“Green” bromination of ketones with H2O2-HBr “on water”
Ajda Podgoršek, Stojan Stavber, Marko Zupan and Jernej Iskra*
Laboratory for Organic and Bioorganic Chemistry, ˝Jožef Stefan˝ Institute, Jamova 39, 1000 Ljubljana, Slovenia and Faculty of Chemistry and Chemical Technology, University of
Ljubljana, Aškerčeva 5, 1000 Ljubljana, Slovenia
jernej.iskra@ijs.si
Table of contents
General...................................................................................................................................2 Typical reaction procedure for bromination of ketones in aqueous H2O2-HBr system.........2 2-bromo-2-methylcyclohexane-1,3-dione (3b, Table 2)...................................................3 2-bromo-1,3-diphenylpropane-1,3-dione (5b, Table 2).....................................................3 2-Bromo-1-phenyl-butane-1,3-dione (6b, Table 2)...........................................................3 2,2-dibromo-1-phenylbutane-1,3-dione (6c, Table 2).......................................................4 1-Bromo-2-oxo-cyclopentanecarboxylic acid ethyl ester (7b, Table 2)............................4 2-Benzyl-2-bromo-3-oxo-butyric acid ethyl ester (8b, Table 2).......................................4 2-Bromo-cyclooctanone (9b, Table 2)...............................................................................4 α-bromo-4-methylacetophenone (10b, Table 2)................................................................5 2-bromo-1,2-diphenylethanone (11b, Table 2)..................................................................5 2-bromo-1,3-diphenylpropan-1-one (12b, Table 2)...........................................................5 2-bromo-1-phenylpropan-1-one (13b, Table 2).................................................................6 (1-bromo-cyclobutyl)-phenyl-methanone (14b, Table 2)..................................................6 4-bromononan-5-one (15b, Table 2)..................................................................................6 3-bromo-2-nonanon (16b, Table 2)...................................................................................7 1-bromo-2-nonanone (16d, Table 2)..................................................................................7 2-bromo-2,4-dimethylpentan-3-one (17b, Table 2)...........................................................7 1-bromo-1-phenylpropan-2-one (18b, Table 3).................................................................7 1-(3-Bromo-4-methoxy-phenyl)-propan-2-one (19d, Table 3).........................................8 4-(3-Bromo-4-methoxy-phenyl)-butan-2-one (20d, Table 3)............................................8 2-bromo-indane-1-one (21b, Table 4)...............................................................................8 2,2-dibromo-indane-1-one (21c, Table 4)..........................................................................9 2-bromo-1-tetralone (23b, Table 4)...................................................................................9 Tandem oxidation and bromination of sec-alcohol...............................................................9 2-Bromo-cycloheptanone (28b, Table 5).........................................................................10 2-bromopentan-3-one (29b, Table 5)...............................................................................10 NMR experiments................................................................................................................11 References............................................................................................................................11
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General
All chemicals were obtained form commercial sources and were used without further purification. Column and thin layer chromatography was carried out using silica gel 60 (0.063-0.200 mm) and silica 60F-245 plates, respectively. 1H and 13C NMR spectra were recorded in CDCl3 using a Varian Inova 300 MHz spectrometer. The chemical shifts (δ) are reported in ppm units relative to TMS as an internal standard for 1H NMR and CDCl3 for 13C NMR spectra. Melting points were determined using a Büchi 535 melting point apparatus. Mass spectra were obtained using an Autospec Q mass spectrometer with electron impact ionization (EI, 70 eV).
