Microwave assisted synthesis of dihydropyrrole by AgOAc catalyzed intramolecular cyclization reaction of homopropargyl amine

Article abstract of DOI:10.1007/s11164-016-2442-x

A series of 5-aryl dihydropyrrole was synthesized from the intramolecular cyclization reaction of homopropargyl amine in the presence of AgOAc as catalyst under microwave irradiation reaction conditions. The homopropargyl amine was prepared by the reaction of propargyl bromide with N-tosyl aldimine under a sonochemical Barbier-type reaction condition. Further aromatization reaction of 5-aryl dihydropyrrole in KOtBu/DMSO can afford 2-aryl pyrrole under microwave irradiation reaction conditions.

Full text of DOI:10.1007/s11164-016-2442-x

Res Chem Intermed
DOI 10.1007/s11164-016-2442-x
Microwave assisted synthesis of dihydropyrrole
by AgOAc catalyzed intramolecular cyclization
reaction of homopropargyl amine
1
1
•
Adam Shih-Yuan Lee
1
Yu-Ting Chang
•
Szu-Huio Ma Lee
Received: 20 November 2014 / Accepted: 5 March 2015
Ó Springer Science+Business Media Dordrecht 2016
Abstract
A series of 5-aryl dihydropyrrole was synthesized from the
intramolecular cyclization reaction of homopropargyl amine in the presence of
AgOAc as catalyst under microwave irradiation reaction conditions. The homo-
propargyl amine was prepared by the reaction of propargyl bromide with N-tosyl
aldimine under a sonochemical Barbier-type reaction condition. Further aromati-
zation reaction of 5-aryl dihydropyrrole in KOtBu/DMSO can afford 2-aryl pyrrole
under microwave irradiation reaction conditions.
Keywords Homopropargyl amine Á Dihydropyrrole Á 2-Aryl pyrrole Á
Sonochemical Barbier-type reaction Á Microwave irradiation
Introduction
Pyrroles bearing aryl substituents at the 2-position are often found in a large number
of biologically important natural products [1–5], which exhibit interesting
biological properties such as the antibacterial [6–9], antifungal [10–12], antitumor
[
13–15], and used as functional material [16, 17]. Over the years much effort has
been directed towards the development of new strategies for 2-arylpyrrole and
oligopyrrole synthesis [18–25]. Continuing interest in the development of the
synthetic methodology of dihydropyrrole synthesis provides the impetus to initiate a
project designed to develop a new and more expedient route to the formation of
pyrrole rings. Dihydropyrroles may be employed as important synthetic interme-
diates for synthesis of pyrroles. Our group reported a sonochemical Barbier-type
reaction of propargyl bromide with aldehyde to generate homopropargyl alcohol at
room temperature [26] and an intramolecular cyclization of homoallyl alcohol to
&
Adam Shih-Yuan Lee
adamlee@mail.tku.edu.tw
1
Department of Chemistry, Tamkang University, New Taipei 25137, Taiwan
123

A. S.-Y. Lee et al.
Scheme 1 Synthetic route to homopropargyl amine and dihydropyrrole
afford tetrahydrofuran in the presence of L-proline as a promoter [27]. Our attention
was attracted to the formation of homopropargyl amine, which may be achieved by
reaction of propargyl bromide with aldimine under our sonochemical Barbier-type
reaction conditions, and then this undergoes intramolecular cyclization (5-endo-dig)
[
28] to yield the desired dihydropyrrole (Scheme 1).
Results and discussion
N-Tosylphenyl aldimine was initially chosen as the substrate to be investigated.
Treatment of N-tosylphenyl aldimine with propargyl bromide under previously
developed sonochemical Barbier-type reaction conditions should generate the
expected N-tosyl homopropargyl amine product. To a reaction mixture of N-
tosylphenyl aldimine (1.0 eq.) were added zinc powder (5.0 eq.) and 1,2-
1
diiodoethane (1.0 eq.) Propargyl bromide (1.5 eq.) in anhydrous THF (5 mL)
2
was sonicated for 2.5 h and the expected N-tosylphenyl homopropargyl amine
(
78 %) was obtained (Scheme 2). It is worth noting that protection of the alkynyl
proton of propargyl bromide was not necessary under this sonochemical Barbier-
type reaction conditions [29–36].
