Facile, diversity-oriented, normal-electron-demand Diels-Alder reactions of 6-amino-2 H-pyran-2-ones with diethyl acetylenedicarboxylate, 1,4-naphthoquinone, and N-phenylmaleimide

Article abstract of DOI:10.1055/s-0034-1379397

A series of 6-amino-4-methoxyphenyl-2H-pyran-2-ones, having an electron-rich diene system, capable of undergoing normal-electron-demand (NED) Diels-Alder reaction, were synthesized. The Diels-Alder reaction of these pyrones with electron-deficient dienophiles - diethyl acetylene dicarboxylate, 1,4-naphthoquinone, and N-phenylmaleimide - followed three different pathways and gave structurally diverse products, aminobenzenes, aminoanthraquinones, and aminopolycyclic diimides, respectively. The amino group at the 6-position activated substantially the pyrone ring towards NED Diels-Alder reaction and the reaction has a potential to generate great structural diversity.

Full text of DOI:10.1055/s-0034-1379397

SYNTHESIS
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
© Georg Thieme Verlag Stuttgart · New York
2015, 47, 343–350
paper
343
A. I. Khatri, S. D. Samant
Paper
Synthesis
Facile, Diversity-Oriented, Normal-Electron-Demand Diels–Alder
Reactions of 6-Amino-2H-pyran-2-ones with Diethyl Acetylene-
dicarboxylate, 1,4-Naphthoquinone, and N-Phenylmaleimide
OMe
Adil I. Khatri
R
R
R
R
Shriniwas D. Samant*
O
N
O
N
EtO
EtO
O
Department of Chemistry, Institute of Chemical Technology,
N. M. Parekh Road, Matunga, Mumbai 400019, India
+
9
1
2
(
2
2
)
2
6
9
2
1
0
2
O
N
samantsd@yahoo.com
O
O
sd.samant@ictmumbai.edu.in
N
OMe
OMe
O
N
R
O
R
6 examples
78–96%
5 examples
56–86%
4 examples
57–90%
Received: 11.08.2014
Accepted after revision: 13.10.2014
Published online: 13.11.2014
spective adducts without loss of CO2. Surprisingly, the 3,5-
halo derivatives of 2-pyrones show ambident diene behav-
ior, that is, they undergo the reaction by normal-electron-
demand (NED) as well as inverse-electron-demand (IED)
pathways.20,21 Intramolecular DA reaction on pyrones has a
potential to generate complex systems.22,23 The DA reaction
of 2-pyrones has been employed in the synthesis of many
natural products and related compounds,24–26 like qui-
nones,14,15 benzenoids,27,28 and complex bicyclo com-
pounds.29
The diene behavior of 2-pyrones can be modified by in-
troducing appropriate substituents on the ring. For the NED
Diels–Alder reaction, an electron-rich diene is required, and
hence an electron-donating group on the pyrone ring facili-
tates the reaction. Thus, the DA reactions of the pyrones
bearing OMe and Me groups at the C6 position are reported.
In spite of having electron-donating ability of OMe at C6 po-
sition, the DA reaction of 6-methoxypyrone requires long
reaction time.30,31
In an effort to build polycyclic compounds bearing an
amino group, which are difficult to synthesize otherwise,
we thought of introducing an amino group at the 6-position
of 2-pyrone through the DA reaction of the 2-pyrones and
using this substrate as a diene. Surprisingly, the dienes con-
taining an amino group at C6 position have not attracted at-
tention. The amino group is not only expected to activate
the diene, but also would provide amino group-substituted
unusual products, which may be biologically interesting.
While studying the NED Diels–Alder reaction of these 6-
amino-2-pyrones with some symmetrical dienophiles we
found that the reaction followed different pathways and
gave structurally diverse products, exhibiting a diversity
oriented synthesis (DOS). Thus, we are presenting our re-
sults on the facile, NED, diversity-oriented DA reaction of 6-
amino-2-pyrones with diethyl acetylenedicarboxylate, 1,4-
naphthoquinone (NQ), and N-phenylmaleimide (NPMA),
DOI: 10.1055/s-0034-1379397; Art ID: ss-2014-f0505-op
Abstract A series of 6-amino-4-methoxyphenyl-2H-pyran-2-ones,
having an electron-rich diene system, capable of undergoing normal-
electron-demand (NED) Diels–Alder reaction, were synthesized. The
Diels–Alder reaction of these pyrones with electron-deficient dieno-
philes – diethyl acetylene dicarboxylate, 1,4-naphthoquinone, and N-
phenylmaleimide – followed three different pathways and gave struc-
turally diverse products, aminobenzenes, aminoanthraquinones, and
aminopolycyclic diimides, respectively. The amino group at the 6-posi-
tion activated substantially the pyrone ring towards NED Diels–Alder re-
action and the reaction has a potential to generate great structural
diversity.
