One-Pot Synthesis of Cyclic Carbonates from Aldehydes, Sulfur Ylide, and CO₂

Abstract

Treatment of aldehydes with sulfur ylide (CH₂=SOMe₂ or CH₂=SMe₂), in the presence of CO₂ (1 atm) bubbled sequentially under mild conditions, produces cyclic carbonates in preparative yields. Sodium iodide formed in situ promotes the reaction between epoxide as intermediate and CO₂ at ambient conditions, thus constituting a powerful metal-free synthesis of organic cyclic carbonates directly from aldehydes.

Key words

cyclization - epoxides - insertion - carbon dioxide - cyclic carbonates

Carbon dioxide is one of the major constituents of greenhouse gases, and to control its rapidly increased concentration in atmosphere is a major challenge for scientific communities.[1] Global-warming concern has dramatically increased interest in using CO₂ as a feedstock for the preparation of value-added chemicals.[1j] Although CO₂ is an attractive nonhazardous C₁ synthon in abundance, its utilization in chemical transformations remains challenging because of its high thermodynamic stability and low chemical reactivity.[2] In particular, the synthesis of low-energy target molecules (e.g., organic carbonates) represents a promising alternative to overcome this thermodynamics. Organic cyclic carbonates are biodegradable chemicals that find tremendous applications as electrolytic materials in lithium ion batteries, polar aprotic solvents, intermediates in the production of pharmaceuticals and fine chemicals, as well as for developing engineered polymeric materials.[3] Biologically active molecules that contain a cyclic carbonate moiety have also been isolated from various natural sources.[4] In literature, cyclic carbonates are generally prepared by the cycloaddition of CO₂ with epoxides in the presence of many activating reagents such as quaternary ammonium salts,[5a] [b] [c] azaphosphatranes,[5d] metal–salen complexes derived from Al, Zn, Mg, and other first-row transition metals.[6] Other methods of their synthesis include the reaction of CO₂ with styrenes,[7] propargyl alcohols,[8] allyl alcohols,[9] diols,[10] or halohydrins.[11] Although these reported methods provide a simple route for the environmentally benign chemical fixation of CO₂ to produce cyclic carbonates, these have certain limitations such as dependence on epoxides as starting materials, use of toxic or costly reagents, relatively high pressure and temperature, often requiring a tedious workup procedure for their isolation. Sulfur ylides have been widely employed in the conversion of aldehydes into epoxides (Corey–Chaykovsky reaction) in organic synthesis, thereby serving as C₁ carbon source under ambient conditions.[12] In this note, we wish to disclose an efficient and metal-free, one-pot procedure for the synthesis of organic cyclic carbonates by the sequential reaction of aldehydes with sulfur ylides (CH₂=SOMe₂ or CH₂=SMe₂) followed by its reaction with CO₂ (1 atm) in the absence of heavy-metal additives under ambient conditions (Scheme [1]).

Scheme 1 Synthesis of cyclic carbonates from aldehydes, sulfur ylide, and CO₂

Preliminary experiments have shown that when all the three components (aldehyde, sulfur ylide, and CO₂) were treated together at 25 °C in DMSO, a stable, colorless adduct[12] (mp 135–137 °C) was obtained instantaneously due to the preferential reaction of sulfur ylide with CO₂. It was then reasoned that CO₂ could be bubbled sequentially after the in situ formation of epoxide from aldehyde and sulfur ylide.

Table 1 Optimization Parameters for Cyclic Carbonates^a

Entry	Solvent	Temp (°C)	Time (h)	Yield of 2a (%)b	Yield of 3a (%)b	Yield of 4a (%)b
1	DMSO	25	12	95	–	–
2	DMSO	40	12	–	65	30
3	DMSO	60	12	–	53	41
4	DMSO	80	12	–	23	71
5	DMSO	100	12	–	–	87
6	DMSO–THF(1:1)	25	12	96	–	–
7	DMSO–THF(1:1)	40	6	–	–	94

^a Aldehyde (3 mmol), NaH (3.3 mmol), Me₃SOI (3.3 mmol), solvent (20 mL).

^b Isolated yield after column chromatographic purification.

