Formal [4 + 1] cycloaddition strategy for the synthesis of dihydrobenzofurans via Michael addition of 2-(2-nitrovinyl)-phenols and malonate esters (C1 synthon) and subsequent iodine-catalyzed oxidative annulation

Article abstract of DOI:10.1016/j.tet.2018.09.028

A novel [4 + 1] cycloaddition protocol for the synthesis of dihydrobenzo(naphtho)furan skeletons from readily available 2-(2-nitrovinyl)-phen(naphth)ols and malonate esters via a tandem Michael addition/iodine-catalyzed oxidative annulation has been devel

Full text of DOI:10.1016/j.tet.2018.09.028

Accepted Manuscript
Formal [4 + 1] cycloaddition strategy for the synthesis of dihydrobenzofurans via
Michael addition of 2-(2-nitrovinyl)-phenols and malonate esters (C1 synthon) and
subsequent iodine-catalyzed oxidative annulation
Jiaying Leng, Jiang Meng, Xiaoyan Luo, Wei-Ping Deng
PII:
S0040-4020(18)31107-4
10.1016/j.tet.2018.09.028
TET 29800
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 30 August 2018
Revised Date: 12 September 2018
Accepted Date: 14 September 2018
Please cite this article as: Leng J, Meng J, Luo X, Deng W-P, Formal [4 + 1] cycloaddition strategy for
the synthesis of dihydrobenzofurans via Michael addition of 2-(2-nitrovinyl)-phenols and malonate esters
(C1 synthon) and subsequent iodine-catalyzed oxidative annulation, Tetrahedron (2018), doi: https://
doi.org/10.1016/j.tet.2018.09.028.
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Formal [4 + 1] Cycloaddition Strategy for the
Synthesis of Dihydrobenzofurans via Michael
Addition of 2-(2-nitrovinyl)-phenols and Malonate
Esters (C1 Synthon) and Subsequent Iodine-catalyzed
Oxidative Annulation
Leave this area blank for abstract info.
Jiaying Leng, Jiang Meng, Xiaoyan Luo,* and Wei-Ping Deng*
Shanghai Key Laboratory of New Drug Design, School of Pharmacy, East China University of Science and
Technology, Shanghai 200237, China

ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Formal [4 + 1] Cycloaddition Strategy for the Synthesis of Dihydrobenzofurans via
Michael Addition of 2-(2-nitrovinyl)-phenols and Malonate Esters (C1 Synthon) and
Subsequent Iodine-catalyzed Oxidative Annulation
Jiaying Leng, Jiang Meng, Xiaoyan Luo,* and Wei-Ping Deng*
Shanghai Key Laboratory of New Drug Design, School of Pharmacy, East China University of Science and Technology, Shanghai 200237, China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A novel [4 + 1] cycloaddition protocol for the synthesis of dihydrobenzo(naphtho)furan
skeletons from readily available 2-(2-nitrovinyl)-phen(naphth)ols and malonate esters via a
tandem Michael addition/iodine-catalyzed oxidative annulation has been developed. This
method provides a new and facile application of malonate esters as 1,1-nucleophilic/electrophilic
type C1 synthons without a pre-functionalization step and the plausible reaction mechanism is
proposed.
Available online
2017 Elsevier Ltd. All rights reserved
.
Keywords:
Iodine-catalyzed
dihydrobenzofurans
nitroalkenes
malonate esters
1. Introduction
Figure 1. Pharmaceutical compounds containing 2,3-
dihydrobenzofuran rings
Five-membered heterocycles such as dihydrobenzofuran
represent pivotal structural motifs found in a large number of
biologically active molecules, drugs, and materials (Figure 1).1
Thus, the development of novel and highly efficient
methodologies for their synthesis has attracted continuous
attention from synthetic chemists. As known, cycloaddition
reactions such as [3 + 2] are powerful and well-studied tools for
the construction of five-membered rings.2 Comparatively, the
less-studied [4 + 1] annulations providing alternative and
versatile approaches to obtain these compounds are attracting
more and more attentions owing to their distinct synthetic
advantages.3 According to the literatures, carbon monoxide,
fischer carbenes, nucleophilic carbenes, isocyanides, diazo
reagents and sulfur/phosphine ylides are widely used as one-
carbon(C1) synthons in the [4 + 1] annulations.4 Based on these
C1 synthons, a variety of highly efficient methodologies toward
five-membered heterocycles have been reported. However, there
are rare methodologies being developed based on a new C1
synthon for it is a rather challenging work. Thus, the novel [4 +
1] annulation to construct five-membered heterocycles relied on
new C1 synthons or strategies is worth to explore.
Differing from the aforementioned C1 synthons, the
compounds with active methylene group such as 1,3-dicarbonyl
compounds also can be used as C1 synthons for that they can be
easily transformed into carbon dianion under basic conditions
(scheme 1A).5 Therefore, they are commonly used as 1,1-
bisnucleophilic type C1 synthons in the [4 + 1] annulations,
while the aforementioned nucleophilic carbenes, isocyanides,
diazo reagents and sulfur/phosphine ylides are used as 1,1-
nucleophilic/electrophilic type ones owing to their special
structures or characters such as with leaving groups. In 2011, Xie
et al6 and co-workers reported a noval cycloaddition to construct
dihydrobenzofuran using α-halo-1,3-dicarbonyl compound as C1
synthon to react with salicylic aldehyde derivatives (scheme 1B).
