Synthesis of 1-(3H)isobenzofuranone compounds by tin powder promoted cascade condensation reaction

Article abstract of DOI:10.1002/aoc.6249

An efficient approach for the construction of phthalide compounds is developed through tin powder mediated cascade condensation reaction of 2-formylbenzoic acids with allyl bromides or α-bromoketone under mild reaction conditions. This method is easy to operate and can tolerate various functional groups to give the corresponding phthalides in good to excellent yields. The phthalides produced from α-bromoketone can be further transformed to 3,3a-dihydro-8H-pyrazolo[5, l-a]isoindol-8-one and 8H-pyrazolo[5, l-a]isoindol-8-one.

Full text of DOI:10.1002/aoc.6249

Received: 24 December 2020
DOI: 10.1002/aoc.6249
Revised: 10 March 2021
Accepted: 12 March 2021
F U L L P A P E R
Synthesis of 1-(3H)isobenzofuranone compounds by tin
powder promoted cascade condensation reaction
Shangxian Wang1
Yulai Hu1,2
| Ke-Hu Wang1
| Bo Chang1
| Danfeng Huang1
|
1College of Chemistry and Chemical
Engineering, Northwest Normal
University, Lanzhou, China
2State Key Laboratory of Applied Organic
Chemistry, Lanzhou University, Lanzhou,
China
An efficient approach for the construction of phthalide compounds is
developed through tin powder mediated cascade condensation reaction of
2-formylbenzoic acids with allyl bromides or α-bromoketone under mild
reaction conditions. This method is easy to operate and can tolerate various
functional groups to give the corresponding phthalides in good to excellent
yields. The phthalides produced from α-bromoketone can be further trans-
formed to 3,3a-dihydro-8H-pyrazolo[5, l-a]isoindol-8-one and 8H-pyrazolo[5, l-
a]isoindol-8-one.
Correspondence
Danfeng Huang and Yulai Hu, College of
Chemistry and Chemical Engineering,
Northwest Normal University,
967 Anning East Road, Lanzhou 730070,
China.
K E Y W O R D S
Email: huangdf@nwnu.edu.cn;
huyl@nwnu.edu.cn
allyl bromide, phthalide compounds, tin powder, α-bromoketone
Funding information
Key Laboratory of Polymer Materials of
Ministry of Education of Ecological
Environment; Key Laboratory Polymer
Materials of Gansu Province (Northwest
Normal University); National Natural
Science Foundation of China, Grant/
Award Numbers: 21462037, 21861033;
State Key Laboratory of Applied Organic
Chemistry (Lanzhou University)
1 | INTRODUCTION
to now, many synthetic approaches have been developed
for the synthesis of phthalides derivatives, which can be
Among the oxygen-containing heterocyclic compounds,
phthalide is one of the most common molecular structure
in medicine, natural products, perfume and food additive
molecules[1] (Figure 1A–H). The phthalide derivatives
usually exhibit a broad spectrum of biological activities
such as anti-cancer, antibacterial, anti-inflammatory,
anti-viral, antioxidant, anti-HIV, and blood pressure low-
ering.[2] In addition, they also act as versatile building
blocks in organic synthesis, particularly in the synthesis
of functionalized naphthalenes, anthracenes, and
naphthacene natural products.[3] Thus, considerable
attention has been paid to the methodological develop-
ment of the construction of phthalide derivatives.[4] Up
classified as follows: addition/cyclization reaction of
organometallic reagent with aldehydes/ketones,[5] transi-
tion metal catalyzed intramolecular hydroacylation of
ketones,[6] coupling reaction of transition metal-catalyzed
aryl boric acids with 2-formyl benzoate alkyl esters,[7]
copper(I)-catalyzed interrupted click reaction,[8] and
other methods.[9] Among these various methods, metal
promoted addition/cyclization process of allyl bromides
with 2-formylbenzoic acids or esters is more direct and
convenient way without the use of transition metal cata-
lysts. For instance, zinc[5a], indium,[5b] and chromium
chloride[5c] have been used to promoted the addition/
cyclization of allyl bromides with 2-formylbenzoic acids
Appl Organomet Chem. 2021;e6249.
wileyonlinelibrary.com/journal/aoc
© 2021 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.6249

