An Efficient Synthesis of Phenanthridines via a Transition-Metal-Free Process

Hsieh et al. have reported an efficient synthesis of phenanthridines via a transition-metal-free process. The reaction includes lithium triethylborohydride-induced anionic cyclization by a nucleophilic aromatic substitution (SNAr) reaction, with the cleavage of the C-Br bond. They proposed the reaction mechanism involving the chelating of biaryl bromonitriles to a lithium cation and addition of a hydride to the nitrile. The procedure can be applied to the syntheses of a range of polysubstituted phenanthridines including natural alkaloids.