Issue in Honor of Prof. Atta-ur-Rahman ARKIVOC 2007 (vii) 291-300
Crystallization from dichloromethane furnished meso-9 as a pure sample m.p. 233–235°C (ref. 5:
m.p. 235–238°C). Bis(methoxycarbonylphenylmethyl)ether (5) (diastereomeric mixture). 1H-NMR (400 MHz, CDCl3) d 3.69, 3.72 (6H, 2s), 5.00, 5.02 (2H, 2s), 7.32–7.40 (6H, m), 7.41–7.49 (4H, m); 13C- NMR (100 MHz, CDCl3) d 52.3, 78.6, 78.8, 127.4, 127.6, 128.7, 135.3, 135.4, 170.4, 170.5; EI- MS (70 eV), m/z (%) 255 ([M-CO2CH3]+, 26), 150 (34) ,149 (100), 121 (45). The ratio of the singlets at 3.69/3.72 and 5.00/5.02 indicates a 1.14:1 diastereomeric mixture. cis-Dimethyl 2,3-diphenyloxirane-2,3-dicarboxylate (8) by Darzens condensation. To a solution of potassium tert.-butylate (10 ml, 1-molar) in THF a mixture of methyl abromophenylacetate (2.2 g, 10 mmol) and methyl phenylglyoxylate (1.65 g, 10 mmol) in THF (1 ml) was added dropwise at -10°C. The mixture was allowed to stand overnight at 20°C. The mixture was brought to pH 4 by addition of acetic acid and poured into ice water (30 ml). After extraction with ether (4×40 ml) the organic phase was washed with brine (2×50 ml), dried over Na2SO4 and the solvent removed on a rotary evaporator. The crude product (3.1 g) was purified by recrystallization from methanol followed by recrystallization from pentane/dichloromethane, yield: 2.0 g (64%), m.p. 131–132°C. 1H-NMR (400 MHz, CDCl3) d 3.82 (6H, s), 7.11–7.17 (6H, m), 7.30–7.36 (4H, m); 13C-NMR (100 MHz, CDCl3) 53.2 , 68.9, 127.5, 127.8, 128.6, 130.7, 167.5; EI-MS (70 eV), m/z: (%) 312 (M+·, 4), 266 (36), 253 (10), 238 (16), 221 (27), 193 (10), 179 (98), 165 (21), 151 (27), 149 (19), 121 (37), 105 (100), 77 (43). cis-2,3-Diphenyloxirane-2,3-dicarboxylic acid (10). The diester 8 was saponificated to the dibasic acid 10 as described in ref. 2, yield: 79%, m.p. 121–123°C. 1H-NMR (400 MHz, CDCl3) d 7.13–7.21 (6H, m), 7.31–7.41 (4H, m); 13C-NMR (100 MHz, CDCl3) d 69.7, 128.3, 128.5, 129.1, 132.8, 168.3; EI-MS (70 eV), m/z 266 ([M-H2O]+·). cis-1,5-Diphenyl-3,6-dioxabicyclo[3.10]hexane-2,4-dione (11). Dehydration of 10 to the anhydride 11 is performed according to ref. 2, yield 42%, m.p. 141–142°C. 1H-NMR (400 MHz, acetone-d6) 7.34–7.42 (6H, m), 7.53–7.59 (4H, m); 13C-NMR (100 MHz, acetone-d6) 69.3, 125.4, 129.1, 129.2, 131.0, 165.7; EI-MS (70 eV), m/z 266 (M+·). Crystal structure analysis of compounds 8 and 11
Crystals suitable for a single crystal X-ray diffraction investigation were grown from solutions in dichloromethane/pentane. Data were collected at a temperature of 173(2) K on a Stoe IPDS 2T diffractometer using Mo-Ka irradiation (. = 0.71073 Å) and were corrected for Lorentz and polarization effects. Crystal structure analysis of 8: C18H16O5, M = 312.31. Crystal size 0.50 × 0.30 × 0.08 mm. Monoclinic, space group C2/c, a = 16.024(4), b = 7.0035(14), c = 28.674(7) Å, ß = 102.41(4)°, Z = 8. Theta range for data collection: 3.19 to 29.41°, 25521 reflections collected, 4258 independent reflections [R(int) = 0.0484], direct methods, full-matrix least-squares refinement on F2, 211 parameters, GooF = 1.046, R1 [I>2s(I)] = 0.0432, wR2 (all data) = 0.1081, largest diff. peak and hole: 0.266 and -0.227 e Å-3.
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