Alkoxide-functionalized imidazolium betaines for CO2 activation and catalytic transformation

Article abstract of DOI:10.1039/c3gc42346h

Alkoxide-functionalized imidazolium betaines (AFIBs), including an alkoxide anion and an imidazolium cation, were synthesized by treating potassium tert-butoxide with 1-(2-hydroxyethyl)-2,3-disubstituted imidazolium bromide. The novel betaines were able to quickly capture CO₂, affording carboxylate zwitterions (AFIB-CO₂ adducts). In the presence of adventitious water, the transformation of the AFIB-CO₂ adducts into the corresponding bicarbonate salts was observed by ¹H and ¹³C NMR spectroscopy. The structures of the AFIB bicarbonate salts were solved using single crystal X-ray crystallography. Furthermore, the dithiocarboxylate zwitterions (AFIB-CS₂ adducts), which are more stable to moisture in comparison with their CO₂ adducts, were prepared by reacting CS₂ with the corresponding betaines. X-Ray single crystal analysis revealed the bent geometry of the binding CS₂ in the dithiocarboxylate zwitterions with a S-C-S angle of 126.6-126.9°, which indirectly confirms the structures of the AFIB-CO₂ adducts in hand. These AFIB-CO₂ adducts were found to function as organocatalysts for the coupling reaction of propargylic alcohols with CO ₂ for selectively producing valuable cyclic carbonates under mild and solvent-free reaction conditions. the Partner Organisations 2014.

Full text of DOI:10.1039/c3gc42346h

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Alkoxide-functionalized imidazolium betaines for
CO2 activation and catalytic transformation†
Cite this: Green Chem., 2014, 16,
2266
Yan-Bo Wang, Dong-Sheng Sun, Hui Zhou, Wen-Zhen Zhang and Xiao-Bing Lu*
Alkoxide-functionalized imidazolium betaines (AFIBs), including an alkoxide anion and an imidazolium
cation, were synthesized by treating potassium tert-butoxide with 1-(2-hydroxyethyl)-2,3-disubstituted
imidazolium bromide. The novel betaines were able to quickly capture CO2, affording carboxylate zwitter-
ions (AFIB-CO2 adducts). In the presence of adventitious water, the transformation of the AFIB-CO2
adducts into the corresponding bicarbonate salts was observed by 1H and 13C NMR spectroscopy. The
structures of the AFIB bicarbonate salts were solved using single crystal X-ray crystallography. Further-
more, the dithiocarboxylate zwitterions (AFIB-CS2 adducts), which are more stable to moisture in com-
parison with their CO2 adducts, were prepared by reacting CS2 with the corresponding betaines. X-Ray
single crystal analysis revealed the bent geometry of the binding CS2 in the dithiocarboxylate zwitterions
with a S–C–S angle of 126.6–126.9°, which indirectly confirms the structures of the AFIB-CO2 adducts in
hand. These AFIB-CO2 adducts were found to function as organocatalysts for the coupling reaction of
propargylic alcohols with CO2 for selectively producing valuable cyclic carbonates under mild and
solvent-free reaction conditions.
Received 15th November 2013,
Accepted 20th December 2013
DOI: 10.1039/c3gc42346h
www.rsc.org/greenchem
More recently, a new concept of frustrated Lewis pair (FLP)
introduced by Stephan et al. represents a fundamental and
Introduction
The use of CO2 as a C1 feedstock for preparing useful fine novel strategy to straightforwardly sequester CO2.6 Although
chemicals has became a flourishing area of research in recent considerable progress on CO2 activation by carbon or nitrogen
decades.1 However, the biggest obstacle for transforming CO2 atom as a nucleophilic site has been achieved, oxygen atoms
into value-added chemicals lies in its remarkable thermodynamic as a nucleophilic position is poorly explored.7
and kinetic stability, since CO2 is at the highest oxidation
It is generally well known that a betaine shown in
state of carbon. In view of the discrepancy of electronegativity Scheme 1, named as N,N,N-trimethylglycine, consists of an
between the carbon and oxygen atoms, CO2 prevalently quaternary ammonium positive ion center bearing no hydro-
behaves as an electrophile, and thus is easily activated by gen atoms and a carboxylate anionic moiety that is not adja-
strong nucleophiles or low-valent metal reagents. Generally, cent to the cationic site. On the whole, betaine could be
CO2 as a η1 or η2 ligand can be coordinated with various low- regarded as a neutral compound. In view of the special struc-
valent metal complexes, which has been demonstrated by ture, much effort for establishing a reasonable chemical cir-
several research groups.2 On the other hand, a variety of metal- cumstance between the cationic and anionic centres was
free activation systems based on carbon and nitrogen atoms as conducted for achieving Lewis acid–base synergistic effects.
