Silver-catalyzed cascade radical cyclization of sodium sulfinates and o-(allyloxy)arylaldehydes towards functionalized chroman-4-ones

Article abstract of DOI:10.1016/j.tetlet.2020.151704

An efficient method for the synthesis of functionalized Chroman-4-ones via cascade radical cyclization of sodium sulfinates and o-(allyloxy)arylaldehydes using silver as catalyst and K₂S₂O₈ as oxidant was presented. The de

Full text of DOI:10.1016/j.tetlet.2020.151704

Tetrahedron Letters 61 (2020) 151704
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Silver-catalyzed cascade radical cyclization of sodium sulfinates and
o-(allyloxy)arylaldehydes towards functionalized chroman-4-ones
b
Qing-Qing Han a,1, Guang-Hui Li a,1, Yuan-Yuan Sun a, De-Mao Chen a, Zu-Li Wang a, , Xian-Yong Yu ,
⇑
Xin-Ming Xu c
a College of Chemistry and Pharmaceutical Sciences, Qingdao Agricultural University, Qingdao 266109, China
b School of Chemistry and Chemical Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
c College of Chemistry and Chemical Engineering, Yantai University, Yantai 264005, China
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient method for the synthesis of functionalized Chroman-4-ones via cascade radical cyclization of
sodium sulfinates and o-(allyloxy)arylaldehydes using silver as catalyst and K2S2O8 as oxidant was pre-
sented. The desired products with various groups were isolated in moderate to good yields.
Ó 2020 Elsevier Ltd. All rights reserved.
Received 9 January 2020
Revised 31 January 2020
Accepted 2 February 2020
Available online 4 February 2020
Keywords:
Chroman-4-ones
Sodium sulfinates
Silver-catalyze
Persulfates
Introduction
boxylic acids and o-(allyloxy)arylaldehydes. With ammonium per-
sulfate as the oxidant, the dihydroflavonoid derivatives can be
The chroman-4-ones are highly valuable structural scaffolds in
various natural products, medicinal compounds and biologically
active compounds [1–3]. Consequently, significantly efforts have
been focused on developing economical, practical and environ-
mentally benign protocols for their preparation [4,5]. As we all
know, radical cyclization reaction has been used widely in organic
synthesis [6–11]. The radical cyclization reaction using o-(allyloxy)
arylaldehydes [12] as substrate represents one of the most efficient
way for the synthesis of chroman-4-ones (Fig. 1). For example, Li
group synthesize phosphonate chroman-4-ones using silver salt
as the catalyst and K2S2O8 as an oxidant under mild conditions.
This strategy could also extend to azido and hydroxyl radicals,
and the synthesis of the corresponding functionalized chroman-
4-ones was achieved smoothly [12a]. In 2018, Silver-catalyzed
decarboxylative cascade radical cyclization of tertiary carboxylic
acids and o-(allyloxy)arylaldehydes was presented by Yu group
to synthesize 3-alkyl-substituted chroman-4-one derivatives [13].
Wu and co-workers developed a silver nitrate-catalyzed cascade
decarboxylation and oxidative cyclization reaction of a-oxocar-
obtained with moderate to good yields [14a]. Zhu group describe
a novel visible light-induced tandem radical addition–cyclization
of alkenyl aldehydes with
a -bromocarbonyl compounds. The cor-
responding products are synthesized with high efficiency and good
functional group compatibility at room temperature [14b].
As cheap, easily handled strong oxidants, persulfates have been
widely used in organic synthesis [15–17]. Persulfates may decom-
pose to sulfate radical anions under heating, light irradiation or
transition-metal reductive conditions [18–20]. In 2013, the synthe-
sis of 3-arylthioindoles from indoles and diaryl disulfides using
ammonium persulfate in methanol was presented by Kumar and
his co-workers [21]. Liu’s group found that (NH4)2S2O8 was good
oxidant for oxidative CAH functionalization of naphthoquinones
with alkenes [22]. The direct CAH alkylation of heteroarenes with
inactivated ethers promoted by potassium persulfate was devel-
oped by Barriault [23]. In view of the above reports, and given
our continuing interest in functionalization of heterocyclic com-
pounds [24–29]. Herein, we present Ag/persulfate promoted
cyclization of sodium sulfinates and o-(allyloxy)arylaldehydes.
Functionalized chroman-4-ones with moderate to high yield can
be isolated using this method.
⇑
Corresponding author.
E-mail address: wangzulichem@163.com (Z.-L. Wang).
1
These authors contributed equally to this article.
https://doi.org/10.1016/j.tetlet.2020.151704
0040-4039/Ó 2020 Elsevier Ltd. All rights reserved.

