Reaction Steps
(R/S)-1-(4-Iodo-5-methoxy-2-nitrophenyl)-2,2-dimethyl-1-propyl (1S)-camphanate (3.4 g) was dissolved in boiling ethanol (150 ml), the solution was kept in a warm oil bath and slowly cooled to room temperature and stood overnight. Needle crystals were formed gradually and collected by filtration to yield pure single diastereomer (R)-1-(4-iodo-5-methoxy-2-nitrophenyl)-2,2-dimethyl-1-propyl (1S)-camphanate (870 mg, 51%). The remaining mother liquor was concentrated in vacuo, and the residue was dissolved again in boiling ethanol (150 ml), and the solution was quickly cooled to room temperature and needle crystals were formed within two hours. The crystals were collected by filtration to yield pure single diastereomer (S)-1-(4-iodo-5-methoxy-2-nitrophenyl)-2,2-dimethyl-1-propyl (1S)-camphanate. The crystallization process was repeated twice to yield additional pure (S)-diastereomer (total 1.07 g, 63%). 1H NMR (400 MHz, CDCl3) for (R)-1-(4-iodo-5-methoxy-2-nitrophenyl)-2,2-dimethyl-1-propyl (1S)-camphanate: δ 8.48 (s, 1H, Ph-H), 6.94 (s, 1H, Ph-H), 6.84 (s, 1H, Ph-CH), 3.93 (s, 3H, OCH3), 2.42 (m, 1H, CH), 2.11 (m, 1H, CH), 1.92 (m, 1H, CH2), 1.75 (m, 1H, CH2), 1.11 (s, 3H, CH3), 1.05 (s, 3H, CH3), 0.97 (s, 9H, C(CH3)3), 0.86 (s, 3H, CH3). 1H NMR (400 MHz, CDCl3) for (S)-1-(4-iodo-5-methoxy-2-nitrophenyl)-2,2-dimethyl-1-propyl (1S)-camphanate: δ 8.48 (s, 1H, Ph-H), 6.95 (s, 1H, Ph-H), 6.80 (s, 1H, Ph-CH), 3.96 (s, 3H, OCH3), 2.37 (m, 1H, CH), 1.92 (m, 2H, CH2), 1.66 (m, 1H, CH), 1.14 (s, 3H, CH3), 1.07 (s, 3H, CH3), 1.06 (s, 3H, CH3), 0.98 (s, 9H, C(CH3)3).