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WANG ET AL.
FIGURE 1 Selected typical bioactive
molecules containing phthalide units
to functional groups and high selectivity in reactions.[10]
We have developed the tin-powder promoted one-pot
reaction of allyl bromides or 2-bromoacrylic acid
esters, carbonyl compounds and hydrazides to afford
homoallylic N-acylhydrazines or α-methylene-γ-lac-
tams[10a,11]. In addition, we also investigate the C-C cou-
pling reaction of in-situ formed allyltin bromide with
benzylic carbocations.[12] In order to further expand the
application of tin-powder promoted reactions in organic
synthesis, we investigated the tin-powder promoted
allylation-lactonization reactions of 2-formyl benzoic
acids with allyl bromides or α-bromo ketones to produce
phthalides.
2 | RESULTS AND DISCUSSION
In the initial exploration, the mixture of 2-formylbenzoic
acid (1a, 1.0 equiv), allyl bromide (2a, 1.0 equiv) and Sn
powder (1.0 equiv) was refluxed in THF for 6 hr, and the
desired product phthalide 3a was obtained in 75% yield
after work-up (Table 1, entry 1). To optimize the reaction
conditions, the molar ratio of the reactants was explored,
and it was found that the substrate molar ratios had a
great impact on the product yield. When the amount of
allyl bromide and Sn powder increased, the product
yields improved (Table 1, entries 2–5). When the molar
ratio of 1a: 2a: Sn reached 1: 2.0: 2.0, the yield of product
3a went up to 96% (Table 1, entry 5). Further increasing
the molar ratio of allyl bromide and Sn powder did not
lead the improvement of the product yield. (Table 1,
entries 6 and 7). Afterwards, the effect of different sol-
vents on the reaction were examined. The results indi-
cated that the reaction in toluene or 1,4-dioxane afforded
the product 3a in good yield (Table 1, entries 8 and 9),
but the reaction in other solvents, such as CH3CN, DMF,
DCE, EtOH, MeOH and H2O, gave the product in lower
yield (Table 1, entries 10–12 and 14–16). Thus, the
SCHEME 1 Methods for synthesizing derivatives of phthalides
under promotion of metal and metal reagent
or esters, and allyl silanes are also applied for the allylic
addition/cyclization[5d] (Scheme 1a–d). However, some of
the reaction conditions are harsh and require transition
metal catalysis.
In our research group, we are interested in metal
tin-mediated organic reactions due to their good stability
toward heat, hydrolysis, and oxidants with good tolerance

WANG ET AL.
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TABLE 1 Optimization of the
reaction conditionsa
Entry
1
Mole Ratio of 1a: 2a: Sn
1.0:1.0:1.0
1.0:1.5:1.0
1.0:1.0:1.5
1.0:1.5:2.0
1.0:2.0:2.0
1.0:2.0:2.5
1.0:2.5:2.5
1.0:2.0:2.0
1.0:2.0:2.0
1.0:2.0:2.0
1.0:2.0:2.0
1.0:2.0:2.0
1.0:2.0:2.0
1.0:2.0:2.0
1.0:2.0:2.0
1.0:2.0:2.0
Solvent
THF
Time (hr)
Yieldb (%)
6
6
6
6
6
6
6
7
7
7
9
8
8
8
8
8
75
78
79
88
96
96
93
92
91
50
51
78
0
2
THF
3
THF
4
THF
5
THF
6
THF
7
THF
8
toluene
1,4-dioxane
CH3CN
DMF
9
10
11
12
13
14
15
16
DCE
DCM
EtOH
MeOH
H2O
71
65
47
aReaction conditions: 1a (0.3 mmol), 2a and tin powder were refluxed in solvent (4 mL).
bIsolated yields.
optimized reaction conditions were to reflux the 1a, 2a,
and tin powder in THF with the molar ratio of 1a, 2a,
and tin powder being 1:2:2.
aldehyde groups of 2-formylbenzoic acids (Table 3, 4a,
4k, 4l, and 4m). When R2 groups of allyl bromides were
aryl groups, the allyl bromides with both electron-
donating and electron-withdrawing substitutes on their
phenyl rings afforded the corresponding products in good
yields, but the allyl bromides with electron-withdrawing
substitutes on their phenyl rings produced the products
in slightly higher yields than those with electron-
donating groups (Table 3, 4e−4g vs. 4h). When the allyl
bromide compounds are ethyl-2-(bromomethyl)acrylate,
methyl-4-bromocrotonate and ethyl-4-bromocrotonate,
the target compounds could also be obtained in good
yields (Table 3, 4j, 4k, and 4l).
In order to further expand the substrate scope, the
reactions were conducted with α-bromo-ketones instead
of allyl bromides. Under the above optimized reaction
conditions, 2-formylbenzoic acid (1a) reacted with
α-bromo-acetophenone (5a) in the presence of tin pow-
der, but the yield of 6a was only 31%. Thus, reaction con-
ditions were re-optimized (for details, see Table S1). It
was found that the product 6a could be obtained in 89%
Under the optimized reaction condition, the general-
ity of 2-formylbenzoic acid derivatives to this reaction
was investigated (Table 2). The results indicated that the
2-formylbenzoic acid derivatives with both electron-
donating and electron-withdrawing groups on their
phenyl rings gave the corresponding products 3a–3j in
excellent yields. By comparison, the substrates with
electron-withdrawing groups on their phenyl rings pro-
duced the products in slightly higher yields than those
with the electron-donating ones (Table 2, 3a–3 f vs. 3g–3j).
Subsequently, various substituted allyl bromides were
applied in the reaction (Table 3). The results showed that
all of β- and γ-substituted allyl bromides could produce
the corresponding products in good to excellent yields.
As indicated by the product structures, the tin-powder
promoted addition of allyl bromides to aldehyde group in
2-formylbenzoic acids was γ-addition, that is, the carbon
in γ-position of allyl bromides were added to the

