“…After the addition of 100 mg of THBQ, the product was stored at -5 °C. Preparative high-performance LC (0.8% EtOAc/hexane) gave 1.97 g (48%) of viscous yellow ester 24 as a single isomer to analytical highperformance LC (3% EtOAc/hexane): IR (film) 1695 (C=0), 1600 (C=C), 1580,1390,1350,1240,1150,1040,975,890,840 cm"1; NMR (CDC13) 1.00 (t, J = 8 Hz, 3, Ctf3CH2C), 1.07 (s, 6, C-16 and C-17 CH3), 1.32 (t, J = 6 Hz, 3, CH3CH20), 1.4-1.7 (m, 4, C-2 and C-3 CH2), 2.02 (s, 3, C-19 CHg), 1.9-2.15 (m, 4, C-4 and C-18 CH2), 2.39 (d, J = 1 Hz, 3, C-20 CH3), 4.19 (q, J = 7.5 Hz, 2, COOCH2), 5.78 (s, 1, C-14 C=CH), 6.03-6.40 (m, 4, C-7, C-8, and C-12 HC=CH, C-10 C=CH), 6.94 and 7.06 (dd, J = 15 and 12 Hz, 1, C-ll HC=CH); 13C NMR (CDClg) 13.0 (C-19), 13.5 and 14.0 (C-20, CCHgCHg), 14.4 (OCH2CHg), 19.6 (C-3), 28.0 (CH2CHg), 29.1 (C-16 and C-17), 30.0 (C-4), 34.5 (C-l), 40.1 (C-2), 59.5 (OCHg), 118.8 (C-14), 128.8,129.6, and 130.8 (C-7, C-10 and C-ll), 135.4 and 135.7 (C-5 and C-12), 136.6 and 137.7 (C-6 and C-8), 139.4 (C-9), 152.4 (C-13), 167.0 ppm (C-15); UV Xmaz (EtOH) 351 nm (t 3.37 X 104), 242 (e 8.6 X 103). MS Caled for C^HgA: 342.2559.…”