Diastereo- and enantioselective hydrogenation of a challenging enamide derived from 4-phenyl-2-tetralone: an appealing shortcut towards enantiopure cis-2-aminotetraline derivatives

A clean, efficient, and diasteroselective (dr >95%) catalytic hydrogenation of the enamide N-(4-phenyl-3,4-dihydronaphthalen-2-yl)propionamide (2 a) using palladium on carbon is performed. This procedure provides the Melatonin Receptor ligand (+/-)-cis-4-phenyl-2-propionamidotetralin (cis-4-P-PDOT, 1 a) and its 8-methoxy analog. Furthermore, Rh and Ru catalyzed homogeneous asymmetric hydrogenation of the challenging racemic endocyclic enamide 2 a with several chiral phosphine ligands is studied. The best results, in terms of enantioselectivity, for both diastereomers are obtained when chiral Rh-Josiphos is used as the catalyst.