Synthesis of pyrrolobenzoxazepinones by CuI/L-proline-catalyzed intramolecular coupling reactions

Article abstract of DOI:10.1016/j.tet.2012.11.009

A copper-catalyzed process for the construction of pyrrolobenzoxazepinones from 2-(2-iodophenoxy)-1-(1H-pyrrol-2-yl)ethanones is described. The reaction afforded avariety of products in good to excellent yields.

Full text of DOI:10.1016/j.tet.2012.11.009

Tetrahedron 69 (2013) 642e646
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Synthesis of pyrrolobenzoxazepinones by CuI/ -proline-catalyzed
L
intramolecular coupling reactions
*
*
Aiping Huang, Lei Feng , Zhi Qiao, Wei Yu, Qingqing Zheng, Chen Ma
School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A copper-catalyzed process for the construction of pyrrolobenzoxazepinones from 2-(2-iodophenoxy)-1-
(1H-pyrrol-2-yl)ethanones isdescribed. The reaction afforded avarietyofproductsingood toexcellent yields.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 29 August 2012
Received in revised form 26 September
2012
Accepted 2 November 2012
Available online 7 November 2012
Keywords:
Copper-catalyzed process
Pyrrolobenzoxazepinones
Bioactive compounds
Synthesis
1. Introduction
Transition-metal-catalyzed reactions have beenwidely employed
in the construction of carbonenitrogen bonds.2e13 Recently, copper-
Substituted pyrrolobenzoxazepinones (PBOs) are pharmaceuti-
cally important heterocycles that display various important bi-
ological activities,1 such as antitumor 1,1e anti-HIV-1 2,1a and
antiviral 31d properties. Additionally, many of pyrrolobenzox-
azepinones are non-nucleoside inhibitors of human adenosine ki-
nase 4 (Fig. 1).1b
catalyzed Ullmann N-arylations have made significant progress, and
the N-arylation strategy has been used for the synthesis of nitrogen
heterocycles.14e29 Ma and co-workers first applied CuI/amino acid
catalyzed Ullmann N-arylation, leading to the intermolecular and
intramolecular N-arylation at low temperature.10,15,16 Their research
also demonstrated that CuI/amino acid was an efficient system in the
intermolecular N-arylation of pyrroles.15,16 Many other groups also
made significant process in the intermolecular N-arylation of
pyrroles.17e19 Until recently, there are few synthetic routes leading to
pyrrolobenzoxazepinones. Only Campiani and co-workers reported
palladium or phosphorus pentachloride catalyzed method for the
construction of pyrrolobenzoxazepinone derivatives. These methods
required higher costs of Pd catalysts, harsh reaction conditions, or
inconvenient operations. Therefore, an efficient and economical
method for the synthesis of these heterocycles is still desirable.
Moreover, the intramolecular N-arylation of pyrrole is very few.14,20
Herein, we report an efficient copper-catalyzed process for the con-
struction of pyrrolobenzoxazepinones from 2-(2-iodophenoxy)-1-
(1H-pyrrol-2-yl)ethanones (Scheme 1).
O
O
O
N
N
N
O
1
2
O
S
O
O
N
N
3
4
2. Results and discussion
Fig. 1. Structures of some biologically important pyrrolobenzoxazepinones.
2-(2-Iodophenoxy)-1-(1H-pyrrol-2-yl)ethanones7were obtained
by the reaction of 2-iodophenols30,315 with 2-chloro-1-(1H-pyrrol-2-
yl)ethanone32 6 in the presence of potassium carbonate in refluxing
acetonitrile (Scheme 2). The reactions afforded 7 in good yields.
