Lanthanide/B(C 6 F 5 ) 3 -Promoted Hydroboration Reduction of Indoles and Quinolines with Pinacolborane.

We have developed a lanthanide/B(C 6 F 5 ) 3 -promoted hydroboration reduction of indoles and quinolines with pinacolborane (HBpin). This reaction provides streamlined access to a range of nitrogen-containing compounds in moderate to excellent yields. Large-scale synthesis and further transformations to bioactive compounds indicate that the method has potential practical applications. Preliminary mechanistic studies suggest that amine additives promote the formation of indole-borane intermediates, and the lanthanide/B(C 6 F 5 ) 3 -promoted hydroboration reduction proceeds via hydroboration of indole-borane intermediates with HBpin and in situ-formed BH 3 species, followed by the protodeborylation process.