Cooperative Multifunctional Organocatalysts for Ambient Conversion of Carbon Dioxide into Cyclic Carbonates

Article abstract of DOI:10.1021/acscatal.8b01925

A series of pincer-type compounds possessing an N-heterocyclic carbene precursor and a carboxyl group as proton transfer agent were synthesized and used as organocatalysts for the cycloaddition of epoxides with CO₂. In this context, we have demonstrated the high activity of these one-component organocatalysts in the CO₂ transformation to cyclic carbonates under ambient conditions (room temperature, 1 bar of CO₂). The catalytic potential of these multifunctional organocatalysts on challenging internal epoxides is particularly deserving of mention because organocatalysts that are able to mediate the cycloaddition reaction of internal epoxides with CO₂ under mild conditions remain scarce. The intramolecular synergistic activation mechanism was elucidated by control experiments and DFT calculations.

Full text of DOI:10.1021/acscatal.8b01925

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Article
Cooperative Multi-Functional Organocatalysts for Ambient
Conversion of Carbon Dioxide into Cyclic Carbonates
Ning Liu, Ya-Fei Xie, Chuan Wang, Shi-Jun Li, Dong-Hui Wei, Min Li, and Bin Dai
ACS Catal., Just Accepted Manuscript • Publication Date (Web): 14 Sep 2018
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Cooperative MultiꢀFunctional Organocatalysts for
Ambient Conversion of Carbon Dioxide into Cyclic
Carbonates
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†
Ning Liu,*, YaꢀFei Xie,† Chuan Wang,‡ ShiꢀJun Li,§ Donghui Wei,*,§
†
Min Li,† Bin Dai,*,
†School of Chemistry and Chemical Engineering, Key Laboratory for
Green Processing of Chemical Engineering of Xinjiang Bingtuan, Shihezi
University, North Fourth Road, Shihezi, Xinjiang, 832003, People’s
Republic of China
‡Department of Chemistry, University of Science and Technology of
China, 96 Jinzhai Road, Hefei, Anhui 230026, People’s Republic of
China
§College of Chemistry and Molecular Engineering, Center of
Computational Chemistry, Zhengzhou University, 100 Science Avenue,
Zhengzhou, Henan Province, 450001, People’s Republic of China
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ABSTRACT: A series of pincerꢀtype compounds possessing an Nꢀheterocyclic
carbene precursor and a carboxyl group as proton transfer agent were synthesized
and used as organocatalysts for the cycloaddition of epoxides with CO2. In this
context, we have demonstrated the high activity of these oneꢀcomponent
organocatalysts in the CO2 transformation to cyclic carbonates under ambient
conditions (room temperature, 1 bar of CO2). The catalytic potential of these
multiꢀfunctional organocatalysts on challenging internal epoxides is particularly
deserved to be mentioned because organocatalysts being able to mediate the
cycloaddition reaction of internal epoxides with CO2 under mild conditions remain
scarce. The intramolecular synergistic activation mechanism was elucidated by
control experiments and DFT calculations.
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KEYWORDS: carbon dioxide, cyclic carbonate, multiꢀfunctional organocatalyst,
metalꢀfree, cycloaddition
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Introduction
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Carbon dioxide utilized as an abundant, inexpensive, and renewable C1 building
block for the synthesis of cyclic carbonates represents a much more sustainable
alternative to the use of phosgene.1 Cyclic carbonates are an important class of
compounds that can be utilized as intermediates for preparation of fine chemicals,2
as electrolytes in lithium ion batteries,3 and raw materials for polymers.4 Given the
importance of cyclic carbonates, many catalytic systems for this transformation
have been developed over the past decade to achieve this type of compounds.5
Among these methods of organocatalyzed cycloadditons between CO2 and
epoxides represents an attractive approach to cyclic carbonates, because
organocatalysts are usually lowꢀcost, readily available, and free of metal
contaminants.6 To date, a wide range of organocatalysts for this transformation
have been developed, such as imidazolium salts,7 organic amines,8 phosphonium
salts,9 ammonium salts,10 and phenols,11 have been developed. Despite the growing
number of organocatalysts, organocatalytic systems aforementioned still suffer
from some disadvantages in the synthetic point of view: low activity, high catalyst
loading, poor substrate scope, and harsh reaction conditions.12 Recent
developments in the area of cyclic carbonates synthesis have demonstrated that
careful design of catalysts plays a significant role for tuning the catalytic activity.
For instance, Shirakawa et al. demonstrated that triethylamine hydroiodide is an
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effective oneꢀcomponent catalyst for the coupling of terminal epoxides with CO2 at
40 °C under ambient pressure.13 D’Elia et al. discovered an environmentally
benign binary system of ascorbic acid with TBAI (tetrabutylammonium iodide).
This work reported the successful conversion of terminal epoxides with CO2 to
cyclic carbonates under ambient conditions.14 Another contribution by Lu and
coꢀworkers was described that the phosphorus ylide CO2 adducts are able to
effectively catalyze the conversion of terminal epoxides and CO2 into cyclic
carbonates under ambient conditions.15 More recently, Kleij and coꢀworkers
developed binary organocatalytic systems based on squaramide scaffold that are
highly active catalysts for the cycloaddition reaction between internal epoxides and
CO2 at 80 °C under 30 bar of CO2.16 Therefore, the development of a
oneꢀcomponent catalyst that can be effective for the conversion of internal
epoxides under mild conditions is a still a challenging task.
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Recent reports have demonstrated that bifunctional imidazolium halides or
quaternary phosphonium salts possessing a hydroxyl17 or carboxyl groups,18 play
an imperative role in activating of epoxides by the hydrogenꢀbonding donor group.
Meanwhile, He and coꢀworkers have proved that the amino acid salts are capable
of capturing one equivalent of CO2 through the insertion of CO2 into NꢀH bond.19
Bowen et al. found that CO2 can bind to the quinoline N atom to form the
(quinolineꢀCO2) anionic complex.20 In addition, previously reported catalysts and
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catalytic systems showed that NHC (Nꢀheterocyclic carbenes) can react with CO2
to form NHCꢀCO2 adducts.18b,f These recent advances promoted our interest in the
design of effective multiꢀfunctional catalysts which allow the simultaneous
activation of CO2 and the epoxide. Since the pyridine ring is a typical electronic
transfer structure, it is an alternative bridge for the design of multiꢀfunctional
catalysts through varying functional groups attached. Recently, we reported
pyridineꢀbridged benzimidazolium salt and pincerꢀtype iron(II) complexes that
show interesting potential toward epoxide/CO2 couplings.21 Amino acids are
readily available and environmentally benign natural products,22 which consist of a
combination of a carboxyl group as a Brønsted acid and an amino group as CO2
activating agent. It is highly desired to design and synthesize a multiꢀfunctional
catalyst, which is composed of a Brønsted acidic site, a nucleophilic site, and CO2
absorbent and activating sites through introduction of a benzimidazolium salt and
an amino acid to a pyridine ring (Figure 1). In this work, we demonstrate that
oneꢀcomponent, neat, and highly active multiꢀfunctional catalysts can offer a
competitive alternative to metal catalysis in the conversion of terminal and internal
epoxide under mild conditions.
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Figure 1. Design and active sites of catalyst.
