Diasteroselective cyclizations with enantiopure malonaldehyde monocycloacetals

The synthesis of a series of enantiopure malonaldehyde monocycloacetals is described. Treatment of 8b with L-tryptophan methyl ester, 5-methoxytryptamine, and tryptamine, respectively, in the Pictet-Spengler condensation gave the corresponding enantiomerically pure key precursors 1-3 and 17-21 in only two steps. Using a chiral amino-diol successfully realized the kinetic resolution of racemic carbolines 23 and 24.