Key words 6-amino-2H-pyrone, normal-electron-demand Diels–Alder
reaction, diversity-oriented synthesis, aminobiphenyls, anthraqui-
nones, polycyclic diimides
2-Pyrones are six-membered heterocycles having weak
aromatic character and hence exhibiting diene character in
cycloadditions. Diels–Alder (DA) reaction of 2-pyrone is
known. In fact, the first report of the DA reaction of 2-py-
rones appeared in 1931.1 The peculiarity of this reaction is
that the reaction gives a bicyclic lactone product, which un-
dergoes decarboxylation via a facile retro-DA reaction, to
form a stable product. A variety of dienophiles have been
employed in the reaction over the years.2–9 The DA reac-
tions of modified pyrones, like fused 2-pyrones,10,11 and
highly substituted 2-pyrones are reported.12 The DA reac-
tions of 3-hydroxy-2-pyrone requires a base as a catalyst,13–15
longer reaction times or harsh conditions,16 while the DA
reactions of protected amino group at C3 position of pyrone
lead to amino-substituted polycyclic compound.7,12,17 Py-
rones containing thio group like 3-phenylsulfenyl-2-py-
rone18 and 3-phenylsulfonyl-2-pyrone19 react with
electron-poor and electron-rich dienophiles to afford re-
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 343–350

344
A. I. Khatri, S. D. Samant
Paper
Synthesis
providing aminobenzenes, aminoanthraquinones, and ami-
nopolycyclic diimides, respectively. Such compounds are
useful, but difficult to obtain otherwise. For example, poly-
substituted aromatic amines are useful in many fields like
pharmaceuticals, dyes, and natural products.32 Derivatives
of phthalates are biologically active.33–35 3-Amino-substi-
tuted phthalic acid derivatives show IMP-1 metallo-β-lact-
amase inhibitory activity.36 Aminoanthraquione is one of
the core structures for drugs, dyes, etc.37–42 1-Amino-9,10-
anthraquinones have anticancer properties.43,44 The polycy-
clic diimides are one of the important building blocks in or-
ganic synthesis.17 Moreover, bicyclo[2.2.2]octenes with
amino group at the bridgehead are not common,45 and their
derivatives possess antiprotozoal activity.46,47
Table 1 Synthesis of 6-Amino-2-pyrones 6a
Entry
Amine 5
2-Pyrone 6
Yield (%)b
1
2
3
4
5
6
piperidine (5a)
6a
6b
6c
6d
6e
6f
94
86
83
84
87
81
dimethylamine (5b)
morpholine (5c)
pyrollidine (5d)
dibutylamine (5e)
diethylamine (5f)
a Reaction conditions: 4 (2 mmol), amine 5 (2.4 mmol), Et3N (2 mmol),
CH2Cl2 (12 mL), 0 °C to r.t., 3.5 h.
b Isolated yield.
The 6-amino-2-pyrones 6 were synthesized as shown in
Scheme 1. Acid 3 was synthesized by reacting anisole (1)
with acetone dicarboxylic acid (2), prepared in situ from
citric acid and concentrated sulfuric acid.48 Acid 3 was
treated with phosphorus pentachloride to obtain the corre-
sponding 6-chloro derivative 4,21 which on reacting with di-
alkylamines 5 in the presence of triethylamine as a base
gave the required 6-amino-2-pyrones 6 (Table 1).
The 6-amino-2-pyrones 6 were then used in Diels–Alder
reactions with diethyl acetylenedicarboxylate in boiling tol-
uene, leading to highly substituted benzeneamine deriva-
tives 8a–f (Scheme 2,Table 2). The normal-electron-
demand Diels–Alder reaction first led to the formation of a
bicyclic lactone 7, which underwent decarboxylation to
form the aromatized product 8.
OMe
OMe
OMe
HO
OH
PCl5
concd H2SO4
0 °C to r.t.
O
+
O
O
O
0 °C to r.t.
OH
1
2
O
O
Cl
HO
O
3
4
OMe
OMe
H
Et3N, CH2Cl2
0 °C to r.t.
N
+
R
R
5a–f
R
O
O
Cl
O
O
N
R
4
6a–f
Scheme 1 Synthesis of 6-amino-2-pyrones 6
OMe
O
R
R
OEt
O
O
N
OMe
OEt
O
O
EtO
EtO
toluene
110–120 °C
+
O
– CO2
O
O
N
R
R
O
O
N
R
R
EtO
EtO
OMe
8a–f
6a–f
7
not isolated
Scheme 2 DA reaction of 6-amino-2-pyrones 6 with diethyl acetylenedicarboxylate
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 343–350

345
A. I. Khatri, S. D. Samant
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Synthesis
Table 2 Reaction of 6-Amino-2-pyrones 6 with Diethyl Acetylenedi-
Table 3 Reaction of 6-Amino-2-pyrones 6 with 1,4-Naphthoquinonea
carboxylatea
Entry
2-Pyrone 6
Product 11
Yield (%)b
Entry
2-Pyrone 6
Product 8
Yield (%)b
1
2
3
4
5
6a
6b
6c
6d
6e
11a
11b
11c
11d
11e
83
56
74
85
86
1
2
3
4
5
6
6a
6b
6c
6d
6e
6f
8a
8b
8c
8d
8e
8f
78
92
96
85
79
95
a Reaction conditions: pyrone 6 (0.5 mmol): 1,4-naphthoquinone (1
mmol), toluene (5 mL), reflux (110–120 °C), 3 h.
b Isolated yield.
a Reaction conditions: pyrone 6 (0.5 mmol), diethyl acetylenedicarboxylate
(1 mmol), toluene (5 mL), reflux (110–120 °C), 2 h.
b Isolated yield.
