), 275 (18), 260 (15), 247 (35), 236 (42), 197
(15), 179 (22), 129 (30). Anal. calcd. for C20H17NO2: C, 79.21; H, 5.61; N, 4.62%.
Found: C, 79.19; H, 5.64; N, 4.71%.
10-Hydroxy-4,5,6,7-tetrahydro-indolo[3,2,1-d,e]phenanthridin-8-one (6d).
Yellowish white solid; mp 198 ꢀC; yield: 52 mg (18%); IR (KBr, cmꢁ1) nmax: 3427,
1
2930, 1635; H NMR (400 MHz, CDCl3) (ppm) d: 12.51 (s, 1H, C10-H), 8.02 (d,
1H, C1-H, J ¼ 7.82 Hz), 7.72 (d, 1H, C13-H, J ¼ 8.26 Hz), 7.54 (t, 1H, C2-H,
J ¼ 7.82 Hz), 7.45 (d, 1H, C11-H, J ¼ 8.26 Hz), 7.38 (t, 1H, C12-H, J ¼ 8.26 Hz),
7.08 (d, 1H, C3-H, J ¼ 7.82 Hz), 3.10–3.07 (m, 2H, C7-H2), 2.72–2.69 (m, 2H,
C4-H2), 1.96–1.91 (m, 4H, C5- & C6-H2); 13C NMR (125 MHz, CDCl3) (ppm) d:
160.33 (CO), 146.83 (C10), 141.98 (C3b), 130.18 (C3b0), 128.53 (C7a), 126.13 (C9a),
124.83 (C13b), 123.12 (C12), 122.76 (C3), 120.41 (C2), 119.15 (C13a), 118.51 (C3a),
117.40 (C1), 116.11 (C11), 110.58 (C13), 25.47 (C4), 23.73 (C7), 21.23 (C5), 21.10
(C6); MS: m=z (%) 289 (Mþ, 100), 288 (76), 271 (36), 215, (30), 163 (12), 113 (44).
Anal. calcd. for C19H15NO2: C, 78.89; H, 5.19; N, 4.84%. Found: C, 78.80; H,
5.22; N, 4.78%.
3,4,5,6-Tetrahydroisochromeno[3,4-a]carbazol-2(13H)-one (7d). Yellow
solid; mp 211 ꢀC; yield: 202 mg (70%); IR (KBr, cmꢁ1) nmax: 3391, 2924, 1689,
1
1545; H NMR (400 MHz, CDCl3) (ppm) d: 8.75 (b s, 1H, N13-H), 8.61 (d, 1H,
C9-H, J ¼ 7.88 Hz), 8.12 (d, 1H, C7-H, J ¼ 8.40 Hz), 7.78 (d, 1H, C12-H, J ¼ 7.88),
7.50 (t, 1H, C11-H, J ¼ 7.88 Hz), 7.42 (d, 1H, C8-H, J ¼ 8.40 Hz), 7.24 (t, 1H,
C10-H, J ¼ 7.88 Hz), 2.96–2.92 (m, 2H, C3-H2), 2.65–2.61 (m, 2H, C6-H2),

FURO- AND PYRANO-CARBAZOLES
2977
1.95–1.90 (m, 4H, C4- & C5-H); 13C NMR (125 MHz, CDCl3) (ppm) d: 161.58 (CO),
140.89 (C6a), 139.35 (C13b), 136.36 (C12a), 127.42 (C2a), 124.18 (C8b), 123.41
(C13a), 122.68 (C11), 121.38 (C10), 120.36 (C8a), 118.19 (C9), 117.48 (C6b), 114.96 (C8),
112.41 (C12), 110.43 (C7), 26.37 (C6), 23.12 (C3), 21.69 (C5), 21.46 (C4); MS: m=z (%)
289 (Mþ, 100), 285 (75), 233, (32), 209 (15), 181 (10), 164 (12), 115 (20). Anal. calcd.
for C19H15NO2: C, 78.89; H, 5.19; N, 4.84%. Found: C, 78.93; H, 5.16; N, 4.78%.