The CO₂ insertion into epoxide can be further facilitated by NaI as promoter formed in the reaction. However, when CO₂ (1 atm) was bubbled into the reaction mixture at 25 °C after one hour (by which time the complete formation of epoxide has taken place), only epoxide 2a was isolated in 95% yield (Table [1], entry 1). At 40 °C, it gave the desired cyclic carbonate 4a (30%) along with significant amount of iodo alcohol 3a (65%). Subsequently it was found that the yield of 4a was, however, dependent linearly on temperature (Table [1], entries 3–5). At this stage, it was thought that by reducing the polarity of the solvent, the nucleophilicity of the iodo alkoxide 3 (Scheme [2]) could be increased for its reaction with CO₂ so as to maximize the yield of 4a.[11] Thus, when the reaction was carried out with a relatively low polar solvent system (DMSO–THF, 1:1) at 25 °C under CO₂ (1 atm), no cyclic carbonate was observed; only epoxide 2a was again obtained in 96% yield. Finally, at 40 °C, a dramatic improvement in yield of 4a (94%) was achieved with the same solvent system Table [1], entry 7). Unfortunately, other bases (KOH, NaOH, KOt-Bu)[13] were not as effective as NaH. With the optimized reaction conditions in hand,[16] we then examined the substrate scope of the reaction (Table [2]). Even lower members of cyclic carbonates of commercial importance (4b and 4c) can be prepared in moderate to good yields. Further, aldehydes bearing halo, cyano, nitro, methoxy, and methylene dioxy groups on the aromatic nucleus and functionalized aliphatic aldehydes underwent this sequential reaction smoothly to afford the corresponding cyclic carbonates 4a–v in high yields. Among the substrates screened, aldehdyes with halo 4k–n and cyano 4t substituents on the aromatic nucleus were found to be the best substrates for this methodology.

Volatile aliphatic and conjugated aldehydes[14] were also converted into the corresponding cyclic carbonates 4b–h in high yields (Table [2], entries 2–8). Also, chiral amino aldehyde 1u gave the corresponding cyclic carbonate 4u efficiently under the reaction conditions (Table [2], entry 21). Cyclic carbonates 4a–v have exhibited a strong IR absorption in the range 1792–1822 cm^–1 due to the C=O stretching vibration of the cyclic carbonate moiety.

Table 2 Cyclic Carbonates from Aldehydes and CH₂=SOMe₂ or CH₂=SMe₂ with CO₂ ^a

Entry	Aldehydes 1	Yield of cyclic carbonates (%)b
1	benzaldehyde (1a)	4a 94
2	acetaldehyde (1b)	4b 40
3	propionaldehyde (1c)	4c 65
4	isobutyraldehyde (1d)	4d 73
5	n-pentanal (1e)	4e 89
6	n-heptanal (1f)	4f 94
7b	acrolein (1g)	4g 65
8b	cinnamaldehyde (1h)	4h 98
9	2-methoxybenzaldehyde (1i)	4i 85
10	3,4,5-trimethoxybenzaldehyde (1j)	4j 90
11	4-fluorobenzaldehyde (1k)	4k 90
12	4-chlorobenzaldehyde (1l)	4l 87
13	2-bromobenzaldehyde (1m)	4m 96
14	4-trifluoromethylbenzaldehyde (1n)	4n 98
15	2-nitrobenzaldehyde (1o)	4o 79
16	3-nitrobenzaldehyde (1p)	4p 75
17	piperonal (1q)	4q 86
18	3-benzyloxy-1-propanal (1r)	4r 80
19	3-phenylpropanal (1s)	4s 77
20	3,4-(OMe)2-2-CN-phenyl-propanal (1t)	4t 83
21	(S)-(α-NHBoc)-3-phenyl-propanal (1u)	4u 79
22	4-thiomethylbenzaldehyde (1v)	4v 90

^a Reaction conditions: aldehyde (3 mmol), NaH (3.3 mmol), Me₃SOI (3.3 mmol), DMSO (10 mL), THF (10 mL), 25 °C, 1 h, then CO₂ bubbling 40 °C, 6 h.

^b Dimethylsulfonium methylide was used instead of dimethyloxosulfonium methylide.

