Cu(II)/TBAI-catalyzed esterification of acid hydrazides via C(sp3)-H oxidative coupling

Article abstract of DOI:10.1055/s-0034-1379478

A Cu²⁺/TBAI-cocatalyzed allylic ester synthesis was developed, which allows a direct coupling of acid hydrazides and cycloalkanes. This process makes use of commercially available, inexpensive, and abundant starting materials. Based on the extensive experimental data, a plausible radical mechanism was suggested.

Full text of DOI:10.1055/s-0034-1379478

2908▌
LETTER
lCettuer (II)/TBAI-Catalyzed Esterification of Acid Hydrazides via C(sp3)–H Oxida-
tive Coupling
Esterification of Acid Hydrazides
Guifeng Liu,*a,b Can Jin,a,b Guomin Wua,b
a
Institute of Chemical Industry of Forest Products, Chinese Academy of Forestry, Key Laboratory of Biomass Energy and Material of Jiangsu
Province, Key and Open Laboratory on Forest Chemical Engineering, State Forestry Administration, National Engineering Laboratory for
Biomass Chemical Utilization, Nanjing 210042, P. R. of China
Fax +86(25)85482457; E-mail: liuguifeng067@163.com
b
Research Institute of New Technology, Chinese Academy of Forestry, Beijing 10091, P. R. of China
Received: 20.08.2014; Accepted after revision: 22.09.2014
catalytic synthesis of C–O bonds via C–H functionaliza-
Abstract: A Cu2+/TBAI-cocatalyzed allylic ester synthesis was de-
tion is of great interest.4 Among them, C–H activation to
veloped, which allows a direct coupling of acid hydrazides and cy-
form C(sp3)–O bond is a more challenging task. In the late
1950s, Kharasch and Sosnovsky reported the allylic oxi-
cloalkanes. This process makes use of commercially available,
inexpensive, and abundant starting materials. Based on the exten-
sive experimental data, a plausible radical mechanism was suggest- dation of olefins to afford allyl esters with tert-butyl per-
oxybenzoates (the Kharasch–Sosnovsky reaction)5 in the
presence of a copper catalyst. After that, a great deal of re-
search effort has been directed to improve the efficiency
of this allylic oxidation of olefins.6
ed.
Key words: Cu2+/TBAI cocatalysis, direct coupling, acid hydra-
zides
A few decades later, direct esterfication of an alkenes us-
ing aromatic acids were also attached.7 Recently, some
further significant progress in this area that cycloallyl es-
ters were synthesized directly from cycloalkanes using ar-
omatic aldehydes8 or alkylbenzenes9 as benzoyl source,
respectively, has been made. Herein, we report the synthe-
sis of cycloallyl esters via C(sp3)–H oxidative coupling
process using stable and accessible solids of acid hydra-
zides as benzoyl source and Cu(II)/TBAI as catalyst
(Scheme 1).
During the past ten years, C–H activation has emerged as
an attractive strategy to prepare organic building blocks in
a step- and atom-economical fashion.1 Much research has
been devoted to this C–H functionalization, and a lot of
selective conversions have been achieved, including C–C,
C–O, C–N, and C–X (X = F, Cl, Br, I) bond formation.2
Among these, some expensive metal catalysts containing
palladium, rhodium, and iridium salts were always need-
ed,1,2 the high price of which limits the practical industrial
applications. The use of inexpensive, nontoxic and com-
mercially available iron or copper salts would be of great
value.