Recently, Lei et al7 reported a novel N-iodosuccinimide-
mediated decarboxylative [4 + 1] oxidative annulation between
2-vinylpyridine derivatives and malonate monoesters to construct
indolizine derivatives by utilizing malonate monoesters as a C1
synthons, in which the in situ formed 2,2-diiodoacetate was the
active intermediate, which reacted with 2-vinylpyridine
derivatives through an electro-philic/radical reaction path way
(scheme 1C). With the sustaining interests in heterocycle
synthesis, we have reported the novel iodine-catalyzed [3 + 2]
annulations of allenes with 1,3-dicarbonyl compounds or
enamines for synthesis of polysubstituted furans and pyrroles, in
which the ɑ-carbon anion with potential nucleophilic reactivity of
the intermediate could be inverted into electrophilic site under
oxidative conditions.8 With this information in mind, we
envisioned that the compounds with active methylene group
would find new application for they can first be used as
nucleophile in the reaction and then converted into electrophile
under
oxidative
conditions
without
a
necessary

2
Te rt hae dro n
ACCEPTED MANUSCRIPT
prefunctionalization step. This strategy would endow these
traditional 1,1-bisnucleophiles the new reactivity as 1,1-
nucleophilic/electrophilic type C1 synthons which are equal to
diazo reagents, α-halo carbonyl compounds and sulfur/phosphine
ylides (scheme 1D).
After initial screening of the reaction conditions, 2-(2-
nitrovinyl)-naphthol 1a and methyl malonate 2a were
chosen as the substrates and NaHCO3 was chosen as base
for the further optimization of the formal [4 + 1] oxidative
annulation (see the Supplementary Material for the details,
Table 1). When KI (20 mol %) was used as the catalyst and
TBHP (70 wt % in H2O) as oxidant in 1,4-dioxane, the
desired dihydronaphthofurans 3aa was obtained in 47%
yield (Table 1, entry 1). The examination of catalysts
revealed that NIS (20 mol %) gave a better result and the
yield of 3aa was increased to 60% after prolonging the
reaction time to 36 h (Table 1, entry 2), while I2 (20 mol %)
afforded the nearly same result (Table 1, entry 3). Other
catalyst like NaBr could not trigger this reaction (Table 1,
entry 4). The further screening of catalysts proved that
when the same molar quantity of iodide was employed, the
reaction that employing I2 as catalyst would perform better
and the improvement of the catalyst loading could
deteriorate the desired reaction (Table 1, entries 5-6). Some
other oxidants (such as DTBP and H2O2) failed to improve
the yield of 3aa (Table 1, entries 7 and 8). Surprisingly, the
result was dramatically increased to 82% when using
TBHP (5.5 M in decane) as oxidant (Table 1, entry 9). This
encouraging result implied that the water in oxidant might
deteriorate the reaction. To our surprised, the use of dried
THF as solvent did not improve the yield (Table 1, entry
10). Further experiments showed that 90% of 3aa would be
obtained by increasing the amount of methyl malonate 2a
to 1.8 equiv (Table 1, entry 11) and 71% of 3aa could still
be got after reducing the catalyst loading to 5 mol % (Table
1, entry 12). Control experiments exhibited that both
NaHCO3 and catalyst are necessary for this transformation
(Table 1, entry 13 and 15). Our initial screening of the
reaction conditions showed that the stronger base such as
K2CO3 was not suitable for this reaction for which would
unambiguously lead to intramolecular ester interchange
side reaction (see the Supplementary Material for the
details, Table 1). When replacing NaHCO3 with K2CO3, a
considerable drop in yield is observed unsurprisingly
(Table 1, entry 14), but the reaction time was shorten to 2 h.
Scheme 1. The reaction modes of active methylene groups as C1
synthons
2. Results and discussion
The reaction of nitroalkenes based on salicylaldehydes
and malonate esters was designed to test our hypothesis. It
was envisaged that malonate esters would first react with
nitroalkenes to form the Michael adducts, which could be
further oxidized under oxidative conditions and captured
by phenolic hydroxyl to construct dihydrobenzofurans
(scheme 2). The possible side reactions such as the
Table 1. The optimization of reaction conditions for the
oxidation of phenol and
ɑ-carbon of nitroalkane,
formal [4 + 1] annulationa
intramolecular ester interchange of phenolic hydroxyl with
ester along with some intermolecular reactions would
unambiguously increase the difficulty of the designed [4 +
1] reaction, not to mention the compatibility of Michael
addition reaction and the crucial oxidative step.9 Herein,
we report the first iodine-catalyzed formal [4 + 1] oxidative
annulation of malonate esters and readily available 2-(2-
nitrovinyl)-naphthols or 2-(2-nitrovinyl)-phenols for the
synthesis of dihydrobenzo(naphtho)furans with the new
entry
cat.
oxidant
equiv yield(%)b
of 2a
reactivity
of
active
methylenes
as
1,1-
1
2
3
4
5
6
7
KI (20 mol %)
NIS (20 mol %)
I2 (20 mol %)
TBHPc
TBHPc
TBHPc
1.2
1.2
1.2
1.2
1.2
1.2
1.2
47
nucleophilic/electrophilic type C1 synthons.
60
Scheme 2. Initial design and its challenges
58
NaBr (20 mol %) TBHPc
nr
I2 (10 mol %)
NIS (10 mol %)
I2 (10 mol %)
TBHPc
TBHPc
DTBP
67
64
trace
8
I2 (10 mol %)
I2 (10 mol %)
I2 (10 mol %)
I2 (10 mol %)
H2O2
1.2
1.2
1.8
1.8
43
82
64
90
9
10e
TBHPd
TBHPd
TBHPd
11

12
I2 (5 mol %)
I2 (10 mol %)
I2 (10 mol %)
none
TBHPd
TBHPd
TBHPd
TBHPd
1.8
ACC7E1PTED MANUSCRIPT
13f
14g
15
1.8
1.8
1.8
trace
64
np
aStandard conditions: 1a (0.2 mmol), I2 (10 mol %), TBHP (5.5 M in decane) (2
equiv), NaHCO3 (1 equiv), THF (1.5 mL), 30 oC, and 24 h. bIsolated yield. cTBHP
(70 wt.% in H2O) was used. dTBHP (5.5 M in decane) was used. edry THF was
used. fno NaHCO3. gK2CO3 was used instead of NaHCO3. DTBP = di-tert-butyl
peroxide. nr = no reaction. np = no product.
