Reactions of propargylic bromides with sodium sulfinates

Article abstract of DOI:10.1055/s-0033-1340377

A one-pot, palladium-catalyzed synthesis of substituted 2,3-bissulfonylpropenes starting with propargylic bromides and sodium sulfinates (RSO₂Na) in the presence of n-Bu₄NF under refluxing aqueous 1,4-dioxane conditions for eight hours in moderate yields is described. Georg Thieme Verlag Stuttgart. New York.

Full text of DOI:10.1055/s-0033-1340377

LETTER
▌411
lRetteeractions of Propargylic Bromides with Sodium Sulfinates
Synthesis of Substituted 2,3-Bissulfonylpropenes
Meng-Yang Chang,* Ming-Hao Wu
Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 807, Taiwan
Fax +886(7)3125339; E-mail: mychang@kmu.edu.tw
Received: 16.09.2013; Accepted after revision: 17.11.2013
a one-pot methodology for preparing substituted skeleton
1 using the treatment of propargylic bromides 2 with so-
dium sulfinates (RSO2Na, 3) in the presence of a different
additive under refluxing aqueous 1,4-dioxane conditions.
Initially, after treatment of propargyl bromide (2a) with
one equivalent of benzenesulfinic sodium salt (3a) in the
presence of a phase-transfer reagent propargylic benzene-
sulfone was isolated in 88% yield. However, when the re-
action of propargyl bromide (2a) was treated with three
equivalents of compound 3a, compound 1a was isolated
in 43% yield. This is an interesting result. To improve the
yield, some additives and reaction conditions were
screened (Table 1).
Abstract: A one-pot, palladium-catalyzed synthesis of substituted
2,3-bissulfonylpropenes starting with propargylic bromides and so-
dium sulfinates (RSO2Na) in the presence of n-Bu4NF under reflux-
ing aqueous 1,4-dioxane conditions for eight hours in moderate
yields is described.
Key words: cross-coupling, domino reaction, elimination, sul-
fones, palladium
Unsaturated sulfones and their related derivatives are the
versatile intermediates in the preparation of diversified
and functionalized sulfone-containing frameworks due to
their interesting reaction mechanism and synthetic appli-
cations.1 Among the literature on unsaturated sulfones,
substituted sulfones are the subunits in the design of mul-
ticoupling reagents.2 Various chemical transformations
from vinylic, allylic, and propargylic sulfones to useful
acyclic or heterocyclic skeletons have been demonstrated
by Padwa via nucleophilic substitution or radical cycliza-
tion. The three-carbon backbone of 2,3-bisarenesulfonyl-
propenes, including the combination of a vinylic and
allylic sulfone, offers many advantages to a sulfonyl
group.3 There are a number of processes available to gen-
erate this skeleton, but generally, they are described as a
nucleophilic substitution of propargylic sulfones with
thiophenol and triethylamine followed by oxidation of the
resulting sulfur substituent with H2O2 or MCPBA
(Scheme 1).3–5 Consequently, development of a one-pot
protocol for constructing 2,3-bisarenesulfonylpropenes
has stimulated considerable interest.6
Table 1 Reaction Conditions of Compounds 2a and 3aa,b
O
O
O
S
S
additives
Ph
H
Ph
Na
+
O
O
Br
1,4-dioxane–H
2O (5:1)
O
S
Ph
2a
3a
1a
Entry
Catalyst (mmol%), PTR (equiv)
Yield (%)b
1
2
3
4
5
6
7
8
9
Pd/C (5), n-Bu4NCl (0.1)
77
60
64
60
55
70
80
86
50
CuCl2·H2O (5), n-Bu4NCl (0.1)
FeCl3·6H2O (5), n-Bu4NCl (0.1)
CeCl3·6H2O (5), n-Bu4NCl (0.1)
CrCl3·6H2O (5), n-Bu4NCl (0.1)
PdCl2· (5), n-Bu4NCl (0.1)
10% Pd/C (5), n-Bu4NF (0.1)
10% Pd/C (10), n-Bu4NF (0.2)
10% Pd/C (10), n-Bu4NF (0)
1) base, RSH
H
H
O
O
X
S
2) oxidation conditions
R
X = Cl, Br
O
O
S
R = Ph, Tol
oxidation conditions
(1) H2O2, HOAc
a The reactions were run on a 1.0 mmol scale with propargyl bromide
(2a) (80% in toluene, 1.0 mmol), PhSO2Na (3a) (3.0 equiv), 1,4-diox-
ane (5 mL) and H2O (1 mL), reflux temperature, 8 h.
b Crystalline 2,3-bisbenzenesulfonylpropene 1a was >95% pure as de-
termined by NMR analysis.