Results and Discussion
Seven multiꢀfunctional organocatalysts 1a−g (Scheme 1) were prepared according
to procedures reported previously.23 We first report a series of organocatalysts with
multiꢀactive sites: amino groups, pyridine N atom and preꢀNHC (NHC,
Nꢀheterocyclic carbenes precursor) for CO2 capture and activation, carboxyl
groups for epoxides activation and halide anion for nucleophilic ring opening.
Scheme 1. Synthesis of multiꢀfunctional organocatalysts.
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The catalytic performance of all the resultant multiꢀfunctional catalysts 1a−g was
investigated, and the coupling between PO (propylene epoxide) and CO2 was
chosen as a benchmark reaction at 80 °C with CO2 pressure of 5 bar. The obtained
results indicated that the catalyst 1e containing phenolic hydroxyl group (Table 1,
entry 5) was catalytically more active than other catalysts (Table 1, entries 1ꢀ4).
The function of carboxyl group and phenolic hydroxyl group in this reaction is
generally used as a hydrogen bond donor. To investigate the hydrogen bonding
interaction between PO and two hydrogen bond donors, in situ FTIR studies were
carried out (see the Supporting Information for details). When PO was added into
the catalysts, the characteristic FTIR band at 1725 cmꢀ1 reduced continuously
which corresponds to the v(C=O) stretching vibration of carboxyl group (Figure
S1). However, the v(OH) bending vibration of phenolic hydroxyl group in the
range of 700ꢀ800 cmꢀ1 has not significant change during the addition of PO into the
catalyst system (Figure S2). Qualitative NMR titration methods were also used to
investigate the function of two hydrogen bond donors. Upon addition of PO to the
catalyst 1e, shifting of the resonance of COOH proton and OH proton was not
observed (Figure S5). However, gradual weakening of the resonance of COOH
proton was observed (Figure S5), which was consistent with what observed in the
in situ FTIR analysis. In order to exclude the HꢀD exchange between COOH
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1
proton and deuterium reagents, a H NMR detection of catalyst 1e in deuterium
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reagents without adding PO for overnight was performed. The result indicated that
the chemical signal of COOH proton was unchanged. The resonance of carbon of
COOH shifted downfield from δ = 174.60 to 175.17 ppm, however, shifting of the
resonance of aromatic carbon attaching OH was not observed (Figure S6). These
results indicated that COOH reacted with PO through a proton transfer process
rather than remaining at the stage of the hydrogen bonding interactions. We have
additionally considered the pathway where the epoxide is activated by the phenol
via transition state TS2’’ (Figure S8). The energy barrier via transition state TS2’’
is 25.0 kcal/mol, which is higher than that via transition state TS2 (21.2 kcal/mol),
so we can safely exclude the pathway using phenol as the Brønsted acid.
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The effect of the counterꢀanions on the catalytic performance was also studied.
The catalytic activity of 1e, 1f, and 1g, which bear I−, Br−, and Cl− ions,
respectively, increased in the order 1e > 1f > 1g (I−, Br−, and Cl−; Table 1, entries
5, 6, and 7). Subsequently, we investigated the performance of catalyst under
various reaction conditions (Table 1, entries 8–14). When the reaction temperature
was lowered from 80 °C to room temperature, we were delighted to observe a 26%
yield of 3a in 4 h (Table 1, entry 10) and a slightly higher yield (37%) could be
obtained by a prolonged reaction time to 24 h (Table 1, entry 11). Furthermore, the
influence of the CO2 pressures on the outcome of the reaction was also evaluated.
When the CO2 pressure was decreased from 5 bar to 1 bar, the yield was reduced
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from 37% to 29% (Table 1, entries 11 and 12). To our delight, the catalyst loading
has an evident effect on catalytic performance. When the catalyst loading of 1e
was increased from 1 mol% to 4 mol%, the yield of 3a reached 96% at ambient
condition (Table 1, entry 14).
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Table 1. Optimization of PC Synthesisa
entry catalyst (mol%)
temperature (°C)
CO2 (bar)
time (h) yield (%)
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8
1a (1.0)
1b (1.0)
1c (1.0)
1d (1.0)
1e (1.0)
1f (1.0)
1g (1.0)
1e (1.0)
1e (1.0)
1e (1.0)
1e (1.0)
1e (1.0)
1e (2.0)
1e (4.0)
80
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80
80
80
80
80
60
40
r.t.
r.t.
r.t.
r.t.
r.t.
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4
24
24
24
24
77
68
52
57
99
79
61
79
53
26
37
29
75
96
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5
1b
1b
1b
aReaction conditions unless specified otherwise: PO (10.0 mmol), catalyst (as indicated in this
table), neat, the reactions involving a CO2 pressure higher than 1 bar were carried out in a 25 mL
stainless steel autoclave, yield was determined by GC using biphenyl as an internal standard.
bCO2 balloon.
Under the optimized reaction conditions, the terminal epoxides scope was then
evaluated, and the results are demonstrated in Table 2. This protocol can tolerate
the presence of various aliphatic substituents of the terminal epoxides and give
cyclic carbonate products 3a−3j in 73%−95% yield under ambient (room
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temperature, one bar of CO2), solventꢀfree and additiveꢀfree conditions. The
electronic effect of the substituents of terminal epoxides is significant. The
terminal epoxides bearing aliphatic groups had relatively high reactivity than those
with aryl groups (3a−3j vs 3l). The terminal epoxides 2l required an increased the
reaction temperature to 40 °C, to achieve 89% yield (3l in Table 2). Upon
increasing the temperature to 40 °C while still maintaining a bar of CO2, substrate
2m reacted smoothly to obtain 87% yield (3m in Table 2). Moreover, substrate 2k
also required a higher reaction temperature (40°C) due to its high melting point (3k
in Table 2).
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Table 2. Scope of terminal epoxidesa
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aConditions: PO (10.0 mmol), 1e (0.4 mmol, 4 mol%), room temperature, 1 bar of CO2 (balloon),
24 h, neat. isolated yield. b40 °C.
Internal epoxides are challenging substrates in cycloaddition reaction with CO2
owing to their high steric hindrance (Table 3). These were also evaluated in our
catalytic system. Increased reaction temperature were required to achieve the high
yields of desired products. For example, when 1,2ꢀdimethyloxirane was used, the
cyclic carbonate product 4a was obtained with 83% yield at 80 °C with a CO2 of 1
bar. Next, several bicyclic epoxides were examined and could be converted into
their cyclic carbonates 4bꢀd in good yields and chemoselectivities. In addition to
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sixꢀmembered bicyclic cyclohexene oxide was converted into the corresponding
carbonate 4b in an isolated yield of 95%, fiveꢀmembered bicyclic epoxides could
be also converted into their carbonates 4c and 4d in good yields. Oxetanes are
particularly challenging substrates because of their lower ring strain. When an
unsubstituted oxetane was employed as substrate only yield of 37% was obtained
(4e in Table 3).
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The conversion of internal epoxides such as epoxidized fatty acid esters is
challenging because of highly steric hindrance.24 Subsequently, the scope of our
protocol for the synthesis of fatty acid based bioꢀcarbonates was investigated
(Table 3). Under the reaction conditions of 100 °C and 5 bar of CO2, carbonate 4f
was isolated in a yield of 51%. The epoxidized ethyl oleate was also converted and
the corresponding carbonate 4g was obtained in a moderate yield. The cyclic
carbonate 4h originating from erucic acid was also isolated in a yield of 48%. Two
epoxideꢀfunctionalized carbonate 4i was obtained in an isolated yield of 43%,
although the reaction time had to be prolonged to 48 h.