We began our investigation by examining the coupling of
benzoic acid hydrazide (1a, 0.2 mmol) and cyclohexane
(2a, 2 mL) in the presence of different copper salts and ox-
idants to optimize the reaction conditions. The catalytic
system using 10 mol% of Cu(OAc)2 as catalyst and TBHP
(3 equiv) as oxidant gave an encouraging yield of 35% for
3a (Table 1, entry 1). However, other copper salts gave
The C–O bond is a major structural motif found in a broad
range of natural and unnatural structures.3 Due to the bio-
medical and industrial importance of these molecules, the
efficient and selective construction of C–O bonds has
been paid a topic of long-standing attention. Recently, the
H
O
H
H
OX
+
+
O
(X = Ot-Bu or H), ref. 5–7
ref. 9
O
O
O
H
H
H
+
NHNH2
+
this work
ref. 8
Scheme 1 Direct C–H functionalization routes for the synthesis of allyl esters
SYNLETT 2014, 25, 2908–2912
Advanced online publication: 17.10.2014
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0034-1379478; Art ID: st-2014-w0703-l
© Georg Thieme Verlag Stuttgart · New York

LETTER
Esterification of Acid Hydrazides
2909
Table 1 Optimization of Conditionsa
poor results (Table 1, entries 2–4). When adding 20 mol%
additive of TBAI (Bu4NI), the yield of 3a increased to
61% (Table 1, entry 5) unexpectedly. KI could not afford
the higher yield (entry 6), but KCl and KBr reduced the
yield (<5%, Table 1, entries 7 and 8). Control experiments
carried out in the absence of either Cu(OAc)2/TBAI or
TBHP failed to give the target product (Table 1, entries 9,
11), but TBAI only manifested some catalytic activity
(Table 1, entry 10). Increasing the amount of catalyst, ox-
idant, additive, or using other oxidants did not improve
the yield (Supporting Information Table 1, entries 11–20).
H
O
O
catylst
additive
O
NHNH2
+
oxidant
1a
2a
3a
Entry
Catalyst
Oxidant
Additive Yield (%)b
1
2
Cu(OAc)2
CuCl
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
No
–
35
5
–
With the optimized reaction conditions (Table 1, entry 5),
the substrate scope was then examined (Scheme 2). Sub-
strates bearing various aryl-substituted acid hydrazides
could afford the corresponding borate esters in good to ex-
cellent yields (Scheme 2). Both electron-withdrawing and
electron-donating substitutions on the aromatic ring were
successfully esterificated (Scheme 2, 3a–h), however, the
substrates with electron-withdrawing group reduced the
reaction yield (3b–d vs. 3e–h). In addition, heterocyclic
aromatic acid hydrazides also gave the target products in
a lower yield (3i,j). It is a pity that aliphatic acid hydra-
zides gave no results (3k,l). Other cycloalkanes also gave
the good yield of target products (3m–o) except hexane
(3p).
3
CuBr
–
8
4
CuI
–
14
61
47
<5
<5
0
5
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
–
TBAI
KI
6
7
KCl
KBr
–
8
9
10
11
–
TBAI
TBAI
24
0
Cu(OAc)2
a Reaction conditions: 1a (0.2 mmol), cyclohexane (2a, 2 mL), cata-
lyst (10 mol%), oxidant (0.6 mmol), additive (20 mol%), 140 °C, N2,
To gain some insight of the reaction mechanism and un-
derstand the roles of each component in the transforma-
tion, control experiments were performed (Scheme 3). We
36 h.
b Isolated yield.
O
O
H
Cu(OAc)2
TBAI
O
NHNH2
R
R
+
TBHP
1
2
3
O
O
O
O
MeO
MeO
MeO
O
O
O
O
MeO
3a, 61%
3b, 70%
3d, 72%
3c, 58%
O
O
O
O
O
O
O
O
Br
O2N
F
Cl
3e, 39%
3f, 30%
3h, 45%
3g, 33%
O
O
O
O
O
O
O
O
O
S
3l, 0
3k, 0
3i, 37%
3j, 21%
O
O
O
O
O
O
O
O
3p, 0
3o, 68%
3m, 65%
3n, 43%
Scheme 2 The scope of the aryl-substituted acid hydrazides
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 2908–2912

2910
G. Liu et al.
LETTER
tained. This result indicated that the current transforma-
tion might proceed via formation of radical species.6–9
Furthermore, benzoic acid hydrazide reacted in MeCN
under standard conditions without cyclohexane gave 45%
yield of benzoic acid (Scheme 3, a). Subsequently, benzo-
ic acid was used to react with cyclohexane under standard
conditions giving 58% yield of 3a (based on benzoic acid,
Scheme 3, c). When the reaction was carried out in the ab-
sence of 1a, cyclohexene were detected by 1H NMR spec-
troscopy (Scheme 3, d). Finally, 1a was used to react with
ten equivalents cyclohexene giving 71% yield of 3a
(Scheme 3, e). It is suggested that the catalytic cycle might
proceed via cyclohexene and benzoic acid as the interme-
diates.