Typical reaction procedure for bromination of ketones in aqueous H2O2-HBr system One mmol of substrate was suspended in 0.5 mL of water (in case of performing reaction with additional water) and the flask was covered with an aluminium foil to shield the reaction mixture from light. Then 0.057 mL (0.5 mol equiv.) of 48% aqueous solution of HBr was added and after stirring the mixture at room temperature for 5 minutes 0.051 mL (0.5 mol equiv.) of 30% aqueous solution of H2O2 was added. This procedure (0.5 mol equiv. HBr, stirring for 5 minutes, 0.5 mol equiv H2O2) was then repeated every 2-3 hours until the appropriate amount of bromide and oxidant had been added (See Tables 1, 2, 3 and 4). The progress of the reaction was monitored by TLC. After completion of the reaction (8 to 24 hours), the work-up procedure depended on the aggregate state of products. Work-up procedure for liquid products:
The reaction mixture was first dissolved in 5 mL of appropriate mixture of hexane and ethylacetate (20:1 or 10:1), solid NaHSO3 was then added to reduce any unreacted Br2 and H2O2 and the solution was dried over anhydrous Na2SO4. The insoluble material was then filtered off and the organic solvent evaporated under reduced pressure. The crude reaction mixture was then analyzed by 1H NMR spectroscopy. Finally, the products were isolated by column chromatography (SiO2, hexane/EtOAc) and structure determined by comparison with the literature data.
Work-up procedure for solid products:
The reaction mixture was filtered off and rinsed with 10 mL of water. The crude reaction mixture was then analyzed by 1H NMR spectroscopy. Finally, products were isolated by
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column chromatography (SiO2, hexane/EtOAc) or purified by crystallization and their structures determined by comparison with the literature data. 2-Bromo-2-methylcyclohexane-1,3-dione (3b, Table 2)1
126 mg (1.0 mmol) of 3a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol H2O2), 0.114 mL (1.0 mmol) HBr, 0.5 mL H2O, stirring for 8 h at room temperature; work-up for liquid products. Column chromatography gave 185 mg (90%) of pure product 3b; δH(300 MHz; CDCl3; Me4Si) 1.67-1.81 (m, 1H, CH2), 1.82 (s, 3H, CH3), 2.20-2.34 (m, 1H, CH2), 2.58 (dt, J 16.2 and 4.9 Hz, 2H, CH2), 3.36 (ddd, J 16.2, 11.6 and 5.8 Hz, 2H, CH2); δC(76 MHz; CDCl3; Me4Si) 17.9 (CH3), 19.2 (CH2), 35.7 (CH2), 59.9 (CBr), 201.0 (CO); m/z (EI, 70 eV) 206 (2%, M++2), 204 (2%, M+), 126 (9%), 97 (64%), 82(24%), 80 (24%), 70 (16%), 55 (100%).
2-Bromo-1,3-diphenylpropane-1,3-dione (5b, Table 2)2
224 mg (1.0 mmol) of 5a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.114 mL (1.0 mmol) HBr, 0.5 mL H2O, stirring for 9 h at room temperature; work-up for solid products. Crystallization from EtOH gave 248 mg (82%) of pure solid product 5b; mp 88-89 °C; δH(300 MHz; CDCl3; Me4Si) 6.57 (s, 1H, CHBr), 7.45-7.50 (m, 4H, ArH), 7.58-7.63 (m, 2H, ArH), 7.99-8.01 (m, 4H, ArH); δC(76 MHz; CDCl3; Me4Si) 52.6 (CHBr), 129.0 (Ar-C), 129.2 (Ar-C), 133.7 (Ar-C), 134.2 (Ar-C), 188.9 (CO); m/z (EI, 70 eV) 304 (0.7%, M++2), 302 (0.7%, M+), 223 (37%), 105 (100%), 77 (41%). 2-Bromo-1-phenylbutane-1,3-dione (6b, Table 2)3