Table 3. Scope of internal epoxidesa
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aConditions: PO (10.0 mmol), 1e (0.4 mmol, 4 mol%), 80 °C, 1 bar of CO2 (balloon), 24 h, neat.
isolated yield. b100 °C, 5 bar of CO2, 24 h. c100 °C, 5 bar of CO2, TBAI (12 mol%), 48 h.
Table 4 lists several reported organocatalytic systems employed under ambient
conditions. D’Elia and coꢀworkers reported ascorbic acid/TBAI catalytic system.14
Under ambient conditions, a TON of 16 and a TOF of 0.7 were achieved using PO
as model substrate (Table 4, entry 1). The TON = 18 and TOF = 3 was reported by
Lu et al. using the phosphorusꢀylideꢀCO2 adducts as catalysts (Table 4, entry 2).15
To the best of our knowledge, this is the highest TON and/or TOF for the
literatures reported organocatalysts under ambient conditions. When 4 mol%
catalyst loading was employed, a TON of 24 and a TOF of 1.0 were achieved in
our developed catalytic system (Table 4, entry 3). Lowing catalyst loading to 2
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mol% could increase slightly TON and TOF value (Table 4, entry 4). These results
indicated that this work also are proved to be highly active catalysts, which are
commensurate with the catalysts reported by Lu et al.15
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Table 4. Comparison of Catalytic Activity of Catalysts
entry ref.
yield (%)
TON
16
18
24
38
TOF (hꢀ1)
0.70
3.0
1.0
1.6
1
2
3
4
Ref. 14a
64
90
96
75
Ref. 15b
this workc
this workd
a
Conditions: PO (25.0 mmol), ascorbic acid (4 mol%), TBAI (8 mol%), r.t., 1 bar of CO2
(balloon), neat, 23 h. PO (10.0 mmol), PꢀYlideꢀCO2ꢀadducts (5 mol%), r.t., 1 bar of CO2
(balloon), neat, 6 h. PO (10.0 mmol), 1e (4 mol%), r.t., 1 bar of CO2 (balloon), neat, 24 h. PO
(10.0 mmol), 1e (2 mol%), r.t., 1 bar of CO2 (balloon), neat, 24 h. TON, turnover number; TOF,
turnover frequency (TOF = TON/reaction time (h)).
b
c
d
The use of enantiopure terminal epoxides as substrates gave us the opportunity
to gain insight into the reaction mechanism. We investigated the mechanism of this
multiꢀfunctionalꢀcatalyzed reaction from the viewpoint of stereochemistry using
(R)ꢀ2l. As shown in scheme 2, the (R)ꢀ2l was converted preferentially into the
(R)ꢀ3l with the retention of the configuration in a ratio of 85:15. The retention of
the configuration in the cyclic carbonate product (R)ꢀ3l suggests that (R)ꢀ2l attacks
preferentially at the methylene carbon (less hindered carbon atom).
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Scheme 2. Investigation of the Reaction Mechanism by Using an Optically Pure Epoxide.
To clarify the effect of the counterꢀanions on the catalysts, we used pure
transꢀ2,3ꢀepoxybutane to reveal some mechanistic insights into reaction pathways
(Table 5). When 1f (Brꢀ) and 1g (Clꢀ) are used as catalysts, transꢀ3n and cisꢀ3n
were obtained in a ratio of 92:8 and 97:3, respectively (Table 5, entries 2 and 3).
However, the use of the organocatalyst 1e resulted in some epimerization from the
original configuration of the starting epoxides (Table 5, entry 1). This result
suggests that the 1eꢀmediated reaction undergoes different reaction pathway
compared with 1f and 1g.
Table 5. Possible Reaction Pathways for 1e−g Catalyzed the Conversion of
transꢀ2,3ꢀEpoxybutane into cisꢀ and transꢀCyclic Carbonate.a
entry
catalyst
1e
1f
cisꢀ4a (%)b
57
8
transꢀ4a (%)b
43
92
97
total yield (%)c
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58
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3
3
1g
aConditions: transꢀ2,3ꢀepoxybutane (10.0 mmol), catalyst (0.4 mmol, 4 mol%), 80 °C, 1 bar of
CO2 (balloon), 24 h, neat, isolated yield. bDetermined by 1H and 13C NMR (CDCl3) from the raw
reaction mixture.5d,25 cIsolated yield.
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In order to prove the synergistic action between the imidazolium and amino acid
moieties whether occurs in intramolecular interactions or in intermolecular
interactions. A control experiment was carried out using a binary catalyst system
combining a pyridineꢀsubstituted benzimidazolium salt (1h in Scheme 3, eqn. 1)
with a pyridineꢀsubstituted tyrosine (1i in Scheme 3, eqn. 1). Previous literatures
reported that phenol is an active organocatalytic moiety for the cycloaddition of
CO2 to epoxides. So the 1h/phenol binary system was also tested for the
cycloaddition of CO2 to PO under ambient conditions. However, only 5% yield of
product was obtained (Scheme 3, eqn. 2). The results showed that twoꢀcomponent
catalytic system was proved to be difficult to trigger this reaction at ambient
condition (Scheme 3, eqns. 1 and 2), suggesting that the unique pincerꢀtype
structures of our developed catalysts provide CO2 and epoxides a chance for
intramolecular interactions.
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To explore the effect of carboxyl group on this reaction, a catalyst was
synthesized by the esterification of carboxylic acid (1j in Scheme 3, eqn. 3). In the
absence of carboxyl proton, only 9% of yield was obtained (Scheme 3, eqn. 3). The
results showed that the existence of carboxyl group is essential for the highly
catalytic performance.
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The effect of amino group were also investigated (Scheme 3, eqn. 4). When
amino group being protected by methyl group (1k in Scheme 3, eqn. 4), the
catalytic activity of catalyst 1k is almost not affected and a slightly lower yields
(93% yield in Scheme 3, eqn. 4) was obtained compared with the catalyst 1e (96%
yield in Table 1, entry 14). We also investigated possible process of CO2 binding to
amino group by DFT calculations. However, this process is impossible due to the
high Gibbs free energy barrier, and more details can be found in the Supporting
Information. The results suggest that the effect of amino group is negligible in this
reaction.
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Scheme 3. Study on Active Sites of Catalysts.
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To determine whether CO2 preferentially binds to the C2 position of the
benzimidazolium ring, a catalyst was designed by introducing the methyl group to
the C2 position of the benzimidazolium ring (1l in Scheme 3, eqn. 5). The result
showed that the alkylation of the C2 position leads to a significant decrease of
product yield, which might be caused by the lack of interaction between CO2 and
the C2 position of catalyst.
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In addition, we have considered and investigated the two possible activation
processes of CO2 catalyzed by both of the two different nitrogen atoms (i.e. the N
atoms of amino group and pyridine) using DFT calculations (Scheme S1). The
calculated results indicated that the free energy changes and Gibbs free energy
barrier of the possible pathways would be too high to overcome, so we think the
pyridine N atom cannot directly work as catalyst to activate the CO2 molecule.