O
O
H
(a)
Cu(OAc)2 (10 mol%)
TBHP (3 equiv)
O
NHNH2
+
TBAI (20 mol%)
scavengers
3a, 0
1a
2a
(b)
(c)
O
O
H
Cu(OAc)2 (10 mol%)
TBHP (3 equiv)
OH
NHNH2
+
TBAI (20 mol%)
No
MeCN
45%
1a
O
O
H
Cu(OAc)2 (10 mol%)
TBHP (3 equiv)
O
OH
+
TBAI (20 mol%)
On the basis of these preliminary results, possible mecha-
nisms are proposed (Scheme 4). Initially, TBHP can give
the t-Bu and OH radicals catalyzed by TBAI, according to
Szabó6d and Wan.7c Subsequently, benzoic acid hydrazide
is oxidized to give benzoic acid. Meanwhile, cyclohexane
undergoes dehydrogenation to cyclohexene, according to
Pérez’s suggestion.10 This dehydrogenative olefination of
cyclohexane to give cyclohexene has been reported with
various platinum, iridium, or rhenium catalysts.11 Finally,
a similar oxidative coupling as described in Wan’s work7c
to form the target product 3a12 was performed.
1a
58%
2a
(d)
(e)
O
H
Cu(OAc)2 (10 mol%)
TBHP (3 equiv)
OH
+
TBAI (20 mol%)
1H NMR detected
No
O
2a
H
Cu(OAc)2 (10 mol%)
TBHP (3 equiv)
NHNH2
3a, 71%
+
In summary, we have successfully developed
a
TBAI (20 mol%)
Cu2+/TBAI cocatalyzed allylic ester synthesis allowing a
direct coupling of acid hydrazides and cycloalkanes. This
radical process makes use of commercially available, in-
expensive, and abundant starting materials. Based on the
extensive experimental data, we have proposed a plausi-
ble radical mechanism. Further studies concerning the de-
tailed mechanism are currently under way in our
laboratory.
1a
Scheme 3 Control experiments
found that the addition of radical scavengers, such as
1,1-diphenylethene or TEMPO (Scheme 3, a), completely
inhibited the reaction, and no desired products were ob-
H
H
H
Cu+
OH
O
+
(a)
(b)
O
OH
Cu+
1/2 I2
Or
Or Cu2+
I
HCu(OAc)
TBHP
O
O
+
3a
O
NHNH2
O
H2O
O
+
N2
OH
O
H2O
O
O
Cu2+
Scheme 4 The possible mechanism
Synlett 2014, 25, 2908–2912
© Georg Thieme Verlag Stuttgart · New York

LETTER
Esterification of Acid Hydrazides
2911
Shi, Z.-J. Catal. Sci. Technol. 2011, 1, 191; and references
cited therein.
Acknowledgment
The authors are grateful for the support of the Special Fund for Fun-
damental Research from the Institute of New Technology of the
Chinese Academy of Forestry (CAFINT2012C04).
(7) (a) García-Cabeza, A. L.; Marín-Barrios, R.; Moreno-
Dorado, F. J.; Ortega, M. J.; Massanet, G. M.; Guerra, F. M.
Org. Lett. 2014, 16, 1598. (b) Chen, L.; Shi, E.; Liu, Z. J.;
Chen, S. L.; Wei, W.; Li, H.; Xu, K.; Wan, X. Chem. Eur. J.
2011, 17, 4085. (c) Shi, E.; Shao, Y.; Chen, S. L.; Hu, H. Y.;
Liu, Z. J.; Zhang, J.; Wan, X. B. Org. Lett. 2012, 14, 3384.
(d) Xue, Q.; Xie, J.; Xu, P.; Hu, Y.; Cheng, Y.; Zhu, C. ACS
Catal. 2013, 3, 1365.