162 mg (1.0 mmol) of 6a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.114 mL (1.0 mmol) HBr, 0.5 mL H2O, stirring for 9 h at room temperature; work-up for liquid products. Column chromatography gave 190 mg (79%) of 6b; δH(300 MHz; CDCl3; Me4Si) 2.46 (s, 3H, CH3), 5.63 (s, 1H, CHBr), 7.44-7.54 (m, 2H, ArH), 7.58-7.67 (m, 1H, ArH), 7.96-8.00 (m, 2H, ArH); δC (76 MHz; CDCl3; Me4Si) 27.08 (CH3), 52.86 (CHBr), 128.93 (Ar-C), 129.17 (Ar-C), 133.63 (Ar-C), 134.42 (Ar-C), 189.85 (CO), 198.11 (CO); m/z (EI, 70 eV) 242 (0.5%, M++2 ), 240 (0.5%, M+), 200 (5%), 198 (5%), 105 (100%), 77 (40%); and
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2,2-dibromo-1-phenylbutane-1,3-dione (6c, Table 2)4 (16 mg, 5%)
δH(300 MHz; CDCl3; Me4Si) 2.53 (s, 3H, CH3), 7.45-7.50 (m, 2H, ArH), 7.58-7.64 (m, 1H, ArH), 8.05-8.10 (m, 2H, ArH); δC(76 MHz; CDCl3; Me4Si) 24.7 (CH3), 68.8 (CBr2), 128.6 (Ar-C), 130.6 (Ar-C), 130.8 (Ar-C), 134.3 (Ar-C), 185.4 (CO), 191.7 (CO). Ethyl 1-bromo-2-oxo-cyclopentanecarboxylate (7b, Table 2)1
156 mg (1.0 mmol) of 7a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.114 mL (1.0 mmol) HBr, 0.5 mL H2O, stirring for 8 h at room temperature; work-up for liquid products. Column chromatography gave 200 mg (85%) of pure product 7b; δH(300 MHz; CDCl3; Me4Si) 1.33 (t, J 7.1 Hz, 3H, CH3), 2.10-2.23 (m, 2H, CH2), 2.26-2.39 (m, 1H, CH2), 2.43-2.62 (m, 2H, CH2), 2.72-2.83 (m, 1H, CH2), 4.31 (q, J 7.1 Hz, 2H, CH2); δC(76 MHz; CDCl3; Me4Si) 13.9 (CH3), 19.4 (CH2), 35.1(CH2), 38.7 (CH2), 62.1(CH2), 63.2 (CBr), 166.9 (CO), 205.9 (CO); m/z (EI, 70 eV) 236 (7%, M++2), 234 (7%, M+), 190 (15 %), 188 (15%), 109 (100%).
Ethyl 2-benzyl-2-bromo-3-oxobutanoate (8b, Table 2)5
220 mg (1.0 mmol) of 8a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.228 mL (2.0 mmol) HBr, 0.5 mL H2O, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave 284 mg (95%) of pure product 8b; δH(300 MHz; CDCl3; Me4Si) 1.21 (t, J 7.10, 3H, CH3), 2.34 (s, 3H, CH3), 3.51 (d, J 14.5 Hz, 1H, CH2), 3.64 (d, J 14.5 Hz, 1H, CH2), 4.21 (q, J 7.1 Hz, 2H, CH2), 7.20-7.30 (m, 5H, ArH); δC(76 MHz; CDCl3; Me4Si) 13.7 (CH3), 26.8 (CH3), 42.6 (CH2), 53.4 (CH2), 63.1 (CBr), 127.5 (Ar-C), 128.1 (Ar-C), 130.4 (Ar-C), 134.6 (Ar-C), 167.1 (CO), 197.7 (CO); m/z (EI, 70 eV) 258 (10%), 256 (10%), 219 (35%), 173 (83%), 131 (58%), 91 (35%), 78 (100%).
2-Bromo-yclooctanone (9b, Table 2)6
126 mg (1.0 mmol) of 9a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.125 mL (1.1 mmol) HBr, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave 141 mg (69%) of pure product 9b; δH(300 MHz; CDCl3; Me4Si) 1.11-1.25 (m, 1H, CH2), 1.35-1.48 (m, 1H, CH2), 1.50-1.97 (m, 6H,
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CH2), 2.26-2.46 (m, 3H, CH2), 2.81-2.91 (m, 1H, CH2), 4.28 (dd, J 10.8 and J 4.6 Hz, 1H, CHBr); δC(76 MHz; CDCl3; Me4Si) 23.9 (CH2), 25.4 (CH2), 26.5 (CH2), 28.7 (CH2), 32.6 (CH2), 36.2 (CH2), 54.3 (CHBr), 208.6 (CO); m/z (EI, 70 eV) 125 (4%), 98 (100%), 55 (83%).
