An in situ formed Ca2+-crown ether complex and its use in CO2-fixation reactions with terminal and internal epoxides

Article abstract of DOI:10.1039/c7gc01114h

Herein we report an efficient catalytic system based on readily available calcium iodide and 18-crown-6 ether for the atom economical addition of CO₂ to epoxides. ¹H NMR experiments revealed the selective in situ formation of a crown ether complex. This catalyst allows the conversion of various terminal epoxides under 1 atm CO₂ pressure even at room temperature. Remarkably, a broad range of internal epoxides with various substitution patterns and substituents were smoothly converted which confirms the high efficiency and capability of the protocol. Notably, most of the internal carbonates were synthesized in high yields and diastereoselectivities of up to ≥99%. Furthermore, this system operates under solvent-free conditions without any co-catalysts e.g. onium salts.

Full text of DOI:10.1039/c7gc01114h

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An in situ formed Ca2+–crown ether complex and
its use in CO2-fixation reactions with terminal and
internal epoxides†
Cite this: DOI: 10.1039/c7gc01114h
J. Steinbauer, A. Spannenberg and T. Werner
*
Herein we report an efficient catalytic system based on readily available calcium iodide and 18-crown-6
1
ether for the atom economical addition of CO2 to epoxides. H NMR experiments revealed the selective
in situ formation of a crown ether complex. This catalyst allows the conversion of various terminal
epoxides under 1 atm CO2 pressure even at room temperature. Remarkably, a broad range of internal
epoxides with various substitution patterns and substituents were smoothly converted which confirms the
high efficiency and capability of the protocol. Notably, most of the internal carbonates were synthesized
in high yields and diastereoselectivities of up to ≥99%. Furthermore, this system operates under solvent-
free conditions without any co-catalysts e.g. onium salts.
Received 12th April 2017,
Accepted 12th May 2017
DOI: 10.1039/c7gc01114h
rsc.li/greenchem
These systems are mainly based on metal complexes7 and
metal organic frameworks8 as well as some organocatalysts9
Introduction
The interest in the use of CO2 as an abundant, low cost, non- which are commonly used in combination with onium salts as
toxic and renewable C1 synthon consistently increases from co-catalysts. Whereas the synthesis of terminal cyclic carbon-
the academic and the industrial points of view.1 In this context ates is well established, the synthesis of internal cyclic carbon-
the synthesis of cyclic carbonates from epoxides and CO2 is a ates is still an open field. Kleij et al. recently reported the latest
well-known but still very vibrant research area (Scheme 1).2 developments in this area, showing that the synthesis of
This is due to the diversified applications of cyclic carbonates, internal cyclic carbonates under mild conditions (T < 100 °C)
e.g. as solvents,3 electrolytes,4 raw materials for polymers2f,5 is still very challenging and of great interest.2c
and synthetic building blocks.6 Various catalytic systems have
Alkali metal salts2b are amongst the most extensively
been developed for the synthesis of cyclic carbonates but so studied catalysts in cyclic carbonate synthesis from terminal
far only a few systems operate under ambient conditions (T ≤ epoxides. The most frequently used salt is potassium iodide2b
25 °C, p(CO2) ≤1 atm).2
which has been applied in combination with 18-crown-6 ether
(18C6)10 or polydibenzo-18-crown-6 11 as ligands at elevated
temperatures. For the conversion of epoxides with CO2 under
mild conditions an electrophilic activation of the epoxide is
crucial in those systems. Due to the weak Lewis acidic charac-
ter of the K+ cation an electrophilic co-catalyst must be pro-
vided. Recently, hydrogen bond donors have been reported as
co-catalysts, activating the epoxide through hydrogen
bonding12 allowing the conversion even at a reaction tempera-
ture of T = 40 °C.13 Furthermore, Lu et al. reported an Al-salen
complex in combination with KI/18C6 operating even at room
temperature.14 In this system the Al complex acts as the elec-
trophilic co-catalyst. In contrast to alkali metal salts, alkaline
earth metal salts are less investigated.2b Particularly, calcium-
based systems are hardly investigated, which is quite surpris-
ing since calcium is one of the six metals (Na, K, Ca, Ti, Fe, Al)
classified as abundant,15 inexpensive and environmentally
benign.16 So far, calcium-based protocols have only been
Scheme 1 Synthesis of cyclic carbonates from epoxides and CO2.
Leibniz Institute for Catalysis at the University of Rostock (LIKAT Rostock), Albert
Einstein Str. 29a, 18059 Rostock, Germany. E-mail: Thomas.Werner@catalysis.de
†Electronic supplementary information (ESI) available. CCDC 1532107 and
1542896. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c7gc01114h
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reported for the synthesis of cyclic carbonates at temperatures
of ≥100 °C.2b Troev and co-workers used CaCl2 as a co-catalyst
for tetraalkylammonium or phosphonium halides at 170 °C.17
Furthermore, Bai et al. reported a Ca2+–BINOL complex with
tetraalkylammonium salts as co-catalysts at 120 °C.18 Moreover
He and co-workers established a catalyst system based on
CaBr2 and DBU which efficiently promotes the reaction at
100 °C in DMF.19 We recently reported the design and appli-
cation of organocatalytic20 as well as sustainable metal-based
systems.11,12,21a–c In this work, we investigated the potential of
calcium salts as catalysts in the synthesis of cyclic carbonates
from epoxides and CO2 under mild conditions.
Fig. 1 Molecular structure of CaI2/18C6-complex 3·2DMF in the
crystal. Displacement ellipsoids correspond to 30% probability.
Hydrogen atoms are omitted for clarity. Operator for generating equi-
valent atoms: −x, −y + 1, −z. CCDC 1532107 contains the supplementary
crystallographic data for this paper.23
Results and discussion
Catalyst screening and parameter optimization
The conversion of tert-butylglycidyl ether (1a) with CO2 was
studied as a model reaction (Table 1). The synthesis of glycidyl
ether based carbonates is of particular interest, because glyci-
dyl can be synthesized from glycerol, which can be obtained
from renewables.22 The first screening experiments were per-
formed at 25 °C and a CO2 pressure of 10 bar for 4 h with a
catalyst loading of 2.5 mol%. Our initial efforts focused on the
screening of several calcium salts in combination with 18C6 as
a ligand under these conditions.23 Notably, catalysts with non-
nucleophilic counter anions such as AcO− and TfO− showed
no catalytic activity under these conditions (entries 1 and 2).
CaCl2 with the nucleophilic Cl− anion also did not show any
activity which is probably due to the poor leaving group abil-
ities of Cl− (entry 3). In contrast, CaBr2 and CaI2 showed cata-
In the absence of 18C6 the yield dropped from 64% to 7%
(entry 6).
The complexation of Ca2+ by 18C6 leads to an increased
solubility of the metal salt and enhanced dissociation of the
iodide anion.24 Overall this led to a catalyst which enables the
efficient synthesis of cyclic carbonates even at room tempera-
ture. We continued our investigations by optimizing the reac-
tion parameters. An increase of the reaction time to 24 h led to
an excellent yield of 99% (entry 8). Remarkably, the catalytic
system performed well even at lower CO2 pressures (entries 9
and 10). Notably, even at 23 °C and being purged with CO2
under atmospheric pressure a yield of 65% was obtained (entry
10). We increased the catalyst loading from 2.5 mol% to
5 mol% to achieve a quantitative conversion of the epoxide 1a
(entry 11). Moreover we were able to isolate 3·2DMF by recrys-
tallization of complex 3 from DMF (Fig. 1). This complex gives
comparable results to the in situ system (Table 1, entry 10).
Thus, we assumed complex 3 to be the catalytically active
species which is formed in situ under the reaction conditions.
It is worth mentioning that this metal complex is one of the
rare examples, which is active under ambient conditions in the
absence of further co-catalysts.25
lytic activity under these conditions (entries
4 and 5).
Surprisingly, CaI2 gave a good yield of 64% after only 4 h (entry 3).
