Copper(I)-Catalyzed Desulfinative Carboxylation of Sodium Sulfinates using Carbon Dioxide

Article abstract of DOI:10.1002/adsc.201500101

A copper(I)-catalyzed desulfinative carboxylation of sodium sulfinates using carbon dioxide has been developed. This reaction showed wide functional group tolerance. A series of sodium aryl- and alkenylsulfinates could be converted into the corresponding carboxylic acids in good to excellent yields. Additionally, the reaction mechanism was studied by in situ NMR analysis and isotopic labeling experiments.

Full text of DOI:10.1002/adsc.201500101

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DOI: 10.1002/adsc.201500101
Copper(I)-Catalyzed Desulfinative Carboxylation of Sodium
Sulfinates using Carbon Dioxide
Song Sun,a Jin-Tao Yu,a Yan Jiang,a and Jiang Chenga,b,*
a
School of Petrochemical Engineering, Jiangsu Key Laboratory of Advanced Catalytic Materials & Technology, Jiangsu
Province Key Laboratory of Fine Petrochemical Engineering, Changzhou University, Changzhou 213164, People’s
Republic of China
E-mail: jiangcheng@cczu.edu.cn
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, People’s Republic of China
b
Received: February 2, 2015; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201500101.
Abstract: A copper(I)-catalyzed desulfinative car-
boxylation of sodium sulfinates using carbon diox-
ide has been developed. This reaction showed wide
functional group tolerance. A series of sodium aryl-
and alkenylsulfinates could be converted into the
corresponding carboxylic acids in good to excellent
yields. Additionally, the reaction mechanism was
studied by in situ NMR analysis and isotopic label-
ing experiments.
Scheme 1. The employment of CO2 in carboxylation reac-
tions.
Keywords: carbon dioxide fixation; carboxylation;
copper; desulfination; sodium sulfinates
sensitive organometallic reagents or excess alkylzinc
compounds as reducing reagent remains a drawback
to be overcome.
On the other hand, sodium sulfinates are stable and
Recently, increasing attention has been paid in the accessible from sulfonyl chlorides.[8] As a result, vari-
carboxylation reaction of carbon nucleophiles with ous transition metal-catalyzed desulfinative coupling
CO2, where CO2 serves as an important one-carbon reactions such as desulfinative Heck-type reactions,[9]
source.[1] However, CO2 is an inert electrophile. Only addition reactions to double or triple bonds,[10] as well
organometallic reagents with high nucleophilicity as homo-[11] and cross-coupling[12] reactions have been
such as Grignard or organolithium reagents could well developed. Meanwhile, the desulfinative coupling
react with CO2 directly. But these strong nucleophiles reactions of sodium arylsulfinates with different elec-
suffer from poor functional group tolerance, thus lim- trophiles have also been established.[13] These results
iting their application scope. To circumvent it, the encouraged us to investigate the nucleophilic reac-
transition metal-catalyzed carboxylation of less reac- tions of sodium sulfinates with the inert electrophile
tive nucleophiles such as organozinc,[2] organoboron,[3] CO2 (Scheme 1, eq 3). Herein, we wish to report
and organotin[4] compounds have been well-docu- these results.
mented with good functional group tolerance
We initially explored the desulfination/carboxyla-
(Scheme 1, eq 1). Alternatively, arylhalides and al- tion of sodium benzenesulfinate (1a) as the model re-
kenes could act as ideal pre-nucleophiles for the fixa- action catalyzed by copper salts under 1 atm of CO2.
tion of CO2.[5] For instance, Martin and co-workers re- Control experiments in the absence of either the
ported Ni- or Pd-catalyzed carboxylation of aryl- and copper source, ligand, base or CO2 confirmed that
alkylhalides using CO2 in the presence of Zn or dia- these species played critical roles in such transforma-
lkylzinc as reducing agent (Scheme 1, eq 2).[6] Rovis tion (Table 1, entries 1–5). Meanwhile, the use of
developed a nickel-catalyzed direct carboxylation of DMSO as solvent gave better results than that of
À
styrene C H bond using CO2, where excess alkylzinc CH3CN, DMF or dioxane (Table 1, entries 6–8).
is essential for this transformation (Scheme 1, eq 2).[7] Other copper sources such as CuCl2, CuBr, CuI were
Nevertheless, the use of a stoichiometric amount of also efficient for this reaction, and CuI was the best
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Song Sun et al.