3-Aminopyrano[2,3-a]carbazol-2(11H)-ones (9) and
3-Mercaptopyrano[2,3-a]carbazol-2(11H)-ones (10)
General procedure. To a mixture of respective 1-hydroxy carbazole-2-
carbaldehydes (1, 0.5 mmol) and glycine=thioglycolic acid (1 mmol) in 5 ml pyridine
was added 0.2 mL of piperidine at 80 ꢀC. Then the temperature was raised to 130 ꢀC
and maintained for 4 h. The reaction was monitored by TLC. After completion of
reaction, the excess solvent was removed and the reaction mixture was poured into
ice water and neutralized with 1:1 HCl. The solid was filtered, dried, and purified by
column chromatography over silica gel using petroleum ether=ethyl acetate (85:15)
as eluant to get the corresponding 3-aminopyrano[2,3-a]carbazol-2(11H)-ones (9)
and 3-mercapto-pyrano[2,3-a]carbazol-2(11H)-ones (10). The compound thus
obtained was recrystallized from ethanol.
3-Amino-8-methylpyrano[2,3-a]carbazol-2(11H)-one (9a). Brown solid;
mp 267 ꢀC; yield: 87 mg (66%); IR (KBr, cmꢁ1) nmax: 3422, 3341, 3208, 2918,
1
1708; H NMR (500 MHz, CDCl3) (ppm) d: 8.34 (b s, 1H, N11-H), 8.03 (s, 1H,
C7-H), 7.83 (d, 1H, C5-H, J ¼ 7.80 Hz), 7.48 (d, 1H, C10-H, J ¼ 7.46 Hz), 7.34–7.25
(m, 2H, C6-, C9-H), 6.50 (s, 1H, C4-H), 4.26 (s, 2H, C3-NH2), 2.54 (s, 3H, C8-
CH3); 13C NMR (125 MHz, CDCl3) (ppm) d: 159.60 (C2), 139.23 (C10a), 136.52
(C3), 132.24 (C11b), 129.20 (C11a), 128.41 (C8), 128.30 (C6b), 123.11 (C7), 119.80
(C9), 118.84 (C4a), 116.90 (C6), 116.52 (C4), 112.73 (C5), 111.06 (C10), 104.64
(C6a), 21.04 (C8-CH3); MS: m=z (%) 264 (Mþ, 100), 263 (28), 247 (60), 223 (12),
179 (27), 129 (8), 104 (15). Anal. calcd. for C16H12N2O2: C, 72.72; H, 4.45; N,
10.60%; Found: C, 72.66; H, 4.47; N, 10.56%.
3-Amino-9-methylpyrano[2,3-a]carbazol-2(11H)-one (9b). Brown solid;
mp 280 ꢀC; yield: 84 mg (64%); IR (KBr, cmꢁ1) nmax: 3425, 3309, 3204, 2919,
1
1710; H NMR (500 MHz, CDCl3) (ppm) d: 8.48 (b s, 1H, N11-H), 7.99 (d, 1H,
C7-H, J ¼ 7.50 Hz), 7.87 (d, 1H, C5-H, J ¼ 7.25 Hz), 7.26–7.12 (m, 3H, C6-, C8,
C10-H), 6.53 (s, 1H, C4-H), 4.32 (s, 2H, C3-NH2), 2.58 (s, 3H, C9-CH3); 13C NMR
(125 MHz, CDCl3) (ppm) d: 159.01 (C¼O), 142.45 (C10a), 136.35 (C3), 132.88
(C11b), 132.18 (C9), 129.18 (C11a), 121.36 (C8), 120.82 (C6b), 120.27 (C7), 118.40
(C4a), 117.00 (C6), 114.12 (C4), 112.91 (C10), 112.71 (C5), 104.72 (C6a), 21.40 (C9-
CH3); MS: m=z (%) 264 (Mþ, 100), 263 (45), 247 (80), 223 (16), 208 (10), 179 (12),
129 (22), 77 (35). Anal. calcd. for C16H12N2O2: C, 72.72; H, 4. 45; N, 10.60%; Found:
C, 72.69; H, 4.43; N, 10.51%.
3-Amino-10-methylpyrano[2,3-a]carbazol-2(11H)-one (9c). Brown solid;
mp 316 ꢀC; yield: 89 mg (68%); IR (KBr, cmꢁ1) nmax: 3419, 3320, 3217, 2921,
1
1704; H NMR (500 MHz, CDCl3) (ppm) d: 8.39 (b s, 1H, N11-H), 7.87 (d, 1H,

2978
K. PRABAKARAN AND K. J. R. PRASAD
C7-H, J ¼ 7.25 Hz), 7.69 (d, 1H, C5-H, J ¼ 8.50 Hz), 7.32–7.15 (m, 3H, C6-, C8,
C9-H), 6.51 (s, 1H, C4-H), 4.22 (s, 2H, C3-NH2), 2.61 (s, 3H, C10-CH3); 13C NMR
(125 MHz, CDCl3) (ppm) d: 159.18 (C¼O), 136.51 (C3), 137.25 (C10a), 132.29
(C11b), 128.19 (C6b), 127.50 (C11a), 125.08 (C8), 123.11 (C10), 120.80 (C9), 119.00
(C4a), 118.31 (C7), 116.91 (C6), 114.55 (C4), 113.12 (C5), 104.60 (C6a), 17.28 (C10-
CH3); MS: m=z (%) 264 (Mþ, 100), 263 (25), 248 (32), 247 (55), 208 (10), 195 (20),
179 (18), 135 (16), 105 (12). Anal. calcd. for C16H12N2O2: C, 72.72; H, 4.45; N,
10.60%; Found: C, 72.76; H, 4.44; N, 10.66%.
