Cooperative Multifunctional Organocatalysts for Ambient Conversion

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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 Downloaded from http://pubs.acs.org on September 14, 2018

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Cooperative Multi-Functional Organocatalysts for Ambient Conversion of Carbon Dioxide into Cyclic Carbonates †

†

Ning Liu,*, Ya-Fei Xie, Chuan Wang,‡ Shi-Jun 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 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 multi-functional 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.

KEYWORDS: carbon dioxide, cyclic carbonate, multi-functional organocatalyst, metal-free, cycloaddition

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Introduction 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 low-cost, 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 one-component 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 co-workers 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 co-workers 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 one-component catalyst that can be effective for the conversion of internal epoxides under mild conditions is a still a challenging task. 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 hydrogen-bonding donor group. Meanwhile, He and co-workers have proved that the amino acid salts are capable of capturing one equivalent of CO2 through the insertion of CO2 into N-H bond.19 Bowen et al. found that CO2 can bind to the quinoline N atom to form the (quinoline-CO2) anionic complex.20 In addition, previously reported catalysts and


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catalytic systems showed that NHC (N-heterocyclic carbenes) can react with CO2 to form NHC-CO2 adducts.18b,f These recent advances promoted our interest in the design of effective multi-functional 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 multi-functional catalysts through varying functional groups attached. Recently, we reported pyridine-bridged benzimidazolium salt and pincer-type 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 multi-functional 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 one-component, neat, and highly active multi-functional 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 multi-functional organocatalysts 1a−g (Scheme 1) were prepared according to procedures reported previously.23 We first report a series of organocatalysts with multi-active sites: amino groups, pyridine N atom and pre-NHC (NHC, N-heterocyclic carbenes precursor) for CO2 capture and activation, carboxyl groups for epoxides activation and halide anion for nucleophilic ring opening.

Scheme 1. Synthesis of multi-functional organocatalysts.


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The catalytic performance of all the resultant multi-functional 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 1-4). 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 cm-1 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 700-800 cm-1 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 H-D exchange between COOH proton and deuterium reagents, a 1H 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. The effect of the counter-anions 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). Table 1. Optimization of PC Synthesisa

entry catalyst (mol%) temperature (°C) CO2 (bar) time (h) yield (%) 1 1a (1.0) 80 5 4 77 2 1b (1.0) 80 5 4 68 3 1c (1.0) 80 5 4 52 4 1d (1.0) 80 5 4 57 5 1e (1.0) 80 5 4 99 6 1f (1.0) 80 5 4 79 7 1g (1.0) 80 5 4 61 8 1e (1.0) 60 5 4 79 9 1e (1.0) 40 5 4 53 10 1e (1.0) r.t. 5 4 26 11 1e (1.0) r.t. 5 24 37 b 12 1e (1.0) r.t. 1 24 29 13 1e (2.0) r.t. 1b 24 75 b 14 1e (4.0) r.t. 1 24 96 a Reaction 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. b CO2 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), solvent-free and additive-free 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). Table 2. Scope of terminal epoxidesa


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a

Conditions: 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 1,2-dimethyloxirane 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 4b-d in good yields and chemoselectivities. In addition to


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six-membered bicyclic cyclohexene oxide was converted into the corresponding carbonate 4b in an isolated yield of 95%, five-membered 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). 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 bio-carbonates 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 epoxide-functionalized 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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a

Conditions: 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 co-workers 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 phosphorus-ylide-CO2 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 Table 4. Comparison of Catalytic Activity of Catalysts

entry ref. yield (%) TON TOF (h-1) a 1 64 16 0.70 Ref. 14 2 90 18 3.0 Ref. 15b c 3 96 24 1.0 this work 4 75 38 1.6 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. bPO (10.0 mmol), P-Ylide-CO2-adducts (5 mol%), r.t., 1 bar of CO2 (balloon), neat, 6 h. cPO (10.0 mmol), 1e (4 mol%), r.t., 1 bar of CO2 (balloon), neat, 24 h. dPO (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)).