Table 1 Catalyst screening and parameter optimization for the conver-
sion of tert-butyl glycidyl ether (1a) with CO2
Subsequently we performed several 1H NMR experiments to
confirm the in situ formation of complex 3. Fig. 2a shows the
1H NMR spectrum of 18C6 with a specific resonance at
3.50 ppm. The addition of 1 equiv. CaI2 led to a downfield
shift to 3.82 ppm (Fig. 2b). This is characteristic for the com-
plexation of cations by crown ethers.26 Thus, the 1H NMR
experiments revealed the selective in situ formation of a Ca2+–
crown ether complex 3 from a 1 : 1 mixture of CaI2 and 18C6.
Notably, the formation of 3 was also observed in the presence
of cis-stilbene oxide, 5 mol% CaI2 and 18C6 suggesting the for-
mation of 3 even under solvent free reaction conditions
(Fig. 2c).
Entry Catalyst
Cat./mol% T/°C p/bar
t/h Yield 2aa/%
1
2
Ca(OAc)2/18C6 2.5
Ca(OTf)2/18C6 2.5
25
25
25
25
25
25
25
25
25
23
23
10
10
10
10
10
10
10
10
5
4
4
4
4
4
4
4
0
0
0
16
64
7
3
4
5
6
CaCl2/18C6
CaBr2/18C6
CaI2/18C6
CaI2/–
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
5
7
8
9
10
11
–/18C6
0
CaI2/18C6
CaI2/18C6
CaI2/18C6
CaI2/18C6
24 99
24 99
1 atm 24 65 (88)b
1 atm 24 99
a Reaction conditions: 1.0 equiv. 1a (15.4 mmol), 0.025–0.050 equiv.
catalyst and 18C6 (1 : 1), solvent-free. Yield determined by 1H NMR
with mesitylene as an internal standard. b Complex 3 was prepared
prior to the reaction.
Substrate scope I: conversion of terminal epoxides
Having established that CaI2/18C6 is a highly efficient catalyst
system for organic carbonate formation, we subsequently
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copolymerization products, which contain a carbonate unit in
the polymer.28 The epoxide 1g which contains a furfuryl
moiety can be synthesized from renewables29 and was con-
verted to the corresponding carbonate 2g in 89% yield. Silyl-
functionalized carbonates are of particular interest because
they have potential application possibilities as electrolytes,30
for surface modification and as precursors for the synthesis of
non-isocyanate polyhydroxyurethane hybrid materials.31 For
this reason we were delighted to isolate 97% of the silyl-
functionalized carbonate 2h. The highly fluorinated carbon-
ates 2i–k can be used as electrolytes in lithium batteries.32
We were able to prepare them under the standard reaction con-
ditions in excellent yields of up to 97%. Subsequently, we
applied the protocol to terminal alkyl and aryl substituted
Fig. 2 1H NMR investigations regarding the in situ formation of the epoxides (Scheme 3). Aliphatic substituted carbonates 5a–5d
catalyst. All mixtures were prepared in acetonitrile and CD3CN was used
were synthesized in very good to excellent yields of up to 97%.
as a deuterated solvent. (a) 1H NMR spectrum of 18C6. (b) 1H NMR
Particularly, propylene carbonate (5a) is of high interest,
spectrum of CaI2 and 18C6 (1 : 1). (c) 1H NMR of cis stilbene oxide. (d)
Mixture of cis stilbene oxide (1 equiv.) and 5 mol% CaI2/18C6 (1 : 1).
because it is used as an electrolyte4 and considered as one of
the most sustainable alternative solvents in organic chem-
istry.33 Furthermore, enantiopure (R)-propylene oxide (5a) was
converted to the desired carbonate with full retention of the
focused on the evaluation of its outstanding potential. At first
stereochemical information. The retention of the configuration
we investigated the substrate scope with respect to terminal
indicates that the nucleophilic ring-opening occurs at the
epoxides. Under the optimized reaction conditions (23 °C, 1
atm CO2, 24 h) we applied the catalyst system to a broad
variety of (un-)functionalized glycidyl ethers and esters 1a–k,
providing the respective cyclic carbonates 2a–k (Scheme 2).
All glycidyl derivatives 1 besides glycidol (1b) itself were
smoothly converted under ambient conditions yielding exclu-
sively the desired carbonates 2a–k in very good to excellent
β-carbon atom.34 However, it should be mentioned that the
retention of configuration is also achieved by two consecutive
SN2 substitutions at the α-carbon atom which leads to a
double inversion of the configuration. Due to the high vola-
tility of butylene oxide (4b) we converted 4b also in an auto-
clave under 1 bar CO2 pressure and we were able to improve
the yield of 5b from 83% up to 96%. The epichlorohydrin (4e)
yields of up to 99%. The conversion of glycidol (1b) which is
was converted to the corresponding carbonate 5e in 88% yield,
prone to polymerization27 was converted to glycerol carbonate
2b in 42% yield. The alkyl and alkyne substituted carbonates
2a, 2c and 2d were synthesized in distinguished yields of
88–99%. Furthermore, we were pleased to isolate the unsatu-
rated carbonates 2e and 2f in excellent yields of up to 96%.
These derivatives are potential building blocks for homo- and
but due to halide exchange with CaI2, the product was
obtained as a mixture of the Cl and the I substituted carbonate
in a ratio of 9 : 1 (Cl/I). Notably, the selective conversion of
terminal epoxides in the presence of internal epoxides is poss-
ible. Under ambient conditions the selective conversion of 4f
to the monocarbonate 5f was achieved. The desired product 5f
Scheme 3 Substrate scope for the conversion of terminal epoxides 4.
Reaction conditions: 1.0 equiv. 4 (2 g), 5 mol% CaI2/18C6 (1 : 1), 23 °C,
Scheme 2 Substrate scope for the conversion of glycidyl ethers 1.
Reaction conditions: 1.0 equiv. 1 (2 g), 5 mol% CaI2/18C6 (1 : 1), 23 °C,
24 h, 1 atm CO2 (purged), solvent-free. Isolated yields are given.
24 h, 1 atm CO2 (purged), solvent-free. Isolated yields are given. a (R)-4a
was employed. b p(CO2) = 1 bar. c A mixture of Cl− and I− carbonate was
isolated (Cl/I 9 : 1). d (R)-4h was employed.
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Scheme 4 Substrate scope for the conversion of disubstituted terminal
epoxides 6. Reaction conditions: 1.0 equiv. 6 (2 g), 5 mol% CaI2/18C6
(1 : 1), 23 °C, 24 h, 1 atm CO2 (purged), solvent-free. Isolated yields are
given.
was isolated in a yield of 92%. Furthermore morpholino sub-
stituted carbonate 5g was synthesized in a yield of 93%.
Additionally, we converted the aryl substituted styrene oxide
4h. The reaction of racemic 4h with CO2 led to the respective
carbonate 5h in 82% yield.
Scheme 5 Substrate scope for the synthesis of bicyclic internal car-
bonates 9. Reaction conditions: 1.0 equiv. 8 (2 g), 5 mol% CaI2/18C6
(1 : 1), 45 °C, 48 h, solvent-free. Isolated yields are given. The cis/trans
ratio was determined by 1H and/or 13C NMR spectroscopy. a Acetonitrile
was employed as a solvent. Yield was determined by 1H NMR.
In contrast to the propylene oxide (R)-4a which was con-
verted with full retention of the stereoinformation, styrene
oxide (4h) is prone to a SN1-type mechanism, which might
lead to a partial racemization of the product 5h.34 Indeed
when (R)-4h was converted under the standard reaction con-
ditions partial racemization was observed and 5h was isolated
in an enantiomeric excess of 42%. After having established a
general protocol for the conversion of monosubstituted term-
inal epoxides under ambient conditions, we applied our cata-
lytic system to the conversion of disubstituted epoxides
(Scheme 4). Remarkably, the substrates 6a–6e also smoothly
reacted to yield the respective cyclic carbonates under our stan-
dard reaction conditions. The alkyl and halide substituted car-
bonates 7a–7c were isolated in yields of 84–92%. It is note-
worthy that the conversion of an acceptor substituted epoxide
6d, which is a challenging substrate,35 gave the corresponding
carbonate 7d in a distinguished yield of 96%.
Finally, we converted the alkyl aryl disubstituted epoxide 6e
and isolated 23% of the carbonate 7e. These combined
results clearly show the amplified scope of CaI2/18C6 for
the conversion of terminal epoxides, even under ambient
conditions.