3-Aminopyrano[2,3-a]carbazol-2(11H)-one (9d). Brown solid; mp 238 ꢀC;
1
yield: 86 mg (69%); IR (KBr, cmꢁ1) nmax: 3426, 3321, 3203, 2921, 1715; H NMR
(500 MHz, CDCl3) (ppm) d: 8.29 (b s, 1H, N11-H), 7.77 (d, 1H, C7-H, J ¼ 7.50 Hz),
7.59 (d, 1H, C5-H, J ¼ 8.25 Hz), 7.25–7.19 (m, 4H, C6-, C8, C9-, C10-H), 6.50 (s, 1H,
C4-H), 4.28 (s, 2H, C3-NH2); 13C NMR (125 MHz, CDCl3) (ppm) d: 159.61 (C¼O),
136.08 (C10a), 136.15 (C3), 132.40 (C11b), 130.22 (C11a), 126.71 (C9), 125.62 (C6b),
120.16 (C8), 119.80 (C7), 118.67 (C4a), 116.76 (C6), 115.02 (C4), 113.10 (C10),
112.13 (C5), 104.97 (C6a); MS: m=z (%) 250 (Mþ, 100), 249 (22), 233 (62), 209
(10), 164 (18), 115 (15), 91 (12). Anal. calcd. for C15H10N2O2: C, 72.00; H, 4.00;
N, 11.20%; Found: C, 71.92; H, 4.03; N, 11.24%.
3-Mercapto-8-methylpyrano[2,3-a]carbazol-2(11H)-one
(10a). Yellow
solid; mp > 300 ꢀC; yield: 84 mg (60%); IR (KBr, cmꢁ1) nmax: 3425, 2925, 2635,
1
1714, 1607; H NMR (500 MHz, CDCl3) (ppm) d: 10.23 (b s, 1H, N11-H), 7.98 (s,
1H, C7-H), 7.79 (d, 1H, C5-H, J ¼ 8.16 Hz), 7.72 (s, 1H, C4-H), 7.41 (d, 1H,
C10-H, J ¼ 8.00 Hz), 7.19–7.15 (m, 2H, C6-, C9-H), 4.24 (s, 1H, C3-SH), 2.44 (s,
3H, C8-CH3); 13C NMR (125 MHz, CDCl3) (ppm) d: 162.60 (C2), 139.37 (C10a),
134.32 (C11b), 130.24 (C8), 129.30 (C6b), 128.91 (C11a), 128.00 (C4a), 126.51 (C4),
125.40 (C7), 122.32 (C9), 120.41 (C6), 119.23 (C3), 117.40 (C6a), 112.52 (C5),
111.46 (C10), 21.20 (C8-CH3); MS: m=z (%) 281 (Mþ, 100), 280 (62), 248 (15), 247
(72), 223 (15), 178 (18), 127 (16), 114 (25). Anal. calcd. for C16H11NO2S: C, 68.32;
H, 3.91; N, 4.98; S, 11.39%; Found: C, 68.39; H, 3.94; N, 4.85; S, 11.44%.