For comparative studies, it was of interest to investigate the effect of temperature on cycloaddition of styrene epoxide with CO₂ using various alkali metal iodides. Thus, when styrene epoxide was treated with CO₂ (1.0133 bar) in the presence of NaI (100 mol%) in DMSO–THF (1:1) at 25 °C for 12 hours, no reaction took place. However, when the same reaction was carried out at 40 °C for six hours, the corresponding styrene cyclic carbonate was obtained in 95% yield. Also, other alkali metal iodides (KI and LiI, in stoichiometric amount) under the same reaction conditions, could be employed to give the styrene cyclic carbonate in 73% and 83% yield, respectively. NaI could also be used in catalytic amount (10 mol%) to give styrene cyclic carbonate in 91% yield, although it took 38 hours to completion. From the above investigations, we strongly believe that a slightly higher temperature (40 °C) is needed for the activation of styrene epoxide by alkali metal iodide.

Based on the above observations, a probable mechanistic pathway for the formation of cyclic carbonates is shown in Scheme [2].[15] Firstly, aldehydes 1a–v react with sulfur ylide (generated in situ from O=SMe₃I and NaH in ­DMSO) to form epoxide 2 which was isolated and characterized. Subsequently, NaI formed in situ in the reaction medium promotes the regioselective ring opening of epoxide 2 to give iodo alkoxide complex 3 (confirmed by isolation and characterization of iodoalcohol 3a, see Table [1]). This is followed by its simultaneous insertion with CO₂ producing the intermediate I, cyclization of which results in the formation of cyclic carbonates 4a–v.

Scheme 2 Pathway for the formation of cyclic carbonates from aldehydes, sulfur ylide, and CO₂

In summary, we have described, for the first time, a novel ‘one-pot’ procedure that involves reaction of aldehydes 1a–v with sulfur ylides, followed by CO₂ insertion in a ­sequential fashion leading to the high-yield synthesis of cyclic carbonates 4a–v. The salient features of the methodology are as follows: (1) unprecedented one-pot synthesis of organic cyclic carbonates directly from aldehydes; (2) inexpensive and commercially available starting materials; (3) metal-free synthesis; (4) water-soluble NaI acts as a promoter; (5) milder reaction conditions; (6) functional-group tolerance; and (7) high yields of cyclic carbonates.

Acknowledgment

We sincerely thank CSIR, New Delhi, India (NWP-0021B) for financial support. RDA and BSK thank CSIR, New Delhi, India for research fellowships. Authors also thank Dr V. V. Ranade, Chair, Chemical Eng. & Process Develop. Div. and Dr B. D. Kulkarni, Distinguished Scientist for their constant encouragement and support.

