A sulfur ylides-mediated domino benzannulation strategy to construct biaryls, alkenylated and alkynylated benzene derivatives

Article abstract of DOI:10.1002/adsc.201400176

An efficient domino benzannulation strategy with the participation of sulfur ylides for the construction of biaryl compounds is disclosed. It could also be extended to the synthesis of alkenylated and alkynylated benzene derivatives under mild conditions. This versatile strategy combined with traditional metal-catalyzed cross-coupling methods should offer a practical route to construct complex multiaryl compounds.

Full text of DOI:10.1002/adsc.201400176

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DOI: 10.1002/adsc.201400176
A Sulfur Ylides-Mediated Domino Benzannulation Strategy to
Construct Biaryls, Alkenylated and Alkynylated Benzene
Derivatives
Fei Gaoa and You Huanga,*
a
State Key Laboratory and Institute of Elemento-organic Chemistry, Collaborative Innovation Center of Chemical Science
and Engineering (Tianjin), Nankai University, Tianjin 300071, Peopleꢀs Republic of China
Fax : (+86)-22-2350-3159; e-mail: hyou@nankai.edu.cn
Received: February 17, 2014; Revised: April 9, 2014; Published online: July 17, 2014
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201400176.
Abstract: An efficient domino benzannulation strat-
egy with the participation of sulfur ylides for the
construction of biaryl compounds is disclosed. It
could also be extended to the synthesis of alkeny-
lated and alkynylated benzene derivatives under
mild conditions. This versatile strategy combined
with traditional metal-catalyzed cross-coupling
methods should offer a practical route to construct
complex multiaryl compounds.
thetic strategies for accessing such motifs mainly
focus on transition metal-catalyzed cross-coupling re-
actions.[2] Recently, benzannulation reactions have at-
tracted considerable attention.[3] Tang and Liu have
reported two methods to construct multiply substitut-
ed benzenes without metal catalysts. Our group has
reported on phosphine-mediated benzannulation re-
actions.[3a,b,e] So far, to the best of our knowledge, no
multiaryl compounds have been directly constructed
from sulfonium salts.
Keywords: benzannulation; biaryls; domino reac-
tions; multiaryl compounds; sulfur ylides
Sulfur ylides, which have been developed as valua-
ble and versatile synthetic reagents in organic synthe-
sis,[4] are widely applied, also in domino reactions.
Corey and Chaykovsky,[5] Aggarwal,[6] Tang,[7] Xiao[8]
and others[9] have developed a series of elegant
domino reactions of sulfur ylides that include tradi-
Biaryl skeletons are the key blocks of many natural tional cyclization reactions to build three-membered
products, bioactive molecules and functional materi- ring compounds (such as epoxides,[6a–d,f,g] aziri-
als.[1] Consequently, efficient strategies to construct
dines,[6e,7g,9d] and cyclopropanes[6h,7b,e,9e]) and some an-
ACHTUNGTRENNUNG
multiaryl compounds are of the utmost importance nulation processes to form the 5- and 6-membered
and have been intensively investigated. Current syn- heterocyclic compounds.[7a–d,8,9a–c,h–k] In further investi-
Scheme 1. Reactions of crotonate-derived sulfonium salts.
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A Sulfur Ylides-Mediated Domino Benzannulation Strategy
Table 1. Optimization of the domino benzannulation reac-
gations, Tang et al. reported a tandem Michael addi-
tion/ylide epoxidation of the crotonate-derived sulfo-
nium salt with a,b-unsaturated ketones for the synthe-
sis of functionalized cyclohexadiene epoxides in high
efficiency (Scheme 1, A).[7e] Recently, Zhang and co-
workers reported an appealing domino approach
using thw crotonate-derived sulfonium salt with elec-
tion with sulfur ylides.[a]
tron-deficient
[3.1.0]hexenes (Scheme 1, B).[9g]
Based upon these studies, we were keen to develop
an efficient, practical benzannulation strategy to con-
struct multisubstituted biaryls with sulfur ylides for
the first time (Scheme 1, C).
