Cascade C-C and C-N Bond Formation: A Straightforward Synthesis of Phenanthridines and Fused Quinolines

Article abstract of DOI:10.1002/ejoc.201600220

A Pd-catalyzed cascade process has been developed for the synthesis of quinoline and phenanthridine derivatives from various β-chloro α,β-unsaturated aldehydes and 2-chloroaryl aldehydes, respectively, in good to high yields. The reaction proceeds through Pd-catalyzed cascade carbon-carbon and carbon-nitrogen bond formation in a single reaction vessel. The requisite β-chloro α,β-unsaturated aldehydes were efficiently synthesized from their corresponding carbonyl compounds. The use of the ligand Sphos with Pd(OAc)₂ is crucial for the successful implementation of the present cascade process. This synthetic protocol is also applied for the gram-scale synthesis of a trispheridine alkaloid.

Full text of DOI:10.1002/ejoc.201600220

DOI: 10.1002/ejoc.201600220
Full Paper
Domino Reactions
Cascade C–C and C–N Bond Formation: A Straightforward
Synthesis of Phenanthridines and Fused Quinolines
Ashwini Borah[a] and Pranjal Gogoi*[a]
Abstract: A Pd-catalyzed cascade process has been developed requisite ꢀ-chloro α,ꢀ-unsaturated aldehydes were efficiently
for the synthesis of quinoline and phenanthridine derivatives synthesized from their corresponding carbonyl compounds. The
from various ꢀ-chloro α,ꢀ-unsaturated aldehydes and 2-chloro- use of the ligand Sphos with Pd(OAc)2 is crucial for the success-
aryl aldehydes, respectively, in good to high yields. The reaction ful implementation of the present cascade process. This syn-
proceeds through Pd-catalyzed cascade carbon–carbon and thetic protocol is also applied for the gram-scale synthesis of a
carbon–nitrogen bond formation in a single reaction vessel. The trispheridine alkaloid.
Introduction
Nitrogen-containing fused six-membered arenes, such as quin-
olines and phenanthridines, are important structural motifs that
are found in many natural bioactive alkaloids, pharmaceuticals,
and agrochemicals.[1] Such compounds are also used as ligands
for asymmetric synthesis and in functional materials.[2] In phar-
maceuticals, quinolines are used for the treatment of parasitic
infections such as malaria[3] and leishmaniasis.[4] They are also
integral to a large number of synthetic drug substances that
exhibit anti-inflammatory, antineoplastic, antifungal, antiseptic/
anti-infective, antitumor, and analgesic properties.[5] On the
other hand, phenanthridines are an important group of natural
alkaloids, typified by trispheridine, decarine, chelerythine, nitid-
ine, which demonstrate expansive biological activity including
nematodial, antitumor, antibacterial, antifungal, and cytotoxic
Figure 1. Examples of natural products containing a phenanthridine core unit.
activity (Figure 1).[6]
Molecules containing these structural units have received
copper-catalyzed and other methods have been reported for
the synthesis of quinoline derivatives.[10] However, most of the
reported methods for both cases are not fully satisfactory with
regards to yields and reaction conditions. Furthermore, byprod-
uct formation,[10g] and limited availability of starting materi-
als[10h] are unavoidable problems associated with some of the
reported methods.
Alternatively, Pd-catalyzed cascade approaches have gained
immense popularity in recent years because they offer advanta-
ges of relatively mild reaction conditions and high functional
group tolerance.[11] Additionally, cascade approaches using eas-
ily achievable starting materials offer a more atom-economical
approach relative to other conventional reactions. In this regard,
Pd-mediated Ullmann cross-coupling/reductive cyclization,[12]
Suzuki cross-coupling/Michael addition reaction[13] or conden-
sation[14] sequences are well-known approaches for quinolines,
isoquinolones, and phenanthridines. However, in the Pd-medi-
ated Ullmann cross-coupling cascade approach, homocoupled
side-products are formed together with the desired product.
Moreover, in the reported Suzuki cross-coupling cascade ap-
considerable attention in medicinal and material chemistry;
therefore, much effort has been focused on developing syn-
thetic methods to access quinolines and phenanthridine deriva-
tives.[1b,7] Bischler–Napieralski cyclization, Pictet–Hubert con-
densation, Skraup, and Doebner–Miller synthesis are classical
methods to achieve these structural units.[8] Although these tra-
ditional approaches are simple and practical, they have limita-
tions such as long synthetic pathways, limited substrate scope,
low functional group tolerance, and harsh reaction conditions.
To improve the synthesis of the phenanthridine skeleton, vari-
ous radical-mediated reactions, metal-catalyzed cross-cou-
plings, cycloadditions, and other synthetic methods have been
reported.[9] Additionally, Friedländer-type, halogen-mediated,
[a] Medicinal Chemistry Division, CSIR – North East Institute of Science and
Technology,
Jorhat 785006, India
E-mail: gogoipranj@yahoo.co.uk
http://www.rrljorhat.res.in
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejoc.201600220.