To understand the scope of this sonochemical Barbier-type reaction for synthesis
of N-tosyl homopropargyl amine, a series of N-tosyl aldimines was prepared and
investigated, and the results are shown in Table 1.
As shown in Table 1, reactions using aliphatic aldimines (entry 1), electron-poor
entry 3–4) or electron-rich (entries 5, 6) aromatic aldimines, or heteroaromatic
(
aldimines (entries 8, 9) gave the desired N-tosyl homopropargyl amines in
reasonable to good yields. N-tosyl aldimines with highly electron-withdrawing
nitro-substituent (entry 4) did not undergo the additional reactions under this
sonochemical Barbier-type reaction.
N-Tosylhomopropargyl amines were successfully prepared by the sonochemical
Barbier-type reaction conditions. Therefore, the intramolecular cyclization reaction
of homopropargyl amine for generating the desired dihydropyrrole was further
investigated [37]. N-Tosylphenyl homopropargyl amine (Table 1, entry 2) was
chosen as the investigated substrate for the intramolecular cyclization reaction (5-
endo-dig).
1
The addition of 1,2-diiodomoethane was used for the activation of metal, and it reacted with Zn powder
2
in situ to generate Lewis acid ZnI and ethene.
2
The ultrasonic cleaning bath (Elma-T490DH, 50 kHz) should be filled with water containing some
–5 % detergent. In our laboratory, we used Decon 90, which permits much more even cavitation in bath
water.
3
1
23

Microwave assisted synthesis of dihydropyrrole by AgOAc…
Scheme 2 Synthesis of homopropargyl amine by sonochemical Barbier-type reaction
Table 1 Synthesis of homopropargyl amines
a
The yields were determined after chromatographic purification
b
No reaction and recovery of starting material
After introducing 0.1 eqivalent of AgOAc to N-tosylphenyl homopropargyl
amine in acetone, the reaction mixture was stirred at 56 °C for 3 days to produce a
35 % yield of dihydropyrrole. In order to shorten the reaction time, the
intramolecular cyclization reaction was tested by using a different energy source
123

A. S.-Y. Lee et al.
such as microwaves [38–40]. The reaction mixture of AgOAc and N-tosylphenyl
homopropargyl amine in acetone was irradiated by microwaves at 50 °C ,and the
improvment of the dihydropyrrole yield to 54 % was observed after 15 min-
irradiation (Scheme 3). It is worth noting that using acetonitrile as solvent instead of
acetone dramatically improved the yield from 54 to 76 % under the microwave
reaction conditions. Introducing 0.05 equivalent of AgOAc catalyst to homopropar-
gyl amine afforded the same formation yield of dihydropyrrole as provided by using
0
.1 equivalent of AgOAc. Other Ag(I)-catalysts were also investigated, and it is
interesting to note that generation of dihydropyrrole was not obtained when AgOTf
and AgF were used as catalysts, respectively.
To understand the scope of this AgOAc catalyzed intramolecular cyclization of
homopropargyl amine, a series of homopropargyl amines was investigated under
microwave irradiation conditions and the results are shown in Table 2. As shown in
Table 2, all homopropargyl amines were transformed to their corresponding
5
-substituted dihydropyrroles with moderate to high yields. Both alkyl- and aryl
homopropargyl amines can undergo this Ag(I)-catalyzed intramolecular cyclization
reaction and gave the desired products.
