Synthesis of 7a-phenyl-1a,7a-dihydrobenzopyrano[2,3-b]azirin-7-ones via photoisomerization reaction

Article abstract of DOI:10.1039/c4ra12542h

A novel protocol has been developed for the synthesis of 7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b] azirin-7-ones via the photoisomerization of 4-phenyl-5-(2-hydroxyphenyl)isoxazoles. This procedure involves a photo-catalyzed ring opening of isoxazole and

Full text of DOI:10.1039/c4ra12542h

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Synthesis of 7a-phenyl-1a,7a-dihydro-
benzopyrano[2,3-b]azirin-7-ones via
photoisomerization reaction†
Cite this: RSC Adv., 2015, 5, 4788
Qiuya Wang,ab Zunting Zhang, a Xi Zhang,a Jin Zhang,a Yang Kanga and Jufang Penga
*
A novel protocol has been developed for the synthesis of 7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b]
azirin-7-ones via the photoisomerization of 4-phenyl-5-(2-hydroxyphenyl)isoxazoles. This procedure
involves a photo-catalyzed ring opening of isoxazole and subsequent intramolecular nucleophilic
addition between a 2H-azirine intermediate and a phenolic hydroxyl group. The synthetic method offers
several notable advantages including operational simplicity, mild reaction conditions, moderate to high
yields and environmental friendliness.
Received 16th October 2014
Accepted 8th December 2014
DOI: 10.1039/c4ra12542h
www.rsc.org/advances
2H-azirines could be employed to synthesize aziridines by the
addition with O-, S-, N-, C-nucleophiles and hydride.17 Although
Introduction
the preparation methods of aziridines and its derivatives have
been well developed, the synthesis of fused aziridine derivatives
was scarce due to the inconvenience of starting materials,
nitrene source, catalysts and the harsh reaction conditions.
In the previous work, we have synthesized 2H-phenanthro
[9,10-c]pyrazoles by the intramolecular photocyclization and
dehydration of 3,4-diaryl-1H-pyrazoles in EtOH–H2O (1 : 1,
v/v).18 Following our investigations on the development of new
methodologies for the access to novel polyheterocyclic deriva-
tives, we expect to synthesize phenanthro[9,10-c]isoxazoles 3 by
the photocyclization of 4-phenyl-5-(2-hydroxyphenyl)isoxazoles 2.
Under the same conditions, the unexpected products, 7a-phenyl-
1a,7a-dihydro-benzopyrano[2,3-b]azirin-7-ones 1 were isolated and
identied instead of phenanthro[9,10-c]isoxazoles 3 (Scheme 3). As
yet, only Buggle19 reported the synthesis of 7a-phenyl-1a,7a-
dihydro-benzopyrano[2,3-b]azirin-7-one as a byproduct in 11%
yield. In this paper, a series of 7a-phenyl-1a,7a-dihydro-benzo-
pyrano[2,3-b]azirin-7-one analogues were successfully synthe-
sized via the photoisomerization reaction of 4-phenyl-5-(2-
hydroxyphenyl)isoxazoles 2 in EtOH–H2O (1 : 1, v/v).
Organic photochemical reactions play an important role in the
context of green chemistry and total synthesis.1 The photons
can be considered as the ideal clean reagent for organic
synthesis in contrast to toxic chemical activators.2 Another big
advantage of reactions in the excited state is their applications
in the synthesis of polycyclic or highly functionalized molecules
which would be difficult to access with standard chemistry
reactions in the ground state.3 Therefore, organic photochem-
ical reactions have received considerable interest in the
academic and industry.4
Aziridines, the smallest saturated aza-heterocycles, are
versatile synthetic intermediates, which have been paid great
attentions due to their important and wide applications in
organic synthesis and medicinal chemistry.5 For an instance,
natural fused aziridines such as mitomycins,6 azinomycins,7
cellomycin8 displayed signicant antibiotic and antitumor
activities (Scheme 1).
Current preparation of aziridines mainly included the cycli-
zation reactions,9 nitrene addition to olens,10 carbene and
ylide addition to imines,11,12 addition of azirines,13 aza-Darzen
approaches14 and ring contraction.15 Another interesting
methodology was affording 2H-azirines by the photo-cleavage
reaction of isoxazoles (Scheme 2).16 It was known that
Results and discussion
Optimization of the photoisomerization conditions
On the basis of the literature,20 4-phenyl-5-(2-hydroxyphenyl)
isoxazoles 2 were prepared by the condensation of isoavones
aKey Laboratory of the Ministry of Education for Medicinal Resources and Natural
Pharmaceutical Chemistry, National Engineering Laboratory for Resource
Development of Endangered Crude Drugs in Northwest of China, School of and hydroxylamine hydrochloride with Et3N as a base in
Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an 710062,
reuxing EtOH. The yields of 4-phenyl-5-(2-hydroxyphenyl)
isoxazoles 2 were in the range of 72–90%. Initially, 4-phenyl-5-
People's Republic of China. E-mail: zhangzunting@sina.com; Fax: +86-29-85303940
bCollege of Chemistry and Life Science, WeiNan Normal University, WeiNan 714000,
(2-hydroxyphenyl)isoxazole (2a) was irradiated in EtOH–H2O
People's Republic of China
(1 : 1, v/v) with a 500 W middle-pressure mercury lamp at about
20 ꢀC according to the methods of our previous work.18 Based on
† Electronic supplementary information (ESI) available: Part experimental details,
spectroscopic data. CCDC 1017876. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c4ra12542h
the careful isolation and characterization, it was surprised to
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Scheme 1 Fused aziridines in the natural products.
withdrawing substituents. The functionalities such as Me,
OMe, i-OPr, OBz, OH, F, Br and CF3 were all tolerated, leading to
the desired products 1a–w. While the electronic effect of
different substituents had an inuence on the yields of products
1. The substrates bearing electron-donating substituents
including Me, OMe, i-OPr, OBz or OH gave the corresponding
products in good yield (60–76%, entries 2–13), and when
electron-withdrawing substituents such as F, Br or CF3 were
present, the corresponding products were obtained in relative
lower yields (34–50%, entries 14–23).