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proaches, aryliodides or arylbromides are used as coupling part- bases except Cs2CO3 gave low yield of product. Although
ners with organoboron compounds, which are unstable and Cs2CO3 gave a similar result to that with K3PO4, the latter was
mixtures of other halogenated undesired products are formed used for the rest of the reactions because it is less expensive
during their synthesis. On the other hand, there is great interest and readily available (entry 16).
in the challenge of using aryl chlorides in Suzuki cross-coupling
reactions for the synthesis of pharmaceutically important com-
Table 1. Optimization studies.[a]
pounds because they are readily available, inexpensive, and en-
vironmentally strategic reagents. However, they are much more
difficult to activate than aryl bromides and iodide. Therefore,
the development of catalyst system for the synthesis of impor-
tant compounds employing arylchloride is highly desirable. To
our knowledge, there is no report on the synthesis of quinolines
Entry Ligand
Base
Solvent
Temp. (°C)
Yield (%)[b]
and phenanthridines from aryl chloride using a cascade strat-
egy.
1
PPh3
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
Na2CO3
K2CO3
Cs2CO3
KOAc
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
THF
dioxane
DMF
CH3CN
DCE
120
120
120
120
120
120
120
120
80
30
25
45
87
65
91
53
65
71
45
39
15
77
53
57
89
61
2
3
4
5
6
7
8
rac-BINAP
(Cy)3P
Xphos
Mephos
Sphos
Ruphos
–
Results and Discussion
In the context of our interest in the chemistry of ꢀ-halo α,ꢀ-
unsaturated aldehydes,[15] we report herein a cascade Suzuki
cross-coupling reaction/condensation reaction of easily accessi-
ble ꢀ-chloro α,ꢀ-unsaturated aldehydes[15b] and commercially
available 2-chloroaryl aldehydes with (2-aminoaryl)boronic acid
pinacol esters to provide quinolines and phenanthridines in ex-
cellent yields (Scheme 1).
9
Sphos
Sphos
Sphos
Sphos
Sphos
Sphos
Sphos
Sphos
Sphos
10
11
12
13
14
15
16
17
100
120
80
80
DMSO
DMSO
DMSO
DMSO
120
120
120
120
[a] Reaction conditions: 2-chlorobenzaldehyde (1 mmol), (2-aminophenyl)-
boronic pinacol ester (1.2 mmol), Pd(OAc)2 (2.5 mol-%), ligand (5 mol-%), base
(2 mmol), solvent (2 mL). [b] Yield of isolated product.
Under the optimized reaction conditions, the synthetic po-
tential of our cascade strategy was investigated; the results are
summarized in Table 2. The cascade reaction took place
smoothly, affording excellent yields of quinolines and phenan-
Scheme 1. Synthesis of phenanthridines and quinolines.
Initially, the catalyst system was optimized on a model reac- thridines. To establish the substrate scope of the reaction lead-
tion between 2-chlorobenzaldehyde (1a) and (2-aminophenyl)- ing to phenanthridines, a selection of 2-chloroaryl aldehydes
boronic pinacol ester (2a) in the presence of 2.5 mol-% 3a–i were then subjected to the optimized conditions (Table 2).
Pd(OAc)2 as catalyst. After a ligand screen with various ligands
(Figure 2) was performed in dimethyl sulfoxide (DMSO) as sol-
vent and K3PO4 as base, Sphos emerged as the most efficient,
yielding 3a in 91 % yield.
As shown in Table 2, both electron-rich and -poor 2-chloro-
aryl aldehydes afforded the corresponding products in excellent
yields, in spite of their electronic nature. However, 2-chloroaryl
aldehyde bearing electron-rich groups gave higher yield com-
Other solvents including tetrahydrofuran (THF), 1,2-dichloro- pared with those with electron-poor groups. Notably, the reac-
ethane (DCE), acetonitrile, dioxane, and N,N-dimethyl- tion conditions are compatible with alkyl, methoxy, methylene-
formamide (DMF) were tested and all of them led to a decrease dioxy, fluoro, and trifluoromethyl group on the aryl ring (3b–
in reaction yield (Table 1, entries 9–13). In the optimization h). Our synthetic strategy was also applied to the synthesis of
study, various bases such as Na2CO3, K2CO3, Cs2CO3, and KOAc natural alkaloid trisphaeridine (3g), which represents the basic
were also tested (entries 14–17). However, most of the tested skeleton of the Amaryllideceae alkaloids and also appears in a
Figure 2. Phosphine ligands utilized in optimization studies.
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Table 2. Synthesis of phenanthridines and quinolines.[a]
ciently used to synthesize these structurally diverse fused quin-
olines. The requisite ꢀ-chloro α,ꢀ-unsaturated aldehydes were
efficiently synthesized through Vilsmeier–Haack–Arnold chloro-
formylation reaction.[15] ꢀ-Chloro α,ꢀ-unsaturated aldehydes
derived from various tetralones gave excellent yield of the de-
sired quinoline derivatives. However, 4-chloro-2H-chromene-3-
carbaldehyde and 2-chlorocyclohept-1-enecarbaldehyde de-
rived from 4-chromanone and cycloheptanone, respectively,
gave moderate yields of their corresponding fused quinolines
(3o and 3p; Table 2). Aza-arene with more than one nitrogen
atom and azathio-arenes were also prepared by using our cas-
cade strategy. Pyridine-, thiophene-, and benzothiophene-de-
rived aldehydes were tolerated in this cascade strategy and sev-
eral interesting heterofused quinolines were synthesized (3q–s;
Table 2).
