Synthesis of pyrrolo[1,2-f]phenanthridine-annulated polycyclic heterocycles from palladium-catalyzed intramolecular direct arylation reaction

Article abstract of DOI:10.1007/s00706-011-0564-9

A concise synthesis of pyrrolo[1,2-f]phenan-thridine-annulated polycyclic heterocycles has been achieved in good yields by palladium-catalyzed intramolecular direct arylation reaction.

Full text of DOI:10.1007/s00706-011-0564-9

Monatsh Chem (2012) 143:119–125
DOI 10.1007/s00706-011-0564-9
ORIGINAL PAPER
Synthesis of pyrrolo[1,2-f]phenanthridine-annulated polycyclic
heterocycles from palladium-catalyzed intramolecular direct
arylation reaction
•
Brindaban Roy Rajendra Narayan De
•
Somjit Hazra
Received: 15 March 2011 / Accepted: 26 June 2011 / Published online: 19 July 2011
Ó Springer-Verlag 2011
Abstract A concise synthesis of pyrrolo[1,2-f]phenan-
thridine-annulated polycyclic heterocycles has been
achieved in good yields by palladium-catalyzed intramo-
lecular direct arylation reaction.
prompted several groups of chemists to develop efficient
synthetic methods [13, 14] for this class of compounds.
One of the most efficient approaches for synthesizing
polycyclic compounds is to use domino reactions [15–19].
Especially attractive are those reactions that involve C–H
bond activation reactions, because these preclude the
presence of additional functional groups in the substrates.
A number of metal-catalyzed C–H bond activations have
recently been described for the synthesis of heterocyclic
compounds [13, 14], e.g., specifically using Pd [20–31], Pt
[32, 33], Ru [34–37], and Rh [38–44]; also see Refs.
[45–49]. In particular, the ability of palladium to activate
C–H bonds has been used extensively in organic synthesis
[50–56]. Thus, we envisioned that palladium-catalyzed
C–H bond activation of N-arylpyrroles 3 would afford the
polycyclic heterocycles 4 (Scheme 2) that would have
potential bioactivity and useful physical properties. Herein,
we report our results.
Keywords Phenanthridine Á Arylation Á
Palladium catalysis Á Heterocycles Á C–H bond activation
Introduction
Phenanthridines are an important class of compounds
because of their wide occurrence in natural products [1–3]
as well as a broad spectrum of biological activities and
unusual pharmacological utility that make them suitable for
antineoplastic application [4–6]. The high charge mobility
of this planar heterocyclic system provides effective
photoconducting and photovoltaic properties, required in
the field of electroluminescence and dye lasers [7–10].
Several pyrrolo[1,2-f]phenanthridine ring systems (PPHs)
have shown interesting antiproliferative activity against
Friend erythroleukemia cells (FLC) and multi-drug resis-
tant cell lines (DRTL) [11]. These planar compounds
inhibit HIV-1 and probably interact with the binding site of
non-nucleoside reverse transcriptase inhibitors (NNRTs)
[12]. Some PPHs are able to reduce the virus-induced
cytopathogenicity and stimulate the growth of MT cells, a
crucial factor in anti-AIDS therapy [12].
Results and discussion
We prepared the N-arylpyrroles 3a–3h in 62–78% yield by
the Paal–Knorr condensation reactions of 1,4-diketones
2a–2d with either 6-amino-5-bromocoumarin (1a), 6-amino-
5-bromoquinolones 1b, 1c, or 2-amino-1-bromonaphtha-
lene (1d) (Scheme 1) in anhydrous toluene at its boiling
point in the presence of p-toluenesulfonic acid.
The potentially useful pharmacological activities and
unique polycyclic structure of pyrrolophenanthridines have
Then, arylpyrrole 3a was refluxed with Pd(OAc)2
(10 mol%) in anhydrous toluene in the presence of a base
(Scheme 2) for trapping HBr (110 °C, 15 h) under various
conditions (Table 1). The use of KOAc as a base led to the
polycyclic compound 4a in 30% yield (entry 7).The activity
of most Pd-catalyzed reactions could be enhanced by the
addition of tetrabutylammonium bromide (TBAB) as a
B. Roy (&) Á R. N. De Á S. Hazra
Department of Chemistry, University of Kalyani,
Kalyani 741235, WB, India
e-mail: broybs@rediffmail.com
123

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B. Roy et al.