adduct 14 (Scheme 4). Thermal Diels–Alder reactions of 2-
pyrone gives exo,exo-fused ring products with a plane of
symmetry.17,49
The Diels–Alder reaction of 6 with 1,4-naphthoquinone
in boiling toluene gave 1-amino-3-aryl- 9,10-anthraqui-
nones 11a–e (Scheme 3). This reaction took place in a dif-
ferent manner. The initial reaction gave a bicyclic lactone 9,
which underwent decarboxylation to form a dihydroanth-
raquinone derivative, which could not be isolated. 1,4-
Naphthoquinone, being an oxidizing agent, probably oxi-
dized the intermediate 10 to form the red colored 1-amino-
3-(4-methoxyphenyl)-9,10-anthraquinones 11a–e (Table
3). 1,4-Naphthoquinone is a known oxidant for the adducts
in the Diels–Alder reaction.14
One of the most important synthetic routes for the syn-
thesis of bicyclo[2.2.2]octenes is the Diels–Alder reaction of
2-pyrones.17,49 The Diels–Alder reaction of 6 with N-phenyl-
maleimide gave polycyclic diimides 14a–d (Table 4). The
reaction took place via a tandem DA reaction–decarboxyl-
ation–DA reaction sequence. The intermediate 12 under-
went decarboxylation to form a very reactive diene 13,
which reacted further with N-phenylmaleimide to form the
Thus, the DA reaction of 6-amino-2-pyrones leads to
amino-substituted products. The reaction can be used in
the synthesis of more complex structures; however, the re-
action of electronically neutral dienophiles, like phenyl-
acetylene, failed to give the desired product.
In conclusion, we have found the synthetic utility of 6-
amino-2-pyrones in the synthesis of diverse compounds
with high complexity, which is otherwise difficult to syn-
thesize. This is the first report of DA reaction of 2-pyrones
with amino group at the C6 position. The amino group en-
hances the reactivity of the pyrone as a diene, much better
than a methoxy group does, and the reaction proceeds un-
der the mild thermal conditions, through the normal elec-
tron demand pathway. The amino group is incorporated in
the final product. Thus, the reaction represents a diversity-
oriented synthesis. The products obtained may be commer-
cially important and may find many applications in diverse
fields.
OMe
O
O
MeO
O
O
toluene
110–120 °C
+
N
R
R
O
O
N
R
O
O
R
6a–f
(2 equiv)
9
not isolated
R
R
R
R
O
N
O
O
N
oxidation
CO2
O
OMe
OMe
10
11a–e
not isolated
Scheme 3 DA Reaction of 6-amino-2-pyrones 6 with 1,4-naphthoquinone
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 343–350

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A. I. Khatri, S. D. Samant
Paper
Synthesis
OMe
OMe
O
O
R
toluene
N
O
+
N
110–120 °C
O
R
O
O
O
O
N
R
N
(2 equiv)
R
6a–e
12
not isolated
OMe
OMe
O
O
R
O
N
HN
NPMA
N
O
O
N
N
O
R
R
R
13
not isolated
14a–d
Scheme 4 DA Reaction of 6-amino-2-pyrones 6 with NMPA
Table 4 Reaction of 6-Amino-2-pyrones 6 with NMPAa
was separated and washed with brine (50 mL), dried (Na2SO4), and
the solvent evaporated under reduced pressure. The crude product
was purified on silica gel (60–120 mesh) column chromatography us-
ing EtOAc–PE with increasing quantity of EtOAc; yield: 6 g (60%); pale
yellow solid; mp 110–112 °C (Lit.50 mp 216–217 °C).
Entry
2-Pyrone 6
Product 14
Yield (%)b
1
2
3
4
6a
6b
6d
6e
14a
14b
14c
14d
87
90
87
57
IR (KBr): 1717, 1597, 1251, 1025, 817 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 3.88 (s, 3 H), 6.36 (d, J = 1.2 Hz, 1 H),
6.54 (d, J = 1.2 Hz, 1 H), 7.00 (d, J = 8.8 Hz, 2 H), 7.54 (d, J = 8.8 Hz, 2 H).
a Reaction conditions: pyrone 6 (0.5 mmol), NMPA (1 mmol), toluene (5
mL), reflux (110–120 °C), 2 h,
13C NMR (100 MHz, CDCl3): δ = 55.5, 104.0, 106.1, 114.8, 126.7, 128.3,
149.5, 155.5, 161.3, 162.3.
b Isolated yield.
6-Amino-2H-pyrones 6; General Procedure
Pyranone 4 (473 mg, 2 mmol) was added to a 100 mL round-bot-
tomed flask containing CH2Cl2 (12 mL), and equipped with a magnetic
stirring. The reaction mixture was cooled using an ice-water bath. To
the above solution, amine 5 (2.4 mmol) was added slowly followed by
the addition of Et3N (200 mg, 2 mmol). Ice-bath was removed after 30
min and the reaction mixture was further stirred for 3.5 h. The sol-
vent was evaporated under reduced pressure and the crude product
was purified by column chromatography on silica gel using EtOAc–PE
by gradually increasing the quantity of EtOAc to afford the pure prod-
uct.
