Facile Catalytic Hydrosilylation of Pyridines

摘要

The catalytic hydrosilylation of imines has emerged as an important method for the preparation of amines, whereas the hydrosilylation of other nitrogen-containing substrates remains a significant synthetic challenge. Only a handful of catalytic methods for the hydrosilylation of nitriles to amines nitriles to irnines, amides to amines, and nitroarenes to anilines are known. The addition of silanes to pyridines is even rarer. The synthesis of silylated 1,2- and/or 1,4-dihydropyridines is of importance as a potential method for the preparation of partially reduced pyridines, which are often used as selective reducing agents and could be valuable building blocks for organic synthesis. Harrod and co-workers reported the only example to date of a homogeneous hydrosilylation of pyridines. The use of a titanium catalyst at 80 °C gave silylated dihydropyridines; however, these reactions were compromised by the concomitant hydrogenation of the products to tetrahydropyridines. In related studies, Crabtree and co-workers developed a reduction of quinolines by silanes in the presence of [Rh(nbd)-(PPh3)2]PF6 (nbd = norbornadiene), which catalyzes the generation of the highly active product SiH4 from H3SiPh. The stoichiometric insertion of pyridine into an Fe-Si bond to give an η~3-1-silyl-1,4-dihydropyridinyl complex was described by Tobita and co-workers.