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WANG ET AL.
TABLE 2 Substrate scope of 2-formylbenzoic acidsa
aReaction conditions: 1 (0.3 mmol), 2a (0.6 mmol), and tin powder (0.6 mmol) were 80ꢀC in THF (4 mL). Isolated yields.
yield when 20 mol% of BF3ÁEt2O was added and the DCE
was used as solvent (Table 4, 6a). Afterwards, different
α-bromo-acetophenones (5) were reacted with
2-formylbenzoic acids. The results indicated that both
electron-withdrawing and electron-donating substituted
α-bromo-acetophenones produced the corresponding
products 6 in good to excellent yields. However,
when the substitutes on phenyl rings of α-bromo-
acetophenones were at ortho-position, the products were
obtained in relatively lower yields (Table 4, 6e and 6i).
When amino and hydroxyl group were attached on the
phenyl rings of α-bromo-acetophenones, the reaction did
not produce the corresponding products (Table 4, 6k and
6m).
Next, 2-formylbenzoates were used to replace
2-formylbenzoic acid to perform the reaction. When
methyl or ethyl 2-formylbenzoates (7a or 7b) reacted with
allyl bromide in the presence of tin powder in THF under
80ꢀC reflux, the product 3a obtained in 91% or 94%
yields, respectively (Scheme 2).
9a in 68% yield, but there was no product 9b
formed when 2-benzoyl-benzoic acid was used in the
reaction.
To explore the practical utility of this method, a
gram-scale experiment was performed by using
2-formylbenzoic acid 1a (1.051 g, 7 mmol), allyl bromide
2a (1.694 g, 14 mmol) and Sn (1.662 g, 14 mmol) under
the standard reaction conditions. The desired product 3a
obtained in 93% yield. This demonstrated that the proto-
col was scalable and practical (Scheme 4).
Further transformation of products 6 was tried. For
example, the compound 6a was refluxed with hydrazine
in ethanol and product 10 obtained in 78% yield, which
further oxidized by DDQ to give the compound 11 in 84%
yield (Scheme 5).
Finally, the reaction mechanism was proposed
based on the experimental results and literature
(Scheme 6).[10a,11a] First, allyl bromides 2 reacted with tin
powder to generate in situ the allyl tin bromides 12[13]
which
underwent
γ-addition
reaction
with
2-Acylbenzoic acids 8 were also tested as substrates
(Scheme 3). It was found that the 2-acetyl-benzoic
acid reacted with allyl bromide to afford the product
2-formylbenzoic acids 1 to give intermediates 14. The
hydrolysis of intermediates 14 produced the final target
products 4.

WANG ET AL.
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TABLE 3 Substrate scope of allyl bromidesa
aReaction conditions: 1 (0.3 mmol), 2 (0.6 mmol), and tin powder (0.6 mmol) were refluxed at 80ꢀC in THF (4 mL). Isolated yields.
bDetermined by HPLC analysis.
3 | CONCLUSION
operate and has good tolerance to various functional
groups. The reaction proceeds smoothly under mild condi-
tions, and the corresponding products can be obtained in
good yields. The method further expanded the application
of tin powder promoted allylation reactions in organic syn-
thesis, especially in synthesis of heterocyclic compounds.
In summary, we have established a simple method for syn-
thesizing phthalide compounds through one-pot reaction
of 2-formylbenzoic acids and allyl bromides or α-bromo
ketones promoted by tin powder. The method is easy to

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WANG ET AL.
TABLE 4 Substrate scope of α-bromo ketonesa
aReaction conditions: 1 (0.3 mmol), 5 (0.6 mmol), BF3ÁEt2O (0.06 mmol) and tin powder (0.6 mmol) were refluxed in DCE (4 mL). Isolated yields.

