Cp2TiCl2-catalyzed hydrocarboxylation of alkynes with CO2: formation of α,β-unsaturated carboxylic acids

Article abstract of DOI:10.1039/c6ra25003c

Cp₂TiCl₂-catalyzed hydrocarboxylation of alkynes with CO₂ (atmospheric pressure) has been reported. A range of alkynes were transformed to the corresponding α,β-unsaturated carboxylic acids in high yields with high regioselectivity. The reaction proceeded with hydrotitanation, transmetalation, and subsequently carboxylation with CO₂

Full text of DOI:10.1039/c6ra25003c

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Cp2TiCl2-catalyzed hydrocarboxylation of alkynes
with CO2: formation of a,b-unsaturated carboxylic
acids†
Cite this: RSC Adv., 2017, 7, 3534
a
a
a
ab
*
*
Peng Shao, Sheng Wang, Gaixia Du and Chanjuan Xi
Received 10th October 2016
Accepted 22nd November 2016
Cp2TiCl2-catalyzed hydrocarboxylation of alkynes with CO2 (atmospheric pressure) has been reported. A
range of alkynes were transformed to the corresponding a,b-unsaturated carboxylic acids in high yields
with high regioselectivity. The reaction proceeded with hydrotitanation, transmetalation, and
subsequently carboxylation with CO2.
DOI: 10.1039/c6ra25003c
www.rsc.org/advances
Introduction
a,b-Unsaturated carboxylic acids are important chemicals,1 and
can be used as basic materials in the production of plastics,
superabsorbent, polymers, and rubbers. Various synthetic
methodologies for their synthesis have been developed, for
example, oxidation of propene over heterogeneous catalysts at
high temperature yielded the a,b-unsaturated carboxylic acids2
and hydrocarboxylation of alkynes utilization of metal
carbonyls complexes also formed the a,b-unsaturated carbox-
ylic acids.3 From the viewpoint of sustainable chemistry, the
development of efficient routes with high atom and step-
economy under mild conditions could be highly desirable.
Carbon dioxide (CO2) is an environmental friendly, low-toxic
and abundant carbon source. Many reaction have been devel-
oped utilization of CO2 as a C1 feedstock in organic synthesis.4
The addition of CO2 to alkynes could serve as a most powerful
synthetic route for construction of the a,b-unsaturated carbox-
ylic acids. Recently, Ma and co-workers reported a nickel-
catalyzed hydrocarboxylation of alkynes with diethyl zinc and
CO2 to form the a,b-unsaturated carboxylic acids.5 In the
meantime, Tsuji and co-workers developed a copper-catalyzed
hydrocarboxylation of alkynes with CO2 by using hydrosilane
as hydrogen source to afford the a,b-unsaturated carboxylic
acids.6 On the other hand, direct reaction of vinylmagnesium
halides with CO2 could also afford the a,b-unsaturated carbox-
ylic acids, however, the vinylmagnesium reagents are required
preparation in advanced and thus limitation their use.7 It was
reported that alkynes reacted with isobutylmagnesium bromide
(iBuMgBr) in the presence of a catalytic amount of Cp2TiCl2 to
Scheme 1 Cp2TiCl2-catalyzed hydrocarboxylation of alkynes with
CO2 in the presence of Grignard reagent.
afford
alkenylmagnesium
halides,8
in
which
iso-
butylmagnesium bromide is not only as a hydrogen source but
also as a transmetallation reagent. Encouraged by this work and
as part of our ongoing project on group IV metal complex in
organic synthesis,9 Herein we reported a Cp2TiCl2-catalyzed
hydrocarboxylation of alkynes with CO2 in the presence of iso-
butylmagnesium halide to afford the a,b-unsaturated carboxylic
acids (Scheme 1).
Results and discussion
In initial study, we carried out the rst trial in the utilization of
diphenylacetylene 1a as the substrate, 5 mol% of Cp2TiCl2 as
a catalyst in the presence of isobutylmagnesium bromide in
diethyl ether. The reaction mixture was stirred at 30 ꢀC for 6 h.
Subsequently, CO2 balloon was connected to the reaction
ꢀ
mixture and the mixture was stirred at 30 C overnight under
CO2 atmosphere to obtain an a,b-unsaturated carboxylic acid 2a
in 75% yield (eqn (1)).
