Copper-phenanthroline catalysts for regioselective synthesis of pyrrolo[3′,4′:3,4]pyrrolo[1,2-a]furoquinolines/phenanthrolines and of pyrrolo[1,2-a]phenanthrolines under mild conditions

Article abstract of DOI:10.3762/bjoc.10.62

A new series of pyrrolo[3′,4′:3,4]pyrrolo[1,2-a]furoquinolines/ phenanthrolines and pyrrolo[1,2-a]phenanthrolines were efficiently built up from an 8-hydroxyquinoline derivative or phenanthroline via 1,3-dipolar cycloaddition reaction involving non-stabilized azomethine ylides, generated in situ from the parent furo[3,2-h]quinoliniums/phenanthroliums, in presence of a copper(II) chloride-phenanthroline catalytic system. The methodology combines general applicability with high yields.

Full text of DOI:10.3762/bjoc.10.62

Copper–phenanthroline catalysts for regioselective
synthesis of pyrrolo[3′,4′:3,4]pyrrolo[1,2-a]furo-
quinolines/phenanthrolines and of
pyrrolo[1,2-a]phenanthrolines under mild conditions
Rupankar Paira, Tarique Anwar, Maitreyee Banerjee, Yogesh P. Bharitkar,
Shyamal Mondal, Sandip Kundu, Abhijit Hazra, Prakas R. Maulik
and Nirup B. Mondal*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2014, 10, 692–700.
Department of Chemistry, Indian Institute of Chemical Biology,
Council of Scientific and Industrial Research, 4 Raja S.C. Mullick
Road, Jadavpur, Kolkata-700032, India
doi:10.3762/bjoc.10.62
Received: 18 December 2013
Accepted: 21 February 2014
Published: 20 March 2014
Email:
Nirup B. Mondal* - nirup@iicb.res.in
Associate Editor: B. Stoltz
* Corresponding author
© 2014 Paira et al; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
copper(II) chloride–phenanthroline; 1,3-dipolar cycloaddition;
furo[3,2-h]quinoliniums; phenanthroliums;
pyrrolo[1,2-a]phenanthrolines;
pyrrolo[3′,4′:3,4]pyrrolo[1,2-a]furoquinolines/phenanthrolines
Abstract
A new series of pyrrolo[3′,4′:3,4]pyrrolo[1,2-a]furoquinolines/phenanthrolines and pyrrolo[1,2-a]phenanthrolines were efficiently
built up from an 8-hydroxyquinoline derivative or phenanthroline via 1,3-dipolar cycloaddition reaction involving non-stabilized
azomethine ylides, generated in situ from the parent furo[3,2-h]quinoliniums/phenanthroliums, in presence of a copper(II)
chloride–phenanthroline catalytic system. The methodology combines general applicability with high yields.
Introduction
The chemistry of the 1,3-dipolar cycloaddition has always been recent years, there have been many attempts to synthesize
a fascinating undertaking especially when azomethine ylides are diversely modified pyrrolidines, both symmetric and asym-
involved as the key component [1-9]. These ylides, both stabi- metric in nature. Several of these attempts involved 1,3-dipolar
lized or non-stabilized 1,3-dipoles, can easily enter the reaction cycloaddition reactions involving azomethine ylides to give
independent of their stability and lead to the formation of a cycloadducts, which were further explored as potential antiviral,
pyrrolidine core, a structural motif of immense interest from antifungal, antitumor and anti-HIV candidates [1-15]. We
both chemical and pharmacological points of view [10]. In have also been pursuing the cycloaddition methodology
692