Scheme 6 Substrate scope for the synthesis of internal carbonates 11.
Reaction conditions: 1.0 equiv. 10 (2 g), 5 mol% CaI2/18C6 (1 : 1), 45 °C,
48 h, solvent-free. Isolated yields are given. The cis/trans ratio was
determined by 1H and/or 13C NMR spectroscopy. a Acetonitrile was
employed as a solvent. b T = 23 °C, 24 h. c Yield determined by 1H NMR.
d Ratio of the products was determined by 1H NMR.
Substrate scope II: conversion of internal epoxides
The synthesis of internal carbonates from epoxides and CO2 is
a challenging task and is often neglected in the evaluation of ESI†).23 We were delighted that it was possible to convert even
the substrate scope. This reaction typically requires reaction these demanding substrates under milder conditions (45 °C,
temperatures above 100 °C, high CO2 pressures and/or long p(CO2) = 10 bar, 48 h) compared to the state of the art cata-
reaction times. After the application of the catalyst system to lysts.2c,7e,20c,36 Initially we studied the synthesis of bicyclic
the conversion of terminal epoxides, we challenged the cata- carbonates 9 (Scheme 5). It is worth mentioning that all
lytic potential of the CaI2/18C6-system with the more demand- products 9a–9i were prepared in excellent diastereoselectivities
ing conversion of internal epoxides (Schemes 5 and 6). We of ≥99%. This is of special interest, since cyclic carbonates can
initially tested the standard protocol (5 mol% CaI2/18C6, 1 be used as precursors for the diastereoselective synthesis of
atm CO2, 23 °C) in the conversion of cyclohexene oxide (8c). diols.36a Using cyclopentene oxide (8a) and the dihydrofuran-
Under these conditions 5% of the desired cyclic carbonate 9c derived epoxide 8b as substrates, the yields of 98% and 76%
was obtained. Based on this result, the reaction conditions for for the respective carbonates were obtained. The application of
the conversion of internal epoxides were optimized (see the the catalyst system to the epoxides 8c–8f led to the carbonates
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in yields of 45–99%. The synthesis of biscarbonates is cur-
rently intensively studied, because they can be used as mono-
mers for the synthesis of non-isocyanate polyurethanes
(NIPUs).2f,37
In this regard, we were pleased to achieve a good yield of
67% for the synthesis of biscarbonate 9g. For the conversion
of cycloheptene oxide an excellent yield of 97% was achieved.
Even the conversion of the very demanding cyclooctene oxide
was possible though only a low yield of 4% was observed.
Finally, we evaluated the substrate scope for the synthesis of
disubstituted carbonates 11a–11h (Scheme 6).
Fig. 3 Molecular structure of 11i in the crystal. Displacement ellipsoids
correspond to 30% probability. CCDC 1542896 contains the supplemen-
tary crystallographic data for this paper.23
The conversion of trans-1,2-butylene oxide (10a) led to 86%
of the trans carbonate 11a with a cis/trans ratio of ≥1 : 99,
whereas the cis-carbonate 11b was obtained with a similar
yield of 87%, but with a cis/trans ratio of 91 : 9. Usually the
reaction proceeds via two consecutive SN2 steps which leads to
an overall retention of the stereochemistry. However, appar-
ently a SN1-type mechanism is in operation to some extent
leading to the formation of 8% trans-11b as the thermo-
dynamically favored product. The conversion of trans-stilbene
oxide (10c) led selectively to 11c in an excellent yield of 98%
with a cis/trans ratio of ≥1 : 99. Notably, a similar result was
obtained even at 23 °C underlining the great efficiency of this
catalyst system. To the best of our knowledge, this is the first
report of a room temperature conversion of an internal
epoxide resulting in an exceptional yield of 94% in only 24 h.
Moreover, we employed the catalyst to cis-stilbene oxide (10d)
and 81% of the carbonate was obtained. The isomerisation
towards the trans-product increased compared to the conver-
sion of substrate 10b. Due to the phenyl substituent the SN1-
pathway leading to the trans-product is favoured. Thus, the
observed cis/trans ratio for 11d was 43 : 57. The carbonate 11e
was synthesized with a yield of 90% and a cis/trans ratio of
≥1 : 99. Remarkably, the acceptor substituted carbonates 11f
and 11g were obtained in yields of 51% and 71% with excellent
cis/trans ratios. The conversion of 10h resulted in a quite sur-
prising result, because the expected product 11h only was the
minor product. Interestingly, the terminal carbonate 11i is the
major product of this transformation. The products were
obtained with a ratio of 11h/11i 12 : 88. Product 11i is probably
Scheme 7 Proposed mechanism for the formation of cyclic carbonates
from epoxides and CO2.
formed by CO2 insertion into the O–H bond of the hydroxyl vation facilitates the nucleophilic ring-opening and the result-
moiety of 10h and a nucleophilic epoxide ring-opening of the ing alkoxide anion B is stabilized by the Ca2+-complex. At this
resulting carboxylate anion. This alternative mechanism for stage the reaction might proceed via an SN1 or SN2 pathway
cyclic carbonate synthesis from hydroxyl functionalized epo- which has previously been proposed for other catalytic
xides has recently been reported by Kleij and co-workers.38 systems.39 Based on the observed diastereoselectivities for the
Furthermore, we were able to recrystallize the product 11i from conversion of the internal epoxides 11b we propose the SN2-
CH2Cl2 to obtain crystals which were suitable for X-ray crystal- pathway as the most likely reaction pathway for substrates
lographic analysis (Fig. 3).
which do not stabilize cationic intermediates. This leads to an
overall retention of the relative and absolute stereochemistry,
respectively. Thus, the addition of CO2 leads to carbonates C
Mechanism
Based on the results of the NMR spectroscopic investigations and a subsequent SN2 reaction to the desired product. This is
and the conversion of chiral terminal and cis-substituted also supported by the result for the conversion of the enantio-
internal carbonates, we propose the mechanism shown in pure propylene oxide (R)-4a, where the absolute configuration
Scheme 7. After the in situ formation of complex 3, which was is fully retained.
monitored by 1H NMR spectroscopy (Fig. 2), the epoxide is
In contrast, in the conversion of substrates bearing substitu-
activated by the Lewis-acidic complex 3 leading to A. This acti- ents capable of stabilizing cationic intermediates such as 10d
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the reaction might follow a SN1-pathway to some extent Coupling reaction of CO2 and internal epoxides (GP2)
leading to E. Under these reaction conditions the nucleophilic
ring-closure will most likely yield the thermodynamically pre-
A stainless-steel autoclave was charged with 5.0 mol% CaI2,
5.0 mol% 18-crown-6 ether, and 1.0 equiv. epoxide 8 or 10
ferred trans-product as observed in the conversion of cis-stil-
(0.50–2.00 g), and in the case of a solid epoxide additionally
bene oxide (10d). In this case actually the trans-carbonate 11c
1.5 mL solvent were added. The autoclave was sealed, con-
was the major product. This is also supported by the partial
stantly purged with 10 bar CO2, and the reaction mixture was
racemization in the conversion of the enantiopure styrene
stirred for 48 h at 45 °C. Subsequently the reactor was cooled
oxide ((R)-4h). In this case an ee of 42% was obtained for the
to ≤20 °C with an ice bath and CO2 was released slowly. The
product 5h. These results show that at the stage of the inter-
reaction mixture was filtered over silica gel (SiO2) with
cyclohexane : ethyl acetate = 2 : 1 or purified by flash chromato-
graphy. After the removal of all volatiles in vacuo the product 9
mediate B the reaction can also proceed via a SN1-pathway. In
the SN1-pathway the alkoxide activates CO2 and D is formed,
but afterwards the cationic intermediate E is formed and the
or 11 was obtained. It has to be considered that in some cases
ring is closed via a SN1-type mechanism. The reaction proceeds
by addition of the epoxide to the catalyst a very exothermic
reaction was observed. This should be considered especially
via this pathway if the SN2-pathway leads to a thermo-
dynamically non-favoured product. Furthermore, substituents
for upscaling experiments.
which stabilize the cationic intermediate E promote the SN1-
pathway, too.