(1)
aKey Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Ministry of
Education, Department of Chemistry, Tsinghua University, Beijing 100084, China
bState Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin
300071, China. E-mail: cjxi@tsinghua.edu.cn
Following the hydrocarboxylation of a variety of symmetrical
internal alkynes was carried out in the presence of BuMgBr as
i
hydride source. The representative results are summarized in
Table 1. The diaryl alkynes bearing methyl group at any position
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra25003c
3534 | RSC Adv., 2017, 7, 3534–3539
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
a
Table 1 Preparation of functionalized acrylic acids by Cp2TiCl2-catalyzed hydrocarboxylation of symmetrical alkynes with CO2
Entry
Alkyne
Product
Yieldb (%)
1
80
77
2
3
4
66
43
5
62
6
7
41
43
8
9
53
65
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 3534–3539 | 3535

View Article Online
RSC Advances
Paper
Table 1 (Contd.)
Entry
Alkyne
Product
Yieldb (%)
10
73
a
i
Reaction conditions: (i) alkynes (1 mmol), Cp2TiCl2 (0.05 mmol), BuMgBr (1.1 mmol), Et2O (4 mL), 30 ꢀC; (ii) CO2 balloon, 30 ꢀC, overnight.
Isolated yield.
b
of the phenyl ring could proceed smoothly and afforded the
Based on the above results and literatures about hydro-
corresponding diaryl substituted a,b-unsaturated carboxylic magnesiation of unsaturated hydrocarbons,8 a possible reaction
acids (entries 2–4). When electron-withdrawing group such as F mechanism was proposed as shown in Scheme 2. First, reduc-
or Cl was tolerated on the phenyl ring, the hydrocarboxylative tion of Cp2TiCl2 by Grignard reagent gives species Cp2TiiBu,
acids were obtained with a slightly reduced yield (entries 5 and which was followed by b-hydride elimination to give Cp2TiH.8
6). Notably, for more electron-decient alkyne, such as di-(4- Then addition of alkyne affords an intermediate A, which
CF3-phenyl) acetylene was used, no hydrocarboxylative product undergoes transmetallation with the Grignard reagent to
was obtained. When dinaphthyl or dithienyl substituted alkynes produce complex B and release hydromagnesiated product C.
were employed as a substrate, the corresponding a,b-unsatu- The hydromagnesiated C reacts with CO2 and subsequent
rated carboxylic acids 2h and 2i could also be obtained in hydrolysis to afford the a,b-unsaturated carboxylic acids 2. The
acceptable yields, respectively (entries 7 and 8). Moreover, b-hydride elimination of the complex B to regenerate species of
internal alkynes possessing aliphatic substituents could also be Cp2TiH.
applied in this system, giving the corresponding product 2j and
2k in good yield (entries 9 and 10).
Conclusion
In further to examine the scope of hydrocarboxylation of
alkynes, unsymmetrical internal alkynes were selected as
substrates, and the representative results are shown in Table 2.
When 1-phenyl-1-propyne 1l was used, the hydrocarboxylation
worked well with good regioselectivity, affording desired prod-
ucts with the CO2H group connected to the sp2 carbon atom
bearing the phenyl group as a major product in good yield (entry
1). Utilization of unsymmetrical internal alkynes with some
We have developed Cp2TiCl2-catalyzed an efficient hydro-
carboxylation of alkynes with CO2, affording the corresponding
carboxylic acids in good yields with high regioselectivity. This
protocol provides a convenient pathway for the synthesis of the
a,b-unsaturated carboxylic acids by use of CO2 as a renewable
source of carbon in organic synthesis.
t
other alkyl moieties, such as Et, Bu, cyclopropyl or ether, also
Experimental section
General information
proceeded smoothly to afford the corresponding disubstituted
acrylic acids with good regioselectivity (entries 2–4 and 6). It is
noteworthy that the hydrocarboxylation of the alkyne with
hydroxyl group took place regioselectively in moderate yield,
albeit one more equivalent of iBuMgBr was necessary (entry 5).
The large steric hindrance group TMS was also tolerated in this
system with good regioselectivity (entry 7). Alkyne with phenyl
and cyclohexenyl groups gave a mixture of two products in 7 : 1
ratio (entry 8). However, when 1-phenyl-2-thienyl acetylene 1t
and 1-(4-F-phenyl)-2-phenyl acetylene 1u were used as
substrates, the reaction could proceed, while the regioselectivity
of products decreased (entries 9 and 10). When 1-(3,3-
dimethylbut-1-yn-1-yl)-4-uorobenzene 1v was employed in the
reaction, less amount of 2v was observed and 3-methylbutanoic
acid was obtained as a major product (entry 11). Utilization of 1-
(3,3-dimethylbut-1-yn-1-yl)-4-methoxybenzene 1w in this reac-
tion and desired product was obtained in 46% yield (entry 12).