The synthesis of 5-aryl dihydropyrroles was exploited and further aromatized to
their corresponding pyrroles, which are valuable precursors in the synthesis of
biologically active compounds and materials. Therefore, the ability to access the
aromatization reaction to generate aryl pyrrole was investigated. Conventional
aromatizating agents such as P-Chloranil (tetrachloro-1,4-benzoquinone) and DDQ
(
2,3-dichloro-5,6-dicyano-1,4-benzoquinone) failed to generate the expected 2-aryl
pyrrole. Many products were obtained, and the structures of these formed
compounds were not identified. Thus, other reaction conditions were examined to
investigate their affects on the oxidation of 5-aryl dihydropyrrole to 2-aryl pyrrrole.
We Introduced 5.0 equivalents of potasium tert-butyloxide to 5-phenyl dihydropy-
rrole in DMSO, and the reaction mixture was stirred at room temperature for 4 h.
Only the recovered starting material was observed. The reaction mixture of t-BuOK
and 5-phenyl dihydropyrrole in DMSO was irradiated by microwaves at 50 °C for
5
min, and the expected product 2-phenyl pyrrole was obtained with 47 % yield
(
Scheme 4). It should be noted that the N-tosyl group of pyrrole was not resistant
under this basic reaction condition and was hydrolyzed to its corresponding 1H-
pyrrole.
Thus, a series of 5-aryl dihydropyrroles was investigated under the microwave
irradiation conditions, and the results are shown in Table 3. As shown in Table 3, all
5-aryl dihydropyrroles were transformed to their corresponding 2-aryl pyrroles with
reasonable yields.
In conclusion, a new method for preparation of homopropargyl amine was
developed by the reaction of propargyl bromide with aldimine under sonochemical
Barbier-type reaction conditions. 5-Aryl dihydropyrrole was synthesized from the
AgOAc catalyzed intramolecular cyclization reaction of homopropargyl amine
under microwave irradiation reaction conditions. Further aromatization reaction of
5-aryl dihydropyrrole in KOtBu/DMSO affords 2-aryl pyrrole under microwave
irradiation reaction conditions.
1
23

Microwave assisted synthesis of dihydropyrrole by AgOAc…
Scheme 3 Optimization of cyclization reaction of homopropargyl amine
Experimental section
All reagents were purchased from Aldrich, Merck and Riedel–deHaen, and all were
used directly without further purification. The microwave irradiation reaction was
1
carried out in a CEM Discover microwave reactor. The H-NMR (proton nuclear
magnetic resonance) spectra were recorded at 300 MHz (Bruker-AC300P) with
deuteriochloroform (CDCl , Aldrich 99.8 atom% D) as the solvent and the internal
3
1
standard. The C-NMR (carbon nuclear magnetic resonance) spectra were recorded
3
at 75.5 MHz (Bruker-AC300P) with CDCl as the solvent and the internal standard.
3
Column chromatography was performed using silica gel (Merck 230–400 mesh) and
ethyl acetate/hexane mixture as the eluent.
A representative procedure for synthesis of homopropargyl amines
A solution of N-tosylphenyl aldimine (1.0 mmol) and propargyl bromide
(
1.5 mmol) in anhydrous THF (5 mL) was added dropwise to a reaction mixture
of zinc (5.0 mmol) and 1,2-diiodoethane (see footnote 1) (1.0 mmol) in anhydrous
THF (25 mL) under sonication in a commercial ultrasonic cleaning bath (see
footnote 2) (Elma-T490DH, 50 kHz) for 2.5 h at around 43 °C. After sonication, an
aqueous 2M HCl (10 mL) was added, and the filtrate was extracted with ether
(
with MgSO , filtered, and then the organic solvent was removed under reduced
30 mL 9 3). The combined organic layer was washed with brine (20 mL), dried
4
pressure. Further purification was achieved on a flash chromatograph with ethyl
acetate/hexane as eluent.
A representative procedure for synthesis of 5-substituted dihydropyrroles
A reaction mixture of homopropargyl amine (1.0 mmol), AgOAc (0.05 mmol) in
CH CN (4 mL) was introduced in a pressure tube with a threaded Teflon cap, and
the reaction mixture was microwave-irradiated for 15 min at 100 W, 100 psi, and
3
123

A. S.-Y. Lee et al.
Table 2 Synthesis of N-tosyl dihydropyrroles
a
The yields were determined after chromatographic purification
8
0 °C reaction condition. The reaction mixture was cooled to room temperature, and
the resulting product was passed through a short Celite column to remove metals.