Supporting Information for this article is available online
at
http://www.thieme-connect.com/products/ejournals/journal/
10.1055/s-00000083.SunpfgIpi
m
o
nr
i
(8) Zhao, J.; Fang, H.; Han, J.; Pan, Y. Org. Lett. 2014, 16, 2530.
(9) Rout, S. K.; Guin, S.; Ali, W.; Gogoi, A.; Patel, B. K. Org.
Lett. 2014, 16, 3086.
References and Notes
(1) (a) Handbook of C−H Transformations: Applications in
Organic Synthesis; Dyker, G., Ed.; Wiley-VCH: Weinheim,
2005. For recent reviews on this topic, see: (b) Li, C.-J. Acc.
Chem. Res. 2009, 42, 335. (c) Dobereiner, G. E.; Crabtree,
R. H. Chem. Rev. 2010, 110, 681. (d) Colby, D. A.;
Bergman, R. G.; Ellman, J. A. Chem. Rev. 2010, 110, 624.
(e) Lyons, T. W.; Sanford, M. S. Chem. Rev. 2010, 110,
1147. (f) Sun, C.-L.; Li, B.-J.; Shi, Z.-J. Chem. Rev. 2011,
111, 1293. (g) Gutekunst, W. R.; Baran, P. S. Chem. Soc.
Rev. 2011, 40, 1976. (h) Arockiam, P. B.; Bruneau, C.;
Dixneuf, P. H. Chem. Rev. 2012, 112, 5879. (i) Kuhl, N.;
Hopkinson, M. N.; Wencel-Delord, J.; Glorius, F. Angew.
Chem. Int. Ed. 2012, 51, 10236. (j) Engle, K. M.; Mei, T.-S.;
Wasa, M.; Yu, J.-Q. Acc. Chem. Res. 2012, 45, 788.
(k) Engle, K. M.; Yu, J.-Q. J. Org. Chem. 2013, 78, 8927.
(2) C–H functionalization in total synthesis: (a) Taber, D. F.;
Stiriba, S.-E. Chem. Eur. J. 1998, 4, 990. (b) Godula, K.;
Sames, D. Science 2006, 312, 67. (c) Davies, H. M. L.;
Manning, J. R. Nature (London, U.K.) 2008, 451, 417.
(d) Gutekunst, W. R.; Baran, P. S. Chem. Soc. Rev. 2011, 40,
1976. (e) McMurray, L.; O’Hara, F.; Gaunt, M. J. Chem.
Soc. Rev. 2011, 40, 1885. (f) Brückl, T.; Baxter, R. D.;
Ishihara, Y.; Baran, P. S. Acc. Chem. Res. 2012, 45, 826.
(g) Yamaguchi, J.; Yamaguchi, A. D.; Itami, K. Angew.
Chem. Int. Ed. 2012, 51, 8960.
(3) (a) Ley, S. V.; Thomas, A. W. Angew. Chem. Int. Ed. 2003,
42, 5400. (b) Science of Synthesis; Vol. 27; Forsyth, C. J.,
Ed.; Thieme: Stuttgart, 2008.
(4) For selected references, see: (a) Wang, D. H.; Engle, K. M.;
Shi, B. F.; Yu, J.-Q. Science 2010, 327, 315. (b) Engle, K.
M.; Mei, T.-S.; Wasa, M.; Yu, J.-Q. Acc. Chem. Res. 2012,
45, 788.
(5) (a) Kharasch, M. S.; Sosnovsky, G.; Yang, N. C. J. Am.
Chem. Soc. 1959, 81, 5819. (b) Kharasch, M. S.; Sosnovsky,
G. J. Am. Chem. Soc. 1958, 80, 756. (c) Akermark, B.;
Magnus Larsson, E.; Oslob, J. D. J. Org. Chem. 1994, 59,
5729. (d) Shi, E.; Shao, Y.; Chen, S.; Hu, H.; Liu, Z.; Zhang,
J.; Wan, X. Org. Lett. 2012, 14, 3384.