Melting points were determined on a Analab apparatus (Model-
μThermocal 10) in open capillary tubes and are uncorrected. NMR
spectra were recorded on Varian Mercury plus 300 spectrometer at
300 MHz or Bruker Avance spectrometer at 400 MHz using TMS as an
internal standard. The coupling constants (J) are given in hertz. IR
spectra were recorded on a Perkin-Elmer Spectrum 100 spectropho-
tometer as KBr pellet/CHCl3. The starting compound 3 was prepared
according to the reported procedure.48 All other reagents and solvents
are of commercial grade and used as such. Petroleum ether (PE) refers
to the fraction boiling in the 60–80 °C range.
4-(4-Methoxyphenyl)-6-(piperidin-1-yl)-2H-pyran-2-one (6a)
Yield: 536 mg (94%); yellow solid; mp 156–158 °C.
6-Chloro-4-(4-methoxyphenyl)-2H-pyran-2-one (4)50
IR (KBr): 2939, 1738, 1569, 1366, 1228, 1022 cm–1
.
To an ice cold, magnetically stirred, solution of PCl5 (17 g, 82 mmol) in
CH2Cl2 (60 mL) was added 3 (10 g, 42 mmol) portionwise. Vigorous
reaction occurred during the addition. After stirring for 15 min, the
ice bath was removed and the reaction mixture was stirred further for
3.5 h. The mixture was quenched with crushed ice, the organic layer
1H NMR (400 MHz, CDCl3): δ = 1.67 (6 H), 3.5 (4 H), 3.85 (s, 3 H), 5.64
(s, 1 H), 5.42 (s, 1 H), 6.95 (d, J = 8.4 Hz, 2 H), 7.52 (d, J = 8.8 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 24.1, 25.2, 45.9, 55.4, 80.8, 92.6, 114.2,
128.1, 130.3, 159.4, 161.2, 161.3, 162.5.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 343–350

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A. I. Khatri, S. D. Samant
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Synthesis
MS (ESI): m/z = 286 [M + H]+.
ESI-MS: m/z calcd for C17H20NO3 + H [M+ + H]: 286.1443; found:
1H NMR (300 MHz, CDCl3): δ = 1.26 (t, J = 7.2 Hz, 6 H), 3.47 (q, J = 7.2
Hz, 4 H), 3.86 (s, 3 H), 5.30 (s, 1 H), 5.61 (s, 1 H), 6.96 (d, J = 8.7 Hz, 2
H), 7.53 (d, J = 8.7 Hz, 2 H).
286.1430.
13C NMR (100 MHz, CDCl3): δ = 13.1, 42.9, 55.4, 91.3, 114.2, 128.1,
130.5, 159.5, 161, 161.2, 162.6.
MS (EI): m/z = 273 [M]+.
4-(4-Methoxyphenyl)-6-dimethylamino-2H-pyran-2-one (6b)
Yield: 422 mg (86%); yellow solid; mp 174–176 °C.
ESI-MS: m/z calcd for C16H20NO3 + H [M+ + H]: 274.1443; found:
FTIR (KBr): 2928, 1709, 1607, 1242, 1023, 797 cm–1
.
274.1444.
1H NMR (300 MHz, CDCl3): δ = 3.16 (s, 6 H), 3.86 (s, 3 H), 5.31 (d, J =
1.2 Hz, 1 H), 5.65 (d, J = 1.2 Hz, 1 H), 6.96 (d, J = 8.7 Hz, 2 H), 7.54 (d, J =
8.7 Hz, 2 H).
Cycloaddition of 6-Amino-2-pyrones 6 with Diethyl Acetylenedi-
carboxylate; General Procedure
13C NMR (100 MHz, CDCl3): δ = 30.9, 37.5, 55.4, 80.1, 92, 114.2, 128.1,
To a solution of 6-amino-2-pyrone 6 (0.5 mmol) in toluene (5 mL) was
added diethyl acetylenedicarboxylate (170 mg, 1 mmol) and the reac-
tion mixture was refluxed under N2 atmosphere for 2 h. Toluene was
evaporated under reduced pressure and the crude product was puri-
fied by silica gel column chromatography (60–120 mesh) using
EtOAc–PE by gradually increasing the quantity of EtOAc to afford the
pure product.
130.2, 159.3, 161.2, 162.0, 162.4.
MS (EI): m/z = 245 [M]+.
ESI-MS: m/z calcd for C14H16NO3 + H [M+ + H]: 246.1130; found:
246.1128.
4-(4-Methoxyphenyl)-6-(morpholin-4-yl)-2H-pyran-2-one (6c)51
Yield: 477 mg (83%); yellow solid; mp 138–140 °C (Lit.51 mp 148–
149 °C).
Diethyl 3-(Piperidin-1-yl)-5-(4-methoxyphenyl)benzene-1,2-di-
carboxylate (8a)
FTIR (KBr): 2912, 1727, 1607, 1229, 1111, 798, 770 cm–1
.
Yield: 156 mg (78%); white crystals; mp 83–85 °C.
1H NMR (300 MHz, CDCl3): δ = 3.48 (t, J = 4.8 Hz, 4 H), 3.80 (t, J = 4.8
Hz, 3 H), 3.85 (s, 3 H), 5.42 (d, J = 1.5 Hz, 1 H), 5.76 (d, J = 1.5 Hz, 1 H),
6.96 (d, J = 8.7 Hz, 2 H), 7.52 (d, J = 8.7 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 44.8, 55.4, 66, 81.1, 94.7, 114.3, 128.1,
129.8, 159, 161.4, 161.4, 162.0.