WANG ET AL.
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4 | EXPERIMENTAL
4.1 | General information
column chromatography was carried out using silica gel
60 (230–400 mesh). Analytical thin layer chromatography
(TLC) was done using silica gel GF254. TLC plates were
analyzed by an exposure to ultraviolet (UV) light and/or
submersion in phosphomolybdic acid solution or submer-
sion in KMnO4 solution or in I2. High-resolution mass
spectra were recorded on Fourier transform ion cyclotron
resonance mass spectrometer. NMR experiments were car-
ried out in chloroform-d1 (CDCl3) and Dimethyl
The solvents were distilled by standard methods. Reagents
were obtained from commercial suppliers and used with-
out further purification unless otherwise noted. Silica gel
1
sulfoxide-d6 ([CD3]2SO). H NMR, 13C{1H} NMR spectra
were recorded at 400 or 600 MHz and 100 or 150 MHz
spectrometers, respectively. 19F NMR spectra were
recorded at 376 MHz spectrometers. Chemical shifts are
reported as δ values relative to internal TMS (δ 0.00 for 1H
1
NMR), chloroform (δ 7.26 for H NMR), dimethyl sulfox-
SCHEME 2 Reaction of 2-formylbenzoates with allyl bromide
1
1
ide (δ 2.50 for H NMR), acetone (δ 2.05 for H NMR),
chloroform (δ 77.16 for 13C{1H} NMR), dimethyl sulfoxide
(δ 39.52 for 13C{1H} NMR), and acetone (δ 206.26 for 13C
{1H} NMR) in parts per million (ppm). The following
abbreviations are used for the multiplicities: s: singlet, d:
doublet, dd: doublet of doublet, t: triplet, q: quartet, m:
multiplet, br: broad signal for proton spectra. Coupling
constants (J) are reported in Hertz (Hz). Melting
points were uncorrected (Supporting information). The
compounds 1b–1j[14a], 2d–2j,[14b] and 5b–5m[14c] were pre-
pared according to the reported literature procedures.
SCHEME 3 Reaction of 2-acylbenzoic acids with allyl bromide
4.2 | General procedure for the synthesis
of compounds 3 and 4
2-Formylbenzoic acids 1 (0.3 mmol, 1 equiv), allyl bro-
mides 2 (0.6 mmol, 2 equiv), tin powder (0.6 mmol,
SCHEME 4 Gram-scale synthesis of 3a
SCHEME 5 Further transformation of product 6a
SCHEME 6 Proposed mechanistic pathway

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WANG ET AL.
2 equiv) and THF (4 mL) were put into a dried round-
bottom flask (50 mL). The mixture was stirred and
refluxed. The mixture was stirred for another 5–9 h at
80ꢀC reflux. The reaction was monitored by TLC until
the starting material disappeared, and then cooled to
room temperature. THF was removed under vacuum.
The saturated NH4Cl solution (5 mL) was poured into
the mixture and stirred for 10 min. The mixture was
extracted with EtOAc (3 × 10 mL). The combined
organic phase was dried over MgSO4 and then concen-
trated. Purification of the residue by silica gel column
chromatography using petroleum ether/ethyl acetate
(5/1) as the eluent furnished the pure products
3 and 4.
acquisition; methodology. Yulai Hu: Funding acquisi-
tion; methodology; project administration.
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are avail-
able in the supplementary material of this article.
ORCID
Shangxian Wang https://orcid.org/0000-0001-9648-
4983
Ke-Hu Wang https://orcid.org/0000-0001-8246-3559
Bo Chang https://orcid.org/0000-0002-6168-4165
Danfeng Huang https://orcid.org/0000-0002-5848-1164
Yulai Hu https://orcid.org/0000-0002-9630-4150
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4.3 | General procedure for the synthesis
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Natural Science Foundation of China (Grant
No. 21462037 and 21861033); Key Laboratory Polymer
Materials of Gansu Province (Northwest Normal
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istry of Education of Ecological Environment; and State
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CONFLICT OF INTEREST
There is no conflict of interest to declare.
AUTHOR CONTRIBUTIONS
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Shangxian Wang: Data curation; formal analysis; inves-
tigation; methodology; validation. Ke-Hu Wang: Data
curation; validation. Danfeng Huang: Funding

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How to cite this article: Wang S, Wang K-H,
Chang B, Huang D, Hu Y. Synthesis of 1-(3H)
isobenzofuranone compounds by tin powder
promoted cascade condensation reaction. Appl
Organomet Chem. 2021;e6249. https://doi.org/10.
1002/aoc.6249