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 multi-functional-catalyzed 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 counter-anions on the catalysts, we used pure trans-2,3-epoxybutane to reveal some mechanistic insights into reaction pathways (Table 5). When 1f (Br-) and 1g (Cl-) are used as catalysts, trans-3n and cis-3n 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 1e-mediated reaction undergoes different reaction pathway compared with 1f and 1g. Table 5. Possible Reaction Pathways for 1e−g Catalyzed the Conversion of trans-2,3-Epoxybutane into cis- and trans-Cyclic Carbonate.a

entry catalyst cis-4a (%)b trans-4a (%)b total yield (%)c 1 57 43 83 1e 2 8 92 58 1f 3 3 97 12 1g a Conditions: trans-2,3-epoxybutane (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 pyridine-substituted benzimidazolium salt (1h in Scheme 3, eqn. 1) with a pyridine-substituted 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 two-component catalytic system was proved to be difficult to trigger this reaction at ambient condition (Scheme 3, eqns. 1 and 2), suggesting that the unique pincer-type structures of our developed catalysts provide CO2 and epoxides a chance for intramolecular interactions. 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.

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. 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 C-C bond and C-H bond stretching vibration of the pyridine ring in the range of 700-1100 cm-1 have no change in wavelengths during the addition of CO2 into the catalyst system (Figures S3-4). 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, pre-NHC can be transferred to NHC (N-heterocyclic 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 trans-R1, which is accompanied with the three-membered 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 five-membered 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 cis-P 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 rate-determining 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 trans-P. As depicted in Scheme 4, the negatively charged oxygen of intermediate M1 can also nucleophilically attack on the epoxy carbon of reactant trans-R1 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 trans-P can be dissociated with the intermediate M1 through a SN2-type transition state TS6 (Scheme 4). As shown in Figure 2, the process associated with TS6 is the rate-determining step for this pathway leading to the trans-P. 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 pre-NHC and the epoxy ring opening through nucleophilic attack by I-, was also investigated, and more details can be found in the Supporting Information. When X is I, we think the stereoselectivity is kinetically controlled, and the energy barrier of the whole reaction leading to cis-P via TS2 (23.6 kcal/mol) is


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slightly lower than that leading to trans-P via TS6 (24.0 kcal/mol), which aligns well with the experimental observation that the ratio of cis-P:trans-P 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 trans-P should be the main product.


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Scheme 4. The Suggested Catalytic Cycles.

39.5 TS2'

Relative Gibbs free energies (kcal/mol)

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21.2 TS2

21.6 TS6

9.6 TS5

trans-R1

0.0

CO2

1.2 TS1

4.9 M3

NHC+CO2 -2.4 M1

11.1 M5 5.1 TS3 -4.9 TS4

-2.1 M2 -13.0 M4

-11.2 -10.3 trans-P cis-P

Reaction Coordinate Figure 2. The Energy Profiles of the Possible Reaction Pathways Leading to the Products cis-P and trans-P.

In summary, we have demonstrated that one-component, neat, and highly active multi-functional 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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ACS Catalysis

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 open-ring 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. Experimental Section General Procedure for the Synthesis of organocatalysts 1a−g. A mixture of 2,6-dibromopyridine (5 mmol), amines (10 mmol), CuI (1 mmol), tetramethylethane-1,2-diamine (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,

2-bromo-6-substituent-pyridine (5 mmol), amino acids (7.5 mmol), CuI (1 mmol), N,N-dimethylethylenediamine (2 mmol) and K2CO3 (15 mmol) in DMSO (20 mL) was allowed to react under nitrogen atmosphere. The resultant 2,6-disubstituent-pyridine (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 multi-functional 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 yellowish solid (1.468 g, 61%), M.P. = 159.1–159.6 °C; 1H NMR (400 MHz, DMSO-d6): 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), 7.81-7.71 (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 Hz, 2H), 1.05-0.98 (m, 9H), ppm;

13

C NMR (100 MHz, DMSO-d6): 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 [M-I]+ 353.1972, found 353.1969.


23

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 39

Data for 1b are as follows: Purification by flash chromatography (DCM/MeOH = 25:1): a yellowish solid (1.227 g, 49%), M.P. = 113.2–114.3 °C; 1H NMR (400 MHz, DMSO-d6): 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), 7.80-7.70 (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), 4.41-4.35 (m, 1H), 2.02 (sext, J = 7.6 Hz, 2H), 1.75-1.60 (m, 2H), 1.01-0.95 (m, 6H), 0.88 (d, J = 6.4 Hz, 3H), ppm;

13

C NMR (100 MHz, DMSO-d6): 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 [M-I]+ 367.2129, found 367.2125. Data for 1c are as follows: Purification by flash chromatography (DCM/MeOH = 15:1): a yellowish solid (0.905 g, 35%), M.P. = 93.5–93.9 °C; 1H NMR (400 MHz, DMSO-d6): 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), 7.82-7.68 (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), 4.59-4.52 (m, 3H), 2.67-2.61 (m, 2H), 2.07-2.00 (m, 6H), 1.00 (t, J = 7.6 Hz, 3H), ppm;

13

C

NMR (100 MHz, DMSO-d6): 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 [M-I]+ 385.1693, found 385.1699. Data for 1d are as follows: Purification by flash chromatography (DCM/MeOH = 10:1): a yellowish solid (1.309 g, 49%), M.P. = 115.6–116.3 °C; 1H NMR (400 MHz, DMSO-d6): 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), 7.77-7.73 (m, 3H), 7.71 (d, J = 8.0 Hz, NH), 7.32-7.25 (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), 4.70-4.66 (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, DMSO-d6): 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 [M-I]+ 401.1972, found 401.1970. Data for 1e are as follows: Purification by flash chromatography (DCM/MeOH = 40:1): a yellowish solid (1.671 g, 61%), M.P. = 136.5–137.2 °C; 1H NMR (400 MHz, DMSO-d6): 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), 7.78-7.66 (m, 3H), 7.65 (d, J = 8.0 Hz, NH), 7.11 (d, J = 8.0 Hz, 2H), 7.06


24

Page 25 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

(d, J = 8.0 Hz, 1H), 6.84 (d, J = 8.0 Hz, 1H), 6.66 (d, J = 8.0 Hz, 2H), 4.61-4.52 (m, 3H), 3.09 (dd, J = 14.0 Hz, 4.8 Hz, 1H), 2.94-2.88 (m, 1H), 2.02 (sext, J = 7.6 Hz, 2H), 0.99 (t, J = 7.6 Hz, 3H), ppm; 13C NMR (100 MHz, DMSO-d6): δ 174.94, 158.51, 156.32, 146.09, 142.04, 140.21, 132.04, 130.53, 129.91, 128.58, 127.79, 127.39, 116.46, 115.41, 114.38, 103.87, 56.55, 49.05, 36.89, 22.50, 11.25, ppm; HRMS (MALDI) calcd for C24H25N4O3I [M-I]+ 417.1921, found 417.1911. Data for 1f are as follows: Purification by flash chromatography (DCM/MeOH = 25:1): a yellowish solid (1.056 g, 50%), M.P. = 141.0–141.5 °C; 1H NMR (400 MHz, DMSO-d6): 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), 7.77-7.70 (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), 4.58-4.51 (m, 3H), 3.10 (dd, J = 14.0 Hz, 4.8 Hz, 1H), 2.93-2.87 (m, 1H), 2.01 (sext, J = 7.6 Hz, 2H), 0.99 (t, J = 7.6 Hz, 3H), ppm; 13C NMR (100 MHz, DMSO-d6): 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 [M-Br]+ 417.1921, found 417.1917. Data for 1g are as follows: Purification by flash chromatography (DCM/MeOH = 20:1): a yellowish solid (0.972 g, 46%), M.P. = 112.3–112.9 °C; 1H NMR (400 MHz, DMSO-d6): δ 10.38 (s, 1H, NCHN), 8.37 (d, J = 8.0 Hz, 1H), 8.14 (d, J = 8.0 Hz, 1H), 7.70-7.65 (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), 2.89-2.82 (m, 1H), 1.98 (sext, J = 7.6 Hz, 2H), 0.99 (t, J = 7.6 Hz, 3H), ppm; 13C NMR (100 MHz, DMSO-d6): 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 [M-Cl]+ 417.1921, found 417.1913. Data for 1h are as follows: Purification by flash chromatography (DCM/MeOH = 20:1): a yellowish solid (1.366 g, 72%), M.P. = 157.2–157.7 °C; 1H NMR (400 MHz, DMSO-d6): δ 10.62 (s, 1H), 8.77 (d, J = 4.8 Hz, 1H), 8.47-8.44 (m, 1H), 8.33-8.25 (m, 2H), 8.16 (d, J = 8.0 Hz, 1H), 7.76-7.70 (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;

13

C NMR (100 MHz, DMSO-d6): 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 [M-I]+ 238.1339, found 238.1329.


25

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 39

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, DMSO-d6): 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), 7.36-7.28 (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), 4.61-4.56 (m, 1H), 3.08 (dd, J = 14.0 Hz, 4.8 Hz, 1H), 2.90 (dd, J = 14.0 Hz, 9.6 Hz, 1H), ppm; 13C NMR (100 MHz, DMSO-d6): 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 yellowish solid (1.681 g, 61%), M.P. = 109.3–109.9 °C; 1H NMR (400 MHz, DMSO-d6): δ 10.31 (s, 1H, NH), 8.22-8.19 (m, 2H), 7.81-7.72 (m, 4H), 7.12-7.09 (m, 3H), 6.87 (d, J = 8.0 Hz, 1H), 6.68 (d, J = 8.0 Hz, 2H), 4.71-4.66 (m, 1H), 4.56 (t, J = 7.2 Hz, 2H), 3.63 (s, 3H), 3.09-2.93 (m, 2H), 2.01 (sext, J = 7.2 Hz, 2H), 0.99 (t, J = 7.2 Hz, 3H), ppm;

13

C NMR (100 MHz,

DMSO-d6): 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 [M-I]+ 431.2078, found 431.2072. Data for 1k are as follows: Purification by flash chromatography (DCM/MeOH = 15:1): a yellowish solid (0.791 g, 31%), M.P. = 112.3–112.9 °C; 1H NMR (400 MHz, DMSO-d6): δ 10.24 (s, 1H), 8.16 (d, J = 8.0 Hz, 1H), 8.05-7.98 (m, 1H), 7.82 (t, J = 8.0 Hz, 1H), 7.75-7.67 (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), 3.22-3.04 (m, 2H), 2.96 (s, 3H), 1.98 (sextet, J = 7.2 Hz, 2H), 0.96 (t, J = 7.2 Hz, 3H), ppm; 13C NMR (100 MHz, DMSO-d6): 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 [M-I]+ 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, DMSO-d6): δ 8.20 (d, J = 8.0 Hz, 1H), 7.84-7.60 (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), 4.51-4.46 (m, 1H), 3.08 (dd, J = 14.0 Hz, 4.4 Hz, 2H), 2.89 (s, 3H), 1.95 (sextet, J = 7.2 Hz, 2H), 1.07 (t, J = 7.2 Hz, 3H), ppm; 13C NMR (100 MHz, DMSO-d6): δ 174.74, 159.12, 156.34, 151.78, 144.23, 140.06, 131.26, 130.98, 130.52,


26

Page 27 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

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 [M-I]+ 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. 4-Methyl-1,3-dioxolan-2-one (3a).5d Purification by flash chromatography (petroleum ether/EtOAc = 2:1) gave a colorless oil (949.2 mg, 93%). 1H NMR (400 MHz, CDCl3) δ 4.90-4.82 (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. 4-Ethyl-1,3-dioxolan-2-one

(3b).15

Purification

by

flash

chromatography

(petroleum

ether/EtOAc = 2:1) gave a yellow oil (1.003 g, 87%). 1H NMR (400 MHz, CDCl3) δ 4.70-4.63 (m, 1H), 4.53 (t, J = 8.0 Hz, 1H), 4.09 (t, J = 8.0 Hz, 1H), 1.87-1.72 (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. 4-Hexyl-1,3-dioxolan-2-one (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 4.73-4.66 (m, 1H), 4.52 (t, J = 8.0 Hz, 1H), 4.06 (t, J = 8.0 Hz, 1H), 1.83-1.63 (m, 2H), 1.49-1.28 (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. 4-Butyl-1,3-dioxolan-2-one

(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 4.74-4.67 (m, 1H), 4.53 (t, J = 8.0 Hz, 1H), 4.07 (t, J = 8.0 Hz, 1H), 1.86-1.65 (m, 2H), 1.49-1.34 (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. 4-(Chloromethyl)-1,3-dioxolan-2-one (3e).5d Purification by flash chromatography (petroleum ether/EtOAc = 2:1) gave a yellow oil (1.272 g, 93%). 1H NMR (400 MHz, CDCl3) δ 5.02-4.96 (m, 1H), 4.61(t, J = 8.0 Hz, 1H), 4.42 (dd, J = 8.8 Hz, J = 5.6 Hz, 1H), 3.83-3.73 (m, 2H), ppm; 13

C NMR (100 MHz, CDCl3) δ 154.54, 74.54, 66.99, 44.20, ppm.


27

ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 39

4-(Chloromethyl)-4-methyl-1,3-dioxolan-2-one (3f).21b Purification by flash chromatography (petroleum ether/EtOAc = 2:1) gave a yellow oil (1.426 g, 95%). 1H NMR (400 MHz, CDCl3) δ 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. 4-(but-3-en-1-yl)-1,3-dioxolan-2-one (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 5.84-5.74 (m, 1H), 5.12-5.05 (m, 2H), 4.77-4.70 (m, 1H), 4.54 (t, J = 8.0 Hz, 1H), 4.09 (t, J = 8.0 Hz, 1H), 2.31-2.15 (m, 2H), 1.99-1.90 (m, 1H), 1.83-1.75 (m, 1H), ppm; 13C NMR (100 MHz, CDCl3) δ 154.96, 136.08, 116.43, 69.33, 33.07, 28.66, ppm. 4-(butoxymethyl)-1,3-dioxolan-2-one (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 4.84-4.78 (m, 1H), 4.50 (t, J = 8.0 Hz, 1H), 4.39 (dd, J = 8.0 Hz, 6.0 Hz, 1H), 3.70-3.59 (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), ppm;

13

C NMR (100 MHz, CDCl3) δ 154.98, 75.10, 71.91, 69.64, 66.32, 31.52, 19.15, 13.83,

ppm. 4-((allyloxy)methyl)-1,3-dioxolan-2-one

(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 5.92-5.83 (m, 1H), 5.31-5.21 (m, 2H), 4.86-4.81 (m, 1H), 4.51 (t, J = 8.0 Hz, 1H), 4.41 (dd, J = 8.0 Hz, 6.0 Hz, 1H), 4.07-4.04 (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. 4-(Phenoxymethyl)-1,3-dioxolan-2-one (3j).15 Purification by flash chromatography (petroleum ether/EtOAc = 2:1) gave a white solid (1.648 g, 85%), M.P. = 100.9-101.2°C. 1H 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), 5.08-5.02 (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 = 10.4 Hz, J = 4.4 Hz, 1H), 4.17 (dd, J = 10.8 Hz, J = 3.6 Hz, 1H), ppm;

13

C NMR (100 MHz,

CDCl3) δ 157.77, 154.71, 129.71, 121.99, 114.63, 74.18, 66.90, 66.25, ppm. 4-(((9H-Carbazol-4-yl)oxy)methyl)-1,3-dioxolan-2-one

(3k).21b

Purification

by

flash

chromatography (DCM) gave a white solid (2.153 g, 76%), M.P. = 215.7-216.2°C. 1H NMR (400 MHz, DMSO-d6) δ 11.33 (s, 1H), 8.13 (d, J = 8.0 Hz, 1H), 7.48 (d, J = 8.0 Hz, 1H), 7.38-7.31 (m, 2H), 7.16-7.13 (m, 2H), 6.72 (d, J = 8.0 Hz, 1H), 5.35 (s, 1H), 4.78 (t, J = 8.4 Hz,


28

Page 29 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

1H), 4.65-4.41 (m, 3H), ppm; 13C NMR (100 MHz, DMSO-d6) 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. 4-Phenyl-1,3-dioxolan-2-one (3l).5d

Purification

by flash chromatography

(petroleum

ether/EtOAc = 10:1) gave a yellow solid (1.459 g, 89%), M.P. = 50.0-51.4°C. 1H NMR (400 MHz, CDCl3) δ 7.48-7.43 (m, 3H), 7.38-7.36 (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. 4,4-Dimethyl-1,3-dioxolan-2-one (3m).5d Purification by flash chromatography (petroleum ether/EtOAc = 5:1) gave a colorless oil (1.010 g, 87%). 1H 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)-4,5-dimethyl-1,3-dioxolan-2-one (4a).21b Purification by flash chromatography (petroleum ether/EtOAc = 2:1) gave a colorless oil (963.1 mg, 83%). trans-4a: 1H NMR (400 13

MHz, CDCl3) δ 4.33-4.26 (m, 2H), 1.41-1.39 (m, 6H), ppm;

C NMR (100 MHz, CDCl3) δ

154.54, 79.93, 18.27, ppm. Hexahydrobenzo[d][1,3]dioxol-2-one (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 4.67-4.62 (m, 2H), 1.88-1.74 (m, 4H), 1.57-1.48 (m, 2H), 1.41-1.31 (m, 2H), ppm;

13

C NMR (100 MHz,

CDCl3) δ 155.38, 75.78, 26.62, 19.03, ppm. (3aR,6aS)-Tetrahydro-4H-cyclopenta[d][1,3]dioxol-2-one

(4c).16

Purification

by

flash

1

chromatography (petroleum ether/EtOAc = 5:1) gave a white solid (998.7 mg, 78%). H NMR (400 MHz, CDCl3): δ 5.14-5.10 (m, 2H), 2.18-2.13 (m, 2H), 1.85-1.63 (m, 4H), ppm; 13C NMR (100 MHz, CDCl3) δ 155.47, 81.85, 33.19, 21.57, ppm. (3aR,6aS)-Tetrahydrofuro[3,4-d][1,3]dioxol-2-one

(4d).16

Purification

by

flash

chromatography (petroleum ether/EtOAc = 5:1) gave a white solid (976.3 mg, 75%). 1H NMR (400 MHz, CDCl3): δ 5.22-5.21 (m, 2H), 4.28-4.25 (m, 2H), 3.59-3.55 (m, 2H), ppm; 13C NMR (100 MHz, CDCl3) δ 154.39, 80.04, 73.02, ppm. 1,3-Dioxan-2-one (4e).21a Purification by flash chromatography (petroleum ether/EtOAc = 5:1) gave a colorless oil (378.5 mg, 37%). 1H NMR (400 MHz, CDCl3) δ 4.40-4.32 (m, 4H), 2.11-2.00 (m, 2H), ppm; 13C NMR (100 MHz, CDCl3) δ 148.62, 68.09, 21.62, ppm.


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Methyl

Page 30 of 39

8-(5-octyl-2-oxo-1,3-dioxolan-4-yl)octanoate

(4f).24c

Purification

by

flash

chromatography (petroleum ether/EtOAc = 10:1) gave a colorless oil (1.817 g, 51%, cis:trans=19:81). trans-4g: 1H NMR (400 MHz, CDCl3) δ 4.25-4.20 (m, 2H), 3.67 (s, 3H), 2.31 (t, J = 8.0 Hz, 2H), 1.62-1.28 (m, 26H), 0.88 (t, J = 6.8 Hz, 3H), ppm;

13

C NMR (100 MHz,

CDCl3) δ 174.17, 154.71, 82.02, 81.98, 51.46, 33.99, 33.82, 33.80, 31.78, 29.30, 29.17, 29.12, 28.96, 28.91, 24.81, 24.64, 24.60, 22.62, 14.07, ppm. Ethyl

(4g).24c

8-(5-octyl-2-oxo-1,3-dioxolan-4-yl)octanoate

Purification

by

flash

chromatography (petroleum ether/EtOAc = 10:1) gave a colorless oil (2.083 g, 56%). as a mixture of two diastereoisomers (cis:trans=17:83); trans-4h: 1H NMR (400 MHz, CDCl3) δ 4.25-4.19 (m, 2H), 4.03 (q, J = 6.8 Hz, 2H), 2.29 (t, J = 7.6 Hz, 2H), 1.72-1.24 (m, 28H), 0.88 (t, J = 6.8 Hz, 3H), ppm; 13C NMR (100 MHz, CDCl3) δ 173.73, 154.67, 81.98, 81.94, 60.17, 34.24, 33.78, 31.75, 29.14, 29.08, 28.94, 28.88, 24.80, 24.60, 24.57, 22.59, 14.22, 14.04, ppm. Methyl 12-(5-octyl-2-oxo-1,3-dioxolan-4-yl)dodecanoate (4h).24c Purification by flash chromatography (petroleum ether/EtOAc = 20:1) gave a colorless oil (1.979 g, 48%). trans-4i: 1

H NMR (400 MHz, CDCl3) δ 4.25-4.20 (m, 2H), 3.67 (s, 3H), 2.30 (t, J = 7.6 Hz, 2H),

1.74-1.27 (m, 36H), 0.88 (t, J = 6.8 Hz, 3H), ppm;

13

C NMR (100 MHz, CDCl3) δ 174.30,

154.74, 82.02, 51.43, 34.09, 33.83, 31.78, 29.47, 29.41, 29.37, 29.32, 29.30, 29.22, 29.17, 29.12, 24.93, 24.64, 22.62, 14.07, ppm. Methyl

8-(2-oxo-5-((2-oxo-5-pentyl-1,3-dioxolan-4-yl)methyl)-1,3-dioxolan-4-yl)octanoate

(4i).24c Purification by flash chromatography (petroleum ether/EtOAc = 2:1) gave a colorless oil (1.783 g, 43%). A mixture of four diastereroisomers dr=53:21:10:16; 1H NMR (400 MHz, CDCl3) δ 4.79-4.67 (m, 2H, isomer 1), 4.56-4.47 (m, 2H, isomer 2), 4.44-4.36 (m, 2H, isomer 3), 4.30-4.25 (m, 2H, isomer 4), 3.63 (s, 3H), 2.29-2.24 (m, 2H), 2.18-1.96 (m, 2H), 1.81-1.48 (m, 8H), 1.39-1.22 (m, 12H), 0.89-0.85 (m, 3H), ppm;

13

C NMR (100 MHz, CDCl3) δ 174.20,

154.68, 154.57, 153.66, 153.63, 82.54, 82.48, 82.08, 81.98, 79.44, 79.33, 79.26, 75.71, 74.50, 74.43, 51.46, 34.03, 33.91, 33.51, 33.29, 31.72, 31.25, 28.93, 28.80, 28.50, 25.38, 25.14, 24.71, 24.45, 24.26, 22.52, 22.35, 13.85, ppm. Computational Details All the theoretical calculations in the study were performed using Gaussian16 program package.27 All the geometries were optimized at the M06-2X28/6-31G** level in gas phase, and


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ACS Catalysis

the harmonic vibrational frequency calculations were performed at the same level to confirm the local minima and transition state. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. NMR spectra of the organocatalysts and prepared cyclic carbonates. AUTHOR INFORMATION Corresponding Author *E-mail for N.L.: [email protected]; [email protected]. Fax: (+0086)-0993-205-7270; phone: (+0086)-0993-205-7277. *E-mail for D.W.: [email protected]. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources Support was provided by the National Natural Science Foundation of China. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT


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ACS Catalysis

The one-component, neat, and highly active multi-functional catalysts have applied successfully for the cycloaddition of terminal epoxides with CO2 under ambient conditions. 169x67mm (300 x 300 DPI)


Cooperative Multifunctional Organocatalysts for Ambient Conversion

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