Beilstein J. Org. Chem. 2014, 10, 692–700.
for several years and established some synthetic routes copper(II) chloride–phenanthroline as the best catalytic pair for
towards indolizines, pyrrolo[1,2-a]quinolines/isoquinolines, this purpose. Herein we wish to present the results of our recent
oxazadicyclopenta[a,h]naphthalenes etc., some of which have synthetic efforts to synthesize a series of unique pentacyclic
been evaluated as potential antibacterial and antifungal agents pyrrolo[3′,4′:3,4]pyrrolo[1,2-a]furoquinolines/phenanthrolines
[16-19]. In order to explore the possibility of using structurally using the above catalytic system. To the best of our knowledge,
more complex dipoles and dipolarophiles to construct more this is the first report of the application of this catalyst for the
interesting structural networks, we replaced simple alkenes/ regioselective 1,3-dipolar cycloaddition reaction, involving
alkynes with maleimide derivatives. Our preference for this azomethine ylides derived from structurally complex quinoline-
dienophile was dictated by a recent patent on the lifespan based N-heterocycles.
altering properties of cycloadducts involving maleimide
dienophiles [20]. Moreover, very recently we have character- Results and Discussion
ized some furo[3,2-h]quinoliniums as potent non-detergent Our studies started with the preparation (Scheme 1 and
spermicides [19], which encouraged us for further modification Scheme 2) of maleimides 4a–c employing maleic anhydride (1)
and derivatization of furoquinoline analogues in search and different aromatic amines 2a–c, and of furo[3,2-h]quinolin-
for more potent agents. Thus we became interested in the iums 9a–d from 5-chloro-8-hydroxy-7-iodoquinoline 5 [19,24].
construction of a number of structurally complex pentacyclic However, attempted condensation of 4a with the 1,3-dipole
pyrrolo[3′,4′:3,4]pyrrolo[1,2-a]furoquinolines, for possible generated in situ from 9a, employing protocols from our
identification of new antibacterial/antifungal/spermicidal/
lifespan altering agents, where furo[3,2-h]quinoliniums were
employed as dipole precursors and maleimide derivatives as
dipolarophiles.
We initially employed the protocols from our recently devel-
oped green methodologies [21-25], which however failed to
give any promising outcome and forced us to explore new
catalytic systems. While searching for this goal, we were
attracted by the possible application of copper-catalysis, which
has always been an effective tool especially with Diels–Alder
reactions [26,27]. Thus, we studied the effect of a number of
Scheme 1: Preparation of maleimide dipolarophiles 4a–c.
catalytic systems and after an extensive screening, we found
Scheme 2: Preparation of 1,3-dipole precursors 9a–d.
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Beilstein J. Org. Chem. 2014, 10, 692–700.
recently developed methodologies, did not succeed, affording copper catalysts in this particular reaction over the others;
products only in low yields (10–19%, Table 1, entries 1–7).
CuCl2 appeared to be the catalyst of choice (Table 1, entries
8–32). In order to explore the effect of ligands, a number of
We then studied the feasibility of a metal-catalyzed 1,3-dipolar phosphines, bis-oxazocines, pyrazolyl-pyrimidines and phenan-
cycloaddition strategy. A thorough screening of different cata- throline analogues were employed (Figure 1). As represented in
lysts, as summarized in Table 1, revealed the supremacy of Table 1, the monodentate ligands are in general less effective
Table 1: Optimization of conditions of reaction between 4a and 9a.
Entry
Catalytic system
Solventa
Time (h)
Temp. (°C)
Yieldb
1
Basic alumina
Amberlite IRA 402 (OH)
K-10 clay
None
0.3
10
0.3
3
80
90
80
rt
10c
16
12c
17
15
19
12
NR
NR
NR
NR
11
15
28
12
32
47
23
45
57
58
58
56
58
55
65
67
65
74
71
94
94
2
H2O
3
None
4
Triton X-114 (60 mM)
SDS (60 mM)
TTAB (80 mM)
CTAB (90 mM)
SnCl4
H2O
5
H2O
3
rt
6
H2O
6
rt
7
H2O
5
rt
8
Toluene
DCM
8
80
rt
9
Sc(OTf)3
10
10
10
10
8
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Sc(OTf)3
Toluene
DCM
80
rt
Mg(ClO4)3
Mg(ClO4)3
Toluene
DCM
80
rt
Cu(OTf)2
Cu(OTf)2
Toluene
DCM
8
80
rt
Cu(OAc)2
8
Cu(OAc)2
Toluene
MeCN
DCM
8
80
65
rt
Cu(OAc)2
8
CuCl2
6
CuCl2
Toluene
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
6
80
65
65
65
65
65
65
65
65
65
65
65
65
65
CuCl2
3
CuCl2/PPh3
3
CuCl2/PMePh2
CuCl2/PCy3
3
3
CuCl2/P(3-ClC6H4)3
CuCl2/P(3-OMeC6H4)3
CuCl2/DPEphos
CuCl2/xantphos
CuCl2/pyphos
CuCl2/bis-oxazocine
CuCl2/pyrimidine
CuCl2/phenanthroline (L1)
CuCl2/phenanthroline (L2)
3
3
3
3
3
3
3
3
3
aAll the reactions were performed in presence of DBU; bIsolated yield; cThe reactions were performed under microwave irradiation at 180 W.
694