Under the optimal conditions, the substrate scope of this
synthetic protocol was evaluated. Various malonate esters were
suitable reaction partners for 1a to afford corresponding
dihydronaphthofurans (Table 2). Methyl, ethyl and isopropyl
malonates
reacted
smoothly
with
1a
to
deliver
dihydronaphthofurans 3aa-ac in excellent yields. When tert-butyl
malonate was used, product 3ad was obtained in 67% yield after
8 days presumably owing to the steric hindrance. Furthermore,
changing one of the methyl group in 2a to benzyl afforded 3ae in
67% yield (dr = 1.5/1), while the reaction of benzyl malonate 2f
with 1a gave 3af in 93% yield after prolonging reaction time to
43 h. Unfortunately, further extending the substrate scope of
malonate esters to ethyl acetoacetate, methyl cyanoacetate and
acetoacetone was proved to be unsuitable for the reaction under
the current conditions, even employing K2CO3 as base or adding
Takemoto catalyst.
aStandard conditions: 1a (0.2 mmol), 2a (0.36 mmol), I2 (10 mol %), TBHP (5.5 M
in decane) (2 equiv), NaHCO3 (1 equiv), THF (1.5 mL), 30 oC. bNR = no reaction.
cNP = no product. dTakemoto catalyst was used.
Table 3. Synthesis of dihydrobenzofurans from malonate esters
with various 2-(2-nitrovinyl)-phenolsa
After testing the limitation of malonate esters, we moved
forward to examine substitution patterns for various 2-(2-
nitrovinyl)-phenols (Table 3). As indicated in table 3, 2-(2-
nitrovinyl)-phenols 1b reacted smoothly with the methyl, ethyl
and isopropyl malonates in good to excellent yields to afford
dihydrobenzofurans 3ba-bc. Also, various substituted 2-(2-
nitrovinyl)-phenols 1c-j were found suitable for this
transformation, delivering the desired products 3ca-ja in 65-99%
yields. These results revealed that the reactions were
insignificantly affected by positions or electronic properties of
the substituents. However, it should be noted that the reaction of
6-Cl substituted 2-(2-nitrovinyl)-phenols 1e with methyl
malonate 2a needed longer time to complete the transformation,
which implied that the nucleophilic property of the phenolic
hydroxyl might influence this transformation.
Table 2. Synthesis of dihydronaphthofurans from 2-(2-
nitrovinyl)-naphthol 1a with various malonate estersa
aStandard conditions: 1a (0.2 mmol), 2a (0.36 mmol), I2 (10 mol %),
TBHP (5.5 M in decane) (2 equiv), NaHCO3 (1 equiv), THF (1.5 mL).
As mentioned above, the dihydrobenzo(naphtho)furan
ring systems represent the privileged skeletons prevalent in
an increasing number of biologically active natural
products and pharmaceuticals. To date, a great deal of
research efforts have been devoted to the development of
new methods for the synthesis of these ring systems.10 In
spite of the significant achievements, most methods used
for the preparation of these ring systems still need a
necessary pre-functionalization step to prepare the
substrates or rely on some special substrates.11 This method
here provided a new perspective for solving the problem.

4
Te rt hae dro n
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To gain insight into the reaction pathway, several control
experiments were conducted. As is known, 1,3-dicarbonyl
compounds can react with molecular iodine (I2) or N-
iodosuccinimide (NIS) under basic conditions to form
ɑ-
monoiodinated 1,3-dicarbonyl compounds, in which I2 and
NIS act as I+ sources.12 As indicated in scheme 3, 1
equivalent of I2 or NIS was used without additional oxidant
to promote the reaction. Obviously, the desired product
could also be obtained, but only in less than 10% and 43%
yield respectively with a rather low conversion after
prolonging reaction time to 48 h. These results revealed
that iodinated 1,3-dicarbonyl compounds may be included
in this reaction, but they are not the real active
intermediates and I2 is not the active catalyst. At the
beginning of the reaction conditions screening, Michael
product was obtained when using TBAI as catalyst (see the
Supporting Information for the details, Table 1), which
indicated the Michael adduct could be the key intermediate
of this transformation. Thus, the Michael adduct of 2-(2-
nitrovinyl)-phenols 1b and methyl malonate 2a was
obtained to test the hypothesis. As shown in scheme 4, the
intermediate 3ba’ was transformed into product 3ba in 73%
yield after 12 h under standard conditions, while only trace
amount of product 3ba was obtained without NaHCO3.
These results proved that the Michael adducts are indeed
the intermediate and base is necessary in both steps of
Michael addition and oxidative annulation in this reaction.
Moreover, the intermediate 3ba’ could not be further
converted into 3ba with 1 equivalent of I2 and NaHCO3,
which further confirmed that I2 is not the active species.
Moreover, the addition of TEMPO did not retard the
desired reaction under standard conditions, which indicated
that the oxidative annulation might not proceed through a
radical pathway (scheme 5).
According to Ishihara and co-workers’ pioneered work
and our previous reports, the potential actual oxidant
species, [IO2]−, could be generated by oxidation of I2 with
TBHP under basic conditions.13 Thus,
a
tentative
mechanism is proposed in scheme 6 based on the results of
control experiments described above and other related
work. As depicted in scheme 6, I2 could be transformed
into hypoiodite [IO]− under basic conditions initially, then,
which is further oxidized by TBHP to form the iodite
[IO2]−. The Michael adduct formed by the reaction of
malonate ester 2a and nitroalkene 1b could possibly react
with the in situ formed reactive species [IO2]− to give the
intermediate [I]-3ba’
, which could be captured by
intramolecular
phenolic
hydroxyl
to
construct
dihydrobenzofuran and releasing hypoiodite species [IO]−
for the next catalytic cycle.
