Synthesis of dibenzo[e,g]isoindol-1-ones via photoinduced intramolecular annulation of 3,4-diphenyl-1H-pyrrol-2(5H)-ones

Article abstract of DOI:10.1016/j.tet.2021.131981

An efficient, oxidant and photocatalyst-free approach for the synthesis of polycyclic-fused isoindolinone derivatives is reported via annulation of 3,4-diphenyl-3-pyrrolin-2-ones along with release of the hydrogen gas under an argon atmosphere in EtOH by

Full text of DOI:10.1016/j.tet.2021.131981

Tetrahedron 84 (2021) 131981
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Tetrahedron
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Synthesis of dibenzo[e,g]isoindol-1-ones via photoinduced
intramolecular annulation of 3,4-diphenyl-1H-pyrrol-2(5H)-ones
Yang Kang, Yun He, Jingzhi Sui, Tao Wang, Yong Liang 1, Zunting Zhang*
Key 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, And School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an,
710119, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient, oxidant and photocatalyst-free approach for the synthesis of polycyclic-fused isoindolinone
derivatives is reported via annulation of 3,4-diphenyl-3-pyrrolin-2-ones along with release of the
hydrogen gas under an argon atmosphere in EtOH by irradiation with a 500 W mercury lamp at room
temperature. The described approach is atom-economic and environmentally friendly and tolerates
various electron-donating and electron-withdrawing groups. In addition, selected annulation products,
dibenzo[e,g]isoindole-1-ones, were successfully oxidized into dibenzo[e,g]isoindole-1,3(2H)- diones in
DMSO in the presence of CH3ONa at room temperature.
Received 21 November 2020
Received in revised form
9 January 2021
Accepted 24 January 2021
Available online 15 February 2021
Keywords:
Dibenzo[e,g]isoindole-1-ones
Photoinduced
© 2021 Elsevier Ltd. All rights reserved.
Hydrogen evolution
Photocatalyst-free
1. Introduction
two methoxy groups are required as the electron-donating group at
each of the aromatic rings (Scheme 1a) [8]. Later, the same condi-
Isoindolinones are an important class of nitrogen heterocycles
and their derivatives are in some bioactive natural products and
drug molecules [1]. Selected isoindolinone derivatives with certain
biological activities are shown in Fig. 1. For instance, indoprofen
serves as an anti-inflammatory agent [2]. Chlortalidone was used as
a diuretic and antihypertensive prescription drug [3]. Indolo-
tions were used to synthesize benzo[a]carbazoles and indolo[2,3-a]
carbazole analogues by Pelkey’s group, which eliminated the
requirement of methoxy group, but indoles are still electron-rich
and nucleophilic [9]. Regarding to the Pelkey’s work for the syn-
thesis of dibenzo[e,g]isoindol-1-ones, the reaction generally re-
quires not only the electron-rich arenes, but also the position of
methoxy group is critical.
€
carbazole analogue Go6976 has been employed in selective PKC
Photochemical reactions have become an important tool for
organic chemists. The photons have been recognized as an ideal
clean reagent for organic synthesis comparing to toxic chemical
activators [10]. Polycyclic aromatic hydrocarbons (PAHs) could be
easily achieved with the photochemical reactions, whereas, it
would be difficult to access with traditional chemical conditions
[11e13]. Furthermore, milder reaction condition, broad functional
group could be tolerated, and high atom efficiency are other ad-
vantages of photochemical reactions to thermochemical reactions
[14,15].
Given our interest in the development of transition-metal and/
or additive-free photoinduced intramolecular dehydrogenative
cyclization of 2,3-diaryl-4H-chromen-4-ones and 3,4-diarylfuran-
2(5H)-ones for the synthesis of oxygen heterocycles [16,17], we
would like to describe the synthesis of dibenzo[e,g]isoindol-1-ones
with good functional group tolerance via the annulation of 3,4-
inhibitor and HIV-1 antagonist [4]. Moreover, heterocyclic fused
isoindolinones have also been reported and pyrrolocarbazole
(X ¼ NH; Y]S) was found to be a potent inhibitor of mixed-lineage
kinases (MLK1/3) [5].
Although, plenty of approaches have been reported for the
preparation of isoindolinones [6], there is only a small number of
known reports discussing the synthesis of dibenzo[e,g]isoindol-1-
one [7]. Dibenzo[e,g]isoindol-1-one derivatives were obtained by
the Scholl-type oxidative cyclization reaction in the presence of
PhI(O2CCF3)2 and BF3ꢀEt2O at ꢁ40 ꢂC for 4 h. However, the annu-
lation is limited to arenes contanining methoxy group, since at least
* Corresponding author.
E-mail address: zhangzunting@sina.com (Z. Zhang).
Present Address: Department of Molecular Medicine, Beckman Research Insti-
1
tute of City of Hope, Duarte, California 91,010, United States (Y.L.).
https://doi.org/10.1016/j.tet.2021.131981
0040-4020/© 2021 Elsevier Ltd. All rights reserved.

Y. Kang, Y. He, J. Sui et al.
Tetrahedron 84 (2021) 131981
Fig. 1. Biologically active isoindolinone derivatives.
Table 1
Optimization of intramolecular cyclization of 2aa.
entry
conc. (mM)
solvent (v/v)
time (h)
yield (%)b
1
2
3
4
5
6
7
8
10
10
10
10
10
10
5
15
10
10
10
Me2CO
DMF
6
6
6
6
6
6
6
6
4
8
6
21
N.D.
N.D.
trace
37
61
54
Toluene
CH2Cl2
MeOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
49
50
9
10
11
58
46c
a
2a (35.3 mg, 0.150 mmol) was irradiated with a 500 W high-pressure mercury
lamp in various solvents at room temperature under an Ar atmosphere. N.D.: not
detected.
b
Isolated yield.
Open air.
Scheme 1. Synthetic approaches to polycyclic-fused isoindolinones.
c
diphenyl-3-pyrrolin-2-ones in EtOH at room temperature (Scheme
1c), which avoids usage of any oxidant and photocatalyst. Most
importantly, the described method overcomes the shortcoming of
Scholl-type oxidative cyclization reactions [8,9], since the presence
of methoxy groups is not required.
irradiation of 2a in EtOH (10 mM) at room temperature for 6 h was
determined to be the optimal condition. The results of detecting the
hydrogen and emission spectrum of the 500 W high-pressure
mercury lamp are shown in the Support Information (SI,
Figures S3-5).
With the optimized conditions in hand, generality of the
annulation was examined and the yields of 3 are summarized in
Table 2. It was found that no significant substituent effect was
observed for the substrates (3a-3h) bearing either electron-
withdrawing groups (e.g., F, CN) or electron-donating groups (e.g.,
Me, OMe), since the yields of annulation products are close (57%e
67%). Naphthalene and N-methyl substituted substrate were also
subjected to the optimal condition and 3i-3k, 3af were also ob-
tained in similar yields (51e60%). Moreover, thiophenyl and furanyl
substituted substrate also gave desired products (3l-3m) in mod-
erate yields (52%, 71%) with only half of the irradiation time (3 h),
which is likely due to the higher activity of heteroaromatics. Finally,
irradiation of the N-acetyl-substituted substrates (1a, 1b, 1g, 1e, 1l)
also yielded the annulation products (3aa-3ae) but with slightly
higher yields (64e78%) in significant shortened time (1h), which
could be explained by the presence of an acetyl on the nitrogen
atom. The structures of annulation products 3 were characterized
by 1H NMR, 13C NMR, 19F NMR, HRMS and IR.
2. Results and discussion
Substrate 1-acetyl-3,4-diphenyl-1,5-dihydropyrrol-2-one (1a)
and 3,4-diphenyl-3-pyrrolin- 2-one (2a) were synthesized ac-
cording to the literature report [18]. Irradiation of 3,4-diphenyl-3-
pyrrolin-2-one 2a in various solvents under different conditions
was performed and corresponding data are presented in Table 1.
Initially, irradiation of 2a in Me2CO (15 mL) with a 500 W high-
pressure mercury lamp at ambient temperature under an argon
atmosphere for 6 h gave annulation product 3a in 21% (Table 1,
entry 1). Replacement of Me2CO with other aprotic solvents, e.g.
N,N-dimethylformamide (DMF), toluene, dichloromethane (DCM),
resulted in inferior yields of 3a (entries 2e4). To our delight, the
yields of 3a were improved to 37% and 61% with polar protic sol-
vents (entries 5e6). Meanwhile, different concentrations were
explored (entries 6e8) and it is noticed that 3a was obtained in
highest yield with 10 mM concentration (entry 6, 61%). Finally,
irradiation time (4e8 h) was screened and the annulation product
3a was obtained in 50%, 61% and 58% separately (entries 6, 9 and
10). It is important to note that the 3a could be also obtained under
open air, but with slightly decreased yield (entry 11, 46%). Thus,
Based on the mechanism studies [16,17,19,20] and experimental
evidences, a plausible mechanism for the formation of 3a is put
forward and shown in Scheme 2. Irradiation of 3,4-diphenyl-3-
2

Y. Kang, Y. He, J. Sui et al.
Tetrahedron 84 (2021) 131981
Table 2
substrate Scopea.