1) base, RSH
R
O
O
2) oxidation conditions
S
(2) MCPBA, CH2Cl2
R
1
Scheme 1 General route toward 2,3-bisarenesulfonylpropenes
After screening six additives (10% Pd/C, CuCl2·H2O,
FeCl3·6H2O, CeCl3·6H2O, CrCl3·6H2O, PdCl2) and two
phase-transfer reagents (PTR, n-Bu4NCl, or n-Bu4NF),
we found that entry 8 (Table 1) provided the optimized
conditions and best yield. Therefore, this reaction must be
controlled by 10% Pd/C (10 mmol%) in the presence of n-
Bu4NF (0.2 equiv) under refluxing conditions for eight
hours; otherwise, compound 1a will be isolated in lower
yields (Table 1, entries 2–6). Without the addition of
Since the synthetic procedures of substituted 2,3-bissulfo-
nylpropenes 1 are almost all repeated thiophenol-mediat-
ed nucleophilic substitution followed by oxidation under
different reaction conditions, this work intends to explore
SYNLETT 2014, 25, 0411–0416
Advanced online publication: 10.12.2013
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0033-1340377; Art ID: ST-2013-W0881-L
© Georg Thieme Verlag Stuttgart · New York

412
M.-Y. Chang, M.-H. Wu
LETTER
Table 2 Synthesis of Skeleton 1a (continued)
n-Bu4NF, compound 1a provided an only 50% yield (Ta-
ble 1, entry 9). Recently, there have been a number of in-
vestigations for a one-pot reaction of a reactive
intermediate with RSO2Na using palladium-mediated
cross-coupling reactions.7,8 Based on the above-men-
tioned phenomenon, compounds 1b–m were obtained by
a one-pot palladium-catalyzed synthetic protocol; the re-
sults are summarized in Table 2.9,10
O
O
O
S
Pd/C, n-Bu4NF
R
X
R
S
Na
+
O
S
Br
1,4-dioxane–H2O (5:1)
8 h
O
2a, X = H
2b, X = Et
O
X
R
3
1
Entry
Skeleton 1
Yield (%)
O
O
S
Compounds 1a–m, with different bisarenesulfonyl groups
were also synthesized in 65–90% yields via palladium-
mediated reaction of propargylic bromides 2a,b (X = H,
Et) and sodium sulfinates (RSO2Na) 3a–k in the presence
of n-Bu4NF under the refluxing aqueous 1,4-dioxane con-
ditions for eight hours. Furthermore, the structures of
compounds 1e and 1m were determined by single-crystal
X-ray crystallography (Figure 1).11 Compared with the
isolated yields of products with different arene substitu-
ents, it was found that skeleton 1, with the electron-with-
drawing substituent 1b (4-fluorophenyl), was slightly
poorer than the other analogues. Compound 1g, with an
electron-donating group, provided a better yield (90%).
From this phenomenon, we believe that the electron-rich
group delocalized to the benzylic position easily and fa-
vored a palladium-mediated double nucleophilic attack of
compound 2a. The Pd/C catalyst plays the key promoter
to increase the yields of skeleton 1.