Synthesis of cyclic carbonates
4-(tert-Butoxymethyl)-1,3-dioxolan-2-one (2a).20b According
to GP1, 2-(tert-butoxymethyl)oxirane 1a (2.00 g, 15.4 mmol),
Conclusions
CaI2 (226 mg, 0.769 mmol), 18-crown-6 ether (206 mg,
In summary, we have reported a Ca2+-complex as an extraordi- 0.779 mmol) and CO2 were converted to the desired carbonate.
nary efficient catalyst for the synthesis of a broad range of The product 2a (2.64 g, 15.2 mmol, 99%) was obtained as a
1
cyclic carbonates from CO2 and epoxides. The selective in situ colourless liquid. H NMR (300 MHz, CDCl3, 25 °C): δ = 1.13
formation of the catalyst from CaI2 and 18-crown-6 ether was (s, 9H), 3.46 (dd, J = 10.3 Hz, 3.6 Hz, 1H), 3.55 (dd, J = 10.3 Hz,
confirmed by 1H NMR experiments. The catalyst is based on 4.5 Hz, 1H), 4.32 (dd, J = 8.3 Hz, 5.9 Hz, 1H), 4.41 (dd, J =
calcium which is a cheap, earth-abundant, nontoxic metal. 8.2 Hz, 8.2 Hz, 1H), 4.64–4.77 (m, 1H) ppm.
Notably, this catalytic system does not require any co-catalysts.
4-(Hydroxymethyl)-1,3-dioxolan-2-one (2b).20b According to
19 terminal and 5 terminal disubstituted carbonates were pre- GP1, glycidol 1b (2.00 g, 27.0 mmol), CaI2 (396 mg,
pared at room temperature and under a CO2 atmosphere 1.35 mmol), 18-crown-6 ether (358 mg, 1.35 mmol) and CO2
under solvent-free conditions in yields of up to 99%. were converted to the desired carbonate. The product 2b
Remarkably, 17 internal epoxides were also converted with (1.35 g, 11.4 mmol, 42%) was obtained as a colourless liquid.
CO2 under comparatively mild conditions (reaction tempera- 1H NMR (300 MHz, CDCl3, 25 °C): δ = 2.92 (t, J = 6.3 Hz, 1H),
ture ≤45 °C) in yields of up to 99%. Additionally, the evalu- 3.64 (ddd, J = 6.9, 6.0, 3.5 Hz, 1H), 3.92 (ddd, J = 7.2 Hz,
ation of the substrate scope shows the tolerance for a great 5.7 Hz, 3.0 Hz, 1H), 4.36–4.52 (m, 2H), 4.71–4.82 (m, 1H) ppm.
number of functional moieties of the catalytic protocol. In
4-(Methoxymethyl)-1,3-dioxolan-2-one (2c).40 According to
general, this work clearly indicates the potential of calcium GP1, 2-(methoxymethyl)oxirane 1c (2.00 g, 22.7 mmol), CaI2
catalysts in ring-opening reactions and we expect that these (335 mg, 1.14 mmol), 18-crown-6 ether (301 mg, 1.14 mmol)
results will trigger further research in this area.
and CO2 were converted to the desired carbonate. The product
2c (2.63 g, 19.9 mmol, 88%) was obtained as a colourless
liquid. 1H NMR (300 MHz, CDCl3, 27 °C): δ = 3.42 (s, 3H), 3.56
(dd, J = 11.0 Hz, 3.8 Hz, 1H), 3.64 (dd, J = 11.0 Hz, 3.8 Hz, 1H),
4.37 (dd, J = 8.3 Hz, 6.1 Hz, 1H), 4.49 (dd, J = 8.4 Hz, 8.4 Hz,
1H), 4.76–4.86 (m, 1H) ppm.
Experimental
Coupling reaction of CO2 and terminal epoxides under
ambient conditions (GP1)
4-((Prop-2-yn-1-yloxy)methyl)-1,3-dioxolan-2-one (2d).35a
A Schlenk flask was charged with 5 mol% CaI2, 5 mol% According to GP1, 2-((prop-2-yn-1-yloxy)methyl)oxirane 1d (2.00 g,
18-crown-6 ether and 1 equiv. epoxide 1, 4 or 6 (2.00 g). The 17.8 mmol), CaI2 (260 mg, 0.885 mmol), 18-crown-6 ether
flask was constantly purged with CO2 under atmospheric (236 mg, 0.893 mmol) and CO2 were converted to the desired
pressure. The reaction mixture was stirred for 24 h at 23 °C. carbonate. The product 2d (2.68 g, 17.2 mmol, 97%) was
The reaction mixture was filtered over silica gel (SiO2) with obtained as a colourless liquid. 1H NMR (300 MHz, CDCl3,
cyclohexane : ethyl acetate = 1 : 1. After the removal of all 25 °C): δ = 2.49 (t, J = 2.4 Hz, 1H), 3.69–3.83 (m, 2H), 4.15–4.30
volatiles in vacuo the product 2, 5 or 7 was obtained. It has (m, 2H), 4.39 (dd, J = 8.4 Hz, 6.1 Hz, 1H), 4.51 (t, J = 8.4, 1H),
to be considered that in some cases by addition of the 4.81–4.91 (m, 1H) ppm.
epoxide to the catalyst a highly exothermic reaction was
observed. This should be considered especially by upscaling GP1, 2-((allyloxy)methyl)oxirane 1e (2.00 g, 17.5 mmol), CaI2
4-((Allyloxy)methyl)-1,3-dioxolan-2-one (2e).20b According to
experiments.
(260 mg, 0.885 mmol), 18-crown-6 ether (231 mg, 0.874 mmol)
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and CO2 were converted to the desired carbonate. The product
4-((2,2,3,3,3-Pentafluoropropoxy)methyl)-1,3-dioxolan-2-one
2e (2.56 g, 16.2 mmol, 93%) was obtained as a colourless (2j).32a According to GP1, 2-((2,2,3,3-tetrafluorobutoxy)methyl)
liquid. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 3.61 (dd, J = oxirane 1j (2.00 g, 9.80 mmol), CaI2 (143 mg, 0.49 mmol),
11.0 Hz, 3.8 Hz, 1H), 3.69 (dd, J = 11.0 Hz, 3.9 Hz, 1H), 18-crown-6 ether (128 mg, 0.49 mmol) and CO2 were converted
3.99–4.12 (m, 2H), 4.40 (dd, J = 8.3 Hz, 6.1 Hz, 1H), 4.50 (dd, to the desired carbonate. The product 2j (2.27 g, 9.1 mmol,
1
J = 8.3 Hz, 8.3 Hz, 1H), 4.77–4.88 (m, 1H), 5.19–5.33 (m, 2H), 93%) was obtained as a colourless liquid. H NMR (300 MHz,
5.78–5.97 (m, 1H) ppm.
CDCl3, 23 °C): δ = 3.94 (m, 4H), 4.45 (m, 2H), 4.85 (m, 1H)
2-(Oxo-1,3-dioxolan-4-yl)methyl methacrylate (2f).20b ppm.
According to GP1, oxiran-2-ylmethyl methacrylate 1f (2.01 g,
4-(((2,2,3,3,4,4,5,5-Octafluoropentyl)oxy)methyl)-1,3-dioxolan-
14.1 mmol), CaI2 (210 mg, 0.715 mmol), 18-crown-6 ether 2-one (2k). According to GP1, 2-(((2,2,3,3,4,4,5,5-octafluoro-
(187 mg, 0.707 mmol) and CO2 were converted to the desired pentyl)oxy)methyl)oxirane 1k (2.00 g, 6.94 mmol), CaI2
carbonate. The product 2f (2.54 g, 13.6 mmol, 96%) was (105 mg, 0.357 mmol), 18-crown-6 ether (95 mg, 0.359 mmol)
obtained as a colourless liquid. 1H NMR (300 MHz, CDCl3, and CO2 were converted to the desired carbonate. The product
25 °C): δ = 1.93–1.97 (m, 3H), 4.29–4.39 (m, 2H), 4.39–4.47 2k (2.24 g, 6.74 mmol, 97%) was obtained as a colourless
(m, 1H), 4.51–4.67 (m, 1H), 4.92–5.04 (m, 1H), 5.61–5.72 liquid. 1H NMR (300 MHz, CDCl3, 22 °C): δ = 3.88 (ddd, J =
(m, 1H), 6.08–6.23 (m, 1H) ppm.