FTIR (KBr): 2926, 1726, 1604, 1514 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 1.37 (t, J = 7.2 Hz, 3 H), 1.42 (t, J = 7.2
Hz, 3 H), 1.53–1.56 (m, 2 H), 1.64–1.69 (m, 4 H), 2.96 (m, 4 H), 3.86 (s,
3 H), 4.35 (q, J = 7.2 Hz, 2 H), 4.42 (q, J = 7.2 Hz, 2 H), 6.99 (d, J = 8.8 Hz,
2 H), 7.51–7.53 (m, 3 H), 7.90 (d, J = 1.2 Hz, 1 H)
13C NMR (100 MHz, CDCl3): δ = 14.2, 14.3, 24.2, 26.6, 24.2, 26.6, 54.2,
55.4, 61.3, 61.4, 114.3, 123.8, 124.1, 128.3, 129.1, 132.3, 142.5, 153.0,
159.7, 165.7, 168.8.
MS (EI): m/z = 287 [M]+.
4-(4-Methoxyphenyl)-6-(pyrolidin-1-yl)-2H-pyran-2-one (6d)
Yield: 456 mg (84%); yellow solid, mp 162–164 °C.
MS (EI): m/z = 413 [M]+.
ESI-MS: m/z calcd for C24H30NO5 + H [M+ + H]: 412.2124; found:
IR (KBr): 2923, 1706, 1588, 1245, 1028, 792 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 2.00–2.09 (m, 4 H), 3.48–3.52 (m, 4 H),
3.85 (s, 3 H), 5.22 (s, 1 H), 5.61 (s, 1 H), 6.68 (d, J = 8.7 Hz, 2 H), 7.54 (d,
J = 8.7 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 25.20, 46.71, 55.40, 91.27, 114.18,
128.08, 130.22, 159.15, 160.27, 161.18, 162.71.
MS (EI): m/z = 271 [M]+.
ESI-MS: m/z calcd for C16H18NO3 + H [M+ + H]: 272.1287; found:
412.2125.
Diethyl 3-Dimethylamino-5-(4-methoxyphenyl)benzene-1,2-di-
carboxylate (8b)
Yield: 170 mg (92%); white crystals; mp 92–94 °C.
FTIR (KBr): 2981, 1726, 1600, 1519 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 1.35–1.40 (m, 6 H), 2.81 (s, 6 H), 3.86
(s, 3 H), 4.35 (q, J = 7.2 Hz, 2 H), 4.41 (q, J = 7.2 Hz, 2 H), 6.99 (d, J = 8.8
Hz, 2 H), 7.53 (d, J = 8.8 Hz, 2 H), 7.54 (d, J = 1.6 Hz, 1 H), 7.79 (d, J = 1.6
Hz, 1 H).
272.1281.
4-(4-Methoxyphenyl)-6-dibutylamino-2H-pyran-2-one (6e)
Yield: 573 mg (87%); yellow solid; mp 82–84 °C.
FTIR (KBr): 2958, 2923, 1720, 1526, 1248, 1023, 797 cm–1
1H NMR (300 MHz, CDCl3): δ = 0.94–0.99 (m, 6 H), 1.25–1.39 (m, 4 H),
1.40–1.68 (m, 4 H), 3.37 (t, J = 7.5 Hz, 4 H), 3.85 (s, 3 H), 5.29 (s, 2 H),
5.6 (s, 1 H), 6.96 (d, J = 9 Hz, 2 H), 7.51 (d, J = 9 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 14.1, 14.2, 45.1, 55.4, 61.4, 61.5, 114.3,
122.2, 122.4, 128.3, 128.9, 130.0, 132.4, 142.5, 152.5, 159.7, 166.1,
169.0.
MS (EI): m/z = 371 [M]+.
ESI-MS: m/z calcd for C21H25NO5 + Na [M+ + Na]: 394.1630; found:
.
13C NMR (100 MHz, CDCl3): δ = 13.9, 20.2, 29.8, 48.6, 55.4, 80, 91.2,
394.1616.
114.2, 128.1, 130.5, 159.3, 161.1, 161.3, 162.6.
MS (EI): m/z = 329 [M]+.
ESI-MS: m/z calcd for C20H28NO3 + H [M+ + H]: 330.2069; found:
Diethyl 3-(Morpholin-4-yl)-5-(4-methoxyphenyl)benzene-1,2-di-
carboxylate (8c)
Yield: 198 mg (96%); white crystals; mp 116–118 °C.
330.2063.
FTIR (KBr): 2956, 1724, 1600, 1521 cm–1
.
4-(4-Methoxyphenyl)-6-diethylamino-2H-pyran-2-one (6f)
1H NMR (400 MHz, CDCl3): δ = 1.36–1.43 (m, 6 H), 3.05 (m, 4 H), 3.80
(m, 4 H), 3.87 (s, 3 H), 4.40 (m, 4 H), 7.01 (d, J = 8.8 Hz, 2 H), 7.53 (d, J =
8.8 Hz, 2 H), 7.54 (d, J = 1.6 Hz, 1 H), 7.97 (d, J = 1.6 Hz, 1 H).
Yield: 443 mg (81%); yellow solid; mp 128–130 °C.
