A silver-mediated free-radical cascade cyclization of isocyanides with potassium alkyl trifluoroborates was developed. The procedure tolerates a series of functional groups, including chloro, bromo, ester, ketone, and amide. Additionally, it is not sensitive to steric hindrance. Thus, this reaction represents a very useful strategy for the production of 6-alkylated phenanthridine derivatives. The addition of alkyl radical to the isonitrile, followed by a radical aromatic cyclization, is involved in this transformation.