O
S
Cl
O
3
73
Cl
O
1d
O
S
O
O
S
4
5
6
82
84
90
1e
O
O
S
O
O
Table 2 Synthesis of Skeleton 1a
S
O
O
O
S
S
Pd/C, n-Bu4NF
R
X
R
Na
+
O
O
Br
1,4-dioxane–H2O (5:1)
8 h
O
S
1f
2a, X = H
2b, X = Et
X
R
3
1
O
O
S
Entry
Skeleton 1
Yield (%)
O
O
S
MeO
O
O
S
O
S
O
MeO
F
1
65
1g
O
O
S
F
O
O
1b
S
Et
O
O
S
7
80
O
S
O
Et
Cl
2
77
1h
O
O
S
Cl
O
1c
S
O
8
82
1i
Synlett 2014, 25, 411–416
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of Substituted 2,3-Bissulfonylpropenes
413
Table 2 Synthesis of Skeleton 1a (continued)
(R = Ar) of sodium sulfinates 3 was changed to a methyl
group (3l, R = Me). Under the above-mentioned reaction
conditions, only a trace of compound 1n (ca. 10%) was
yielded. The major 2,3-bismethylsulfonylpropan-1-ol (4)
was isolated in 66% yield via a palladium-mediated 1,4-
addition of compound 1n with water (Scheme 2). The
structure of compound 4 was determined by single-crystal
X-ray crystallography (Figure 2).11
O
O
O
S
Pd/C, n-Bu4NF
R
X
R
S
Na
+
O
O
Br
1,4-dioxane–H2O (5:1)
8 h
O
S
2a, X = H
2b, X = Et
X
R
3
1
Entry
Skeleton 1
Yield (%)
O
O
S
O
O
S
9
83
1j
O
O
Figure 1 X-ray crystal structures of compounds 1e and 1m
S
O
S
O
10
82
1k
O
O
S
O
S
O
11
80
Figure 2 X-ray crystal structures of compounds 4 and 5a
For treatment of compound 1e (R = Tol) or 1n (R = Ms)
with three equivalents of 4-TsSO2Na (3e) or MeSO2Na
(3l), 1,3-bistoluenesulfonylpropene (5a) or 1,3-bistolu-
enesulfonylpropene (5b) was provided in 74% or 60%
yield and compound 1e or 1n was recovered in 18% or
31% yield via one-pot palladium-catalyzed 1,2-shift rear-
rangement of the 4-tosyl or methyl group (Scheme 3).
This is a novel cascade route to conversion from the skel-
eton of 2,3-bissulfonylpropene 1 to 1,3-bissulfonylpro-
pene 5. The structure of compound 5a was determined by
single-crystal X-ray crystallography (Figure 2).11 For the
palladium-catalyzed cross-coupling reaction of propargyl
bromide (2a) with n-BuSO2Na (3m), when the reaction
solvent was changed from aqueous 1,4-dioxane to water,
compounds 6 (56%) and 7 (22%) were observed and no
1l
O
O
S
O
S
O
12
82
1m
a Isolated compounds 1a–m were >95% pure as determined by 1H
NMR analysis.
products with the bissulfonyl group were generated.12
A
To further examine the palladium-catalyzed cross-cou-
pling reaction of propargyl bromide (2a), an aryl group plausible mechanism was proposed as shown in Scheme
O
O
O
O
O
S
S
S
Pd/C, n-Bu4NF
Me
Me
Me
Na
2a
+
+
O
O
O
O
1,4-dioxane–H2O (5:1), 8 h
O
S
HO
S
Me
1n (~10%)
Me
4 (66%)
3l
Scheme 2 Reaction of compound 2a with 3l
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 411–416

414
M.-Y. Chang, M.-H. Wu
LETTER
4. The initial event may be considered as the generation of ing skeletons 8–10. When sodium sulfinate 3a or 3e
2,3-bissulfonylpropene via double nucleophilic addition played the role of base to deprotonate the δ-proton, com-
of compound 2a with 3m. 1,2-Sulfonyl migration affords pound 8a or 8b was formed by protonation of the δ-carb-
1,3-bissulfonylpropene. Two structures in brackets are the anion under basic conditions. For the formation of
reasonable intermediates. Under the basic aqueous condi- compound (Z)-9a or 9b, we believe that sodium sulfinate
tions, compound 7 should be formed via water-mediated 3a or 3e should serve as the nucleophile and the δ-carbon
allylic desulfonation. Followed by 1,4-addition of water, of sulfonyl allene was attacked from the less hindering
product 6 was generated. To demonstrate this 1,4-addition face to produce the skeleton of 2,3-bissulfonyl butene fol-
from compound 6 to compound 7, treatment of sole com- lowed by nucleophilic substitution of the allylic sulfone
pound 7 with the above reaction conditions provided com- with water. Furthermore, compound 10a or 10b was iso-
pound 6 with 76% yield.
lated via the δ-attack of compound 8a or 8b with sodium
sulfinate 3a or 3e followed by α-protonation. To examine
this δ-attack (1,6-addition) from skeleton 8 to 10, treat-
ment of sole compound 8b with the above conditions pro-
vided compound 10b with only 32% yield. And, an
unknown complex mixture was isolated as the major
product. The structure 10b was determined by single-
crystal X-ray crystallography (Figure 3).11 Among the iso-
lated products, skeleton 9 was observed in good yield.
