Palladium-catalyzed heck-type coupling via C-N cleavage

Article abstract of DOI:10.1055/s-0034-1379911

Abstract A palladium-catalyzed Heck-type coupling method between arenes and ketone Mannich bases via C-N cleavage to synthesize chalcones is reported. This protocol offers good yields and tolerates a broad range of functional groups. Based on the extensive experimental data, we propose a plausible coulping mechanism.

Full text of DOI:10.1055/s-0034-1379911

SYNLETT
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
© Georg Thieme Verlag Stuttgart · New York
2015, 26, 1253–1257
letter
1253
W. Fan et al.
Letter
Synlett
Palladium-Catalyzed Heck-Type Coupling via C–N Cleavage
Weizheng Fan1
Faming Liu1
O
O
Heck-type coupling
C–N cleavage
no additional base
Pd(OAc)2
ArH
R
N(R')2
R
Ar
Bainian Feng*
Ag2CO3, Ag2O
ketone Mannich bases
School of Pharmaceutical Science, Jiangnan University,
Wuxi 214122, P. R. of China
fengbainian@jiangnan.edu.cn
Received: 02.02.2015
Accepted after revision: 17.03.2015
Published online: 02.04.2015
studies, the most important intermediate was in situ gener-
ated α,β-unsaturated ketone,9,10 and subsequent oxidative
dehydrogenation to finish the reaction.10
DOI: 10.1055/s-0034-1379911; Art ID: st-2015-w0079-l
Abstract A palladium-catalyzed Heck-type coupling method between
arenes and ketone Mannich bases via C–N cleavage to synthesize chal-
cones is reported. This protocol offers good yields and tolerates a broad
range of functional groups. Based on the extensive experimental data,
we propose a plausible coulping mechanism.
previous work:
O
O
ArH
+
R
H
Ar
oxidative
dehydrogenation
R
saturated ketones
Key words palladium-catalyzed, Heck-type coupling, C–N cleavage,
control experiment, mechanism
this work:
O
O
R1
ketone Mannich bases
N(R2)2
+
ArH
R1
Ar
Chalcones and their heterocyclic analogues are promi-
nent structural motifs of many bioactive natural products,2
pharmaceuticals,3 and functional materials.4 Recently, in-
tense efforts have focused on the development of effective
methods to synthesize these compounds. Traditionally,
chalcones are synthesized by the aldol condensation be-
tween aromatic aldehydes and ketones with the proper
bases.5 Because of some groups sensitive to bases, research-
ers developed other synthetic methods,6,7 including palladi-
um-catalyzed Sonogashira coupling of electron-deficient
aryl halides with aryl 1-propargyl alcohols6a,b and palladi-
um-catalyzed carbonylative Heck coupling of aryl halides
with styrenes.6c,d
The direct metal-catalyzed C–H bond formation has at-
tracted more attention in synthetic chemistry, providing an
atom economical strategy and reducing the production of
toxic byproducts which contributes to the growing field of
reactions with decreased environmental impact.8 Inspired
by this C–H activation idea, Su9 reported a versatile method
for the facile synthesis of chalcone through palladium-cata-
lyzed dehydrogenative cross-coupling between arenes and
aryl ethyl ketones (Scheme 1). In his detailed mechanistic
C–N cleavage
Scheme 1 Direct C–H functionalization routes for chalcone synthesis
Encouraged by this in situ generated method, ketone
Mannich bases, successfully employed in Heck-type cou-
pling,11 were chosen as precursors to do the same reaction.
Herein, a palladium-catalyzed Heck-type coupling method
between arenes and ketone Mannich bases via C–N cleav-
age to synthesize chalcones is reported. Some control ex-
periments suggest that this reaction proceeds through a
similar olefin intermediate in situ and a subsequent oxida-
tive coupling mechanism.9,10
Initially,
3-(dimethylamino)-1-phenylpropan-1-one
(1a) and a highly electron-deficient pentafluorobenzene
(2a)12 were chosen as model substrates in the presence of
different palladium catalysts, oxidants, and solvents to opti-
mize the reaction conditions. To our delight, when the re-
action was conducted with Pd(OAc)2 (0.05 equiv) and Ag2CO3
(1.5 equiv) in DMSO at 120 °C, 3a was formed in 65% yield
(Table 1, entry 1). Other palladium catalysts [PdCl2,
Pd(OTf)2, and Pd2(dba)3] showed less activity (Table 1, en-
tries 2–4). Further reaction attempts with other oxidants
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1253–1257

