Scheme 1. Reagents and conditions: i) SOCl₂, DMF (cat.) reflux, 8 h; ii) ethane-1,2-diamine, CH₂Cl₂, 0–25 °C, 18 h; iii) Ph₃P CHCO₂Et, EtOH, 25 °C, 18 h, chromatography; iv) DIBAL-H, −78 °C, 1 h; v) MnO₂, CH₂Cl₂, 25 °C, 18 h; vi) Na(OAc)₃BH, THF, 25 °C, 18 h.