2-(1-Bromo-1-methyl-ethyl)-2-methyl-[1,3]dioxolane

Juan M. Castro, Pablo J. Linares-Palomino, Sofía Salido, Joaquín Altarejos,* Manuel Nogueras and Adolfo Sánchez

Departamento de Química Inorgánica y Orgánica, Facultad de Ciencias Experimentales, Universidad de Jaén, 23071 Jaén, Spain. Tel.: 34-953-002743, fax: 34-953-012141

 E-mail: [email protected]

Received: 16 February 2004 / Accepted: 25 March 2004 / Published: 29 March 2004

Keywords: Bromination, a-bromoketone, dioxolane ring.

A solution of bromine (0.3 mL, 5.90 mmol) in CCl₄ (2 mL) was slowly added over a stirred mixture of 3-methyl-butan-2-one (1) (505 mg, 5.90 mmol) and AcOH (0.33 mL) at room temperature. After complete addition of bromine it was left reacting for 1 h and then, the reaction was quenched by pouring carefully aqueous NaHSO₃ (25 mL, 40% w/v). The organic layer was washed with 40% NaHSO₃ (25 mL), saturated NaHCO₃ (3×25 mL) and brine (3×25 mL). The organic layer was dried over anhydrous Na₂SO₄, and 15 mL of MeOH were added to evaporate the azeotrope under reduced pressure. The residue (1.03 g), which contains mainly 3-bromo-3-methyl-butan-2-one (2), was resolved in benzene (20 mL) and anhydrous p-TsOH (171 mg, 1.00 mmol) and  ethyleneglycol (928 mg, 14.90 mmol) were added. Then a Dean-Stark trap device was fit and the reaction refluxed for 4.5 h. The crude reaction was worked up by washing with saturated NaHCO₃ (3×25 mL) and brine (4×25 mL) and the organic layer dried over anhydrous Na₂SO₄, after that, MeOH (15 mL) was added to evaporate the azeotrope under reduced pressure. The residue (811 mg) was purified by reduced pressure distillation (0.15 mmHg, 32 ºC) to yield the title compound 3 (770 mg, 3.70 mmol, 62% from 1) as a colorless liquid.

IR (neat, n, cm^-1): 1161, 1093, 1045, 951 (C-O-C), 649 (C-Br).

¹H NMR (300 MHz, CDCl₃, d, ppm): 1.52 (3H, s, Me-2), 1.79 (6H, s, 2Me-1’), 4.05 (4H, br s, H-4, H-5).

¹³C NMR (75 MHz, CDCl₃, d, ppm): 20.52 (Me-2), 29.51 (C-2’, Me-1’), 65.93 (C-4, C-5), 69.99 (C-1’), 111.92 (C-2).

MS (70 eV, m/z): 195 ([M+2]⁺–Me, 1%), 193 (M⁺–Me, 2), 129 (M⁺–Br, 5), 153 (C₃H₆⁸¹Br⁺, 1), 121 (C₃H₆⁷⁹Br⁺, 1), 114 (M⁺–Br–Me, 6), 99 (M⁺–Br–2Me, 5), 87 (C₄H₇O₂⁺, 98), 69 (9), 57 (22), 43 (100).

Acknowledgements:

We wish to thank the Ministerio de Ciencia y Tecnología for financial support (R+D Project PPQ2000-1665) and the Ministerio de Educación, Cultura y Deporte for a fellowship to J. M. Castro.

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