* Corresponding authors. Tel.: þ86 531 8836 4464; fax: þ86 531 8856 4464;
e-mail addresses: Feng_Lei@sdu.edu.cn (L. Feng), chenma@sdu.edu.cn (C. Ma).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.11.009

A. Huang et al. / Tetrahedron 69 (2013) 642e646
643
Under the optimized conditions, we investigated the scope of
substrates for the assembly of substituted pyrrolobenzox-
azepinones (Table 2). As shown in Table 2, the electronic properties
of 7 had little influence on the yields of this process, which is evi-
dent from the fact that 7 bearing both electron-withdrawing
groups (entries 2e8) and electron-donating groups (entries 9e11)
worked well, giving the corresponding 2-subsitututed pyrrolo-
benzoxazepinones in good yields. It is noteworthy that not only the
substrates bearing an iodine substituent worked well under the
optimized conditions, but also the substrate with a bromide group
afforded the desired product pyrido[3,2-b]pyrrolo[1,2-d][1,4]oxa-
zepin-7(6H)-one in good yield (entry 12). The substrates bearing an
iodine group (entries 1e8) reacted smoothly in this process, and the
substrates bearing two iodines were also compatible with these
conditions (entries 9e11). However, the electronic influence of
substituent on 7 had a marked effect on the reaction rate. It was
found that reactions of 7 with an electron-withdrawing group
(entries 2e8) required much more time than those with electron-
donating group (entries 9e12).
O
O
N
O
X
CuI,
L-proline, K2CO3
R
O
R
HN
Y
DMSO, 80°C
Y
7
8
X = I, Br
Y = C, N
Scheme 1. The reaction of 2-(2-iodophenoxy)-1-(1H-pyrrol-2-yl)ethanones.
O
O
X
OH
X
HN
Cl
K2CO3, CH3CN
reflux
R
R
+
HN
O
Y
Y
5
7
6
Scheme 2. The reaction of 2-iodophenols with 2-chloro-1-(1H-pyrrol-2-yl)ethanone.
The Cu-catalyzed intramolecular coupling reaction of the 2-(2-
iodophenoxy)-1-(1H-pyrrol-2-yl)ethanone 7a was chosen as
a model reaction to screen for suitable reaction conditions (Table 1).
The reaction was conducted under the following conditions: CuI
3. Conclusion
(10 mol %), L-proline (L
, 20 mol %), K2CO3 (2.5 equiv) in DMF at 80 ꢀC
In summary, we have developed an efficient synthetic method
for the synthesis of pyrrolobenzoxazepinones. A variety of pyrro-
lobenzoxazepinone derivatives were synthesized from 2-(2-
iodophenoxy)-1-(1H-pyrrol-2-yl)ethanones by intramolecular Cu-
catalyzed Ullmann N-arylations in good to excellent yields. This
process has potential applications in the synthesis of biologically
and medicinally relevant compounds.
(entry 1). It was found that the desired cyclic product 8a could be
obtained in 74% yield. To optimize the reaction conditions, we ex-
amined different solvents, bases, and ligands. The results are
summarized in Table 1. We investigated the effect of the solvents
(entries 1e7). Dioxane, toluene, and NMP gave the products in
moderate yields (entries 2, 3, and 5). The yields of the products in
THF and CH3CN were much lower (entries 4 and 6). DMSO proved
to be the most effective solvent. We then investigated the effect of
the bases (entries 7e9). K2CO3 and Cs2CO3 provided the similar
results (entries 7 and 8). K3PO4 was less successful (entry 9). K2CO3
was the most suitable base in the reaction (entry 7). Under these
reaction conditions, two other ligands (1,10-phenanthronine and
DMEDA) gave the product 8a in relatively low yields (entries 10 and
11). We also investigated the following conditions: CuI, 1,10-
phenanthronine, K2CO3 in toluene and CuI, 1,10-phenanthronine,
K3PO4 in dioxane, and the yields of 8a were 55% and 62%, re-
spectively. Consequently, the optimized reaction condition was CuI
4. Experimental section
4.1. General
2-Iodophenols26,27 and 2-chloro-1-(1H-pyrrol-2-yl)ethanone28
were prepared according to literature procedures. Potassium car-
bonate, cesium carbonate, potassium phosphate, L-proline, 1,10-
phenanthronine, DMEDA, CuI, and solvents were commercially
available. All reactions were monitored by thin-layer chromatog-
raphy (TLC). 1H NMR spectra were recorded on a Bruker Avance 400
or 300 spectrometer at 400 or 300 MHz, using CDCl3 or DMSO-d6 as
solvent and tetramethylsilane (TMS) as internal standard. 13C NMR
spectra were run in the same instrument at 100 or 75 MHz. Melting
points were determined on an XD-4 digital micro melting point
apparatus. HRMS spectra were determined on a Q-TOF6510 spec-
trograph (Agilent).