We initiated our investigation by subjecting enone-
ester 1a[10] to sulfonium salt 2a in the presence of
Cs2CO3 in CH3CN at room temperature. To our de-
light, the biaryl compound 3a was obtained in 77%
yield (Table 1, entry 1). The configuration of the prod-
uct 3a was confirmed by combination of NMR, HR-
MS and X-ray crystallographic analysis[11] (see the
Supporting Information). Encouraged by this result,
we next explored the influence of other bases on this
reaction. As shown in Table 1, other bases, such as
enynes
to
construct
bicyclo-
ACHTUNGTRENNUNG
Entry
Base
Solvent
Time [h]
Yield [%][b]
1
2
3
4
Cs2CO3
K2CO3
DBU
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH2Cl2
CHCl3
5
5
4.5
4.5
5
4
9
6
7
2
2
6
6
12
5
5
6
5
77
67
51
62
NR
75
41
45
43
58 (48)
57 (45)
70
86
NR
80
71
57
84
Et3N
5
t-BuOK
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
6[c]
7
8
9
THF
DMF
10[d]
11[d]
12[j]
13[e]
14
15[f]
16[g]
17[h]
18[i]
DMSO
C2H5OH
CH3OH
toluene
CH3OH
CH3OH
CH3OH
CH3OH
K2CO3, DBU (1,8-diazabicycloACTHUNTGRNEUNG[5.4.0]undec-7-ene),
Et3N gave no better results than Cs2CO3 (Table 1, en-
tries 2–4). When t-BuOK was used, no product was
obtained (Table 1, entry 5). These results indicate that
Cs2CO3 shows the highest activity for the reaction.
With the addition of 20 mL H2O as additive,[7f] the
yield could not be improved (Table 1, entry 6). On
screening for solvents, we found that the reaction also
worked in CHCl3, CH2Cl2 THF albeit in somewhat
low yields (entries 7–9). Reactions in polar solvents,
such as DMF, DMSO gave moderate yields rapidly
(entries 10 and 11). However, this reaction could not
proceed in the non-polar solvent toluene (Table 1,
entry 14). It is worthwhile to note that the reaction
gave higher yields in the polar protic solvents
(Table 1, entries 12 and 13). We also found that the
product 3a underwent a transesterification process
with methanol and ethanol as solvent. On decreasing
the amount of Cs2CO3, the yield of 3a also decreased
(Table 1, entries 15 and 16). Changing the ratio of 1a/
2a did not improve the yield (Table 1, entries 17 and
18). Finally, we established the optimal reaction con-
ditions as follows: the ratio of 1a/2a was 1:2, with
4.0 equivalents of Cs2CO3, in CH3OH (3 mL) at room
temperature for the synthesis of compounds 3.
[a]
Unless otherwise noted, the reactions were carried out
on a 0.3 mmol scale, using 4.0 equivalents of base, in sol-
vent (3 mL) at room temperature. The ratio of 1a/2a was
1:2.
Yields of isolated products.
20 mL of H2O were added.
In parentheses are the yields obtained when the reaction
time was extended to 6 h.
The transesterification product 3c.
3 equivalents of Cs2CO3 were used.
2 equivalents of Cs2CO3 were used.
The ratio of 1a/2a was 1:1.
[b]
[c]
[d]
[e]
[f]
[g]
[h]
[i]
The ratio of 1a/2a was 1:3.