Scheme 6. Tentative Mechanism
Scheme 3. The reaction of 2-(2-nitrovinyl)-phenols 1a with
ɑ
-monoiodinated methyl malonate
Finally, to demonstrate the further applications of this
strategy for the application of malonate esters as 1,1-
nucleophilic/electrophilic type C1 synthons, the reaction of
ortho-quinone methides (o-QMs) 4a and malonate ester 2a
was examined. As a result, the reaction was performed
smoothly to deliver desired product 5aa in 50% yield with
K2CO3 as base (scheme 7, eq 1). An intending to convert
the primary nitro derivative 3aa to acid14 gave methyl
naphtho[2,1-b]furan-2-carboxylate 6aa in 69% yield
(scheme 7, eq 2), which provided a novel approach to
obtain this useful skeleton. The naphtho[2.1-b]furan
Scheme 4. Investigation of the reaction intermediate
skeleton is proved to have analgesic activity.15 Moreover
，
we can also obtain a new kind of tricyclic skeleton 7ea via
simple reduction and cyclization (scheme 7, eq 3).16
Scheme 7. Further applications
Scheme 5. Transformation of reaction intermediate with
radical scavenger

A yellow solid (62 mg, 90% yield), Mp: 145-147 °C. 1H NMR
ACCEPTED MANUSCRIPT
(400 MHz, Chloroform-d) δ 7.87 (d, J = 8.2 Hz, 1H), 7.82 (d, J =
8.9 Hz, 1H), 7.73 (d, J = 8.3 Hz, 1H), 7.63-7.53 (m, 1H), 7.46-
7.37 (m, 1H), 7.26 (d, J = 8.9 Hz, 1H), 5.49 (t, J = 5.9 Hz, 2H),
4.78 (d, J = 5.9 Hz, 1H), 3.88 (s, 3H), 3.82 (s, 3H). 13C NMR
(100 MHz, Chloroform-d) δ 167.7, 165.9, 155.3, 132.1, 130.6,
129.7, 129.1, 128.4, 124.5, 121.4, 114.4, 112.3, 91.1, 73.0, 54.2,
53.8, 46.1. HRMS (EI-TOF): calcd for, C17H15NO7
[M]+:345.0849; found, 345.0848.
4.2.2.
Diethyl 1-(nitromethyl)naphtho[2,1-b]furan-2,2(1H)-
dicarboxylate (3ab)
A yellow solid (69 mg, 92% yield), Mp: 103-105 °C. 1H NMR
(400 MHz, Chloroform-d) δ 7.87 (d, J = 8.2 Hz, 1H), 7.81 (d, J
= 8.9 Hz, 1H), 7.72 (d, J = 8.3 Hz, 1H), 7.60-7.56 (m, 1H), 7.43-
7.39 (m, 1H), 7.26 (d, J = 8.9 Hz, 1H), 5.51 (dd, J = 8.0, 3.8 Hz,
1H), 4.83-4.74 (m, 2H), 4.43-4.18 (m, 4H), 1.34 (t, J = 7.2 Hz, 3
H), 1.28 (t, J = 7.1 Hz, 3H). 13C NMR (100 MHz, Chloroform-d)
δ 167.1, 165.5, 155.4, 131.9, 130.6, 129.6, 129.2, 128.3, 124.4, 1
21.4, 114.6, 112.3, 91.2, 73.1, 63.5, 63.3, 45.7, 14.0, 13.9. HRM
S (EI-TOF): calcd for, C19H19NO7 [M]+, 373.1162; found, 373.11
64.
3. Conclusion
In conclusion, a novel [4 + 1] strategy by employing malonate
esters as 1,1-nucleophilic/electrophilic type C1 synthons through
a tandem Michael addition/iodine-catalyzed oxidative annulation
has been developed. This method provides a facile synthetic
protocol for the construction of dihydrobenzo(naphtho)furan ring
systems from readily available 2-(2-nitrovinyl)-phen(naphth)ols
and malonate esters in good to excellent yields (up to 99%) under
mild conditions. Notably, this tactic can also be applied to the
reaction of o-QMs and malonate esters. Further explorations of
this strategy are ongoing in our laboratory and will be reported in
due course.
4.2.3. Diisopropyl 1-(nitromethyl)naphtho[2,1-b]furan-2,2(1H)-d
icarboxylate (3ac)
A yellow solid (73 mg, 91% yield), Mp: 145-147 °C. 1H
NMR (400 MHz, Chloroform-d) δ 7.86 (d, J = 8.2 Hz, 1H), 7.80
(d, J = 8.9 Hz, 1H), 7.71 (d, J = 8.3 Hz, 1H), 7.59-7.55 (m, 1H),
7.42-7.38 (m, 1H), 7.25 (d, J = 8.2 Hz, 1H), 5.49 (dd, J = 9.1, 2.7
Hz, 1H), 5.18-5.04 (m, 2H), 4.85 (dd, J = 15.3, 9.2 Hz, 1H), 4.74
(dd, J = 15.2, 2.7 Hz, 1H), 1.34 (d, J = 6.3 Hz, 3H), 1.32 (d, J =
6.4 Hz, 3H), 1.29 (d, J = 6.2 Hz, 3H), 1.24 (d, J = 6.3 Hz, 3H).
13C NMR (100 MHz, Chloroform-d) δ 166.7, 165.1, 155.5,
131.9, 130.5, 129.6, 129.2, 128.3, 124.3, 121.4, 114.7, 112.3,
91.2, 72.9, 72.1, 71.2, 45.3, 21.7, 21.6, 21.5, 21.3. HRMS (EI-
TOF): calcd for, C21H23NO7 [M]+, 401.1475; found, 401.1476.