When terminal alkynes, for example phenylacetylene and 1-
octyne, were applied in this reaction, no hydrocarboxylative
products were detected.
All the reactions were carried out in oven-dried Schleck tubes
under N2 atmosphere. Unless indicated, all materials were ob-
tained from commercial sources and used as received. THF and
diethyl ether were fresh distilled. Column chromatography was
1
performed on silica gel (particle size 200–300 mesh). H NMR
and 13C NMR spectra were recorded on 400 MHz at ambient
temperature with CDCl3 or DMSO-d6 as the solvent. Chemical
shis (d) were given in ppm, referenced to the residual proton
resonance of CDCl3 (7.26), to the carbon resonance of CDCl3
(77.16). Coupling constants (J) were given in hertz (Hz). The
term m, d, s referred to multiplet, doublet, and singlet.
General procedure for synthesis of 2a–w
To an oven-dried Schleck tube was added Cp2TiCl2 (5 mol%),
which was degassed and relled with N2 for 3 times. Dry diethyl
ether (4 mL) was added via syringe, followed by the dropwise
i
addition of BuMgBr (1.1 mmol, 2 M in diethyl ether) at room
temperature. Then, the alkynes 1a–t (1 mmol) was added. The
3536 | RSC Adv., 2017, 7, 3534–3539
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
a
Table 2 Preparation of functionalized acrylic acids by Cp2TiCl2-catalyzed hydrocarboxylation of unsymmetrical alkynes with CO2
Entry
1
Alkyne
Yieldb (%)
69
Ratio of productc
2l : 2l0 (97 : 3)
2
3
4
60
51
77
2m : 2m0 (96 : 4)
2n : 2n0 (96 : 4)
2o : 2o0 (95 : 5)
5d
6
60
41
2p : 2p0 (99 : 1)
2q : 2q0 (99 : 1)
7
8
49
2r : 2r0 (94 : 6)
2s : 2s0 (7 : 1)
63e
9
51e
2t : 2t0 (2 : 1)
10
54e
2u : 2u0 (2 : 1)
11f
Trace
2v : 2v0 (100 : —)
12
46
2w : 2w0 (92 : 8)
a
i
b
c
Reaction conditions: alkyne (1 mmol), Cp2TiCl2 (0.05 mmol), BuMgBr (1.1 mmol), Et2O (4 mL). Isolated yield of major product. NMR ratio.
2.1 equiv. iBuMgBr was used. e Combined yield. f 3-Methylbutanoic acid was obtained as major product.
d
ꢀ
resulting mixture was stirred at 30 C for 6 h under N2 atmo- The residue was puried by silica gel (petroleum ether/ethyl
sphere. Then the solution was stirred overnight under CO2 acetate ¼ 5/1) to give the corresponding products 2a–w.
balloon at room temperature. Aer that, the reaction was
(E)-2,3-Diphenylacrylic acid (2a). White solid, 168 mg, yield:
quenched with HCl solution (2 M) till pH ¼ 3–4. Then the 75%, mp 166–168 ꢀC; 1H NMR (CDCl3, 400 MHz): d 7.07 (d, J ¼
mixture was extracted with ethyl acetate (5 mL ꢁ 3) and the 8 Hz, 2H), 7.16 (t, J ¼ 8 Hz, 2H), 7.23–7.25 (m, 3H), 7.35–7.40 (m,
combined organic phase was dried over anhydrous Na2SO4, 3H); 13C NMR (CDCl3, 101 MHz): 128.1, 128.4, 128.8, 129.6,
followed by ltration and concentration by rotary evaporator. 129.9, 131.0, 131.9, 134.4, 135.5, 142.5, 173.3; GC-MS m/z: 224.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 3534–3539 | 3537

View Article Online
RSC Advances
Paper
249.1 Hz), 163.3 (d, JC–F ¼ 253.4 Hz), 173.3; HRMS (ESIꢂ) calcd
ꢂ
for C15H9F2O2 259.0576; found: 259.0572.