Next, a one-pot, palladium-catalyzed reaction of 1-bro-
mobut-2-yne (2c) with compound PhSO2Na (3a) or 4-
TsSO2Na (3e) in refluxing water for 72 hours was exam-
ined, as shown in Scheme 5. However, three skeletons of
1-sulfonylbutadienes 8a or 8b, (Z)-2-sulfonylbut-2-en-1-
ols 9a or 9b, and (E)-1,4-bissulfonylbut-2-enes 10a or
10b were isolated in different yields.13–15 The two shown
intermediates with monosulfonyl alkyne and allene
should be the key intermediates (in brackets) for provid-
O
O
O
1
S
R
S
Pd/C, n-Bu4NF
3
2
3
R
1e, R = Tol (18%)
1n, R = Me (31%)
O
O
O
O
R
+
1,4-dioxane–H2O (5:1), 8 h
TolSO2Na 3e (for 1e) or
MeSO2Na 3l (for 1n)
S
S
O
R
1e, R = Tol
1n, R = Me
5a, R = Tol (74%)
5b, R = Me (60%)
Scheme 3 Formation of compound 5a or 5b
O
O
O
O
O
Pd/C, n-Bu4NF
S
OH
S
n-Bu
n-Bu
n-Bu
S
O
Na
2a
+
+
H2O, 8 h
OH
OH
3m
6 (56%)
7 (22%)
H2O
O
S
O
O
S
H2O
n-Bu
n-Bu
O
O
O
O
S
S
n-Bu
O
n-Bu
Scheme 4 Reaction of compound 2a with 3m
R
Me
O
S
Br
10a, R = Ph (trace)
10b, R = Tol (~10%)
2c
O
Pd/C, n-Bu4NF
+
O
O
1,4-dioxane–H2O (5:1),
72 h
O
R
S
R
S
Na
Me
S
O
R
O
O
3a, R = Ph
3e, R = Tol
+
for 10a,b
HO
9a, R = Ph (71%)
9b, R = Tol (69%)
for 8a,b
α
δ
3a or 3e
O
O
H
S
H
S
for 9a,b
δ
R
Me
C
O
O
O
β
8a, R = Ph (18%)
8b, R = Tol (15%)
S
O
R
R
Scheme 5 Reaction of compound 2c with 3a or 3e
Synlett 2014, 25, 411–416
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of Substituted 2,3-Bissulfonylpropenes
415
alized biphenyls will be conducted and published in due
course.
Acknowledgment
The authors would like to thank the National Science Council of the
Republic of China for its financial support (NSC 102-2113-M-037-
005-MY2).
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnuIpofoiprmntgirStanoIuifpog
r
t
iornat
References and Notes
Figure 3 X-ray crystal structure of compound 10b
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To extend this one-pot domino protocol for the applica-
tion of 1,4-dibromobut-2-yne (2d), we found that com-
pounds 11a or 11b with the symmetrical bis-(E,E)-
vinylsulfonyl group was observed for the above palladi-
um-mediated reaction of compounds 2d with sodium sul-
finates 3a or 3e, as shown in Scheme 6.16 From the
experimental results, we envisioned that two intermedi-
ates with bissulfonyl alkyne and allene (in brackets) must
be formed. After deprotonation of the allenic proton with
sodium sulfinates 3a or 3e, compound 11a or 11b could
be separated in high yield via the sequential protonation.
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R
O
Br
Br
S
2d
Pd/C, n-Bu4NF
O
+
O
1,4-dioxane–H2O (5:1), 8 h
O
O
S
R
S
Na
R
O
(4) Wu, Z.; Shen, R.; Ren, L.; Huang, X. Synthesis 2005, 2171.
(5) (a) Kazmaier, U.; Wesquet, A. Synlett 2005, 1271.
