Reaction Steps
To a mixture of trimethyl phosphonoacetate (2.5 mL, 15.3 mmol) and tBuOK (1.7 g, 15.3 mmol) in THF (20 mL) at 0° C. (1 h) was added a THF (10 nmL) solution of 18 (1.2 g, 3.7 mmol). The mixture was stirred at reflux for 36 h. Purification of the crude residue by flash chromatography (hexane/EtOAc 92:8) followed by preparative HPLC (hexane/EtOAc 92:8, Novapak normal phase cartridge column, 10 mL/min), afforded in order of elution; 18 (123.3 mg, 10%), 19E (387.0 mg, 27%) and 19Z (609.3 mg, 43%) as clear oils: 19E; 1H NMR (300 MHz, CDCl3) δ0.28 (s, 9H), 0.99 (t, J=7.6 Hz, 3H), 2.99 (q, J=7.6 Hz, 2H), 3.42 (s, 3H), 3.75 (s, 3H), 4.02 (s, 3H), 4.47 (s, 2H), 4.72 (s, 2H), 5.8 (s, 1H), 6.84 (s, 1H); 13C NMR (75 MHz, CDCl3) δ−2.0, 12.3, 14.2, 26.6, 51.2, 53.4, 55.3, 61.9, 96.7, 115.4, 118.9, 121.1, 150.9, 160.3, 162.2, 164.9, 166.2; IR (film, NaCl, cm−1) 2949, 1723, 1341, 1042, 840; LRMS (70 eV, EI) m/z (rel int %) 367 (M+), 352, 322, 308 (100), 290, 276, 246, 232, 99, 57; HRMS m/z calcd for C18H29NO5Si (M+) 367.1815,m found 367.1802. 19Z: 1H NMR (300 MHz, CDCl3) δ0.26 (s, 9H), 1.11 (t, J=7.2 Hz, 3H), 2.38-2.48 (m, 2H), 3.4 (s, 3H), 3.53 (s, 3H), 3.99 (s, 3H), 4.35 (d, J=10.2 Hz, 1H), 4.51 (d, J=10.2 Hz, 1H), 4.66 (dd, J=6.3 and 14.2 Hz, 2H), 5.94 (s, 1H), 6.72 (s, 1H); 13C NMR (75 MHz, CDCl3 δ−1.9, 11.4, 33.1, 51.1, 53.2, 55.2, 61.9, 96.5, 114.5, 116.3, 120.6, 150.0, 159.0, 161.7, 164.3, 165.6; IR (film, NaCl, cm−1) 2941, 1732, 1559, 1457, 1342, 1054, 836; LRMS (70 eV, EI) m/z (rel int %) 367 (M+), 322, 290, 278, 262, 139 (100), 89, 73; HRMS m/z calcd for C18H29NO5Si (M+) 367.1815, found 367.1820.