α-Bromo-4-methylacetophenone (10b, Table 2)7
134 mg (1.0 mmol) of 10a was transformed using the following reaction reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.125 mL (1.1 mmol) HBr, 0.5 mL H2O, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave 166 mg (78%) of pure solid product 10b; mp 47-48°C (mp7 51-52ºC); δH(300 MHz; CDCl3; Me4Si) 2.43 (s, 3H, CH3), 4.43 (s, 2H, CH2), 7.29 (d, J 8.3 Hz, 2H, ArH), 7.88 (d, J 8.3 Hz, 2H, ArH); δC(76 MHz; CDCl3; Me4Si) 21.7 (CH3), 31.0 (CH2Br), 129.0 (Ar-C), 129.5 (Ar-C), 131.4 (Ar-C), 145.0 (Ar-C), 190.9 (CO); m/z (EI, 70 eV) 214 (4%, M++2), 212 (4%, M+), 119 (100%), 105 (15 %), 91 (47 %), 77 (8%), 65 (23%).
2-Bromo-1,2-diphenylethanone (11b, Table 2)8
196 mg (1.0 mmol) of 11a was transformed using the following reaction reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.171 mL (1.5 mmol) HBr, 0.5 mL H2O, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave 242 mg (88%) of pure solid product 11b; mp 45-46 °C (mp8 44-46 °C); δH(300 MHz; CDCl3; Me4Si) 6.39 (s, 1H, CHBr), 7.31-7.58 (m, 8H, ArH), 7.91-8.01 (m, 2H, ArH); δC(76 MHz; CDCl3; Me4Si) 51.0 (CHBr), 128.8 (Ar-C), 129.0 (Ar-C), 129.1 (Ar-C), 133.7 (Ar-C), 134.1 (Ar-C), 135.6 (Ar-C), 191.0 (CO); m/z (EI, 70 eV) 276 (0.4%, M++2), 274 (0.4%, M+), 195 (7%), 105 (100%), 90 (10%), 77 (20%).
2-Bromo-1,3-diphenylpropan-1-one (12b, Table 2)9
210 mg (1.0 mmol) of 12a was transformed using the following reaction conditions: 0.114 mL (2.0 mmol) H2O2, 0.171 mL (1.5 mmol) HBr, 0.5 mL H2O, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave 248 mg (86%) of pure product 12b; δH(300 MHz; CDCl3; Me4Si) 3.35 (dd, J 14.3 and J 7.1 Hz, 1H, CH2), 3.67 (dd, J 14.3 and J 7.5 Hz, 1H, CH2), 5.32 (dd, J 7.5 and J 7.1 Hz , 1H, CHBr), 7.16-7.32 (m, 5H, ArH), 7.39-7.48 (m, 2H, ArH), 7.52-7.59 (m, 1H, ArH), 7.95-7.98 (m, 2H, ArH); δC(76
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MHz; CDCl3; Me4Si) 39.4 (CH2), 46.6 (CHBr), 127.0 (Ar-C), 128.6 (Ar-C), 128.7 (Ar-C), 128.8 (Ar-C), 129.4 (Ar-C), 133.7 (Ar-C), 134.3 (Ar-C), 137.5 (Ar-C), 192.7 (CO); m/z (EI, 70 eV) 290 (2%, M++2), 289 (12%, M+-H+2), 288 (2%, M+), 287 (9%, M+-H), 209 (100%), 131 (11%), 105 (72%), 77 (33%).
2-Bromo-1-phenylpropan-1-one (13b, Table 2)10
134 mg (1.0 mmol) of 13a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.228 mL (2.0 mmol) HBr, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave 166 mg (78%) of pure product 13b; δH(300 MHz; CDCl3; Me4Si) 1.91 (d, J 6.6 Hz, 3H, CH3), 5.30 (q, J 6.6 Hz, 1H, CHBr), 7.49 (t, J 7.4 Hz, 2H, ArH), 7.59 (tt, J 7.4 and 1.5 Hz, 1H, ArH), 8.02 (dd, J 7.4 and 1.5 Hz, 2H, ArH); δC(76 MHz; CDCl3; Me4Si) 20.1 (CH3), 41.4 (CHBr), 128.7 (Ar-C), 128.9 (Ar-C), 133.7 (Ar-C), 134.0 (Ar-C), 193.3 (CO); m/z (EI, 70 eV) 214 (2%, M++2), 212 (2%, M+), 105 (100%), 77 (36%).