The structure of transesterification product 3a’ is:
[j]
With the optimized reaction conditions in hand, we
explored the substrate scope of the benzannulation acetonitrile (CH3CN) as the solvent to avoid transes-
reaction. As shown in Table 2, the desired products 3 terification in some cases, which could also give mod-
were achieved in good to excellent yields, irrespective erate to good yields (Table 2, entries 11–15). To our
of the electronic properties and the position of the delight, the alkyl- and furan-2-yl-substituted unsatu-
substituents on the benzene ring of 1 (Table 2, en- rated enone-esters 1 could react smoothly to construct
tries 1–10). Also, increasing the size of the ester group the monobenzene skeleton and heterocyclic aromatic
in the sulfonium salt 2 decreased the yield of 3 ring system (Table 2, entries 16 and 17). Afterwards,
(Table 2, entries 2, 14 and 15). In addition, we chose the substrate scope was further expanded. Substituted
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Fei Gao and You Huang
Table 2. Investigating the scope of the sulfur ylides participating in the domino benzannulation reaction.[a]
Entry
1
R1
n
R2
R3
Time [h]
Product
Yield [%][b]
1
2
3
4
5
6
7
8
1b
1c
1d
1e
1f
1g
1h
1i
C6H5
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
1
1
2
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
5
5
5
5
5
5
5
2
4
5
5
4.5
4.5
5
5
3
3b
3c
3d
3e
3f
3g
3h
3i
82
94
86
83
65
78
75
73
68
60
80
53
58
89
76
81
61
84
82
72
4-BrC6H4
4-ClC6H4
4-FC6H4
4-CH3C6H4
4-OCH3C6H4
4-BnOC6H4
3-BrC6H4
2-CH3C6H4
2,4-ClC6H3
4-BrC6H4
4-ClC6H4
4-CH3C6H4
4-BrC6H4
4-BrC6H4
CH3
9
1j
3j
10
11[c]
12[c]
13[c]
14[c]
15[c]
16
17
18
19
20[d]
1k
1a
1l
1m
1c
1c
1p
1q
1r
3k
3a
3l
3m
3n
3o
3p
3q
3r
Et
Et
Me
Me
Me
Me
Me
Me
Me
iPr
Me
Me
Me
Me
Me
furyl
5
4
4
6
4-BrC6H4
4-CH3C6H4
4-BrC6H4
1s
1c
3s
3c
[a]
Reaction conditions: 1 (1.0 equiv., 0.3 mmol), 2 (2.0 equiv.), Cs2CO3 (4.0 equiv.), CH3OH (3 mL) at room temperature.
Isolated yields.
The solvent was CH3CN.
Multigram scale experiment.
[b]
[c]
[d]
(E)-methyl 4-oxo-4-arylbutenoates[12] 1r and 1s were zene derivatives. The reactions of enynones[14] 6a–6d
also successfully employed in the reaction (Table 2, with sulfonium salt 2a proceeded smoothly in a short
entries 18 and 19).
time at room temperature, although with slight lower
To test the practicality of the current methodology, yields (Table 4). The low yields of products 7 are
a gram-scale reaction was carried out (Table 2, probably due to polymerization of enynones 6 under
entry 20) whereby 5 mmol 1c and 10 mmol 2a in alkaline conditions. Although further optimization of
70 mL methanol gave 1.35 g of the desired product the reaction conditions could not improve the yield of
(72% yield) in 6 h.
products
7
(see the Supporting information,
Encouraged by the successful synthesis of the biaryl Table S1), to the best of our knowledge, this is the
products as described above, we envisioned that this first report on the construction of alkynylated ben-
strategy could also be used for the preparation of al- zene products in a transition metal-free manner.
kenylated benzene derivatives. Delightfully, various
To demonstrate the versatility of this domino reac-
dienones 4a–4d,[13] bearing phenyl(4a), electron-defi- tion, the transformations of 3c, 3i and 5b into the cor-
cient aryl (4b, 4c) and electron-rich aryl (4d) groups responding more complex multiaryl compounds 3c’,
reacted with sulfonium salt 2a to afford the corre- 3i’and 5b’ were realized by traditional cross-coupling
sponding products 5a–5d in modest yields (Table 3).
methods (Figure 2). Therefore, we believe that the
When the unsymmetrical dienone 4e was used, combination of sulfur ylides participating in a domino
a mixture of products 5e and 5e’ was obtained in 42% benzannulation strategy with the traditional metal-
yieldACHTUNGTRENNUNG(Figure 1). The ratio of the two isomers was 4.8:1 catalyzed cross-coupling methods should offer a plat-
1
as determined by H NMR analysis. Unfortunately, it form to construct complex multiaryl compounds.
was hard to determine which one was the main prod-
uct.
On the basis of our experimental results[3a,10a,9h] and
previous related studies,[7f,9g,3c,d] several possible mech-
Stimulated by the above investigations, we were anisms are depicted in Scheme 2. The sulfonium salt 2
pleased to find that this domino benzannulation strat- could be converted to allyic ylides A and B with the
egy could also be used to construct alkynylated ben- aid of Cs2CO3, then Michael addition of B to enone-
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A Sulfur Ylides-Mediated Domino Benzannulation Strategy
Table 3. The synthesis of the alkenylated benzene products 5.[a]
Entry
Substrate
R
Time [h]
Product
Yield [%][b]
1
2
3
4
4a
4b
4c
4d
H
5
5
6
6
5a
5b
5c
5d
43
65
54
49
Br
Cl
Me
[a]
Reaction conditions: 4 (1.0 equiv., 0.3 mmol), 2a (3.0 equiv.), Cs2CO3 (4.0 equiv.), CH3OH (3 mL) at room temperature.