(10 mol %),
L-proline (L, 20 mol %), K2CO3 (2.5 equiv) in DMSO at
80 ꢀC.
Table 1
Optimization of the intramolecular cyclizationa
O
O
N
O
I
CuI, ligand, base
O
HN
7a
solvent, temperature
4.2. General experimental procedure for the preparation of 2-
8a
(2-iodophenoxy)-1-(1H-pyrrol-2-yl)ethanones 7
Entry Ligand
Base
Temperature Solvent
Yieldb (%)
74
A mixture of 2-iodophenols 5 (2 mmol), 2-chloro-1-(1H-pyrrol-
2-yl)ethanone 6 (2 mmol), and K2CO3 (2.4 mmol) in acetonitrile
was refluxed and TLC monitored at the end of the reaction. Then the
mixture was cooled to room temperature, diluted with brine
(30 mL), and extracted with dichloromethane twice (2ꢁ15 mL). The
combined organic layers were dried over MgSO4 and the solvent
was removed in vacuo to afford a residue. The residue was purified
by column chromatography on silica gel to afford 7.
1
2
3
4
5
6
7
8
L
L
L
L
L
L
L
L
L
-Proline
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
80 ꢀC
DMF
-Proline
-Proline
-Proline
-Proline
-Proline
-Proline
-Proline
-Proline
Reflux
Reflux
Reflux
80 ꢀC
Dioxane 52
Toluene 50
THF
34
56
27
79
78
42
47
35
NMP
Reflux
CH3CN
DMSO
DMSO
DMSO
DMSO
DMSO
80 ꢀC
Cs2CO3 80 ꢀC
K3PO4
9
80 ꢀC
80 ꢀC
80 ꢀC
Reflux
Reflux
10
11
12
13
1,10-Phenanthronine K2CO3
DMEDA K2CO3
1,10-Phenanthronine K2CO3
1,10-Phenanthronine K3PO4
4.2.1. 2-(2-Iodophenoxy)-1-(1H-pyrrol-2-yl)ethanone (7a). White
Toluene 55
Dioxane 62
solid (89%). Mp 214e215 ꢀC. 1H NMR (400 MHz, CDCl3):
d 9.57
(1H, s, br), 7.27 (2H, m), 7.08 (1H, d, J¼0.88 Hz), 6.80 (1H, d,
a
Reaction conditions: 2-(2-iodophenoxy)-1-(1H-pyrrol-2-yl)ethanone 7a
J¼7.84 Hz), 6.75 (1H, m), 6.33 (1H, m), 5.05 (1H, s); 13C NMR
(1 equiv), CuI (0.1 equiv), ligand (0.2 equiv), base (2.5 equiv), solvent (3 mL).
b
Isolated yield.
