aReagents and conditions:
(a) CH3I, NaH, THF, rt, 0.5 h; (b) (CH3CO)2O, Et3N, CH2Cl2, rt; (c) Concentrated HCl, ethylene glycol, refluxed; d) Separation of enantiomers of 24b on HPLC: column: Chiralcel OD; mobile phase: 35% isopropanol in hexane; flow rate: 4.0 mL/min; (+)-enantiomer at 15 min and (-)-enantiomer at 30 min;