Reaction Steps
Prepared according to general procedure A using freshly distilled hydrocinnamaldehyde (32.4 mL, 0.246 mmol). The reaction was stirred for 22 h to give a diastereomeric mixture of carboxylic acids in a 75:25 ratio. After esterification, both diastereomers (anti-20 and syn-20) were purified by column chromatography to give a pale yellow oil (71.7 mg, 94%, combined yield for both diastereoisomers). The diastereomeric ratio of the esters was found to be 79:21 (anti-20:syn-20) by 1H-NMR spectroscopic analysis. CSP-HPLC analysis. Chiralpak OJ-H (4.6 mm×25 cm), hexane/IPA: 80/20, 0.5 mL min-1, RT, UV detection at 254 nm, retention times: anti-20 52.6 min. (major enantiomer) and 76.2 min. (minor enantiomer); syn-20 66.5 min. (major enantiomer) and 106.6 min. (minor enantiomer). TLC (hexanes:EtOAc, 8:2 v/v): Rf=0.35; anti-20: 1H NMR (600 MHz, CDCl3): δ=8.15 (d, J=7.8 Hz, 1H), 7.59 (app. t, 1H), 7.47 (app. t, 1H), 7.35-7.25 (m, 3H), 7.25-7.15 (m, 3H), 4.91-4.84 (m, 1H), 3.92 (d, J=6.8 Hz, 1H), 3.76 (s, 3H), 2.92-3.02 (m, 1H), 2.83-2.75 (m, 1H), 2.13-2.03 (m, 1H), 1.97-1.87 (m, 1H); 13C NMR (100 MHz, CDCl3): δ=170.6, 164.0, 140.6, 136.0, 134.3, 130.7, 128.9, 128.7, 128.6, 127.3, 126.40, 124.7, 78.3, 52.9, 48.7, 35.7, 31.3; syn-20: 1H NMR (600 MHz, CDCl3): δ=8.15 (d, J=7.9 Hz, 1H), 7.56 (app. t, 1H), 7.48 (app. t, 1H), 7.35-7.25 (m, 2H), 7.25-7.15 (m, 4H), 4.60-4.53 (m, 1H), 3.83 (d, J=3.2, 1H), 3.68 (s, 3H), 3.02-2.92 (m, 1H), 2.90-2.83 (m, 1H), 2.30-2.21 (m, 1H), 2.14-2.02 (m, 1H); 13C NMR (100 MHz, CDCl3): δ=169.4, 164.8, 140.5, 136.8, 133.9, 130.9, 129.2, 128.8, 128.7, 127.4, 126.42, 125.5, 77.3, 52.8, 48.1, 34.5, 31.4; IR (neat): 3062, 3027, 2952, 2927, 2860, 1723, 1603, 1457, 1244, 1159, 1120, 1086, 700 cm−1; HRMS (ESI): calcd. for [M+Na]+O19H18O4Na requires 333.1103. found 333.1103.