Scheme 2. Plausible reaction mechanism.
pyrrolin-2-one 2a with 500 W Hg lamp at room temperature
generated intermediate A via an intramolecular 6 -electron cycli-
p
zation [19], followed by a thermal suprafacial [1,5]-H shift [20] to
give intermediate B, which is driven by the rearomatization of the
benzene ring. Subsequently, a more stable syn-isomer intermediate
C is obtained via the keto-enol isomerization of B. In the end, the
annulation product 3a is obtained by hydrogen evolution via syn-
elimination. Which shares similar transformations reported in
literature [16,17]. It is important to note that the annulation product
3a is also obtained in low yield under the open air (in presence of
oxygen, Table 1, entry 11), which indicated the photochemical
cyclization proceeded through the S1 state [11b,16].
Scheme 3. Detection of the only byproduct H2 for irradiation 1g.
proved solid evidence for the proposed mechanism (Scheme 2).
It has been reported that treatment of 3,4-diphenyl-1H-pyrrol-
2(5H)-one 2a with NaH in DMF under an oxygen atmosphere at 0 ꢂC
Most importantly, the presence of H2 byproduct was success-
fully detected via GC during annulation of 1g (Scheme 3), which
3

Y. Kang, Y. He, J. Sui et al.
Tetrahedron 84 (2021) 131981
1 mmol) in acetic anhydride (3.3 mL) at 0 ꢂC and was stirred at
room temperature for 12 h. When the reaction was completed
(detected by TLC), the reaction mixture was partitioned with water
and ethyl acetate. Organic layer was combined, washed (saturated
citric acid solution, saturated NaHCO3 solution and brine), dried
and concentrated in vacuo. The residue was purified by silica col-
umn chromatography (ethyl acetate/petroleum ether, 1:5) to give
corresponding product 1a (207.8 mg, 75%) [18]. Similarly, products
1b-1m were obtained with the same method as described above.
Scheme 4. Synthesis of dibenzo[e,g]isoindole-1,3(2H)-dione.
4.2.1. 1-Acetyl-3,4-diphenyl-1,5-dihydropyrrol-2-one (1a) [18]
1H NMR (600 MHz, CDCl3)
d
(ppm) 7.41e7.28 (m, 10H), 4.76 (s,
gave 3,4-diphenyl-1H-pyrrole-2,5-dione in moderate yields [21].
Since maleimide moiety has been extensively found in drugs,
pesticides and dyes [22], these conditions were used to convert 3a
and 3aa into dibenzo[e,g]isoindole-1,3(2H)-dione 4 under an oxy-
gen atmosphere (Scheme 4). Sodium methoxide was added to the
solution of 3a or 3aa in DMSO at room temperature to provide
direct access to dibenzo[e,g]isoindole-1,3(2H)-dione 4 in 72% and
60%, which further confirmed the practical feasibility of the new
developed method.
2H), 2.65 (s, 3H); 13C NMR (151 MHz, CDCl3)
d
(ppm) 170.6, 169.8,
150.9, 132.1, 131.9, 131.0, 130.5, 130.2, 129.6, 129.0, 128.8, 128.1,
50.02, 24.8.
4.2.2. 1-Acetyl-3-(4-methoxyphenyl)-4-phenyl-1,5-dihydropyrrol-
2-one (1b)
Yellow solid. Yield: 69%, 211.8 mg. mp: 160.1e161.9 ꢂC. 1H NMR
(600 MHz, CDCl3)
2H), 4.72 (s, 2H), 3.83 (s, 3H), 2.65 (s, 3H); 13C NMR (151 MHz,
CDCl3) (ppm) 170.6, 170.1, 156.0, 149.9, 132.4, 131.4, 130.9, 130.3,
129.0, 128.0, 123.1, 114.3, 55.4, 50.0, 24.8; IR (KBr),
(cmꢁ1) 3059,
d
(ppm) 7.37e7.30 (m, 7H), 6.91 (d, J ¼ 8.7 Hz,
3. Conclusion
d
n
In summary, we have successfully demonstrated the synthesis
of dibenzo[e,g]isoindol-1-one derivatives via annulation of 3,4-
diphenyl-3-pyrrolin-2-one in EtOH with irradiation a 500 W mer-
cury lamp under room temperature along with hydrogen evolution.
Compared with reported methods, the described method offers
several notable advantages: a) tolerates electron-donating and
electron-withdrawing groups and heteroaromatics, such as thio-
phene and furan, b) eliminates the usage of any expensive
transition-metal catalyst or photocatalyst, and c) atom-economic
and environmental friendly with H2 as the only byproduct. Addi-
tionally, annulation products 3a and 3aa were successfully oxidized
into dibenzo[e,g]isoindole-1,3(2H)-dione analogue 4 in moderate
yields that demonstrate the practical applications of this method.
2928, 1705, 1605, 1340, 1300, 1159, 899, 766, 633; HRMS (ESI) m/z:
calcd for C19H17NO3Na [M þ Na]þ 330.1101; found 330.1110.
4.2.3. 1-Acetyl-3-(30,40-dimethoxyphenyl)-4-phenyl-1,5-
dihydropyrrol-2-one (1c)
White solid. Yield: 71%, 267.7 mg. mp: 138.2e139.9 ꢂC. 1H NMR
(600 MHz, CDCl3)
d (ppm) 7.38e7.36 (m, 3H), 7.35e7.31 (m, 2H),
6.99 (dd, J ¼ 8.3, 1.9 Hz, 1H), 6.88 (d, J ¼ 8.3 Hz, 1H), 6.85 (d,
J ¼ 1.8 Hz, 1H), 4.73 (s, 2H), 3.90 (s, 3H), 3.73 (s, 3H), 2.65 (s, 3H); 13
C
NMR (151 MHz, CDCl3)
d (ppm) 170.6, 169.9, 150.1, 149.6, 149.1,
132.3, 131.5, 130.4, 129.0, 128.1, 123.3, 122.5, 112.6, 111.4, 56.0, 55.9,
50.0, 24.8; IR (KBr), n
(cmꢁ1) 2933, 1716, 1691, 1514, 1377, 1257, 1139,
1022, 769, 536; HRMS (ESI) m/z: calcd for C20H19NO4Na [M þ Na]þ
360.1206; found 360.1212.
4. Experimental section
4.2.4. 1-Acetyl-4-phenyl-3-(o-tolyl)-1,5-dihydropyrrol-2-one (1d)
White solid. Yield: 66%, 192.1 mg. mp: 156.1e157.9 ꢂC. 1H NMR
4.1. General information
(600 MHz, CDCl3)
4.89 (d, J ¼ 19.1, 1H), 4.84 (d, J ¼ 19.1, 1H), 2.67 (s, 3H), 2.14 (s, 3H);
13C NMR (151 MHz, CDCl3)
(ppm) 170.5, 169.8, 150.7, 136.9, 132.4,
131.9, 131.1, 130.7, 129.8, 129.0, 129.0, 127.5, 126.5, 49.7, 24.7, 19.9; IR
d
(ppm) 7.37e7.26 (m, 8H), 7.17 (d, J ¼ 7.5 Hz, 1H),
All reactions were determined by thin layer chromatography
(TLC). TLC used 60 mesh silica gel. The crude products were per-
formed by flash column chromatography (200e300 mesh) on silica
gel. The starting materials were purchased from Energy Chemical.
1H and 13C NMR spectra were recorded on Bruker 400 or 600 MHz
spectrometer in CDCl3 and DMSO. All chemical shifts were given as
d
(KBr),
n
(cmꢁ1) 3057, 2923, 1716, 1688, 1340, 1298, 1197, 1037, 902,
761, 541; HRMS (ESI) m/z: calcd for C19H17NO2Na [M þ Na]þ
314.1151; found 314.1160.
d
value (ppm) with referenced to the residual solvent peaks [CDCl3
(7.26 ppm) or DMSO‑d6 (2.50)] for 1H NMR and the CDCl3
(77.16 ppm) or DMSO‑d6 (39.52) for 13C NMR spectra. High-
resolution mass spectra (HRMS) were obtained using the
electron-spray ionization (ESI) and (APCI) technique. Melting
points (uncorrected) were measured with a X-5 micro-melting
point apparatus. IR spectra were recorded with a Nicollet 170SX
FT-IR spectrophotometer with KBr pellets. All the irradiation ex-
periments were performed in a BL-GHX-V photo-chemical reactor
equipped with a 500 W high-pressure mercury lamp at room
temperature. The emission spectrum of the 500 W high-pressure
mercury lamp is provided in Supporting Information (Figure S5).
4.2.5. 1-Acetyl-3-phenyl-4-(p-tolyl)-1,5-dihydropyrrol-2-one (1e)
White solid. Yield: 69%, 200.28 mg. mp: 147.1e148.9 ꢂC. 1H NMR
(600 MHz, CDCl3)
d
(ppm) 7.39e7.35 (m, 5H), 7.24 (d, J ¼ 8.2 Hz, 2H),
7.11 (d, J ¼ 8.1 Hz, 2H), 4.74 (s, 2H), 2.64 (s, 3H), 2.34 (s, 3H); 13C
NMR (151 MHz, CDCl3) d (ppm) 170.6,169.9, 150.9, 141.1, 131.2, 131.1,
129.7, 129.6, 129.1, 128.8, 128.7, 128.0, 49.9, 24.8, 21.6; IR (KBr),
n
(cmꢁ1) 2923, 1720, 1650, 1604, 1346, 1292, 1118, 819, 540; HRMS
(ESI) m/z: calcd for C19H17NO2Na [M þ Na]þ 314.1151; found
314.1158.