18.9 Hz, 11.1 Hz, 3.5 Hz, 2H), 3.95–4.20 (m, 2H), 4.40 (dd, J =
4-((Furan-2-ylmethoxy)methyl)-1,3-dioxolan-2-one
(2g). 8.5 Hz, 6.1 Hz, 1H), 4.53 (dd, J = 8.5 Hz, 8.5 Hz, 1H), 4.80–4.90
According to GP1, furfuryl glycidyl ether 1g (2.02 g, (m, 1H), 6.05 (tt, J = 51.9 Hz, 5.4 Hz, 1H) ppm; 13C{1H} NMR
13.1 mmol), CaI2 (191 mg, 0.650 mmol), 18-crown-6 ether (300 MHz, CDCl3, 25 °C): δ = 65.7 (CH2), 68.3 (t, J = 25.8 Hz,
(171 mg, 0.647 mmol) and CO2 were converted to the desired CH2), 71.5 (CH2), 74.6 (CH), 109.5–119.4 (m, 3 × CF2), 107.6 (tt,
carbonate. The product 2g (2.31 g, 11.7 mmol, 89%) was J = 254.5 Hz, 30.8 Hz, CHF2), 154.7 (CvO) ppm; 19F NMR
obtained as a pale yellow liquid. 1H NMR (300 MHz, CDCl3, (300 MHz, CDCl3, 22 °C): δ = (−137.3)–(−136.8) (m, 2F),
23 °C): δ = 3.62 (dd, J = 11.0 Hz, 3.8 Hz, 1H), 3.70 (dd, J = 11.0 (−130.0)–(−129.6) (m, 2F), (−125.2)–(−124.9) (m, 2F), (−119.5)–
Hz, 4.2 Hz, 1H), 4.33 (dd, J = 8.4 Hz, 6.2 Hz, 1H), 4.35–4.58 (m, (−119.2) (m, 2F) ppm; HRMS (ESI-TOF/MS): m/z calcd
3H), 4.75–4.82 (m, 1H), 6.34–6.37 (m, 2H), 7.42 (dd, J = 1.38 C9H8F8O4Na [M+ + Na]: 355.0187; m/z found C9H8F8O4Na
Hz, 1.29 Hz, 1H) ppm; 13C{1H} NMR (75 MHz, CDCl3, 23 °C): [M+ + Na]: 355.0191; EA: calcd (%) for C9H8F8O4 (332.15 g mol−1):
δ = 65.2 (CH2), 66.2 (CH2), 68.4 (CH2), 74.8 (CH), 110.1 (CH), C 32.55, H 2.43; found: C 32.86, H 2.25.
110.4 (CH), 143.1 (CH), 150.6 (C), 154.8 (CvO) ppm; HRMS
4-Methyl-1,3-dioxolan-2-one (5a).20b According to GP1,
(EI): m/z calcd C9H10O5 [M+]: 198.0523; m/z found C9H10O5 2-methyloxirane 4a (2.00 g, 34.4 mmol), CaI2 (504 mg,
[M+]: 198.0525; EA: calcd (%) for C9H10O5 (198.17 g mol−1): 1.71 mmol), 18-crown-6 ether (459 mg, 1.74 mmol) and CO2
C 54.55, H 5.09; found: C 54.60, H 5.02.
were converted to the desired carbonate. The product 5a
4-(((tert-Butyldimethylsilyl)oxy)methyl)-1,3-dioxolan-2-one (2.97 g, 29.1 mmol, 85%) was obtained as a colourless liquid.
(2h). According to GP1, tert-butyldimethyl(oxiran-2-ylmethoxy) 1H NMR (300 MHz, CDCl3, 25 °C): δ = 1.47 (d, J = 6.2 Hz, 3H),
silane 1h (2.00 g, 10.6 mmol), CaI2 (160 mg, 0.544 mmol), 4.01 (dd, J = 8.4 Hz, 7.2 Hz, 1H), 4.54 (dd, J = 8.4 Hz, 7.7 Hz,
18-crown-6 ether (141 mg, 0.533 mmol) and CO2 were con- 1H), 4.76–4.94 (m, 1H) ppm.
verted to the desired carbonate. The product 2h (2.40 g,
4-Ethyl-1,3-dioxolan-2-one (5b).20b According to GP1,
1
10.3 mmol, 97%) was obtained as a colourless solid. H NMR 1,2-epoxybutane 4b (2.00 g, 27.7 mmol), CaI2 (408 mg,
(300 MHz, CDCl3): δ = 0.07–0.12 (m, 6H), 0.88–0.93 (m, 9H), 1.39 mmol), 18-crown-6 ether (370 mg, 1.40 mmol) and CO2
3.73 (dd, J = 11.7 Hz, 2.8 Hz, 1H), 3.92 (dd, J = 11.6 Hz, 3.5 Hz, were converted to the desired carbonate. The product 5b
1H), 4.41–4.52 (m, 2H), 4.70–4.78 (m, 1H) ppm; 13C{1H} NMR (2.68 g, 23.1 mmol, 83%) was obtained as a colourless liquid.
(300 MHz, CDCl3, 25 °C): δ = −5.6 (d, J = 3.3 Hz, 2 × CH3), 1H NMR (300 MHz, CDCl3, 27 °C): δ = 1.02 (t, J = 7.4 Hz, 3H),
18.1 (C), 25.6 (3 × CH3), 62.4 (CH2), 65.8 (CH2), 76.0 (CH), 1.66–1.89 (m, 2H), 4.08 (dd, J = 8.4 Hz, 7.0 Hz, 1H), 4.52 (dd,
155.1 (CvO) ppm; 29Si{1H} NMR (400 MHz, CDCl3, 25 °C): J = 8.1 Hz, 8.1 Hz, 1H), 4.60–4.72 (m, 1H) ppm.
δ = 23.2 ppm; HRMS (ESI-TOF/MS): m/z calcd C10H20O4Na
4-Butyl-1,3-dioxolan-2-one (5c).20b According to GP1, 2-butyl-
[M+ + Na]: 255.1023; m/z found C10H20O4Na [M+ + Na]: oxirane 4c (2.00 g, 20.0 mmol), CaI2 (293 mg, 0.997 mmol),
255.1026; EA: calcd (%) for C10H20O4Si (232.35 g mol−1): 18-crown-6 ether (267 mg, 1.01 mmol) and CO2 were converted
C 51.69, H 8.68; found: C 51.38, H 8.69.
to the desired carbonate. The product 5c (2.79 g, 19.4 mmol,
1
4-((2,2,3,3-Tetrafluoropropoxy)methyl)-1,3-dioxolan-2-one 97%) was obtained as a colourless liquid. H NMR (300 MHz,
(2i).32b According to GP1, 2-((2,2,3,3-tetrafluoropropoxy) CDCl3, 27 °C): δ = 0.92 (t, J = 7.1 Hz, 3H), 1.31–1.53 (m, 4H),
methyl)oxirane 1i (2.00 g, 10.6 mmol), CaI2 (156 mg, 1.62–1.88 (m, 2H), 4.07 (dd, J = 8.4 Hz, 7.2 Hz, 1H), 4.52 (dd,
0.53 mmol), 18-crown-6 ether (141 mg, 0.533 mmol) and J = 8.1 Hz, 8.1 Hz, 1H), 4.64–4.77 (m, 1H) ppm.
CO2 were converted to the desired carbonate. The product 2i
4-Hexyl-1,3-dioxolan-2-one (5d).20b According to GP1, 2-hexyl-
(2.25 g, 9.7 mmol, 91%) was obtained as a colourless liquid. oxirane 4d (2.00 g, 15.6 mmol), CaI2 (229 mg, 0.779 mmol),
1H NMR (300 MHz, CDCl3, 23 °C): δ = 3.84 (m, 4H), 4.50 18-crown-6 ether (208 mg, 0.787 mmol) and CO2 were con-
3
3
(t, J = 8.5 Hz, 1H), 4.50 (q, J = 5.9 Hz, 1H), 4.83 (m, 1H), 5.88 verted to the desired carbonate. The product 5d (2.62 g,
(tt, 2J = 53 Hz, 3J = 4.7 Hz, 1H) ppm.