Further purification was achieved on a flash chromatograph with silica gel and ethyl
acetate/hexane as eluent.
A representative procedure for synthesis of 2-substituted pyrroles
A reaction mixture of dihydropyrrole (1.0 mmol) and KOtBu (5.0 mmol) in DMSO
(
Dimethyl sulfoxide, 4 mL) was introduced in a pressure tube with a threaded
Teflon cap, and the reaction mixture was microwave-irradiated for 5 min at 100 W,
00 psi, and 50 °C reaction conditions. The reaction mixture was cooled to room
1
temperature, and ether (30 mL) was added. The resulting solution was passed
through a short Celite column to remove metals. The combined organic layer was
1
23

Microwave assisted synthesis of dihydropyrrole by AgOAc…
Scheme 4 Optimization of aromitization of dihydropyrrole
washed with water (20 mL 9 3), brine (20 mL), dried with MgSO , filtered, and
4
then the organic solvent was removed under reduced pressure. Further purification
was achieved on a flash chromatograph with silica gel and ethyl acetate/hexane as
eluent.
N-(1-cyclohexylbut-3-ynyl)-4-methylbenzenesulfonamide (Table 1, Entry 1)
1
H-NMR: d0.91 (m, 2H), 1.07 (m, 3H), 1.53 (m, 6H), 1.92 (m, 1H), 2.17 (m, 1H),
2
7
7
.27 (m, 1H), 2.41 (s, 3H), 3.08 (m, 1H), 4.71 (s, 1H), 7.27 (d, J = 8.4 Hz, 1H),
1
3
.73 (d, J = 8.4 Hz, 1H). C-NMR: d21.3, 22.0, 25.6, 28.0, 29.2, 39.8, 56.3, 71.0,
9.5, 126.8, 129.3, 137.9, 143.0.
4
-methyl-N-(1-phenylbut-3-ynyl)benzenesulfonamide (Table 1, Entry 2)
1
H-NMR: d1.97 (t, J = 2.6 Hz, 1H), 2.38 (s, 3H), 2.64 (m, 2H), 4.50 (q, 1H), 5.02
d, J = 6.8 Hz, 1H), 7.14–7.23 (m, 7H), 7.62 (d, J = 8.2 Hz, 2H). C-NMR:
1
3
(
d21.3, 27.1, 55.8, 71.8, 79.1, 126.5, 126.9, 127.6, 128.2, 129.2, 137.1, 139.0, 143.1.
N-(1-(4-fluorophenyl)but-3-ynyl)-4-methylbenzenesulfonamide (Table 1,
Entry 3)
1
H-NMR: d1.99 (t, J = 2.5 Hz 1H), 2.39 (s, 3H), 2.58–2.61 (m, 2H), 4.45 (q, 1H),
5
2
1
.17 (s, 1H), 6.86–6.92 (m, 2H), 7.12 (m, 2H), 7.17 (m, 2H), 7.58 (d, J = 8.25 Hz,
1
3
H). C-NMR: d21.4, 27.2, 55.1, 72.2, 78.8, 115.0, 127.0, 128.2, 129.4, 134.9,
37.0, 143.4, 160.9, 163.3.
N-(1-(4-methoxyphenyl)but-3-ynyl)-4-methylbenzenesulfonamide (Table 1,
Entry 5)
1
H-NMR: d1.98 (t, 1H), 2.39 (s, 3H), 2.62 (m, 2H), 3.76 (s, 3H), 4.44 (m, 1H), 5.02
d, J = 6.82 Hz, 1H), 6.72 (d, J = 6.7 Hz, 2H), 7.07 (d, J = 6.7 Hz, 2H), 7.18 (d,
(
1
3
J = 8.3 Hz, 2H), 7.62 (d, J = 8.3 Hz, 2H). C-NMR: d21.4, 27.5, 29.3, 55.5, 55.7,
0.8, 71.8, 79.5, 114.1, 127.4, 128.2, 129.4, 131.4, 137.4, 143.1, 159.1.