Table 1. Selected results in the optimization of reaction con-
ditions.[a]
Entry Catalyst Ligand Base
Solvent Yield [%][b]
1
2
–
phen
phen
–
KOtBu DMSO
DMSO
KOtBu DMSO 30
KOtBu DMSO
KOtBu DMSO 64
KOtBu CH3CN 32
KOtBu dioxane trace
0
0
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl2
CuBr
CuI
CuI
CuI
CuI
CuI
CuI
CuI
–
3
4[c]
5
phen
phen
phen
phen
phen
phen
phen
phen
phen
phen
bipy
py
0
6
7
8
9
10
11
12
13
14
15
16[f]
17[g]
KOtBu DMF
KOtBu DMSO 73
53
KOtBu DMSO 75
KOtBu DMSO 81 60[d] 71[e]
LiOtBu DMSO 17
K2CO3
DMSO 74
KOtBu DMSO 45
KOtBu DMSO 24
KOtBu DMSO 58
phen
phen
KOtBu DMSO
<10
[a]
Reaction conditions: 1a (0.2 mmol), catalyst (10 mol%),
ligand (30 mol%) (phen=o-phenanthroline, bipy=2,2’-
bipyridine, py=pyridine), base (0.6 mmol), solvent
(2.5 mL), at 1408C under 1 atm of CO2 for 12 h, in
Figure 1. Scope of sodium sulfinates.[a]
a sealed Schlenk tube, unless otherwise noted.
Isolated yield.
under N2.
3 h.
7 h.
[b]
[c]
[d]
[e]
[f]
ed the desired carboxylation products in good to ex-
cellent yields. A variety of reactive functional groups,
such as chloro, bromo, acetyl and cyano groups, which
are potentially suitable for further functionalization,
survived in these reactions. Additionally, sodium p-cy-
anoarenesulfinate showed relatively low activity. For-
tunately, 88% yield was obtained when the catalyst
under N2 + CO2.
under O2 + CO2.
[g]
choice (Table 1, entries 5, 9–11). Other bases such as loading was increased to 30 mol% (2m). It was note-
LiOtBu and K2CO3 were inferior to KOtBu (Table 1, worthy that the steric effect had profound effect on
entries 12–13). Among the ligands tested, o-phenan- the reaction. For example, sodium 2,4,6-trimethylare-
throline was the most effective one (Table 1, en- nesulfinate produced the corresponding carboxylic
tries 14–15). The reaction could proceed in an atmos- acid 2e in 82% yield. However, the more bulky
phere of N2 and CO2, albeit in the slightly decreased sodium 2,4,6-triisopropylarenesulfinate resulted in no
yield (Table 1, entry 16). However, the yield sharply product at all (2g). Further experiments also demon-
decreased in an atmosphere of O2 and CO2, which strated that sodium naphthalenesulfinates were also
was at least partly due to the oxidation of the active good substrates for this carboxylation reaction, as
catalyst species to an inactive analogue (Table 1, shown for the successful formation of 2n and 2o in
entry 17).[14] After considerable experimentation, we 65% and 70% yields under the present reaction con-
found that the combination of CuI (10 mol%), o-phe- ditions, respectively.
nanthroline (30 mol%) and KOtBu (3 equiv), deliv-
ered the desired carboxylation product in 81% yield extended to sodium alkenylsulfinates. Under the opti-
(Table 1, entry 11). mal conditions, sodium 2-phenylethenesulfinate could
To our delight, the substrate scopes could also be
With the optimized reaction conditions in hand, we be carboxylated by CO2 to generate cinnamic acid 2p
then explored the scope and generality of this trans- in moderate yield.
formation in the presence of a variety of functional
In order to confirm whether CO2 participated in
groups on the sodium arylsulfinates. As shown in this reaction, the desulfinative carboxylation of 1a
Figure 1, the reactions of a wide range of sodium aryl- with 13CO2 was carried out (Scheme 2). To our de-
sulfinates with CO2 proceeded smoothly and generat- light, the reaction ran smoothly under the standard
2
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Copper(I)-Catalyzed Desulfinative Carboxylation
mation). After the introduction of 13CO2 into the
NMR tube, the color of the reaction mixture gradual-
ly changed from dark green to dark red. Meanwhile,
a new broad singlet appeared at 170 ppm which could
be assigned to the copper benzoate complex and was
in agreement with the result reported by Baba
(Figure 2, (3)).[15] After the addition of five drops of
1m HCl into the NMR tube, the color changed to
light green immediately. The broad singlet at
Scheme 2. The 13C-labelling study.
condition to generate the desired benzoic acid 2a-13C 170.0 ppm disappeared, and a singlet at 168.6 ppm ap-
with 13C-labelled carboxyl group in about 75% yield, peared, which could be assigned to the free benzoic
which was confirmed by EI-MS (m/z [M+]: 123, [M+] acid generated from the hydrolysis of the copper ben-
- OH:=106; [M+] - 13COOH:=77) and the 13C NMR zoate complex (Figure 2, (4)). These results indicated
(the strong signal at 172.0 ppm in CDCl3) (see Figures that the copper benzoate species were the intermedi-
S1 and S2 in the Supporting Information).
ates during this transformation.