This was also confirmed by in situ FTIR. The CꢀC bond and CꢀH bond stretching
vibration of the pyridine ring in the range of 700ꢀ1100 cmꢀ1 have no change in
wavelengths during the addition of CO2 into the catalyst system (Figures S3ꢀ4).
More details can be found in the Supporting Information.
In order to clarify the detailed mechanisms, we have additionally carried out
theoretical calculations by using DFT method, which has been widely applied in
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the mechanistic studies.26 As shown in Scheme 4, preꢀNHC can be transferred to
NHC (Nꢀheterocyclic carbene) by the release of a molecule of HX (X=I, Br, and
Cl), so the efficiency of catalyst would be the best when X=I, which is in
agreement with the experimental observation that the yield is the highest when X is
I. Firstly, the carbene carbon of NHC catalyst would nucleophilically attack on the
carbon atom of CO2 to generate zwitterionic intermediate M1 via transition state
TS1. Secondly, the negatively charged oxygen nucleophilically attacks on the
epoxy carbon of reactant transꢀR1, which is accompanied with the
threeꢀmembered ring opening and a proton transfer process for the formation of
intermediate M2 via transition state TS2. Then, the intermediate M2 can be
structurally transformed to intermediate M3 by the C−C single bond rotation.
Subsequently, it is the fiveꢀmembered ring closure process coupled with the other
proton transfer for affording intermediate M4 via transition state TS3. The last
process is the dissociation of NHC catalyst with product cisꢀP via transition state
TS4. As shown in Figure 2, the Gibbs free energy barriers via the transition states
TS1, TS2, TS3, and TS4 are 1.2, 23.6, 0.2, and 8.1 kcal/mol, so the epoxy ring
opening should be the rateꢀdetermining step. Interestingly, the organocatalyst has
two functions, the one is to work as Lewis base NHC to activate the CO2, and the
other is to provide and abstract the proton as Brønsted acid/base.
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Alternatively, we also considered the possible pathways associated with the
product transꢀP. As depicted in Scheme 4, the negatively charged oxygen of
intermediate M1 can also nucleophilically attack on the epoxy carbon of reactant
transꢀR1 from the other side, which leads to the formation of intermediate M2′ via
transition state TS2′. However, the energy barrier via TS2′ is extremely high (39.5
kcal/mol, Figure 2), so we can safely exclude this pathway. Besides, the
intermediate M2 can also react with another molecule of CO2 to form intermediate
M5 via transition state TS5, and then the product transꢀP can be dissociated with
the intermediate M1 through a SN2ꢀtype transition state TS6 (Scheme 4). As
shown in Figure 2, the process associated with TS6 is the rateꢀdetermining step for
this pathway leading to the transꢀP. It should be mentioned that the energy
(without the correction) of intermediate M5 is lower than that of transition state
TS5, but the free energy (with the thermal correction) of intermediate M5 (11.1
kcal/mol) is slightly higher than that of transition state TS5 (9.6 kcal/mol).
Furthermore, other possible pathway, including the activation processes of CO2
catalyzed by preꢀNHC and the epoxy ring opening through nucleophilic attack by
Iꢀ, was also investigated, and more details can be found in the Supporting
Information.
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When X is I, we think the stereoselectivity is kinetically controlled, and the
energy barrier of the whole reaction leading to cisꢀP via TS2 (23.6 kcal/mol) is
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slightly lower than that leading to transꢀP via TS6 (24.0 kcal/mol), which aligns
well with the experimental observation that the ratio of cisꢀP:transꢀP is 57:43.
When X is Br or Cl, the HX would be more difficult to dissociate with the NHC
catalyst, we think the efficiency of NHC catalyst would become lower and the
stereoselectivity is thermodynamically controlled, and thus the more stable transꢀP
should be the main product.
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Scheme 4. The Suggested Catalytic Cycles.
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TS2'
21.2
TS2
21.6
TS6
9.6
trans
-R1
TS5
11.1
M5
5.1
CO2
1.2
TS1
TS3
4.9
M3
0.0
-4.9
NHC+CO2
TS4
-2.1
M2
-2.4
M1
-10.3
cis
-13.0
M4
-11.2
trans
-P
-P
Reaction Coordinate
Figure 2. The Energy Profiles of the Possible Reaction Pathways Leading to the Products
cisꢀP and transꢀP.
In summary, we have demonstrated that oneꢀcomponent, neat, and highly active
multiꢀfunctional catalysts can offer a competitive alternative to metal catalysis in
the conversion of epoxide with CO2 under mild conditions. This potential is clearly
proven in the conversion of internal epoxides which are generally difficult
substrates to activate, especially by the organocatalytic systems. The control
experiments and DFT calculations suggest that the reaction was realized by
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combining the carbene as catalyst for the activation of CO2 with the carboxyl
group as proton transfer agent. In contrast with many organocatalysts in which
halide anion is using as the nucleophilic agent for openꢀring of epoxide, in our
catalytic system halide anion was using as a carbene initiator by the deprotonation.
The knowledge obtained through these studies provides insight and new concept
into the rational design of highly active catalysts.
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Experimental Section
General Procedure for the Synthesis of organocatalysts 1a−g. A mixture of
2,6ꢀdibromopyridine (5 mmol), amines (10 mmol), CuI (1 mmol), tetramethylethaneꢀ1,2ꢀdiamine
(2 mmol) and K2CO3 (15 mmol) in DMSO (20 mL) was stirred for 30 min at room temperature,
and then heated to 90 °C for 24
h
under nitrogen atmosphere. Thereafter,
2ꢀbromoꢀ6ꢀsubstituentꢀpyridine (5 mmol), amino acids (7.5 mmol), CuI (1 mmol),
N,Nꢀdimethylethylenediamine (2 mmol) and K2CO3 (15 mmol) in DMSO (20 mL) was allowed
to react under nitrogen atmosphere. The resultant 2,6ꢀdisubstituentꢀpyridine (5 mmol), and alkyl
halides (10 mL) was heated to the desired temperature and the reaction stirred for 8 h under air
atmosphere, and affording a series of multiꢀfunctional organocatalysts 1a−g. The solvent was
concentrated under vacuum and the product of organocatalysts 1a−g was isolated by flash
chromatography.
Data for 1a are as follows: Purification by flash chromatography (DCM/MeOH = 20:1): a
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yellowish solid (1.468 g, 61%), M.P. = 159.1–159.6 °C; H NMR (400 MHz, DMSOꢀd6): δ
12.68 (br., 1H, COOH), 10.29 (s, 1H, NCHN), 8.39 (d, J = 8.0 Hz, 1H), 8.20 (d, J = 7.2 Hz, 1H),
7.81ꢀ7.71 (m, 3H), 7.47 (d, J = 8.0 Hz, NH), 7.08 (d, J = 7.2 Hz, 1H), 6.96 (d, J = 7.6 Hz, 1H),
4.55 (t, J = 6.8 Hz, 2H), 4.33 (t, J = 5.6 Hz, 1H), 2.23 (sext, J = 6.8 Hz, 1H), 2.02 (sext, J = 7.2
13
Hz, 2H), 1.05ꢀ0.98 (m, 9H), ppm; C NMR (100 MHz, DMSOꢀd6): δ 174.49, 158.93, 146.05,
142.14, 140.17, 132.09, 129.95, 127.80, 127.43, 116.44, 114.39, 103.92, 59.74, 49.04, 30.33,
22.50, 19.80, 18.85, 11.26, ppm; HRMS (MALDI) calcd for C20H25N4O2I [MꢀI]+ 353.1972,
found 353.1969.