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• 16 General Description Solvents were purified and dried by standard procedures before use; PE of boiling range 60–80 °C was used. Melting points are uncorrected and recorded on a Buchi B-542 instrument. ¹H NMR and ¹³C NMR spectra were recorded on Bruker AC-200 spectrometer unless mentioned otherwise. Elemental analysis was carried out on a Carlo Erba CHNS-O analyzer. Infrared spectra were recorded on Shimadzu FTIR-8400 spectrometer and absorption is expressed in cm^–1. HRMS data for new compounds were recorded on a Thermo Scientific Q-Exactive, Accela 1250 pump. Purification was done using column chromatography (230–400 mesh). General Experimental Procedure for the Preparation of Cyclic Carbonates 4a–v NaH (0.132 g, 3.3 mmol; previously washed with anhydrous PE to remove oil) was taken in an oven-dried three-necked flask, followed by addition of anhydrous DMSO (10 mL) through a septum to it, and the whole slurry was stirred at 25 °C under N₂ atmosphere. Solid Me₃SOI (0.726 g, 3.3 mmol) was added to the slurry with stirring over a period of 5 min via a solid addition funnel until it becomes a homogeneous solution. A solution of aldehyde 1a–v (3 mmol), dissolved in anhydrous THF (10 mL), was added dropwise to the reaction mixture. After 1 h, CO₂ (1 atm) was then bubbled slowly via a needle into the reaction mixture, (after ascertaining that aldehyde was completely converted into epoxide, monitored by TLC) at 40 °C, for 6 h. Water (10 mL) was added to quench the reaction. It was then extracted with EtOAc (3 × 20 mL); the organic layer was washed with brine and dried over anhydrous Na₂SO₄ and the solvent concentrated, product purified by silica gel column chromatography (100–200 mesh) using PE and EtOAc (70:30) as eluent to afford pure cyclic carbonates 4a–v. 4-Phenyl-1,3-dioxolan-2-one (4a) Yield 94% (463 mg, 2.82 mmol); colorless solid; mp 53–54 °C (lit. mp 51–53 °C). IR (CHCl₃): ν_max = 769, 1068, 1168, 1328, 1458, 1812 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 4.29 (t, J = 7.9 Hz, 1 H), 4.77 (t, J = 7.9 Hz, 1 H), 5.64 (t, J = 7.9 Hz, 1 H), 7.32–7.42 (m, 5 H). ¹³C NMR (50 MHz, CDCl₃): δ = 70.9, 77.8, 125.7, 129.0, 129.4, 135.8, 154.6. Anal. Calcd (%) for C₉H₈O₃: C, 65.85; H, 4.91. Found: C, 65.84; H, 4.90. 4-Methyl-1,3-dioxolan-2-one (4b) Yield 40% (122.5 mg, 1.2 mmol); colorless oil; IR (CHCl₃): ν_max = 711, 776, 1051, 1120, 1183, 1354, 1389, 1793 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 1.49 (d, J = 6.1 Hz, 3 H), 4.02 (dd, J = 8.2, 1.0 Hz, 1 H), 4.55 (t, J = 8.0 Hz, 1 H), 4.77–4.94 (m, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 19.0, 70.4, 73.4, 154.8. Anal. Calcd (%) for C₄H₆O₃: C, 47.06; H, 5.92. Found: C, 47.04; H, 5.91. 