4.2.6. 1-Acetyl-3-(40-fluorophenyl)-4-phenyl-1,5-dihydropyrrol-2-
one (1f)
4.2. General procedure for the synthesis of 1-Acetyl-3,4-diphenyl-
White solid. Yield: 62%, 182.9 mg. mp: 184.5e185.9 ꢂC. 1H NMR
1,5-dihydropyrrol-2-one (1)
(600 MHz, CDCl3)
d
(ppm) 7.39e7.32 (m, 7H), 7.07 (t, J ¼ 8.7 Hz, 2H),
4.74 (s, 2H), 2.64 (s, 3H); 13C NMR (151 MHz, CDCl3)
d (ppm) 170.5,
Triethylamine (2.3 mL, 16 mmol) was slowly added to the so-
lution of N-(2-oxo-2-phenylethyl)-2-phenylacetamide (253 mg,
169.7, 163.0 (d, 1J ¼ 247.21 Hz), 151.1, 131.9, 131.5 (d, 3J ¼ 8.31 Hz),
130.8, 130.6, 129.1, 128.0, 126.8 (d, 4J ¼ 3.18 Hz), 115.9 (d,
4

Y. Kang, Y. He, J. Sui et al.
Tetrahedron 84 (2021) 131981
2J
d
¼
21.33 Hz), 50.0, 24.7; 19F NMR (376 MHz, CDCl3)
(ppm) ꢁ112.17; IR (KBr),
(cmꢁ1) 3064, 2927, 1710, 1510, 1336,
129.6, 129.0, 128.9, 128.0, 127.8 (d, 4J ¼ 3.25 Hz), 126.9, 126.5, 125.9,
124.9, 116.2 (d, 2J ¼ 21.78 Hz), 49.9, 24.7; 19F NMR (376 MHz, CDCl3)
n
1294, 1155, 1097, 975, 850, 769, 686, 526; HRMS (ESI) m/z: calcd for
d
(ppm) ꢁ107.96; IR (KBr),
n
(cmꢁ1) 3062, 1720, 1510, 1303, 1201,
C
18H14FNO2Na [M þ Na]þ 318.0901; found 318.0902.
966, 840, 800, 624; HRMS (ESI) m/z: calcd for C22H16FNO2Na [M þ
Na]þ 368.1057; found 368.1058.
4.2.7. 4-(1-Acetyl-2-oxo-4-phenyl-2,5-dihydropyrrol-3-yl)
benzonitrile (1g)
4.2.12. 1-Acetyl-4-phenyl-3-(thiophen-2-yl)-1,5-dihydropyrrol-2-
one (1l)
Gray solid. Yield: 64%, 193.3 mg. mp: 191.1e192.9 ꢂC. 1H NMR
(600 MHz, CDCl3)
2H), 7.42 (t, J ¼ 7.4 Hz, 1H), 7.35 (t, J ¼ 7.7 Hz, 2H), 7.28 (d, J ¼ 7.4 Hz,
2H), 4.77 (s, 2H), 2.64 (s, 3H); 13C NMR (151 MHz, CDCl3)
(ppm)
170.3,168.9, 153.3, 135.7, 132.5,131.3, 131.1, 130.5,130.1, 129.3,128.0,
118.6, 112.5, 50.3, 24.8; IR (KBr),
(cmꢁ1) 2927, 2227, 1697, 1344,
d
(ppm) 7.66 (d, J ¼ 8.3 Hz, 2H), 7.50 (d, J ¼ 8.3 Hz,
White solid. Yield: 72%, 203.8 mg. mp: 90.6e91.8 ꢂC. 1H NMR
(600 MHz, CDCl3)
7.34 (d, J ¼ 3.6 Hz,1H), 7.01 (dd, J ¼ 4.9, 3.8 Hz,1H), 4.67 (s, 2H), 2.67
(s, 3H); 13C NMR (151 MHz, CDCl3)
(ppm) 170.4,168.9, 150.1, 132.6,
131.2, 130.5, 129.2, 128.4, 127.9, 127.5, 127.0, 125.6, 51.0, 24.8; IR
d
(ppm) 7.47e7.42 (m, 5H), 7.37 (d, J ¼ 5.1 Hz, 1H),
d
d
n
1298, 1112, 975, 854, 769, 547; HRMS (ESI) m/z: calcd for
(KBr), n
(cmꢁ1) 3082, 1717, 1294, 1151, 970, 845, 700; HRMS (ESI) m/
C
19H14N2O2Na [M þ Na]þ 325.0947; found 325.0954.
z: calcd for C16H13SNO2Na [M þ Na]þ 306.0559; found 306.0567.
4.2.8. 1-Acetyl-3-(30,40-dimethoxyphenyl)-4-(40-fluorophenyl)-1,5-
dihydropyrrol-2-one (1h)
4.2.13. 1-Acetyl-3-(furan-2-yl)-4-phenyl-1,5-dihydropyrrol-2-one
(1m)
Yellow solid. Yield: 60%, 213.0 mg. mp: 154.6e155.9 ꢂC. 1H NMR
Yellow solid. Yield: 67%, 178.9 mg. mp: 114.5e115.9 ꢂC. 1H NMR
(600 MHz, CDCl3)
d
(ppm) 7.39e7.35 (m, 2H), 7.04e7.00 (m, 2H),
(600 MHz, CDCl3)
7.13 (d, J ¼ 3.4 Hz, 1H), 6.49 (dd, J ¼ 3.4, 1.8 Hz, 1H), 4.67 (s, 2H), 2.64
(s, 3H); 13C NMR (151 MHz, CDCl3)
(ppm) 170.3,168.0,148.5,145.6,
142.8, 132.6, 130.4, 128.6, 128.2, 121.2, 112.5, 111.5, 50.7, 24.8; IR
d
(ppm) 7.47e7.42 (m, 5H), 7.35 (d, J ¼ 1.2 Hz,1H),
6.94 (dd, J ¼ 8.3, 1.9 Hz, 1H), 6.88 (d, J ¼ 8.3 Hz, 1H), 6.85 (d,
J ¼ 1.8 Hz,1H), 4.70 (s, 2H), 3.90 (s, 3H), 3.76 (s, 3H), 2.64 (s, 3H); 13
C
d
NMR (151 MHz, CDCl3)
d (ppm) 170.5, 169.8, 163.7 (d,
1J ¼ 251.17 Hz), 149.6, 149.2, 148.8, 131.4, 130.1 (d, 3J ¼ 8.35 Hz),
128.3 (d, 4J ¼ 3.18 Hz), 123.1, 122.4, 116.2 (d, 2J ¼ 21.76 Hz), 112.4,
111.5, 56.0, 56.0, 49.9, 24.8; 19F NMR (376 MHz, CDCl3)
(KBr), n
(cmꢁ1) 2931, 1722, 1684, 1346, 1139, 815, 736, 536; HRMS
(ESI) m/z: calcd for C16H13NO3Na [M þ Na]þ 290.0788; found
290.0794.
d
(ppm) ꢁ108.74; IR (KBr),
n
(cmꢁ1) 3062, 2937, 1726, 1681, 1595,
1512, 1309, 1245, 1137, 1016, 813, 756, 655; HRMS (ESI) m/z: calcd
for C20H18FNO4Na [M þ Na]þ 378.1112; found 378.1116.
4.3. General procedure for the synthesis of 3,4-diphenyl-1H-pyrrol-
2(5H)-one (2)
4.2.9. 1-Acetyl-3-(naphthalen-1-yl)-4-phenyl-1,5-dihydropyrrol-2-
one (1i)
A solution of sodium methoxide in MeOH (500 mL, 0.5 mmol,
30%) was added to the solution of 1-acetyl-3,4-diphenyl-1,5-
dihydropyrrol-2-one 1a (138.5 mg, 0.500 mmol) in dry MeOH
(25 mL) at 0 ꢂC under an Ar atmosphere. When the reaction was
White solid. Yield: 70%, 228.9 mg. mp: 183.5e184.9 ꢂC. 1H NMR
(600 MHz, CDCl3)
d
(ppm) 7.90 (dd, J ¼ 15.6, 8.2 Hz, 2H), 7.63 (d,
J ¼ 8.4 Hz, 1H), 7.53e7.49 (m, 1H), 7.46 (t, J ¼ 7.4 Hz, 1H), 7.40e7.35
completed (detected by TLC), acetic acid (61 mL,1 mmol) was slowly
(m, 2H), 7.25e7.22 (m, 1H), 7.20 (d, J ¼ 7.5 Hz, 2H), 7.14 (t, J ¼ 7.7 Hz,
added and the reaction mixture was concentrated in vacuo. After
partition with water and CH2Cl2, the organic layer was combined,
washed (brine), and concentrated in vacuo. The residue was puri-
fied by silica column chromatography (ethyl acetate/dichloro-
methane, 1:3) to afford the corresponding product 2a (70.5 mg,
60%) [18]. Similarly, compounds 2b-2m were obtained with the
same method as described above.
2H), 4.96 (s, 2H), 2.63 (s, 3H); 13C NMR (151 MHz, CDCl3)
d (ppm)
170.6,170.1,152.1,134.0,131.5,131.3,130.8,129.5,129.3,129.0,128.8,
128.0, 127.9, 126.8, 126.4, 125.8, 125.0, 50.0, 24.7; IR (KBr),
n
(cmꢁ1
)
3053, 2923,1720, 1692, 1338, 1296, 1201,1099, 904, 800, 545; HRMS
(ESI) m/z: calcd for C22H17NO2Na [M þ Na]þ 350.1151; found
350.1152.