4. Experimental section
4.1 General
Melting points were obtained in open capillary tubes using
SGW X-4 micro melting point apparatus which were
1
4.2.4. Ditertbutyl 1-(nitromethyl)naphtho[2,1-b]furan-2,2(1H)-di
carboxylate (3ad)
uncorrected. H NMR spectrum were recorded on a Bruker DPX
400 MHz spectrometer in CDCl3. Chemical shifts were reported
in ppm with the internal TMS signal at 0.0 ppm as a standard.
The spectra are interpreted as: s = singlet, d = doublet, t = triplet,
m = multiplet, dd = doublet of doublets, dt = doublet of triplets,
dq = doublet of quartets, coupling constant(s) J are reported in Hz
and relative integrations are reported. 13C NMR (100 MHz)
spectrum were recorded on a Bruker DPX 400 MHz spectrometer
in CDCl3. Chemical shifts were reported in ppm with the internal
chloroform signal at 77.0 ppm as a standard. Mass spectra were
recorded on TOF mass spectrometer. TLC (thin-layer
chromatography) was performed using commercially prepared
100−400 mesh silica gel plates, and visualization was effected at
254 or 365 nm.
A yellow solid (58 mg, 67% yield), Mp: 137-139 °C. 1H NMR
(400 MHz, Chloroform-d) δ 7.85 (d, J = 8.2 Hz, 1H), 7.78 (d, J
= 8.9 Hz, 1H), 7.69 (d, J = 8.3 Hz, 1H), 7.56-7.52 (m, 1H), 7.40-
7.36 (m, 1H), 7.24 (d, J = 8.8 Hz, 1H), 5.51 (dd, J = 8.3, 2.8 Hz,
1H), 4.80 (dd, J = 15.7, 8.4 Hz, 1H), 4.72 (dd, J = 15.7, 2.9 Hz, 1
H), 1.54 (s, 9H), 1.47 (s, 9H). 13C NMR (100 MHz, Chloroform-
d) δ 165.8, 164.6, 155.5, 131.7, 130.5, 129.6, 129.2, 128.1, 124.2,
121.4, 115.1, 112.3, 92.0, 85.7, 84.0, 73.4, 44.7, 27.9 (3C), 27.8
+
.
(3C). HRMS (EI-TOF): calcd for, C23H27NO7 [M] , 429.1788; fo
und, 429.1783
4.2.5. 2-benzyl 2-methyl 1-(nitromethyl)naphtho[2,1-b]furan-2,2(
1H)-dicarboxylate (3ae)
1
A yellow oil (57 mg, 67% yield) (dr = 1.5:1). H NMR (400
4.2 General procedure
MHz, Chloroform-d) δ 7.87-7.84 (m, 1.67H) (overlapping), 7.82-
7.79 (m, 1.67H) (overlapping), 7.70 (d, J = 8.3 Hz, 1.67H)
(overlapping), 7.56 (t, J = 7.6 Hz, 1.67H) (overlapping), 7.43-
7.23 (m, 11.69H) (overlapping), 5.51-5.47 (m, 1.67H)
(overlapping), 5.42 (d, J = 12.1 Hz, 0.67H) (minor), 5.28 (d, J =
12.3 Hz, 1H) (major), 5.18 (d, J = 12.3 Hz, 1H) (major), 5.13 (d,
J = 12.1 Hz, 0.67H) (minor), 4.82-4.72 (m, 3.34H) (overlapping),
3.76 (s, 3H) (major), 3.70 (s, 2H) (minor). 13C NMR (100 MHz,
2-(2-nitrovinyl)-phenol or 2-(2-nitrovinyl)-naphthol 1, base, Cat.,
and 1.5 mL solvent were added to an oven-dried tube,
successively. Then malonate ester or related compound 2 and
oxidant were added. The reaction mixture was then stirred in air
until the reaction was nearly completed, as determined by TLC.
Once 1 consumed, the reaction mixture was cooled to ambient
temperature. The resulting mixture was concentrated in vacuo
and directly purified by column chromatography (petroleum
ether/ethyl acetate= 7:1~5:1) on silica gel to give the desired
products 3.
Chloroform-d)
δ 167.4(minor), 166.8(major), 165.6(major),
165.1(minor), 155.3(major), 155.3(minor), 134.7, 134.2, 131.98,
131.95, 130.5, 130.5, 129.5, 129.04, 129.02, 128.8, 128.7,
128.57, 128.56, 128.56, 128.5, 128.3, 128.3, 127.9, 127.9, 124.4,
124.4, 121.3, 114.37, 114.36, 112.24, 112.20, 91.1(major), 91.0,
72.95, 72.89(major), 68.7, 68.5(major), 53.9, 53.5(major),
4.2.1. Dimethyl 1-(nitromethyl)naphtho[2,1-b]furan-2,2(1H)-
dicarboxylate (3aa)

6
Te rt hae dro n
ACCEPTED MANUSCRIPT
45.9(major), 45.8. HRMS (EI-TOF): calcd for, C23H19NO7
4.2.12. Dimethyl 7-chloro-3-(nitromethyl)benzofuran-2,2(3H)-
dicarboxylate (3ea)
[M]+, 421.1162; found, 421.1165.