2-Bromo-2-cyclobutyl-1-phenylethanone (14b, Table 2)11
160 mg (1.0 mmol) of 14a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.228 mL (2.0 mmol) HBr, stirring for 24 h at room temperature; work-up for solid products. Crystallization from EtOH gave 182 mg (76%) of pure solid product 14b; mp 57-58°C (mp11 54-55 ºC); δH(300 MHz; CDCl3; Me4Si) 1.80-1.93 (m, 1H, CH2), 2.34-2.49 (m, 1H, CH2), 2.71-2.82 (m, 2H, CH2), 3.08-3.19 (m, 2H, CH2), 7.42-7.49 (m, 2H, ArH), 7.54 (tt, J 7.4 and 1.5 Hz, 1H, ArH), 8.03 (dd, J 7.4 and 1.5 Hz, 2H, ArH); δC(76 MHz; CDCl3; Me4Si) 16.5 (CH2), 37.0 (CH2), 59.6 (CBr), 128.3 (Ar-C), 130.1 (Ar-C), 132.2 (Ar-C), 133.2 (Ar-C), 194.5 (CO); m/z (EI, 70 eV) 240 (1%, M++2), 238 (1%, M+), 159 (1%), 105 (100%), 77 (35%).
4-Bromononan-5-one (15b, Table 2)12
142 mg (1.0 mmol) of 15a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.228 mL (2.0 mmol) HBr, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave 176 mg (80%) of pure product 15b; δH(300 MHz; CDCl3; Me4Si) 0.90-0.97 (m, 6H, CH3), 1.28-1.66 (m, 6H, CH2), 1.84-2.04 (m, 2H, CH2), 2.58-2.78 (m, 2H, CH2), 4.26 (dd, J 8.1 and 6.0 Hz, 1H, CHBr); δC(76
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MHz; CDCl3; Me4Si) 13.4 (CH3), 13.8 (CH3), 20.6 (CH2), 22.2 (CH2), 26.0 (CH2), 35.3 (CH2), 38.6 (CH2), 53.5 (CHBr), 204.4 (CO); m/z (EI, 70 eV) 222 (0.5%, M++2), 220 (0.5%, M+), 180 (4%), 178 (4%), 85 (100%), 57 (71%). 3-Bromononan-2-one (16b, Table 2)13
142 mg (1.0 mmol) of 16a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.228 mL (1.0 mmol) HBr, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave mixture of 16b (74 mg, 33%); δH(300 MHz; CDCl3; Me4Si) 0.86-0.90 (m, 3H, CH3), 1.19-1.40 (m, 6H, CH2), 1.41-1.55 (m, 2H, CH2), 1.85-2.06 (m, 2H, CH2), 2.36 (s, 3H, CH3), 4.23 (dd, J 8.1 and 6.5 Hz, 1H, CHBr); δC(76 MHz; CDCl3; Me4Si) 14.0 (CH3), 22.4 (CH2), 27.2 (CH2), 28.6 (CH2), 28.9 (CH2), 31.4 (CH2), 33.5 (CH3), 54.4 (CHBr), 202.0 (CO); and 1-Bromo-2-nonanone (16d, Table 2)14 (32 mg, 14%)
δH(300 MHz; CDCl3; Me4Si) 0.86-0.90 (m, 3H, CH3), 1.19-1.40 (m, 8H, CH2), 1.57-1.66 (m, 2H, CH2), 2.65 (t, 2H, J 7.4 Hz, CH2), 3.89 (s, 2H, CH2); δC(76 MHz; CDCl3; Me4Si) 14.0 (CH3), 22.5 (CH2), 23.8 (CH2), 26.0 (CH2), 28.90 (CH2), 31.6 (CH2), 34.3 (CH2), 39.8 (CH2Br), 202.1 (CO).