Scheme 1
Scheme 2
Ph
Br
COOEt
Catalyst, base
Solvent
N
COOEt
N
O
O
O
O
3a
4a
Table 1 Optimization of
cyclization conditions from
3a to 4a
Entry
Conditions
Temp/°C
Time/h
Yield/%
1
2
3
4
5
6
7
8
9
Pd(OAc)2, TBAB, KOAc, DMF
Pd(OAc)2, TBAB, KOAc, DMF
Pd(OAc)2, TBAB, KOAc, toluene
Pd(OAc)2, TBAB, KOAc, PPh3, toluene
Pd(OAc)2, TBAB, Cs2CO3, toluene
Pd(OAc)2, TBAB, K2CO3, toluene
Pd(OAc)2, KOAc, toluene
90
120
110
110
110
110
110
110
110
10
15
15
15
15
15
15
15
15
50
68
80
62
47
55
30
n.r.
47
PdCl2, TBAB, KOAc, toluene
Pd(PPh3)2Cl2, TBAB, KOAc, toluene
n.r. no reaction
cocatalyst [57]. Thus, the formation of product 4a was
increased to 80% yield by using TBAB in addition to KOAc
(entry 3). Although the role of TBAB in C–C bond formation
is not clear, it may be associated with a shorter induction
period for activation of Pd(II) [58] and hence more efficient
reduction of Pd(II) to catalytically active Pd(0) [59].
Sometimes addition of ligand to the reaction mixture offers
better yields [60, 61], and hence we used PPh3 as ligand, but
obtained a somewhat negative result (entry 4). If the base
was changed to Cs2CO3 or K2CO3 the yields were also
lowered (entries 5, 6). When PdCl2 was used as catalyst,
no cyclization took place, which might be due to the
123

Synthesis of pyrrolo[1,2-f]phenanthridine-annulated polycyclic heterocycles
121
poor solubility of PdCl2 in toluene, whereas catalyst
Pd(PPh3)2Cl2 led to moderate yield (entries 8, 9). However,
the reactions in DMF instead of toluene gave moderate
yields (entries 1, 2). Careful scrutiny of various conditions
revealed that the use of Pd(OAc)2 as catalyst and KOAc as
base in conjunction with TBAB in anhydrous toluene was
the most suitable condition to achieve better yields.
Using these optimized reaction conditions, we synthe-
sized a good number of pyrrolo[1,2-f]phenanthridines
4a–4h (Table 2).
Table 2 Yields of
intramolecular direct arylation
reactions of 3 to 4
Yield
Entry
1
Substrate
Product
/%a
80
82
68
3a
3b
3c
4a
4b
4c
2
3
4
5
6
76
71
76
3d
3e
3f
4d
4e
4f
7
8
70
3g
3h
4g
4h
87
a
Isolated yield
123

122
B. Roy et al.
ArH), 7.40 (d, 1H, J = 8.4 Hz, ArH), 8.07 (d, 1H,
J = 9.6 Hz, ArH) ppm; 13C NMR (100 MHz, CDCl3):
d = 12.1, 14.5, 59.7, 110.3, 113.6, 117.0, 118.7, 119.8,
124.6, 127.2, 128.1, 128.3, 131.8, 132.9, 134.1, 134.6, 137.9,
The outcome of the reaction reveals that ester and acetyl
functional groups are well tolerated in the ring closure.
N-Naphthylpyrrole 3h affords a better yield than pyr-
rolocoumarins 3a, 3b, whereas pyrroloquinolones 3d–3g
give somewhat lower yields (Table 2). The pyrrolocoum-
arin 3c gives only 68% of compound 4c, the lowest yield
among the reactions performed.
ꢀ
142.3, 154.2, 159.1, 165.3 ppm; IR (KBr): m = 3,030, 2,977,
1,749, 1,703 cm-1
;
MS: m/z = 452 (M? ? H), 454
(M? ? 2 ? H).
In conclusion, we have reported a concise Pd-catalyzed
cyclization leading to polycyclic heterocycles. The key
step of this ring closure is an intramolecular direct arylation
reaction via C–H bond activation. The reaction is mild and
straightforward and can be utilized for the construction of
condensed heterocycles, especially pyrrolo[1,2-f]naph-
thyridines in good to very good yields. To the best of our
knowledge, such this ring system has not been reported
earlier.