7
123

A. S.-Y. Lee et al.
Table 3 Synthesis of 2-substituted pyrroles
a
The yields were determined after chromatographic purification
N-(1-(benzo[d] [1,3] dioxol-5-yl)but-3-ynyl)-4-methylbenzenesulfonamide
Table 1, Entry 6)
(
1
H-NMR: d2.00 (s, 1H), 2.39 (s, 3H), 2.57 (m, 2H), 4.36 (m, 1H), 5.15 (m, 1H), 5.88
d, J = 5.6 Hz 1H), 6.59 (m, 3H), 7.18 (d, J = 8.1 Hz, 2H), 7.59 (d, J = 8.1 Hz,
(
1
3
2
H). C-NMR: d21.4, 27.2, 55.6, 72.0, 79.1, 101.0, 106.9, 107.8, 120.2, 127.0,
1
29.3, 133.0, 137.1, 143.2, 147.0, 147.4.
4-methyl-N-(1-(naphthalen-2-yl)but-3-ynyl)benzenesulfonamide (Table 1,
Entry 7)
1
H-NMR: d1.99 (m, 1H), 2.33 (s, 3H), 2.79 (m, 2H), 5.27 (m, 2H), 7.06 (d,
J = 7.9 Hz, 2H), 7.32 (d, J = 7.9 Hz, 1H), 7.42 (m, 3H), 7.44 (m, 2H), 7.55 (m,
1
23

Microwave assisted synthesis of dihydropyrrole by AgOAc…
1
3
1
H), 7.57(m, 1H). C-NMR: d21.5, 26.8, 56.0, 72.6, 79.2, 124.5, 125.8, 126.4,
1
26.6, 127.3, 127.5, 128.6, 129.1, 129.4, 130.2, 133.9, 134.5, 137.1, 143.4.
N-(1-(furan-2-yl)but-3-ynyl)-4-methylbenzenesulfonamide (Table 1, Entry
)
8
1
H-NMR: d1.98 (s, 1H), 2.39 (s, 3H), 2.65 (m, 2H), 4.58 (m, 1H), 5.18 (d,
J = 8.40 Hz, 1H), 6.12 (d, J = 3.3 Hz 1H), 6.19 (m, 1H), 7.23 (m, 1H), 7.29 (s,
1
3
1
1
H), 7.68 (d, J = 8.4 Hz, 1H). C-NMR: d21.4, 25.0, 49.9, 71.8, 78.7, 107.6,
10.2, 127.0, 129.5, 137.3, 142.2, 143.3, 151.4.
4-methyl-N-(1-(thiophen-2-yl)but-3-ynyl)benzenesulfonamide (Table 1,
Entry 9)
1
H-NMR: d2.02 (t, J = 2.6 Hz, 1H), 2.41 (s, 3H), 2.72 (dd, J = 2.6, 2.8 Hz, 2H),
4
.76 (m, 1H), 5.12 (d, J = 8.1 Hz, 1H), 6.83 (m, 2H), 7.14 (m, 1H), 7.23 (d,
1
3
J = 8.2 Hz, 1H), 7.68 (d, J = 8.2 Hz, 1H). C-NMR: d21.5, 27.6, 51.6, 72.5, 78.7,
1
25.2, 126.6, 127.1, 129.5, 137.2, 142.8, 143.5.
2
-cyclohexyl-1-tosyl-2,3-dihydro-1H-pyrrole (Table 2, Entry 1)
1
H-NMR: d1.08 (m, 3H), 1.16 (m, 5H), 1.73 (m, 3H), 2.14 (m, 2H), 2.42 (s, 3H),
.58(m, 1H), 5.06 (m, 1H), 6.28(m, 1H), 7.27 (d, J = 8.3 Hz, 2H), 7.64 (d,
3
13
J = 8.3 Hz, 2H). C-NMR: d21.3, 22.0, 25.8, 29.2, 39.8, 56.3, 76.0, 79.5, 127.1,
1
29.1, 137.9, 143.0.