(E)-2,3-Bis(4-chlorophenyl)acrylic acid (2g). White solid,
120 mg, yield: 41%, mp 178–180 ꢀC; 1H NMR (CDCl3, 400 MHz):
d 7.00 (d, J ¼ 8 Hz, 2H), 7.15–7.19 (m, 4H), 7.36 (d, J ¼ 8 Hz, 2H),
7.90 (s, 1H); 13C NMR (CDCl3, 101 MHz): 128.8, 129.2, 131.0,
131.3, 132.0, 132.5, 133.3, 134.5, 135.9, 141.7, 172.2; GC-MS m/z:
292. Data were in accordance with those previously reported in
the literature.6
(E)-2,3-Di(naphthalen-2-yl)acrylic acid (2h). Yellow solid,
139 mg, yield: 43%, mp 237–239 ꢀC; 1H NMR (d6-DMSO, 400
MHz): d 6.82 (d, J ¼ 8 Hz, 1H), 7.00 (t, J ¼ 8 Hz, 1H), 7.20 (d, J ¼
8 Hz, 1H), 7.35 (t, J ¼ 8 Hz, 1H), 7.42–7.49 (m, 2H), 7.55 (t, J ¼
8 Hz, 1H), 7.63 (t, J ¼ 8 Hz, 1H), 7.70 (d, J ¼ 8 Hz, 1H), 7.81 (t, J ¼
8 Hz, 2H), 7.86–7.91 (m, 2H), 8.20 (d, J ¼ 8 Hz, 1H), 8.68 (s, 1H);
13C NMR (d6-DMSO, 101 MHz): 124.3, 125.4, 125.4, 126.0, 126.4,
126.8, 126.9, 127.4, 128.0, 128.3, 128.9, 129.1, 129.4, 131.7,
132.2, 132.4, 133.4, 133.5, 134.5, 135.1, 139.2, 168.8; HRMS
Scheme 2 Possible reaction mechanism.
ꢂ
(ESIꢂ) calcd for C23H15O2 323.1072; found: 323.1070.
Data were in accordance with those previously reported in the
literature.5
(Z)-2,3-Di(thiophen-2-yl)acrylic acid (2i). Yellow solid,
125 mg, yield: 53%, mp 239–241 ꢀC; 1H NMR (d6-DMSO, 400
MHz): d 7.00 (d, J ¼ 4 Hz, 3H), 7.04–7.07 (m, 1H), 7.14–7.16 (m,
1H), 7.49 (d, J ¼ 4 Hz, 1H), 7.63 (d, J ¼ 4 Hz, 1H), 7.73 (d, J ¼
8 Hz, 1H), 8.12 (s, 1H); 13C NMR (d6-DMSO, 101 MHz): 127.4,
128.2, 128.9, 129.3, 133.0, 135.7, 136.8, 167.5; GC-MS m/z: 236.
Data were in accordance with those previously reported in the
literature.6
(E)-2,3-Bis(4-methoxyphenyl)acrylic acid (2b). Yellow solid,
227 mg, yield: 80%, mp 206–208 ꢀC; 1H NMR (CDCl3, 400 MHz):
d 3.82 (s, 3H), 3.83 (s, 3H), 6.87–6.95 (m, 5H), 7.40–7.43 (m, 4H);
13C NMR (CDCl3, 101 MHz): 55.4, 55.5, 114.1, 114.2, 128.2,
128.2, 129.9, 130.1, 131.6, 132.2, 159.7, 159.9, 174.9; GC-MS m/z:
284. Data were in accordance with those previously reported in
the literature.5
(E)-2-Ethylpent-2-enoic acid (2j). Yellow oil, 83 mg, yield:
65%; 1H NMR (CDCl3, 400 MHz): d 1.03 (t, J ¼ 8 Hz, 3H), 1.07 (t, J
¼ 8 Hz, 3H), 2.19–2.27 (m, 2H), 2.28–2.34 (m, 2H), 6.88 (t, J ¼
8 Hz, 1H); 13C NMR (CDCl3, 101 MHz): 13.4, 14.0,ꢂ19.7, 22.0,
132.9, 146.5, 173.9; HRMS (ESIꢂ) calcd for C7H11O2 127.0759;
found: 127.0763.