To further explore the scope of our cascade strategy, other
(2-aminoaryl)boronic acid pinacolate esters were also examined
as coupling partners. In these experiments, 2-chlorobenzalde-
hyde efficiently coupled with (2-aminoaryl)boronic acid pinacol-
ate esters under the standard reaction conditions, affording
phenanthridines in excellent yields (3t–v; Table 2). The requisite
starting (2-aminoaryl)boronic acid pinacolate esters were easily
prepared from the corresponding halide through palladium-cat-
alyzed cross-coupling reaction with pinacolborane.[16] Alterna-
tively, we planned to achieve phenanthridine 3a from 2-chloro-
aniline and (2-formylphenyl)boronic acid under the optimized
catalytic conditions (Scheme 3). In a separate experiment, 2-
chloroaniline (1 mmol) was treated with (2-formylphenyl)-
boronic acid (1.2 mmol) in the presence of Pd(OAc)2 (2.5 mol-
%), Sphos (5 mol-%) and K3PO4 (2 mmol) in DMSO at 120 °C for
8 h. In this case, the desired product 3a was obtained in only
trace amounts (ca. 8 % yield). These results suggested that the
neighboring formyl group of 1a might have some role in the
Pd-catalyzed cascade process.
[a] Reaction conditions: 2-chlorobenzaldehyde (1 mmol), (2-aminophenyl)-
boronic pinacol ester (1.2 mmol), Pd(OAc)2 (2.5 mol-%), Sphos (5 mol-%),
K3PO4 (2 mmol), DMSO (2 mL). [b] Yield of isolated product.
wide range of natural alkaloids and possesses excellent antitu-
mor effects and antiretroviral activity. To demonstrate the prac-
tical application of our method, gram-scale synthesis of tris-
pheridine was also conducted (Scheme 2). Alternatively, (2-
aminophenyl)boronic acid was also used instead of its pinacol
ester 2a for the synthesis phenanthridine 3a. Arylboronic acid
and 2a show similar reactivity in the cascade process and pro-
duced 3a in 90 % yield.
Scheme 3. Synthesis of phenanthridine 3a from 2-chloroaniline and (2-form-
ylphenyl)boronic acid.
Regarding the mechanism, it is presumed that the reaction
initially proceeds through the generation of Pd0 species in situ
from Pd(OAc)2 in the presence of ligand and base, which cata-
lyzes the coupling of chloroaldehydes with organoboron com-
pounds. This cross-coupling reaction is probably facilitated by
the intramolecular coordination of the neighboring carbonyl
oxygen to the palladium to form intermediate I[15a] during the
oxidative addition step (Figure 3). Intermediate I undergoes
transmetalation with organoboronate followed by reductive
Scheme 2. Gram-scale synthesis of trispheridine.
We next sought to explore the versatility of our reaction with elimination to form intermediate A. Finally, the latter intermedi-
other important nitrogen-containing arene quinolines (3j–p; ate gives the desired product 3 through intramolecular conden-
Table 2). Various ꢀ-chloro α,ꢀ-unsaturated aldehydes were effi- sation of the amine and the aldehyde.
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acetate–hexane) to give the desired products 2b–d in 61–83 %
yield (see the Supporting Information).
General Procedure for the Synthesis of Phenanthridines and
Quinolines: An oven-dried round-bottomed flask (50 mL) contain-
ing a stirrer bar was charged with Pd(OAc)2 (0.025 mmol), SPhos
(0.05 mmol), and K3PO4 (2 mmol). After degassing three times with
argon, dimethyl sulfoxide (DMSO) (2 mL) was added and the reac-
tion mixture was stirred at room temperature for 30 min. Chloro-
aldehyde 1 (1 mmol) and (2-aminoaryl)boronic acid pinacol ester 2
(1.2 mmol) were added to the mixture and the whole reaction mix-
ture was vigorously stirred and heated at 120 °C for 8 h under argon
atmosphere. After cooling to room temperature, EtOAc (15 mL) was
added and the mixture was washed with H2O (3 × 5 mL) to remove
the DMSO, dried with Na2SO4, and concentrated in vacuo. The
crude product was then purified by flash chromatography on silica
gel (ethyl acetate and hexane) to give the desired products 3a–s in
64–93 % yields.
Figure 3. Proposed mechanism and intermediate I.
Phenanthridine (3a):[17] Compound 3a was prepared according to
the general experimental procedure as above, yield 0.163 g (91 %);
yellow solid; m.p. 102–105 °C. 1H NMR (500 MHz, CDCl3): δ = 9.30
(s, 1 H), 8.51–8.71 (m, 2 H), 8.21 (dd, J = 8.1, 1.2 Hz, 1 H), 8.06 (d,
J = 7.9 Hz, 1 H), 7.80–7.98 (m, 1 H), 7.62–7.81 (m, 3 H) ppm. 13C
NMR (125 MHz, CDCl3): δ = 153.4, 144.2, 132.6, 131.2, 129.9, 128.8,
Conclusions
We have developed a Pd-catalyzed cascade strategy for the syn-
thesis of fused quinoline and phenanthridine derivatives from
ꢀ-chloro α,ꢀ-unsaturated aldehydes and 2-chloroaryl aldehydes,
respectively. The ꢀ-chloro α,ꢀ-unsaturated aldehydes were syn-
thesized from their corresponding ketones by using the Vils-
128.7, 127.5, 127.2, 126.3, 124.1, 122.2, 121.9 ppm. IR (CHCl3): ν =
˜
1619, 1487, 1457, 1445 cm–1. LC-MS (ESI): m/z = 180.0 [M + 1]+.
C13H9N (179.22): calcd. C 87.12, H 5.06, N 7.82; found C 87.13, H
meier–Haack–Arnold chloroformylation reaction. This cascade 5.08, N 7.88.