5-Bromo-6-(2,5-diphenyl-1H-pyrrol-1-yl)-2H-chromen-2-
one (3b, C25H16BrNO2)
Recrystallized from ethyl acetate/petroleum ether (1:2). Yield
1
73%, white solid, m.p.: 171–172 °C; H NMR (400 MHz,
CDCl3): d = 6.46 (d, 1H, J = 9.6 Hz, ArH), 6.52 (s, 2H,
ArH), 7.09–7.11 (m, 4H, ArH), 7.15–7.18 (m, 6H, ArH), 7.24
(d, 1H, J = 8.4 Hz, ArH), 7.49 (d, 1H, J = 8.8 Hz, ArH),
7.94 (d, 1H, J = 10.0 Hz, ArH) ppm; 13C NMR (100 MHz,
CDCl3): d = 110.8, 114.2, 115.4, 121.1, 124.5, 126.5, 127.0,
128.0,129.1,136.1,137.2,139.5,140.2,151.0,161.2 ppm;IR
-1
ꢀ
(KBr): m = 3,029, 2,925, 1,732 cm
.
Experimental
5-Bromo-6-(4,5,6,7-tetrahydro-2-phenyl-1H-indol-1-yl)-
2H-chromen-2-one (3c, C23H18BrNO2)
Melting points were determined in open capillaries. IR
spectra were recorded using solid samples on KBr disks on
a PerkinElmer L 120-000A spectrophotometer, and NMR
spectra were measured in CDCl3 with TMS as internal
standard (d in parts per million) on a Bruker Ultrashield
400 MHz. Elemental analyses were done at the University
of Kalyani on a Perkin Elmer CHN analyzer 2400 series II,
and mass spectra were done on a Jeol JMS600 instrument
at the Indian Institute of Chemical Biology, Kolkata, India.
Silica gel (60–120 mesh) was used for chromatographic
separation. Silica gel-G (Spectrochem, India) was used for
TLC. Petroleum ether refers to the fraction boiling between
60 and 80 °C.
Recrystallized from ethyl acetate/petroleum ether (1:2).
Yield 62%, yellow solid, m.p.: 158–159 °C; 1H NMR
(400 MHz, CDCl3): d = 1.75–1.83 (m, 4H), 2.18–2.32 (m,
2H), 2.57–2.67 (m, 2H), 6.28 (s, 1H, ArH), 6.53 (d, 1H,
J = 10.0 Hz, ArH), 7.07–7.09 (m, 2H, ArH), 7.12–7.16
(m, 3H, ArH), 7.28 (d, 1H, J = 8.8 Hz, ArH), 7.39 (d, 1H,
J = 8.8 Hz, ArH), 8.09 (d, 1H, J = 10.0 Hz, ArH) ppm;
13C NMR (100 MHz, CDCl3): d = 22.5, 23.0, 23.2, 23.6,
108.7, 116.7, 118.3, 118.8, 119.5, 124.4, 126.1, 127.4,
128.3, 131.3, 133.0, 133.2, 133.8, 136.0, 142.7, 153.7,
-1
ꢀ
159.5 ppm; IR (KBr): m = 3,059, 2,832, 1,732 cm
.
Ethyl 1-(5-bromo-1,2-dihydro-1-methyl-2-oxoquinolin-
6-yl)-2-methyl-5-phenyl-1H-pyrrole-3-carboxylate
(3d, C24H21BrN2O3)
Preparation of compound 3a
Recrystallized from ethyl acetate/petroleum ether (3:1).