4.2.10. 1-Acetyl-3-(naphthalen-1-yl)-4-(p-tolyl)-1,5-dihydropyrrol-
2-one (1j)
4.3.1. 3,4-Diphenyl-1H-pyrrol-2(5H)-one (2a) [18]
1H NMR (600 MHz, DMSO)
d
(ppm) 8.48 (s, 1H), 7.32e7.23 (m,
White solid. Yield: 69%, 235.3 mg. mp: 162.1e163.6 ꢂC. 1H NMR
10H), 4.33 (s, 2H); 13C NMR (151 MHz, DMSO)
d
(ppm) 172.4, 150.4,
(600 MHz, CDCl3)
d
(ppm) 7.93 (dd, J ¼ 13.7, 8.2 Hz, 2H), 7.66 (d,
133.3, 132.4, 131.8, 129.3, 129.0, 128.6, 128.2, 127.7, 127.5, 47.5.
J ¼ 8.4 Hz, 1H), 7.54 (t, J ¼ 7.3 Hz, 1H), 7.49 (t, J ¼ 7.4 Hz, 1H), 7.41 (t,
J ¼ 6.5 Hz, 2H), 7.12 (d, J ¼ 8.2 Hz, 2H), 6.97 (d, J ¼ 8.2 Hz, 2H), 4.97
4.3.2. 3-(40-Methoxyphenyl)-4-phenyl-1H-pyrrol-2(5H)-one (2b)
(s, 2H), 2.66 (s, 3H), 2.25 (s, 3H); 13C NMR (151 MHz, CDCl3)
d
(ppm)
[23]
170.6, 170.2, 152.1, 141.4, 134.0, 131.4, 130.3, 129.7, 129.6, 129.4,
128.8,128.7,128.0,127.8,126.7,126.3,125.8,125.1, 49.9, 24.7, 21.5; IR
1H NMR (600 MHz, DMSO)
d
(ppm) 8.47 (s, 1H), 7.33 (s, 5H), 7.22
(d, J ¼ 8.7 Hz, 2H), 6.90 (d, J ¼ 8.7 Hz, 2H), 4.32 (s, 2H), 3.76 (s, 3H);
13C NMR (151 MHz, DMSO)
(ppm) 172.6, 158.8, 149.2, 133.6, 131.1,
(KBr),
n
(cmꢁ1) 3043, 2923, 1905, 1708, 1632, 1294, 1195, 1095, 966,
d
794, 547; HRMS (ESI) m/z: calcd for C23H19NO2Na [M þ Na]þ
130.5, 128.8, 128.6, 127.4, 124.3, 113.6, 55.0, 47.4.
364.1308; found 364.1318.
4.3.3. 3-(30,40-Dimethoxyphenyl)-4-phenyl-1H-pyrrol-2(5H)-one
4.2.11. 1-Acetyl-4-(40-fluorophenyl)-3-(naphthalen-1-yl)-1,5-
dihydropyrrol-2-one (1k)
(2c) [8]
1H NMR (600 MHz, DMSO)
d
(ppm) 8.48 (s, 1H), 7.37e7.33 (m,
5H), 6.93e6.88 (m, 2H), 6.84 (d, J ¼ 1.7 Hz, 1H), 4.32 (s, 2H), 3.75 (s,
3H), 3.56 (s, 3H); 13C NMR (151 MHz, DMSO)
(ppm) 172.5, 149.5,
Yellow solid. Yield: 65%, 224.2 mg. mp: 190.5e192.1 ꢂC. 1H NMR
(600 MHz, CDCl3)
d
(ppm) 7.94 (dd, J ¼ 17.5, 8.2 Hz, 2H), 7.62 (d,
d
J ¼ 8.4 Hz, 1H), 7.55 (t, J ¼ 7.6 Hz, 1H), 7.50 (t, J ¼ 7.5 Hz, 1H), 7.40 (t,
J ¼ 8.1 Hz, 2H), 7.21 (dd, J ¼ 8.7, 5.3 Hz, 2H), 6.86 (t, J ¼ 8.6 Hz, 2H),
4.97 (d, J ¼ 19.1 Hz, 1H), 4.93 (d, J ¼ 19.1 Hz, 1H), 2.66 (s, 3H); 13C
148.5, 148.2, 133.7, 131.2, 128.8, 128.6,127.6, 124.5, 121.9, 113.0, 111.5,
55.4, 55.2, 47.5.
NMR (151 MHz, CDCl3)
d
(ppm) 170.6, 169.9, 163.9 (d,
4.3.4. 4-Phenyl-3-(o-tolyl)-1H-pyrrol-2(5H)-one (2d)
1J ¼ 251.74 Hz), 150.8, 134.1, 131.2, 131.0, 130.0 (d, 2J ¼ 8.62 Hz),
White solid. Yield: 68%, 84.7 mg. mp: 174.1e175.5 ꢂC. 1H NMR
5

Y. Kang, Y. He, J. Sui et al.
Tetrahedron 84 (2021) 131981
(600 MHz, DMSO)
(m, 3H), 7.04 (d, J ¼ 7.4 Hz, 1H), 4.46 (dd, J ¼ 19.2, 23.2 Hz, 2H), 2.04
(s, 3H); 13C NMR (151 MHz, DMSO)
(ppm) 172.5, 149.9, 136.4,
133.1, 133.0,132.9, 130.0, 129.7, 129.2, 128.6, 128.0, 126.9, 125.9, 47.2,
19.4; IR (KBr),
(cmꢁ1) 3435, 3277, 3055, 2918, 1693, 1448, 1360,
d
(ppm) 8.47 (s, 1H), 7.31e7.25 (m, 5H), 7.23e7.18
4.3.10. 3-(Naphthalen-1-yl)-4-(p-tolyl)-1H-pyrrol-2(5H)-one (2j)
Yellow solid. Yield: 69%, 103.1 mg. Mp: 222.4e223.8 ꢂC. 1H NMR
d
(600 MHz, DMSO)
d
(ppm) 8.54 (s, 1H), 7.97 (t, J ¼ 8.1 Hz, 2H), 7.63
(d, J ¼ 8.4 Hz, 1H), 7.55 (dd, J ¼ 8.1, 7.1 Hz, 1H), 7.52e7.48 (m, 1H),
7.41e7.38 (m, 1H), 7.32 (dd, J ¼ 7.0, 1.0 Hz, 1H), 7.05 (d, J ¼ 8.3 Hz,
2H), 6.96 (d, J ¼ 8.1 Hz, 2H), 4.59 (d, J ¼ 19.0, 1H), 4.53 (d, J ¼ 19.0,
n
1217, 1084, 754, 638; HRMS (ESI) m/z: calcd for C17H15NONa [M þ
Na]þ 272.1046; found 272.1050.
1H), 2.16 (s, 3H); 13C NMR (151 MHz, DMSO)
d (ppm) 173.0, 151.4,
138.9, 133.3, 131.4, 131.2, 130.8, 130.0, 129.1, 128.3, 128.1, 127.5, 127.0,
126.2, 126.0, 125.7, 125.3, 47.4, 20.8; IR (KBr),
n
(cmꢁ1) 3269, 1688,
4.3.5. 3-Phenyl-4-(p-tolyl)-1H-pyrrol-2(5H)-one (2e)
1443, 1352, 1225, 1016, 889, 777, 656; HRMS (ESI) m/z: calcd for
Yellow solid. Yield: 72%, 89.6 mg. mp: 209.1e210.9 ꢂC. 1H NMR
C
21H17NONa [M þ Na]þ 322.1202; found 322.1210.
(600 MHz, DMSO)
J ¼ 6.8 Hz, 2H), 7.20 (d, J ¼ 8.1 Hz, 2H), 7.12 (d, J ¼ 8.0 Hz, 2H), 4.33 (s,
2H), 2.27 (s, 3H); 13C NMR (151 MHz, DMSO)
(ppm) 172.5, 150.4,
138.7, 132.5, 131.1, 130.4, 129.3, 129.2, 128.2, 127.6, 127.4, 47.5, 20.8;
d (ppm) 8.48 (s, 1H), 7.37e7.30 (m, 3H), 7.27 (d,
d
4.3.11. 4-(40-Fluorophenyl)-3-(naphthalen-1-yl)-1H-pyrrol-2(5H)-
one (2k)
IR (KBr),
n
(cmꢁ1) 3184, 3063, 2868, 1686, 1447, 1366, 1225, 702;
Yellow solid. Yield: 63%, 95.4 mg. Mp: 209.1e210.8 ꢂC. 1H NMR
HRMS (ESI) m/z: calcd for C17H15NONa [M þ Na]þ 272.1046; found
(600 MHz, DMSO)
d
(ppm) 8.61 (s, 1H), 7.98 (dd, J ¼ 8.1, 4.5 Hz, 2H),
272.1048.
