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DOI: 10.1055/s-2007-968009
Deprotection of Acetals and Ketals in a Colloidal Suspension Generated by Sodium Tetrakis(3,5-trifluoromethylphenyl)borate in Water
Publication History
Publication Date:
24 January 2007 (online)
Abstract
Deprotection of acetals and ketals can be achieved by using sodium tetrakis(3,5-trifluoromethylphenyl)borate (NaBArF 4) as the catalyst in water at 30 °C. For example, a quantitative conversion of 2-phenyl-1,3-dioxolane into benzaldehyde was accomplished within five minutes by using this sodium salt (0.1 mol%) in water.
Key words
acetals - phase-transfer catalysis - hydrolysis - sodium - protecting groups
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References and Notes
Typical Procedure for Hydrolysis: A mixture of NaBArF 4×2H2O (5 ¥ 10-3 mmol) [11] and acetal (5.0 mmol) in H2O (10 mL) was placed in a 25-mL flask. The resulting suspension was stirred vigorously at 30 °C for a certain period as shown in Table [2] . After the completion of the reaction, the reaction mixture was extracted with CH2Cl2 (2 ¥ 5 mL). The extracts were dried and filtered through a short column of silica gel to remove the sodium salt. Upon concentration, the desired carbonyl products were obtained in pure form. For all products reported in Table [2] , full 1H and 13C NMR data were compared with those of the pure sample obtained from commercial sources, or with reported data. [25]
14
Spectral Data for the Hydrolyzed Products:
1,2-
O
-Isopropylidene-α-d-glucofuranose:
[18]
mp 154-158 °C (dec.).1H NMR (400 MHz, D2O): δ = 5.90 (d, J = 4 Hz, 1 H), 4.58 (d, J = 4 Hz, 1 H), 4.20 (s, 1 H), 3.97 (d, J = 8 Hz, 1 H), 3.78 (m, 1 H), 3.68 (d, J = 12 Hz, 1 H), 3.97 (d, J = 8 Hz, 1 H), 3.52 (dd, J = 6 Hz, 1 H), 1.39 (s, 3 H), 1.24 (s, 3 H). 13C NMR (100 MHz, D2O): δ = 112.5 (C), 104.6 (CH), 84.3 (CH), 79.6 (CH), 78.6 (CH), 68.2 (CH), 63.4 (CH2), 25.4 (CH3), 25.0 (CH3).
4-Propylbenzaldehyde:
[21]
1H NMR (400 MHz, CDCl3): δ = 9.98 (s, 1 H), 7.81 (d, J = 6.8 Hz, 2 H), 7.34 (d, J = 6.8 Hz, 2 H), 2.68 (t, J = 7 Hz, 2 H), 1.68 (m, 2 H), 0.96 (t, J = 7 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 191.64 (CH), 150.1 (C), 134.4 (C), 129.9 (CH), 129.2 (CH), 39.0 (CH2), 26.2 (CH2), 14.2 (CH3).
4-(
tert
-Butyldimethylsilyloxymethyl)benzaldehyde:
[22]
1H NMR (300 MHz, CDCl3): δ = 10.01 (s, 1 H), 7.85 (d, J = 8 Hz, 2 H), 7.49 (d, J = 8 Hz, 2 H), 4.82 (s, 2 H), 0.96 (s, 9 H), 0.13 (s, 6 H). 13C NMR (100 MHz, CDCl3): δ = 191.6 (CH), 148.6 (C), 135.3 (C), 129.9 (CH), 126.3 (CH), 65.0 (CH2), 26.7 (CH3), 19.3 (C), -4.3 (CH3).
4-Hydroxymethylbenzaldehyde:
[23]
1H NMR (400 MHz, CDCl3): δ = 9.96 (s, 1 H), 7.84 (d, J = 6.8 Hz, 2 H), 7.50 (d, J = 6.8 Hz, 2 H), 4.78 (s, 2 H). 13C NMR (100 MHz, CDCl3): δ = 191.7 (CH), 147.7 (C), 135.6 (C), 130.1 (CH), 127.0 (CH), 65.1 (CH2).
3-Ethoxypropionaldehyde:
[24]
1H NMR (400 MHz, CDCl3): δ = 9.78 (t, J = 2 Hz, 1 H), 3.76 (t, J = 6.4 Hz, 2 H), 3.50 (q, J = 6.8 Hz, 2 H), 2.67 (td, J = 1.6, 6 Hz, 2 H), 1.20 (t, J = 6.4 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 200.9 (CH), 67.1 (CH2), 64.6 (CH2), 64.6 (CH2), 44.6 (CH2), 16.0 (CH3).
Methyl 4-Formylbenzoate:
[25]
1H NMR (400 MHz, CDCl3): δ = 10.09 (s, 1 H), 8.18 (d, J = 8 Hz, 2 H), 7.94 (d, J = 8 Hz, 2 H), 3.95 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ = 191.6 (CH), 166.0 (C), 139.1 (C), 135.1 (C), 130.2 (CH), 129.5 (CH), 52.6 (CH3).
Preparation of 20: A solution of 17 (0.32 g, 2 mmol) and Et3N (0.38 mL, 2.8 mmol) in anhyd CH2Cl2 (5 mL) was cooled in an ice-water bath under dried nitrogen. Chlorotrimethylsilane (0.31 mL, 2.4 mmol) was slowly added to the above solution with stirring. After the addition, the resulting mixture was heated to reflux for 6 h. The mixture was filtered to remove the ammonium salt and the filtrate was evaporated under reduced pressure to remove the excess amine and chlorotrimethylsilane. The residue was dissolved in CH2Cl2 (10 mL) and washed with sat. NaHCO3. The organic extract was dried over MgSO4 and concentrated to give the desired compound 20 (0.46 g, 100%). 1H NMR (400 MHz, CDCl3): δ = 3.64 (d, J = 12 Hz, 2 H), 3.55 (s, 2 H), 3.52 (d, J = 12 Hz, 2 H), 1.41 (s, 3 H), 1.37 (s, 3 H), 0.79 (s, 3 H), 0.09 (s, 9 H). 13C NMR (100 MHz, CDCl3): δ = 97.5 (C), 66.2 (CH2), 65.2 (CH2), 35.0 (C), 27.0 (CH3), 21.2 (CH3), 18.3 (CH3), -0.1 (CH3). Anal. Calcd for C11H24O3Si: C, 56.85; H, 10.41. Found: C, 56.77; H, 10.21.