(E)-2-Propylhex-2-enoic acid (2k). Yellow oil, 114 mg, yield:
73%; 1H NMR (CDCl3, 400 MHz): d 0.90–0.97 (m, 6H), 1.40–1.53
(m, 4H), 2.16–2.22 (m, 2H), 2.27 (t, J ¼ 8 Hz, 2H), 6.92 (t, J ¼
8 Hz, 1H); 13C NMR (CDCl3, 101 MHz): 14.0, 14.1, 22.1, 22.5,
28.5, 30.9, 131.8, 145.6, 173.9; GC-MS m/z: 156. Data were in
accordance with those previously reported in the literature.5
(E)-2-Phenylbut-2-enoic acid (2l). White solid, 112 mg, yield:
69%, mp 115–117 ꢀC; 1H NMR (CDCl3, 400 MHz): d 1.77 (d, J ¼
8 Hz, 3H), 7.18–7.20 (m, 2H), 7.24–7.39 (m, 4H); 13C NMR
(CDCl3, 101 MHz): 15.9, 127.7, 128.2, 129.9, 134.3, 134.5, 142.9,
172.7; GC-MS m/z: 162. Data were in accordance with those
previously reported in the literature.6
(E)-2,3-Di-p-tolylacrylic acid (2c). White solid, 194 mg, yield:
77%, mp 184–186 ꢀC; 1H NMR (CDCl3, 400 MHz): d 2.27 (s, 3H),
2.38 (s, 3H), 6.98 (s, 4H), 7.12 (d, J ¼ 8 Hz, 2H), 7.18 (d, J ¼ 8 Hz,
2H), 7.89 (s, 1H); 13C NMR (CDCl3, 101 MHz): 21.5, 129.1, 129.6,
129.7, 130.7, 131.0, 131.8, 132.6, 137.8, 139.9, 142.4, 173.7; GC-
MS m/z: 252. Data were in accordance with those previously
reported in the literature.5
(E)-2,3-Di-m-tolylacrylic acid (2d). White solid, 167 mg, yield:
66%, mp 153–155 ꢀC; 1H NMR (CDCl3, 400 MHz): d 2.19 (s, 3H),
2.33 (s, 3H), 6.82–6.84 (s, 1H), 6.92 (s, 1H), 7.01–7.06 (m, 4H),
7.17 (d, J ¼ 8 Hz, 1H), 7.25 (d, J ¼ 8 Hz, 1H), 7.89 (s, 1H); 13C
NMR (CDCl3, 101 MHz): 21.3, 21.5, 126.8, 127.9, 128.2, 128.7,
128.9, 130.3, 130.4, 131.6, 132.1, 134.4, 135.4, 137.9, 138.4,
142.5, 173.4; GC-MS m/z: 252. Data were in accordance with
those previously reported in the literature.5
(E)-2,3-Di-o-tolylacrylic acid (2e). White solid, 108 mg, yield:
43%, mp 165–167 ꢀC; 1H NMR (CDCl3, 400 MHz): d 2.14 (s, 3H),
2.43 (s, 3H), 6.66 (d, J ¼ 8 Hz, 1H), 6.81 (t, J ¼ 8 Hz, 1H), 7.04 (d, J
¼ 8 Hz, 1H), 7.08–7.25 (m, 5H), 8.21 (s, 1H); 13C NMR (CDCl3,
101 MHz): 19.7, 20.2, 125.6, 126.1, 128.2, 129.0, 129.3, 130.1,
130.3, 130.3, 131.7, 133.5, 134.8, 136.8, 138.2, 140.9, 172.8; GC-
MS m/z: 252. Data were in accordance with those previously
reported in the literature.5
(E)-2-Phenylpent-2-enoic acid (2m). Colorless oil, 106 mg,
yield: 60%; 1H NMR (CDCl3, 400 MHz): d 1.02 (t, J ¼ 8 Hz, 3H),
2.12 (m, 2H), 7.16–7.20 (m, 3H), 7.29–7.38 (m, 3H); 13C NMR
(CDCl3, 101 MHz): 13.3, 23.3, 127.7, 128.1, 129.8, 132.8, 134.8,
149.3, 172.8; GC-MS m/z: 176. Data were in accordance with
those previously reported in the literature.6
(E)-2,3-Bis(4-uorophenyl)acrylic acid (2f). White solid,