A white solid (67 mg, 92% yield), Mp: 150-152 °C. 1H NMR
(400 MHz, Chloroform-d) δ 7.28 (d, J = 8.0 Hz, 1H), 7.04-7.01
(m, 1H), 6.94 (t, J = 7.8 Hz, 1H), 5.09 (t, J = 6.7 Hz, 1H), 4.83
(dd, J = 14.3, 6.5 Hz, 1H), 4.66 (dd, J = 14.3, 7.0 Hz, 1H), 3.89
(s, 3H), 3.87 (s, 3H). 13C NMR (100 MHz, Chloroform-d) δ
166.8 165.9, 153.7, 130.9, 125.2, 123.9, 122.6, 116.5, 90.0, 74.6,
54.4, 53.9, 46.4. HRMS (EI-TOF): calcd for, C13H12Cl35NO7
[M]+, 329.0302; found, 329.0303.
4.2.6. Dibenzyl 1-(nitromethyl)naphtho[2,1-b]furan-2,2(1H)-
dicarboxylate (3af)
A yellow solid (92 mg, 93% yield), Mp: 118-120 °C. 1H NMR
(400 MHz, Chloroform-d) δ 7.86 (d, J = 8.2 Hz, 1H), 7.81 (d, J =
8.9 Hz, 1H), 7.69 (d, J = 8.2 Hz, 1H), 7.58-7.54 (m, 1H), 7.43-
7.39 (m, 1H), 7.34-7.27 (m, 6H), 7.25-7.21 (m, 3H), 7.16-7.13
(m, 2H), 5.50 (dd, J = 8.7, 3.1 Hz, 1H), 5.31 (d, J = 12.1 Hz, 1H),
5.16 (d, J = 12.3 Hz, 1H), 5.10 (dd, J = 12.2, 3.6 Hz, 2H), 4.85-
4.70 (m, 2H). 13C NMR (100 MHz, Chloroform-d) δ 166.9,
165.1, 155.4, 134.5, 134.0, 132.0, 130.5, 129.5, 129.1, 128.8,
128.7 (4C), 128.5 (2C), 128.5, 128.3, 128.0 (2C), 124.4, 121.4,
114.4, 112.3, 91.1, 72.9, 68.8, 68.6, 45.9. HRMS (EI-TOF):
calcd for, C29H23NO7 [M]+, 497.1475; found, 497.1477.
4.2.13. Dimethyl 6-methoxy-3-(nitromethyl)benzofuran-2,2(3H)-
dicarboxylate (3fa)
A yellow solid (60 mg, 92% yield), Mp: 140-142 °C. 1H
NMR (400 MHz, Chloroform-d) δ 7.01 (d, J = 8.3 Hz, 1H), 6.57
(d, J = 2.2 Hz, 1H), 6.53 (dd, J = 8.4, 2.2 Hz, 1H), 4.95 (t, J = 6.8
Hz, 1H), 4.76 (dd, J = 13.9, 6.7 Hz, 1H), 4.58 (dd, J = 14.0, 6.9
Hz, 1H), 3.86 (s, 3H), 3.86 (s, 3H), 3.77 (s, 3H). 13C NMR (100
MHz, Chloroform-d) δ 167.3, 166.2, 162.0, 158.7, 124.7, 114.9,
108.9, 97.2, 90.5, 75.2, 55.7, 54.2, 53.8, 45.4. HRMS (EI-TOF):
calcd for, C14H15NO8 [M]+, 325.0798; found, 325.0795.
4.2.7. Dimethyl 3-(nitromethyl)benzofuran-2,2(3H)-dicarboxylate
(3ba)
A yellow solid (53 mg, 89% yield), Mp: 85-87 °C. 1H NMR
(400 MHz, Chloroform-d) δ 7.27 (t, J = 7.8 Hz, 1H), 7.14 (d, J =
7.8 Hz, 1H), 7.01-6.98 (m, 2H), 5.04 (t, J = 6.7 Hz, 1H), 4.80
(dd, J = 14.2, 6.8 Hz, 1H), 4.64 (dd, J = 14.2, 6.7 Hz, 1H), 3.87
(s, 3H), 3.85 (s, 3H). 13C NMR (100 MHz, Chloroform-d) δ
167.3, 166.3, 157.4, 130.5, 124.4, 123.3, 122.9, 110.9, 89.8, 74.9,
54.2, 53.8, 45.8. HRMS (EI-TOF): calcd for, C13H13NO7 [M]+,
295.0692; found, 295.0693.
4.2.14.
Dimethyl
6-(benzyloxy)-3-(nitromethyl)benzofuran-
2,2(3H)-dicarboxylate (3ga)
A yellow solid (52 mg, 65% yield), Mp: 122-124 °C. 1H NMR
(400 MHz, Chloroform-d) δ 7.42-7.33 (m, 5H), 7.01 (d, J = 8.3
Hz, 1H), 6.63 (d, J = 2.0 Hz, 1H), 6.60 (dd, J = 8.3, 2.2 Hz, 1H),
5.02 (s, 2H), 4.95 (t, J = 6.8 Hz, 1H), 4.76 (dd, J = 14.0, 6.7 Hz,
1H), 4.57 (dd, J = 14.0, 6.9 Hz, 1H), 3.86 (s, 3H), 3.85 (s, 3H).
13C NMR (100 MHz, Chloroform-d) δ 167.3, 166.2, 161.2,
158.7, 136.5, 128.8 (2C), 128.3, 127.6 (2C), 124.7, 115.3, 109.8,
98.2, 90.5, 75.2, 70.5, 54.2, 53.8, 45.4. HRMS (EI-TOF): calcd
for, C20H19NO8 [M]+, 401.1111; found, 401.1108.