Scheme
isoxazoles.
2 The formation of 2H-azirines via photo-cleavage of
nd that 7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b]azirin-7-
one (1a) was obtained in 56% yield (entry 1) (Table 1).
Subsequently, other solvents were screened for the photo-
isomerization reaction. When replacing EtOH–H2O (1 : 1, v/v)
with organic solvent (CH2Cl2, Me2CO, MeCN, MeOH, and
EtOH), the yields of 1a were decreased (21–43%, entries 2–6).
And using MeCN–H2O (1 : 1, v/v) and MeOH–H2O (1 : 1, v/v) as
solvents, the yields of 1a were 60% and 48%, respectively
(entries 7 and 8). Although the yield of 1a in MeCN–H2O (1 : 1,
v/v) was slightly higher than that in EtOH–H2O (1 : 1, v/v), while
from the economical and environmental point of view,
EtOH–H2O (1 : 1, v/v) was nally chosen as the reaction
medium. Ultimately, the optimized conditions included the
irradiation of 2a (C ¼ 10ꢁ2 mol Lꢁ1) in EtOH–H2O (1 : 1, v/v)
with a 500 W medium-pressure mercury lamp (l $ 300 nm)
Characterization of the products
All the products, 7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b]
azirin-7-ones 1 were characterized by IR, NMR and HRMS. In
1
the H NMR (DMSO-d6) spectra of 1, two doublets showed up
around 4.7 ppm and 5.4 ppm. When one drop of D2O was added
to the DMSO-d6 solution, a doublet at about 4.7 ppm dis-
appeared completely, and the doublet at 5.4 ppm was replaced
by singlet. The results of deuterium (2H)-exchange showed that
two signals around 4.7 ppm and 5.4 ppm belonged to –NH– and
–CH– of aziridine ring. Simultaneously, in the 13C NMR spectra
of 1, the peak at 188–191 ppm indicated the generation of
carbonyl group (–C]O). The appearance of the peaks at about
47 ppm and 70 ppm validated the existence of two saturated
carbon atoms (C7a and C1a) in the aziridine ring. In addition, the
single crystal of 1k was obtained from methanol, and single
crystal X-ray diffraction analysis also established the postulated
structures unequivocally (Fig. 1).
ꢀ
under an argon atmosphere at about 20 C (entry 1).
The scope of the substrates
In order to explore the reaction scope, different substituted
substrates 2a–w were irradiated under the optimized reaction
conditions, which generated a structurally divergent 7a-phenyl-
Mechanism of the photoisomerization reaction
1a,7a-dihydro-benzopyrano[2,3-b]azirin-7-ones 1a–w in moderate A proposed mechanism for the formation of 7a-phenyl-
to good yields (Table 2). Obviously, the reaction was practicable 1a,7a-dihydro-benzopyrano[2,3-b]azirin-7-one is depicted in
for substrates bearing either electron-donating or electron- Scheme 4. According to the photochemical characteristics of
Scheme 3 Irradiation of 4-phenyl-5-(2-hydroxyphenyl)isoxazoles.
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Table 1 Optimization for the photoisomerization conditions of 2aa
Entry
Solvent
Time (min)
Yieldb (%)
1
2
3
4
5
6
7
8
EtOH–H2O (1 : 1)
CH2Cl2
Me2CO
MeCN
MeOH
EtOH
MeCN–H2O (1 : 1)
MeOH–H2O (1 : 1)
60
120
120
90
90
90
56
21
28
43
34
39
60
48
Fig. 1 X-ray crystal structure of 1k showing 30% probability ellipsoids.
substituted isoxazoles,16 the rst step of this photo-
isomerization reaction has been suggested to occur through
homolytic cleavage of the labile N–O bond of isoxazole I with the
generation of a diradical II, followed by giving a stable benzylic
radical III, which then forms a 2H-azirine intermediate IV by
coupling with the nitrogen centered radical. Second, an intra-
molecular nucleophilic addition reaction occurs between the
phenolic hydroxyl group (–OH) of IV and the C]N bond of
2H-azirines ring. The N atom of 2H-azirine rst accepts a proton
60
60
a
The intermediate 2a (1 mmol) was dissolved in different solvents (100
mL). The solution was irradiated at l $ 300 nm with a 500 W medium-
pressure mercury lamp under an argon atmosphere at about 20 ꢀC.
b
Yield of isolated product aer column chromatography based on 2a.
Table 2 Synthesis of 7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b]azirin-7-ones (1) via the photoisomerizationa
Entry
Substrate
R1
R2
R3
R4
Product
Time (min)
Yieldb (%)
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
2o
2p
2q
2r
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Br
F
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
H
H
H
H
H
1a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
1q
1r
60
40
50
70
60
70
70
70
50
60
60
70
80
80
90
100
90
90
56
68
75
71
60
72
74
70
73
61
76
72
61
44
35
39
43
46
40
34
41
50
48
i-OPr
i-OPr
i-OPr
OH
OH
OMe
OBz
OMe
H
OMe
OMe
H
H
H
OMe
Me
H
OMe
OMe
OMe
H
OMe
H
Me
Me
H
H
F
F
F
OMe
F
CF3
CF3
CF3
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
H
H
H
H
F
i-OPr
OMe
H
H
H
2s
2t
2u
2v
2w
1s
1t
1u
1v
1w
80
F
120
120
100
100
H
H
H
OMe
i-OPr
a
Conditions: 2 (1 mmol) was irradiated at l $ 300 nm with a 500 W high-pressure mercury lamp in 100 mL EtOH–H2O (1 : 1, v/v) under an argon
atmosphere at about 20 ꢀC until it was consumed completely indicative by TLC. b Isolated yields aer silica chromatography.