To gain more insights into the mechanism of this
On the basis of these experimental results and the
reaction, a 13C NMR monitoring reaction of 1a with similar work reported previously,[9,10,16] a plausible
13CO2 was carried out (Figure 2). Firstly, a slight mechanism is outlined in Scheme 3. Firstly, coordina-
change in the 13C NMR spectrum to that of 1a was tion of the sodium sulfinates to copper(I) provides in-
observed in the NMR scale reaction of 1a with CuI termediate A, which is similar with the Pd-catalyzed
(1 equiv), o-phenanthroline (30 mol%), KOtBu desulfinative reactions.[9,10] Subsequently, desulfinative
(3 equiv) at 1408C in [D6]DMSO under N2 after 12 h carboxylation of intermediate A assisted by carbon
(Figure 2, (1) vs (2)). For instance, the resonance aris- dioxide affords copper benzoate species B or C, along
ing from the sulfinate carbon shifts from 158.6 ppm to with the extrusion of SO2.[17] However, the possibility
159.5 ppm after the reagents are added. The chemical of the sequential desulfination followed by carboxyla-
shifts of other aromatic carbons also look different. tion could not be thoroughly ruled out, owing to the
Based on these results, copper sulfinate would have low sensitivity of 13C NMR. Then, metathesis of the
been generated in this step which is similar with that copper benzoate species by KOtBu gives the potassi-
of Pd-catalyzed desulfinative reactions.[9–12] (For de- um carboxylate D and regenerates the copper(I) cata-
tails, see Figures S3 and S7 in the Supporting Infor- lyst, which is comparable with the work reported by
Figure 2. Combined 13C NMR spectra of the successive carboxylation and hydrolysis reaction of complex 1a (75 MHz,
[D6]DMSO).
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Song Sun et al.
Technology (BM2012110), State Key Laboratory of Coordi-
nation Chemistry of Nanjing University and the Priority Aca-
demic Program Development of Jiangsu Higher Education
Institutions (PAPD) for financial support.
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In conclusion, a copper(I)-catalyzed desulfinative
carboxylation of sodium sulfinates using CO2 has
been developed. This reaction showed wide generality
with good functional group tolerance. A series of
sodium aryl- and alkenylsulfinates could be converted
to the corresponding carboxylic acids in good to ex-
cellent yields. Thus, this method represents a practical
procedure for the fixation of CO2.
Experimental Section
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sodium sulfinates with CO2
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The sodium sulfinate (0.2 mmol), CuI (0.02 mmol), o-phe-
nanthroline (0.06 mmol), KOtBu (0.6 mmol) and DMSO
(2.5 mL) were added into a 10 mL Schlenk tube equipped
with a stir bar under air. The reaction vessel was evacuated
to about À0.1 MPa (last for 30 seconds per time) and back-
filled with CO2 (1 atm); this sequence was repeated three
times. The reaction mixture was stirred in the sealed
Schlenk tube at 1408C for about 12 h. After the reaction
mixture had been cooled to room temperature, 1m HCl
(1 mL) was added to terminated the reaction and convert
the carboxylate into a carboxylic acid. The reaction mixture
was diluted with EtOAc and washed with water. The organic
layer was dried over anhydrous MgSO4 and concentrated in
vacuum. The residue was purified by flash column chroma-
tography on silica gel with petroleum ether/ethyl acetate as
eluent to give the desired product.
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We thank the National Natural Science Foundation of China
(no. 21272028, 21202013), “Innovation & Entrepreneurship
Talents” Introduction Plan of Jiangsu Province, the Natural
Science Foundation of Zhejiang Province (no. R4110294),
Jiangsu Key Laboratory of Advanced Catalytic Materials &
4
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6 Copper(I)-Catalyzed Desulfinative Carboxylation of Sodium
Sulfinates using Carbon Dioxide
Adv. Synth. Catal. 2015, 357, 1 – 6
Song Sun, Jin-Tao Yu, Yan Jiang, Jiang Cheng*
6
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