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Data for 1b are as follows: Purification by flash chromatography (DCM/MeOH = 25:1): a
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yellowish solid (1.227 g, 49%), M.P. = 113.2–114.3 °C; H NMR (400 MHz, DMSOꢀd6): δ
12.66 (br., 1H, COOH), 10.27 (s, 1H, NCHN), 8.37 (d, J = 8.0 Hz, 1H), 8.19 (d, J = 7.6 Hz, 1H),
7.80ꢀ7.70 (m, 3H), 7.62 (d, J = 8.0 Hz, NH), 7.06 (d, J = 7.2 Hz, 1H), 6.83 (d, J = 7.6 Hz, 1H),
4.53 (t, J = 7.6 Hz, 2H), 4.41ꢀ4.35 (m, 1H), 2.02 (sext, J = 7.6 Hz, 2H), 1.75ꢀ1.60 (m, 2H),
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1.01ꢀ0.95 (m, 6H), 0.88 (d, J = 6.4 Hz, 3H), ppm; C NMR (100 MHz, DMSOꢀd6): δ 175.72,
158.67, 146.27, 142.17, 140.25, 132.09, 130.01, 127.72, 127.43, 116.46, 114.38, 103.98, 52.65,
49.04, 24.98, 23.36, 22.47, 21.81, 11.27, ppm; HRMS (MALDI) calcd for C21H27N4O2I [MꢀI]+
367.2129, found 367.2125.
Data for 1c are as follows: Purification by flash chromatography (DCM/MeOH = 15:1): a
1
yellowish solid (0.905 g, 35%), M.P. = 93.5–93.9 °C; H NMR (400 MHz, DMSOꢀd6): δ 12.75
(br., 1H, COOH), 10.29 (s, 1H, NCHN), 8.40 (d, J = 8.0 Hz, 1H), 8.20 (d, J = 8.0 Hz, 1H),
7.82ꢀ7.68 (m, 3H), 7.67 (d, J = 8.0 Hz, NH), 7.09 (d, J = 8.0 Hz, 1H), 6.84 (d, J = 8.0 Hz, 1H),
4.59ꢀ4.52 (m, 3H), 2.67ꢀ2.61 (m, 2H), 2.07ꢀ2.00 (m, 6H), 1.00 (t, J = 7.6 Hz, 3H), ppm; 13C
NMR (100 MHz, DMSOꢀd6): δ 175.00, 158.65, 146.24, 142.18, 140.33, 132.09, 129.99, 127.76,
127.44, 116.55, 114.37, 104.15, 53.06, 49.05, 31.18, 30.38, 22.48, 14.97, 11.27, ppm; HRMS
(MALDI) calcd for C20H25N4O2SI [MꢀI]+ 385.1693, found 385.1699.
Data for 1d are as follows: Purification by flash chromatography (DCM/MeOH = 10:1): a
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yellowish solid (1.309 g, 49%), M.P. = 115.6–116.3 °C; H NMR (400 MHz, DMSOꢀd6): δ
12.90 (br., 1H, COOH), 10.25 (s, 1H, NCHN), 8.28 (d, J = 8.0 Hz, 1H), 8.19 (d, J = 8.0 Hz, 1H),
7.77ꢀ7.73 (m, 3H), 7.71 (d, J = 8.0 Hz, NH), 7.32ꢀ7.25 (m, 4H), 7.18 (t, J = 7.6 Hz, 1H), 7.04 (d,
J = 7.2 Hz, 1H), 6.82 (d, J = 8.4 Hz, 1H), 4.70ꢀ4.66 (m, 1H), 4.52 (t, J = 7.6 Hz, 2H), 3.22 (dd, J
= 14.0 Hz, 4.8 Hz, 1H), 3.02 (dd, J = 14.0 Hz, 4.8 Hz, 1H), 2.01 (sext, J = 7.6 Hz, 2H), 0.99 (t, J
= 7.6 Hz, 3H), ppm; 13C NMR (100 MHz, DMSOꢀd6): δ 174.52, 158.45, 146.08, 142.16, 140.32,
138.41, 132.07, 129.96, 129.58, 128.66, 127.78, 127.42, 126.91, 116.35, 114.39, 104.14, 55.91,
49.02, 37.53, 22.49, 11.25, ppm; HRMS (MALDI) calcd for C24H25N4O2I [MꢀI]+ 401.1972,
found 401.1970.
Data for 1e are as follows: Purification by flash chromatography (DCM/MeOH = 40:1): a
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yellowish solid (1.671 g, 61%), M.P. = 136.5–137.2 °C; H NMR (400 MHz, DMSOꢀd6): δ
12.80 (br., 1H, COOH), 10.28 (s, 1H, NCHN), 9.19 (s, 1H, OH), 8.28 (d, J = 8.0 Hz, 1H), 8.20
(d, J = 8.0 Hz, 1H), 7.78ꢀ7.66 (m, 3H), 7.65 (d, J = 8.0 Hz, NH), 7.11 (d, J = 8.0 Hz, 2H), 7.06
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(d, J = 8.0 Hz, 1H), 6.84 (d, J = 8.0 Hz, 1H), 6.66 (d, J = 8.0 Hz, 2H), 4.61ꢀ4.52 (m, 3H), 3.09
(dd, J = 14.0 Hz, 4.8 Hz, 1H), 2.94ꢀ2.88 (m, 1H), 2.02 (sext, J = 7.6 Hz, 2H), 0.99 (t, J = 7.6 Hz,
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3H), ppm; C NMR (100 MHz, DMSOꢀd6): δ 174.94, 158.51, 156.32, 146.09, 142.04, 140.21,
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36.89, 22.50, 11.25, ppm; HRMS (MALDI) calcd for C24H25N4O3I [MꢀI]+ 417.1921, found
417.1911.
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Data for 1f are as follows: Purification by flash chromatography (DCM/MeOH = 25:1): a
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yellowish solid (1.056 g, 50%), M.P. = 141.0–141.5 °C; H NMR (400 MHz, DMSOꢀd6): δ
10.29 (s, 1H, NCHN), 9.20 (s, 1H, OH), 8.30 (d, J = 8.0 Hz, 1H), 8.19 (d, J = 8.0 Hz, 1H),
7.77ꢀ7.70 (m, 3H), 7.61 (d, J = 8.0 Hz, NH), 7.10 (d, J = 8.0 Hz, 2H), 7.03 (d, J = 8.0 Hz, 1H),
6.82 (d, J = 8.0 Hz, 1H), 6.64 (d, J = 8.0 Hz, 2H), 4.58ꢀ4.51 (m, 3H), 3.10 (dd, J = 14.0 Hz, 4.8
Hz, 1H), 2.93ꢀ2.87 (m, 1H), 2.01 (sext, J = 7.6 Hz, 2H), 0.99 (t, J = 7.6 Hz, 3H), ppm; 13C NMR
(100 MHz, DMSOꢀd6): δ 174.70, 158.51, 156.36, 146.11, 142.15, 140.21, 132.07, 130.51,
129.96, 128.51, 127.78, 127.39, 116.46, 115.40, 114.36, 103.87, 56.42, 49.00, 36.87, 22.49,
11.24, ppm; HRMS (MALDI) calcd for C24H25N4O3Br [MꢀBr]+ 417.1921, found 417.1917.