15.2 mmol, 97%) was obtained as a colourless liquid. H NMR
1
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(300 MHz, CDCl3, 27 °C): δ = 0.89 (t, J = 6.8 Hz, 3H), 1.25–1.52 carbonate. The product 7b (2.45 g, 16.3 mmol, 86%) was
(m, 8H), 1.62–1.88 (m, 2H), 4.06 (dd, J = 8.3 Hz, 7.2 Hz, 1H), obtained as a pale yellow liquid. 1H NMR (300 MHz, CDCl3,
4.52 (dd, J = 8.1 Hz, 8.1 Hz, 1H), 4.64–4.77 (m, 1H) ppm.
25 °C): δ = 1.61 (s, 3H), 3.59 (d, J = 12.0 Hz, 1H), 3.72 (d, J =
4-(Chloromethyl)-1,3-dioxolan-2-one (5e).20b According to 12.0 Hz, 1H), 4.16 (d, J = 8.8 Hz, 1H), 4.50 (d, J = 8.8 Hz, 1H)
GP1, epichlorohydrin 4e (2.00 g, 21.6 mmol), CaI2 (315 mg, ppm.
1.07 mmol), 18-crown-6 ether (291 mg, 1.10 mmol) and CO2
4-(Chloromethyl)-4-ethyl-1,3-dioxolan-2-one (7c). According
were converted to the desired carbonate. The product 5e to GP1, 2-(chloromethyl)-2-ethyloxirane 6c (2.03 g, 16.8 mmol),
(2.76 g, 18.9 mmol, 88%) was obtained as a colourless liquid CaI2 (244 mg, 0.830 mmol), 18-crown-6 ether (219 mg,
with a chloride to iodine ratio of 90 : 10. 1H NMR (300 MHz, 0.829 mmol) and CO2 were converted to the desired carbonate.
CDCl3, 25 °C): C4H5ClO3: δ = 3.72 (dd, J = 12.2 Hz, 3.8 Hz, 1H), The product 7c (2.55 g, 15.5 mmol, 92%) was obtained as a
1
3.80 (dd, J = 12.2 Hz, 5.2 Hz, 1H), 4.40 (dd, J = 8.9 Hz, 5.7 Hz, pale yellow liquid. H NMR (300 MHz, CDCl3, 21 °C): δ = 1.04
1H), 4.59 (t, J = 8.6 Hz, 1H), 4.93–5.05 (m, 1H) ppm; C4H5IO3: (t, 3H), 1.80–2.00 (m, 2H), 3.63 (d, J = 12.0 Hz, 1H), 3.73 (d, J =
δ = 3.35 (dd, J = 10.7 Hz, 7.4 Hz, 1H), 3.41 (dd, J = 10.7 Hz, 12.0 Hz, 1H), 4.20 (d, J = 8.8 Hz, 1H), 4.47 (d, J = 8.8 Hz, 1H)
4.3 Hz, 1H), 4.21 (dd, J = 8.9 Hz, 6.2 Hz, 1H), 4.59 (t, J = 8.6 Hz, ppm; 13C{1H} NMR (75 MHz, CDCl3, 21 °C): δ = 6.9 (CH3), 28.8
1H), 4.75–4.86 (m, 1H), 4.93–5.05 (m, 1H) ppm.
(CH2), 46.8 (CH2), 70.3 (CH), 83.9 (C), 153.9 (CvO) ppm;
4-(7-Oxabicyclo[4.1.0]heptan-3-yl)-1,3-dioxolan-2-one (5f).36a HRMS (ESI-TOF/MS): m/z calcd C6H9ClO3 [M+ + H]: 165.0313;
According to GP1, 3-(oxiran-2-yl)-7-oxabicyclo[4.1.0]heptane 4f m/z found C6H9ClO3 [M+ + H]: 165.0314 m/z calcd C6H9ClO3
(2.00 g, 14.3 mmol), CaI2 (210 mg, 0.715 mmol), 18-crown-6 [M+ + H]: 167.0285; m/z found C6H9ClO3 [M+ + H]: 167.0284.
ether (190 mg, 0.719 mmol) and CO2 were converted to the
Methyl
4-methyl-2-oxo-1,3-dioxolane-4-carboxylate
(7d).
desired carbonate. The crude product was purified by flash According to GP1, methyl 2-methyloxirane-2-carboxylate 6d
chromatography (SiO2, cyclohexane/ethyl acetate = 1 : 1 to 1 : 2) (2.07 g, 17.8 mmol), CaI2 (253 mg, 0.861 mmol), 18-crown-6
and after the removal of all volatiles in vacuo the product 5f ether (228 mg, 0.863 mmol) and CO2 were converted to the
(2.41 g, 13.1 mmol, 92%) was obtained as a colourless liquid. desired carbonate. The product 7d (2.74 g, 17.1 mmol, 96%)
1H NMR (300 MHz, CDCl3, 27 °C) of a mixture of diastereo- was obtained as a colourless liquid. 1H NMR (300 MHz, CDCl3,
isomers: δ = 1.02–2.40 (m, 7H), 3.13–3.30 (m, 2H), 4.10–4.23 25 °C): δ = 1.72 (s, 3H), 3.84 (s, 3H), 4.21 (d, J = 8.9 Hz, 1H),
(m, 1H), 4.35–4.55 (m, 2H) ppm.
4.65 (d, J = 8.9 Hz, 1H) ppm; 13C{1H} NMR (75 MHz, CDCl3,
4-(Morpholinomethyl)-1,3-dioxolan-2-one (5g).35a According 25 °C): δ = 22.0 (CH3), 53.5 (CH3), 72.6 (CH2), 80.9 (C), 153.4
to GP1, 4-(oxiran-2-ylmethyl)morpholine 4g (2.00 g, (CO3), 169.8 (CO2) ppm; HRMS (ESI-TOF/MS): m/z calcd
14.0 mmol), CaI2 (207 mg, 0.704 mmol), 18-crown-6 ether C6H9O5 [M+ + H]: 161.0445; m/z found C6H9O5 [M+ + H]:
(187 mg, 0.707 mmol) and CO2 were converted to the desired 161.0446 m/z calcd C6H8O5Na [M+ + Na]: 183.0264; m/z found
carbonate. The product 5g (2.44 g, 13.0 mmol, 93%) was C6H8O5Na [M+ + Na]: 183.0266; EA: calcd (%) for C6H8O5
obtained as a colourless liquid. 1H NMR (400 MHz, CDCl3, (160.13 g mol−1): C 45.01, H 5.04; found: C 44.98, H 5.07.
24 °C): δ = 2.50–2.60 (m, 4H), 2.65–2.71 (m, 2H), 3.69 (t, J =
4.7 Hz, 4H), 4.23 (dd, J = 8.5 Hz, 7.0 Hz, 1H), 4.53 (dd, J = GP1, 2-methyl-2-phenyloxirane 6e (2.00 g, 14.9 mmol), CaI2
8.3 Hz, 8.3 Hz, 1H), 4.78–4.87 (m, 1H) ppm. (220 mg, 0.749 mmol), 18-crown-6 ether (200 mg, 0.757 mmol)
4-Methyl-4-phenyl-1,3-dioxolan-2-one (7e).41 According to
4-Phenyl-1,3-dioxolan-2-one (5h).20b According to GP1, and CO2 were converted to the desired carbonate. The crude
2-phenyloxirane 4h (2.00 g, 16.6 mmol), CaI2 (246 mg, product was purified by flash chromatography (SiO2, cyclo-
0.837 mmol), 18-crown-6 ether (222 mg, 0.840 mmol) and CO2 hexane/ethyl acetate = 20 : 1 to 5 : 1) and after the removal of
were converted to the desired carbonate. The crude product all volatiles in vacuo the product 7e (0.599 g, 3.36 mmol, 23%)
1
was purified by flash chromatography (SiO2, cyclohexane/ethyl was obtained as a colourless solid. H NMR (300 MHz, CDCl3,
acetate = 5 : 1 to 1 : 1) and after the removal of all volatiles 22 °C): δ = 1.84 (s, 3H), 4.49 (s, 2H), 7.33–7.47 (m, 5H) ppm.