2
-phenyl-1-tosyl-2,3-dihydro-1H-pyrrole (Table 2, Entry 2)
1
H-NMR: d2.42 (m, 4H), 2.86 (m, 1H), 4.69 (m, 1H), 5.09 (m, 1H), 6.51 (m, 1H),
.23 (m, 1H), 7.27 (m, 7H), 7.53 (d, J = 8.2 Hz, 2H). C-NMR: d21.6, 40.8, 63.0,
1
3
7
1
09.9, 126.6, 127.7, 127.9, 129.6, 129.8, 131.0, 134.2, 143.7, 147.1.
2
-(4-fluorophenyl)-1-tosyl-2,3-dihydro-1H-pyrrole (Table 2, Entry 3)
1
H-NMR: d2.35 (m, 4H), 2.83 (m, 1H), 2.75 (m, 1H), 4.67 (m, 1H), 5.10 (m, 1H),
1
3
.51 (m, 1H), 6.95 (m, 2H), 7.27 (m, 4H), 7.59 (d, J = 8.2 Hz, 2H). C-NMR:
6
d21.4, 40.5, 62.2, 110.0, 127.0, 127.4, 127.8, 127.9, 129.5, 129.6, 130.6, 133.6,
1
38.4, 143.8, 160.8, 163.2.
2
-benzo [1,3] dioxol-1-tosyl-2,3-dihydro-1H-pyrrole (Table 2, Entry 4)
1
H-NMR: d2.42 (s, 3H), 2.46 (m, 1H), 2.87 (m, 1H), 3.78 (s, 3H), 4.64 (m, 1H), 5.09
m, 1H), 6.49 (m, 1H), 6.81 (d, J = 6.6 Hz, 2H), 7.22 (m, 4H), 7.59 (d, J = 8.2 Hz,
(
1
3
2
H). C-NMR: d21.6, 32.2, 32.8, 34.6, 55.3, 62.4, 64.2, 64.8, 84.9, 85.5, 89.8,
1
13.9, 127.3, 127.8, 128.1, 129.8, 133.8, 134.9, 136.0, 143.5, 158.9.
123

A. S.-Y. Lee et al.
2
-(4-methoxyphenyl)-1-tosyl-2,3-dihydro-1H-pyrrole (Table 2, Entry 5)
1
H-NMR: d2.42(s, 3H), 2.50(m, 1H), 2.91(m, 1H), 4.72(m, 1H), 5.11(m, 1H),
.52(m, 1H), 7.29(m, 6H), 7.61(d, J = 8.00 Hz, 2H). C-NMR: d21.7, 40.8, 63.1,
1
3
6
1
10.2, 126.4, 126.6, 127.6, 127.7, 128.7, 129.7, 129.8, 130.9, 142.8, 143.8.
2
-(naphthalen-2-yl)-1-tosyl-2,3-dihydro-1H-pyrrole (Table 2, Entry 6)
1
H-NMR: d2.42 (s, 3H), 2.43 (m, 1H), 3.06 (m, 1H), 5.15 (s, 3H), 5.35 (m, 1H), 6.65
1
3
(
m, 1H), 7.27 (m, 2H), 7.42 (m, 3H), 7.54 (m, 3H), 7.75 (m, 2H), 7.85 (m, 1H). C-
NMR: d21.5, 29.6, 40.2, 110.4, 122.9, 124.2, 125.3, 125.4, 125.9, 127.6, 128.0,
29.0, 129.5, 129.8, 130.9, 133.5, 134.0, 137.4, 143.7.
