1-(2,2-Dibromo-1-chlorocyclopropyl)ethanol (1f). CH3I (2.0 g, 14.2 mmol) was slowly added to Mg (0.28 g, 12.0 mmol) in dry diethyl ether (20 mL). The mixture was refluxed for 30 min and cooled to rt. The methylmagnesium iodide solution was slowly added to a solution of 1b (2.6 g, 10.0 mmol) in dry diethyl ether at 0 oC. After addition the reaction mixture was refluxed for an additional 30 min and was then quenched by adding saturated aqueous NH4Cl (20 mL). The hydrolysate was extracted with diethyl ether (3 x 20 mL), and the combined organic phases were dried (MgSO4) and concentrated. Flash chromatography (hexane:ethyl acetate, 80:20) afforded 1f (2.42 g, 88%) as a colorless oil. IR (film): 3800-3050 (s), 3078 (w), 2982 (s), 2958 (w), 2931 (s), 2870 (w), 1446 (m), 1420 (m), 1375 (m), 1267 (m), 1173 (m), 1110 (m), 1076 (m), 1031 (w), 1001 (m), 949 (w), 916 (m), 824 (w), 699 (m) cm-1; 1H NMR (200 MHz; CDCl3): d 4.00 (quintet, J = 6.4 Hz, 1H), 2.29 (d, J = 6.4 Hz, 1H), 2.02 (d, J = 9.3 Hz, 1H, A part of an AB system), 1.93 (d, J = 9.3 Hz, 1H, B part of and AB system), 1.45 (d, J = 6,4 Hz, 3H); 13C NMR (50 MHz; CDCl3): d 68.4, 52.5, 34.7, 29.5, 14.8; MS (EI).: m/z 276 (12), 274 (22), 260 (12), 201 (10), 183 (20), 181 (30), 153 (42), 128 (12), 103 (25), 82 (100); HRMS calcd. for [M]+. ([C5H7Br2ClO]+.) 275.8552, found 275.8564.
1-(2,2-Dibromo-1-chlorocyclopropyl)ethanone (1g). A solution of CrO3 (1.77 g, 17.7 mmol), concentrated sulphuric acid (1.6 mL), and H2O (4.8 mL) was slowly added to a mixture of 1f (2.78 g, 10.0 mmol) and acetone (8 mL) kept on ice bath. After stirring for 4 h, water (50 mL) was added and the product mixture was extracted with CH2Cl2 (3 x 50 mL). The combined organic phases were dried (MgSO4) and concentrated. Flash chromatography (hexane:ethyl acetate, 97.5:2.5) afforded 1g (2.0 g, 73%) as a colourless oil. IR (film): 3448 (w), 3087 (w), 3003 (w), 2925 (w), 1723 (m), 1417 (m), 1387 (w), 1359 (m), 1276 (m), 1205 (w), 1059 (w), 1030 (m), 1012 (m), 931 (w), 801 (w), 699 (m), 624m, 610m cm-1; 1H NMR (200 MHz; CDCl3): d 2.79 (d, J = 9.1 Hz, 1H, A part of an AB system), 2.55 (s, 3H), 1.96 (d, J = 9.1 Hz, 1H, B part of an AB system); 13C NMR (50 MHz; CDCl3): d 198.6, 53.1, 34.8, 27.0, 14.9; MS (EI): m/z 277 (12), 233 (30), 197 (88), 169 (52), 153 (9), 131 (16), 116 (100), 107 (8), 87 (27), 73 (52), 61 (7); HRMS calcd. for [M]+. ([C5H5Br2ClO]+.) 273.8396, found 273.8385.
2-(2,2-Dibromo-1-chlorocyclopropyl)-1,3-dithiolane (1h). Procedure 1. A mixture of 1a (6.7 g, 20 mmol), 1,2-ethanedithiol (2.0 mL, 25 mmol), and silica chloride (3.0 g, 30 mmol) in CH2Cl2 (50 mL) was stirred at rt for 4 h. The silica chloride was removed by filtration and washed with CH2Cl2 (50 mL). The organic phase was washed with 10% (w/w) aqueous NaOH (50 mL), H2O (100 mL), dried over MgSO4 and concentrated. Flash chromatography (hexane:ethyl acetate, 90:10) afforded 1h (5.3 g, 78%) as a colourless oil.
Procedure 2.12 Aldehyde 1b (2.6 g, 10 mmol) and 1,2-ethanedithiol (1.6 mL, 20 mmol) was dissolved in CHCl3 (50 mL) and stirred for 1 h at 20 oC. The reaction mixture was then cooled to 0 oC and boron trifluoride diethyl etherate (2.0 mL, ~ 3.8 M) was added dropwise over 10 min. The reaction mixture was then stirred at 0 oC for further 12 h. The reaction mixture was washed with 10 % (w/w) aqueous NaOH (20 mL), H2O (20 mL), aqueous saturated NaCl (20 mL) and dried over MgSO4. The solvent was evaporated and flash chromatography (hexane:ethyl acetate, 90:10) afforded 1h (2.6 g, 78%) as a colourless oil.
