The N-acetalphthalimide 3 was obtained by treatment of phthalimide and bromoacetal in the presence of KOH as base and toluene as solvent at 80 C. Reaction of 2 with 3 in the presence of BF3-OEt2 resulted in the desired ring-closed product 4 in high yield and good diastereoselectivity based on a chiral auxiliary mediated Pictet-Spengler reaction.6 Removal of the chiral auxiliary proceeded without racemization upon treatment with HCl in ethanol at 0 C. The ...