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Synlett 2014; 25(2): 197-200
DOI: 10.1055/s-0033-1340109
DOI: 10.1055/s-0033-1340109
letter
A New Entry to Sonochemical/Efficient Agitation Switching: Alkene Formation through Epoxide Deoxygenation
Further Information
Publication History
Received: 16 September 2013
Accepted after revision: 08 October 2013
Publication Date:
13 November 2013 (online)
![](https://www.thieme-connect.de/media/synlett/201402/lookinside/thumbnails/10.1055-s-0033-1340109-1.jpg)
Abstract
‘Sonochemical switching’ whereby the pathway of a reaction is changed under sonication conditions was first reported by Ando, and in fact could just be the consequence of efficient agitation. We herein report a new addition to this switching phenomenon in which epoxides are converted to cyclic carbonates by addition of CO2 under standard heating/electrolysis conditions but are ‘switched’ to alkenes under deoxygenating sonochemical conditions.
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References and Notes
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- 10 Representative Procedure for the Standard Synthesis of Phenyl Ethylene Carbonate (Ref. 2): Styrene oxide (1; 0.12 g, 1.0 mmol) and CO2 (balloon) in MeCN (150 mL) were electrolysed (constant current: 60 mA) for 6 h in a single compartment cell [Mg anode and copper(0) cathode] containing Bu4NBr (0.32 g, 1.0 mmol) as supporting electrolyte at 50 °C. On completion the reaction mixture was washed with aq 0.1 M HCl (50 mL) followed by extraction with Et2O (3 × 35 mL). The combined organic extracts were then dried over MgSO4 and evaporated under reduced pressure to afford an amber oil, which was suspended in EtOAc (100 mL). After 1 h the precipitated Bu4NBr (0.30 g, 95%) was removed by filtration and the solvent evaporated under reduced pressure to afford an amber oil. This crude material was purified by column chromatography on silica gel eluting with EtOAc–light petroleum to yield a colourless solid (conversion: 99%; yield: 0.12 g, 96%); mp 49–51 °C. IR (CH2Cl2): 1167 (C–O), 1789 (C=O) cm–1. 1H NMR (400 MHz, CDCl3/Me4Si): δ = 4.35 (dd, J = 7.9, 8.4 Hz, 1 H), 4.80 (dd, J = 8.5 Hz, 1 H), 5.68 (dd, J = 7.99 Hz, 1 H), 7.35–7.45 (m, 5 H). 13C NMR (100 MHz, CDCl3/Me4Si): δ = 71.2, 78.0, 125.9, 129.3, 129.8, 135.8, 154.8.
- 11 Representative Procedure for the Sonochemical Synthesis of Styrene (2): Styrene oxide (1; 0.12 g, 1.0 mmol) and CO2 (balloon) in MeCN (150 mL) were electrolysed (constant current: 60mA) for 6 h in a single compartment cell [Mg anode and copper(0) cathode] containing Bu4NBr (0.32 g, 1.0 mmol) as supporting electrolyte. The reaction vessel was submerged in a sonication bath at 50–60 Hz. On completion the reaction mixture was washed with aq 0.1 M HCl (50 mL) followed by extraction with Et2O (3 × 35 mL). The combined organic extracts were then dried over MgSO4 and evaporated under reduced pressure to afford an amber oil, which was suspended in EtOAc (100 mL). After 1 h the precipitated Bu4NBr (0.30 g, 95%) was removed by filtration and the solvent evaporated under reduced pressure to afford an amber oil. This crude material was purified by column chromatography on silica gel eluting with EtOAc–light petroleum to yield a colourless liquid (0.094 g, 90%). IR (CH2Cl2): 1442 (C=C), 1610 (C=C) cm–1. 1H NMR (400 MHz, CDCl3/Me4Si): δ = 5.25 (dd, J = 0.8, 11.0 Hz, 1 H), 5.75 (dd, J = 1.2, 17.5 Hz, 1 H), 6.72 (dd, J = 11.0, 17.5 Hz, 1 H), 7.24–7.41 (m, 5 H). 13C NMR (100 MHz, CDCl3/Me4Si): δ = 113.7, 126.2, 127.8, 128.5, 137.0, 137.7.
- 12 General Procedure for Cyclic Carbamate Formation: The aziridine (2.0 mmol) in MeCN (20 mL) was added to a solution of supporting electrolyte Bu4NBr (0.64 g, 2.0 mmol) in MeCN (130 mL), and the resulting solution was flushed with CO2 for 1 h, followed by heated electrolysis at 50 ºC with constant stirring at a constant current of 60 mA for 6 h under a CO2 balloon, in a single compartment cell containing a magnesium anode and copper cathode. On completion the reaction mixture was filtered to remove the precipitated MgCO3 and evaporated to dryness followed by addition of EtOAc (50 mL). After 1 h the precipitated Bu4NBr (ca. 70% recovered) was removed by filtration and the solvent evaporated under reduced pressure. The crude carbamate was then analysed by 1H NMR spectroscopy to determine the regioselectivity and then purified by column chromatography on silica gel eluting with EtOAc–light petroleum.
- 13 3-Benzyl-4-methyloxazolidin-2-one (3): colourless oil, mixture of regioisomers observed in a 95:5 ratio in favour of the title compound (conversion: 98%; yield: 0.34 g, 87%). IR (CH2Cl2): 1181 (C–N), 1255 (C–O), 1416 (C=C), 1721 (C=O) cm–1. 1H NMR (400 MHz, CDCl3/Me4Si): δ = 1.21 (d, J = 6.0 Hz, 3 H), 2.97 (dd, J = 6.8, 8.6 Hz, 1 H), 3.50 (dd, J = 8.4 Hz, 1 H), 4.37–4.46 (m, 2 H), 4.57–4.67 (m, 1 H), 7.26–7.33 (m, 5 H). 13C NMR (100 MHz, CDCl3/Me4Si): δ = 18.3, 46.7, 50.8, 64.7, 127.8, 127.9, 128.3, 128.8, 158.3. 3-Benzyl-5-phenyloxazolidin-2-one (4): colourless solid, single regioisomer observed (conversion: 51%; yield: 0.162 g, 32%); mp 61–63 °C. IR (CH2Cl2): 1157 (C–N), 1250 (C–O), 1454 (C=C), 1752 (C=O) cm–1. 1H NMR (400 MHz, CDCl3/Me4Si): δ = 3.30 (dd, J = 7.5, 8.8 Hz, 1 H), 3.75 (dd, J = 8.8 Hz, 1 H), 4.41–4.56 (m, 2 H), 5.45 (dd, J = 8.3 Hz, 1 H), 7.21–7.40 (m, 10 H). 13C NMR (100 MHz, CDCl3/Me4Si): δ = 45.9, 48.5, 74.6, 125.5, 126.3, 128.1, 128.2, 128.8, 128.9, 135.7, 138.6, 158.0.
- 14 Clegg W, Harrington RW, North M, Pasquale R. Chem. Eur. J. 2010; 16: 6828
- 15 This was confirmed by subjecting phenyl ethylene carbonate instead of styrene oxide to the reaction conditions reported in reference 11. Only phenyl ethylene carbonate and supporting electrolyte was observed in the crude reaction 1H NMR spectrum.
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