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Scheme 4 Proposed mechanism for the photoisomerization of 4-phenyl-5-(2-hydroxyphenyl)isoxazoles.
from the phenolic hydroxyl group to produce an azirine car-
bonium ion V. Next, the phenoxyl anion attacks the carbonium
ion to obtain the target product VI. Compared with the irradi-
ation of 3,4-diaryl-1H-pyrazoles to synthesize 2H-phenanthro
[9,10-c]pyrazoles,18 4-phenyl-5-(2-hydroxyphenyl)isoxazoles have
undergone the photoisomerization to produce the 7a-phenyl-
1a,7a-dihydro-benzopyrano[2,3-b]azirin-7-ones owing to the
labile N–O bonds.
General procedure for synthesis of 7a-phenyl-1a,7a-dihydro-
benzopyrano[2,3-b]azirin-7-one (1a–w)
4-Phenyl-5-(2-hydroxyphenyl)isoxazoles 2a–w (1 mmol) was
dissolved in 50 mL EtOH and 50 mL redistilled water. The
solution was contained in 100 mL quartz tubes, deaerated by
bubbling Ar for 30 min and irradiated at l $ 300 nm with a
500 W medium-pressure mercury lamp, which were cooled to
about 20 ꢀC with tap water by means of an internal cold nger.
The progress of reaction was monitored by TLC at regular
intervals until the intermediate 2a–w has disappeared
completely. Then, the solvent was removed under reduced
pressure, and the residue was puried by column chromatog-
raphy on silica gel using petroleum ether–ethyl acetate to give
the corresponding products (1a–w), and they are characterized
by 1H NMR, 13C NMR, IR and HRMS spectra.
7a-Phenyl-1a,7a-dihydro-benzopyrano[2,3-b]azirin-7-one (1a).
Yield: 56%; yellow solid; m.p. 80.6–81.5 ꢀC. 1H NMR (400 MHz,
DMSO-d6), d (ppm) 4.61 (d, 1H, J ¼ 6.6 Hz), 5.44 (d, 1H, J ¼ 6.6
Hz), 7.09–7.17 (m, 2H), 7.34–7.42 (m, 5H), 7.61 (m, 1H), 7.80 (dd,
1H, J ¼ 7.8, 1.6 Hz); 1H NMR (600 MHz, DMSO-d6 + D2O), d
(ppm) 5.40 (s, 1H), 7.07 (d, 1H, J ¼ 8.4 Hz), 7.12–7.15 (m, 1H),
7.32–7.38 (m, 5H), 7.58–7.61 (m, 1H), 7.76–7.77 (m, 1H); 13C
NMR (100 MHz, DMSO-d6), d (ppm) 48.3, 70.1, 117.8, 119.5,
122.2, 126.8, 128.0, 128.9, 134.1, 135.8, 155.4, 190.1; IR (KBr), n
(cmꢁ1) 3552, 3476, 3415, 1675, 1614, 1465, 1216, 751, 616;
HRMS (m/z): calc. for C15H11NO2 [M + Na]+ 260.0687, found
260.0675.
Conclusions
In summary, a simple and efficient protocol has been developed
for the synthesis of 7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b]
azirin-7-ones via the photoisomerization of 4-phenyl-5-(2-
hydroxyphenyl)isoxazole in EtOH–H2O (1 : 1, v/v) at l $ 300
nm with a 500 W medium-pressure mercury lamp. This method
offers several notable advantages including the operational
simplicity, mild reaction conditions, moderate to high yields
and friendly to environment. The formation of 7a-phenyl-
1a,7a-dihydro-benzopyrano[2,3-b]azirin-7-one involves a photo-
catalyzed ring opening of isoxazole and subsequent intra-
molecular nucleophilic addition between 2H-azirine interme-
diate and phenolic hydroxyl group.
Experimental sections
4-Isopropoxy-7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b]azirin-
7-one (1b). Yield: 68%; white solid; m.p. 123.8–124.7 ꢀC. 1H NMR
(300 MHz, DMSO-d6), d (ppm) 1.29 (d, 6H, J ¼ 6.0 Hz), 4.59 (d,
1H, J ¼ 6.6 Hz), 4.75 (m, 1H), 5.39 (d, 1H, J ¼ 6.6 Hz), 6.58 (d, 1H,
J ¼ 2.1 Hz), 6.71 (dd, 1H, J ¼ 8.8, 2.1 Hz), 7.36–7.40 (m, 5H), 7.73
(d, 1H, J ¼ 8.8 Hz); 1H NMR (400 MHz, DMSO-d6 + D2O), d (ppm)
1.25 (d, 6H, J ¼ 6.0 Hz), 4.67 (m, 1H), 5.35 (s, 1H), 6.52–6.54 (m,
1H), 6.67–6.69 (m, 1H), 7.33–7.36 (m, 5H), 7.69–7.71 (m, 1H);
13C NMR (100 MHz, DMSO-d6), d (ppm) 21.6, 47.3, 70.1, 70.5,
102.2, 111.3, 112.5, 127.9, 128.0, 128.6, 128.8, 134.5, 157.5,
163.7, 188.6; IR (KBr), n (cmꢁ1) 3473, 3250, 2978, 1651, 1617,
1444, 1381, 1297, 1246, 1113, 946, 853, 768, 691, 611; HRMS
(m/z) calc. for C18H17NO3 [M + H]+ 296.1287, found 296.1286.