9-Methylphenanthridine (3b):[18] Compound 3b was prepared ac-
cording to the general experimental procedure as above, yield
0.173 g (90 %); reddish brown solid; m.p. 82–86 °C. 1H NMR
(500 MHz, CDCl3): δ = 9.21 (s, 1 H), 8.54 (d, J = 8.1 Hz, 1 H), 8.36 (s,
1 H), 8.17 (d, J = 8.1 Hz, 1 H), 7.92 (d, J = 8.1 Hz, 1 H), 7.72 (t, J =
7.6 Hz, 1 H), 7.65 (t, J = 7.6 Hz, 1 H), 7.51 (d, J = 8.0 Hz, 1 H), 2.64
(s, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 153.2, 144.5, 141.5,
132.6, 129.9, 129.2, 128.6, 128.5, 126.8, 124.5, 123.9, 122.1, 121.4,
strategy was also applied to the direct one-pot synthesis of
pyridine-, thiophene-, and benzothiophene-fused quinolines.
This procedure demonstrates an operationally simple, inexpen-
sive, and scalable strategy for the direct synthesis of quinoline
and phenanthridine derivatives under mild conditions.
Experimental Section
22.4 ppm. IR (CHCl3): ν = 2921, 1623, 1590, 1459 cm–1. LC-MS (ESI):
˜
m/z = 194.0 [M + 1]+. C14H11N (193.25): calcd. C 87.01, H 5.74, N
1
General Methods: H and 13C NMR spectra were obtained with a
7.25; found C 87.05, H 5.71, N 7.28.
Bucker Advance 500 MHz spectrometer with CDCl3 as solvent and
TMS as internal standard. Melting points were determined with a
Buchi M-560 apparatus and are uncorrected. IR spectra were re-
corded as thin films on a silicon disk with a PerkinElmer FTIR spec-
trometer. ESI mass spectra were recorded with a Bucker Daltonic
Data analysis 2.0 spectrometer. Reactions were monitored by thin-
layer chromatography (TLC) using aluminum-backed MERCK 60 sil-
ica gel plates (0.2 mm thickness); the chromatograms were visual-
ized first with ultraviolet light (254 nm) and then by immersion
in solutions of p-anisaldehyde followed by heating. Flash column
chromatography was performed with Merck silica gel 60 (230–
400 mesh). (2-Aminophenyl)boronic acid pinacolate ester (2a) was
obtained commercially and used directly without further purifica-
tion.
8-Methoxyphenanthridine (3c):[19] Compound 3c was prepared
according to the general experimental procedure as above, yield
0.194 g (93 %); dark-brown liquid. 1H NMR (500 MHz, CDCl3): δ =
9.21 (s, 1 H), 8.49 (t, J = 8.8 Hz, 2 H), 8.10–8.21 (m, 1 H), 7.66 (m, 2
H), 7.48 (dd, J = 8.9, 2.6 Hz, 1 H), 7.37 (d, J = 2.4 Hz, 1 H), 3.98 (s, 3
H) ppm. 13C NMR (125 MHz, CDCl3): δ = 158.9, 152.7, 143.5, 129.9,
127.7, 127.1, 126.9, 124.2, 123.6, 122.1, 121.7, 107.9, 55.6 (one signal
missing due to overlap) ppm. IR (CHCl3): ν = 2928, 1621, 1589, 1577,
˜
1530, 1486, 1462, 1369 cm–1. LC-MS (ESI): m/z = 210.1 [M + 1]+.
C14H11NO (209.25): calcd. C 80.36, H 5.30, N 6.69; found C 80.40, H
5.33, N 6.71.
8-Fluorophenanthridine (3d):[13] Compound 3d was prepared ac-
cording to the general experimental procedure as above; Yield:
0.175 g (89 %); reddish brown sticky mass. 1H NMR (500 MHz,
CDCl3): δ = 9.19 (s,1 H), 8.55 (dd, J = 8.9, 4.9 Hz, 1 H), 8.47 (d, J =
7.8 Hz, 1 H), 8.18 (d, J = 7.9 Hz, 1 H), 7.50–7.79 (m, 4 H) ppm. 13C
NMR (125 MHz, CDCl3): δ = 161.4 (d, J = 249.4 Hz), 152.3 (d, J =
3.6 Hz), 143.9, 130.2, 129.2 (d, J = 1.2 Hz), 128.5, 127.5, 127.4, 124.6
(d, J = 8.3 Hz), 123.7, 121.9, 120.2 (d, J = –23.9 Hz), 112.7 (d, J =
General Procedure for the Synthesis of Pinacolate 2-Aminoaryl-
boronates: To a mixture of 2-bromoaniline (5.0 mmol), Et3N
(2.8 mL, 20.0 mmol), and (dppf)PdCl2·CH2Cl2 (4 mol-% of 2-bromo-
aniline) in 1,4-dioxane (10 mL), was added 4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (2.17 mL, 15.0 mmol) dropwise. The resultant mixture
was heated to reflux at 120 °C. After 12 h, the mixture was cooled
to room temperature and diluted with NH4Cl (20 mL). The resulting
aqueous phase was extracted with CH2Cl2 (2 × 20 mL) and the
combined organic phases were washed with brine (30 mL). The
resulting organic phase was dried with Na2SO4, filtered, concen-
20.6 Hz) ppm. IR (CHCl3): ν = 1625, 1531, 1484, 1460 cm–1. LC-MS
˜
(ESI): m/z = 198.0 [M + 1]+. C13H8FN (197.21): calcd. C 79.18, H 4.09,
N 7.10; found C 79.19, H 4.10, N 7.12.