1254
W. Fan et al.
Letter
Synlett
Table 1 Optimization of the Conditionsa
O
F
F
H
F
F
O
F
F
F
Ph
Pd catalyst
oxidant, solvent
+
Ph
N(Me)2
F
F
F
1a
2a
3a
Entry
Pd cat. (5 mol%)
Oxidant (1.5 equiv)
Yield (%)b
1
2
Pd(OAc)2
PdCl2
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2O
65
15
43
<5
51
<5
0
3
Pd(OTf)2
Pd2(dba)3
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
no
4
5
6
O2
7
PhI(OAc)2
DDQ
8
0
9
Ag2CO3 + Ag2O (1:1)
Ag2CO3 + Ag2O (1:1)
no
81
<5
0
10
11
Pd(OAc)2
a Reaction conditions: 1a (0.2 mmol), 2a (0.6 mmol), catalyst (5 mol%), oxidant (1.5 equiv), DMSO (3 mL), 120 °C, 24 h
b Isolated yield.
showed that a mixture of Ag2CO3 and Ag2O (1:1, Table 1, en-
try 9) afforded the best yield of 81% (Table 1, entries 5–9).
The use of other solvents, increasing the amount of loading
catalyst or carrying out the standard reaction under inert
argon atmosphere, led to no significant improvement on
the yield (see Supporting Information, SI Tables 1). In the
absence of catalysts or oxidants, it showed less or no activi-
ty (Table 1, entries 10 and 11).
With the optimized reaction conditions in hand
[Pd(OAc)2 (5 mol%), Ag2CO3 + Ag2O (1.5 equiv, 1:1), DMSO
(3.0 mL), and 120 °C], we first examined the substrate scope
of this reaction (Scheme 2). Some other perfluoroarenes
also showed good activity (2a–e, 71–81%), similar to
Zhang’s work.12 However, electron-rich substrates (2f,g)
showed less or no activity. Subsequently, the other elec-
tron-deficient heterocycles were screened. Both electron-
withdrawing and electron-donating substituents on thio-
phene furnished good yields (3h–l, 59–84%), in which elec-
tron-withdrawing substituents show a litter lower activity.
Note that 3k containing a Cl group always got good yield
(63%) without dehalogenation. In contrast, unsubstituted
heteroarenes 3m and 3n afforded very poor yields (35% and
39%, respectively). It’s a pity that we did not isolate any 3o,
which might be due to the strong coordination to palladium
and poisoning the catalyst. The reaction occurred exclusive-
ly at the 5-position of monosubstituted thiophene or furan
rings, which might involve an electrophilic process.
Next, we evaluated the scope of aryl ketone Mannich
bases by using 2-methyl thiophene as a coupling partner
(Scheme 3). Variations of substitution positions and elec-
tronic effect did not much influence the product yields, ex-
hibiting good yields (3p–v, 65–85%). When R1 was changed
to Me, Et, or n-Bu, the yield of 3v was also influenced a lit-
tle. It suggests that there was no N(R1)2 group involved
in the catalytic intermediates. Note that all the products
3a–v18 showed E regioselectivity due to the high tempera-
ture (120 °C).
To understand the role of each compound in this forma-
tion, control experiments were performed (see SI-1 in the
Supporting Information). First, the reaction of 1a was
stirred under standard conditions and 78% yield of phenyl
vinyl ketone (1a′) was detected by 1H NMR spectroscopy in
five hours. When the reaction finished, adding one equiva-
lent of 2h and stirring for 12 hours afforded 82% yield of 3h
(Scheme 4). Second, (E)-3-(5-methylthiophen-2-yl)-1-
phenylprop-2-en-1-one (3h′)9,15 reacting under standard
conditions for 48 hours only got 15% yield of 3h. These re-
sults agree with a β-amino elimination first and subsequent
oxidative dehydrogenation mechanism (Scheme 5).9,10,12
In summary, a palladium-catalyzed Heck-type coupling
method between arenes and ketone Mannich bases via C–N
cleavage to synthesize chalcones is reported. This protocol
offers good yields and tolerates a broad range of functional
groups. Based on the extensive experimental data, we pro-
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1253–1257