Melting points were measured by a X-5 micromelting point
apparatus and are uncorrected. NMR spectra were recorded on a
Bruker AM 300, 400 or 600 instrument using TMS as internal
standard and DMSO-d6 as solvent. High resolution mass spec-
trometry (HRMS) were recorded using electron-spray ionization
(ESI) technique and IR spectra were recorded on a Nicollet
170SX FT-IR spectrophotometer with KBr pellets. The crystal
diffraction data were collected on a Bruker Smart-1000 CCD
diffractometer. All the irradiation experiments were performed
in a BL-GHX-V photochemical reactor equipped with a 500 W
medium-pressure mercury lamp. TLC was performed on silica
gel 60-GF254 plate. The silica gel (size 200–300 mesh) used for
the column chromatography was purchased from Qingdao
Haiyang Chemistry Plant (China).
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ꢀC. 1H NMR (400 MHz, DMSO-d6), d (ppm) 3.77 (s, 3H), 4.41 (d, J ¼
6.8 Hz, 1H), 5.20 (s, 2H), 5.39 (d, J ¼ 6.8 Hz, 1H), 6.69 (d, J ¼ 2.1
Hz, 1H), 6.80–6.82 (m, 1H), 6.93–6.95 (m, 2H), 7.32–7.37 (m, 3H),
7.39–7.47 (m, 4H), 7.74 (m, 1H); 13C NMR (100 MHz, DMSO-d6), d
(ppm) 47.0, 55.1, 69.7, 70.5, 101.9, 110.0, 113.0, 113.4, 126.3,
127.8, 128.1, 128.5, 128.6, 130.1, 136.2, 157.4, 158.9, 164.3, 189.0;
IR (KBr), n (cmꢁ1) 3553, 3476, 3414, 3272, 2926, 1612, 1510, 1444,
1244, 1171, 1026, 835, 624; HRMS (ESI) calc. for C23H19NO4 [M +
H]+ 374.1392, found 374.1370.
4-Methoxy-7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b]azirin-
7-one (1i). Yield: 73%; yellow solid; m.p. 103.0–104.1 ꢀC. 1H NMR
(400 MHz, DMSO-d6), d (ppm) 3.84 (s, 3H), 4.51 (d, J ¼ 6.4 Hz, 1H),
5.42 (d, J ¼ 6.4 Hz, 1H), 6.62 (d, J ¼ 2.1 Hz, 1H), 6.75 (dd, J ¼ 8.8,
2.1 Hz, 1H), 7.36–7.41 (m, 5H), 7.76 (d, J ¼ 8.8 Hz, 1H); 13C NMR
(100 MHz, DMSO-d6), d (ppm) 47.4, 55.8, 70.5, 100.9, 110.5, 112.8,
127.9, 128.0, 128.5, 128.8, 134.4, 157.5, 165.4, 188.7; IR (KBr),
n (cmꢁ1) 3633, 3213, 1656, 1609, 1572, 1493, 1440, 1285, 1244,
1187, 1024, 839, 587; HRMS (ESI) calc. for C16H13NO3 [M + H]+
268.0974, found 268.0974.
4-Isopropoxy-7a-(4-methoxyphenyl)-1a,7a-dihydro-benzo-
pyrano[2,3-b]azirin-7-one (1c). Yield: 75%; yellow solid; m.p.
1
ꢀ
128.3–128.8 C. H NMR (400 MHz, DMSO-d6), d (ppm) 1.29 (d,
6H, J ¼ 6.0 Hz), 3.77 (s, 3H), 4.39 (d, J ¼ 6.8 Hz, 1H), 4.74 (m, 1H),
5.38 (d, J ¼ 6.8 Hz, 1H), 6.57 (d, J ¼ 2.0 Hz, 1H), 6.70 (dd, J ¼ 8.8,
2.0 Hz, 1H), 6.94 (d, J ¼ 8.8 Hz, 2H), 6.94 (d, J ¼ 8.8 Hz, 2H),
7.72 (d, J ¼ 8.8 Hz, 1H); 13C NMR (100 MHz, DMSO-d6), d (ppm)
21.6, 46.9, 55.1, 70.1, 70.5, 102.1, 111.2, 112.6, 113.4, 126.4, 128.6,
130.1, 157.5, 158.9, 163.6, 188.8; IR (KBr), n (cmꢁ1) 3553, 3477,
3415, 3265, 2977, 1649, 1613, 1515, 1448, 1292, 1246, 1188, 1115,
1028, 947, 825, 748, 624; HRMS (ESI) calc. for C19H19NO4 [M + H]+
326.1392, found 326.1379.
4-Isopropoxy-7a-(4-methylphenyl)-1a,7a-dihydro-benzo-
pyrano[2,3-b]azirin-7-one (1d). Yield: 71%; white solid; m.p.
156.2–157.1 ꢀC. 1H NMR (400 MHz, DMSO-d6), d (ppm) 1.29 (d,
6H, J ¼ 6.0 Hz), 2.32 (s, 3H), 4.43 (d, J ¼ 6.0 Hz, 1H), 4.74 (m,
1H), 5.35 (d, J ¼ 6.0 Hz, 1H), 6.58 (s, 1H), 6.70 (d, J ¼ 8.8, 1H),
7.19 (d, J ¼ 6.8 Hz, 2H), 7.28–7.30 (m, 2H), 7.72–7.74 (m, 1H);
13C NMR (100 MHz, DMSO-d6), d (ppm) 20.7, 21.6, 47.1, 70.1,
70.5, 102.2, 111.3, 112.6, 128.5, 128.6, 128.7, 131.5, 137.1, 157.5,
163.7, 188.7; IR (KBr), n (cmꢁ1) 3447, 3271, 2978, 2025, 1652,
1613, 1443, 1388, 1247, 1188, 1110, 854, 752, 642; HRMS (ESI)
calc. for C19H19NO3 [M + Na]+ 332.1263, found 332.1245.