nucleophiles have been reported. The former mainly refers to Ooi and co-workers have demonstrated the great potential of
the study of N-heterocyclic carbene (NHC)3 or N-heterocyclic betaines as catalysts for asymmetric reactions.8 The synthesis
olefin (NHO).4 The latter concerns amidine or guanidine com- of cyclic carbonates through the coupling reaction of epoxides
pounds containing nitrogen heterocycles, which were with CO2 using betaines as catalyst has been described by
described to react with CO2, expectantly affording zwitterionic
adducts.5 However, in most cases bicarbonate salts were unex-
pectedly produced owing to the presence of adventitious water.
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian
116024, China. E-mail: lxb-1999@163.com
†Electronic supplementary information (ESI) available: Crystallography and
copies of NMR. CCDC 971543–971545. For ESI and crystallographic data in CIF
Scheme 1 The structures of betaine and alkoxide-functionalized imi-
or other electronic format see DOI: 10.1039/c3gc42346h
dazolium betaine (AFIB).
2266 | Green Chem., 2014, 16, 2266–2272
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Sakai et al.7b Notably, the Arnold group successfully syn-
thesized various copper, potassium and silver complexes
bearing alkoxide-functionalized N-heterocyclic carbenes as
ligands.9 Furthermore, Rossi and colleagues have shown that
the reaction of commercially available tetrabutylammonium
methoxide or ethoxide as intermolecular ion pairs with CO2
yields the corresponding methyl and ethyl tetrabutyl-
ammonium carbonates.7a Based on the above studies, great
interest has been aroused to explore alkoxide-functionalized
imidazolium betaines for CO2 activation and further trans-
formations, since the alkoxide anion has enough potential
nucleophilicity for CO2 sequestration. Herein, we describe for
the first time, the syntheses of various CO2 adducts and CS2
adducts of alkoxide-functionalized imidazolium betaines
(AFIBs) and further explore these AFIB-CO2 adducts as
effective organocatalysts for CO2 transformations to valuable
chemicals.
Scheme 3 The transformation of 2a–2d to 3a–3d in the presence of
H2O.
Results and discussion
To avoid the interference of reactive hydrogen atoms on the
deprotonation step in preparing AFIB, compounds 1a–1d
(Scheme 2) with methyl or iso-propyl substituted at the 2-posi-
tion of the imidazolium ring were used for synthesizing AFIBs
by reaction with potassium tert-butoxide under anhydrous con-
ditions. The resultant AFIB solution was covered with an
atmosphere of CO2, resulting in immediate precipitation of a
white solid 2. Obvious differences in the chemical shifts were
Fig. 1 Molecular structure of 3c with thermal ellipsoids drawn at 30%
probability. Selected bond lengths (Å) and angles (°) in complexes 3c as
follow: O(1)–C(2) 1.415(6), O(2)–C(1) 1.326(4), O(3)–C(1) 1.255(4),
O(4)–C(1) 1.246(4), O(2)–C(1)–O(3) 117.9(3), O(2)–C(1)–O(4) 116.9(3),
O(3)–C(1)–O(4) 125.2(3).
1
observed in the H and 13C NMR spectra of compounds 1 and
example, when trace water was introduced to a DMSO-d6 solu-
1
tion of 2c, obvious changes in the H and 13C NMR chemical
2 (see ESI, Fig. S1†). In comparison with the 2-methylene adja-
cent to alcoholic hydroxyl group of compounds 1a–1d, the
chemical shift of methylene at the same position in 2a–2d
clearly moves downfield. Meanwhile, the 13C NMR spectra of
compounds 2a–2d show strong carboxylate carbon signals at
153.3–153.4 ppm. Dependent on the substituent groups in the
imidazolium ring, the CvO stretching frequencies of the car-
boxylates in the FTIR spectra of 2a–2d change from 1671 cm−1
to 1694 cm−1, similar to that of methyl and ethyl tetrabutyl-
ammonium carbonates (1670 cm−1).7a
Although much effort was paid to cultivating the single
crystals of the AFIB-CO2 adducts 2a–2d in hand, we failed to
isolate them, perhaps due to their sensitivities towards water.