Yield 65%, white solid, m.p.: 166–167 °C; 1H NMR
(400 MHz, CDCl3): d = 1.39 (t, 3H, J = 7.2 Hz,
–CH2CH3), 2.32 (s, 3H, –CH3), 3.73 (s, 3H, –NCH3),
4.33 (q, 2H, J = 7.2 Hz, –CH2CH3), 6.83 (s, 1H, ArH),
6.84 (d, 1H, J = 9.6 Hz, ArH), 7.09–7.17 (m, 5H, ArH),
7.35 (d, 1H, J = 8.8 Hz, ArH), 7.39 (d, 1H, J = 8.8 Hz,
ArH), 8.15 (d, 1H, J = 10.0 Hz, ArH) ppm; 13C NMR
(100 MHz, CDCl3): d = 12.2, 14.6, 30.1, 59.7, 110.1, 113.3,
114.3, 120.5, 124.0, 125.7, 127.0, 128.0, 128.3, 131.5, 132.0,
A mixture of 0.240 g 6-amino-5-bromo-2H-chromen-2-one
(1a, 1 mmol), 0.248 g ethyl 2-acetyl-4-oxo-4-phenylbu-
tanoate (2a, 1 mmol), and 0.017 g 4-methylbenzenesulfonic
acid (10 mol%) in anhydrous toluene was refluxed in a
Dean–Stark apparatus for 7 h. On purification by column
chromatography compound 3a was obtained in 0.320 g
(71%) yield. Compounds 3b–3h were prepared following the
same procedure.
Ethyl 1-(5-bromo-2-oxo-2H-chromen-6-yl)-2-methyl-5-
phenyl-1H-pyrrole-3-carboxylate (3a, C23H18BrNO4)
Recrystallized from ethyl acetate/petroleum ether (2:1).
Yield 71%, white solid, m.p.: 135–136 °C; 1H NMR
(400 MHz, CDCl3):d = 1.39(t, 3H, J = 7.2 Hz, –CH2CH3),
2.32 (s, 3H, –CH3), 4.33 (q, 2H, J = 7.2 Hz, –CH2CH3), 6.55
(d, 1H, J = 9.6 Hz, ArH), 6.82 (s, 1H, ArH), 7.08–7.10 (m,
2H, ArH), 7.14–7.19 (m, 3H, ArH), 7.33 (d, 1H, J = 8.8 Hz,
132.4, 134.1, 137.9, 138.2, 140.9, 161.5, 165.4 ppm; IR
-1
ꢀ
(KBr): m = 2,982, 2,925, 1,678, 1,654 cm
.
6-(3-Acetyl-2-methyl-5-phenyl-1H-pyrrol-1-yl)-5-bromo-1-
methylquinolin-2(1H)-one (3e, C23H19BrN2O2)
Recrystallized from ethyl acetate/petroleum ether (2:1).
Yield 65%, yellow solid, m.p.: 123–124 °C; 1H NMR
(400 MHz, CDCl3): d = 2.34 (s, 3H, –CH3), 2.52 (s, 3H,
123

Synthesis of pyrrolo[1,2-f]phenanthridine-annulated polycyclic heterocycles
123
–COCH3), 3.73 (s, 3H, –NCH3), 6.76 (s, 1H, ArH), 6.84 (d,
138.4, 165.6 ppm; IR (KBr): ꢀm = 3,065, 2,977, 2,929,
1H, J = 9.6 Hz, ArH), 7.05–7.07 (m, 2H, ArH), 7.11–7.15
(m, 3H, ArH), 7.35 (d, 1H, J = 9.2 Hz, ArH), 7.38 (d, 1H,
J = 8.8 Hz, ArH), 8.14 (d, 1H, J = 10.0 Hz, ArH) ppm;
13C NMR (100 MHz, CDCl3): d = 12.7, 28.8, 30.8, 110.4,
114.3, 120.5, 121.8, 124.1, 125.5, 127.2, 128.1, 128.4,
131.3, 131.9, 132.1, 133.9, 137.8, 137.9, 141.0, 161.5,
1,696 cm-1
.
Preparation of compound 4a
A mixture of 150 mg 3a (0.332 mmol), 268 mg TBAB
(0.830 mmol), 49 mg anhydrous KOAc (0.498 mmol),
7 mg Pd(OAc)2 (0.033 mmol), and 5 cm3 of dry toluene
was heated under nitrogen atmosphere in an oil bath at
110 °C for 15 h. Toluene was removed under reduced
pressure. The yield was 87 mg (80%) of compound 4a after
purification by flash column chromatography. Compounds
4b–4h were synthesized similarly.
ꢀ
195.3 ppm; IR (KBr): m = 2,997, 2,851, 1,659 (broad)
cm-1
.
Ethyl 1-(5-bromo-1-ethyl-1,2-dihydro-2-oxoquinolin-6-yl)-
2-methyl-5-phenyl-1H-pyrrole-3-carboxylate
(3f, C25H23BrN2O3)
Recrystallized from ethyl acetate/petroleum ether (2:1).