161 mg, yield: 62%, mp 171–173 ꢀC; 1H NMR (CDCl3, 400 MHz):
(E)-4,4-Dimethyl-2-phenylpent-2-enoic acid (2n). White
1
ꢀ
d 1.77 (d, J ¼ 8 Hz, 3H), 7.18–7.20 (m, 2H), 7.24–7.39 (m, 4H); 13
C
solid, 104 mg, yield: 51%, mp 138–140 C; H NMR (d6-DMSO,
400 MHz): d 0.92 (s, 9H), 7.12–7.16 (m, 3H), 7.29–7.31 (m, 3H);
13C NMR (d6-DMSO, 101 MHz): 30.3, 34.5, 127.6, 127.7, 130.2,
130.8, 135.7, 155.8, 173.8; GC-MS m/z: 204. Data were in accor-
dance with those previously reported in the literature.6
NMR (CDCl3, 101 MHz): 115.7 (d, JC–F ¼ 21.6 Hz), 116.1 (d, JC–F
¼ 21.4 Hz), 130.3 (d, JC–F ¼ 3.7 Hz), 130.9 (d, JC–F ¼ 3.4 Hz), 131.7
(d, JC–F ¼ 8.0 Hz), 132.9 (d, JC–F ¼ 8.5 Hz), 141.9, 162.7 (d, JC–F
3538 | RSC Adv., 2017, 7, 3534–3539
¼
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
(E)-3-Cyclopropyl-2-phenylacrylic acid (2o). White solid,
145 mg, yield: 55%, mp 93–95 C; H NMR (CDCl3, 400 MHz):
d 0.70–0.74 (m, 2H), 0.89–0.94 (m, 2H), 1.49–1.55 (m, 1H), 6.54
(d, J ¼ 8 Hz, 1H), 7.24–7.39 (m, 5H); 13C NMR (CDCl3, 101 MHz):
9.56, 13.0, 127.6, 128.1, 130.3, 130.5, 135.0, 153.2, 172.5; GC-MS
m/z: 188. Data were in accordance with those previously re-
ported in the literature.10
RSC Advances
Othmer Encyclopedia of Chemical Technology, ed. A. Seidel,
Wiley, Hoboken, 2004, vol. 1, pp. 342–369.
2 M. Cokoja, C. Bruckmeier, B. Rieger, W. A. Herrmann and
F. E. Kuhn, Angew. Chem., Int. Ed., 2011, 50, 8510.
3 M. Beesu and M. Periasamy, J. Organomet. Chem., 2012, 705,
30.
4 For selected reviews, see: (a) P. Braunstein, D. Matt and
D. Nobel, Chem. Rev., 1988, 88, 747; (b) X. Yin and
J. R. Moss, Coord. Chem. Rev., 1999, 181, 27; (c) M. Aresta
and A. Dibenedetto, Dalton Trans., 2007, 2975; (d) A. Correa
1
ꢀ
(E)-4-Hydroxy-2-phenylbut-2-enoic acid (2p). Light-yellow
solid, 107 mg, yield: 60%, mp > 300 ꢀC; 1H NMR (d6-DMSO,
400 MHz): d 3.97 (d, J ¼ 8 Hz, 2H), 4.98 (s, 1H), 6.91–6.94 (m,
1H), 7.15 (d, J ¼ 8 Hz, 2H), 7.31–7.38 (m, 3H), 12.6 (s, 1H); 13C
NMR (d6-DMSO, 101 MHz): 59.0, 128.0, 128.3, 130.0, 133.5,
´
and R. Martın, Angew. Chem., Int. Ed., 2009, 48, 6201; (e)
R. Martın and A. W. Kleij, ChemSusChem, 2011, 4, 1259; (f)
´
ꢂ
135.5, 144.1, 168.2; HRMS (ESIꢂ) calcd for C10H9O3 177.0552;
Y. Tsuji and T. Fujihara, Chem. Commun., 2012, 48, 9956;
(g) B. Yu, Z. F. Diao, C. X. Guo and L. N. He, J. CO2 Util.,
2013, 1, 60; (h) L. Zhang and Z. Hou, Chem. Sci., 2013, 4,
3395; (i) K. Huang, C. Sun and Z. Shi, Chem. Soc. Rev.,
2011, 40, 2435; (j) Q. Liu, L. Wu, R. Jackstell and M. Beller,
Nat. Commun., 2015, 6, 1.
found: 177.0556.