2-Bromo-2,4-dimethylpentan-3-one (17b, Table 2)15
114 mg (1.0 mmol) of 17a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.228 mL (2.0 mmol) HBr, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave 148 mg (77%) of pure product 17b; δH(300 MHz; CDCl3; Me4Si) 1.18 (d, J 6.7 Hz, 6H, CH3), 1.87 (s, 6H, CH3), 3.45 (sept, J 6.7 Hz, 1H, CH); δC(76 MHz; CDCl3; Me4Si) 29.3 (CH3), 34.5 (CH3), 64.5 (CH), 96.0 (CBr), 209.9 (CO); m/z (EI, 70 eV) 194 (0.3%, M++2), 192 (0.3%, M+), 123 (11%), 121 (11%), 85 (11%), 71 (100%).
1-Bromo-1-phenylpropan-2-one (18b, Table 3)3
134 mg (1.0 mmol) of 18b was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.228 mL (2.0 mmol) HBr, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography (SiO2, CH2Cl2) gave 187 mg (88%) of
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pure product 18b; δH(300 MHz; CDCl3; Me4Si) 2.30 (s, 3H, CH3), 5.44 (s, 1H, CHBr), 7.34-7.46 (m, 5H, ArH); δC(76 MHz; CDCl3; Me4Si) 27.1 (CH3), 57.3 (CHBr), 127.7 (Ar-C), 129.7 (Ar-C), 129.8 (Ar-C), 130.1 (Ar-C), 130.2 (Ar-C), 135.1 (Ar-C), 200.2 (CO); m/z (EI, 70 eV) 214 (2%, M++2), 212 (2%, M+), 171 (46%), 169 (50%), 133 (100%), 118 (15%), 105 (25%), 90 (43%), 77 (15%).
1-(3-Bromo-4-methoxyphenyl)propan-2-one (19d, Table 3)
164 mg (1.0 mmol) of 19a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.114 mL (1.0 mmol) HBr, 0.5 mL H2O, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave 230 mg (95%) of 19d; δH(300 MHz; CDCl3; Me4Si) 2.16 (s, 3H, CH3), 3.62 (s, 2H, CH2), 3.87 (s, 3H, CH3), 6.86 (d, J 8.4 Hz, 1H, ArH), 7.10 (dd, J 8.4 and 2.1 Hz, 1H, ArH), 7.38 (d, J 2.1 Hz, 1H, ArH); δC(76 MHz; CDCl3; Me4Si) 29.2 (CH3), 49.3 (CH2), 56.1 (CH3), 111.6 (Ar-C), 112.0 (Ar-C), 127.6 (Ar-C), 129.4 (Ar-C), 134.0 (Ar-C), 154.9 (Ar-C), 205.8 (CO); m/z (EI, 70 eV) 244 (30%, M++2), 242 (30%, M+), 201 (100%), 199 (100%), 105 (48%), 77 (62%); found: C, 49.51; H, 4.65. C10H11BrO2 requires C, 49.41; H, 4.56%. 4-(3-Bromo-4-methoxyphenyl)butan-2-one (20d, Table 3)16
178 mg (1.0 mmol) of 20a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.114 mL (1.0 mmol) HBr, 0.5 mL H2O, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave 246 mg (96%) of 20d; δH(300 MHz; CDCl3; Me4Si) 2.13 (s, 3H, CH3), 2.76 (m, 4H, CH2), 3.85 (s, 3H, CH3), 6.81 (d, J 8.4 Hz, 1H, ArH), 7.08 (dd, J 8.4 and 2.1 Hz, 1H, ArH), 7.36 (d, J 2.1 Hz, 1H, ArH); δC(76 MHz; CDCl3; Me4Si) 28.3 (CH3), 30.0 (CH2), 44.9 (CH2), 56.1 (CH3), 111.4 (Ar-C), 111.8 (Ar-C), 128.2 (Ar-C), 132.9 (Ar-C), 134.6 (Ar-C), 154.1 (Ar-C), 207.5 (CO); m/z (EI, 70 eV) 258 (57%, M++2), 256 (57%, M+), 201 (100%), 199 (100%), 178 (26%), 134 (41%), 121 (65%), 77 (32%).
