Ruthenium-catalysed enantioselective hydrogenation of trisubstituted enamides derived from 2-tetralone and 3-chromanone: Influence of substitution on the amide arm and the aromatic ring

Cyclic enamides were prepared in one step from tetralone and chromanone derivatives and primary amides under acidic conditions. The enantioselective hydrogenation of these enamides bearing an endocyclic trisubstituted carbon-carbon double bond was performed at room temperature in the presence of ruthenium catalysts. On the one hand, the nature of the amide group had little influence on the enantioselectivity of the hydrogenation when mononuclear precatalysts were used. On the other hand, the presence of a coordinating atom at some specific position on the tetralone and chromanone skeleton led to a dramatic decrease of the enantiomeric excesses.