Therefore, the stability of all the AFIB-CO2 adducts towards
water was further studied (Scheme 3). Take compound 2c for
shifts were observed within minutes (see ESI, Fig. S2†). A new
signal appears at 3.71 ppm, which is attributable to the chemi-
cal shift of the methene adjacent to the alcoholic hydroxyl
group in the 1H NMR spectra, the value of which was nearly
the same as the corresponding 2-methene in compound 1c.
Meanwhile, a new signal at 158.7 ppm in the 13C NMR spectra
was ascribed to the CvO of the hydrogen carbonate salt.10
Compound 2c was almost transformed to hydrogen carbonate
salt 3c overnight. The crystal structure of compound 3c is
described in Fig. 1. The detail spectra difference between
2a–2b, 2d and 3a–3b, 3d are shown in the ESI, Fig. S3.†
It is well known that CS2 has a higher electroaffinity than
CO2, while their structures are nearly same in both the ground
and activation states. Therefore, we reasonably assumed that
the structure of the AFIB-CS2 adducts should reflect that of the
corresponding AFIB-CO2 adducts. Various AFIB-CS2 adducts
4a–4d were synthesized by the reaction of CS2 with compounds
1a–1d pretreated by KOtBu in THF solution at ambient temp-
erature (Scheme 4). They are more stable towards moisture
than the corresponding AFIB-CO2 adducts. Moreover, the
structures of compounds 4b and 4c were clearly characterized
by X-ray crystallography (Fig. 2). The bent geometry of the
binding CS2 was revealed in the dithiocarboxylate zwitterions
with a S–C–S angle of 126.6–126.9°. These results indirectly
confirmed the structures of the AFIB-CO2 adducts in hand.
Scheme 2 The synthesis of the AFIB-CO2 adducts.
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Table 1 Optimization of the reaction conditions for the carboxylative
a
cyclization of 2-methylbut-3-yn-2-ol (5a) with CO2
Scheme 4 The synthesis of the AFIB-CS2 adducts.
Entry
Cat
T (°C)
P (MPa)
Yieldb (%)
1
2
3
4c
5
6
7
8
2a
2a
2a
2a
2a
2b
2c
2d
80
60
40
60
60
60
60
60
2
2
2
2
0.5
2
2
87
90
34
76
64
82
92
97
2
a Reaction conditions: substrate 5a (3 mmol), 5 h. b Yield determined
by 1H-NMR spectroscopy, using durene as an internal standard.
c 1 mol% 2a.
Fig. 2 Molecular structures of 4b and 4c with thermal ellipsoids drawn
at 30% probability. Hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (°) in complexes 4b and 4c as
follow: 4b S(1)–C(1) 1.687 (2), S(2)–C(1) 1.676(2), O(1)–C(1) 1.363(2), O(1)–
C(2) 1.442(2), S(2)–C(1)–S(1) 126.6(1). 4c S(1)–C(1) 1.665(3), S(2)–C(1)
1.692(3), O(1)–C(1) 1.372(3), O(1)–C(2) 1.444(3), S(1)–C(1)–S(2) 126.9(2).
Table 2 Carboxylative cyclization of various propargylic alcohols with
CO2 to give α-alkylidene cyclic carbonates by 2da
The successful synthesis of these AFIB-CO2 adducts may
afford the opportunity to examine the catalytic performance
referred to in the transformations of CO2 into desirable, high
value-added chemicals. We note that one of the most promis-
ing routes that effectively utilizes CO2 is the synthesis of alkyli-
dene cyclic carbonates through the coupling reaction of
propargylic alcohol with CO2. Although this coupling reaction
can be smoothly carried out by the aid of metal catalysts of
Ag,11 Cu,12 Pd,13 Co14 and Ru,15 the use of organocatalysts for
this transformation is very limited. Only the use of NHC,16
NHO,4 tertiary phosphines17 and guanidine18 as catalysts for
the selective synthesis of various alkylidene cyclic carbonates
have been reported. As a result, there is great interest in these
AFIB-CO2 adducts as catalysts for the coupling reaction of pro-
pargylic alcohols with CO2. Initially, we attempted the coup-
ling reaction of 2-methylbut-3-yn-2-ol (5a) with CO2 using
2 mol% 2a under solvent-free reaction conditions, giving the
desired product 6a in 87% yield at 80 °C within 5 h (Table 1,
entry 1). Encouraged by the above result, further optimization
Entry
Substrate
R1
R2
R3
Yieldb
1
2
3
5b
5c
5d
5e
5e
5f
5g
5h
5i
H
H
H
H
H
H
H
H
Ph
Me
Me
Et
Ph
–(CH2)5–
–(CH2)4–
–(CH2)4–
94
88
75
8
87
94
92
35
30
4
5c
6c
7c
8c
9c
Me
Et
Me
Me
Hex
Et
iPr
Me
a Reaction conditions: substrate 5 (3 mmol), catalyst 2d (2 mol%),
60 °C, 2 MPa CO2, 5 h. b Yield determined by 1H-NMR spectroscopy,
using durene as an internal standard. c The reaction was carried out
under an enhanced catalyst loading of 5 mol% 2d for 24 h.