8-(Trifluoromethyl)phenanthridine (3e):[18] Compound 3e was
trated, and purified by column chromatography on silica gel (ethyl prepared according to the general experimental procedure as
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above, yield 0.215 g (87 %); white solid; m.p. 96–99 °C. 1H NMR 233.1 [M + 1]+. C17H13N (231.30): calcd. C 88.28, H 5.67, N 6.06;
(500 MHz, CDCl3): δ = 9.20 (s, 1 H), 8.64 (d, J = 8.6 Hz, 1 H), 8.53 (d,
J = 7.4 Hz, 1 H), 8.28 (s, 1 H), 8.20 (dd, J = 8.2, 0.9 Hz, 1 H), 8.00 (dd,
J = 8.6, 1.6 Hz, 1 H), 7.77–7.83 (m, 1 H), 7.66–7.74 (m, 1 H) ppm. 13C
NMR (125 MHz, CDCl3): δ = 152.9, 145.0, 134.5, 130.3, 129.9, 129.3
(q, J = 33 Hz), 127.7, 126.7 (q, J = 3 Hz), 126.1 (q, J = 4.2 Hz), 125.4,
found C 88.27, H 5.68, N 6.03.
10-Methoxy-7,8-dihydrobenzo[k]phenanthridine (3k): Com-
pound 3k was prepared according to the general experimental pro-
cedure as above, yield 0.240 g (92 %); dark reddish gummy. 1H NMR
(500 MHz, CDCl3): δ = 8.77 (s, 1 H), 8.43 (d, J = 8.5 Hz, 1 H), 8.13 (d,
J = 8.4 Hz, 1 H), 7.90 (d, J = 8.0 Hz, 1 H), 7.65 (t, J = 7.5 Hz, 1 H),
7.52 (t, J = 7.6 Hz, 1 H), 6.92 (s, 2 H), 3.87 (s, 3 H), 2.76–2.95 (m, 4
H) ppm. 13C NMR (125 MHz, CDCl3): δ = 159.8, 149.8, 148.5, 142.1,
139.5, 130.4, 129.7, 129.6, 128.1, 126.3, 125.2, 124.6, 124.4, 113.8,
123.8 (q, J = 272.2 Hz), 123.1, 122.9, 122.5 ppm. IR (CHCl3): ν = 1629,
˜
1329, 1277, 1220 cm–1. LC-MS (ESI): m/z = 248.0 [M + 1]+. C14H8F3N
(247.22): calcd. C 68.02, H 3.26, N 5.67; found C 68.05, H 3.25, N
5.66.
8,9-Dimethoxyphenanthridine (3f):[17] Compound 3f was pre-
pared according to the general experimental procedure as above,
yield 0.220 g (92 %); brown solid; m.p. 126–131 °C. 1H NMR
(500 MHz, CDCl3): δ = 9.16 (s, 1 H), 8.45 (d, J = 8.1 Hz, 1 H), 8.16 (d,
J = 8.1 Hz, 1 H), 7.89 (s, 1 H), 7.62–7.73 (m, 2 H), 7.36 (s, 1 H), 4.15
(s, 3 H), 4.08 (s, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 152.8,
151.6, 149.9, 143.8, 130.0, 128.1, 127.7, 126.5, 123.8, 121.6, 107.7,
101.7, 56.1, 56.0 (one signal is missing due to overlap) ppm. IR
111.5, 55.2, 29.3, 26.4 ppm. IR (CHCl3): ν = 2932, 2849, 1647,
˜
1618 cm–1. LC-MS (ESI): m/z = 262.3 [M + 1]+. C18H15NO (261.32):
calcd. C 82.73, H 5.79, N 5.36; found C 82.77, H 5.77, N 5.34.
11-Methoxy-7,8-dihydrobenzo[k]phenanthridine (3l): Com-
pound 3l was prepared according to the general experimental pro-
cedure as above, yield 0.235 g (90 %); reddish brown gummy mass.
1H NMR (500 MHz, CDCl3): δ = 8.71 (s, 1 H), 8.40 (d, J = 8.5 Hz, 1 H),
8.05 (d, J = 8.4 Hz, 1 H), 7.56 (t, J = 7.6 Hz, 1 H), 7.41–7.46 (m, 2 H),
7.18 (d, J = 8.2 Hz, 1 H), 6.79 (dd, J = 8.2, 1.8 Hz, 1 H), 3.74 (s, 3 H),
2.62–2.79 (m, 4 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 157.9, 150.1,
148.6, 139.1, 132.6, 132.1, 130.9, 129.9, 128.8, 128.0, 126.6, 124.9,
(CHCl3): ν = 2930, 1615, 1524, 1504, 1469, 1439, 1393, 1266,
˜
1158 cm–1. LC-MS (ESI): m/z = 240.0 [M + 1]+. C15H13NO2 (239.27):
calcd. C 75.30, H 5.48, N 5.85; found C 75.35, H 5.50, N 5.81.