4-Ethyl-1,3-dioxolan-2-one (4c) Yield 65% (226.4 mg, 1.95 mmol); colorless oil. IR (CHCl₃): ν_max = 1060, 1177, 1377, 1797 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 1.03 (t, J = 7.4 Hz, 3 H), 1.72–1.87 (m, 2 H), 4.1 (dd, J = 8.2, 1.5 Hz, 1 H), 4.55 (t, J = 8.2 Hz, 1 H), 4.63–4.73 (m, 1 H). ¹³C NMR (50 MHz, CDCl₃): δ = 7.9, 26.2, 68.5, 77.6, 154.6. Anal. Calcd (%) for C₅H₈O₃: C, 51.72; H, 6.94. Found: C, 51.75; H, 6.91. 4-Isopropyl-1,3-dioxolan-2-one (4d) Yield 73% (285 mg, 2.19 mmol); colorless oil. IR (CHCl₃): ν_max = 1075, 1175, 1392, 1789 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 0.95 (d, J = 6.8 Hz, 3 H), 1.04 (d, J = 6.5 Hz, 3 H), 1.90–2.00 (m, 1 H), 4.12–4.18 (m, 1 H), 4.37–4.53 (m, 2 H). ¹³C NMR (50 MHz, CDCl₃): δ = 16.4, 16.8, 31.4, 67.2, 80.9, 154.6. HRMS (ESI⁺): m/z = calcd for (C₆H₁₀O₃)⁺ [M + H]⁺: 131.0709; found: 131.0708. Anal. Calcd (%) for C₆H₁₀O₃: C, 55.37; H, 7.75. Found: C, 55.40; H, 7.71. 4-Butyl-1,3-dioxolan-2-one (4e) Yield 89% (384.9 mg, 2.6 mmol); gum. IR (CHCl₃): ν_max = 1066, 1173, 1797 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 0.88–0.95 (m, 3 H), 1.23–1.40 (m, 3 H), 1.68–1.80 (m, 3 H), 4.05 (dd, J = 8.2, 1.0 Hz, 1 H), 4.51 (t, J = 8.2 Hz, 1 H), 4.62–4.76 (m, 1 H). ¹³C NMR (50 MHz, CDCl₃): δ = 13.8, 22.2, 26.4, 33.6, 69.3, 76.9, 154.9. Anal. Calcd (%) for C₇H₁₂O₃: C, 58.32; H, 8.39. Found: C, 58.34; H, 8.38%. 4-Hexyl-1,3-dioxolan-2-one (4f) Yield 94% (486 mg, 2.82 mmol); gum. IR (CHCl₃): ν_max = 772, 1065, 1170, 1802 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 0.86–0.93 (m, 3 H), 1.30–1.49 (m, 8 H), 1.69–1.80 (m, 2 H), 4.06 (t, J = 7.2 Hz, 1 H), 4.51 (t, J = 8.0 Hz, 1 H), 4.62–4.76 (m, 1 H). ¹³C NMR (50 MHz, CDCl₃): δ = 13.9, 22.4, 24.3, 28.7, 31.4, 33.8, 69.2, 76.8, 154.8. Anal. Calcd (%) for C₉H₁₆O₃: C, 62.77; H, 9.36. Found: C, 62.73; H, 9.40. 4-Vinyl-1,3-dioxolan-2-one (4g) Yield 65% (222.5 mg, 1.95 mmol); yellow oil. IR (CHCl₃): ν_max = 772, 991, 1060, 1168, 1385, 1510, 1805 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 4.17 (t, J = 7.8 Hz, 1 H), 4.61 (t, J = 8.4 Hz, 1 H), 5.12 (dd, J = 14.9, 7.5 Hz, 1 H), 5.48 (t, J = 16.5 Hz, 2 H), 5.83–6.0 (m, 1 H). ¹³C NMR (50 MHz, CDCl₃): δ = 68.8, 76.8, 120.9, 132.2, 154.2. HRMS (ESI⁺): m/z calcd for (C₅H₆O₃)⁺ [M + H]⁺: 115.0396; found: 115.0392; Anal. Calcd (%) for C₅H₆O₃: C, 52.63; H, 5.30. Found: C, 52.61; H, 5.32. (E)-4-Styryl-1,3-dioxolan-2-one (4h) Yield 98% (559 mg, 2.94 mmol); colorless solid; mp 115–116 °C. IR (CHCl₃): ν_max = 1049, 1070, 1168, 1648, 1800 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 4.23 (t, J = 8.0 Hz, 1 H), 4.64 (t, J = 8.2 Hz, 1 H), 5.26 (q, J = 7.9 Hz, 1 H), 6.15 (dd, J = 15.7, 7.7 Hz, 1 H), 6.73 (d, J = 15.7 Hz, 1 H), 7.26–7.40 (m, 5 H). ¹³C NMR (50 MHz, CDCl₃): δ = 69.2, 77.6, 122.4, 126.9, 128.8, 129.0, 134.8, 136.6, 154.4. HRMS (ESI⁺): m/z calcd for (C₁₁H₁₀O₃)⁺ [M + Na]⁺: 213.0527; found: 213.0522. Anal. Calcd (%) for C₁₁H₁₀O₃: C, 69.46; H, 5.30. Found: C, 69.41; H, 5.33. 