Yield 67%, white solid, m.p.: 160–161 °C; 1H NMR
(400 MHz, CDCl3): d = 1.35–1.40 (m, 6H, –CH2CH3,
–CH2CH3), 2.32(s, 3H, –CH3), 4.26–4.34(m, 2H, –CH2CH3),
4.36–4.44 (m, 2H, –CH2CH3), 6.82–6.84 (m, 2H, ArH),
7.10–7.16 (m, 5H, ArH), 7.34–7.40 (m, 2H, ArH), 8.16(d, 1H,
J = 9.6 Hz, ArH) ppm; 13C NMR (100 MHz, CDCl3):
d = 12.2, 12.9, 14.6, 38.2, 59.7, 110.1, 113.3, 114.1, 120.8,
124.1, 125.8, 127.0, 128.0, 128.3, 131.4, 132.0, 132.2, 134.1,
Ethyl 7-methyl-12-oxo-12H-pyrano[3,2-a]pyrrolo-
[1,2-f]phenanthridine-6-carboxylate (4a, C23H17NO4)
Recrystallized from ethyl acetate/petroleum ether
(3:1). Yield 80%, yellow solid, m.p.: 182–183 °C; 1H
NMR (400 MHz, CDCl3): d = 1.43 (t, 3H, J = 7.2 Hz,
–CH2CH3), 3.22 (s, 3H, –CH3), 4.38 (q, 2H, J = 7.2 Hz,
–CH2CH3), 6.54 (d, 1H, J = 10.0 Hz, ArH), 7.41 (s, 1H,
ArH), 7.43–7.48 (m, 2H, ArH), 7.57 (t, 1H, J = 7.2 Hz,
ArH), 7.93 (d, 1H, J = 8.4 Hz, ArH), 8.07 (d, 1H,
J = 8.0 Hz, ArH), 8.47 (d, 1H, J = 9.2 Hz, ArH), 8.59
(d, 1H, J = 10.0 Hz, ArH) ppm; 13C NMR (100 MHz,
CDCl3): d = 14.5, 16.7, 60.2, 103.7, 115.6, 115.8, 115.9,
117.1, 120.8, 123.0, 123.3, 123.5, 125.8, 128.1, 129.0,
129.5, 130.4, 131.9, 132.9, 142.8, 152.3, 159.9, 165.4 ppm;
IR (KBr): ꢀm = 2,977, 2,924, 1,729, 1,691 cm-1; MS:
m/z = 372 (M? ? H).
ꢀ
137.9, 138.3, 140.0, 161.1, 165.5 ppm; IR (KBr): m = 3,065,
2,970, 1,695, 1,660 cm-1
.
6-(3-Acetyl-2-methyl-5-phenyl-1H-pyrrol-1-yl)-5-bromo-1-
ethylquinolin-2(1H)-one (3g, C24H21BrN2O2)
Recrystallized from ethyl acetate/petroleum ether (2:1).
Yield 62%, white solid, m.p.: 150–151 °C; 1H NMR
(400 MHz, CDCl3): d = 1.37 (t, 3H, J = 7.2 Hz,
–NCH2CH3), 2.35 (s, 3H, –CH3), 2.52 (s, 3H, –COCH3),
4.27–4.31 (m, 1H, –NCH2CH3), 4.40–4.45 (m, 1H,
–NCH2CH3), 6.76 (s, 1H, ArH), 6.83 (d, 1H, J = 10.0 Hz,
ArH), 7.11–7.13 (m, 2H, ArH), 7.16–7.18 (m, 3H, ArH), 7.35
(d, 1H, J = 9.2 Hz, ArH), 7.38 (d, 1H, J = 8.8 Hz, ArH), 8.15
(d, 1H, J = 10.0 Hz, ArH) ppm; 13C NMR (100 MHz,
CDCl3): d = 12.7, 12.8, 29.6, 38.2, 110.4, 114.1, 120.8,
121.7, 124.1, 125.7, 127.2, 128.1, 128.4, 131.3, 131.9, 133.9,
7-Phenyl-12H-pyrano[3,2-a]pyrrolo[1,2-f]phenanthridin-
12-one (4b, C25H15NO2)
Recrystallized from ethyl acetate/petroleum ether (2:1).
