Asymmetric Pictet–Spengler Reactions Employing N,N ‐Phthaloyl Amino Acids as Chiral Auxiliary Groups

Both aromatic and aliphatic Schiff bases 1 can be cyclized asymmetrically in the presence of titanium alkoxides if N,N-phthaloyl-protected amino acids are employed as chiral auxiliaries. The desired heterocycles 3, which are suitable for alkaloid syntheses, are formed with diastereomer ratios of up to 99%. R  nPr, iPr; R1  Me, Et, iPr, Ph, Ar; R2  Me, iPr, tBu.