1255
W. Fan et al.
Letter
Synlett
or
O
H
Pd(OAc)2
O
S
X
O
H
Pd(OAc)2
Ag2CO3, Ag2O
H
+
O
S
+
Ar
N(R1)2
Ag2CO3 + Ag2O
Ar
Ph
NMe2
Ar
Ph
Rf
R2
1
2i
3
1a
O
2
3
O
R2 = OMe
3p, 85%
3q, 76%
3r, 79%
S
O
O
2 = Cl
F
F
R
R
F
2 = NO2
F
F
R2
Ph
Ph
Ph
O
F
F
F
R2 = Me
3s, 75%
3t, 76%
3u, 71%
F
F
S
S
F
2 = Cl
2 = F
F
F
R
R
3a, 81%
3b, 74%
3c, 71%
R2
O
F
O
O
O
R1 = Me
3v, 68%
3v, 71%
3v, 65%
F
F
F
R
R
1 = Et
1 = n-Bu
Ph
Ph
Ph
OMe
F
F
CN
F
Scheme 3 The scope of the aryl ketone Mannich bases. Reagents and
conditions: 1 (0.2 mmol), 2 (0.6 mmol), Pd(OAc)2 (5 mol%), Ag2CO3 +
Ag2O (1:1, 1.5 equiv), DMSO (3 mL), 120 °C, 24 h, yields are isolated
yields.
F
3d, 79%
3e, 77%
3f, 0%
O
O
O
S
3i, 75%
S
S
Ph
Ph
Ph
Ph
C4H9
O
O
3g, 15%
3h, 84%
Pd(OAc)2
N(Me)2
O
O
Ag2CO3, Ag2O
O
1a
1a', 78%
S
S
O
S
Ph
Cl
Ph
Ph
O
OEt
S
O
O
standard
H
S
S
conditions
3j, 59%
3k, 63%
3l, 72%
+
Ph
Ph
Ph
O
O
1a', 78%
2h
O
3h, 82%
N
O
Ph
Ph
O
Ph
standard
conditions
S
Ph
3m, 35%
3n, 39%
3o, 0%
3h'
3h, 15%
Scheme 2 The scope of the arenes and heterocycles. Reagents and con-
ditions: 1 (0.2 mmol), 2 (0.6 mmol), Pd(OAc)2 (5 mol%), Ag2CO3 + Ag2O
(1:1, 1.5 equiv), DMSO (3 mL), 120 °C, 24 h, yields are isolated yields.
Scheme 4 Control experiments
O
O
pose a plausible coupling mechanism. Further studies con-
cerning the detailed mechanism and the broader scope of
substrates are currently in progress.
PdX2
N(Me)2
C–N cleavage
Pd(II)
1a
S
H
Acknowledgment
O
O
This work was supported financially by grants from the National Nat-
ural Science Foundation of China (grants 21302066) and Young Pro-
gram, SCF of Jiangsu Province (BK20130129). Delhi, for a SERB-Young
Scientist award (Registration No: CS-271/2014) and financial assis-
tance.
S
2h
Ph
Ph
Pd(II)
C–H olefination
3h
1a'
Scheme 5 A possible mechanism
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1253–1257

1256
W. Fan et al.
Letter
Synlett
Supporting Information
(9) Shang, Y.-P.; Jie, X.-M.; Zhou, J.; Hu, P.; Huang, S.-J.; Su, W.-P.
Angew. Chem. Int. Ed. 2013, 52, 1299.
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0034-1379911.
(10) For the reactions that involve dehydrogenation to olefins fol-
lowed by a coupling process, see: (a) Terao, Y.; Kametani, Y.;
Wakui, H.; Satoh, T.; Miura, M.; Nomura, M. Tetrahedron 2001,
57, 5967. (b) Ueno, S.; Shimizu, R.; Kuwano, R. Angew. Chem. Int.
Ed. 2009, 48, 4543. (c) Stang, E. M.; White, M. C. J. Am. Chem. Soc.
