Prof. Dr. Herbert Waldmann, Dipl.-Chem. Gunther Schmidt, Dr. Henning Henke and Dr. Michael Burkard
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.