1. Step 4. The crude mixture from previous step was dissolved in a mixture of EtOH (16 mL, 268 mmol, 50 equiv.) and EtOAc (12 mL) and treated with 38% aqueous HCl (10 mL, 118 mmol, 22 equiv.) on a salt ice bath (ca. ?5 �C). The solution was stirred at r.t. (ca. 20 �C) for 25 h (R f (27) 0.35, CHCl 3 -EtOH 20:3, brown color with H 3 PO 4 stain and heating) and neutralized with Amberlyst A21 (25 g;Anionite was filtered off and washed with EtOH