Data for 1g are as follows: Purification by flash chromatography (DCM/MeOH = 20:1): a
1
yellowish solid (0.972 g, 46%), M.P. = 112.3–112.9 °C; H NMR (400 MHz, DMSOꢀd6): δ
10.38 (s, 1H, NCHN), 8.37 (d, J = 8.0 Hz, 1H), 8.14 (d, J = 8.0 Hz, 1H), 7.70ꢀ7.65 (m, 3H), 7.47
(s, NH), 7.06 (d, J = 8.0 Hz, 2H), 7.00 (d, J = 8.0 Hz, 1H), 6.77 (d, J = 8.0 Hz, 1H), 6.61 (d, J =
8.0 Hz, 2H), 4.52 (t, J = 7.6 Hz, 3H), 3.10 (dd, J = 14.0 Hz, 4.8 Hz, 1H), 2.89ꢀ2.82 (m, 1H), 1.98
(sext, J = 7.6 Hz, 2H), 0.99 (t, J = 7.6 Hz, 3H), ppm; 13C NMR (100 MHz, DMSOꢀd6): δ 175.19,
158.72, 156.23, 146.13, 142.10, 139.87, 132.03, 130.50, 129.90, 129.24, 127.82, 127.26, 116.71,
115.27, 114.22, 102.97, 57.49, 48.92, 37.20, 22.51, 11.21, ppm; HRMS (MALDI) calcd for
C24H25N4O3Cl [MꢀCl]+ 417.1921, found 417.1913.
Data for 1h are as follows: Purification by flash chromatography (DCM/MeOH = 20:1): a
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yellowish solid (1.366 g, 72%), M.P. = 157.2–157.7 °C; H NMR (400 MHz, DMSOꢀd6): δ
10.62 (s, 1H), 8.77 (d, J = 4.8 Hz, 1H), 8.47ꢀ8.44 (m, 1H), 8.33ꢀ8.25 (m, 2H), 8.16 (d, J = 8.0
Hz, 1H), 7.76ꢀ7.70 (m, 3H), 4.62 (d, J = 8.0 Hz, 2H), 2.06 (sext, J = 7.2 Hz, 1H), 1.01 (t, J = 7.2
Hz, 3H), ppm; 13C NMR (100 MHz, DMSOꢀd6): δ 149.77, 147.84, 142.52, 140.96, 132.08,
129.88, 128.15, 127.55, 125.47, 117.54, 116.46, 114.62, 49.29, 22.51, 11.32, ppm; HRMS
(MALDI) calcd for C15H16N3I [MꢀI]+ 238.1339, found 238.1329.
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Data for 1i are as follows: Purification by flash chromatography (DCM/MeOH = 20:1): a
yellowish solid (1.224 g, 65%), M.P. = 117.9–118.3 °C; 1H NMR (400 MHz, DMSOꢀd6): δ 8.77
(S, 1H), 8.14 (d, J = 8.0 Hz, 1H), 7.74 (d, J = 7.2 Hz, 1H), 7.60 (t, J = 8.0 Hz, 1H), 7.36ꢀ7.28 (m,
3H), 7.12 (d, J = 8.0 Hz, 2H), 6.94 (d, J = 8.0 Hz, 1H), 6.67 (d, J = 8.0 Hz, 2H), 6.60 (d, J = 8.0
Hz, 1H), 4.61ꢀ4.56 (m, 1H), 3.08 (dd, J = 14.0 Hz, 4.8 Hz, 1H), 2.90 (dd, J = 14.0 Hz, 9.6 Hz,
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1H), ppm; C NMR (100 MHz, DMSOꢀd6): δ 175.07, 158.31, 156.33, 148.38, 144.62, 142.60,
139.84, 132.31, 130.51, 128.58, 124.05, 123.10, 120.19, 115.43, 114.19, 101.58, 56.55, 49.07,
36.92, ppm; HRMS (MALDI) calcd for C21H18N4O3 [M]+ 374.1373, found 374.1376.
Data for 1j are as follows: Purification by flash chromatography (DCM/MeOH = 15:1): a
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yellowish solid (1.681 g, 61%), M.P. = 109.3–109.9 °C; H NMR (400 MHz, DMSOꢀd6): δ
10.31 (s, 1H, NH), 8.22ꢀ8.19 (m, 2H), 7.81ꢀ7.72 (m, 4H), 7.12ꢀ7.09 (m, 3H), 6.87 (d, J = 8.0 Hz,
1H), 6.68 (d, J = 8.0 Hz, 2H), 4.71ꢀ4.66 (m, 1H), 4.56 (t, J = 7.2 Hz, 2H), 3.63 (s, 3H), 3.09ꢀ2.93
(m, 2H), 2.01 (sext, J = 7.2 Hz, 2H), 0.99 (t, J = 7.2 Hz, 3H), ppm; 13C NMR (100 MHz,
DMSOꢀd6): δ 173.65, 163.56, 158.20, 156.48, 146.05, 142.12, 140.47, 132.08, 130.53, 129.92,
127.88, 127.70, 127.42, 116.13, 115.52, 114.51, 104.45, 56.28, 52.41, 49.09, 36.97, 22.48, 11.25,
ppm; HRMS (MALDI) calcd for C25H27N4O3I [MꢀI]+ 431.2078, found 431.2072.
Data for 1k are as follows: Purification by flash chromatography (DCM/MeOH = 15:1): a
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yellowish solid (0.791 g, 31%), M.P. = 112.3–112.9 °C; H NMR (400 MHz, DMSOꢀd6): δ
10.24 (s, 1H), 8.16 (d, J = 8.0 Hz, 1H), 8.05ꢀ7.98 (m, 1H), 7.82 (t, J = 8.0 Hz, 1H), 7.75ꢀ7.67 (m,
2H), 7.06 (d, J = 8.0 Hz, 1H), 7.00 (d, J = 8.0 Hz, 2H), 6.82 (d, J = 8.0 Hz, 1H), 6.56 (d, J = 8.0
Hz, 2H), 5.41 (s, 1H), 4.50 (t, J = 7.2 Hz, 2H), 3.22ꢀ3.04 (m, 2H), 2.96 (s, 3H), 1.98 (sextet, J =
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7.2 Hz, 2H), 0.96 (t, J = 7.2 Hz, 3H), ppm; C NMR (100 MHz, DMSOꢀd6): δ 173.26, 158.71,
156.10, 145.37, 142.25, 141.32, 132.07, 130.18, 129.82, 128.73, 127.84, 127.37, 115.91, 115.39,
114.47, 107.50, 104.04, 60.45, 49.01, 33.95, 22.45, 11.22, ppm; HRMS (MALDI) calcd for
C25H27N4O3I [MꢀI]+ 431.2078, found 431.2075.