1
N-(1-(furan-2-yl)but-3-ynyl)-4-methylbenzenesulfonamide (Table 2, Entry
7
)
1
H-NMR: d2.41 (s, 3H), 2.61 (m, 1H), 2.83 (m, 1H), 5.05 (m, 1H), 5.15 (m, 1H),
.43 (m, 1H), 6.89 (m, 1H), 7.17 (m, 1H), 7.26 (d, J = 8.2 Hz, 2H), 7.60 (d,
6
1
3
J = 8.2 Hz, 2H). C-NMR: d21.4, 36.2, 56.4, 70.1, 74.7, 107.4, 110.3, 110.5,
1
27.0, 128.7, 129.5, 133.6, 142.3, 153.2
2
-(thiophen-2-yl)-1-tosyl-2,3-dihydro-1H-pyrrole (Table 2, Entry 8)
1
H-NMR: d2.41 (s, 3H), 2.61 (m, 1H), 2.83 (m, 1H), 5.05 (m, 1H), 5.15 (m, 1H),
.43 (m, 1H), 6.89 (m, 1H), 7.17 (m, 1H), 7.26 (d, J = 8.2 Hz, 2H), 7.60 (d,
6
1
3
J = 8.2 Hz, 2H). C-NMR: d21.6, 32.8, 34.7, 60.5, 85.6, 89.9, 124.9, 125.4, 126.8,
27.3, 127.6, 130.0, 135.9, 143.7, 147.3.
1
Acknowledgments We thank the National Science Council in Taiwan (NSC 101-2113-M-032-003) and
Tamkang University for financial support.
References
1. R.J. Sundberg, in Comprehensive Heterocyclic Chemistry, vol. 4, ed. by A.R. Katritzky, C.W. Rees
(Pergamon Press, Oxford, 1984), p. 313
2
. G.P. Bean, in Pyrroles, ed. by R.A. Jones (Wiley, New York, 1990), p. 105
. R.J. Sundberg, in Comprehensive Heterocyclic Chemistry II, vol. 2, ed. by A.R. Katritzky, C.W.
Rees, E.F.V. Scriven (Elsevier, Oxford, 1996), p. 119
3
4. G.W. Gribble, in Comprehensive Heterocyclic Chemistry II, vol. 2, ed. by A.R. Katritzky, C.W. Rees,
E.F.V. Scriven (Elsevier, Oxford, 1996), p. 207
5
. R.M. Baughman, J.L. Bredas, R.L. Elsenbaumer, L.W. Shacklette, Chem. Rev. 82, 209 (1982)
. R.D’. Alessio, A. Bargiotti, O. Carlini, F. Colotta, M. Ferrari, P. Gnocchi, A. Isetta, N. Mongelli, P.
Motta, A. Rossi, M. Rossi, M. Tibolla, E. Vanotti, J. Med. Chem. 43, 2557 (2000)
. M.A. Galindo, J. Hannant, R.W. Harrington, W. Clegg, B.R. Horrocks, A.R. Pike, A. Houlton, Org.
Biomol. Chem. 9, 1555 (2011)
6
7
8. J.T. Gupton, Top Heterocycl. Chem. 2, 53 (2006)
9. M. Biava, G.C. Porretta, G. Poce, S. Supino, D. Deidda, R. Pompei, P. Molicotti, F. Manetti, M.
Botta, J. Med. Chem. 49, 4946 (2006)
1
23

Microwave assisted synthesis of dihydropyrrole by AgOAc…
1
0. R. Martin, A. J a¨ ger, M. B o¨ hl, S. Richter, R. Fedorov, D.J. Manstein, H.O. Gutzeit, H.J. Kn o¨ lker,
Angew. Chem. Int. Ed. 48, 8042 (2009)
