A New Synthesis of Rizatriptan Based on Radical Cyclization

Abstract

A new methodology useful for preparation of indole derivatives bearing a 2-(dialkylamino)-ethyl substituent at the 3-position has been developed. Application of this methodology to the synthesis of N,N-dimethyl-2-{5-[(1H-1,2,4-triazol-1-yl)methyl]-1H-indol-3-yl}ethan-1-amine (rizatriptan; 3) is described. The key reaction step is based on the radical cyclization of N-[4-(dimethylamino)but-2-yn-1-yl]-N-{2-iodo-4-[(1H-1,2,4-triazol-1-yl)methyl]phenyl}-acetamide (21), easily available by the Mannich reaction, and subsequent isomerization of the primarily formed methylidene derivative 22.