Beilstein J. Org. Chem. 2014, 10, 692–700.
Figure 2: ORTEP diagram showing the molecular structure of 10a at
30% probability level.
Figure 1: Bi-/tridentate ligands used for the optimization of the reac-
tion conditions.
The plausible mechanism of this cycloaddition is presented in
(55–58% yield; Table 1, entries 21–25) than bi-/tridentate Scheme 3. The base (DBU) abstracts the acidic proton of
ligands (65–94% yield; Table 1, entries 26–32), and phos- furo[3,2-h]quinolinium 9a to generate the 1,3-dipole I. The
phines in general proved less effective in terms of product yield Cu(II)–phenanthroline system activates the maleimide dipo-
(Table 1, entries 21–28). Bis-oxazocines and pyrazolyl-pyrim- larophile via coordination with the carbonyl group to undergo a
idines on the other hand showed some promising results [3 + 2] cycloaddition with the 1,3-dipole to form the
(Table 1, entries 29 and 30). However, both in terms of yield cycloadduct 10a, releasing the Cu(II) complex to enter another
and cleaner reaction profile, 1,10-phenanthrolines (L1, L2) were cycle.
identified as the best partners for CuCl2 (Table 1, entries 31 and
32). Thus, the 1,3-dipolar cycloaddition reaction between 9a In order to establish the general applicability of this protocol,
(1 equiv) and 4a (1.1 equiv) yielded 94% of 10a within 3 h, we reacted different furo[3,2-h]quinoliniums 9a–d and
when 5 mol % CuCl2 and 5 mol % of either L1 or L2 were maleimide dipolarophiles 4a–c under the standardized reaction
employed with DBU as the base in acetonitrile solvent at 65 °C. conditions. As obvious from the results summarized in
This was taken as the best conditions to perform the reaction.
Scheme 4, all the reactions proceeded smoothly to give
cycloadducts with excellent yields, which were fully character-
The structure of 10a was deduced from the appearance of a new ized by mass and NMR analysis.
doublet of doublets at δ 5.50 and δ 6.20. Another doublet at
δ 3.90 and a new multiplet at δ 3.50 also indicated the success In order to test its general applicability further, we replaced
of the reaction, as these signals could be attributed to the new furo[3,2-h]quinoliniums with phenanthroliniums 12a,b. These
pyrrolidine core. Besides, the cluster in the aromatic region phenanthroliniums were synthesized (Scheme 5) from phenan-
(δ 6.60–8.50) indicated the presence of 19 aromatic protons in throline (11) and 2′-bromoacetophenones 8a and 8d, under
the cycloadduct 10a. This interpretation was also well basic alumina/microwave (180 W) conditions. These were then
supported by the 13C NMR of 10a. Peaks for the four sp3- subjected to the optimized [3 + 2] cycloaddition protocol with
methine carbons of the newly formed pyrrolidine motif different N-phenylmaleimide dipolarophiles 4a–c, which even-
appeared at δ 47.2, 47.4, 61.0 and 66.5 as expected. Two tually produced similar cycloadducts 14a–c in high yield. It is
methine carbon signals appearing at δ 101.6 and 110.8 could be interesting to note that every reaction proceeded only up to the
assigned to the CH units present in the dihydroquinoline ring. cycloaddition stage, without any aromatization of the final
Moreover, the presence of peaks for three carbonyl carbons at cycloadduct. However, a similar reaction of phenanthroliniums
δ 174.9, 176.6, 194.5, and for ten other quaternary carbons and 12a,b with alkyne dipolarophiles like acetylenedicarboxylates
19 methine carbons in the aromatic region (δ 116.0–159.8) also or monocarboxylates 13a–d proceeded with aromatization of
confirmed the structure. The relative orientations of H-1, H-18, the putative dihydroaromatic intermediates to produce the final
H-19 and H-20 could be determined unambiguously by the cycloaddition products 14d–g.
single-crystal X-ray diffraction analysis of 10a; the ORTEP
diagram is presented in Figure 2. No other diastereomer could Characterization of the products was done via mass and NMR
be detected.
spectral studies. Furthermore, the single-crystal X-ray study of
695