7.63 (d, J ¼ 8.4 Hz, 1H), 7.56 (dd, J ¼ 8.1, 7.1 Hz, 1H), 7.53e7.49 (m,
1H), 7.43e7.39 (m, 1H), 7.34 (d, J ¼ 7.0 Hz, 1H), 7.23e7.18 (m, 2H),
7.04 (t, J ¼ 8.9 Hz, 2H), 4.62 (d, J ¼ 19.2,1H), 4.55 (d, J ¼ 19.2,1H); 13
C
4.3.6. 3-(40-Fluorophenyl)-4-phenyl-1H-pyrrol-2(5H)-one (2f)
White solid. Yield: 70%, 88.5 mg. Mp: 189.5e190.9 ꢂC. 1H NMR
NMR (151 MHz, DMSO)
d
(ppm) 172.8, 162.3 (d, 1J ¼ 246.28 Hz),
150.3, 133.3, 131.5, 131.1, 131.0, 129.4 (d, 4J ¼ 3.13 Hz), 129.3 (d,
(600 MHz, DMSO)
d (ppm) d 8.55 (s, 1H), 7.34e7.30 (m, 7H), 7.18 (t,
3J ¼ 8.50 Hz), 128.4, 128.3, 127.6, 126.2, 126.1, 125.8, 125.2, 115.6 (d,
J ¼ 8.9 Hz, 2H), 4.36 (s, 2H); 13C NMR (151 MHz, DMSO)
d (ppm)
2J ¼ 21.69 Hz), 47.5; 19F NMR (376 MHz, DMSO)
d
ꢁ111.36; IR (KBr),
n
172.3, 161.7 (d, 1J ¼ 243.19 Hz), 150.7, 133.3, 131.4 (d, 3J ¼ 8.32 Hz),
130.6, 129.1, 128.7, 128.6 (d, 4J ¼ 3.03 Hz), 127.5, 115.2 (d,
(cmꢁ1) 3182, 3063, 2849, 1684, 1510, 1352, 1232, 1016, 891, 779;
HRMS (ESI) m/z: calcd for C20H14FNONa [M þ Na]þ 326.0952; found
326.0960.
2J ¼ 21.40 Hz), 47.6; 19F NMR (376 MHz, DMSO)
(ppm) ꢁ109.15; IR
d
(KBr),
n
(cmꢁ1) 3192, 3049, 1678, 1506, 1371, 1227, 1090, 974, 770,
590; HRMS (ESI) m/z: calcd for C16H12FNO Na [M þ Na]þ 276.0795;
found 276.0802.
4.3.12. 4-Phenyl-3-(thiophen-2-yl)-1H-pyrrol-2(5H)-one (2l)
Yellow solid. Yield: 70%, 84.3 mg. Mp: 177.7e178.9 ꢂC. 1H NMR
(600 MHz, DMSO)
d (ppm) 8.66 (s, 1H), 7.51e7.41 (m, 6H), 7.29 (d,
4.3.7. 4-(2-Oxo-4-phenyl-1H-pyrrol-3-yl)benzonitrile (2g)
J ¼ 3.0 Hz, 1H), 7.00 (dd, J ¼ 5.0, 3.7 Hz, 1H), 4.28 (s, 2H); 13C NMR
White solid. Yield: 64%, 83.2 mg. Mp: 203.3e204.9 ꢂC. 1H NMR
(151 MHz, DMSO)
d (ppm) 171.4, 149.8, 134.0, 132.5, 129.1, 128.8,
(600 MHz, DMSO)
(d, J ¼ 8.3 Hz, 2H), 7.39e7.34 (m, 3H), 7.31e7.30 (m, 2H), 4.41 (s,
2H); 13C NMR (151 MHz, DMSO)
(ppm) 171.6, 153.0, 137.4, 132.8,
d
(ppm) 8.66 (s, 1H), 7.82 (d, J ¼ 8.3 Hz, 2H), 7.48
127.7, 127.0, 126.8, 126.6, 124.9, 48.7; IR (KBr), n
(cmꢁ1) 3186, 3065,
2839, 1688, 1362, 845, 700; HRMS (ESI) m/z: calcd for C14H11SNONa
d
[M þ Na]þ 264.0454; found 264.0459.
132.1, 130.3, 130.1, 129.5, 128.8, 127.6, 118.8, 110.3, 47.9; IR (KBr),
n
(cmꢁ1) 3290, 3194, 3045, 2230, 1680, 1447, 1367, 1086, 980, 770,
546; HRMS (ESI) m/z: calcd for C17H12N2ONa [M þ Na]þ 283.0842;
found 283.0845.
4.3.13. 3-(Furan-2-yl)-4-phenyl-1H-pyrrol-2(5H)-one (2m)
White solid. Yield: 58%, 65.2 mg. Mp: 138.1e139.9 ꢂC. 1H NMR
(600 MHz, DMSO)
d
(ppm) 8.62 (s, 1H), 7.60 (d, J ¼ 0.9 Hz, 1H), 7.48
(dd, J ¼ 7.9, 1.6 Hz, 2H), 7.43e7.39 (m, 3H), 7.07 (d, J ¼ 3.3 Hz, 1H),
4.3.8. 3-(30,40-Dimethoxyphenyl)-4-(400-fluorophenyl)-1H-pyrrol-
2(5H)-one (2h)
6.55 (dd, J ¼ 3.3, 1.8 Hz,1H), 4.32 (s, 2H); 13C NMR (151 MHz, DMSO)
d
(ppm) 170.7, 148.4, 146.9, 142.8, 133.9, 129.0, 128.2, 128.0, 120.9,
White solid. Yield: 68%, 106.4 mg. Mp: 190.1e191.4 ꢂC. 1H NMR
111.3, 110.9, 48.2; IR (KBr),
n
(cmꢁ1) 3192, 3067, 2881, 1697, 1447,
(600 MHz, DMSO)
d
(ppm) 8.48 (s, 1H), 7.40 (dd, J ¼ 8.7, 5.6 Hz, 2H),
1352, 1227, 1013, 878, 743; HRMS (ESI) m/z: calcd for C14H11NO2Na
7.20 (t, J ¼ 8.8 Hz, 2H), 6.94 (d, J ¼ 8.3 Hz, 1H), 6.87 (dd, J ¼ 8.3,
[M þ H]þ 248.0682; found 248.0688.
1.8 Hz, 1H), 6.84 (d, J ¼ 1.7 Hz, 1H), 4.31 (s, 2H), 3.76 (s, 3H), 3.59 (s,
3H); 13C NMR (151 MHz, DMSO)
d (ppm) 172.46, 162.17 (d,
1J
¼
245.29 Hz), 148.55, 148.31, 148.28, 131.28, 130.12 (d,
4.3.14. 1-Methyl-3,4-diphenyl-1H-pyrrol-2(5H)-one (2n) [24]
4J ¼ 2.92 Hz), 129.83 (d, 4J ¼ 7.33 Hz), 124.33, 121.89, 115.58 (d,
1H NMR (600 MHz, CDCl3)
d
(ppm)
7.34e7.27 (m, 8H), 4.29 (s, 2H), 3.18 (s, 3H); 13C NMR (151 MHz,
CDCl3) (ppm) 171.00, 147.19, 133.43, 133.01, 132.23, 129.65, 129.20,
d 7.41e7.40 (m, 2H),
2J ¼ 21.66 Hz), 112.89, 111.59, 55.40, 55.29, 47.45; 19F NMR
(376 MHz, DMSO)
d
(ppm) ꢁ112.10; IR (KBr),
n
(cmꢁ1) 3169, 3057,
d
2841, 1680, 1514, 1366, 1254, 1138, 1024, 837, 750, 579; HRMS (ESI)
128.83, 128.51, 128.18, 127.71, 54.58, 29.54.
m/z: calcd for C18H16FNO3Na [M þ Na]þ 336.1006; found 336.1007.
4.4. General procedure for the synthesis of 2,3-dihydro-1H-dibenzo
4.3.9. 3-(Naphthalen-1-yl)-4-phenyl-1H-pyrrol-2(5H)-one (2i)
White solid. Yield: 65%, 92.6 mg. Mp: 212.1e213.4 ꢂC. 1H NMR
[e,g]isoindol-1-one (3a-3m, 3af)
(600 MHz, CDCl3)
d
(ppm) 8.50 (s,1H), 7.91 (t, J ¼ 7.3 Hz, 2H), 7.76 (d,
The solution of 3,4-diphenyl-1H-pyrrol-2(5H)-one 2a (35.3 mg,
0.150 mmol) in EtOH (15 mL) in a quartz tube irradiated with a
high-pressure mercury lamp (500 W) at 25 ꢂC for 6 h under an
argon atmosphere. Volatiles were removed under reduced pressure
and the residue was purified by column chromatography on silica
(ethyl acetate/dichloromethane, 1:3) to give 3a (21.3 mg, 61%).
Similarly, compounds 3b-3m, 3af were obtained with the same
method as described above.
J ¼ 8.4 Hz, 1H), 7.56e7.51 (m, 1H), 7.48 (t, J ¼ 7.4 Hz, 1H), 7.43e7.39
(m, 2H), 7.21e7.18 (m, 1H), 7.14e7.09 (m, 4H), 4.53 (s, 2H); 13C NMR
(151 MHz, CDCl3)
130.5, 129.5, 128.9, 128.7, 128.6, 127.9, 127.3, 126.5, 126.2, 125.9,
125.6, 48.5; IR (KBr),
(cmꢁ1) 3437, 3184, 3057, 2851, 1684, 1447,
d (ppm) 175.3, 152.0, 134.1, 132.7, 132.3, 131.7,
n
1352, 1221, 1103, 779, 640, 534; HRMS (ESI) m/z: calcd for
C
20H15NONa [M þ Na]þ 308.1046; found 308.1050.