in vacuo the product 5h (2.24 g, 13.6 mmol, 82%) was obtained
cis-Tetrahydro-8H-cyclopenta-1,3-dioxol-2-one (9a).20b According
as a colourless solid. 1H NMR (300 MHz, CDCl3, 27 °C): δ = to GP2, 6-oxabicyclo[3.1.0]hexane 8a (2.01 g, 23.9 mmol), CaI2
4.35 (dd, J = 8.6 Hz, 7.9 Hz, 1H), 4.81 (dd, J = 8.4 Hz, 8.4 Hz, (349 mg, 1.19 mmol), 18-crown-6 ether (314 mg, 1.19 mmol)
1H), 5.68 (dd, J = 8.0 Hz, 8.0 Hz, 1H), 7.33–7.50 (m, 5H) ppm.
and CO2 were converted to the desired carbonate at 45 °C and
4,4-Dimethyl-1,3-dioxolan-2-one (7a).35a According to GP1, p(CO2) = 10 bar in 48 h. The product 9a (2.98 g, 23.3 mmol,
2,2-dimethyloxirane 6a (2.00 g, 27.7 mmol), CaI2 (407 mg, 98%) was obtained as a colourless solid. 1H NMR (300 MHz,
1.38 mmol), 18-crown-6 ether (370 mg, 1.40 mmol) and CDCl3, 25 °C) δ = 1.58–1.83 (m, 4H), 2.08–2.17 (m, 2H),
CO2 were converted to the desired carbonate. The product 7a 5.07–5.12 (m, 2H) ppm.
(2.72 g, 23.4 mmol, 84%) was obtained as a colourless liquid.
1H NMR (400 MHz, CDCl3, 24 °C): δ = 1.52 (s, 6H), 4.15 (s, 2H) to GP2, 3,6-dioxabicyclo[3.1.0]hexane 8b (1.97 g, 22.9 mmol),
cis-Tetrahydrofuro[3,4-d][1,3]dioxol-2-one (9b).20b According
ppm.
CaI2 (341 mg, 1.16 mmol), 18-crown-6 ether (307 mg,
4-(Chloromethyl)-4-methyl-1,3-dioxolan-2-one (7b).10 According 1.16 mmol) and CO2 were converted to the desired carbonate
to GP1, 2-(chloromethyl)-2-methyloxirane 6b (2.01 g, at 45 °C and p(CO2) = 10 bar in 48 h. The product 9b (2.28 g,
1
18.9 mmol), CaI2 (276 mg, 0.939 mmol), 18-crown-6 ether 17.5 mmol, 76%) was obtained as a colourless solid. H NMR
(248 mg, 0.938 mmol) and CO2 were converted to the desired (300 MHz, CDCl3, 25 °C) δ = 3.56 (ddd, J = 12.3 Hz, 2.1 Hz,
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1.1 Hz, 2H), 4.24 (dd, J = 11.0 Hz, 1.3 Hz, 2H), 5.21 (dd, J = 2.1 1H NMR (300 MHz, CDCl3, 25 °C): δ = 1.25–1.37 (m, 2H),
Hz, 1.2 Hz, 2H) ppm. 1.41–1.55 (m, 1H), 1.58–1.69 (m, 1H), 1.74–2.01 (m, 6H),
cis-Cyclohexene carbonate (9c).20b According to GP2, cyclo- 4.78–4.86 (m, 2H) ppm.
hexene oxide 8c (2.01 g, 20.5 mmol), CaI2 (299 mg,
trans-4,5-Dimethyl-1,3-dioxolan-2-one (11a).20b According to
1.02 mmol), 18-crown-6 ether (269 mg, 1.02 mmol) and CO2 GP2, trans-2,3-dimethyloxirane 10a (1.97 g, 27.3 mmol), CaI2
were converted to the desired carbonate at 45 °C and p(CO2) = (408 mg, 1.39 mmol), 18-crown-6 ether (367 mg, 1.39 mmol)
10 bar in 48 h. The product 9c (2.85 g, 20.1 mmol, 98%) was and CO2 were converted to the desired carbonate at 45 °C and
obtained as a colourless solid. 1H NMR (300 MHz, CDCl3, p(CO2) = 10 bar in 48 h. The product 11a (2.73 g, 23.5 mmol,
25 °C) δ = 1.35–1.47 (m, 2H), 1.54–1.67 (m, 2H), 1.84–1.93 86%) was obtained as a colourless solid. 1H NMR (300 MHz,
(m, 4H), 4.64–4.71 (m, 2H) ppm.
CDCl3, 25 °C) of the trans isomer: δ = 1.40–1.46 (m, 6H),
cis-3a,4,5,7a-Tetrahydrobenzo[d][1,3]dioxol-2-one (9d).42 4.28–4.37 (m, 2H) ppm.
According to GP2, 7-oxabicyclo[4.1.0]hept-2-ene 8d (1.97 g,
cis-4,5-Dimethyl-1,3-dioxolan-2-one (11b).20b According to
22.9 mmol), CaI2 (341 mg, 1.16 mmol), 18-crown-6 ether GP2, cis 2,3-dimethyloxirane 10b (1.97 g, 27.3 mmol), CaI2
(307 mg, 1.16 mmol) and CO2 were converted to the desired (408 mg, 1.39 mmol), 18-crown-6 ether (367 mg, 1.39 mmol)
carbonate at 45 °C and p(CO2) = 10 bar in 48 h. The product 9d and CO2 were converted to the desired carbonate at 45 °C and
(2.28 g, 17.5 mmol, 76%) was obtained as a colourless solid. p(CO2) = 10 bar in 48 h. The product 11b (2.76 g, 23.8 mmol,
1H NMR (300 MHz, CDCl3, 25 °C): δ = 1.86–1.97 (m, 1H), 87%) was obtained as a colourless solid and with a cis : trans
1.99–2.14 (m, 2H), 2.23–2.36 (m, 1H), 4.87–4.93 (m, 1H), ratio of 91 : 9. 1H NMR (300 MHz, CDCl3, 25 °C) of the cis
4.99–5.03 (m, 1H), 5.74–5.80 (m, 1H), 6.19–6.35 (m, 1H) ppm.
isomer: δ = 1.29–1.37 (m, 6H), 4.77–4.87 (m, 2H); trans isomer:
5-Methylhexahydrobenzo[d][1,3]dioxol-2-one (9e).36a According δ = 1.40–1.45 (m, 6H), 4.29–4.34 (m, 2H) ppm.
to GP2, 3-methyl-7-oxabicyclo[4.1.0]heptane 8e (2.03 g,
trans-4,5-Diphenyl-1,3-dioxolan-2-one (11c).20b According to
18.1 mmol), CaI2 (262 mg, 0.891 mmol), 18-crown-6 ether GP2, trans stilbene oxide 10c (0.508 g, 2.59 mmol), CaI2
(236 mg, 0.893 mmol) and CO2 were converted to the desired (37 mg, 1.26 mmol), 18-crown-6 ether (34 mg, 1.29 mmol) and
carbonate at 45 °C and p(CO2) = 10 bar in 48 h. The product 9e CO2 were converted to the desired carbonate at 45 °C and
(1.28 g, 8.20 mmol, 45%) was obtained as a colourless liquid. p(CO2) = 10 bar in 48 h. The product 11c (0.608 g, 2.53 mmol,
1H NMR (300 MHz, CDCl3, 25 °C) of a mixture of diastereo- 98%) was obtained as a colourless solid. 1H NMR (300 MHz,
isomers dr = 50 : 50; δ = 0.94–0.99 (m, 6H), 1.15–1.24 (m, 2H), CDCl3, 25 °C): δ = 5.45 (s, 2H), 7.31–7.36 (m, 4H) 7.43–7.48 (m,
1.32–1.42 (m, 2H), 1.54–1.75 (m, 6H), 2.01–2.33 (m, 4H), 6H) ppm.