4-(2-Methoxyphenyl)-1,3-dioxolan-2-one (4i) Yield 85% (495 mg, 2.55 mmol); gum. IR (CHCl₃): ν_max = 757, 1076, 1166, 1249, 1494, 1812 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 3.86 (s, 3 H), 4.25 (dd, J = 8.4, 1.1 Hz, 1 H), 4.82 (t, J = 8.4 Hz, 1 H), 5.81 (t, J = 8.0 Hz, 1 H), 6.90–7.04 (m, 2 H), 7.32–7.38 (m, 2 H). ¹³C NMR (50 MHz, CDCl₃): δ = 55.4, 70.5, 74.7, 110.5, 120.9, 124.9, 126.1, 130.3, 154.9, 156.1. Anal. Calcd (%) for C₁₀H₁₀O₄: C, 61.85; H, 5.19. Found: C, 61.79; H, 5.14. 4-(3,4,5-Trimethoxyphenyl)-1,3-dioxolan-2-one (4j) Yield 90% (686 mg, 2.7 mmol); brown solid; mp 133–134 °C. IR (CHCl₃): ν_max = 1068, 1125, 1243, 1510, 1796 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 3.84 (s, 3 H), 3.88 (s, 6 H), 4.31 (t, J = 8.3 Hz, 1 H), 4.78 (t, J = 8.4 Hz, 1 H), 5.60 (t, J = 7.9 Hz, 1 H), 6.54 (s, 2 H). ¹³C NMR (50 MHz, CDCl₃): δ = 56.1, 60.7, 71.1, 78.0, 102.6, 131.2, 138.8, 153.8, 154.5. HRMS (ESI⁺): m/z calcd for (C₁₂H₁₄O₆)⁺ [M + H]⁺: 255.0869; found: 255.0855. Anal. Calcd (%) for C₁₂H₁₄O₆: C, 56.69; H, 5.55. Found: C, 56.62; H, 5.50. 4-(4-Fluorophenyl)-1,3-dioxolan-2-one (4k) Yield 90% (492 mg, 2.7 mmol); colorless solid; mp 91–92 °C. IR (CHCl₃): ν_max = 773, 840, 1069, 1161, 1210, 1385, 1514, 1818 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 4.31 (t, J = 8.2 Hz, 1 H), 4.80 (t, J = 8.3 Hz, 1 H), 5.66 (t, J = 8.0 Hz, 1 H), 7.08–7.19 (m, 2 H), 7.32–7.40 (m, 2 H). ¹³C NMR (50 MHz, CDCl₃): δ = 71.0, 77.3, 116, 116.5, 127.9, 128.0, 131.6, 154.4, 160.84, 165.8. Anal. Calcd (%) for C₉H₇FO₃: C, 59.35; H, 3.87. Found: C, 59.37; H, 3.86. 4-(4-Chlorophenyl)-1,3-dioxolan-2-one (4l) Yield 87% (518 mg, 2.61 mmol); colorless solid; mp 70–71 °C (lit. mp 68–69 °C). IR (CHCl₃): ν_max = 770, 829, 1071, 1167, 1384, 1494, 1816 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 4.29 (t, J = 8.4 Hz, 1 H), 4.80 (t, J = 8.4 Hz, 1 H), 5.65 (t, J = 7.8 Hz, 1 H), 7.28–7.33 (m, 2 H), 7.36–7.44 (m, 2 H). ¹³C NMR (50 MHz, CDCl₃): δ = 70.9, 77.1, 127.2, 129.4, 134.4, 135.7, 154.3. Anal. Calcd (%) for C₉H₇ClO₃: C, 54.43; H, 3.55. Found: C, 54.37; H, 3.56. 4-(2-Bromophenyl)-1,3-dioxolan-2-one (4m) Yield 96% (700 mg, 2.88 mmol); gum. IR (CHCl₃): ν_max = 763, 969, 1072, 1125, 1159, 1208, 1473, 1817 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 4.24 (dd, J = 6.8, 1.7 Hz, 1 H), 4.99 (t, J = 8.4 Hz, 1 H), 5.94 (t, J = 8.0 Hz, 1 H), 7.28–7.39 (m, 1 H), 7.43–7.62 (m, 3 H). ¹³C NMR (50 MHz, CDCl₃): δ = 70.4, 76.3, 120.1, 126.0, 128.1, 130.4, 132.96, 136.3, 154.3. Anal. Calcd (%) for C₉H₇BrO₃: C, 44.47; H, 2.90. Found: C, 44.45; H, 2.86. 