(10) Conde, A.; Vilella, L.; Balcells, D.; Díaz-Requejo, M. M.;
Lledós, A.; Pérez, P. J. J. Am. Chem. Soc. 2013, 135, 3887.
(11) (a) Choi, J.; MacArthur, A. H. R.; Brookhart, M.; Goldman,
A. S. Chem. Rev. 2011, 111, 1761. (b) Haibach, M. C.;
Kundu, S.; Brookhart, M.; Goldman, A. S. Acc. Chem. Res.
2012, 45, 947.
(12) Synthesis of 3a–p
A mixture of 1 (0.2 mmol), cycloalkane (2 mL), Cu(OAc)2
(10 mol%), TBAI (20 mol%), and TBHP (3 equiv) was
stirred at 140 °C under N2 atmosphere for 36 h. The reaction
mixture was washed with H2O 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
product.
Compound 3a: yield 61%. 1H NMR (500 MHz, CDCl3): δ =
8.06 (d, J = 8.4 Hz, 2 H), 7.55 (m, 1 H), 7.42 (dd, J = 8.2, 7.0
Hz, 2 H), 6.01 (m, 1 H), 5.85 (m, 1 H), 5.51 (m, 1 H), 2.15
(m, 1 H), 2.04 (m, 1 H), 1.96 (m, 1 H), 1.84 (m, 1 H), 1.68
(m, 1 H). 13C NMR (125 MHz, CDCl3): δ = 166.2, 132.8,
132.7, 130.8, 129.5, 128.2, 125.7, 68.5, 28.4, 24.9, 18.9.
HRMS: m/z calcd for C13H14O2 [M]+: 202.2491; found:
202.2488.
Compound 3b: yield 70%. 1H NMR (500 MHz, CDCl3): δ =
8.00 (d, J = 9.0 Hz, 2 H), 6.90 (d, J = 9.0 Hz, 2 H), 5.96 (m,
1 H), 5.81 (m, 1 H), 5.45 (m, 1 H), 3.82 (s, 3 H), 2.04 (m, 3
H), 1.82 (m, 2 H), 1.67 (m, 1 H). 13C NMR (125 MHz,
CDCl3): δ = 165.9, 163.2, 132.5, 131.5, 125.9, 123.2, 113.4,
68.2, 55.3, 28.4, 24.9, 18.9. HRMS: m/z calcd for C14H16O3
[M]+: 232.2750; found: 232.2755.
Compound 3c: yield 58%. 1H NMR (500 MHz, CDCl3): δ =
7.70 (m, 2 H), 7.13 (m, 2 H), 5.80 (m, 1 H), 5.68 (m, 1 H),
5.35 (m, 1 H), 2.20 (m, 3 H), 1.99–1.65 (m, 6 H). 13C NMR
(125 MHz, CDCl3): δ = 165.8, 137.5, 133.1, 132.2, 130.3,
129.6, 127.7, 126.4, 125.2, 68.0, 28.1, 24.6, 20.8, 18.6..
HRMS: m/z calcd for C14H16O3 [M]+: 232.2750; found:
232.2753
(6) Several groups have described transition-metal-catalyzed
C–H oxidation for allylic ester, see: (a) Grennberg, H.;
Bäckvall, J.-E. Chem. Eur. J. 1998, 4, 1083. (b) Chen, M. S.;
White, M. C. J. Am. Chem. Soc. 2004, 126, 1346. (c) Chen,
M. S.; Prabagaran, N.; Labenz, N. A.; White, M. C. J. Am.
Chem. Soc. 2005, 127, 6970. (d) Pilarski, L. T.; Selander, N.;
Böse, D.; Szabó, K. J. Org. Lett. 2009, 11, 5518. (e) Stang,
E. M.; White, M. C. Nat. Chem. 2009, 1, 547. (f) Thiery, E.;
Aouf, C.; Belloy, J.; Harakat, D.; Le Bras, J.; Muzart, J. J.
Org. Chem. 2010, 75, 1771. (g) Henderson, W. H.; Check,
C. T.; Proust, N.; Stambuli, J. P. Org. Lett. 2010, 12, 824.
(h) Campbell, A. N.; White, P. B.; Guzei, I. A.; Stahl, S. S.