4-Hydroxy-7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b]azirin-
7a-(4-Methoxyphenyl)-1a,7a-dihydro-benzopyrano[2,3-b]azirin-
1
ꢀ
7-one (1j). Yield: 61%; yellow solid; m.p. 83.8–84.9 C. H NMR
(400 MHz, DMSO-d6), d (ppm) 3.77 (s, 3H), 4.53 (d, J ¼ 6.4 Hz, 1H),
5.44 (d, J ¼ 6.4 Hz, 1H), 6.94–6.96 (m, 2H), 7.09–7.18 (m, 2H), 7.35
(d, J ¼ 8.8 Hz, 2H), 7.61–7.64 (m, 1H), 7.80–7.82 (m, 1H); 13C NMR
(100 MHz, DMSO-d6), d (ppm) 47.9, 55.1, 70.2, 113.5, 117.8, 119.5,
122.2, 126.1, 126.8, 130.2, 135.7, 155.4, 159.0, 190.3; IR (KBr), n
(cmꢁ1) 3552, 3476, 3415, 2922, 1617, 1517, 1464, 1292, 1250, 1027,
825, 752, 623; HRMS (ESI) calc. for C16H13NO3 [M + Na]+ 290.0793,
found 290.0781.
1
ꢀ
7-one (1e). Yield: 60%; white solid; m.p. 81.3–82.1 C. H NMR
(600 MHz, DMSO-d6), d (ppm) 4.38 (d, J ¼ 6.0 Hz, 1H), 5.38 (d, J ¼
6.0 Hz, 1H), 6.33 (s, 1H), 6.54 (d, J ¼ 9.0 Hz, 1H), 7.29–7.34 (m,
5H), 7.62–7.64 (m, 1H); 13C NMR (150 MHz, DMSO-d6), d (ppm)
47.7, 70.9, 102.9, 111.8, 112.3, 128.3, 128.4, 129.3, 129.4, 135.2,
158.0, 164.9, 188.9; IR (KBr), n (cmꢁ1) 3522, 3444, 3280, 2025,
1679, 1626, 1515, 1484, 1443, 1400, 1265, 1219, 1159, 995, 740,
565; HRMS (ESI) calc. for C15H11NO3 [M + Na]+ 276.0637, found
276.0616.
4-Methoxy-6-methyl-7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-
b]azirin-7-one (1k). Yield: 76%; yellow solid; m.p. 132.1–132.9 ꢀC.
1H NMR (400 MHz, DMSO-d6), d (ppm) 2.51 (s, 3H), 3.81 (s, 3H),
4.37 (d, J ¼ 6.4 Hz, 1H), 5.40 (d, J ¼ 6.4 Hz, 1H), 6.47–6.56 (m, 2H),
7.35–7.40 (m, 5H); 13C NMR (100 MHz, DMSO-d6), d (ppm) 22.0,
49.6, 55.6, 69.7, 99.5, 112.5, 112.9, 127.8, 127.9, 129.1, 134.7, 142.6,
158.4, 163.5, 190.6; IR (KBr), n (cmꢁ1) 3479, 3247, 3056, 2924, 1665,
1610, 1573, 1446, 1356, 1281, 1245, 1205, 1142, 1045, 885, 840, 751,
698, 594; HRMS (ESI) calc. for C17H15NO3 [M + H]+ 282.1130, found
282.1131.
4-Hydroxy-7a-(4-methoxyphenyl)-1a,7a-dihydro-benzopyrano
[2,3-b]azirin-7-one (1f). Yield: 72%; yellow solid; m.p. 109.8–
1
ꢀ
110.7 C. H NMR (400 MHz, DMSO-d6), d (ppm) 3.76 (s, 3H),
4.30 (d, J ¼ 6.8 Hz, 1H), 5.32 (d, J ¼ 6.8 Hz, 1H), 6.37 (d, J ¼ 2.1
Hz, 1H), 6.58 (dd, J ¼ 8.8, 2.1 Hz, 1H), 6.93 (d, J ¼ 8.8 Hz, 2H),
7.31 (d, J ¼ 8.8 Hz, 2H), 7.66–7.68 (m, 1H); 13C NMR (100 MHz,
DMSO-d6), d (ppm) 46.8, 55.1, 70.4, 102.4, 111.2, 111.8, 113.4,
4-Methoxy-7a-(4-methylphenyl)-1a,7a-dihydro-benzopyrano
[2,3-b]azirin-7-one (1l). Yield: 72%; yellow solid; m.p. 135.7–
126.6, 128.9, 130.1, 157.5, 158.9, 164.3, 188.7; IR (KBr), n (cmꢁ1
)
1
ꢀ
136.5 C. H NMR (400 MHz, DMSO-d6), d (ppm) 2.32 (s, 3H),
3.84 (s, 3H), 4.46 (d, J ¼ 6.0 Hz, 1H), 5.38 (d, J ¼ 6.0 Hz, 1H),
6.61 (s, 1H), 6.73–6.75 (m, 1H), 7.18 (d, J ¼ 8.8 Hz, 2H), 7.28–
7.30 (m, 2H), 7.75 (dd, J ¼ 8.8, 2.1 Hz, 1H); 13C NMR (100 MHz,
DMSO-d6), d (ppm) 20.7, 47.2, 55.8, 70.5, 101.0.110.4, 112.9,
3553, 3477, 3415, 3239, 2929, 2361, 1616, 1254, 622, 483; HRMS
(ESI) calc. for C16H13NO4 [M + H]+ 284.0923, found 284.0909.