Beilstein J. Org. Chem. 2014, 10, 692–700.
Scheme 3: Plausible mechanistic pathway for the synthesis of pyrrolo[3′,4′:3,4]pyrrolo[1,2-a]furoquinolines.
cycloadduct 14e undoubtedly confirmed the structure of these stirred for 30 min. Then 5 mol % CuCl2 and 5 mol % of either
cycloadducts, as obvious from the ORTEP diagram presented in L1, L2 were added to the reaction mixture and stirred continu-
Figure 3.
ously for 3 h at 65 °C. After completion of the reaction (moni-
tored by TLC), the reaction mixture was partitioned between
brine and ethyl acetate. The organic layer was then evaporated
and purified by column chromatography (ethyl acetate:hexane).
Conclusion
In conclusion, a simple CuCl2–phenanthroline catalyzed
methodology has been developed to synthesize a series of
unique heteroaromatic polycycles 10a–h, 14a–g by a 1,3- NMR data and crystal data of some representative com-
dipolar cycloaddition reaction, using furo[3,2-h]quinolinium/ pounds: a) spectral data of 10a: Yellow solid. 94% yield;
phenanthrolinium dipole precursors and maleimide/acetylene- mp 246–248 °C; Rf (20% ethyl acetate–hexane) 0.35; 1H NMR
carboxylate dipolarophiles. High atom-economy, good to very (300 MHz, CDCl3) δ 3.65 (t, J = 8.1 Hz, 1H), 3.84 (s, 3H), 3.89
good isolated yield of the products, short reaction time and ease (m, 1H), 5.52 (m, 1H), 6.18 (m, 1H), 6.64 (s, 1H), 6.76 (s, 1H),
of separation coupled with general applicability are the key 6.98 (m, 8H), 7.11 (m, 1H), 7.20 (m, 2H), 7.65 (t, J = 7.5 Hz,
features of this methodology.
2H), 7.76 (d, J = 7.2 Hz, 1H), 8.48 (d, J = 7.2 Hz, 1H);
13C NMR (150 MHz, CDCl3) δ 47. 2 (CH), 47.4 (CH), 55.5
(CH3), 61.0 (CH), 66.5 (CH), 101.6 (CH), 110.8 (CH), 114.5
Experimental
General procedure to synthesize pyrrolo[3′,4′:3,4]pyrrolo- (2CH), 116.0 (C), 119.7 (CH), 124.0 (CH), 124.6 (2CH), 127.6
[1,2-a]furoquinolines 10a–h, pyrrolo[3′,4′:3,4]pyrrolo[1,2- (2CH), 127.6 (C), 128.4 (3CH), 128.4 (C), 128.8 (C), 129.3 (C),
a]phenanthrolines 14a–c, and pyrrolo[1,2-a]phenanthro- 129.4 (2CH), 129.6 (2CH), 131.2 (C), 133.1 (C), 134.4 (CH),
lines 14d–g: A mixture of 3.3 mmol furo[3,2-h]quinolinium 140.6 (C), 157.0 (C), 159.8 (C), 174.9 (C), 176.6 (C), 194.5
derivatives 9a–d/phenanthroliniums 12a,b and 3.3 mmol (C); HRMS (ESI) m/z: [M + Na]+ calcd for C36H25ClN2NaO5+
N-phenylmalimide derivatives 4a–d/dialkyl acetylenedicar- 623.1344; found, 623.1353. b) Spectral data of 14a: Yellow
boxylates 13a–b/monoalkyl acetylenemonocarboxylates 13c,d solid. 81% yield; mp 242–243 °C; Rf (20% ethyl
was placed in a round bottomed flask (25 mL). To this MeCN acetate–hexane) 0.31; 1H NMR (300 MHz, CDCl3) δ 2.26 (s,
(50 mL) and DBU (1 mmol) were added and the mixture was 6H), 3.65 (m, 1H), 3.74 (m, 1H), 5.94 (m, 1H), 6.18 (m, 1H),
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Beilstein J. Org. Chem. 2014, 10, 692–700.
Scheme 4: Synthesis of pyrrolo[3′,4′:3,4]pyrrolo[1,2-a]furoquinoline analogues under the optimized protocol.
6.54 (m, 1H), 7.00 (m, 3H), 7.07 (m, 2H), 7.19 (m, 2H), 7.64 (ESI) m/z: [M + Na]+ calcd for C32H25N3NaO3+ 522.1788;
(m, 4H), 7.85 (m, 1H), 8.33 (m, 2H); 13C NMR (75 MHz, found, 522.1799. c) Spectral data of 14e: Brown solid. 91%
CDCl3) δ 19.5 (CH3), 19.7 (CH3), 46.9 (CH), 47.5 (CH), 63.4 yield; mp 233–234 °C; Rf (20% ethyl acetate–hexane) 0.33;
(CH), 67.0 (CH), 116.9 (CH), 120.4 (CH), 121.1 (C), 121.6 1H NMR (300 MHz, CDCl3) δ 1.06 (t, J = 7.2 Hz, 3H), 1.38 (t,
(CH), 123.7 (CH), 126.4 (CH), 126.9 (CH), 127.3 (CH), 128.2 J = 7.2 Hz, 3H), 3.72 (m, 1H), 3.88 (m, 1H), 4.38 (m, 2H), 7.33
(C), 128.7 (2CH), 128.8 (2CH), 129.1 (C), 129.4 (C), 130.2 (m, 1H), 7.51 (t, J = 7.4 Hz, 2H), 7.60 (m, 1H), 7.69 (d,
(CH), 132.9 (CH), 134.6 (C), 136.0 (CH), 137.7 (C), 137.9 (C), J = 9.3 Hz, 1H), 7.83 (m, 2H), 8.01 (m, 1H), 8.17 (d,
138.5 (C), 145.3 (CH), 175.7 (C), 176.9 (C), 196.6 (C); HRMS J = 7.8 Hz, 3H), 8.57 (d, J = 9.3 Hz, 1H); 13C NMR (75 MHz,
697

