Scheme 1. Reagents and conditions: (i) POCl₃, DMF, 0 °C, 2 h; (ii) NaClO₂, NH₂HSO₃, CH₂Cl₂, 0 °C, 3 h; (iii) thionyl chloride, reflux; 1-benzylpiperidin-4-amine (4), K₂CO₃, CH₂Cl₂, rt, 8 h; (iv) thionyl chloride, reflux; 2-(1-benzylpiperidin-4-yl)ethanamine (5), K₂CO₃, CH₂Cl₂, rt, 8 h.