Cyano Group Removal from Cyano-Promoted Aza-Diels–Alder Adducts: Synthesis and Structure–Activity Relationship of Phenanthro­indolizidines and Phenanthro­quinolizidines

Phenanthro­indolizidines and phenanthro­quinolizidines were concisely synthesized by the reductive decyanization of cyano-promoted intramolecular aza-Diels–Alder cycloadducts followed by aryl–aryl coupling. Cyano groups were removed from α-amino­acrylonitriles via treatment with sodium borohydride in 2-propanol in almost quantitative yields; a possible mechanism was proposed and examined using D-labeling experiments. A systematic study of the effects of the phenanthrene substitution pattern on the anticancer activity against three human cancer cell lines was discussed.