Data for 1l are as follows: Purification by flash chromatography (DCM/MeOH = 15:1): a
yellowish solid (0.763 g, 27%), M.P. = 125.3–125.7 °C; 1H NMR (400 MHz, DMSOꢀd6): δ 8.20
(d, J = 8.0 Hz, 1H), 7.84ꢀ7.60 (m, 4H), 7.12 (d, J = 8.0 Hz, 2H), 6.95 (d, J = 8.0 Hz, 2H), 6.69
(d, J = 8.0 Hz, 2H), 4.58 (t, J = 7.6 Hz, 2H), 4.51ꢀ4.46 (m, 1H), 3.08 (dd, J = 14.0 Hz, 4.4 Hz,
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2H), 2.89 (s, 3H), 1.95 (sextet, J = 7.2 Hz, 2H), 1.07 (t, J = 7.2 Hz, 3H), ppm; C NMR (100
MHz, DMSOꢀd6): δ 174.74, 159.12, 156.34, 151.78, 144.23, 140.06, 131.26, 130.98, 130.52,
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128.58, 127.19, 126.90, 115.38, 113.98, 113.72, 108.81, 56.36, 47.19, 36.88, 22.32, 12.16, 11.38,
ppm; HRMS (MALDI) calcd for C25H27N4O3I [MꢀI]+ 431.2078, found 431.2075.
General Procedure for the Synthesis of Cyclic Carbonates. Epoxides (10.0 mmol), and
organocatalyst 1e (0.4 mmol) were successively put into a 25 mL Schlenk flask. The reaction
mixture was stirred at room temperature for 24 h under a CO2 atmosphere (1 atm, using a
balloon). The reaction mixtures were added to brine (50 mL) and extracted three times with
dichloromethane (3×50 mL). The solvent was removed under reduced pressure, and the products
were isolated by flash chromatography.
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4ꢀMethylꢀ1,3ꢀdioxolanꢀ2ꢀone (3a).5d Purification by flash chromatography (petroleum
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ether/EtOAc = 2:1) gave a colorless oil (949.2 mg, 93%). H NMR (400 MHz, CDCl3) δ
4.90ꢀ4.82 (m, 1H), 4.56 (t, J = 8.0 Hz, 1H), 4.03 (t, J = 8.0 Hz, 1H), 1.50 (t, J = 6.4 Hz, 3H),
ppm; 13C NMR (100 MHz, CDCl3): δ 155.16, 73.76, 70.68, 19.03, ppm.
4ꢀEthylꢀ1,3ꢀdioxolanꢀ2ꢀone (3b).15 Purification by flash chromatography (petroleum
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ether/EtOAc = 2:1) gave a yellow oil (1.003 g, 87%). H NMR (400 MHz, CDCl3) δ 4.70ꢀ4.63
(m, 1H), 4.53 (t, J = 8.0 Hz, 1H), 4.09 (t, J = 8.0 Hz, 1H), 1.87ꢀ1.72 (m, 2H), 1.04 (t, J = 8.0 Hz,
3H), ppm; 13C NMR (100 MHz, CDCl3) δ 155.21, 78.11, 69.06, 26.79, 8.38, ppm.
4ꢀHexylꢀ1,3ꢀdioxolanꢀ2ꢀone (3c).18b Purification by flash chromatography (petroleum
ether/EtOAc = 5:1) gave a colorless oil (1.537 g, 89%). 1H NMR (400 MHz, CDCl3) δ 4.73ꢀ4.66
(m, 1H), 4.52 (t, J = 8.0 Hz, 1H), 4.06 (t, J = 8.0 Hz, 1H), 1.83ꢀ1.63 (m, 2H), 1.49ꢀ1.28 (m, 8H),
0.87 (t, J = 7.2 Hz, 3H), ppm; 13C NMR (100 MHz, CDCl3) δ 155.15, 77.15, 69.43, 33.76, 31.46,
28.73, 24.26, 22.39, 13.91, ppm.
4ꢀButylꢀ1,3ꢀdioxolanꢀ2ꢀone (3d).5d Purification by flash chromatography (petroleum
ether/EtOAc = 5:1) gave a colorless oil (1.299 g, 90%). 1H NMR (400 MHz, CDCl3) δ 4.74ꢀ4.67
(m, 1H), 4.53 (t, J = 8.0 Hz, 1H), 4.07 (t, J = 8.0 Hz, 1H), 1.86ꢀ1.65 (m, 2H), 1.49ꢀ1.34 (m, 4H),
0.93 (t, J = 8.0 Hz, 3H), ppm; 13C NMR (101 MHz, CDCl3) δ 155.2, 77.2, 69.5, 33.6, 26.5, 22.3,
13.8, ppm.
4ꢀ(Chloromethyl)ꢀ1,3ꢀdioxolanꢀ2ꢀone (3e).5d Purification by flash chromatography (petroleum
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ether/EtOAc = 2:1) gave a yellow oil (1.272 g, 93%). H NMR (400 MHz, CDCl3) δ 5.02ꢀ4.96
(m, 1H), 4.61(t, J = 8.0 Hz, 1H), 4.42 (dd, J = 8.8 Hz, J = 5.6 Hz, 1H), 3.83ꢀ3.73 (m, 2H), ppm;
13C NMR (100 MHz, CDCl3) δ 154.54, 74.54, 66.99, 44.20, ppm.
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4ꢀ(Chloromethyl)ꢀ4ꢀmethylꢀ1,3ꢀdioxolanꢀ2ꢀone (3f).21b Purification by flash chromatography
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4.54 (d, J = 8.4 Hz, 1H), 4.11 (d, J = 8.4 Hz, 1H), 3.77 (d, J = 12.4 Hz, 1H), 3.53 (d, J = 12.4 Hz,
1H), 1.45 (s, 3H), ppm; 13C NMR (100 MHz, CDCl3) δ 155.48, 84.04, 71.50, 65.80, 21.29, ppm.
4ꢀ(butꢀ3ꢀenꢀ1ꢀyl)ꢀ1,3ꢀdioxolanꢀ2ꢀone (3g).13 Purification by flash chromatography (petroleum
ether/EtOAc = 5:1) gave a colorless oil (1.115 g, 78%). 1H NMR (400 MHz, CDCl3) δ 5.84ꢀ5.74
(m, 1H), 5.12ꢀ5.05 (m, 2H), 4.77ꢀ4.70 (m, 1H), 4.54 (t, J = 8.0 Hz, 1H), 4.09 (t, J = 8.0 Hz, 1H),
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2.31ꢀ2.15 (m, 2H), 1.99ꢀ1.90 (m, 1H), 1.83ꢀ1.75 (m, 1H), ppm; C NMR (100 MHz, CDCl3) δ
154.96, 136.08, 116.43, 69.33, 33.07, 28.66, ppm.
4ꢀ(butoxymethyl)ꢀ1,3ꢀdioxolanꢀ2ꢀone (3h).15 Purification by flash chromatography (petroleum
ether/EtOAc = 5:1) gave a colorless oil (1.271 g, 73%). 1H NMR (400 MHz, CDCl3) δ 4.84ꢀ4.78
(m, 1H), 4.50 (t, J = 8.0 Hz, 1H), 4.39 (dd, J = 8.0 Hz, 6.0 Hz, 1H), 3.70ꢀ3.59 (m, 2H), 3.51 (t, J
= 6.4 Hz, 2H), 1.56 (quint, J = 6.4 Hz, 2H), 1.36 (sext, J = 8.0 Hz, 2H), 0.92 (t, J = 8.0 Hz, 3H),
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ppm; C NMR (100 MHz, CDCl3) δ 154.98, 75.10, 71.91, 69.64, 66.32, 31.52, 19.15, 13.83,
ppm.