2011, 133, 14892. (d) Leskinen, M. V.; Yip, K.-T.; Valkonen, A.;
Pihko, P. M. J. Am. Chem. Soc. 2012, 134, 5750. (e) Moon, Y.;
Kwon, D.; Hong, S. Angew. Chem. Int. Ed. 2012, 51, 11333.
(11) (a) Reichwald, C.; Shimony, O.; Sacerdoti-Sierra, N.; Jaffe, C. L.;
Kunick, C. Bioorg. Med. Chem. Lett. 2008, 18, 1985.
(b) Reichwald, C.; Shimony, O.; Dunkel, U.; Sacerdoti-Sierra, N.;
Jaffe, C. L.; Kunick, C. J. Med. Chem. 2008, 51, 659.
(12) Zhang, X.-G.; Fan, S.-L.; He, C.-Y.; Wan, X.-L.; Min, Q.-Q.; Yang, J.;
Jiang, Z.-X. J. Am. Chem. Soc. 2010, 132, 4506.
(13) Pennell, M. N.; Sheppard, T. D.; Unthank, M. S.; Turner, P. J. Org.
Chem. 2011, 76, 1479.
(14) Musumarra, G.; Ballistreri, F. P. Org. Magn. Reson. 1980, 14, 384.
(15) Mori, A.; Miyakawa, Y.; Ohashi, E.; Haga, T.; Maegawa, T.; Sajiki,
H. Org. Lett. 2006, 8, 3279.
(16) Ranu, B. C.; Jana, R. J. Org. Chem. 2005, 70, 8621.
(17) Liu, D.-N.; Tian, S.-K. Chem. Eur. J. 2009, 15, 4538.
(18) Synthesis of 3a–p
S
u
p
p
ortioInfgrmoaitn
S
u
p
p
ortiInfogrmoaitn
References and Notes
(1) The authors contributed equally to this work.
(2) For a review on the bioactivity of chalcones, see: Dimmock, J. R.;
Elias, D. W.; Beazely, M. A.; Kandepu, N. M. Curr. Med. Chem.
1999, 6, 1125.
(3) (a) Konieczny, M. T.; Konieczny, W.; Sabisz, M.; Skladanowski,
A.; Wakiec, R. J. Med. Chem. 2007, 42, 729. (b) Kumar, D.; Kumar,
N. M.; Akamatsu, K.; Kusaka, E.; Harada, H.; Ito, T. Bioorg. Med.
Chem. Lett. 2010, 20, 3916. (c) Ducki, S.; Forrest, R.; Hadfield, J.
A.; Kendall, A.; Lawrence, N. J.; McGown, A. T.; Rennison, D.
Bioorg. Med. Chem. Lett. 1998, 8, 1051. (d) Edenharder, R.;
Petersdorff, I. V.; Rauscher, R. Mutat. Res. 1993, 287, 261.
(e) Pandeya, S. N.; Sriram, D.; Nath, G.; DeClercq, E. Eur. J. Med.
Chem. 1999, 9, 25. (f) Buolamwini, J. K.; Assefa, H. J. Med. Chem.
2002, 45, 841. (g) Nowakowska, Z. Eur. J. Med. Chem. 2007, 42,
125. (h) Ram, V. J.; Saxena, A. S.; Srivastava, S.; Chandra, S.
Bioorg. Med. Chem. Lett. 2000, 10, 2159.
(4) For selected examples of the syntheses of organic functional
materials from chalcones, see: (a) Ribierre, J.-C.; Cheval, G.;
Huber, F.; Mager, L.; Fort, A.; Muller, R.; Mery, S.; Nicoud, J. F. J.
Appl. Phys. 2002, 91, 1710. (b) Melzer, C.; Barzoukas, M.; Fort,
A.; Mery, S.; Nicoud, J.-C. Appl. Phys. Lett. 1997, 71, 2248.
(5) Thebtaranonth, C.; Thebtaranonth, Y. In The Chemistry of
Enones; Vol. 29; Patai, S.; Rappoport, Z., Eds.; Wiley: New York,
1989, 199.
(6) (a) Müller, T. J. J.; Ansorge, M.; Aktah, D. Angew. Chem. Int. Ed.
2000, 39, 1253. (b) Braun, R. U.; Ansorge, M.; Müller, T. J. J.