[1,3]Dioxolo[4,5-j]phenanthridine (3g):[17] Compound 3g was
124.4, 115.4, 113.4, 55.4, 27.9, 26.8 ppm. IR (CHCl3): ν = 2935, 2834,
˜
1558, 1230 cm–1. LC-MS (ESI): m/z = 262.3 [M + 1]+. C18H15NO
(261.32): calcd. C 82.73, H 5.79, N 5.36; found C 82.76, H 5.80, N
5.38.
prepared according to the general experimental procedure as
1
above, yield 0.201 g (90 %); pale-yellow solid; m.p. 112–127 °C. H
NMR (500 MHz, CDCl3): δ = 9.01 (s, 1 H), 8.27 (d, J = 6.9 Hz, 1 H),
8.07 (d, J = 8.1 Hz, 1 H), 7.81 (s, 1 H), 7.52–7.64 (m, 2 H), 7.24 (s, 1
H), 6.08 (s, 2 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 151.6, 151.5,
148.2, 143.8, 130.3, 129.8, 128.0, 126.7, 124.2, 122.9, 121.9, 105.5,
10,11-Dimethoxy-7,8-dihydrobenzo[k]phenanthridine
(3m):
Compound 3m was prepared according to the general experimen-
tal procedure as above, yield 0.268 g (92 %); dark-brown gum. 1H
NMR (500 MHz, CDCl3): δ = 8.80 (s, 1 H), 8.48 (d, J = 7.9 Hz, 1 H),
8.16 (dd, J = 8.4, 0.9 Hz, 1 H), 7.68 (m, 1 H), 7.56 (m, 1 H), 7.52 (s, 1
H), 6.92 (s, 1 H), 3.98 (s, 3 H), 3.94 (s, 3 H), 2.78–2.95 (m, 4 H) ppm.
13C NMR (125 MHz, CDCl3): δ = 149.6, 149.5, 148.3, 147.2, 139.9,
133.6, 130.0, 129.6, 128.3, 126.5, 125.0, 124.4, 124.2, 112.9, 111.4,
101.9, 99.9 ppm. IR (CHCl3): ν = 1638, 1465, 1257 cm–1. LC-MS (ESI):
˜
m/z = 224.1 [M + 1]+. C14H9NO2 (223.23): calcd. C 75.33, H 4.06, N
6.27; found C 75.35, H 4.10, N 6.25.
[1,3]Dioxolo[4,5-i]phenanthridine (3h):[20] Compound 3h was
prepared according to the general experimental procedure as
1
56.4, 55.9, 28.5, 26.6 ppm. IR (CHCl3): ν = 1639, 1606, 1554, 1501,
˜
above, yield 0.192 g (86 %); pale-yellow solid; m.p. 148–150 °C. H
1384 cm–1. LC-MS (ESI): m/z = 292.0 [M + 1]+. C19H17NO2 (291.35):
NMR (500 MHz, CDCl3): δ = 9.30 (s, 1 H), 8.38 (d, J = 7.1 Hz, 1 H),
8.11 (dd, J = 7.8, 0.9 Hz, 1 H), 8.05 (br. s, 1 H), 7.56–7.71 (m, 2 H),
7.36 (s, 1 H), 6.21 (s, 2 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 146.5,
145.6, 143.7, 143.2, 130.9, 130.2, 127.8, 127.4, 127.1, 124.1, 121.9,
calcd. C 78.33, H 5.88, N 4.81; found C 78.35, H 5.90, N 4.81.
9,11-Dimethyl-7,8-dihydrobenzo[k]phenanthridine (3n): Com-
pound 3n was prepared according to the general experimental pro-
cedure as above, yield 0.235 g (91 %); dark-brown liquid. 1H NMR
(500 MHz, CDCl3): δ = 8.82 (s, 1 H), 8.45 (d, J = 8.5 Hz, 1 H), 8.14
(dd, J = 8.4, 0.9 Hz, 1 H), 7.63–7.69 (m, 2 H), 7.55 (m, 1 H), 7.11 (br.
s, 1 H), 2.76–2.89 (m, 4 H), 2.42 (s, 3 H), 2.41 (s, 3 H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 149.9, 148.7, 139.9, 135.7, 135.2, 134.9, 131.8,
131.7, 130.7, 129.9, 128.0, 127.8, 126.4, 125.5, 124.7, 26.4, 24.0, 21.3,
115.2, 113.2, 102.6 ppm. IR (CHCl3): ν = 1573, 1463, 1287, 1231 cm–1
.
˜
LC-MS (ESI): m/z = 224.0 [M + 1]+. C14H9NO2 (223.23): calcd. C 75.33,
H 4.06, N 6.27; found C 75.35, H 4.07, N 6.28.
Benzo[k]phenanthridine (3i):[9f] Compound 3i was prepared ac-
cording to the general experimental procedure as above, yield
0.147 g (64 %); brown solid; m.p. 108–110 °C. 1H NMR (500 MHz,
CDCl3): δ = 9.34 (s, 1 H), 9.19 (d, J = 7.1 Hz, 1 H), 9.09 (dd, J = 8.2,
4.4 Hz, 1 H), 8.33 (d, J = 8.1 Hz, 1 H), 7.90–8.10 (m, 3 H), 7.70–7.84
(m, 4 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 152.5, 145.8, 135.2,
131.2, 130.2, 129.0, 128.9, 128.8, 128.2, 128.1, 127.8, 127.0, 126.9,
126.8, 125.1, 120.2 (one signal missing due to overlap) ppm. IR
19.9 ppm. IR (CHCl3): ν = 2927, 1641, 1564, 1503 cm–1. LC-MS (ESI):
˜
m/z = 260.1 [M + 1]+. C19H17N (259.35): calcd. C 87.99, H 6.61, N
5.40; found C 87.98, H 6.66, N 5.41.