(E)-5-Methoxy-2-phenylpent-2-enoic acid (2q). Yellow oil,
1
85 mg, yield: 41%; H NMR (CDCl3, 400 MHz): d 2.36–2.41 (m,
2H), 3.30 (s, 3H), 3.44 (t, J ¼ 8 Hz, 2H), 7.18–7.24 (m, 3H), 7.31–
7.37 (m, 3H); 13C NMR (CDCl3, 101 MHz): 30.4, 58.7, 71.0, 127.8,
128.2, 129.8, 134.6, 134.8, 144.0, 172.2; HRMS (ESIꢂ) calcd for
5 S. Li, W. Yuan and S. Ma, Angew. Chem., Int. Ed., 2011, 50,
2578.
ꢂ
C
12H13O3 205.0865; found: 205.0868.
6 T. Fujihara, T. Xu, K. Semba, J. Terao and Y. Tsuji, Angew.
Chem., Int. Ed., 2011, 50, 523.
7 (a) I. Mutule and E. Suna, Tetrahedron, 2005, 61, 11168; (b)
L. N. Mander and S. P. Sethi, Tetrahedron Lett., 1983, 24,
5425.
8 (a) H. L. Finkbeiner and G. D. Cooper, J. Org. Chem., 1961, 26,
4779; (b) G. D. Cooper and H. L. Finkbeiner, J. Org. Chem.,
1962, 27, 1493; (c) H. L. Finkbeiner and G. D. Cooper, J.
Org. Chem., 1962, 27, 3395; (d) E. C. Ashby and
R. D. Ainslie, J. Organomet. Chem., 1983, 250, 1; (e) F. Sato,
H. Ishikawa and M. Sato, Tetrahedron Lett., 1981, 22, 85; (f)
F. Sato, J. Organomet. Chem., 1985, 285, 53.
(E)-2-Phenyl-3-trimethylsilylacrylic acid (2r). Light-yellow
solid, 108 mg, yield: 49%; mp 110–112 ꢀC; 1H NMR (CDCl3,
400 MHz): d 0.09 (s, 9H), 7.39–7.42 (m, 2H), 7.52–7.54 (m, 3H);
13C NMR (CDCl3, 101 MHz): 0.73, 127.8, 128.1, 129.5, 137.7,
146.9, 148.5, 172.0; HRMS (ESIꢂ) calcd for C12H15O2Siꢂ
219.0841; found: 219.0837.
(E)-2-(4-Methoxyphenyl)-4,4-dimethylpent-2-enoic acid (2w).
White solid, 108 mg, yield: 46%; mp 176–178 ꢀC; 1H NMR
(CDCl3, 400 MHz): d 0.94 (s, 9H), 3.81 (s, 3H), 6.85–6.87 (d, 2H),
7.05–7.07 (d, 2H), 7.16 (s, 1H); 13C NMR (CDCl3, 101 MHz): 30.4,
34.5, 55.3, 113.2, 131.3, 156.1, 159.0, 174.2. HRMS (ESIꢂ) calcd
ꢂ
for C14H17O3 233.1183; found: 233.1183.
9 For selected reviews, see: (a) X. Yan and C. Xi, Acc. Chem. Res.,
2015, 48, 935; (b) X. Yan and C. Xi, Coord. Chem. Rev., 2016,
308, 22; (c) C. Chen and C. Xi, Chin. Sci. Bull., 2010, 55, 3235;
(d) P. Shao, S. Wang, C. Chen and C. Xi, Chem. Commun.,
2015, 51, 6640; (e) Y. Zhou, C. Chen, X. Yan and C. Xi,
Organometallics, 2014, 33, 844; (f) C. Xi, X. Yan, W. You and
T. Takahashi, Angew. Chem., Int. Ed., 2009, 48, 8120; (g)
C. Chen, C. Xi, Y. Jiang and X. Hong, J. Am. Chem. Soc.,
2005, 127, 8024; (i) P. Shao, S. Wang, C. Chen and C. Xi,
Org. Lett., 2016, 18, 2050; (j) S. Wang, P. Shao, C. Chen and
C. Xi, Org. Lett., 2015, 17, 5112.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21472106 and 21272132) and the
National Key Basic Research Program of China (973 program)
(2012CB933402). We also thank Dr Chao Chen in Tsinghua
University for his kind discussion.
References
1 (a) B. E. Maryanoff and A. B. Reitz, Chem. Rev., 1989, 89, 863;
(b) S. E. Kelly, in Comprehensive Organic Synthesis, Pergamon,
Oxford, 1991, vol. 1, pp. 729–817; (c) W. Bauer Jr, in Kirk-
10 X. Wang, M. Nakajima and R. Martin, J. Am. Chem. Soc.,
2015, 137, 8924.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 3534–3539 | 3539