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3a, R = Ph
3e, R = Tol
11a, R = Ph (84%)
11b, R = Tol (80%)
R
R
O
R
O
O
O
S
S
S
O
O
H
C
O
H
S
R
O
3a or 3e
Scheme 6 Reaction of compound 2d with 3a or 3e
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In summary, a synthetic methodology for producing sev-
eral substituted 2,3-bissulfonylpropenes 1 has been suc-
cessfully presented using the one-pot facile palladium-
catalyzed coupling of propargylic bromides 2 with sodi-
um sulfinates 3 in good yields in the presence of n-Bu4NF
conditions. The one-pot synthesis of functionalized sulfo-
nyl skeletons 6–10 was investigated under aqueous condi-
tions. The structures of the key products were confirmed
by X-ray crystal analysis. The one-pot synthetic approach
begins with simple starting materials and provides a po-
tential methodology for the synthetic research of vinylic
or allylic sulfonyl derivatives. Further investigation of
skeleton 1 regarding a one-pot synthesis of multifunction-
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Quiclet-Sire, B.; Seguin, S.; Zard, S. Z. C. R. Acad. Sci., Ser.
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aryl sulfinates, see: (a) Ortigies, D. H.; Barthelme, A.; Aly,
S.; Desharnais, B.; Rioux, S.; Forgione, P. Synthesis 2013,
45, 694. (b) Zhao, F.; Tan, Q.; Xiao, F.; Zhang, S.; Deng, G.-
J. Org. Lett. 2013, 15, 1520. (c) Chen, W.; Zhou, X.; Xiao,
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© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 411–416

416
M.-Y. Chang, M.-H. Wu
LETTER
(8) For palladium-catalyzed cross-coupling with aryl sulfinates,
see: (a) Chandrasekhar, S.; Jagadeshwar, V.; Saritha, B.;
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(9) Representative Synthetic Procedure of Skeleton 1
n-Bu4NF (1.0 M in THF, 0.2 mL, 0.2 mmol) was added to a
solution of propargyl bromide (2a) (80% in toluene, 150 mg,
1.0 mmol) or 1-bromopent-2-yne (2b, 150 mg, 1.0 mmol) in
1,4-dioxane (5 mL) at r.t. Then, RSO2Na 3 (3.0 mmol) in hot
H2O (1 mL) was slowly added to the reaction mixture. The
reaction mixture was stirred at r.t. for 10 min. Next, Pd/C
(10% in carbon, 11 mg, 0.1 mmol) was added to the stirred
solution at r.t. The reaction mixture was stirred at reflux for
8 h. The reaction mixture was cooled, filtered, washed, and
concentrated under reduced pressure. The residue was
diluted with H2O (10 mL), and the mixture was extracted
with EtOAc (3 × 20 mL). The combined organic layers were
washed with brine, dried, filtered, and evaporated to afford
crude product. Purification on silica gel (hexanes–EtOAc,
6:1 to 2:1) afforded skeleton 1.
2 H), 7.32 (J = 8.0 Hz, 2 H), 7.31 (d, J = 8.0 Hz, 2 H), 7.20
(t, J = 7.6 Hz, 1 H), 4.17 (s, 2 H), 2.71–2.65 (m, 4 H), 2.37–
2.30 (m, 2 H), 1.65–1.57 (m, 4 H), 1.38–1.30 (m, 4 H), 1.09
(t, J = 7.6 Hz, 3 H), 0.93 (t, J = 7.6 Hz, 3 H), 0.92 (t, J = 7.6
Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 152.91, 150.03,
149.35, 136.65, 136.25, 131.20, 129.20 (2×), 129.11 (2×),
128.43 (2×), 128.40 (2×), 53.93, 35.62, 35.59, 33.10 (2×),
23.69, 22.23, 22.19, 13.82 (2×), 12.49.Single-crystal X-ray
diagram: Crystal of 1m was grown by slow diffusion of
EtOAc into a solution of 1m in CH2Cl2 to yield colorless
prisms. The compound crystallizes in the monoclinic crystal
system, space group P121/c1, a = 29.984 (3) Å,
b = 5.2734(5) Å, c = 15.4864(17) Å, V = 2408.6(4) Å3,
Z = 4, dcalcd = 1.276 g/cm3, F(000) = 992, 2θ range 0.69–
26.40°; R indices (all data): R1 = 0.1069, wR2 = 0.1900.