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Q.-Q. Han et al. / Tetrahedron Letters 61 (2020) 151704
reaction, 36% yield of the product was isolated (Table 1, entry 1).
Other solvents such as CH3CN:H2O (1:1), DCE:H2O (1:1), PhCl:
H2O (1:1) were also suitable for this transformation (Table 1,
entries 2, 3, 7), but the yields were not high. When the reaction
was conducted in CH2Cl2:H2O (1:1), toluene:H2O (1:1) or THF:
H2O (1:1), only trace amount of the products were observed
(Table 1, entries 4–6). Dioxane:H2O (1:1) and DMSO:H2O (1:1)
are proved to be effective for this reaction, providing the desired
products in 76% and 78% yields (Table 1, entries 8–9). We next turn
our attention to investigate the effect of oxidants on the reaction
(Table 1, entries 10–15). K2S2O8 was found to be more effective
than other oxidant, such as TBHP, DTBP, TBPB, Na2S2O8 and (NH4)2-
S2O8. The sliver catalysts also play an important role in this reac-
tion. Ag2O, Ag2SO4, Ag2CO3 and AgOAc could all catalyze the
reaction, delivering the desired products in 69–75% yields (Table 1,
entries 16–19). No desired product was generated when the reac-
tion proceeded in the absence of sliver catalyst (Table 1, entry 21).
This result shows the important role of the sliver catalyst in this
transformation. In addition, a slightly lower yield was obtained
when the reaction was conducted in air (Table 1, entry 20). Differ-
ent ratio of DMSO/H2O were also investigated (Table 1, entry 22–
23), showing that DMSO/H2O (1:1) was the optimal result.
With the optimized reaction conditions in hand, the substrate
scope and limitations of the cyclization reaction were investigated
by evaluating a variety of sodium sulfinates and o-(allyloxy)ary-
laldehydes. There was no obvious electronic and steric effect for
this reaction (3a–3g, 3m, 3n). For example, CH3, F, Cl and Br groups
are all well tolerated in this system and afford the corresponding
products in 62–78% yield. For the substituted o-(allyloxy)arylalde-
hydes, electron-withdrawing and electron-donating groups did not
show obvious influence on the yield (3k–3p). The desired products
can be isolated in moderate to high yields. Moreover, halogen
atoms (F, Cl, and Br) were well compatible, rendering the product
Fig. 1. Synthesis of functionalized chroman-4-ones.
Results and discussion
We initiated our study with examination of the reaction
between sodium benzenesulfinate and 2-(allyloxy)benzaldehyde.
To our delight, when DMF:H2O = 1:1 was used as solvent for this
Table 1
Optimization of the reaction conditions.a
Entry
Catalyst (20 mol%)
Oxidant (3 equiv.)
Solvent (2 mL)
Yield (%)
1
2
3
4
5
6
7
8
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
AgNO3
Ag2O
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
DMF:H2O = 1:1
CH3CN:H2O = 1:1
DCE:H2O = 1:1
CH2Cl2:H2O = 1:1
Toluene:H2O = 1:1
THF:H2O = 1:1
36
50
10
trace
trace
trace
12
76
78
NR
NR
NR
74
69
trace
70
69
75
69
67
PhCl:H2O = 1:1
Dioxane:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:1
DMSO:H2O = 1:2
DMSO:H2O = 2:1
9
K2S2O8
10
11
12
13
14
15
16
17
18
19
20b
21
22
23
TBHP(in H2O)
TBHP(in decane)
DTBP
Na2S2O8
(NH4)2S2O8
TBPB
K2S2O8
K2S2O8
K2S2O8
K2S2O8
Ag2SO4
Ag2CO3
AgOAc
AgNO3
–
K2S2O8
K2S2O8
K2S2O8
K2S2O8
NR
71
66
AgNO3
AgNO3
a
Reaction conditions: A (0.2 mmol), B (0.4 mmol), catalyst (20 mol%), oxidant (3.0 equiv), solevent (2 mL = 1:1), 100 , N2, 24 h.
Under air.
b

Q.-Q. Han et al. / Tetrahedron Letters 61 (2020) 151704
3
for further functionalizations readily. It should be noted that 2-(al-
lyloxy)-1-naphthaldehyde and 2-hydrosulfonylthiophene are also
good substrates for this reaction, albeit the yields of the products
was not high (3q, 3r) (Table 2).
In order to further understand the possible mechanism of this
novel reaction, a series of control experiments were performed,
as shown in Scheme 1. When radical scavenger tempo, BHT or
1,1-diphenylethylene was added to this reaction, the reaction
was completely inhibited. Compound 3s has been confirmed by
Table 2
Reaction scope.a
3b,68%
3c,73%
3f,72%
3a, 78%
3d,69%
3e,62%
3h,65%
3i,64%
3l,65%
3g,62%
3j,64%
3k,65%
3n,64%
3m,72%
3o,63%
3r,36%
3q,41%
3p,64%
a
Reaction conditions: A (0.2 mmol), B (0.4 mmol), AgNO3 (20 mol%), K2S2O8 (3.0 equiv), DMSO:H2O = 1:1 (2 mL),
100 °C, N2, 24 h.
Scheme 1. Control experiments.

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Q.-Q. Han et al. / Tetrahedron Letters 61 (2020) 151704
Scheme 2. Proposed reaction mechanism.
HRMS. This result indicating that a radical process may be pro-
posed for this reaction.
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Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tetlet.2020.151704.

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