of the reaction conditions showed that the reaction tempera- substituted (Table 1, entries 2 and 6). It was found that the use
ture has a profound impact on the efficiency of this reaction of 2d provided the best yield of 97%, possibly due to its good
and a better yield of 90% was obtained at 60 °C (Table 1, entry solubility (Table 1, entries 8).19
2). However, a lower catalyst loading or decrease in CO2
With the optimized conditions established, we further
pressure led to a decreased yield (Table 1, entries 4 and 5). It is investigated the reaction scope using a variety of propargylic
interesting that the structures of the AFIB-CO2 adducts have an alcohols as the substrates, and the results are outlined in
important influence on the catalytic activity. The results from Table 2. The coupling reaction of most propargyl alcohols with
Table 1 exhibited that the N-isopropyl-substituted AFIB-CO2 CO2 proceeded smoothly to give the corresponding α-alkyli-
adduct showed a slightly higher catalytic activity than the dene cyclic carbonates in good to excellent yields. The reaction
N-methyl-substituted AFIB-CO2 adduct (Table 1, entries 2 activity depended on the substitute groups of propargylic alco-
and 7). Surprisingly, the 2-isopropyl-substituted AFIB-CO2 hols. Surprisingly, the 1-ethynyl cyclopentanol 5e gave inferior
adduct presented a lower catalytic activity than the 2-methyl- results relative to 1-ethynyl cyclohexanol 5d (Table 2, entry 3
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Experimental
Unless otherwise statement, all manipulations were performed
using standard Schlenk techniques under a dry nitrogen
atmosphere. NMR spectra were recorded on a Bruker Avance II
400 M type (1H NMR, 400 MHz; 13C NMR, 100 MHz) spectro-
meter. High resolution mass spectra (HRMS) were recorded on
a Q-TOF mass spectrometry (Micromass, Wythenshawe, UK)
equipped with a Z-spray ionization source. Infrared spectra
(IR) was measured using a Nicolet NEXUS FT-IR spectro-
photometer. Carbon dioxide (99.999%) was used as received
without further purification. Tetrahydrofuran, diethyl ether
and hexane were distilled from sodium/benzophenone under a
N2 atmosphere. CS2 and acetonitrile were distilled from phos-
phorus pentoxide under a N2 atmosphere. DMSO-d6 was dis-
tilled from calcium hydride under reduced pressure and stored
over 4 Å molecular sieves. Commercially available terminal
propargylic alcohols were used without further purification.
Internal propargylic alcohol (5i) was prepared by the Sono-
gashira coupling reaction of the corresponding 2-methyl-3-butyn-
2-ol with iodobenzene according to the literature method with
some modifications.20
Scheme 5 Plausible mechanism for the AFIB-CO2 adduct catalyzed
carboxylative cyclization of propargylic alcohols with CO2.
vs. 4). Sterically hindered substrates 5f–5h could yield the
desired products at a higher catalyst loading and prolonged
reaction time. However, in the case of internal propargylic
alcohol 5i as substrate (Table 2, entry 9), α-alkylidene cyclic
carbonate 6i was obtained in low yield. These results reflected
that the present catalyst system seemed to be more favorable
for terminal propargylic alcohols than internal propargylic
alcohols.
Preparation of 1-(2-hydroxyethyl)-2,3-disubstituted-
imidazolium bromine (1a–1d)
The synthesis of 1a. To a three-necked round-bottomed
flask containing 1,2-dimethyl imidazole (3.84 g, 40 mmol) was
added acetonitrile (20 mL) and 2-bromoethanol (7.50 g,
60 mmol). The mixture was heated to 80 °C under N2 and
stirred for 24 h and then cooled to room temperature. After
the solvent was removed under the reduced pressure, the
residue was washed with THF (3 × 20 mL). The product 1a was
On the basis of the above results and previous work,4,16,17
a
possible mechanism was proposed, which is shown in
Scheme 5. CO2 was firstly activated by AFIB to form an
AFIB-CO2 adduct in which the carboxylate anion moiety could
firstly attack the triple bond of propargylic alcohol to form
intermediate A. Then the new intermediate B was produced by
hydrogen migration from the hydroxyl group of the alcohol.