(75 MHz, CDCl3):
d 86.1, 111.3, 112.4, 118.1, 123.5, 125.3, 129.6,

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A. Huang et al. / Tetrahedron 69 (2013) 642e646
Table 2
Synthesis of pyrrolobenzoxazepinones 8a
O
O
N
O
X
CuI, L-proline, K2CO3
R
O
R
HN
Y
Y
DMSO, 80°C
7
8
Entry
1
Substrate
Time (h)
2
Product
Yieldb (%)
79
7a
8a
8b
8c
8d
2
3
4
4
82
80
76
7b
7c
2
2.5
7d
5
6
6
84
76
8e
8f
7e
7f
1.5
7
8
9
3
79
83
71
7g
7h
7i
8g
8h
1
0.5
8i
10
11
0.5
87
92
7j
8j
0.15
7k
8k
12
3
58
7l
8l
a
Reaction conditions: 2-(2-iodophenoxy)-1-(1H-pyrrol-2-yl)ethanones 7 (1 equiv), CuI (0.1 equiv), L
-proline (0.2 equiv), K2CO3 (2.5 equiv), DMSO (3 mL), 80 ꢀC.
Isolated yield.
b

A. Huang et al. / Tetrahedron 69 (2013) 642e646
645
139.8, 156.9, 184.3. HRMS calcd for C12H10INO2 327.9856; found:
327.9823.
J¼2.1 Hz), 7.56 (1H, t, J¼2.1 Hz), 7.17 (1H, dd, J¼4.1, 1.8 Hz), 6.56 (1H,
t, J¼2.9 Hz), 4.71 (2H, s), 2.07 (3H, s); 13C NMR (100 MHz, CDCl3):
d
23.9, 78.2, 92.6, 111.9, 113.8, 119.4, 126.5, 127.1, 131.4, 131.6, 132.5,
4.3. Procedure for the preparation of pyrrolobenzox-
azepinones 8
132.8, 137.8, 145.0, 168.5, 188.1; HRMS calcd for C14H12N2O3
256.0848; found: 256.0811.
A mixture of 2-(2-iodophenoxy)-1-(1H-pyrrol-2-yl)ethanone 7
4.3.8. 2-Phenylbenzo[b]pyrrolo[1,2-d][1,4]oxazepin-7(6H)-one
(1 mmol), 10 mol % of CuI (0.1 mmol), 20 mol % of
L-proline
(8h). White solid (83%). Mp 268e269 ꢀC. 1H NMR (300 MHz,
(0.2 mmol), and K2CO3 (2.5 mmol) in 3 mL DMSO and under ni-
trogen, was heated at 80 ꢀC, and TLC monitored at the end of the
reaction. After that, the reaction was cooled to room temperature,
quenched with water (10 mL), and diluted with 10 mL of ethyl
acetate. The layers were separated, and the aqueous layer was
extracted with ethyl acetate (2ꢁ10 mL). The combined organic
layers were dried over MgSO4 and the solvent was removed in
vacuo to afford a residue. The residue was purified by column
chromatography on silica gel to afford 8.
CDCl3): d 7.58 (2H, m), 7.53 (3H, m), 7.49 (1H, m), 7.35 (3H, m), 6.50
(1H, dd, J¼3.9, 2.7 Hz), 4.73 (2H, s); 13C NMR (75 MHz, CDCl3):
d
79.5, 112.0, 120.4, 121.6, 123.2, 126.5, 126.7, 127.0, 129.0, 133.2,
133.7, 139.5, 139.6, 150.1, 188.9; HRMS calcd for C18H13NO2
275.0946; found: 275.0936.
4.3.9. 2-Chloro-4-iodobenzo[b]pyrrolo[1,2-d][1,4]oxazepin-7(6H)-
one (8i). White solid (71%). Mp 251e252 ꢀC. 1H NMR (300 MHz,
CDCl3):
d
7.75 (1H, d, J¼2.4 Hz), 7.37 (1H, d, J¼2.1 Hz), 7.32 (1H, dd,
J¼2.7, 1.8 Hz), 6.51 (1H, dd, J¼3.9, 2.7 Hz), 4.68 (2H, s); 13C NMR
4.3.1. Benzo[b]pyrrolo[1,2-d][1,4]oxazepin-7(6H)-one
(8a). White
7.39 (1H, m),
(100 MHz, CDCl3): d 78.5, 92.9, 112.6, 121.0, 123.3, 126.5, 128.8,
solid (79%). Mp 221e222 ꢀC. 1H NMR (300 MHz, CDCl3):
d
130.9, 132.4, 136.3, 149.1, 187.8; HRMS calcd for C12H7ClINO2
358.9210; found: 358.9197.
