Reaction Steps
Prepared according to general procedure B from ethyl vinyl ketone (59 μL, 0.59 mmol), trans-2-methyl-1,3-pentadiene (94 μL, 0.89 mmol), 70% aqueous perchloric acid (10.2 μL, 0.12 mmol) and (2S, 5S)-5-benzyl-3-methyl-2-(5-methyl-furan-2-yl)-imidazolidin-4-one (32 mg, 0.12 mmol) in ethanol (590 μL) for 4.5 days at −30° C. Purification by silica gel chromatography (9:1 pentane:ether) provided the title compound as a single diastereomer (as judged by GLC analysis) in 90% yield (90 mg, 0.54 mmol) and 90% ee. IR (film) 2964, 2937, 2874, 2833, 1711, 1452, 1377, 1343, 1227, 1195, 1123, 1038, 984.2, 886.0, 841.6 cm−1; 1H NMR (300 MHz, CDCl3) δ 5.37 (m, 1H, CH═CCH3), 2.60 (m, 2H, CHCO and CHCH3), 2.50 (dq, J=17.4, 7.5 Hz, 1H, C(H)HCO), 2.37 (dq, J=17.4, 7.5 Hz, 1H, C(H)HCO), 1.94 (m, 2H, ═CCH2), 1.68 (m, 2H, CH2CH), 1.64 (s, 3H, CH3C═CH), 1.05 (dd, J=7.5, 7.5 Hz, 3H, CH2CH3), 0.76 (dd, J=6.9, 6.9 Hz, 3H, CH3CH); 13C NMR (75 MHz, CDCl3) δ 214.0, 133.7, 126.3, 50.5, 34.6, 31.7, 30.2, 23.8, 19.0, 16.8, 8.1. [α]D=+16.7 (c=1.0, CHCl3). Product ratios were determined by GLC analysis (100° C., 23 psi); (1R, 2S) endo isomer tr=21.3 min, and (1S, 2R) endo isomer tr=20.4 min, exo isomers tr=15.4, 16.6 min.