Finally, the alkoxide anion of intermediate B attacked the
carbonyl carbon to release the desired product and AFIB,
which rapidly captures free CO2 to regenerate the AFIB-CO2
adduct and finish the catalytic cycle.
1
isolated as a white solid in 88% yield. 1a: H NMR (400 MHz,
DMSO-d6): δ = 7.65 (d, 1H, J = 2.4 Hz, NCH), 7.63 (d, 1H, J =
2.4 Hz, NCH), 5.09 (t, 1H, J = 1.2 Hz, CH2OH), 4.20 (t, 2H, J =
5.2 Hz, CH2CH2), 3.78 (s, 3H, NCH3), 3.68 (q, 2H, CH2CH2),
2.60 (s, 3H, CCH3). 13C NMR (100 MHz, DMSO-d6): δ = 145.3,
122.6, 121.7, 60.1, 50.7, 35.3, 10.5. HRMS (ESI, m/z) calcd for
C7H13BrN2 [M − Br]+:141.1028, found: 141.1026.
Complex 1b was synthesized in a similar manner to 1a,
however, starting from 1-methyl-2-isopropyl imidazole (2.48 g,
20 mmol)21 to give complex 1b as a white solid in 71% yield.
1
1b: H NMR (400 MHz, DMSO-d6): δ = 7.69 (d, 1H, J = 2.4 Hz,
CHvCH), 7.67 (d, 1H, J = 2.4 Hz, CHvCH), 5.14 (t, 1H, J =
2.4 Hz, CH2OH), 4.27 (t, 2H, J = 5.2 Hz, CH2CH2), 3.89 (s, 3H,
NCH3), 3.68 (m, 3H, CH2CH2 and CH(CH3)2), 1.36 (d, 3H, J =
Conclusions
In summary, alkoxide-functionalized imidazolium betaines 7.2 Hz, CH(CH3)2). 13C NMR (100 MHz, DMSO-d6): δ = 149.4,
(AFIBs) bearing an alkoxide anion and an imidazolium cation 123.4, 121.5, 59.6, 50.4, 35.9, 24.1, 18.4. HRMS (ESI, m/z) calcd
were found to have strong tendencies for CO2 and CS2 seques- for C9H17BrN2 [M − Br]+: 169.1341, found: 169.1343.
tration, affording
a
CO2 or CS2 adducts (AFIB-CO2 or
Complex 1c was synthesized in a similar manner to 1a,
AFIB-CS2), in which the binding CS2 exhibits a bent geometry however, starting from 1-isopropyl-2-methyl imidazole (2.48 g,
with an S–C–S angle of 126.6–126.9°. AFIB-CO2 adducts as 20 mmol)4 to give complex 1c as a white solid in 77% yield. 1c:
organocatalysts could effectively catalyze the coupling reac- 1H NMR (400 MHz, DMSO-d6): δ = 7.87 (d, 1H, J = 1.6 Hz,
tions of propargylic alcohols with CO2 under mild and solvent- CHvCH), 7.71 (d, 1H, J = 1.6 Hz, CHvCH), 5.11 (s, 1H,
free reaction conditions, selectively affording functionalized CH2OH), 4.69 (m, 1H, CH(CH3)2), 4.20 (t, 2H, J = 4.8 Hz,
cyclic carbonates.
CH2CH2), 3.71 (m, 2H, CH2CH2), 2.66 (s, 3H, CCH3), 1.43 (d,
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3H, J = 6.4 Hz, CH(CH3)2). 13C NMR (100 MHz, DMSO-d6): δ = 1H, J = 5.2 Hz, CH2CH2), 3.97 (t, 2H, J = 5.2 Hz, CH2CH2), 3.67
144.2, 122.8, 118.3, 60.1, 50.8, 50.6, 22.6, 10.4. HRMS (m, 1H, CH(CH3)2), 1.28 (d, 6H, J = 7.2 Hz CH(CH3)2). 13C NMR
(ESI, m/z) calcd for C9H17BrN2 [M − Br]+: 169.1337, found: (100 MHz, DMSO-d6): δ = 153.4, 149.7, 135.2, 128.9, 128.2,
169.1341.