Chem. Eur. J. 2006, 12, 9081. (c) Wu, X.-F.; Neumann, H.; Beller,
M. Angew. Chem. Int. Ed. 2010, 49, 5284. (d) Wu, X.-F.;
Neumann, H.; Spannenberg, A.; Schulz, T.; Jiao, H.; Beller, M. J.
Am. Chem. Soc. 2010, 132, 14596.
A mixture of 1 (0.2 mmol), 2 (0.6 mmol), DMSO (3 mL),
Pd(OAc)2 (5 mol%), and Ag2CO3 and Ag2O (1.5 equiv, 1:1) was
stirred at 120 °C under air atmosphere for 24 h. To the reaction
mixture was added H2O and EtOAc, and the aqueous phase was
extracted with EtOAc (3×). The combined organic layer was
washed with brine, dried over Na2SO4, and evaporated under
reduced pressure. The crude product was purified by silica gel
column chromatography to give the corresponding products
(3a,12 3g,13 3h,14 3i–l,9 3m,16 3n,17 3p,q,s–v9 according to the lit-
erature).
(E)-3-(2,3,4,6-Tetrafluorophenyl)-1-phenylprop-2-en-1-one
(3b)
Yield 74%. 1H NMR (500 MHz, CDCl3): δ = 7.85 (d, J = 7.2 Hz, 2
H), 7.78–7.50 (m, 4 H), 7.35 (d, J = 16.8 Hz, 1 H), 7.08 (m, 1 H).
13C NMR (125 MHz, CDCl3): δ = 190.2, 153.0 (dm, J = 248.0 Hz),
149.9 (dm, J = 251.0 Hz), 148.5 (dm, J = 249.6 Hz), 139.2 (dm,
J = 241.2 Hz), 136.8, 135.9 (m), 131.5, 128.6, 126,9, 115.8, 114.1
(m), 102.9 (m). 19F NMR (282 MHz, CDCl3): δ = –118.5 (t, J = 9.6
Hz, 1 F), –134.9 (m, 1 F), –138.7 (dd, J = 19.5, 5.5 Hz, 1 F), –163.8
(m, 1 F). HRMS: m/z calcd for C15H8OF4: 280.0511; found:
280.0517.
(7) (a) Wang, D.; Zhang, Y.; Harris, A.; Gautam, L. N. S.; Chen, Y.; Shi,
X.-D. Adv. Synth. Catal. 2011, 353, 2584. (b) Albaladejo, M. J.;
Alonso, F.; Yus, M. Chem. Eur. J. 2013, 19, 5242. (c) Bukhari, S. N.
A.; Jasamai, M.; Jantan, I.; Ahmad, W. Mini-Rev. Org. Chem. 2013,
10, 73.
(8) For selected books and reviews, see: (a) C–HActivation, In Topics
in Current Chemistry; Vol. 292; Yu, J.-Q.; Shi, Z.-J., Eds.; Springer:
Berlin, 2010. (b) Kakiuchi, F.; Chatani, N. Adv. Synth. Catal. 2003,
345, 1077. (c) Satoh, T.; Miura, M. Chem. Lett. 2007, 36, 200.
(d) Chen, X.; Engle, K. M.; Wang, D.-H.; Yu, J.-Q. Angew. Chem.
Int. Ed. 2009, 48, 5094. (e) Li, C.-J. Acc. Chem. Res. 2009, 42, 335.
(f) Daugulis, O.; Do, H.-D.; Shabashov, D. Acc. Chem. Res. 2009,
42, 1074. (g) Ackermann, L.; Vicente, R.; Kapdi, A. R. Angew.
Chem. Int. Ed. 2009, 48, 9792. (h) Lyons, T. W.; Sanford, M. S.
Chem. Rev. 2010, 110, 1147. (i) Yeung, C. S.; Dong, V. M. Chem.
Rev. 2011, 111, 1215. (j) Bugaut, X.; Glorius, F. Angew. Chem. Int.
Ed. 2011, 50, 7479. (k) Liu, C.; Zhang, H.; Shi, W.; Lei, A. Chem.
Rev. 2011, 111, 1780. (l) Wencel-Delord, J.; Droge, T.; Liu, F.;
Glorius, F. Chem. Soc. Rev. 2011, 40, 4740. (m) Colby, D. A.;
Bergman, R. G.; Ellman, J. A. Chem. Rev. 2010, 110, 624.