6

Y. Kang, Y. He, J. Sui et al.
Tetrahedron 84 (2021) 131981
4.4.1. 2,3-Dihydro-1H-dibenzo[e,g]isoindol-1-one (3a)
4.4.7. 2,3-Dihydro-3-oxo-1H-dibenzo[e,g]isoindole-6-carbonitrile
(3g)
White solid. Yield: 61%, 21.3 mg. mp: 258.2e259.7 ꢂC. 1H NMR
(600 MHz, DMSO)
8.75 (s, 1H), 8.10 (d, J ¼ 7.8 Hz, 1H), 7.83 (t, J ¼ 7.2 Hz, 1H), 7.78e7.73
(m, 3H), 4.79 (s, 2H); 13C NMR (151 MHz, DMSO)
(ppm) 171.8,
144.5, 131.2, 129.8, 128.8, 127.5, 127.4, 127.3, 127.0, 126.6, 124.5,
124.3, 123.8, 123.5, 123.4, 43.9; IR (KBr),
(cmꢁ1) 3069, 2893, 1699,
d
(ppm) 9.28e9.23 (m, 1H), 8.94e8.88 (m, 2H),
Yellow solid. Yield: 67%, 25.9 mg. mp: 289.2e290.9 ꢂC. 1H NMR
(600 MHz, DMSO)
(d, J ¼ 8.2 Hz, 1H), 8.87 (s, 1H), 8.12 (d, J ¼ 7.7 Hz, 1H), 8.05 (d,
J ¼ 8.3 Hz, 1H), 7.88 (t, J ¼ 7.4 Hz, 1H), 7.83 (t, J ¼ 7.3 Hz, 1H), 4.81 (s,
d
(ppm) 9.42 (s, 1H), 9.33 (d, J ¼ 8.3 Hz, 1H), 9.02
d
n
2H); 13C NMR (151 MHz, DMSO)
d (ppm) 170.6, 147.2, 130.0, 129.3,
1423, 1337, 1092, 988, 760, 540; HRMS (APCI) m/z: calcd for
C
129.3, 128.9, 128.4, 128.2, 128.0, 126.6, 124.2, 124.0, 123.7, 123.5,
16H12NO [M þ H]þ 234.0913; found 234.0913.
118.6, 109.1, 43.7; IR (KBr), n
(cmꢁ1) 3074, 2874, 2228, 1690, 1450,
1070, 760, 554; HRMS (APCI) m/z: calcd for C17H11N2O [M þH]þ
259.0866; found 259.0875.
4.4.2. 2,3-Dihydro-9-methoxy-1H-dibenzo[e,g]isoindol-1-one (3b)
White solid. Yield: 59%, 23.3 mg. mp: 251.3e252.9 ꢂC. 1H NMR
(600 MHz, DMSO)
d
(ppm) 9.16 (d, J ¼ 8.9 Hz,1H), 8.93 (d, J ¼ 8.3 Hz,
4.4.8. 2,3-Dihydro-6-fluoro-9,10-dimethoxy-1H-dibenzo[e,g]
isoindol-1-one (3h)
1H), 8.69 (s, 1H), 8.27 (s, 1H), 8.05 (d, J ¼ 7.8 Hz, 1H), 7.80 (t,
Yellow solid. Yield: 62%, 28.9 mg. mp: 276.3e278.1 ꢂC. 1H NMR
J ¼ 7.5 Hz, 1H), 7.74 (t, J ¼ 7.3 Hz, 1H), 7.38 (d, J ¼ 8.6 Hz, 1H), 4.73 (s,
2H), 4.01 (s, 3H); 13C NMR (151 MHz, DMSO)
d (ppm) 171.9, 158.3,
(600 MHz, DMSO)
d
(ppm) 8.68 (dd, J ¼ 17.3, 5.5 Hz, 3H), 8.14 (s,1H),
141.8, 131.7, 130.7, 128.3, 127.5, 127.0, 125.0, 124.4, 124.4,124.2, 121.7,
8.07 (dd, J ¼ 8.8, 6.1 Hz, 1H), 7.55e7.52 (m, 1H), 4.70 (s, 2H), 4.03 (s,
n
(cmꢁ1) 1697, 1337, 1220, 1153,
3H), 3.93 (s, 3H); 13C NMR (151 MHz, DMSO)
d (ppm) 171.9, 162.0 (d,
117.3, 105.0, 55.5, 43.8; IR (KBr),
1098, 858, 733; HRMS (APCI) m/z: calcd for C17H14NO2 [M þ H]þ
1J ¼ 243.07 Hz), 150.0, 149.2, 141.8, 132.8 (d, 3J ¼ 8.89 Hz), 127.0 (d,
3J ¼ 9.19 Hz), 124.3 (d, 4J ¼ 3.54 Hz), 123.1, 122.8, 122.7, 115.2 (d,
2J ¼ 24.39 Hz), 108.9 (d, 2J ¼ 22.15 Hz), 104.9, 103.6, 55.9, 55.4, 43.7;
264.1019; found 264.1027.
19F NMR (376 MHz, DMSO)
d
(ppm) ꢁ110.94; IR (KBr),
n )
(cmꢁ1
4.4.3. 2,3-Dihydro-9,10-dimethoxy-1H-dibenzo[e,g]isoindol-1-one
3071, 1686, 1522, 1431, 1261, 1157, 1026, 829, 781, 608; HRMS (APCI)
(3c) [8]
m/z: calcd for C18H15FNO3 [M þ H]þ 312.1030; found 312.1038.
1H NMR (400 MHz, DMSO)
d
(ppm) 8.85 (d, J ¼ 8.4 Hz, 1H), 8.72
(s, 2H), 8.20 (s, 1H), 8.01 (d, J ¼ 7.8 Hz, 1H), 7.76 (t, J ¼ 7.2 Hz, 1H),
7.66 (t, J ¼ 7.4 Hz,1H), 4.72 (s, 2H), 4.03 (s, 3H), 3.93 (s, 3H); 13C NMR
4.4.9. 12,13-Dihydro-11H-benzo[e]naphtho[2,1-g]isoindol-11-one
(3i)
(151 MHz, DMSO)
d (ppm) 172.1, 149.6, 149.1, 142.1, 130.8, 128.1,
White solid. Yield: 54%, 22.9 mg. mp: 238.1e239.9 ꢂC. 1H NMR
126.2, 125.8, 124.7, 124.3, 123.8, 123.7, 122.3, 104.4, 103.7, 55.7, 55.4,
43.7.
(600 MHz, DMSO)
d
(ppm) 9.95 (d, J ¼ 8.3 Hz, 1H), 8.95 (d,
J ¼ 8.4 Hz, 1H), 8.88 (d, J ¼ 9.5 Hz, 2H), 8.13 (dd, J ¼ 15.0, 8.5 Hz, 2H),
8.05 (d, J ¼ 7.6 Hz, 1H), 7.85 (t, J ¼ 7.5 Hz, 1H), 7.77 (t, J ¼ 7.3 Hz, 1H),
4.4.4. 2,3-Dihydro-11-methyl-1H-dibenzo[e,g]isoindol-1-one (3d)
Yellow solid. Yield: 57%, 21.1 mg. mp: 212.2e214.1 ꢂC. 1H NMR
7.65 (m, 2H), 4.89 (s, 2H); 13C NMR (151 MHz, DMSO)
d (ppm) 171.8,
146.8,132.6,131.3,129.3,129.1,129.1,128.0,127.5,127.3,126.7,126.5,
(600 MHz, DMSO)
d
(ppm) 8.88 (d, J ¼ 8.4 Hz,1H), 8.76 (d, J ¼ 8.2 Hz,
126.3, 126.0, 124.9, 124.2, 124.2, 121.4, 43.9; IR (KBr),
n
(cmꢁ1) 3094,
1H), 8.57 (s, 1H), 8.05 (d, J ¼ 7.8 Hz, 1H), 7.80 (t, J ¼ 7.3 Hz, 1H), 7.73
2901, 1680, 1406, 1119, 797, 758, 538; HRMS (APCI) m/z: calcd for
(t, J ¼ 7.4 Hz, 1H), 7.61 (t, J ¼ 7.7 Hz, 1H), 7.52 (d, J ¼ 7.1 Hz, 1H), 4.78
20H14NO [M þ H]þ 284.1070; found 284.1079.
(s, 2H), 3.03 (s, 3H); 13C NMR (151 MHz, DMSO)
d (ppm) 171.6, 146.7,
C
135.8, 131.8, 131.4, 130.6, 129.1, 127.5, 127.0, 126.6, 126.5, 126.4, 124.1,
123.9, 121.2, 43.9, 25.1; IR (KBr),
1456, 1261, 1097, 804, 527; HRMS (APCI) m/z: calcd for C17H14NO
[M þ H]þ 248.1070; found 248.1079.
n
(cmꢁ1) 3072, 2924, 2855, 1695,
4.4.10. 3-Methyl-12,13-dihydro-11H-benzo[e]naphtho[2,1-g]
isoindol-11-one (3j)
Yellow solid. Yield: 60%, 26.7 mg. mp: 256.4e257.9 ꢂC. 1H NMR
(600 MHz, DMSO)
d
(ppm) 9.94 (d, J ¼ 8.4 Hz,1H), 8.90 (d, J ¼ 9.1 Hz,
1H), 8.80 (d, J ¼ 19.2 Hz, 2H), 8.12 (d, J ¼ 9.0 Hz,1H), 8.05 (dd, J ¼ 7.5,
4.4.5. 2,3-Dihydro-6-methyl-1H-dibenzo[e,g]isoindol-1-one (3e)
Yellow solid. Yield: 64%, 23.7 mg. mp: 250.5e251.9 ꢂC. 1H NMR
(600 MHz, DMSO)
4.9 Hz, 2H), 7.65 (dd, J ¼ 10.7, 3.9 Hz, 1H), 7.61 (dd, J ¼ 10.2, 4.8 Hz,
2H), 4.86 (s, 2H), 2.65 (s, 3H); 13C NMR (151 MHz, DMSO)
d (ppm)
d (ppm) 9.26e9.19 (m, 1H), 8.90e8.85 (m, 1H),
171.9, 146.8, 139.0, 132.6, 131.5, 131.3, 129.2, 129.2, 129.0, 127.8,
127.3, 126.7, 126.2, 125.4, 124.9, 124.6, 124.1, 123.7, 121.5, 43.9, 21.9;
8.73 (s, 1H), 8.69 (s, 1H), 7.98 (d, J ¼ 8.1 Hz, 1H), 7.71 (dd, J ¼ 9.0,
4.8 Hz, 2H), 7.59 (d, J ¼ 8.1 Hz, 1H), 4.75 (s, 2H), 2.62 (s, 3H); 13C
IR (KBr), n
(cmꢁ1) 3072, 2854, 1670, 1450, 1337, 1215, 1028, 760, 644;
NMR (151 MHz, DMSO)
d (ppm) 171.9, 144.6, 138.6, 131.3, 129.6,
HRMS (APCI) m/z: calcd for C21H16NO [M þ H]þ 298.1226; found
129.0, 127.5, 127.3, 126.8, 124.5, 124.3, 123.5, 123.5, 123.5, 123.4,
43.9, 21.8; IR (KBr),
n
(cmꢁ1) 3179, 3065, 2885, 1691, 1454, 1339,
298.1225.