127.0, 122.6, 122.5, 61.3, 51.0, 49.0, 24.3, 18.8. IR (Film)
Compound 1d was synthesized in a similar manner to 1a, 1694 cm−1 (vs).
however, starting from 1-benzyl-2-isopropyl imidazole (4.00 g,
The synthesis of 4a–4d. 1-(2-Hydroxyethyl)-2,3-disubstituted
20 mmol) according to the reported synthesis method of 1-iso- imidazolium bromine (2 mmol) and KOtBu (2.4 mmol, 0.27 g)
propyl-2-methyl imidazole with modification21 to give 1d as a were added to a solution of THF (15 mL) and the mixture was
white solid in 63% yield. 1d: 1H NMR (400 MHz, DMSO-d6): δ = stirred at ambient temperature for 2 h. During the reaction
7.80 (d, 1H, J = 1.6 Hz, CHvCH), 7.76 (d, 1H, J = 1.6 Hz, course, the solution colour gradually changed to yellow. After
CHvCH), 7.24–7.43 (m, 5H, Ph) 5.58 (s, 2H, CH2Ph), 5.21 filtration to remove the salt, CS2 (6 mmol, 0.46 g) was added to
(t, 2H, J = 6.4 Hz, OH), 4.30 (m, 2H, J = 5.2 Hz, CH2CH2), the yellow filtrate. A precipitate was formed immediately and
3.69–3.78 (m, 3H, CH2CH2 and CH(CH3)2), 1.26 (d, 6H, J = 7.2 was collected via filtration. The pure 4a and 4b were obtained
Hz, CH(CH3)2). 13C NMR (100 MHz, DMSO-d6): δ = 150.4, by washing the yellow precipitate with cold methanol
135.6, 129.4, 128.8, 127.6, 123.0, 122.9, 59.9, 51.5, 51.1, 24.8, (2 × 10 mL). Washing the yellow precipitate with cold aceto-
19.4. HRMS (ESI, m/z) calcd For C15H21BrN2 [M − Br]+: nitrile (2 × 10 mL) afforded pure 4c. The pure 4d was obtained
245.1662, found: 245.1654.
by washing the precipitate with THF (2 × 10 mL).
4a, yellow powder, 35% yield. 1H NMR (400 MHz, DMSO-
d6): δ = 7.62 (s, 1H, CHvCH), 4.56 (t, 2H, J = 4.8 Hz, CH2CH2),
4.31 (t, 2H, J = 4.8 Hz, CH2CH2), 3.76 (s, 3H, NCH3), 2.68 (s,
Preparation of AFIB-CO2 adducts (2a–2d) and AFIB-CS2
adducts (4a–4d)
The synthesis of 2a–2d. 1-(2-Hydroxyethyl)-2,3-disubstituted 3H, CCH3). 13C NMR (100 MHz, DMSO-d6): δ = 228.3, 145.0,
imidazolium bromine (2 mmol) and KOtBu (2.4 mmol, 0.27 g) 122.3, 121.3, 67.7, 47.2, 34.7, 9.5. IR (KBr) 1093, 1075 cm−1
were added to a solution of THF (15 mL) and the mixture was (vs).
stirred at ambient temperature for 2 h. During the reaction
4b, yellow powder, 41% yield. 1H NMR (400 MHz, DMSO-
course, the solution colour gradually changed to yellow. After d6): δ = 7.64 (d, 1H, J = 2.0 Hz, CHvCH), 7.63 (d, 1H, J =
filtration to remove the salt, the yellow filtrate filled in an anti- 2.0 Hz, CHvCH), 4.56 (t, 1H, J = 4.8 Hz, CH2CH2), 4.49 (t, 2H,
pressure Schlenk flask was transferred to a Schlenk line J = 4.8 Hz, CH(CH3)2). 13C NMR (100 MHz, DMSO-d6): δ =
equipped with a CO2 source and the flask was degassed at 228.9, 150.1, 124.1, 122.0, 68.7, 47.7, 36.4, 24.6, 19.1. IR (KBr)
−78 °C in vacuo, and filled with 1 atm CO2. The solution was 1082, 1067 cm−1 (vs).
stirred to room temperature for 2 hours. The precipitate was
4c, yellow powder, 38% yield. 1H NMR (400 MHz, DMSO-
formed and collected via filtration. Subsequently the solid was d6): δ = 7.82 (d, 1H, J = 2.0 Hz, CHvCH), 7.67 (d, 1H, J =
washed with THF (2 × 10 mL) and Et2O (2 × 10 mL) to afford 2.0 Hz, CHvCH), 4.67 (m, 1H,CH(CH3)2), 4.59 (t, 2H, J = 4.8
the corresponding AFIB-CO2 adducts and then pumped to Hz, CH2CH2), 4.42 (t, 2H, J = 4.8 Hz, CH2CH2), 2.72 (s, 3H,
dryness.