Isolated yields.
[b]
could lead to F, which could subesquently undergo
proton transfer and isomerization to furnish G (Path
A). Elimination of dimethyl sulfide could afford cy-
clohexadiene H which finally would give product 3
via dehydration.
Intermediate E may also give E1 through intramo-
lecular epoxidation and elimination of Me2S (Path B).
Then product 3 is formed by base-mediated ring
opening and dehydration. In order to get additional
information on possible reaction intermediates E1, we
have tried the reaction at low temperatures, unfortu-
nately, no formation of intermediate E1 could be ob-
served (see the Supporting Information, Table S2). In-
termediate E could also undergo nucleophilic addi-
tion and a sulfur-Wittig-type reaction followed by oxi-
dative aromatization to deliver the corresponding
product 3 (Path C). However, when the reaction was
conducted under an N2 atmosphere, no cyclohexa-
diene F1 could be isolated, instead, product 3 was ob-
tained in high yield (see the Supporting Information).
In addition, no DMSO could be detected by MS even
Figure 1. The reaction of the unsymmetrical dienone 4e and
sulfonium salt 2a.
ester 1 would lead to enolate C, which could be fur- in the gram-scale reaction. Therefore, we consider
ther transferred to E by proton transfer and isomeri- that path A is the more reasonable pathway for the
zation. Intramolecular nucleophilic addition of E reaction.
Table 4. The synthesis of alkynylated benzene products 7.[a]
Entry
Substrate
R
Time [min]
Product
Yield [%][b]
1
2
3
4
6a
6b
6c
6d
H
Br
Cl
CH3O
10
15
10
40
7a
7b
7c
7d
29
34
36
25
[a]
Reaction conditions: 6 (1.0 equiv., 0.3 mmol), 2a (2.0 equiv.), Cs2CO3 (4.0 equiv.), CH3OH (3 mL) at room temperature.
Isolated yields.
[b]
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Fei Gao and You Huang
Figure 2. Synthetic transformations of products 3c, 3i, and 5b (DME=dimethoxyethane).
Scheme 2. Plausible mechanism for the formation of compounds 3.
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A Sulfur Ylides-Mediated Domino Benzannulation Strategy
Research Fund for the Doctoral Program of Higher Educa-
tion of China (20120031110002). We also thank the reviewers
for their useful suggestions about the reaction mechanism.
In conclusion, we have developed a versatile, effi-
cient domino benzannulation strategy with participa-
tion of sulfur ylides for the construction of biaryl
compunds in moderate to high yields under mild con-
ditions. Also, alkenylated and alkynylated benzene
derivatives could also be constructed through this pro-
cedure. Thus, our domino benzannulation strategy
combined with traditional metal-catalyzed cross-cou-
pling methods should provide an efficient route to
construct complex multiaryl compounds. Further ef-
forts toward the application of this strategy in organic
synthesis and investigations on the detailed mecha-
nism are currently ongoing in our laboratory.
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Experimental Section
General Procedure for the Synthesis of Biaryls 3
Cesium carbonate (390 mg, 1.20 mmol) was added to
a stirred mixture of sulfonium salt 2 (0.6 mmol) and enone-
ester 1 (0.3 mmol) in CH3OH (3 mL) at room temperature.
The resulting mixture was stirred at the same temperature
until the reaction was completed (as monitored by TLC).
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was purified by column chromatography on silica gel (gradi-
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afford biaryls 3.
General Procedure for the Synthesis of Alkenylated
Benzene Products 5
To a stirred mixture of sulfonium salt 2a (216 mg, 0.9 mmol)
and dienone 4 (0.3 mmol) in CH3OH (3 mL) cesium carbon-
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temperature. The resulting mixture was stirred at the same
temperature until the reaction was completed (as monitored
by TLC). All volatiles were removed under vacuum and the
residue was purified by column chromatography on silica
gel (gradient eluent: petroleum ether/ethyl acetate=40:1–
30:1) to afford alkenylated benzene products 5.
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General Procedure for the Synthesis of Alkynylated
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and enynone 6 (0.3 mmol) in CH3OH (3 mL). The resulting
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Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (21172115, 20972076) and the
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Fei Gao and You Huang
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