Yield 82%, yellow solid, m.p.: 174–175 °C; 1H NMR
(400 MHz, CDCl3): d = 6.50 (d, 1H, J = 10.0 Hz, ArH),
6.69 (d, 1H, J = 3.6 Hz, ArH), 7.05 (d, 1H, J = 3.6 Hz,
ArH), 7.10 (d, 1H, J = 9.2 Hz, ArH), 7.41–7.49 (m, 6H,
ArH), 7.58 (t, 1H, J = 7.6 Hz, ArH), 7.70 (d, 1H,
J = 9.2 Hz, ArH), 8.01 (d, 1H, J = 8.4 Hz, ArH), 8.07
(d, 1H, J = 8.0 Hz, ArH), 8.64 (d, 1H, J = 10.0 Hz, ArH)
ppm; 13C NMR (100 MHz, CDCl3): d = 102.7, 115.6,
116.0, 116.6, 121.7, 122.1, 123.3, 123.5, 125.2, 127.9,
128.1, 128.3, 128.6, 129.0, 129.1, 129.2, 131.4, 131.6,
137.7, 137.8, 137.9, 140.0, 161.1, 195.3 ppm; IR (KBr):
-1
ꢀ
m = 2,962, 2,922, 1,663 (broad) cm
.
Ethyl 1-(1-bromonaphthalen-2-yl)-2-methyl-5-phenyl-1H-
pyrrole-3-carboxylate (3h, C24H20BrNO2)
Recrystallized from ethyl acetate/petroleum ether (1:2).
Yield 78%, white solid, m.p.: 98–99 °C; 1H NMR (400 MHz,
CDCl3):d = 1.39(t, 3H, J = 7.2 Hz, –CH2CH3), 2.33(s, 3H,
–CH3), 4.32 (q, 2H, J = 7.2 Hz, –CH2CH3), 6.86 (s, 1H,
ArH), 7.06–7.09 (m, 3H, ArH), 7.11–7.14 (m, 2H, ArH),
7.27 (d, 1H, J = 8.4 Hz, ArH), 7.59–7.60 (m, 2H, ArH),
7.82 (d, 1H, J = 8.8 Hz, ArH), 7.88 (d, 1H, J = 7.6 Hz,
ArH), 8.31 (d, 1H, J = 8.0 Hz, ArH) ppm; 13C NMR
(100 MHz, CDCl3): d = 12.2, 14.6, 59.7, 110.0, 113.1,
124.7, 126.8, 127.1, 127.8, 127.9, 128.0, 128.2,
128.3, 128.4, 128.8, 132.2, 132.4, 133.8, 134.0, 135.6,
131.8, 134.9, 142.8, 151.9, 160.2 ppm; IR (KBr):
-1
ꢀ
m = 2,919, 2,850, 1,735, 1,725 cm
.
10,11,12,13-Tetrahydro-2H-indolo[1,2-f]pyrano-
[3,2-a]phenanthridin-2-one (4c, C23H17NO2)
Recrystallized from ethyl acetate/petroleum ether (2:1).
Yield 68%, yellow solid, m.p.: 191–192 °C; 1H NMR
(400 MHz, CDCl3): d = 1.25–1.33 (m, 2H), 1.87–1.89
(m, 1H), 1.97–2.00 (m, 1H), 2.79 (t, 2H, J = 5.6 Hz), 3.27
(t, 2H, J = 5.2 Hz), 6.51 (d, 1H, J = 10.0 Hz, ArH), 6.85
123

124
B. Roy et al.
(s, 1H, ArH), 7.36 (t, 1H, J = 8.4 Hz, ArH), 7.43 (d, 1H,
J = 9.2 Hz, ArH), 7.52 (t, 1H, J = 8.0 Hz, ArH), 7.94 (d,
1H, J = 8.0 Hz, ArH), 8.01 (d, 1H, J = 8.0 Hz, ArH),
8.35 (d, 1H, J = 9.6 Hz, ArH), 8.63 (d, 1H, J = 10.0 Hz,
ArH) ppm; 13C NMR (100 MHz, CDCl3): d = 22.6, 22.7,
24.0, 24.3, 101.6, 115.2, 115.5, 115.7, 119.9, 121.0, 122.7,
122.9, 124.0, 124.7, 126.4, 128.0, 128.3, 128.7, 128.9,
13C NMR (100 MHz, CDCl3): d = 13.1, 14.5, 16.6, 37.9, 60.1,
103.3, 113.3, 116.7, 117.6, 119.8, 121.1, 123.2, 123.8, 123.9,
125.6, 128.0, 128.9, 129.0, 130.2, 132.5, 137.4, 138.0, 138.2,
161.1, 165.6 ppm; IR (KBr): ꢀm = 3,067, 2,977, 1,698,
1,651 cm-1
.