FTIR (KBr): 2978, 1708, 1605, 1176, 794 cm–1
.
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13C NMR (100 MHz, CDCl3): δ = 14.2, 14.3, 53.5, 55.4, 61.4, 61.6, 67.4,
114.4, 124.0, 124.6, 128.3, 129.2, 131.9, 132.1, 142.8, 151.3, 159.9,
165.4, 168.7.
under reduced pressure and the crude product was purified by silica
gel column chromatography (60–120 mesh) using EtOAc–PE by grad-
ually increasing the quantity of EtOAc to afford the pure product.
MS (EI): m/z = 413 [M]+.
ESI-MS: m/z calcd for C23H28NO6 + H [M+ + H]: 414.1917; found:
1-(Piperidin-1-y1)-3-(4-methoxyphenyl)-9,10-anthraquinone
(11a)
414.1891.
Yield: 165 mg, 83%; dark red crystals; mp 186–188 °C.
FTIR (KBr): 2923, 1668, 1664, 1579, 1243, 1028, 827 cm–1
.
Diethyl 3-(Pyrolidin-1-yl)-5-(4-methoxyphenyl)benzene-1,2-di-
carboxylate (8d)
1H NMR (300 MHz, CDCl3): δ = 1.67–1.73 (m, 2 H), 1.84–194 (m, 4 H),
3.21–3.24 (t, J = 6.8 Hz, 4 H), 3.88 (s, 3 H), 7.22 (d, J = 12 Hz, 2 H), 7.55
(d, J = 2.4 Hz, 1 H), 7.66–7.79 (m, 4 H), 8.12 (d, J = 2.4 Hz, 1 H), 8.24 (d,
J = 8.4 Hz, 1 H), 8.30 (d, J = 8.4 Hz, 1 H).
13C NMR (100 MHz, CDCl3): δ = 24.2, 26.1, 54.2, 55.4, 114.5, 118.4,
120.7, 122.3, 126.4, 127.3, 128.5, 131.9, 132.5, 132.7, 134.1, 134.3,
135.7, 136.9, 146.1, 154.9, 160.3, 181.2, 184.6.
Yield: 170 mg (85%); white crystals; mp 108–112 °C.
FTIR (KBr): 2974, 1722, 1602, 1516 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 1.35–1.38 (m, 6 H), 1.93–1.97 (m, 4 H),
3.35 (t, J = 6.4 Hz, 4 H), 3.85 (s, 3 H), 4.31–4.38 (m, 4 H), 6.97 (d, J = 8.8
Hz, 2 H), 7.02 (d, J = 1.2 Hz, 1 H), 7.36 (d, J = 1.2 Hz, 1 H), 7.51 (d, J = 8.8
Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 14.0, 14.3, 25.8, 50.0, 55.4, 61.4, 61.6,
114.2, 116.2, 116.4, 117.9, 128.4, 131.8, 133.1, 142.3, 146.6, 159.6,
167.5, 170.1.
MS (ESI): m/z = 398.2 [M + H]+.
ESI-MS: m/z calcd for C26H23NO3 + H [M+ + H]: 398.1756; found:
398.1755.
MS (EI): m/z = 397 [M]+.
ESI-MS: m/z calcd for C23H28NO5 + H [M+ + H]: 398.1967; found:
1-Dimethylamino-3-(4-methoxyphenyl)-9,10-anthraquinone
(11b)
398.1968.
Yield: 100 mg (56%); red crystals; mp 176–178 °C.
FTIR (KBr): 2925, 1666, 1641, 1590, 1248, 1033, 812, 707 cm–1
.
Diethyl 3-(Dibutylamino)-5-(4-methoxyphenyl)benzene-1,2-di-
carboxylate (8e)
1H NMR (400 MHz, CDCl3): δ = 3.06 (s, 6 H), 3.88 (s, 3 H), 7.03 (d, J =
8.8 Hz, 2 H), 7.46 (d, J = 1.6 Hz, 1 H), 7.66–7.91 (m, 4 H), 8.03 (d, J = 1.6
Hz, 1 H), 8.24–8.27 (m, 2 H).
13C NMR (100 MHz, CDCl3): δ = 44.3, 55.4, 114.4, 116.9, 118.3, 119.6,
126.5, 127, 128.5, 132.1, 132.6, 134.1, 136, 136.7, 145.7, 153.8, 160.3,
181.1, 184.5.
Yield: 178 mg (79%); gum.
FTIR (KBr): 2980, 1726, 1600, 1514, 1178 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 0.86 (t, J = 6.8 Hz, 6 H), 1.23–1.46 (m,
14 H), 2.98 (m, 4 H), 3.86 (s, 3 H), 4.33–4.42 (m, 4 H), 7.00 (d, J = 8.8
Hz, 2 H), 7.52 (d, J = 8.8 Hz, 2 H), 7.54 (d, J = 1.6 Hz, 1 H), 7.93 (d, J = 1.6
Hz, 1 H).
ESI-MS: m/z calcd for C23H19NO3 + H [M+ + H]: 358.1443; found:
358.1432.