4.2.8. Diethyl 3-(nitromethyl)benzofuran-2,2(3H)-dicarboxylate
(3bb)
A yellow solid (63 mg, 97% yield); 1H NMR (400 MHz,
Chloroform-d) δ 7.28-7.24 (m, 1H), 7.13 (d, J = 7.4 Hz, 1H),
7.01-6.96 (m, 2H), 5.04 (t, J = 6.8 Hz, 1H), 4.81 (dd, J = 14.1,
6.8 Hz, 1H), 4.63 (dd, J = 14.1, 6.9 Hz, 1H), 4.39-4.21 (m, 4H),
1.31 (td, J = 7.2, 3.0 Hz, 6H).
4.2.15. Dimethyl 5-methyl-3-(nitromethyl)benzofuran-2,2(3H)-
dicarboxylate (3ha)
A yellow solid (49 mg, 79% yield), Mp: 60-62 °C. H NMR
4.2.9.
dicarboxylate (3bc)
Diisopropyl
3-(nitromethyl)benzofuran-2,2(3H)-
1
(400 MHz, Chloroform-d) δ 7.08-7.03 (m, 1H), 6.93 (s, 1H), 6.87
(d, J = 8.2 Hz, 1H), 4.99 (t, J = 6.8 Hz, 1H), 4.79 (dd, J = 14.2,
6.7 Hz, 1H), 4.62 (dd, J = 14.2, 6.8 Hz, 1H), 3.86 (s, 3H), 3.85 (s,
3H), 2.28 (s, 3H). 13C NMR (100 MHz, Chloroform-d) δ 167.4,
166.4, 155.3, 132.6, 130.9, 124.7, 123.3, 110.5, 89.9, 74.9, 54.1,
53.7, 45.9, 20.9. HRMS (EI-TOF): calcd for, C14H15NO7 [M]+,
309.0849; found, 309.0850.
1
A yellow solid (66 mg, 94% yield); Mp: 82-84 °C. H NMR
(400 MHz, Chloroform-d) δ 7.27-7.23 (m, 1H), 7.12 (d, J = 7.5
Hz, 1H), 7.00-6.95 (m, 2H), 5.19-5.09 (m, 2H), 5.01 (t, J = 6.9
Hz, 1H), 4.83 (dd, J = 14.1, 6.6 Hz, 1H), 4.63 (dd, J = 14.1, 7.2
Hz, 1H), 1.32-1.28 (m, 12H). 13C NMR (100 MHz, Chloroform-
d) δ 166.1, 165.2, 157.5, 130.2, 124.2, 123.7, 122.6, 110.7, 89.8,
74.9, 71.7, 71.3, 45.3, 21.5, 21.45, 21.40, 21.38. HRMS (EI-
TOF): calcd for, C17H21NO7 [M]+, 351.1318; found, 351.1314.
4.2.16. Dimethyl 4-methoxy-3-(nitromethyl)benzofuran-2,2(3H)-
dicarboxylate (3ia)
A yellow solid (49 mg, 75% yield), Mp: 79-81 °C. H NMR
4.2.10. Dimethyl 7-methyl-3-(nitromethyl)benzofuran-2,2(3H)-
dicarboxylate (3ca)
1
(400 MHz, Chloroform-d) δ 7.23-7.19 (m, 1H), 6.62 (d, J = 8.1
Hz, 1H), 6.51 (d, J = 8.3 Hz, 1H), 5.11 (dd, J = 8.4, 3.2 Hz, 1H),
4.98 (dd, J = 14.9, 3.3 Hz, 1H), 4.75 (dd, J = 14.9, 8.4 Hz, 1H),
3.85 (s, 3H), 3.83 (s, 3H), 3.83 (s, 3H). 13C NMR (100 MHz,
Chloroform-d) δ 167.5, 166.3, 158.4, 156.3, 131.6, 109.5, 104.8,
103.7, 89.9, 72.1, 55.7, 54.1, 53.6, 45.1. HRMS (EI-TOF): calcd
for, C14H15NO8 [M]+, 325.0798; found, 325.0799.
A yellow oil (57 mg, 91% yield); 1H NMR (400 MHz,
Chloroform-d) δ 7.07 (d, J = 7.4 Hz, 1H), 6.95 (d, J = 7.5 Hz,
1H), 6.89 (t, J = 7.5 Hz, 1H), 5.03 (t, J = 6.8 Hz, 1H), 4.79 (dd, J
= 14.2, 7.1 Hz, 1H), 4.61 (dd, J = 14.2, 6.6 Hz, 1H), 3.86 (s, 3H),
3.84 (s, 3H), 2.29 (s, 3H). 13C NMR (100 MHz, Chloroform-d) δ
167.5, 166.5, 155.9, 131.7, 122.8, 122.6, 121.6, 121.3, 89.6, 74.9,
54.1, 53.7, 46.2, 15.2. HRMS (EI-TOF): calcd for, C14H15NO7
[M]+, 309.0849; found, 309.0851.
4.2.17. Dimethyl 4-fluoro-3-(nitromethyl)benzofuran-2,2(3H)-
dicarboxylate (3ja)
4.2.11. Dimethyl 7-methoxy-3-(nitromethyl)benzofuran-2,2(3H)-
dicarboxylate (3da)
A yellow solid (54 mg, 86% yield), Mp: 100-102 °C. 1H NMR
(400 MHz, Chloroform-d) δ 7.28-7.22 (m, 1H), 6.80 (d, J = 8.2
Hz, 1H), 6.71 (t, J = 8.7 Hz, 1H), 5.19 (dd, J = 7.8, 3.6 Hz, 1H),
4.95 (dd, J = 15.0, 3.7 Hz, 1H), 4.82 (dd, J = 15.0, 7.8 Hz, 1H),
3.88 (s, 3H), 3.85 (s, 3H). 13C NMR (101 MHz, Chloroform-d) δ
166.9, 165.9, 159.2 (d, J = 7.6 Hz), 158.8 (d, J = 249.4 Hz),
157.6, 132.0 (d, J = 8.7 Hz), 109.8 (d, J = 19.7 Hz), 109.8 (d, J =
19.7 Hz), 106.9, 90.1, 72.5, 54.3, 53.8, 44.6. HRMS (EI-TOF):
calcd for, C14H12FNO7 [M]+, 313.0598; found, 313.0596.