7.29 (5H, m), 6.48 (1H, dd, J¼3.8, 2.8 Hz), 4.70 (2H, s); 13CNMR(75MHz,
CDCl3): d 79.5, 111.9, 120.3, 122.8, 122.9, 126.1, 126.7, 127.9, 133.1, 133.6,
150.8, 188.9; HRMS calcd for C12H9NO2 199.0633; found: 199.0623.
4.3.10. 2-Bromo-4-iodobenzo[b]pyrrolo[1,2-d][1,4]oxazepin-7(6H)-
one (8j). White solid (87%). Mp 246e247 ꢀC. 1H NMR (300 MHz,
4.3.2. 2-Methylbenzo[b]pyrrolo[1,2-d][1,4]oxazepin-7(6H)-one
CDCl3):
J¼1.8 Hz), 7.23 (1H, dd, J¼2.7, 1.8 Hz), 6.51 (1H, dd, J¼3.9, 2.7 Hz),
4.68 (2H, s); 13C NMR (75 MHz, CDCl3):
78.4, 93.3, 112.7, 118.96,
121.0, 126.1, 126.5, 133.4, 138.9, 149.6, 187.8; HRMS calcd for
C12H7BrINO2 402.8705; found: 402.8681.
d
7.89 (1H, d, J¼2.1 Hz), 7.51 (1H, d, J¼2.4 Hz), 7.32 (1H, q,
(8b). White solid (82%). Mp 230e231 ꢀC.1H NMR (300 MHz, CDCl3):
d
7.30 (2H, m), 7.20 (1H, m), 7.16 (1H, s), 7.09 (1H, m), 6.47 (1H, dd,
d
J¼3.9, 2.7 Hz), 4.67 (2H, s), 2.40 (3H, s); 13C NMR (75 MHz, CDCl3):
d
21.47, 80.1,112.3,120.6,122.9,123.7,127.1,128.9, 133.6,136.4,149.1,
189.4; HRMS calcd for C13H11NO2 213.0790; found: 213.0777.
4.3.11. 2,4-Diiodobenzo[b]pyrrolo[1,2-d][1,4]oxazepin-7(6H)-one
4.3.3. 2-Ethylbenzo[b]pyrrolo[1,2-d][1,4]oxazepin-7(6H)-one
(8k). White solid (92%). Mp 247e248 ꢀC. 1H NMR (400 MHz,
(8c). Yellow oil (80%). 1H NMR (300 MHz, CDCl3):
d
7.29 (2H, m), 7.20
CDCl3):
J¼4.0, 1.7 Hz), 7.23 (1H, dd, J¼2.6, 1.9 Hz), 6.50 (1H, dd, J¼3.9,
2.9 Hz), 4.67 (2H, s); 13C NMR (100 MHz, CDCl3):
78.5, 89.3, 93.8,
d
8.07 (1H, d, J¼1.9 Hz), 7.67 (1H, d, J¼1.9 Hz), 7.31 (dd,
(2H, d, J¼8.1 Hz), 7.11 (1H, dd, J¼7.1, 1.5 Hz), 6.47 (1H, dd, J¼3.9,
2.7 Hz), 4.67 (2H, s); 2.69 (2H, q, J¼7.8 Hz), 1.27 (3H, t, J¼7.8 Hz); 13C
d
NMR (100 MHz, CDCl3):
d
15.52, 28.37, 79.55, 111.74, 120.14, 122.14,
112.6, 121.0, 126.6, 131.9, 133.4, 134.6, 144.7, 150.4, 187.8; HRMS
calcd for C12H7I2NO2 450.8566; found: 450.8523.