13C NMR (100 MHz, CDCl3): δ = 14.0, 14.1, 14.2, 20.4, 29.6, 54.8, 55.4,
61.2, 61.4, 114.4, 124.1, 126.1, 128.3, 129.2, 132.30, 133.1, 142.0,
151.0, 159.7, 165.7, 168.9.
MS (EI): m/z = 455 [M]+.
ESI-MS: m/z calcd for C27H37NO5 + H [M+ + H]: 456.2750; found:
3-(4-Methoxyphenyl)-1-(morpholin-4-yl)-9,10-anthraqunone
(11c)
Yield: 148 mg (74%); red solid; mp 138–140 °C.
FTIR (KBr): 2922, 2860, 1663, 1583, 1250, 1025, 944, 715 cm–1
.
456.2749.
1H NMR (300 MHz, CDCl3): δ = 3.27–3.33 (m, 4 H), 3.89 (s, 3 H), 4.06–
4.09 (m, 4 H), 7.03–7.07 (m, 2 H), 7.66–7.7 (m, 2 H), 7.56 (s, 1 H), 7.7–
7.82 (m, 2 H), 8.22–8.31 (m, 3 H).
Diethyl 3-Diethylamino-5-(4-methoxyphenyl)benzene-1,2-dicar-
boxylate (8f)
Yield: 190 mg (95%); gum.
FTIR (KBr): 2980, 1726, 1602, 1715 cm–1
1H NMR (400 MHz, CDCl3): δ = 1.04 (m, 6 H), 1.4 (m, 6 H), 3.06 (m, 4
H), 3.89 (s, 3 H), 4.35–4.46 (m, 4 H), 7.02 (dd, J = 8.8, 2 Hz, 2 H), 7.99
(d, J = 2 Hz, 1 H), 7.57 (d, J = 2 Hz, 1 H), 7.55 (dd, J = 8.8, 2 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 53.1, 55.5, 67.1, 114.5, 119.5, 121.2,
121.8, 126.5, 127.4, 128.5, 131.5, 132.4, 133, 134.2, 135.5, 137.0,
146.6, 154.0, 160.5, 181.4, 184.3.
ESI-MS: m/z calcd for C25H21NO4 + H [M+ + H]: 400.1549; found:
400.1541.
.
13C NMR (100 MHz, CDCl3): δ = 12.8, 14.2, 14.2, 48.8, 55.4, 61.1, 61.5,
114.4, 124.5, 126.6, 128.3, 129.0, 132.2, 134.0, 142.1, 150.3, 159.8,
165.6, 168.8.
MS (EI): m/z = 399 [M]+.
ESI-MS: m/z calcd for C23H30NO5 + H [M+ + H]: 400.2124; found:
3-(4-Methoxyphenyl)-1-(pyrolidin-1-yl)-9,10-anthraquinone
(11d)
Yield: 162 mg (85%); bright red solid; mp 196–198 °C.
FTIR (KBr): 2933, 1667, 1664, 1580, 1243, 1029, 827 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 2.06 (br, 4 H), 3.38 (br, 4 H), 3.87 (s, 3
H), 7.02 (dd, J = 9, 2.4 Hz, 2 H), 7.38 (s, 1 H), 7.99 (s, 1 H), 7.64–7.78
(m, 4 H), 8.12–8.25 (m, 2 H).
13C NMR (100 MHz, CDCl3): δ = 26.0, 31.0, 52.7, 55.4, 114.4, 115.5,
117.1, 117.5, 126.5, 126.6, 128.5, 132.3, 132.3, 132.7, 134, 136, 136.6,
145.2, 150.1, 160.1, 181.2, 184.5.
400.2131.
Cycloaddition of 6-Amino-2-pyrones 6 with 1,4-Naphthoquinone;
General Procedure
To a solution of 6-amino-2-pyrone 6 (0.5 mmol) in toluene (5 mL) was
added 1,4-naphthoquinone (158 mg, 1 mmol). The reaction mixture
was refluxed under N2 atmosphere for 3 h. Toluene was evaporated
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ESI-MS: m/z calcd for C25H21NO3 + H [M+ + H]: 384.1600; found:
384.1592.
13-(4-Methoxyphenyl)-7-(pyrolidin-1-yl)-4,10-diphenyl-4,10-di-
azatetracyclo[5.5.2.02,6.08,12]tetradeca-13-ene-3,5,9,11-tetrone
(14c)
1-(Dibutylamino)-3-(4-methoxyphenyl)-9,10-anthraquinone
(11e)
Yield: 250 mg (87%); white solid; mp 234–236 °C (turned yellow).
FTIR (KBr): 2962, 1770, 1714, 1600, 1188 cm–1
.
Yield: 190 mg (86%); dark pink crystals; mp 85–87 °C.
FTIR (KBr): 2952, 1631, 1660, 1588, 1245, 1029, 837, 715 cm–1
1H NMR (400 MHz, CDCl3): δ = 0.87 (t, J = 7.2 Hz, 6 H), 1.29 (m, 4 H),
1.84 (q, J = 7.2 Hz, 4 H), 3.62 (t, J = 7.2 Hz, 4 H), 3.89 (s, 3 H), 7.03 (d, J =
8.8 Hz, 2 H), 7.66 (d, J = 8.8 Hz, 2 H), 7.52 (d, J = 1.2 Hz, 1 H), 7.68–7.78
(m, 2 H), 8.03 (d, J = 1.2 Hz, 1 H), 8.26 (t, J = 8.8 Hz, 2 H).