1223, 1036, 779; HRMS (APCI) m/z: calcd for C17H14NO [M þ H]þ
248.1070; found 248.1082.
4.4.11. 3-Fluoro-12,13-dihydro-11H-benzo[e]naphtho[2,1-g]
isoindol-11-one (3k)
4.4.6. 2,3-Dihydro-9-fluoro-1H-dibenzo[e,g]isoindol-1-one (3f)
Yellow solid. Yield: 63%, 23.7 mg. mp: 264.8e265.9 ꢂC. 1H NMR
Yellow solid. Yield: 52%, 23.5 mg. mp: 260.1e261.9 ꢂC. 1H NMR
(600 MHz, DMSO)
d
(ppm) 9.94 (d, J ¼ 8.4 Hz, 1H), 8.87 (s, 1H), 8.80
(600 MHz, DMSO)
d
(ppm) 9.27 (dd, J ¼ 8.9, 6.4 Hz, 1H), 8.87 (d,
(d, J ¼ 9.1 Hz, 1H), 8.72 (dd, J ¼ 12.0, 2.2 Hz, 1H), 8.19 (dd, J ¼ 8.8,
J ¼ 8.1 Hz, 1H), 8.78 (s, 1H), 8.66 (dd, J ¼ 11.7, 2.4 Hz, 1H), 8.07 (d,
6.0 Hz,1H), 8.10 (d, J ¼ 9.0 Hz, 1H), 8.04 (d, J ¼ 7.4 Hz, 1H), 7.68e7.61
J ¼ 7.6 Hz,1H), 7.83e7.76 (m, 2H), 7.61 (m,1H), 4.75 (s, 2H); 13C NMR
(m, 3H), 4.84 (s, 2H); 13C NMR (151 MHz, DMSO)
d (ppm) 171.6,
(151 MHz, DMSO)
d
(ppm) 171.6, 161.1 (d, 1J ¼ 242.02 Hz), 143.8,
162.5 (d, 1J ¼ 244.45 Hz), 146.6, 133.3 (d, 3J ¼ 9.00 Hz), 132.9, 131.5,
128.9, 128.9 (d, 4J ¼ 4.38 Hz), 128.0, 127.3, 127.2 (d, 3J ¼ 9.27 Hz),
127.0, 126.7, 125.8, 125.0, 123.5, 121.7, 116.7 (d, 2J ¼ 24.18 Hz), 109.2
132.0 (d, 3J ¼ 8.38 Hz), 130.6 (d, 4J ¼ 4.20 Hz), 128.8, 128.1, 127.0,
126.0 (d, 3J ¼ 8.76 Hz), 124.5, 124.3, 124.1, 124.1, 116.1 (d,
2J ¼ 23.43 Hz), 108.8 (d, 2J ¼ 22.40 Hz), 43.9; 19F NMR (376 MHz,
(d, 2J
¼
22.86 Hz), 43.9; 19F NMR (376 MHz, DMSO)
DMSO)
d
(ppm) ꢁ112.19; IR (KBr),
n
(cmꢁ1) 3069, 2883, 1691, 1522,
d
(ppm) ꢁ109.25; IR (KBr),
n
(cmꢁ1) 3072, 1666, 1423, 1263, 1219,
1441, 1340, 1178, 1140, 829, 762, 594; HRMS (APCI) m/z: calcd for
1016, 870, 760, 596; HRMS (APCI) m/z: calcd for C20H13FNO [M þ
C
16H11FNO [M þ H]þ 252.0819; found 252.0828.
H]þ 302.0976; found 302.0982.
7

Y. Kang, Y. He, J. Sui et al.
Tetrahedron 84 (2021) 131981
4.4.12. 8,9-Dihydro-10H-benzo[e]thieno[3,2-g]isoindol-10-one (3l)
Yellow solid. Yield: 71%, 25.4 mg. mp: 261.2e262.9 ꢂC. 1H NMR
1126, 976, 841, 756, 538; HRMS (APCI) m/z: calcd for C19H13N2O2
[M þ H]þ 301.0972; found 301.0976.
(600 MHz, DMSO)
d
(ppm) 8.85 (s, 1H), 8.62 (d, J ¼ 8.2 Hz, 1H), 8.29
(d, J ¼ 5.3 Hz,1H), 8.10 (d, J ¼ 8.0 Hz,1H), 7.99 (d, J ¼ 5.2 Hz,1H), 7.77
4.5.4. 2-Acetyl-6-methyl-2,3-dihydro-1H-dibenzo[e,g]isoindol-1-
one (3ad)
(t, J ¼ 7.4 Hz, 1H), 7.68 (t, J ¼ 7.4 Hz, 1H), 4.85 (s, 2H); 13C NMR
(151 MHz, DMSO)
d (ppm) 170.1, 140.9, 137.1, 130.1, 129.7, 128.4,
White solid. Yield: 73%, 31.6 mg. mp: 293.5e294.9 ꢂC. 1H NMR
128.1, 126.3, 126.0, 124.9, 124.9, 124.5, 122.1, 45.1; IR (KBr), n )
(cmꢁ1
(600 MHz, CDCl3)
d (ppm) 9.15e9.13 (m, 1H), 8.65e8.63 (m, 1H),
3180, 3072, 2876, 1693, 1346, 1167, 966, 868, 766; HRMS (APCI) m/z:
8.46 (s, 1H), 7.75 (d, J ¼ 8.1 Hz, 1H), 7.70 (dd, J ¼ 6.2, 3.3 Hz, 2H), 7.50
calcd for C14H10NOS [M þ H]þ 240.0478; found 240.0485.
(d, J ¼ 8.1 Hz, 1H), 4.95 (s, 2H), 2.74 (s, 3H), 2.66 (s, 3H); 13C NMR
(151 MHz, CDCl3)
d (ppm) 171.0, 168.9, 143.1, 140.6, 133.2, 130.3,
4.4.13. 8,9-Dihydro-10H-benzo[e]furo[3,2-g]isoindol-10-one (3m)
White solid. Yield: 52%, 17.4 mg. mp: 248.4e249.9 ꢂC. 1H NMR
129.4, 128.1, 127.5, 127.4, 124.3, 124.3, 123.9, 123.7, 123.0, 122.7, 46.8,
24.9, 22.6; IR (KBr), n
(cmꢁ1) 3072, 1728, 1684, 1290, 1192, 972, 891,
(600 MHz, DMSO)
d
(ppm) 8.73 (s, 1H), 8.42 (d, J ¼ 8.2 Hz, 1H), 8.20
777, 735, 584; HRMS (APCI) m/z: calcd for C19H16NO2 [M þ H]þ
(d, J ¼ 2.0 Hz, 1H), 8.11 (d, J ¼ 8.2 Hz, 1H), 7.78e7.75 (m, 1H), 7.70 (d,
290.1176; found 290.1186.
J ¼ 2.0 Hz, 1H), 7.66e7.64 (m, 1H), 4.85 (s, 2H); 13C NMR (151 MHz,
DMSO)
d (ppm) 168.5, 146.1, 145.6, 141.9, 128.8, 128.3, 125.6, 125.0,
124.5, 124.5, 123.6, 117.7, 106.1, 44.9; IR (KBr),
n
(cmꢁ1) 3179, 3069,
4.5.5. 9-Acetyl-8,9-dihydro-10H-benzo[e]furo[3,2-g]isoindol-10-
one (3ae)
2876, 1701, 1393, 1346, 1175, 1015, 885, 771, 646; HRMS (APCI) m/z:
calcd for C14H10NO2 [M þ H]þ 224.0706; found 224.0711.