4.58–4.76 (m, 4H) ppm.
trans-4-Methyl-5-phenyl-1,3-dioxolan-2-one (11e).43 According
cis-5-Vinylhexahydrobenzo[d][1,3]dioxol-2-one (9f).36a According to GP2, trans 2-methyl-3-phenyloxirane 10e (1.95 g,
to GP2, 3-vinyl-7-oxabicyclo[4.1.0]heptane 8f (1.99 g, 14.5 mmol), CaI2 (219 mg, 0.745 mmol), 18-crown-6 ether
16.0 mmol), CaI2 (237 mg, 0.806 mmol), 18-crown-6 ether (197 mg, 0.745 mmol) and CO2 were converted to the desired
(213 mg, 0.806 mmol) and CO2 were converted to the desired carbonate at 45 °C and p(CO2) = 10 bar in 48 h. The product
carbonate at 45 °C and p(CO2) = 10 bar in 48 h. The product 9f 11e (2.32 g, 13.0 mmol, 90%) was obtained as a colourless
(2.65 g, 15.8 mmol, 99%) was obtained as a colourless liquid. solid. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 1.55 (d, J = 6.2 Hz,
1H NMR (300 MHz, CDCl3, 25 °C) of a mixture of diastereo- 3H), 4.56–4.65 (m, 1H), 5.13 (d, J = 8.0 Hz, 1H), 7.34–7.40 (m,
isomers dr = 50 : 50; δ = 1.11–1.24 (m, 1H), 1.28–1.43 (m, 2H), 2H), 7.40–7.48 (m, 3H) ppm.
1.52–1.86 (m, 5H), 1.95–2.03 (m, 1H), 2.10–2.39 (m, 5H),
4.61–4.80 (m, 4H), 4.98–5.08 (m, 4H), 5.67–5.80 (m, 2H) ppm.
trans-Ethyl-2-oxo-5-phenyl-1,3-dioxolane-4-carboxylate (11g).35b
According to GP3, trans ethyl 3-phenyloxirane-2-carboxylate
cis-5-(2-Oxo-1,3-dioxolan-4-yl)hexahydrobenzo[d][1,3]dioxol- 10g (1.962 g, 10.2 mmol), CaI2 (153 mg, 0.521 mmol),
2-one (9g).36a According to GP2, 3-(oxiran-2-yl)-7-oxabicyclo 18-crown-6 ether (138 mg, 0.522 mmol) and CO2 were con-
[4.1.0]heptane 8g (1.96 g, 14.0 mmol), CaI2 (33 mg, verted to the desired carbonate at 45 °C and p(CO2) = 10 bar in
0.112 mmol), 18-crown-6 ether (29 mg, 0.110 mmol) and CO2 48 h. The product 11g (1.723 g, 7.29 mmol, 71%) was obtained
1
were converted to the desired carbonate at 45 °C and p(CO2) = as a colourless liquid. H NMR (300 MHz, CDCl3, 25 °C): δ =
10 bar in 48 h. The product 9g (2.15 g, 9.42 mmol, 67%) was 1.36 (t, J = 7.1 Hz, 3H), 4.33–4.41 (qd, J = 7.1, 1.1 Hz, 2H),
obtained as a colourless liquid. 1H NMR (300 MHz, CDCl3, 4.91 (d, J = 5.6 Hz, 1H), 5.66 (d, J = 5.7 Hz, 1H), 7.36–7.50 (m,
27 °C) of a mixture of diastereoisomers; δ = 1.23–1.38 (m, 2H), 5H) ppm.
1.45–1.64 (m, 2H), 1.62–1.81 (m, 4H), 1.91–2.05 (m, 2H),
2.02–2.20 (m, 2H), 2.30–2.42 (m, 2H), 4.18–4.24 (m, 2H), According to GP3, trans (3-phenyloxiran-2-yl)methanol 10h
4.51–4.61 (m, 4H), 4.71–4.91 (m, 4H) ppm. (0.507 g, 3.38 mmol), CaI2 (49 mg, 0.167 mmol), 18-crown-6
trans-4-(Hydroxymethyl)-5-phenyl-1,3-dioxolan-2-one (11h).39a
cis-Hexahydro-4H-cyclohepta[d][1,3]dioxol-2-one (9h).36a ether (44 mg, 0.166 mmol) and CO2 were converted at 45 °C
According to GP2, 8-oxabicyclo[5.1.0]octane 8h (0.519 g, and p(CO2) = 10 bar in 48 h. The product of this conversion
4.63 mmol), CaI2 (66 mg, 0.225 mmol), 18-crown-6 ether was a mixture of 11h and 11i in a ratio of 12 : 88. This mixture
(59 mg, 0.223 mmol) and CO2 were converted to the desired (0.538 g, 2.77 mmol, 82%) was obtained as a colourless solid.
carbonate at 45 °C and p(CO2) = 10 bar in 48 h. The product 9h 1H NMR (300 MHz, CDCl3, 25 °C): δ = 3.30–3.33 (m, 1H),
(0.702 g, 4.49 mmol, 97%) was obtained as a colourless solid. 4.31–4.38 (m, 2H), 4.82–4.93 (m, 2H), 7.34–7.48 (m, 5H).
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4-(Hydroxy(phenyl)methyl)-1,3-dioxolan-2-one
(11i).38
Ed., 2015, 54, 11686–11690; (c) R. Ninokata, T. Yamahira,
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A. W. Kleij, J. Am. Chem. Soc., 2016, 138, 14194–14197;
(e) L.-C. Yang, Z.-Q. Rong, Y.-N. Wang, Z. Y. Tan, M. Wang
and Y. Zhao, Angew. Chem., Int. Ed., 2017, 56, 2927–2931.
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Chem. – Eur. J., 2010, 16, 6828–6843; (b) A. Buchard,
M. R. Kember, K. G. Sandeman and C. K. Williams, Chem.
Commun., 2011, 47, 212–214; (c) J. A. Castro-Osma,
K. J. Lamb and M. North, ACS Catal., 2016, 6, 5012–5025;
(d) J. A. Castro-Osma, M. North and X. Wu, Chem. – Eur. J.,
2016, 22, 2100–2107; (e) X. Wu and M. North,
ChemSusChem, 2016, 10, 74–78.
8 (a) M. H. Beyzavi, R. C. Klet, S. Tussupbayev, J. Borycz,
N. A. Vermeulen, C. J. Cramer, J. F. Stoddart, J. T. Hupp
and O. K. Farha, J. Am. Chem. Soc., 2014, 136, 15861–15864;
(b) Z.-R. Jiang, H. Wang, Y. Hu, J. Lu and H.-L. Jiang,
ChemSusChem, 2015, 8, 878–885; (c) P.-Z. Li, X.-J. Wang,
J. Liu, J. S. Lim, R. Zou and Y. Zhao, J. Am. Chem. Soc.,
2016, 138, 2142–2145; (d) A. C. Kathalikkattil, R. Roshan,
J. Tharun, R. Babu, G.-S. Jeong, D.-W. Kim, S. J. Cho and
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According to GP3, trans (3-phenyloxiran-2-yl)methanol 10h
(0.507 g, 3.38 mmol), CaI2 (49 mg, 0.167 mmol), 18-crown-6
ether (44 mg, 0.166 mmol) and CO2 were converted at 45 °C
and p(CO2) = 10 bar in 48 h. The product of this conversion
was a mixture of 11h and 11i in a ratio of 12 : 88. This mixture
(0.538 g, 2.77 mmol, 82%) was obtained as a colourless solid.
1H NMR (300 MHz, CDCl3, 25 °C) of the trans isomer: δ =
3.03–3.07 (m, 1H), 3.76–3.83 (m, 1H), 4.04–4.10 (m, 1H),
4.57–4.62 (m, 1H), 5.62 (d, J = 7.1 Hz, 1H) 7.34–7.48 (m, 5H)
ppm.
Acknowledgements
This research project is part of the Leibniz ScienceCampus
Phosphorus Research Rostock and is co-funded by the funding
line strategic networks of the Leibniz Association. Furthermore
we thank Christoph Grimmer, Lars Longwitz and Prof.
Dr Matthias Beller for their support and advice.
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