1H NMR (300 MHz, CDCl3): δ = 1.98 (br, 4 H), 3.30 (br, 4 H), 3.36 (dd,
J = 8.4, 0.8 Hz, 2 H), 3.53 (d, J = 8.4 Hz, 2 H), 3.82 (s, 3 H), 4.08 (s, 1 H),
6.65 (s, 1 H), 6.89 (d, J = 8.4 Hz, 2 H), 7.03 (d, J = 7.2 Hz, 4 H), 7.30–7.39
(m, 6 H), 7.43 (d, J = 8.4 Hz, 2 H).
ESI-MS: m/z calcd for C35H31N3O5 + H [M+ + H]: 574.2336; found:
574.2326.
.
13C NMR (100 MHz, CDCl3): δ = 14.0, 20.3, 29.8, 52.8, 54.4, 114.5,
117.4, 120.2, 123.1, 126.4, 127.1, 128.4, 132.0, 132.5, 132.6, 134.0,
136, 136.9, 145.3, 153.1, 160.2, 180.6, 184.6.
13-(4-Methoxyphenyl)-7-(dibutylamino)-4,10-diphenyl-4,10-di-
azatetracyclo[5.5.2.02,6.08,12]tetradeca-13-ene-3,5,9,11-tetrone
(14d)
ESI-MS: m/z calcd for C29H31NO3 + H [M+ + H]: 442.2382; found:
Yield: 179 mg (57%); white solid; mp 238–240 °C (turned yellow).
442.2376.
FTIR (KBr): 2591, 1772, 1723, 1603, 1504, 1182 cm–1
.
Cycloaddition of 6-Amino-2-pyrones 6 with NMPA; General Proce-
dure
1H NMR (400 MHz, CDCl3): δ = 0.98 (t, J = 7.2 Hz, 6 H), 0.88 (t, J = 7.2
Hz, 6 H), 1.22 (m, 2 H), 1.43 (m, 4 H), 1.79 (m, 2 H), 2.86 (t, J = 8 Hz, 2
H), 3.12 (t, J = 8 Hz, 2 H), 3.35 (d, J = 8.8 Hz, 2 H), 3.36 (d, J = 8.8 Hz, 2
H), 3.48 (d, J = 8.8 Hz, 2 H), 3.81 (s, 3 H), 4.38 (s, 1 H), 6.49 (s, 1 H), 6.89
(d, J = 8.8 Hz, 2 H), 7.03 (d, J = 7.6 Hz, 4 H), 7.28–7.39 (m, 8 H).
13C NMR (100 MHz, CDCl3): δ = 14.1, 14.3, 20.1, 20.9, 32.19, 36.7, 36.9,
44.6, 45.5, 50.9, 52.7, 55.3, 68.8, 114.5, 122.8, 126.2, 127.1, 128.2,
128.6, 129.1, 131.6, 140.2, 160.1, 173.5, 175.3.
To a solution of 6-amino-2-pyrone 6 (0.5 mmol) in toluene (5 mL) was
added NPMA (173 mg, 1 mmol). The reaction mixture was refluxed
under N2 for 2 h. Toluene was evaporated under reduced pressure and
the crude product was washed with cold Et2O (2 × 4 mL) to afford the
sufficiently pure product.
7-(Piperidin-1-y1)-13-(4-methoxyphenyl)-4,10-diphenyl-4,10-di-
azatetracyclo[5.5.2.02,6.08,12]tetradeca-13-ene-3,5,9,11-tetrone
(14a)
ESI-MS: m/z calcd for C39H41N3O5 + H [M+ + H]: 632.3124; found:
632.3100.
Yield: 255 mg (87%); white solid; mp 264–266 °C (turned yellow).
FTIR (KBr): 2926, 1772, 1714, 1602, 1502, 1182 cm–1
.
Acknowledgment
1H NMR (300 MHz, CDCl3): δ = 1.50 (br, 4 H), 1.82 (br, 2 H), 3.24 (br, 4
H), 3.35 (dd, J = 8.4, 2.7 Hz, 2 H), 3.55 (d, J = 8.4 Hz, 2 H), 3.82 (s, 3 H),
4.38 (dt, J = 3, 1.5 Hz, 2H), 6.69 (s, 1 H), 6.88 (d, J = 8.7 Hz, 2 H), 7.02 (d,
J = 6.6 Hz, 4 H), 7.27–7.45 (m, 8 H).
13C NMR (100 MHz, CDCl3): δ = 25.3, 26.2, 27.6, 36.4, 44.7, 45.5, 47,
47.6, 55.3, 67.8, 114.4, 121.6, 126.3, 127, 128.6, 129.1, 131.6, 140.4,
160.1, 173.9, 175.3.
A.I.K. is grateful to CSIR, Delhi (India) for a fellowship. The authors are
thankful to the Institute for Intensive Research in Basic Sciences
(IIRBS), M. G. University, Kottayam, Kerala (India), and Guru
Jambheshwar University of Science and Technology (GJUST), Hissar,
Harayana (India) for providing the NMR facility.
MS (ESI): m/z = 588.2 [M]+.
ESI-MS: m/z calcd for C36H33N3O5 + H [M+ + H]: 588.2498; found:
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 343–350