4-[4-(Trifluoromethyl)phenyl]-1,3-dioxolan-2-one (4n) Yield 98% (683 mg, 2.94 mmol); gum. IR (CHCl₃): ν_max = 771, 844, 1071, 1167, 1264, 1327, 1426, 1822 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 4.30 (t, J = 7.8 Hz, 1 H), 4.85 (t, J = 8.4 Hz, 1 H), 5.74 (t, J = 7.9 Hz, 1 H), 7.48 (d, J = 8.0 Hz, 1 H), 7.70–7.74 (d, J = 8.2 Hz, 2 H). ¹³C NMR (50 MHz, CDCl₃): δ = 70.8, 76.8, 126.0, 126.2, 126.3, 126.4, 139.9, 154.2. HRMS (ESI⁺): m/z calcd for (C₁₀H₇F₃O₃)⁺ [M + H]⁺: 233.0426; found: 233.0426. Anal. Calcd (%) for C₁₀H₇F₃O₃: C, 51.74; H, 3.04. Found: C, 51.71; H, 3.06. 4-(2-Nitrophenyl)-1,3-dioxolan-2-one (4o) Yield 79% (496 mg, 2.37 mmol); brown solid; mp 95–96 °C. IR (CHCl₃): ν_max = 1073, 1167, 1350, 1527, 1819 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 4.27 (dd, J = 9.0, 3.3 Hz, 1 H), 5.17 (t, J = 8.9 Hz, 1 H), 6.28 (dd, J = 8.7, 2.7 Hz, 1 H), 7.60–7.68 (m, 1 H), 7.83 (d, J = 4.0 Hz, 2 H), 8.26 (d, J = 8.2 Hz, 1 H). ¹³C NMR (50 MHz, CDCl₃): δ = 71.2, 74.3, 125.6, 126.2, 129.9, 134.1, 135.1, 145.9, 154.2 Anal. Calcd (%) for C₉H₇NO₅: C, 51.68; H, 3.37; N, 6.70. Found: C, 51.71; H, 3.35; N, 6.66. 4-(3-Nitrophenyl)-1,3-dioxolan-2-one (4p) Yield 75% (470 mg, 2.25 mmol); brown solid; mp 97–98 °C. IR (CHCl₃): ν_max = 1071, 1166, 1349, 1530, 1805 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 4.35 (dd, J = 8.7, 1.1 Hz, 1 H), 4.91 (t, J = 8.5 Hz, 1 H), 5.81 (t, J = 7.8 Hz, 1 H), 7.64–7.78 (m, 2 H), 8.24–8.33 (m,2 H). ¹³C NMR (50 MHz, CDCl₃): δ = 70.7, 76.3, 120.9, 124.5, 130.5, 131.4, 138.2, 148.6, 153.8. HRMS (ESI⁺): m/z calcd for (C₉H₇NO₅)⁺ [M + Na]⁺: 232.0221; found: 232.0214. Anal. Calcd (%) for C₉H₇NO₅: C, 51.68; H, 3.37; N, 6.70. Found: C, 51.72; H, 3.34; N, 6.68. 4-{Benzo[d][1,3]dioxol-5-yl}-1,3-dioxolan-2-one (4q) Yield 86% (537 mg, 2.58 mmol); gum. IR (CHCl₃): ν_max = 1070, 1164, 1251, 1505, 1791 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 4.32 (t, J = 8.4 Hz, 1 H), 4.75 (t, J = 8.5 Hz, 1 H), 5.58 (t, J = 8.0 Hz, 1 H), 6.01 (s, 2 H), 6.84 (s, 3 H). ¹³C NMR (50 MHz, CDCl₃): δ = 71.0, 78.0, 101.5, 106.1, 108.6, 120.3, 129.2, 148.5, 148.8, 154.6. Anal. Calcd (%) for C₁₀H₈O₅: C, 57.70; H, 3.87. Found: C, 57.72; H, 3.84. 4-[2-(Benzyloxy)ethyl]-1,3-dioxolan-2-one (4r) Yield 80% (533 mg, 2.4 mmol); gum. IR (CHCl₃): ν_max = 1061, 1173, 1364, 1454, 1794 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 2.02–2.10 (m, 2 H), 3.58–3.65 (m, 2 H), 4.17 (dd, J = 8.4, 1.0 Hz, 1 H), 4.47–4.52 (m, 3 H), 4.79–4.93 (m, 1 H), 7.29–7.40 (m, 5 H). ¹³C NMR (50 MHz, CDCl₃): δ = 32.0, 33.9, 61.5, 65.3, 69.1, 69.6, 73.1, 73.3, 75.0, 127.5, 127.8, 128.3, 128.4, 137.5, 154.7. Anal. Calcd (%) for C₁₂H₁₄O₄: C, 64.85; H, 6.35. Found: C, 64.82; H, 6.31. 