J. Am. Chem. Soc. 2010, 132, 15116. (i) Yin, G.; Wu, Y.;
Liu, G. J. Am. Chem. Soc. 2010, 132, 11978. (j) Lumbroso,
A.; Koschker Vautravers, P. N. R.; Breit, B. J. Am. Chem.
Soc. 2011, 133, 2386. (k) For a review, see: Li, H.; Li, B.-J.;
Compound 3d: yield 72%. 1H NMR (500 MHz, CDCl3): δ =
7.52 (dd, J = 8.4, 2.0 Hz, 1 H), 7.40 (d, J = 2.0 Hz, 1 H), 6.69
(m, 1 H), 5.83 (m, 1 H), 5.68 (m, 1 H), 5.28 (m, 1 H), 3.75
(s, 3 H), 3.70 (s, 3 H), 2.20–1.40 (m, 6 H). 13C NMR (125
MHz, CDCl3): δ = 165.4, 152.4, 148.1, 132.0, 125.5, 123.0,
122.8, 111.5, 109.7, 67.9, 55.4, 28.1, 24.5, 18.2. HRMS: m/z
calcd for C15H18O4 [M]+: 262.3010; found: 262.3013.
Compound 3e: yield 39%. 1H NMR (500 MHz, CDCl3): δ =
7.90 (d, J = 8.6 Hz, 2 H), 7.56 (d, J = 8.6 Hz, 2 H), 6.01 (m,
1 H), 5.832 (m, 1 H), 5.50 (m, 1 H), 2.05 (m, 3 H), 1.83 (m,
2 H), 1.70 (m, 1 H). 13C NMR (125 MHz, CDCl3): δ = 165.3,
132.8, 131.4, 130.99, 129.7, 127.67, 125.9, 68.8, 28.4, 24.8,
18.2.. HRMS: m/z calcd for C13H13BrO2 [M]+: 281.1451;
found: 281.1450.
Compound 3f: yield 30%. 1H NMR (500 MHz, CDCl3): δ =
8.28 (d, J = 8.8 Hz, 2 H), 8.22 (d, J = 8.8 Hz, 2 H), 6.05 (m,
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 2908–2912

2912
G. Liu et al.
LETTER
1 H), 5.84 (m, 1 H), 5.55 (m, 1 H), 2.19–1.72 (m, 6 H). 13
NMR (125 MHz, CDCl3): δ = 164.0, 150.1, 135.9, 133.9,
C
5.89 (m, 1 H), 5.67 (m, 1 H), 2.3 (m, 3 H), 1.88 (m, 2 H), 1.78
(m, 1 H). 13C NMR (125 MHz, CDCl3): δ = 162.5, 134.9,
134.1, 132.9, 132.0, 128.3, 125.9, 68.8, 28.5, 24.3, 18.1.
HRMS: m/z calcd for C11H12O3 [M]+: 192.2112; found:
192.2110.
130.4, 124.7, 123.2, 69.6, 28.0, 24.7, 18.6. HRMS: m/z calcd
for C13H13NO4 [M]+: 247.2466; found: 247.2463.
Compound 3g: yield 33%. 1H NMR (500 MHz, CDCl3): δ =
8.07 (m, 2 H), 7.10 (m, 2 H), 6.01 (m, 1 H), 5.82 (m, 1 H),
5.50 (m, 1 H), 2.06 (m, 3 H), 1.85 (m, 2 H), 1.70 (m, 1 H).
13C NMR (125 MHz, CDCl3): δ = 166.9, 165.2, 164.3, 132.9,
132.1, 132.0, 126.9, 125.5, 115.4, 115.2, 68.7, 28.3, 24.9,
18.9. HRMS: m/z calcd for C13H13FO2 [M]+: 220.2395;
found: 220.2393.