6-Acetyl-11-ethyl-7-methylbenzo[a]pyrrolo-
[2,1-c][4,7]phenanthrolin-12(11H)-one(4g, C24H20N2O2)
Recrystallized from ethyl acetate/petroleum ether (4:1).
Yield 70%, yellow solid, m.p.: 254–255 °C; 1H NMR
(400 MHz, CDCl3): d = 1.46 (t, 3H, J = 7.2 Hz,
–CH2CH3), 2.63 (s, 3H, –COCH3), 3.22 (s, 3H, –CH3),
4.48 (q, 2H, J = 7.2 Hz, –CH2CH3), 6.81 (d, 1H,
J = 10.0 Hz, ArH), 7.34 (s, 1H, ArH), 7.43 (t, 1H,
J = 8.0 Hz, ArH), 7.53 (d, 1H, J = 9.2 Hz, ArH), 7.56
(t, 1H, J = 8.0 Hz, ArH), 8.05 (d, 1H, J = 8.0 Hz, ArH),
8.06 (d, 1H, J = 7.2 Hz, ArH), 8.48 (d, 1H, J = 9.2 Hz,
ArH), 8.56 (d, 1H, J = 10.0 Hz, ArH) ppm; 13C NMR
(100 MHz, CDCl3): d = 12.9, 13.2, 29.2, 38.1, 103.2,
113.9, 119.2, 121.0, 121.4, 123.4, 125.3, 126.1, 126.5,
126.9, 127.5, 127.9, 131.3, 131.7, 131.9, 137.2, 137.7,
ꢀ
132.6, 143.1, 151.3, 161.3 ppm; IR (KBr): m = 2,922,
2,850, 1,729 cm-1
.
Ethyl 11,12-dihydro-7,11-dimethyl-12-oxobenzo[a]-
pyrrolo[2,1-c][4,7]phenanthroline-6-carboxylate
(4d, C24H20N2O3)
Recrystallized from ethyl acetate/petroleum ether (4:1).
Yield 76%, yellow solid, m.p.: 252–253 °C; 1H NMR
(400 MHz, CDCl3): d = 1.43 (t, 3H, J = 7.2 Hz,
–CH2CH3), 3.22 (s, 3H, –CH3), 3.84 (s, 3H, –NCH3),
4.38 (q, 2H, J = 7.2 Hz, –CH2CH3), 6.82 (d, 1H,
J = 10.0 Hz, ArH), 7.40 (s, 1H, ArH), 7.42 (d, 1H,
J = 10.4 Hz, ArH), 7.48–7.55 (m, 2H, ArH), 8.02–8.06
(m, 2H, ArH), 8.47 (d, 1H, J = 9.2 Hz, ArH), 8.56 (d, 1H,
J = 8.8 Hz, ArH) ppm; 13C NMR (100 MHz, CDCl3):
d = 14.5, 16.6, 30.0, 60.1, 103.3, 113.4, 116.4, 117.2,
119.8, 121.1, 123.0, 123.2, 123.8, 124.1, 125.7, 125.9,
ꢀ
139.7, 161.3, 195.2 ppm; IR (KBr): m = 2,969, 2,923,
2,852, 1,655 (broad) cm-1
.
Ethyl 7-methylbenzo[a]pyrrolo[1,2-f]phenanthridine-6-
carboxylate (4h, C24H19NO2)
128.9, 129.0, 132.6, 135.3, 136.6, 138.0, 161.5, 165.2 ppm;
-1
ꢀ
IR (KBr): m = 3,060, 2,984, 1,693, 1,663 cm
.
Recrystallized from ethyl acetate/petroleum ether (1:1).