(10) The RSO2Na 3 is prepared in accordance with the known
method, see: Crowell, T. A.; Halliday, B. D.; McDonald, J.
H. III.; Indelicato, J. M.; Pasini, C. E.; Wu, E. C. Y. J. Med.
Chem. 1989, 32, 2436.
(11) CCDC 942165 (1e), 957847 (1m), 942167 (4), 942166 (5a),
and 942219 (10b) contain the supplementary
crystallographic data for this paper.
This data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
+44(1223)336033; E-mail: deposit@ccdc.cam.ac.uk].
(12) (a) Najera, C.; Sansano, J. M. Tetrahedron 1991, 47, 5193.
(b) Najera, C.; Perez-Pinar, A.; Sansano, J. M. Tetrahedron
1991, 47, 6337. (c) Najera, C.; Yus, M. J. Org. Chem. 1989,
54, 1491. (d) Niyazymbetov, M. E.; Konyushkin, L. D.;
Niyazymbetova, Z. I.; Kalugin, V. E.; Litvinov, V. P.;
Petrosyan, V. A. Tetrahedron Lett. 1991, 32, 1099.
(13) (a) Mauleon, P.; Nunez, A. A.; Alonso, I.; Carretero, J. C.
Chem. Eur. J. 2003, 9, 1511. (b) Hwang, S. H.; Kurth, M. J.
Tetrahedron Lett. 2002, 43, 53. (c) Zhu, X. Q.; Liang, H.;
Zhu, Y.; Cheng, J.-P. J. Org. Chem. 2008, 73, 8403.
(14) Carpino, L. A.; Philbin, M. J. Org. Chem. 1999, 64, 4315.
(15) (a) Ju, Y.; Kumar, D.; Varma, R. S. J. Org. Chem. 2006, 71,
6697. (b) Blackwell, H. E.; O’Leary, D. J.; Chatterjee, A. K.;
Washenfelder, R. A.; Bussmann, D. A.; Grubbs, R. H. J. Am.
Chem. Soc. 2000, 122, 58. (c) Howsam, R. W.; Stirling, C. J.
M. J. Chem. Soc., Perkin Trans. 2 1972, 847.
Compound 1e: yield 82% (287 mg); colorless solid; mp 154–
155 °C. ESI-HRMS: m/z calcd for C17H19O4S2 [M+ + 1]:
351.0725; found: 351.0726. 1H NMR (400 MHz, CDCl3):
δ = 7.62–7.57 (m, 4 H), 7.28–7.25 (m, 4 H), 6.64 (d, J = 0.8
Hz, 1 H), 6.49 (d, J = 0.8, 1.6 Hz, 1 H), 4.02 (d, J = 1.2 Hz,
2 H), 2.43 (s, 3 H), 2.42 (s, 3 H). 13C NMR (100 MHz,
CDCl3): δ = 145.29, 145.09, 139.67, 134.74, 134.69, 130.43,
129.95 (2×), 129.79 (2×), 128.48 (2×), 128.39 (2×), 54.05,
21.66, 21.64.
Single-crystal X-ray diagram: Crystal of 1e was grown by
slow diffusion of EtOAc into a solution of 1e in CH2Cl2 to
yield colorless prisms. The compound crystallizes in the
monoclinic crystal system, space group P121/c1,
a = 15.6737(5) Å, b = 11.2694(4) Å, c = 19.6400(6) Å,
V = 3298.69(19) Å3, Z = 8, dcalcd = 1.411 g/cm3,
F(000) = 1472, 2θ range 2.11–26.39°; R indices (all data):
R1 = 0.1105, wR2 = 0.2077.
Compound 1m: yield 82% (379 mg); colorless solid; mp
106–108 °C. ESI-HRMS: m/z calcd for C25H35O4S2 [M+ +
1]: 463.1977; found: 463.1974. 1H NMR (400 MHz,
CDCl3): δ = 7.71 (d, J = 8.4 Hz, 2 H), 7.66 (d, J = 8.4 Hz,
(16) (a) Zoller, T.; Uguen, D. Eur. J. Org. Chem. 1999, 1545.
(b) Wang, X.; Ni, Z.; Lu, X.; Hollis, A.; Banks, H.;
Rodriguez, A.; Padwa, A. J. Org. Chem. 1993, 58, 5377.
Synlett 2014, 25, 411–416
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