Selective Reduction of Amides to Amines by Boronic Acid Catalyzed Hydrosilylation

摘要

Amines constitute important intermediates for the pharmaceutical, agrochemical, and chemical industry. Regarding their preparation, the reduction of carboxamides constitutes a convenient arid straightforward synthetic access. Conventionally, amides have been reduced using aluminum or boron hydrides, but these protocols show only limited functional-group tolerance. However, for the efficient construction of functionalized complex molecules, achieving high chemo-selectivity is crucial in organic synthesis. For instance, among the top 20 drugs (based on sales) in 2010, five are amine derivatives having additional reducible moieties, such as ester and cyano groups. In contrast to stoichiometric reductions, catalytic routes offer the possibility to control selectivity by modifying the catalyst metal and the surrounding ligands. In this respect, catalytic hydrosilylation has recently become the method of choice for chemoselective reductions of carboxamides. Compared to hydrogenation, a variety of noble-metal catalysts based on Rh,Ru,Pt, Ir, as well as others can be applied in this transformation.