Yield 87%, yellow solid, m.p.: 119–120 °C; 1H NMR
(400 MHz, CDCl3):d = 1.44(t, 3H, J = 7.2 Hz, –CH2CH3),
3.25 (s, 3H, –CH3), 4.39 (q, 2H, J = 7.2 Hz, –CH2CH3),
7.41–7.44 (m, 2H, ArH), 7.49–7.56 (m, 2H, ArH), 7.61 (dd,
1H, J = 7.2, 8.8 Hz, ArH), 7.88 (d, 1H, J = 9.2 Hz, ArH),
7.95 (d, 1H, J = 8.0 Hz, ArH), 8.10 (d, 1H, J = 8.0 Hz,
ArH), 8.38 (d, 1H, J = 9.2 Hz, ArH), 8.53 (d, 1H,
6-Acetyl-7,11-dimethylbenzo[a]pyrrolo[2,1-c][4,7]-
phenanthrolin-12(11H)-one (4e, C23H18N2O2)
Recrystallized from ethyl acetate/petroleum ether (4:1).
Yield 71%, yellow solid, m.p.: 256–257 °C; 1H NMR
(400 MHz, CDCl3): d = 2.63 (s, 3H, –COCH3), 3.22 (s,
3H, –CH3), 3.85 (s, 3H, –NCH3), 6.83 (d, 1H, J = 9.6 Hz,
ArH), 7.34 (s, 1H, ArH), 7.44 (t, 1H, J = 7.6 Hz, ArH),
7.52 (d, 1H, J = 9.2 Hz, ArH), 7.56 (t, 1H, J = 7.2 Hz,
ArH), 8.06 (d, 1H, J = 7.6 Hz, ArH), 8.08 (d, 1H,
J = 7.2 Hz, ArH), 8.48 (d, 1H, J = 9.2 Hz, ArH), 8.57
(d, 1H, J = 10.0 Hz, ArH) ppm; 13C NMR (100 MHz,
CDCl3): d = 13.1, 28.1, 29.0, 102.4, 112.4, 116.3, 119.7,
120.1, 122.1, 123.0, 123.5, 124.8, 127.1, 127.9, 128.0,
J = 8.4 Hz, ArH), 8.81 (d, 1H, J = 8.4 Hz, ArH) ppm; 13
C
NMR (100 MHz, CDCl3): d = 14.6, 16.8, 60.0, 102.5, 116.8,
116.9, 120.0, 123.0, 125.2, 125.4, 125.5, 126.5, 127.2, 127.5,
127.6, 127.9, 128.1, 128.2, 129.7, 130.2, 131.4, 132.3, 132.7,
-1
ꢀ
165.8 ppm; IR (KBr): m = 2,977, 2,925, 1,704 cm
.
Acknowledgments We thank the UGC and CSIR (New Delhi,
India) and the University of Kalyani for financial support. R. N. De is
grateful to UGC (New Delhi, India) and S. Hazra is grateful to CSIR
(New Delhi, India) for their fellowships. We also thank the DST (New
Delhi) for providing the Bruker NMR spectrometer (400 MHz),
Perkin-Elmer CHN analyzer, and IR spectrometer under its FIST
programme.
128.1, 129.4, 130.8, 131.1, 137.0, 137.6, 160.5, 195.2 ppm;
-1
ꢀ
IR (KBr): m = 2,925, 2,854, 1,652 (broad) cm
.
Ethyl 11-ethyl-11,12-dihydro-7-methyl-12-
oxobenzo[a]pyrrolo[2,1-c][4,7]phenanthroline-6-
carboxylate (4f, C25H22N2O3)
Recrystallized from ethyl acetate/petroleum ether (4:1).
Yield 76%, yellow solid, m.p.: 163–164 °C; 1H NMR
(400 MHz, CDCl3): d = 1.39–1.47 (m, 6H, –CH2CH3,
–CH2CH3), 3.23 (s, 3H, –CH3), 4.38 (q, 2H, J = 6.8 Hz,
–CH2CH3), 4.50 (q, 2H, J = 7.2 Hz, –CH2CH3), 6.81 (d, 1H,
J = 10.0 Hz, ArH), 7.41–7.44 (m, 2H, ArH), 7.51–7.56
(m, 2H, ArH), 8.05 (t, 2H, J = 8.4 Hz, ArH), 8.49 (d, 1H,
J = 9.6 Hz, ArH), 8.57 (d, 1H, J = 10.0 Hz, ArH) ppm;
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