Compound 3m: yield 65%. 1H NMR (500 MHz, CDCl3): δ
= 8.02 (d, J = 8.4 Hz, 2 H), 7.53 (t, J = 7.2 Hz, 1 H), 7.40 (m,
2 H), 6.18 (m, 1 H), 5.92 (m, 2 H), 2.65 (m, 1 H), 2.33 (m, 2
H), 1.90 (m, 1 H). 13C NMR (125 MHz, CDCl3): δ = 166.6,
137.7, 132.7, 130.7, 129.5, 129.4, 128.2, 81.1, 31.2, 29.9.
HRMS: m/z calcd for C12H12O2 [M]+: 288.2225; found:
188.2220.
Compound 3h: yield 45%. 1H NMR (500 MHz, CDCl3): δ =
7.98 (d, J = 8.4 Hz, 2 H), 7.40 (d, J = 8.4 Hz, 2 H), 6.01 (m,
1 H), 5.82 (m, 1 H), 5.50 (m, 1 H), 2.05 (m, 3 H), 1.83 (m, 2
H), 1.70 (m, 1 H). 13C NMR (125 MHz, CDCl3): δ = 165.2,
139.0, 132.9, 130.9, 129.1, 128.5, 125.4, 68.8, 28.3, 24.8,
18.8. HRMS: m/z calcd for C13H13ClO2 [M]+: 236.6941;
found: 236.6945.
Compound 3n: yield 43%. 1H NMR (500 MHz, CDCl3): δ =
8.08 (m, 2 H), 7.57 (m, 1 H), 7.42 (m, 2 H), 5.91 (m, 1 H),
5.79 (m, 1 H), 5.66 (m, 1 H), 2.27 (m, 1 H), 2.14 (m, 1 H),
2.01 (m, 2 H), 1.90–1.66 (m, 3 H), 1.53–1.45 (m, 1 H). 13
C
NMR (125 MHz, CDCl3): δ = 166.1, 133.7, 133.0, 132.2,
130.9, 129.8, 128.5, 74.9, 33.1, 28.8, 26.9, 26.8. HRMS: m/z
calcd for C14H16O2 [M]+: 216.2756; found: 216.2751.
Compound 3o: yield 68%. 1H NMR (500 MHz, CDCl3): δ =
8.02 (d, J = 8.4 Hz, 2 H), 7.55 (t, J = 8.4 Hz, 1 H), 7.43 (t,
J = 7.6 Hz, 2 H), 5.93 (m, 1 H), 5.72 (m, 1 H), 5.61 (m, 1 H),
2.33 (m, 1 H), 2.15 (m, 1 H), 2.04 (m, 1 H), 1.66 (m, 6 H),
1.42 (m, 1 H). 13C NMR (125 MHz, CDCl3): δ = 166.0,
132.7, 130.7, 130.7, 129.8, 129.5, 128.2, 73.0, 35.1, 28.8,
26.4, 25.9, 23.4. HRMS: m/z calcd for C15H18O2 [M]+:
230.3022; found: 230.3019.
Compound 3i: yield 37%. 1H NMR (500 MHz, CDCl3): δ =
7.80 (m, 1 H), 7.53 (m, 1 H), 7.08 (m, 1 H), 6.00 (m, 1 H),
5.81 (m, 1 H), 5.47 (m, 1 H), 2.03 (m, 3 H), 1.84 (m, 2 H),
1.68 (m, 1 H). 13C NMR (125 MHz, CDCl3): δ = 161.8,
134.3, 133.1, 132.9, 132.0, 127.5, 125.4, 68.8, 28.2, 24.8,
18.8. HRMS: m/z calcd for C11H12SO2 [M]+: 208.2768;
found: 208.2770.
Compound 3j: yield 21%. 1H NMR (500 MHz, CDCl3): δ =
7.92 (m, 1 H), 7.64 (m, 1 H), 7.15 (m, 1 H), 6.21 (m, 1 H),
Synlett 2014, 25, 2908–2912
© Georg Thieme Verlag Stuttgart · New York

Copyright of Synlett is the property of Georg Thieme Verlag Stuttgart and its content may not
be copied or emailed to multiple sites or posted to a listserv without the copyright holder's
express written permission. However, users may print, download, or email articles for
individual use.