4-Phenethyl-1,3-dioxolan-2-one (4s) Yield 77% (444 mg, 2.31 mmol); gum. IR (CHCl₃): ν_max = 1061, 1165, 1796 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 1.94–2.17 (m, 2 H), 2.72–2.91 (m, 2 H), 4.01 (dd, J = 8.3, 1.1 Hz, 1 H), 4.44 (t, J = 8.2 Hz, 1 H), 4.62–4.68 (m, 1 H), 7.15–7.34 (m, 5 H). ¹³C NMR (50 MHz, CDCl₃): δ = 30.8, 35.6, 69.1, 75.8, 126.5, 128.3, 128.7, 139.6, 154.6. Anal. Calcd (%) for C₁₁H₁₂O₃: C, 68.74; H, 6.29. Found: C, 68.71; H, 6.26. 4,5-Dimethoxy-2-(2-oxo-1,3-dioxolan-4-yl)benzonitrile (4t) Yield 83% (690.42, 2.49 mmol); gum. IR (CHCl₃): ν_max = 1064, 1168, 1270, 1516, 1793, 2218 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 2.09 (q, J = 7.8 Hz, 1 H), 2.89–2.98 (m, 1 H), 3.89 (s, 3 H), 3.94 (s, 3 H), 4.14 (dd, J = 8.3, 1.6 Hz, 1 H), 4.54 (t, J = 8.2 Hz, 1 H), 4.62–4.73 (m, 1 H), 6.80 (s, 1 H), 7.03 (s, 1 H). ¹³C NMR (50 MHz, CDCl₃): δ = 29.5, 35.0, 56.1, 69.0, 75.6, 103.0, 112.3, 114.2, 118.0, 138.1, 147.9, 152.9, 154.5. HRMS (ESI⁺): m/z calcd for (C₁₄H₁₅NO₅)⁺ [M + H]⁺: 278.1023; found: 278.1026. Anal. Calcd (%) for C₁₄H₁₅NO₅ C, 60.64; H, 5.45; N, 5.05. Found: C, 60.60; H, 5.40; N, 5.10. tert-Butyl {(S)-1-[(S)-2-Oxo-1,3-dioxolan-4-yl]-2-phenylethyl}carbamate (4u) Yield 79% (728 mg, 2.37 mmol); colorless solid; mp 148–149 °C. IR (CHCl₃): ν_max = 1061, 1169, 1249, 1366, 1689, 1800 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 1.40 (s, 9 H), 2.82–2.89 (m, 2 H), 4.09 (m, 1 H), 4.28–4.44 (m, 2 H), 4.67 (m, 2 H), 7.22–7.33 (m, 5 H). ¹³C NMR (50 MHz, CDCl₃): δ = 28.2, 38.5, 52.8, 66.5, 76.1, 80.4, 127.1, 128.88, 129.2, 136.4, 154.6, 155.9. Anal. Calcd (%) for C₁₆H₂₁NO₅: C, 62.53; H, 6.89; N, 4.56. Found: C, 62.57; H, 6.91; N, 4.60. 4-[4-(Methylthio)phenyl]-1,3-dioxolan-2-one (4v) Yield 90% (573 mg, 2.73 mmol); yellow solid; mp 55–57 °C. IR (CHCl₃): ν_max = 817, 895, 1062, 1173, 1384, 1514, 1767 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 2.49 (s, 3 H), 4.30 (t, J = 8.1 Hz, 1 H), 4.76 (t, J = 8.2 Hz, 1 H), 5.61 (t, J = 8.0 Hz, 1 H), 7.27 (s, 4 H). ¹³C NMR (100 MHz, CDCl₃): δ = 15.0, 70.7, 77.5, 125.8, 131.9, 140.7, 154.5. Anal. Calcd (%) for C₁₀H₁₀SO₃: C, 57.13; H, 4.79. Found: C, 57.17; H, 4.86. HRMS (ESI⁺): m/z calcd for (C₁₀H₁₀O₃S)⁺ [M + H]⁺: 211.0429; found: 211.0441. 2-Iodo-1-phenylethan-1-ol (3a) Gum. IR (CHCl₃): ν_max = 699, 1054, 1174, 1452, 3404 cm^–1. ¹H NMR (200 MHz, CDCl₃): δ = 2.44 (br s, 1 H), 3.33–3.52 (m, 2 H), 4.80–4.84 (m, 1 H), 7.31–7.38 (m, 5 H). ¹³C NMR (50 MHz, CDCl₃): δ = 1502, 74.0, 125.7, 128.3, 128.6, 141.1. Anal. Calcd (%) for C₈H₉IO: C, 38.74; H, 3.66. Found: C, 38.70; H, 3.63.