Synthesis of 8-aryl substituted benzo[a]phenanthridine derivatives by consecutive three component tandem reaction and 6-endo carbocyclization

A concise construction of benzo[a]phenanthridines involving multicomponent tandem reaction/carbocyclization in a sequential format is described. The reaction proceeds initially via formation of a 4-aryl-3-arylethynyl-isoquinoline from 2-bromobenzaldehyde/tert-butylamine/1,3-diyne in a three component format followed by a second ring closure either via gold/silver catalyzed intramolecular hydroarylation or via iodo-catalyzed regioselective 6-endo-dig electrophilic cyclization. The salient feature of the strategy involves a three component reaction followed by transformation of the resulting product in to polyheterocycles with increased structural complexity in two steps.