8,9,10,11-Tetrahydro-7H-cyclohepta[c]quinolines (3o):[12] Com-
pound 3o was prepared according to the general experimental pro-
cedure as above, yield 0.130 g (66 %); orange crystalline solid; m.p.
64–67 °C. 1H NMR (500 MHz, CDCl3): δ = 8.67 (s, 1 H), 8.11 (t, J =
8.5 Hz, 2 H), 7.62–7.66 (m, 1 H), 7.51–7.55 (m, 1 H), 3.24–3.28 (m, 2
H), 2.98–3.01 (m, 2 H), 1.66–1.76 (m, 6 H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 151.3, 148.5, 147.0, 135.6, 129.8, 128.1, 126.7, 126.2,
(CHCl3): ν = 2923, 1579, 1451, 1381 cm–1. LC-MS (ESI): m/z = 230.0
˜
[M + 1]+. C17H11N (229.28): calcd. C 89.06, H 4.84, N 6.11; found C
89.06, H 4.82, N 6.12.
7,8-Dihydrobenzo[k]phenanthridine (3j):[12] Compound 3j was
prepared according to the general experimental procedure as
above, yield 0.206 g (89 %); light-yellow gummy mass. 1H NMR
(500 MHz, CDCl3): δ = 8.82 (s, 1 H), 8.48 (d, J = 8.5 Hz, 1 H), 8.15 (d,
J = 8.4 Hz, 1 H), 7.98 (d, J = 7.3 Hz, 1 H), 7.68 (t, J = 7.4 Hz, 1 H),
7.55 (t, J = 7.6 Hz, 1 H), 7.30–7.48 (m, 3 H), 2.78–3.00 (m, 4 H) ppm.
13C NMR (125 MHz, CDCl3): δ = 150.1, 148.6, 140.2, 139.3, 131.9,
123.1, 33.2, 32.4, 28.0, 27.2, 26.2 ppm. IR (CHCl ): ν = 2924, 2852,
3
˜
1723, 1507, 1505, 1453, 1273 cm–1. LC-MS (ESI): m/z = 198.0 [M +
1]+. C14H15N (197.28): calcd. C 85.24, H 7.66, N 7.10; found C 85.25,
H 7.67, N 7.12.
6H-Chromeno[3,4-c]quinolines (3p): Compound 3p was prepared
130.7, 129.9, 129.0, 128.8, 128.2, 128.1, 126.6, 126.4, 125.2, 124.5, according to the general experimental procedure as above, yield
28.9, 26.4 ppm. IR (CHCl3): ν = 1638, 1503 cm–1. LC-MS (ESI): m/z = 0.151 g (65 %); reddish brown liquid. 1H NMR (500 MHz, CDCl3): δ =
˜
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1
8.74 (s, 1 H), 8.51 (d, J = 8.5 Hz, 1 H), 8.16 (d, J = 8.5 Hz, 1 H), 8.08
(dd, J = 7.8, 1.5 Hz, 1 H), 7.4 (m, 1 H), 7.50 (m, 1 H), 7.39 (td, J = 7.8,
7.6, 1.5 Hz, 1 H), 7.15–7.23 (m, 2 H), 5.15 (s, 2 H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 157.3, 149.2, 146.4, 134.8, 130.9, 130.2, 128.9,
above, yield 0.210 g (85 %); white solid. H NMR (500 MHz, CDCl3):
δ = 9.29 (d, J = 7.6 Hz, 1 H), 8.42–8.65 (m, 2 H), 7.96–8.14 (m, 2 H),
7.80–7.96 (m, 1 H), 7.65–7.80 (m, 1 H), 7.50 (s, 1 H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 154.9, 149.0, 145.0, 131.9, 131.6, 128.9, 127.9,
128.5, 127.3, 125.9, 124.8, 123.5, 122.1, 121.9, 118.0, 67.0 ppm. IR 126.2, 123.9, 122.6, 121.6, 120.7, 120.5 (d, J = 258.1 Hz), 120.3 ppm.
(CHCl3): ν = 2852, 1641, 1483, 1245 cm–1. LC-MS (ESI): m/z = 234.1
IR (CHCl3): ν = 3064, 2928, 1618, 1462, 1260 cm–1. LC-MS (ESI): m/z =
˜
˜
[M + 1]+. C16H11NO (233.27): calcd. C 82.38, H 4.75, N 6.00; found C
82.37, H 4.78, N 6.02.
248.0 [M + 1]+. C14H8F3N (247.22): calcd. C 68.02, H 3.26, N 5.67;
found C 68.06, H 3.28, N 5.66.
Benzo[h][1,6]naphthyridine (3q):[9f] Compound 3q was prepared
according to the general experimental procedure as above, yield
0.149 g (83 %); brown solid; m.p. 95–97 °C. 1H NMR (500 MHz,
CDCl3): δ = 9.31 (s, 1 H), 9.19 (dd, J = 4.4, 1.7 Hz, 1 H), 9.15 (m, 1
H), 8.36 (dd, J = 8, 1.7 Hz, 1 H), 8.22 (d, J = 8.2 Hz, 1 H), 7.86 (m, 1
H), 7.77 (m, 1 H), 7.65 (dd, J = 7.9, 4.4 Hz, 1 H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 153.3, 152.6, 148.6, 146.6, 135.9, 130.3, 129.4,
Supporting Information (see footnote on the first page of this
article): Experimental details, spectroscopic data and selected cop-
ies of 1H and 13C NMR spectra of some (2-aminoaryl)boronic acid
pinacolate esters and all final products.
