IBX-mediated oxidative addition of isocyanides to cyclic secondary amines: total syntheses of alangiobussine and alangiobussinine
Present study describes a robust and general method for the synthesis of C(1)-carboxamides through IBX-mediated oxidative addition of isocyanides to the tryptolines and 1,2,3,4-tetrahydroisoquinolines. In this transformation, IBX plays a dual role of oxidant as well as Lewis acid to activate the imine facilitating the isocyanide addition. Detailed mechanistic investigations were performed by isotopic labeling and real-time NMR experiments. The method was utilized for the gram scale syntheses of two alkaloids alangiobussine and alangiobussinine in 63 % and 45 % overall yield respectively.