2-Bromoindane-1-one (21b, Table 4)17
132 mg (1.0 mmol) of 21a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.125 mL (1.1 mmol) HBr, stirring for 24 h at room temperature; work-up for solid products. Column chromatography gave 184 mg (87%) of 21b; mp 37-38
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°C (mp1 37-38 °C); δH(300 MHz; CDCl3; Me4Si) 3.42 (dd, J 18.1 and 3.2 Hz, 1H, CH2), 3.84 (dd, J 18.1 and 7.5 Hz, 1H, CH2), 4.65 (dd, J 7.5 and 3.2 Hz, 1H, CHBr), 7.40-7.46 (m, 2H, ArH), 7.64-7.69 (m, 1H, ArH), 7.81-7.84 (m, 1H, ArH); δC(76 MHz; CDCl3; Me4Si) 37.9 (CH2), 44.0 (CHBr), 125.0 (Ar-C), 126.4 (Ar-C), 128.2 (Ar-C), 133.5 (Ar-C), 135.9 (Ar-C), 151.1 (Ar-C), 199.5 (CO); m/z (EI, 70 eV) 212 (13%, M++2), 210 (13%, M+), 131 (100%), 103 (46 %), 77 (28%); and
2,2-Dibromoindane-1-one (21c, Table 4)17 (11mg, 4%)
mp 133-134 °C (mp17 133-134 °C) δH(300 MHz; CDCl3; Me4Si) 4.30 (s, 2H, CH2), 7.42 (d, J 7.70 Hz, 1H, ArH), 7.51 (t, J 7.7 Hz, 1H, ArH), 7.75 (dt, J 7.7 and 1.2 Hz, 1H, ArH), 7.96 (d, J 7.7 Hz, 1H, ArH); δC(76 MHz; CDCl3; Me4Si) 52.3 (CH2), 56.8 (CBr2), 126.0 (Ar-C), 126.6 (Ar-C), 128.7 (Ar-C), 129.0 (Ar-C), 136.9 (Ar-C), 147.1 (Ar-C), 192.7 (CO); m/z (EI, 70 eV) 292 (18%, M++4), 290 (34%, M++2), 288 (18%, M+), 211 (95%), 209 (100%), 198 (5%), 196 (5%), 130 (27%), 102 (89%), 89 (18%), 75 (37%). 2-Bromo-1-tetralone (23b, Table 4)17
146 mg (1.0 mmol) of 23a was transformed using the following reaction conditions: 0.204 mL (2.0 mmol) H2O2, 0.125 mL (1.1 mmol) HBr, stirring for 24 h at room temperature; work-up for liquid products. Column chromatography gave 203 mg (90%) of pure product 23b; δH(300 MHz; CDCl3; Me4Si) 2.41-2.60 (m, 2H, CH2), 2.90 (dt, J 17.2 and J 4.5 Hz, 1H, CH2), 3.26-3.37 (m, 1H, CH2), 4.73 (t, J 4.5 Hz, 1H, CHBr), 7.25 (d, J 7.9 Hz, 1H, ArH), 7.34 (t, J 7.9 Hz, 1H, ArH), 7.51 (td, J 7.9 and J 1.5 Hz, 1H, ArH), 8.09 (dd, 1H, 7.9 and 1.4 Hz, 1H, ArH); δC(76 MHz; CDCl3; Me4Si) 26.1 (CH2), 31.9 (CH2), 50.4 (CHBr), 127.1 (Ar-C), 128.6 (Ar-C), 128.7 (Ar-C), 129.9 (Ar-C), 134.1 (Ar-C), 142.9 (Ar-C), 190.5 (CO); m/z (EI, 70 eV) 226 (18%, M++2), 224 (18%, M+), 144 (33%), 118 (100%), 115 (32%), 90 (42%). Tandem oxidation and bromination of sec-alcohol
1.0 mmol of sec-alcohol was suspended in 0.5 mL of water and the flask was covered with an aluminum foil. Then 0.057 mL (0.5 mol equiv.) of 48% aqueous solution of HBr was added. After stirring at room temperature for 5 minutes, to the mixture was added 0.051 mL (0.5 mol equiv.) of 30% aqueous solution of H2O2. This procedure (0.5 mol equiv. of HBr, stirring for 5 minutes, 0.5 mol equiv. of H2O2) were then repeated every four hours until the appropriate amount of HBr and H2O2 had been added (Table 5). After completion of the reaction the
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Supplementary Material (ESI) for Green Chemistry This journal is © The Royal Society of Chemistry 2007
crude reaction mixture was isolated following the work-up procedure for liquid products and isolated by column chromatography (SiO2, hexane/EtOAc).
