1h. IR (film): 3080 (w), 2978 (s), 2930 (m), 2897 (m), 2881 (m), 1480 (w), 1444 (m), 1422 (m), 1372 (s), 1354 (m), 1295 (w), 1268 (m), 1248 (m), 1184 (s), 1108 (s), 1072 (s), 1010 (m), 964 (w), 702 (m), 668 (m), 629 (m) cm-1; 1H NMR (200 MHz; CDCl3): d 4.85 (s, 1H), 3.60-3.47 (m, 2H), 3.37-3.26 (m, 2H), 2,15 (d, J = 9.4 Hz, 1H, A part of an AB system), 2.08 (d, J = 9.4 Hz, 1H, B part of and AB system); 13C NMR (50 MHz; CDCl3): d 61.4, 40.1, 39.8, 38.1, 31.8, 30.4; MS (EI): m/z 336 (9), 275 (11), 243 (14), 185 (30), 176 (12), 141 (12), 123 (7), 111 (10), 103 (74), 75 (100), 67 (9); HRMS calcd. for [M]+. ([C6H7Br2ClS2]+.), 335.8044, found 335.8051.
Ring opening of 1b-1h under PTC in the presence of ethanol. General procedure
To a cold (0 oC) mixture of one of the 1,1-dibromo-2-chlorocyclopropane derivatives 1b-1h, TEBA, and CH3CH2OH in CH2Cl2 (25-50 mL) was added 50% (w/w) aqueous NaOH. The cooling bath was removed and the reaction mixture was stirred vigorously at room temperature until all the starting material was consumed (monitored TLC). Water was added, the products were extracted with dichloromethane, and the combined extracts were dried with magnesium sulfate, filtered and evaporated under vacuum. The products, except from 1c, were isolated from the residue by flash chromatography.
To aldehyde 1b (1.3 g, 5.0 mmol), TEBA (0.2 g) and CH3CH2OH (0.92 g, 20.0 mmol) in CH2Cl2 (25 mL) was added NaOH (2.1 mL, 40 mmol) dropwise during 15 min and the reaction mixture stirred for further 24 h. At this point all the starting material was consumed. H2O (25 mL) was added and the reaction mixture was extracted with CH2Cl2 (3 x 25 mL). The combined organic extracts were combined, dried (MgSO4) and concentrated to yield a reaction crude product of 0.8 g. Chromatographic investigation showed a complex reaction mixture that contained at least 12 products from which we were not able to isolate reasonably pure samples any of the components (see text).
To acid 1c (1.4 g, 5.0 mmol), TEBA (0.2 g) and CH3CH2OH (0.92 g, 20.0 mmol) in CH2Cl2 (25 mL) was added NaOH (2.1 mL, 40 mmol) dropwise during 15 min and the reaction mixture stirred for further 24 h. H2O (25 mL) was added and the water phase was washed with CH2Cl2 (3 x 25 mL). The water phase was then made slightly acidic (~ 4, pH paper) with 2 M HCl and then extracted with CH2Cl2 (3 x 25 mL). Evaporation of the solvent gave 2,2-diethoxybut-3-ynoic acid (2c) (0.65 g, 75%) as a semisolid which melted gradually when heated.
2c. IR (film): 3750- 2550 (m), 3252 (w), 2980 (s), 2931 (s), 2889 (m), 2628 (w), 2115 (w), 1714 (s), 1441 (m), 1396 (m), 1371 (w), 1265 (m), 1220 (m), 1153 (m), 1120 (s), 1081 (s), 1054 (s), 890 (m), 733 (w) 700 (w); 1H NMR (200 MHz, CDCl3): d 9.28 (s, 1H), 3.90-3.42 (m, 4H), 2.62 (s, 1H), 1.29-1.05 (m, 6H); 13C NMR (50 MHz, CDCl3): d 173.1, 100.1, 83.2, 79.1, 63.0, 15.0; MS (EI): m/z 173 (30), 172 (40), 127 (55), 103 (100), 60 (12), 45 (15) m/z; HRMS calcd. for [M- OEt]+ ([C6H7O3]+) 127.0402 found 127.0410.
To ester 1d (1.5 g, 5.0 mmol), TEBA (0.2 g) and CH3CH2OH (0.92 g, 20 mmol) in CH2Cl2 (25 mL) was added NaOH (2.1 mL, 40 mmol) dropwise during 15 min and the reaction mixture stirred for further 20 h. Water (25 mL) was added and the two phases were separated. The water phase was extracted with CH2Cl2 (3 x 25 mL) and the combined organic extracts were dried