CCH3), 1.41 (d, 6H, J = 6.8 Hz, CH(CH3)2). 13C NMR (100 MHz,
2a, white powder, 87% yield. 1H NMR (400 MHz, DMSO-d6): DMSO-d6): δ = 228.3, 143.9, 122.1, 117.6, 67.5, 49.9, 47.0, 21.9,
δ = 7.60 (s, 1H, CHvCH), 7.59 (s, 1H, CHvCH), 4.20 (t, 2H, J = 9.5. IR (KBr) 1080, 1066 cm−1 (vs).
5.6 Hz, CH2CH2), 3.89 (t, 2H, J = 5.6 Hz, CH2CH2), 3.76 (s, 3H,
4d, yellow powder, 90% yield. 1H NMR (400 MHz, DMSO-
NCH3), 2.59 (s, 3H, CCH3). 13C NMR (100 MHz, DMSO-d6): δ = d6): δ = 7.77 (d, 1H, J = 1.6 Hz, CHvCH), 7.72 (d, 1H, J =
153.3, 144.7, 122.1, 121.3, 61.3, 48.6, 34.6, 9.22. IR (KBr) 1.6 Hz, CHvCH), 7.23–7.43 (m, 5H, Ph), 5.57 (s, 2H, CH2Ph),
1671 cm−1 (vs).
4.67 (t, 2H, J = 4.8 Hz, CH2CH2), 4.56 (t, 2H, J = 4.8 Hz,
2b, white powder, 82% yield. 1H NMR (400 MHz, DMSO-d6): CH2CH2), 3.73 (m, 1H, CH(CH3)2),1.33 (d, 6H, J = 7.2 Hz, CH
δ = 7.60 (s, 1H, CHvCH), 7.59 (s, 1H, CHvCH), 4.27 (t, 2H, J = (CH3)2). 13C NMR (100 MHz, DMSO-d6): δ = 228.5, 150.0, 135.0,
4.8 Hz, CH2CH2), 3.89–3.91 (m, 5H, CH2CH2 and NCH3), 3.63 128.9, 128.3, 127.0, 122.7, 122.5, 67.9, 51.1, 47.5, 24.4, 19.1.
(m, 1H, CH(CH3)2), 1.39 (d, 6H, J = 6.4 Hz, CCH3). 13C NMR IR (KBr) 1070 cm−1 (vs).
(100 MHz, DMSO-d6): δ = 153.3, 149.4, 123.3, 121.6, 61.4, 48.7,
35.8, 24.2, 18.3. IR (Film) 1682 cm−1 (vs).
2c, white powder, 85% yield. 1H NMR (400 MHz, DMSO-d6):
Representative experimental procedure for the carboxylation
cyclization of propargylic alcohols with CO2
δ = 7.83 (d, 1H, J = 1.2 Hz, CHvCH), 7.66 (d, 1H, J = 1.2 Hz,
CHvCH), 4.68 (m, 1H, NCH(CH3)2), 4.20 (t, 2H, J = 4.8 Hz, A 10 mL oven dried autoclave containing a stir bar was
CH2CH2), 3.89 (t, 2H, J = 4.8 Hz, CH2CH2), 3.64 (s, 3H, CCH3), charged with 5a (0.25 g, 3 mmol) and 2a (11 mg, 0.06 mmol)
1.41 (d, 6H, J = 6.4 Hz, CH(CH3)2). 13C NMR (100 MHz, DMSO- after purging the autoclave with CO2 three times. The sealed
d6): δ = 153.3, 143.5, 122.2, 117.4, 61.2, 49.8, 48.5, 21.9, 9.2. IR autoclave was pressurized to 2 MPa CO2. The reaction mixture
(Film) 1686 cm−1 (vs).
was stirred at 60 °C for 5 h, then the autoclave was cooled to
2d, white powder, 80% yield. 1H NMR (400 MHz, DMSO-d6): room temperature and the remaining CO2 was vented slowly.
1
δ = 7.71 (d, 1H, J = 1.6 Hz, CHvCH), 7.68 (d, 1H, J = 1.6 Hz, The yields of the target products were determined by H NMR
CHvCH), 7.22–7.43 (m, 5H, Ph), 5.54 (s, 2H, CH2Ph), 4.31 (m, analysis.