1. M.G. Thomas, M.D. Burkart, C.T. Walsh, Chem. Biol. 9, 171 (2002)
2. J. Regourd, A.A. Ali, A. Thompson. J. Med. Chem. 50, 1528 (2007)
3. D. Feh e´ r, R.S. Barlow, P.S. Lorenzo, T.K. Hemscheidt, J. Nat. Prod. 2008, 71 (1970)
4. M. Rene, J. Anne, J.K. Hans, Synlett 19, 2795 (2011)
1
1
1
1
1
5. H. Yoshimura, K. Kikuchi, S. Hibi, K. Tagami, T. Satoh, T. Yamauchi, A. Ishibahi, K. Tai, T. Hida,
N. Tokuhara, M. Nagai, J. Med. Chem. 43, 2929 (2000)
16. C.P. Gonzalo, J.A. Pomposoa, J.A. Alduncin, M. Salsamendi, A.I. Mikhaleva, L.B. Krivdin, B.A.
Trofimov, Electrochim. Acta 52, 4784 (2007)
17. C. Simon, T. Constantieux, J. Rodriguez, Eur. J. Org. Chem. 2004, 4957 (2004)
18. H. Shiraishi, T. Nishitani, S. Sakaguchi, Y. Ishii, J. Org. Chem. 63, 6234 (1998)
19. X. Lin, Z. Mao, X. Dai, P. Lu, Y. Wang, Chem. Commun. 47, 6620 (2011)
20. O.A. Attanasi, G. Favi, F. Mantellini, G. Moscatelli, S. Santeusanio, J. Org. Chem. 76, 2860 (2011)
21. E. Ghabraie, S. Balalaie, M. Bararjanian, H.R. Bijanzadeh, F. Rominger, Tetrahedron 67, 5415
(2011)
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
2. C.R. Reddy, M.D. Reddy, B. Srikanth, K.R. Prasad, Org. Biomol. Chem. 9, 6027 (2011)
3. B.M. Trost, J.-P. Lumb, J.M. Azzarelli, J. Am. Chem. Soc. 133, 740 (2011)
4. A.V. Gulevich, A.S. Dudnik, N. Chernyak, V. Gevorgyan, Chem. Rev. 113, 3084 (2013)
5. H.C. Brown, U.R. Khire, G. Narla, U.S. Racherla, J. Org. Chem. 60, 544 (1995)
6. A.S.-Y. Lee, S.-F. Chu, S.-H. Wang, Y.-T. Chang, Tetrahedron Lett. 45, 1551 (2004)
7. A.S.-Y. Lee, K.-W. Tsao, Y.-T. Chang, S.-F. Chu, Tetrahedron Lett. 48, 6790 (2007)
8. J.E. Baldwin, J. Chem. Soc. Chem. Commun. 734 (1976)
9. A.S.-Y. Lee, Y.-T. Chang, F.-Y. Su, J. Chin. Chem. Soc. 61(2), 290 (2014)
0. A.S.-Y. Lee, Y.-T. Chang, Tetrahedron Lett. 51, 3800 (2010)
1. A.S.-Y. Lee, C.-H. Chung, S.-F. Chu, Y.-T. Chang, J. Chin. Chem. Soc. 56, 202 (2009)
2. A.S.-Y. Lee, K.-W. Tsao, Y.-T. Chang, S.-F. Chu, J. Chin. Chem. Soc. 54(2), 519 (2007)
3. A.S.-Y. Lee, Y.-T. Chang, S.-F. Chu, K.-W. Tsao, Tetrahedron Lett. 47, 7085 (2006)
4. A.S.-Y. Lee, Y.-T. Chang, S.-H. Wang, S.-F. Chu, Tetrahedron Lett. 43, 8489 (2002)
5. A.S.-Y. Lee, R.-Y. Cheng, O.-G. Pan, Tetrahedron Lett. 38, 443 (1997)
6. A.S.-Y. Lee, W.-C. Dai, Tetrahedron 53, 859 (1997)
7. H.M. Wisniewska, E.R. Jarvo, Chem. Sci. 2, 807 (2011)
8. B.L. Hayes, Microwave Synthesis (CEM Publishing, London, 2002)
9. A.S.-Y. Lee, Y.-C. Wu, Y.-T. Chang, B.-C. Wang, Res. Chem. Intermed. 40(6), 2277 (2014)
0. A.S.-Y. Lee, C.-H. Chung, Y.-T. Chang, P.-L. Chen, J. Appl. Sci. Eng. 15(3), 311 (2012)
123