2-Bromocycloheptanone (28b, Table 5)18
114 mg (1.0 mmol) of 26 was transformed using the following reaction conditions: 0.408 mL (4.0 mmol) H2O2, 0.170 mL (1.5 mmol) HBr, stirring for 10h at room temperature. Column chromatography gave 168 mg (88%) of pure product 28b; δH(300 MHz; CDCl3; Me4Si) 1.30-1.44 (m, 1H, CH2), 1.49-2.06 (m, 5H, CH2), 2.29-2.52 (m, 3H), 2.81-2.90 (m, 1H, CH2), 4.37 (dd, J 9.6 and 5.1 Hz, 1H, CHBr); δC(76 MHz; CDCl3; Me4Si) 24.9 (CH2), 26.8 (CH2), 29.5 (CH2), 34.2 (CH2), 39.33 (CH2), 53.7 (CHBr), 206.2 (CO); m/z (EI, 70 eV) 192 (4%, M++2), 190 (4%, M+), 149 (3%), 137 (2%), 123 (2%), 111 (45%), 83 (28%), 69 (29%), 55 (100%). 2-Bromopentan-3-one (29b, Table 5)19
88 mg (1.0 mmol) of 27 was transformed using the following reaction conditions: 0.408 mL (4.0 mmol) H2O2, 0.170 mL (1.5 mmol) HBr, stirring for 10h at room temperature. Column chromatography gave 152 mg (92%) of pure product 29b; δH(300 MHz; CDCl3; Me4Si) 1.12 (t, J 7.3 Hz, 3H, CH3), 1.75 (d, J 6.8 Hz, 3H, CH3), 2.60 (qd, J 7.3 and 17.9 Hz, 1H, CH2), 2.87 (qd, J 7.3 and 17.9 Hz, 1H, CH2), 4.43 (q, J 6.8 Hz, 1H, CHBr); δC(76 MHz; CDCl3; Me4Si) 8.1 (CH3), 20.1 (CH3), 31.9 (CH2), 47.2 (CHBr), 205.1 (CO); m/z (EI, 70 eV) 166 (20%, M++2), 164 (20%, M+), 137 (15%), 135 (15%), 109 (70%), 107 (70%), 84 (63%), 57 (100%).
Determination of concentration of bromine and hydrogen peroxide in H2O2-HBr system 1.60 mL (14.0 mmol) of a 48% aqueous solution of HBr and 2.86 mL (28.0 mmol) of a 30% aqueous solution of H2O2 were added to 7.0 mL of water. The flask was covered with an aluminium foil and stirred at room temperature. Time dependence of the concentration of bromine and hydrogen peroxide was followed periodically by iodometric titration. Small portions (100 μL) of solution were transferred into 10 mL 0.05 M aqueous solution of potassium iodide. First, the concentration of bromine was determined with instantaneous titration of liberated iodine with 0.05 M aqueous solution of Na2S2O3. Then, 0.55 mL of 10% aqueous solution of H2SO4 was added and after 30 minutes the liberated iodine was titrated to determine the concentration of hydrogen peroxide.
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Supplementary Material (ESI) for Green Chemistry This journal is © The Royal Society of Chemistry 2007
NMR experiments
Spectrum A: 55 mg (0.25 mmol) of 2-benzyl-3-oxo-butyric acid ethyl ester 8a was dissolved in 0.8 mL of CDCl3. Spectrum B: 55 mg (0.25 mmol) of 8a was dissolved in 0.32 mL of DMSO-d6 and 0.48 mL of D2O was added. Spectrum C: 55 mg (0.25 mmol) of 8a was dissolved in 0.32 mL of DMSO-d6 and 0.48 mL of D2O and 0.028 mL (0.25 mmol) of 48% aqueous solution of HBr were added. 1H NMR spectra were recorded in 1 hour time after preparation of samples.
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