4-Methoxy-7a-(4-methoxyphenyl)-1a,7a-dihydro-benzopyrano
[2,3-b]azirin-7-one (1g). Yield: 74%; yellow solid; m.p. 142.7–
1
ꢀ
143.9 C. H NMR (400 MHz, DMSO-d6), d (ppm) 3.77 (s, 3H),
3.84 (s, 3H), 4.40 (d, J ¼ 6.8 Hz, 1H), 5.40 (d, J ¼ 6.8 Hz, 1H),
6.60 (d, J ¼ 2.1 Hz, 1H), 6.94 (d, J ¼ 8.8 Hz, 2H), 7.32 (dd, J ¼ 8.8,
2.1 Hz, 2H) 7.74 (d, J ¼ 8.8 Hz, 2H); 13C NMR (100 MHz, DMSO-
d6), d (ppm) 47.0, 55.1, 55.8, 70.5, 100.9, 110.4, 112.8, 113.4,
128.5, 128.7, 131.4, 137.2, 157.5, 165.3, 188.8; IR (KBr), n (cmꢁ1
)
3520, 3443, 3278, 2930, 2025, 1670, 1609, 1513, 1443, 1386,
1245, 1189, 1107, 836, 570; HRMS (ESI) calc. for C17H15NO3 [M
+ Na]+ 304.0950, found 304.0934.
7a-(4-Methylphenyl)-1a,7a-dihydro-benzopyrano[2,3-b]azirin-
7-one (1m). Yield: 61%; yellow solid; m.p. 83.8–84.9 ꢀC. 1H NMR
(400 MHz, DMSO-d6), d (ppm) 2.32 (s, 3H), 4.58 (d, J ¼ 6.4 Hz,
1H), 5.43 (d, J ¼ 6.4 Hz, 1H), 7.10–7.21 (m, 4H), 7.30–7.32 (m,
2H), 7.61–7.65 (m, 1H), 7.82 (d, J ¼ 8.0 Hz, 1H); 13C NMR
(100 MHz, DMSO-d6), d (ppm) 20.7, 48.1, 70.2, 117.8, 119.5,
122.2, 126.8, 128.6, 128.8, 131.1, 135.7, 137.3, 155.4, 190.2; IR
126.4, 128.5, 130.1, 157.5, 158.9, 165.3, 189.0; IR (KBr), n (cmꢁ1
)
3552, 3476, 3415, 3239, 2926, 2361, 1723, 1617, 1515, 1439, 1247,
1024, 838, 624, 482; HRMS (ESI) calc. for C17H15NO4 [M + Na]+
320.0899, found 320.0880.
4-Benzyloxy-7a-(4-methoxyphenyl)-1a,7a-dihydro-benzopyrano
[2,3-b]azirin-7-one (1h). Yield: 70%; yellow solid; m.p. 101.8–102.7
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(KBr), n (cmꢁ1) 3552, 3415, 3240, 2027, 1616, 1517, 1464, 1395, Hz), 165.4, 188.6; IR (KBr), n (cmꢁ1) 3444, 3255, 2025, 1663,
1285, 1215, 1143, 986, 812, 752, 6; HRMS (ESI) calc. for 1613, 1513, 1440, 1403, 1246, 1155, 1101, 1031, 831, 767, 679,
C16H13NO2 [M + H]+ 252.1025, found 252.1013.
569; HRMS (ESI) calc. for C16H12FNO3 [M + Na]+ 308.0699,
5-Bromo-7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b]azirin- found 308.0687.
7-one (1n). Yield: 44%; yellow solid; m.p. 56.5–57.3 ꢀC. 1H NMR
4-Fluoro-7a-(4-methoxyphenyl)-1a,7a-dihydro-benzopyrano
(400 MHz, DMSO-d6), d (ppm) 4.85 (d, J ¼ 6.4 Hz, 1H), 5.52 (d, J ¼ [2,3-b]azirin-7-one (1s). Yield: 40%; yellow solid; m.p. 57.9–58.2
6.4 Hz, 1H), 7.13 (d, J ¼ 8.8 Hz, 1H), 7.37–7.45 (m, 5H), 7.79 (dd, J ꢀC. 1H NMR (600 MHz, DMSO-d6), d (ppm) 3.76 (s, 3H), 4.60 (d, J ¼
¼ 8.8, 2.1 Hz, 1H), 7.88 (d, J ¼ 2.50 Hz, 1H); 13C NMR (100 MHz, 6.6 Hz, 1H), 5.45 (d, J ¼ 6.6 Hz, 1H), 6.93–6.94 (m, 2H), 7.15–7.18
DMSO-d6), d (ppm) 48.2, 70.4, 113.8, 120.6, 121.2, 128.0, 128.1, (m, 1H), 7.33–7.34 (m, 2H), 7.48–7.51 (m, 2H); 13C NMR (150 MHz,
128.8, 128.9, 133.6, 138.1, 154.5, 189.0; IR (KBr), n (cmꢁ1) 3555, DMSO-d6), d (ppm) 48.1, 55.6, 70.9, 112.2 (d, 2J ¼ 23.7 Hz), 114.0,
3479, 3414, 3274, 3060, 2922, 2360, 1678, 1597, 1468, 1420, 1262, 120.5 (d, 3J ¼ 7.6 Hz), 120.8 (d, 3J ¼ 6.5 Hz), 123.6 (d, 2J ¼ 24.3 Hz),
1219, 1184, 1126, 982, 817, 746, 694, 587, 501; HRMS (ESI) calc. 126.3, 130.7, 152.2, 157.5 (d, 1J ¼ 238.4 Hz), 159.6, 190.2; IR (KBr),
for C15H10BrNO2 [M + H]+ 315.9973, found 315.9960.
n (cmꢁ1) 3520, 3443, 3279, 2930, 2026, 1670, 1609, 1513, 1443,
10-Fluoro-7a-phenyl-1a,7a-dihydro-benzopyrano[2,3-b]azirin- 1387, 1244, 1189, 1106, 1018, 836, 769, 681, 570; HRMS (ESI) calc.
7-one (1o). Yield: 35%; yellow solid; m.p. 78.9–80.2 ꢀC. 1H NMR for C16H12FNO3 [M + Na]+ 308.0699, found 308.0684.