(n) Engle, K. M.; Mei, T.-S.; Wasa, M.; Yu, J.-Q. Acc. Chem. Res.
2012, 45, 788. (o) Brückl, T.; Baxter, R. D.; Ishihara, Y.; Baran, P.
S. Acc. Chem. Res. 2012, 45, 826.
(E)-3-(2,4,6-Trifluorophenyl)-1-phenylprop-2-en-1-one (3c)
Yield 71%. 1H NMR (500 MHz, CDCl3): δ = 7.84 (d, J = 7.0 Hz, 2
H), 7.62–7.50 (m, 4 H), 7.34 (d, J = 16.6 Hz, 1 H), 6.96 (t, J = 9.0
Hz, 2 H). 13C NMR (125 MHz, CDCl3): δ = 189.8, 165.2 (dm,
J = 248.8 Hz), 139.1, 135.8 (m), 130.5, 128.9, 127.8, 117.1, 111.9
(m), 101.9 (m). 19F NMR (282 MHz, CDCl3): δ = –105.7 (m, 1 F), –
113.1 (t, J = 8.2 Hz, 2 F). HRMS: m/z calcd for C15H9OF3:
262.0605; found: 262.0613.
(E)-3-(2,3,5,6-Tetrafluorophenyl)-1-phenylprop-2-en-1-one
(3d)
1
Yield 79%. H NMR (500 MHz, CDCl3): δ = 7.837–7.75 (m, 3 H),
7.68–7.59 (m, 3 H), 7.35 (d, J = 17.4 Hz, 1 H), 7.15 (m, 1 H). 13C
NMR (125 MHz, CDCl3): δ = 190.3, 149.5 (dm, J = 256.4 Hz),
145.8 (dm, J = 262.5 Hz), 138.7 (m), 137.1, 128.5, 127.6, 118.3
(m), 114.5, 103.6 (t, J = 22.8 Hz). 19F NMR (282 MHz, CDCl3): δ =
–139.7 (m, 2 F), –144.8 (m, 2 F). HRMS: m/z calcd for C15H8OF4:
280.0511; found: 280.0508.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1253–1257

1257
W. Fan et al.
Letter
Synlett
(E)-3-(4-Cyano-2,3,5,6-tetrafluorophenyl)-1-phenylprop-2-
found: 305.0471.
en-1-one (3e)
(E)-3-(5-Methyl-2-thienyl)-1-(4-nitrophenyl)-2-propen-1-
one (3r)
Yield 77%. 1H NMR (500 MHz, CDCl3): δ = 8.04–8.02 (m, 2 H),
7.98 (d, J = 16.0 Hz, 1 H), 7.78 (d, J = 16.0 Hz, 1 H), 7.67–7.55 (m,
3 H). 13C NMR (125 MHz, CDCl3): δ = 188.9, 148.5 (dm, J = 246.3
Hz), 145.3 (dm, J = 257.9 Hz), 138.5 (m), 135.4, 129.9, 128.3,
128.4, 127.5, 116.1 (t, J = 13.7 Hz), 114.7, 99.3 (m). 19F NMR (282
MHz, CDCl3): δ = –132.5 (dd, J = 21.6, 8.0 Hz, 2 F), –138.4 (dd,
J = 21.6, 8.2 Hz, 2 F). HRMS: m/z calcd for C16H7ONF4: 305.0464;
Yield 79%. 1H NMR (500 MHz, CDCl3): δ = 8.14 (d, J = 8.0 Hz, 2
H), 7.95 (d, J = 15.4 Hz, 1 H), 7.68 (d, J = 8.0 Hz, 2 H), 7.34 (d,
J = 3.6 Hz, 1 H), 7.25 (d, J = 15.4 Hz, 1 H), 6.88 (d, J = 3.6 Hz, 1 H),
2.62 (s, 3 H). 13C NMR (125 MHz, CDCl3): δ = 189.8, 146.8, 140.2,
140.0, 139.3, 137.5, 134.2, 129.9, 128.5, 127.3, 118.4, 16.1.
HRMS: m/z calcd for C14H11NO3S: 273.0460; found: 273.0465.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1253–1257