A yellow solid (66 mg, 99% yield), Mp: 132-134 °C. 1H NMR
(400 MHz, Chloroform-d) δ 6.95 (t, J = 7.9 Hz, 1H), 6.86 (d, J =
8.0 Hz, 1H), 6.73 (d, J = 7.5 Hz, 1H), 5.06 (t, J = 6.8 Hz, 1H),
4.82 (dd, J = 14.3, 6.9 Hz, 1H), 4.64 (dd, J = 14.3, 6.7 Hz, 1H),
3.90 (s, 3H), 3.86 (s, 3H), 3.84 (s, 3H). 13C NMR (100 MHz,
Chloroform-d) δ 167.3, 166.2, 145.9, 144.9, 124.4, 123.8, 115.9,
113.3, 90.1, 74.8, 56.2, 54.2, 53.8, 46.4. HRMS (EI-TOF): calcd
for, C14H15NO8 [M]+, 325.0798; found, 325.0799.

Wang, B.; Zhang, X. J. Am. Chem. Soc. 2002, 124, 13400; (c)
4.2.18. Dimethyl 2-(1-(2-hydroxyphenyl)-2-nAitroCetChyEl)mPaTloEnaDte MANUSCRIPT
Chen, C.; Li, X.; Schreiber, S. L. J. Am. Chem. Soc. 2003, 125,
10174; (d) Blum, T. R.; Zhu, Y.; Nordeen, S. A.; Yoon, T. P.
Angew. Chem. 2014, 126, 11236.
(3ba’)
A yellow oil (59 mg, 99% yield). 1H NMR (400 MHz,
Chloroform-d) δ 7.16-7.06 (m, 1H), 6.83 (td, J = 7.6, 0.9 Hz,
1H), 6.70 (d, J = 7.8 Hz, 1H), 6.65 (s, 1H), 5.08 (dd, J = 13.1, 8.9
Hz, 1H), 4.92 (dd, J = 13.1, 4.8 Hz, 1H), 4.41-4.35 (m, 1H), 4.29
(d, J = 10.1 Hz, 1H), 3.78 (s, 3H), 3.54 (s, 3H). 13C NMR (100
MHz, Chloroform-d) δ 168.5, 168.3, 154.1, 130.7, 129.8, 121.9,
120.9, 116.4, 76.1, 53.2, 53.0, 52.8, 40.4.
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132, 2550.
4.2.19.
Dimethyl(E)-7-styryl-[1,3]dioxolo[4,5-f]benzofuran-
6,6(7H)-dicarboxylate (5aa)
A colorless oil (19 mg, 50% yield). 1H NMR (400 MHz,
Chloroform-d) δ 7.37 – 7.21 (m, 5H), 6.63 (d, J = 15.8 Hz, 1H),
6.60 – 6.54 (m, 2H), 6.06 (dd, J = 15.8, 9.0 Hz, 1H), 5.95 – 5.87
(m, 2H), 4.93 (d, J = 9.0 Hz, 1H), 3.87 (s, 3H), 3.69 (s, 3H).
6. Li, Q.-B.; Zhou, F.-T.; Liu, Z.-G.; Li, X.-F.; Zhu, W.-D.; Xie, J.-
W. J. Org. Chem. 2011, 76, 7222.
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Caiuby, C. A. D.; Ali, A.; Santana, V. T.; Lucas, F. W. D. S.;
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Kirschning, A.; Zhdankin, V. V. Synthesis 2010, 3681.
4.2.20. Methyl naphtho[2,1-b]furan-2-carboxylate (6aa)
A yellow solid (31 mg, 69% yield). 1H NMR (400 MHz,
Chloroform-d) δ 8.15 (s, 1H), 8.03 (s, 1H), 7.97 (d, J = 8.1 Hz,
1H), 7.88 (d, J = 9.1 Hz, 1H), 7.70 (d, J = 9.1 Hz, 1H), 7.65 (t, J
= 7.6 Hz, 1H), 7.55 (t, J = 7.6 Hz, 1H), 4.02 (s, 3H).
4.2.21.
Methyl5-chloro-3-oxo-1,2,3,8b-tetrahydro-3aH-
benzofuro[2,3-c]pyrrole-3a-carboxylate (7ea)
1
A white soild (25 mg, 60% yield), Mp: 210-212 °C. H NMR
(400 MHz, Chloroform-d) δ 8.00 (s, 1H), 7.21 (dt, J = 8.0, 1.0
Hz, 1H), 7.09 (dt, J = 7.5, 1.2 Hz, 1H), 6.92 (t, J = 7.8 Hz, 1H),
4.44 – 4.39 (m, 1H), 4.03 (dd, J = 10.2, 7.4 Hz, 1H), 3.87 (s, 3H),
3.60 – 3.53 (m, 1H). 13C NMR (101 MHz, Chloroform-d) δ
170.6, 167.4, 154.2, 130.2, 128.5, 123.4, 122.5, 116.3, 90.3, 53.5,
47.2, 47.0. HRMS (EI-TOF): calcd for, C12H10ClNO4 [M]+,
267.0298; found, 267.0296.
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Acknowledgments
This work was financially supported by the Shanghai
Comittee of Science and Technology (no.17ZR1407600).
References and notes
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Supplementary Material
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2. (a) Gothelf, A. S.; Gothelf, K. V.; Hazell, R. G.; Jørgensen, K. A.
Angew. Chem., Int. Ed. 2002, 41, 4236; (b) Longmire, J. M.;