(400 MHz, DMSO-d6), d (ppm) 4.73 (d, J ¼ 6.8 Hz, 1H), 5.50 (d, J ¼
4-Fluoro-7a-(4-uorophenyl)-1a,7a-dihydro-benzopyrano[2,3-
6.8 Hz, 1H), 7.21–7.22 (m, 1H), 7.39–7.44 (m, 5H), 7.51–7.53 (m, b]azirin-7-one (1t). Yield: 34%; yellow solid; m.p. 139.5–140.1 ꢀC.
2H); 1H NMR (400 MHz, DMSO-d6 + D2O), d (ppm) 5.46 (s, 1H), 1H NMR (600 MHz, DMSO-d6), d (ppm) 4.72 (d, J ¼ 6.60 Hz, 1H),
7.15–7.19 (m, 1H), 7.36–7.40 (m, 5H), 7.47–7.52 (m, 2H); 13C 5.49 (d, J ¼ 6.60 Hz, 1H), 7.17–7.22 (m, 3H), 7.48–7.53 (m, 4H);
NMR (100 MHz, DMSO-d6), d (ppm) 48.1, 70.3, 111.7 (d, 2J ¼ 23.6 13C NMR (150 MHz, DMSO-d6), d (ppm) 47.9, 70.8, 112.2 (d, 2J ¼
3
2
Hz), 120.0, 120.1, 120.3 (d, J ¼ 6.6 Hz), 123.2 (d, J ¼ 24.2 Hz), 23.7 Hz), 115.3 (d, 2J ¼ 21.3 Hz), 120.5 (d, 3J ¼ 7.6 Hz), 120.7 (d, 3J
128.1 (d, 3J ¼ 5.8 Hz), 128.9, 133.8, 151.7, 157.0 (d, 1J ¼ 238.4 Hz), ¼ 6.9 Hz), 123.7 (d, J ¼ 24.3 Hz), 130.6, 131.6 (d, J ¼ 8.5 Hz),
189.5; IR (KBr), n (cmꢁ1) 3479, 3412, 3298, 3080, 1675, 1624, 152.1, 157.5 (d, 1J ¼ 238.5 Hz), 162.4 (d, 1J ¼ 243.5 Hz), 189.8; IR
1483, 1441, 1345, 1264, 1212, 1161, 1125, 1041, 990, 942, 822, (KBr), n (cmꢁ1) 3612, 3522, 3444, 3281, 2025, 1679, 1626, 1604,
744, 699, 612; HRMS (ESI) calc. for C15H10FNO2 [M + H]+ 1516, 1484, 1402, 1265, 1219, 1159, 1126, 995, 829, 763, 740, 700,
2
3
256.0774, found 256.0765.
565; HRMS (ESI) calc. for C15H9F2NO2 [M + Na]+ 296.0499, found
7a-(4-Fluorophenyl)-1a,7a-dihydro-benzopyrano[2,3-b]azirin-7- 296.0482.
1
ꢀ
one (1p). Yield: 39%; yellow solid; m.p. 104.0–104.9 C. H NMR
7a-(4-Triuoromethylphenyl)-1a,7a-dihydro-benzopyrano[2,3-
(400 MHz, DMSO-d6), d (ppm) 4.65 (d, J ¼ 6.8 Hz, 1H), 5.48 (d, J ¼ b]azirin-7-one (1u). Yield: 41%; yellow solid. m.p. 106.1–107.0 ꢀC.
6.8 Hz, 1H), 7.11–7.25 (m, 4H), 7.47–7.51 (m, 2H), 7.62–7.66 (m, 1H NMR (400 MHz, DMSO-d6), d (ppm) 4.82 (d, J ¼ 6.6 Hz, 1H),
1H), 7.81–7.83 (m, 1H); 13C NMR (100 MHz, DMSO-d6), d (ppm) 5.51 (d, J ¼ 6.6 Hz, 1H) 7.13–7.21 (m, 2H), 7.64–7.70 (m, 3H), 7.77
47.7, 70.1, 114.9 (d, 2J ¼ 21.3 Hz), 117.8, 119.4, 122.3, 126.8, 130.4, (d, J ¼ 8.4 Hz, 2H), 7.84 (dd, J ¼ 8.0, 2.1 Hz, 1H); 13C NMR
131.1 (d, 3J ¼ 8.4 Hz), 135.8, 155.4, 161.8 (d, 1J ¼ 242.9 Hz), 189.9; (150 MHz, DMSO-d6), d (ppm) 47.8, 70.1, 117.9, 119.3, 122.4,
IR (KBr), n (cmꢁ1) 3553, 3477, 3414, 3293, 3044, 1662, 1613, 1509, 124.2 (q, 1J ¼ 270.6 Hz), 124.8 (q, 3J ¼ 3.8 Hz), 126.9, 128.5 (q, 2J ¼
1470, 1292, 1218, 1155, 1104, 1012, 899, 812, 747, 622; HRMS (ESI) 31.5 Hz), 129.8, 136.0, 138.7, 155.3, 189.5; IR (KBr), n (cmꢁ1) 3669,
calc. for C15H10FNO2 [M + Na]+ 278.0593, found 278.0580.
3284, 3072, 1671, 1610, 1470, 1413, 1331, 1296, 1219, 1164, 1113,
1067, 1010, 903, 858, 815, 752; HRMS (ESI) calc. for C16H10F3NO2
4-Isopropoxy-7a-(4-uorophenyl)-1a,7a-dihydro-benzo-
pyrano[2,3-b]azirin-7-one (1q). Yield: 43%; yellow solid. [M + Na]+ 328.0561, found 328.0549.
m.p. 98.8–99.5 ꢀC. 1H NMR (400 MHz, DMSO-d6), d (ppm)
4-Methoxy-(4-triuoromethylphenyl)-1a,7a-dihydro-benzo-
1.29 (d, 6H, J ¼ 6.0 Hz), 4.52 (d, J ¼ 6.0 Hz, 1H), 4.75 (m, 1H), pyrano[2,3-b]azirin-7-one (1v). Yield: 50%; yellow solid; m.p.
