Synthesis of enantiomerically pure 1,2,3,4-tetrahydro-beta-carbolines and N-acyl-1-aryl ethylamines by rhodium-catalyzed hydrogenation

The rhodium-catalyzed asymmetric hydrogenation of different enamides, in particular, dihydro-p-carboline derivates, was investigated in the presence of chiral phosphorus ligands. Enantioselectivities of up to 99% ee were obtained after ligand screening and optimization of the reaction conditions. The scope and limitation of the catalysts were shown in the synthesis of optically active tetrahydro-beta-carbolines and other benchmark N-acyl-1-aryl ethylamines.