(a) TBDPSCl, Et3N, DMAP, CH2Cl2, 18 h, rt; 89%. (b) KOt-Bu, 0 °C, 1h; methyl bromoacetate, rt, 18 h; 50% (72% BORSM). (c) N-methylaminoethanol, NaOMe, THF, rt, 2 h; 73%. (d) LDA, LiCl, THF, −78 °C, 1 h; 0 °C, 15 min; rt, 5 min; Me2C=C=CHCH2Br (15), 0 °C, 2 h; 93%. (e) dimethyl carbonate, NaOMe, CH2Cl2, rt, 18 h; 96%.