Reaction of chiral diamine 3.11a with succindialdehyde (3.19, obtained by treatment of 2,5-dimethoxytetrahydrofuran with 0.1 M HC1) and benzotriazole in CH2C12 at room temperature for 24 h readily afforded Bt intermediate 3.22 as a single enantiomer in 81% yield (Scheme 3-6). The stereochemistry of 3.22 was determined by NOE NMR experiments. H NMR spectra of 3.22 show that H(3), H(7a) and H(5) appear at 3.7 ppm multipleet, 5.1 ppm (doublet-doublet) and 6.0 ppm (triplet), respectively. A significant positive NOE effect was observed between H(3) and H(5), and no NOE effect was observed between H(7a) with either H(3) or H(5). Thus, NOE analysis demonstrates that H(3) and H(5) in 3.22 are in a cis-orientation whereas H(3) and H(7a) are in trans- orientation. Treatment of 3.22 with 2 equiv of AlC13 did not afford the desired 3.23, but gave a decomposed mixture possibly due to the labile NCHN moiety in the presence of a Lewis acid. 3.3 Conclusion In summary, starting from easily available N-Boc-a-amino-acids, we have developed an efficient method for the preparation of novel enantiopure 1,2,3,5,10,10a- hexahydroimidazo[1,5-b]isoquinolines 3.1a-c, 2,3,10,1 a-tetrahydroimidazo[ 1,5- b]isoquinolin-l(5H)-ones 3.15a-c and 3.18a-c via Lewis acid promoted iminium cation intramolecular cyclizations. 3.4 Experimental Section Column chromatography was performed on silica gel (200-425 mesh). All of reactions were carried out under nitrogen.