Reagents and conditions. (i)
(a) 2.5 equiv BrCH(CO2Et)2, MeOH, rt, 20 min,
(b) 3.0 equiv amino alcohol a–g,
rt, 1 h; (ii) 6.0 equiv mCPBA, CH2Cl2, rt, 1–5 h; (iii) ClSO2NCO, HCO2H, DMA 0 °C → rt, 3 h; (iv) NaOH, MeOH, 0 °C to
rt, 2–4 h; then Amberlite IR120-H+.