1
ꢀ
5.41 (d, J ¼ 6.0 Hz, 1H), 6.59 (s, 1H), 6.70–6.72 (m, 1H), 7.19– 132.3–133.2 C. H NMR (400 MHz, DMSO-d6), d (ppm) 3.85 (s,
7.24 (m, 2H), 7.45–7.48 (m, 2H), 7.73 (dd, J ¼ 8.8, 2.4 Hz, 3H), 4.72 (d, J ¼ 6.6 Hz, 1H), 5.47 (d, J ¼ 6.6 Hz, 1H), 6.65 (d, J ¼
1H); 13C NMR (100 MHz, DMSO-d6), d (ppm) 21.6, 46.7, 70.1, 2.4 Hz, 1H), 6.76 (dd, J ¼ 8.4, 2.4 Hz, 1H), 7.68 (d, J ¼ 8.4 Hz, 2H),
70.4, 102.2, 111.3, 112.4, 114.8 (d, 2J ¼ 21.3 Hz), 128.6, 7.74–7.78 (m, 3H); 13C NMR (100 MHz, DMSO-d6), d (ppm) 46.9,
3
1
130.7, 131.1 (d, J ¼ 8.3 Hz), 157.5, 161.7 (d, J ¼ 242.8 Hz), 55.9, 70.5, 101.0, 110.7, 112.6, 124.2 (q, 1J ¼ 270.5 Hz), 124.7 (q, 3J
163.7, 188.4; IR (KBr), n (cmꢁ1) 3520, 3443, 3277, 2930, 2025, ¼ 3.7 Hz), 128.5 (q, 2J ¼ 31.6 Hz), 128.9, 129.8, 139.1, 157.5, 165.5,
1670, 1609, 1514, 1443, 1385, 1245, 1189, 1159, 1110, 1017, 188.1; IR (KBr), n (cmꢁ1) 3553, 3476, 3414, 3238, 2361, 1616, 1440,
836, 769, 680, 570; HRMS (ESI) calc. for C18H16FNO3 [M + 1325, 1247, 1171, 1134, 1065, 1022, 869, 832, 620, 482; HRMS
Na]+ 336.1012, found 336.0989.
(ESI) calc. for C17H12F3NO3 [M + Na]+ 358.0667, found 358.0650.
4-Methoxy-7a-(4-uorophenyl)-1a,7a-dihydro-benzopyrano
4-Isopropoxy-(4-triuoromethylphenyl)-1a,7a-dihydro-ben-
[2,3-b]azirin-7-one (1r). Yield: 46%; yellow solid; m.p. 112.8– zopyrano[2,3-b]azirin-7-one (1w). Yield: 48%; yellow solid;
1
1
ꢀ
ꢀ
113.1 C. H NMR (400 MHz, DMSO-d6), d (ppm) 3.84 (s, 3H), m.p. 107.5–108.9 C. H NMR (600 MHz, DMSO-d6), d (ppm)
4.54 (d, J ¼ 6.0 Hz, 1H), 5.44 (d, J ¼ 6.0 Hz, 1H), 6.63 (s, 1H), 1.29 (d, 6H, J ¼ 6.0 Hz), 4.69 (d, J ¼ 6.8 Hz, 1H), 4.76 (m, 1H),
6.74–6.76 (m, 1H), 7.19–7.24 (m, 2H), 7.46–7.49 (m, 2H), 5.44 (d, J ¼ 6.8 Hz, 1H), 6.61 (d, J ¼ 2.4 Hz, 1H), 6.73 (dd, J ¼
7.74–7.77 (m, 1H); 13C NMR (100 MHz, DMSO-d6), d (ppm) 8.4, 2.4 Hz, 1H), 7.66 (d, J ¼ 8.4 Hz, 2H), 7.74–7.76 (m, 3H); 13
C
46.8, 55.8, 70.4, 101.0, 110.5, 112.7, 114.8 (d, 2J ¼ 21.4 Hz), NMR (150 MHz, DMSO-d6), d (ppm) 21.5, 46.8, 70.1, 70.5,
3
1
1
3
128.6, 130.7, 131.1 (d, J ¼ 8.4 Hz), 157.5, 161.8 (d, J ¼ 242.7 102.2, 111.5, 112.3, 124.2 (q, J ¼ 270.6 Hz), 124.7 (q, J ¼ 3.6
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2
Hz), 128.4 (q, J ¼ 31.6 Hz), 129.8, 139.1, 128.7, 157.5, 163.9,
188.0; IR (KBr), n (cmꢁ1) 3553, 3477, 3415, 3290, 2986, 1654,
1617, 1572, 1500, 1445, 1331, 1279, 1248, 1165, 1113, 1066,
1015, 925, 856, 816, 610, 484; HRMS (ESI) calc. for
S. P. Smith, J. Org. Chem., 1977, 42, 3317; (d) F. Nakatsubo,
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and T. Nakashima, J. Antibiot., 1986, 39, 1527; (b) K. Yokoi,
K. Nagaoka and T. Nakashima, Chem. Pharm. Bull., 1986,
34, 4554; (c) S. Ishizeki, M. Ohtsuka, K. Irinoda, K. Kukita,
K. Nagaoka and T. Nakashima, J. Antibiot., 1987, 40, 60.
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F. Reusser, Biochemistry, 1977, 16, 3406.
C
19H19F3NO3 [M + H]+ 364.1161, found 364.1147.
Acknowledgements
We are grateful for the nancial support from the National
Natural Science Foundation of China (no. 21372150), the
Fundamental Funds Research for the Central Universities
(no. GK261001095) and Innovation Funds of Graduate
Programs of Shaanxi Normal University (no. 2012 CXB016) for
nancial support of this research.
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