Beilstein J. Org. Chem. 2014, 10, 692–700.
Scheme 5: Construction of pyrrolo[3′,4′:3,4]pyrrolo[1,2-a]phenanthrolines 14a–c and of pyrrolo[1,2-a]phenanthrolines 14d–g.
CDCl3) δ 13.6 (CH3), 14.3 (CH3), 60.4 (CH2), 61.4 (CH2), data and conventional R = 0.041 for 2932 F-values with
104.0 (C), 120.2 (CH), 122.5 (CH), 125.3 (CH), 125.6 (C), I>2σ(I), (Δ/σ)max = 0.000, S = 0.617 for all data and 398 para-
126.8 (C), 126.0 (CH), 126.7 (CH), 127.7 (C), 128.1 (2CH), meters, Δρmax, min (e/Å3) = 0.214, −0.197. e) Crystal data for
129.0 (C), 130.0 (2CH), 130.7 (C), 132.2 (CH), 135.9 (CH), 13f: C28H22N2O5, M = 466.48 , monoclinic, P21/c,
137.3 (C), 137.4 (C), 137.9 (C), 145.7 (CH), 163.5 (C), 165.5 a = 11.9766(8), b = 17.281(1), c = 11.6975(8) Å,
(C), 184.4 (C); HRMS (ESI) m/z: [M + Na]+ calcd for β = 109.484(3)°, V = 2282.4(3) Å3, Z = 4, Dc = 1.358 g cm−3,
C28H22N2NO5+ 489.1421; found, 489.1437. d) Crystal data µ = 0.094 mm−1, F(000) = 976, λ (Mo Kα) = 0.71073 Å,
for 10a: C36H25N2O5Cl, M = 601.03 , monoclinic, P21/c, yellowish block, crystal size: 0.17 × 0.11 × 0.09 mm, 25248
a = 15.687(2), b = 19.297(2), c = 9.848(1) Å, β = 99.478(8)°, reflections measured (Rint = 0.0552), 3534 unique reflections,
V = 2940.5(7) Å3, Z = 4, Dc = 1.358 g cm−3, µ = 0.178 mm−1, wR(F2) = 0.1976 for all data and conventional R = 0.0501 for
F(000) = 1248, λ(MoKα) = 0.71073 Å, reddish block, crystal 2741 F-values with I>2σ(I), (Δ/σ)max = 0.000, S = 1.504 for all
size: 0.7 × 0.25 × 0.19 mm, 37123 reflections measured data and 319 parameters, Δρmax, min (e/Å3) = 0.267, −0.351.
(Rint = 0.0477), 3620 unique reflections, wR(F2) = 0.155 for all Unit cell determinations and intensity data collections for both
698

Beilstein J. Org. Chem. 2014, 10, 692–700.
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Supporting Information
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Acknowledgements
We would like to thank The Council of Scientific and Indus-
trial Research (CSIR), New Delhi, for financial support in the
form of fellowships to R.P., S.M., A.H. and Emeritus Scientist
ship to P.R.M. and N.B.M. We are indebted Dr B. Achari,
Ex-Emeritus Scientist, CSIR, for critical suggestions and
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