122.54, 126.61, 126.63, 127.25, 133.21, 133.24, 142.33, 148.75, 189.26;
HRMS calcd for C14H13NO2 227.0946; found: 227.0935.
4.3.12. Pyrido[3,2-b]pyrrolo[1,2-d][1,4]oxazepin-7(6H)-one
4.3.4. 2-Isopropylbenzo[b]pyrrolo[1,2-d][1,4]oxazepin-7(6H)-one
(8l). White solid (58%). Mp 222e223 ꢀC. 1H NMR (300 MHz, CDCl3):
(8d). Yellow oil (76%). 1H NMR (400 MHz, CDCl3):
d
7.28 (2H, m),
7.22 (2H, m), 7.13 (1H, dd, J¼6.2, 1.5 Hz), 6.46 (1H, t, J¼3.2 Hz), 4.66
(2H, s); 13C NMR (100 MHz, CDCl3):
23.9, 33.7, 79.5, 111.7, 120.1,
d
8.31 (1H, dd, J¼4.5,1.5 Hz), 8.03 (1H, dd, J¼2.7, 2.1 Hz), 7.62 (1H, dd,
J¼7.8, 1.5 Hz), 7.43 (1H, q, J¼1.8 Hz), 7.24 (1H, dd, J¼7.8, 3.0 Hz), 6.51
d
(1H, dd, J¼3.9, 3.0 Hz), 4.70 (2H, s); 13C NMR (100 MHz, CDCl3):
120.8, 122.5, 125.8, 126.6, 133.2, 147.0, 148.7, 189.2; HRMS calcd for
C15H15NO2 241.1103; found: 227.1088.
d 78.5, 111.9, 122.2, 122.8, 127.4, 128.9, 131.4, 131.9, 144.6, 145.4, 186.6;
HRMS calcd for C11H8IN2O2 200.0586; found: 200.0578.
4.3.5. 2-(tert-Butyl)benzo[b]pyrrolo[1,2-d][1,4]oxazepin-7(6H)-one
Acknowledgements
(8e). White solid (84%). Mp 232e234 ꢀC. 1H NMR (300 MHz,
CDCl3):
d
7.37 (1H, m), 7.31 (3H, m), 7.21 (1H, d, J¼8.4 Hz), 6.49 (1H,
We are grateful to the National Science Foundation of China (No.
21172131) for financial support of this research.
dd, J¼3.60, 3.00 Hz), 4.68 (2H, s), 1.36 (9H, s); 13C NMR (75 MHz,
CDCl3): d 31.4, 34.7, 79.5, 111.7, 119.9, 120.1, 122.1, 124.9, 126.6, 132.9,
133.2, 148.5, 149.4, 189.3; HRMS calcd for C16H17NO2 255.1259;
found: 255.1257.
Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2012.11.009.
4.3.6. 2-(Benzyloxy)benzo[b]pyrrolo[1,2-d][1,4]oxazepin-7(6H)-one
(8f). White solid (76%). Mp 246e248 ꢀC. 1H NMR (300 MHz, CDCl3):
d
7.39 (5H), 7.29 (1H, dd, J¼3.9, 1.8 Hz), 7.20 (2H, m), 6.99 (1H, d,
J¼2.7 Hz), 6.87 (1H, dd, J¼8.7, 3.0 Hz), 6.47 (1H, dd, J¼3.9, 2.7 Hz),
5.09 (2H, s), 4.66 (2H, s); 13C NMR (100 MHz, CDCl3):
79.7, 109.8,
References and notes
d
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4.3.7. N-(7-Oxo-6,7-dihydrobenzo[b]pyrrolo[1,2-d][1,4]oxazepin-2-
yl)acetamide (8g). Yellow solid (79%). Mp 250e251 ꢀC. 1H NMR
(300 MHz, CDCl3):
d
10.17 (1H, s), 8.02 (1H, d, J¼2.0 Hz), 7.81 (1H, d,

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