Acknowledgments
127.6, 125.2, 123.7, 122.7, 120.9 ppm. IR: ν = 1589, 1440 cm–1. LC-
˜
The authors thank the Department of Science and Technology,
New Delhi for financial support [SB/FT/CS-036/2014 (CSIR-NEIST
project number GPP 293)] and Director, CSIR-North East Insti-
tute of Science and Technology, Jorhat, India for his keen inter-
est in this work and facilities.
MS (ESI): m/z = 181.0 [M + 1]+. C12H8N2 (180.21): calcd. C 79.98, H
4.47, N 15.55; found C 79.97, H 4.45, N 15.50.
Thieno[2,3-c]quinoline (3r):[21] Compound 3r was prepared ac-
cording to the general experimental procedure as above, yield
0.159 g (86 %); white solid; m.p. 86–87 °C. 1H NMR (500 MHz, CDCl3):
δ = 9.31 (s, 1 H), 8.27 (d, J = 8.1 Hz, 1 H), 8.23 (d, J = 8.3 Hz, 1 H),
7.96 (d, J = 5.1 Hz, 1 H), 7.84 (dd, J = 5.2, 1.3 Hz, 1 H), 7.71 (t, J =
7.6 Hz, 1 H), 7.64 (t, J = 7.6 Hz, 1 H) ppm. 13C NMR (125 MHz,CDCl3):
δ = 144.9, 144.1, 141.3, 133.3, 131.6, 129.7, 127.7, 126.8, 124.3, 123.2,
Keywords: Synthetic methods · Domino reactions ·
Palladium · C–C coupling · Nitrogen heterocycles
121.4 ppm. IR (CHCl3): ν = 2922, 2845, 1566, 1499, 1463, 1362, 1220,
˜
1619, 1487, 1457, 1445 cm–1. LC-MS (ESI): m/z = 286.1 [M + 1]+.
C11H7NS (185.24): calcd. C 71.32, H 3.81, N 7.56; found C 71.33, H
3.79, N 7.53.
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Benzo[4,5]thieno[2,3-c]quinolines (3s):[14b] Compound 3s was
prepared according to the general experimental procedure as
above, yield 0.207 g (88 %); brown solid; m.p. 128–131 °C. H NMR
(500 MHz, CDCl3): δ = 9.34 (s, 1 H), 8.87 (dd, J = 6.7, 2.9 Hz, 1 H),
8.83 (dd, J = 7.0, 1.8 Hz, 1 H), 8.31 (dd, J = 6.7, 2.9 Hz, 1 H), 8.04
(dd, J = 6.8, 2.2 Hz, 1 H), 7.75 (m, 2 H), 7.62 (m, 2 H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 145.5, 145.4, 141.3, 135.3, 135.0, 133.3, 130.6,
127.7, 127.4, 127.3, 125.9, 125.3, 123.6, 122.8 (one signal missing
1
due to overlap) ppm. IR (CHCl3): ν = 3060, 2921, 1500, 1317,
˜
1217 cm–1. LC-MS (ESI): m/z = 236.0 [M + 1]+. C15H9NS (235.30):
calcd. C 76.57, H 3.86, N 5.95; found C 76.55, H 3.88, N 5.94.
3-Methylphenanthridine (3t):[22] Compound 3t was prepared ac-
cording to the general experimental procedure as above, yield
0.171 g (89 %); brown gum. H NMR (500 MHz, CDCl3): δ = 9.24 (s,
1 H), 8.27–8.67 (m, 2 H), 7.88–8.10 (m, 2 H), 7.80 (m, 1 H), 7.63 (m,
1 H), 7.45 (m, 1 H), 2.58 (s, 3 H) ppm. 13C NMR (125 MHz, CDCl3):
δ = 153.3, 144.1, 138.8, 132.5, 130.9, 129.2, 128.8, 128.7, 126.9, 125.9,
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121.9, 121.7, 121.6, 21.5 ppm. IR (CHCl3): ν = 3062, 2922, 1616,
˜
1480 cm–1. LC-MS (ESI): m/z = 194.0 [M + 1]+. C14H11N (193.25):
calcd. C 81.01, H 5.74, N 7.25; found C 81.09, H 5.71, N 7.26.
3-Fluorophenanthridine (3u):[18] Compound 3u was prepared ac-
cording to the general experimental procedure as above, yield
0.177 g (90 %); white solid. H NMR (500 MHz, CDCl3): δ = 9.26 (d,
J = 7.7 Hz, 1 H), 8.39–8.63 (m, 2 H), 8.01 (s, 1 H), 7.75–7.92 (m, 2 H),
7.60–7.74 (m, 1 H), 7.32–7.54 (m, 1 H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 162.5 (d, J = 248.5 Hz), 154.6, 145.3 (d, J = 11.7 Hz),
132.3, 131.5, 128.9, 127.4, 125.8, 121.5, 120.7, 124.1 (d, J = 9 Hz),
1
116.2 (d, J = 23.8 Hz), 114.3 (d, J = 21 Hz) ppm. IR (CHCl3): ν = 3062,
˜
2926, 1618, 1465, 1262 cm–1. LC-MS (ESI): m/z = 198.0 [M + 1]+.
C13H8FN (197.21): calcd. C 79.17, H 4.09, N 7.10; found C 79.18, H
4.11, N 7.09.
3-(Trifluoromethyl)phenanthridine (3v):[23] Compound 3v was
prepared according to the general experimental procedure as
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Received: February 25, 2016
Published Online: April 6, 2016
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© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim