Cooperative Multifunctional Organocatalysts for Ambient Conversion

Research Article Cite This: ACS Catal. 2018, 8, 9945−9957

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Cooperative Multifunctional Organocatalysts for Ambient Conversion of Carbon Dioxide into Cyclic Carbonates Ning Liu,*,† Ya-Fei Xie,† Chuan Wang,‡ Shi-Jun Li,§ Donghui Wei,*,§ Min Li,† and Bin Dai*,†

ACS Catal. 2018.8:9945-9957. Downloaded from pubs.acs.org by KAOHSIUNG MEDICAL UNIV on 11/07/18. For personal use only.

†

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 450001, People’s Republic of China S Supporting Information *

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 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. KEYWORDS: carbon dioxide, cyclic carbonate, multifunctional 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 the preparation of fine chemicals,2 as electrolytes in lithium ion batteries,3 and as 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 these types of compounds.5 Among these methods, organocatalyzed cycloadditions between CO2 and epoxides represents an attractive approach to cyclic carbonates, because organocatalysts are usually inexpensive, 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 Despite the growing number of organocatalysts, the aforementioned organocatalytic © 2018 American Chemical Society

systems still suffer from some disadvantages from a synthetic point of view: low activity, high catalyst loading, poor substrate scope, and harsh reaction conditions.12 Recent developments in the area of cyclic carbonate synthesis have demonstrated that the careful design of catalysts plays a significant role in tuning the catalytic activity. For instance, Shirakawa et al. demonstrated that triethylamine hydroiodide is an 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 described that phosphorus ylide CO2 adducts are able to effectively catalyze Received: May 18, 2018 Revised: September 13, 2018 Published: September 14, 2018 9945

DOI: 10.1021/acscatal.8b01925 ACS Catal. 2018, 8, 9945−9957

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ACS Catalysis

Figure 1. Design and active sites of catalyst.

Scheme 1. Synthesis of Multifunctional Organocatalysts

of a combination of a carboxyl group as a Brønsted acid and an amino group as a CO2 activating agent. It is highly desirable to design and synthesize a multifunctional 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 multifunctional catalysts can offer a competitive alternative to metal catalysis in the conversion of terminal and internal epoxide under mild conditions.

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 a 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 group18 play an imperative role in activation of epoxides by the hydrogen-bonding donor group. Meanwhile, He and co-workers have proved that the amino acid salts are capable of capturing 1 equiv 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 quinolineCO2 anionic complex.20 In addition, previously reported catalysts and catalytic systems showed that NHCs (Nheterocyclic carbenes) can react with CO2 to form NHCCO2 adducts.18b,f These recent advances prompted our interest in the design of effective multifunctional 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 multifunctional catalysts through the attachment of varying functional groups. Recently, we reported pyridine-bridged benzimidazolium salt and pincertype 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

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RESULTS AND DISCUSSION The seven multifunctional organocatalysts 1a−g (Scheme 1) were prepared according to procedures reported previously.23 We first report a series of organocatalysts with multiple active sites: amino groups, pyridine N atoms, and pre-NHCs (Nheterocyclic carbene precursors) for CO2 capture and activation, carboxyl groups for epoxide activation, and halide anions for nucleophilic ring opening. The catalytic performance of all the resultant multifunctional catalysts 1a−g was investigated, and the coupling between PO (propylene epoxide) and CO2 was chosen as a benchmark reaction at 80 °C with a CO2 pressure of 5 bar. The obtained results indicated that the catalyst 1e containing a phenolic hydroxyl group (Table 1, entry 5) was more catalytically active than the other catalysts (Table 1, entries 1−4). The function of the carboxyl group and phenolic hydroxyl group in this reaction is generally 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 9946


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ACS Catalysis Table 1. Optimization of PC Synthesisa

entry

catalyst (mol %)

1 2 3 4 5 6 7 8 9 10 11 12 13 14

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)

temp (°C) 80 80 80 80 80 80 80 60 40 room room room room room

temp temp temp temp temp

CO2 (bar)

time (h)

yield (%)

5 5 5 5 5 5 5 5 5 5 5 1b 1b 1b

4 4 4 4 4 4 4 4 4 4 24 24 24 24

77 68 52 57 99 79 61 79 53 26 37 29 75 96

used to investigate the function of two hydrogen bond donors. Upon addition of PO to the catalyst 1e, shifting of the resonances of the COOH proton and OH proton was not observed (Figure S5). However, gradual weakening of the resonance of the COOH proton was observed (Figure S5), which was consistent with what observed in the in situ FTIR analysis. In order to exclude H−D exchange between the COOH proton and deuterium reagents, a 1H NMR detection of catalyst 1e in deuterium reagents overnight without addition of PO was performed. The result indicated that the chemical signal of the COOH proton was unchanged. The resonance of the carbon of COOH shifted downfield from δ 174.60 to 175.17 ppm; however, shifting of the resonance of the aromatic carbon attached to 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); therefore, we can safely exclude the pathway using phenol as the Brønsted acid. The effect of the counteranions on the catalytic performance was also studied. The catalytic activities of 1e−g, which bear I−, Br−, and Cl− ions, respectively, increased in the order 1e > 1f > 1g (I−, Br−, and Cl−; Table 1, entries 5−7). Subsequently, we investigated the performance of catalysts 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 an increase in the reaction time to 24 h (Table 1, entry 11). Furthermore, the influence of the CO2 pressure on the outcome of the reaction was also evaluated. When the

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, and the yield was determined by GC using biphenyl as an internal standard. bCO2 balloon.

(see the Supporting Information for details). When PO was added to the catalysts, the characteristic FTIR band at 1725 cm−1 continuously decreased, which corresponds to the ν(C O) stretching vibration of the carboxyl group (Figure S1). However, the ν(OH) bending vibration of the phenolic hydroxyl group in the range of 700−800 cm−1 did not change significantly during the addition of PO to the catalyst system (Figure S2). Qualitative NMR titration methods were also Table 2. Scope of Terminal Epoxidesa

a

Conditions unless specified otherwise: PO (10.0 mmol), 1e (0.4 mmol, 4 mol %), room temperature, 1 bar of CO2 (balloon), 24 h, neat. Isolated yields are given. b40 °C. 9947


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ACS Catalysis Table 3. Scope of Internal Epoxidesa

Conditions unless specified otherwise: PO (10.0 mmol), 1e (0.4 mmol, 4 mol %), 80 °C, 1 bar of CO2 (balloon), 24 h, neat. Isolated yields are given. b100 °C, 5 bar of CO2, 24 h, TBAI (12 mol %). c100 °C, 5 bar of CO2, TBAI (12 mol %), 48 h.

a

unsubstituted oxetane was employed as a substrate, only a yield of 37% was obtained (4e in Table 3). The conversion of internal epoxides such as epoxidized fatty acid esters is challenging because of high steric hindrance.24 Subsequently, the scope of our protocol for the synthesis of fatty acid based biocarbonates 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%. The doubly epoxide functionalized carbonate 4i was obtained in an isolated yield of 43%, although the reaction time had to be prolonged to 48 h. Table 4 gives several reported organocatalytic systems employed under ambient conditions. D’Elia and co-workers reported the ascorbic acid/TBAI catalytic system.14 Under

CO2 pressure was decreased from 5 to 1 bar, the yield was reduced 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 to 4 mol %, the yield of 3a reached 96% under ambient conditions (Table 1, entry 14). Under the optimized reaction conditions, the terminal epoxide 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−j in 73%−95% yields under ambient (room temperature, 1 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 higher reactivity in comparison to those with aryl groups (3a−j vs 3l). The terminal epoxides 2l required an increase in the reaction temperature to 40 °C, to achieve 89% yield (3l in Table 2). When the temperature was increased to 40 °C while still 1 bar of CO2 was maintained, substrate 2m reacted smoothly to give an 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). Internal epoxides are challenging substrates in cycloaddition reactions with CO2 owing to their high steric hindrance (Table 3). These were also evaluated in our catalytic system. Increased reaction temperatures were required to achieve high yields of the 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 pressure 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 the six-membered bicyclic cyclohexene oxide being converted into the corresponding carbonate 4b in an isolated yield of 95%, five-membered bicyclic epoxides could be also converted into their carbonates 4c,d in good yields. Oxetanes are particularly challenging substrates because of their lower ring strain. When an

Table 4. Comparison of Catalytic Activity of Catalystsa

ref

yield (%)

TON

TOF (h−1)

14 15c this workd this worke

64 90 96 75

16 18 24 38

0.70 3.0 1.0 1.6

entry 1 2 3 4

b

a

Abbreviations: TON, turnover number; TOF, turnover frequency (TOF = TON/reaction time (h)). bConditions: PO (25.0 mmol), ascorbic acid (4 mol %), TBAI (8 mol %), room temperature, 1 bar of CO2 (balloon), neat, 23 h. cConditions: PO (10.0 mmol), P ylideCO2 adducts (5 mol %), room temperature, 1 bar of CO2 (balloon), neat, 6 h. dConditions: PO (10.0 mmol), 1e (4 mol %), room temperature, 1 bar of CO2 (balloon), neat, 24 h. eConditions: PO (10.0 mmol), 1e (2 mol %), room temperature, 1 bar of CO2 (balloon), neat, 24 h. 9948


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that the 1e-mediated reaction undergoes a different reaction pathway in comparison with 1f,g. In order to prove whether the synergistic action between the imidazolium and amino acid moieties 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, eq 1) with a pyridine-substituted tyrosine (1i in Scheme 3, eq 1). Previous literature reported that phenol is an active organocatalytic moiety for the cycloaddition of CO2 to epoxides. Therefore, the 1h/phenol binary system was also tested for the cycloaddition of CO2 to PO under ambient conditions. However, only a 5% yield of product was obtained (Scheme 3, eq 2). The results showed that a two-component catalytic system had difficulty in triggering this reaction under ambient conditions (Scheme 3, eqs 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 groups on this reaction, a catalyst was synthesized by the esterification of carboxylic acid (1j in Scheme 3, eq 3). In the absence of carboxyl protons, only a 9% yield was obtained (Scheme 3, eq 3). The results showed that the existence of carboxyl groups is essential for high catalytic performance. The effects of amino groups were also investigated (Scheme 3, eq 4). When an amino group was protected by a methyl group (1k in Scheme 3, eq 4), the catalytic activity of catalyst 1k was almost not affected and a slightly lower yield (93% yield in Scheme 3, eq 4) was obtained in comparison with the catalyst 1e (96% yield in Table 1, entry 14). We also investigated the possible process of CO2 binding to amino groups 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 groups is negligible in this reaction. To determine whether CO2 preferentially binds to the C2 position of the benzimidazolium ring, a catalyst was designed by introducing a methyl group to the C2 position of the benzimidazolium ring (1l in Scheme 3, eq 5). The result showed that alkylation of the C2 position leads to a significant decrease in product yield, which might be caused by the lack of interaction between CO2 and the C2 position of the 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 the amino group and pyridine) using DFT calculations (Scheme S1). The calculated results indicated that the free energy changes and Gibbs free energy barriers of the possible pathways would be too high to overcome; therefore, we think that the pyridine N atom cannot directly work as a catalyst to activate the CO2 molecule. This was also confirmed by in situ FTIR. The C−C and C−H bond stretching vibrations of the pyridine ring in the range of 700−1100 cm−1 had no change in wavelengths during the addition of CO2 to the catalyst system (Figures S3 and S4). 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 methods, which have been widely applied in 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, Cl), and so the efficiency of the catalyst

ambient conditions, a TON of 16 and a TOF of 0.7 were achieved using PO as model substrate (Table 4, entry 1). TON = 18 and TOF = 3 were reported by Lu et al. using 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 organocatalysts reported in the literature 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). Lowering the catalyst loading to 2 mol % slightly increased the TON and TOF value (Table 4, entry 4). These results indicated that the catalysts developed in this work also are highly active catalysts, with results commensurate with those for the catalysts reported by Lu et al.15 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 multifunctionalcatalyzed reaction from the viewpoint of stereochemistry using (R)-2l. As shown in Scheme 2, (R)-2l was converted Scheme 2. Investigation of the Reaction Mechanism by Using an Optically Pure Epoxide

preferentially into (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). To clarify the effect of the counteranions on the catalysts, we used pure trans-2,3-epoxybutane to obtain some mechanistic insights into the reaction pathways (Table 5). When 1f (Br−) and 1g (Cl−) were used as catalysts, trans-3n and cis-3n were obtained in a ratios 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 Table 5. Possible Reaction Pathways for 1e−g Catalysis of the Conversion of trans-2,3-Epoxybutane into Cis and Trans Cyclic Carbonatesa

entry

catalyst

cis-4a (%)b

trans-4a (%)b

total yield (%)c

1 2 3

1e 1f 1g

57 8 3

43 92 97

83 58 12

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. bDetermined by 1 H and 13C NMR (CDCl3) from the raw reaction mixture.5d,25 c Isolated yield. 9949


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ACS Catalysis Scheme 3. Study on Active Sites of Catalysts

addition, 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 the 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 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, another 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 = I, we think that the stereoselectivity is kinetically controlled, and the energy barrier of the whole reaction leading to cis-P via TS2 (23.6 kcal/mol) is slightly lower than that leading to trans-P via TS6 (24.0 kcal/mol), which aligns well with the experimental observation that the cis-P:trans-P ratio is 57:43. When X = Br, Cl, HX would have more difficulty in dissociating with the NHC catalyst; we think that the efficiency of the NHC catalyst would become lower and the stereoselectivity would be thermodynamically controlled, and thus the more stable trans-P should be the main product. In summary, we have demonstrated that one-component, neat, and highly active multifunctional catalysts can offer a competitive alternative to metal catalysts in the conversion of epoxide with CO2 under mild conditions. This potential is clearly proven in the conversion of internal epoxides which are

would be the best when X = I, which is in agreement with the experimental observation that the yield is the highest when X = I. First, the carbene carbon of the NHC catalyst would nucleophilically attack the carbon atom of CO2 to generate the zwitterionic intermediate M1 via transition state TS1. Second, the negatively charged oxygen nucleophilically attacks the epoxy carbon of the reactant trans-R1, which is accompanied by a 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 a C−C single-bond rotation. Subsequently, a five-membered-ring closure process occurs, coupled with another proton transfer to afford intermediate M4 via transition state TS3. The last process is the dissociation of the NHC catalyst to give the product cis-P via transition state TS4. As shown in Figure 2, the Gibbs free energy barriers via the transition states TS1−TS4 are 1.2, 23.6, 0.2, and 8.1 kcal/mol, respectively; therefore, the epoxy ring opening should be the rate-determining step. Interestingly, the organocatalyst has two functions: one is to work as a Lewis base NHC to activate the CO2, and the other is to provide and abstract the proton as a Brønsted acid/base. 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 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), and so we can safely exclude this pathway. In 9950


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ACS Catalysis Scheme 4. Suggested Catalytic Cycles

CO2 with the carboxyl group as a proton transfer agent. In contrast with many organocatalysts in which halide anion is used as the nucleophilic agent for ring opening of epoxide, in our catalytic system halide anion was used as a carbene initiator by deprotonation. The knowledge obtained through these studies provides insight and new concepts to 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 2,6-dibromopyridine (5 mmol), amine (10 mmol), CuI (1 mmol), tetramethylethane-1,2diamine (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 a nitrogen atmosphere. Thereafter, 2bromo-6-substituted pyridine (5 mmol), amino acid (7.5 mmol), CuI (1 mmol), N,N-dimethylethylenediamine (2 mmol), and K2CO3 (15 mmol) in DMF (20 mL) were allowed to react at 120 °C for 48 h under a nitrogen atmosphere. The resultant 2,6-disubstituted pyridine (5 mmol) and alkyl halide (10 mL) were heated to the desired temperature, and the reaction mixture was stirred for 8 h in an air atmosphere, affording the series of multifunctional organocatalysts 1a−g. The solvent was concentrated under

Figure 2. Energy profiles of the possible reaction pathways leading to the products cis-P and trans-P.

generally difficult substrates to activate, especially by organocatalytic systems. The control experiments and DFT calculations suggest that the reaction was realized a combination of the carbene as a catalyst for the activation of 9951


Research Article

ACS Catalysis

= 8.0 Hz, 2H), 7.06 (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), yellowish solid (1.056 g, 50%), mp 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; 13 C 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), yellowish solid (0.972 g, 46%), mp 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), yellowish solid (1.366 g, 72%), mp 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; 13C 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. Data for 1i are as follows: purification by flash chromatography (DCM/MeOH = 20/1), a yellowish solid (1.224 g, 65%), mp 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; 13 C 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), yellowish solid (1.681 g, 61%),

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), yellowish solid (1.468 g, 61%), mp 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; 13C NMR (100 MHz, DMSOd6) 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. Data for 1b are as follows: purification by flash chromatography (DCM/MeOH = 25/1), yellowish solid (1.227 g, 49%), mp 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; 13C 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), yellowish solid (0.905 g, 35%), mp 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; 13C 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), yellowish solid (1.309 g, 49%), mp 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; 13 C 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): yellowish solid (1.671 g, 61%), mp 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 9952


Research Article

ACS Catalysis mp 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; 13C 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), yellowish solid (0.791 g, 31%), mp 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), yellowish solid (0.763 g, 27%), mp 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, 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. An epoxide (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; 13 C 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; 13C NMR (100 MHz, CDCl3) δ 154.54, 74.54, 66.99, 44.20 ppm. 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; 13C 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%), mp 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; 13C 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%), mp 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 9953


Research Article

ACS Catalysis (m, 2H), 6.72 (d, J = 8.0 Hz, 1H), 5.35 (s, 1H), 4.78 (t, J = 8.4 Hz, 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%), mp 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 MHz, CDCl3) δ 4.33−4.26 (m, 2H), 1.41−1.39 (m, 6H) ppm; 13 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; 13C 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 chromatography (petroleum ether/ EtOAc = 5/1) gave a white solid (998.7 mg, 78%): 1H 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. Methyl 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; 13C 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 8-(5-Octyl-2-oxo-1,3-dioxolan-4-yl)octanoate (4g).24c 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, 1 H 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, 1H 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; 13C 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%), as 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; 13C 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 of the theoretical calculations in the study were performed using the Gaussian16 program package.27 All of the geometries were optimized at the M062X28/6-31G** level in the gas phase, and the harmonic vibrational frequency calculations were performed at the same level to confirm the local minima and transition state.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acscatal.8b01925. NMR spectra of the organocatalysts and prepared cyclic carbonates (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*N.L.: e-mail, [email protected], [email protected]; fax, (+0086)-0993-205-7270; tel, (+0086)-0993-205-7277. *D.W.: e-mail, [email protected]. *B.D.: e-mail, [email protected]. ORCID

Ning Liu: 0000-0001-7299-0400 Chuan Wang: 0000-0002-9219-1785 Shi-Jun Li: 0000-0001-9872-6245 Donghui Wei: 0000-0003-2820-282X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for the support from the National Natural Science Foundation of China (Grant Nos. U1603103 and 21466033).

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REFERENCES

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