4ꢀ((allyloxy)methyl)ꢀ1,3ꢀdioxolanꢀ2ꢀone (3i).15 Purification by flash chromatography
(petroleum ether/EtOAc = 5:1) gave a colorless oil (1.279 g, 81%). 1H NMR (400 MHz, CDCl3)
δ 5.92ꢀ5.83 (m, 1H), 5.31ꢀ5.21 (m, 2H), 4.86ꢀ4.81 (m, 1H), 4.51 (t, J = 8.0 Hz, 1H), 4.41 (dd, J =
8.0 Hz, 6.0 Hz, 1H), 4.07ꢀ4.04 (m, 2H), 3.70 (dd, J = 10.8 Hz, J = 3.6 Hz, 1H), 3.62 (dd, J = 10.8
Hz, J = 3.6 Hz, 1H), ppm; 13C NMR (100 MHz, CDCl3) δ 154.95, 133.67, 117.94, 75.04, 72.61,
68.85, 66.29, ppm.
4ꢀ(Phenoxymethyl)ꢀ1,3ꢀdioxolanꢀ2ꢀone (3j).15 Purification by flash chromatography (petroleum
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ether/EtOAc = 2:1) gave a white solid (1.648 g, 85%), M.P. = 100.9ꢀ101.2°C. H NMR (400
MHz, CDCl3) δ 7.33 (t, J = 8.0 Hz, 2H), 7.04 (t, J = 8.0 Hz, 1H), 6.94 (d, J = 8.0 Hz, 2H),
5.08ꢀ5.02 (m, 1H), 4.64 (t, J = 8.4 Hz, 1H), 4.56 (dd, J = 8.8 Hz, J = 6.0 Hz, 1H), 4.26 (dd, J =
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10.4 Hz, J = 4.4 Hz, 1H), 4.17 (dd, J = 10.8 Hz, J = 3.6 Hz, 1H), ppm; C NMR (100 MHz,
CDCl3) δ 157.77, 154.71, 129.71, 121.99, 114.63, 74.18, 66.90, 66.25, ppm.
4ꢀ(((9HꢀCarbazolꢀ4ꢀyl)oxy)methyl)ꢀ1,3ꢀdioxolanꢀ2ꢀone (3k).21b Purification by flash
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chromatography (DCM) gave a white solid (2.153 g, 76%), M.P. = 215.7ꢀ216.2°C. H NMR
(400 MHz, DMSOꢀd6) δ 11.33 (s, 1H), 8.13 (d, J = 8.0 Hz, 1H), 7.48 (d, J = 8.0 Hz, 1H),
7.38ꢀ7.31 (m, 2H), 7.16ꢀ7.13 (m, 2H), 6.72 (d, J = 8.0 Hz, 1H), 5.35 (s, 1H), 4.78 (t, J = 8.4 Hz,
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1H), 4.65ꢀ4.41 (m, 3H), ppm; 13C NMR (100 MHz, DMSOꢀd6) δ 155.51, 154.54, 141.64, 139.44,
126.89, 125.22, 122.55, 121.88, 119.21, 111.85, 110.96, 105.04, 100.98, 75.41, 67.82, 66.67,
ppm.
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ether/EtOAc = 10:1) gave a yellow solid (1.459 g, 89%), M.P. = 50.0ꢀ51.4°C. H NMR (400
MHz, CDCl3) δ 7.48ꢀ7.43 (m, 3H), 7.38ꢀ7.36 (m, 2H), 5.69 (t, J = 8.0 Hz, 1H), 4.81 (t, J = 8.0
Hz, 1H), 4.34 (t, J = 8.0 Hz, 1H), ppm; 13C NMR (100 MHz, CDCl3) δ 154.95, 135.87, 129.72,
129.23, 125.94, 78.05, 71.21, ppm.
4,4ꢀDimethylꢀ1,3ꢀdioxolanꢀ2ꢀone (3m).5d Purification by flash chromatography (petroleum
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ether/EtOAc = 5:1) gave a colorless oil (1.010 g, 87%). H NMR (400 MHz, CDCl3) δ 4.13 (s,
2H), 1.50 (s, 6H), ppm; 13C NMR (100 MHz, CDCl3) δ 154.64, 81.81, 75.37, 25.95, ppm.
(4R,5S)ꢀ4,5ꢀdimethylꢀ1,3ꢀdioxolanꢀ2ꢀone (4a).21b Purification by flash chromatography
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(petroleum ether/EtOAc = 2:1) gave a colorless oil (963.1 mg, 83%). transꢀ4a: H NMR (400
MHz, CDCl3) δ 4.33ꢀ4.26 (m, 2H), 1.41ꢀ1.39 (m, 6H), ppm; 13C NMR (100 MHz, CDCl3) δ
154.54, 79.93, 18.27, ppm.
Hexahydrobenzo[d][1,3]dioxolꢀ2ꢀone (4b).15 Purification by flash chromatography (petroleum
ether/EtOAc = 5:1) gave a colorless oil (1.337 g, 95%). 1H NMR (400 MHz, CDCl3): δ 4.67ꢀ4.62
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(m, 2H), 1.88ꢀ1.74 (m, 4H), 1.57ꢀ1.48 (m, 2H), 1.41ꢀ1.31 (m, 2H), ppm; C NMR (100 MHz,
CDCl3) δ 155.38, 75.78, 26.62, 19.03, ppm.
(3aR,6aS)ꢀTetrahydroꢀ4Hꢀcyclopenta[d][1,3]dioxolꢀ2ꢀone (4c).16 Purification by flash
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chromatography (petroleum ether/EtOAc = 5:1) gave a white solid (998.7 mg, 78%). H NMR
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(400 MHz, CDCl3): δ 5.14ꢀ5.10 (m, 2H), 2.18ꢀ2.13 (m, 2H), 1.85ꢀ1.63 (m, 4H), ppm; C NMR
(100 MHz, CDCl3) δ 155.47, 81.85, 33.19, 21.57, ppm.
(3aR,6aS)ꢀTetrahydrofuro[3,4ꢀd][1,3]dioxolꢀ2ꢀone
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chromatography (petroleum ether/EtOAc = 5:1) gave a white solid (976.3 mg, 75%). H NMR
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(400 MHz, CDCl3): δ 5.22ꢀ5.21 (m, 2H), 4.28ꢀ4.25 (m, 2H), 3.59ꢀ3.55 (m, 2H), ppm; C NMR
(100 MHz, CDCl3) δ 154.39, 80.04, 73.02, ppm.
1,3ꢀDioxanꢀ2ꢀone (4e).21a Purification by flash chromatography (petroleum ether/EtOAc = 5:1)
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gave a colorless oil (378.5 mg, 37%). H NMR (400 MHz, CDCl3) δ 4.40ꢀ4.32 (m, 4H),
2.11ꢀ2.00 (m, 2H), ppm; 13C NMR (100 MHz, CDCl3) δ 148.62, 68.09, 21.62, ppm.
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