2270 | Green Chem., 2014, 16, 2266–2272
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Characterization of alkylidene cyclic carbonates (6a–6i)
δ = 157.2, 151.8, 90.0, 86.4, 37.1, 24.2, 16.5, 16.2. IR (Film)
1820, 1682 cm−1. HRMS (ESI, m/z) calcd for C8H12NaO3
4,4-Dimethyl-5-methylene-1,3-dioxolan-2-one (6a). 1H NMR [M + Na]+: 179.0684, found: 179.0688.
(400 MHz, CDCl3): δ = 4.78 (d, J = 4.0 Hz, 1H, CHvCH), 4.32
(Z)-5-Benzylidene-4,4-dimethyl-1,3-dioxolan-2-one
(6i). 1H
(d, J = 4.0 Hz, 1H, CHvCH), 1.62 (s, 6H, CH3). 13C NMR NMR (400 MHz, CDCl3): δ = 7.53–7.55 (m, 2H, C6H5), 7.23–7.37
(100 MHz, CDCl3): δ = 158.8, 151.4, 85.4, 84.7, 27.7. IR (Film) (m, 3H, C6H5), 5.50 (s, 1H, CvCH), 1.68 (s, 6H, CH3). 13C NMR
1824, 1684 cm−1. HRMS (ESI, m/z) calcd for C6H8O3Na [M + (100 MHz, CDCl3): δ = 151.4, 150.8, 132.5, 128.7, 128.6, 127.7,
Na]+: 151.0371, found: 151.0368.
4-Methyl-4-ethyl-5-methylene-1,3-dioxolan-2-one
101.6, 85.7, 27.8. IR (Film) 1835, 1814, 1701 cm−1. HRMS (ESI,
(6b). 1H m/z) calcd for C12H12NaO3 [M + Na]+: 227.0684, found:
NMR (400 MHz, CDCl3): δ = 4.82 (d, 1H, J = 4.0 Hz, CHvCH), 227.0676.
4.27 (d, 1H, J = 4.0 Hz, CHvCH), 1.87–1.96 (m, 1H, CH2CH3),
1.70–1.77 (m, 1H, CH2CH3), 1.59 (s, 3H, CCH3), 0.99 (t, 3H, J =
4.0 Hz, CH2CH3). 13C NMR (100 MHz, CDCl3): δ = 157.6, 151.7,
Acknowledgements
87.6, 85.7, 33.5, 26.1, 7.5. IR (Film) 1832, 1687 cm−1. HRMS
(ESI, m/z) calcd for C7H10NaO3 [M + Na]+: 165.0528, found: This work was financially supported by the National Natural
165.0533.
Science Foundation of China (U1162101), and the Program for
4-Methyl-5-ethylene-4-phenyl-1,3-dioxolan-2-one
(6c). 1H Changjiang Scholars and Innovative Research Team in Univer-
NMR (400 MHz, CDCl3): δ = 7.47–7.49 (m, 2H, C6H5), 7.38–7.44 sity (IRT13008). X.-B. Lu gratefully acknowledges the Chang
(m, 3H, C6H5), 4.95 (d, 1H, J = 4.0 Hz, CHvCH), 4.47 (d, 1H, Jiang Scholars Program (no. T2011056) from Ministry of Edu-
J = 4.0 Hz, CHvCH), 1.97 (s, 6H, CH3). 13C NMR (100 MHz, cation, People’s Republic of China.
CDCl3): δ = 157.5, 151.3, 139.3, 129.3, 129.0, 124.8, 88.3, 87.3,
27.6. IR (Film) 1821, 1686 cm−1. HRMS (ESI, m/z) calcd for
C11H10O3Na [M + Na]+: 213.0528, found: 213.0534.
Notes and references
5-Ethylene-1,3-dioxaspiro[4.5]decan-2-one (6d). 1H NMR
(400 MHz, CDCl3): δ = 4.76 (d, J = 4.0 Hz, 1H, CHvCH), 4.29,
(d, J = 4.0 Hz, 1H, CHvCH), 2.62 (t, J = 7.6 Hz, 2H), 1.99–2.06
(m, 2H), 1.58–1.73 (m, 7H), 1.26–1.38 (m, 1H). 13C NMR
(100 MHz, CDCl3): δ = 158.8, 151.6, 86.5, 85.6, 36.6, 24.4, 21.7.
IR (Film) 1838, 1814, 1682 cm−1. HRMS (ESI, m/z) calcd for
C9H12O3Na [M + Na]+: 191.0684, found: 191.0680.
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NMR (400 MHz, CDCl3): δ = 4.80 (d, J = 4.0 Hz, 1H, CHvCH),
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2272 | Green Chem., 2014, 16, 2266–2272
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