3-Mercapto-9-methylpyrano[2,3-a]carbazol-2(11H)-one
(10b). Yellow
solid; mp > 300 ꢀC; yield: 88 mg (63%); IR (KBr, cmꢁ1) nmax: 3308, 2950, 2631,
1
1718, 1599; H NMR (500 MHz, CDCl3) (ppm) d: 10.16 (b s, 1H, N11-H), 7.96 (d,
1H, C7-H, J ¼ 7.98 Hz), 7.77 (d, 1H, C5-H, J ¼ 8.20 Hz), 7.70 (s, 1H, C4-H),
7.22–7.17 (m, 2H, C6-, C8-H), 7.12 (s, 1H, C10-H), 4.22 (s, 1H, C3-SH), 2.50 (s,
3H, C9-CH3); 13C NMR (125 MHz, CDCl3) (ppm) d: 162.34 (C¼O), 137.09 (C10a),
134.80 (C11b), 130.84 (C9), 129.10 (C11a), 128.71 (C4a), 126.45 (C4), 122.40 (C6b),
121.45 (C8), 121.01 (C7), 120.94 (C6), 119.64 (C3), 117.52 (C6a), 112.34 (C10),
112.16 (C5), 21.22 (C9-CH3); MS: m=z (%) 281 (Mþ, 100), 280 (40), 265 (15), 248
(72), 247 (15), 223 (12), 178 (15), 127 (16). Anal. calcd. for C16H11NO2S: C, 68.32;
H, 3.91; N, 4.98; S, 11.39%; Found: C, 68.36; H, 4.88; N, 4.95; S, 11.32%.
3-Mercapto-10-methylpyrano[2,3-a]carbazol-2(11H)-one (10c). Yellow
solid; mp > 300 ꢀC; yield: 87 mg (62%); IR (KBr, cmꢁ1) nmax: 3250, 2931, 2632,
1
1711; H NMR (500 MHz, CDCl3) (ppm) d: 10.42 (b s, 1H, N11-H), 7.95 (d, 1H,
C7-H, J ¼ 7.50 Hz), 7.80 (d, 1H, C5-H, J ¼ 8.28 Hz), 7.68 (s, 1H, C4-H), 7.12–7.02
(m, 3H, C6-, C8-H, C9-H), 4.29 (s, 1H, C3-SH), 2.55 (s, 3H, C10-CH3); 13C NMR

FURO- AND PYRANO-CARBAZOLES
2979
(125 MHz, CDCl3) (ppm) d: 162.94 (C¼O), 137.36 (C10a), 135.21 (C11b), 129.64
(C11a), 128.22 (C4a), 126.12 (C4), 125.89 (C8), 124.76 (C6b), 122.44 (C10), 121.08
(C9), 120.12 (C6), 119.94 (C3), 118.40 (C7), 117.34 (C6a), 113.41 (C5), 17.80 (C10-
CH3); MS: m=z (%) 281 (Mþ, 100), 280 (28), 248 (20), 247 (44), 208 (24), 178 (30),
105 (12). Anal. calcd. for C16H11NO2S: C, 68.32; H, 3.91; N, 4.98; S, 11.39%; Found:
C, 68.39; H, 4.90; N, 4.84; S, 11.46%.
3-Mercaptopyrano[2,3-a]carbazol-2(11H)-one (10d). Yellow solid; mp >
300 ꢀC; yield: 87 mg (65%); IR (KBr, cmꢁ1) nmax: 3301, 2939, 2620, 1705; 1H
NMR (500 MHz, CDCl3) (ppm) d: 10.34 (b s, 1H, N11-H), 7.82 (d, 1H, C7-H,
J ¼ 7.55 Hz), 7.75 (d, 1H, C5-H, J ¼ 8.25 Hz), 7.62 (s, 1H, C4-H), 7.55 (d, 1H,
C10-H, J ¼ 7.75 Hz), 7.23–7.13 (m, 3H, C6-, C8-, C9-H), 4.28 (s, 1H, C3-SH); 13C
NMR (100 MHz, CDCl3) (ppm) d: 162.10 (C¼O), 136.30 (C10a), 135.45 (C11b),
128.50 (C11a), 128.11 (C4a), 126.42 (C4), 125.48 (C6b), 122.96 (C9), 120.78 (C7),
120.18 (C6), 119.63 (C8), 119.16 (C3), 117.41 (C6a), 112.73 (C5), 112.49 (C10); MS:
m=z (%) 267 (Mþ, 100), 266 (32), 234 (16), 233 (36), 209 (25), 164 (25), 114 (10). Anal.
calcd. for C15H9NO2S: C, 67.41; H, 3.37; N, 5.24; S, 11.98%; Found: C, 67.48; H,
3.35; N, 5.18; S, 11.92%.
ACKNOWLEDGMENTS
K. P. thanks the Council of Scientific and Industrial Research (CSIR), New
Delhi for providing a CSIR-senior research fellowship. Our sincere thanks go to
the director, ISO Quality Assurance Cell, Indian Institute of Chemical Technology,
Hyderabad, and SAIF, Indian Institute of Technology Madras, Chennai, and the
Chairman, NMR Research Centre, IISc, Bangalore, for providing access to their
mass and NMR spectral facilities, respectively.
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