Yellow solid. Yield: 64%, 27.0 mg. mp: 243.2e244.9 ꢂC. 1H NMR
(600 MHz, CDCl3, TFA-d1)
d
(ppm) 8.40 (d, J ¼ 8.2 Hz, 1H), 8.00 (d,
4.5. General procedure for the synthesis of 2-Acetyl-2,3-dihydro-
1H-dibenzo [e,g]isoindol-1-one (3aa-3ae)
J ¼ 5.2 Hz, 1H), 7.90 (d, J ¼ 8.1 Hz, 1H), 7.81 (t, J ¼ 7.5 Hz, 1H), 7.76 (d,
J ¼ 5.2 Hz, 1H), 7.67 (t, J ¼ 7.5 Hz, 1H), 5.09 (s, 2H), 2.81 (s, 3H); 13
C
NMR (151 MHz, CDCl3, TFA-d1)
d (ppm) 174.1, 168.0, 139.7, 138.4,
The solution of 1-acetyl-3,4-diphenyl-1,5-dihydropyrrol-2-one
1a (41.6 mg, 0.150 mmol) in EtOH (15 mL) in a quartz tube irradi-
ated with a high-pressure mercury lamp (500 W) at 25 ꢂC for 1 h
under an argon atmosphere. Volatiles were removed under
reduced pressure and the residue was purified by column chro-
matography on silica (ethyl acetate/petroleum ether, 1:5) to give
3aa (28.9 mg, 70%). Similarly, compounds 3ab-3ae were obtained
with the same method as described above.
132.2, 130.5, 130.1, 128.7, 127.1, 125.4, 125.1, 124.6, 122.9, 121.7, 48.4,
24.4; IR (KBr), n
(cmꢁ1) 3098, 2924, 1722, 1688, 1344, 1134, 968, 872,
727, 623, 534; HRMS (APCI) m/z: calcd for C16H12NO2S [M þ H]þ
282.0583; found 282.0589.
4.5.6. 2,3-Dihydro-2-methyl-1H-dibenzo[e,g]isoindol-1-one (3af)
[7b]
1H NMR (600 MHz, CDCl3)
d (ppm) 9.34e9.33 (m, 1H), 8.67 (d,
J ¼ 8.3 Hz, 1H), 8.64 (d, J ¼ 8.9 Hz, 1H), 7.76 (d, J ¼ 7.9 Hz, 1H),
4.5.1. 2-Acetyl-2,3-dihydro-1H-dibenzo[e,g]isoindol-1-one (3aa)
White solid. Yield: 70%, 28.9 mg. mp: 226.2e227.9 ꢂC. 1H NMR
7.72e7.67 (m, 3H), 7.61 (t, J ¼ 7.4 Hz, 1H), 4.57 (s, 2H), 3.28 (s, 3H);
13C NMR (151 MHz, CDCl3)
d (ppm) 170.24, 140.83, 131.85, 130.41,
(600 MHz, CDCl3)
8.65e8.63 (m, 1H), 7.84 (d, J ¼ 7.9 Hz, 1H), 7.80 (t, J ¼ 7.6 Hz, 1H),
7.73e7.70 (m, 2H), 7.67 (t, J ¼ 7.4 Hz, 1H), 4.94 (s, 2H), 2.74 (s, 3H);
d
(ppm) 9.14e9.12 (m, 1H), 8.67 (d, J ¼ 8.3 Hz,1H),
128.42, 127.70, 127.65, 127.22, 127.14, 126.62, 125.62, 124.68, 123.78,
123.60, 122.76, 50.84, 29.53.
13C NMR (151 MHz, CDCl3)
d (ppm) 171.0, 168.8, 143.0, 133.0, 130.6,
130.1, 128.3, 127.8, 127.8, 127.2, 126.0, 124.4, 124.3, 123.8, 123.6,
4.6. General procedure for the synthesis of 1H-dibenzo[e,g]
isoindole-1,3(2H)-dione (4)
123.0, 46.8, 25.0; IR (KBr),
n
(cmꢁ1) 1726, 1684, 1379, 1302, 1126,
895, 754, 617; HRMS (ESI) m/z: calcd for C18H13NO2Na [M þ Na]þ
298.0838; found 298.0830.
Sodium methoxide in MeOH (100 mL, 0.1 mmol, 30%) was added
to the solution of 3a or 3aa (0.1 mmol) in DMSO (5 mL) at room
temperature under an oxygen atmosphere. When the reaction was
completed (detected by TLC), water was added and extracted with
CH2Cl2. The organic layer was combined, washed (brine), and
concentrated in vacuo. The residue was purified by silica column
chromatography (ethyl acetate/petroleum ether, 1:2) to afford the
product 4 in 72% and 60%.
4.5.2. 2-Acetyl-9-methoxy-2,3-dihydro-1H-dibenzo[e,g]isoindol-1-
one (3ab)
Yellow solid. Yield: 72%, 32.9 mg. mp: 277.2e278.9 ꢂC. 1H NMR
(600 MHz, CDCl3, TFA-d1)
J ¼ 8.4 Hz, 1H), 7.89 (d, J ¼ 1.8 Hz, 1H), 7.74 (t, J ¼ 7.5 Hz, 1H),
7.64e7.59 (m, 2H), 7.25 (dd, J ¼ 6.7, 2.0 Hz, 1H), 4.67 (s, 2H), 4.01 (s,
d
(ppm) 8.77 (d, J ¼ 8.9 Hz, 1H), 8.48 (d,
3H), 2.71 (s, 3H); 13C NMR (151 MHz, CDCl3, TFA-d1)
d (ppm) 174.3,
168.8, 159.0, 141.0, 132.4, 132.3, 130.3, 128.0, 125.8, 125.5, 124.5,
4.6.1. 1H-dibenzo[e,g]isoindole-1,3(2H)-dione (4) [17b]
123.8, 122.5, 121.0, 117.5, 105.4, 55.7, 46.9, 24.3; IR (KBr),
n
(cmꢁ1
)
1H NMR (600 MHz, DMSO)
d
(ppm) 11.30 (s, 1H), 8.99e8.94 (m,
4H), 7.89e7.86 (m, 2H), 7.84e7.82 (m, 2H); 13C NMR (151 MHz,
DMSO) (ppm) 170.6, 132.7, 129.3, 128.4, 127.5, 125.1, 124.8, 123.7.
2937, 2837, 1726, 1679, 1522, 1342, 1124, 1042, 895, 762, 627, 544;
HRMS (APCI) m/z: calcd for C19H16NO3 [M þ H]þ 306.1125; found
306.1134.
d
4.5.3. 2-Acetyl-3-oxo-2,3-dihydro-1H-dibenzo[e,g]isoindole-6-
carbonitrile (3ac)
4.7. Synthesis of 1 mmol Scale 3aa
Yellow solid. Yield: 78%, 35.1 mg. mp: 293.5e294.9 ꢂC. 1H NMR
The solution of 1-acetyl-3,4-diphenyl-1,5-dihydropyrrol-2-one
1a (277.0 mg, 1 mmol) in EtOH (100 mL) in a quartz tube irradiated
with a high-pressure mercury lamp (500 W) at 25 ꢂC for 4.5 h under
an argon atmosphere. Volatiles were removed under reduced
pressure and the residue was purified by column chromatography
on silica (ethyl acetate/petroleum ether, 1:5) to afford the corre-
sponding products 3aa (176.0 mg, 64%).
(600 MHz, CDCl3, TFA-d1)
d
(ppm) 9.31 (d, J ¼ 8.4 Hz, 1H), 9.10 (s,
1H), 8.76 (d, J ¼ 8.4 Hz, 1H), 8.09 (d, J ¼ 7.9 Hz, 1H), 8.02e7.98 (m,
2H), 7.89 (t, J ¼ 7.5 Hz, 1H), 5.27 (s, 2H), 2.87 (s, 3H); 13C NMR
(151 MHz, CDCl3, TFA-d1)
d (ppm) 174.9, 168.6, 147.3, 132.3, 132.1,
130.8, 130.1, 129.9,129.7, 129.1, 126.3, 125.6, 125.1, 124.1, 122.5, 110.3,
47.6, 24.5; IR (KBr),
n
(cmꢁ1) 3099, 2930, 2226, 1726, 1686, 1306,
8

Y. Kang, Y. He, J. Sui et al.
Tetrahedron 84 (2021) 131981
S.Z. Whetzel, A.E. Corbin, T.A. Pugsley, T.G. Heffner, L.D. Wise, Bioorg. Med.
4.8. Detection of H2 generated by Annulation of 1g
Chem. Lett 8 (1998) 1499e1502.
ꢀ
[2] F. Csende, F. Miklos, A. Porkolab, ARKIVOC 2 (2013) 378e388.
Using Ar as carrier gas, thermal conductivity detector (TCD
temperature: 120 ꢂC) and stainless steel column (column length:
2 m, column temperature: 40 ꢂC, Tam TDS-01: 60e80 mesh) were
used for gas chromatography analysis. Under the condition of gas
velocity of 0.06 Mpa and the flow rate of 50 mL/min, gas was
analyzed at room temperature. The ethanol (125 mL) was degassed
for an hour by ultrasonic at room temperature. Then, sodium sulfite
(14 g) and hydroquinone (1.1 g) was added and the mixture was
refluxed for 3 h to remove the oxygen in the solvent. The compound
of 1g (151 mg, 0.500 mmol) was dissolved in 50 mL deoxidization
chromatographic ethanol at room temperature in a quartz tube I. In
the same conditions, quartz tube II without compound 1g was
prepared. All operations discussed above were performed under
argon atmosphere. With strict sealing, quartz tube I and II were
irradiated with a high-pressure mercury lamp (500 W) at room
temperature for 1.5 h. According to the experiment data, the
reference substance H2 retention time tR1 was 1.413 min
(Figure S3); the retention time tR2 in quartz tube I was 1.381 min
(Figure S4), indicating the presence of H2 in the tube I. However, H2
was not observed in quartz tube II, further confirming the presence
of H2 was generated during the annulation of 1g.
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The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
Acknowledgements
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