Synthesis of 6-aryl-substituted azocino-[5,4-b]indoles from 1-aryl-substituted 2-ethyltetrahydro-β-carbolines

We optimized the reaction of tetrahydropyridine ring expansion in 1-aryl-substituted tetrahydro-β-carbolines by the action of activated alkynes and achieved higher than 70% yields of the target indoloazocines. The substituents in the 1-aryl ring and at the indole nitrogen atom were shown to affect the rate and selectivity of this transformation. © 2014 Springer Science+Business Media New York.